i
INVESTIGATION ON QUALITY OF HYDROXYAPATITE ADHESION ON
INVESTMENT CASTING MOULD
AMIR FEREIDOUNI LOTFABADI
A thesis submitted in fulfillment of the
requirements for the award of the degree of
Master of Engineering (Mechanical Engineering)
Faculty of Mechanical Engineering
Universiti Teknologi Malaysia
JULY 2008
iii
To my beloved father and mother
Amir
28/7/2008
iv
ACKNOWLEDGEMENT
In this research, I was in contact with many people, researchers,
academicians, and practitioners. They have contributed towards my understanding
and thoughts. In particular, I wish to express my sincere appreciation to my main
thesis supervisor, Associate Professor Dr. Hasbullah Haji Idris, for support, guidance,
critics and friendship. I am also very thankful to my co-supervisors Dr. Mohd Rafiq.
Foundry lab technicians in Universiti Teknologi Malaysia had very kind and helpful
cooperation with me during my research as well. Furthermore my Friends Mr.
Hessam Majd and Mr. Ali Akhavan Farid had very helpful guidance and sympathy
during my research time.
v
ABSTRACT
Quality of Hydroxyapatite adhesion on investment casting mould was
investigated in this project. Investment casting is a new method for HAp coating onto
the metals. First stage of applying this method is making appropriate investment
casting mould. Appropriate investment casting mould should have specific properties
such as: sufficient strength, proper shape for obtaining sound casting, and the must
important one, enough amount of HAp should adhered onto the inner layer of
investment casting mould to defuse into the metal during casting for desirable
coating. For this purpose appropriate methods used to stick sufficient amount of
Hydroxyapatite onto inner layer of ceramic investment casting mould to prepare it for
metal coating by casting. therefore 3 different HAp-water mixture viscosities: 5, 7.5
and 10 seconds, were applied to find out which of them was support enough amount
of Hydroxyapatite after dewaxing and firing. Dewaxing in three different
temperatures 100°, 200° and 300° C applied as well to investigate the effect of the
dewaxing temperature on the quality of HAp adhesion on to the moulds. Finally after
gathering the results of dewaxing; moulds that have the desirable properties were
fired at 600° C to study the effect of firing process on the quality of hydroxyapatite
adhesion on moulds. After all XRD, EDAX tests and 3D microscope supervision
were done to find out the results. By considering these tests 5 seconds viscosity of
HAp-water mixture and 300°C dewaxing temperature had the desirable properties for
making sufficient investment casting moulds for metal coating.
vi
TABLE OF CONTENTS
CHAPTER
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGMENT
iv
ABSTERACT
v
TABLE OF CONTENTS
vi
LIST OF TABLES
ix
LIST OF FIGUERES
x,xi
1
INTRODUCTION
1
2
TISSUE ENGINEERING
4
2.1 Introduction
4
2.2 Bio-active materials for tissue engineering
6
2.2.1 Ceramics
8
2.2.1.1 Nonabsorbable or Relatively Bioinert Bioceramics
10
2.2.1.2 Biodegradable or Resorbable Ceramics
11
2.2.1.3 Bioactive or Surface-Reactive Ceramics
12
2.2.1.4 Bioceramics Calcium Phosphate base
13
2.2 Hydroxyapatite
14
2.2.1 Identification
15
2.2.2 Advantage of Hydroxyapatiate
15
2.2.3 Disadvantage of Hydroxyapatite
16
vii
CHAPTER
3
4
TITLE
PAGE
2.2.4 Hydroxyapatite coatings
16
2.2.5 Coating Techniques
16
2.3 Related works on usage of Hydroxyapatite
18
2.3.1 Bioactive coatings on 316L Stainless Steel implants
18
2.3.2 Hydroxyapatite coating on cobalt base alloys
19
METHODOLOGY AND EXPERIMENTAL PROCEDURE
23
3.1 Introduction
23
3.2 Methodology and Experiment
24
3.2.1 Design
26
3.2.1.1 Pattern Design
26
3.2.1.2 Design of wax mould
27
3.2.2 Mould Fabrication
30
3.2.3 Wax pattern manufacture
31
3.2.4 Ceramic mould fabrication
33
3.2.4.1 Preparing wax samples
34
3.2.4.2 Preparing Hydroxyapatite for coating
34
3.2.4.3 Coating of samples
35
3.2.4.4 Slurry preparation
37
3.2.4.5 Investment casting mould making
39
3.2.5 Effect of dewaxing temperature
42
3.2.5.1 Introduction
42
3.2.5.2 Dewaxing
42
3.2.6 Firing process
44
3.2.7 Tests
44
RESULTS AND DISCCUSION
48
4.1 XRD Result
48
4.2 EDAX Result
59
4.3 3D microscope
63
viii
CHAPTER
5
TITLE
PAGE
COCLUSTION
64
REFRENCES
66
ix
LIST OF TABLES
TABLE NO.
TITLE
PAGE
2.1
Coating techniques of Hydroxyapatite
16-17
2.2
Summarized related works on HAp Coatings
20-22
4.1
XRD test results – Reference Materials
52
4.2
XRD test results for different viscosities
57
4.3
EDAX result for 600°C temperature
60
4.4
EDAX result for actual samples, Fluka
62
x
LIST OF FIGUERS
FIGURE NO.
TITLE
PAGE
2.1
Hydroxyapatite structure projected
14
3.1
Flowchart of the process
25
3.2
Drawing of a sample
27
3.3
Base part of pattern mould
28
3.4
Middle part of the pattern mould
29
3.5
Top part of the pattern mould
29
3.6
Disassembled pattern mould
31
3.7
Assembled mould for wax pattern
31
3.8
Solid wax pattern inside the mould
33
3.9
Wax patterns hanged for drying
33
3.10
Mixing HAp and mineral water
35
3.11
Measuring the viscosity of HAp-water mixture
36
3.12
Preparing ceramic slurry
38
3.13
Coating wax patterns with ceramic slurry
40
3.14
Coated wax pattern with slurry
40
3.15
Moulds after stuccoing
41
3.16
Moulds after final coating
41
3.17
Making holes inside the wax
43
3.18
Moulds inside the furnace
43
3.19
Broken samples parts for tests
47
3.20
Prepared powder for XRD test
47
xi
FIGURE NO.
TITLE
PAGE
4.1
XRD result for Fluka
49
4.2
XRD result for Granumas
50
4.3
XRD result for Iran
51
4.4
XRD result for reference materials
53
4.5
XRD result for 5S viscosity and 600°C
54
4.6
XRD result for 7.5 viscosity and 600° C
55
4.7
XRD result for 10 viscosity and 600° C
56
4.8
Material amount vs. Temperature in 5S viscosity
58
4.9
Material amount vs. Temperature in 7.5S viscosity
58
4.10
Material amount vs. Temperature in 10S viscosity
59
4.11
Adhesion of HAp onto the inner layer of mould
64
CHAPTER 1
INTRODUCTION
Hydroxylapatite, also called hydroxyapatite, is a mineral. It is a naturally
occurring form of calcium apatite with the formula Ca5 (PO4)3 (OH), but is usually
written Ca10 (PO4)6(OH)2 to denote that the crystal unit cell comprises two molecules.
Hydroxylapatite is the hydroxyl endmember of the complex apatite group. The OHion can be replaced by fluoride, chloride or carbonate. It crystallizes in the hexagonal
crystal system. It has a specific gravity of 3.08 and is 5 on the Mohs hardness scale.
Pure hydroxylapatite powder is white. Naturally occurring apatites can however also
have brown, yellow or green colorations..
Hydroxylapatite can be found in teeth and bones, within the human body.
Therefore, it can be used as a filler to replace amputated bone or as a coating to
promote bone ingrowth into prosthetic implants. Although many other phases exist
with similar or even identical chemical makeup, the body responds much differently
to them.
Many modern implants, e.g hip replacements and dental implants, are coated
with hydroxyapatite. It has been suggested that this may promote osseointegration
and there is good evidence for this. Because of its poor mechanical strength must of
2
the time it is needed to use it as a coating of any other materials such as Titanium
alloys, Cobalt alloys and medical grade Stainless steel.
There are various ways for coating HAp on to different materials each method
of coating has its own advantage and disadvantages; The method of coating is dipend
on the usage of the implant, accuracy, amount of HAp that was needed to coat and
the cost of the method as well. Some of these methods are summarized in table 2.1. in
chapter 2.
One of the most new methods for coating HAp on to the metallic materials is
coating by investment casting method, also called lost-wax casting, is one of the
oldest known metal-forming techniques. From 5,000 years ago, when beeswax
formed the pattern, to today’s high-technology waxes, refractory materials and
specialist alloys, the castings allow the production of components with accuracy,
repeatability, versatility and integrity in a variety of metals and high-performance
alloys. Lost foam casting is a modern form of investment casting that eliminates
certain steps in the process. Investment casting consist of 3 main stage, at first
making the wax and preparing ceramic shell on it, second dewaxing the moulds and
finally fire the dewaxed moulds.
This method of coating firstly used to coat HAp on to Cobalt alloys [J.C.
Escobedo, et. al. 2006]. This method of coating has its own advantages and
disadvantages. This method is very cheap regarding to other coating methods and it is
very simple as well. Also according to using simple methods control of the elements
which are involved in the finale results is easier than other coating methods like
plasma spraying or electro chemical methods for coating.
In this project finding the best dewaxing temperature for moulds aimed. And
investigation to find out what is the best viscosity of HAp-water mixture for coating
the inner layer of investment casting moulds was targeted as well.
3
This report started from introduction on tissue engineering and highlight its
history and importance through human life also mentioned the materials and methods
that used and being in the process from past until now.
Afterward the properties, composition and classification of bioceramics
discussed in detail especially for hydroxyapatite. Also the related works,
investigations and applying of several bioceramics issued in several tables.
At 3rd chapter methodology and experimental procedure discussed, 4th and 5th
chapter talked about on results and conclusion as well.
4
CHAPTER2
TISSUE ENGINEERING
2.1 Introduction
Biomedical engineering (BME) is the application of engineering principles
and techniques to the medical field. It combines the design and problem solving skills
of engineering with the medical and biological science to help improve patient health
care and the quality of life of healthy individuals.
As a relatively new discipline, much of the work in biomedical engineering
consists of research and development, covering an array of fields: bioinformatics,
medical imaging, image processing, physiological signal processing, biomechanics,
biomaterials and bioengineering, systems analysis, 3-D modeling, etc. Examples of
concrete applications of biomedical engineering are the development and
manufacture of biocompatible protease.
Tissue Engineering is the use of a combination of cells, engineering and
materials methods, and suitable biochemical and physio-chemical factors to improve
or replace biological functions. While most definitions of tissue engineering cover a
broad range of applications, in practice the term is closely associated with
applications that repair or replace portions of or whole tissues (i.e., bone, cartilage,
blood vessels, bladder, etc). Often, the tissues involved require certain mechanical
and structural properties for proper function. The term has also been applied to efforts
5
to perform specific biochemical functions using cells within an artificially-created
support system (e.g. an artificial pancreas, or a bioartificial liver). The term
regenerative medicine is often used synonymously with tissue engineering, although
those involved in regenerative medicine place more emphasis on the use of stem cells
to produce tissues. Natural bone surface is quite often contains features that are about
100 nm across. If the surface of an artificial bone implant were left smooth, the body
would try to reject it. Smooth surface is likely to cause production of fibrous tissue
covering the surface of the implant. This layer reduces the bone-implant contact,
which may result in loosening of the implant and further inflammation. It was
demonstrated that by creating nano-sized features on the surface of the hip or knee
prosthesis one could reduce the chances of rejection as well as to stimulate the
production of osteoblasts. The osteoblasts are the cells responsible for the growth of
the bone matrix and are found on the advancing surface of the developing bone.The
effect was demonstrated with polymeric, ceramic and, more recently, metal materials.
More than 90% of the human bone cells from suspension adhered to the
nanostructured metal surface [Gutwein, LG, et. al. 2003], but only 50% in the control
sample. In the end this findings would allow to design a more durable and longer
lasting hip or knee replacements and to reduce the chances of the implant getting
loose.
Titanium is a well-known bone repairing material widely used in orthopaedics
and dentistry. It has a high fracture resistance, ductility and weight to strength ratio.
Unfortunately, it suffers from the lack of bioactivity, as it does not support sell
adhesion and growth well. Apatite coatings are known to be bioactive and to bond to
the bone. Hence, several techniques were used in the past to produce an apatite
coating on titanium. Those coatings suffer from thickness non-uniformity, poor
adhesion and low mechanical strength. In addition, a stable porous structure is
required to support the nutrients transport through the cell growth.
It was shown that using a biomimetic approach – a slow growth of
nanostructured apatite film from the simulated body fluid – resulted in the formation
6
of a strongly adherent, uniform nanoporous layer [Ma J, et. al. 2003]. The layer was
found to be built of 60 nm crystallites, and possess a stable nanoporous structure and
bioactivity.
A real bone is a nanocomposite material, composed of hydroxyapatite
crystallites in the organic matrix, which is mainly composed of collagen. The bone is
mechanically tough and, at the same time, plastic, so it can recover from a
mechanical damage. The actual nanoscale mechanism leading to this useful
combination of properties is still debated.
2.1 Bio-active materials for tissue engineering:
The first generation of biomedical materials used within the body was largely
biologically inert, or nearly-inert. The goal at the time was to achieve a suitable
combination of physical properties to match those of the replaced tissue with a
minimal toxic response in the host. It was once thought that all materials, when
placed inside the body, would elicit a foreign body response, the formation of a nonadherent fibrous capsule around the implant. However the discovery, in 1969, of a
four-component glass which could bond to living tissue showed that it is possible for
certain materials to elicit a controlled action and reaction in the physiological
environment. By the mid-1980s bioactive materials had reached clinical use in a
variety of orthopaedic and dental applications, including various compositions of
bioactive glasses, ceramics, glass-ceramics and composites. Another advance in this
second generation of materials for medicine was the development of resorbable
biomaterials, designed to break down chemically and be resorbed at an equivalent
rate to tissue regrowth. Ultimately the foreign material is replaced by regenerating
tissue and the implant site becomes virtually indistinguishable from the host tissue.
An example of this is the biodegradable suture, in which the polymer composed of
polylactic (PLA) and polyglycolic (PGA) acids decomposes and metabolises into
CO2 and H2O.
7
Developments throughout the last century, such as drugs, vaccines, water
treatment and improved hygiene have resulted in a vast increase in the average life
expectancy in developed countries. While the clinical success of bioinert, bioactive
and resorbable implants has greatly improved the quality of life for tens of millions
of people, research shows that a third to half of prostheses fail within 10–25 years
and patients require revision surgery. Twenty years of research have had only small
effects on failure rates. In fact the improvement of first- and second-generation
materials is limited as all man-made biomaterials used for the repair or restoration of
the body represents a compromise. Synthetic materials cannot respond to changing
physiological loads or biochemical stimuli, unlike living tissues. This limits the
lifetime of artificial body parts. Thus there is a need to consider a shift towards a
more biologically based method for the repair and regeneration of tissues.
The new challenge in biomaterials is to enhance the body’s own regenerative
capacity by stimulating genes which initiate repair at the site of damage or disease. A
third generation of biomaterials is being developed to do this. The separate concepts
of bioactive and resorbable materials have been combined to make bioactive
materials resorbable. Third generation bioactive glasses and macroporous foams are
being designed to activate genes that stimulate regeneration of living tissues.
Molecular modifications of resorbable polymer systems elicit specific cellular
responses.
Tissue-engineered constructs can be produced by seeding progenitor cells
onto modified resorbable scaffolds. The cells grow outside the body, become
differentiated and mimic naturally occurring tissues. The construct can then be
implanted into a patient. In time the scaffold is resorbed and replaced by host tissue
that includes a viable blood supply and nerves. The living construct will adapt to the
physiological environment and should provide long-lasting repair.
Biomaterials can be used in situ in the form of powders, solutions or doped
microparticles to stimulate local tissue repair. The materials release chemicals in the
8
form of ionic dissolution products, or growth factors such as bone morphogenic
protein (BMP), at controlled rates, by diffusion or network breakdown, which
activates the cells in contact with the stimuli. The cells produce additional growth
factors that in turn stimulate multiple generations of growing cells to self-assemble
into the required tissues in situ. For example, when a particulate bioactive glass is
used to fill a bone defect there is rapid regeneration of bone that matches the
architecture and mechanical properties of bone at the site of repair. [V.J shirtliff,LL
Hench 2003].
2.1.1 Ceramics
Ceramics are defined as the art and science of making and using solid articles
that have as their essential component, inorganic nonmetallic materials [Kingery et
al., 1976]. Ceramics are refractory, polycrystalline compounds, usually inorganic,
including silicates, metallic oxides, carbides and various refractory hydrides, sulfides,
and selenides. Oxides such as Al2O3, MgO, SiO2, and ZrO2 contain metallic and
nonmetallic elements and ionic salts, such as NaCl, CsCl, and ZnS [Park and Lakes,
1992]. Exceptions to the preceding include covalently bonded ceramics such as
diamond and carbonaceous structures like graphite and pyrolized carbons [Park and
Lakes, 1992].
Ceramics in the form of pottery have been used by humans for thousands of
years. Until recently, their use was somewhat limited because of their inherent
brittleness, susceptibility to notches or micro cracks, low tensile strength, and low
impact strength. However, within the last 100 years, innovative techniques for
fabricating ceramics have led to their use as “high tech” materials. In recent years,
humans have realized that ceramics and their composites can also be used to augment
or replace various parts of the body, particularly bone. Thus, the ceramics used for
the latter purposes are classified as bioceramics. Their relative inertness to the body
fluids, high compressive strength, and aesthetically pleasing appearance led to the use
of ceramics in dentistry as dental crowns. Some carbons have found use as implants
9
especially for blood interfacing applications such as heart valves. Due to their high
specific strength as fibers and their biocompatibility, ceramics are also being used as
reinforcing components of composite implant materials and for tensile loading
applications such as artificial tendon and ligaments [Park and Lakes, 1992].
Unlike metals and polymers, ceramics are difficult to shear plastically due to
the (ionic) nature of the bonding and minimum number of slip systems. These
characteristics make the ceramics non-ductile and are responsible for almost zero
creep at room temperature [Park and Lakes, 1992]. Consequently, ceramics are very
susceptible to notches or microcracks because instead of undergoing plastic
deformation (or yield) they will fracture elastically on initiation of a crack. At the
crack tip the stress could be many times higher than the stress in the material away
from the tip, resulting in a stress concentration which weakens the material
considerably. The latter makes it difficult to predict the tensile strength of the
material (ceramic). This is also the reason ceramics have low tensile strength
compared to compressive strength. If a ceramic is flawless, it is very strong even
when subjected to tension. Flawless glass fibers have twice the tensile strengths of
high strength steel (approximately 7 GPa) [Park and Lakes, 1992].
Ceramics are generally hard. Diamond is the hardest, with a hardness index of
10 on Moh’s scale, and talc (Mg3Si3O10COH) is the softest ceramic (Moh’s hardness
1), while ceramics such as alumina (Al2O3; hardness 9), quartz (SiO2; hardness 8),
and apatite (Ca5P3O12F; hardness 5) are in the middle range. Other characteristics of
ceramic materials are
I. Their high melting temperatures
II. Low conductivity of electricity and heat. These characteristics are due to
the chemical bonding within ceramics.
Ceramics used in fabricating implants can be classified as nonabsorbable
(relatively inert), bioactive or surface reactive (semi-inert) [Hench, 1991, 1993] and
biodegradable or resorbable (non inert) [Hentrich et al., 1971] and[Graves et al.,
10
1972]. Alumina, zirconia, silicone nitrides, and carbons are inert bioceramics. Certain
glass ceramics and dense hydroxyapatites are semi-inert (bioreactive) and calcium
phosphates and calcium aluminates are resorbable ceramics [Park and Lakes, 1992].
Desired Properties of Implantable Bioceramics
i.
Should be nontoxic.
ii.
Should be no carcinogenic.
iii.
Should be no allergic.
iv.
Should be no inflammatory.
v.
Should be biocompatible.
vi.
Should be biofunctional for its lifetime in the host.
Bioceramics are devided to 3 major classes
i.
Nonabsorbable or Relatively Bioinert Bioceramics,
ii.
The second class is Biodegradable or Resorbable Ceramics
iii.
Third is Bioactive or Surface-Reactive Ceramics.
2.1.1.1. Nonabsorbable or Relatively Bioinert Bioceramics:
Relatively bioinert ceramics maintain their physical and mechanical
properties while in the host. They resist corrosion and wear and have all the
properties listed for bioceramics. Examples of relatively bioinert ceramics are dense
and porous aluminum oxides, zirconia ceramics, and single phase calcium
aluminates. (Relatively bioinert ceramics are typically used as structural-support
implants. Some of these are bone plates, bone screws, and femoral heads. Examples
of nonstructural support uses are ventilation tubes, sterilization devices [Feenstra and
de Groot, 1983] and drug delivery devices.
11
Examples of Relatively Bioinert Bioceramics:
i.
Pyrolitic carbon coated devices
ii.
Dense and nonporous aluminum oxides
iii.
Porous aluminum oxides
iv.
Dense hydroxyapatites
v.
Zirconia ceramics
Uses of Bioinert Bioceramics
i.
In the repair of the cardiovascular area.
ii.
As bone plates and screws.
iii.
In the form of ceramic-ceramic composites.
iv.
In the form of ceramic-polymer composites.
v.
As drug delivery devices.
vi.
As femoral heads.
vii.
As middle ear ossicles.
viii.
In the reconstruction of orbital rims.
ix.
As components of total and partial hips.
x.
In the form of sterilization tubes.
xi.
As ventilation tubes.
xii.
In reconstruction of acetabular cavities.
2.1.1.2. Biodegradable or Resorbable Ceramics
Although Plaster of Paris was used in 1892 as a bone substitute [Peltier,
1961], the concept of using synthetic resorbable ceramics as bone substitutes was
introduced in 1969 [Hentrich et. al., 1969] and [Graves et. al., 1972]. Resorbable
ceramics, as the name implies, degrade upon implantation in the host. The resorbed
material is replaced by endogenous tissues. The rate of degradation varies from
12
material to material. Almost all bioresorbable ceramics except Biocoral and Plaster of
Paris (calcium sulfate dihydrate) are variations of calcium phosphate. Examples of
resorbable ceramics are aluminum calcium phosphate, coralline, Plaster of Paris,
hydroxyapatite, and tricalcium phosphate.
Examples of Biodegradable Bioceramics:
i.
Glass Fibers and their composites.
ii.
Corals.
iii.
Calcium Sulfates, including Plaster of Paris
iv.
Zinc-Calcium-Phosphorous Oxides.
v.
Hydroxyapatites.
vi.
Tricalcium Phosphate.
vii.
Ferric Calcium Phosphorous Oxides
viii.
Aluminum-Calcium-Phosphorous Oxides.
2.1.1.3. Bioactive or Surface-Reactive Ceramics
Upon implantation in the host, surface reactive ceramics form strong bonds
with adjacent tissue. Examples of surface reactive ceramics are dense nonporous
glasses, Bioglass and Ceravital, and hydroxyapatites (Table 3.5). One of their many
uses is the coating of metal prostheses. This coating provides a stronger bonding to
the adjacent tissues, which is very important for protheses. A list of the uses of
surface-reactive ceramics is shown in (Table 3.5).
Examples of Surface Reactive Bioceramics:
i.
For coating of metal prostheses
ii.
In reconstruction of dental defects.
iii.
For filling space vacated by bone screws, donor bone
13
iv.
As bone plates and screws
v.
As replacements of middle ear ossicles.
vi.
In replacing subperiosteal teeth.
vii.
For correcting periodontal defects.
viii. For lengthening of rami.
2.1.1.4. Bio ceramics calcium phosphate base
The concept of using synthetic resorbable ceramics as bone substitutes was
introduced in 1969 [Hentrich et al., 1969] , [Graveset al., 1972].
Resorbable ceramics , as the name implies, degrade upon implantation in the
host. The resorbed material is replaced by endogenous tissues. The rate of
degradation varies from material to material. Almost all bioresorbable ceramics
except Biocoral and Plaster of Paris (calcium sulfate dihydrate) are variations of
calcium phosphate.
Calcium phosphate has been used in the form of artificial bone. This material
has been synthesized and used for manufacturing various forms of implants, as well
as for solid or porous coatings on other implants. Calcium phosphate can be
crystallized into salts such as hydroxyapatite and β-whitlockite depending on the
Ca:P ratio, presence of water, impurities, and temperature. In a wet environment and
at lower temperatures (<900°C), it is more likely that hydroxyl- or hydroxyapatite
will form, while in a dry atmosphere and at a higher temperature, β-whitlockite will
be formed [Park and Lakes 1992]. Both forms are very tissue compatible and are
used as bone substitutes in a granular form or a solid block. The apatite form of
calcium phosphate is considered to be closely related to the mineral phase of bone
and teeth.
The mineral part of bone and teeth is made of a crystalline form of calcium
phosphate similar to hydroxyapatite [Ca10 (PO4)6(OH)2]. The apatite family of
mineral [A10 (BO4)6X2] crystallizes into hexagonal rhombic prisms and has unit cell
dimensions
α=
9.432
Å
and
c=
6.881
Å.
The
atomic
structure
of
14
. Note that the hydroxyl ions lie on the corners of the projected basal plane and they
occur at equidistant intervals (3.44 Å) along the columns perpendicular to the basal
plane and parallel to the c-axis. Six of the ten calcium ions in the unit cell are
associated with the hydroxyls in these columns, resulting in strong interactions
among them [Park and Lakes, 1992].
Figure 2.1: Hydroxyapatite structure projected down the c-axis onto the basal
plane.
2.2. Hydroxyapatite
Hydroxylapatite, also called hydroxyapatite, is a mineral. It is a naturally
occurring form of calcium apatite with the formula Ca5 (PO4)3(OH), but is usually
written Ca10 (PO4)6(OH)2 to denote that the crystal unit cell comprises two molecules.
Hydroxylapatite is the hydroxyl endmember of the complex apatite group. The OHion can be replaced by fluoride, chloride or carbonate. It crystallizes in the hexagonal
crystal system. It has a specific gravity of 3.08 and is 5 on the Mohs hardness scale.
Pure hydroxylapatite powder is white. Naturally occurring apatites can however also
have brown, yellow or green colorations.
70% of bone is made up of the inorganic mineral hydroxylapatite.
Carbonated-calcium deficient hydroxylapatite is the main mineral of which dental
enamel and dentin are comprised. Hydroxyapatite crystals are also found in the small
15
calcifications (within the pineal gland and other structures) known as corpora
arenacea or 'brain sand'.
2.2.1. Identification:
Molecular Weight: 502.31 gm
Color: Colorless, White, Gray, Yellow, Yellowish green
Crystal habit: Massive to crystalline, major bone forming mineral
Crystal system: Hexagonal - Dipyramidal
Cleavage: Indistinct
Mohs scale hardness: 5
Luster: Vitreous to dull
Refractive index: nω = 1.651 nε = 1.644
Optical Properties: Uniaxial (-)
Birefringence: δ = 0.007
Streak: White
Specific gravity: 3.08
Density: 3.156 g/cm^3
Diaphaneity: Transparent to Opaque
2.2.2. Advantages of Hydroxyapatite
The beneficial biocompatible properties of hydroxyapatite are well
documented. It is rapidly integrated into the human body, while at the same time the
body is none the wiser as to the invasion by a foreign body, albeit a friendly invasion.
Perhaps it’s most interesting property is that hydroxyapatite will bond to bone
forming indistinguishable unions.
16
2.2.3. Disadvantages of Hydroxyapatite
However, poor mechanical properties (in particular fatigue properties) mean
that hydroxyapatite cannot be used in bulk form for load bearing applications such as
orthopaedics.
2.2.4. Hydroxyapatite Coatings
Coatings of hydroxyapatite have good potential as they can exploit the
biocompatible and bone bonding properties of the ceramic, while utilizing the
mechanical properties of substrates such as Ti6Al4V and other biocompatible alloys.
While the metallic materials have the required mechanical properties, they benefit
from the hydroxyapatite which provides an osteophilic surface for bone to bond to,
anchoring the implant and transferring load to the skeleton, helping to combat bone
atrophy.
2.2.4.1. Coating Techniques:
There are several methods for coating of HAp in the table 2.1 some of them
was shown:
Table 2.1: Coating techniques of Hydroxyapatite
Technique
Thickness Advantages
Disadvantages
Dip Coating
0.05-
Inexpensive
Requires
0.5mm
Coatings
Thermal
coat
sintering
applied temperatures
quickly
Can
high
expansion
complex mismatch
substrates
Sputter
Coating
0.02-1µm
Uniform
thickness
substrates
coating Line of sight technique
on
flat Expensive Time consuming
Cannot coat complex
substrates Produces coating
17
Technique
Hot
Thickness Advantages
Pressing 0.2-
and
Disadvantages
Produces dense coatings
Hot 2.0mm
HP cannot coat complex
substrates
Isostatic
High temperature required
Pressing
Thermal
expansion
mismatch
Elastic property differences
Expensive
Removal/Interaction
of
encapsulation material
Electrophoretic 0.1-
Uniform
Deposition
thickness
free coatings
Rapid deposition rates
Requires
2.0mm
Can
coat
coating Difficult to produce crack-
high
sintering
complex temperatures
substrates
Thermal
30-200µm High deposition rates
Spraying
Line of sight technique
High temperatures induce
decomposition
Rapid
cooling
produces
amorphous coatings
Sol-Gel
<1µm
Can
coat
complex Some
processes
shapes Low processing controlled
require
atmosphere
temperatures Relatively processing
cheap as coatings are Expensive raw materials
very thin
18
2.3. Related Works on usage of hydroxyapatite:
2.3.1. Bioactive coatings on 316L stainless steel implants:
Bioactive hydroxyapatite has a substantial interest because of its chemical
similarity to the calcium phosphate minerals in biological hard tissue, and its ability
to form a strong chemical bond with bone1. But the fracture toughness of the
hydroxyapatite ceramics does not exceed the value of about 1 MPa.m1/2. Therefore,
the hydroxyapatite ceramic materials cannot be used as heavy-loaded implants, such
as artificial bone or teeth.
Metallic implants (316L stainless steel, titanium, Ti-6Al-4V, etc.) are having
high strength and fracture toughness, but their bonding ability to bone tissue is very
low. In order to obtain bioactive and strong materials, the formation of hydroxyaptite
on an implant with good mechanical properties is considered a good approach.
Biphasic calcium phosphate coating is preferred when implant resorbability is
desired.
Coatings of hydroxyapatite on metallic implants have been prepared by a
variety of techniques, including plasma spraying, sol-gel, r.f sputtering, detonation
gun coating, high velocity oxy-fuel coating, electrophoretic deposition, laser ablation,
hydrothermal and biomimetic methods. At present, plasma spraying is the most
commonly used method for preparation of the hydroxyapatite coatings. However,
plasma-spraying method suffers with hydroxyapatite phase stability, lack of
crystallanity and poor adhesion to the substrate. The electrophoretic methods have
problems with poor adhesion and formation of other phases. The r.f sputtering suffers
with amorphous nature of the coating material. This paper describes a simple dipcoating method, which produces a thin and adherent HA and BCP coatings on 316L
stainless steel. Therefore for conclusion:
19
a) Dip coating is a simple method to produce hydroxyapatite or biphasic
calcium phosphate coating on stainless steel substrates.
b) The dense, fracture free coating can improve adhesion with the substrate
and also acts as barrier layer between implant surface and body fluids.
c) By dip-coating method, it’s possible to obtain a very thin coating of
thickness 5-10 (m for both hydroxyapatite and biphasic calcium phosphate coatings
on 316L stainless steel.
2.3.2. Hydroxyapatite coating on a cobalt base alloy by investment casting:
A cobalt alloy was cast into preheated molds previously coated with
hydroxyapatite powder. Two molds were used, one made of investment material and
the other of pure graphite. Selected samples were heat treated. Both heat and non heat
treated samples were immersed in simulated body fluid for 21 days at 37 _C. A
ceramic layer, identified as hydroxyapatite, was formed on all the samples. A thicker
layer was formed on the sample cast into the investment mold without heat treatment.
A chemical interaction between the investment mold and hydroxyapatite takes place
leading to a higher in vitro bioactivity.A cobalt base alloy was cast into a mold in
which the cavities were coated with hydroxyapatite powder. Bioactive ceramic
particles were embedded on the surface of the alloy. A dense and homogeneous
bonelike apatite layer was formed on the as cast cobalt alloy surface after 21 days of
immersion in SBF. A decrease in bioactivity was observed in the heat treated samples
due to the decomposition of HA.
20
Table4.1: Summarized related works on HAp coatings
Authors Name
Title & Methods
Conclusions
1- J.C. Escobedo , J.C. Hydroxyapatite coating on
A
decrease
in
Ortiz, J.M. Almanza, D.A. a cobalt base alloy by bioactivity was observed in
Corte´s, Scripta Materialia investment casting
the heat treated samples
vol.54 (2006)
due to the decomposition
of HAp.
2- TuantuanliI, Junhee Lee Hydroxyapatite coating by The dipping method is an
,Takayuki Kobayashi,
dipping method, and bone effective
Hideki Aoki Journal of
bonding strength
technique
for
preparing
HA
coated
material science, Materilas
titanium
materials
in Medicine, 7 (1996) 355
complicated shapes. The
357
material
had
with
good
biocompatibility and may
be effective for use as
prostheses.
3- A. De Carlos et. al. J
In
vitro
testing
of The
calcium
phosphate
Mater Science: Mater Med Nd:YAG laser processed coatings obtained by the
17:1153–1160 (2006)
calcium
coatings
phosphate Nd:YAG laser cladding
technique
showed
a
behaviour similar to the
reference
materials,
Ti-
6Al-4V alloy and CaP
coatings
produced
by
plasma spray, respective to
cell
morphology(SEM
observations),cell
proliferation (Alamar Blue
assay) and cytotoxicity of
extracts (MTT assay).
21
Authors Name
Title & Methods
Conclusions
4- Bunyamin Aksakal C. Bioceramic dip-coating on Cheap,
Hanyaloglu,Sci:
easy,
repeatable
Mater Ti–6Al–4V and 316L SS with high production rate
Med 2007
implant materials
of bioceramic coatings of
the Ti6Al4V and 316L SS
implant
materials
achieved
by
are
using
a
dipping method
5-
D.A.
Cortes,
A.A. Biomimetic apatite
Results indicate that the
Nogiwa , J.M. Almanza , coating onMg-PSZ/Al2O3
biomimetically treated
S.
zirconia composites, by
Ortega.
Materials composites. Effect of the
Letters 59 1352– 1355 immersion method
using the re-immersion
(2005)
method, show a high
in vitro bioactivity and
may exhibit a bonebonding ability through the
apatite layer.
6- H.H. Rodrı´guez H.H.
Electrophoretic deposition
The apatite formed on the
Rodrı´guez, G. Vargas,
of bioactive wollastonite
porcelain coating after the
D.A. Corte´s. Ceramics
and porcelain–
dissolution
International (2007)
wollastonite coatings on
wollastonite layer, seemed
316L stainless steel
to be strongly attached.
of
the
The heat treatment of the
samples
after
electrophoretic deposition
has a positive effect on the
bioactivity,
since
no
apatite was formed on the
non-sintered
wollastonite
coated samples.
22
Authors Name
8-
Jie
Weng
Biomoterials
(1997)
et.
Title & Methods
al. Formation and
vol.18 characteristics of the
Conclusions
The HA structure of the
heated
coating
apatite layer on plasma-
critical
for
sprayed hydroxyapatite
nucleate in SBF without
coatings in simulated
sufficient dissolution of the
body fluid
coating to increase the
local
apatite
supersaturation
calcium
ions.
is
and
not
to
of
phosphate
CHAPTER 3
METHODOLOGY AND EXPERIMENTAL PROCEDURE:
3.1. Introduction:
In this project the quality of adhesion of Hydroxyapatite on the investment
casting mould was investigated. Viscosity of HAp-water mixture, dewaxing
temperature and firing temperature had the main effect on the quality of adhesion of
HAp on to the inner layer of investment casting mould. so investigation through
different viscosities , dewaxing and firing temperature and finding the differentiation
of them was the main objective, to find out the best HAp-water mixture , dewaxing
temperature and firing temperature for this purpose.
The project will be conducted within the below boundaries:
i. 3different hydroxyapatite slurry viscosities (3 different viscosities)
ii. 3different dewaxing temperature (3 different temperatures)
iii. Shell investment casting mould with 5 layers thickness will be employed.
For this purpose at first it needed to design appropriate parts and belongings
of them to do sound casting and obtain correct results.
24
3.2 Methodology and Experiment
i. Preparing the raw materials and equipments which are needed for investment
casting and testing the prepared specimen, for this reason enough raw materials was
prepared, the materials were:
a. Hydroxyapatite as a main material that was used for coating on to the
investment casting mould.
b. Hyfill wax was used as the material of the pattern for investment casting.
c. Aluminum rod that was used for making appropriate mould for making wax
patterns.
d. Zircon powder as the base material of investment casting mould
e. Stucco in 2 different sizes fine () and coarse.
f. Mineral water as a solvent for HAp.
g. Cooking oil
And necessary equipments for the experiment were:
a. Mixer machine
b. appropriate containers
c. Ordinary lathe machines for manufacturing the Aluminum mould for
making patterns.
d. Drill machine
e. Firing furnace (that is used for both firing and dewaxing process) it should
heat up to 1000 C.
ii. After preparing needed equipments and materials designing the experiment is the
significant point for doing the project. The experimental process was started from
designing an appropriate mould for manufacturing of the wax patterns. Then its go
through coating the patterns with HAp-water mixture, ceramic mould making and
dewaxing, finally chosen moulds were fired in the furnace for 1 hour in 600 C to
increase the strength of the mould and supervise the effect of the heat on the coated
25
HAp layer. For obtaining the results 3 kinds of test were applied. XRD EDAX
3Dmicroscope. The whole process of the project was shown in a flowchart in figure
3.1.
START
Checking Requirements
Preparing mould for making patterns
Making Wax Patterns
Coating patterns with HAp
Making Ceramic Mould
Dewaxing the moulds
100 C
200 C
300 C
Choosing the best Dewaxed
300 C
Fire the moulds up to 600 C
Doing the tests
XRD
EDAX
Supervise
Figure 3.1: Flowchart of the process
3Dmicroscop
END
26
Defined objectives of the project were to investigate what is the best
dewaxing temperature for dewaxing the moulds and also find out which of the HApwater mixture viscosities would be the best one for coating the inner layer of the
moulds.
3.2.1 Design:
3.2.1.1 Pattern Design:
At the first stage of experiment the shape of the pattern for the mould
designed. Regarding to the limitations of the project which were
i.
High price of HAP
ii. Previous experiment
iii. Desired characteristics
iv. Equipment availability
v. Simplifying the experiment
vi. Number of required samples for different testes, etc
The patterns consist of a pouring cup and three cylindrical samples were
designed. Dimensions and general view of the pattern is shown in figure3.2 for
making this pattern from the wax Aluminum mould was designed. This mould has
ability to make three wax samples and a pouring cup. According to high price of
HAp and objective of the project the size of the samples were minimized Regarding
to the even condition of the coating the samples were designed in cylindrical shape.
For increasing the number of samples, easier casting and to overcome the defects that
may occur during the solidification process the pouring cup with stated dimensions
designed. This part provides the pouring cup for uniform molten metal flow in to the
samples as well.
27
In accordance with previous investment casting experiments and estimated
thickness of the ceramic mould which is based on the number of layers, the
arrangement of the samples and the distance between them were calculated. and was
shown in figure 3.2. Indeed, based on the shape of the patterns for investment
casting, it was required to prepare a mould for pattern fabrication.
17mm
20mm
15mm
Figure 3.2: Drawing of a sample
3.2.1.2 Design of Wax mould:
The design of considered mould was consisted of separation lines of different
part of the mould, tapering, and easy final releasing of the patterns from the mould.
The mould was designed in three parts for the purpose of even heat removal and good
surface finish. The mould for wax pattern production consisyed of three parts; the
Base which was met to produce a uniform surface finish of the wax pattern at the
bottom of the samples. Middle part that contains three desired cylindrical samples.
28
The upper part separated into two parts for easy remove of the patterns from the
mould. The drawings of each part are shown in figures 3.3-3.6.
Figure 3.3 Base part of pattern mould
29
Figure 3.4 Middle part of the pattern mould
Figure 3.5 Top part of the pattern mould
30
3.2.2 Mould Fabrication
Regarding to prepared drawings and available materials, Aluminum was
selected. Available materials for making the mould were aluminum and Stainless
steel. Regarding to the melting temperature of the wax as the base material of the
patterns, high thermal resistance of the mould material was not considerable.
Furthermore easy machining characteristics for rapid and accurate machining with
better final surface finish comparing to stainless steel were the key points for
selecting aluminum rather than stainless steel.
The raw material was an aluminum rod which was cut in 63mm diameter and
100mm height. This work piece was cut into three parts that each of them showed in
the drawings. For machining of this work piece a conventional lathe machine was
used. The machine tool was normal HSS regarding to the machining condition and
base material which was Aluminum.
During machining the surface finish and accuracy of the work piece was
supervised regarding to precision casting of the wax and easy releasing of samples
from the mould.
31
Middle part
Top part
Base part
Figure 3.6 Disassembled pattern mould
Figure3.7. Assembled mould for wax patter
3.2.3 Wax pattern manufacture
On the subject of the characteristics of the wax that was applied to make
investment casting mould, the melting temperature of the wax is around 100
32
centigrade degree. Therefore simple electric heater was a good option for melting the
wax. A simple container made from aluminum was used as a pot for the melting of
the wax. Solid clean pieces of wax were melted in the container by means of the
electric heater. The electric heater adjusted on the 250 centigrade degree.
For easy removal and releasing of the wax pattern form the mould, a good
lubricant was needed. For this purpose cooking oil would be a good selection,
because of its characteristics as a lubricant which is not toxic, and inflammable at the
wax melts temperature.
After coating inner parts of the mould with the cooking oil (Corn Oil), the
melted wax was poured into the mould to make the required pattern with the desired
shape. Also a hanging grip is put onto the top surface of the molten wax, so that when
it solidifies it is easy to hang the patterns. Hanging the samples is required for next
processes especially during coating process and ceramic mould making process steps.
Solidification of the wax inside the mould takes around 15 minutes time. For making
the solidification faster water was used as an extra cooler. Regarding to the mixing of
water and molten wax while using water as a coolant, it should be used carefully.
Therefore, the surface layer of the wax pattern which is in contact with the air should
be solidified first otherwise the water can penetrate into the wax and form a nonhomogeneous mixture. Then the mould can be put into the cold water container for
final and complete cooling process. A solidified wax pattern was shown in figure
After removing wax pattern from the mould, pattern was hanged from its
hanging part for further use and next levels.
33
Figure 3.8 Solid wax patterns inside the mould
Wax Pattern
Figure 3.9 Wax patterns hanged for drying
3.2.4. Ceramic mould fabrication:
This stage consists of several stages those are respectively:
34
i. Preparing the wax samples for coating of hydroxylapatite.
ii. Preparing 3 different Hydroxyl apatite viscosities for coating.
iii. Coating the wax samples with hydroxylapatite.
iv. Preparing the slurry for making the shells of investment casting mould.
v. Fabrication of Ceramic mould, stuccoing, and final sealing
3.2.4.1. Preparing Wax Samples:
In this step, wax samples were washed by a simple detergent to remove extent
oil remained from the surface of the samples in wax casting stage. Remaining of oil
on the surface of the samples will affect the stickiness of the first coating layer and
the quantity of hydroxylapatite that would be coated on the surface. For washing the
samples enough amount of detergent was mixed with water in an appropriate
container, and then samples were washed inside the container. Subsequently, enough
time should be taken until all the samples become completely dried.
3.2.4.2. Preparing Hydroxylapatite for coating
After preparing all the samples, sufficient amount of Hydroxylapatite mixed
with water. The mixing process is described as following:
As there was no information about the mixture ratio of Hydroxylapatite and
water to obtain the desired viscosity, a step by step method was chosen. In this
method the volume of water that was enough for soaking a sample or pattern into the
mixture of water and HA applied then step by step HA added to the water and the
mixture was stirred up continuously. Besides, the viscosity of the mixture was
measured concurrently until the desired viscosity was achieved. The desired
35
viscosities for this purpose were 5, 7.5 and 10 seconds as previously mentioned in the
scopes of the project. For measuring the viscosities a Zhan’s cup was used.
Obtaining the viscosities more than 10 seconds was not applicable because of
creamy characteristic of HA-water mixture. Regarding to this characteristic of HAwater mixture, using the mixing machines was not considered suitable as well.
Indeed, the mixture was stirred manually and by hand during the preparation of the
mixture to obtaining the desired viscosities.
For coating of HAp-water mixture on the samples, there were several
methods. However, in this project soaking in to the HAp-water mixture was applied.
Therefore samples were soaked into different viscosities for 30 seconds to make sure
enough HAp was adhered to the samples, and then all of them hanged for about 2
hours to be dried completely. In figure 3.10 mixing process of HAp and water was
shown in figure 3.10.
Figure 3.10 Mixing HAp and mineral water
36
3.2.4.3-Coating of samples
There are different ways to coat HAp on to the samples i.e. as it was
illustrated in literature review… applied paint brush to coat samples with HAp-water
mixture. As investment casting was applied in this project, the samples were dipped
into the mixture of water and HAp. In this case, soaking of samples into the Hp-water
mixtures was done. All the samples were divided to 3 groups each group contains 9
samples as it was shown in the table below.
Initially the samples were dipped into the mixture for 30 seconds and then
they were removed and hanged for about 2 hours to be almost dried. In case of any
defects or crakes the samples were dipped again to make sure that the coating is
sound. Based on the preliminary experiments it was concluded that complete dryness
of Hap coating layer will result in some defects which is mostly crakes. These crakes
can affect the thickness and quality of Hap coating layer which is not good for the
purpose of this process and experiment. Therefore incomplete dryness is appropriate
method to overcome this problem and prepare the samples for slurry coating. In
figure 3.11 measuring the viscosity of HAp-water mixture was shown.
37
Figure 3.11 Measuring the viscosity of HAp-Water mixture
3.2.4.4. Slurry preparation
To prepare the investment casting slurry in this project Zircon powder and
Colloidal Silica were mixed together with specific viscosities (20,25 and at last
coating 20 again). At first Colloidal Silica was poured in to the container and Zircon
powder was mixed gradually while the mixture was continuously stirred by a mixer
to make homogenous slurry and even properties in the whole slurry. Figure 3.12 was
shown the mixing process.
The appropriate viscosity was achieved after several tests. The measurement
tool was a standard Zhan’s cup with a 5 millimeter hole. To measure the viscosity the
cup was filed up of the slurry and the time for pour out of slurry was measured by a
chronometer.
38
Figure 3.12 Preparing ceramic slurry from colloidal silica and zircon powder.
39
3.2.4.5. Investment casting mould making
The mould was built with 7 layers. For the first layer and sealing layer (last
layer) higher viscosity was selected. Desired viscosity was 25 seconds. Higher
viscose slurry will take less time to become dry and have higher stickiness due to less
flow ability. Therefore it provides better overall quality and sufficient thickness for
the first layer and last layer.
For the back up coats layers the viscosity of 20 seconds was selected. It will
provide enough stickiness for stucco particles and sufficient thickness as a layer of
the mould as well.
They were 5 back up coats slurry layers which all were completely covered
with the stucco. They were two available stucco sizes; fine and coarse. Based on the
initial experiments the combination of fine and coarse was selected. After the first
layer the fine stucco size was applied to cover the first middle slurry layer and
followed by coarse stucco size for the second layer. This sequence was employed for
all 5 middle layers which mean that first, third and fifth middle layers were covered
with fine stucco while second and fourth middle layers were covered with coarse
stucco. This mixture provided two important properties which are good strength and
good permeability that are resulted from fine and coarse stucco respectively.
Indeed there were seven layers with the following order: HAp coat, slurry,
five layers back up coats, and final sealing coat. The making of the investment
casting mould used for the investigation was shown in figures 3.13 to 3.16.
40
Figure 3.13: Coating wax samples with ceramic slurry
Figure 3.14: Coated wax pattern with slurry
41
Figure 3.15: Moulds after stuccoing
Figure 3.16: Moulds after final coating
42
3.2.5. Effect of dewaxing temperature:
3.2.5.1. Introduction
Three dewaxing temperatures were chosen 100 C, 200 C and 300 C to
determine it’s effect on HAp coatings.
Dewaxing was conducted in an electric resistance furnace prior to dewaxing
seven holes were drilled on the wax at the pouring cup Figure3.17.
Prior to insert the moulds into the furnace; the furnace was heated to the
required temperature, once the temperature needed, the moulds were placed in the
arrangement shown in figure 3.18. the moulds were removed from the furnace after 1
hour. The procedure was repeated for the temperatures of 200 and 300 C
Considering the scope of the project three dewaxing temperatures were tested.
Generally the dewaxing temperature for investment casting is between 100 to 300
degrees centigrade. Selected temperatures were 100,200 and 300 degrees centigrade
to find out the appropriate dewaxing temperature for the process.
3.2.5.2. Dewaxing
Dewaxing process was done in resistance furnace with the following
specifications. Figures:
The moulds were put upside down in the furnace for one hour to melt the wax
and for wax removal from the moulds. Regarding to initial test moulds the expansion
of the wax during dewaxing process leaded to mould cracks, to prevent this defect
there are several solutions, in this project a new method was applied to overcome the
problem. New method was reducing the amount of the wax inside the mould. For this
purpose the wax was removed from the open head of the mould by drilling. As it was
shown in figures5.12, 6 or 7 holes were drilled in the pouring cup of the mould with
the appropriate depth. Depths of the holes were around 1.5 cm to assure that they
43
will not reach the mould’s body. The moulds were not heated up from environment
temperature to the dewaxing temperature. Therefore the furnace turned on and heated
up to desired temperature and then the moulds were put in the furnace for one hour to
remove the wax.
Figure 3.17 Making holes inside the wax
Figure 3.18 Moulds inside the furnace
44
3.2.6 Firing process:
Dewaxed moulds must be fired for several purposes. The most important
objectives of firing process specifically for this project include complete removal of
remain wax in the moulds and increasing the strength of the moulds by sintering the
layers.
Firing process was carried out with the same furnace that had been used for
dewaxing process. In addition, the process was also similar to the dewaxing process
which means that the furnace was heated up to the selected firing temperature and the
moulds were put in the furnace for one hour to perform the firing process.
Regarding to defined scope and objectives of this project three different firing
temperatures were selected. In addition this selection was regarding to the properties
and characteristics of applied bio active material (Hydroxyl apatite). The structural
phase of this material changes according to specific temperature range.The starting
temperature for phase modification is 800 degree centigrade. Hydroxyl apatite is
thermally unstable compound, decomposing at temperature from about 800 to 1200
degree centigrade depending on its stoichiometry. Based on this fact and the
conditions of this research three different firing temperatures were selected including
600, 800 and 1000 degree centigrade. These temperatures were selected to study the
effect of different temperatures below the range, above the range and exactly at the
border of the range. Therefore the behavior of the Hydroxyl apatite with different
firing temperature can be studied.but for the purpose of understanding which
viscosity and dewaxing temperature is the best selection for moulds only 600 degree
centigrade was applied.
3.2.7. Tests
The final part of the project includes test results and discussions about them to
evaluate the achieved results of the experiments. These results will clarify the best
45
combination of experimental factors for better and effective casting results that
depends on the factors that are needed for production of medical implants in future.
The experimental tests consist of XRD (X Ray Diffraction), EDAX (Energydispersive X-ray spectroscopy), SEM (Scanning Electron Microscope), 3D
microscope imaging.
XRD: X-ray scattering techniques are a family of non-destructive analytical
techniques which reveal information about the crystallographic structure, chemical
composition, and physical properties of materials and thin films. These techniques
are based on observing the scattered intensity of an x-ray beam hitting a sample as a
function of incident and scattered angle, polarization, and wavelength or energy.
EDAX: Energy dispersive X-ray spectroscopy (EDS, EDX or EDXRF) is an
analytical technique used for the elemental analysis or chemical characterization of a
sample. As a type of spectroscopy, it relies on the investigation of a sample through
interactions between electromagnetic radiation and matter, analyzing x-rays emitted
by the matter in response to being hit with the electromagnetic radiation. Its
characterization capabilities are due in large part to the fundamental principle that
each element has a unique atomic structure allowing x-rays that are characteristic of
an element's atomic structure to be indentified uniquely from each other.
To stimulate the emission of characteristic x-rays from a specimen, a high
energy beam of charged particles such as electrons or protons, or a beam of x-rays, is
focused into the sample being studied. At rest, an atom within the sample contains
ground state (or unexcited) electrons in discrete energy levels or electron shells
bound to the nucleus. The incident beam may excite an electron in an inner shell,
ejecting it from the shell while creating an electron hole where the electron was. An
electron from an outer, higher-energy shell then fills the hole, and the difference in
energy between the higher-energy shell and the lower energy shell is released in the
form of an x-ray. The x-ray released by the electron is then detected and analyzed by
46
the energy dispersive spectrometer. These x-rays are characteristic of the difference
in energy between the two shells, and of the atomic structure of the element form
which they were emitted.
For performing XRD, EDAX and 3Dmicroscope tests, moulds were broken
carefully (Figure 3.19) to prepare required samples for each test. For XRD test the
required amount of powder were scratched from the adhered HAp of the mould wall
(Figure 3.20).
In addition for EDAX and SEM tests a small part of the mould with HAp on
the wall was selected. This selection was because of the required size for EDAX and
SEM machine. Sizing for EDAX and SEM samples were done by technicians of the
machines at UTHM, Batu Pahat.
For 3D microscope the down part of the mould were taken which had vertical
walls of the mould with HAp on it this was selected for better showing of adhesion of
the HAp to the moulds wall.(Figure 3.19)
47
Figure 3.19 Broken parts of the samples for tests.
Figure 3.20 Prepared powder for XRD test
CHAPTER4
RESULT AND DISCCUSION
As mentioned above four kinds of tests had been performed to analyze the
samples and verify the results with available standards. The results were categorized
based on the tests that were carried out. At first XRD results are presented and
discussed to confirm the existence of suitable chemical compositions in the produced
samples. Next EDAX results had been issued to verify the existence of necessary
elements and confirm the desired ratio of required elements. Moreover SEM results
were presented to show the micro structure of the adhered HAp on the inner surface
of the mould. Finally 3D microscope images had been taken to show the thickness
and stickiness of HAp to the mould.
4.1. XRD Result
To specify a reference and understanding the initial available components in
the considered base materials XRD test was performed on all three kinds of the
materials. Provided materials for this project were from three different suppliers that
are Fluka, Granumas, Plasma Tech Co. Figures 4.1 to 4.3 show the XRD results of
Fluka, Granumas, Plasma Tech Co. respectively.
18000
17000
16000
15000
14000
13000
12000
11000
Lin (Counts)
Figure 4.1 XRD result for Fluka
Fluka
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
4
10
20
30
40
50
60
2-Theta - Scale
Fluka - File: Fluka.raw - Type: 2Th/Th locked - Start: 3.000 ° - End: 129.999 ° - Step: 0.020 ° - Step time: 15.5 s - Temp.: 25 °C (Room) - Time Started: 10 s - 2-Theta: 3.000 ° - Theta: 1.500 ° - Chi: 0.00 ° - Ph
Operations: Background 1.000,1.000 | Import
00-024-0033 (D) - Hydroxylapatite - Ca5(PO4)3(OH) - Y: 8.37 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.43200 - b 9.43200 - c 6.88100 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (1
00-055-0592 (*) - Hydroxylapatite, syn - (Ca)10(PO4)6(OH)2 - Y: 22.36 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41890 - b 9.41890 - c 6.88270 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive 00-009-0432 (I) - Hydroxylapatite, syn - Ca5(PO4)3(OH) - Y: 7.20 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41800 - b 9.41800 - c 6.88400 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/
00-003-0747 (D) - Hydroxylapatite - Ca10(PO4)6(OH)2 - Y: 5.50 % - d x by: 1. - WL: 1.5406 00-001-1008 (D) - Hydroxyapatite - Ca10(OH)2(PO4)6 - Y: 7.89 % - d x by: 1. - WL: 1.5406 -
49
18000
17000
16000
15000
14000
13000
12000
11000
Lin (Counts)
Figure 4.2 XRD result granumas
Granumas
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
3
10
20
30
40
50
60
2-Theta - Scale
Granumas - File: Granumas.raw - Type: 2Th/Th locked - Start: 3.000 ° - End: 69.990 ° - Step: 0.020 ° - Step time: 15.5 s - Temp.: 25 °C (Room) - Time Started: 10 s - 2-Theta: 3.000 ° - Theta: 1.500 ° - Chi: 0.00 ° - Phi
Operations: Background 1.000,1.000 | Import
00-024-0033 (D) - Hydroxylapatite - Ca5(PO4)3(OH) - Y: 15.63 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.43200 - b 9.43200 - c 6.88100 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (176) - 2 00-009-0432 (I) - Hydroxylapatite, syn - Ca5(PO4)3(OH) - Y: 14.33 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41800 - b 9.41800 - c 6.88400 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (176)
00-055-0592 (*) - Hydroxylapatite, syn - (Ca)10(PO4)6(OH)2 - Y: 42.83 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41890 - b 9.41890 - c 6.88270 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (
00-003-0747 (D) - Hydroxylapatite - Ca10(PO4)6(OH)2 - Y: 8.52 % - d x by: 1. - WL: 1.5406 00-001-1008 (D) - Hydroxyapatite - Ca10(OH)2(PO4)6 - Y: 10.19 % - d x by: 1. - WL: 1.5406 -
50
18000
17000
16000
15000
14000
13000
12000
11000
Lin (Counts)
Figure 4.3 XRD result Iran
Iran
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
4
10
20
30
40
50
60
2-Theta - Scale
Iran - File: iran.raw - Type: 2Th/Th locked - Start: 3.000 ° - End: 69.990 ° - Step: 0.020 ° - Step time: 15.5 s - Temp.: 25 °C (Room) - Time Started: 10 s - 2-Theta: 3.000 ° - Theta: 1.500 ° - Chi: 0.00 ° - Phi: 0.00 ° - X: 0
Operations: Background 1.000,1.000 | Import
00-024-0033 (D) - Hydroxylapatite - Ca5(PO4)3(OH) - Y: 0.73 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.43200 - b 9.43200 - c 6.88100 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (176) - 2 00-009-0432 (I) - Hydroxylapatite, syn - Ca5(PO4)3(OH) - Y: 0.62 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41800 - b 9.41800 - c 6.88400 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (176) 00-055-0592 (*) - Hydroxylapatite, syn - (Ca)10(PO4)6(OH)2 - Y: 1.51 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41890 - b 9.41890 - c 6.88270 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (1
51
52
A brief summary of XRD results for base materials and available chemical
compositions in these materials are listed in Table4.1
Table4.1: XRD Test Results – Reference Materials
XRD Test Results – Reference Materials
Material
Hydroxlyapatite
[Ca5(PO4)3(OH)]
Hydroxlyapatite,syn
[Ca10(PO4)6(OH)2]
Hydroxlyapatite,syn
[Ca5(PO4)3(OH)]
Hydroxlyapatite
[Ca10(PO4)6(OH)2]
Hydroxyapatite
[Ca10(OH)2(PO4)6]
Material
Code
Fluka
Granumas
Plasma
Tech Co.
0033
1550
2900
250
0592
4050
7600
350
0432
1400
2550
200
0747
650
1600
-
1008
1450
1850
-
Regarding to exsiccating limitations that include availability, price, and
appropriate chemical composition the HAp provided by Fluka was selected. It can be
seen from the table that HAp from Fluka and Granumas offered required chemical
compositions better than Plasma Tech and indeed Plasma Tech was rejected (Figure
204). On the other hand, with considering the price of available materials it was
concluded to apply Fluka instead of Granumas.
53
XRD Results - Reference Materials
8000
7000
6000
Lin (Counts)
5000
Hydroxlyapatite - [Ca5(PO4)3(OH)]
Hydroxlyapatite, syn - [Ca10(PO4)6(OH)2]
Hydroxlyapatite, syn - [Ca5(PO4)3(OH)]
Hydroxlyapatite - [Ca10(PO4)6(OH)2]
Hydroxyapatite - [Ca10(OH)2(PO4)6]
4000
3000
2000
1000
0
Fluka
Granumas
Plasma Tech Co.
Company
Figure 4.4 XRD result for reference materials
XRD test was also performed for three moulds that were fired in 600 C
temperature to figure out the remaining chemical compositions of the materials. It
will illustrate effect of firing temperature and viscosities result in higher amount of
necessary component for medical use and next steps. In this project availability and
quality of adhered HAp is the main objective. Therefore this illustration can clarify
the best procedure for producing moulds.
Actual XRD test results for all nine samples were shown in figures 4.5-4.7
18000
17000
16000
15000
14000
13000
12000
11000
Lin (Counts)
Figure 4.5 Result of XRD for 5 s viscosity and 600 C
5S600C
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
4
10
20
30
40
50
60
2-Theta - Scale
5S600C - File: 5S600C.raw - Type: 2Th/Th locked - Start: 3.000 ° - End: 69.990 ° - Step: 0.020 ° - Step time: 15.5 s - Temp.: 25 °C (Room) - Time Started: 11 s - 2-Theta: 3.000 ° - Theta: 1.500 ° - Chi: 0.00 ° - Phi: 0.0
Operations: Background 1.000,1.000 | Import
00-024-0033 (D) - Hydroxylapatite - Ca5(PO4)3(OH) - Y: 8.31 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.43200 - b 9.43200 - c 6.88100 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (176) - 2 00-055-0592 (*) - Hydroxylapatite, syn - (Ca)10(PO4)6(OH)2 - Y: 19.30 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41890 - b 9.41890 - c 6.88270 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (
00-009-0432 (I) - Hydroxylapatite, syn - Ca5(PO4)3(OH) - Y: 7.20 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41800 - b 9.41800 - c 6.88400 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (176) 00-003-0747 (D) - Hydroxylapatite - Ca10(PO4)6(OH)2 - Y: 6.05 % - d x by: 1. - WL: 1.5406 00-001-1008 (D) - Hydroxyapatite - Ca10(OH)2(PO4)6 - Y: 7.26 % - d x by: 1. - WL: 1.5406 -
54
18000
17000
16000
15000
14000
13000
12000
11000
Lin (Counts)
Figure 4.6 result of XRD for 7.5 s viscosity and 600 C
7.5S600C
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
3
10
20
30
40
50
60
2-Theta - Scale
7.5S600C - File: 7.5S600C.raw - Type: 2Th/Th locked - Start: 3.000 ° - End: 69.990 ° - Step: 0.020 ° - Step time: 15.5 s - Temp.: 25 °C (Room) - Time Started: 10 s - 2-Theta: 3.000 ° - Theta: 1.500 ° - Chi: 0.00 ° - Phi:
Operations: Background 1.000,1.000 | Import
00-024-0033 (D) - Hydroxylapatite - Ca5(PO4)3(OH) - Y: 5.20 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.43200 - b 9.43200 - c 6.88100 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (176) - 2 00-055-0592 (*) - Hydroxylapatite, syn - (Ca)10(PO4)6(OH)2 - Y: 13.37 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41890 - b 9.41890 - c 6.88270 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (
00-009-0432 (I) - Hydroxylapatite, syn - Ca5(PO4)3(OH) - Y: 5.52 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41800 - b 9.41800 - c 6.88400 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (176) 00-003-0747 (D) - Hydroxylapatite - Ca10(PO4)6(OH)2 - Y: 4.88 % - d x by: 1. - WL: 1.5406 00-001-1008 (D) - Hydroxyapatite - Ca10(OH)2(PO4)6 - Y: 8.23 % - d x by: 1. - WL: 1.5406 -
55
18000
17000
16000
15000
14000
13000
12000
11000
Lin (Counts)
Figure 4.7 Result of XRD for 10 s viscosity and 600 C
10S600C
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
4
10
20
30
40
50
60
2-Theta - Scale
10S600C - File: 10S600C.raw - Type: 2Th/Th locked - Start: 3.000 ° - End: 69.990 ° - Step: 0.020 ° - Step time: 15.5 s - Temp.: 25 °C (Room) - Time Started: 10 s - 2-Theta: 3.000 ° - Theta: 1.500 ° - Chi: 0.00 ° - Phi:
Operations: Background 1.000,1.000 | Import
00-055-0592 (*) - Hydroxylapatite, syn - (Ca)10(PO4)6(OH)2 - Y: 20.93 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41890 - b 9.41890 - c 6.88270 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (
00-024-0033 (D) - Hydroxylapatite - Ca5(PO4)3(OH) - Y: 7.10 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.43200 - b 9.43200 - c 6.88100 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (176) - 2 00-009-0432 (I) - Hydroxylapatite, syn - Ca5(PO4)3(OH) - Y: 6.44 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 9.41800 - b 9.41800 - c 6.88400 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P63/m (176) 00-003-0747 (D) - Hydroxylapatite - Ca10(PO4)6(OH)2 - Y: 6.10 % - d x by: 1. - WL: 1.5406 00-001-1008 (D) - Hydroxyapatite - Ca10(OH)2(PO4)6 - Y: 8.33 % - d x by: 1. - WL: 1.5406 -
56
57
In table 6.2 the results were summarized for better comparison. To separate
the results for each viscosity, the results of XRD test for each viscosity 600 C firing
temperature are shown in Figures 214-219.
Table 4.2: XRD results for different viscosities
Dewaxing
300
Temperature (°C)
Viscosity (s)
5
7.5
10
600
600
600
0033
1500
1000
1400
0592
3500
2450
3750
0432
1350
1050
1250
0747
1100
600
1200
1008
1400
1500
1500
Firing
Temperature (°C)
Material
Hydroxlyapatite
[Ca5(PO4)3(OH)]
Hydroxlyapatite,syn
[Ca10(PO4)6(OH)2]
Hydroxlyapatite,syn
[Ca5(PO4)3(OH)]
Hydroxlyapatite
[Ca10(PO4)6(OH)2]
Hydroxyapatite
[Ca10(OH)2(PO4)6]
Material Code
Figures 4.8, 4.9 and 4.10show the intensities of desired chemical
compositions of three different viscosities of HAp slurry. It can be realized that in
600 degree centigrade the highest amount of these desired components is available in
10 s viscosity.
58
Material Amount vs. Temperature - 5s Viscosity
4000
3500
3000
Lin (Counts)
2500
Hydroxlyapatite - [Ca5(PO4)3(OH)]
Hydroxlyapatite, syn - [Ca10(PO4)6(OH)2]
2000
Hydroxlyapatite, syn - [Ca5(PO4)3(OH)]
Hydroxlyapatite - [Ca10(PO4)6(OH)2]
Hydroxyapatite - [Ca10(OH)2(PO4)6]
1500
1000
500
0
600
Firing Temperature (C)
Figure 4.8: Material amount vs. temperature in 5 s viscosity
Material Amount vs. Temperature - 7.5s Viscosity
3000
2500
Lin (Counts)
2000
Hydroxlyapatite - [Ca5(PO4)3(OH)]
Hydroxlyapatite, syn - [Ca10(PO4)6(OH)2]
1500
Hydroxlyapatite, syn - [Ca5(PO4)3(OH)]
Hydroxlyapatite - [Ca10(PO4)6(OH)2]
Hydroxyapatite - [Ca10(OH)2(PO4)6]
1000
500
0
600
Firing Temperature (C)
Figure 4.9: Material vs. Temperature 7.5 viscosity
59
Material Amount vs. Temperature - 10s Viscosity
4000
3500
3000
Lin (Counts)
2500
Hydroxlyapatite - [Ca5(PO4)3(OH)]
Hydroxlyapatite, syn - [Ca10(PO4)6(OH)2]
2000
Hydroxlyapatite, syn - [Ca5(PO4)3(OH)]
Hydroxlyapatite - [Ca10(PO4)6(OH)2]
Hydroxyapatite - [Ca10(OH)2(PO4)6]
1500
1000
500
0
600
Firing Temperature (C)
Figure 4.10: Material amount vs. temperature 10s viscosity
4.2 EDAX result
The purpose of EDAX test is to specify the structural elements of the adhered
HAp to the wall of the mould. This test will clarify the changes of the elements
during the firing process regarding to the amount of the material adhered to the
mould from different quantity of viscosity. The main elements that are study in this
EDAX test are Phosphor and Calcium. These elements are the base and most
significant components of HAp. The amount ratio of these elements is a key issue to
specify the existence and phase of HAp.
At first, original base materials which were provided by the three suppliers
were tested. The results of these tests had beneficial conclusions regarding to the
standard ratio between main elements of HAp. The most desirable ration of Calcium
and Phosphate is 1.67 which shows the presence of Hydroxyapatite. In addition, the
Ca/P ratio of 1.5 and 2 proves the presence of TCP (Tri-Calcium Phosphate) and
TTCP respectively. Indeed these results would support key points for analyzing the
60
base materials and finally to select the best material between these three and consider
it as a reference to study the changes according to firing temperatures. The results of
EDAX tests for base materials are listed in Table 203. According to achieved EDAX
results, it can be obviously understood that Fluka provides the best base material for
the purpose of this project and also medical uses based on proven ratios reported in
previous papers. This is due to the average ratio of the Ca/P which must vary from
1.5 to 2. By looking at the EDAX results of two other companies, they show higher
average ratio of Ca/P that can not be accepted. Also these results along with XRD
results confirm the better quality of Fluka’s Hydroxyapatite.
Table 4.3 EDAX results for 600 C temperatures
EDAX Test Results – Actual Samples, Fluka
Dewaxing
300
Temperature (°C)
Viscosity (s)
Firing
Temperature (°C)
Test
5
7.5
10
600
600
600
Element
1
Ca/P Ratio
1.87616
2.15128
1.90722
2
Ca/P Ratio
1.67288
1.95871
1.85714
3
Ca/P Ratio
1.4548
1.91933
1.75
1.66795
2.00977
1.83812
Ca/P Ratio
Average
61
Next, as it was necessary to confirm the existence of these principal elements
after the firing process, all nine samples were taken for EDAX test. The results are
shown in Table 6.3. By taking a glance at the results of the EDAX samples, it can be
easily understood that the experimental conditions are well considered due to the
existence and logical ratio of Ca/P. Most of the calculated Ca/P ratios can be found in
the standard and desirable range.
On the other hand, there are a few number of test results that do not show the
appropriate ratio of Ca/P. However, by considering all the recognized elements in the
result, it can be understood that it is the error of the technicians or some other
environmental error due to the existence of high amount of Zircon and Silicon which
means that the wall of the mould was taken for the test instead of HAp layer adhered
to the wall. In conclusion, all other accurate test results are in the standard range of
Ca/P ratio which is from 1.5 to 2. Table 4.4.
62
Table 4.4: EDAX Test Results – Actual Samples, Fluka
EDAX Test Results – Actual Samples, Fluka
Dewaxing(°C)
Test
300
Viscosity (s)
5
7.5
10
Firing Temp(°C)
600
600
600
Be
4.33
0
32.48
C
1.81
2.92
0.23
Si
0.9
0
0.01
P
17.07
18.31
1.94
Ca
32.026
39.39
3.7
Zr
0
0
0
Be
0
5.35
35.91
C
3.14
1.05
0
Si
0
0
0
P
20.91
16.71
0.07
Ca
34.98
32.73
0.13
Zr
0
0
0
Be
0
0
35.9
C
2.01
1.9
0
Si
1.96
0
0
P
21.68
19.71
0.08
Ca
31.54
37.83
0.14
Zr
0
0
0
Element
1
2
3
1
Ca/P Ratio
1.87616
2.15128
1.90722
2
Ca/P Ratio
1.67288
1.95871
1.85714
3
Ca/P Ratio
1.4548
1.91933
1.75
Ca/PRatioAverage
1.66795
2.00977
1.83812
63
4.3 3D microscopes:
One of the main objectives of the project is measuring the thickness of HAp
layer adhered to the inner wall of the mould. For this purpose 2D microscope was
needed but for applying this kinds of microscopes the surface of the detecting
samples should be in good finishing condition. Therefore proper surface finishing is
needed but because of brittle manner of adhered HAp, surface finishing is not
applicable. So 3Dmicroscope will be a good choice that can detect the surface.
3d microscope pictures were taken to prove the adherence of HAp on to the
walls of the mould; these pictures are shown in figure 6.11. In all of these samples a
layer of HAp with minimum thickness of 0.5mm can be detected. Indeed, this
confirms the validity of investment casting method for coating of HAp and its
existence on the walls of the moulds to provide this bio active material on to bio
metallic materials which can be produced by casting method.
Figure 4.11: Adhesion of HAp to the inner layer of mould
CHAPTER 5
CONCLUSION
After all from the result that reached from the tests, the project objectives as
were mentioned in methodology: finding the best dewaxing temperature and also find
the best viscosity of HAp-water mixture for coating the inner layer of investment
casting mould, obtained.
For dewaxing temperature 300 C is the best because the maximum wax was
removed from the investment casting mould and it dose not have any worst effect on
the quality of the layers.
For viscosities HAp viscosity of 5 second shows the best ratio Ca: P i.e 1.7
and fewer cracks during the process instead of 7.5 and 10 second viscosities.
Regarding to this project and the other projects that were done for coating the
HAp on to the different materials, in can be concluded that this method (investment
casting method for coating) will be an appropriate method in the subject of coating
HAp on to the metallic materials.
As it discussed before this method is very cheap regarding to other coating
methods and it is very simple as well and according to using simple methods control
of the elements which are involved in the finale results is easier than other coating
methods like plasma spraying or electro chemical methods for coating.
65
Simplifying and decreasing the cost of the process will directly affect on the
price of the final product therefore it can help to make cheaper and more popular
implants that will increase the life style for the people who need appropriate implants.
But should be assure the accuracy of the final product and weather it is not accurate
find better methods or optimize current method.
A system alternate found to portray the least crack and enhanced with drilling
the wax to reduce cracks. It is a new method to minimize the effect of wax expansion
during the dewaxing process. This method is easy and cheap and don’t have any
effect on the quality of the mould. It is possible in all the simple workshops.
Regarding to hole making inside the wax pattern to assure crack-less mould
during dewaxing process Indeed, the use of Investment casting method can assure the
minimum requirements of the coating process of HAp (bioactive material) onto biometallic materials (base material of medical implants).
Finally some other options can be a good research area for finding new
methods and helping to obtain better result in this method; also it can help us to
figure out the behavior of HAp water mixture and effects of the other materials and
temperatures on it during the process. In example the temperature affect on the color
of adhered HAp on the inner layer of the ceramic mould. Also one of the problems
that occurred in this project was the measuring the viscosity of HAp-water mixture,
because of its creamy characteristic.
As it was mentioned before the brittleness of HAp layer was also a difficulty
to obtain accurate results during the test for example measuring the thickness of HAp
layer was to hard and using usual measuring methods was impossible thus finding
new methods and new materials to decrease the brittleness of HAp layer can be a
good subject.
66
References
Abrams L, Bajpai PK. 1994. Hydroxyapatite ceramics for continuous delivery of
heparin. Biomed. Sci. Instrumen. 30:169–174
Bajpai PK and Fuchs CM. 1985. Development of a Hydroxyapatite Bone Grout. In:
Proceedings of the First Annual Scientific Session of the Academy of Surgical
Research. San Antonio, Texas. C. W. Hall, Ed. p. 50–54. Pergamon Press, New
York, NY.]
Bajpai PK. 1992. Ceramics: A Novel Device for Sustained Long Term Delivery of
Drugs. In: Bioceramics Volume 3. JA Hulbert and SF Hulbert, Eds. p. 87–99. RoseHulman Institute of Technology, TerraHaute, IN]
Bajpai PK. 1994. Ceramic Drug Delivery Systems. In: Biomedical Materials
Research in The Far East (I). Xingdong Zhang and Yoshito Ikada, Eds. p. 41–42,
1994. Kobunshi Kankokai Inc., Kyoto, Japan.Parker and Bajpai, 1993]
Bajpai PK. 1992. Ceramics: A Novel Device for Sustained Long Term Delivery of
Drugs. In: Bioceramics Volume 3. JA Hulbert and SF Hulbert, Eds. p. 87–99. RoseHulman Institute of Technology, Terra Haute, IN]
Bunyamin Aksakal C. Hanyaloglu, Bioceramic dip-coating on Ti–6Al–4V and 316L
SS implant materials, Sci:Mater Med 2007]
67
Cition. American Ceramic Society 26 th Annual Meeting Conference Proceedings.
2003] Gutwein, LG.; Webster, TJ. Affects of alumina and titania nanoparticulates on
bone cell foundation]
D.A. Cortes, A.A. Nogiwa , J.M. Almanza , S. Ortega., coating onMg-PSZ/Al2O3
composites. Effect of the immersion method, Materials Letters 59 1352– 1355
(2005)]
De la Isla A, Brostow W, Bujard B, Estevez M, Rodriguez JR, Vargas S, Castano
VM. Nanohybrid scratch resistant coating for teeth and bone viscoelasticity
manifested in tribology. Mat Resr Innovat. 2003;7:110–114.].
Feenstra L and de Groot K. 1983. Medical Use of Calcium Phosphate Ceramics. In:
Bioceramics of calcium phosphate. K de Groot, Ed. p. 131–141, CRC Press, Boca
Raton, FL]
Gutwein, LG.; Webster, TJ. Affects of alumina and titania nanoparticulates on bone
cell function. American Ceramic Society 26 th Annual Meeting Conference
Proceedings. 2003]
Hench LL. 1993. Bioceramics: From concept to clinic. American Ceramic Society
Bulletin, 72:93–98].
Hench LL. 1991. Bioceramics: From concept to clinic. J. Am. Ceram. Soc. 74:1487–
1510]
Hentrich RL Jr, Graves GA Jr, Stein HG, and Bajpai PK. 1971. An evaluation of
inert and resorbable ceramics for future clinical applications. J. Biomed. Mater. Res.
5:25–51]
68
H.H. Rodrı´guez H.H. Rodrı´guez, G. Vargas, D.A. Corte´s., Electrophoretic
deposition of bioactive wollastonite and porcelain–wollastonite coatings on 316L
stainless steel, Ceramics International (2007)]
Jarcho M, Salsbury RL, Thomas MB, and Doremus RH. 1979. Synthesis and
fabrication of β-tricalcium phosphate (whitlockite) ceramics for potential prosthetic
applications. J. of Mater. Science. 14:142–150]
J.C. Escobedo, et al; Hydroxyapatite coating on a cobalt base alloy by investment
casting Scripta Materialia 54 (2006) 1611–1615]
Jie Weng , Formation and characteristics of the apatite layer on plasma-sprayed
hydroxyapatite coatings in simulated body fluid, Biomoterials vol.18 (1997)]
Kingery WD, Bowen HK, and Uhlmann DR. 1976. Introduction to Ceramics, 2nd
ed., p.368, J. Wiley, New York]
Ma J, Wong H, Kong LB, Peng KW. Biomimetic processing of nanocrystallite
bioactive apatite coating on titanium. Nanotechnology. 2003;14:619– 623. doi:
10.1088/0957-4484/14/6/310.]
N. Ramesh Babu et al. Trends Biomater. Artif. Organs. Vol. 17(2) pp 43-47 (2004)]
Park JB and Lakes RS. 1992. Biomaterials—An Introduction, 2nd ed., Plenum Press,
New York].
Peltier LF. 1961, The use of plaster of Paris to fill defects in bone. Clin. Orthop,
21:1–29]
69
Piattelli A and Trisi P. 1994. A light and laser scanning microscopy study of
bone/hydroxyapatite-coated titanium implants interface: Histochemical evidence of
unmineralized material in humans. J. Biomed. Mater. Res. 28:529–536]
R.M. Trommer, Alternative technique for hydroxyapatite coatings, Flame Assisted
Chemical Vapor Deposition (FACVD)Surface & Coatings Technology 201 (2007)]
TuantuanliI, Junhee Lee ,Takayuki Kobayashi, Hideki Aoki, Hydroxyapatite coating
by dipping method, and bone bonding strength, Journal of material science, Materilas
in Medicine, 7 (1996) 355 357]