Material Properties of Chemically Bonded
Phosphate Ceramic/Wood Interfaces
M.J. Benjamin, K.R. Englund, D.F. Bahr
School of Mechanical and Materials Engineering
Washington State University
Introduction
Results and Analysis
Chemically bonded phosphate ceramics (CBPCs) are
man made inorganic solids that lie in between hydraulic
cements and ceramics . Normally, ceramics are sintered
at temperatures ranging from 700-2000⁰C, but the bonds
in CBPCs form after the addition of water, like in hydraulic
cements such as Portland concrete. However, the
covalent or ionic bonds that form in CBPCs are much
stronger than those found in other hydraulic cements,
resulting in more ceramic like material properties than
would be expected.
Vickers Hardness
HV = (1.8544 L )/ D2
Where L is the load in kilograms-force, and D is average
diagonal in mm ((D1+D2)/2).
• Polished sample (1 μm) shows ISE at 50gf and 100gf.
Benefits:
•Stability at range of pH values
Indentation Size Effect in CBPC Samples
•Increased compressive strength
• High resistance to wear and heat
Top: CBPC Composite
Sample
• Interest as structural ceramic, and many other applications
Experimental Method
CBPC
Magnesium Phosphate Ceramic
Test Method Microindentation using Vickers Diamond
Tip (.490-19.62N Load) for
Microhardness, Optical Microscopy
Sample
CBPC/Basswood Composite
CBPC - 60% CaSiO3/40% CBPC Dry,
+21.5% Water
Vibrated into Mold w/ Basswood
3 Day Minimum Curing Time
Preparation Sectioning with Diamond Saw (5-10 μm
rough surface), Diamond Lapping
Polishing to 1 μm
• Indicates distinct trend that the CBPC at the interface
is less hard than noninterface cement from the same
specimen
Crystal Growth
ISE
•Faster setting time than cements like Portland concrete
• Near neutral pH, allowing CBPCs to bind many
hazardous and waste materials as aggregates
Interface/Cement Comparison Cont.
As noted in other materials, there is an
Indentation Size Effect (ISE) present in this CBPC.
• Plotting HV vs Load (analogous to HV vs Depth)
ISE is present, and especially pronounced in
samples that had not undergone polishing, and were
simply smooth casted
• Plotting Average D vs Load
A power slope of .5 is expected. However, this
unpolished sample produced a slope of .703, an
indicator of ISE. Fixed regressions at a slope of .5
closely match data after loads of 50 grams-force.
Interface/Cement Comparison
Left: Unpolished Diamond
Cut Composite Sample
• Crystal growth was
evident in fractured
interfaces examined
under optical
microscopy.
• Could indicate
structure of interface
Conclusion
This magnesium phosphate CBPC has
demonstrated lower hardness at its interface with
basswood, which might indicate greater fracture
toughness at the interface. ISE seems to decrease when
the indentation surface becomes more fine, indicating
0.1 μm polishing could minimize ISE further. Polishing to
less than 1 μm could also make fractures more
observable, allowing for calculation of fracture
toughness, if used in conjunction with nanoindentation.
Observing possible crystal growth at the interface with
a Scanning Electron Microscope (SEM) would also be
advisable, if possible.
References
M. B. Zbib, M. C. Tarun, M. G. Norton, D. F. Bahr, R. Nair, N. X. Randall, E. W. Osborne,
2010, Mechanical properties of polycrystalline silicon solar cell feed
stock grown via fluidized bed reactors, Journal of Materials Science, no. 6, pg. 1560
Wagh, A.S., 2004, Chemically Bonded Phosphate Ceramics, Elsevier, Kidlington, 283 p.
• Polished, the power slope of the cement more
closely matches the expected value
Right: 1 μm Polished
Diamond Cut Composite
Sample
• Data shows larger diagonal indentation distances on
the interface, indicating lower hardness
Acknowledgements
Special thanks are in order for M. B. Zbib and Dr. Bellou for their help in training on
various pieces of equipment, as well as the NSF for funding this project.
This work was supported by the National Science Foundation’s REU program under
grant number DMR-0755055.