Magic Suspensions
Developer:
Dr. Mary R. Reidmeyer
Project for Grade Level:
High School
Discipline:
Materials, Chemistry
Topic Area:
Binder Gelation, Crosslinking
Time Required:
Goals:
Demonstrate the ability to form spherical shapes based on the
gelation of seaweed derived material.
Objectives:
Observe the crosslinking of high molecular weight polymer into a
gel with exposure to highly charged cations in a solution.
Create spherical balls by allowing drops of a ceramic/polymer
solution to fall into a soluble salt solution.
Discuss what can be created with these ceramic/polymer spheres.
Materials:
Ammonium alginate powder
Talc powder
Nepheline Syenite powder
Calcium chloride
Plastic syringe 12ml with 16 GA blunt needle
Beakers 100ml 250ml, 400ml
Wire Strainer
Stir Bars
Magnetic stirrer
Balance
University of Missouri-Rolla – Ceramic Engineering Department
http://campus.umr.edu/ceramics
116092419
Safety Precautions:
Follow the instructions. Wear proper safety equipment such as goggles
and vinyl gloves. Dispose of the materials properly.
Procedure:
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Prepare a 1 wt% solution of ammonium alginate. Place a 400ml beaker
(with stir bar) on a magnetic stir plate that contains 297g of deionized
water. With stirrer creating a moderate vortex, gradually sprinkle the 3g
ammonium alginate powder into the water. Do not clump it together. If
you do, it will not dissolve in a reasonable amount of time (normally 1530 minutes.) Since the alginate is a dried polymer, first the granules must
be dispersed in the water then swelled and disentangled.
Prepare a 10wt% solution of calcium chloride. Stir 40g of calcium
chloride into 360g of deionized water in a 400ml beaker.
Prepare a 25vol% ceramic slurry using the prepared 1 wt% sodium
alginate solution. To 75ml of ammonium alginate solution stir in 15g of
nepheline syenite and 40g of talc powder. Stir thoroughly for several
minutes until the slurry becomes smooth.
Place the calcium chloride solution on the magnetic stir and set to stir very
slowly.
Take the syringe and draw up approximately 6ml of 1wt% sodium alginate
solution. Hold the syringe over the beaker containing the calcium chloride
solution. Gently press the syringe plunger so that drops of solution are
formed on the tip of needle. Allow the drops to fall into the calcium
chloride solution.
After several dozen transparent spheres of alginate can be observed in the
calcium chloride beaker cease dropping solution. Allow the spheres to
circulate in the beaker for several minutes.
Place the wire strainer over the top of a clean 400ml beaker and pour the
sphere containing solution through the strainer. Retain the calcium
chloride solution for future use.
Gently rinse the spheres in the strainer with deionized water. Rinse some
out of the strainer into a glass dish for observation. Examine others with
your fingers and determine their properties.
Set your calcium chloride solution back on the magnetic stirrer. Squirt the
remaining alginate solution in the syringe into a waste container.
Stir the ceramic slurry again to homogenize it. Take the syringe and draw
up approximately 6ml of ceramic slurry. Hold the syringe over the beaker
containing the calcium chloride solution. Gently press the syringe plunger
so that drops of slurry are formed on the tip of the needle. Allow the drops
to fall into the calcium chloride solution.
University of Missouri-Rolla – Ceramic Engineering Department
http://campus.umr.edu/ceramics
116092419
11.
12.
After dozens of ceramic spheres are created, allow them set a few minutes
then strain and wash them as done previously with the alginate sphere.
Examine the ceramic spheres.
Observations and Questions:
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7.
Describe what happens when high molecular weight ionic polymer is
exposed to highly charged cations.
How would potassium chloride or magnesium chloride solutions interact
with the sodium alginate solution?
What would happen if you accidentally stirred the alginate solution with
the spatula (dirty) you used to stir the calcium chloride solution? (Try
pouring a small amount of each solution together in another beaker.)
How would the alginate solution behave if was mixed with a less soluble
salt such as calcium sulfate. (Hint: Calcium chloride salt is highly soluble,
calcium sulfate is slightly soluble.)
What variables would you control to change the size of the spheres
created?
What would happen if you extruded a column of alginate solution into the
calcium chloride solution?
What are some practical uses of this gelation process? (Think about
dentistry, foods, cosmetics, etc.)
Teacher’s Note:
Supplemental MaterialVocabulary:
Alginate- A salt of alginic acid, such as sodium or ammonium alginate.
Alginic acid- An insoluble colloidal acid in the form of a polysaccharide that is
abundant in the cell walls of brown algae, kelp.
Crosslink- an atom or group that connects parallel chains in a complex chemical
molecule.
Gel- a colloidal mixture of solid and liquid of jelly-like consistency.
Molecular weight- The sum of the atomic weights of all the atoms in a molecule. Also
called formula weight.
University of Missouri-Rolla – Ceramic Engineering Department
http://campus.umr.edu/ceramics
116092419
Nepheline syenite- K2O·Na2O·4Al2O3·9SiO2; hardness (Mohs) 6; sp. gr. 2.60; an
igneous rock consisting of a mixture of potash feldspar and soda feldspar used in
ceramics to lower the firing temperature.
Salt- A chemical compound formed by replacing all or part of the hydrogen ions of an
acid with metal ions or electropositive radicals.
Slurry- A thin mixture of a liquid, especially water, and any of several finely divided
substances, such as cement, plaster of Paris, or clay particles.
Solution- A homogeneous mixture of two or more substances, which may be solids,
liquids, gases, or a combination of these.
Talc- 3MgO·4SiO2·H2O; m.p. above 1400°C; sp. gr. 2.7; hardness (Mohs) 1- 1.5; a
natural hydrous magnesium silicate commonly used in low fire pottery bodies.
Background Information:
Gums and ResinsMany different materials are used as additives in the processing of ceramic
materials. Polymer molecules are adsorbed between ceramic particles and can provide a
temporary bond between the particles to allow molding or forming of articles. Depending
on the nature of the organic additive it can burn cleanly way during heating or leave
behind inorganic components which can react with the particles. Many organic binders
such as cellulose, gums, polysaccharides (starch), lignin, alginates, glycols, polymerized
alcohols and acrylic resins burn away during the heating process before ceramic bonds
are formed. These binders can be purchased in different molecular weights and grades.
Some of the favorite additives are also used extensively in the food industry as thickening
or emulsion controlling additives. The salts of alginic acid, such as ammonium alginate
and sodium alginate, are derived from an extract of Kelp seaweed. The empirical formula
for sodium alginate is C6H7NaO6. Algin polymers will react with most polyvalent cations
(except magnesium) to form crosslinkages. As the concentration of polyvalent cations
increase, the algin solution, thickens, gels, and can even precipitate. Calcium is one of the
most common polyvalent cations used to gel alginates. Highly soluble calcium
compounds can be used to from insoluble filaments, films and spheres. Calcium alginate
is not water soluble. Slowly dissolving calcium compounds can gradually thicken a
solution. Fortunately alginates in solution are compatible with a wide variety of materials
including other thickeners, synthetic resins, sugars, oils, fats, waxes, pigments and
various surfactants. Because of this we can create gels and insoluble filaments that
contain a wide variety of materials.
University of Missouri-Rolla – Ceramic Engineering Department
http://campus.umr.edu/ceramics
116092419
What is Gelation?
Gelation occurs in solutions that contain long chain molecules when something causes
the chains to interact. When the long chain molecules interact, they produce a threedimensional structure. Commonly this interaction is cause by a thermal or chemical
change. Depending on the nature of that interaction the gelation may be reversible or
irreversible. In a sodium alginate solution when calcium cations are introduced into the
solution, a chemical change occurs;
Nan alginate(sol) + n/2 Ca2+(solution) → n Na+(solution) + Can/2 alginategel)
This chemical gelation is practically irreversible.
An example of reversible gelation is a methyl cellulose solution. Upon heating the
cellulose molecules in the solution dehydrate and three dimensional bonds form creating
a gel. Upon cooling the cellulose molecules rehydrate, the bonds are broken and the
gelation disappears.
Forming MethodsA great many forming methods are used to create useful objects from powdered
materials. For ceramics, binders help hold the powder particles together in the desired
shape until heat treatment forms a permanent strong bond. The method used depends on
the objects size, geometry, surface finish, required tolerances and the productivity
required. Powders can be pressed into shapes but these shapes relatively simple. Objects
can be cast from powder/water suspensions into porous multipart molds to produce more
complex shapes. This method while very effective is labor intensive. Soft plastic mixtures
of powders and binders can be extruded like pasta and simple cross-sectional objects can
be produced in large quantities. Similar mixtures can be injection molded like a plastic.
While these methods can form greater quantities or more complex objects, the amount of
binder required can affect the ability to produce these easily and quickly. Many creative
methods are developed and used by material engineers and scientists. The gelling of
alginate solutions containing powder is just one example of these creative forming
methods.
University of Missouri-Rolla – Ceramic Engineering Department
http://campus.umr.edu/ceramics
116092419