Che5700 陶瓷粉末處理
Processing Aids
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May include the followings:
Liquid/solvent
Surfactant (wetting agent)
Deflocculant
Coagulant
Binder/flocculant
Plasticizer
Foaming agent
Antifoam
Lubricant
Bactericide/fungicide
Che5700 陶瓷粉末處理
Surfactants
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Mostly having both polar and non-polar end-groups
(hydrophobic and hydrophilic groups)
Classified as: non-ionic surfactants; cationic
surfactants (mostly with Cl- ) & anionic surfactants
(e.g. Na+, NH4+ ions; sulfonate, carboxylate, etc)
Lyo- solvent; lyophobic,
lyophilic;
Surfactants (II)
• Sodium dodecyl sulfate (sodium laural sulfate) – ionic
surfactant CH3-(CH2)11-O-SO3- Na+ (other examples:
sulfonate, lignosulfonate, carboxylate, phosphates, etc.)
• Cationic surfactant: dodecyltrimethylammonium chloride:
[C12H25N(CH3)3]+ Cl- (commonly toxic materials)
• Surfactants can reduce surface tension: improve wetting
property of liquid on solid
• Polyelectrolytes: polymer molecules with repeating
ionizable groups (usually through electrical attraction onto
solid surface) – sometimes also classified as surfactants
Che5700 陶瓷粉末處理
HLB Values
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In oil-water system, the surfactant is called emulsifier;
Whether oil-in-water or water-in-oil: which one is the
continuous phase, which one the dispersed phase?
(relative quantity & …)
Bancroft rule: the continuous phase is the one in which
the emulsifier is more stable; (both oil drops and water
drops are formed and adsorb surfactants; if if oil-oil
coalescence is faster, oil will be the continuous phase;)
HLB: an index to rate the relative strengths of
hydrophobic and hydrophilic groups in a surfactant;
HLB = 20 ( 1 – S/A) [scale of 0 – strong hydrophobic
group; to 20 – strong hydrophilic group] (empirical)
S: saponification number; A = acid umber of separated
acid
HLB and CMC
• HLB = Σhydrophilic group No. – Σliophilic group No. + 7
• assigning numbers to structural groups (i.e. chemical nature
of surfactants)
• e.g. –SO4Na (38.7); -COOK (21.1); -COONa (19.1); -COOH
(2.1); -OH (1.9); -O- (1.3);
• for liophilic groups: -CH-, or –CH2-, or –CH3, or =CH- all
0.475
• properties related to HLB: heat of hydration, micellization,
dielectric constant, etc.
• log (CMC) = a + b log (HLB)
• critical micelle concentration: minimum concentration of
surfactant molecules to form micelles (form aggregates)
• taken from book by Vold and Vold, 1983.
Taken from JS
Reed, 1995;
•Dispersed in
water: HLB > 8;
•in oil: HLB < 6
•Too much
surfactant 
form micelle
(CMC)
Che5700 陶瓷粉末處理
Uses of Binders
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Quite a few uses are often found for a binder:
Wetting agent (may improve wetting of particle)
Thickener (increase apparent viscosity)
Suspension aid: reduce settling velocity
Rheological aid:control flow of a slurry
Body plasticizer: help with pressing, extrusion;
Liquid retention agent: reduce liquid migration
(evaporation) in matrix;
 Consistency aid: alter amount of liquid required to
produce a particular type of flow;
 Binder: improve strength of green body
Types of
Binders:
inorganic and
organic
Che5700 陶瓷粉末處理
Binder Materials
•Organic binders: be
aware of different
molecular weight effect;
•MBI index: adsorption of
methyl blue dye/particle
surface area; often used
for inorganic binder
•PVA: polyvinyl alcohol;
common binder material;
partially hydrolyzed or fully
hydrolyzed
Binder MW: significant
effect on viscosity;
some may use
viscosity data to
determine MW;
Gelation: some binder
-solvent system,,
when change in
temperature, become
poor solvency and gel;
mostly reversible
process; may use
chemical methods to
gel (e.g. pH change to
PZC, reversibility poor
here)
Vinyl Binders
Backbone: C-C
Cellulose Binder
•Modified by R1, R2 and
R3;
•Methyl cellulose: R = CH3
for all Rs
•Degree of substitution DS
= average number of OH
on anhydroglucose unit
that have been reacted (03 range); molar substitution; DS = 1.6 – 2.0
provides water solubility of
methyl cellulose binder
Hydroxyethyl cellulose: HEC, ethylene oxide substitute some
H, -CH2-CH2O-; Molar substitution MS = average number of
substitution by ethylene oxide
Che5700 陶瓷粉末處理
More Binders
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polysaccarides: refined starch, easily dissolved in water;
Some cellulose contain soluble function groups  ionic
type binder; e.g. Na carboxymethyl cellulose (Na-CMC)
PEG: polyethylene glycol, HO-(CH2-CH2-O-)n-H, large
variation of MW, several hundred – 20,000 g/mole
Wax: paraffin compounds; microcrystalline wax – are
saturated hydrocarbons, less crystalline, stronger but
tougher than paraffins;
In general: binder need to dissolve in solvent, then add
ceramic powder, continue processing. ..problem of
solvent selection
Che5700 陶瓷粉末處理
General Effects of Binders
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In general: small amount of non-ionic binder 
stabilization; increase concentration 
bridging flocculation; further increase  may
stabilize system again;
For ionic binders, pH becomes very important;
 influence charge on both particle and binder,
and hence adsorption behavior;
Cellulose binders are les flexible than vinyls,
waxes, and glycols;  elastic effect
Binders adsorbed may reduce surface
roughness and coefficient of friction  very
specific to binder molecules
•Different behaviors
of polymers:
•Linear polymers: its
chain can twist and
coil  e.g. HDPE;
•branched polymers:
not so free to twist
and coil  LDPE;
•Cross-linked
polymers: usually
rigid structure, having
a yield strength
Che5700 陶瓷粉末處理
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Plasticizers
For a binder system: glassy state (brittle, movement of
molecule limited;)  rubbery state (segment of
molecules is able to flow and realign); elastic behavior
to viscoelastic behavior ( increase of temperature)
Glass transition temperature Tg
Polymer films exhibit changes in resistance to
mechanical deformation, thermal expansion, and
specific heat at Tg
Plasticizer: small molecules to reduce van der Waals
forces between polymers, to cause polymers to pack
less densely, to increase flexibility;  decrease of Tg
Adsorbed water: can function as a plasticizer
Hydrolyzed PVA, its Tg vs
Temp. effect on elastic
modulus; fromJS Reed, 1995; plasticizer and adsorbed
moisture
Che5700 陶瓷粉末處理
Common Plasticizers
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Ethylene glycol: cheap, often used; effect related to
MW;
Stearic and oleic acid are plasticizers for waxes; oils
and wax are used for thermoplastic polymers (PE, PS)
Che5700 陶瓷粉末處理
Foaming and Anti-foaming Agents
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Foaming agent: reduce surface tension of
the foaming solution; used in fabricate light
weight concrete and in beneficiation of
some minerals (flotation)
Anti-foam agent: defoaming agent;
examples include – fluorocarbon,
dimethylsilicones, higher-molecular weight
alcohols and glycols, Ca and Al stearate;
Che5700 陶瓷粉末處理
Lubricants
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Reduce resistance to relative movement (sliding); to get
objects out of a mold
Boundary lubricant: adsorbed film of high lubricity; high
adhesion strength, low shear strength
Solid lubricants: fine particles with a laminar structure
and smooth surface; plate-like particles: graphite, talc,
graphitic BN etc.