Questions and answers
Ceramics
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Questions: 81
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Question 31
Consider the role of water in solid powder particles behaviour
- Wetting the surface of ceramic particle and decrease of the friction coefficient - Introduction of liquid with high viscosity among powder particles - Dissolution of polymers - Dispersion of solid particles in the liquid
Question 32
What is the meaning of “zero point charge” in suspension of powder particles
Isolectrical point = point of zero charge (pzc) occures at pH, where: [MO-] = [MOH2+]
Question 33
Describe electrical double layer (EDL)
EDL is of a given thickness; the effective diameter of a particle is higher if measured with EDL EDL shows the effective chargé ζ Both, the thickness and the chargé of EDL can be changed via pH It is convenient to measure pH value for zeta potential ζ=0 (isoelectrical point)
Question 34
How DLVO describes behaviour of particles in the liquid medium?
Particles could produce attractive and repulsive forces. If the repulsive forces are stronger then attractive a suspension is stable, if not particles coagulate
Question 35
What is the origin of electrostatic repulsion of ceramic particles in the polar liquid?
electrostatic repulsion forces: repulsion of two identical charged ions
Question 36
What are the means of suspension stabilization?
- pH-changing agents - polymer - sulfactants
Question 37
Requirements (3) for polymer stabilization of suspension
-efficient thickness of polymer layer - total cover on particle surface by polymer - effective anchoring of polymer on particle Surface
Question 38
What is the role of surfactants in stabilization of suspension?
Increase distance between particles suspension
Question 39
How can you describe “a stable suspension”?
- Sedimentation is very slow - Sediment is well packed - The liquid over a sediment is „misty/cloudy” – it contains fine particles
Question 40
List the types (4) of intergranular bonding of particles in water presence
a) bridged b) suspended c )capilary d) droplet
Question 41
41. Give the stages of granules formation from the solution
Sprying solution -&rt; Powder -&rt; Wetting and absorbing -&rt; Solidified -&rt; Solid Briedge -&rt; Final Granules
Question 42
List the main constituents (4) of suspension for casting
Solvent - controls viscosity, Binder - improves mechanical properties, Plasticizer- it gives elasticity, Defflocculant – it keeps dispersion of particles
Question 43
Give the names of various casting (3)
Slip-casting a ceramic part, Centrifugal casting of ceramics, Tape casting
Question 44
Describe the meaning of “slip” and “slurry”
Slip – water suspension of fine clay particles Slurry – complex suspension of fine powder in water or in solvent
Question 45
Stages of slip casting to porous moulds
Making the slip -&rt; Pouring suspension (slip) into a mould of plaster -&rt; Water passes via capillary action into porous plaster -&rt; Sintering