Ceramics

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

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+]

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)

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

What is the origin of electrostatic repulsion of ceramic particles in the polar liquid?

electrostatic repulsion forces: repulsion of two identical charged ions

What are the means of suspension stabilization?

- pH-changing agents - polymer - sulfactants

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

What is the role of surfactants in stabilization of suspension?

Increase distance between particles suspension

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

List the types (4) of intergranular bonding of particles in water presence

a) bridged b) suspended c )capilary d) droplet

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

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

Give the names of various casting (3)

Slip-casting a ceramic part, Centrifugal casting of ceramics, Tape casting

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

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