Pytania i odpowiedzi
ceramics
Zebrane pytania i odpowiedzi do zestawu.
Ilość pytań: 81
Rozwiązywany: 2283 razy
Pytanie 21
Obligatory requirement for self-propagating high-temperature synthesis (SHS) powder
exothermic reaction - the rate of heat losses from the closed system is slower from the rate of the heat evolution: borides, carbides, nitrides, silicides - ignition
Pytanie 22
Give examples of chemical methods of ceramics powders manufacturing
Wet chemical methods: -spray frying; - freeze drying; - co-precipation; - pecchini method with critic acid; - hydrothermal methods; - SOL-GEL
Pytanie 23
Description of spray-drying method fo ceramic powder
Spray-drying is a process of producing a granulates ,flowable powder of uniform bulk density. It is process by which fluid feed material is transformed in a dry powderby spraying the feed into a hot drying medium (gas) EVAPORATION -&rt; PRECIPITATION -&rt; DRYINGE -&rt; DECOMPOSITION
Pytanie 24
Description of freeze drying method for ceramic powder
Freeze-drying is used to create a formable powder from a sprayed slurry mist. Freeze-drying creates softer particles with a more homogeneous chemical composition than traditional hot spray drying, but it is also more expensive.
Pytanie 25
.List the reagents (3) in sol-gel method for ceramic powder production
- water - alkoxides - acid
Pytanie 26
Principles of ceramic nanopowder production via gas-phase methods
EVAPORATION-CONDENSATION, DECOMPOSITION OF GASEOUS COMPOUNDS, REACTIONS BETWEEN GAS PHASES
Pytanie 27
What does it mean: “rheology”
RHEOLOGY: hydrodynamics of dispersed systems: solid+liquid
Pytanie 28
Parameters describing powder properties(3)
Particle size distribution, Apparent mean size, Specific Surface area (SSA)
Pytanie 29
Why powder particles from agglomerates?
Because it wants to reduce the surface energy
Pytanie 30
How water presence affect Hamaker’s constant of powder?
Water presence reducecs Hamaker's constant
Pytanie 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
Pytanie 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+]
Pytanie 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)
Pytanie 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
Pytanie 35
What is the origin of electrostatic repulsion of ceramic particles in the polar liquid?
electrostatic repulsion forces: repulsion of two identical charged ions
Pytanie 36
What are the means of suspension stabilization?
- pH-changing agents - polymer - sulfactants
Pytanie 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
Pytanie 38
What is the role of surfactants in stabilization of suspension?
Increase distance between particles suspension
Pytanie 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
Pytanie 40
List the types (4) of intergranular bonding of particles in water presence
a) bridged b) suspended c )capilary d) droplet