Questions and Answers (1 / 2)
Ceramics
1.
Examples of engineering, dielectric, optical ceramics
Engineering: oxide: Al2O3, non oxide: SiC Dielectric : strontium titanate (ST), calcium titanate (CT), magnesium titanate (MT), Optical ceramics: Al2O3, YAG, Nd: YAG, Yttrium oxide (Y2O3)
2.
Examples of ceramics with ionic bonding
MgO, CaO, Al2O3, ZrO2
3.
Examples of ceramics with covalent bonding
SiC, TiC, AlN, Si3N4
4.
Give a basic differences between the monocrystalline oxide compound and ceramics
Monocrystalline oxide is not necessarily sintered, Ceramics are sintered material and we know the way of the uprising
5.
Examples (3) of advanced ceramics
Si3N4, Zr2O3, SiC
6.
Examples (3) of traditional ceramics
faience (quartz+ feldspar), porcelain (kaolin+quartz+feldspar), stoneware (stoneware products are produced from clay raw materials)
7.
Main stages of ceramic technology
Raw materials → Chemical treatment → Milling → Batching → Mixing → Forming → Drying → Sintering → Final machining
8.
What parameters are essential for characterization of the given powder?
particle size (granulometry), particle shape (morhpology), deegre of fragmentation, chemical composition, purity, degree of crystallinity and concentration of defects
9.
How the surface energy of powder could be decreased?
Surface energy can be reduced by adding wetting agents
10.
Difference between an aggregate and an agglomerate
Aggregate - a collection of crystallites of common borders, An agglomerate - a collection of crystallites or aggregates that contact each other pointwise
11.
Difference between an agglomerate and a granule
The agglomerate is a spontaneously formed porous form composed of crystallites or aggregates contacting each other pointwise. Granula is a powder specially formulated in agglomerates with regular shapes, minimized porosity, created under conditions that allow slipping and dense packing.
12.
Types of bonding in granules
Van der Waals or resulting from binder, electrostatic bonding
13.
Types of bonding in agglomerates
Electrostatic or van der Waals, polymer
14.
List examples (3) of natural raw materials for ceramic industry
Clay, Silica, Kaolinite
15.
List the names (2) of natural hydroxides of alumina-silicates
Kaolinite (Al4[Si4O10](OH)8), Illite K0.6-0.85Al2(Si,Al)4O10(OH)2
16.
Give examples (2) of equipment for crushing brittle raw materials
Hammer Crusher,, Jaw Crusher
17.
Give examples (3) of mills used in ceramic industry
Ball mill, Roller mill, Atritor mill
18.
Could you explain a term “calcination”
Calcination is a heat treatment in order to decompose the materials especially carbonate to its oxide state. It’s use only to simple oxides, is a endothermic reaction,
19.
Give an example (1 reaction) of solid state synthesis of mixed oxides
CaO + TiO2 -&rt; CaTiO3 (perovskite, ferroelectric)
20.
Give an example (1 reaction) of carbothermal synthesis of non-oxide ceramic powder
Si + C = SiC (???) Si3N4 + 3C ⇌ 3SiC + 2N2 (???)
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
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
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
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.
25.
.List the reagents (3) in sol-gel method for ceramic powder production
- water - alkoxides - acid
26.
Principles of ceramic nanopowder production via gas-phase methods
EVAPORATION-CONDENSATION, DECOMPOSITION OF GASEOUS COMPOUNDS, REACTIONS BETWEEN GAS PHASES
27.
What does it mean: “rheology”
RHEOLOGY: hydrodynamics of dispersed systems: solid+liquid
28.
Parameters describing powder properties(3)
Particle size distribution, Apparent mean size, Specific Surface area (SSA)
29.
Why powder particles from agglomerates?
Because it wants to reduce the surface energy
30.
How water presence affect Hamaker’s constant of powder?
Water presence reducecs Hamaker's constant
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
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+]
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)
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
35.
What is the origin of electrostatic repulsion of ceramic particles in the polar liquid?
electrostatic repulsion forces: repulsion of two identical charged ions
36.
What are the means of suspension stabilization?
- pH-changing agents - polymer - sulfactants
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
38.
What is the role of surfactants in stabilization of suspension?
Increase distance between particles suspension
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
40.
List the types (4) of intergranular bonding of particles in water presence
a) bridged b) suspended c )capilary d) droplet
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
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
43.
Give the names of various casting (3)
Slip-casting a ceramic part, Centrifugal casting of ceramics, Tape casting
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
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
46.
Why the casted objects shrink during drying?
because of water/solvent removal
47.
How water is removed from the casted object during casting to non-porous (plastic) moulds?
The water is removed from the casted thanks to rotation of the mould
48.
Characterization of tape casting
Tape casting has been used to produce thin layers of ceramics. The Tape Casting process involves the casting the slurry onto a flat moving carrier surface. The slurry usually consists of a ceramic powder with the appropriate additions of solvents plasticisers and binders.
49.
Why the thin ceramic foil can be produced from the viscous suspension?
Selection of the suitable composition of the suspension assures its good fl uidity and obtainment of the thin homogenous layers with the uniform structure
50.
Which parameter control viscosity of ceramic suspension?
Amount of Solvent