Ceramic solids

Because of the larger surface area (compared with solid-ceramic refractories) the chemical resistance of fibers is relatively poor. Their acid resistance is good, but they have less alkah resistance than solid materials because of the absence of resistant aggregates. Also, because they have less bulk, fibers have lower gas-velocity resistance. Besides... 

Ionic conductors, used in electrochemical cells and batteries (Chapter 6), have high point defect populations. Slabs of solid ceramic electrolytes in fuel cells, for instance, often operate under conditions in which one side of the electrolyte is held in oxidizing conditions and the other side in reducing conditions. A signihcant change in the point defect population over the ceramic can be anticipated in these conditions, which may cause the electrolyte to bow or fracture. 

SOE cells utilize solid ceramic electrolytes (e.g. yttria stabilized zirconia) that are good oxygen ion (0 ) conductors at very high temperatures in the range of 1000°C [8]. The operating temperature is decided by the ionic conductivity of the electrolyte. The feed gas, steam mixed with hydrogen, is passed through the cathode compartment. At the cathode side, the reaction is... 

Some of these modules were fabricated in solid ceramic materials allowing chemical reactions with highly corrosive reactants or products or even at very high temperatures. Also special ceramic foams were developed which can be used as a catalyst carrier. 

Ford Motor Co [312] obtained a patent for a method of producing sodium which uses a solid ceramic (P-alumina) that conducts sodium ions as a divider for a two-compartment cell. This method allows low melting sodium salts or salt mixtures to be used to produce sodium [312-315], The cell operates at 200°C and 6 V instead of the conventional 7 V for Downs cells, making sodium at 600°C. The average current efficiency is 100% compared to 85-92% for Downs cells. The power consumption of the process at the same productivity is 20-30% lower than for the Downs cell. This process has, however, not been operated on a large scale because the P-A1203 does not have sufficient lifetime. 

THE USE OF FIRE TO transform CLAY PASTE into solid ceramic vessels may have been one of the earliest efforts at chemistry. Since the earliest times, pottery has been made by using clays formed by the weathering of rocks. Sedimentary deposits containing clay minerals also contain fragments of other minerals that are broken from the source rocks as they weather. The chemical composition of the sediments used as a clay source determined some of the characteristics of the pottery that was produced. 

Exposure limits for silicon carbide and powders of zirconium compounds (including zirconium dioxide) have been established by ACGIH. TLV —TWA s are 10 mg/m3 and 5 mg/m3, respectively. OSHA guidelines for zirconium compounds call for a PEL of 5 liig/m3. There are no exposure limits for silicon nitride powder, but prudent practice suggests a TLV—TWA of 0.1 mg/m3. The solid ceramics present no apparent health hazard. In machining such ceramics, however, care should be taken to prevent inhalation of respirable particles in amounts in excess of established limits. Disposal should be in approved landfills the materials are inert and should pose no danger to the environment. 

In solid phase reaction s3mthesis, there are three types of chemical reactions oxidation or reduction of a solid, thermal decomposition of a solid, and solid state reaction between two t3 s of solid. With liquid phase ssmthesis of ceramic powders, there are five different methods drying of a liquid, precipitation, sol-gel sjmthesis, hydrothermal S5m-thesis, and reactions of a liquid metal melt with a gas to give a solid ceramic. There are basically three operational principles for precipitation temperature change, evaporation, and chemical reaction. Sol—gel... 

Sometimes, a part of the ceramic material melts and provides a liquid phase during sintering. This liquid phase provides a medium for faster flow of material to fill the pores because the liquid can (1) act as a flux and dissolve the solid ceramic materials of the porous ceramic green body, (2) provide a pathway for fast diffiision compared to solid state diffusion, and (3) precipitate the final ceramic material in the pore thereby filling it. As a result sintering is a complex phenomena. 

FIGURE 16.39 Schematic of a phase diagram for a ceramic B and a metal A without any solubility of the solid ceramic A in the liquid A. When both A and B are liquid we have an immiscibility gap. 

FIGURE 6.29 Concepts of membrane reactor based on gas-liquid-solid ceramic membrane contactors. 

The early preparations of mesoporous silica film were conducted by growth from solution.[20,276]. The basic principle for the synthesis of ordered mesoporous films by growth from solution is to bring the synthesis solution (including a solvent, surfactant, and inorganic precursor) into contact with a second phase, e.g. solid (ceramic), gas (air), or another liquid (oil). The two-phase system is kept under specific conditions and the ordered film is formed at the interface. When the second phase is solid, it is the support on which the ordered film or membrane is grown. When the second phase is air or oil, the solid films are self-standing. 

Solid oxide fuel cell (SOFC) uses solid ceramic material, such as Y2O3 stabilized Zr02 (YSZ), as an electrolyte. As SOFC operates at high temperature (600-1000° C), a variety of fuels, e.g., hydrogen, methane, and carbon monoxide, can directly be utilized. The high temperature places severe constraints on material selection and results in difficult fabrication process. Co-ZrO (or Ni-ZrO) and SrO doped LaMn03 have often been used for anode and cathode materials, respectively. 

Williams, Richard J. Mullins, 0. "A System Using Solid Ceramic Oxygen Electrolyte Cells to Measure Oxygen Fugacities in Gas-Mixing Systems" Technical Memorandum TMX-58167,... 

Sood S K, Fong C, Kalyanam K M, Busigin A, Kvelton O K and Ruthven D M (1992), A new pressure swing adsorption (PSA) process for recovery of tritium from the ITER solid ceramic breeder helium purge gas . Fusion Technol, 21, 299. 

Carbon and Silicon Netuuork Atomic Solids Ceramics Semiconductors... 

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