Ceramic hot pressing

Fig. 3. Stress mpture behavior in air at 1200°C for SiC stmctural ceramics —hot-pressed -, reaction-bonded , sintered alpha —sintered beta. To...

When you squeeze snow to make a snowball, you are hot-pressing a ceramic. Hot-pressing of powders is one of several standard sintering methods used to form ceramics which require methods appropriate to their special properties. 

M. H. Leipold, "Hot Pressing," ia F. F. Y. Wang, ed.. Treatise on Materials Science and Technology, Vol. 9 (Ceramic Fabrication Processes), Academic Press, New York, 1976. 

Fig. 2. Strength as a function of temperature for representative SiC stmctural ceramics A, sintered (Y2O2 added) , hot-pressed (2% AI2O2) sintered...

Fig. 4. Thermal diffusivity of silicon-based stmctural ceramics (a) reaction-bonded SiC (b) hot-pressed and sintered SiC (c) hot-pressed (1% MgO,...

Fig. 11. Micrographs of (a) a hot-pressed alumina—TiC ceramic showing a white TiC phase and a dark alumina phase (3) and (b) a fracture surface of an...

Beryllium Nitride. BeryUium nitride [1304-54-7], Be N2, is prepared by the reaction of metaUic beryUium and ammonia gas at 1100°C. It is a white crystalline material melting at 2200°C with decomposition. The sublimation rate becomes appreciable in a vacuum at 2000°C. Be2N2 is rapidly oxidized by air at 600°C and like the carbide is hydrolyzed by moisture. The oxide forms on beryllium metal in air at elevated temperatures, but in the absence of oxygen, beryllium reacts with nitrogen to form the nitride. When hot pressing mixtures of beryUium nitride and sUicon nitride, Si N, at 1700°C, beryllium sUicon nitride [12265-44-0], BeSiN2, is obtained. BeSiN2 may have appHcation as a ceramic material. 

Uses. Apphcations for boron carbide relate either to its hardness or its high neutron absorptivity ( B isotope). Hot-pressed boron carbide finds use as wear parts, sandblast no22les, seals, and ceramic armor plates but in spite of its hardness, it finds Httie use as an abrasive. However, this property makes it particulady usehil for dressing grinding wheels. 

There are two further processes. Silicon-based ceramics can be fabricated by sintering or by hot-pressing. But a new route, reaetion bonding (Fig. 19.6), is cheaper and gives good precision. If pure silicon powder is heated in nitrogen gas, or a mixture of silicon and carbon powders is sintered together, then the reactions... 

If the temperature and supersaturation are sufficiently high in a CVD reaction, the product is primarily powder precipitated from the gas phase (see Ch. 2). Such powders have few impurities provided that the CVD precursors are carefully purified. Their small diameter and great uniformity are important factors in the production of high quality hot-pressed or sintered ceramic bodies with good mechanical and electrical properties. In addition, the sintering temperatures required for CVD powders are lower than those for conventional powders. 

Early tests [37] utilized a cell design similar to that of early MCFC experiments. The assembled cell, machined from graphite blocks, is shown as Fig. 24. The electrodes and current collectors were machined from graphite and dense carbon, respectively. The electrolyte was a mixture of 63% Na2S, 37% Li2S, believed to melt near 850 °C the melting point after several days of operation was below 700 °C, probably because of polysulfide formation. The electrolyte was immobilized in a matrix of MgO, the whole formed by hot-pressing a mixture of electrolyte and ceramic powders. 

Hot melt silicones, 22 35 Hot molding, 12 733 Hot-pressed carbon brick, 12 764 Hot pressing, ceramics processing,... 

Sol-gel processing in which a network of precipitated colloidal particles is treated by a conventional processing technique, such as cold pressing, hot pressing or sintering, in order to produce a ceramic article. 

Figure 4. A typical setup for hot pressing PLZT ceramics...

Sobolev, I. A., Stefanovsky, S. V., Omelianenko, B. I., Ioudintsev, S. V., Vance, E. R. Jostsons, A. 19974. Comparative study of Synroc-C ceramics produced by hot-pressing and inductive melting. Materials Research Society Symposium Proceedings, 465, 371-378. 

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