Ceramic products

Fig. 9. Strength ranges for glass and glass-ceramic products. To convert MPa to psi, multiply by 145.

The development of the principles of nucleation and growth eady in the twentieth century (2) ultimately led to the discovery that certain nucleating agents can induce a glass to crystallize with a fine-grained, highly uniform microstmcture that offers unique physical properties (3). The first commercial glass-ceramic products were missile nose cones and cookware. 

Heating the ammonium beryUium carbonate solution to 95°C causes nearly quantitative precipitation of beryUium basic carbonate [66104-24-3], Be(OH)2 2BeC02. Evolved carbon dioxide and ammonia are recovered for recycle as the strip solution. Continued heating of the beryUium basic carbonate slurry to 165°C Hberates the remaining carbon dioxide and the resulting beryUium hydroxide [13327-32-7] intermediate is recovered by filtration. The hydroxide is the basic raw material for processing into beryUium metal, copper—beryUium and other aUoys, and beryUia [1304-56-9] for ceramic products. Approximately 90% of the beryUium content of bertrandite is recovered by this process. 

Any product that depends on aesthetics for consideration for purchase and use will be improved by the use of color. Hence, many ceramic products, such as tile, sanitary ware, porcelain enameled appHances, tableware, and some stmctural clay products and glasses, contain colorants. 

For both economic and technical reasons, the most effective way to impart color to a ceramic product is to apply a ceramic coating that contains the colorant. The most common coatings, gla2es and porcelain enamels, are vitreous in nature. Hence, most appHcations for ceramic colorants involve the coloring of a vitreous material. 

The Marshall group has optimized reaction (14) to obtain a poly-si lazane with Mw A000 Daltons which can be hand drawn to give 10-20 pm preceramic fibers. These fibers are then rendered Infusible by exposure to humid air and pyrolyzed to give fibers with the same ceramic yields, 55+%, as found by Verbeek et al. The ceramic products are mainly amorphous SiC and SijN with some Si02 (a consequence of the humidity treatments). 

Table I lists the molecular weights and viscoelastic properties for the precursors and selected polymers produced in reaction (34). It also contains the ceramic yields obtained on pyrolysis to 900°C and the composition of the ceramic product.

While these silylamide-catalyzed reactions provided a good way to solve the problem of the low ceramic yield in the pyrolysis of [(CH3SiH)x (CH3Si)y]n, the problem of the elemental composition of the ceramic product remained (i.e., the problem of Si/C ratios greater than one) since only catalytic quantities of the silylamide were used. 

The ceramic products obtained in the pyrolysis of the "combined" polymers have not been studied in detail, but some of them have been analyzed for C, N, and Si. The compositions of the ceramic materials obtained cover the range 1 Si3N4 + 3.3 to 6.6 SiC + 0.74 to 0.85 C. Thus, as expected, they are rich in silicon carbide and the excess Si which is obtained in the pyrolysis of the [(CH3SiH)x(CH3Si)y]n materials alone is not present, so that objective has been achieved. By proper adjustment of starting material ratios, we find that the excess carbon content can be minimized [11]. 

Lead is produced from both primary (i.e., mined ore) and secondary (i.e., scrap metal and wastes) sources, and is imported by the United States. In 1997, production from primary and secondary sources was 343,000 metric tons and 1.1 million metric tons, respectively (Smith 1998), and imports reached 265,000 metric tons (Larrabee 1998 Smith 1998). Approximately 1.6 million metric tons of lead were consumed in the United States in 1997 (Smith 1998). Of lead used in 1997, 86.9% was used for storage batteries, 7.8% was used in metal products, and 5.3% was used in miscellaneous applications (Smith 1998). Because of the adverse health effects associated with exposure to lead, its use in paints, ceramic products, gasoline additives (now banned), and solder has declined dramatically in recent years. In 1997,... 

Table II. Ceramic Products from Metal Powder-Polysilazane Composites Pyrolyzed to 1500 °C under a Flow of Argon.

Used industrially as a rodenticide, raw material for glass and ceramic production, and intermediate for preparation of other arsenical products. 

Drue, I. C., Burger, R. L., Zamojska, R., and Magny, P. (2001). Ancon and Garagay ceramic production at the time of Chavin de Huantar. Journal of Archaeological Science 28 29 43. 

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