White ceramics

To produce a ceramic material containing only Si3N4, the white solid polysilazane derived from DHCD of the oil obtained by ammonolysis of 6 1 CH3SiHCl2/CH3SiCl3 was pyrolyzed in a stream of ammonia (to 1000°C). A white ceramic residue containing only 0.36% by weight C resulted. 

Primary clay, for example kaolin, is colorless, and when such clay is heated to a high temperature it produces white ceramic materials. Most pottery, however, is colored its color is due to the fact that most of it was, and still is, made not from primary but from secondary clay. Secondary clay contains minerals other than clay, and colored metal ions in them endow the pottery with their color. Iron ions (in iron oxides), for example, tend to make pottery yellow, brown, or red, and manganese ions (in pyrolusite, a mineral composed of manganese oxide) make it either dark or black. 

All specifications apply for a diffusely reflecting matt white ceramic target... 

Fig. 5.12. DIP of a JEOL JMS-700 sector instrament for use with El, chemical ionization (Cl) and field ionization (FI). The copper probe tip holds the glass sample vial and is fitted to a temperature-controlled heater (left). The heater, a thermocouple, and circulation water cooling are provided inside. The (white) ceramics insulator protects the operator from the high voltage of the ion source.

NIR spectra are acquired using dried tissue, either whole or ground. The reflectance is measured relative to a so-called white reference, which is a highly reflective surface, such as Gore-Tex or white ceramic. Near-infrared reflectance spectra, or absorbance spectra, defined as log(l/R), with R being the reflectance, look rather flat. For analysis purposes the second derivative of the spectra is often used, because it enhances certain spectral features. 

Yellowness Index. The yellowness of the 50-mil plaques used for stabilization studies was measured directly from a Hunter D-25 color difference meter equipped with a 90° sphere attachment. The samples were placed in the reflectance port of the sphere using a standard white ceramic as backing. The instrument is designed to give direct yellowness index values as described in ASTM D-1925. 

These polymers may be used in the preparation of high-purity silicon nitride if the pyrolysis is carried out in a steam of ammonia (a reactive gas) rather than under nitrogen or argon. Thus pyrolysis to 1000 °C of the DHCD product of the ammonolysis product (THF) of the 1 1 mixture in a stream of ammonia gave a white ceramic residue in high yield, which contained only 0.29% C, with the remainder being silicon nitride. 

Fibers could be drawn from concentrated syrups of these products in toluene. The drawn fibers could not directly be converted to ceramic fibers, because they melted on being heated, and a cure step was required to render them infusible. The required cure could be accomplished by UV irradiation of the fibers. Following this treatment, pyrolysis of the fibers in a stream of argon gave black ceramic fibers, and pyrolysis in a stream of ammonia gave white ceramic fibers. 

Diffraction data (Table 4.4) were collected from a white ceramic plate. Using the Mineral Database and 3 strongest of the 15 observed peaks identify the material. 

A hard, fine-grained, non-POROUS, white CERAMIC ware that is fired at high temperature. 

T. Takahashi, Y. Katsumura, and H. Suzuki, Cutting performance of white ceramics tools having high strength, J. Jpn. Soc. Powd. Powd. Metall. 1994, 41, 33-37. 

G J Oliver and R N White, Ceram Research Limited, Stoke-on-Trent, UK... 

Standard, white reflectance n. In general usage, may refer to a physical white standard which is nearly a perfect white diffuser, such as pressed barium sulfate of high purity, pressed magnesium oxide or freshly smoked magnesium oxide. Other less perfectly diffusing or reflective materials, such as white ceramics, may be calibrated in reference to the perfect diffuser or to one of the near-perfect materials, and used in place of the material relative to which it is cahbrated. Such a white reference standard should properly be called a secondary reference standard. 

White ceramics, with a high reflective index in the visible and near-UV regions. Used as linings in steel furnaces. 

An important application for zirconium oxide is as an alloying element in aluminum oxide ceramics. Sintered aluminum oxide is brittle. It has been found that the toughness can be considerably improved by mixing aluminum oxide with 4-15% zirconium oxide and sintering the two together. Then a white ceramic , tough enough for many applications, e.g. tools, is obtained. 

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