Brown powder Browning process

Silicon is prepared commercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be prepared as a brown powder, which can be easily melted or vaporized. The Gzochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process. 

If lighter colors than these are desired it is necessary to decolorize all the melanin in the hair in a preliminary step, and then add color back to the desired depth in a second treatment. This is known as a double-process treatment. The decolorization step consists of treating the hair with an alkaline mixture of persulfate salts and peroxide. The persulfate is added to the peroxide as a dry powder immediately before applying to the hair. Although the persulfate salts alone do not have any bleaching effect, the persulfate—peroxide mixture can remove all the melanin in the hair. Dark brown or darker hair can be lightened to a light blonde shade in about an hour. 

Iron Browns. Iron browns are often prepared by blending red, yellow, and black synthetic iron oxides to the desired shade. The most effective mixing can be achieved by blending iron oxide pastes, rather than dry powders. After mixing, the paste has to be dried at temperatures around 100°C, as higher temperatures might result in the decomposition of the temperature-sensitive iron yellows and blacks. Iron browns can also be prepared directiy by heating hydrated ferric oxides in the presence of phosphoric acid, or alkaU phosphates, under atmospheric or increased pressure. The products of precipitation processes, ie, the yellows, blacks, and browns, can also be calcined to reds and browns. 

The menstmum niobium—carbide process (7) utilizes either columbite [1310-23-2] mineral concentrates or ferroniobium as starting materials. A low level of TaC in soHd solution with NbC commonly occurs, as Ta and Nb occur together in ores. The properties of NbC are given in Table 1. The grayish brown NbC powder is used in cemented carbides to replace TaC. TaC—NbC soHd solutions that have 3 1, 2 1, 1 1, and 1 2 ratios and the corresponding ternary and quaternary soHd solutions with TiC and WC are common. 

Compaction Rate Processes The performance of compac tion techniques is controlled by the ability of the particulate phase to uniformly transmit stress and the relationship between apphed stress and the compaction and strength characteristics of the final compacted particulate phase. The general area of study relating compac tion and stress transmission is referred to as powder mechanics (Brown Richards, Principles of Powder Mechanics, Pergamon Press Ltd., Oxford, 1970). 

Tour s work showed that polymerization is still a preferred process even though large excesses ofradical traps (1,4-cyclohexadiene) were employed. They obtained poly( 1,4-naphthalene) only as an insoluble brown powder by polymerization of 1,2-diethynylbenzene in benzene solution. This route appears to be an attractive approach to a new dielectric medium ... 

Diphenylamine behaves not only as a stabilizer, but also as an indicator of the oxidation and decomposition processes which occur in powders. It was noticed long ago that powders containing diphenylamine assume under certain conditions colours ranging from greenish or bluish shades to dark blue or almost black and sometimes to yellow or brown, i.e. ... 

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