Opacified powders

Fig. 1-7 Apparent thermal conductivities of typical cryogenic insulation material (a) multilayer insulations (b) opacified powders (c) glass fibers (cf) powders (e) foams, powders, and fibers, according to Ref. 1. [1 Btu in/h ft2 ° F = 144 mW/m °C]...

Paper studies were first made to determine a basis for design work. This covered pipe sizes from 1/2 in. through 8 in. and included analysis of vacuum insulation systems using perlite, CS-5 opacified powder and two different grades of superinsulation, SI-12 and SI-4. BoA cost and performance were compared. Comparison was based on application in hydrogen service and return of investment over a two-year period based on both depreciation and the savings due to the reduction of evaporation losses. For the purposes of this study the arbitrarily assumed value of liquid hydrogen is. 50/lb. 

After some study, it was found that of the total heat transport through the coarser, heavier powders such as perlite, contribution due to solid conduction amounts to over 70, the remainder being attributable to radiation. As there seemed to be no practical way of reducing this "intrinsic" solid conductivity, it was concluded that powders of this type did not offer much opportunity for further improvement instead, it was decided that opacifying powders of very low solid conductivity which are, however, essentially transparent, in order to reduce the radiative mode of heat transport, would, in all likelihood, be the more fruitful approach. 

Opacifiers are fine inorganic powders, usually white, that are used to reduce the transparency of ceramic gla2es and porcelain enamels. The coating becomes opaque because the particles of the opacifter scatter and reflect the incident light. When inorganic pigments are combined with white opacifiers, pastel colors are obtained. 

Microporous insulation materials consist mainly of highly dispersed silica with a particle size of only 5-30 nm. The highly dispersed silica powder is pressed to plates, which receive heat treatment up to 800 °C, after which the plates are self-supporting and possess a micropore structure with pore diameter of 0.1pm. The addition of opacifiers to the highly dispersed silica starting material reduces the loss of heat by radiation. The dates for such insulation boards are shown in Table 18. 

Stannic oxide, SnC>2, is a white powder, insoluble in acids and alkalis. It is an excellent glaze opacifier, a component of pink, yellow and maroon ceramic stains and of dielectric and refractory bodies. 

Deterrents are used to coat the powder, reducing the initial bum rate, and lowering the burn temperature. Deterrents used include dinitrotoluenes, ethyl centralite, methyl centralite, and phthalates. Inorganic additives such as earth metal salts are added as flash suppressants, and opacifiers such as carbon black can be added to increase the reproducibility of the burn rate [34], Note that several of the listed additive chemicals serve multiple purposes, as summarized in Table 5. Ethyl centralite can be applied as a stabilizer, a plasticizer, and a deterrent. Similarly, dinitrotoluenes can be used as both a plasticizer and a deterrent. Table 6 represents composition data from six powder... 

Cerium 58 Ce Polishing powders, opacifier for porcelain coatings, glass decolouriser and melting accelerator, photographic materials, textiles, arc lamps, ferrous and non-ferrous alloys including high-temperature Mg alloys, automotive catalytic converters, misch metal... 

Zinc stearate is primarily used in pharmaceutical formulations as a lubricant in tablet and capsule manufacture at concentrations up to 1.5% w/w. It has also been used as a thickening and opacifying agent in cosmetic and pharmaceutical creams and as a dusting powder. See Table I. 

Zirconia powder serves as a polishing agent, as an opacifier in glazes and enamels and as a component of chemically resistant glasses and enamels stabilized Zr02 is used in the manufacture of highly refractory ceramics. 

Properties White powder. Insoluble in water. Efficient flux in glasses containing zirconium dioxide. Recommended as a flux in zirconium-opacified enamels, glazes, and porcelains. 

Titania. Titania powders are used as pigments, catalytic supports, membranes, opacifiers, photocatalysts and fillers in industrial applications . Titania particles have been prepared by a number of methods, such as hydrolysis, sol-gel, microemulsion and hydrothermal synthesis. Titania exists naturally in two tetragonal forms, the metastable phase anatase, and the stable phase rutile. On heat treatment, anatase transforms into rutile. The phase transition temperature depends on the starting materials and the preparation procedure. 

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