Precipitated silica

About: Precipitated silica is a research topic. Over the lifetime, 1401 publications have been published within this topic receiving 20992 citations.

Characterization of rice hull ash

Abstract: Rice hulls, a byproduct of the rice industry, contain 60-90% silica and are unique within nature. The annual worldwide output of rice-hull-derived silica is more than 3.2 million tons, which poses environmental concerns because of disposal issues. Burning rice hulls, as a preparative step for energy production, is a useful solution to the growing environmental concern, a desirable outcome would be the economic use of the resulting silica-rich hull ash. The economical usefulness of this silica ash in the filler market has been undermined by its limited dispersion abilities and poor interaction capability with polymers. In this study, some of the reasons for the poor performance of silica ash as a reinforcing filler in various polymeric composites were linked to its inherent characteristics: factors such as its impurity, irregular topography, porosity, and chemical and thermodynamic nature arising from its surface polarity that negatively influence the filler-matrix interactions. The silica ash obtained from a novel combustion process had about 6% (w/w) impurity, of which around 3% was volatile. We also propose that the silanation efficiency of silica ash is lower compared to other commercial silicas because of its porosity, which could hide a fraction of the silane used. Also, processing changed the particle size distribution, and this could have affected the agglomerating tendencies and seriously marked the reinforcing capabilities of the silica ash. The estimation of the surface silanol groups of the rice hull ash by thermogravimetric studies indicated that the surface silanol density was about 16/nm2. On a comparative scale, this value is comparable to the silanol density on precipitated silica, but a thermodynamic study of silica ash surface revealed a high surface free energy that contributed to its high aggregation tendencies and poor distribution and dispersion abilities.

Process of treating silica with a siloxane and product thereof

Abstract: A finely-divided hydrophobic silica filler having reduced tendency to induce structure when incorporated in a siloxane convertible to the solid, elastic state (see Group IV (a)) consists of silica aerogel, fume silica or precipitated silica coated with octamethyl-cyclotetrasiloxane. The treatment of the silica may be effected either (1) by mixing it with the cyclic siloxane in amount from 5 to 10 per cent by weight of the silica and heating the mixture at 150 DEG to 350 DEG C. and at normal or reduced pressure to cause volatilization of the siloxane and diffusion thereof through the silica particles with consequent replacement of moisture on the silica by a thin film of the siloxane; or (2) by continuously introducing, in a heated atmosphere the finely-divided silica and siloxane into an air-jet mill (see article entitled "Efficient Particle-Size Reduction" in July, 1955 issue of "Chemical Processing".ALSO:A composition having reduced structure and lower knit time comprises (1) an organopolysiloxane convertible to the cured, solid, elastic state and containing an average of from 1.98 to 2.05 organic radicals per Si atom, and (2) a structure inducing filler, selected from silica aerogel, fume silica and precipitated silica, treated with octamethylcyclotetrasiloxane (see Group III). The convertible siloxane may contain methyl, ethyl, propyl, vinyl, allyl, phenyl, tolyl, xylyl, benzyl, phenylethyl, naphthyl, chlorophenyl or tetrachlorophenyl radicals bonded to silicon. Siloxanes containing methyl or methyl and phenyl radicals are preferred. The structure-inducing filler may be used in amount from 10 to 200 per cent by weight of the siloxane. Non-reinforcing fillers, untreated or treated as above, may also be added, e.g. titania, lithopone, zinc oxide, ferric oxide, zirconium silicate, diatomaceous earth, fine sand, and calcium carbonate. The compositions may be cured by means of curing agents, e.g. benzoyl peroxide, tertiary butyl perbenzoate or bis-(2 : 11-dichlorobenzoyl) peroxide or by highenergy electron irradiation. The compositions may be moulded, e.g. at 100 DEG to 200 DEG C. from 5 to 30 minutes at pressures from 10 to 1000 p.s.i., and further heat-treated for 1 to 36 hours at 150 DEG to 250 DEG C. Examples are given. Where desired, solvents, e.g. toluene, xylene and butanol, may be used to make dispersions for coating and impregnating sheet materials, e.g. glass cloth, asbestos cloth and mica sheets, fibres and finely-divided fillers, e.g. mica, glass fibres and asbestos floats, for subsequent use in making heater ducts or for electrical insulation.