Silica compounds physical processes

Silica compounds are generally processed in conventional internal mixers, preferably with intermeshing rotors. These mixers are designed and optimized for carbon black-fiUed compounds in which mixing is based only on physical processes. When a silica-silane reinforcing system is used, additionally a chemical reaction, the sUanization, occurs. One of the main influencing factors of the silanization reaction is the concentration of ethanol in the compound as well as in the mixer [25,26]. As the silanization finally reaches an equilibrium, low concentrations of ethanol in the compound are expected to enhance the reaction rate. 

Organo-silica compounds are widely used in a range of industries such as printing, oil production, and mining as lubricants and polishing compounds. They also find domestic use in silicon rubber and aerosol sprays because of their special physical properties, such as viscosity and dielectric constant. These compounds are also recognized as poisons/inhibitors in different catalytic processes, such as in atmospheric scrubbers, automobile exhausts, flammable gas... 

Rubber compounds very often contain smaU-particle fillers such as carbon black and silica, to improve processability and physical properties, and to reduce material costs. The most common filler is carbon black, use of which as a pigment dates to ca. 4000 BC. Methods to incorporate fillers, and the effect of their distribution and dispersion on properties, are central considerations, with... 

For all processes that involve the adsorption step, such as physical processes of separation or catalytic transformations, the usage of solid materials with optimised activity as adsorbents and catalysts is necessary. Various solids, such as porous materials (zeolites—molecular sieves with hierarchical porosities and natural clays), activated carbons, mesoporous silica-based materials, pillared clays and metal oxides, have shown the ability to act as adsorbents or as catalysts for the conversions of previously mentioned atmospheric pollutants. Solid materials are also used for the removal of pollutants that can be found in wastewaters. The possibilities to remove polyaromatic hydrocarbons (PAHs) and heavy metal particles using the adsorptive characteristics of activated carbon and porous materials from wastewaters have been proven [15-17]. The same classes of solids are used for the elimination of organic pollutants form wastewaters by heterogeneous catalytic oxidation processes one of the most important tasks is to eliminate phenolic compounds [13]. 

Other additives such as silanes, titanates and zirconates are also used to overcome the processing characteristics of silica fillers. Silanes not only give improved processability of silica-filled compounds, but also provide improved crosslinks between the silica particle surface and the rubber molecular chains giving increased physical properties. The use of silane coupling agents at a... 

Nitrile mbber is much like SBR in its physical properties. It can be compounded for physical strength and abrasion resistance using traditional fillers such as carbon black, silica, and reinforcing clays. The primary benefit of the polymer is its oil and solvent resistance. At a medium ACN content of 34% the swell in IRM 903 oil at 70°C is typically 25—30%. Nitrile mbber processes on conventional mbber equipment and can be compression, transfer, or injection molded. It can also be extmded easily. 

On silica gel and alumina, the PAHs show a wide range of photolytic activity suggesting a relationship between structure and activity. On the fly ash, similar half-lives were observed that would indicate, in this instance, that the process is independent of the PAH structure and dependent on the physical and chemical properties of the substrate. The PAHs are more stable on the carbon black and there is little variation among the different compounds. For comparison, the vapor-phase half-lives have been calculated and in most instances are shorter than those observed on the particles. Pyrene is a noted exception showing more rapid degradation on silca gel and alumina than by the hydroxyl radical process in the vapor phase. 

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