Wollastonite processing

Miyamoto, M., N. Onuma, and H. Takeda (1979). Wollastonite whiskers in the Allende meteorite and their bearing on a possible post condensation process. Geochem. J. 13 1-5. 

The silanization process has also been employed to permit tailoring, for various applications, surfaces such as kaolin clays, Wollastonite, talc, and sodium aluminum silicate with amino, epoxy, mercapto, methacryloxy and vinyl groups. 

The moisture resistance properties of filled molding compounds are enhanced by the treatment of the fillers with silane adhesion promoters prior to compounding. Silane promoters on wollastonite fillers in thermoplastic polyester molding compounds (50 percent filled) will improve the flexural strength after 16 h in 50°C water by as much as 40 percent. Silane-treated silica fillers have been found to significantly increase the moisture resistance of epoxy adhesives used in the electronics industry for chip, surface-mounted, and printed-circuit processes.8... 

Nonfibrous reinforcements are also employed as reinforcements and fillers. They result in increased tensile strength and deflecdon temperature, but usually decrease impact resistance. Nonfibrous reinforcements are preferred when fabricating with exceptional flatness. The nonfibrous include mica, glass beads, and minerals such as wollastonite (talc, calcium carbonate, and kaolin are considered fillers). Unlike fibrous reinforcements the nonfibrous reinforcements can be processed by many different technologies. 

A supersaturated bioinspired solution was used to coat alumina and zirconia substrates with a thin, poorly crystalline layer of OCP that after heat treatment at 1050 °C for 1 h was converted to hydroxyapatite with particle size of 300 nm (Pribosic, Beranic-Klopcic and Kosmac, 2010). Stefanic et al. (2012) applied a related method to rapidly deposit an OCP layer by a two-step process onto yttria-stabilised tetragonal zirconia polycrystal (Y-TZP). 80vol% Mg-PSZ/20 vol% alumina substrates were used by Nogiwa and Cortes (2006) to deposit biomimetically by immersion in 1.4 SBF a bone-like apatite coating of 15-30 pm thickness, using a bed of either wollastonite ceramics or bioactive glass as an additional source of Ca2+ ions. 

It is the length of a particle divided by its diameter. For spherical or cubical particles, the aspect ratio equals to one. For calcium carbonate particles, the aspect ratio is typically 1-3. For talc, the aspect ratio is typically in the range of 5-20. For milled glass fiber, it is between 3 and 25. For mica, it is 10-70. For wollastonite, it is between 4 and 70. For chopped glass fiber, it is between 250 and 800. For natural fibers, such as cellulose, the aspect ratio can be from 20-80 to thousands. Low aspect ratio is below 10. However, the above figures are given for fillers not processed in a compounder and/or an extruder. Upon processing, aspect ratio can decrease from dozens and hundreds to as low as 3-10. 

The process involves blending PPCO with a resin or its blend that is to be foamed. The blend is then heated to T > 300°C, sufficient to melt the principal resin and to decompose PPCO. Talc, wollastonite, clay, CaCOj or citric acid can be used as a nucleating agent. The densities of the molded articles were reduced by at least 50%. Most recently, foaming of the engeneering resims by supercritical CO was introduced. 

CaCOs compounds. Wollastonite s fiber-like shape provides similar properties as those of the glass fibers discussed below, and also like glass, its abrasiveness can damage processing equipment. However, unlike other mineral fiber, asbestos, its particles are nonhazardous [1-1, 3-4, 7-6, 7-13, 7-15]. 

---