Silica, fusion

Recently, Foo et al. (2006) produced some novel nanocomposites from spider silk-silica fusion (chimeric) proteins. The composite morphology and structure could be regulated by controlling processing conditions to produce films and fibers. Silk and biomineralization being natural inspiration sources will allow production of numerous new materials in various fields of application. 

Mieszawska, A. J., Nadkami, L. D., Perry, C. C., and Kaplan, D. L. (2010). Nanoscale control of silica particle formation via silk-silica fusion proteins for bone regeneration. Chem. Mater. 22, 5780-5785. 

Wong Po Foo, G., Patwardhan, S. V, Belton, D. J. et al. 2006. Novel nanocomposites from spider silk-silica fusion (chimeric) proteins. Proc Natl Acad Sci USA, 103 9428-33. 

Vitreous silica (silica glass) is essentially a supercooled Hquid formed by fusion and subsequent cooling of crystalline silica. It is found ia nature ia fulgerites, ie, fused bodies resulting from lightning striking quart2 sand. 

Chemical methods to determine the crystalline content in silica have been reviewed (6). These are based on the solubility of amorphous silica in a variety of solvents, acids or bases, with respect to relatively inert crystalline silica, and include differences in reactivity in high temperature fusions with strong bases. These methods ate qualitative, however, and fail to satisfy regulatory requirements to determine crystallinity at 0.1% concentration in bulk materials. 

Transparent fused silica can be formed at a temperature of 1200°C and a pressure of 13.8 MPa (2000 psi) from silica powder consisting of 15 nm ultimate particles (92) or by electric arc fusion of pure silica sand having low iron and alkali metal contents. The cooled product is ground to the desired particle size. Fused sihca is primarily manufactured by C-E Minerals, Minco, and Precision Electro Minerals in the United States by Chuo Denko, Denki Kagaku Kogyo, NKK, Showa Denko, and Toshiba Ceramics in Japan. Based on 1988 data and projected growth, an estimated 135,000 metric tons of fused siUca were used in 1994 as a sacrificial component or investment casting in the manufacture of metals and as a component in refractory materials (62). 

Substances which are insoluble or only partially soluble in acids are brought into solution by fusion with the appropriate reagent. The most commonly used fusion reagents, or fluxes as they are called, are anhydrous sodium carbonate, either alone or, less frequently, mixed with potassium nitrate or sodium peroxide potassium pyrosulphate, or sodium pyrosulphate sodium peroxide sodium hydroxide or potassium hydroxide. Anhydrous lithium metaborate has found favour as a flux, especially for materials containing silica 12 when the resulting fused mass is dissolved in dilute acids, no separation of silica takes place as it does when a sodium carbonate melt is similarly treated. Other advantages claimed for lithium metaborate are the following. 

Oxide glasses have been reported by Crisp Wilson (1978a,b, 1979), Wilson et al. (1980), and Hill Wilson (1988a). The fusion mixtures contain silica, alumina and calcium carbonate to which sodium carbonate or calcium orthophosphate may be added. They may be represented thus, with fusion temperature given in parentheses ... 

This is the earliest and the most commonly used casting process. It has the advantages of wide metal suitability, low cost, and simple operation. It uses sand as a refractory material. Many types of sand are utilized by the foundry industry. However, because of its wide availability and relatively low cost, silica sand is the one that makes most metal castings. Silica sand is composed of the mineral quartz (Si02), which has a fusion point of approximately 1670°C (3090°F), which is often lowered by the presence of appreciable quantities of minerals with lower fusion points. 

Iron-centered tetradecker sandwiches, when in contact with oxygen on silica, undergo oxidative fusion with ejection of iron to generate 12-vertex Co2C4B8 clusters.83 The cluster geometry, however, depends on the nature of the substituent X at B(3) in the iron sandwich. When X = H or Cl, the isolated species are of type 62, also obtained directly from C0C2B3 complexes as described in Section 3.01.4.1 64 when X = Me, the cluster produced is 77.84... 

The product of the fusion of silica with sodium carbonate, sodium silicate (strictly called sodium poly trioxosilicate but usually metasilicate), dissolves in water to give a clear, viscous solution known as waterglass . It hydrolyses slowly and silica is precipitated. Besides the metasilicate, other silicates of sodium are known, e.g. the poly-tetroxosilicate (orthosilicate), Na4Si04. Only the silicates of the alkali metals are soluble in water. Other silicates, many of which occur naturally, are insoluble, and in these substances the polysilicate anions can have highly complicated structures, all of which are constructed from a unit of one silicon and four oxygen atoms arranged tetrahedrally (cf. the structure of silica). Some of these contain aluminium (the aluminatesilicates) and some have import ant properties and uses. 

Figure 6. Diagram of our 1-atm ion mobility spectrometer (IMS) apparatus (a) stainless steel source gas dilution volume, (b) septum inlet, (c) needle valve, (d) Nj source gas supply, (e) source and drift gas exhaust, (f) flow meter, (g) pressure transducer, (h) insulated box, (i) drift tube, (j) ion source, (k) Bradbury-Nielson gate, (I) Faraday plate/MS aperture, (m) drift gas inlet, (n) universal joint, (o) electrostatic lens element, (p) quadrupole mass filter, (q) 6"-diffusion pump, (r) first vacuum envelope, (s) channeltron electron multiplier, (t) second vacuum envelope, (u) 3"-dif-fusion pump, (v) Nj drift gas, (w) leak valve, (x) on/off valves, (y) fused silica capillary, (z) 4-liter stainless steel dilution volume, (aa) Nj gas supply.

---