Silica, Quartz Fibers

The extmders were monitored using a pair of custom-made transmission probes inserted into the extruder die just downstream from the screws. Each probe consisted of a sapphire window brazed into a metal body a quartz rod behind the window piped the light to the end of the probe low-OH silica fiber-optic bundles connected the probe to the NIR analyzer, an LT Quantum 12001. Optical path lengths were typically between 0.3 and 2.0 cm. 

Initial attempts to prepare Cf metal using metallothermic reduction methods (Section II,A) were less than successful due to the high vapor pressure of Cf metal 28, 46). Reduction of californium oxide with La metal (Section II,B) and collection of the product Cf metal on a fused silica fiber (in the apparatus shown schematically in Fig. 15), were found to give metal with usable X-ray diffraction patterns (5). Later, the same method was used to collect Cf metal both on a fused silica fiber for X-ray diffraction analysis and on an electron microscopy grid for electron diffraction analysis 56). As more Cf became available, preparations via this method were carried out on 0.4-1.0-mg samples of californium oxide (55), using fibers of quartz. Be, or C (suitable for direct X-ray diffraction analysis) to collect the product Cf metal. 

Ceramic Ablators, Several types of subliming or melting ceramic ablators have been used or considered tor use in dielectric applications particulady with quartz or boron nitride [10043-11-5] fiber reinforcements to form a nonconductive char. Fused silica is available in both nonporous (optically transparent) and porous (slip cast) forms. Ford Aerospace manufactures a 3D silica- fiber-reinfo reed composite densified with colloidal silica (37). The material, designated AS-3DX, demonstrates improved mechanical toughness compared to monolithic ceramics. Other dielectric ceramic composites have been used with performance improvements over monolithic ceramics (see Composite materials, ceramic matrix). 

Typical fillers carbon black, calcium carbonate, dolomite, clays, calcinated clays, talc, soapstone, zinc oxide, filmed silica, borates, iron oxide, zinc oxide, magnesium carbonate, pulverized polyurethane foam, barium and strontium ferrites, magnesium aluminum silicate, nylon fibers, quartz in EMI shielding field silver plated aluminum, silver plated nickel, silver coated glass spheres, silver plated copper, silver, nickel and carbon black... 

The RPC to be used as a prospective repair material contains a Type II cement, silica fume, silica sand, quartz powder, steel fiber, and a superplasticizer. The mix design of the RPC repair material is also displayed in Table 1. The flexural strength of RC in comparison with its repair materials is shown in Table 2. The bending beams had dimensions of 100 mm x 100 mm x350 mm as shown in Fig. 1. 

Quartz fibers are made from natural quartz crystals by softening quartz rods in an oxy-hydrogen flame and drawing rods into filaments. Because high purity quartz crystals are rare, the cost of quartz fibers is considerable higher than that of glass fiber and high silica fibers. 

Quartz filaments have assumed a role as high-temperature resistant fibers, and are produced in considerable quantities for high temperature and corrosion-resistant applications. They are widely used as filtration and insulation materials at temperatures above those of mineral silicate fibers. Quartz and silica fiber RPs are used in jet aircrafts, rocket nozzles, nose cones, and reentry heat shields for spacecraft. 

Most LOC devices require detection in the UV-VIS spectrum for biomaterial applications. These wavelengths require quartz or doped silica core fibers, since glass and plastic will not transmit very efficiently below 400 nm. Doped silica fibers with high hydroxyl (—OH) content for UV-VlS, or low hydroxyl (—OH) content for... 

Temperatures above 1800°C would be required to contain a fiber forming silica melt in a bushing. A requirement like this would by far exceed the practical capability of most precious metal and/or other practical alloy materials. As a result, pure silica glass fibers are downdrawn from solid silica preform rods (Figure 14). Gas flame or electrical furnaces soften the ends of the quartz rods, and thereby facilitate the formation of continuous silica fibers. Preforms made from natural silica contain 99.99% Si02 and impurities include 20-50 ppm Al, <5 ppm OH", and <4 ppm Na. Preforms made by oxidation of SiCl4 in a plasma flame [60] afford even purer silica fibers (<1 ppm Al, <0.1 ppm OH, <1 ppm Na, and <50 ppm Cl). 

Structural silica or quartz fibers made by downdrawing have diameters ranging from 7 to 14 jm rovings are made with up to 4800 filaments. These fibers offer superior heat resistance since they retain useful strength at very high temperatures. They also possess the high ablation resistance and the dielectric, acoustic, optical and chemical properties of quartz from... 

Ultrapure silica or quartz fibers are used in fabrics, yams, rovings and threads. Fabrics are used to reinforce radomes, antenna windows for missiles, high temperature circuit boards, and rocket nose cones. Braided yarns provide high temperature electrical insulation, e.g., for coaxial cables, thermocouple wires, and space separators. Rovings are used to reinforce polymer matrix composites for ablative and electrical uses, as well as high performance sporting goods, e.g., tennis racquets and skis, especially when hybridized with carbon fibers. Threads are used to stitch cable tray insulation for nuclear power plants. 

As must be obvious, we have only touched on the natural occurrences of crystalline fibrous Si02- For example, Si02, usually quartz, often replaces fibrous minerals of another composition as rock masses are altered. Si02 also occurs in fibrous form within some plants (phytoliths) and in the soil. To summarize, in addition to the usual and common occurrences of the mineral quartz and its varieties, several silica polymorphs occur as fibers in a variety of biologic and geologic environments. 

Silicon is the most important constituent of igneous and many sedimentary rocks, occurring in combination with oxygen in feldspars, micas, quartz, sands and shales. The element is used in electronic devices, while silicon in combination with oxygen as silica and silicates finds application in concrete, bricks, pottery, enamels, glasses, optical fibers for telecommunications, and refractory (high-temperature resistant) materials. 

The glass fibers and fused-silica glass (Thermal American Fused Quartz Co.) were crushed and then dispersed in water. The pH of this near-neutral suspension was varied using KOH or HNO,. In some experiments, a hydrolyzed solution of y-APS was added to this suspension. Here, the initial pH was 10. The electrophoretic mobilities of glass fragments suspended in these solutions were measured without any further treatment except for the addition of electrolyte (10-3 M KNO,). These analyses were performed using a Rank Brothers Particle Micro-Electrophoresis Apparatus Mark II or a Pen Kem System 3000 Automated Electrokinetics Analyzer. 

---