Quartz 572 Ceramic Materials

Ceramic materials are typically noncrystalline inorganic oxides prepared by heat-treatment of a powder and have a network structure. They include many silicate minerals, such as quartz (silicon dioxide, which has the empirical formula SiO,), and high-temperature superconductors (Box 5.2). Ceramic materials have great strength and stability, because covalent bonds must be broken to cause any deformation in the crystal. As a result, ceramic materials under physical stress tend to shatter rather than bend. Section 14.22 contains further information on the properties of ceramic materials. 

Egyptian faience A non-ceramic material made from a mixture of quartz, lime, soda, alumina, and feldspar, which is fired and covered with a layer of usually blue, alkaline glaze. 

Material Quartz and ceramic materials (Barium titanate (BaTiOQ, Lead metaniobate (PbNb2Os) and the mixed crystal Lead-zirconate titanate) Nickel or an alloy of Nickel. Also, some other high-tech alloys with ferrite materials (MFe204, M = divalent metal like Ni, Zn and Pb)... 

Domenech A, Sanchez S, Yusa DJ, Moya M, Gimeno JV, Bosch F (2004) Determination of the borondead ratio in ceramic materials based on electrochemical quartz crystal microbalance. Electroanalysis 16 1814-1822. 

The distinctly differentiated results obtained, for example, for different faces of quartz or feldspar crystal, with clear observed differences depending on structure and compactness of the material under test, are an argument for wide use of the Mackensen blower in the study of engineering properties of rocks and ceramic materials and also in hardness estimation of minerals. 

The practical application of ultrasonics requires effective transducers to change electrical energy into mechanical vibrations and vice versa. Transducers are usually piezoelectric, ferroelectric, or magnetostrictive. The application of a voltage across a piezoelectric crystal causes it to deform with an amplitude of deformation proportional to the voltage. Reversal of the voltage causes reversal of the mechanical strain. Quartz and synthetic ceramic materials are used. 

The two most common substrates for thin film electrodes are various types of glass—soda-lime, Pyrex, and various forms of quartz or fused silica—and silicon wafers that have been treated to produce an insulating surface layer (typically a thermally grown oxide or nitride). Other possible substrates include mica, which can be readily cleaved to produce an ordered surface, and various ceramic materials. All of these materials can be produced in very flat, smooth... 

On heating to 1500 °C/6 h/Ar, the Zr material crystallizes to a mixture of monoclinic and tetragonal zirconia and crystobalite with loss of considerable original surface area (36 m2 g 1). The Hf material behaves similarly, although it partially crystallizes at 1000 °C to produce cubic or tetragonal hafnia. Cristobalite is only observed in materials heated to 1400 °C. Finally, thin films of the Zr and Hf derivatives could be cast from hydrocarbon solutions on quartz and then converted to thin films of the corresponding amorphous or ceramic materials. 

Aluminium oxide is the oldest ceramic material used in medicine. Bauxite and corundum are the main natural sources of aluminium oxide. Bauxite is a mixture of diaspore, gibbsite, iron hydroxides, clay minerals and quartz. It is formed by the tropical weathering of silicate rocks during which quartz and the elements sodium, calcium, magnesium and potassium are largely washed away. This is the reason why the remaining material becomes richer in the resistant elements titanium, iron and aluminium. The latter is extracted from this mixture in the form of aluminium hydroxide. In its turn this compound is converted into aluminium oxide by heating the mixture to 1200-1300 °C, this is called calcination. The hydroxide is thus made anhydrous. 

A number of ceramic materials meet these specifications fairly well. Thus, synthetic mullite having a melting point of about 1835°C. and an expansion coefficient of 45 X 10-7 cm./cm./°C. between 20° and 1320°C., and synthetic zircon having a melting point of 1775°C. and an expansion coefficient of 42 X 10 7 between 20° and 1550°C. are suitable materials. However, both ceramics start to decompose under vacuum conditions above 1300°C. and show a not negligible vapor pressure of SiO and Si02 at considerably lower temperatures. In spite of this, mullite and zircon are better than fused quartz in the temperature range up to 1200°C. Moreover, they are cheaper and easier to be sealed to the vacuum system. 

To confer electroconductivity upon porous ceramics these materials were coated with a layer of pyrolytic carbon. The deposition of carbon was carried out in the gas phase by pyrolysis of natural gas. The ceramic materials were placed in a quartz reactor under 50 mL/min flow of natural gas. The pyrolysis took place at 900°C for 30 min. 

Temperature Limit Like any other ceramic material, many factors affect the maximum use temperature of high purity silica products. In general, 2000°F is the highest temperature limit for cyclic service. When the temperature goes above 2000°F, the vitreous/fused silica grains will crystallize to cristobalite and quartz. If the operating temperature is then cycled, the various silica inversions can take place which will tear the brick apart. When operation is restricted to continuous service only, then the maximum use temperature is approximately 3000°F. 

A detailed diagram of the FID sensor is shown in Fig. 1. The body and the cylindrical electrode is usually made of stainless steel and stainless-steel fittings connect the detector to the appropriate gas supplies. The jet and the electrodes are insulated from the main body of the sensor with appropriate high-tem-perature insulators. Some care must be taken in selecting appropriate insulators as many glasses (with the exception of fused quartz) and some ceramic materials become conducting at high temperatures (200-300°C) [3]. 

Quartz is abundant and hence inexpensive, relatively hard and chemically inert. Similar to other ceramics, high hardness is a useful property of quartz. Knoop hardness data for a number of ceramic materials including quartz are given in Table 5 [32], The densities of a number of ceramic materials including quartz are given in Table 6 [32],... 

Table 5 Knoop hardness for quartz and some common ceramic materials [32]...

The types of substance that are thermoluminescent, either in their natural state or after radiation bombardment, include (112) the alkali metal halides, calcite, dolomite, fluorite, aluminum oxide, magnesium oxide, gypsum, quartz, glass, feldspars, feldspathoids, certain dried clays, and ceramic materials. Of over 3000 rock samples examined for thermoluminescence, some 75% showed visible fight emission (112). Nearly all limestones and acid igneous rocks are naturally thermoluminescent, due mainly to the presence of trace elements of uranium, thorium, and so on. Calcium and magnesium... 

This is also the basis for thermoluminescence dating. When geologic minerals like quartz, feldspars, etc as well as ceramic materials like fired clay are exposed to high energy cosmic... 

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