Glass-ceramics electrical properties

The glass-ceramic phase assemblage, ie, the types of crystals and the proportion of crystals to glass, is responsible for many of the physical and chemical properties, such as thermal and electrical characteristics, chemical durabiUty, elastic modulus, and hardness. In many cases these properties are additive for example, a phase assemblage comprising high and low expansion crystals has a bulk thermal expansion proportional to the amounts of each of these crystals. 

Certain glass-ceramic materials also exhibit potentially useful electro-optic effects. These include glasses with microcrystaUites of Cd-sulfoselenides, which show a strong nonlinear response to an electric field (9), as well as glass-ceramics based on ferroelectric perovskite crystals such as niobates, titanates, or zkconates (10—12). Such crystals permit electric control of scattering and other optical properties. 

Oxides. Although not widespread commercially, glass-ceramics consisting of various oxide crystals in a matrix of siUceous residual glass offer properties not available with mote common siUcate crystals. In particular, glass-ceramics based on spinels and perovskites can be quite refractory and can yield useful optical and electrical properties. 

Plasma processing technologies ate used for surface treatments and coatings for plastics, elastomers, glasses, metals, ceramics, etc. Such treatments provide better wear characteristics, thermal stability, color, controlled electrical properties, lubricity, abrasion resistance, barrier properties, adhesion promotion, wettability, blood compatibility, and controlled light transmissivity. 

Alpha-quartz has many useful properties which lead to its wide use in industry as a glass, ceramic and molecular sieve. However, undoubtedly its most technically important use occurs by virtue of its piezo-electric properties, which allow it to be used as a frequency regulating device in satellites, computers, and the ubiquitous quartz-watch . Unfortunately, it has been found that quartz crystals are susceptible to damage by radiation, and that this is associated with the presence of defects in the crystal lattice. These defects, particularly aluminum and hydrogen, are grown into the crystal and so far have proved impossible to remove. This problem has been the cause of intensive research, which has led to some information on the possible types of defects involved, but has failed to produce details of their geometries, and the way in which they interact. 

Beryllium oxide shows excellent thermal conductivity, resistance to thermal shock, and high electrical resistance. Also, it is unreactive to most chemicals. Because of these properties the compound has several applications. It is used to make refractory crucible materials and precision resistor cores as a reflector in nuclear power reactors in microwave energy windows and as an additive to glass, ceramics and plastics. 

Many of the fundamental relationships and concepts governing the electrical properties of materials have been introduced in the previous section. In this section, we elaborate upon those topics that are more prevalent or technologically relevant in ceramics and glasses than in metals, such as electrical insulation and superconductivity, and introduce some topics that were omitted in Section 6.1.1, such as dielectric properties. 

The discovery of glass-ceramics as a new type of solid with unusual parameters and their rapid laboratory development have outrun the possible applications. At present, glass-ceramics have found chief application in technical fields where their specific mechanical, thermal, electrical and other properties are exploited, and in the building industry which has been focusing its attention at elements made from cheap natural or waste materials. 

Electrical properties of glass ceramics are determined by the properties of both the crystalline phases and the residual glass. Electrical conductivity and dielectric loss (at low frequencies) are dominated by the concentration and mobility of alkali ions in the glass phase. The dielectric constant is dominated by the crystalline phase, especially when that phase consists of high dielectric constant materials such as ferroelectric crystals. The... 

Delaney JS, Dyar MD, Sutton SR, Bajt S (1998) Redox ratios with relevant resolution Solving an old problem using the synchrotron microXANES probe. Geology 26 139-142 Dhar RN, Mandal SS, Roy SR (1959) Electrical properties of Indian micas—d.c. resistivity. Central Glass Ceramic Inst Bull (India) 6 29036... 

The mechanical, optical, and electrical properties of glasses are discussed in detail, along with other ceramics, in those topical chapters. 

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