Electrically insulating ceramics

Figure C2.11.4. A commercial spark plug witli its electrically insulating ceramic body comprised of alumina and glass (white portion).

PN-69/E-06307. Elektroizolacyjne materialy ceramiczne. Metody badan (Electrical Insulating Ceramic Materials. Test Methods) (binding since 1.7.70). 

Compatibility Screening Tests on Electrically Insulating Ceramics... 

As a first step, we need a compatibility screening test for the development of insulator coatings Results of compatibility tests on electrically insulating ceramic candidates in liquid Li are shown in Table In general, compatibility of ceramic insulators with liquid Li follows the criterion for thermodynamic stability. Although some ceramic materials are considered to be thermodynamically stable materials, e.g., sintered AIN and SiC (applied... 

The thermal conductivity of most (electrically insulating) ceramics increases with increasing temperature. True or False ... 

Electrical Insulators Ceramic or Glass 400-450 K Hermeticity, compatibility with gas loop... 

Glasses and electrically insulating ceramics can be used as crucibles and are often desirable because of their chemical inertness with many molten materials. Typical crucible ceramics are Th02, BeO, stabilized Zr02 (i.e. additions of Hf02 and CaO to ZrO, AI2O3, MgO, BN, and fused silica. Kohl has written an extensive review of the oxide and nitride materials that may be of interest as crucible materials. The ceramics can be heated by conduction or radiation... 

Cases can be classified as either hermetic or nonhermetic, based on their permeabiUty to moisture. Ceramics and metals are usually used for hermetic cases, whereas plastic materials are used for nonhermetic appHcations. Cases should have good electrical insulation properties. The coefficient of thermal expansion of a particular case should closely match those of the substrate, die, and sealing materials to avoid excessive residual stresses and fatigue damage under thermal cycling loads. Moreover, since cases must provide a path for heat dissipation, high thermal conductivity is also desirable. 

Standard ceramic processing conditions are controlled so that the resulting ceramic microstmcture is composed of semiconducting 2inc oxide grains (pZnO < IHcm) and electrically insulating grain boundaries > 10 0cm)). The microstmcture is thus similar to that of the BaTiO thermistor and... 

The insulation around the central electrode is an example of a non-metallic material - in this case, alumina, a ceramic. This is chosen because of its electrical insulating properties and because it also has good thermal fatigue resistance and resistance to corrosion and oxidation (it is an oxide already). 

The transport of charged ions in alkali halides and, later on, in (insulating) ceramics is a distinct parepisteme, because electric fields play a key role. This large field is discussed in Schmalzried s 1995 book, already mentioned, and also in a review by one of the pioneers (Nowick 1984). This kind of study in turn led on to the developments of superionic conductors, in which ions and not electrons carry substantial currents (touched on again in Chapter 11, Section 11.3.1.1). 

All metals conduct electricity on account of the mobility of the electrons that bind the atoms together. Ionic, molecular, and network solids are typically electrical insulators or semiconductors (see Sections 3.f3 and 3.14), but there are notable exceptions, such as high-temperature superconductors, which are ionic or ceramic solids (see Box 5.2), and there is currently considerable interest in the electrical conductivity ol some organic polymers (see Box 19.1). 

The stability of ceramic materials at high temperatures has made them useful as furnace liners and has led to interest in ceramic automobile engines, which could endure overheating. Currently, a typical automobile contains about 35 kg of ceramic materials such as spark plugs, pressure and vibration sensors, brake linings, catalytic converters, and thermal and electrical insulation. Some fuel cells make use of a porous solid electrolyte such as zirconia, Zr02, that contains a small amount of calcium oxide. It is an electronic insulator, and so electrons do not flow through it, but oxide ions do. 

The technique is referred to by several acronyms including LAMMA (Laser Microprobe Mass Analysis), LIMA (Laser Ionisation Mass Analysis), and LIMS (Laser Ionisation Mass Spectrometry). It provides a sensitive elemental and/or molecular detection capability which can be used for materials such as semiconductor devices, integrated optical components, alloys, ceramic composites as well as biological materials. The unique microanalytical capabilities that the technique provides in comparison with SIMS, AES and EPMA are that it provides a rapid, sensitive, elemental survey microanalysis, that it is able to analyse electrically insulating materials and that it has the potential for providing molecular or chemical bonding information from the analytical volume. 

Thermo luminescence is the emission of light by moderately heated electrically insulating solids. Many minerals, rocks, and ceramics, when heated to a high temperature but below that required for them to become incandescent, emit light. The emission of light is related to the structure and previous environmental conditions of the solids. All solids on the earth s... 

Aluminum is produced commercially by the electrolysis of cryolite, Na3AlF6, but bauxite, A1203, is the usual naturally occurring source of the metal. The oxide is a widely used catalyst which has surface sites that function as a Lewis acid. A form of the oxide known as activated alumina has the ability to adsorb gases and effectively remove them. Other uses of the oxide include ceramics, catalysts, polishing compounds, abrasives, and electrical insulators. 

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