Built-up mica

Built-Up Mica. When the primary property needed for a particular appHcation is insulation, budt-up mica made by binding layered mica spHttings together serves as a substitute for the more expensive sheet mica. The principal uses for built-up mica are segment plate, molding plate, flexible plate, heater plate, and tape (7). 

Segment plate, used as insulation between copper commutator segments on direct-current universal motors and generators, accounts for the primary use for built-up mica. Phlogopite built-up mica is preferred for these segments because it wears at the same rate as the copper segments. 

Some types of built-up mica are bound to special paper (qv), silk (qv), linen, muslin, glass cloth, or plastic. These products are very flexible and are produced in continuous wide sheets. These sheets are either shipped in roUs or cut into ribbons, tapes, or other desired shapes (Table 7). 

Table 7. Built-Up Mica Sold or Used in the United States by Product...

Built-up mica Silicone Epoxy Shellac Polyester ... 

Mica paper - Mica paper is a fabricated alternative to natural sheet and built-up mica products. Scrap mica is delaminated through a combination of thermal, chemical, and mechanical treatments. The mica pulp is then processed on a papermaking machine into a continuous, homogeneous sheet of imiform thickness. 

In some weathering environments, Fe and Mg are ejected from the mica structure to counter the excess positive charge built up in the trioctahedral sheet as Fe " is oxidized. In the process, Mg may form a Mg(OH>2 sheet between the 2 1 layers, forming chlorite as an intermediate weathering product. 

Many crystals can be considered as built up of parallel layers, especially if the forces operative between layers are of less consequence than those acting within layers. In some materials such as graphite the layers may be monotonic, but in others such as micas or clay materials they may be several atoms deep. Much attention has been directed toward the study of reactions enhanced by molecular catalysts intercalated in smectite clays [66,67]. Because of the ability of these minerals to imbibe water, a solution-like environment can exist between layers and, provided the layers are sufficiently swollen to permit rapid diffusion of reactants, many reactions involving cations or neutral molecules can be carried out. Photocatalytic and photochemical reactions in/on clays or clay-modified materials (electrodes) have been studied and discussions of these experiments are presented in the monographs of Thomas [68] and of Kalyanasundaram [69] and in the... 

It seems reasonable to connect variety and frequency of occurrence with structural stability. The wide range of conditions under which the TOT layer is stable on its own occurs in talc and pyrophyllite, built up by this layer only. The TOT layers are even able to survive through reactions generating other minerals [cf Baronnet (1997) and Buseck (1992) and references therein] including other micas (cf Ferraris et al. 2001a). 

The insulation of the coil sides is built up as continuous tape isolation, i.e., both the straight sections of the coil and the core ends are wound with tape. The insulation consists of epoxy-impregnated mica glass-tape. Both the preimpregnated MICAREX system and the vacuum-pressme impregnated MICAPACT system satisfy the requirements for temperature class F (155°C). The insulation systems used are described in more detail in separate brochures. 

The whole apparatus was built to chemically identify an isotope of Rf decaying by SF with a half-life of 0.3 seconds, that had previously been synthesized and identified by a team of physicists at Dubna. In a number of experiments, I. Zvara and co-workers identified multiple SF tracks in the mica detectors when they used glass surfaces and temperatures of 300°C [104], They had shown in preparatory experiments with Hf, that indeed the transfer of Hf through the apparatus occurred within less than 0.3 s, and thus, that the experimental set-up was suited to study the short-lived Rf isotope [81]. A number of possible sources of SF tracks in the mica detectors other than the SF decay of an Rf isotope were discussed and ruled out. Further experiments with a slightly modified apparatus [106] were conducted immediately after the experiments described here. A total of 63 SF events were attributed to the decay of an Rf nuclide. 

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