Molybdenum thermal properties

In appUcations in which electrical conductivity is required, metals, copper, tungsten, molybdenum, and Kovar [12606-16-5] are the preferred chip-carrier materials. Metals have exceUent thermal conductivities. Tables 2 and 3 Ust the various materials used for substrates, along with their mechanical, electrical, and thermal properties. 

A mixture of molybdenum hexacarbonyl and 4-chlorophenol is effective in performing al-kyne metathesis of dipropynylated dialkylbenzenes. Alkyne metathesis of these precursors leads to the clean formation of dialkyl poly( paraphenyleneethynylene)s (PPEs) in high yield and with high molecular weights. This facile yet effective access to the PPEs has allowed study of their spectroscopic, structural, and thermal properties. While PPEs have been made before, the dialkyl-PPEs turned out to have particularly interesting optical and liquid-crystalline properties that can be explained in terms of the conformation of the main chains. The PPEs have also been utilized to construct light-emitting diodes and other semiconductor devices. This chapter discusses the interplay of structure, chromicity, and electronic properties of the dialkyl-PPEs. 

Although eighty percent of molybdenum production is used in the metallurgical industries, the fastest-growing sector of use is in chemicals, which has more than doubled in the past thirty years. The most widely-used compound is probably molybdenum disulphide. Apart from its use in lubrication, it is used as an additive to thermoplastics, where it improves the mechanical and thermal properties. It also has a number of potential applications in high density electric batteries, although the extent of commercial use is not clear. 

Tungsten is mainly used for heating conductors, electric bulbs, thermionic valves and electrodes. Because of its suitable electrical and thermal properties, molybdenum is used in high temperature furnaces. 

The mechanical properties reported in the literature for molybdenum and its alloys are frequently at variance. That this should be so is not surprising as the properties of molybdenum and its alloys are greatly affected by the prior history of the material, both thermal and mechanical. Far too often values are used without reference to the sources of the material, various states of heat treatment, etc. When mechanical properties are an important feature of the design application, advice should always be sought on the suitability as only the manufacturer has the complete data on the history of his own product. Physical and some typical mechanical properties given for general guidance are shown in Tables 5.2 and 5.3. 

Properties of deposits Deposits are often more adherent, coherent and temperature-stable than those produced by alternative coating methods. Adhesion can be adversely affected by spurious reactions between the metal-gas and impurities in (e.g. as observed during the deposition of molybdenum on steel ) and also where the thermal coefficients of expansion of A/, and differ widely. The purity of reactants can affect that of A/,. crystal size is reduced by raising the reactant concentrations, or by lowering the plating temperature. 

Optimum conditions for the formation of CdS by the acidic method on metallic A1 substrate at 25 °C have been reported as follows pH 2.3, potential -1 V vs. SCE, and electrolysis time > 2 h [44]. Thermal treatment improved the characteristics of the films and their photovoltaic properties, which were evaluated by evaporating a CU2S layer on the CdS/Al film, to form a heterojunction cell. The influence of the deposition substrate on the formation and morphology of CdS was found to be important. The aluminum substrates gave the best results among Pt, Mo, and Al. In the case of molybdenum, surface blocking by adsorbed sulfur was considered. 

The optical properties and photoconductivity of thin crystals of molybdenum disulfide have been investigated53-58. The thermal expansion properties of MoS2 have also been reported59. The coefficient of thermal expansion is 10.7 x 10-6/deg K. 

The properties of silica- and/or alumina-supported molybdena catalysts for propene metathesis were studied by Handzlik and coworkers. These materials could be prepared by thermal spreading of Mo02(acac)2 with well-dispersed molybdenum in a wide range of its loading. The selective metathesis activity depends on the substrate and on the surface molybdenum concentration. For example, a higher activity is found for the molybdena-alumina system at high Mo loadings. 

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