Spray molybdenum

Flame sprayed molybdenum articles have poor corrosion resistance, no doubt owing to the porosity of the coating. However, modern plasma spraying techniques produce a dense coating and this should lead to more widespread use of clad materials such as molybdenum clad steel where the clad product should have the same corrosion resistance as the solid material. 

In cases where very high adherence is necessary an undercoating of sprayed molybdenum is applied. Owing to the volatile nature of its oxide this metal presents a clean surface to the workface and with most metals (except copper) very high adhesion is obtained. To a limited extent arc-sprayed aluminium bronze will also form a strongly adherent base coating. 

Spraying conditions make hardness values so variable that unless they are accurately known no comparisons are possible. Brinell hardness figures for sprayed molybdenum vary from 350 when produced with a reducing flame to 725 with an oxidising flame, and while a thick sprayed deposit of 0-8% carbon steel can give a figure of 330, the hardness of a particle obtained by micro hardness methods will be about 550. 

The Tribaloy aUoy T-800, is from an aUoy family developed by DuPont in the eady 1970s, in the search for resistance to abrasion and corrosion. Excessive amounts of molybdenum and sUicon were aUoyed to induce the formation during solidifica tion of hard and corrosion-resistant intermetaUic compounds, known as Laves phase. The Laves precipitates confer outstanding resistance to abrasion, but limit ductUity. As a result of this limited ductUity the aUoy is not generaUy used in the form of plasma-sprayed coatings. 

Immersed Molybdenum has good resistance to synthetic sea water, the rate of attack up to 60° C being less than 0-1 mm/y" and it is only slightly corroded when exposed to synthetic sea water spray at 60°C for periods of 10, 20 and 30 days. 

The US Bureau of Mines found the chemical and galvanic corrosion behaviour of both the TZM and Mo-30W alloy to be generally equal or superior to that of unalloyed molybdenum in many aqueous solutions of acids, bases and salts. Notable exceptions occurred in 6-1 % nitric acid where both alloys corroded appreciably faster than molybdenum. In mercuric chloride solutions the TZM alloy was susceptible to a type of crevice corrosion which was not due to differential aeration. The alloys were usually not adversely affected by contact with dissimilar metals in galvanic couple experiments, but the dissimilar metals sometimes corroded galvanically. Both alloys were resistant to synthetic sea water spray at 60°C. 

Plasma spraying Metals, or refractory materials or composites are applied by melting in an ionised inert gas M, tantalum, molybdenum, alumina, zirconia M2 a variety of metallic substrates... 

Properties of the deposits Almost any material which can be melted is suitable for plasma spraying, giving a vast range of possible coatings of single or mixed metallic or non-metallic substances. It is often possible to produce types of coatings which are not obtainable in any other way. Typical of the materials which are plasma sprayed are copper, nickel, tantalum, molybdenum. Stellites, alumina, zirconia, tungsten and boron carbides, and stainless steels. 

Spray plates with (1) 0.1% 2, 7 -dichloroflnorescein, (2) 1% AICI3 in ethanol, (3) 1% aqneons FeClj solution warm the plates to about 45°C briefly between sprays Prepare solution 1 4% solution of molybdic oxide in 70% H2SO4 add 0.4-g powdered molybdenum to 100 ml of solution 1 add 200-ml HjO and filter final spray consists of 100 ml of preceding and 200 ml HjO and 240-ml acetic acid... 

Hardfaeing and Wear-resistant Alloys. These materials, essentially quaternary alloys of cobalt chromium, tungsten (or molybdenum) and carbon, are widely used for industrial hardfaeing purposes. They can be deposited by welding techniques, sprayed on as powders, or produced as separate castings. By using the weld deposition technique, a highly alloyed heat-, wear-, and corrosion-resistant surface can be applied to a... 

Thompson and Zao [170] have described a solvent extraction-inductively coupled plasma atomic emission spectrometric method for the determination of down to 0.02 - 0.03 xg/g of molybdenum in soils. The soil sample is pressure-leached with 6 M hydrochloric acid and at 120 °C for 15 minutes. The digest is then extracted with heptan-2-one to separate molybdenum from potentially interfering elements such as iron, aluminium, calcium and magnesium. This organic extract is then directly sprayed into an inductively coupled plasma atomic emission spectrometer operated at 1.65 to 1.7 kW power. 

Teflon self-lubricating plastic bearings can be used in situations where a lubricant might contaminate the system. There are also a variety of nonoily lubricants such as silicone lubricant (usually dispensed as a spray) and molybdenum disulfide (suspended in petroleum distillates that evaporate to leave a dry coating). Molybdenum disulfide is an excellent alternative to graphite for lubrication of moving parts in a high-vacuum system. 

Because of this ready adherence to a substrate, molybdenum disulphide films can be produced in a wide variety of different ways, including flotation from the surface of a liquid, spraying, brushing or dipping in a volatile dispersant, bonding with adhesive or polymeric compounds, rubbing with powder, transfer, and vacuum sputtering. The nature of the initial film produced depends on the way in which it is applied, and all the important types will be discussed in subsequent chapters. 

Much thicker films can be produced by the use of dispersions of molybdenum disulphide powder in volatile liquids. The dispersion can be applied to a solid surface by dipping, brushing or spraying, and the liquid is then allowed to evaporate, either at room temperature or with additional heating. Although the dry films are much... 

Another chemical aspect which seems to have been clearly established is the generally unsatisfactory performance of molybdenum disulphide on a copper or copper alloy substrate. There is some evidence that sputtered molybdenum disulphide will not adhere properly to copper either in the initial formation of a film or in transfer to a counterface. Reid and Schey also found indications that with their sprayed and burnished films copper became intermingled with the film and transferred to the counterface. 

Dispersions can be applied to a bearing surface by brushing, dipping or spraying. The most suitable process depends on the size and shape of the component, and the viscosity and concentration of the dispersion. The liquid then evaporates, with or without the use of heat or enhanced airflow, leaving a thin but uniform and often adherent film of molybdenum disulphide powder. The adherence... 

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