Molybdenum in steels

The above procedure may be adapted to the determination of molybdenum in steel. Dissolve a 1.00 g sample of the steel (accurately weighed) in 5 mL of 1 1 hydrochloric acid and 15 mL of 70 per cent perchloric acid. Heat the solution until dense fumes are evolved and then for 6-7 minutes longer. Cool, add 20 mL of water, and warm to dissolve all salts. Dilute the resulting cooled solution to volume in a 1 L flask. Pipette 10.0 mL of the diluted solution into a 50 mL separatory funnel, add 3 mL of the tin(II) chloride solution, and continue as detailed above. Measure the absorbance of the extract at 465 rnn with a spectrophotometer, and compare this value with that obtained with known amounts of molybdenum. Use the calibration curve prepared with equal amounts of iron and varying quantities of molybdenum. If preferred, a mixture of 3-methylbutanol and carbon tetrachloride, which is heavier than water, can be used as extractant. 

Takahashi T. and Shimamura T. (1994) Determination of zirconium, niobium and molybdenum in steel by glow discharge mass spectrometry, Anal Chem 66 3274—3280. 

H. Bergamin-Filho, F.J. Krug, B.F. Reis, J.A. Nobrega, M. Mesquita, I.G. Souza, On-line electrolytic dissolution of alloys in flow injection analysis. Part 2. Spectrophotometric determination of molybdenum in steels, Anal. Chim. Acta 214 (1988) 397. 

F. J. Krug, 0. Bahia F, and E. A. G. Zagatto, Determination of Molybdenum in Steels by Flow Injection Spectrophotometry. Anal. Chim. Acta, 161 (1984) 245. 

A. Varghese, A.M.A. Khadar, and B. Kalluraya. Simultaneous determination of titanium and molybdenum in steel samples using derivative spectrophotometry in neutral micellar medium. Spectrochimica Acta Part A 64 383-390, 2006. 

Manning, Ball, and Menis (162) have carried out polarographic and coulometric reductions of molybdenum (VI) in a nitrilotriacetic acid medium and have applied their findings to the analysis of thorium-uranium oxide mixtures. The determination of molybdenum in steel using coulometric techniques has been reported by Ibrahim and Nair (163) who reduced molybdenum at —0.40 V vs. SCE in a sodium acetate buffered chloride medium. Chromium interference can be removed by pre-reduction with alcohol. The catalytic effect of lower oxidation states of molybdenum in the reduction of perchlorate has been used as an indirect electro-analytical method for the determination of perchlorate (159, 164). 

Molybdenum hexafluoride is classified as a corrosive and poison gas. It is stored and shipped in steel, stainless steel, or Monel cylinders approved by DOT. Electronic and semiconductor industries prefer the cylinders equipped with valves which have Compressed Gas Association (CGA) 330 outlets. 

Hydrogen at elevated temperatures can also attack the carbon in steel, forming methane bubbles that can link to form cracks. Alloying materials such as molybdenum and chromium combine with the carbon in steel to prevent decarburization by hydrogen (132). 

High strength, low alloy (HSLA) steels often contain 0.10—0.30% molybdenum. These steels exhibit toughness at low temperatures and good weldabiHty. They are used extensively for undersea pipelines (qv) transporting gas and oil from offshore weUs to pumping stations on shore, and are also used extensively in remote Arctic environments. 

Heavy metals on or in vegetation and water have been and continue to be toxic to animals and fish. Arsenic and lead from smelters, molybdenum from steel plants, and mercury from chlorine-caustic plants are major offenders. Poisoning of aquatic life by mercury is relatively new, whereas the toxic effects of the other metals have been largely eliminated by proper control of industrial emissions. Gaseous (and particulate) fluorides have caused injury and damage to a wide variety of animals—domestic and wild—as well as to fish. Accidental effects resulting from insecticides and nerve gas have been reported. 

Other acids Formic acid is more liable to cause pitting than is acetic acid, and it must be considered with particular care at higher temperatures. Citric, oxalic, lactic and sebacic acids are also liable to cause appreciable attack in strong solutions at the higher temperatures, and for the borderline conditions molybdenum is a useful addition to the steel. On the other hand, many organic acids are less corrosive than acetic, and non-molybdenum austenitic steels may be used with them without trouble even at 100°C. Such acids... 

Fertilisers For nitrates, non-molybdenum austenitic steels are satisfactory, but in the manufacture of ammonium sulphate some free acid is often present, so that evaporators and centrifugal dryer baskets in this case are generally made from molybdenum-bearing steels. For super-phosphates this has limited application. 

Cellulose produds There is little scope for the use of austenitic steels in the alkali processes for the digestion of wood pulp, but both molybdenum-free and molybdenum-bearing steels are extensively used for sulphite pulp digestion, choice depending on concentration, temperature and working experience. 

Relatively small amounts of molybdenum in Ni-Cr-Fe alloys, as in stainless steels, render passivation much easier and it may be seen from Fig. 4.25... 

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. 

---