2012-11-14   来源:润滑油情报网 网友评论 0

摘要:Pharmacists and doctors claim that beans, cucumbers, collard greens and spinach are some of the healthiest foods, because among other minerals they contain molybdenum...

Pharmacists and doctors claim that beans, cucumbers, collard greens and spinach are some of the healthiest foods, because among other minerals they contain molybdenum. Consumed regularly and in right proportion, molybdenum is said to promote alertness and concentration, metabolism of fats and carbohydrates, dental health, protection against stomach cancer, and much more.

   Dietary benefits aside, moly has shaped the development and evolution of homo-technicus. And it has taken 20th century technology to efficiently extract molybdenite ore and turn it into useful molybdenum metal, compounds and derivatives.

   Long ago molybdenum was confused with lead, hence the name (from the Greek word “molybdos” which means lead or lead-like). Today we know that it is the 54th most abundant element in the Earth’s crust and 25th most abundant in the oceans, but in its pure metallic form, as molybdenum, it is very scarce.

   In the distant future, some bold astrophysicists may discover a planet with pure molybdenum metal deposits, but on Earth extraction requires heroic effort. Deep underground, where it comes from — and there are few primary molybdenum mines in the world — miners have to mine more than 2,000 pounds of ore, which then has to be crushed and milled, in order to recover some four to six pounds of molybdenum.  

   Even when found co-deposited alongside other ores, such as in copper surface mines, moly must be painstakingly separated from the primary output. Then, about 75 percent of this freshly minted moly will go into production of alloy steels, while the rest is used as molybdenum metal and in chemical and specialty applications, according to the International Molybdenum Association (IMoA).

   Most commercial deposits are along the spine of North and South America (Canada, the United States, Mexico, Chile and Peru) and in China, and most of the output from these mines will find use as an alloying element. In only very small proportions, molybdenum oxides give iron and steel the characteristics needed for modern engineering — strength, superior toughness at low or high temperatures, and resistance to corrosion and wear.

   That should ring a bell with lubricant formulators, because similar characteristics are needed in lubricants and greases. Here, sulfur complexes are used, rather than oxides, the most common and popular being molybdenum disulfide (MoS2 ). MoS2 occurs naturally in the ore, at concentrations of 0.02 to 0.4 percent. It is extracted from the ore and then purified for direct use in lubrication. (It also can be synthesized at high heat, by direct union   of the elements Mo and S.) “Since MoS2 is of geothermal origin, it has the durability to withstand heat and pressure,” notes the IMoA.        Molybdenum disulfide’s use as a lubricant dates back to the 18th century, although it was not widely used as a grease additive until the mid-1950s. Today, lubricants still represent only about 1.5 percent of the total molybdenum market, points out Tom Risdon, a longtime expert in solid lubricants. “Worldwide, the lubricant-grade MoS2 market is about 6.5 million pounds, or 3,000 metric tons,” he said — about the same level as five years ago, prior to the recession. “The selling price of lubricant grade MoS2 has risen at about the same rate as the price of many petroleum additives and metals such as nickel, cobalt, copper and others.”

   Formerly with Climax Molybdenum Co., Risdon is an independent consultant and head of Solid Lubricant Solutions in Dexter, Mich. “MoS2 is recovered from the ore by physical beneficiation (repetitive grinding and flotation) or by acid leaching, a procedure that usually isolates more than 99 percent pure MoS2 concentrate,” he explained to Lubes’n’Greases.

   Moly is also used in “greases and in other fluid lubricants as anti-wear and extreme-pressure additives,” Risdon continued.

   But dry applications of MoS2 — which comes in the form of a black powder — also are found in industry, “as solid film lubricants, as bonded coatings, rubbed on films, or as friction modifiers in automotive brake pads.”

   “Besides MoS2 , the lubricant industry uses organo-molybdenum compounds as well,” said Glenn Mazzamaro, director of global sales at specialty chemical manufacturer R.T. Vanderbilt Co. “Most makers of organo-molybdenum compounds use molybdenum trioxide as raw material, which is converted from the disulfide by roasting.” Based in Norwalk, Conn., R.T. Vanderbilt buys high-purity molybdenum to produce organic compounds that are used in lubricant additives.

   These include a variety of organomolybdenum compounds, like MoDTC (molybdenum dithiocarbamates). “These are generally used as friction   reducers in engine and powertrain lubricants,” Mazzamaro said.

   MoS2 is recommended by some equipment manufacturers in their grease specifications because they have found no better alternative, Mazzamaro continued. “From 2005 to 2008, when moly pricing started to surge, many companies considered evaluation of alternatives and some were identified and began to be used.”

   When MoS2 is not specified by the end user or by performance requirements, such substitutes can include graphite, mixtures of MoS2 and graphite, or multi-component solid lubricants such as those containing zinc phosphate, calcium carbonate, graphite and MoS2 ,” Risdon observed. Boron   nitride is another solid lubricant that is gaining traction in the lubricants market, and tungsten disulfide (WS2 ) has been used as well, but it is actually much more expensive than MoS2 , Risdon said. Plus, due to its specific gravity of 7.5, WS2 provides fewer lubricating particles per unit mass than MoS2 , he added.

   Greases fortified with MoS2 are found in automotive, off-road and mining machinery applications — anywhere high loads must be handled. “Examples include wheel bearings, ball joints, constant velocity joints and pivot pins,” Risdon said. “Typical MoS2 content in greases ranges from 1.5 percent to 5 percent.”

   Among the organic additives, other   alternatives to organic molybdenum include friction modifiers like glycerol mono-oleate. “But these materials cannot achieve the level of friction reduction observed in organo-molybdenum compounds,” asserted Mazzamaro. “In many cases, the organic friction modifiers are good enough and are used extensively. But when moly compounds are used as friction modifiers in engine oils, they are typically used above 300 parts per million moly, and even above 600 ppm.” Even at lower levels, moly acts as excellent antioxidant and antiwear synergist with other additive components in the engine oil package, he said.

   Molybdenum prices rose sharply in recent years, in an even more breathtaking   manner than crude oil. After opening the century below $5 per pound, molybdenum trioxide (the most widely quoted grade) peaked above $45 five years later. Prices eased back somewhat after the 2008 oil price run-up, but remain in the range of $16 per pound — roughly triple what they were when the decade started.

   Prices could be on the rise again, according to a presentation given last month by Kevin Loughrey, chairman and CEO of Thompson Creek Metals, a big U.S. primary miner of molybdenum. “The supply-demand dynamic for molybdenum looks quite positive,” he said when unveiling the company’s firstquarter results. “There’s more opportunity on the upside than on the downside in prices.”

   Being such a small consumer of moly, lubricants have little influence on its price in the marketplace; that’s actually driven by the supply-demand fluctuations in the metals industries, emphasized Risdon of Solid Lubricants Solutions. “The price often quoted in the media is primarily for metallurgical grade molybdenum trioxide. It is also priced on contained molybdenum, which is higher than the product price.”

   He added that lubricant-grade MoS2 prices have been relatively stable over the past year and a half, and are independent of the fluctuations seen in the metallurgical sector.

   The future of molybdenum could stretch beyond the traditional steel, specialty chemical and lubricant applications. Researchers are trying to prove that MoS2 could be an alternative to silicon in manufacturing computer chips. One advantage is its two-dimensional molecular structure, whereas silicon is three-dimensional. Some believe it will be possible to isolate sheets of molybdenum that are just 0.65-nanometer thick — much thinner than silicon chips — without restricting the movement of electrons.

   If they’re right, that could open a whole new chapter for moly and homo technicus — and a new world of competition for this essential mineral.  


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