Duplex Stainless Steel Containing Molybdenum Is Used in Xiamen Mountains-to-Sea Trail

Carbon steel is widely used around the globe for the construction of bridges of sizes ranging from the very large to the very small, but now many bridges around the world are approaching the end of their useful life because carbon steel bridges do not have the corrosion resistance benefits offered by chromium, molybdenum and other alloying elements. 

The forward-looking design of the Soderstrom Bridge with duplex stainless steel highlights the benefits of building bridges from structural stainless steel in coastal areas or where deicing salts are used. Molybdenum-containing stainless steels will play an ever-increasing role in much-needed infrastructure upgrades and new builds around the world for the benefit of the environment and the people who depend on them.

Duplex stainless steel bridge structures were praised for their attractive appearance when they were first introduced, with novel designs emerging such as Singapore's Double Helix Bridge and the world's longest mono-cable suspension bridge with a curved deck in Xiamen, China. Nowadays, designers are increasingly looking at the properties of the material beyond its aesthetics. In many applications, even in concealed applications, its strength and corrosion resistance are used to create structures that are lighter than carbon steel in the past. The materials used and less maintenance is required.

All duplex grades are at least twice as strong as 316 stainless steel and have good weldability for a wide range of applications. This material of bridge structures is gaining popularity around the world due to their longer service life and lower maintenance requirements.

While all steel is 100% recyclable, options with stainless steel have a lower environmental footprint. If the stainless steel is selected correctly, the bridge structure will not fail over time. Stainless steel can achieve a near-infinite life expectancy when properly maintained to specification requirements. It also does not require any environmentally harmful surface treatment to resist corrosion

The Soderstrom Bridge was built with 2404 duplex stainless steel, the first bridge to be designed with this grade of stainless steel. This stainless steel contains 1.6% molybdenum, which contributes significantly to its crevice corrosion and pitting resistance. In fact, this type of stainless steel not only has twice the yield strength of 316 stainless steel, but also has improved atmospheric corrosion resistance.

Xiamen Mountains-to-Sea Trail (Health Footpaths) starts at Dongdu Cruise Plaza and ends at Guanyin Mountain Beach. It includes an 11km elevated trail and seven long-span node bridges, as well as newly remodeled green spaces along the walkways. The project also connects eight mountain ranges, namely Huwei Mountain, Xianyue Mountain, Yuanshan Mountain, Xueling Mountain, Hutou Mountain, Jinshan Mountain, Huzi Mountain and Guanyin Mountain, as well as 3 waters of Yundang Lake, Wuyuanwan and Hubin Reservoir. The idea of the walkway is to connect these oasis of harmony and tranquility with bridges, creating a continuous path independent of the busy life of the city below.

The construction time of Xiamen health footpaths was short, and the hills and forests in the environment were extremely challenging. Therefore, designers chose to use highly prefabricated components. Due to their low weight, these components could be transported to the site without heavy machinery, with minimal damage to vegetation.

Stainless steel containing molybdenum is used through the all footpath. For example, Hemei Bridge, one of seven footbridges that are part of the Xiamen Mountains to Sea Trail, a 23-kilometre large-scale network of footpaths, elevated walkways, and footbridges, the suspension system consists of a three-part main cable (fully locked steel cables) and 36 hanger cables (stainless steel spiral strands). The main cable joins the tips of the V-shaped mast and connects the mast to the abutments. The eccentrically arranged hanger cables connect the curved deck to the main cable. The V-shaped mast is situated along the central symmetry axis, stabilized by four guy cables.

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Molybdenum Can Increase the Strength and Hardness of Cast Iron

Molybdenum-base alloys and the metal itself have useful strength at temperatures above which most other metals and alloys are molten. The major use of molybdenum, however, is as an alloying agent in the production of ferrous and nonferrous alloys, to which it uniquely contributes hot strength and corrosion resistance, e.g., in jet engines, combustion liners, and afterburner parts. It is one of the most effective elements for increasing hardenability of iron and steel, and it also contributes to the toughness of quenched and tempered steels.

Molybdenum can increase the strength and hardness of cast iron by lowering the pearlite transition temperature. It can also improve the high temperature strength and creep resistance of the material. Compared with molybdenum-free high-chromium cast iron, high-chromium cast iron containing 2-3% molybdenum has significantly higher impact toughness, and is very suitable for use in harsh wear conditions such as mining, grinding, and crushing. 

The performance of these cast iron castings is qualified, and expensive heat treatment is not necessary. It is a cost-effective alternative to other abrasive materials. The reduction in the content of austenite forming elements such as nickel and manganese also minimizes the retention of the low-temperature austenite phase that is a potential cause of premature component failure. 

The application of high silicon-molybdenum ductile iron with a silicon content of up to 4% and a molybdenum content of 1% has aroused increasing interest. They have good strength at temperatures as high as 600°C and become feasible and cost-effective materials for high-temperature applications to replace higher alloyed steel materials, such as turbocharger housings, engine exhaust manifolds and heating furnace components as well as other applications.

Austenitic austempered ductile iron has a unique microstructure, its strength can exceed 1000 MPa (145 ksi), and it has good impact toughness. Their outstanding performance is very suitable for key applications such as large gears and crankshafts required for power generation, ship propulsion and large mining equipment.

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"Water and Soil Disease" Caused by Molybdenum Lack

The average contents of molybdenum is 1.3 PPM, in the earth crust. Fossil fuels containing molybdenum in natural water body is in very low concentrations, and molybdenum in sea water of the average concentration is 14 micrograms/l.

But due to the Human activities widely used molybdenum and burning of molybdenum content fuel , so increase the molybdenum in the environment circulation.

What is more Weathering make the molybdenum released from the rock. Molybdenum distribution are not regularly, thus cause some areas lack of molybdenum and appear "water and soil disease".

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Molybdenum and Alloy Steel

Molybdenum is used efficiently and economically in alloy steel & iron to
-improve hardenability
-reduce temper embrittlement
-resist hydrogen attack & sulphide stress cracking
-increase elevated temperature strength
-improve weldability, especially in high strength low alloy steels (HSLA)

In the present section the focus is on grades and properties of Mo containing alloy steel and iron. End uses cover the whole world of engineered products for :
-Automotive, shipbuilding
-aircraft and aerospace
-Drilling, mining, processing
-Energy generation, including boilers, steam turbines and electricity generators
-Vessels, tanks, heat exchangers
-Chemical & Petrochemical processing
-Offshore; Oil Country Tubular Goods (OCTG)

In most cases molybdenum is needed to meet the high end of the application properties, which is accomplished with comparatively small molybdenum additions. In fact, with the exception of High Speed Steel and Maraging Steel the Mo content often ranges between 0.2 and 0.5% and rarely exceeds 1%.

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Molybdenum Biochemistry

The most important role of the molybdenum in living organisms is as a metal heteroatom at the active site in certain enzymes. In nitrogen fixation in certain bacteria, the nitrogenase enzyme, which is involved in the terminal step of reducing molecular nitrogen, usually contains molybdenum in the active site (though replacement of Mo with iron or vanadium is also known). The structure of the catalytic center of the enzyme is similar to that in iron-sulfur proteins: it incorporates a Fe4S3 and multiple MoFe3S3 clusters.

In 2008, evidence was reported that a scarcity of molybdenum in the Earth's early oceans was a limiting factor for nearly two billion years in the further evolution of eukaryotic life (which includes all plants and animals) as eukaryotes cannot fix nitrogen, and must therefore acquire most of their oxidized nitrogen suitable for making organic nitrogen compounds, or the organics themselves (like proteins) from prokaryotic bacteria.

The scarcity of molybdenum resulted from the relative lack of oxygen in the early ocean. Most molybdenum compounds have low solubility in water, but the molybdate ion MoO42− is soluble and forms when molybdenum-containing minerals are in contact with oxygen and water. Once oxygen made by early life appeared in seawater, it helped dissolve molybdenum into soluble molybdate from minerals on the sea bottom, making it available for the first time to nitrogen-fixing bacteria, and allowing them to provide more fixed usable nitrogen compounds for higher forms of life.

Although oxygen once promoted nitrogen fixation via making molybdenum available in water, it also directly poisons nitrogenase enzymes. Thus, in Earth's ancient history, after oxygen arrived in large quantities in Earth's air and water, organisms that continued to fix nitrogen in aerobic conditions were required to isolate and protect their nitrogen-fixing enzymes in heterocysts, or similar structures protecting them from too much oxygen. This structural isolation of nitrogen fixation reactions from oxygen in aerobic organisms continues to the present..Molybdenite

Though molybdenum forms compounds with various organic molecules, including carbohydrates and amino acids, it is transported throughout the human body as MoO42−.At least 50 molybdenum-containing enzymes were known by 2002, mostly in bacteria, and their number is increasing with every year;[59][60] those enzymes include aldehyde oxidase, sulfite oxidase and xanthine oxidase. In some animals, and in humans, the oxidation of xanthine to uric acid, a process of purine catabolism, is catalyzed by xanthine oxidase, a molybdenum-containing enzyme. The activity of xanthine oxidase is directly proportional to the amount of molybdenum in the body. However, an extremely high concentration of molybdenum reverses the trend and can act as an inhibitor in both purine catabolism and other processes. Molybdenum concentrations also affect protein synthesis, metabolism and growth.

In animals and plants a tricyclic compound called molybdopterin (which, despite the name, contains no molybdenum) is reacted with molybdate to form a complete molybdenum-containing cofactor called molybdenum cofactor. Save for the phylogenetically-ancient molybdenum nitrogenases discussed above, which fix nitrogen in some bacteria and cyanobacteria, all molybdenum-using enzymes so far identified in nature use the molybdenum cofactor. Molybdenum enzymes in plants and animals catalyze the oxidation and sometimes reduction of certain small molecules, as part of the regulation of nitrogen, sulfur and carbon cycles.

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The Molybdenum Properties

1. Physical properties
In its pure form, molybdenum is a silvery-grey metal with a Mohs hardness of 5.5. It has a melting point of 2,623 °C (4,753 °F); of the naturally occurring elements, only tantalum, osmium, rhenium, tungsten, and carbon have higher melting points.Weak oxidation of molybdenum starts at 300 °C. It has one of the lowest coefficients of thermal expansion among commercially used metals.The tensile strength of molybdenum wires increases about 3 times, from about 10 to 30 GPa, when their diameter decreases from ~50–100 nm to 10 nm.Molybdenite ,Molybdenite on quartz

2. Compounds and chemistry
Molybdenum is a transition metal with an electronegativity of 2.16 on the Pauling scale and a standard atomic weight of 95.96 g/mol.It does not visibly react with oxygen or water at room temperature, and the bulk oxidation occurs at temperatures above 600 °C, resulting in molybdenum trioxide:
2 Mo + 3 O2 → 2 MoO3

The trioxide is volatile and sublimates at high temperatures. This prevents formation of a continuous protective oxide layer, which would stop the bulk oxidation of metal.Molybdenum has several oxidation states, the most stable being +4 and +6 (bolded in the table). The chemistry and the compounds show more similarity to those of tungsten than that of chromium. An example is the instability of molybdenum(III) and tungsten(III) compounds as compared with the stability of the chromium(III) compounds. The highest oxidation state is common in the molybdenum(VI) oxide (MoO3), whereas the normal sulfur compound is molybdenum disulfide MoS2.

Molybdenum(VI) oxide is soluble in strong alkaline water, forming molybdates (MoO42−). Molybdates are weaker oxidants than chromates, but they show a similar tendency to form complex oxyanions by condensation at lower pH values, such as [Mo7O24]6− and [Mo8O26]4−. Polymolybdates can incorporate other ions into their structure, forming polyoxometalates.The dark-blue phosphorus-containing heteropolymolybdate P[Mo12O40]3− is used for the spectroscopic detection of phosphorus.[16] The broad range of oxidation states of molybdenum is reflected in various molybdenum chlorides:

Molybdenum(II) chloride MoCl2 (yellow solid)molybdenum
Molybdenum(III) chloride MoCl3 (dark red solid)
Molybdenum(IV) chloride MoCl4 (black solid)
Molybdenum(V) chloride MoCl5 (dark green solid)
Molybdenum(VI) chloride MoCl6 (brown solid)
The structure of the MoCl2 is composed of Mo6Cl84+ clusters with four chloride ions to compensate the charge.

Like chromium and some other transition metals, molybdenum is able to form quadruple bonds, such as in Mo2(CH3COO)4. This compound can be transformed into Mo2Cl84−, which also has a quadruple bond.

The oxidation state 0 is possible with carbon monoxide as ligand, such as in molybdenum hexacarbonyl, Mo(CO)6.

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Relationships of Copper and Molybdenum to Iron Metabolism

Both copper and molybdenum influence the internal transport and release of iron. There is evidence that copper, as a component of ceruloplasmin, increases the rate of oxidation of ferrous to ferric iron for transport by plasma transferrin; and that molybdenum, as a component of xanthine oxidase, participates in the reduction of cellular ferric to ferrous ferritin.

An excess of either copper or molybdenum, by giving rise to a relatively undissociable Cu-Mo-S complex, may produce a deficit of the metal in marginal supply. As dietary excess of copper is known to be common in the United States, and preliminary data suggest that molybdenum intake may not be optimal, it is possible that a conditioned deficit of molybdenum may contribute to abnormalities of iron metabolism and utilization.

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Molybdenum's Influence on Rats at Different Copper Levels of Diet

1.Male WAG/Cpb inbred rats fed on rations with approximately 1-5 rng copper/kg (deficient), 6.0 mg copper/kg (adequate) and 25.0mg copper/kg (excess) are supplemented with varying amounts of molybdenum (0, 50, 150 and 500 mg/kg diet) (as ammonium heptamolybdate) and the effect on the copper concentration of blood, plasma, liver and kidney,the caeruloplasmin activity of plasma and the molybdenum concentration of liver and kidney are studied. Copper is supplied as copper(II) nitrate.

2. Molybdenum increases the copper concentration of blood, plasma, liver and kidney and the molybdenum concentration of liver and kidney.

3. In the plasma of molybdenum-supplemented rats the presence of a copper-containing fraction is demonstrated, the copper of which did not react with dithiocarbamate and was not related to caeruloplasmin. The copper in this fraction is not able to increase the caeruloplasmin activity in the plasma of copper-deficient molybdenum-supplemented rats. The copper concentration of the erythrocytes does not seem to have been increased by the molybdenum treatment.

4.When compared to copper-adequate rats the effect of molybdenum on the copper distribution is reduced both by copper deficiency and copper excess. This decreased effect of molybdenum is explained by reduced uptake or retention of molybdenum in the body as observed in the liver and kidney.

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The Element Molybdenum

Atomic Number: 42
Atomic Weight: 95.96
Melting Point: 2896 K (2623°C or 4753°F)
Boiling Point: 4912 K (4639°C or 8382°F)
Density: 10.2 grams per cubic centimeter
Phase at Room Temperature: Solid
Element Classification: Metal
Period Number: 5    Group Number: 6    Group Name: none
Estimated Crustal Abundance: 1.2 milligrams per kilogram
Estimated Oceanic Abundance: 1×10-2 milligrams per liter
Number of Stable Isotopes: 6   (View all isotope data)
Ionization Energy: 7.092 eV
Oxidation States: +6

Molybdenum was discovered by Carl Welhelm Scheele, a Swedish chemist, in 1778 in a mineral known as molybdenite (MoS2) which had been confused as a lead compound. Molybdenum was isolated by Peter Jacob Hjelm in 1781. Today, most molybdenum is obtained from molybdenite, wulfenite (PbMoO4) and powellite (CaMoO4). These ores typically occur in conjunction with ores of tin and tungsten. Molybdenum is also obtained as a byproduct of mining and processing tungsten and copper.

Molybdenum has a high melting point and is used to make the electrodes of electrically heated glass furnaces. Some electrical filaments are also made from molybdenum. The metal is used to make some missile and aircraft parts and is used in the nuclear power industry. Molybdenum is also used as a catalyst in the refining of petroleum.

Molybdenum is primarily used as an alloying agent in steel. When added to steel in concentrations between 0.25% and 8%, molybdenum forms ultra-high strength steels that can withstand pressures up to 300,000 pounds per square inch. Molybdenum also improves the strength of steel at high temperatures. When alloyed with nickel, molybdenum forms heat and corrosion resistant materials used in the chemical industry.

Molybdenum disulphide (MoS2), one of molybdenum's compounds, is used as a high temperature lubricant. Molybdenum trioxide (MoO3), another molybdenum compound, is used to adhere enamels to metals. Other molybdenum compounds include: molybdic acid (H2MoO4), molybdenum hexafluoride (MoF6) and molybdenum phosphide (MoP2).

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Molybdenum Applications

Molybdenum is a silvery grey metal that is not found in a pure state in nature. It is usually associated with other elements, such as is the case of sulfurated ores, from which one can also obtain copper. Thus it is common for molybdenum to be regarded as a byproduct of the copper extraction operation.

In the periodic table of chemical elements, molybdenum is identified with number 42 and the symbol Mo. It melts at a temperature of 2,610 degrees Celsius.

Its name originates from the Greek word, “molybdos”, meaning “lead-like”, in a clear allusion to its color. Although some say that it was known in ancient times, it was only during the World War I that its use in steel alloys was made known. Molybdenum was utilized instead of wolfram (aka tungsten) that in those times was scarce, and so began its commercial application.

Its main characteristics are durability, strength and resistance to corrosion and high temperatures.

Molybdenum is a metal used as raw material in order to obtain alloys, among which more resistant steel stands out. Approximately two thirds of this metal is used for this purpose, also known as inox, with contents up to 6%.

The steel alloy withstands high temperatures and pressures, being very resistant. This is why it is used in construction, to manufacture airplane parts and wrought car parts. Molybdenum wires are utilized in electronic tubes and the metal also functions as electrode in glass furnaces.

Among its many applications is a superalloy that can be obtained from a nickel base, to produce catalysts which are used to eliminate sulfur in the oil industry.

In addition, it is utilized in the industrial process of lubricants (molybdenum disulfide is resistant to high temperatures, reduces wear and friction of motor parts – as may be the case of vehicle brakes), in the manufacture of linings and solvents, in the chemical industry (pigments for plastics, paints and rubber compounds) and in the electronic industry (electric conductors).

Molybdenum is also deemed to be a strategic material and has multiple applications in the aerospace and automobile industries, for surgical tools, as well as for manufacturing light bulbs (filament) and LCD screens, for water treatment and even for applying laser beams.

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Molybdenum in the Environment

Molybdenum differs from the other micronutrients in soils in that it is less soluble in acid soils and more soluble in alkaline soils, the result being that its availability to plants is sensitive to pH and drainage conditions. Some plants can have up to 500 ppm of the metal when they grow on alkaline soils.

Molybdenite is the chief mineral ore, with wulfenite being less important. Some molybdenite is obtained as a by-product of tungsen and copper production. The main mining areas are the USA, Chile, Canada and Russia, with world production being around 90.000 tonnes per year, and reserves amounting to 12 million tonnes of which 5 million tonnes are in the USA.

Health effects of molybdenum

Based on animal experiments, molybdenum and its compounds are highly toxic. Some evidence of liver dysfunction with hyperbilirubinemia has been reported in workmen chronically exposed in a Soviet Mo-Cu plant. In addition, signs of gout have been found in factory workers and among inhabitants of Mo-rich areas of Armenia. The main features were joint pains in the knees, hands, feet, articular deformities, erythema, and edema of the joint areas

Environmental effects of molybdenum

Molybdenum is essential to all species. As with other trace metals, though, what is essential in tiny amounts can be highly toxic at larger doses. Animal experiment have shown that too much molybdenum causes fetal deformities. Fodder with more than 10 ppm of molybdenum would put most livestok at risk.

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Occurrence of Molybdenum

Molybdenum is the 54th most abundant element in the Earth's crust and the 25th most abundant element in the oceans, with an average of 10 parts per billion; it is the 42nd most abundant element in the Universe. The Russian Luna 24 mission discovered a molybdenum-bearing grain (1 × 0.6 µm) in a pyroxene fragment taken from Mare Crisium on the Moon.

The comparative rarity of molybdenum in the Earth's crust is offset by its concentration in a number of water-insoluble ores, often combined with sulfur, in the same way as copper, with which it is often found. Though molybdenum is found in such minerals as wulfenite (PbMoO4) and powellite (CaMoO4), the main commercial source of molybdenum is molybdenite (MoS2). Molybdenum is mined as a principal ore, and is also recovered as a byproduct of copper and tungsten mining.

Historically, the Knaben mine in southern Norway, opened in 1885, was the first dedicated molybdenum mine. It closed from 1973–2007, but is now reopened. Large mines in Colorado (such as the Henderson mine and the Climax mine) and in British Columbia yield molybdenite as their primary product, while many porphyry copper deposits such as the Bingham Canyon Mine in Utah and the Chuquicamata mine in northern Chile produce molybdenum as a byproduct of copper mining.

The world's production of molybdenum was 250,000 tonnes in 2011, the largest producers being China (94,000 t), United States (64,000 t), Chile (38,000 t), Peru (18,000 t) and Mexico (12,000 t). The total reserves are estimated at 10 million tonnes, and are mostly concentrated in China (4.3 mt), US (2.7 mt) and Chile (1.2 mt). By continent, 93% of world molybdenum production is about evenly split between North America, South America (mainly in Chile), and China. Europe and the rest of Asia (mostly Armenia, Russia, Iran and Mongolia) produce the remainder.

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History of Molybdenum

Molybdenite—the principal ore from which molybdenum is now extracted—was previously known as molybdena. Molybdena was confused with and often utilized as though it were graphite. Like graphite, molybdenite can be used to blacken a surface or as a solid lubricant. Even when molybdena was distinguishable from graphite, it was still confused with the common lead ore PbS (now called galena); the name comes from Ancient Greek Μόλυβδος molybdos, meaning lead. (The Greek word itself has been proposed as a loanword from Anatolian Luvian and Lydian languages).

Although apparent deliberate alloying of molybdenum with steel in one 14th-century Japanese sword (mfd. ca. 1330) has been reported, that art was never employed widely and was later lost. In in the West in 1754, Bengt Andersson Qvist examined molybdenite and determined that it did not contain lead, and thus was not the same as galena.

 By 1778 Swedish chemist Carl Wilhelm Scheele stated firmly that molybdena was (indeed) not galena nor graphite. Instead, Scheele went further and correctly proposed that molybdena was an ore of a distinct new element, named molybdenum for the mineral in which it resided, and from which it might be isolated. Peter Jacob Hjelm successfully isolated molybdenum by using carbon and linseed oil in 1781.

For about a century after its isolation, molybdenum had no industrial use, owing to its relative scarcity, difficulty extracting the pure metal, and the immaturity of appropriate metallurgical techniques. Early molybdenum steel alloys showed great promise in their increased hardness, but efforts to manufacture them on a large scale were hampered by inconsistent results and a tendency toward brittleness and recrystallization.

In 1906, William D. Coolidge filed a patent for rendering molybdenum ductile, leading to its use as a heating element for high-temperature furnaces and as a support for tungsten-filament light bulbs; oxide formation and degradation require that molybdenum be physically sealed or held in an inert gas. In 1913, Frank E. Elmore developed a flotation process to recover molybdenite from ores; flotation remains the primary isolation process.

During the first World War, demand for molybdenum spiked; it was used both in armor plating and as a substitute for tungsten in high speed steels. Some British tanks were protected by 75 mm (3 in) manganese steel plating, but this proved to be ineffective. The manganese steel plates were replaced with 25 mm (1 in) molybdenum-steel plating allowing for higher speed, greater maneuverability, and better protection.

The Germans also used molybdenum-doped steel for heavy artillery. This was because traditional steel melted at the heat produced by enough gunpowder to launch a one ton shell. After the war, demand plummeted until metallurgical advances allowed extensive development of peacetime applications. In World War II, molybdenum again saw strategic importance as a substitute for tungsten in steel alloys.

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Molybdenum Compounds

Molybdenum is a transition metal with an electronegativity of 2.16 on the Pauling scale and a standard atomic weight of 95.96 g/mol. It does not visibly react with oxygen or water at room temperature, and the bulk oxidation occurs at temperatures above 600 °C, resulting in molybdenum trioxide: 2 Mo + 3 O2 → 2 MoO3

The trioxide is volatile and sublimates at high temperatures. This prevents formation of a continuous protective oxide layer, which would stop the bulk oxidation of metal. Molybdenum has several oxidation states, the most stable being +4 and +6 (bolded in the table). The chemistry and the compounds show more similarity to those of tungsten than that of chromium. An example is the instability of molybdenum(III) and tungsten(III) compounds as compared with the stability of the chromium(III) compounds. The highest oxidation state is common in the molybdenum(VI) oxide (MoO3), whereas the normal sulfur compound is molybdenum disulfide MoS2.

Molybdenum(VI) oxide is soluble in strong alkaline water, forming molybdates (MoO42−). Molybdates are weaker oxidants than chromates, but they show a similar tendency to form complex oxyanions by condensation at lower pH values, such as [Mo7O24]6− and [Mo8O26]4−. Polymolybdates can incorporate other ions into their structure, forming polyoxometalates. The dark-blue phosphorus-containing heteropolymolybdate P[Mo12O40]3− is used for the spectroscopic detection of phosphorus. The broad range of oxidation states of molybdenum is reflected in various molybdenum chlorides:

Molybdenum(II) chloride MoCl2 (yellow solid)
Molybdenum(IV) chloride MoCl4 (black solid)Molybdenum(III) chloride MoCl3 (dark red solid)
Molybdenum(V) chloride MoCl5 (dark green solid)
Molybdenum(VI) chloride MoCl6 (brown solid)

The structure of the MoCl2 is composed of Mo6Cl84+ clusters with four chloride ions to compensate the charge. Like chromium and some other transition metals, molybdenum is able to form quadruple bonds, such as in Mo2(CH3COO)4. This compound can be transformed into Mo2Cl84−, which also has a quadruple bond. The oxidation state 0 is possible with carbon monoxide as ligand, such as in molybdenum hexacarbonyl, Mo(CO)6.

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Isotopes of Molybdenum

There are 35 known isotopes of molybdenum, ranging in atomic mass from 83 to 117, as well as four metastable nuclear isomers. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. Of these naturally occurring isotopes, only molybdenum-100 is unstable.

Molybdenum-98 is the most abundant isotope, comprising 24.14% of all molybdenum. Molybdenum-100 has a half-life of about 1019 y and undergoes double beta decay into ruthenium-100. Molybdenum isotopes with mass numbers from 111 to 117 all have half-lives of approximately 150 ns. All unstable isotopes of molybdenum decay into isotopes of niobium, technetium, and ruthenium.

As also noted below, the most common isotopic molybdenum application involves molybdenum-99, which is a fission product. It is a parent radioisotope to the short-lived gamma-emitting daughter radioisotope technetium-99m, a nuclear isomer used in various imaging applications in medicine.[9] In 2008, the Delft University of Technology applied for a patent on the molybdenum-98-based production of molybdenum-99.

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About Molybdenum

Molybdenum is a Group 6 chemical element with the symbol Mo and atomic number 42.

The name is from Neo-Latin Molybdaenum, from Ancient Greek Μόλυβδος molybdos, meaning lead, since its ores were confused with lead ores.[4] Molybdenum minerals have been known into prehistory, but the element was "discovered" (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm.

Molybdenum does not occur naturally as a free metal on Earth, but rather in various oxidation states in minerals. The free element, which is a silvery metal with a gray cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of world production of the element (about 80%) is in making many types of steel alloys, including high strength alloys and superalloys.

 Most molybdenum compounds have low solubility in water, but the molybdate ion MoO42− is soluble and forms when molybdenum-containing minerals are in contact with oxygen and water. Industrially, molybdenum compounds (about 14% of world production of the element) are used in high-pressure and high-temperature applications, as pigments and catalysts.

Molybdenum-containing enzymes are by far the most common catalysts used by some bacteria to break the chemical bond in atmospheric molecular nitrogen, allowing biological nitrogen fixation. At least 50 molybdenum-containing enzymes are now known in bacteria and animals, although only bacterial and cyanobacterial enzymes are involved in nitrogen fixation, and these nitrogenases contain molybdenum in a different form from the rest. Owing to the diverse functions of the various other types of molybdenum enzymes, molybdenum is a required element for life in all higher organisms (eukaryotes), though not in all bacteria.

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Molybdenum and TZM Alloy Plastic Processing

When stress of the metal exceeds the elastic limit, there will have plastic deformation occurs. Adjacent atomic planes have relative tangential motion. Besides, when the shear stress is large enough, the atomic will from the equilibrium position go into another equilibrium position. But when the external force disappear the atomic planes which after tangential motion can not move back to the original position, thus producing irreversible permanent deformation, that is, plastic processing.

Deformation resistance refers to a kind of ability for resistance plastic deformation. The metal material in order to maintain the original state, there will produce deformation resistance to resist deformation at certain of temperature, speed and deformation degree. From the microscopic point, the external forces make the distance between atoms to change resulting in an imbalance of attraction and repulsion. Molybdenum and TZM alloy in the rolling process will produce deformation resistance, and the main factors which influence the deformation resistance is material chemical composition, metallurgical properties, geometry, friction of deformation outer zone, material work hardening and the deformation zone of thermodynamic parameters.

Molybdenum and TZM alloy plastic processing method mainly includes rolling, extrusion, drawing, stamping, forging, die forging and the equipments include used include rolling mill, extrusion machines, stretching machines, punching machine, forging machines and rolling machine and so on. Molybdenum and TZM alloy only through plastic processing can obtain the desired shape such as wire, strip, rods, tubes and other products with customized shapes and can apply to different areas as well. The main plastic processing method of TZM or molybdenum rod is rolling and model rolling. On the other hand, the wire and tubes usually through stretching machine to produce, and the products of sheet, strip and foil mainly through rolling method.

Using rolling method for material plastic processing mainly puts metal blank in the gap of a pair of rotating rollers (the desired shape), through the compression of rotating rollers to decrease cross-section and to increase the length of the material, then to obtain high quality products. Rolling method is mainly used for the production of bar, sheet and tube. Using rolling mill can obtain good quality product, having low metal burning rate, high productivity, high degree of mechanization, and therefore it is widely used. Rolling can be divided into cold rolling and hot rolling.

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Why Is Molybdenum Used in Stainless Steel?

Molybdenum primarily increases the corrosion resistance of stainless steels. Molybdenum containing grades of stainless steels are generally more corrosion resistant than molybdenum-free grades. They are used in applications that are more corrosive, such as chemical processing plants or in marine applications.There are many grades of stainless steels with different molybdenum (and chromium, nickel, nitrogen, etc.) contents.The best grade for a given application is selected based on the corrosivity of the service environment.

As a large atom, molybdenum increases the elevated temperature strength of stainless steels through solid solution hardening.  This effect is used in heat exchangers and other elevated temperature equipment such as in automotive exhaust systems.

To discuss the influence of molybdenum on the metallurgy of stainless steels, it is useful to look at the metallurgy of stainless steels in general.  Based on their microstructure, stainless steels are divided into the following families: austenitic、ferritic、martensitic、duplex and precipitation hardenable.

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Introduction of Molybdenum Sheet

Standard: ASTM B386

Material: Mo >99.95%
Density: >10.2g/cc

Molybdenum sheet is made of the material of molybdenum, so that molybdenum sheet owns the properties of molybdenum. Molybdenum sheet can stand extreme temperatures and keep its strength and stiffness at high temperatures. Molybdenum sheet also has good thermal conductivity and lower thermal expansion. It can provide excellent corrosion resistance that is similar to tungsten sheet. Our molybdenum products are widely used in aviation, aerospace, nuclear high-temperature furnace, glass, ceramic, crystal production, medical, illumination and vacuum sputtering etc. molybdenum sheet, suitable for light, electric vacuum device and electric semiconductor device.

Molybdenum sheet is processed to obtain maximum ductility for applications involving bending, spinning, drawing or stamping. It is this objective that also gives the impression of molybdenum sheet special advantages. If the customer designates their specific application, we can supply the best material suited for their use, to meet their requirements of product-molybdenum sheet. It is this objective that also gives the impression of molybdenum sheet special advantages. If the customer designates their specific application, we can supply the best material suited for their use, to meet their requirements of product-molybdenum sheet.

Application:

Molybdenum sheet is used for making electric light source parts, components of electric vacuum and electric power semiconductor. It is also used for producing molybdenum boats, heat shield and heat bodies in high temperature furnace.

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Molybdenum in the Environment

Molybdenum differs from the other micronutrients in soils in that it is less soluble in acid soils and more soluble in alkaline soils, the result being that its availability to plants is sensitive to pH and drainage conditions. Some plants can have up to 500 ppm of the metal when they grow on alkaline soils.

Molybdenite is the chief mineral ore, with wulfenite being less important. Some molybdenite is obtained as a by-product of tungsen and copper production. The main mining areas are the USA, Chile, Canada and Russia, with world production being around 90.000 tonnes per year, and reserves amounting to 12 million tonnes of which 5 million tonnes are in the USA.

Health effects of molybdenum

Based on animal experiments, molybdenum and its compounds are highly toxic. Some evidence of liver dysfunction with hyperbilirubinemia has been reported in workmen chronically exposed in a Soviet Mo-Cu plant. In addition, signs of gout have been found in factory workers and among inhabitants of Mo-rich areas of Armenia. The main features were joint pains in the knees, hands, feet, articular deformities, erythema, and edema of the joint areas

Environmental effects of molybdenum

Molybdenum is essential to all species. As with other trace metals, though, what is essential in tiny amounts can be highly toxic at larger doses. Animal experiment have shown that too much molybdenum causes fetal deformities. Fodder with more than 10 ppm of molybdenum would put most livestok at risk.

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