Molybdenum is a transition metal element of the sixth group (chromium group) in the fifth cycle of the periodic table.Element symbol Mo, atomic number 42, relative atomic mass 95.95.The relative density is 10.28g/cm ³, the melting point is 2622 ℃, and the boiling point is 4825 ℃.The resistivity is 5.2X10 Ω Ω · m (20 ℃).[1]
Molybdenum has the characteristics of high strength, high hardness, excellent mechanical properties, and can still maintain high strength and high hardness at high temperatures.Molybdenum is mainly used for steelmaking. Alloy steel mixed with molybdenum has high strength, high toughness, outstanding heat resistance and corrosion resistance.Molybdenum inElectronic tube、transistor、rectifierAnd other electronic devices.[7]
The important compounds of molybdenum include molybdenum oxide, molybdenum sulfide, molybdate and molybdate.Molybdenite (mainly molybdenum disulfide) exists in nature.Molybdenum oxide at high temperature is molybdenum oxide, which is reduced by hydrogen or aluminothermic method to obtain simple molybdenum.It is mainly used for special alloys, electrodes and catalysts.It is an essential trace element for human body.[1]
Chinese name
molybdenum
Foreign name
molybdenum[1]
CAS login number
7439-98-7
EINECS login number
231-107-2
Melting point
2622 ℃[1]
Boiling point
4825 ℃[1]
Density
10.28 g/cm³[1]
Appearance
Silver white metal
Application
Special steel, alloy steel, tool steel, structural steel, etc
Before the end of the 18th century, both were sold under the name of "molybdenite" in the European market.
In 1778, Scheler's organization studied a mineral called molybdenite.[4]
In 1782, Elm, the owner of a Swedish mine, used the mixture of charcoal and molybdic acid mixed with linseed oil for closed burning to separate metal molybdenum from molybdenite, named molybdenum, and the element symbol was determined as MoBeziliusAnd others.[2]
In 1953, it was confirmed that molybdenum was an essential trace element for human body, animals and plants.
Physical and chemical properties
Announce
edit
physical property
Molybdenum rod in ampoule
Molybdenum is a hard silver white metal in cubic crystal system.The relative density is 10.28g/cm ³, the melting point is 2622 ℃, and the boiling point is 4825 ℃.The resistivity is 5.2X10 Ω Ω · m (20 ℃).It is resistant to corrosion due to the oxide film on the surface. It is not oxidized by air at room temperature, and is insoluble in hydrochloric acid or hydrofluoric acid. It is soluble in hot concentrated sulfuric acid, nitric acid and molten potassium nitrate.The oxidation state includes+2,+4 and+6, and+6 is the main oxidation state.[1]
chemical property
Reaction of molybdenum with air
At room temperature, molybdenum does not react with air or oxygen (O ₂).In red heat, molybdenum can react with oxygen to form molybdenum oxide (Ⅵ) MoO ≮.[4]
Reaction of Molybdenum with Halogen
Molybdenum reacts directly with fluorine gas (F ₂) at room temperature to form molybdenum fluoride (Ⅵ) MoF ₆.[4]
Carefully control the reaction conditions of molybdenum and chlorine (Cl ₂) to generate molybdenum chloride (V) MoCl ≮.[4]
Preparation method
Announce
edit
Powder metallurgy
After compression and solidification, molybdenum powder is sintered in hydrogen or vacuum.In the state of compression and sintering, the density of molybdenum powder is 90-95% of the theoretical value. After mechanical processes such as rolling and molding, the molybdenum powder can reach the theoretical density.[8]
Vacuum arc casting
Molybdenum powder is mixed with machine tool chips and continuously pressed into electrodes.The electrodes are continuously fed into the water-cooled copper mold.The potential difference in the mold forms an arc, which melts the end of the electrode, and the molten metal solidifies in the mold.In vacuum arc casting process, molybdenum is very dense due to casting.However, the cast molybdenum is coarse grain, so machining including recrystallization tempering is required to refine the grain and obtain excellent performance.The casting structure is usually destroyed first by high temperature extrusion operation.The extruded billet is usually recrystallized before further forging or rolling.[8]
application area
Announce
edit
Industrial use
Electrode for melting glass
Molybdenum is a good electrode material because of its high strength at operating temperature and good conductivity. The possible molybdenum oxide does not discolor most glasses.[8]
Heating furnace components
Molybdenum has high thermal strength, which makes it widely used in vacuum heating furnace, neutral or reducing atmosphere heating furnace, such as making heating elements, reflector andBoat vessel。[8]
Electrical and electronic components
Molybdenum wire is a good conductorIncandescent light bulbsIt is widely used to support tungsten wire.Radio vacuum tubes, X-ray tubes and many electronic devices need molybdenum to make components with high thermal strength.[8]
Mold
A more important use of TZM molybdenum base alloy is to make cores and molds for brass, aluminum and steel die castings.Even some zinc die-casting parts use TZM mold to achieve good results.TZM alloy has the advantages of high thermal strength, good heat dissipation and heat crack resistance.[8]
Hot working die
TZM molybdenum base alloy has high thermal strength, so it can be used to make forging dies, stamping dies, punching rods and other dies.[8]
Medical use
Molybdenum-99It is one of the radioisotopes of molybdenum and is used to prepare technetium-99 in hospitals.Technetium-99 is a radioisotope, which can be used for internal organs radiography after taking by patients.Molybdenum-99 used for this purpose is usually absorbed by aluminum oxide powder and stored in relatively small containers whenMolybdenum-99Generated during decayTechnetium-99If necessary, technetium-99 can be taken from the container to the patient.[6]
Distribution
Announce
edit
Molybdenum crucible
There is no free metal molybdenum in nature.The main minerals of molybdenum areMolybdenite(Molybdenum disulfide, MoS ₂).[4]
The reserves of molybdenum on the earth are small, accounting for 0.001% of the weight of the crust. The total reserves of molybdenum ore are about 15 million tons, mainly distributed inU.S.A, China, Chile, Russia, Canada, etc.China's proven molybdenum reserves are 1.72 million tons and its basic reserves are 3.43 million tons, ranking second only to the United States in the world.Molybdenum deposits are concentrated in Shaanxi, Henan, Jilin and Liaoning provinces.
Safety measures
Announce
edit
Environmental hazards
Average of molybdenum in the crustabundance1.3ppm, mostly inMolybdenite、Molybdenite, hydromolybdite.Mineral fuels also contain molybdenum.The concentration of molybdenum in natural water is very low, and the average concentration of molybdenum in seawater is 14 μ g/l.Molybdenum in the atmosphere is mainly composed of molybdate andMolybdenum oxideThe state exists, the concentration is very low, and the molybdenum compound is usually less than 1 μ g/m.
Health hazards
Molybdenum deficiency
Molybdenum in diet is easily absorbed.But sulfate radical (SOfour2-）The absorption of molybdenum is affected because it can form molybdenum sulfate with molybdenum.At the same time, sulfate can also inhibit the reabsorption of molybdenum by renal tubules and increase its excretion from the kidney.So the bodySulfur-containing amino acidThe increase of can promote the excretion of molybdenum in urine.Molybdenum is mainly excreted in urine, but a small part can be excreted with bile.
Molybdenum deficiency is mainly seen in hereditary molybdenum metabolism defects. It has been reported that molybdenum deficiency occurs during total parenteral nutrition.Molybdenum deficiency can be manifested as growth retardation or even deathuric acid、xanthine、HypoxanthineIncreased excretion.
Molybdenum excess
Excessive molybdenum is harmful to human health.It can make the process of energy metabolism in the body appear obstacles, myocardial hypoxia and focal necrosis, prone to kidney stones and urethral stones, increase the risk of iron deficiency anemia, and cause dental caries[3]。
Both human and animal bodies have a strong internal stability mechanism for molybdenum, and oral intake of molybdenum compounds is not easy to cause poisoning.It is reported that the daily molybdenum intake of residents living in Armenia is up to 10-15mg;The local incidence of gout is particularly high and is considered to be related to this.Workers in molybdenum smelters may also ingest too much molybdenum due to inhalation of molybdenum containing dust.According to the survey, these workers' serum molybdenum level, xanthine oxidase activity, blood and urine uric acid levels are significantly higher than the general population.
Toxicological data
Almost all molybdenum compounds are highly toxic and can cause deformities.[4]
Storage and transportation
Store in a cool and ventilated warehouse.Keep away from kindling and heat sources.Protect from direct sunlight.Packing and sealing.It shall be stored separately from fluorine, acid and edible chemicals, and mixed storage is strictly prohibited.Explosion proof lighting and ventilation facilities shall be adopted.It is prohibited to use mechanical equipment and tools that are easy to generate sparks.The storage area shall be equipped with appropriate materials to contain leakage.[5]
test method
Announce
edit
Molybdenum is determined by digesting the sample with HNO ≮ - HCIO ₄ and dissolving it with hydrochloric acid.ThiocyanateIt reacts with molybdenum and becomes an orange yellow complex under the action of reducing agent. The aluminum content in the solution can be determined by isopropyl ether solvent extraction and spectrophotometer colorimetry.[9]
