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Calcium tungstate

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Calcium tungstate, also known as "artificial scheelite", white powder, is a very effective luminescent material under the excitation of X-ray, electron beam and ultraviolet light, and is a very important chemical raw material. It is mainly used to produce ammonium paratungstate Tungsten trioxide Tungsten products such as ferrotungsten, alloy steel, hard alloy, tungsten material, tungsten wire and tungsten alloy. It is used as raw material of tungsten series chemical products.

Chinese name: Calcium tungstate
Foreign name: Calcium tungstate
Chinese alias: artificial Scheelite

Molecular formula: CaWO4
molecular weight: two hundred and eighty-seven point nine three
CAS: 7790-75-2

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brief introduction

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Molecular structure diagram of calcium tungstate

Chinese name: calcium tungstate

Chinese alias: artificial Scheelite

English name: Calcium tungstate

English alias: Calciumtungstatewethipowder; calcium wolframate, not of a kind used as a luminophore; calcium wolframate, of a kind used as a luminophore; Calciumtetrahydrogendiphosphatemonhydrate; Calcium orthotungstate; Calcium wolframate; calcium dioxido(dioxo)tungsten

Molecular formula: CaWO four

Molecular weight: 287.93

In the molecular formula CaWO four The valence of W is+6.^[1]

Numbering system

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CAS No.: 7790-75-2

MDL No.: MFCD00010913

EINECS No.: 232-219-4

PubChem No.: 24854944^[1]

Physical property data

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Character: white tetragonal crystal, square crystal system structure.

Density (g/mL 25 º C): 6.062

Melting point (º C): 1580

Refractive index (n20/D): 1.93

Solubility: slightly soluble in water Ammonium chloride solution , decompose in hot hydrochloric acid.^[1]

toxicology data

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Exposure to tungsten compounds will cause irritation and inflammation of the upper and deep respiratory tracts. Irritating to skin.^[1]

Ecological data

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Generally speaking, it is harmless to water. If there is no government permission, do not discharge materials into the surrounding environment.^[1]

Properties and stability

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It will not decompose if used and stored according to specifications.

Avoid contact with acid and alkali. It can be decomposed into yellow tungstic acid by hydrochloric acid or nitric acid, and can also be decomposed into sodium tungstate by molten sodium carbonate. Operators shall wear gas masks, dust-proof clothes, gloves and glasses. Dust leakage shall be prevented at all stages of preparation and use of tungsten and its compounds. Slightly soluble in water, soluble in Ammonium chloride solution 。 Insoluble in ethanol. It decomposes in hydrochloric acid. For manufacturing Luminous paint Fluorescent lamp, X-ray fluorescent screen, medicine, scintillation counter and laser, etc.^[1]

characteristic

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Calcium tungstate is a self activating phosphor, which is very effective under X-ray, electron beam and ultraviolet excitation Luminescent material 。 Blue fluorescence is generated under 253.7 nm ultraviolet radiation, and the peak wavelength of the emission spectrum is 423 nm, and the half width is 120 nm. Blue light is emitted under the excitation of cathode ray, anode voltage is 3kV, peak wavelength is 415nm, and optical efficiency is 851m/W.^[1]

Storage method

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Keep the container sealed. Store in a tight container in a cool, dry place.^[1]

synthetic method

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1. Calcium oxide or calcium hydroxide With tungsten oxide or tungsten hydroxide in alkali metal hydroxide Or in carbonate solution to produce calcium tungstate. Sodium tungstate is mixed with sodium sulfide, dissolved with water, added with zinc chloride aqueous solution, filtered, and treated with pure calcium chloride to obtain calcium tungstate.

2. Sodium tungstate solution and Calcium chloride solution It can be processed by natural scheelite.

3. Use tungsten trioxide and calcium carbonate It is made of raw materials by burning at 1070 ℃. It can also be controlled by Sodium tungstate Solution vs calcium chloride Solution action or natural scheelite Processed.^[1]

purpose

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Calcium tungstate is a very important chemical raw material, mainly used for production Ammonium paratungstate 、 Tungsten trioxide , ferrotungsten, alloy steel Hard alloy , tungsten material Tungsten wire and tungsten alloy etc. Tungsten products 。 Used as tungsten Raw materials for a series of chemical products; Also used for Fluorescent coating , light screen tube for photography, medicine, X-ray pictures, fluorescent lamps, etc. It is used for fluorescent coatings, light screen tubes for photography, medicine, X-ray pictures, fluorescent lamps, etc. Calcium tungstate is also used to make Luminous paint Fluorescent lamp, neon lamp, X-ray fluorescent screen, medicine, scintillation counter and laser, etc.^[2]