Reactions of Sodium Tungstate Preparation

Sodium tungstate is the inorganic compound with the formula Na2WO4. This white, water-soluble solid is the sodium salt of tungstic acid. It is useful as a source of tungsten for chemical synthesis. It is an intermediate in the conversion of tungsten ores to the metal.

Treatment of sodium tungstate with hydrochloric acid gives the trioxide:

    Na2WO4 + 2 HCl → WO3 + 2 NaCl + H2O

This reaction can be reversed using aqueous solution of sodium hydroxide

 

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Preparation and Structure of Sodium Tungstate

The predominant route to this salt is the extraction of tungsten ores, almost all of which are tungstates. Thus, the ores are treated with a base to give sodium tungstate, as illustrated in the case of wolframite:
Fe/MnWO4 + 2 NaOH + 2 H2O → Na2WO4•2H2O + Fe/Mn(OH)2

Scheelite is treated similarly using sodium carbonate.

Sodium tungstate can also be produced by treating tungsten carbide with a mixture of sodium nitrate and sodium hydroxide in a fusion process which overcomes the high exothermicity of the reaction involved.

Several polymorphs of sodium tungstate are known, three at only one atmosphere pressure. They feature tetrahedral orthotungstate dianions but differ in the packing motif. The WO42− anion adopts a structure like sulfate (SO42−).


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Salts of Tungstic Acid-I

Tungstic acid resembles molybdic acid in that it reacts with bases to form many different types of salts. A satisfactory classification of these salts has long been, and still is, a matter of difficulty, owing to the fact that many of the compounds are only described by individual investigators, whose work is either insufficient in detail or has lacked confirmation by later workers. The existence of the di- and tri-tungstates prepared by Lefort has not been established. Laurent, in 1847, suggested that there were at least five distinct acids (combinations of tungstic anhydride with water in different proportions) with corresponding series of salts, and although the preparation and properties of all these acids have been described, it is now recognised, largely owing to the work of Riche, Scheibler, and Marignac, that only two different acids are definitely known to exist, namely, ordinary tungstic acid, H2WO4, and metatungstic acid, H2W4O13.aq. The former is insoluble in water and reacts with bases to form normal di-, tri-, and para-tungstates; the latter is soluble in water and yields a well-defined series of salts, the metatungstates.


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Colloidal Tungstic Acid-I

When dilute hydrochloric acid is added to a solution of sodium tungstate until the liquid becomes slightly acid, a colloidal solution of tungstic acid is obtained. If the solution of sodium tungstate is concentrated, a white gelatinous precipitate is obtained on the addition of the acid. This precipitate, after washing by decantation at a low temperature (0° to 5° C.) with as little exposure to air as possible, may be dissolved in a concentrated solution of oxalic acid and the liquid subjected to dialysis. If the outer water is repeatedly changed, the oxalic acid may be completely removed, leaving a colloidal solution of tungstic acid.


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Chemical Equations of Tungsten Acid Preparations

1, By mixing the calcium tungstate and hydrochloric acid, washed, dried and pulverized to obtain acid products.


2, By acidifing pure ammonium tungstate solution with hydrochloric acid, and then dehydrated, dried and pulverized to obtain acid products.



 

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The Main Types of Tungsten Carbide Tipped Tools (1)

Tungsten carbide tipped tools are referred to the cutting tools whose cutting edges are comprised of tungsten carbide as a separate piece of material that welded, brazed or clamped on to the tool body. Generally, the main types of tungsten carbide tipped tools include,

Milling Cutters



Milling cutters are normally applied in milling machines and machining centres. For the industrial milling applications, for instance face milling ,slot milling and profile milling, end mills as one of most popular milling cutters are widely adopted. Fly cutters also could be cataloged into this type. It carries one or two inserted tool bits which generate small facing cuts while the whole units are rotating.


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The Main Types of Tungsten Carbide Tipped Tools (2)

Beside the milling cutters, the other two main types of tungsten carbide tipped tools are listed as follows,



Tool Bits

Tool bits are referred to the non-rotary cutting tools which make effort in the devices like shapers, planers and metal lathes. In the practice, tool bits are also addressed as single point cutting tools. In addition, The cutting edge is ground to suit a particular machining operation and may be resharpened or reshaped as needed.

Saw Blades

Saw blades are the cutting tools comprise a hard blade and several cutting edges along the cutting site of the saw, which own ability to cut through materials such as, wood, plywood, laminated board, plastic, grass, aluminum and some other metals. The saw blade's teeth are welded with small pieces of sharp tungsten carbide block.


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Tungsten Carbide Removable Cutting Tips Advantages

Tungsten carbide removable cutting tips are referred to the cutting tips that are not welded or brazed to the tool body which could flip or rotate independently. They also addressed as inserts.

The main advantages regarded to this kind of cutting tips include,

Time saving in manufacturing as the fresh cutting edges are able to perform periodically without set up changes, tool grinding and update new values in the operation program.

It is much easier for the manufacturer to produce the small tungsten carbide inserts instead of producing the whole solid tool from the the same material. In addition the cost is less if only the cutting edge’s material is tungsten carbide, and the rest of the tool made from other cheaper material.

The hardness of the tungsten carbide removable cutting tips offer a longer working life for the cutting tools.


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The Classification of Tungsten Radiation Collimators

There two kinds of tungsten collimators, tungsten panoramic collimators and tungsten directional collimators. Collimators contain and direct the beam of radiation during exposure. This results in improved radiograph quality and safer operating conditions. Tungsten panoramic collimators consist of a stainless steel housing containing two tungsten inserts. Tungsten directional collimators direct the radiation beam from a side port as a 60° conical side throw. A wide range of collimators have been developed to meet the variety of applications and techniques used.

 

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Polymer–Nonleaded Metal Tungsten Composites

Nonleaded metal–polymer tungsten and sendust composite can be applied for X-ray shielding as a reliable substitute material for lead. The lamination order of tungsten film and sendust composite film affects the final performance of the laminated composites.Polymer–nonleaded metal tungsten composites had been studied the effects of multilayer structure on X-ray shielding ability. Though the metals were nonleaded, the metal contents were low, and the composite films were thin, the composite films showed favorable X-ray shielding ability due to the uniform dispersion of metal particles in the polymer matrix and the flake alignment of tungsten. This means that multi-layered particles can effectively absorb the penetrating photons and they fill the pin holes in the composite. More uniformly aligned tungsten shows better shielding effect than randomly oriented lead.

 

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