The thermal decomposition of ammonium paratungstate hydrate was investigated in dynamic air and inert gas (nitrogen and argon) atmospheres by simultaneous thermo-gravimetric analysis (TGA), differential thermal analysis (DTA) and mass spectroscopy (MS). The intermediate and end products obtained during thermal decomposition of ammonium paratungstate hydrate were characterized by X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR).

It was found that the kind of gas was not effective on the thermal decomposition mechanism of ammonium paratungstate hydrate below 665K. In the first decomposition step, anhydrous ammonium paratungstate was obtained by dehydration. In the second decomposition step, only deammoniation occurred and ammonium hydrogen tungstate was obtained. During the third decomposition step, dehydration, deammoniation and reduction of some tungsten atoms to lower valences were observed. At this stage, first, ammonium hydrogen tungsten oxide bronze and later ammonium tungsten oxide bronze were formed by two serial reactions. In the fourth step which occurs after 665 K, ammonium tungsten oxide bronze formed stoichiometric tungsten oxide in air atmosphere and tungsten suboxide in inert gas atmosphere.

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Tungsten metal products are made using a chemically refined intermediate ammonium paratungstate (APT) product. APT is produced by processing tungsten concentrates containing scheelite (calcium tungstate) or wolframite (iron/manganese tungstate). The processing steps usually include several impurity removal steps to make an APT product of the desired purity.

In the process for recovering tungsten from a tungsten concentrate wherein the tungsten content of said concentrate is separated therefrom, purified and converted into solid ammonium paratungstate (APT) by crystallization from ammoniacal solution, of which a portion is off-grade material, the improvement for recovering said off-grade APT with a minimum number of processing cycles which comprises mixing said off-grade APT with an ammonia solution containing about 2.5% to about 12%, by weight, of NH3 and autoclaving said mixture at a temperature above the boiling point thereof for a time sufficient to dissolve substantially all of said APT and recrystallizing solid APT from the resulting solution to yield a solid APT product.

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Ammonium metatungstate(APT) solutions are prepared from relatively insoluble APT by (a) forming an aqs. suspension containing up to 22% wt APT, calculated on the content of WO3; (b) maintaining the pH of the aqs. suspension at 1-75-3.5 by the addition of hydrogen ions, and (c) maintaining the temperature of the suspension at 50-120 degrees C until the APT has been dissolved and converted into metatungstate. The process enables ammonium metatungstate solutions to be more cheaply prepared, as ammonium paratungstate is cheaper than ammonium metatungstate. The process is convenient and efficient, and can be carried out using the commercially available refracting form of ammonium paratungstate. - Concentrated solutions of the metatungstate can be easily prepared.

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(a) providing an aqueous solution of ammonium paratungstate(APT);

(b) adding aqueous potassium hydroxide solution to the aqueous solution of APT as a doping substance, wherein the mole ratio of potassium to ammonium is 0.1 to 10, thereby forming an ammonium potassium paratungstate;

(c) converting the ammonium potassium paratungstate to potassium-doped tungsten blue oxide;

(d) reducing the doped tungsten blue oxide to doped tungsten powder; and

(e) compacting the doped tungsten powder and drawing doped tungsten wire from the compacted powder.

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A process for producing APT from a heavy metal alloy containing tungsten comprising introducing the heavy metal alloy into an electrolytic cell as an anode, said cell comprising an inert cathode and an aqueous electrolyte solution comprising ammonium hydroxide and ammonium nitrate, passing a direct electric current through said cell, said ammonium hydroxide and ammonium nitrate being maintained at a suitable concentration for oxidizing tungsten and forming ammonium paratungstate. After the desired concentration of ammonium paratungstate is reached in the electrolyte solution, the reaction may be stopped and the electrolyte withdrawn. The resulting ammonium paratungstate may be purified by conventional methods known in the art.

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When cutting tungsten carbide cutting tools, tungsten carbide cutting tools for cutting the amount of wear has a significant impact, especially in cutting speed. Different cutting speed on the wear of tungsten carbide cutting tools have different variations. In general, the greater the cutting speed, the greater the amount of flank wear, the more severe tools wear. Uncoated tungsten carbide tools in high-speed cutting, the rapid rise in the amount of flank wear, cutting the distance is very short, but the amount is much larger than the amount of wear and wear low-speed cutting. When the cutting speed reaches 100m / min or more, the coating due to friction during cutting off, the substrate is exposed to participate in a cutting tool. Lead to increased wear of tungsten carbide cutting tools, and ultimately failure.

Different grades of tungsten carbide cutting tools wear is as cutting speed increases. Low speed cutting with adhesive wear as the main wear mechanism, high-speed cutting wear and diffusion wear oxide as the main wear mechanism. This is because with the increase in cutting speed and tools - chip contact surface temperature with increasing pressure, knife - contact debris from sliding contact between the adhesive into contact. Under the adhesion force in the tools and workpiece contact surface friction generated by the process, the tools material fine particles from peeling or cutting. When the cutting temperature reaches 800 ~ 900 ℃, decomposition occurs between the workpiece and the tools element and the diffusion element to each other, the strength of the tools is reduced, resulting in tungsten carbide cutting tools wear or breakage failure.




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Tungsten carbide tools wear process is divided into early wear, normal wear and severe wear of three phases.

1. Wear the early stages
Tungsten carbide cutting tools and the workpiece during the fourth year, as the new tools sharpening surface roughness and micro-cracks, defects such as oxidation or decarbonization layer, so that the actual contact area is small, the contact point bonding serious, so the tools wear faster. As the cutting proceeds, the tools surface micro peak peak gradually rubbed off, the surface roughness values decrease, the actual contact area increases, increased number of contact points, so tungsten carbide tools wear rate decreased. Coated tungsten carbide cutting tools at low speed, the wear more evenly. When the speed increases, the wear and tear is beginning to show a parabolic band.

2. Normal wear stage
After the initial worn, rough surfaces and polished tungsten carbide cutting tools gradually phase into the normal wear and tear. This stage is relatively slow uniform wear, with the growth of the amount of wear and the cutting time is approximately proportional to the increase. This stage is the stage of effective working tool. When the tools wear stage into the normal wear and tear, wear, Deputy Regional flank wear was uniform phenomenon. Especially coated tungsten carbide cutting tools, wear range presents a uniform wear strip. Compared with uncoated tungsten carbide cutting tools, wear it more slowly into the normal wear stage.

3. Severe wear stage
When the amount of wear tungsten carbide cutting force reaches a certain value will increase sharply, cutting temperature rises rapidly, the flank wear values will increase significantly decreased mechanical efficiency, precision loss, abnormal vibration and noise, the final result cutting tools fall, resulting in the loss of tungsten carbide cutting ability.

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Swaged rods final diameter of about 3 mm. Available swaging draw blank drawing production, but also the production of usable rolling method; rolling billet production pass deformation large, relatively homogeneous, in favor of subsequent processing. Drawn tungsten tungsten blanks with "warm brushed" method. First, pull on the chain stretching machine to a diameter of 1.3 mm, respectively, and then pull through coarse, medium and fine pull pull so diameter of less than 0.06 mm 0.2,0.06.

With the reduced diameter, so that the heating temperature should drop, drawing speed. Pass deformation is generally between 10 to 20%. Drawing coal gas - air mixture is heated at a temperature of 900 ~ 400 ℃. Pull thick wire with carbide dies, diamond mold is used to pull the filaments. Mold material, pass, grinding technology has a great influence on the quality of the wire, graphite lubricant quality, particle size, proportion, coating methods also affect the quality of the wire. Inhomogeneity wire diameter is one of the most important reason of broken wires when used, there are 0.2 to 0.4 micron deviation will cause a vacuum in the tungsten filament life is greatly reduced.

Diameter filament material can be used gravimetric method or vacuum measurement standard current law. In the drawing process, as the diameter decreases, the deformation resistance is increased (e.g., fracture strength tungsten wire diameter of 0.1 to 0.3 mm can be up to 350 kgf / mm 2), the plastic is reduced accordingly. In order to further improve the processing performance, generally eliminate the need for intermediate stress annealing. In addition, the electrolytic etching can be processed into a wire filament diameter of less than 0.01 mm.

Plate Rolling

Tungsten can be divided into hot-rolled plate rolling, warm rolling and cold rolling. Due to the large deformation resistance of tungsten, ordinary rolls not fully meet the requirements of the tungsten plate rolling, you should use special materials roll. When rolling, the roll is preheated, depending on rolling conditions, preheating temperature of 100 ~ 350 ℃.




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 Process for the continuous preparation of ammonium paratungstate hydrate directly in the reextraction of a tungsten-laden organic phase with an ammonia-containing aqueous solution in a mixer-settler apparatus, which comprises carrying out the reextraction at an NH3:W molar ratio of from 0.83 to 1.30, and a volume feed ratio of the tungsten-laden organic phase to the ammonia-containing aqueous solution of from 5 to 25 wherein the reextraction in the mixer is carried out so that a solids concentration of the ammonium paratungstate hydrate, based on the ammonia-containing aqueous phase in the mixer, of from 100 to 1200 g/l, is established and wherein the tungsten-laden organic phase and the ammonia-containing aqueous solution are introduced into a stirrer region of the mixer and in that that a three-phase mixture is formed and is taken off both from the upper region, via a free overflow, and from the stirrer region, of the mixer, so that a stationary ratio of tungsten-laden organic phase (OP) and ammonia-containing aqueous solution (AP) in a phase ratio (OP:AP) in the range from 1:5 to 1:70 is established in the mixer.

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Ammonium paratungstate is normally prepared by any one of several well known techniques. One technique involves the dissolution of tungstic acid in ammonium hydroxide to produce ammonium tungstate followed by filtration and evaporation to crystallize ammonium paratungstate. Another technique involves addition of ammonium chloride to sodium tungstate solution to precipitate ammonium paratungstate and leave sodium chloride in solution. Still another technique involves the extraction of a metatungstate species with an organic extracting agent followed by stripping with ammonium hydroxide to produce ammonium tungstate which is evaporated to produce ammonium paratungstate crystals. Another technique involves addition of ammonium hydroxide to ammonium metatungstate solution to precipitate ammonium paratungstate crystals.

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