Cobalt is the metal with shiny steel gray. The tool made by steel containing a certain amount of cobalt can significantly improve the wear resistance and cutting performance, so cobalt often used for making carbide. The content of cobalt at tungsten carbide surface affects its performance, specific performance as bellows:
1. The cobalt content of outermost layer is lower than the nominal cobalt content, and then the carbide will have high hardness and wear resistance;
2. The cobalt content of middle layer is higher than the nominal cobalt content, and then the carbide will have good hardness and abrasion resistance.



In this paper, a method that preparing tungsten carbide with gradient cobalt content change at surface from ammonium paratungstate, the carbide produced has normal core tissue, the mechanical properties and service life are improved. Steps are as follows:
1. Prepare a paste of ammonium paratungstate
APT is dissolved at a concentration of 2%~4% polyvinyl alcohol solution to obtain a paste of ammonium paratungstate, the amount of APT added is 6~8 times the amount of polyvinyl alcohol solution;
2. Carbide surface infiltration tungsten
Wrapping carbide in the paste ammonium paratungstate, and heated to 800~900°C in a hydrogen atmosphere, continually heated to 1400~1460°C after incubation for 20~40 minutes heating, then incubation for 1~2 hours, taken out and cooling down under a hydrogen atmosphere;
3. The solid carburizing
Add carbon black at a temperature of 1420~1450°C for 0.5~2 hours
4. Decarburization phase generated
Ammonium paratungstate is heated to about 900°C at a hydrogen atmosphere, activity W and tungsten oxide can be obtained, and then reacted at a constant temperature 1400~1460°C for some time, thus to get tungsten carbide with gradient cobalt content change at surface.

Another purpose of this experiment is to show that the experimental data on the number of polycrystalline diamond composite button impact on the resistance of polycrystalline diamond buttons, tungsten carbide substrate by more marked hole inserts welded certain number of polycrystalline diamond can effectively improve the wear resistance of tungsten carbide buttons. The schematic diagram of 1-4 PCD inserts welded tungsten carbide - polycrystalline diamond composite buttons as follow:

From the figure we can be more clearly seen in the PCD carbide ball symmetrically distributed around the button tip, the tip of the general impact of the maximum stress endured so cemented carbide substrate is usually not tip inserts welded polycrystalline diamond PCD damaged by great impact energy. Experimental results show that a polycrystalline diamond insert welded carbide - polycrystalline diamond composite ball gear not rupture under impact action 30J-70J, that within the impact resistance of safety values. For φ16mm diameter high pressure DTH drill site operations in the approximate range withstand the impact energy also falls within this range, it is considered that a polycrystalline diamond insert welded carbide - polycrystalline diamond compact button able to meet the requirements of DTH drill. However, when the hole of tungsten carbide basis is more than 3, its impacting resistance will remarkably decrease (starting to destroy when the impact energy is higher than 50J). Therefore, for tungsten carbide – polycrystalline diamond button, the more polycrystalline diamond does not mean the better properties, which has a optimum range and the effect subjects to normal distribution.

Tungsten carbide – polycrystalline diamond button is based on tungsten carbide and punching for polycrystalline diamond welding, which makes this composite buttons not only have excellent hardness and impact resistance, but also the defect of wear resistance can be made up by polycrystalline diamond. Theoretically, tungsten carbide – polycrystalline diamond buttons can be perfectly suitable for the requirements of impacting resistance of DTH drills. In order to prove this inference, related researchers design the interior impact test, which was calculated using the results of DTH drill buttons at the construction site of the state power to withstand the impact of granite, the impact test simulates the maximum extent carbide - PCD composite buttons as the actual working environment DTH drill buttons.

The experiments use tungsten carbide – polycrystalline diamond button reference φ115 DTH drill diameter edge button φ16mm by comparing the number of different inserts welded polycrystalline diamond (1-4) composite ball gear respectively 30J, 50J, 70J the number of times the impact energy of the impact, the impact is 100 times. If tungsten carbide – polycrystalline diamond buttons do not break within 100 times under the impact energy, we can confirm that this impact energy within the safety value. Afterwards, combining different types of DTH drill requirements for impact resistance buttons, it is possible to obtain more rigorous carbide - polycrystalline diamond composite buttons can meet the respective DTH drill impact resistance requirements.

Tantalum, an inactive metal element, symbiosis with niobium, is mainly existed in tantalite, with moderate hardness and full scalability, low coefficient of expansion. Since the tantalum surface will produce stable protective film of Ta₂O₅, thus blocking the continually reaction, and makes that tantalum has a very good corrosion resistance.

Tantalum carbide is based on tungsten carbide alloy composed of cobalt and titanium, its composition is of complexity. Tungsten can be easily recovered in the form of ammonium paratungstate because of the large amount; however, niobium and tantalum with the low levels, therefore only recovered as a general enrichment, so there are a variety of recycling processes have been developed. Zinc Treatment and Molten Sodium Nitrate Enrichment are two of the common methods, the steps seen as following.

Zinc Treatment Method
1. The sintered carbide is decomposed with liquid zinc at 800℃, to break down the bonds of carbide particles and bonds between titanium and cobalt;
2. The decomposition products are carried out vacuum distillation to separate the zinc out which can be recycled;
3. The products after removal of zinc are oxidation and finely grounded, and then go on with alkali treatment and flooding, etc., to make tungsten leaching into the fluid in the form of NaWO₃, thereby ammonium paratungstate is prepared to recycle tungsten;
4. Use sulfuric acid to leach cobalt and titanium, the leaching residue obtained is the tantalum and niobium concentrate, then further separation to recover cobalt and. tantalum.

Molten Sodium Nitrate Enrichment Method
1. The waste carbide together with sodium nitrate are melt processed at the temperature of 700~800℃ to make the carbide decomposition and oxidation;
2. Add water into the melting for leaching out tungsten, thereby preparing ammonium paratungstate to recover tungsten;
3. Filtration, separation the Tungsten-containing solution and residue, and then add hydrochloric acid to leaching out cobalt to recover cobalt;
4. Finally, recover tantalum and niobium concentrate in hydrochloric acid leaching residue thus to recovery of tantalum and niobium.

Metatungstate is one of many types of tungstate, the only compound which the structures have been identified as colorless crystals. It has high solubility in water, and can be derived from metatungstate. Since the metatungstate itself is extremely unstable and easily degradable, therefore, it has a large difficulty in preparation. In the traditional way, sodium tungstate often used to prepare metatungstate crystals, but the complex process, high production costs, low productivity, poor product quality and the environmental pollution and other defects make the way no to be better. Nowadays, harmonious environment, cost savings, simplified procedures are promoted, so its necessary to develop a process which has the simplified process, low cost and environmental pollution, and also conducive to industrial producing metatungstate.

Studies have pointed out that ammonium paratungstate (APT) can be used to prepare metatungstate solution. The steps as following:
1. APT powder heated to 270℃~350℃ for 30-60 minutes to dissociate, thus to generate ammonium metatungstate;
2. Add ammonium metatungstate powder into deionized water to leaching with stirring to get an emulsion;
3. Carry out filtration to remove insoluble, and the filtrate was placed in a water bath of 60~90℃ aging for 4~24 hours;
4. Filtered again, and exchanged by Cation Resin, then we get metatungstate solution.

As we can see from the above, the method APT used as raw material to prepare metatungstate solution has the advantages like: simplify process, easy to control, and low cost; In addition, since the reaction process doesn’t introduce any impurity element, so the purity and quality of metatungstate can be ensured; finally, the production process does not use ether and other volatile organic compounds, with minimal impact on the environment, so it is suitable for industrial mass production.

Tungsten trioxide prepared by nanometer tungsten trioxide by the hydrothermal method and calcination treatment, which is characterized by higher non-symmetry axis and the second symmetry axis, the symmetry plane is more complicated. Monoclinic tungsten trioxide has a strong heterogeneity, which has three principal refractive indexes.

Taking Na₂WO₄·2H₂O as raw materials, DL- malice acid as supplement aid, in this context, which can be synthesized in a three-dimensional spherical shape containing precursor (WO_3·xH₂O). It shows that the addition of malice acid dose of WO_3·xH₂O morphology and crystalline phase having a significant impact. Thus gas test shows that the optimum operating temperature of three samples reaches to 250 ℃, and square-shaped monoclinic tungsten trioxide shows the highest sensitivity, which mainly due to its unique and innovative three-dimensional porous structure. At 300 ℃, the optimum operating temperature is the lowest detectable concentration of material, which can reach 0.1ppm, material optimum calcination temperature is determined at500 ℃,the sensitivity of 5ppm acetone sample gas reaches to 7.9; in the relative humidity conditions , the sensitivity of 5ppm acetone resistance remains 5.72.

In tests of different gases (such as acetone, methanol, ethanol, ammonia, etc.) in the gas sensing of different working conditions, monoclinic tungsten trioxide gas shows high selectivity and sensitivity. Taking Na₂WO₄·2H₂O as raw materials, which are used by Na₂C₂O₄, Na₂SO₄ and H₂C₂O₄ supplement. The hydrothermal conditions keep 24 hours at 180 ℃. Experimental results show that the solution plays the role in Na⁺、SO₄^-、C₂O₂^-、HC₂O₄^-  ions and H₂C₂O₄ nano WO₃ crystal nucleation and growth process. The results show that three different adjuvant does not effect on crystal of product system. Subsequent tests show Na₂WO₄ assisting synthesis of WO₃ nimrods at 320 ℃ for certain have concentrations to gas sensing, which mainly due to its high degree of dispersion and crystalline.

Preparation Process:
Preparing various samples at different sintering temperatures after the samples were prepared, than measuring different sets of samples according to voltammeters, impedance spectroscopy and dielectric spectroscopy curves. We can obtain micron tungsten trioxide nonlinear coefficient polyethylene composite samples by calculating the nonlinear coefficients of main sample data. In the composite sample, the tungsten trioxide particles in the sample content has polyethylene nonlinear coefficients, and the nonlinear coefficient of the sintered samples, sintering the other samples at 250 ℃, up to 98%. When the organic matter content of polyethylene is 80%, the sample becomes an insulator; the prepared tungsten trioxide polyethylene material is more stable.

Sample Analysis
The experimental methods commonly is based on varistor methods, and calculating barrier trends, comparing barrier with nonlinear coefficient, typical sample is made by six-phase morphology in the structural analysis. Comparing samples with nonlinear in the function of the body as well as micro particles and nanoparticles composite sample, which shows the trends of barrier are consistent with nonlinear coefficients.

Test results of morphology and electrical properties show that polyethylene resistance and nonlinear crystal polyethylene material are applied in the electric field of tungsten trioxide samples, which resulting shift toward low-resistance crystalline phase, and it has a close relationship. The results of nonlinear of typical sample with impedance spectroscopy show the bias under the grain boundary resistance are not changed significantly. Resistance is low because their low resistances phase structures that are mainly monoclinic.