Hydrothermal is the study of geologist simulating the natural mineralization in 19th century. Hydrothermal method is a category of liquid chemical method. Hydrothermal method is a method in a sealed pressure vessel, chemical reaction at high temperature and pressure conditions. Hydrothermal reaction depends on the type of reaction that can be divided into hydrothermal oxidation, hydrothermal reduction, hydrothermal precipitation, hydrothermal synthesis, water, thermal hydrolysis, hydrothermal crystallization. The material is dissolved in an aqueous nutrient medium in the heat, in the form of ions, molecules become into the solution.

Single tungsten trioxide material properties in the structure are flaws, they can not meet all the needs of practical application, in order to improve the performance of tungsten trioxide to meet the needs of more areas, we use the following method to prepare tungsten trioxide, which doping molybdenum trioxide, complexes were characterized on the structure and composition to improve the value of the actual use of composite tungsten trioxide.

Incorporating trioxide molar percentage of 0%, 1%, 5%, 8%, 10%, 12% ratio, a certain quality and 1.000g of sodium molybdate was dubbed to sodium tungstate solution, mixing them well. The above solution was dropped to 2ml hydrochloric acid, stirring 0.5h, transferring to a stainless steel autoclave, containing it at 100 ℃ about 24h. Drying it in forced air oven 6-7h, then placing it in a muffle furnace , burning it 400 ℃ 3h, tungsten trioxide is complex at last.

Continued from the preceding page, the advantages of tungsten carbide ball valve are given as follow:

5. It has bidirectional sealing property, which make the process more stable;

6. When fully open or fully closed, the ball and seat sealing surface and the medium is completely isolated state, which makes high-speed flow of the media is not prolonged contact with the sealing surface of the seat caused by erosion;

7. It is light in weight, has compact structure and suitable for high-temperature and low-temperature media system (In a range of -204℃-815℃);

8. Ball valve has symmetrical structure so that it can endure the pressure from pipeline perfectly;

9. Overall fully welded ball valve body can also be directly buried in the ground, so that the valve member from erosion, oil and gas pipelines in the most ideal type of valves, maximum useful life of 30 years.

In addition, to ensure the stability of tungsten carbide valve ball, the choice of the material of tungsten carbide ball seat is also can not be ignored. It requires that smaller coefficient of friction, stable physicochemical properties, broader range of temperature, excellent sealing property and so on. Common materials include copolymers of tetrafluoroethylene (PTFE), nylon and some synthetic rubber. However, these materials have also some defects, such as tetrafluoroethylene has a higher coefficient of thermal expansion, poor thermal conductivity, for lack of sensitivity to temperature, when the sealing material hardens, sealing it also decreases, especially when the pressure difference is low. Some synthetic rubber is limited by media types or temperature range, if there is no lubricant, it will be stuck.

Tungsten carbide valve ball uses ball as device for start and stop, which has many functions, such as cutting, distributing and changing the flow direction of the media, specially designed can regulate the flow. From the design of the ball valve, compared with conventional valve, it has many advantages, such as simple structure, excellent sealing property, light in weight, low consumption, small setting size, small volume in a range of certain nominal diameter, small driving moment, easily to start or stop quickly, which becomes the rapidest developing valve in recent years gradually. Tungsten carbide ball combines the advantages of tungsten carbide (high hardness, high strength, high melting point, excellent chemical stability and wear and corrosion resistance) with ball valve can be suitable to the strict conditions of many industries today.

The advantages of tungsten carbide ball valve are given as follow:

1. It has the lowest flow resistance theoretically (Flow resistance refers to the steady state airflow, sound-absorbing material is applied to the sample and the pressure difference across the air flow through the sample line speed ratio.);

2. It has excellent chemical stability and wear or corrosion resistance, which can be contact with most of liquid and some media with corrosive property;

3. It has excellent sealing property at high temperature and high pressure (Nominal pressure from vacuum to 42MPa);

4. Tungsten carbide valve ball using ball as the device for start and stop so that it affected by friction slightly and can be starting or stopping quickly (in a range of 0.05-0.1s), and has small operating impact. In addition, spherical device can endure the higher pressure differential when it close and can achieve automatic position;

When the doping concentration is 0.2mol% and the sintering temperature is about 1100 ℃, the density of the WO₃ ceramics doped Bi₂O₃ can reach 91%. When the doping concentration is 0.2mol% , WO₃ ceramics densification will decline; the sintering temperature is lower than 1100 ℃, the density increases gradually, but when the sintering temperature is 1100 or higher than 1100 ℃, the density of the ceramic will decline ; the best sintering time is 2h, extend the time will make the ceramics sintered density decreases. After analysis, the major causes for this phenomenon are: WO₃ melting point is 1273 ℃, Bi₂O₃ melting point is 860 ℃, the formation of the sublimation are the two substances .

Comparing with non-doped WO₃ ceramics, WO₃ ceramics doped Bi₂O₃ varistor voltage declines rapidly, this shows the rapid growth of the ceramic grains causing breakdown voltage drop. When the sintering temperature of WO₃ doped Bi₂O₃ ceramics is 900 ℃, WO₃ ceramics do not have pressure-sensitive properties, when the temperature is 900 ℃ ~ 1100 ℃, the pressure-sensitive is maximum coefficient, when the sintering temperature is 1100 ℃, the pressure-sensitive decreases with the temperature rises, it disappears after sintering temperature is higher than 1100 ℃. When Bi₂O₃ doping concentration is 0.5mol%, the sintering time is 2h.

Doping Bi₂O₃ having a significant effect on the microstructure of WO₃ ceramics; doping can play a role to help promote sintering ceramics; doping can improve the characteristics of the ceramic varistor.

Bismuth trioxide (Bi₂O₃) is known as yellow powder, it dissolves in water, and it does not dissolve in acid generating bismuth (III) salt. Its melting point is 824 ℃, the boiling point is 1890 ℃. Bismuth trioxide may be obtained from natural bismuth Hua (a mineral), its main source is copper, and bismuth powder can be obtained bismuth trioxide in the air combustion. Bismuth oxide is mainly used in the chemical industry (such as chemical reagents, bismuth salt manufacturing, etc.), glass industry (mainly used for coloring), and the electronics industry (electronic ceramics, etc.). Among them, the electronics industry is the most widely used bismuth oxide industry; it is mainly used in varistors, thermistors, and CRT oxide surge arresters and other fields. In addition, Bi₂O₃ has high refractive index and dielectric constant, significant fluorescence characteristics and inert to water. Therefore, Bi₂O₃ is potential decomposition and degradation of water pollutants visible catalyst.

Bi₂O₃ doping WO₃ceramics, when the doping has smaller number, the presence of single phase is WO₃; when the doping concentration is greater than 0.2mol%, and it will begin to appear as Bi₂WO₆ phase. Bi₂WO₆ phase becomes bigger with the sintering temperature increasing. WO₃ phase will disappear in the solid phase reaction sintering process. Bi₂O₃ can promote the rapid growth of WO₃ ceramic grain, compact structure, porosity reduction, and a high concentration of Bi₂O₃ doped in the grain boundary formation of the second phase Bi₂WO₆ , which increasing the sintering temperature and time, which can promote the growth of WO₃ ceramic grains form more Bi₂WO₆ phase. According to the analysis results, we can get Bi₂O₃ doping can be formed during the sintering process in the reaction; the transfer material ultimately provides the energy for the growth of the ceramic grains.

Tungsten disulfide can take place of molybdenum disulfide in almost every field with even more wider application. Molybdenum and tungsten is in the same phrator of chemical element, chemical property of tungsten is more stable and higher molecular weight. Molybdenum is widely used due to its low price and high efficiency of marketing supplement. In fact, tungsten disulfide is not newly developed product, its application history is all the way with molybdenum disulfide. Due to its high price, it is firstly used in NASA aerospace, military, automobile industry and so on. A few years ago, price of tungsten disulfide is ten times higher than molybdenum disulfide. Nowadays price of molybdenum disulfide is increasing rapidly. And the price of these two materials is the same. So it would be more valuable if tungsten disulfide is used.

Differences between tungsten disulfide and molybdenum disulfide:

Note：PSI=6.89×103Pa

From the thermo dynamics of view, Equilibrated at the point of contact of the solid and liquid phases must meet γ_S = γ_SL + γ_Lcosθ. θ is the wetting angle or contact angle, when completely wet, θ = 0 °, then γ_S = γ_SL + γ_L; partial wetting, 0 °< θ < 90 °; completely non-wetting, θ> 90 °, this time γ_S ≥ γ_SL + γ_L. Liquid phase sintering occurs must satisfy θ < 90 °, only with complete wetting liquid or partially wet to penetrate the pores and grain gap, forming a network-like structure of the coating. If θ > 90 °, the liquid produced during sintering will quickly bleed sintered body, densification can not be successfully completed, so that the group of tungsten copper alloy phase changes occurs.

View from the classical liquid-phase humidification theory, Only when we can see the surface energy of the solid and liquid phases is greater than the sum of the solid - liquid interfacial energy, that WSL = γS + γL - γSL in WSL> 0, when the liquid in order to effectively wet the solid surface. Solid phase has certain solubility in the liquid phase will help to improve wettability, promoting an increase in the number of liquid can be carried out by means of liquid mass transfer, and dissolved in a liquid phase in the process of dissolving precipitated solute portion may be carried out to fill the solid phase defects and particle clearance particle surface, thereby further improving the solid phase particle distribution uniformity. The quantity of liquid phase required to meet the solid particles fill the gaps, reduce the porosity of the material, increasing the density of the material, generally 20% -50% of the volume of liquid phase sintering of the best accounts, exceed prone to sintering deformation is insufficient so that the liquid can not be filled solid tungsten skeleton pore and solid particles come into contact with each other and the grains will grow up.

Tungsten copper electrode has both advantages of tungsten (W) and copper (Cu), such as high melting point, high density and high hardness of tungsten, excellent thermal and electrical conductivity of copper. Due to the big difference between tungsten and copper (the melting point of tungsten is 3387℃, the melting point of copper only 1083℃), it makes tungsten copper sintering become a typical liquid-phase sintering.

During the liquid-phase sintering process, Solid solubility in the liquid phase, the solid and liquid phases of liquid interfacial energy and the ability to penetrate the solid phase along the grain boundaries greatly affected the speed of change in the sintering and microstructure. In addition, the parameters, such as the granularity of particle distribution, powder purity, sintering temperature, sintering time, sintering atmosphere and the compact density are all the significant influencing factors of tungsten copper electrode. Liquid-phase sintering must meet wettability, solubility, phase number three conditions, the wettability of the solid, liquid surface tension (specific surface energy) interfacial tension γ_S, γ_L and two-phase (interfacial energy) γ are decided.