Recently, zirconium tungstate is the best isotropic negative thermal expansion compound, and also the typical compound which have attracted great interest from the crystal structure to heat-shrinkable properties in new negative thermal expansion compound. Studies have pointed out that dope the other elements into basal body of can change its properties, and it will have a very broad application prospect. A method that use ammonium paratungstate as raw material to prepare cerium-doped zirconium tungstate negative thermal expansion ceramic powder, steps as follows:

1. Take materials: weight eight water zirconium oxychloride, ammonium paratungstate and cerium ammonium nitrate according to a certain stoichiometry, mix the zirconium oxychloride and cerium ammonium nitrate and dissolved in deionized water; at the same time, ammonium paratungstate also dissolved in deionized water, and make sure the concentration of W equals to the summation of concentration of Ce and Zr;
2. Mix the deionized water and concentrated hydrochloric acid at a certain volume ratio to get the hydrochloric acid solution at a concentration of 6-10mol/L;
3. Dropping the mixed solution of zirconium oxychloride and cerium ammonium nitrate, ammonium paratungstate into deionized water by the double-dropping-method with stirring, and control the temperature between 60-80℃, continually stirring for 4-8 hours;
4. Raising the temperature to 80-90°C, dropping the hydrochloric acid solution into the mixture under constant stirring conditions, until the H + concentration in the final solution is 1.5-3mol/L, and then stirring was continued for 16 to 24 hours ;
5. Translating the mixture obtained in step 3 into a teflon-lined autoclave, and heated for 12-72 hours at temperature of 165-220℃, then suction, dried at 60-85℃, so the precursor generated;
6. Placed the precursor in a muffle furnace and heated to 600-700℃, and incubated for 6-12 hours to give a final product--zirconium tungstate cerium-doped ceramic powder.

Trace element and other additives are also the common method for improving wear resistance of tungsten carbide buttons. People add some elements with specific additives and excellent performance to change the composition and properties of carbide itself to adapt to different requirements of works More common additives such as grain growth inhibitor (refined grains, inhibit grain growth), corrosion of some components (to improve corrosion resistance), some of the rare earth element or refractory metals (carbide corresponding optimization performance). The principles of influencing factors of additives on wear resistance of tungsten carbide buttons are different, some uniforms the structure by grain refined, some improves the binding strength of interface by improving the wettability of cobalt (Co) on tungsten carbide (WC).

Finally, we introduce the effects of chemical treatment on wear resistance of tungsten carbide button. Theoretically, heat treatment of tooth carbide ball can change the organizational structure of the matrix corresponding compound distribution and coordination, so as to give full play to the composite materials’ advantage. Therefore, the relevant domestic and foreign scholars and researchers have carried out extensive research on the mechanism of heat treatment on tungsten carbide button, and draw different conclusions.

At present, there are two explanations of tungsten carbide buttons heat treatment mechanism: one is thought tungsten (W) supplementary heat treatment was dissolved in Co binder phase, the contiguity of WC grain size decreased, while the WC and Co contiguity rise, thus wear resistance of tungsten carbide buttons is improved; another is thought heat treatment changes the stress state phase structure and internal Cu alloy phase, which can keep the face-centered cubic structure (fcc) a-Co binder phase at high temperatures to a large extent, reduce HCP (hexagonal closepacked structure) e-Co. The former is a plastic material, and the latter is a brittle material, thus tungsten carbide button abrasion resistance corresponding increases. In addition, there are carburizing, boron, lanthanum and other chemical heat treatment and laser treatment, ion injection, etc.

Take tungsten carbide (WC-Co) as a example, it has high hardness, high density, high strength and excellent chemical stability, but its wear resistance is poor. Related researchers have conducted extensive research, which includes three influencing factors on the wear resistance of tungsten carbide buttons, such as the grain size of solid phase (WC), trace element or additives and chemical heat treatment, etc.

According to the principle that material micro-structure determines the surface property, the researcher propose the granularity of solid phase (WC) in tungsten carbide has a great impact on the wear resistance and they do o lot of extensive researches. The experimental data shows that when the cemented carbide (WC-Co) in the hard phase (WC) grain size is reduced to sub-micron or less, to the material hardness, strength, toughness and wear resistance have been improved to some extent. The relationship of wear rate and WC grain size given as follow:

From the figure we can clearly see in the lower hardness, the hard phase tungsten carbide (WC) hardness plays a major role, while at higher hardness values, the toughness of the material take effects. With the increasing size of the WC particles, accelerated wear, wear rate did rise, but can not be considered biased nano-scale tungsten carbide (WC) particles and wear properties will certainly be advantageous for the wear mechanism and conditions are mutually reinforcing. Generally, the finer the crystal grain size that is smaller defect, the binder phase of cobalt (Co) smaller average freedom, corresponding high hardness and bending strength. With increasing hardness of tungsten carbide, WC grain size and relative sizes of the abrasive is close, no significant correlation between the wear volume losses with the hardness of the alloy.

Cesium is a golden yellow metal, low melting point active metal, easily oxidized in air and can react violently with water to produce hydrogen and even explode. There is no elemental form of cesium in nature, cesium minimal distribution in the ocean in the form of cesium salt. Cesium tungsten bronze is widely used because of its low resistance, excellent visible light transmittance, near-infrared shielding properties. Also it is widely used in preparing conductive thin film, since being the glass transparent insulation coating as insulating agent, it has excellent properties like low resistance, excellent visible light transmittance and near-infrared shielding performance. The article provides a method that using ammonium paratungstate and cesium nitrate as raw materials to produce Cesium-tungsten oxide ultrafine powder, the specific steps are as follows:



1. Weighing the cesium nitrate, ammonium paratungstate by the molar ratio of Cs/W being 1: (1.5 to 2.8), and adding chelating agent and alcohol reagent, reacting at 170°C for 3 hours;
2. Loading the mixture obtained in step 1 in a pressure vessel shells, raising the temperature to 260~270°C for reacting for 5 to 8 hours;
3. The reaction obtained in step 2 is carried out alcohol washing, centrifugation; then dried in the conditions of 80°C in vacuum, thus to generate complete crystalline cesium-tungsten powder.

Using this method to prepare cesium-tungsten oxide ultrafine powder has many advantages, such as: saving the materials, thus to save costs; shorten the preparation period, make it advantaged for industrial production; products prepared are ultrafine powders with a very low resistance.

Zirconium tungstate belongs to ceramic materials, its widest temperature range of negative effects of expansion, high negative thermal expansion and maintain isotropic, making it one of the hot negative thermal expansion material of a Subsidiary . Zero expansion or low expansion material can significantly improve the thermal stability and geometric impact resistance. In this article, nano-scale zirconium tungstate with uniform particle size and negative good expansion properties is prepared from ammonium paratungstate and zirconium oxychloride by hydrothermal synthesis method.



Steps as follows:
1. Take an appropriate amount of ammonium paratungstate and thermal decompensate under a certain conditions to obtain ammonium metatungstate;
2. Respectively take and weight the zirconium oxychloride and ammonium metatungstate according to a certain proportion, and then formulate into zirconium oxychloride and ammonium metatungstate solution;
3. Stirring the AMT solution, and adding zirconium oxychloride solution at the same time, continually stirring and preheating the solution to 60~70 ° C for I~3 hours; and then adding hydrochloric acid solution with stirring and heating to 80~100°C for 2.5~3.5 hours, then zirconium tungstate precursor suspension got;
4. Zirconium tungstate precursor suspension is carried out hydrothermal reaction at 170~190°C for 4~6 hours, and then cooled down, the precipitate was collected and washed to remove Cl^-; after dried, the precipitate is calcined at a 800~KKKTC for 1~5 hours to obtain the product we need.

Using fused salt electrolysis method for rare earth metals production need to use refractory and corrosion metal as cathode and cathode material usually chooses molybdenum electrode or tungsten electrode. Fused salt electrolysis method for rare earth metals production usually requires high temperature and the cathode should has corrosion resistance property. Tungsten electrode and molybdenum electrode has good high temperature performance and corrosion resistance property, therefore become the preferred cathode material. However, comparing molybdenum electrode with tungsten electrode, molybdenum electrode corrosion resistance is poorer than tungsten electrode, and consumption is faster. On the other hand, some rare earth has a strict requirement on impurity content and molybdenum is one of impurity element of rare earth. So many manufacturers will use tungsten electrode as cathode using in fused salt electrolysis for rare earth production instead of using molybdenum electrode.

Tungsten electrode production usually uses powder metallurgy method and the key process of this method is sintering. When tungsten bar diameter is less than 20mm, they usually directly use vertical furnace for tungsten bar sintering. When tungsten bar diameter is larger than 20mm need to use intermediate frequency sintering furnace for sintering and after sintering need to process forge. However, both methods require higher sintering equipment and there will have welding difficult as well. Thus, most manufacturers choose activated sintering method for tungsten electrode sintering. This method is using physical or chemical means to reduce sintering temperature and increase sintering speed, thereby increasing the density and associated performance of electrode.

Using activated sintering method to produce tungsten electrode so it can use in fused salt electrolysis for rare earth metal production and the detail production processes are as follow:
1. Mixing powder: making a small amount of the activator nickel salt dissolves in ethanol, and then pours this solution into tungsten powder and mixing well.
2. Pressing: mixed tungsten powder to dry under the protection of hydrogen, nickel will coat on tungsten particle surface, then using cold isostatic pressing presses tungsten powder into a billet.
3. Sintering: after pressing to sinter pressed tungsten powder into a billet can obtain tungsten electrode.

The experiment found that using nickel-coated tungsten powder as raw material for tungsten electrode production which produces by activated sintering method has better property than traditional tungsten and molybdenum electrodes.

Electric Conductivity Test: It is a relative simple process that put tungsten copper (W-Cu) sintered body with high surface roughness grinded by metallographic abrasive paper on the equipment, and generally use alternating current bridge method, first determine the resistivity of the formula, and then through the relationship between conductivity and resistivity calculate the conductivity, but also during the relative conductivity values were calculated (based on the relative value of conductivity international standard soft copper is annealed conductivity of copper is 100% 1.7241μΩ • cm conductivity).

Shrinkage Test: It is essential that Measure the diameter and thickness of the blank with a caliper, sintered tungsten copper will be erased and the surface of the sintered powder with a caliper at this time of the diameter and thickness were measured again. According to the formula to calculate the radial shrinkage of the shrinkage of the sintered body (S_D = (D-D_S) / D × 100%, D is the diameter of the green body, D_S is the diameter of a sintered body, S_D is a radial shrinkage of the sintered body).

SEM: (Scanning electron microscope) SEM adapts a focused electron beam on the surface of tungsten copper samples at a predetermined time and space sequence gate intensive scanning secondary electron interaction with the sample signal transmission, the transmission must change after two photoelectric conversion by point presentation on the microscopic screen, whereby the reaction of the sample surface topography secondary electron image. In addition, the sample of SEM can be block or powder, but it should be noticed that vacuum can ensure the stability. For magnetic sample should be demagnetized in advance in case that the electron beam was observed to prevent being affected by magnetic fields.