While for tungsten copper (W-Cu) two phases heat sink material, it has lower coefficient of thermal expansion, which thermal expansion behavior is much more complex than a single-phase material. The experiment shows that t lower temperatures, tungsten-copper composite material showed a negative thermal expansion, but only when the temperature exceeds a certain value showed positive expansion. Tungsten copper sample coefficient of thermal expansion of injection molding and compression molding process under more stable than copper infiltration sample, the magnitude of change is smaller.

This is due to the phase change, as well as the internal organization of the reasons magnetic stretch, thermal expansion of the material will show some special law. By increasing the degree of constraint W phase at elevated temperatures in the expansion phase of Cu, thereby reducing the thermal expansion coefficient of tungsten copper composite material. In addition, since the difference of the coefficient of thermal expansion of the materials, tungsten copper composite material will produce complex stress inside, whose distribution will restrain the thermal expansion behavior.

As for the electrical conductivity, it was detected by eddy current method. When an alternating current is cut coil (also called probes) near the surface of a conductive material, since the coil alternating magnetic field, it has an effect on the material surface and near surface induced swirling current, which called the vortex. Materials and eddy currents generate their own magnetic field coil reacts, which is related to the size of the surface conductivity near the surface. Non-ferromagnetic conductive material can be directly detected by eddy current sensor. After testing found that the sample injection molded tungsten copper has the highest conductivity, reaches 37.43%IACS, which is higher than molding sample (29.85%IACS) and infiltrated sample (33.18%IACS).

Except test of hardness, density and micro-structure, for tungsten copper composite materials, which is widely used in EDM electrode, high-voltage discharge tube and heat sink, test of thermal properties (includes thermal conductivity and the coefficient of thermal expansion) and electrical conductivity are also essential. There is the test result of thermal and electrical conductivity by three different kinds of process:

From the graph above, we can clearly see that among the three kinds of process, tungsten copper composite powder by PIM (Powder Injection Molding) has the highest thermal conductivity, reaches 217W/(m·k), compared with molding process and Cu infiltration. Combined with micro-structure of them, the researchers conclude some main reasons:

1. Although tungsten copper composite material has uniform distribution of W and Cu phase in the molding process, it still remains some porosity, which has a great impact on thermal conductivity of tungsten copper composite material;

2. Under the optimum Cu infiltration, there is no pore inside the sample, but Cu phase can not connect and form net structure. W and Cu phases distribute unevenly, in the process of heat conduction, part of thermal conductivity convey by W phase so that it is a critical factor of the lower thermal conductivity;

3. Relatively, injection molding process can effectively avoid the two defects, not only improve the density of tungsten copper products, but also W and Cu two-phase evenly distributed, thus it has a higher thermal conductivity.

Theoretically, thermal expansion of solid materials is due to the thermal vibrations of atoms as a center from its equilibrium position, which called crystal vibration non-harmonic effect. When the sintering temperature is increasing, atomic vibrations also stronger, the greater the energy of atomic vibrations, so that the microscopic atomic lattice parameters increase, the macro is manifested in the thermal expansion of solid materials. For single-phase material, the thermal expansion will increase as the temperature rises.

Multiple composite rare earth tungsten electrodes have good weldability, and non-radioactive, so it is the best alternative for thorium tungsten electrode. However, this electrode has low finished products rate and high production cost, thus greatly limiting its application range. Doping rare earth can help to reduce the work function of the electrode, improving the welding performance. However, the rare earth element will impede tungsten grain growth. And during processing, the rare earth will increase the recovery and recrystallization temperature of tungsten electrode, so that the deformation resistance of electrode is increased, making the sintering process not easy to control the, and finished products having low rate.

To improve multiple composite rare earth tungsten electrodes production technology will help improve the finished products rate and reduce production cost. To produce multiple composite rare earth tungsten electrodes using APT and rare earth nitrate as raw materials, doped with La, Y and Ce and other rare earth elements, can achieve uniform doping. Using two-stage reduction can produce good performance rare earth tungsten metal powder. During the restore process, you can use a large temperature gradient reduction method to control particle size. At sintering process, before the sintering neck grows up to closure making rare earth uniformly distributed in the tungsten bar, which can be obtained good performance sintered billet. In the process, appropriate increase processing temperature in the initial stage of the process, using multi-pass deformation processing technology, making the tungsten bar uniform deformation and improve processing rate and yield.

By strictly controlling multiple composite rare earth tungsten electrode manufacturing process technology can not only improve productivity, but also can obtain excellent performance tungsten electrode. In addition, it is also beneficial to composite rare earth tungsten electrode industrial production realization to reduce production costs and expand its application range.

Among tungsten electrodes, thoriated tungsten electrode, having good weldability, is the most widely used tungsten electrodes. But because thorium has radioactive contamination so in the production and using process will endanger human health and pollute the environment. Through continuous research and development, the researchers developed multiple composite rare earth tungsten electrodes, and it is considered the best material to replace thoriated tungsten electrodes.

Rare earth doped as the active material doped to tungsten matrix can effectively reduce the work function of the tungsten electrode material to improve the welding performance. In multiple composite rare earth tungsten electrodes, the doped rare earth elements include La, Y and Ce. These three different rare earth elements at different temperatures have diffusion rates. Among these elements, Ce first diffused to the surface, reducing the work function of the surface, so click arc easy. When arc burning stable, La has largest surface coverage, and plays an important role at this process. While working in high current, Y timely migration to the surface, so the electrode can stably operate at high current conditions. Synergy of these three rare earth elements, so that the performance of multiple composite rare earth electrodes better than thoriated tungsten electrode.

On the other hand, the rare earth is conducive to refine reduction powder, and easy to promote the β-W formation. β-W makes the sintering process not easy to control. In the tungsten electrode sintering process, not only the rare earth will impede tungsten grain growth, but it will improve the recovery and recrystallization temperature of tungsten electrode such that the deformation resistance increases of electrode will increase, resulting in sintering process not easy to control. This is also one of reasons that multiple composite rare earth tungsten electrode has low finished produced rate and high production costs.

In the future, studies should toward production technology development direction to research. To improve the multiple composite rare earth tungsten electrodes finished produced rate and to reduce production costs make it more widely used.

Near-infrared(NIR, IR-A DIN), is defined by the water absorption, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO2 glass (silica) medium. Image intensifiers are sensitive to this area of the spectrum. Examples include night vision devices such as night vision goggles.

Recently, shielding not only ultraviolet rays but also infrared rays has been attracted attentions in terms of saving resource and energy and creating comfortable life space. Cs doped tungsten bronze (CsxWO3) which has suitable amounts of free electrons in crystal is one of the candidate materials of inorganic infrared rays shielding materials, since it can shield ultraviolet and infrared rays by interband transition and plasma oscillation of free electrons, respectively. Nanoparticles of CsxWO3 particles were synthesized by solvothermal reaction of WCl6 and CsOH・H2O in ethanol and ethanol aqueous solutions at 200 ℃ for 12-47 h. After that, CsxWO3 particles were heated in 500 ml/min NH3 gas flow at 400 ℃ for 1 h. Sheet-like and rod-like nanopartricles of CsxWO3 were synthesized in ethanol and 42.9 vol% ethanol aqueous solution at 200 ℃, respectively. The samples formed in 42.9 vol% ehanol aqueous showed higer crystallinity but lower Cs/W atomic ratio than those in ethanol. Sheet-like particles showed higher visible light transparency, while rod-like particles showed more excellent infrared shielding properties, indicating that rod-like particles were more suitable for shielding infrared rays. Moreover, the visible light transparency and infrared shielding properties could be improved by improving the dispersion state of the particles by agitating with ZrO2 beads. The electric conductivity of the pressed pellet of rod-like particles could be increased by heating in NH3 gas atmosphere at 400 ℃.