A new material that emits short-wavelength thermal radiation when heated could be used in systems that convert waste heat into electrical energy. Created by an international team co-led by researchers at Purdue University, the University of Alberta and Hamburg University of Technology, the material comprises alternating layers of 20 nm of tungsten oxide and 100 nm of hafnium oxide.

Tungsten oxide is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkalis to produce WO3. It is insoluble in H2O and acids, but soluble in hot alkalis. It is n type semiconductor material, the special physical and chemical property make it used in various filed and become the important functional material in modern scientific research.

The structure was chosen so that the emission of long-wavelength infrared photons from the material is suppressed while the emission of shorter wavelength photons is enhanced. These shorter wavelength photons have enough energy to drive a photovoltaic cell, while the longer wavelength photons do not. The research team tested the material by heating it to 1000˚C and using it to power a photovoltaic cell. They found that the new material produced 90% more electrical energy than a conventional black-body infrared emitter. It could someday be used to generate electricity from the waste heat produced by industrial processes and even automobile engines.

In all kinds of sintering technology, microwave heating with heating speed, the overall heating, selective heating and non-thermal effects of traditional heat conduction heating methods do not have the characteristics. WC-Co powder compacts have good coupling absorption to microwave, and the penetration depth of microwaves in the compacts of the mixture is very large. Therefore, the preparation of high-performance tungsten carbide by microwave sintering technology has the traditional heat conduction heating preparation method Unmatched advantages. These advantages are shown in the following aspects: 1, micro-high-performance wave heating fast, holistic not only can significantly shorten the preparation cycle and reduce the sintering temperature, simplifying the process, and can prepare a uniform microstructure, grain Small material. 2, because of the high energy efficiency of microwave and its environment-friendly features, it can at lower cost and less environmental pollution to create greater economic value. 3, the characteristics of microwave heating is very conducive to the development of nano-fine grain hard alloy, gradient cemented carbide, carbide coating and other new high-performance carbide. These advantages make the development of tungsten carbide and microwave sintering technology combined into an inevitable trend.

The WC-Co high performance tungsten carbide was successfully prepared by microwave sintering at the University of Pennsylvania. Compared with the traditional sintering method, microwave sintering can obtain the same degree of shrinkage at lower sintering temperature and shorter holding time. The sintered samples have the same degree of shrinkage in the three dimensional direction, while the traditional sintering method in the vertical direction And the microwave sintered samples have more fine WC grains and more uniform Co phase distribution than the traditional sintered samples. The hardness is higher and the chemical corrosion performance is better. In addition, it was found that there were almost no W atoms in the bonding phase of microwave sintered samples, which was very different from the case of the traditional sintered samples with about 20 wt% W atoms.

Dortmund University of Germany, using W, C and Co mixed powder crushed to microwave sintering, compared to the traditional process of WC and Co mixture briquette sintering, this process not only the synthesis of WC powder and WC-Co green compact Sintering two steps together, effectively simplifying the process, shortening the production cycle of cemented carbide, but also make full use of the carbon atoms in the WC between the release of heat, reducing the energy consumption of sintering. The high-performance tungsten carbide materials obtained by this process are denser, the organization is more compact, and the mechanical properties are improved.


 

The results show that the pure magnetic field heating can not complete the post-sintering of the alloy, because at 1100 ℃ above, the Co in the alloy will change from ferromagnetism to paramagnetism, so that the magnetic field can absorb the microwave magnetic field collapse, so that the magnetic field loss to temperature The sintering temperature of the alloy sample can not be increased continuously. However, WC-Co cemented carbide induction of microwave electromagnetic field mainly in the form of dielectric loss, therefore, the use of pure electric field and electromagnetic hybrid field heating can complete the whole densification of the alloy, and the prepared alloy has a good mechanics The WC grains in the microstructure are uniform, and the Co phase is evenly distributed, forming a good lattice structure.

In addition, for the decarburization in the sintering process, studies have shown that by adding carbon black in the mixture and adding carbon black in the filler can inhibit this decarbonization phenomenon, thereby enhancing the performance of microwave sintered cemented carbide. The results show that when the amount of carbon black is 0.4% (mass fraction), the flexural strength of the alloy is up to 2250 MPa. When the carbon black is added into the filler, the bending strength can be increased to 3172 MPa.

Invention and application of modern tungsten carbide materials is the change of  history material, which known as the "industrial teeth", fully reflects the ability of human transformation of nature with tools to enhance the material and improve.

Tungsten carbide tool as a cutting tool, widely used in all aspects of modern manufacturing, with its excellent performance is to guide the high-quality metal cutting market development. China's consumption of cutting tools, about 69% of high-speed steel cutting tools, carbide cutting tools accounted for only about 28% (the rest of the tool system, diamond and cubic boron nitride cutting tools, etc.). Even with the import of tools, cutting tool consumption in China, about 53% for high-speed steel cutting tools, and carbide cutting tools for 45%, while the diamond and cubic boron nitride tool only 2%. The proportion of the world's cutting tool consumption is probably: high-speed steel cutting tools accounted for 35%, 10% of diamond and cubic boron nitride cutting tools, while the welding carbide cutting tools, solid carbide and carbide can be indexed the rest section.


 

This shows that the cutting tool market in China's tool consumption structure can not reach the world average. We can see China as the world's largest metal cutting market its overall level is not enough, high-end carbide cutting tools is not yet developed. This is for the production of carbide is a big country vigilance!

The overall low level of processing and our rising labor costs and the appreciation of the renminbi have hidden the risks of making our Chinese manufacturing less competitive. Economists and entrepreneurs in some countries, including the United States, are considering Will have moved some of the manufacturing enterprises in Asia moved back to their home. To enable us to continue to attract global enterprises to land manufacturing in China, we need to improve our competitiveness, including, of course, improve the manufacturing level. But also in line with the CPC Central Committee on our "second Five-Year" period to change the mode of development requirements, that is, from the number of low-value, high consumption of manufacturing, to the heavy level, high value-added, green manufacturing.

Direction of development for cutting tool market must be high value-added, high-performance carbide cutting tools and other high-end superhard cutting tools become mainstream, high-speed steel and other traditional materials, tool overcapacity, performance and other factors is restricting China's high-end carbide Tool development is an important bottleneck.

Under the effect of National Day’s holiday, although some enterprises are still waiting to stimulate tungsten market, raw material market is in nervous status, manufacturers only purchase raw material without selling. Dealing amount is decreasing.