2019年5月20日星期一

The Metal Zirconium Tungstate Composite Material

Thermal expansion and contraction are common physical phenomena.

However, there are some materials which do not act according to common sense and show the opposite phenomenon of thermal expansion and cold expansion, such materials are known as negative thermal expansion materials, and zirconium tungstate is one of the negative thermal expansion materials.

The results show that the zirconium tungstate ZrW2O8 has a stable negative thermal expansion performance in the range of 0.3 to 1050.0K in the temperature range, negative thermal expansion coefficient alpha can reach -9 * 10-6K-1, and is isotropic. Therefore, zirconium tungstate can be used alone as a heat shrinkable material, and can also be mixed with other materials to form composite material.

Zirconium tungstate metal substrate is using a powder metallurgy method principle, adding zirconium tungstate composite material in the metal. Because of its excellent conductivity and thermal conductivity, the composite of zirconium tungstate and metal can make the composites not only have low thermal expansion characteristics, but also have excellent properties of metals. This kind of metal-based zirconium tungstate composite with low thermal expansion and high thermal conductivity has wide application prospect in microelectronics, the metal material, which is usually compounded with zirconium tungstate, is predominantly aluminum, titanium, and copper, and the object is more aluminum.

metal based zirconium tungstate image

In the field of microelectronics, such as aerospace industry structure components, electronic packaging, measuring instruments, optical devices, sensitive components, satellite antennas and other high-precision devices, it often requires materials with lower thermal expansion coefficients, such as below 15 x 10-6K-1 or even below 10 * 10-6K-1, so that the material can maintain dimensional stability when subjected to temperature changes, and the general negative thermal expansion material "aluminum" is difficult to achieve this requirement. Therefore, some scholars have combined aluminum and zirconium tungstate into aluminium based zirconium tungstate composite, the thermal expansion coefficient was reduced to 8.7 * 10-6K-1, and the bottleneck problem was solved easily.

The traditional preparation methods of metal base tungstic acid composite material are heating sintering and pressing. Aluminum alloy zirconium tungstate composite material was successfully prepared by powder metallurgy method and sintered by pulse current sintering of aluminum and zirconium tungstate. Dai Enbin and other scholars at Central South University successfully prepared ZrW2O8/6013Al composites by pressure melt infiltration method, the results show that the coefficient of thermal expansion of aluminum based zirconium tungstate composite is lower and the performance is more stable than aluminum alloy.

The low heat metal based zirconium tungstate composite can greatly improve the thermal shock resistance of the material, when the material is used in the changing temperature condition, the dimension stability is maintained and the service life of the material is improved, compared with the traditional low expansion alloy, it has the advantages of self-evident. Of course, there has not been a major breakthrough in the preparation of zirconium tungstate. The difficulty of preparation and high cost is the main problem. With the development of China's material industry, it is believed that the cost of zirconium tungstate will be solved soon.

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Ceramic Zirconium Tungstate Composite

Thermal expansion and contraction are common physical phenomena. However, in industrial practice, it is found that zirconium tungstate is a heterogeneous species.

It is shown by the "heat shrinkable cold expansion". This phenomenon is called "negative thermal expansion" of zirconium tungstate. It should not be underestimated in zirconium tungstate. It can be used in industrial production.

The results show that the zirconium tungstate ZrW2O8 has a stable negative thermal expansion performance in the range of 0.3 to 1050.0K in the temperature range, negative thermal expansion coefficient alpha can reach -9 * 10-6K-1, and is isotropic. Therefore, zirconium tungstate can be used alone as a heat shrinkable material, and can also be mixed with other materials to form composite material.

The material obtained by the composite process of ceramic and zirconium tungstate is called zirconium tungstate composite based on ceramic. The ceramic based zirconium tungstate composite is an important structural and functional material. Compared with the metal based zirconium tungstate composite, its thermal expansion coefficient is more compatible with the matrix and easier to combine.

ceramic zirconium tungstate laser device image

Ceramic matrix composites are prepared by mixing ZrW2O8 powders with a certain mass of ZrO2 or other materials, in sealed platinum crucible, calcined for 2 hours at 1180 °C, cooled by liquid nitrogen, and finally obtained low thermal expansion ZrO2 - ZrW2O8 material, some scholars also compare ZrO2 and WO3 at a certain mass ratio, ceramic based zirconium tungstate composite was prepared by high pressure and high temperature ball milling. But in general, the above methods need to be improved, and there is not yet a perfect production plan.

In recent years, the study of ceramic based zirconium tungstate negative thermal expansion materials has become a hot topic in the world. The biggest characteristic of this kind of materials can be precise control of material expansion coefficient, the coefficient of thermal expansion of a material is controlled as a set positive value, negative value, or zero. For example, the ceramic based zirconium tungstate composite material and the regular positive thermal expansion material are made into composite materials in a certain manner and proportion, the utility model can be used for the precise optical focusing and optical path collimation of special glass manufacture, telescope, laser equipment and optical communication system, so that the utility model is not affected by temperature fluctuation, and has the advantages of stable performance and long service life.

At present, there is no better solution to the cost of zirconium tungstate. Therefore, the ceramic based zirconium tungstate composite material is mostly applied in the high-end technology field. But the current research of zirconium tungstate is still in the initial stage, improving costs is only a matter of time. In the near future, products made from ceramic based zirconium tungstate materials may soon permeate all aspects of our lives.

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Polymerized Resin Zirconium Tungstate Composite

Zirconium tungstate is a new kind of negative thermal expansion material, which is different from common physical phenomena of thermal expansion and cold contraction.

In nature, it exhibits the physical phenomenon of "heat expansion and cold expansion", which is quite uncommon and unusual. Zirconium tungstate has attracted much attention in industrial production.

In the field of industry, the traditional negative thermal expansion materials are aluminum, titanium, zirconium, polymer resin and so on. In general, polymerized resins are used mainly in traditional electronic circuits, as well as in instrumentation, packaging materials, and protective coatings. For a long time, the polymerization of resin with its easy to obtain, the advantages of low prices and become the first choice for industrial applications, however, there is a great thermal expansion coefficient in the process of polymerization into resins.

polymerized resin zirconium tungstate circuit board image

In recent years, with the advent of zirconium tungstate material, this kind of new material with low negative thermal expansion has attracted more and more fans, of course, like the dazzling star, the high cost of production makes people yearn for zirconium tungstate. Therefore, the scientists retreated to the second place, and changed the amount of zirconium tungstate into the polymerized resin to form a composite resin of zirconium tungstate composite.

The preparation method of polymer based zirconium tungstate composite material is solid phase method, the surface treated zirconium tungstate powder is dispersed into the matrix of the polymerized resin, and then the polymer based zirconium tungstate composite material is obtained by heating, curing and other processes, for example, some scholars have prepared the zirconium tungstate electronic packaging materials by mixing the surface treated zirconium tungstate powder with E-51 epoxy resin at a certain mass ratio, and finally curing and heating up.

The preparation of polymerized zirconium tungstate composite material not only greatly improves the quality of electronic products, to a certain extent, ease the cost pressures of using zirconium tungstate materials alone, especially in the high-end field of electronic products. Using of polymeric zirconium tungstate composites instead of conventional polymeric resins often means better performance and greater competitiveness.

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The Latest Solution of Asphalt Pavement Cracking -- Zirconium Tungstate

Some asphalt pavements often have long, thin, split cracks or web, this kind of situation, we usually call it "cracking".

There are many reasons for cracking, and some vehicles overrun the load too much, and some asphalt material reasons, here we discuss briefly the material factors.

In general, the cause of asphalt pavement cracking of pavement is extreme temperature or temperature fatigue effect. In short, the asphalt pavement has experienced a large expansion and contraction, and once the temperature stress exceeds the fracture strength of asphalt concrete, cracks will arise. Moreover, the cracks in the road is just the beginning, the days later, more sun and rain and traffic rolling, asphalt mixture on the temperature changes will become increasingly sensitive, when the ambient temperature is too high, resulting in high temperature rut; temperature is too low, crack extension re-cracking. It will soon turn into a pothole, and eventually a collapse or even more serious road damage. As a result, pavement cracking is one of the typical diseases of asphalt pavement, the cost of road maintenance at the highway department is staggering every year.

asphalt pavement cracking image

If there is any effective and feasible way to prepare for the rainy day? More and more scholars have come to think that the key is to reduce the sensitivity of the asphalt road to temperature. As is known to all, asphalt mortar plays a decisive role in the performance of asphalt mixture during the process of asphalt synthesis. Therefore, a certain amount of low temperature negative thermal expansion material to the mortar to modify the asphalt is the key to improve the low temperature crack resistance of asphalt mixture. So who can complete the bridges and road protection? Some scholars think of the excellent performance of the negative thermal expansion material zirconium tungstate.

So, is it feasible to solve the problem of asphalt cracking with zirconium tungstate material? Some scholars have done some research on it. Zirconium tungstate is a new type of material. The research report shows that it has different thermal characteristics, such as thermal expansion and cold expansion, in the range of 0 ~ 1005K, some scholars believe that a certain amount of asphalt is added to the asphalt mortar, it can neutralize the thermal expansion and contraction effect of asphalt pavement, and greatly enhance the anti cracking ability of asphalt pavement. In the course of the study, scholars use zirconium tungstate instead of mineral powder as filler of asphalt mortar and compare with traditional asphalt, the results show that the advantage of zirconium tungstate modified asphalt is higher than traditional asphalt, which results in higher adhesion work and tensile strength. That is to say, the resistance to cracking increases greatly, and the disadvantage is that the water loss ability of zirconium tungstate is slightly weaker than traditional asphalt. With the deepening of research, the improvement and upgrading of zirconium tungate is only a matter of time.

The performance of the modified asphalt for zirconium tungstate is good, but to be honest,the cost of preparing zirconium tungstate material is still on the high side, and it is not practical for large-scale projects such as highway asphalt paving, this is also the distance from the laboratory to industrial promotion, but in any case, the use of zirconium tungstate modified asphalt is very promising.

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