2017年9月15日星期五

Development Status of Nano Tungsten Carbide Powder in China

Nanocrystalline cemented carbide is a tool material developed in recent years. It is based on nano tungsten carbide powder.



The cemented carbide with high hardness, high wear resistance and high toughness has been produced under the condition of adding proper binder and grain growth inhibitor, its performance is obviously higher than that of conventional cemented carbide. It has been widely used in hard metal materials, cutting tools, micro drills in the electronics industry, precision molds, medical fields and other fields.

In the aspect of ultrafine or nanocrystalline cemented carbide, there are only a few countries in the world such as the United States, Japan, Sweden and so on, which can produce alloy with both high hardness (HRA>90) and high strength (>3 200 MPa). The main difficulties come from ultrafine and nano tungsten carbide powder and other raw materials and cemented carbide production process.

From 70 to 80s in China began to study the industrial production of submicron and ultrafine WC cemented carbide, the granulated tungsten oxide reduction method and the self reduction tungstate process have been developed; Since the beginning of 90s, ultrafine tungsten carbide powder has been produced by hydrogen plasma reduction, micro - violet tungsten reduction, fluidized bed gas phase reduction carbonization, high frequency plasma method, WC-15Co tungsten cobalt carbide alloy with hardness HRA>90 and strength >3 200 MPa was prepared. But compared with the advanced level in the world, there are still some gaps in product quality, production capacity, cost, production process and continuity.

Tungsten cobalt alloy is also called WC Co cemented carbide. According to cobalt content, can be divided into high cobalt (20%~30%), cobalt (10%~15%) and low cobalt (3%~8%) three categories. The key of tungsten cobalt alloy is the purity of tungsten carbide powder. Although some achievements have been made in the research and production of nano tungsten carbide powder, there is still a big gap compared with the advanced level in the world.

It is proposed to strengthen the research on the basic theory, according to China's actual situation, we should boldly study and adopt new technology and process, it is necessary to study the production process of nanometer tungsten carbide powder which is suitable for the situation of our country and has the world's leading level.


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Tungsten Oxide Nanoparticle as a Catalyst for Malonic Acid Ester Synthesis via Ozonolysis

Ozonolysis is of great interest to synthetic organic chemistry because it is one of the most efficient tools for oxidatively cleaving carbon-carbon double bonds. Ozonolysis is generally used to prepare biologically active molecules. Therefore, the reactions between ozone and organic compounds continue to be a subject of significant interest from mechanistic, synthetic, and environmental perspectives. The importance of O3 reactions with alkenes in the troposphere and solution has led to many experimental and theoretical studies of their kinetics and mechanism.



Scientists addresses tungsten oxide nanoparticle syntheses for use as a catalyst in the novel one-step malonic acid ester synthesis. Malonic acid ester is directly synthesized and esterified via the ozonolysis of palm olein (palm oil fraction), which comprises 10% linoleic acid as an unsaturated fatty acid. The main advantages of using tungsten oxide nanoparticles as the catalyst for this esterification are to shorten the reaction time. Using tungsten oxide nanoparticles also has minor advantages such as simple synthetic operation, excellent yields, and recyclability. The structure and size of the tungsten oxide nanoparticles were investigated via field emission scanning electron microscopy (FE-SEM) and X-ray powder diffraction (XRD). The malonic acid ester was spectroscopically characterized via gas chromatography mass spectroscopy (GC-MS).

The study used a new approach to synthesize malonic acid ester via the direct ozonolysis of palm olein, where the fine bubbles of ozone played an active role to cleave the double bonds. This method was used for the first time with a tungsten trioxide catalyst for the esterification of malonic acid and had the advantages of synthetic simplicity, an excellent 10% yield, short 2 h reaction time, and recyclability. Malonic acid ester was characterized using mass spectroscopy. The prepared nanoparticles have a spherical shape and diameter of 24 nm have been investigated by the FESEM & XRD, respectively.


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Nanocrystalline Tungsten Oxide Thick Film Sensor for the Detection of H2S Gas

Metal oxide semiconductors (MOS) have been utilized as gas sensing active materials for half a century. One of the most promising solid-state MOS chemo sensors is n-type semiconducting tungsten oxide-based  gas  sensor.  They  have  demonstrated  novel sensing  properties  such  as  high  sensitivity,  fast response  time  and  low  operation  temperature.  In particular,  pure  or  doped  tungsten  oxide  is  a  promising material for the detection of various substances, e.g., H2,H2S,NOx, NH3 and ethanol.

Scientists have investigated  the sensing characteristics  of  tungsten oxide nanoparticles  to H2S  in  the 7 to 200 ppm range at working temperatures of the range of 100–225 ℃.  Semiconductor  gas  sensors  based  on nanocrystalline  WO3  powders  were  prepared  by  acid precipitation method. The thick films of the powder were coated on to glass  substrate, annealed at 600 ℃ and its response  to  different  concentration  of  H2S  gas  was studied.  Sensor behavior is presented in detail for representative concentration of 18ppm. The result showed that WOnanoparticles are good candidates for H2S detection at a temperature of 200 ℃.

Resistance variation on the introduction of different concentration of test gas
Sensitive  layers  of  tungsten  oxide  were  prepared  by dispersing  the  prepared  tungsten  oxide  powder  in methanol and drop casting on glass  substrates followed by  overnight  annealing  at  600 ℃.  The obtained crystalline phase of WO3 nanoparticles was triclinic in nature. The structure of sensor was characterized using XRD.  The surface morphology and elemental composition were characterized by scanning electron microscopy and energy dispersive X-ray analysis. It was found that the WO3 samples consisted of crystalline aggregates.  This was confirmed in TEM results.  The particles were spherical in nature.  Gas  sensing properties  of  samples  were  studied  for  the  detection  of H2S  gas.   Resistance  of  the  films  decrease  upon exposure  to  gases  and  attained  a  saturation  value.

Sensor regains its original value after test gas is removed. Sensor exhibit good sensing characteristics to H2S in the concentration range studied, 7 to 200 ppm over the temperature range 100-125 0C. The best results were obtained at operating temperature of 200 ℃ with a sensitivity of 1.3. Response and recovery time of sensor at this optimum temperature was 22 seconds and 4.1 minutes respectively. Lowest measurable concentration is found to be 7ppm. Resistance  always  returned  to  its initial  value  after  the  test  gas  is  shut  off  for  all concentration  studied. Results indicate that response of sensor is reproducible during this test. 


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Carbon Doped Tungsten Oxide Nanorods NO2 Sensor Prepared by Glancing Angle RF Sputtering

Nanostructures such as nanowires, nanorods, nanotubes of metal oxide semiconductor (MOS) materials have recently attracted monumental interest in gas-sensing applications because of their excellent performances owing to their large surface to vol-ume ratio, lower electron recombination rate and high stability. Among various MOS materials, tungsten trioxide (WO3) is a highly promising candidate due to its fast response with high sensitivity toward NOx.

Resistance response of the carbon-doped and undoped tungsten oxide sensor towards NO2
Glancing angle depositio (GLAD) technique is a relatively new method for fabrication of well-ordered and sophisticated nanostructures i.e. nanorods, nanoblade and zigzag nanocolumns. It is a modified physical vapor deposition process, in which substrate surface is rotated and tilted to an angle greater than 80° with respect to the normal of substrate surface or less than 10°with respect to the direction of vapor flux. The vapor molecules directed to the substrate will experience shadowing and limited surface diffusion condition leading to the formation of isolated nanostructures. With this technique, the shape, size and density of nanostructures can be well controlled by deposition parameters such as deposition angle, operating pressure, substrate temperature, deposition power, and so on. In this report, carbon-doped WO3 nanorods is fabricated by GLAD technique using RF magnetron sputtering and investigated for NO2 sensor application. In addition, its performances are comparatively studied with that of the undoped ones.

Carbon-doped and undoped WO3 nanorods gas sensors have successfully been fabricated by the GLAD technique with RF magnetron sputtering.  By this technique, the vertically well-aligned homogeneous WO3 nanorods with very low defect were achieved over a large area. It was found that carbon doping does not change any crystalline structure but increases the grain size and accelerates the nanorods growth leading to relatively high aspect ratios as compared to the undope one. The fabricated carbon-doped tungsten oxide nanorods sensor exhibits high response and selectivity to NO2 at the concentration range of 0.5–5 ppm at an optimum operating temperature of 250℃. In addition, the carbon-doped sensor still works well for NO2 detection at lower operating temperature of 150℃ due to the decrease of activation energy and alteration of the depletion layer. Therefore, carbon-doped well-ordered WO3 nanorods with improved NO2 gas-sensing performances in terms of response, response  time, selectivity and operating temperature has been realized. Moreover, this technique offers distinct advantages over other methods such as high productivity, simplicity and low cost for well-ordered nanostructure construction.


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Defect State Nano Structure Tungsten Oxide Catalyst Is Invented

USTC(University of Science and Technology of China) recently announced that professor Xiong Yujie research group designed a kind of nano structure tungsten oxide in defect state based on inorganic solid accurate preparation of chemical and use crystalline defect project. Under broad spectrum illumination, it shows fine oxidation coupling catalytic property which is expected to realize low cost and low-energy organic chemical technology. Tungsten oxide has good photocatalytic property due to its special structure, it has already been used as varies of catalyst and also other industrial fields. 

Most of catalytic reaction is based on the application of precious metal oxide and motivated by burning of petroleum and coal. It has disadvantages of high cost and high energy consuming. Compared to precious metal catalyst, metal oxide has benefits of low cost. However, it shows shortcomings in oxygen molecular system which can not capture solar energy and pass it into oxygen molecular.

Defect Rich WO3 Nanosheet

In order to solve the problem, Xiong Yujie research group designed a kind of nano structure tungsten oxide. Usually metal atom of metal oxides has coordination saturation property, it can not active oxygen molecular by chemical absorption. During the research, construct of oxygen vacancy defect overcomes the shortcomings and accelerate photo electron transact from metal oxides catalyst to oxygen molecular. Defect state also broadens light absorption range of photocatalyst which enables it to capture solar energy in visible light and near infrared area. The two big steps realize the valid capture of solar energy and energy transaction, solves the bottleneck problems of oxides catalyst in the organic synthesis of photocatalytic activity.



Based on this acknowledgement, researchers are able to adjust solar energy to drive organic oxygen coupling reaction based on crystalline defect project. It provides possibility to use solar energy take place of heat source organic synthesis, and make an improvement for design of photocatalyst material.


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Sodium Tungstate Diet Pills Are Becoming Possible

The metabolic syndrome is associated with increased obesity caused by a group of common metabolic disorder syndrome, the fundamental reason is the imbalance of body energy metabolism.

weight-reducing aid image

With the improvement of people's standard of living, when the body intake of excessive nutrition and energy use is reduced, the remaining nutrients are stored in the body in the form of fats and glycogen, and excessive fat storage causes obesity.

Obesity is the cause of many chronic conditions, it will significantly increase the incidence of diabetes, coronary heart disease, stroke, hypertension, hyperlipidemia and other morbidity and mortality. So far, only two drugs have been approved and accepted for obesity in FDA of the United States: Orlistat and Sibutramine. So people can lose weight better and control their appetites, but synthetic diet pills have side effects, such as headaches, anorexia and gastrointestinal reactions, and western medicine is expensive.

In recent years, researchers in China have discovered as a mineral element of "tungsten", it also has the effect of reducing blood lipids and blood sugar, a large number of studies have shown that tungsten form of tungstate has a strong role in weight loss and anti-diabetes. The body weight of obese rats induced by high calorie diet was significantly decreased, and the weight of the treated group was still lower than the control group even after a long period of withdrawal.

Tungsten is not the first trace element found to have the effect of fighting against metabolic syndrome, sodium vanadate, which is less toxic and highly bioavailable in clinical trials, is in line with the need for safety. In addition, sodium tungstate seems to be much better because sodium tungstate can reduce normal blood glucose levels in type I and type II diabetic patients without causing hypoglycemia.

Sodium tungstate will be a great weight loss medicine in the future, a large number of academic papers show that, both in terms of efficacy or safety, sodium tungstate exhibits a stable, moderate, and natural advantage that is better than western medicine. Therefore, the research and development of sodium tungstate diet pills has broad prospects.


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The Rebirth of Tungsten Tailings -- Glass Ceramics (2)

As we all know, the main raw material of glass is silica, namely quartz, the main raw material of ceramics is kaolin. Coincidentally, the main component of tungsten tailings is also silicon, and may be rich in other kaolin constituents.

glass ceramics image

In the eyes of scientists and technicians, most of the composition of tungsten tailings and glass ceramic raw materials are similar, do not need too complicated to deal with, can be processed into glass ceramics.

Some scholars have prepared glass ceramics by using tungsten tailings after magnetic separation to remove iron, by changing the temperature system in sintering process, the glass ceramics with better properties were obtained, and the crystallization kinetics of glass-ceramic during sintering was further explored.

The crystallization temperature is adjusted between 950~1100 °C, the results show that the main crystalline phases of glass ceramics are calcium feldspar and iron pyroxene. The crystalline phase number and grain size of glass ceramics increase with the increase of crystallization temperature. The crystal morphology is distributed from small to flaky. When the crystal phase is reheated again and the crystallization temperature is 1100 °C, a part of iron and calcium pyroxene changes into gehlenite. Based on the kinetic analysis of crystal growth, it is concluded that the crystalline structure of tungsten tailings glass ceramics is the best with the highest crystallization temperature of 1050 °C, which has the potential as a building material.

Moreover, with the development of tailings such as tungsten, iron, copper and so on, the cost of glass ceramics is greatly reduced. For two simple examples, our Corning glass for cell phone screens is wearable and scratch resistant and can withstand a collision resistance, because it's glass ceramics; Ceramic tile used for decoration, which is more wear-resistant and brighter than traditional glazed tiles, and also uses glass ceramics in glaze. The use of tailings benefits millions of households, and early Corning glass was used only for high-end mobile phones, but it is now standard for all smart phones; Early ceramic tiles cost one hundred or two hundred yuan each, and many prices have now been reduced by half.

Glass ceramics made tungsten tailings realize the magnificent turn from waste to important raw materials. It not only brings convenience to people's life, but also improves environmental pollution problems. In the 2010 long-range plan, the state has planned to focus on the development and environmental protection governance of glass ceramics as a national strategy for comprehensive utilization.


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The Rebirth of Tungsten Tailings -- Glass Ceramics (1)


Tungsten tailings are the wastes left in the production of mines. China is a big producer of tungsten resources.

glass ceramics image

It is said that all large tungsten mines have a large number of tailings reservoirs, and the tailings reservoirs accumulated over several decades or even centuries have become too large to imagine. Some tailings which have reached the marginal grade can be extracted again, but most of the tailings are no longer meaningful. How to find a way out for these tailings?

Tailings treatment has always been a thorny problem in mining enterprises, not only copper and iron, tungsten ore also racking their brains for tailings to find a new way out, the most common tungsten tailings application is the manufacture of cement, tile. However, with the development of industrial technology, people found that it is a waste that tungsten tailings are used to make cement and bricks. In recent years, scientists have invented a material between ceramic and glass, which has remarkable function in the fields of electronics, architecture, biochemistry and so on, it is glass ceramics. Scientists also found that tungsten tailings are the most suitable raw materials for treating glass ceramics.

Glass ceramics, also called microcrystalline jade, is a polycrystalline material prepared by melting, quenching, and controlling crystallization. It concentrates on the three advantages of glass, ceramics and natural stone. Ordinary glass is brittle because of its irregular arrangement of atoms. Glass ceramics, like ceramics, are made up of crystals, with regular atomic arrangement, stronger toughness than glass, and higher brightness than ceramics, and are superior to natural stone in performance. In addition to the building curtain wall and interior high-grade decoration, it is also made into mechanical structural materials, electronic and electrical insulation materials, bottom material of large-scale integrated circuits, microwave oven heat crack ware, chemical engineering and anticorrosion materials and mines wear-resistant materials etc.. It is a new material with great prospects for development.


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