2020年6月24日星期三

Photocatalytic Production of Benzoic Acid with Bismuth Tungstate

Benzoic acid is a flake or needle like crystalline with a smell of benzene or formaldehyde, usually made by selective oxidation of toluene.

photocatalytic production of benzoic acid with bismuth tungstate image

Toluene is obtained by a series of oxidation processes. Benzoic acid is an important food preservative, and is also used in medicine, dye carriers, plasticizers, spices and antibacterial agents. In the traditional chemical process, the production of benzoic acid from toluene requires selective oxidation of toluene under severe conditions, such as high temperature, high pressure, and acidic solvents. Generally speaking, the process is costly and polluting.

Tungstate is a kind of photocatalyst which is widely used in industrial wastewater treatment, but some scholars have made use of the principle of petal type bismuth tungstate photocatalyst to produce benzoic acid. Because bismuth tungstate can use oxygen as oxidant to catalyze the oxidation of toluene and its derivatives, thereby simplifying the preparation of benzoic acid and reducing pollution.

In the process of studying the oxidation of benzoic acid by catalytic oxidation of toluene with bismuth tungstate, it is found that the petal like bismuth tungstate powder has the highest activity. By means of X ray diffraction, scanning electron microscopy, UV Vis absorption spectra and experimental results indicate that surface flower like bismuth tungstate powder showed the best activity for the oxidation of toluene and it is likely to be the largest surface area has a relationship. Because Bi2WO6 is excited by light, electrons are excited by light and leave holes that form electron hole pairs, these photogenerated electron hole pairs give rise to stronger oxidation and reduction signals because of their strong redox power, while electrons and holes play a corresponding role in the oxidation of toluene, thus facilitating the reduction.

In recent years, bismuth tungstate has become a new force for environmental protection because of its good photocatalytic performance, but it is rare in the application of catalysts, the reduction of benzoic acid with bismuth tungstate not only provides a new idea for the oxidation and reduction of toluene, but also provides an effective method for the green production of benzoic acid.

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Tungsten Trioxide Helps Catalyze SCR Soot Denitrification Technology

The nitrogen oxides produced by coal combustion as a pollutant will affect human health.

The most harmful is NO2, which mainly affects the respiratory system of human beings, and can cause bronchitis and emphysema.

SCR selective catalytic reduction technology has become the most widely used and most effective flue gas denitrification technology in the world. It has the advantages of low reaction temperature, high purification rate, reliable operation and small two pollution. After its catalysis, the main non-toxic and non polluting N2 and H2O are produced.

SCR soot denitrification technology image

In the SCR soot denitrification technology selective catalytic reduction system, it is generally composed of ammonia storage system, ammonia and air mixing system, ammonia injection system, reactor system and monitoring control system, the thermal power plant, SCR reactor is usually installed in the boiler economizer and air preheater, here for the high dust temperature arrangement, smoke temperature in this region for SCR denitrification reaction, ammonia injection in the appropriate position in the flue between economizer and SCR reactor, and the flue gas mixture after the reaction with NOx catalyst in the reactor. The catalyst is placed in a solid reactor. The catalyst unit is usually vertically arranged and the flue gas flows up and down.

Catalyst is one of the core of SCR technology, its cost is about 20%~40% of the total cost of SCR system, and the performance of catalyst has a direct impact on the removal efficiency of NOx. For SCR systems, the three main commercial catalysts are noble metal catalysts, metal oxide catalysts, and molecular sieve catalysts. At present, metal oxide catalysts are the most widely used in industry because they are the cheapest. In the past, vanadium titanium catalyst is the main catalyst for selective catalytic reduction system of SCR in China. But in recent years, scientists have found that titanium tungsten vanadium catalysts are more active, selective, antioxidant and anti toxic, and they are expected to be the first choice of catalysts.

Some scholars use imported V2O5 - WO3/TiO2 catalyst to test the effect of SCR, with the help of tungsten trioxide, SCR denitration ratio reached 100%, compared with the traditional vanadium and titanium powder, the effect increased by 30%, the effect is very obvious, but the cost has also increased a lot. For some enterprises, environmental protection measures are only a move, and raising environmental costs is tantamount to their lives, which is the biggest obstacle to the commercial popularization of titanium tungsten vanadium SCR catalyst.

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Single Layer Tungsten Disulfide Challenge Graphene (2)

Tungsten and carbon have many similar physical properties, such as high melting point, high hardness, and better conductivity and thermal conductivity.

So foreign scientists first took aim at tungsten. In recent years, foreign scholars through the study found that single layer tungsten disulfide also has excellent semiconductor performance, it not only has excellent characteristics of graphene, there are more excellent than the characteristics of the semiconductor, two tungsten sulfide has a considerable band gap, and it also shows new properties: As the number of atoms increases, the bandgap becomes tunable, and its electron migration rate is better than that of graphene, which is the ideal choice for transistor materials.

single layer two tungsten sulfide image

There is no doubt that the emergence of graphene and other two-dimensional materials to the world's material industry brought about tremendous changes, as China attaches great importance to the material industry, graphene manufacturing technology has achieved many achievements, the cost of graphene has greatly declined, making the use of two-dimensional materials rapidly spread. In many areas, graphene has the advantage of excellent compatibility and cost control, and is "the king of new materials". But in the field of semiconductor such as transistors, high-performance single layer two tungsten sulfide has the absolute strength beyond the performance of graphene.

China is not only a big producer of graphene, but also a major producer of tungsten. Tungsten is an important strategic resource of non renewable. The price of monolayer tungsten disulfide is one to two times higher than that of graphene, which is probably the main reason why monolayer tungsten disulfide is difficult to produce as much as graphene. However, if a single layer of tungsten disulfide and graphene made of composite material? This may be feasible. Looking forward to the future, we can exploit the advantages of raw materials to develop a microprocessor with Chinese proprietary rights. In the future of the intelligent world, we use those than the performance speed is almost a few times or even hundreds of times the computer, mobile phone, or VR equipment, and even intelligent robots, they can be a real Chinese core.

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Catalytic Synthesis Edible Perfume Butyric Acid Vinegar with Tungsten Silicate

Tungstic acid is a tungsten heteropoly acid, with keggin structure, the appearance of white or pale yellow deliquescence crystals, soluble in water and alcohol.

Butyrate but also known as butyl butyrate, can be used as bananas, pineapple and other fruit essence, used in beverages, cakes and bread food. Its traditional synthesis method is under the catalysis of sulfuric acid, esterification by butyric acid and butanol. However, the method has the disadvantages of long reaction cycle and low yield. Meanwhile, sulfuric acid has a strong corrosion on the equipment and produces wastewater that pollutes the environment.

In recent years, in the food additives industry, tungsten silicate and tungsten phosphate have been widely used in place of traditional acid catalysis. They are both effective and environmentally friendly. They are the gospel of the whole food processing industry.

butyric acid butyl vinegar image

The preparation of butyric acid vinegar is the synthesis of butyric acid vinegar by the catalysis of tungsten silicate, the butyric acid and a certain amount of catalyst, with water and butanol added to the three bottles, with water and butanol three neck bottle, equipped with water separator, built-in quantitative saturated salt water, heated to reflux with an electric hot pot, before the reaction stopped 15min, began with water and excess alcohol distillation, the product is then cooled and butyric acid vinegar is obtained.

Tungsten silicic acid has good catalytic properties. Most of the strong acid needed to catalyze the synthesis of food additives, such as butyl acetate butyrate, isoamyl acetate, octyl acetate, levulinic, can be catalyzed by phosphotungstic acid or tungstic acid with Keggin structure. Because the structure of tungsten heteropoly acid of Keggin structure is simple, the structure is determined, and the structure characteristics of complexes and metal oxides are also included, not only with inorganic acids (such as sulfuric acid) and solid acids (such as molecular sieves), it has the essence of acid catalysts, it also has the function of free or oxygen-containing organic compounds (such as alcohols, ethers, etc.) free in and out of the heteropoly phase, which is called "pseudo liquid phase". Therefore, heteropoly acid as an acid catalyst, its acidity is much stronger than inorganic acid, but it is more environmentally friendly.

Therefore, it is necessary to test the synthesis of similar food additives, which can be safely used with phosphotungstic acid and tungstic acid as the catalysts of the two types of heteropolyacid salts.

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2020年6月1日星期一

Tungsten Silicate Catalytic Synthesis Cinnamic Acid Isopentyl Acetate

Tungsten silicate is a kind of tungsten heteropoly acid with Keggin structure, recently it is widely used as food additives on catalytic synthesis.

cinnamic acid isopentyl acetate image

Its appearance is white or pale yellow deliquescent crystal. Isopentyl cinnamate is a kind of perfume. It is a colorless viscous liquid with cocoa flavor. It is mainly used in food and daily chemical industry. It is a kind of spice which has a bright future to be developed. The traditional synthesis is catalyzed by sulfuric acid, cinnamic acid and isoamyl alcohol process acetification, the main drawback of this method is the existence of long reaction time, low yield, complex process polluted water on environment, sulfate has strong corrosive effect on equipment.

Tungsten silicate is an environmentally friendly green catalyst, it has the structural characteristics of complexes and metal oxides, it has the acid catalysts function as inorganic acids (such as sulfuric acid) and solid acids (such as molecular sieves). In the food additives industry, it has also been used to replace traditional acid catalysts, both effective and environmentally friendly.

Test method for synthesis of cinnamic acid isopentyl acetate is that get some cinnamic acid and a certain amount of catalyst, water carrying agent (benzene) isoamyl alcohol into three bottles, equipped with water separator, the water separator is equipped with quantitative saturated salt water, heat the reflux with an electric pan,  then begin to steam the water carrying agent and the excess alcohol 15min before stopping the reaction, and cool the product down.

The reaction conditions for tungsten silicate catalytic synthesis of cinnamic acid isopentyl acetate is mild, acetification rate is high, less dosage, recyclable. Therefore, tungsten silicate can be used instead of many kinds of food additives in the synthesis of acid catalysts, which is basically a consensus among many scholars.

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Tungsten Silicate Catalyze Preparing Edible Flavor Octyl Acetate

Tungsten silicate is a tungsten heteropoly acid, its appearance is white or pale yellow deliquescent crystal, soluble in water and alcohol, soluble in crystal water itself.

octyl acetate image

When heated, it has decomposition when under 600~650°C. Tungsten heteropoly acid is often used as a catalyst, so as tungsten silicate.

Octyl acetate exist in citrus oil, green tea leaf oils and so on, it also exist in fruit. Octyl acetate is identified as non-toxic food by FEMA (the flavor and Extract Manufacturers Association). The preparation of octyl acetate can not be separated from the strong acid catalyst. Due to the oxidation and strong dehydration of concentrated sulfuric acid, the esterification rate is reduced, the quality of ester is poor, and the equipment is seriously corroded. A lot of waste liquid is produced in the post-treatment process, which pollutes the environment and so on.

Tungsten heteropoly acid is a kind of green environmental friendly catalyst, in recent years, in the food additives industry, it is widely used to replace traditional acid catalyst, it is efficient and environmentally friendly. Phosphotungstic acid and tungsten silicate is that kind of catalyst.

Method for preparing octyl acetate is that a certain amount of acetic acid, octyl alcohol and tungsten silicate in three bottles, oil bath is heated to a certain temperature, after stirring, reflux, and cooling down the reaction liquid, filtering to remove the catalyst, filtrate analysis by gas chromatography, to test the alcohol conversion rate and selectivity of octyl acetate. The optimum conditions for the preparation and esterification of the catalyst were determined by changing the amount of catalyst, the time of calcination, the molar ratio of acetic acid to octanol, the amount of catalyst, the reaction temperature and time. Through a series of evaluation we conclude that the suitable conditions for the catalytic esterification of tungsten silicate is that ratio of acid to alcohol is 1.3:1, the amount of catalyst 0.2g/0.1mol octanol, reaction time for 1H, reaction temperature is 100~118°C. Under this condition, the esterification rate can reach 99.30%.

Tungsten silicate has good catalytic activity in the synthesis of octyl acetate, it has short reaction time, high esterification rate, no waste acid discharge, simple process, the catalyst can be reused, therefore, tungsten silicate is an excellent catalyst for the synthesis of octyl acetate, it has a good prospect of industrial application.

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Single Layer Tungsten Disulfide Challenge Graphene (1)

Graphene, also called monatomic graphene, is a quasi two-dimensional material with only one atomic layer.

Graphene is one of the newest, most powerful, conductive and thermal conductive materials. The "king of transistors" that is expected to replace silicon in the future. Since the first two-dimensional material graphene was discovered in experiments, two-dimensional electronic materials have been studied for more than 10 years. Two dimensional materials are the thickness of only one atom, also known as a single layer of material, they are several hundred times smaller than the thickness of a sheet of paper. Nano monolayer two tungsten sulfide is also a two-dimensional material, moreover, in the field of semiconductor transistors, single layer two tungsten disulfide has a functional advantage that graphene does not have.

single layer two tungsten sulfide image

Transistors refer to all single elements based on semiconductor material. In a transistor, electrons pass from one end (S) to the other via a channel (D), when the process is complete, the delivery of information is complete. Because the speed of electrons is limited, in modern transistors, they usually run at saturation speed, so the time required is basically determined by the length of the channel. The shorter, the faster.

Now we are mainly producing silicon materials for transistors. In the micron era, the smaller the transistor size, the smaller the channel length and the shorter the electron transmission distance. This represents the faster processor chips, higher integration rates, and lower cost.

But by 2005, Inter and AMD, two computer microprocessors, would no longer boost CPU frequency but switch to multicore architectures, as did the development of mobile microprocessors. The reason is that, first, Moore's law, the higher the processor frequency, the greater the power consumption, when the frequency reaches 5G, the computer is a big stove; Two is the silicon wafer size has reached the limit at 20 nm, reducing the most significance, that is, reducing power consumption, performance is very limited. Thus, since then, CPU turned to multi-core architecture optimization, which is later dual core, quad core, eight core CPU appear reasons.

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【Know Tungsten】Tungsten Powder Export

China is a dominant country of tungsten resources and tungsten powder export, and export control conditions of 4xy3, has canceled export quota in 2016 and transferred to goods of export license administration.

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2020年5月1日星期五

Talking About Past and Present -- Flotation

Flotation, also known as flotation separation, is a method of separating useful minerals from ores according to the physical and chemical properties of mineral particles.

In the 18th century, it was known that the gas adhered solid particles rose to the surface of the water; In the 19th century, people used gasification (boiled pulp) or acid and carbonate minerals generated by the reaction of flotation graphite flotation. In the late nineteenth Century, due to the increasing demand for metals, the resources of coarse lead, zinc and copper sulfide ores were reduced gradually, in Australia, the United States and some European countries, flotation has been used to fine grained ores to provide concentrates for smelting.

At the beginning of the industrial age, the most widely used flotation method is the total oil flotation, it is based on the oily and hydrophilic nature of the mineral and is stirred by adding a large amount of oil to the pulp, the lipophilic mineral sticking to the oil layer is scraped out and separated from the hydrophilic gangue minerals. This method began in 1898 for the treatment of lead and zinc sulfide industrial production, but because of small production capacity, poor sorting, fuel consumption costs, and soon be eliminated.

flotation image

In 1902, the Americans proposed a method of pellet flotation, in a small amount of oil and soap agents under the conditions of the slurry in the sulfide ore selective flocculation into pellets, thus, the dispersed gangue can be washed away and separated from the aggregate minerals. This method once replaced the whole oil flotation, but it seems that the time is not long.

The froth flotation process, which we have been using since 1924, is derived from the popularity of flotation reagents. It is the selective separation of solid gas from the suspension of water (pulp) into the solid mineral, and is the selective separation process of the gas liquid solid three-phase interface, foam flotation has been called "miraculous invention" in the history of mineral smelting science and technology, and opened a new era of modern flotation methods.

Now, with the progress of industry, our tungsten ore flotation technology is changing with each passing day, but it is still the category of foam flotation. With the flawless beneficiation of chemicals used, flotation of new methods and new concepts are also constantly invented and created, in the accumulation of a large number of technology, China's tungsten flotation field developing, accumulate steadily, industry technology has been in the international leading position. Even some of the western countries, which have been proud of themselves, have turned their back on copy the flotation method of our country.

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Hunan New ShaoTan Tungsten Ore

In November 13, 2014, Xinshao County, Hunan Province, compiled by the 407 team of Hunan Provincial Geological Prospecting Bureau, successfully filed on the Provincial Bureau of land and resources. 

The report shows that the size of the tungsten ore mine in Xinshao County, Hunan Province is a large-scale tungsten mine, proven tungsten resources reserves of 70,400 tons, associated gold, silver, antimony and other metal elements, is expected to mine service life of about 17 years, the total total economic value of about 8 billion yuan. News once broadcast, it led to a warm reaction to the capital market, the listed company's market value increased significantly, because it is the first record of nonferrous metal mineral exploration in Hunan province since 2000, and the reserves are huge. In China, the shortage of tungsten resources is becoming more and more urgent, and the good news is encouraging.

Hunan new ShaoTan tungsten ore image

Tan Xian tungsten ore is located in the Cao Jia village, Xin Shao county, an area of 10.29 square kilometers, located in the Longshan mountain metallogenic belt, tectonic, magmatic activity is strong, excellent mineralization conditions. Of course, behind the dazzling achievement is full of geological prospecting people's hardships. According to 407 team members described in 2010 when the exploration work began, they found Tan Xi tungsten ore area geological situation is complex, fault fracture zone development, the surface is not obvious, the depth of the exploration line is very wide, the thickness is generally larger than 100m, the distribution range is wide, the area is large and the depth is large. Early drilling is used to expose the construction period, the cost is high and the effect is poor. Later 407 brigade summed up the failure experience and sort out the mineralization of the Tan Xi mine, decided to use geophysical methods to detect. The result is remarkable. It is not only fast, effective, but also saves a lot of costs.

For four years, the project team completed the field work from detailed investigation to exploration, completed a total of 2.15 square kilometers of 1: 2000 geological survey, 34 for construction drilling, 13358.05 meters for drilling footage, 4 for aquatic test and 4 for mineral processing. It is determined that the type of deposit is stratabound skarn type tungsten deposit, and 12 mineralization layers are numbered, and the amount of ore body is estimated, a total of 57 laying ore body, ore body thickness of 0.64 meters to 17.56 meters, the average grade of 0.367%, submitted to the amount of 19.16 million tons of tungsten ore, tungsten resources 70,400 tons.

Relative to the gold, Tan Xi tungsten ore seems to have more comprehensive mining value, in 2013, Hunan Province, 304 Geological Survey team in the mine Li Ping village found a new generation of tungsten antimony ore belt. In the future, the development potential of Tan Xi tungsten mine is abysmal.

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Apple May Secretly Develop Power Batteries in China

According to the first financial news, apple is working with a Chinese power battery manufacturer secretly developed automotive power batteries, confirmed that the U.S. auto project is not just software, as well as hardware. Apple may really be making a car.

One is the Silicon Valley global high-tech giant, and the other is a power battery manufacturer in Fujian, China. Apple and the Ningde era of new energy Polytron Technologies Inc (hereinafter referred to as the "Ningde era", also known as "CATL") is a project based on confidentiality agreements. According to sources close to the collaboration, the first financial services are being co operated in the field of batteries.

Amperex Technology Limited (hereinafter referred to as "ATL") is Apple's consumer electronics products, the world's largest battery supplier. The Ningde era was part of the parent company's ATL power battery division, which became independent power battery manufacturers in 2011. Ningde times founder Ceng Yuqun, President Huang Shilin and many other start-up shareholders have been ATL executives.

clean energy vehicles image

Apple did not announce any news of the cooperation with the Ningde era, while the Ningde era refused to respond to this. CCID Consulting, new energy director Wu Hui told the first financial reporter said, if Apple and Ningde era cooperate in power battery, it does not rule out the possibility of Apple to continue to build cars, one of the core components of automatic driving electric vehicles is the power battery.

At present, Panasonic battery has become the market leader in automotive power batteries, in 2017, Dalian Matsushita automotive power battery project officially put into operation in April 27th, with an annual capacity of 200 thousand power lithium-ion batteries. If Apple is also making a car, then the potential power battery suppliers are also likely to be in China, and even as Apple's mobile phone, most of the production lines are likely to be in China.

The main reason is that China's manufacturing industry under the guidance of the national "Made in China 2025" strategy. China not only has a good scientific research and investment environment, but also cultivate a large number of outstanding skilled workers. And in the production of materials, China's rich mineral resources, iron, copper, tungsten, molybdenum, aluminum and other important materials. And after years of development, steel, tungsten, molybdenum, copper and alloy smelting industry has been in the world advanced level.

In addition, some experts believe that clean energy vehicles will replace the existing fuel vehicles in the next ten years, but due to the problem of thermal power pollution, electricity is still not ideal for clean energy, perhaps solar energy is the cleanest energy source. In recent years, with the development of nano technology and thin film technology, people have found a variety of can be used for solar cell manufacturing materials, such as monocrystalline silicon, monocrystalline tungsten, monocrystalline molybdenum, zirconium tungstate film, tungsten selenide film, these are very valuable solar power materials.

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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.

nano tungsten carbide image

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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2020年4月8日星期三

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.

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.

weight-reducing aid image

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.

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 ceramic.

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.

glass ceramics image

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.

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 image

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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Barium Tungstate Thin Film Preparation by Galvanic Cell Electrochemical Method

Tungstate scheelite structure is a kind of important laser material. They are tetragonal structures at room temperature and emit blue light from the tungstate crystals under UV excitation.

The study shows that the structure of barium tungstate always keeps tetragonal structure from room temperature to melting (1820 K), indicating that it has good structural stability. In view of the superior properties of barium tungstate, barium tungstate thin films are often in short supply in the fields of luminescence and display technology, laser and photoelectron technology, and detection technology. In recent years, the electrochemical technology of galvanic cell has been used more and more in the field of preparation of inorganic functional films because of its advantages of one-step film forming, no post-processing and environmental coordination. Compared with electrolytic electrochemical technology, this technology has the advantage of zero energy consumption. Therefore, electrochemical deposition of galvanic cells is a new and environmentally compatible technique for the preparation of thin films.

barium tungstate thin film image

Barium tungstate thin films were prepared by galvanic electrochemical technique at room temperature. The purity of 99.9% and polished the metal tungsten film as working electrode, immersed in saturated barium hydroxide solution, Pt is used as auxiliary electrode and Ag / AgCl electrode as reference electrode to form primary battery system and sealed electrolytic cell. After the reaction has been completed, samples are removed and rinsed with deionized water several times to dry and to obtain barium tungstate thin films.

The study found that these films are highly crystalline, scheelite structure, and the element valence is also consistent with the theoretical value. Under the condition of primary cell, the quality of the film is obviously improved, and the micro crystal also tends to be regular square conical particles. Under the excitation of ultraviolet light, the barium tungstate thin film produces a blue emission band with a center at 460 nm and a half height of 140 nm. The results show that electrochemical deposition of galvanic cells provides a convenient, cheap and environmentally friendly process for the preparation of barium tungstate.

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2020年2月17日星期一

Scintillation Crystal Material -- Magnesium Tungstate

When the inorganic crystal is subjected to high-energy particles or high-energy rays (such as X-rays, gamma-rays), a phosphor that emits visible light due to excitation of particles or rays, which is a scintillation crystal, and magnesium tungstate is a scintillation crystal.

Magnesium tungstate (MgWO4) single crystal belongs to the wolframite structure, its melting point is 1358 °C. The crystal has a wide emission band of blue white light with a peak value between 480~500 and nm, in which the half width of the spectrum reaches 140nm, the luminescent intensity of magnesium tungstate is sensitive to impurities and excessive grinding, and the emission intensity of the scintillation crystal is weakened regardless of the substance.

magnesium tungstate lamps image

The excitation spectrum of MgWO4 is wider than PbWO4. In early studies of scintillators, MgWO4 has the highest quantum efficiency, it is believed that the efficiency of converting 253.7 nm radiation to visible light is 100%. It is often used as reference samples of magnesium tungstate scintillator when measuring quantum efficiency. The subsequent results show that the actual quantum efficiency is about 85%. The current MgWO4 in the fluorescent lights and white lights have important applications, while quantum efficiency measurements are used as standard sample.

Method for preparing magnesium tungstate with high temperature solid state method and hydrothermal method. In general, the traditional high-temperature solid-state method is not only high calcination temperature, but also only monoclinic tungstate can be obtained. Co precipitation method can not prepare MgWO4 directly under normal temperature and atmospheric pressure. However, the scholars found that the hydrothermal method can obtain tetragonal magnesium tungstate at very low temperature, and less impurity phase formation, the rare earth ions can be doped into them, and can be converted to monoclinic phase at lower temperature, with good luminescence properties. Therefore, the hydrothermal method is more recommended by the method of preparation of magnesium tungstate.

It is often used for magnesium tungstate doped with Er3+, Nd3+, Tm3+, Ho3+, Yb3+ and other rare earth ions to produce near infrared luminescent materials, near infrared light has many special properties, such as large penetration depth, high intensity and light intensity absorbed, it has been widely used in optical fiber communication, laser source, biosensor and fluorescence immunoassay. In summary, the magnesium tungstate material also has great application potential.

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