2020年2月11日星期二

New Material For Scintillation Crystal -- Lead 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 lead tungstate is a scintillation crystal.

lead tungstate crystals image

This property makes lead tungstate an indispensable part in nuclear medicine, high-energy physics, nuclear technology, space physics and petroleum exploration. Scintillation crystal is mainly used for CT machine, particle collider, detector and even laser weapons and other manufacturing, the common oxide scintillation crystals are mainly bismuth germanate, cadmium tungstate, calcium tungstate, cadmium molybdate and calcium molybdate, lead tungstate is a new scintillation crystal found in 1990s relative to other crystals.

Lead tungstate (PbWO4) monocrystalline belongs to the scheelite structure, its melting point is 1123 °C, its scintillation performance is not lower than other tungstate crystals, In 1990, some scholars used Czochralski method to lift the lead tungstate single crystal for the first time. This crystal has crystal coloring defects, and its coloring mechanism can be considered as follows: the formation of oxygen vacancies leads to the formation of color centers, including oxygen vacancies, color centers, defects and Fe2+.

A center of color complex formed by impurity defects; Fe2+ produces light absorption near 4 60nm. The annealing process is carried out in an air atmosphere, enabling the diffusion of oxygen components into the crystals to reduce the number of oxygen vacancies Vo, thus improving the performance of the crystals to some extent. It was also found that the irradiation hardness and transmittance of lead tungstate crystals in short wavelength range (330450 nm) were obviously enhanced by doping some trivalent ions so as to improve the optical properties of the crystal.

Although the lead tungstate crystals have defects of low luminous efficiency, because of its large density, small radiation length, strong radiation hardness and short attenuation time, it is the preferred scintillation crystal for Large Hadron Collider high resolution electromagnetic calorimeter.

Lead tungstate crystals also have a glorious history, in September 20, 2008, the world's largest scientific program, CERN, was formally operated by the Large Hadron Collider (LHC), it began the journey of human beings to reveal the origin of the universe and to find the source of quality. CMS (Compact Muon Selinoid) is one of the four projects of the Hadron Collider project, from May 2005 to March 2008, the Shanghai Silicate Research Institute provided nearly 5000 large size lead tungstate crystals for CMS electromagnetic energy devices. The Shanghai Silicate Institute has also won the CMS Industrial Award top prize awarded by the European Nuclear Center (CERN) in Geneva, Switzerland.

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Photocatalyst Combines - Phosphotungstic Acid mixed Titanium Dioxide

At present, environmental pollution has become one of the most important concerns of mankind, especially organic pollutants.

Their damage to the environment such as water, atmosphere and soil will be damaged if they are not dealt with in time, and cause an irreversible loss. In recent years, photocatalytic degradation has become one of the most important methods for organic pollutants because of its high efficiency, environmental protection and easy operation. 

As far as photocatalytic reaction is concerned, titanium dioxide TiO2 is one of the most studied semiconductors. This is due to its early application, cheapness, ease of handling, large specific surface area, and stability. Photocatalysis has attracted the most attention in the field of wastewater purification and treatment. But what can not be evaded is that TiO2 band gap is wider (about 3.2 e V), it can only be excited by ultraviolet light, the use of solar energy is limited, photoinduced electron recombination with hole is fast. it leads to low photon efficiency, which limits its practical application. 

phosphotungstic acid photocatalytic degradation image

In recent years, phosphotungstic acid has been used as a kind of heteropoly acid type catalytic material, it has become a star because of its unique acidity, quasi - liquid behavior, multifunctional (acid, oxidation and photoelectric catalysis) and the strong absorption of polyoxometalates in the ultraviolet and visible regions. However, compared with TiO2, phosphotungstic acid has the disadvantage of being easily soluble in water, alcohol and acid liquid phase, so it is difficult to recover and reuse.

Titanium dioxide and phosphotungstic acid each has their own specialty, and each has its own characteristics. Try mixing the two together to see whether each of them brings advantages, therefore, some scholars will use sol-gel method to mix TiO2 and phosphotungstic acid. The mixing ratio is 1:0.05, and the process of mixing is as follows:

A certain amount of deionized water and 1/3 anhydrous ethanol were mixed into A solution, a certain amount of four butyl titanate, glacial acetic acid and phospho tungstic acid were added to the 2/3 anhydrous alcohol under a rapid stirring, and then B solution was prepared. Then A solution is slowly dripped into the B solution under rapid agitation, a uniform white solution is obtained. After the white gel is formed, the stirring is stopped, and the obtained colloid is dried for 12 hours at a constant temperature of 80°C. The ethanol on gel stone slowly evaporates, and white solid block is obtained. The white solid block turn into white powder after grinding, and put in the muffle furnace stone, the mixture powder of TiO2 and phosphotungstic acid was obtained at high temperature for a certain time. 

What's the effect of mixing the two? Scholars use titanium dioxide and phosphotungstic acid mixed powder to degrade industrial dye wastewater methylene blue, it is concluded that TiO2 and phosphotungstic acid powder have photocatalytic adsorption effect on methylene blue, at the condition of 0.6g. L-1 catalyzer, and illumination time of 3.0, the decolorization rate of methylene blue reached 91.1%. After 4 times use, the photocatalyst still has high catalytic activity.

The test proved that TiO2 and phosphotungstic acid combines reached the expecting effect, the photocatalytic effect of titanium dioxide is enhanced, and the deficiency of the recovery and reuse of phosphotungstic acid is overcome. Another point can not be ignored, that is the price, the current market price is that phosphotungstic acid is 4.5 times the price of titanium dioxide, using phosphotungstic acid would be more luxury, combining the two not only reduces the cost, and also improves the photocatalytic performance, so it is a flexible and effective degradation of organic waste water price scheme.

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What Can Tungsten Do In The Age of Robots? (1)

In July 26, 2017, in order to commemorate this gentleman, Baidu search engine replaced the home page Logo.

robots image

Joseph Engelberg (Joseph, F, Engelberger), father of the robot, American, born in New York in July 26, 1925. In 1959, George DeVaul authorized patent technology to develop the world's first industrial robot, human beings entered the first year of robotics, and since then, the robot has brought great changes to the industry.

Today, robots are no longer limited to industry, but are beginning to come into our lives. What will happen after ten years in the future, experts have predicted that after ten years of artificial intelligence (AI) will be the rapid development of integrated circuit, with higher speed, the progress of science and technology will be at top speed.

On 2015, Premier Li Keqiang of the State Council put forward the strategy of "made in China 2025", and pointed out that China should enter the strategic target of "manufacturing power ranks" in 2025, intelligent manufacturing as an important direction of the transformation and upgrading of manufacturing industry, bear the dream of the people. As an important part of intelligent intelligence, the robot was promoted to the national strategic level during the 13th Five Year period, and will focus on the development of breakthrough arc welding robot, vacuum (clean) robot, fully self-programming intelligent industrial robot, man-machine collaboration robot, arms robot, heavy load handling robot, fire rescue robot, surgical robot, intelligent public service robot, nursing robot ten iconic products. Then, as an important strategic tungsten resources in China, what role can it play in the robotics industry?

As we all know, tungsten has excellent physical and chemical properties, such as high melting point, high density, high strength, high conductivity / thermal conductivity, low thermal expansion coefficient, good machinability and corrosion resistance. Benefiting from the advantages of tungsten reserves in China, the alloy materials industry has developed rapidly, and it also provides a solid industrial foundation for the main components of robots, tungsten is an important raw material for high quality alloys, and will also play an important role in the era of robotics.


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What Can Tungsten Do In The Age of Robots? (2)

The robots of the future need to have high pressure, high heat resistance, wear resistance, corrosion resistance and other excellent physical conditions.

They can be engaged in fire rescue, heavy load handling and underwater operation. Tungsten has the highest melting point, high temperature strength and creep resistance, as well as excellent thermal conductivity, electrical conductivity and electron emission. It will be an indispensable element in robot body casting, such as tungsten cobalt hard alloy, tungsten copper manufacturing body, can change the arbitrary shape, with a sticky, hydrophobic and high density of tungsten mud, for the robot needs flexible changes in the joint parts.

The future robot needs superior intelligence and accurate judgment, capable of autonomous programming, intelligence, medical surgery, and intelligent care, tungsten thorium alloy and rare earth tungsten alloy can reduce the electronic work, so that the material has a high recrystallization temperature, and is ideal for thermionic emission materials and electrode materials. Tungstate is a typical self - activated luminescent material, which can be used as a scanning module for robots, such as human eyes.

robots image

Future robots also need to work in conditions that ordinary people can not stand, such as high temperature operation, extremely cold operation, zirconium tungstate can be "heat shrinkable, cold expansion", is an excellent negative thermal expansion material, it’s not only for the manufacture of zero expansion devices, but also for robot circuit packaging, in extreme conditions, to ensure that the robot thermal optical instruments, laser equipment, optical communication systems and microelectronic devices of the normal operation. Of course, a robot without energy is impossible, so nano zirconium tungstate film can also be used to make thin-film solar cells, responsible for the operation of the robot.

Hocking, a famous cosmologists, claims that future robots will replace human beings and express concern about artificial intelligence. In my opinion, the kind of highly developed artificial intelligence robot that he points out should not appear in the next thirty years. But now it is foreseeable that, ten years later, the intelligent robot will be like the previous PC and the Internet, to bring about earthshaking changes in our lives, the most direct impact is there will be a large number of people unemployed. But we must not be complacent, if we don’t develope now, it will soon be pull-down by the developed countries such as the United States, Japan and Europe. The modern history of more than 100 years ago is a bitter lesson. Intelligent robots may be another opportunity for us to catch up with developed countries such as Europe, America, Japan and other countries. Tungsten, molybdenum and other important strategic resources will provide us with great help.

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2019年12月23日星期一

Cyclohexanone Catalytic Reaction by Sodium Tungstate and Hydrogen Peroxide Mixed

Cyclohexanone is an important chemical raw material, widely used in fibers, synthetic rubber, industrial coatings, pharmaceuticals, pesticides, organic solvents and other industries.

Cyclohexanone is the main intermediate for the synthesis of caprolactam and adipic acid, and it is also a raw material for the preparation of spices, rubber antioxidants, adhesives, vinegar and fruit preservative phenolic phenol, and can also be used as fine chemical auxiliaries.

cyclohexanone production plant image

The traditional way to produce cyclohexanone is to produce cyclohexanol by hydrogenation of cyclohexanol, and then to reduce the cyclohexanol to the ring chamber by chemical method. There are two conventional preparation methods: One is in zinc catalyzed by 400 to 500 °C under oxidative dehydrogenation to cyclohexanone; The other was prepared by adding chromic acid catalyst with bleaching powder as oxidizing agent under weak acid condition. Among them, there is a problem, that is, there is no ideal catalyst, or the reaction conditions are harsh; or chromic acid is a toxic carcinogen, polluting the environment.

With the further study of sodium tungstate, the scholars found that the synthesis of adipic acid with cyclohexanone can be successfully catalyzed by sodium tungstate and hydrogen peroxide, scholars try again, using sodium tungstate as the main compound of hydrogen peroxide (H2O2), adding oxalic acid or phosphomolybdic acid and other acidic oxidant, made of tungstate compound catalytic agent. Through the catalysis of sodium tungstate composite catalyst, the synthesis process of the ring tunnel is quite smooth, the conclusion is that when the reaction temperature is 80 °C and the reaction time is 6h, only a small amount of tungstic acid compound catalyst mixture is used, the cyclohexanone yield is 98.2%, and the efficiency is 20% higher than the traditional chromic acid oxidizer.

Practice has proved again that sodium tungstate and hydrogen peroxide mixture can not only catalyze the synthesis of adipic acid from cyclohexanone, it also catalyzes the synthesis of cyclohexanol by cyclohexanone and may be a good catalyst for this type of chemical material, the most important thing is that sodium tungstate combined with hydrogen peroxide is not only effective, but also environmentally friendly, and can provide a better production environment for enterprises and society.

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Tin Removal From Waste Tungsten Alloy Recycle

With the shortage of tungsten ore resources, the utilization of tungsten resources becomes more and more urgent.

Waste tungsten alloy is one of the main sources of tungsten recovery, according to statistics, about 35% of the tungsten in Europe and America developed from waste tungsten alloy recycling. With the emphasis on tungsten resources in China, the recycle rate of tungsten resources in China has been increasing year by year, and it has reached 20%.

In the tungsten recycling process, the sodium carbonate melting method of waste tungsten recycle process technology is more mature and wide applicability of the program, but it is inevitable that the leaching process in recycling of waste tungsten, scrap tin, phosphorus, chromium, molybdenum and other impurities may also enter coarse sodium tungstate solution, thus affecting the purity of tungsten products. The main impurities of the waste alloy are different, the treatment method varies according to material, here to introduce tin removal from crude sodium tungstate solution method of tin rich impurities.

 impurities removal in sodium tungstate solution image

In the alkaline process, the purification of sodium tungstate from waste alloy is usually made by magnesium ammonium phosphate method or phosphorus arsenic magnesium salt method. In the impure sodium tungstate solution, a small amount of soluble magnesium salt is added to produce ammonium phosphate, and generated magnesium salt or phosphorus arsenic magnesium salt, so as to remove arsenic and phosphorus.

In the impure sodium tungstate solution, a small amount of soluble magnesium salt is added to produce ammonium phosphate, magnesium salt or phosphorus arsenic magnesium salt, so as to remove arsenic and phosphorus. In the process of pH, silicon can simultaneously remove from the solution, but it can not effectively remove tin and tin, the best filtering stage only in the crude sodium tungstate solution phase, the follow-up process is very difficult to deal with.

For the treatment of tin in crude sodium tungstate solution from waste tungsten alloy recycle, some foreign scholars have proposed the scheme, which can be roughly divided into four stages. (1) Adding ammonium or hydrogen hydroxide to sodium tungstate solution. (2) Adding sulfuric acid, transfer PH to 9.5-10 and stir for half an hour. (3) Adding magnesium chloride into the solution which has been ammoniation and adjusted the pH value, and then the mixture is stirred for a period of about 12 hours to form a slightly soluble tin, arsenic, phosphorus and silicon compounds. (4) Stand aside for about 3 hours. A substance containing tin compounds can be precipitated.

When the insoluble substance is removed, the filter can be used to filter the insoluble matter in the solution and to obtain the purified solution containing tungsten, the content of tin obtained by the purified solution can reach or better than the purity of APT - 0, and it is very economical and feasible to evaluate the content of the waste alloy by the recycling standard of APT.

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Sodium Tungstate Preparation From Scheelite Slime Recycle

Sodium tungstate is an important chemical raw material and an important intermediate product in tungsten metallurgy production.

Generally speaking, industrial production of sodium tungstate mainly uses scheelite concentrate or wolframite concentrate as raw material, and the production cost is higher.

In the tungsten concentrate production process, there are often some tungsten due to process or equipment reasons, lead to part of the tungsten ore grinding machine into powder or no successful flotation into the tailings, forming tungsten fine mud.

scheelite slime recycle image

The conventional recycle process of tungsten slime is tungsten slime - sodium tungstate - ammonium paratungstate. How can the sodium tungstate be recycled more efficiently by using tungsten slime? Compared with wolframite, fine scheelite slime is characterized by lower grade, more impurities, and more calcium containing molybdenum, which is more difficult to purify. In view of the above, we can use hot ball milling alkali decomposition ion exchange APT evaporation crystallization process. It has a strong adaptability to high calcium and low grade ore. It has three main stages:

1. The tungsten fine slime is decomposed by alkali method and hot ball milling, and most impurities are inhibited in the slag, so that the WO3 is transferred into the solution to produce sodium tungstate solution, and most of the impurities (P, As, Si, etc.) are left in the slag. 

2. The obtained sodium tungstate solution is evaporated and crystallized at once, and to recycle the alkali and remove impurities such as P, As, Si etc..

3. Sodium tungstate crystals were dissolved and filtered to obtain sodium tungstate solution. Unlike the sodium tungstate solution obtained from the scheelite concentrate, there is more molybdenum in sodium tungstate solution. The main work of this stage is to remove the molybdenum, can be selected by ion exchange or selective precipitation of tungsten and molybdenum separation. The sodium tungstate solution after molybdenum can be obtained by two times evaporation and crystallization, and can be converted into ammonium tungstate solution by ion exchange method, and then APT is prepared.

4. The above process can effectively deal with low grade and scheelite fine slime containing calcium and molybdenum. Some data show that the process of recycling scheelite fine slime from ore in Hunan, China, has a total recovery rate of 60-70%, and the effect is very good. Moreover, from the cost point of view, the majority of tungsten slime, according to WO3 measurement, the cost is only 60%-70% of the concentrate price. The recycle of tungsten slime is an effective way to reduce the cost of mining and prolong the mining life of the mine.

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