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.

If you have any inquiry of tungsten, please feel free to contact us:
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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.


If you have any inquiry of tungsten, please feel free to contact us:
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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.

If you have any inquiry of tungsten, please feel free to contact us:
Tel.: +86 592 5129696/+86 592 5129595
Fax: +86 592 5129797

Scan QR code of Chinatungsten Wechat platform to follow up the daily latest price and market of tungsten, molybdenum and rare earth.