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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Acute Pancreatitis Detection Method of Phosphorus Magnesium Tungstate Precipitation Method

Hyperlipidemia is one of the causes of hyperlipidemic acute pancreatitis, at the same time, hyperlipidemia is also the manifestation of metabolic disorder of acute pancreatitis.

Patients with acute pancreatitis due to impaired pancreatic function, fat metabolism disorders, during the course of the disease, blood lipids rise dramatically, greatly increasing the amount of fat in the blood, the appearance of the patient's serum is extremely cloudy with milk, which is commonly referred to as severe chylous blood.

acute pancreatitis image

Chylous blood interferes with colorimetric and turbidimetric tests of biochemical tests, leading to the fact that patients with acute pancreatitis are not diagnosed in time. And acute pancreatitis is an acute abdomen, the condition is critical, and even severe shock or death, the clinical need to grasp the relevant inspection data, in order to timely diagnosis.

Some scholars believe that the phosphorus magnesium tungstate precipitation method can effectively get rid of chylemia interference on the detection of acute pancreatitis, chylemia contains glycerin three greases, the principle of magnesium phosphosilicate as precipitant to detect HDL-C is that the polyanion interacts with divalent metal ions, an insoluble complex with apolipoprotein B in serum. Therefore, magnesium phosphotungstate can selectively precipitate apolipoprotein containing apolipoprotein B, VLDL, low density lipoprotein and lipoprotein, high-density lipoprotein (HDL), which contains only apolipoprotein B in serum lipoproteins, can be detected individually.

Through comparative test, scholars believe that the detection results of phosphorus magnesium tungstate precipitation method is accurate, this acute pancreatitis test can effectively eliminate the severe chylous condition in the specimens of patients with acute pancreatitis, conducive to timely diagnosis and treatment of patients, biochemical and phosphorus magnesium tungstate precipitation method for the vast majority of interference will not occur. The method has the advantages of simple operation, quick operation, obvious precipitating effect, convenient reagent source, no special equipment and low cost, suitable for all hospitals in the laboratory, is the ideal specimens of HLAP specimens and other chyme specimens of biochemical testing pre-treatment methods.

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Scintillation Crystal Materials -- Cadmium Tungstate

Cadmium tungstate (CdWO4) single crystal is a scintillation detector with excellent scintillation properties.

Its X ray absorption coefficient is large, the luminous efficiency is high, the afterglow time is short, and the radiation damage resistance is strong. It has extremely important application value in the field of nuclear medicine, X-ray, CT and container detection.

Cadmium tungstate (CdWO4) single crystal belongs to the tungstenite structure (monoclinic), its melting point is 1289 °C, with excellent performance, high luminous efficiency and energy resolution. In the process of growth, the crystal is easy to crack because of the cleavage plane. In 1948, the optical properties of cadmium tungstate crystals were reported for the first time. In 1950, some scholars made the crystals by flame. They were yellow green, but they were of poor quality.

.cadmium tungstate single crystal image

With the development of the preparation technology, it is possible to prepare large size cadmium tungstate single crystals by the Czochralski process. However, the growth of high-quality single crystal cadmium tungstate is still difficult. The main problem is that the optical quality of each CdWO4 crystal is not uniform enough, the reproducibility of single crystal growth in different batches is poor. There are many kinds of crystal defects such as cracking, inclusion and color center, so there are few units for stable growth of cadmium tungstate single crystal at home and abroad. At present, large size cadmium tungstate crystals are mainly grown by Czochralski method and crucible method.

CdWO4 single crystals were grown by Czochralski method, and transparent and nearly colorless CdWO4 single crystals were successfully grown by optimizing the growth process. Through the analysis of SEM, light transmission and fluorescence properties, the results show that the crystal grown has good crystallinity, no macroscopic crystal defect, complete structure and transmittance of 70% in the visible region, the wavelength of the emission peak is in the blue region, but the main problems are as follows: melt volatilization, crystal cleavage along (010) cleavage plane, inclusion formation, crystal coloring, etc..

The crucible reduction method is based on high purity CdO and WO3, and CdWO4 polycrystalline material is synthesized by high temperature solid state reaction. The CdWO4 single crystal was grown by vertical crucible falling method. When the single crystal was grown, the furnace temperature was 1350 °C ~1400 °C, the solid-liquid interface temperature gradient was 30~40 °C /cm, and the crucible descending rate was 0.5 ~ 1.5 mm/h. Compared with the Czochralski method, the crucible method avoids the volatilization of the melt components during the crystal growth process and keeps the homogeneity of the melt composition, the stable temperature field is beneficial to reduce the crystal cracking. Therefore, the method of crucible growth with cadmium tungstate crystal is a process with application and development value.

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Scintillation Crystal Material -- Barium Tungstate

Barium tungstate is an important scintillation crystal material with excellent photoluminescence properties.

Barium tungstate has potential applications in the fields of nuclear spin hole, Raman scattering, solid-state laser and so on. As the core component of the vacuum electronic device, the cathode must have the characteristics of large emitting current, low operating temperature, low evaporation rate and long service life, barium tungstate is a raw material that takes into account the high current, low evapotranspiration, long life cathode.

barium tungstate crystal image

Raman frequency shift technique is a nonlinear optical technique for obtaining a new wavelength laser by using the stimulated Raman scattering effect of Raman medium, barium tungstate crystal is a promising Raman crystal. In recent years, all solid state Raman lasers based on stimulated Raman scattering (SRS) effects of crystalline materials have become an attractive luminescent spot, the laser output from ultraviolet to near infrared band can be obtained by barium tungstate crystal, these include yellow, orange, laser, and eye safe lasers for medical, radar, remote sensing and ocean exploration applications.

Compared with the commonly used barium nitrate, barium tungstate crystal has the characteristics of non deliquescence, wide transparence, excellent thermal mechanical properties, it is easier to obtain large-size single crystals by Czochralski method, moreover, both the nanosecond pulse and picosecond pulse laser pumped higher Raman gain. These advantages make barium tungstate crystals a very promising Raman laser crystal for practical all solid state Raman lasers.

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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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Green Catalytic Activity of Phosphotungstic Acid for Four Hydrogen Sulfide

Four hydrogen sulfide is a chemical intermediate of nitro spray paint, rubber and other solvents, so is often used in the protection of hydr...