2020年4月8日星期三

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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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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