Effect of Time on Ammonium Paratungstate Production
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- Category: Tungsten Information
- Published on Tuesday, 29 December 2015 17:47
Ammonium paratungstate (APT) is an important intermediate product of the production of tungsten metal powder. To ensure the quality of tungsten powder, the average particle size, particle size distribution and crystal morphology should also meet certain requirements while the APT chemical purity does. With the rapid development of modern science and technology, there’re more and more demands for different grain size and shape of tungsten powder production, and thus the requirements of raw material APT are also getting higher. For APT crystallization conditions, the scholars have carried out extensive exploration and discussion, but the overall reports are rare, and the results are not entirely consistent. In order to investigate the basic conditions of APT production, for the preparation of APT crystallization problems, this article attempts to make some analysis and discussion on theory and the process practice based on a number of experimental studies made recently and some views are put forward by reference.
Evaporation and crystallization including the heating time (heating rate) and the evaporation time (evaporation rate). When the heating time is quick, most of the free ammonia in solution were expelled in a short time, so that PH of the solution decreased rapidly, and the over-saturation increases, and a lot of nuclei was formed rapidly, the particle size became finer. Long evaporation time, it will help small crystals dissolve constantly, big crystals continue to grow. the situation of crystal growth becomes more apparent when APT crystalline precipitate for a while before filtered. It was also found in the conditions of a certain degree of vacuum, evaporation speed increases, the bulk density of the resulting APT reduces significantly.
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Effect of the Original Solution Purity on APT Crystallization
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- Category: Tungsten Information
- Published on Tuesday, 29 December 2015 17:42
Ammonium paratungstate (APT) is an important intermediate product of the production of tungsten metal powder. To ensure the quality of tungsten powder, the average particle size, particle size distribution and crystal morphology should also meet certain requirements while the APT chemical purity does. With the rapid development of modern science and technology, there’re more and more demands for different grain size and shape of tungsten powder production, and thus the requirements of raw material APT are also getting higher and higher.
For APT crystallization conditions, the scholars have carried out extensive exploration and discussion, but the overall reports are rare, and the results are not entirely consistent. In order to investigate the basic conditions of APT production, for the preparation of APT crystallization problems, this article attempts to make some analysis and discussion on theory and the process practice based on a number of experimental studies made recently and some views are put forward by reference.
When the impurities contained in ammonium tungstate solution is not too high, the influence on crystal grains is not obvious. test taking into account the normal production, the amount of ammonium chloride in ammonium tungstate solution prepared by ion exchange method was quite different from the one prepared by classic method.
When the impurities contained in ammonium tungstate solution is not too high, the influence on crystal grains is not obvious. test taking into account the normal production, the amount of ammonium chloride in ammonium tungstate solution prepared by ion exchange method was quite different from the one prepared by classic method.
Tests showed that the higher the content of ammonium chloride in the original solution(increased from 10g / L to 100g / L), the finer the particle size of APT (bulk density decreased from 2.1g /cm3 to 1.8g /cm3). The reason may be that there are other substances that have grain adsorption in the solution, but do not participate in the crystalline lattice forming other substances. Since this impurities are adsorbed to the crystal surface, covering the active region of the crystal surface, leaving the crystal growth rate slow, hindering obtain coarse crystalline particles, but beneficial for obtaining fine crystals.
It was also found that if there are solid impurities such as crystalline particles in solution, these particles play a central role in agglomerating to promote early nucleation generation. Different impurity content makes different products in crystal types and thickness. pure ammonium tungstate solution is easy to prepare regular polymorph and even coarse grain, and the physical properties of APT has better results in actual use.
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Tungsten Alloy Shielding Application in PETⅡ
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- Category: Tungsten Information
- Published on Tuesday, 29 December 2015 17:23
PET achieves the human imaging mainly by detecting the rays of radioactive substances. F-FDG is the most commonly used radiopharmaceutical in the PET scanning, the fluorine of its molecular chose the radioisotope fluorine-18 which belongs to the positron emission type. There are some other radioactive substances such as: carbon-11, nitrogen-13 and oxygen-15, etc., which is a type of a positron-emitting radioisotopes. The γ rays, which will irradiate when the radioactive elements and the organization collided, can be detected by PET.
There are many radioactive substances need to be shielded in a PET scanning, such as radiopharmaceutical shielding. The waiting room for people who has injected radiopharmaceutical, also need to shield. Tungsten alloy shielding in medical applications has been used very extensively, its high density, high radiation absorption capacity are also well known. Different types of tungsten alloy shielding can be applied to PET and can achieve the good radiation shielding effects.
For the radiopharmaceuticals, we can use tungsten alloy shielding containers to shield it, i.e., to seal the radiopharmaceuticals in a tungsten alloy shielding container. For the shielding of γ ray in PET scanning process, it’s dependent on adding the tungsten alloy materials into the ring-type detecting components of PET scanner, to absorb a lot of γ-rays, thereby to play a role in weakening rays. In short, the properties of high density and environmentally friendly make tungsten alloy to provide good shielding effects to the radioactive substances or medical equipment,which depends on using a number of radioactive substances to treat diseases, moreover, tungsten alloy shielding have no side effects.
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Cemented Carbide High-end Products
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- Category: Tungsten Information
- Published on Tuesday, 29 December 2015 17:06
With the development of technology and equipments of tungsten carbide, high-end tungsten carbide products are developing to different requirements of customers. The main application of tungsten carbide products are cutting tools, mining tools and some wear parts.
1. Cutting tool
Cutting tool is one of the most significant applications of tungsten carbide, due to its high hardness, high strength, thermal stability and high precision, which dominates the world market of cutting tool gradually. At present, coated tungsten carbide CNC blade, printed circuit board (PCB) micro drill and precision hole overall tungsten carbide tool are the most high-end products in the field. So far, coated tungsten carbide CNC has diverse coating layer meets different requirements, such as aluminum oxide (Al2O3), titanium nitride (TiN), Hf, Zr and some rare earth elements or ceramics powder; PCB micro drills and mills focus on the coated cutting tools with less than 0.3mm diameter; precision hole overall tungsten carbide tools orient to special use and deep processing products.
2. Mining tool
Tungsten carbide has a broad prospect in energy, minerals and offshore drilling. There are three types of high-end tungsten carbide products: one is mineral mining, such as mating buttons for rock drilling; and ultra fine grain tungsten carbide drill bit for offshore drilling and deep well drilling; another one is suitable for complicate stratum cutting and public facilities construction. In a word, high-end tungsten carbide product for mining tools tends to ultra coarse grain and new structure.
3. Wear part
Some mold manufacturing industries requires high hardness, high toughness and excellent electrochemical corrosion resistance, using tungsten carbide will has better precision, strength and suitable for sealing ring bushing or wire drawing die, etc.
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Tungsten Alloy Shielding Application in PETⅠ
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- Category: Tungsten Information
- Published on Tuesday, 29 December 2015 16:29
PET namely positron emission tomography, it is one way of nuclear medicine, which is to utilize a variety of the medical imaging methods for diagnosis and treatment of patients, it is also another functional brain imaging tomography technique since the CT technology appeared. Nuclear medicine techniques typically include: PET, single photon emission computer scanning technique, cardiovascular imaging and bone scans.
In a PET scanning, the patient will be injected a radioactive substance, and then lying on the platform through an annular structure (as shown in the following pic.). This structure, which contains γ-ray detector array, has a series of scintillation crystals, which connected with the photomultiplier tubes(PMT) one by one above the X-ray machine platform. These crystals will convert the γ-rays emitted from the patients into the photons, then the PMT will convert these photons and amplitude into an electric signal, which can be processed by the computer. This process can form a three-dimensional image of the human body after repeated.
It’s well known that the γ-ray has a strong penetrating power, so when exposed to γ-ray, the radiation will enter the bodies interior, and then occurs the ionization with the cells in vivo. The ions generated by ionization will erode the complex organic molecules such as proteins, nucleic acids and enzymes, which are the main components to constitute the living cells and tissues. Once they are damaged, it will lead to the interference of the normal chemical processes in the human bodies, if severely, it will make the cells dead. The tungsten alloy shielding can be applied to PET to weaken the ray intensity, thus weakening radiation, and ensure the doctors and patients’ safety.
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Tungsten Alloy Shielding Application in X-ray MachineⅡ
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- Category: Tungsten Information
- Published on Tuesday, 29 December 2015 16:26
Since X-ray is just a form of ionizing radiation, when the atoms were irradiated with the ordinary light, it does not have a significant impact on the atoms. But when the atoms were irradiated with X-ray photon, it causes the electrons detached from the atoms and form a plasma and a charged particle. The free electrons then collide with other atoms, it creates more ions, the charge from these ions will destroy the DNA chains of cells, leading to cell mutation or cell death.
In the past, many doctors had no conscious to be exposed themselves and their patients to X-rays for a long time, and leading them to suffer from the radiation sickness. Hereafter, the medical community began to recognize this error gradually, and have taken many relative measures to shield the unwanted radiation.
The early shielding, wrapped around the X-ray machine is mainly lead, the shielding effectiveness of lead can’t be denied, but its toxic properties, limited its applications afterwards. With the development of other resources, tungsten, which density is higher than lead and has non-toxic environmental protection properties, as a new material naturally replaced the lead and became the suitable material for shielding producing. The shielding made of tungsten alloy has a high melting point, high temperature, which can resist a large heat generated by X-rays in its generating process. In addition to being used for shielding the radiation of X-ray machines , tungsten alloy shielding can also well reduce the X-ray, which is to prevent it emitted from all directions of the machine, so that the X-rays can only go along with a particular direction, and go through the filtration device then after projected onto the patient. Most importantly, tungsten alloy has a very strong radiation absorption capacity, therefore the tungsten alloy materials are the most suitable for producing X-ray machines shielding. The X-ray machine filtration device can also be made of tungsten alloy material with considered and suitable thickness. It can not only absorb the strong radiation but also diagnose the patient's condition without influences.
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Tungsten Alloy Shielding Application in X-ray MachineⅠ
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- Category: Tungsten Information
- Published on Tuesday, 29 December 2015 16:24
X-ray machine is a device to generate X-rays, and mainly to be used in the medical field for diagnosis, chest X-ray, gastrointestinal diseases checking and so on. X-rays were discovered by German physicist called Wilhelm Röntgen, on the whole, X-rays are the same thing with the visible light. There are three ways to generate X-rays: bremsstrahlung, electron capture and internal conversion. The greater radiation would be caused by X-ray machine, over time, it will cause inevitable damage in humans’ bodies and even lead to cancer. However, if installed with tungsten alloy shielding in X-ray machines, it may be greatly shield the radiation, and weakened the X-ray radiation intensity.
X-ray machine is mainly composed of X-ray tube, X-ray machine power, control circuits and other components, and the X-ray tube is composed of the cathode filament, the anode target and a vacuum glass tube. The core of X-ray machine is the cathode filament and the anode target, they locate in the same vacuum glass tube. The machine can transport the current through the cathode filament and then the filament will be heated , after that, the heat will sputter out the electron of filament surface. As can be seen from the following diagram of X-ray machine working illustration, in addition to the vacuum tube, the cathode filament and the anode target, it is also composed of oil grooves, the shielding, engines and filtration device. The anode of X-ray machine is a roulette, which is made of tungsten, can absorb the electron over from the vacuum tubes. The rotating engine, next to the anode, is mainly used to prevent the melting problem caused by the high heat of violent crashing in the X-ray generation process. The vacuum tube surrounding the cooling oil can also absorb some heats.
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Soda Thermal Decomposition Scheelite to Produce Sodium Tungstate
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- Category: Tungsten Information
- Published on Tuesday, 29 December 2015 09:04
More than 20 kinds of tungsten minerals have been discovered in the nature. But wolframite and scheelite have the value of industrial research. Scheelite is the main raw material of tungsten smelting. The traditional industrial production technology of disposing scheelite requires a high alkaline, high temperature and high pressure leaching technology to achieve a better decomposition rate. At the same time the leachate contains a lot of alkali salts and the impurity ions. So a large amount of industrial waste water containing salt was produced. Therefore, it is imperative to improve the existing production process.
This article introduced a novel process to separate tungsten from gangue material to produce sodium tungstate with high purity, in which the sheelite was used as feed and the flowsheet was dry ball milling activation一roasting一high temperature smelting with slag former adding. The main research work included directly high temperature smelting and ball milling activation一roasting一high temperature smelting. The experimental methods can be divided into three steps in total:
1.The experiment to decompose scheelite by soda through directly high temperature sintering process. The result showed that the decomposition ratio of scheelite was extermely lirnited(all＜60%), even under the conditions when the temperature was higher than 900℃，the addition amount of alkali was 1.0~2.0 times of theory stiochemistry consumption, the reaction time was extend to 180 minutes and the weight percent of additives to the raw material was more than 10%. This result was in accord with theoretical analysis. It proved the process was infeasible. TG-DSC analysis demonstrated that the optimum temperature range for scheelite decomposition was 590℃-850℃.Given comprehensive consideration, the reaction temperature of decomposition should be under 865℃.And the temperature of smelting should be greater than1000℃.Thus, it is necessary to make decompose reaction process and sintering operation separately.
2. The research of soda roasting of sheelite. The results showed that under the conditions: roasting temperature was 595℃,reaction time was 2 hour, alkali additive amount was 2.3 times of theory stiochemistry consumption, the sheelite decomposition ratio reached 93.79%. Adding quartz had a negative effect on decomposition.
3. The high temperature smelting. Without adding of slag formers, the smelting results showed that the separation of sodium tungstate and slag was very difficult only by increasing smelting temperature(from 1100℃to1500℃). With adding of slag formers, the results showed that the decrease of Ca0 ratio in slag former and the increase of temperature could improve the property of slag and effectively separate slag and sodium tungstate. The addition of sodium floride can not obviously improve the srnelting property.
Melting temperature of scheelite decomposition Melting time of scheelite decomposition
In conclusion, the process of dry ball milling activation一roasting一high temperature smelting with slag former adding, not only effectively decompose scheelite (the decomposition ratio was above 98%), but also produce sodium tungstate with high purity through effective separation of tungsten from gangue. T'he purity of sodium tungstate (include sodium molybdate) was above 94%. Molybdenum cannot be separated from tungsten in decomposition and smelting. The residue can be reused for roasting and smelting.
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Sodium Tungstate Application
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- Category: Tungsten Information
- Published on Tuesday, 29 December 2015 09:01
Sodium tungstate is also called sodium tungstate dehydrate. The property of sodium tungstate is colorless crystal or white crystal orthorhombic system. It has the gloss of flaky crystal or crystalline powder. Melting point is 698 ℃ and relative density is 3.25. it effloresces in dry air and loses the crystal water by heating to 100 ℃.Sodium tungstate is soluble in water and aqueous solution is slightly alkaline. But it isn’t insoluble in ethanol and is slightly soluble in ammonia.
Sodium tungstate crystal powder
How to get sodium tungstate? At first, tungsten trioxide reacts with sodium hydroxide or tungsten concentrate boils with sodium hydroxide. Thus sodium tungstate solution can be produced. Then separate impurity components through a series of process, such as purification, filtration, ion exchange and so on. Finally, sodium tungstate products can be got by evaporation and crystallization.
Sodium tungstate has wide uses and the very important industrial application value. It can be mainly summarized as the following points:
1. It is used for analysis reagent, catalyst and water treatment agent.
2. It is used in the manufacture of metal tungsten, tungsten acid and tungsten acid salts, such as phosphotungstic acid salt, boron tungstate and so on.
3. It is used in mordant, pigment, dyestuff, printing ink. Mordant is very useful in chemistry and biology. When dyeing of cells and tissues, it’s available to use cells, tissues and pigment combination drug solution. It can make the material dyed. The drug solution is the mordant. It also refers that dye is dyed to fabric material to reach the purpose of dye.
4. Weavers use it as fabric weighting agent. The mixture of sodium tungstate, ammonium sulfate and ammonium phosphate can be used for fiber fire prevention and waterproof. This kind of fiber can make fire retardant rayon and spun rayon. It can also be used for leather tanning.
5. It is used for plating anticorrosion. Plating can enhance the corrosion resistance and hardness of the metal plating. Wear and tear can be prevented. Electrical conductivity, smoothness and thermal stability can be improved. And surface is beautiful.
6. It is used as a cosolvent introduced porcelain glaze material to reduce the fever temperature and complement colors.
7. It is used in the oil industry and manufacture of aviation and aerospace materials.
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Sodium Tungstate Solution Eliminating Chromium Method
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- Category: Tungsten Information
- Published on Monday, 28 December 2015 19:56
For a long time, Chinese tungsten reserves, production, trade volume is ranking first in the world. In recent years, due to the rapid development of Chinese economy, China' own consumption also ranks the first in the world. Unfortunately, we pay more attention to a long-term exploitation of resources, but not enough attention to tungsten recovery and utilization due to technology, policy and other reasons. This resulted in a waste of resources and damage of the environment. Therefore, utilization of various tungsten resources is becoming urgent. People have done a lot of work on the comprehensive utilization of renewable resources of tungsten for many years. Currently, the rate of recycling waste tungsten has reached more than 20% in the consumption of our country. Sodium carbonate recycling waste tungsten smelting technology is more mature and be of wide applicability. And the annual recovery of sodium tungstate treatment was up to more than two thousand tons. But during leaching of sodium carbonate melting back waste tungsten, a large number of impurity elements also enter in the sodium tungstate solution. So the production of high purity tungsten cannot be met. So in order to effectively recover tungsten secondary resources, we should conduct impurity removal process, especially the removal of chromium.
There are two methods of eliminating chromium from sodium tungstate solution:
1. The acidic solution reduction method
In acidic solution reduction, sodium sulfite, ferrous sulfate are mainly as the reducing agent. the basic process is adjusting the solution to an acidic sodium tungstate. then adding the sodium sulfite and ferrous sulfate reducing agent. restore Cr6+ toCr3+.
2. The alkaline solution reduction method
In the reduction of alkaline solution, sodium sulfide, sodium hydrosulfide are mainly as the reducing agent. the basic process is adding sodium sulfide, sodium hydrosulfide to an alkaline chromium-containing material to realize Cr6 + reduction reaction and form Cr (OH) 3 precipitate.
This paper describes the use of sodium sulfide eliminating chromium process. it's also an alkaline solution of reduction process. Because eliminating molybdenum sulfide has been in part of the curing process of APT tungsten smelting production. so eliminating chromium can be carried out in the procee of molybdenum extraction simultaneously. But there's no vulcanization process. it will lead to Cr (OH) 3 subsequently curing liquid phase dissolved into the tone of acid acid which resulting in extraction, stripping phase difficulties. when it enters upon stripping (NH4) 2WO4 solution,it makes the APT chromium content exceeded. so it's necessary to increase the cvulcanization processing in the part of the curing process on the basis of the original. in addition, in molybdenum sulfide production process, through adding 4 times the theoretical amount of sodium sulfide, controlling the reaction pH value of 8 to 9 and selecting the appropriate temperature and aging time, the better effect of eliminating chromium can be reached.
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