2022年5月27日星期五

Tungsten Ores Directly Produces Coarse-Grain Tungsten Carbide

At present, 50 to 60% of the world's tungsten is used for the manufacture of tungsten carbide. Among them, rock drills in mining tools, three-cone drills in oil extraction, and coarse-grain tungsten carbide used in the hobs of tunnel shield machines account for a considerable part of tungsten carbide.

coarse-grained tungsten carbide image

As the main product of tungsten resource consumption, tungsten carbide can be used as the raw material to synthesize tungsten carbide directly. The tungsten carbide particles can greatly shorten the smelting process, and the ultra coarse grain tungsten carbide particles are widely used in mine rock drilling tools, which have higher added value than the general tungsten carbide.

Some scholars have proposed a method for preparing coarse grained tungsten carbide directly from tungsten ores. The main process is as follows:

Synthetic scheelite was synthesized from pure sodium tungstate and calcium chloride. Spare after drying.

According to the mass ratio of 33:43:8:9:7 to weighing artificial scheelite, reduced iron powder, graphite powder, alumina and silica, the vacuum induction furnace is placed in the vacuum induction furnace, the vacuum degree is less than 10Pa, the 30min is heated to 1600 ℃, and the heating is kept for 1 hours. After natural cooling, the crucible is removed from the induction furnace.

The slag phase and the metal phase are removed from the crucible, then the two phases are separated and the metal phase is removed. The 1:1 hydrochloric acid is added until the metal phase is completely dissolved, and the tungsten carbide is enriched at the bottom of the container.

The WC powder was separated from the solution, washed with water, and then concentrated with hydrochloric acid to remove impurities. After repeated washing, the purified tungsten carbide powder was obtained after drying.

The new method is made of tungsten ore as the main raw material, which is accomplished by reduction of carbonization at high temperature. The molten iron is melted and formed into a metal molten pool. Tungsten enters the molten iron and forms tungsten carbide with its carbon (tungsten is reduced to form tungsten carbide; raw carbon is used as reducing agent to reduce the oxide of tungsten, and tungsten carbide is formed with tungsten). The calcium in the ore will form slag with raw material alumina and raw material silica, and the impurity enters into the slag phase. After rinsing after acid leaching, the coarse grain tungsten carbide particles from several microns to several hundred microns can be obtained. It has low impurity content, complete crystalline form and complete carbonization. It can be used in the production of hard alloy and has great competitive potential.

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Bismuth Tungstate Photocatalysis for Marine Oil Sewage

With the development of shipping industry, marine and river water pollution caused by ships is becoming more and more serious. Some researchers have proposed a scheme of photocatalytic treatment of ship oil sewage by pre separation + fine filtration + deep oxidation.

bismuth tungstate photocatalysis for marine oil sewage image

(1) The oil sewage from the upper part of the tank is pumped into the direction of the upper entrance of the pool in tangential direction, forming a rotating flow, which is divided into a cylindrical type. Under the action of the centrifugal force of water, the oil particles with relatively small relative density converge to the central part of the pool and float up, so that the coarse oil particles are separated out in advance.

(2) Through the pre separated oily sewage into the fine filter, the fine filter is in turn from top to bottom, including overflow trough, filter material partition board, biomass filter layer, filter material bearing layer, filter material separator with pore size less than biomass filter material, filter material bearing layer is made up of gravel layer, so that raw material filter material is fixed on filter material separator and filter. Between the bearing layer, the pre separated oily sewage is brought to the overflow slot, and then the filter material is removed, the biomass filter layer and the filter material bearing layer are passed in order to realize the filtration and removal of the fine oil particles.

(3) The oily sewage is filtered into the deep oxidation unit and the deep oxidation unit is coated with bismuth tungstate photocatalyst. When the ozone is attached to small oil particles and emulsified oil particles with micro bubbles, the air flotation oxidation pool is entered with the flow of water. The floating of oil particles is realized through the buoyancy effect of ozone bubbles, and the oil particles are initially oxidized and degraded at the same time. The light ceramsite with the visible light catalyst of bismuth tungstate floating on the surface of the water, and the light source is irradiated. The energy transition produces a strong oxidizing free radical in the water, and further catalyzes the oxidation degradation of the floating oil particles. The flotation, ozone oxidation and photocatalytic oxidation are carried out in the flotation cell to achieve the separation and degradation of the remaining small oil particles and emulsified oil particles and sewage.

The three stage treatment process of "pre separation + fine filtration + deep oxidation" of marine oil sewage can simultaneously complete the separation and deep degradation of oil in oily sewage. It has the advantages of good separation effect, high purification efficiency, low labor cost and convenient operation.

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The Algae Pollution Treatment by Bismuth Tungstate Porous Material

A large number of domestic sewage and industrial waste water are discharged into rivers and lakes, resulting in eutrophication of water bodies, affecting the safety of water and living environment. The algae outbreak will cause the oxygen depletion in the water to lead to the death of the fish. The toxins released by some algae will poison the organisms. We should deal with the algae pollution quickly and effectively. It is an urgent need to control the water pollution.

algae pollution treatment by bismuth tungstate porous material image

At present, algae removal in water is often done by manual removal, and the treatment efficiency is low. Researchers have developed a new method for purifying algae: magnetic nanomaterials using solid phase, montmorillonite with porous materials as adsorbents, non-toxic and harmless adsorbents, adsorbents for algal porous materials and bismuth tungstate, a photochemical agent used to degrade algae and algae toxins. The method of scheme preparation is as follows:

(1) First, the adsorbents are evenly dispersed in water and then placed in a water bath reaction tank, through nitrogen protection, and then FeCl3•6H2O and FeCl2•4H2O are put into the water bath reaction tank with the molar ratio of 2:1. The mass ratio of adsorbents to magnetic nanomaterials is controlled in 1:0.4-1.4, and the temperature of water bath is controlled at 60°C -90°C. After mixing 15-30min, the ammonia water with a mass fraction of 30% was added, the pH value of the solution was controlled to 11-13, and the reaction for 2-4h was continued, and the unassembled magnetic nanomaterials and adsorbents were removed.

(2) The compound magnetic adsorbent is prepared with the adsorbent. The compound magnetic adsorbent and the bismuth tungstate photocatalyst precursor are added to the hydrothermal reactor. The mass ratio of the compound magnetic adsorbent and the bismuth tungstate is controlled in the 1:3, the hydrothermal method is at 160 -220°C, and the reaction is 10-24h. The magnetic adsorbent was loaded with light catalyst, and then cooled to room temperature after the reaction was completed. After washing and magnetic separation, the magnetic adsorbent and bismuth tungstate photocatalyst were loaded on the magnetic nanomaterials, and the magnetic compound alga removal agent was obtained by drying the adsorbent and the bismuth tungstate photocatalyst at 60-80°C.

(3) The magnetic compound algae removal agent is added to the eutrophic water containing algae according to the dosage of 0.8- 1.5g/L, stirring for 1-10 minutes, leaving the algae flocculant out for 5-10 minutes, and using magnets to remove the algae flocculant out of the water. The quality of the magnetic compound algae removal agent is better than that made of the algae, and the algae removal agent can adsorb and flocculate the algae and water. Pollutants such as nitrogen and phosphorus, improve the transparency of water, and purify the water quality.

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It Can Change Color? Unveil the Hidden Properties of Tungsten Oxide

At present, the market of electrochromic technology is quite extensive. Most of the electrochromic glass windows are made by applying translucent indium tin or fluoride tin oxide film to two pieces of glass to obtain electrical conductivity, and then apply electrochromic tungsten oxide to one of the glass, and then glue two pieces of glass together with a kind of glue like electrolyte.

electrochromism image

Electrochromic materials are divided into inorganic materials and organic materials. Inorganic materials can be divided into metal oxides and covalent metal complexes. The representative material of metal oxide is tungsten trioxide (WO3). The principle of discoloration is mainly that the energy of the inorganic material falls within the energy range of the visible light region, so when the valence of metal oxide changes, it can just cover the visible light area, reflect the color we see in the naked eye, and some special tungsten oxide derivatives. The compounds even possess bipolar characteristics of redox. In addition to tungsten oxide, the common covalent metal malocclusion is Prussian blue (Prussian Blue), and its principle is that absorption energy under different valence changes the absorption spectrum of the material itself.

The hidden function of tungsten oxide is expected to be applied in the field of new energy batteries. Recently, a high capacity and fast charge electrochromic battery has been developed. The battery is positive and negative with tungsten oxide (W18O49) nanowires and metal aluminum. It can establish an interface with users to identify the capacity by color change. When the state is transparent, the quantity of electricity is full, and the color gradually turns blue to mark the consumption of storage electricity, and the electricity is exhausted when the color is the deepest. The pool can be quickly charged by adding a trace of hydrogen peroxide, or using an external power supply to recharge and use the oxygen in the air to self - charge. The battery is more than 6 times as high as the same battery. This technology can change and improve the details and quality of life around us.

Electrochromic battery is a new type of battery which combines battery technology and electrochromic technology. It has unique color change characteristics. It can show the capacity of battery by the difference of its own color. A kind of interface is established between the user and the battery. However, electrochromic cells are facing many challenges at the present stage, and their capacity, charging time and cyclic stability are not ideal, but there is no doubt that electrochromic cells have an unlimited market potential.

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2022年4月27日星期三

Preparation of Nano Tungsten Trioxide Gas Sensing Film by Gas Phase Method

Nano tungsten trioxide is a typical N-type semiconductor gas sensing material, it has a large surface area, stable chemical properties, a wide band gap, a variety of toxic gases have good sensitivity, can effectively improve gas sensor sensitivity and response speed, is a good gas-sensitive film material.

tungsten trioxide gas sensitive film image

The preparation and synthesis of nano tungsten trioxide thin film by gas phase method is mainly to convert the synthesized tungsten trioxide crystal into the state of gas phase of tungsten trioxide through steps of sublimation, evaporation and decomposition. By setting the experimental conditions, the tungsten trioxide is transformed into tungsten trioxide saturated vapor. Finally, as the temperature decreases, saturated steam will crystallize in cold to grow as nanostructured tungsten trioxide crystals.

The preparation of nano tungsten trioxide gas-sensitive film gas method includes two kinds of chemical and physical methods.

Chemical vapor deposition (CVD) principle is the use of gas raw materials in the gas phase to form a chemical reaction and after two stages of nucleation and growth of the final preparation of the desired products (such as films, particles, whiskers). The use of chemical vapor deposition is also a method of preparing WO3 films. W(CO)6 as raw material, heated to 60 ~ 100 ℃, generate steam, and then N2 carrier gas generated steam at 300cm3min-1 flow rate of loading, W(CO)6 in the reaction chamber decomposition, the WO3 deposition to the base. Chemical vapor deposition (CVD) has the characteristics of continuous process, controllable and high purity. At the same time, multi-functional composite films can be prepared continuously by this method.

Physical vapor deposition (PVD) includes many basic particle growth processes such as the nucleation of nanostructured tungsten trioxide particles and the growth and aggregation of WO3 nucleus. The method of completing the particle transfer and transferring the basic unit to a specific location through a basic physical process is called a physical vapor deposition method. The typical method is vacuum evaporation, the principle is under high vacuum or high purity inert atmosphere (Ar, He), the evaporation of material under vacuum heating, WO3 vapor condensation in an inert gas medium to form a thin film. In recent years, they have also developed electron beam evaporation, ion beam assisted evaporation technology.

Regardless of the chemical deposition method or the physical deposition method to prepare the tungsten trioxide film, the prepared film has the advantages of high purity, stable performance and even particle distribution, and is suitable for the preparation of low melting point and single component films, but the shortcomings are also obvious, that is, the high cost, the preparation conditions are strict, the process is complex, and it is not suitable for large area preparation.

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Preparation of Tungsten Trioxide Thin Films by Sol - Gel Method

Sol gel method is widely used abroad, a kind of nano material preparation method, its principle is the prepared precursor (such as inorganic salt or metal alkoxide) dissolved in small molecule solvent in solution by mixing made uniform, solute and solvent hydrolysis reaction, hydrolysis condensation the reaction of nano particles and the formation of integrated sol.

tungsten trioxide film image

On the basis of the prepared sol, different processes can be used to prepare nano thin films and ultrafine powders with different properties. There are several ways to prepare tungsten trioxide thin films by sol-gel method: 1. Tungstic acid hydrochloric acid method; 2. Tungsten powder peroxide polytungstic acid method; 3. Tungstic acid colloid solution is prepared by ion exchange; 4. Polymer method.

The traditional sol-gel method mostly controls the particle size of powders by controlling pH value, temperature and adding surfactants. Recently, some scholars have successfully controlled the particle size of WO3 powders by increasing the viscosity of the reaction medium. After aging, filtration, drying and crystallization at 60 ℃, WO3 between 20 and 30 nm was obtained. Compared with the traditional gel method, CMC increased the viscosity of the hydrolyzate and inhibited the growth of colloidal particles , so using this method can be made of small size nanoparticles.

The sol-gel method has the advantages of low reaction temperature, easy control of product composition, smaller particle size, narrow and uniform particle size distribution and high purity of powder. At the same time, there are also many problems, such as the price of raw materials more expensive, the product is easy to agglomerate in the drying process, the synthesis period is very long, so time is money in the moment, even if the gas sensing properties of tungsten oxide films prepared by the sol-gel method is excellent, but the cost is difficult to control, so it is difficult to scale production.

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Preparation of Nano Tungsten Trioxide Thin Films by Electrodeposition

Nano tungsten trioxide is an excellent N-type semiconductor gas sensor, compared with the traditional materials, nano-tungsten trioxide gas sensor, high sensitivity, faster response speed and faster recovery is the most studied in recent years gas sensitive raw materials.


tungsten trioxide electrodeposition method image

There are methods for the synthesis of nano tungsten oxide films or gas phase method and solid phase method, liquid phase method. Electrodeposition is a gas phase method for preparing nano tungsten trioxide thin film, it is in a certain electrolyte and operating conditions, the metal or alloy from the compound solution, non aqueous solution or molten salt electrochemical deposition.

The basic process of electrodeposition in preparing WO3 thin films is: first, dissolve the W powder in a certain proportion with H2O2, then remove the excess H2O2, get the electrolyte solution and deposit it naturally, then use Pt as the working electrode and the other as the counter electrode. The WO3 thin film can be obtained on the Pt electrode by the electrodeposition of the current. Some scholars have used this method to prepare WO3 films on the surface of Ti matrix. The basic process is as follows: first, add 2G tungsten powder to H2Oof 10 m L 30%, and then add 100mL distilled water and 30m L propanol after the exothermic reaction is finished, then get the electrolyte solution needed to prepare WO3 film. Using a saturated calomel electrode as the counter electrode at room temperature to 450 m V voltage electrolysis for 1 hours, the product repeatedly washed with distilled water and ethanol, and after appropriate heat treatment, you can get WO3 thin film on a substrate.

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Tungsten Trioxide Thin Films Prepared by Sputtering Method

Synthetic nano tungsten trioxide or thin film methods are usually gas phase method, solid phase method, liquid phase method. Sputtering method is a preparation of nano tungsten trioxide film gas phase preparation method.

tungsten trioxide thin films prepared by sputtering method image

The most widely used sputtering method is magnetron sputtering. Some foreign scholars use metal W as a target, and use a mixed gas of Ar and O2 to prepare a WO3 thin film which is more gas-sensitive to NOx by magnetron sputtering. In addition, there are scholars using DC magnetron sputtering device, the target is 99.95% W, in a vacuum degree of 2 × 10-6mbar reaction chamber, Ar (50%) - O2 (50%) the mixed gas is subjected to direct current radio frequency excitation and discharge to deposit the WO3 thinly on the substrate to obtain a WO3 thin film. The electrochromic properties are also studied.

Compared with other coating methods, the sputtering coating method has the following advantages: (1) Any substance can be spattered, especially high melting point, low vapor pressure element and compound. (2) The adhesion between the sputtering film and the substrate is good. High energy particles are deposited on the substrate for energy conversion, producing higher heat energy and enhancing the adhesion between the sputtering atom and the substrate. (3) The sputtering density is high, the pinholes are few, and the purity of the films is high, because there is no such phenomenon as the crucible pollution in the process of sputtering. (4) The thickness of the film is controllable and the reproducibility is good. In addition, a thin film with uniform thickness can be obtained on a large area by the sputtering coating.

In recent years, radio frequency sputtering and magnetron sputtering technology have made great progress in China, and have made some progress in improving sputtering speed and reducing substrate temperature. Sputtering method has also become the main method of preparation of nano tungsten trioxide film, but it needs to be explained that the equipment price of sputtering method is more expensive and the investment in the early stage is larger.

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2022年3月17日星期四

Submicron Tungsten Powder Manufacturing Process

Because the grain uniformity of hard alloy mainly depends on the particle size distribution of WC powder, the particle size distribution of WC powder is hereditary in tungsten powder. Therefore, the preparation technology of tungsten powder and tungsten carbide powder by submicron size and narrow size is very important. The key technical indexes of fine grain, submicron, ultrafine or nanocrystalline cemented carbide for WC powder are the purity, particle size and particle size distribution, and it is clearly stipulated that there is no type of type III coarse in WC powder.

submicron tungsten powder image

Some scholars have adopted the following technical schemes to prepare submicron tungsten powder or tungsten carbide powder, including the following steps:

(1) Ammonium paratungstate (APT) is pyrolyzed to ammonium metatungstate (AMT) and dissolved in ammonia solution or deionized water and filtered to obtain ammonium tungstate solution, or using ammonium paratungstate (APT) production line after ion exchange or crystallization liquid as raw material.

(2) In the ammonium tungstate solution, the dispersant solution and the dispersing agent are added simultaneously and stirred evenly.

(3) Spray drying equipment was used for rapid crystallization drying to obtain fine particle hollow thin-walled spherical ammonium tungstate crystals.

(4) In the presence of hydrogen, nitrogen, nitrogen hydrogen mixture or air, the precursor of tungsten oxide, yellow tungsten, blue tungsten or violet tungsten was pyrolyzed at 500~700°C.

(5) Reduction of submicron and narrow particle size distribution of tungsten powder by hydrogen gas.

(6) In situ forming submicron and narrow particle size tungsten carbide powders by carbon mixing, ball milling and carbonization.

The results show that the average particle size of tungsten powder and tungsten carbide powder prepared by these methods is submicron grade, and has a narrow size distribution range, and it is convenient to prepare the tungsten powder and tungsten carbide powder with the purity of 4N or 5N in submicron size distribution.

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Tungsten Oxide Nanorod Regulation Method

At present, the general method of preparing tungsten oxide is liquid phase method. In the process of preparing tungstic acid in liquid phase, the tungstic acid particles are automatically coalesced because of the unstable thermodynamics. In addition, the free water molecules on the surface of the particles form hydrogen bonds with the free hydroxyl groups, and then form a hydrogen chain with the water molecules on the surface of the adjacent particles to produce a bridging action.

tungsten oxide nanorod image

Some scholars have proposed a method of adjusting the length of tungsten oxide nanorod by oxygen, with a surface functionalized carbon nanotube with a diameter of 2-200 nm and a layer of 1-30 layers as the carrier, tungsten metal salt as the tungsten source, the addition of hydrochloric acid in the carbon nanorod glycol suspension and tungsten metal salt system, and the principle of making the weak acid with strong acid to make tungstate granules. It directly forms on the surface of the carbon nanotubes and grows along the surface of the carbon nanotubes to form tungstate / carbon nanotube rod like composites, which mainly include the following steps:

(1) The 1-50 mg diameter of 2-200 nm and 1-30 layers of carbon nanotubes were soaked in strong acid (one or several mixtures in HCl, nitric acid, sulfuric acid), refluxing, filtering, drying, and then being placed in 10-500 mL ethylene glycol at 100-140°C. The ultrasonic dispersion of 8-24h. A uniform carbon nanotube glycol suspension was obtained.

(2) Tungsten metal salt is completely dissolved in solvent (deionized water, ethylene glycol or mixture of both), and a tungsten metal salt solution with a concentration of 0.01-0.5 mol /L is obtained.

(3) The carbon nanoscale glycol suspension is added to the tungsten metal salt solution and is mixed uniformly under the action of mechanical stirring (constant temperature magnetic agitator or ultrasonic oscillator), in which the molar ratio of tungsten metal salt and carbon nanotube is 1:1-40:1, and then added to them (using micro injector, drip tube or hydrochloric acid atomization, etc. The concentration of 1-20 mL was 5-12 mol/L hydrochloric acid, and the pH value of the solution was adjusted to 1-5; 5-48h was reflued under the constant temperature oil bath at 80-140°C, then vacuum filtration, washing and drying were carried out. The drying temperature was 100-150°C, and the drying time was 3-24h, and the tungstate / carbon nanotube rod like complex was obtained.

(4) The composite is spread in the corundum reaction boat and together with the corundum reaction boat together with the horizontal quartz reaction tube in a tubular resistance furnace. When the sample is roasted, different proportions of oxygen and nitrogen are put into the horizontal quartz reaction tube, the flow rate is 30-500 mL/min, and the oxygen content is 0-100% and the heat treatment temperature is at the temperature. At 400-800°C, the heat treatment time is 0.5-12h. When cooled to room temperature, the tungsten oxide nanorods with a length of 20-800nm can be obtained.

With carbon nanotubes as a template, tungstic acid / carbon nanotube nanorods were prepared by liquid phase method. After that, the tungstate / carbon nanotube nanorods were placed in the high temperature reaction zone of the tube furnace. In the process of dehydration of tungstate precursor and conversion of tungsten oxide into the tungsten oxide, the oxidation atmosphere was entered to make the carbon nanotubes burning and generating two oxygen. With the disappearance of carbon nanotubes and the disappearance of the carbon nanotubes, the tungstic acid nanorods break, which interferes with the growth of tungsten oxide along the surface of the tube bundle of carbon nanotubes. Therefore, the preparation of the process is simple and it is easy to popularize.

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Tailings Recycle Wolframite Optimization Design

The wolframite is brittle and easy to smash and produce fine slime, and most of them have fine embedded granularity and more useful metal minerals. The gangue minerals are closely related to tungsten minerals, and the separation is difficult. Many fine grain tungsten can not be recycled. Then it forms tailings.

tailings recycle wolframite image

Some scholars have proposed a comprehensive mineral processing scheme for recycling wolframite from tailings, including the following steps:

(1) Centrifuge gravity separation and tail preconcentration, after the wolframite tailings are adjusted to pulp, the centrifugal concentrator is used to preconcentration and discarding tailings, and the concentrate and tailings of centrifugal gravity separation are obtained.

(2) The concentrate is floated by the first coarse second sweep process, and the flotation tailings and sulfide ore concentrate are obtained.

(3) Magnetic separation of flotation tailings by magnetic separation is carried out, and magnetic separation concentrate and magnetic separation tailings are obtained.

(4) The magnetic separation tailings were enriched by high gradient magnetic separation to obtain wolframite coarse concentrate and high gradient magnetic separation tailings.

(5) Gravity separation of high gradient magnetic separation concentrate was carried out by shaking table separation, and coarse grained tungsten concentrate and grit tailings were obtained.

(6) The floatation tailings were concentrated to 35% ~ 38%, and the flotation flowsheet was made by using coarse crude and fine second sweep.

(7) The wolframite concentrate from gravity separation and flotation to the wolframite concentrate II are combined into the final wolframite concentrate.

In accordance with the characteristics of the separation of coarse fine-grained wolframite, the process has been optimized by the process of "centrifugal enrichment throwing tail - sulphide flotation - magnetic separation iron removal - high gradient magnetic separation - shaking bed gravity separation - black tungsten flotation". The index of mineral separation. Compared with the conventional ore dressing method, the selected ore volume is less than 60% to 65%, and the selection grade is improved and the ore dressing cost is reduced. It is a kind of beneficiation method suitable for the high efficiency recovery of the wolframite from the tailings.

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High Purity Tungsten Reduction Technology

High purity tungsten, which means more than 99.995% of the purity of tungsten, is a key material for the formation of the diffusion barrier in the process of mass integrated circuit and PVD coating. High purity tungsten powder has become an indispensable raw material for the microelectronics industry.

high purity tungsten iamge

Some scholars have put forward the preparation method of high purity tungsten powder for scale integrated circuit, which aims to make the production of high purity tungsten powder with purity not less than 99.999%, and to ensure the controllability of the particle size and morphology of tungsten powder. The process is as follows:

(1) Using the industrial 0 grade ammonium parotungstate in GB/T10116-2007 as raw material, the three band rotary tube air furnace is calcined to form yellow tungsten. The temperature of the three zone is 550 + 5°C, 600 + 5°C, 600 + 5°C.  The concentration of yellow tungsten is dissolved in 10% ammonia water at 50-60°C, the initial concentration of solution is 200-300g/L, and the dissolution is about 4-8h, and then the ammonium tungstate solution is formed.

(2) 10μm and1μm polypropylene filters were selected for two stage filtration of Fe (OH)3, Ca (OH)2 and other insoluble substances in ammonium tungstate solution.

(3) The filtered ammonium tungstate solution is evaporated and crystallized at 90-120°C in the enamel reaction kettle. The stirring frequency is 50Hz~80Hz, and the crystal mother liquid density reaches 1.08-1.1g/cm3 and then stops the crystallization. At this time the crystallization rate is 60-70%.

(4) A centrifuge equipped with polypropylene filter is used to separate the wet ammonium metatungstate from the centrifuge, and ammonium metatungstate is cleaned by deionized water to the washing liquid to be transparent and then sent into the hot air circulation oven at 100~120°C for 18 ~ 24h, and the purified ammonium metatungstate after purification is obtained.

(5) The high pure ammonium metatungstate was reduced by a tube reduction furnace with high purity quartz as furnace tube. Hydrogen flux was 60-100L/min, hydrogen dew point was -60°C, reduction temperature was 800-900°C, reduction time 1.5-2h, and the loading thickness was 10-30mm.

The purity of high purity ammonium metatungstate and high purity tungsten powder after purification is detected. The total content of impurities is less than 10ppm, and the purity is more than 99.999%. It can meet the requirements of the large-scale integrated circuit and semiconductor chip packaging industry.

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2022年2月16日星期三

Ammonium Paratungstate Purification from Complex Scheelite Ore

Tungsten ore is mainly scheelite. The world's scheelite accounts for more than 2/3 of total, and China accounts for 72.1%. Some scholars have improved the method of using ammonium sulphate to decompose scheelite to prepare ammonium partrungstate.

ammonium paratungstate image

(1) Tungsten containing sulphuric acid and phosphorus mixed acid solution, wherein the concentration of tungsten trioxide is 25-150g/L, the concentration of phosphoric acid is 10 ~ 200g/L, and the concentration of sulphuric acid is 1.5 ~ 2.5mol/L.

(2) The obtained tungsten containing mixed solution of sulphuric acid and phosphoric acid was mixed with oil to extract the two phase volume ratio of oil phase: water phase = 3:1-1:3, and the loading organic phase was obtained.

(3) The obtained load organic phase was extracted by distilling water with volume ratio as oil phase: water phase = 3:1-10:1, and the stripping solution was obtained.

(4) Ammonia was added to the stripping solution to control the free ammonia in the solution at 1-2mol/L and the ammonium tungstate solution was obtained.

(5) Ammonium paratungstate was obtained from ammonium tungstate solution by conventional phosphorus removal and evaporation crystallization.

The improved method can be used as an extractant by increasing the acidity of the material and the alcohols with low concentration. Because the alcohol extractant is a weak neutral extractant, the extractants of iron, calcium, manganese, sulfate and phosphate are not extracted, so the high content of impurities can be processed. A high concentration of phosphotungstic acid solution is obtained by using water as a stripping agent, and then ammonia is added to avoid the problem that the organic phase emulsification can be easily caused by the direct contact between the alkaline reflux and the load organic phase in the traditional process, and the blank organic phase after the extraction of water can be directly extracted without the need of the recycling process of the organic phase. The organic phase after stripping does not have the problem of introducing impurities into the original liquid, the process is short, the manufacturing cost is low, the product yield is high, and the green is pollution-free, and it can be industrialized on a large scale.


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Tungsten Tin Ore Dressing Guide

Tungsten tin ore is a brittle mineral, which is extremely easy to be milled and polished during mineral processing, causing inconvenience to mineral processing.

tungsten tin ore dressing image

Some scholars have proposed a method of mineral processing for tungsten tin ores. The content of Sn in the mineral materials is 0.083 to 0.32% and the content of WO3 is 0.035 ~ 0.46%. The steps and the pharmaceutical system are as follows:

(1) The tungsten tin minerals are removed to some monomers and the jigging branch separation technology is used to separate the minerals into coarse heavy minerals and fine grain aggregates, and then the coarse and fine grain aggregate minerals are reselected.

(2) Coarse and heavy minerals are selected by spiral chute, and the coarse concentrate and spiral chute tailings are obtained, and the spiral chute coarse concentrate rocking bed is selected. The coarse tungsten and tin concentrate 1, the rocking bed middle mine 1 and the rocking tailings tailings 1 are obtained.

(3) The fine aggregate mineral is recycled by shaking table and coarse and fine process. Tungsten tin concentrate 2, rocking bed middling 2 and shaking table tailings 2 are obtained.

(4) The spiral chute tailings, the rocking bed middling 1 and the rocking bed tailings 1 and the shaking table middling 2 are combined to regrinding, and the tungsten tin coarse concentrate 3 is obtained.

(5) Tungsten tin coarse concentrate 1, tungsten tin coarse concentrate 2 and tungsten tin concentrate 3 are combined, the sulphuric acid solution of 1000 ~ 2000g/t with mass concentration of 5%, 100 ~ 300g/t of copper sulfate solution with mass concentration, 5% of Ding Ji xanthate solution of mass concentration 1% and 30 to 50g/t of 2# oil raw liquid are used to remove sulfide ore and obtain tungsten tin mixture.

(6) Tungsten tin mixed concentrate was selected under the condition of magnetic field strength 10000 ~ 13500Gs wet strong magnetic separation. Tungsten tin separation was selected under the condition of 8000 ~ 10000Gs wet strong magnetic separation, and tungsten concentrate and tin concentrate were obtained respectively.

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Tungsten Carbide Nitride Conversion Method

Compared with ordinary powder, WC nano powder has advantages of small particle size, large surface area and high reactive activity. It has remarkable advantages in chemical synthesis, fuel cell and other fields. Therefore, it is of great significance to study a method for preparing high-quality single phase tungsten carbide nano powders.

tungsten carbide nitride conversion method image

Some scholars have provided a method for preparing tungsten carbide nitride nanopowders based on nitride conversion method, including the following steps:

10mmol deionized AMT and 50mmol citric acid were dissolved in 100ml deionized water to get clarified mixed solution; complex reaction was carried out at 70°C for 5 hours; filtration and drying for 12 hours at 120°C, the precursor of tungsten oxide was obtained. The WO3 powder was obtained by calcining at 650°C for 3 hours.

The WO3 powder is placed in a tube furnace and nitrided through ammonia gas. The flow rate of ammonia is controlled at 3L/min, the temperature is 700°C, the heating rate is 2°C/min, and the heat preservation is 2 hours, and the W2N powder is obtained.

10 g of tungsten nitride powder is mixed with 0.62g carbon black, with ethanol as solvent and tungsten carbide ball as ball milling medium, mixed for 24 hours on roll ball mill, rotary evaporation drying, W2N/C mixed powder, W2N/C mixed powder in graphite crucible, and heated to 1100°C under the condition of pressure below 200Pa in carbon tube furnace. The WC nanopowders were obtained at 3°C and the average particle size was 120nm.

Using nitrides conversion method, not only is the raw material cheap and easy to be obtained, but also greatly reduces the synthesis temperature, reduces the cost and energy consumption of raw materials, and the preparation process is simple, practical, controllable and easy to realize scale production.

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Microwave Ball Milling Nano Tungsten Powder

Tungsten powder is the main raw material for the processing of powder metallurgy tungsten products and tungsten alloys. With the rapid development of the microelectronics industry, energy, aviation, machinery industry and other fields, the demand of ultrafine tungsten powder is increasing day by day.

microwave ball milling nano tungsten powder image

At present, the main process methods of nano tungsten powder include hydrogen reduction, sol-gel, high energy ball milling, freeze-drying, molten salt electrolysis, self propagating high temperature reduction and spray drying fluidized bed. In order to solve the problem of preparing ultrafine tungsten powder, scholars have provided a processing technology for nanometer tungsten powder.

(1) Ceramic ball mill can be put into a microwave oven by placing a metal powder, a 10-20 micron blue tungsten or yellow tungsten powder, a ceramic ball with a particle size of 0.5 millimeters and the ratio of deionized water to a ceramic ball mill in a proportion of 1:5.

(2) The motor and microwave oven that start the ceramic ball can make tungsten trioxide reduce to tungsten oxide at 500~700°C.

(3) At 700~900°C, tungsten oxide is reduced to tungsten powder. Reduction is often carried out in tubular electric furnace or rotary furnace.

(4) The tungsten based alloy oxide mixed powder was reduced and the tungsten carbon reduction method was used. The reduction temperature was higher than 1050°C, the atmosphere was hydrogen atmosphere and hydrogen, and the ultrafine tungsten based alloy powder less than 0.05μm was obtained.

The tungsten based alloy oxide was prepared by microwave mechanical ball milling, and then the tungsten based alloy oxide was reduced. The nanometer superfine tungsten based alloy powder was obtained. It not only greatly reduced the high temperature of nano oxide powder, but also successfully solved the serious pollution in dry ball milling and the easy agglomeration of the powder.

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2022年2月9日星期三

High Purity Phosphotungstic Acid Preparation

Heteropoly acid is one of the most active catalysts in acid catalytic reaction and redox reaction. Phosphotungstic acid H3PW12O40•nH2O is the most widely used in heteropoly acid. The purity of phosphotungstic acid directly affects the conversion rate of the catalytic system. Therefore, the preparation of high purity phosphotungstic acid is especially important.

high purity phosphotungstic acid image

Some scholars have proposed a purification method for phosphotungstic acid crystals.

(1) The crystal of industrial phosphotungstic acid is dissolved in water and the inorganic acid is added to the solution of phosphotungstic acid containing inorganic acid. The concentration of tungsten trioxide is 50-150g/L, and the volume molar concentration of the inorganic acid is 0.5 ~ 6mol/L.

(2) In the solution of phosphotungstic acid containing inorganic acids, the oil phase organic alcohol extractant was extracted with the volume concentration of 5-50%, and the volume ratio of the two phase was oil phase = 1:1-10:1, and the organic phase loaded with tungsten was obtained.

(3) The organic phase containing tungsten is extracted by distilling water with volume ratio as oil phase: water phase = 3:1-10:1, and the stripping solution is obtained.

(4) High purity phosphotungstic acid crystals can be obtained by heating evaporating crystals or spray drying, and the yield is more than 95.4%.

The new process is short, the preparation cost is low, the environment is not polluted, and it is easier for large-scale industrial production.

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Ammonium Paratungstate Purification from Complex Scheelite Ore

Tungsten ore is mainly scheelite. The world's scheelite accounts for more than 2/3 of total, and China accounts for 72.1%. Some scholars have improved the method of using ammonium sulphate to decompose scheelite to prepare ammonium partrungstate.

ammonium paratungstate image

(1) Tungsten containing sulphuric acid and phosphorus mixed acid solution, wherein the concentration of tungsten trioxide is 25-150g/L, the concentration of phosphoric acid is 10 ~ 200g/L, and the concentration of sulphuric acid is 1.5 ~ 2.5mol/L.

(2) The obtained tungsten containing mixed solution of sulphuric acid and phosphoric acid was mixed with oil to extract the two phase volume ratio of oil phase: water phase = 3:1-1:3, and the loading organic phase was obtained.

(3) The obtained load organic phase was extracted by distilling water with volume ratio as oil phase: water phase = 3:1-10:1, and the stripping solution was obtained.

(4) Ammonia was added to the stripping solution to control the free ammonia in the solution at 1-2mol/L and the ammonium tungstate solution was obtained.

(5) Ammonium paratungstate was obtained from ammonium tungstate solution by conventional phosphorus removal and evaporation crystallization.

The improved method can be used as an extractant by increasing the acidity of the material and the alcohols with low concentration. Because the alcohol extractant is a weak neutral extractant, the extractants of iron, calcium, manganese, sulfate and phosphate are not extracted, so the high content of impurities can be processed. A high concentration of phosphotungstic acid solution is obtained by using water as a stripping agent, and then ammonia is added to avoid the problem that the organic phase emulsification can be easily caused by the direct contact between the alkaline reflux and the load organic phase in the traditional process, and the blank organic phase after the extraction of water can be directly extracted without the need of the recycling process of the organic phase. The organic phase after stripping does not have the problem of introducing impurities into the original liquid, the process is short, the manufacturing cost is low, the product yield is high, and the green is pollution-free, and it can be industrialized on a large scale.

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Carbon Nanotube Supported Platinum Electrocatalysts Coated with Titanium Tungsten Oxide

Carbon supported platinum catalysts are regarded as ideal fuel cell catalysts. However, the interaction between the carbon carrier and platinum is weak, the carbon carrier is easy to corrode. The nano platinum particles can easily migrate on the surface of the carrier, grow up and even lose, which leads to the degradation of the catalyst activity, and eventually leads to the shorter service life of the fuel cell.

titanium tungsten oxide image

In view of the disadvantages of poor stability and activity of existing fuel cell cathode catalysts, some scholars have used sol-gel method to evenly coat titanium tungsten oxide on the surface of carbon nanotubes, and then heat treatment to form titanium tungsten with high crystallinity and high electrical conductivity. The oxide coating, and thus the platinum catalyst, its main process is as follows:

(1) 1 gram of carbon nanotubes, adding 160 ml of concentrated nitric acid, reheating for 3 hours, cooling, diluted by ultra pure water, filtering out the supernatant, centrifuging and washing, drying, and grinding the purified carbon nanotubes.

(2) The mass ratio of 1: 2.5: 1 was called the purification of carbon nanotubes, butyl titanate and sodium tungstate, respectively, according to the volume ratio of 1: 0.2: 0.008, ethanol, ammonia and hydrogen peroxide respectively, of which the concentration of ammonia water was 28%, the mass concentration of the hydrogen peroxide solution was 30%, and the carbon nanotubes were dispersed in the anhydrous ethanol, and the carbon nanotubes were added to the anhydrous ethanol. The dispersion of n-butyl titanate in carbon nanotubes was obtained by ultrasonic stirring for 40 minutes. Sodium tungstate was dissolved in the ammonia water and added to the hydrogen peroxide solution. The ultrasonic oscillation was 15 minutes, and sodium tungstate solution was obtained. The sodium tungstate solution was slowly dripped into the above carbon nanotube titanate dispersion solution. After stirring reaction for 48 hours, the drying was dried. The amorphous titanium tungsten oxide coated carbon nanotube was coated, and the amorphous titanium tungsten oxide coated carbon nanotube was calcined at 650 C in nitrogen or argon atmosphere for 2 hours, cooling to room temperature, washing two times and washing for two times, drying and grinding to obtain the titanium tungsten oxide coated carbon nanotube.

(3) The mass ratio of 1: 1.1: 0.76: 10 was called titanium tungsten oxide coated carbon nanotubes, chloroplatinated acid, citric acid three sodium and sodium borohydride, and the obtained titanium tungsten oxide coated carbon nanotubes were dispersed in ethylene glycol, and ultrasonic stirring for 40 minutes, forming a mass concentration of 3 mg / ml of titanium tungsten oxide coated carbon nanotube dispersions. Then chloroplatin was slowly added to the titanium tungsten oxide coated carbon nanotube dispersions, stirring for 6 hours, and then adding sodium citrate three for 4 hours. Then the sodium hydroxide solution with mass concentration of 5% was adjusted to pH value to 9, and then slowly added to sodium borohydride and stirring for 4 hours, and then centrifuged, washed, washed, vacuum and vacuum. Titanium and tungsten oxide coated carbon nanotube supported platinum electrocatalysts were obtained by drying and grinding.

Titanium tungsten oxide coated carbon nanotube platinum electrocatalysts can be applied to fuel cells with proton exchange membranes as electrolytes, such as hydrogen oxygen proton exchange membrane fuel cells, direct methanol fuel cells and other gas electrodes. It can also be used in various spacecrafts, portable electronic devices, such as cameras, notebook computers, electric toys, etc.

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Tungsten Ores Directly Produces Coarse-Grain Tungsten Carbide

At present, 50 to 60% of the world's tungsten is used for the manufacture of tungsten carbide. Among them, rock drills in mining tools, ...