72 results about "Thermite" patented technology

A layered thermite composite includes alternating layers of metal oxide and reducing metal deposited upon a substrate. A fuzzy interface layer between each metal oxide layer and reducing metal layer includes reducing metal, reducing metal oxide, and metal oxide at least partially intermixed therein. The fuzzy interface layer forms while moving between chambers in a multi-chamber deposition process which minimizes exposure of the reducing metal to oxygen while moving between chambers. The fuzzy interface layer is not expected to grow in thickness after deposition. The combination of the relative thinness of the fuzzy interface layer as well as the presence of reactants as well as reducing metal oxide maintains the sensitivity of the layered thermit structure to mechanical ignition if the structure is used within a primer.

The invention relates to the technical field of thermite, in particular to a thermite system of an ultralow condensed phase combustion product and a preparation method of the thermite system. The preparation method of the aluminothermic system comprises the following steps: S1, synthesizing nanoscale BiF3 particles; s2, immersing a mixed oxidizing agent into a copper nitrate solution, dropwise adding ammonia water into a system, reacting for a period of time, standing and aging the reaction system, performing centrifugal separation, washing, and performing vacuum freeze drying to obtain BiF3-coated TACN core-shell structure particles; and S3, adding the acid-activated nano aluminum powder and the BiF3-coated TACN core-shell structure particles into an n-hexane medium, carrying out ultrasonic treatment, and drying to obtain thermite powder. Through the high reaction interface of the nano-scale bismuth-based fluoride and the activation strategy of the high-energy gas production compound on the interface, the output of ultralow condensed phase combustion products and the efficient release of system energy are realized.

The invention provides a preparation method of a thermite, which comprises the following steps: taking CuN (CN) 2 and aluminum powder as raw materials, adding an organic solvent, mixing, and carrying out vacuum drying to obtain the thermite, the mass ratio of the CuN (CN) 2 to the aluminum powder is (1: 1)-(1: 4). According to the method for preparing the thermite through CuN (CN) 2, a new thought for applying other oxides to an energetic material of the thermite is provided, the thermite can provide the heat of 1528.9 J / g and the gas production pressure of 50 KPa, and it is detected that a high-temperature-resistant material aluminum nitride is generated in a product obtained after combustion.

The invention provides a gas phase change rock breaking device and method based on an aluminothermic reaction, and belongs to the technical field of rock blasting. The rock breaking device comprises a graphite excitation pipe, a liquefied air bag and a sealing cover, the excitation pipe is filled with thermite, and thermite reaction can be carried out to release heat; the liquefied air bag is hermetically sleeved outside the excitation tube, is filled with liquid oxygen or liquid nitrogen and is changed into gas under the action of heat released by the excitation tube, and rock mass fracture is realized by volume expansion. By arranging a multi-section excitation pipe serial connection structure, adopting the industrial graphite excitation pipe, designing a liquid oxygen or liquid nitrogen double-medium system and using the polyethylene degradable material bag body, the safety, the economical efficiency and the environmental adaptability of open-air rock mining are remarkably improved.

The invention discloses a fluoride modified liquid metal medium thermite and a preparation method thereof, and belongs to the technical field of thermite preparation. Liquid metal is prepared by using Gallinstan eutectic; the method comprises the following steps: synthesizing aluminum powder and liquid metal by adopting a physical mixing and ultrasonic treatment method to obtain liquid metal modified aluminum; the preparation method comprises the following steps: adding FeCl3. 6H2O into a perfluorooctanoic acid aqueous solution, stirring and mixing, carrying out hydrothermal reaction, and washing the obtained product to obtain Fe (PFO) 3; the method comprises the following steps: mixing liquid metal modified aluminum with iron perfluorooctanoate, and carrying out ultrasonic treatment to obtain Fe (PFO) 3-coated LM-Al; fe (PFO) 3 (at) LM-Al and ferric oxide are added into absolute ethyl alcohol for ultrasonic stirring and mixing, and Fe (PFO) 3 (at) LM-Al (at) Fe2O3 is prepared. By the adoption of the method, the high-temperature thermal oxidation reaction temperature of the aluminum powder is increased to be before the melting point of 660 DEG C, and the breakthrough progress of the aluminum powder thermal mass transfer process is achieved.

The present invention provides a method for producing a molybdenum-vanadium-aluminum-chromium alloy with high uniformity. The composition of the molybdenum-vanadium-aluminum-chromium alloy is as follows: Mo 25% - 28%, V 24% - 27%, Cr 28% - 31%, with the balance being Al, O ≤ 0.05%, C ≤ 0.05%, and the segregation of the main content being < 0.6%. It relates to the field of metallurgical technology. The technological steps are as follows: (1) Prepare an ammonium molybdate-ammonium dichromate-ammonium metavanadate precursor by hydrothermal method using sodium molybdate, sodium metavanadate, sodium dichromate, and ammonium chloride; (2) Perform high-temperature treatment on the precursor to obtain a MoO3 / V2O5 / CrO3 composite material; (3) Mix the MoO3 / V2O5 / CrO3 composite material, refined aluminum powder, and calcium oxide in proportion, load them into a furnace and ignite to undergo a thermite reaction to obtain a molybdenum-vanadium-aluminum-chromium alloy ingot. Compared with the molybdenum-vanadium-aluminum-chromium alloy produced by the traditional thermite method, the uniformity of the present invention is greatly improved, and it can be used for the production of titanium alloys such as TB2, TB9, TB15, and TB16.

A layered thermite composite includes alternating layers of metal oxide and reducing metal deposited upon a substrate. A fuzzy interface layer between each metal oxide layer and reducing metal layer includes reducing metal, reducing metal oxide, and metal oxide at least partially intermixed therein. The fuzzy interface layer forms while moving between chambers in a multi-chamber deposition process which minimizes exposure of the reducing metal to oxygen while moving between chambers. The fuzzy interface layer is not expected to grow in thickness after deposition. The combination of the relative thinness of the fuzzy interface layer as well as the presence of reactants as well as reducing metal oxide maintains the sensitivity of the layered thermite structure to mechanical ignition if the structure is used within a primer.

The invention relates to a composite thermite for forcible entry and a preparation method thereof. The composite thermite comprises an aluminothermic reaction agent; a fluxing agent; a binder; and a strong oxidant. Wherein the thermit reaction agent is mixed powder composed of fuel metal particles and metal oxide particles, and the surfaces of the fuel metal particles are subjected to coating modification treatment through a fluorine-containing polymer; in the composite thermite, the mass ratio of the thermite reaction agent is 40%-75%, the mass ratio of the fluxing agent is 2%-10%, the mass ratio of the binder is 5%-20%, and the mass ratio of the strong oxidant is 5%-30%. The composite thermite disclosed by the invention is prepared into a blocky or columnar structure through a compression molding process or a curing molding process, is used for forcible entry of metal or non-metal obstacles, improves the forcible entry performance, is high in medicament environment adaptability and good in use effect, and can be produced on a large scale.

The perforating bullet comprises a perforating bullet body, an energy ring is arranged at the opening end of the perforating bullet body, the energy ring can conduct secondary burning and explosion on a perforation channel after the perforating bullet body is shot into the perforation channel, the energy ring comprises a shell made of fluoropolymer materials and a thermite filling layer, the shell is arranged in an annular shape, and the thermite filling layer is arranged in the shell. The shell is filled with the thermite filling layer, and the outer wall of the opening end of the perforating bullet body is sleeved with the shell. According to the utility model, the energy ring is arranged at the opening end of the perforating bullet body, so that during normal perforation, secondary detonation and energy release are carried out on the interior of a perforation channel, and the effects of increasing the volume of the channel, increasing cracks of the perforation channel and cleaning the channel are achieved.

The invention discloses a preparation method of low-gas high-purity chromium. The preparation method comprises the following steps: S1, preparing part of metal chromium by adopting an aluminothermic method, and crushing the metal chromium into powder with the particle size of 60-200 meshes; preparing the other part of metal chromium by adopting an electrolytic method, and crushing the metal chromium into powder with the particle size of 60-200 meshes; s2, the two parts of metal chromium powder and graphite powder are mixed and pressed into a round ingot of 30 mm * (18 + / -2) mm, the round ingot is loaded into a graphite crucible, and the graphite powder accounts for 0.5%-2% of the total mass of the round ingot; s3, the graphite crucible containing the round ingot is put into a vacuum furnace to be smelted; heating is started when the vacuum degree in the vacuum furnace is smaller than or equal to 5 Mpa, the temperature is increased to 1400-1600 DEG C and kept for 10-15 h, then cooling is conducted, when the temperature is reduced to 1200-1100 DEG C, hydrogen is charged into the vacuum furnace to 15-20 Pa, and pressure is kept for 1 h; and S4, after pressure maintaining is finished, the temperature is increased to 1400-1600 DEG C, heat preservation is carried out for 2 h, then cooling is carried out, and when the temperature is reduced to the room temperature, discharging is carried out.

The invention discloses a thermite formula for coating a ceramic layer in a steel pipe and a preparation method of the thermite formula, and relates to the technical field of steel pipe lining metal ceramic, the formula comprises aluminum powder, ferric oxide, silicon dioxide and oxygen, and further comprises copper oxide and diboron trioxide, the content of oxygen is smaller than the amount of oxygen consumed when the aluminum powder is completely oxidized, and the content of silicon dioxide is smaller than the amount of copper oxide consumed when the aluminum powder is completely oxidized. When the oxygen participating in the reaction is exhausted, aluminum which does not participate in the oxidation reaction exists. According to the invention, by adding the diboron trioxide and the copper oxide, a traditional metal ceramic lining steel pipe combined in a mechanical mode can be improved into a metal ceramic inner covering steel pipe combined in a brazing mode, so that the binding force of the inner covering layer and the base pipe is improved, and the surface flatness of the inner covering layer is improved so as to reduce the fluid conveying resistance; the metal ceramic internally-coated steel pipe manufactured through the formula and the specific implementation method has the advantages of being high in bonding force between the internally-coated layer and the base pipe, smooth in surface, resistant to high temperature and high pressure and resistant to corrosion.

A method for preparing an alumina hollow sphere thermal insulation material by using waste residues generated in chromium production relates to a comprehensive utilization method of smelting waste residues, and adopts a mode of replacing a furnace shell, chromium oxide is reduced into metal chromium liquid which is remained at the lower part of the furnace shell, and the upper layer is covered with alumina melt, so that the possibility that the metal chromium is oxidized due to contact with air is avoided; and the efficiency of refining the metal chromium from the aluminum-chromium slag is improved. According to the invention, the slag generated during the production of metal chromium by an aluminothermic method is converted into two products, namely an aluminum oxide hollow ball and a high-grade thermal insulation material; and the other is metal chromium. The two products are high in price, so that high-value utilization in comprehensive resource utilization of the waste aluminum-chromium slag is realized.

The present invention discloses a method for controlling the yield of vanadium-aluminum alloy, which specifically comprises the following steps: (1) using a copper crucible and a graphite furnace body as a thermite reaction vessel; (2) mixing flaky vanadium pentoxide, aluminum particles and a slag-forming agent uniformly and adding the mixture to the thermite reaction vessel; (3) placing the reaction vessel filled with the mixed raw materials in a cooling pool with circulating water and installing a furnace cover; (4) igniting a magnesium strip to initiate the thermite reaction; (5) removing the furnace cover and the furnace body 5 to 8 minutes after the thermite reaction ends; (6) stopping the cooling water supply when the alloy ingot cools to 950°C and installing a heat-insulating furnace cover on the copper crucible; (7) cooling the alloy ingot naturally for 24 to 48 hours, and finishing the alloy after cooling to obtain a vanadium-aluminum alloy product. The present invention can increase the yield of vanadium-aluminum alloy to more than 86%.

The invention provides a low-oxygen low-nitrogen aluminum-niobium intermediate alloy and a preparation method thereof, and belongs to the technical field of intermediate alloys. The preparation method of the low-oxygen low-nitrogen aluminum-niobium intermediate alloy comprises the following steps that a niobium source, an aluminum source and an oxidizing agent are mixed, then charging is conducted under the argon and vibration conditions, and a mixture is obtained; and the mixture is sequentially subjected to a thermit reaction and cooling under the vibration condition, and the low-oxygen low-nitrogen aluminum-niobium intermediate alloy is obtained. According to the method, charging is carried out under the argon and vibration conditions, air remaining in gaps of mixture particles can be eliminated, introduction of oxygen and nitrogen in the thermit reaction process is reduced, and therefore the oxygen and nitrogen content of the aluminum-niobium intermediate alloy is reduced; and the thermit reaction and cooling are carried out under the vibration condition, so that thick dendritic crystals formed in the alloy solidification process can be crushed, the purpose of grain refinement is achieved, fine grain strengthening is achieved, and the obdurability of the aluminum-niobium intermediate alloy is improved.

The invention provides a method for preparing a high-purity niobium ingot by utilizing multistage refining and the high-purity niobium ingot, and the method comprises the following steps: (1) taking aluminum particles, niobium pentoxide, a heat generating agent and a slag former as raw materials, preparing an aluminum-niobium alloy ingot by adopting an exothermic method outside a furnace, and then carrying out surface treatment and crushing treatment to obtain aluminum-niobium alloy particles; (2) the aluminum-niobium alloy particles are subjected to horizontal electron beam smelting, and a smelted niobium plate is obtained; (3) stacking a plurality of smelting niobium plates, and then sequentially performing vacuum diffusion welding and vacuum arc smelting to obtain a primary niobium ingot; and (4) the primary niobium ingot is placed in a double-gun electron beam smelting furnace to be smelted, and the high-purity niobium ingot is obtained. The stable production of the high-RRR value high-purity niobium is realized by adopting a multi-stage refining process coupling system of an aluminothermy method, horizontal electron beam melting, diffusion welding, electric arc melting and double-gun electron beam melting, and the technical problems of high energy consumption, high cost, low production efficiency and the like in the traditional process are effectively solved.

A method and cascade reactor system for producing elemental rare earth metals and rare earth-aluminum alloys via aluminothermic reduction are disclosed. The method involves combining rare earth oxides or halide salts with aluminum powder, initiating a thermite-type reaction under inert or controlled atmospheric conditions, and recovering the molten metal product. Fluxing agents may be used to enhance slag fluidity and phase separation. The cascade reactor comprises multiple thermite zones with staged ignition, thermal transfer mechanisms, and slag separation interfaces, enabling sequential reduction of mixed feedstocks. The system supports both batch and continuous formats and achieves high recovery yields, reduced aluminum contamination, and compatibility with alloying and post-purification processes. The invention is adaptable to individual rare earth species and mixed oxide concentrates, offering a scalable, energy-efficient, and environmentally favorable route to rare earth metal and alloy production.

Disclosed herein are exothermic reaction mixtures that can be used for copper-based thermite reactions. The disclosed exothermic reaction mixtures can be advantageously formulated with synthetically made copper oxide(s), which can improve consistency and stability of thermite reactions. An example exothermic reaction mixture includes an alloy comprising copper and aluminum and a metal oxide comprising Cu2O and CuO. Also disclosed are methods of preparing the exothermic reaction mixture and methods of welding that include the exothermic reaction mixture.

This invention relates to a thermite reaction charge comprising bismuth oxide and aluminium adapted to react with a reaction rate giving a reaction time of 8 to 15 seconds for a thermite reaction charge of 30 to 100 kg from initialisation of the thermite reaction charge to at least 90% of the thermite reaction charge is reacted, a method for forming a three-phased rock-to-rock barrier by applying the thermite reaction charge and a well barrier formed thereof.

This invention discloses a fluoride-modified liquid metal thermite and its preparation method, belonging to the field of thermite preparation technology. It utilizes Galinstan eutectic to prepare liquid metal; aluminum powder and liquid metal are synthesized using physical mixing and ultrasonic treatment to obtain liquid metal-modified aluminum; FeCl3·6H2O is added to a perfluorooctanoic acid aqueous solution and stirred, followed by a hydrothermal reaction; the resulting product is washed to obtain Fe(PFO)3; the liquid metal-modified aluminum is mixed with iron perfluorooctanoate and ultrasonically treated to obtain Fe(PFO)3@LM-Al; Fe(PFO)3@LM-Al and iron oxide are added to anhydrous ethanol and ultrasonically stirred to obtain Fe(PFO)3@LM-Al@Fe2O3. This invention, using the above method, raises the high-temperature thermal oxidation reaction temperature of aluminum powder to before the melting point of 660℃, achieving a breakthrough in the thermal mass transfer process of aluminum powder.

The invention discloses an energy-gathered cutting device for directional forcible entry of a collapsed building, and belongs to the technical field of building forcible entry, the energy-gathered cutting device for directional forcible entry of the collapsed building comprises a double-layer shaped charge liner, and the double-layer shaped charge liner is formed by nesting an outer-layer shaped charge liner made of steel and an inner-layer shaped charge liner made of red copper; the outer-layer shaped charge liner is in an inverted frustum shape, and the inner-layer shaped charge liner is in an inverted frustum shape and comprises a high-detonation-velocity charge section, a thermite particle section and a low-detonation-velocity charge section which are sequentially connected in series; the detonating cord is connected with a high-detonation-velocity charge section, a thermite particle section and a low-detonation-velocity charge section in series, the delay detonator is arranged at the front end of the high-detonation-velocity charge section, and an outer-layer steel shaped charge crushes a concrete matrix through high impact toughness of steel to form an initial radial crack; the inner-layer red copper shaped charge liner generates high-speed energy-gathered jet flow by virtue of ductility of copper, the steel bars are efficiently cut off, and the inner-layer red copper shaped charge liner and the steel bars work cooperatively to improve the breaking efficiency and quality.

Apparatus, systems, and methods are used for activating a downhole tool, powered by an exothermic reaction, for operation, while deploying a tubing string from a wellbore surface. The tubing string comprises a coupling for enabling pressurized activation of the downhole tool, which comprises a fuel (e.g., thermite) for producing the exothermic reaction. The coupling enables fluid to flow into an interior of the coupling through a first flow passage, during descent of the downhole tool. A stopper is dropped and / or seated to cause the coupling interior to pressurize to an activation pressure, which causes an activator to activate a burn within the downhole tool. Once the downhole tool completes its operation, the coupling interior is further pressurized to burst a burst disc, which opens a second flow passage for fluid to flow from the interior to exterior of the coupling, while downhole tool and coupling are raised to the surface.

The present disclosure teaches a system and method for generating power by a thermal power plant. The system and method includes a fuel heating chamber configured to receive a nano-thermite fuel, an induction assembly configured to inductively heat the fuel in the fuel heating chamber, and an electricity generating subsystem configured to convert heat from the heated nano-thermite fuel into electricity.

This invention provides a method for producing a chromium-aluminum-iron alloy, including steps such as raw material mixing. The raw materials used in the mixing process are chromium oxide, aluminum powder, lime, and sodium chlorate. The process employs a two-step smelting method: first, an aluminothermic reduction reaction is used, and second, an electric heating method is employed in a refining furnace. This process homogenizes the molten iron, chromium, and aluminum alloys with different specific gravities, preventing heavier iron and chromium from sinking and lighter aluminum from floating, thus avoiding alloy segregation. The chromium oxide yield produced by this method reaches 93.97%, which is 5-6 percentage points higher than the yield of metallic chromium produced by the conventional aluminothermic method. The metallic aluminum yield reaches 98%-99%, with low aluminum burn-off.

The invention is a multi-layer thermite block, encased in an exterior protective shield with one face exposed. The exposed face is carved out to accommodate a target device such that the block encompasses the target device when placed atop the device. When receiving a data-destruction signal, the block is ignited producing a short-duration blast of heat sufficient to severely damage or destroy all physical data-storing facilities of the target device.

The invention discloses a smelting device for reducing chromium oxide separated and purified from aluminum-chromium slag into metal chromium, and relates to an aluminum-chromium slag smelting device. A furnace frame (1) is connected with a concrete foundation through foundation bolts; the furnace body (6) is arranged on the furnace frame (1), is fixed by a positioning pin and is connected with the furnace frame into a whole; the middle furnace cover (7) falls on the furnace body (6) and is connected with the furnace body through bolts; the upper furnace cover (5) is connected with the upper part of the middle furnace cover (6) through a bolt; a dust extraction opening (4) is formed in the upper furnace cover (5), and smoke generated by the melting reaction in the furnace is discharged through the dust extraction opening (4) and enters a dust removal system; according to the device, aluminum oxide separated from the aluminum-chromium slag is purified and blown into hollow balls, chromium oxide is reduced into metal chromium, aluminum oxide generated during metal chromium production in each furnace is converted into products in time, slag-state solid waste is not generated, the state that a large amount of slag is accumulated during metal chromium production through a traditional aluminothermy method is overcome, the slag treatment problem is solved, and the production efficiency is improved. The invention relates to a smelting device for high-value utilization of waste residues.

The invention discloses an experimental device for realizing oil and gas well plugging by simulating an underground thermite to melt bismuth alloy, which comprises a pressure container, a combustion system, a data acquisition system, a gas supply system and a power supply system, and is characterized in that the combustion system is arranged in the pressure container and comprises an electric ignition experiment table, an experimental sleeve and an electric ignition wire; the outer surface of the experiment sleeve is coated with bismuth alloy, the experiment sleeve is placed on the electric ignition experiment table, the electric ignition wire extends into the experiment sleeve in the using state, the power supply system is connected with the electric ignition wire, the gas supply system is communicated with the pressure container, and a heating device is arranged in the pressure container. The data acquisition system comprises a high-speed camera and a thermocouple signal collector, and the thermocouple signal collector is connected with the thermocouple through a signal line penetrating through the pressure container. According to the invention, by adding the pressure container, the gas supply system and the heating device, the experiment of melting the bismuth alloy by the thermite in the underground environment is simulated, and data support is provided for oil-gas well plugging.

The invention provides a preparation method of a low-cost CuCr25 contact material, and relates to the technical field of preparation of electrical materials, and the preparation method comprises the following steps: preparing and weighing CuCr25 contact raw materials, mixing the CuCr25 contact raw materials, carrying out compression molding on the CuCr25 contact raw materials, sintering a green body, processing and preparing a CuCr25 contact, and cleaning and inspecting the CuCr25 contact. The water atomized copper powder and the aluminothermy chromium powder are adopted as main raw materials, quantitative recycled powder is innovatively added, the cost of the raw materials is successfully and greatly reduced, the optimized solid-phase sintering process ensures that the material forms a uniform and compact microscopic structure, meanwhile, the production energy consumption of the material is effectively reduced, and the production cost is reduced. The key performance of the prepared CuCr25 contact material completely meets the application standard of low-voltage electrical appliances, the conductivity and strength are perfectly balanced, the product advantages of low cost and high performance are constructed, the green manufacturing concept is reflected through waste recycling, and collaborative improvement of economic benefits and product performance is effectively achieved.

A method and associated system of energy production, the method including providing core-shell thermite particles and combusting the core-shell thermite particles in a dispersed group to produce heat. The combustion of the core-shell thermite particles may proceed according to various core-shell thermite group combustion modes.

A thermite composition for a process of plugging and abandoning a petroleum well comprises a tube-scaling composition and a gas leakage-preventing composition. The tube-scaling composition comprises aluminium and a metal oxide, and the gas leakage-preventing composition comprises a metal or an alloy with a melting point ranging from 100-300° C. The tube-scaling composition is arranged at the bottom, followed by the gas leakage-preventing composition. The thermite composition further comprises a tube-opening composition comprising aluminium and a metal oxide. The process of plugging and abandoning a petroleum well using the thermite composition involves introducing the thermite composition which is arranged in layers in the petroleum well to be plugged and abandoned, and initiating an ignition to trigger a thermite reaction, which melts the metal for tube sealing and prevents gas leakage.

A two-step method for producing low-aluminum low-oxygen high-purity chromium metal comprises the following steps: uniformly mixing chromium oxide, aluminum particles, calcined coke and sodium chlorate to obtain a mixed raw material; putting the mixed raw material into a smelting furnace, covering the surface of the mixed raw material in the smelting furnace with magnesium chips, and igniting to finish smelting; after the furnace burden in the smelting furnace is naturally cooled to the room temperature, starting the furnace, finishing furnace slag on the surface of the metal chromium to obtain coarse chromium, crushing and grinding, and performing magnetic separation to remove iron to obtain metal chromium powder; uniformly mixing metal chromium powder with metal chromium sheet powder obtained by an electrolytic method or metal chromium powder obtained by an aluminothermy method to obtain a metal chromium mixture, and pressing the metal chromium mixture into a metal chromium ingot; and the metal chromium ingot is put into a horizontal vacuum furnace, the temperature is increased, vacuum deoxidation is conducted, and the low-aluminum low-oxygen high-purity metal chromium is obtained. The method has the advantages that other carbon sources do not need to be added, the process steps are simplified, and the degassing efficiency is improved; the carbon element in the metal chromium powder is effectively utilized in the degassing process, the content of the carbon element and the content of the oxygen element are reduced, and the purity of the high-purity metal chromium is improved.