RU2200128C2 - Method of preparing tungsten carbide and tungsten carbide prepared by this method - Google Patents

Abstract

FIELD: nonferrous metallurgy. SUBSTANCE: invention can be used for preparing hard alloys, protective high-temperature, erosion-resistant, and emission coatings. Exothermic portion is prepared by blending, wt %: WO₃ 24.6, Mg 23, carbon black 2,4, and recycled synthesis product or NH₄Cl, or MgO, or polystyrene, or polyethylene 35-40, amount of carbon black constituting no larger than 50% stoichiometric excess with regard to WO₃. Resulting blend is placed into reactor, the latter is filled with argon to pressure at least 0.5 MPa and sealed, after which contents are inflamed. When burning stops, reactor is cooled, synthesis product is successively treated with 5-10% sulfuric acid, 5% chromic mixture, washed with water, and dried. Product, after acidic treatment, can be additionally treated with NaOH and KOH solution with concentration at most 2.5%. Tungsten carbide thus obtained represents micro-powder with hexagonal modification characterized by major particle size 0.1-0.2 mcm (natural cut), content of impurities no more than 0.1 wt %, including free carbon no more than 0.05 wt %. Natural cut is expressed by particles with regular hexagonal and rhombohedral forms, splices and druses with sharp facets and angles. EFFECT: improved physical characteristics of product. 7 cl, 4 ex

Description

 The invention relates to powder metallurgy, in particular to the production of tungsten carbide, which has wide applications as a main component for the production of hard alloys, protective high-temperature, erosion-resistant and emission coatings.

There are many known methods for producing tungsten carbide based on carbonization of tungsten with carbon black or reduction of tungsten oxide (WO ₃ ) in a hydrogen atmosphere with an admixture of hydrocarbons or carbon monoxide at a temperature of 1300-1600 ^o С for at least 2 hours (V.I. Tretyakov. Ceramic-metal hard alloys. - M., 1962, p. 270-276).

 The tungsten carbide powder obtained by known methods can have a size from fine-grained (0-1 μm) to coarse-grained (9-25 μm), usually with fused particles. The method for producing such powders is time consuming and energy intensive.

A known method of producing tungsten carbide by heat treatment of a tungsten concentrate with soot at a temperature of 600-950 ^o C for 2-4 hours in the presence of aluminum as a reducing agent, taken in an amount of from 0.3 to 0.6 parts per part of tungsten (patent RU 2006465, C 01 G 41/00, C 22 B 34/36, 1994). The known method allows to obtain tungsten monocarbide with a particle size of 1-5 microns, however, in addition to it, it contains as an impurity (up to 5%) carbide composition W ₂ C, which is undesirable in the production of carbide. Another disadvantage of this method is its duration in time.

A known method of producing refractory inorganic compounds, in particular tungsten carbide, which includes the preparation of an exothermic mixture of tungsten and carbon (soot), taken in stoichiometric ratio to obtain tungsten carbide (WC), pressing the mixture to a relative density of 0.5-0.6, room pour it into a stainless steel glass, evenly pouring it with a mixture of titanium with carbon black, then put the glass in a sealed reactor, which is filled with argon to 0.1-0.2 MPa, ignite the mixture of titanium with carbon black, the combustion process spreads etsya further the mixture was tungsten and carbon, the interaction of components to form WC, after cooling the reactor contents were removed, separated WC (auth. binding. USSR 556110, C 01 B 31/30, 1977). WC is a powder, the particles of which have an indefinite fused shape with sizes of at least 3-5 microns and at least 5% of the content of W ₂ C.

The data of chemical and x-ray phase analyzes show that as a result of the process, a WC is formed having the composition: C total. 6.1 wt.%, With freedom. 0.09 wt.%, W 93.5 wt.% And hexagonal syngony of type WC with lattice parameters: a = 2.903 A, c = 2.834 A. However, an undesired carbide of composition W ₂ C is also formed in the synthesis process in an amount of at least 5 % The production method due to the use of metallic tungsten as a feedstock is unprofitable for industrial development.

A known method of producing tungsten carbide by carbidization of tungsten powder with a specific surface area of at least 2 m ² / g in a stream of methane-hydrogen gas mixture at a heating temperature of 840-1100 ^o C (patent RU 2028273, 01 01 31/34, 1995). The obtained tungsten carbide has a specific surface area of 2.0-8.0 m ² / g, a particle size of the powder of 0.05-0.20 μm, the content of free carbon is not more than 0.1 wt.%. The specified patent is the closest analogue to the claimed tungsten carbide.

A known method of obtaining a macrocrystalline powder of tungsten monocarbide (International publication 30.06.88, WO / 88/04649 according to the application PCT / US 87/03096, C 04 V 35/56, C 01 B 31/34), comprising preparing an exothermic mixture of components containing tungsten component (tungsten ore containing more than 55 wt.% W), calcium carbide, aluminum, iron oxide and iron, the initiation of combustion, after which a self-propagating exothermic reaction and a temperature increase of 4372-4500 ^o F (2412-2482 ^o С ) After the combustion process, the crystalline mass is separated from the slag and WC macrocrystals are separated from it with particle sizes of more than 37 μm. Impurities and reaction by-products are chemically treated to remove iron, manganese, aluminum and other reaction by-products in dilute sulfuric acid, hydrochloric acid with a small addition of hydrofluoric acid. Obtained by the specified method WC contains at least 0.6 weight. % impurities: Fe = 0.17, SiO ₂ = 0.1, Ti≤0.03; Ta≤0.03; Nb≤0.03, C (free) - 0.02 wt.% And C total. 6.14-6.16 wt.%. The obtained WC macrocrystals contain a rather high amount of impurities and require additional grinding and classification before using WC as the main component in hard alloys.

 The known method, which is selected as the closest solution to the claimed method for producing tungsten carbide, has common features with the claimed: preparation of a mixture of components, heat treatment of the mixture in the combustion mode and subsequent processing of the synthesis product with diluted sulfuric acid.

 The disadvantage of this method is the low yield of the target product, which is not more than 90% with respect to tungsten raw materials, as well as a high content of impurities and the need for long-term grinding of tungsten carbide after chemical treatment.

 The objective of the invention is to provide a semi-industrial method for producing tungsten monocarbide with a high yield and a high degree of purity.

The basis for the production of tungsten carbide is an exothermic reaction of the interaction of tungsten oxide WO ₃ , C (soot) and Mg:
WO ₃ + C + 3Mg = WC + 3MgO + Q.

The temperature of this process exceeds 3000 ^o C, which can lead to the decomposition of tungsten carbide, therefore, to reduce the temperature, the target additives are added to the exothermic part of the mixture, both inert and decomposing in the combustion wave with the formation of gaseous products.

 The problem is achieved in that the method of producing tungsten carbide includes preparing a mixture of components consisting of an exothermic part containing tungsten oxide, magnesium, soot, which is taken with no more than 50% excess relative to stoichiometry to tungsten oxide, and the target additive in an amount 30-45.0 wt.%, Which is used as at least one of a series: recycled product, ammonium chloride, magnesium oxide, polystyrene, polyethylene, mainly recycled product or its mixture with ammonium chloride, t The treatment of the mixture is carried out in a combustion mode under argon pressure not lower than 0.50 MPa, the chemical treatment of the synthesis product in order to isolate the target product is carried out by treating the synthesis product first with dilute sulfuric acid, mainly 5-10% concentration, and then mainly with chromium mixture 5 % concentration.

 The recycled product is a synthesis product before chemical treatment and contains tungsten carbide and reaction by-products: magnesium oxide and other uncontrolled impurities.

 Chemical treatment of the isolated product in the first stage is carried out to remove the reaction products, mainly magnesium oxide, using dilute sulfuric acid, mainly 5-10% concentration. In the second stage of the chemical treatment, excess graphite is removed with a 5% chromium mixture (5% solution of potassium or sodium dichromate in concentrated sulfuric acid). The chemical treatment time depends on the volume of the processed product, the content of by-products, but, as a rule, the total time does not exceed 2 hours.

In the case where an impurity of WO ₂ is observed in the target product, additional processing after acidic (third stage) in a dilute solution of sodium or potassium hydroxide is required at a concentration of no higher than 2.5%.

 Tungsten carbide obtained by this method is a micropowder of tungsten monocarbide of the formula WC, hexagonal modification, in the form of a dark gray powder with a predominant particle size of 0.1-0.2 microns, having a natural faceting and containing a total amount of impurities of not more than 0.1 %, including in wt.%: With freedom. no more than 0.04, magnesium no more than 0.005, iron no more than 0.006, moisture + oxygen no more than 0.02.

 Natural faceting of particles means all observed possible forms: single crystals, drusen, intergrowths, etc., a characteristic feature of which is the presence of an acute-angled shape and sharp edges or sharp chips.

 In some samples, the formation of cubic tungsten carbide is assumed, but so far this has not been recorded in sufficient quantities.

 To reduce the process temperature, the target additive is introduced into the exothermic part of the mixture: an inert diluent — magnesium oxide and / or a recycled synthesis product and an easily decomposing diluent — at least one of a number: ammonium chloride, polyethylene, polystyrene, mainly ammonium chloride. Both types of diluent reduce the temperature of the process, and easily decomposing additives also act as a disintegrant and a supplier of the gas phase, providing the target product in the form of micropowder with a main particle size of 0.1-0.2 μm by grinding the product directly in the combustion front. The use of ammonium chloride or a mixture thereof with a recycled product is most preferred since their decomposition products do not pollute the target product. Additives such as polyethylene and polystyrene also grind the target product and at the same time they are also a supplier of carbon black, which allows introducing less free soot into the exothermic part of the mixture.

 The ratio of all components in each case is strictly controlled and determined by calculation. Thus, the introduction of the target additive in an amount of 30-45 wt.% Is the most preferred and leads, along with other features of the method, to obtain a product with desired characteristics.

The essence of the proposed method for producing tungsten carbide is as follows:
- prepare a mixture of the exothermic part of the components: tungsten oxide, carbon black, magnesium, then add the target additive selected at least one of the series: recycled product, ammonium chloride, magnesium oxide, polyethylene, polystyrene,
- the prepared mixture is placed in a sealed reactor,
- fill the reactor with argon to an initial value of not less than 0.50 MPa,
- initiate the combustion process,
- remove the synthesis product, part of which is separated - a recycled product and use it as a target additive - diluent for subsequent developments of tungsten carbide,
- the main part of the synthesis product is subjected to chemical treatment with diluted sulfuric acid of 5-10% concentration until complete removal of by-products, in particular magnesium oxide,
- subsequent processing of the product from free graphite with 5% chromium mixture to the complete removal of soot,
- washing with water until a neutral reaction of washing water, separation and drying of the target product,
- in some cases, after acid treatment, the product can, if necessary, be processed in a dilute (not higher than 2.5%) potassium or sodium hydroxide solution to remove WO ₂ impurities.

 Example 1

The exothermic part of the components is prepared: tungsten oxide WO ₃ (34.6 wt.%), Magnesium (23 wt.%) And 2.4 wt.% Soot, 40 wt.% Of the recycled product are added as the target additive. The excess of carbon black relative to stoichiometry with respect to WO ₃ is 20 wt.%. The powders are loaded into a stainless steel ball mill and mixed for 1 hour. The finished mixture of the starting components is placed in a reactor, filled with argon to an initial pressure of 5 MPa, sealed, and then the mixture is locally ignited with a tungsten spiral. After the combustion process is completed, the reactor with the contents is cooled, the synthesis product is unloaded, part of it is separated and used in subsequent experiments as the target additive, which has the technical term - recycled product, and its main part is sent for chemical treatment. First, the synthesis product is treated in diluted 10% sulfuric acid for 1 hour to remove reaction by-products, in this case mainly magnesium oxide. Then the remaining black residue is treated with a chromium mixture of 5% concentration for no more than 1 hour. During this time, the complete removal of soot occurs, after which the residue is separated, washed with water until the washings are neutral, dried and analyzed.

The isolated product is a dark gray powder, according to x-ray phase analysis is a tungsten monocarbide WC hexagonal modification. The yield of the target product relative to WO ₃ is 99.9%. The analysis of particle sizes shows that WC is a particle with a basic size of 0.1-0.2 μm, while the particles have a natural facet of predominantly hexagonal shape with sharp edges, and a sufficient number of fused particles with acute-angled shapes are also present in the powder.

 Chemical analysis showed that WC has a total impurity content of 0.09 wt. %, including, in wt.%: With freedom. no more than 0.04, magnesium no more than 0.005, iron no more than 0.006, moisture + oxygen no more than 0.02.

 The obtained WC was tested to obtain a hard alloy WC-Co and showed encouraging results when cutting metals.

 Example 2

The exothermic part of the components is prepared: tungsten oxide WO ₃ (37.7 wt.%), Magnesium (25.2 wt.%) And 2.10 wt.% Soot, 30 wt.% Of magnesium oxide and 5 wt.% Polystyrene are added to as target additives, the total amount of which is 35 wt.%. The excess of carbon black relative to stoichiometry with respect to WO ₃ is 10 wt.%. The total amount of the mixture is 30 kg. The powders are loaded into a stainless steel ball mill and mixed for 1 hour. The finished mixture of the starting components is placed in a reactor, filled with argon to an initial pressure of 15 MPa, sealed, and then the mixture is locally ignited with a tungsten spiral. After the combustion process is completed, the reactor with the contents is cooled, the synthesis product is unloaded and sent for chemical treatment. First, the synthesis product is treated in diluted 5% sulfuric acid for 2.5 hours to remove predominantly magnesium oxide in this case. Then the remaining black residue is treated with a chromium mixture of 4.5% concentration for no more than 1 hour. During this time, the complete removal of soot occurs, which at this stage is visually checked by the absence of CO ₂ emission, then the residue is separated, washed with water until the washings are neutral, dried and analyzed.

The isolated product is a dark gray powder, according to x-ray phase analysis is a tungsten monocarbide WC hexagonal modification. The yield of the target product relative to WO ₃ is 99.8%. Particle size analysis shows that WC is a particle with a basic size of 0.1-0.2 microns, while the particles have a natural facet of predominantly hexagonal shape with sharp edges, and there is a sufficient number of particles of acute-angled shape. Chemical analysis showed that WC has a total impurity content of 0.08 wt.%, Including in wt. %: Sv. no more than 0.06, magnesium no more than 0.005, iron no more than 0.006, moisture + oxygen no more than 0.02. The total carbon content is 6.14 wt. %

 Example 3

The exothermic part of the components is prepared: tungsten oxide WO ₃ (41.7 wt.%), Magnesium (12.0 wt.%) And 1.30 wt.% Soot, add 26.0 wt.% Recycled product, 9.00 wt. . % ammonium chloride and 10 wt.% polyethylene (the total number of target additives is 45.0 wt.%). The excess of carbon black relative to stoichiometry with respect to WO ₃ is 45 wt.%. The powders are loaded into a stainless steel ball mill and mixed for 1.5 hours. The finished mixture of the starting components is placed in a reactor, filled with argon to an initial pressure of 0.5 MPa, sealed, and then the mixture is locally ignited with a tungsten spiral. After the combustion process is completed, the reactor with the contents is cooled, the synthesis product is unloaded and sent for chemical treatment.

 Further, as in other examples. The yield of tungsten carbide is 99.5%.

 The target product has the same characteristics as in example 2.

 Example 4

The exothermic part of the components is prepared: tungsten oxide WO ₃ (45.0 wt.%), Magnesium (20.0 wt.%) And 5.0 wt.% Soot, add 23.0 wt.% Recycled product and 7.0 wt. .% ammonium chloride (the total number of target additives is 30 wt.%). The excess carbon black relative to stoichiometry with respect to WO ₃ is 50 wt.%. The powders are loaded into a mill and stirred for 1 hour. The finished mixture of the starting components is poured into the reactor, filled with argon to an initial pressure of 2.5 MPa, sealed, and then the mixture is locally ignited with a tungsten spiral. After the combustion process is completed, the reactor with the contents is cooled, the synthesis product is unloaded and sent for chemical treatment.

Further, the acid treatment, as in other examples, but in the final target product according to x-ray phase analysis, an impurity of WO _{2 was} detected, therefore, to remove it, the product was processed for 30 min in a 2.5% sodium hydroxide solution.

 After processing, the target product has the same characteristics as in other examples.

The yield of the target product relative to WO ₃ is 98.0%.

 Thus, the claimed method allows to obtain tungsten monocarbide with a high yield of not less than 98.0% relative to tungsten oxide. The resulting carbide has a specific particle shape, which is expressed in the presence of acute-angled faces and sharp chips, which positively affects the cutting tool made from these powders.

 The method of producing tungsten carbide is highly efficient, the entire production cycle of the product is a closed process.

Claims (7)

 1. The method of producing tungsten carbide, including the preparation of a mixture of components, heat treatment of the mixture in the combustion mode and subsequent chemical treatment of the synthesis product with diluted sulfuric acid, characterized in that the mixture is prepared from an exothermic part containing tungsten oxide, carbon black and magnesium, in which carbon black is taken from not more than 50% excess relative to stoichiometry for tungsten oxide, and the target additive, which is used as at least one of a series: recycled synthesis product, ammonium chloride, ma Nia, polyethylene, polystyrene, in an amount of 30-45 wt. %, the heat treatment of the mixture is carried out under an initial argon pressure of not lower than 0.5 MPa, and after processing the synthesis product with dilute sulfuric acid, it is treated with a chromium mixture.  2. The method according to p. 1, characterized in that the recycled synthesis product is mainly used as the target additive.  3. The method according to p. 1, characterized in that as the target additive is used predominantly a mixture of ammonium chloride with a recycled product.  4. The method according to any one of paragraphs. 1-3, characterized in that in the chemical treatment, dilute sulfuric acid is used predominantly of 5-10% concentration, and the chromium mixture is predominantly 5% concentration.  5. The method according to any one of paragraphs. 1-4, characterized in that the synthesis product after acid treatment is additionally treated in a dilute solution of sodium or potassium hydroxide at a concentration of not higher than 2.5%.  6. Tungsten carbide obtained by the method according to any one of paragraphs. 1-5, characterized in that it is a micropowder of tungsten monocarbide composition WC hexagonal modification, with a main particle size of 0.1-0.2 μm, having a natural faceting and containing no more than 0.1 wt. % of the total amount of impurities, including not more than 0.05 wt. % impurities of free carbon.  7. Tungsten carbide according to claim 6, characterized in that the natural faceting of the particles is expressed in the form of particles of regular hexagonal and rhombohedral shapes, as well as particles in the form of splices and drusen with sharp edges and corners.