DE2019399B2 - METHOD FOR MANUFACTURING TUNGSTEN CARBIDE - Google Patents

Description

Made of tungsten carbide. With an increase in Carbon dioxide concentration forms pure tungsten, the permissible limits of the carbon dioxide concentration depending on the temperature.

Further details of the invention are described below with reference to drawings, and although shows

F i g. 1 a characteristic temperature equilibrium curve,

Fig. 2 curves that illustrate the volume -% (CO ₂ ) equilibrium as a function of the temperature,

F i g. 3 a first system for the implementation of the Procedure in a schematic representation while

F i g. 4 illustrates a further system for carrying out the method in a schematic representation.

The diagram according to FIG. 1 illustrates the heating of tungsten oxide at a temperature equilibrium of 85O ⁰ C and 1000 ⁰ C in a flowing atmosphere of carbon monoxide. It can be seen from the curves that the reaction which occurs at the higher temperature first generates the metal and then the carbide is formed as the carbon dioxide produced is continuously removed. At the lower temperature the reaction proceeds directly to carbide formation. It has been found that when gas is used at atmospheric pressure, a concentration of carbon dioxide on the order of 5 to 37 volume percent at 1100 ^° C. yields the metal. At 1500 ° C, up to 33% by volume of carbon dioxide can be used for metal formation. It follows that for the production of carbide with U00 ^c C the carbon dioxide concentration must be less than 5% and that the CGyKonzentration must be kept at a low level unfeasible for the formation of the carbide at 1500 ° C.

It is obviously easy to have a relatively low level of carbon dioxide in the reducing atmosphere by adding carbon monoxide accordingly. A high percentage of carbon dioxide is caused by achieved a low intake of carbon monoxide.

Two comparative tests were carried out at 1100 ^° C. on a fixed bed of 400 g of tungsten oxide. This oxide was reduced by carbon monoxide, with the carbon dioxide content of the reducing atmosphere being enriched in the first attempt and the carbon dioxide formed being continuously removed in the second attempt. In the first experiment, the weight analysis showed 99.95% tungsten, 0.03% carbon, 0.02% oxygen. In the second attempt, weight analysis showed 93.8% tungsten, 6.15% carbon, 0.05% oxygen, this analysis corresponding to tungsten carbide formation.

Using the fixed bed described, the reaction was slow and therefore became a Series of experiments carried out with a rotary furnace with fixed blades. These attempts demonstrated that the more efficient gas / solid contact achieved with this device increased the response time significantly reduced compared to the reaction time required in a fixed bed. In addition, a much more uniform product was produced.

The calculated percentage equilibrium concentrations of CO ₂ are shown as a function of the temperature in the diagram according to FIG. 2 for each of the reactions detected by the above equations (1) and (2) who the. It should be noted that the reactions are intricate and do not necessarily proceed as individual reactions and that the curves are therefore only indicative of the equilibrium conditions for the overall reactions. Within the area under each curve, the reactions tend to run from left to right according to equations (1) and (2), and the states at a point χ are such that the "driving force" xz for the process of the Reaction (2) is greater than the "driving force" xy for the course of reaction (1), and if the reaction time is long enough, tungsten carbide is completely formed as the reaction product.

The heat equilibrium curves illustrate that, although in principle both tungsten carbide and tungsten metal ₃ hei CO ₂ concentrations may be formed of, for example 10% by volume at temperatures up to 1500 ⁰ C from WO, it has been found that the formation of Wolf : amkarbid the temperature limits in practice, from a lower limit of about 800 ⁰ C, below which the reaction for practical projects will be too slow, up to the range of 900 to 1050 ⁰ C extended.

As soon as the temperature value increases from the range from 900 to 1050 ^° C., there is an increased tendency towards the formation of the metal as the end point before the carbide formation. This means that within the range which extends below the reaction curves for equations (1) and (2), between temperatures of about 1000 ° C. and 1500 ° C., the reaction according to equation (1) tends to proceed from left to right and generates tungsten metal and CO ₂ , while the reaction of equation (2) tends to proceed from right to left, ie _{to produce WO 3} and CO. The driving force for the formation of tungsten metal and CO ₂ is greater than that for the production of WO ₃ and CO. Within the area under the curve according to equation (2) at temperatures between 1000 ° C and 1500 ^c C, the reaction according to equation (1) tends to run from left to right in order to form tungsten metal, while the reaction according to equation ( 2) tends to run from left to right to again produce tungsten carbide, the driving force for the formation of tungsten metal being greater than that for the production of woolen carbide.

The gaseous reaction product is carbon dioxide, which is converted into carbon monoxide by a reducing agent is reduced and fed back into the cycle.

A plant in which the gaseous reactants are continuously circulated, is used in F i c. 3 shown. A rotating drum reactor 1, which is refractory with a certain amount Metal oxide 2 can be charged and is heated by a heat source 3 is in a cycle switched on, consisting of a fan 4 and a reduction chamber 5. The circuit is closed and can be operated at atmospheric pressure or slightly overpressure. The temperature of the reactor and the amount of gas flow, which is regulated by the fan speed, is dependent of the single oxide to be treated.

The reduction chamber 5 can contain carbon with a temperature of HOO ⁰ C to 1500 ⁰ C

through which the carbon dioxide contained in the exhaust gas bottle 27 is fed through a valve 28 and the

is reduced according to the following reaction: excess of ^ carbon monoxide through a valve 29

discharged.

4CO ₂ + 4C - * 8CO (3) The filter 19 is preferred before the gas circulation

5 pump 20 arranged, so that a substantial er-

Thus, there is a continuous excess of coal lowing the gas temperature upstream of the circulation pump

oxide corresponding to 3CO formed, which occurs through an outlet, so that a special high-temperature circulation

line 6 must be drained. When commissioning the pump is not required.

the plant is a supply of carbon monoxide is required for the production of tungsten, that through the valve 7 in the circuit io carbide of the furnace 10 preferably at one temperature is introduced. of about 85O ° C and the gas circulation pump

A plant for the continuous production of regulated so that it delivers such a quantity of gas,

Tungsten carbide from tungsten oxide is shown in FIG. 4 shows that through the filter 19 and the circulating pump 20

posed. Tungsten oxide powder is no longer released onto an inlet gas flowing into the coke bed 21

funnel8 abandoned, from which it has by a »5 than 20 vol .-% CO ₁ . An oven with one

Screw conveyor 9 to the solids inlet having an inner diameter of 30 cm and a heated one

Rotary kiln 10 is transported. The furnace is easily required length of 6 m for the production of 10 kg

inclined to a slow forward movement of the tungsten carbide per hour a gas flow rate

Oxide powder along its length to the outlet at approximately 0.4 cubic meters per minute

cause where the powder via a weir 11 in a 20 the carbon dioxide concentration of the exhaust gas untei

Hopper is discharged, which through a valve 13 to keep 20 vol .-%.

The coke bed 21 consists of calcined petroleum can. Depending on the physical coke with minimal impurities in the powder, it may be necessary to vibrate the cleaning of hydrocarbons and the sulfur furnace or periodically with 25 connections and its heating units 23 hammer blows to shake a equal to a temperature between 1100 and 1500 ⁰ C moderate powder flow to achieve. hold, as shown in the equilibrium curve

The furnace 10, which from the outside by a row F i g. 2 for the response
is heated by electrical heating devices 15,

consists of a metal tube with gas-tight 30 C + CO ₂ : £ 2CO (4)

bonds by rotating seals 16 can be seen on each.

End with gas inlet and outlet headers 17 respectively. There is a lower limit for the carbon dioxide

18. The outlet head-ück 18 is through a filter 19 concentration, which is at the outlet of the coke bed 21

connected to the inlet of a gas circulation pump 20, can be achieved, with a vol

which the gas to the top of a coke bed 21 35 tration of 1% is acceptable. The excess ar

promotes, which is contained in a container 22, the carbon monoxide is discharged through the valve 29

surrounded by an electrical heating device 23 and the amount discharged can serve as an additive, un

is. Coke contained in a hopper 24 becomes just above atmospheric according to the system pressure

If necessary, through a valve 25 in the vessel 22 to maintain pressure. Part of the through the drain valve

fed. Gas from the bottom of the coke bed 21 is 40 29 derived carbon monoxide can in conventional

Via a jacketed tube 26 through the gas in a rather way to be used to the rotatingei

line header 17 fed into the furnace 10. To put Koh seals 16 under pressure, and a sth;

Fuel monoxide for start-up is drawn from a still remaining residue is put on bottles

For this purpose 3 sheets of drawings

Claims (2)

■ the tungsten oxide is preferably heated to 8500C - claims: wherein the exhaust gas formed has a carbon dioxide content of at most 20 percent by volume, and there 1. Process for the production of tungsten carbon dioxide of the exhaust gas is then adorned with redu carbide in powder form from tungsten oxide powder and fed into the cycle as monoxide. The method according to the invention is characterized by the following advantages: The dangers occurring when using the tungsten oxide to a hydrogen temperature range are avoided from 800 to 1050 ^° C. and heated with carbon monoxide and it Tungsten carbide powder can be brought into contact with a sub and the partial pressure in the micron structure can be generated, since due to the lack of carbon dioxide produced below a level for hydrogen, no water is produced, which could cause undesired grain growth for the formation of the carbide, important value is kept. The method according to the invention is significantly cheaper 2. The method as claimed in claim 1, characterized in that the tungsten oxide goes to 850 ⁰ C 15, since no hydrogen is heated as an additional reducer, the exhaust gas that is formed contains a carbon monoxide to which the carbon monoxide is added 20 percent by volume must be removed and the conversion process runs faster, holds and the gas is then reduced and as the carbon for the production of carbide monoxide is fed into the cycle. is in the gas phase is better control 20 of the stoichiometry of the product possible. The inventive Procedure can therefore also be used for the Tungsten carbide with an excess of carbon can be used, which has been produced in some other way.
25 In the regeneration of carbon monoxide from CH-PS 4 38 241 is a process for producing carbon dioxide, an excess of carbon monoxide position of tungsten carbide is generated from tungsten oxide, which can be taken from the reduced gas, in which a hydrogen as well as an additional and can be used reducing atmosphere containing decarburization gas in the exhaust gas holds undesirable substances such as what is used. In this process, a hot 30 water, which can get into the oxide fed to the furnace, is removed from the fluidized bed of solid particles of tungsten oxide. The fine tungsten carbide powder produced according to the new process in a hydrogen-containing gas phase is suitable, into which a carburizing gas is introduced, especially for the production of tools, which, before the metal oxide particles become metallic, service life compared to the tools that are made of Grostand are reduced and when they meet 35 bem. Wolf agglomeration produced by known methods. This process also provides for the production of ram carbide powder, tripling as long as the carburizing gas and hydrogen could be used. The novel process will preferably be supplied with reducing atmosphere until the tungsten oxide particles are converted to carbide at a reducing atmosphere temperature. 85O ° C carried out, which is much lower than this process is carried out in such a way that in the reduction 40 is the known process, so that by the tion atmosphere as an intermediate product pure tungsten is produced using normal heat-resistant materials, which is converted into tungsten carbide for the systems to carry out the reduction. process as well as saving heating energy This process is very complicated, time-consuming, substantial reduction in the cost of the tungsten carbide produced, and expensive, since two reaction gases, namely hydride compared to the material used according to the known process and a carburizing gas, can be achieved for the use of tungsten carbide,
long and the chemical reactions over a becomes the reducing atmosphere with carbon dioxide expire for a longer period of time. Another disadvantage is enriched, so pure tungsten is formed according to the danger of the pure water used - the following reaction equation:
to see the fabric. Another crucial flaw 50 this process can optionally be carried out by the ^ q _l 3CO -> - W + 3CO (1) Formation of water occur, which is an undesirable ³ "*" ² Can cause grain growth of tungsten carbide. The object of the invention is to develop a The method according to the invention runs according to the following Process for the production of tungsten carbide, the 55 gender chemical reaction equation from:
avoids the disadvantages of the known method described above. _u , _n , _{rn wr ΔΓη} , -. γλ- λ r ι j 1, ■ ,, r ι WD ₃ - \ - 5CO ^ WL ■■) - 4LÜ.J (2) This task is based on a procedure " of the type described above for the production of Tungsten carbide is 60 prerequisite for this reaction to occur in powder form of tungsten oxide powder, by heating tungsten oxide in a reduction that the carbon dioxide content of the reducing atmosphere atmosphere solved by the fact that tungsten oxide is very low on the sphere. heated a temperature range of 800 to 1050 ¹ C Practice has shown that in the reaction in and is brought into contact with carbon monoxide depending on the temperature and the partial and the partial pressure of carbon dioxide produced 65 pressure of carbon dioxide either tungsten carbide below one or pure tungsten intended for the formation of the carbide. When maintaining th equilibrium is maintained. runs at a very low carbon dioxide concentration According to a further feature of the invention, the reaction of equation (2) will and it will