DE2019399A1 - Process and device for the reduction of refractory metal oxides - Google Patents

Description

UNITED 1KBiGIXD.M ATOMIC ENERGY AUTHORITY

11 Charles II Street, L ο ηä ο η, S. W. 1. England

For this application, the priority is derived from the English patent application Έτ. 20865/69 of April 23, 1969 claimed

Method and device for the reduction of refractory metal oxides

The invention relates to the reduction of refractory metal oxides. Refractory metal is a term used in technology for tungsten and similar metals such as titanium. It should be well known that these metals and their carbides are of great importance, for example for special steels, Tool tips and other items.

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In the special case of tungsten, it has heretofore been the practice in the manufacture of either tungsten metal or carbide to reduce tungsten oxide with hydrogen to obtain the metal. This process was carried out at temperatures of up to 100O ⁰ C, using a large excess of hydrogen, which had to be carefully dried before being used again. To produce the carbide, it was common to marry the metal / else prepared in the above V with the calculated amount of carbon in ball mills, to press it to sinter in hydrogen at about 1500 ⁰ C, and finally the obtained sintered solid to a fine powder to shred. It should be noted that both of the manufacturing routes described above are difficult and expensive.

The object of the present invention is to create a new or better way of reducing refractories Metal oxides.

According to the invention there is a method for reducing refractories Metal oxides in that a bed of hot refractory oxide is in contact with a stream of carbon monoxide gas brought and the monoxide / dioxide exhaust gas mixture through a reducing Agent is recirculated to the bed.

In the case of tungsten, the reactions can take place can be represented as follows: _-..- „■■.

3 CO ^ W + 3 CO ₂ .... (1)

WO ₅ + 5 CO - WC + 4 CO ₂ ".... (2)

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In practice it has been found that the product either the carbide or the metal is, depending on the temperature and the partial pressure of the carbon dioxide. So the reaction follows when there is a very low concentration of carbon dioxide equation (2) is maintained and it will made the carbide. On the other hand, if you get the coal ' Dioxide concentration can accumulate, the metal itself is formed, and the permissible limits of the carbon dioxide concentration are dependent on. the temperature, as will be evident in the following.

According to a particular aspect of the invention, the reducing The agent is therefore arranged so that essentially all of the carbon dioxide in the exhaust gas mixtures is reduced to the monoxide and maintaining the bed at a temperature and the carbon dioxide concentration is maintained below an equilibrium level so that the product is the carbide of the metal.

It should be noted that in the in accordance with the In the invention standing reactions no hydrogen is present, so that the dangers of using this material are avoided and, moreover, there is no water, which causes undesirable Korh growth. The simple cycle management The exhaust gas through a reducing agent, such as a bed of hot carbon, converts the carbon dioxide back into the carbon monoxide. It should also be noted be that because of the carbon used in the manufacture of tungsten carbide is in the gas phase, better control of the Stoichiometry of the product is possible. The invention can thus also be used for tempering tungsten carbide Carbon deficit produced in another way.

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Viewed from another side, the invention closes also a process for the production of refractory metal arbides a, according to which a refractory metal oxide is brought into contact with carbon monoxide at an elevated temperature and the partial pressure of the carbon dioxide produced below an equilibrium value dependent on the temperature mentioned is held, "in which the .Carbide formation is the difference by the metal "is favored.

The mentioned partial pressure can be below the mentioned Value can be maintained by regulating the make-up amount of carbon monoxide

According to a further aspect of the invention, a device for reducing refractory metal oxides is provided, which a rotary kiln for receiving a refractory metal oxide, heating units for heating the refractory Metal oxide, means for passing carbon oxide gas through the furnace to bring it into contact with the refractory metal oxide, a reducing agent for the reduction of the gas leaving the furnace to carbon monoxide and means for the circulation of the carbon monoxide from the reducing agent to the Furnace includes.

The apparatus can also be a means of transport for continuously feeding the refractory metal oxide into the furnace and means for the continuous discharge of the by the Reaction with the product produced by carbon monoxide gas exhibit·

To make the present invention more understandable, intended specific embodiments thereof by way of example

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and with reference to the accompanying drawings be, namely shows

Fig _o 1 shows a typical temperature equilibrium curve,

Fig »2 curves, which relate to the volume% (C (^) - equilibrium refer to the temperature,.

"Fig. 3 schematically, an apparatus for the execution of the invention while

Fig. A also schematically shows another apparatus for carrying out the invention.

Referring to Figure 1, tungsten oxide was heated in a thermal equilibrium of 85O ° C and 1000 ⁰ C in a flowing atmosphere of carbon monoxide. It can be seen from the curves that the reaction at the higher temperature goes to the metal first and then to the carbide as the carbon dioxide product produced is carried away. At the lower temperature the reaction goes closer directly to the carbide. It has been found that when using a carbon dioxide concentration of gas in the order of 5-37 by volume ^ at 1100 ⁰ C gives the metal under atmospheric pressure. At 1500 ⁰ C up to 33 Vo 1% carbon dioxide can be used. It follows that in order to produce carbide at 110O ⁰ C the carbon dioxide concentration must be less than 5%, but in order to produce the carbide at 1500 ⁰ C it is necessary that the COo concentration be kept at an impracticably low level must become.

It should be apparent that it is easy to keep a relatively low level of carbon dioxide safe by that one can get an adjusted flow rate of carbon oxide gas On the other hand, if so desired, insures a high rate Having some carbon dioxide is your best bet, yourself, one to insure a low flow rate of carbon oxide.

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INSPECTED

Two comparative tests were carried out at 110o C ⁰ to a fixed bed of 400 g of tungsten oxide. This oxide was reduced by carbon dioxide in the first attempt, allowing the carbon dioxide content of the gas phase to build up, and in the second attempt by removing the carbon dioxide as it was formed

The product was analyzed and, on the first run, weight analysis found 99.95 % tungsten, 0.03 % carbon, 0.02 % oxygen. On the second attempt the weight analysis gave 93.8% tungsten, 6.15% carbon, 0.05% oxygen, and it should be emphasized that this analysis corresponds to the tungsten carbide,

Using the fixed bed described above, the reaction was slow and therefore a number of experiments were carried out using fixed paddle blades. These tests showed that the more effective gas / solids exposure achieved using this type of apparatus _? decreased the reaction time from that which was found to be necessary in the fixed bed. In addition, a much more uniform product was obtained.

The achieved equal weighting tB-'EPGcent concentrations

GOg are shown in Figure 2 plotted against temperature, and zifar for each of the reactions represented by equations (1) and (2) above. It should be pointed out that the events are involved and do not necessarily take place as individual reactions, and that the curves are therefore only relevant for the equilibrium conditions for the "over-everything"=> Hea! betosrf · because ?! have within the area under each curve HeaktioEan $ a © effort from the left "to the right so to verlaufen9 as fiiireh & I.E equations is represented and the Bedingims © a ₉ μβ'ΙΦ, θ at riciftiusages cdae® Poiifct χ shown

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ORIGINAL INSPECTED

-. -: ■■■ - '■ V-. .; ■ -7 - ■. ■■. ■■ .-. ■ ν "

become, the "driving force" xz for the reaction (2) larger is called the "driving force" xy for reaction (1), and if there is enough time for the reaction to complete -, '- the solid reaction product becomes entirely wolf be ramcarbide *

The graphs of the heat equilibrium curves demonstrate that, although in principle both tungsten carbide and tungsten metal can be formed from wO * at COg concentrations of, for example, '"""TO vol% at temperatures as low as 1500 ° 0", it has been shown has it that the formation of tungsten carbide the temperature limits in practice .the from a lower limit of about SOO ⁰ C, below which the reaction for practical projects too slowly, extending up to in the range 900-1050 ⁰ C. -

As soon as the temperature value increases from the range from 900 to 1050 ^° C., there is a tendency for the metal, which is formed as an end product, preferably before the carbide formation, to multiply. In other words, within the area subtended under the curves for the Gleichungen- (1) and (2), the reaction proceeds between the temperatures of about 1000 ⁰ C and 15OQ ⁰ C according to the equation (1) trend moderately from the left to the right and produces tungsten metal and COg »while the reaction according to equation (2) will tend to run from right to left, ie to produce WO * and CO. The driving force to produce tungsten metal and CO2 is greater than that required to produce the WO ^ and CO. Within the area under the curve according to equation (2) at temperatures between 1000 ⁰ C and 1500 ⁰ C, the reaction according to equation (1) tends to go from left to right in order to produce tungsten metal, while the reaction according to equation ( 2) tends to go from left to right to again produce tungsten carbide here, the

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the driving force of tungsten metal is greater than that which is required for the manufacture of tungsten carbide, whence there is a greater tendency for the end product to be Tungsten metal is.

The gaseous reaction product is carbon dioxide, and a characterizing feature of the invention is to pass the exhaust gas through a reducing agent and es.as a to allow essentially pure monoxide to return to the reaction zone.

An example of a device form in which the gaseous reactants are continuously circulated, is shown in Fig. 3, in which a rotating Drum reactor 1, which can be charged with a certain amount of refractory metal oxide 2 and through a heat source 3 is heated, connected to a circuit consisting of a fan 4 and a reduction chamber 5 is. 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 (determined by the number of fan revolutions) depends on the single oxide to be treated.

The reduction chamber 5 can contain carbon, kept at 1100 ° - 1500 ⁰ O, which will reduce the 4 · CO ₂ of equation (2) as follows:

4 CO ₂ + 4-0> 8 OO

Thus, an excess of carbon oxide is continuously formed in accordance with the 3 00 and must be drawn off at point 6 will. A supply of coal is also required for commissioning

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monoxide is required and this is getting started in the circulation introduced through valve 7 "

A pilot plant for continuous production of carbide or metal from the oxide should now be referenced on Fig. 4- "will be described." Powdered oxide will abandoned on a hopper 8, from which it is carried by a screw conveyor 9 to the ieststoffeinlaß of a rotary kiln 10 is transported. The oven is tilted slightly to allow a slow forward movement along its length Cause outlet where the powder over a weir 11 in a Hopper 12 is emptied, through a valve 13 in a Butter barrel-like container 14- can be emptied. Dependent on Due to the physical nature of the powder it may be necessary to vibrate the oven or periodically to shake with hammer blows to get an even To assure powder flow, as is understandable. ; .. "■;

The furnace 10, which is externally heated by a series of electrical heaters 15 -.-, consists of a metal tube in gas-tight connection by rotating seals 16 at each end with gas inlet and outlet headers 17 and 18. The outlet headpiece 18 is through a Filter 19 is connected to the inlet of a gas circulating pump 20 which allows to flow out onto the upper end of a coke bed 21 which is contained in a vessel 22 which is surrounded by an electrical heating device 23. Coke contained in a funnel 24 is fed into the vessel 22 through a valve 25 as required. Gas from the bottom of the coke bed 21 is fed into the furnace 10 via a jacketed pipe 26 through the gas inlet head piece 17; Carbon monoxide for the start-up is added from a bottle 27 through valve 28 and discharged άρν excess of carbon monoxide through a valve 29th,

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- ίο -

It is preferred that the filter 19 not be left behind to let and the gas circulation pump 20 to be fed, so that a substantial decrease in the gas temperature before reaching the circulating pump, which avoids the need for a special high-temperature circulating pump.

In operation, the furnace is operated 10 in a desired manner at a temperature of about 850 ⁰ G and the gas transfer pump adjusted so that it provides such a flow, that the through the filter 19, the circulating pump and 20 the coke bed 21 flowing discharge gas for the production of tungsten carbide does not have more than 20 Vol $ COp. In a particular example, a 30 cm ID, 6 heated length furnace set up to deliver 10 kg of tungsten carbide per hour requires a gas flow rate of approximately 0.4 cubic meters per minute to keep the carbon dioxide concentration below 20 vol.

The coke bed 21 consists of calcined petroleum coke with recirculated to a minimum contamination of hydrocarbons and sulfur compounds and is held by its heating units 23 at a temperature between 1100-1500 ⁰ C as from the equilibrium curve of Fig. 2 for the reaction

Cf + COp ^ == ^ 2 CO can be seen.

There is a lower limit to the carbon dioxide concentration that can be achieved at the outlet of the coke bed 21, but a Tol ^ concentration of 1fs is acceptable. As discussed above, the excess carbon monoxide is discharged through valve 29 and the amount discharged can serve as an additive to keep the SysterM pressure just above atmospheric. Part of the carbon monoxide from the excretory

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valve 29 can be used in a conventional manner., to pressurize the rotating seals 16 and any remaining residue is drawn onto bottles.

While the present invention has been described with reference to the reduction of tungsten oxide, reference should be made thereto pointed out that similar reactions with similar metals' such as tantalum, molybdenum, titanium and the like. In addition, it is not necessary to prepare the pure metals, and the reaction can, for example are carried out for the production of alloys such as iron-tungsten *

The invention also relates to modifications of the embodiment outlined in the accompanying patent claim 1 and refers above all to all inventor tonals> individually - or in combination - ■ in the whole Description and drawing are disclosed.

Claims

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Claims (10)

70 047 Dr Bu / Schm. April 21, 1970 - 12 - claims 1. A method for reducing refractory metal oxides, characterized in that a bed of hot refractory oxide brought into contact with a stream of carbon monoxide gas and the monoxide / dioxide off-gas mixtures are recycled to the bed through a reducing agent. 2. The method according to claim 1 ,. characterized in that the reducing agent for the reduction essentially all ^ n Carbon dioxide in the mixed exhaust gases is set up to monoxide, the bed is kept at elevated temperature and the ·. Carbon dioxide concentration below an equilibrium value is held so that the product is the carbide of the metal. 3. The method according to claim 2 for the production of tungsten carbide, characterized in that the temperature is 850 ⁰ C and the carbon dioxide concentration is kept below 40 percent by volume. 4. Process for the production of refractory metal carbides, characterized in that a refractory metal oxide at increased Temperature brought into contact with carbon monoxide and the partial pressure of the carbon dioxide produced below one Balanced weight is held, which is dependent on the given temperature and at which a preferably conversion to the carbide to the difference between metal. 00984 6/1191 'bad ORiGINAt 5. The method according to claim 4, characterized in that that said partial pressure by regulating the supply of Carbon monoxide below said. Value is held. · ' 6. "The method according to claim 4 or 5, characterized in that the carbon dioxide produced is reduced and as a monoxide is circulated. 7. Refractory metals produced by the process according to claim 1, _ 8. Refractory metal carbides, produced by the method according to any one of claims 1 to 6. · 9. Apparatus for the reduction of refractory metal oxides, characterized by a rotary kiln for receiving a refractory metal oxide, by heating devices for heating the refractory metal oxide, by means for passing carbon monoxide gas through the furnace to act on the refractory metal oxide, by a reducing Agent for reducing the gas exiting the furnace to carbon monoxide and means for circulating the carbon monoxide from the reducing agent to the furnace. ₍ 10. The device according to claim 9, characterized in that that a transport device for the continuous feeding of a refractory metal oxide into the furnace and means for the discharge of the carbon monoxide (gas manufactured product are provided. j 00.9046 / 1 191 Read it out