DE7014849U - DEVICE FOR REDUCING REFRACTORY METAL OXIDES - Google Patents

Description

PATENT LAWYERS

DlPL-ING. ERICH SCHUBERT DIPL-ING. DIPL-W.-1NG. G. ZWiRNER

59 Siegan, Postf cot 325 Eiserner Strasse 227

Telephone: (0271) 32409

Telegrasun-Adr. = Faisdiub., Postal accounts: Cologne 106931, Essen 2S3 £ 2 Bank accounts: Oeutsme Bank AG-, HUalen Siegen and House of Lords «(RhId.)

70 048 Br.Bü / Schm / A

April 21, 1970

United Kingdom Atomic Energy Authority, 11, Charles II Street, L ο η ö

ο η, S.-W..1, England

For this application priority is claimed from "British Patent Application Hr. 20865/69 dated April 23, 1966".

Device for reducing refractory metal oxides

The innovation "concerns the reduction of refractory metal oxides. Refractory metal is a term used in technology for tungsten and similar metals, such as titanium. Ss should be generally 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, "in the manufacture of either tungsten metal or carbide, it was previously common practice to reduce tungsten oxide with hydrogen in order to obtain the metal. This process was carried out at temperatures up to 1000 ^° C. using a large excess of hydrogen that had to be carefully dried before re-use. in order to produce the carbide, it was common to marry the metal produced in the above manner with the calculated amount of carbon in ball mills, to press it to sinter in hydrogen at about 1500 ⁰ C. and finally crushing the obtained sintered plague body into a fine powder It should be noted that both of the above-described manufacturing routes are difficult and expensive.

The task of the innovation is to create a new or better device for the reduction of refractory metal oxides.

The innovation is to reduce refractory metal oxides a bed of hot refractory oxide brought into contact with a stream of carbon monoxide gas and the conoxide / dioxide exhaust gas mixtures is recycled to the bed by a reducing agent.

In the case of tungsten, the reactions can take place can be represented as follows:

....CD

+ 5 CO WC + 4 CO ₂ .... (2)

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In practice it has been found that the product is either the carbide or the metal, depending on the temperature and the partial pressure of the carbon dioxide. Thus, if a very low concentration of carbon dioxide is maintained, the reaction will follow equation (2) and the carbide will be produced. On the other hand, if the carbon dioxide concentration is allowed to accumulate, the metal itself is formed, and the allowable limits of the carbon dioxide concentration depend on the temperature, as will become apparent hereinafter.

According to a particular aspect of the invention, therefore, the reducing agent is arranged so that essentially everything Carbon dioxide in the exhaust gas mixtures is reduced to monoxide and the bed is kept 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 consistent hit the Invention standing Heaktioaen no hydrogen is present, so that the dangers of using this material are avoided and, moreover, no water is produced, which is undesirable Causes grain growth. The simple circulation The exhaust gas through a reducing agent, such as a bed of hot carbon, converts the sole dioxide back in the coal mo: n.o: x ± &. It should also be noted that because the carbon for the manufacture of tungsten carbide is in the gas phase, better control of the Stoichiometry of the product is possible »Thus the invention are also used for tempering tungsten carbide Carbon nitric shot produced in another way became"

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Joined on another side, the invention closes
also a process for the production of refractory metal carbides, according to which a refractory metal oxide is brought into contact with carbon monoxide at an elevated temperature and the partial duration of the carbon dioxide produced - below
an equilibrium value dependent on the mentioned temperature is maintained, at which the carbide formation is favored in contrast to the metal.

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

According to a further aspect of the invention, a ^"T orrichtung for the reduction of refractory metal oxides provided which f a rotary kiln for the A 33 nähm e of a refractory metal oxide, the refractory heaters for heating
Metal oxide, means for passing carbon oxide gas through the furnace to contact the refractory metal oxide, a reducing agent for reducing the gas exiting the furnace to carbon monoxide, and means for circulating the carbon monoxide from the reducing agent around the furnace.

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, and zx ^ ar shows

Pig. Λ a typical temperature equilibrium curve, Pig «, 2 curves, which refer to the volume% (COp) -equal-

relate weight versus temperature, Pig. 3 schematically an apparatus for the execution

of the invention while
Pig. 4 also schematically shows another apparatus for

reproduces the embodiment of the invention.

"" Referring to Pigur 1, tungsten oxide was heated at a VTärmegleichgewicht of 850 ⁰ C to 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 coil dioxide product produced is carried away. At the lower temperature, the reaction goes closer to directly to the carbide. It has been found that when gas is used under atmospheric pressure, a carbon dioxide concentration in the Prosseosösus of 5-37 ¥ ο1τ £ bsi HOO ⁰ G results in the lüetall. At 15QQ ⁰ C tons "up to 33 vol% carbon dioxide can be used. From this it follows that in order to add carbide at" 100 ⁰ C sü

Carbon dioxide concentration must be less than 5 ° / ° , but in order to produce the carbide at 1500 ° C it is necessary that the COp concentration must be kept at an impracticable low.

It should be obvious that it is easy to find a relative to keep low levels of carbon dioxide safely ^ by that one assures oneself of an adapted flow rate of carbon oxide gas »On the other hand, Tsremi it is desired, a high one Share of carbon dioxide si, it is the "best to become one." insure low carbon dioxide rates.

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Two Yergleichsversuehe -were "carried out at 110o C to ⁰ 'a fixed bed; 400 g tungstic oxide was reduced by carbon monoxide in the first attempt, wherein the Kohlendioxidgeäalt the gas phase has been allowed to build up, and in the second experiment by removal of the carbon dioxide as it was formed.

The product was analyzed, and the first try weight analysis gave 99 _S 95% tungsten, 0.03% carbon, / -. 0.02 % oxygen. In the second attempt the weight analysis showed 95.8 % 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 a series of attempts were therefore made executed using fixed blade plates. These experiments showed that the more effective gas / ITContact with solids, which occurs when using this type of apparatus was achieved reduced 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 calculated equilibrium concentrations of CXXj percent, are plotted against temperature, as shown in Figure 2, and that for each of the reactions that are represented by the equations (1) and (2) above. It should be noted that the reactions are intricate and do not necessarily proceed as individual reactions and that the curves are therefore indicative only of the equilibrium conditions for the supreme reactions. However, with this caveat, it is emphasized that within the area under each curve the reactions tend to prevail. left 'to the right as represented by the equations and the conditions, which, so to speak, are represented at a point χ

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become, the "driving force" xz for the Eeaktion (2) larger is as the "driving force" xy for Eeaction (1), and if there is enough time for the reaction to complete, the solid reaction product becomes entirely tungsten carbide be.

The graphic representations of the Wänne equilibrium curves demonstrate that, although in principle both tungsten carbide and tungsten metal can be formed from WCU at CO ^ -X concentrations of, for example, 10% by volume at temperatures up to 1500 ° C., it has been shown that the formation of tungsten carbide the temperature limits, is extending into the region of 900-1050 ⁰ C to up in the! practice from a lower limit of about 800 ⁰ C, below which the Eeaktion for practical projects too slow.

As soon as the temperature value increases from the range from 900 to 1050 ⁰ C, a tendency for the metal, which is formed as an end product preferably before the carbide formation, occurs. In other words: within the range that is below the curves for the If equations (1) and (2) are added, the reaction according to equation (1) tends to run from left to right ^{between temperatures of about 1000 0} C s- ₁ and 1500 ^{0 C and produces tungsten metal and CO2, 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 the woIfram 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 produce tungsten carbide here again, the

the driving force of tungsten metal is greater than that required for the production of tungsten carbide, where there is a greater fairness for the end product Tungsten metal is.

The gaseous reaction product is carbon dioxide and a characterizing feature of the invention "is that Passing exhaust gas through a reducing agent and returning it to the reaction zone as a pure monoxide borrowed in the v / es allow"

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 is heated by a heat source 3" is connected to a circuit 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 (determined by the number of fan revolutions) is depending on the {) single oxide to be treated.

The reduction chamber 5 may contain carbon, kept at 1-100 ° - 1500 ° C, which will reduce the 4 CO ₂ of equation (2) as follows:

4 CO ₂ + 4 C $> 8 CO

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

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

A pilot plant for the continuous production of carbide or advised all of the oxide should now be referenced? 4 ". Powdered oxide is loaded onto a hopper 8, from which it is transported by a screw conveyor 9 to the solids inlet of a rotary kiln 10. The kiln is slightly inclined to allow slow forward movement along its length towards the ~ J to create an outlet where the powder is emptied via a weir 11 into a funnel 12, which can be emptied through a valve 13 into a buttercup-like container 14. Depending on the physical liature of the bulb, it may be necessary to vibrate the oven to move or to shake periodically with hammer blows to ensure an even flow of powder, as this is understandable.

The furnace 10, -. Hich is heated externally by a number of electric heaters 15, made of a metal pipe in a gas tight connection through rotie- • ■ i) Rende seals 16 at the end with gas inlet and feathers Auslaßkopi'stücken 1? or 18. The outlet head piece 18 is connected by a filter 19 to the inlet of a gas circulation pump 20 which allows it to flow out onto the upper end of an Ebksbettes 21 which is contained in a vessel 22 which is surrounded by an electric heater 25. Biscuit contained in a funnel 24 is fed into the vessel 22 via 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 start-up is added from a bottle 27 through a valve 28 and the excess carbon monoxide is discharged through a valve 29.

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It is preferred not to leave the filter 19 behind and to supply the gas circulating pump 20 so that a significant lowering-ung._Ae.r__ £ a_s_ temperature before reaching the circulating pump, which avoids the need for a special high-temperature circulating pump.

In operation, for the production of tungsten carbide, the furnace 10 is operated in the desired manner at a temperature of about 850 C and the gas circulation pump is regulated so that it results in such a flow rate that the exit gas flowing through the filter and the circulation pump 20 to the coke bed 21 is no longer than 20 Yolfo CC ₂ . In a particular example, a 30 cm ID by 6 heated length furnace, set up to supply 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 yol </ o .

The coke bed 21 of purchases 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

C + CO ₂ - ^v 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 vol concentration of 1 ^ is acceptable. As discussed above, the excess carbon monoxide is removed through valve 29 and the amount removed can serve as an additive to keep the system pressure just above atmospheric pressure. Part of the carbon dioxide from the excretory

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

Although the present innovation, by reference on the reduction of tungsten oxide, it should be noted that similar reactions with similar metals Can be made such as tantalum, molybdenum, titanium and the like. In addition, it is not necessary to use the pure metals produce, and the reaction can be carried out, for example, for the production of alloys, such as Eis en-Wo1fram,

The innovation also affects changes to the enclosed Sesutzasspriics 1 outlined execution si orm and "refers primarily to all IT innovation features, the individually - or in combination - in the whole Description and drawing are disclosed.

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Claims (2)

- 12 TC 048 EE / Scism April 21, 1970 Vision claims 1. Apparatus for reducing refractory metal oxides, characterized by a rotary furnace (1, 10} for receiving a refractory metal oxide, by heating devices (3,15) for heating the refractory metal oxide, by means for passing corilermion oxide gas through the furnace (1. 10 ) in addition to "applying the refractory metal oxide" by a reducing agent for the reduction of the gas leaving the furnace (1, 10) to carbon monoxide as well as by means for the jjujokiührmgmg the carbon monoxide from the reducing agent to the furnace (1, 10 ). 2. "Device according to claim 1, characterized in that that a transport device (8,9) for the continuous Feeding a refractory metal oxide into the furnace (10) and means (11-14) for the. Discharge of the reaction with the product made with the carbon dioxide gas are.