WO2020117098A1 - Method for aluminothermic production of metal powders and device for the implementation thereof - Google Patents

Abstract

What is proposed is a method for producing titanium and silicon powders by aluminothermic reduction thereof from liquid tetrachlorides at low temperatures and a pressure of 1.0 to 1,05 atm, whereby a suitable tetrachloride is fed on the surface of an aluminium block in a dripping or jet-dripping mode. The process utilises a conventional cylindrical reactor with a cone-shaped collector for the products at the bottom part thereof. A compact block of ultrapure aluminium is pre-installed in the reactor. The device is provided with a dispensing unit for tetrachloride dosing in a jet-dripping mode and units for controlling and stabilising temperature and pressure.

Description

METHOD FOR ALUMOTHERMIC PRODUCTION OF METAL POWDERS AND DEVICE FOR ITS IMPLEMENTATION

The field of technology.

The present invention relates to the field of metallurgy of light metals in relation to aluminothermic methods and devices for producing powders of titanium and silicon.

The prior art.

Titanium and silicon are neighbors in the periodic system of elements, are included in its fourth group and are the most important structural elements of modern technology (especially titanium), as well as the most important semiconductors (silicon).

М-Л.: Химия, 1964, 1167 с.). По этим причинам представляется ненужным переводить тетрахлориды в газовую фазу и отказаться от технологий восстановления их в несколько сот градусов Кельвина с большим расходом энергии, трудностями герметизации, регулирования процессов, экологическими проблемами и т.д. The technique and production technology of these elements in pure form is based on the reduction of their tetrachlorides from the gas phase. In this case, both tetrachloride have very low melting and boiling points. For TiC14 this is 230 C and +137.30 C, respectively, and for SiC14 it is 700 C and +57.60 C. The liquid state range for titanium chloride is 1600 C and for silicon tetrachloride is 1280 C. (Chemistry Handbook, vol. II Edited by B.P. Nikolsky.

M-L .: Chemistry, 1964, 1167 p.). For these reasons, it seems unnecessary to transfer tetrachlorides to the gas phase and abandon their recovery technologies of several hundred degrees Kelvin with high energy consumption, difficulties in sealing, process regulation, environmental problems, etc.

Among the known methods for the production of titanium powders, metallothermic production of titanium from dioxide or tetrachloride by calcium hydride has spread. The resulting powders, however, contain a large amount of impurities, and the production itself is very energy intensive. (Tarasov A.V. Metallurgy of titanium.- M.: IKC Akademkniga, 2003.327 p., P. 252).

We have proposed a method and apparatus for aluminothermic reduction of titanium with dispersed aluminum from liquid tetrachloride at a temperature of from-230 C to +1370 C (Begunov A.I., Begunov A.A. Pat. RF N ° 2.549.795. Bull. N ° A method for producing titanium (powder) at temperatures (750 - 1100) K in counter turbulent flows of dispersed aluminum and tetrachloride is also proposed. (Begunov A.I., Begunov A.A. Pat. RF Ns 2.559.075. Published. 08/10/2015. Bull. Ns 22).

Finally, another of our inventions is known for the “Device ...”, which also relates to the production of powdered titanium at high temperatures using counter turbulent flows of tetrachloride and dispersed molten aluminum. (Begunov A.I., Begunov A.A. Pat. RF Ns 2.641.914. Publ. 23.01.2018. Bull. Ns 3.).

On the technologies for producing silicon powders in the most fundamental American monograph-reference book, no information is available ^ Herman R. Powder metallurgy from A to Z. - Translation from English. Libenson G.A., Padalko O.V. - Ed. Padalko O.V. - Dolgoprudny: I.D. Intellect, 2009, 335c.). At the same time, the Plazmoterm Company offers silicon powder with a purity of 99.8-99.9% with a cost in the range of 3600-6000 rubles / kg (2018 year http: // www

.plazmotherm.m / catalog / chemical / silicium / item 186.html).

Apparently, the plasmatron reduction technique will never allow to obtain silicon with low energy and material costs, which are necessary for the mass introduction of a product of "solar" quality.

Of the analogues considered, our patents RFN3 2.559.075 and Ns 2.641.941 are difficult to realize counter turbulent flows of superheated chlorides and dispersed metal reducing agents at temperatures of 750-1100K. Very high values of the rate of reduction reactions can be achieved in them, but the process can be difficult to control. Indeed, chlorides of lower valencies will always be present in superheated tetrachlorides and reactions can proceed according to the scheme of branched chain reactions with the possibility of explosion. In addition, the so-called explosive limits in terms of temperature, pressure and component concentrations are poorly controlled and regulated. Perhaps even more so, this applies to the reduction of silicon from SiHC13 trichloride, which is used in most companies and countries.

Therefore, the closest prototype of the invention is our patent Ns 2.549.795 of low-temperature reduction of titanium tetrachloride with changes in device, pressure parameters, as well as device, pressure and process temperature for silicon.

Technical result

This is the ease of dosing, the supply of one of the reagents - liquid tetrachloride in moderate and small mass or volume equivalent, which excludes the possibility of switching to the kinetics mode with branching chains.

The dosing unit for the supply of tetrachloride in the drop or jet-drop mode reproduces, in principle, the classical titration unit of analytical chemistry, the device is elementary simple and infinitely reliable.

The use of aluminum - reducing agent in the form of a compact metal block, on the surface of which the recovery process mainly takes place, allows the excess heat to be removed to the temperature control and stabilization unit located outside the cylindrical part of the reactor ..

Disclosure of invention

The novelty lies in the fact that a massive aluminum block of a reducing metal is installed in the reaction zone, on the surface of which liquid tetrachloride is metered in a drop or jet-drop mode. The purpose of this solution is to guarantee the avoidance of the possibility of "getting" into the field of kinetics with branching chains and uncontrolled high or "explosive" speeds. In addition, quantitatively dosing the liquid is incomparably easier than the dispersed aluminum powder in the invention, the prototype. Finally, the recovery process is somewhat stretched both in time, passing into a liquid film on the surface of an aluminum block, and in the reaction space filled with gaseous tetrachloride. In addition, the aluminum block, having high values of heat capacity and thermal conductivity, is interfaced with the metal walls of the reactor and the exchanger assembly installed externally. This technique also allows you to dump excess energy with its possible further utilization and facilitates process control. The reduction temperature is maintained for silicon in the range from - 700 C to +580 C. For titanium, it remains the same as that provided for in the prototype invention and is not indicated in the formula of this solution (from - 230 C to +1370 C).

To ensure the safety of the process, the pressure in the reactor is maintained close to atmospheric, but slightly higher: from 1.0 to 1.05 at.

It is not advisable to use an inert gas in our process as a reactor aggregate, since any excess component contains impurities that are undesirable in both products. It is better to fill the volume with tetrachloride as the main component of the process, which is also easily subjected to purification by distillation to any desired degree of purity.

Using a vacuum is also impractical, since any violation of the tightness of the reactor will lead to the ingress of impurity amounts of nitrogen and oxygen in it, which is unacceptable.

On the other hand, any slightest outward leak of gaseous tetrachloride is easily detected and can be quickly repaired.

The essence of the process can be expressed by the reaction equation:

ZMS14 railway d + 4A1tv = ZMtv, d + 4A1t13tv. d (1), where MC14 is T 14 or SiC14, M is Ti or Si. Subscripts mean: w, d - liquid, dispersed; tv is solid; tv, d — solid, dispersed state. Equation (1) is the same as the underlying processes in the invention, the prototype, but structurally, reaction (1) in the new invention looks different. Here, A1 is not in a dispersed state, but in a compact state. It is not aluminum powder that is not present here that is dosed when it is fed into the reactor, but liquid dispersed tetrachloride.

Brief description of the FIGURES of the drawings To implement the proposed technical solution, a reactor consisting of a cylindrical part 1 is used to carry out the chemical work of reduction and a cone-shaped collection of reaction products 2 together with excess trichloride 3 (Fig. 1.). The most important part of the device is a compact aluminum cylindrical block made of highly pure metal 4, mounted on a false bottom 5 at the bottom of the reactor. This block is provided with grooves 6 for draining recovery products on them.

Another most important part of the device is the dosing unit for the supply of tetrachloride in the jet - drop mode 7 to the horizontal surface of the aluminum block. On this surface, tetrachloride in the form of droplets, partially spreading into films, interacts with aluminum to form titanium or silicon powders.

The device also comprises a temperature control and stabilization unit 7, covering the cylindrical part of the reactor. The reactor is hermetically sealed with a lid 8, through which the nozzle 9 passes to supply additional amounts of tetrachloride, if necessary, a slight increase in pressure in the system. Another fitting 10 is designed to purge the device with inert gas before shutting down and depressurizing the reactor to install a new reducing agent block. The node for regulating the pressure in the system is connected with the use of the nozzle 9 and is traditional.

The device also contains a locking-outlet device 11, which can operate both in batch and continuous mode.

When MS14 tetrachloride is fed through dosing unit 7 on the surface of a compact aluminum block 4, drops and trickles of chloride spread and interact with this surface, spreading along it in the radial direction. Further, the reduction products in excess tetrachloride flow down the recesses into the lower conical part of the reactor. After discharge from the reactor under slight excess pressure, this mixture is sent to filters to separate titanium or silicon powders, as well as aluminum trichloride from tetrachloride. The residual tetrachloride is vacuum-stripped sequentially at temperatures of about 600 ° C for SiC14, about 1400 ° C for TiC14, and finally about 1820 ° C for A1C13. If necessary, additional drying of each product can be carried out at higher temperatures in vacuum or inert gas.

Information confirming the possibility and feasibility of the invention In chemical thermodynamics of equilibrium states and reversible processes, the main criterion for the possibility of a reaction proceeding is the magnitude of its Gibbs or Helmholtz free energy. If this value is negative, a reaction is possible. According to our calculations, for the process of silicon reduction with aluminum at (273 - 330) K, the value of AG ~ (- 740) KJ, and for titanium at (260 - 410) K it is (265-310) KJ, i.e. under these conditions, both of these reactions have an equilibrium significantly shifted toward products — free silicon and aluminum.

Kinetic and phase barriers under the conditions of the proposed method and device are absent due to clearly turbulent modes of motion of the media, the dispersed nature and the constantly renewed fresh surface of the components.

The feasibility of implementing the regimes for producing silicon powders at temperatures below 1000 ° C and for titanium no higher than 1500 ° C is extremely attractive, because these processes are incomparably less energy intensive. In addition, they can only be carried out in sealed equipment, which is much easier to ensure at low temperatures than with values up to 1000 K and higher. Thus, issues of environmental cleanliness, as well as the predisposition of processes to automation and the elimination of the cost of heavy physical labor, are solved. There is a demand for powders; their cost reaches several thousand rubles / kg.

A sharp decrease in production costs is expected, which increases the chances of the development and mass introduction of solar-silicon energy. Demand for titanium, and in the current conditions is rapidly growing, will increase further with a decrease in its price.

Finally, after the implementation of low-cost methods for producing titanium and silicon powders, it is possible to turn them into ingots, profiles, or single crystals as a result of the application of vacuum thermal melting, zone melting, the Czochralski method, etc.

Claims

Claim 1. The method of producing metal powders of titanium and silicon by aluminothermic reduction of tetrachloride, characterized in that. that tetrachloride is supplied to the surface of the aluminum block at a speed that provides a drip or jet-drop mode of liquid outflow, followed by spreading it over the aluminum surface into the film and mechanical ablation of the reduction products, while the process is carried out under temperature conditions for silicon from -700 С to +580 C and pressure from 1.00 to 1.05 atm for both media of one or another tetrachloride. 2. A device for implementing the method in the form of a reactor with a cylindrical main part and a conical part for collecting and removing reduction products together with excess tetrachloride, characterized in that the aluminum - reducing agent is pre-arranged in the reaction space in the form of a compact metal block, and the reactor is equipped with a unit dosing of tetrachloride supply in a jet - drop mode, as well as by nodes of regulation and stabilization of temperature and pressure within the limits allowing to maintain a predominantly liquid state of aggregation of one or another tetrachloride.