RU2495826C1 - Method of producing titanium carbide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to metallurgy of high-melting compounds. The method of producing titanium carbide involves using aluminium subchloride, titanium tetrachloride and carbon as starting components. Carbon is fed into the reaction in powder or fibre form. Synthesis of titanium carbide is carried out in two steps. At the first step, aluminium carbide is obtained from aluminium subchloride and carbon at temperature of 1100-1250°C. At the second step, titanium carbide is obtained from aluminium carbide and titanium tetrachloride at temperature of 800-900°C.

EFFECT: invention increases output of titanium carbide, eliminates the step of trapping the product from the gas stream.

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Description

The invention relates to the metallurgy of refractory compounds, and in particular to a method for producing titanium carbide.

All known methods for the synthesis of titanium carbide can be divided into four groups. The first, main group should include carbothermic synthesis of titanium carbide by reduction of titanium dioxide by reaction [Kiparisov SS, Levinsky Yu.V., Petrov A.L. Titanium Carbide: Preparation, Properties, Application / M .: Metallurgy, 1987. - 216 p.]:

TiO ₂ + 3C = TiC + 2CO

In practice, carbidization of titanium oxide is carried out at a high temperature of ~ 2000 ° C, which can be attributed to significant disadvantages of this method. At this temperature, a mixture of titanium dioxide with soot compressed into briquettes is aged in an atmosphere of hydrogen or argon. Another disadvantage of the method is the presence of free carbon in the product> 1%, since in order to exclude oxygen-containing compounds, the solid-phase reduction reaction of titanium oxide is carried out with a stoichiometric excess of carbon. The remaining free carbon is difficult to extract from the product. In addition, for solid-phase reactions, preliminary very thorough mechanical mixing of the two reagents is necessary, which also significantly increases the cost of the process. Finally, most carbothermal methods for the synthesis of TiC require a long (tens of hours) grinding of the resulting synthesis product.

Known methods of production from TiO₂ TiC powders with a characteristic size of 2-3 μm at a low carbidization temperature that do not require further grinding, [Simoroz LI, Prilutsky E.V., Domasevich L.T. Carbides and materials based on them. Kiev: ONTI IPM Academy of Sciences of the Ukrainian SSR, 1983. P.48-51; Koc R., Folmer J.S. Carbothermal synthesis of titanium carbide using ultrafine titania powders // Journal of materials science, 32 (1997), P.3101-3111]. For this purpose, it was proposed to use a highly dispersed TiO fraction as a feedstock.₂ 0.1-0.2 microns, which also increases the cost of the final product.

The common disadvantages for all the methods of the first group are the relatively low rate of chemical transformations characteristic of most solid-phase reactions, high synthesis temperature, and the need for thorough mixing of the starting reagents.

The synthesis group should include the method for producing titanium carbide fibers by the sol-gel method using viscose fiber [Raman V., Dhakate SR, Sahare pD Synthesis of titanium carbide whiskers (TiCW) through sol-gel process from rayon fibers // Journal of materials science letters. 2000, 19, P.1897-1898]. Titanium isopropoxide Ti (OC ₃ H ₇ ) is mixed with isopropanol and acetylacetone in a 1: 2 molar ratio to suppress the precipitation of titanium dioxide from the solution. Acetylacetone forms a soluble chelate complex with titanium. A mixture of titanium alkoxide, isopropanol and acetylacetone in a molar ratio of 1: 2: 2 is mixed in a magnetic stirrer for 5 hours to obtain a TiO ₂ sol, which is then used to impregnate viscose fibers, which serve as a carbon source. The weight ratio of titanium alkoxide and viscose fiber is 2: 1. Viscose fibers were impregnated with a TiO ₂ gel, dried at 60 ° C and then heated at a speed of 100-50 degrees per hour under argon to a temperature of 1420 ° C, and then cooled at the same speed to room temperature.

The disadvantage of this method, in addition to the above, is the long duration of the total synthesis time of TiC, reaching up to 30 hours and the use of expensive chemicals.

The second group of methods for the synthesis of TiC should include direct synthesis from elemental titanium and carbon by sintering them at high temperature either by a periodic out-of-furnace method of self-propagating high-temperature synthesis (SHS), or by a continuous method in a high-temperature furnace. Thus, SHS - methods for producing TiC from a mixture of titanium and carbon black powders are known. [Drozdenko V.A., Borovinskaya N.I. et al. Patent RU 2038296 C1, 1995; Merzhanov A.G., Drozdenko V.A. et al. Patent RU 1570225 A1, 2003]. The disadvantage of these methods is the use of expensive titanium powder, as well as the hardware design of the process, which determines its frequency and the need to grind the resulting compact TiC.

Known methods for the continuous production of TiC from a mixture of powders of titanium and carbon black [Alexandrovsky SV, Mushkov SV et al. Patent RU 2066700, 1996; Alexandrovsky S.V., Lee D.V. Patent RU 2175988, 2001]. In it, the synthesis is carried out continuously in a sealed reactor, heated to 1000-1050 ° C. The volume of the reactor exceeds the volume of the loaded mixture of titanium powder and soot by 250-500 times. Alternatively, to increase productivity, the initial mixture is previously kept in vacuum. The disadvantage is the use of expensive titanium powder, low volumetric capacity of the reactor and the need for subsequent grinding of the obtained TiC.

The common disadvantages of the methods of the second group include the need for thorough mixing of the starting reagents, grinding of the obtained titanium carbide and its high cost.

According to the chemistry of the process, the same group includes the method of TiC synthesis by the interaction of titanium powder with the decomposition products of methane or other gaseous hydrocarbons [Kim Y. - J., Chung K, Kang S. - J.L. In situ formation of titanium carbide in titanium powder compacts by gas-solid reaction // Composite: Part A 32 (2001) P.731-738]. In this method, there is no need to mix the reagents, since one of them is in the gas phase, but the titanium carbide yield does not exceed 30%, and it is part of the Ti-TiC composite, which makes it difficult to use in compounds that do not contain elemental titanium.

The third group of methods for the synthesis of TiC includes plasma-chemical methods based on the joint reduction in a hydrogen or hydrocarbon plasma of a gas mixture consisting of TiCl ₄ and hydrocarbon C _n H _m . In the plasma chemical method [Neunschwarner E. // Less-Common Metals. 1966, V.11, N5, P.365-375] the synthesis of TiC was carried out in a stream of hydrogen plasma containing titanium chloride and methane. The use of gasoline and benzene instead of methane for the production of titanium carbide in plasma was proposed in [Panfilov SA, Rezvykh VF, Tsvetkov Yu.V. and others // Phys. and chem. processing materials. 1979, No. 2, C.21-27; Rezvykh V.F., Panfilov S.A., Khaidarov V.V. and others // Phys. and chem. processing materials. 1983, No. 2, S.58-61; Ibragimov A.T., Kalamazov R.I., Tsvetkov Yu.V. // Phys. and chem. processing materials. 1985, No. 5, p. 58-61].

A known method of synthesis of titanium carbide by carbon deposition from anode material in a hydrogen plasma on a titanium surface serving as a cathode [Dostovalov VA, Gordienko NS et al. Patent RU 2424352, 2011]. The disadvantages of this method, in addition to the general disadvantages of plasma-chemical methods, are: the ability to obtain only a thin carbide film on the titanium surface, the difficulty of uniformly coating a complex surface, low productivity, including limited by the rate of erosion processes on the surface of a graphite anode.

A known method of producing TiC coatings by deposition of titanium from a stream of metal plasma generated by a vacuum-arc discharge in benzene vapor [Bystroy Yu.A., Vetrov N.Z., Lisenkov A.A. Plasma-chemical synthesis of titanium carbide on copper substrates // Letters in ZhTF, 2011, V.37, issue 15, p.33-39].

The general disadvantage of plasma-chemical methods is the complexity of the hardware design and the high cost of electrical energy necessary to maintain chemical transformations in the plasma, as well as the use of hydrogen.

The fourth group of methods for the synthesis of titanium carbide should include metallothermic methods, which are based on generalized reactions:

mTiCl _x + M _n C _m → nMCl _{mx / n} + _m TiC

or

TiCl _x + nM + CCl _y → nMCl _{(x + y) / n} + TiC

The first generalized reaction is based on the method of producing titanium carbide using calcium carbide (CaC ₂ ) as a reagent M _n C _m (n = 1, m = 2) [Abramov DS, Nechaev NI and others SU 1809586 A1, 2000]. The synthesis is carried out by introducing into the melt salts of lower titanium chlorides and calcium carbide at a temperature of 700-800 ° C. The disadvantages of this method are the need for preliminary production of lower titanium chlorides soluble in salt melts and expensive calcium carbide, as well as the inevitability of subsequent grinding of the obtained powder.

The second reaction is based on numerous methods of magnetothermal reduction in a melt of a mixture of titanium tetrachloride and carbon [Aleksandrovsky SV, Mushkov SV et al. Patent RU 2083708 C1, 1997; Alexandrovsky S.V. Patent RU 2130424 C1, 1999]. In them, PSs are obtained by reduction of a mixture of titanium and carbon tetrachlorides (or TiCl ₄ and C ₂ Cl ₄ [Aleksandrovsky SV, Lee DV, Sizyakov VM. Obtaining nanopowders of titanium carbide by magnesium thermal reduction of a mixture of chlorides // Izvestiya Vuzov. Non-ferrous metallurgy. 2004, No. 5, pp. 60-65]) magnesium, followed by vacuum separation. In this synthesis using equipment designed to obtain a titanium sponge with magnetermia. Alternatively, a mixture of tetrachlorides or magnesium is saturated with hydrogen to facilitate grinding the resulting titanium carbide to a powder of the desired size before reduction.

The disadvantage of this method is the need to use metallic magnesium, as well as stages of vacuum separation and grinding of the resulting product.

The closest analogue to the claimed method includes an aluminothermic subchloride method for synthesizing titanium carbide by mixing in the gas phase aluminum subchloride, titanium tetrachloride and oxygen-free carbon-containing gas (for example, hydrocarbons (C _n H _m ), chlorohydrocarbons (C _n H _m Cl _k ) or chlorocarbons (CCl ₄ , C ₂ Cl ₆ )) [Zakirov R.A., Parfenov O.G., Pashkov G.L. Subchloride synthesis in titanium metallurgy // Reports of the Academy of Sciences. - 2009. - T. 425. - No. 5, S.631-633; Zakirov RA, Parfenov OG, Pashkov GL Subchloride Synthesis in Titanium Metallurgy // Doklady Chemistry, 2009, Vol.425, Part 2, P.77-79]. The synthesis of titanium carbide, for example, from hydrocarbon is carried out from the gas phase at a temperature of 1000K <T <2000K with the release of heat based on the following generalized chemical reaction:

$${\text{nTiCl}}_{\text{four}}+{\text{C}}_{\text{n}}{\text{N}}_{\text{m}}+\text{2nAlCl}\to \text{nTiC}+{\text{2nAlCl}}_{\text{3}}+{\text{m / 2H}}_{\text{2}}\text{(one)}$$

The use of chlorine-containing carbon compounds instead of hydrocarbons makes it possible to obtain the same target product, but requires an additional consumption of aluminum subchloride to bind chlorine, which is part of chlorocarbons or chlorohydrocarbons, and thereby increases the cost of titanium carbide synthesis.

The method based on reaction (1) allows synthesizing and precipitating from the gas phase powders of titanium carbide of any size - from nanometers to hundreds of microns. Despite the fact that thermodynamics allows an equilibrium yield of titanium carbide close to 100% in a wide temperature range at 300 <T <2000 K, in practice such a high yield cannot be achieved. One of the reasons is the difficulty in separating ultrafine particles of titanium carbide from the gas stream. Another reason is the low probability of three-molecular collisions in reaction (1). In practice, chemical transformations occur as a result of a sequence of two-molecular collisions, and taking into account the kinetics of intermediate chemical transformations that require slightly different optimal temperature conditions, the total yield of titanium carbide in the gas stream is below equilibrium.

The proposed method is aimed at obtaining a technical result, which consists in increasing the completeness of conversion of titanium introduced into the synthesis and in eliminating the stage of product capture from the gas stream.

The achievement of the technical result is ensured by the fact that the subchloride aluminothermic synthesis of titanium carbide at normal pressure by the total reaction (1) is carried out in two stages at different temperatures, at each of them two reagents are involved in chemical transformations, one of them is in the reactor in the gas - in the solid phase.

In the first stage, the synthesis of aluminum carbide from carbon black or another carbon substance (solid phase) and from aluminum subchloride AlCl (gas phase) is carried out, and the subchloride is introduced in a stoichiometric excess with respect to carbon to ensure complete conversion of this carbon to aluminum carbide.

In the second stage, the aluminum carbide powder obtained in the first stage (solid phase) is purged with vapors of titanium tetrachloride. The titanium carbide synthesized in this way is then washed in hydrochloric acid from the residues of aluminum carbide, elemental aluminum and adsorbed aluminum chlorides.

The essence of the proposed method lies in the fact that aluminum subchloride at a temperature above 730 ° C exists in the gas phase and serves as a gas-phase reducing agent for chlorides of less chlorine-active elements, such as titanium or carbon, and with carbon-containing substances, for example, with hydrocarbons, it can form carbides by reactions:

2nAlCl + C _n H _m → n / 3Al ₄ C ₃ + 2n / 3AlCl ₃ + m / 2Н ₂

Or react with elemental carbon (n = 1, m = 0):

$$\text{2AlCl}+\text{C}\to {\text{1 / 3Al}}_{\text{four}}{\text{C}}_{\text{3}}+{\text{2 / 3AlCl}}_{\text{3}}\text{(2)}$$

The carbon-containing substance is fed into the reaction in the form of a powder, thread or film

For the synthesis, it is proposed to use particles of heat-resistant solid carbon substance, for example, soot, coal, graphite, graphene, fullerene or carbon fibers. AlCl ₃ formed along the way sublimates at T> 180 ° C and practically does not pollute solid aluminum carbide.

Reaction (2) on the surface of a carbon particle intensively proceeds at a temperature of 1100-1250 ° C. At T <1100 ° C, the synthesis rate noticeably decreases mainly due to the low partial vapor pressure of AlCl, which increases sharply with temperature. With increasing temperature, the kinetics of the process also improves, the probability of disproportionation of excess aluminum subchloride decreases, and, accordingly, the content of aluminum metal impurity in aluminum carbide decreases. At T> 1250 ° C, technological difficulties arise in protecting the walls of the reactor from chemical erosion.

In the second stage, at normal pressure, titanium carbide is synthesized by the reaction:

$${\text{Al}}_{\text{four}}{\text{C}}_{\text{3}}+\text{3TiCl}=\text{3TiC}+{\text{4AlCl}}_{\text{3}}\text{(3)}$$

The temperature in the reactor does not exceed 900 ° C in order to suppress the associated formation of TiCl ₃ , which becomes noticeable even at a temperature of 1000 ° C and higher, and is accompanied by etching of titanium in carbide with excess tetrachloride by reaction:

TiC + 3TiCl4 = C + 4TiCl ₃

At the end of the second stage, the remaining aluminum carbide, the adsorbed residues of chlorine-containing compounds and the metal aluminum trapped in the solid product in the first stage are removed by washing with TiC in hydrochloric acid.

The introduction of one solid and one gas-phase reagent into the reaction at each stage eliminates the need for preliminary mixing of the reagents and capture of the target product of the chemical reaction from the gas stream.

The resulting TiC was subjected to x-ray diffraction and elemental analysis. A photograph of a scanning electron microscope of the initial soot particles and the obtained TiC powder is shown in Fig. 1. The size of the agglomerates of soot particles used to produce aluminum carbide is about 30 microns. The synthesized TiC powder consisted of agglomerates of ~ 10–20 μm, uniting particles 100–300 nm in size. The admixtures of free carbon, aluminum, aluminum carbide, titanium, and titanium aluminides did not exceed 0.1%; the yield of titanium carbide relative to the titanium tetrachloride introduced into the system was at least 90%. When carbon drags were introduced into the reaction, instead of soot, titanium carbide fibers with a length and diameter close to the length and diameter of the initial carbon fiber were obtained (Fig. 2).

The essence of the invention is illustrated by examples 1-3.

Examples of the method:

Example 1

In the first stage, aluminum subchloride vapor was passed over 150 mg acetylene carbon black for 60 minutes at a temperature of 1250 ° C. Subchloride was supplied in triplicate in relation to stoichiometry. No free carbon was detected in the resulting aluminum carbide particles. In the second stage, the obtained aluminum carbide was maintained at a temperature of 900 ° C in vapors of titanium tetrachloride also for 60 minutes. The resulting product was washed in a hydrochloric acid solution to remove unreacted aluminum carbide and precipitated during the disproportionation of aluminum. The titanium carbide yield was 90%.

Example 2

The first stage is carried out with the same parameters as in example 1. In the second stage, the temperature was 800 ° C. Lowering the temperature of the second stage can reduce the etching rate of TiC with titanium tetrachloride and thus increase the yield of the product and also prevent the release of free carbon. The titanium carbide yield exceeded 98%.

Example 3

The modes of synthesis of TiC were selected as in Example 2, but instead of soot, carbon fibers were introduced into the reactor. The synthesis resulted in the formation of fibers in the form of titanium carbide tubes. A photograph of TiC fibers with different magnifications is shown in Fig. 2.

Claims (1)

A method of producing titanium carbide, including the use of aluminum subchloride, titanium tetrachloride and carbon as starting components, characterized in that the carbon is fed into the reaction in the form of a powder or thread, and the synthesis of titanium carbide from it is carried out in two stages through the preparation in the first stage aluminum carbide from aluminum and carbon subchloride, and in the second stage, titanium carbide from aluminum carbide and titanium tetrachloride.

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