RU2038296C1 - Method for production of titanium carbide and device for its realization - Google Patents

Abstract

FIELD: production of abrasive and wear-resistant materials. SUBSTANCE: method for production of titanium carbide includes preparation of mixture of powders of titanium and carbon black. Carbon black is taken in amount exceeding stoichiometric one by formula C=2,5· K_d· K_g· K_b.r, where C is carbon black excess mas. of total amount of mixture; K_d is mixture density factor, 0,5 ± 0,75; K_d is gas liberation factor, 0.4-0.8; K_b.r is burning rate factor, 0.3-0.9. Mixture is placed in bag of graphitized cloth, lowered into reactor and isolated from reactor walls with powder of ready product. Initiating device is installed into supporting flange. Supporting flange is rigidly secured to lower part of pipeline inside reactor under cover. Pipeline is located in reactor cover coaxial with its center and additionally furnished with filter and heat-protective screen made in form of shell installed under supporting flange. Installed in upper part of pipeline is check valve. Gas exhaust system provides for continuous gas exhaust in course of combustion reaction. Assembled reactor is placed into water bath, and reaction is initiated. Due to increased volume of reactor, the process safety is ensured due to continuous and smooth relief of excessive pressure, and reliable system of water cooling. Use is made of low-cost raw material, and high purity of titanium carbide is maintained. EFFECT: higher efficiency. 2 cl, 1 dwg, 1 tbl

Description

 The invention relates to inorganic chemistry, and in particular to a technology for producing titanium carbide, which can be used as an abrasive material in powders and pastes, grinding wheels, and also used as a wear-resistant material for spraying.

 A known method of producing titanium carbide in a closed volume in a porous graphite shell with intensive cooling followed by depressurization of the resulting gaseous products and evacuation [1] This method produces titanium carbide with good abrasive performance.

 However, the method and especially the device for its implementation have several disadvantages. The process during cooling, which is included before ignition, complicates the design of the reactor, since the reactor must be equipped with a water-cooling jacket and a system for supplying and draining water from the jacket. This reduces the safety of the process, since in the case of sudden cooling during combustion or after a short period of time after its completion, there is the possibility of overheating of the reactor.

 The disadvantage of this method is the subsequent depressurization from the reaction chamber to 0.1 excess atmosphere when pressure is reached after the start of synthesis of 50-100 atm. High pressure values that occur before the start of the discharge complicate the design of the reaction chamber and limit the size.

Closest to the invention is a method and apparatus for producing titanium carbide in a metal reactor in the mode of self-propagating high-temperature synthesis. According to this method, titanium powder is preliminarily subjected to mechanical activation, and the design of the reactor with a water-cooled jacket and graphite lining is additionally equipped with a heat-removing chamber with a perforated base on which graphite filling is placed [2]
The disadvantages of the method are the introduction of an additional operation for the mechanical activation of titanium powder, as well as a low degree of conversion, the amount of bound carbon in such carbide is less than 19 wt. calculated carbon content in carbide 20.08% The low content of bound carbon in titanium carbide is due to the lack of compaction of the initial charge, the presence of free volume in the reaction zone, and the use of coarse-dispersed powders up to 3 mm.

 The known method and device do not provide high performance, simplicity and safety of the process due to the complex gas exhaust system and water cooling.

 The aim of the invention is to increase productivity, simplify and ensure the safety of the process.

The goal is achieved in that in the method for producing titanium carbide in a metal reactor by local ignition of the reaction mixture in a closed volume followed by high-temperature reaction in the combustion mode, the reaction mixture is taken with excess soot from stoichiometric, determined from the ratio
With 2.5 x K _p x K _g x K _and , where C is an excess of soot, wt. to the total amount of the reaction mixture;
To _p the density coefficient of the reaction mixture, 0.5-0.75;
To _{g the} coefficient of gas evolution of the reaction mixture is 0.44-0.8;
K _and the burning rate coefficient 0.3-0.9.

The reactor is placed in a water bath and the process is conducted with a constant discharge of excess pressure. The reactor for producing titanium carbide is equipped with a means for removal of reaction gases, made in the form of a pipe placed in the reactor lid coaxially to its center with a support flange rigidly fixed in its lower part, located inside the reactor under the lid. The pipeline is additionally equipped with a filter fixed to it above the support flange and a heat shield made in the form of a shell. For reliable cooling of the reactor using a water bath. Moreover, the volume of the bath is 20 times the volume of the reactor, and the diameter of the flange is 0.85-0.95 of the diameter of the reactor. Excess soot, determined by the specified formula, allows to obtain titanium carbide with a degree of conversion of up to 99%
The value of 2.5 was obtained experimentally and shows that for all adverse factors, with maximum coefficients equal to unity, this excess of carbon allows to obtain the highest quality titanium carbide.

, где γ_n плотность реакционной шихты, загруженной в реактор, г/см³;
γ_р расчетная плотность всех компонентов шихты, г/см³, определяют из соотношения

+

+

, где
γ₁, γ₂, γ_n расчетная плотность компонентов шихты, г/см³;
х₁ + х₂ ++ х_n 1 части компонентов в шихте.The density coefficient is calculated by the ratio
K _p

where γ _{n the} density of the reaction mixture loaded into the reactor, g / cm ³ ;
γ _{p the} calculated density of all components of the charge, g / cm ³ is determined from the ratio

+

+

where
γ ₁ , γ ₂ , γ _{n the} estimated density of the components of the mixture, g / cm ³ ;
x ₁ + x ₂ ++ x _n 1 parts of the components in the charge.

Technically, K _p varies between 0-1, the goal is achieved when K _p 0.5-0.8.

 If the density coefficient can be calculated by the amount of charge loaded into the reactor, the gas evolution coefficients and the burning rate are determined by burning the sample in an airtight vessel. The magnitude of the change in pressure and pressure rise time determine the coefficients of gas evolution and combustion rate.

полученного газовыделения к максимально допустимому. Для синтеза из элементов карбида титана максимально допустимым газовыделением принято 100 см³/г. Определение газовыделения (согласно методике ИСМАН N М 01034-81) заключается в том, что образующийся в процессе взаимодействия в режиме горения, титана и сажи газ повышает давление в герметичном сосуде, которое фиксируется образцовым манометром. Расчет газовыделения проводится по формуле
Q

где Q газовыделение, см³/г;
Р₁ Р_п 1 атм начальное давление в герметичном сосуде;
P₂ P₁ + Р манометра;
Р манометра показание избыточного давления на манометре;
V объем герметичного сосуда, уменьшенного на объем сжигаемого образца, см³;
m вес образца г;
Т₁; Т₂ начальная и конечная температуры в герметичном сосуде, ^оК.The gas release coefficient is calculated by the formula
K _g

gas evolution to the maximum allowable. For the synthesis of titanium carbide from elements, the maximum allowable gas evolution is 100 cm ³ / g. The determination of gas evolution (according to the ISMAN method N M 01034-81) consists in the fact that the gas generated during the interaction in the combustion mode, titanium and soot increases the pressure in a sealed vessel, which is fixed with an exemplary pressure gauge. The calculation of gas evolution is carried out according to the formula
Q

where Q is the gas evolution, cm ³ / g;
P ₁ P _p 1 ATM initial pressure in an airtight vessel;
P ₂ P ₁ + P pressure gauge;
P pressure gauge indication of gauge pressure;
V volume of the sealed vessel, reduced by the volume of the burned sample, cm ³ ;
m sample weight g;
T ₁ ; T ₂ initial and final temperature in an airtight vessel, ^about K.

Theoretically, the limits of change of K _g 0-1, the goal is achieved when K _g 0.4-0.8.

для синтеза из элементов карбида титана максимально принятая скорость 10 см/с. Теоретически пределы изменения К_п 0-1, цель достигается при К_п 0,3-0,9.The combustion rate coefficient is calculated from the ratio of the true burning rate to the maximum allowable K _p

for the synthesis of titanium carbide elements, the maximum accepted speed is 10 cm / s. Theoretically, the limits of change of K _p 0-1, the goal is achieved when K _p 0.3-0.9.

 Placing the reactor in a water bath simplifies the synthesis process, ensures safety, and simplifies the design of the reactor. Indeed, in the absence of a forced cooling system, there is no need for shut-off, regulating, controlling and safety equipment providing a predetermined reactor cooling mode. Simplification of the design of the reactor is the absence of a cooling jacket.

 Permanent overpressure discharge ensures process safety, increases productivity and simplifies the design of the reactor; the discharge is made through a non-return valve, which is installed on the discharge pipe and opens with excess pressure that occurs during combustion. Reliable operation of the valve is ensured by heat shields and filters, cleaning and cooling the bleed gases. The non-return valve is placed at the bottom of the discharge pipe, the length of which from the reactor to the valve provides additional cooling of the bleed gases and, accordingly, the reliable operation of the non-return valve.

 The use of a gas vent system in the reactor design, which is a pipeline with a non-return valve in its upper part, placed in the reactor cover coaxially to its center, in the lower part of which a support flange is fixed, having a diameter of 0.85-0.95 of the diameter of the reactor, and is additionally equipped filter and heat shield made in the form of a shell and mounted above the support flange under the reactor cover, provides a quick and smooth pressure relief of the reaction gases.

 The drawing shows the design of the reactor to produce titanium carbide.

 The reactor vessel 1 is connected to the cover of volume 2 and sealed with a gasket 3. The support flange is rigidly fixed in the lower part of the discharge pipe 5 under the cover 2. The discharge pipe is additionally equipped with a filter 6 and a heat shield 7 made in the form of a shell and a check valve 8. Reaction charge placed in a shell (bag) 10 made of graphite fabric, isolated from the walls of the reactor with a layer of powder of the final product or its waste 11. The initiation of the combustion reaction is carried out by the initiating device 12, VK hatch spiral and conductive wires. The reactor is cooled in a water bath 13, where the reactor is placed after loading before synthesis.

 PRI me R. Titanium powder of the Transcarpathian pilot plant of powder metallurgy (the quantity and brands used are presented in the table of examples) with carbon black grade P 804T. The amount is calculated according to the presented formula after determining the coefficients of density, gas evolution and burning rate, mixed in a mixer with a displaced axis for 3 hours. The resulting mixture 9 is placed in a bag 10 made of graphite fabric, and then in the body of the reaction volume and isolated from the walls with powder the finished product 11 dispersion less than 1 mm, the layer thickness of 30 mm An electric spiral is installed in the upper part of the charge and connected to the initiating device 12. The cover 2 is connected to the reactor 1 through the sealing gasket 3 by means of quick-release cam mechanisms, while the support flange 4 presses the charge through the layer of insulating filling 11. The assembled reactor is placed in a water bath 13 , the water level must be above the level of the flange to ensure favorable cooling conditions. The initiating device 12 is connected to a source of electric current and by applying voltage to the electric spiral, a combustion reaction in the charge is initiated. A thin layer combustion reaction passes along the charge.

An exothermic interaction of titanium with carbon occurs, as a result of which the synthesized titanium carbide is heated to more than 2000 ^° C. When a combustion front passes through a charge from the reaction volume through the annular gap between the support flange 4 and the reactor wall, a large amount of gases is released. The amount of gas is determined by the coefficient Kg and depends on the contamination of the initial charge and on the density of the charge loaded into the reactor. The exhaust gases from the reaction volume are cooled and purified passing through a thermally insulated filling 11, through an annular gap between the housing 1 and the support flange 4, a heat shield 7, a filter 6, a discharge pipe 5 and a check valve 8.

 The table shows the data of chemical analysis of titanium carbide obtained according to the invention.

 The synthesis of titanium carbide creates difficulties with the discharge of gases from the reaction volume. Slow gas discharge, as in the prototype, upon reaching a pressure of 50 atm complicates the design of the reactor, limits its size due to the high pressures achieved in the reactors (tens, and sometimes hundreds of atmospheres). The discharge of gases with an increase in the flow cross-sections of the discharge pipe leads to unstable operation of the non-return valve, its clogging and burning of the sealing surfaces, i.e., its depressurization. To ensure stable operation of the non-return valve in the reactor design, a gas exhaust system is provided that differs from the similar one in the prototype, which allows creating conditions for a planned change in gas pressure in the reactor, for placement of devices for cleaning bleed gases (filters), devices for cooling gases (screens ), as well as for the accumulation of dust and powder materials, which together with the gas leave the reaction volume, remaining on the filter, then are poured onto the upper part of the support flange.

 The present invention improves the quality of the final product, primarily by increasing the completeness of the reaction (transformation) of the surface layers of the mixture. Another factor determining the improvement in quality is the possibility of manufacturing larger reactors. If previously reactors with a graphite shell reached a maximum volume of 30 liters, then the invention allows the manufacture of reactors with a volume of 80, 100 and 150 liters. This became possible due to simplification of the reactor design: due to a decrease in gas pressure and replacement of the graphite shell with a graphite fabric with heat-insulating backfill of the layer of the final product. Practice shows that the synthesis of large masses of a titanium carbide product improves its quality, the completeness of the reaction of the components of the charge becomes higher.

 A constant discharge of excess pressure does not allow an increase in pressure in the reactor by more than 1 atm. For such pressures, the reactor can be made of thin sheet material. Previously, reactors were made from thick-walled stainless pipes or from forgings. The reduction in pressure in the reactor greatly simplifies the design and increases productivity. It becomes possible to manufacture large reactors. The pressure reduction in the reactor also ensures the safety of the process.

 The advantages of the invention also include the fact that it allows the use of cheap and contaminated raw materials to obtain high purity titanium carbide.

Claims (2)

1. The method of producing titanium carbide by local ignition of the reaction mixture from carbon black and titanium and the closed volume of the reactor and the synthesis of carbide in the combustion mode during cooling of the reactor with water and constant pressure relief, characterized in that, in order to increase productivity, simplify and ensure the safety of the process, soot in the reaction mixture is taken in excess from stoichiometry, determined by the following formula:
C 2.5 · K _p · K _g · K _and ,
where C is the excess of soot, wt. to the total amount of the reaction mixture;
K _p the density coefficient of the reaction mixture, 0.5 0.75;
K _{g the} coefficient of gas evolution of the reaction mixture, 0.4 0.8;
K _and burning rate coefficient, 0.3 0.9;
and the reactor is cooled in a water bath.  2. A device for producing titanium carbide, comprising a cylindrical vertical reactor with a lid, equipped with a fitting for introducing an initiating device and coaxial with the center of the reactor means for removing reaction gases with a check valve, and a water cooling system of the reactor, characterized in that, in order to increase productivity, simplification and safety of the process, the means for the removal of reaction gases is made in the form of a pipeline with a support flange rigidly fixed in its lower part, located inside the reactor under a cover, and is additionally equipped with a filter and a heat shield made in the form of a shell mounted on the pipeline above the support flange, and the water cooling system is a bath.

Images