KR100276110B1 - Method of producing chromium carbide powder by self-propagating high-temperature synthesis - Google Patents

Abstract

Method for preparing pure chromium carbide (Cr ₃ C ₂ ) powder from chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) powder by using a self-propagating high-temperature synthesis Is disclosed. According to the present invention, chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) are weighed in a molar ratio of 3: 9: 4 and chromium carbide (Cr ₃ C ₂ ) is added as a diluent to add alumina ( Al ₂ O ₃ ) wet-mix in N-hexane for about 24 hours in a ball mill. The mixed powder was dried in a vacuum dryer for about 70 ° C. for 24 hours, and then subjected to a molding pressure of 94 to 565 MPa (= pressure corresponding to 50 to 70% of the theoretical density) using a stainless mold, to a diameter of 20 to 30. Pellets of 15 mm and 15 mm in height are made. The pellets thus formed are placed in a self-combustion reactor, and the pellets are ignited and burned under an atmosphere of argon (Ar) gas at 1 atmosphere. The ignited specimen is then milled in an alumina ball mill for about 50 hours and then leached with 25% hydrochloric acid (HCl) solution to remove magnesium oxide (MgO) and other impurities. Finally, it is washed about 3 to 6 times and dried sufficiently in a drier at a temperature of 60 to 70 ° C. As a result, pure chromium carbide (Cr ₃ C ₂ ) powder is obtained.

Description

Method for preparing chromium carbide powder using the self-burning reaction method

The invention provides pure chromium carbide (Cr) powder from chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) powder using a self-propagating High-temperature Synthesis (hereinafter referred to as SHS). ₃ C ₂ ) relates to a method for producing a powder, and in particular, magnesium oxide (MgO) obtained as a by-product after reduction of chromium oxide (Cr ₂ O ₃ ) powder using magnesium (Mg) powder as a reducing agent, and hydrochloric acid (HCl). It is related to a method for producing pure chromium carbide (Cr ₃ C ₂ ) powder by leaching using).

In general, various special rolls used in industries such as steel, fiber, paper, and the like are used by coating a surface by blowing a thermal spray material onto the surface of a base material by using a spraying method. At this time, cemented carbide, metal carbide, etc. are used as a thermal spraying material laminated on the surface of the base material, and these are mainly urgently developed, and thus are urgently developed.

Chromium carbide (Cr ₃ C ₂ ), which is used for high hardness materials, corrosion resistant materials, and thermal spraying methods such as plasma spraying, metal spraying, and J-gun spraying, is not only difficult to manufacture but also costly to produce. It is so high that it is required to manufacture the material more economically.

Until now, there have been known a number of methods for producing chromium carbide (Cr ₃ C ₂ ) powder as described above, but the conventional manufacturing method is complicated and requires a high temperature reactor or a vacuum reactor, and consumes a large amount of energy, so it is economical. There is a drawback to this. Therefore, it has become an important task to develop a method for economically producing chromium carbide (Cr ₃ C ₂ ) powder having the advantages described above in the same reactor.

The present invention has been made to solve the conventional problems as described above, the object of the present invention by using a magnesium (Mg) powder as a reducing agent in the self-combustion reaction to the raw material powder of chromium oxide (Cr ₂ O ₃ ) powder After reduction, magnesium oxide (MgO) obtained as a by-product is leached with hydrochloric acid (HCl) to provide a method for economically preparing pure chromium carbide (Cr ₃ C ₂ ) powder.

1 is a manufacturing process chart of chromium carbide (Cr ₃ C ₂ ) powder according to the present invention,

2 is a schematic representation of the configuration of a self-burning reactor used to carry out the present invention;

3 is a graph showing the change in combustion temperature according to the amount of diluent, and

Figure 4 is a graph showing the X-ray pattern results of the final chromium carbide (Cr ₃ C ₂ ) powder after leaching with 25% hydrochloric acid (HCl) solution.

<Explanation of symbols for main parts of drawing>

10: preheat 12: green pellets

14: Thermocouple 16: Data Collector

20 computer 22 tungsten (W) filament

24: power supply 26: heat-resistant glass

28 vacuum pump 30 inert gas supply source

32: vent 34: cooling device

36: infrared thermometer 100: self-burning reactor

102: reactor chamber

In order to achieve the above object, the present invention,

Mixing chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) (S1);

First drying the mixture formed in the step S1 (S2);

Molding the first dried mixture into pellets (S3);

Charging the pellets into a reactor chamber of a self-combustion reactor to burn (S4);

Taking out the combustion product produced in the step (S4) from the reactor chamber and leaching magnesium oxide (MgO), which is an intermediate phase, from the combustion product (S5);

It provides a method for producing chromium carbide (Cr ₃ C ₂ ) powder comprising the step (S6) of washing the product produced after the step (S5) sufficiently after the second drying (S6).

Hereinafter, a process for preparing pure chromium carbide (Cr ₃ C ₂ ) powder according to the present invention with reference to the accompanying drawings in more detail.

First, FIG. 2 is a diagram schematically showing the configuration of a self-burning reactor used to carry out the present invention. Referring to FIG. 2, the self-burning reactor 100 mainly consists of the reactor chamber 102 and its peripheral devices. The self-burning reactor 100 may have any structure as long as it can create a vacuum or inert gas atmosphere in the reactor chamber 102 and ignite the specimen located in the reactor chamber 102.

The preheating furnace 10 is located in the center of the reactor chamber 102 of the self-burning reactor 100. Preferably, the preheating furnace 10 has a cylindrical shape of 30 cm in diameter and 40 cm in length. In the preheating furnace 10, a green pellet 12 composed of chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) is located. One side of the preheating furnace 10 is equipped with a thermocouple 14 for measuring the temperature of the green pellet 12 to be burned in the preheating furnace 10. Thermocouple 14 is electrically connected to computer 20 via data collector 16.

Within the reactor chamber 102, tungsten filaments 22 for igniting the green pellets 12 located in the preheater 10 are located just above the preheater 10. Tungsten filament 22 receives current from a power source 24 located outside the reactor chamber 102. On one side wall of the reactor chamber 102 is a heat-resistant glass 26 of a disc shape that can be opened and closed. The heat-resistant glass 26 performs the inlet and outlet of the green pellet 12 while opening and closing as needed, and allows the operator to check the combustion state of the green pellet 12 with the naked eye through the heat-resistant glass 26. .

At the bottom of the reactor chamber 102 is connected a vacuum hose 29 for establishing a vacuum in the reactor chamber 102. The vacuum hose 29 extends to a vacuum pump 28 located outside the reactor chamber 102. The vacuum pump 28 draws air in the reactor chamber 102 as needed to create a vacuum. In addition, an inert gas supply hose 31 for introducing an inert gas into the reactor chamber 102 is connected to a lower end of the reactor chamber 102. The inert gas supply hose 31 extends to an inert gas supply source 30 located outside the reactor chamber 102. Inert gas source 30 provides an inert gas, such as argon (Ar), into reactor chamber 102 as needed. In addition, the vent 32 formed on one side of the lower end of the reactor chamber 102 maintains a constant pressure in the reactor chamber 102 or discharges the pressure in the reactor chamber 102 to the outside when the heat-resistant glass 26 is opened. Let's do it.

Cooling devices 34 for maintaining a constant temperature in the reactor chamber 102 are installed in the upper and lower portions of the reactor chamber 102. Above the outer side of the reactor chamber 102, a vacuum instrument panel 36 is provided for notifying the vacuum state formed in the reactor chamber 102.

1 is a manufacturing process chart of chromium carbide (Cr ₃ C ₂ ) powder according to the present invention. A process for producing chromium carbide (Cr ₃ C ₂ ) powder using the self-burning reactor 100 as described above with reference to FIGS. 1 and 2 will be described.

The present invention is a method of obtaining chromium carbide (Cr ₃ C ₂ ) powder by SHS after mixing the raw material chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) in a certain molar ratio. In general, the SHS used in the present invention is a self-combustion reaction method in which a chemical reaction between a solid and a solid is an exothermic reaction and synthesizes a material using its own heat of chemical reaction after ignition of the material without supplying energy from the outside. In other words, SHS synthesizes a ceramic sample, which is generally difficult to synthesize, at a high temperature (1,500 to 4,000 ° C.) in a few seconds using the calorific value of the sample itself, and thus is a synthesis method for obtaining a high purity compound having good sinterability.

Chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) used as starting materials in the present invention have properties and chemical compositions as shown in Tables 1 and 2 below.

Table 1. Properties of Starting Materials

Starting material Average particle size (μm) water(%) Source Cr ₂ O ₃ One 99.0 Taiwan Pharmacological Chemical Coal 0.5 99.9 Aldrich Mg 10 99.8 -

Table 2. Chemical Composition of Starting Materials

Elemental Starting Material impurities(%) Al Ca Fe Na CD Si Mn K Ti Cr ₂ O ₃ 0.15 0.08 0.32 0.15 - - 0.1 0.15 0.05 Coal - 0.02 0.01 - 0.025 0.03 0.004 0.006 0.005 Mg 0.045 0.036 0.023 - - 0.031 0.009 0.056 -

At this time, coal is used as carbon (C).

The chromium oxide (Cr ₂ O _3), magnesium (Mg), and then provided with a carbon (C), the following scheme of chromium oxide, such as _{(Ⅰ) (Cr 2 O 3} ), magnesium (Mg), and carbon (C) Mix uniformly at a constant composition ratio.

3Cr ₂ O ₃ + 9Mg + 4C = 2Cr ₃ C ₂ + 9MgO ━━ (Ⅰ)

Since the calorific value generated in the reaction is very high and the sample is scattered during the reaction, the combustion temperature and rate cannot be measured, and thus a diluent (Cr ₃ C ₂ ) is added. That is, chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) are weighed in a molar ratio of 3: 9: 4, and an appropriate amount of chromium carbide (Cr ₃ C ₂ ) is added as a diluent and mixed uniformly. 3 is a graph showing the change in combustion temperature according to the amount of diluent. 3, it can be seen that as the amount of diluent increases, the combustion temperature is lowered, and the cooling rate is lowered.

After mixing chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C), milling was performed by wet mixing with N-hexane for about 24 hours using an alumina (Al ₂ O ₃ ) ball.

Next, since the mixed powder is easy to oxidize in the air, it is dried for 24 hours at a temperature of about 70 ℃ in a vacuum dryer. Thereafter, using a stainless mold, a compacting pressure of 94 to 565 MPa, which reaches 50 to 70% of the theoretical density, is applied to the dry powder and compressed. Thus, after the preforms having a diameter of 20 to 30 mm and a height of 15 to 25 mm are made, the preforms are preheated and burned in the internal combustion reactor 100.

To this end, the heat-resistant glass 26 of the self-combustion reactor 100 is opened and green pellets 12 made of the compressed mixture are charged into the reactor chamber 102. That is, the green pellet 12 is located in the preheating furnace 10. Under this condition, after closing the heat-resistant glass 26, the vacuum pump 28 is operated to create a vacuum in the reactor chamber 102, or the inert gas source 30 is operated to inert gas, into the reactor chamber 102, Preferably argon (Ar) gas is introduced. After the argon (Ar) atmosphere of 1 atmosphere is formed, the heat-resistant glass 26 is closed, and a preheating of the green pellet 12 to a temperature of 400 ° C is applied by applying a current from the power supply source 24 to the tungsten filament 22. do. After sufficient preheating has occurred, a sufficient amount of current is applied from the power supply 24 to the tungsten filament 22 to ignite and burn the green pellet 12 to ignite and burn the green pellet 12.

Next, the ignited specimen is taken out of the reactor chamber 102 and then milled for about 50 hours using an alumina (Al ₂ O ₃ ) ball. Thereafter, magnesium oxide (MgO) and other impurities are leached off with a 25% hydrochloric acid (HCl) solution to obtain the desired product.

Hereinafter, a preferred embodiment of the present invention will be briefly described.

Example

Chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) are mixed according to the above reaction formula (I) as raw materials. At this time, chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) are weighed in a molar ratio of 3: 9: 4 and an appropriate amount of chromium carbide (Cr ₃ C ₂ ) is added as a diluent to alumina (Al ₂ O ₃ ) Wet mixing with N-hexane in a ball mill for about 24 hours.

Since the mixed powder is easy to oxidize in air, it is dried in a vacuum dryer for about 70 ° C. for 24 hours and then using a stainless mold to form a molding pressure of 94 to 565 MPa (= 50 to 70% of the theoretical density). ) To make pellets with a diameter of 20 to 30 mm and a height of 15 to 25 mm. After the pellets thus shaped are placed in a self-combustion reactor, the pellets are ignited and burned in an inert gas atmosphere, preferably in an argon (Ar) gas atmosphere of 1 atmosphere. The ignited specimen is then milled in an alumina ball mill for about 50 hours and then leached with 25% hydrochloric acid (HCl) solution to remove magnesium oxide (MgO) and other impurities. Next, it wash | cleans about 3-6 times, and fully makes it dry 2nd degree to 60-70 degreeC in a dryer. The generated sample is analyzed by X-ray diffraction (X-Ray Diffraction).

Figure 4 is a graph showing the X-ray pattern results of the final chromium carbide (Cr ₃ C ₂ ) powder after leaching with 25% hydrochloric acid (HCl) solution. 4, it can be seen that pure chromium carbide (Cr ₃ C ₂ ) is obtained.

As mentioned above, in the method for preparing chromium carbide (Cr ₃ C ₂ ) powder according to the present invention, chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) are weighed in a constant molar ratio and the diluent An appropriate amount of chromium carbide (Cr ₃ C ₂ ) is added to form a mixture thereof, followed by drying in a vacuum dryer, followed by ignition and combustion in a self-combustion reactor. Therefore, the high temperature reactor required by the conventional chromium carbide (Cr ₃ C ₂ ) powder production method is unnecessary, and the manufacturing process is simplified. That is, the existing manufacturing technology requires a high vacuum, high temperature furnace, the present manufacturing method can produce chromium carbide (Cr ₃ C ₂ ) having the same or higher quality without such equipment. In addition, the combustion reaction of the reactant proceeds automatically by the self-heating amount is high energy efficiency and economical.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below. I can understand that you can.

Claims (6)

Mixing chromium oxide (Cr ₂ O ₃ ), magnesium (Mg) and carbon (C) (S1); First drying the mixture formed in the step S1 (S2); Molding the first dried mixture into pellets (S3); Charging the pellets into a reactor chamber of a self-combustion reactor to burn (S4); Taking out the combustion product made in the step (S4) from the reactor chamber and leaching magnesium oxide (MgO), which is an intermediate phase, from the combustion product (S5); Method for producing chromium carbide (Cr ₃ C ₂ ) powder comprising the step (S6) of washing the product produced after the step (S5) sufficiently after the second drying (S6). The method according to claim 1, wherein in step S1, the chromium oxide (Cr ₂ O ₃ ), the magnesium (Mg) and the carbon (C) are weighed in a molar ratio of 3: 9: 4 and the diluent is added in a predetermined amount. Method for producing chromium carbide (Cr ₃ C ₂ ) powder, characterized in that the wet mixing for 24 hours by adding as much as added. The method of claim 2 wherein the chromium carbide (Cr ₃ C ₂₎ process for producing a powder, characterized in that the diluent is a chromium carbide (Cr ₃ C _2). The chromium carbide (Cr ₃ C ₂ ) powder according to claim 1, wherein in step S2, pellets having a diameter of 20 to 30 mm and a height of 15 to 25 mm are made by applying a pressure of 94 to 565 MPa to the mixture. Manufacturing method. 2. The method of claim 1, wherein the step (S5), process for producing a chromium carbide (Cr ₃ C ₂₎ powder of the magnesium oxide (MgO) characterized by leaching a mixture of hydrochloric acid (HCl) of 25%. The method for producing chromium carbide (Cr ₃ C ₂ ) powder according to any one of claims 1 to 5, wherein an argon (Ar) gas atmosphere is formed in the reactor chamber.