JPH0372569B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing boron carbide powder, and more particularly to a method for producing boron carbide powder in which a mixture of magnesium borate, magnesium, and carbon is reduced and carbonized. Various methods have been proposed to produce boron carbide powder, but industrially, reducing metals such as magnesium and carbon such as graphite and coke are added to boron-containing substances such as boric acid and boric anhydride.
The method used is to remove moisture and volatile matter at a temperature of °C, then perform a reduction and carbonization reaction at high temperatures, and remove by-product impurities such as magnesium oxide with acid to obtain boron carbide powder. To explain further, in this method, for example, boron dioxide, magnesium and carbon are used as raw materials to perform a reduction and carbonization reaction according to the following formula (1). 2B ₂ O ₃ +6Mg+C→B ₄ C+6MgO...(1) This reaction is exothermic and approximately 280Kcal/
Since a large amount of heat is generated by B ₄ C・mol, once the reaction starts, it progresses rapidly, causing the raw materials to scatter,
In addition to causing safety problems due to undesirable phenomena such as rapid expansion of the produced gas, there are also disadvantages of low yield and poor quality of boron carbide powder. In order to eliminate these drawbacks, the raw materials are heated in advance to a temperature of 300 to 600℃ lower than the starting temperature of the reduction and carbonization reaction.
After heat treatment to remove volatile components such as moisture, the method is heated to the temperature at which boron carbide is produced.However, due to the reaction heat generated, local temperature increases tend to occur during the reductive carbonization reaction. In addition, even if fine particles are used as raw materials, there is a limit to the opportunities for contact between the raw materials, and there is not enough time to complete the reaction, resulting in scattering of the raw materials or the dissipation of magnesium, resulting in lower yields. The disadvantage is that it is difficult to stabilize. The purpose of the present invention is to solve these drawbacks. By using a mixture of magnesium borate, magnesium, and carbon as a raw material and subjecting it to a reduction and carbonization reaction, high-purity boron carbide powder can be obtained in good yield. The present invention aims to provide a method for producing boron carbide powder that can be produced using the following methods. That is, the present invention provides a method for producing boron carbide powder by reacting a mixture of magnesium borate, magnesium, and carbon at high temperature, in which the mixture is heat-treated at a temperature of 700 to 1000°C for 1 to 4 hours, and then
It is further characterized by heat treatment at a temperature of 1450 to 1650°C for at least 0.5 hours or more. The present invention will be further explained in detail below. In the present invention, magnesium borate is 3MgO.
It contains B ₂ O ₃ and/or 2MaO.B ₂ O ₃ as a main component. In the following, the present invention will be explained using magnesium borate containing MgO.B ₂ O ₃ as a main component, but the present invention is not limited thereto. In other words, the reaction using magnesium borate as a raw material produces 3MgO.
Taking B ₂ O ₃ as an example, the reaction is shown by reaction formula (2). 2 (3MgO・B ₂ O ₃ ) + 6Mg + C → B ₄ C
+12MgO...(2) This reaction is decomposed into two basic reactions: 3MgO・B ₂ O ₃ +3Mg→2B+6MgO...(3) 4B+C→B ₄ C...(4). In order to stabilize the yield of boron carbide in reaction formula (2) of reduction and carbonization, it is first necessary to stably complete the reduction reaction in reaction formula (3). However, the starting temperature of this reaction is 600 to 900°C, which is difficult to stabilize, and the magnesium in reaction formula (2) becomes a melt at 650°C, resulting in a significantly high vapor pressure, which easily dissipates out of the reaction system. Further, the boron produced in reaction formula (3) is so-called Moisan boron and is highly active, but it usually contains about several percent of magnesium and oxygen. This boron reacts with carbon mixed in advance to form boron carbide according to reaction formula (4). This reaction progresses rapidly at temperatures above 1450°C, but at the same time, most of the magnesium and oxygen contained in boron are converted to magnesium oxide, etc., and boron carbide is purified. In order to efficiently carry out the reaction, the present invention provides the following features:
The yield is stabilized by holding at a temperature of 700 to 1000°C for 1 to 4 hours to complete the reduction reaction shown in reaction formula (3) while keeping the vapor pressure of magnesium low. It is characterized in that it is heated to a temperature of 1650°C for at least 0.5 hours to form boron carbide. The present invention will be further explained in detail below. In the heat treatment of raw materials, the first stage heat treatment temperature is
The reason why the temperature is limited to 700 to 1000°C is that at temperatures below 700°C, the reduction reaction does not substantially proceed, and at temperatures above 1000°C, magnesium volatilization is significant, making it difficult for the reduction reaction to stabilize and complete. Further, the holding time at this temperature is 1 to 4 hours. This is because if the reaction time is less than 1 hour, the reaction will not proceed sufficiently, and if the reaction time exceeds 4 hours, no further progress of the reaction will be observed. Next, the heat treatment temperature in the second stage is 1450 to 1650℃, and the reason for this limitation is that below 1450℃, the formula
This is because the carbonization reaction (4) does not proceed sufficiently, and when the temperature exceeds 1650°C, the reaction shown in reaction formula (5) becomes rapid and the yield decreases significantly. It is also necessary to hold at this temperature for at least 0.5 hour. If the time is less than 0.5 hours, the reaction will not proceed sufficiently and it will be difficult to obtain highly pure boron carbide. B ₄ C + 5MgO → 4BO↑ + 5Mg↑ + CO↑ ...(5) As explained above, the present invention provides a method for producing boron carbide powder by reacting specific magnesium borate, magnesium, and carbon at high temperature.
A method in which stage heat treatment is performed at 700 to 1000°C for 1 to 4 hours, and second stage heat treatment is performed at 1450 to 1650°C for at least 0.5 hours, and according to the present invention, when manufacturing boron carbide, compared to conventional methods, Since rapid progress of the reaction that occurs can be prevented, there is no problem with safety, and there is an advantage that high quality boron carbide can be obtained in good yield. Example: 1500g of industrial boric acid (manufactured by US Borax),
1500 g of soft industrial magnesium oxide (Star Mag U manufactured by Kamishima Chemical Co., Ltd.) was mixed, and this mixture was placed in an alumina crucible and fired at 1000° C. for 4 hours in an air atmosphere. According to the X-ray diffraction of the powder, 3MgO・
It was a magnesium borate containing B ₂ O ₃ as the main mineral and a small amount of 2MgO.B ₂ O ₃ . To 2054 g of magnesium borate obtained in the above procedure, 828 g of magnesium powder (manufactured by Yamaishi Metal - 100 mesh)
and artificial graphite powder (Lonza product name “KS-15”)
After adding 68 g and thoroughly mixing, the mixture was filled into a graphite crucible and heat-treated under the heating conditions shown in the table under an argon gas atmosphere. After grinding the product in a ball mill, it was heated to a temperature of 90℃ to 15%
By-product magnesium oxide was removed by immersing it in a hydrochloric acid solution. Next, this was filtered out using a glass filter, and the cake was vacuum-dried at 160°C to remove boron carbide 298
I got g. The yield and chemical analysis values are shown in the table. Comparative Example The same procedure as in Example was carried out except that the heat treatment conditions were changed as shown in the table. 【table】

Claims (1)

[Claims] 1. A method for producing boron carbide powder by reacting a mixture of magnesium borate, magnesium and carbon at high temperature, wherein the mixture is heated at a temperature of 700 to 1000.
After heat treatment at ℃ for 1 to 4 hours, further temperature 1450 ~
A method for producing boron carbide powder, characterized by heat treatment at 1650°C for at least 0.5 hours. 2 Magnesium borate is 3MgO・B ₂ O ₃ and/
or 2MgO.B ₂ O ₃ as a main component, the manufacturing method according to claim 1.