WO2020046229A2

WO2020046229A2 - Production of boron carbide, metal carbide and/or metal boride at high temperature and in continuous production line

Info

Publication number: WO2020046229A2
Application number: PCT/TR2019/050300
Authority: WO
Inventors: Semih Durmus; Tughan AKBASAK; Mehmet SOMER; Kamil KIRAZ; Ozge Balci; Bugra CİCEK
Original assignee: Ak-Kim Kimya Sanayi Ve Ticaret Anonim Sirketi
Priority date: 2018-08-27
Filing date: 2019-05-07
Publication date: 2020-03-05
Also published as: WO2020046229A3

Abstract

The present invention relates to a method developed for use in production of zirconium carbide, boron carbide, titanium carbide, titanium diboride and zirconium diboride particularly by means of solid-state reaction.

Description

PRODUCTION OF BORON CARBIDE, METAL CARBIDE AND/OR METAL BORIDE AT HIGH TEMPERATURE AND IN CONTINUOUS PRODUCTION LINE

TECHNICAL FIELD

The present invention relates to production of boron carbide, metal carbide and/or metal boride at high temperature and in continuous production line.

PRIOR ART

Boride and carbide materials essentially have characteristics like high hardness, high melting point, high thermal conductivity, high electrical conductivity, low density and high chemical stability. These characteristics lead to usage of these materials in advanced technology fields. They have usage in a very wide area from metallurgy to electronic sector.

Borides and carbides are chemical components which are used in industrial, defense industry and nuclear energy plants and which are more frequently used every passing day. Light and robust armours, which have high hardness value and which are resistant to corrosion types and which are resistant to high temperature, are produced from boron carbide. Boron carbide is advanced technological ceramic raw material and it shows 70% lightness when compared with other traditional armour materials.

Particularly in defense industry, they are used in vests and helicopter armours where lightness is important. They are industrially used as additive material in steels for providing hardness and resistance to abrasion and in welding electrodes for increasing resistance to abrasion and in abrasives and emeries as additive material.

In the present art, production of boride and carbide with high tonnages and with high purity is a very difficult and high-cost process. Thus, when required, boron carbide production is provided in induction furnaces, electrical arc furnaces and laboratory-scale tube furnaces. However, most of the time, desired purities cannot be provided.

In the invention with publication number US5720911 , a method for boron carbide preparation by means of sintering is described. In said US invention, there is a thermal process comprising a carbonization cycle where boron carbide is mixed with an epoxidized resin in the solution and where a homogenized and granulized mixture is kept in at least two fixed temperatures for predetermined time durations. The temperature increase/time proportion is adjusted in a controlled manner so as to permit discharge of the gases which occur during the decomposition of resin.

As a result, because of all of the abovementioned problems, an improvement is required in the related technical field.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to production of high purity boron carbide in pusher-type continuous furnaces, for eliminating the above mentioned disadvantages and for bringing new advantages to the related technical field.

An object of the present invention is to provide carbide and/or boride material with high purity.

Another object of the present invention is to provide a carbide and/or boride production method with increased efficiency.

Another object of the present invention is to provide a carbide and/or boride production method with reduced cost.

Another object of the present invention is to provide an environment-friendly carbide and/or boride production method.

In order to realize all of the abovementioned objects and the objects which are to be deducted from the detailed description below, the present invention is a method developed for use in production of zirconium carbide, boron carbide, titanium carbide, titanium diboride and zirconium diboride particularly by means of solid-state reaction. Accordingly, said invention is characterized by comprising the following steps respectively:

a) A physical preparation step comprising mechanical breaking/grinding step where the particle size is reduced; a mixing step providing homogeneity; and the step of compressing in the extruder applied for reducing impurity amount and feeding to the pusher-type furnace,

b) Thermal process step comprising the following steps respectively inside a pusher- type furnace: i) a discharge step applied for preventing reacting of oxygen with raw materials and with graphite-based carrier provided in the pusher-type furnace and where the medium gas is removed;

ii) a pre-heating step with two steps comprising a first pre-heating step applied at temperatures between 100°C and 300°C for providing evaporation of the water in the crystal and the humidity in the body, and a second pre-heating step applied at temperatures between 800°C and 1000°C for providing removal of undesired volatile materials,

iii) a heating step applied between 1 hour and 6 hours and at temperatures between 1700°C and 2200°C where the solid-state reactions are realized, c) a cooling step comprising a cooling off step where the product temperature is reduced to 600°C and a cooling step where the product temperature is reduced from 600°C to 100°C and to lower temperatures by realizing cooling with the help of liquid spraying.

In a preferred embodiment of the present invention, in step (a), the mixing process is provided in a vessel like silo by means of helezonic mixing flaps which move from the bottom towards the top from one side and which move from the right to the left from the other side in order to prevent inhomogeneity resulting from the density difference of the raw material inputs.

In another preferred embodiment of the present invention, in step (iii), the heating process continues at least for 120 minutes.

In another preferred embodiment of the present invention, the subject matter method is used in obtaining at least one of zirconium carbide, boron carbide, titanium carbide, titanium diboride and zirconium diboride.

In another preferred embodiment of the present invention, glassy boron oxide is used as the boron source.

In another preferred embodiment of the present invention, in step (b), the raw materials are moved by a pusher inside a pusher-type furnace.

In another preferred embodiment of the present invention, the monoxide gas release, formed as reaction output in the pusher-type furnace, is used again in the pusher-type furnace as fuel. In order to realize all of the abovementioned objects and the objects which are to be deducted from the detailed description below, the present invention relates to a product obtained by means of the abovementioned method. Accordingly, said invention is characterized in that said product is at least one of zirconium carbide, boron carbide, titanium carbide, titanium diboride and zirconium diboride.

In another preferred embodiment of the present invention, the particle size is at most 50 pm.

In another preferred embodiment of the present invention, the amount of impurity is at most 5%.

DETAILED DESCRIPTION OF THE INVENTION

In this detailed description, the subject matter boride or carbide production with high purity in pusher-type continuous furnace is explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.

By means of the subject matter method, production of boride or carbide with high purity can be provided. In the preferred applications, the subject matter method is used in obtaining materials like zirconium carbide, boron carbide, titanium carbide, titanium diboride and zirconium diboride.

In the application of boron carbide, at least one of or specific proportional mixtures of boric acid, glassy boron oxide, amorphous boron oxide is/are used. As the carbon source, at least one of or specific proportional mixtures of graphite, coal, coke coal, active carbon, carbon black is/are used.

In said method, the basic production steps in production of zirconium carbide, boron carbide, titanium carbide, titanium diboride and zirconium diboride comprise the following steps:

a) Physical preparation

b) Thermal process

c) Cooling

In step (a), grinding process is applied to the beginning raw materials for reducing the beginning particle size to the desired level. Bringing the particle size to the desired level is important for the homogeneity of the final product. Afterwards, in order to provide homogeneity to the raw materials for obtaining carbide or boride, mechanical mixing process is applied before the thermal process. Mixing process is realized in a vessel like silo by means of helezonic mixing flaps which move from the bottom towards the top from one side and which move from the right to the left from the other side in order to prevent inhomogeneity resulting from the density difference of the raw material inputs. After the mixing process, the blend is obtained from the mixture of the raw materials. Before the thermal process, the blend is partially compressed in the extruder and the structure is densified. By means of this, the area of contact of the powder formed particles with each other is increased and the thermal conduction between the particles is accelerated during the thermal process. Another important effect of compression is that the contact area of the particles with the outer medium is reduced and the impurities mixed to the blend are minimized.

In step (b), the extruded blend is fed to the pusher-type continuous furnace. Feeding is realized periodically into the graphite based tray/vessel, etc., provided on the furnace, at predetermined amounts particularly for carbide applications. While the material inside the pusher-type continuous furnace advances on the line, it does not stay fixed and it is moved by means of the pushers like piston, etc. provided in the furnace. Thus, the reaction of the material with the graphite base is prevented.

In practice, feeding of the blend to the furnace changes between 5 kg and 35 kg. Preferably feeding of the blend to the furnace is between 8 kg and 20 kg. The blend, which is in compressed form, advances in a discharge part, where the temperature level is low, inside the pusher-type continuous furnace. In order to prevent reaction of the oxygen, existing in the discharge part, with the beginning materials and with the graphite structure, the medium gas is discharged and it is fed by means of non-reactive gases like nitrogen, argon inside the furnace.

After the discharge part, it respectively advances in the pre-heating, heating, cooling off and cooling parts. At the end of the thermal process, the solid-state reactions inside the blend components are completed and the final product is obtained through the pusher-type continuous furnace outlet.

During pre-heating, the volatile substances existing in the crystal and the humidity existing in the blend are completely removed from the body. Besides, the reaction start between the particles is realized in this part as the heating part is approached. Pre-heating has two steps. First of all, in the ranges between 100°C and 300°C, the humidity and the water existing in the crystal are evaporated. Afterwards, in the ranges between 800°C and 1000°C, by means of pre-heating process, the removal of volatile and undesired materials is provided and the duration of heating in the main tank is shortened. Thus, purer and more homogeneous product can be obtained in shorter durations. The pre-heating duration is between 45 minutes and 90 minutes. In the preferred application, the pre-heating process is between 55 minutes and 70 minutes.

Solid-state reaction realized in the heating part can be started at temperatures 1600°C and above. By means of the temperature and process duration parameters, product purity and particle size optimization is realized. Providing the final product as thin powder, agglomerated powder, cinder or solid block depends on this optimization. In the heating part, the product is transformed into waste carbide or boride form. The temperature of the heating part is between 1600°C and 2200°C and the heating duration is between 60 minutes and 360 minutes depending on the material amount. The temperature of the heating part is preferably between 1800°C and 2000°C. While the temperature is between 1700°C and 1900°C, it is estimated that the desired particle size and the purity levels can be obtained by means of duration optimization. The side product is evaluated by means of burning in the CO preheat chamber.

In step c), the boride or carbide material, whose solid-state reaction is completed in the heating part, advances towards the cooling off part. In high temperature tests, instantaneous temperature change shall be avoided. For this reason, during cooling off, the boride or carbide material is firstly left for cooling and afterwards for external cooling before blowing air into the furnace. The cooling off process is realized until the boride or carbide material line decreases under the values in the vicinity of 600°C. By means of this, the particle growth, which occurs afterwards, is prevented without shortening the line lifetime and by removing the product from the hot region. At the same time, the production process is accelerated. In this step, the gas used for protecting oxidation facilitates the cooling process. Preferably, argon gas is used. The estimated process duration is between 1 and 3 hours. The cooling off process lasts preferably for 1 hour.

The material having boride or carbide structure, which exits the cooling off part, advances to the cooling part. In this step, the temperature of the material is reduced from 600°C to lower than 100°C (preferably to room temperature). This is realized for accelerating the production process. The cooling process in the furnace walls equipped with cooling water jacket lasts between 1 and 3 hours. In this step, there is no need to use protective (sweeper) gas. At the end of the process, the trays are automatically discharged and transferred to the first filling step. The product, which is in waste boride or carbide form, is discharged to the collection chamber for the breaking process when needed.

Mechanical breaking process is applied to the obtained product for decreasing the particle size when required. However, grinding process is not needed for the products whose particle size is small and whose purity sensitivity is low (£90%). The big-sized products are reduced to the range between 100 pm and 50 pm by means of mill grinder. Jet grinder is used for between 50 pm and 10 pm and for lower sizes.

The gases used in the pusher-type continuous furnace are used for their gas protecting, sweeping and cooling properties. These gases prevent oxidizing of the material and the medium by means of pushing the oxygen which remains in the medium and by means of their choking characteristic. By means of this, the purity proportion of the product is increased. The carbon monoxide gas occurring during reaction is removed from the medium and the reaction speed is increased, and by means of this, the sweeper characteristic is utilized. Said gases are sprayed onto the hot material and in the final step, they are used for cooling besides the other two characteristics. Methane, hydrogen, argon and nitrogen gases are fed from outside and they are among the gases which are to be used. At the same time, the carbon monoxide gas which is the side product is evaluated in the pre-heating chamber and it is used again and evaluated.

Some of the applications where the subject matter method is used are as follows:

Exemplary application of boron carbide: The glassy boron oxide and acetylene carbon used in the exemplary application realize the following reaction.

At least one of or specific proportions of glassy boron oxide or amorphous boron oxide is used as the boron source in the beginning material. At least one of or specific proportions of acetylene carbon black or graphite or carbon black is used as the carbon source.

The particle size of the used amorphous boron oxide shall be between 300 pm (d35) and 350 pm (d35) and the purity proportion shall be 98%. The particle size of the used glassy boron oxide is between 200 pm (d35) and 275 pm (d35) and the purity proportion shall be 98%. In the preferred application, glassy boron oxide is used. The used acetylene carbon black shall have purity of at least 99%. The particle size of the used graphite shall be between 35 pm (d90) and 45 pm (d90) and shall have purity of at least 98%. The particle size of the black carbon shall be between 40 pm and 50 pm. In the preferred application, acetylene carbon is used. The production process is applied so as to be within the abovementioned scope. The purity percent obtained after boron carbide production by means of pusher-type continuous furnace is at least 95%. The size of the particle obtained is at most 50 pm.

In the subject matter pusher-type continuous furnace, by means of the carbide, boride production method, carbide and boride materials can be produced and particularly boride carbide can be produced not only in several kilograms but in high tonnages. At the same time, thanks to the used material and the applied high temperatures and particularly compression in the extruder, the impurity proportion in the body is reduced.

In carbo-thermal boron carbide production realized by means of the arc furnace and induction furnace, 2.8 kilograms of carbon monoxide gas, which is poisonous and which is harmful to environment, occurs for each 1 kilogram B4C. Another advantage of the described method when compared with the already used boron carbide production methods is that the monoxide gas release is used as fuel in the process and it is minimized. By means of this, production is environment-friendly and at the same time, production has lower cost.

By means of the subject matter production method, since the raw materials fed into the furnace are not loaded in great amounts in a single try and since the raw materials are in the form of smaller blends which follow each other, the heat amount which is required for sintering of the product, particularly of B4C stays at low levels, and the breaking and grinding processes, which are important cost factors, can be realized in an easier manner and in shorter time.

The protection scope of the present invention is set forth in the annexed claims and cannot be restricted to the illustrative disclosures given above, under the detailed description. It is because a person skilled in the relevant art can obviously produce similar embodiments under the light of the foregoing disclosures, without departing from the main principles of the present invention.

Claims

1. A method developed for use in production of zirconium carbide, boron carbide, titanium carbide, titanium diboride and zirconium diboride particularly by means of solid-state reaction, characterized by comprising the following steps respectively: a) A physical preparation step comprising mechanical breaking/grinding step where the particle size is reduced; a mixing step providing homogeneity; and the step of compressing in the extruder applied for reducing impurity amount and feeding to the pusher-type furnace,

b) Thermal process step comprising the following steps respectively inside a pusher- type furnace:

i) a discharge step applied for preventing reacting of oxygen with raw materials and with graphite-based carrier provided in the pusher-type furnace and where the medium gas is removed;

2. The method according to claim 1 , wherein in step (a), the mixing process is provided in a vessel like silo by means of helezonic mixing flaps which move from the bottom towards the top from one side and which move from the right to the left from the other side in order to prevent inhomogeneity resulting from the density difference of the raw material inputs.

3. The method according to claim 1 , wherein in step (iii), the heating process continues at least for 120 minutes.

4. The method according to claim 1 , wherein said method is used in obtaining at least one of zirconium carbide, boron carbide, titanium carbide, titanium diboride and zirconium diboride.

5. The method according to claim 4, wherein glassy boron oxide is used as the boron source.

6. The method according to claim 1 , wherein in step (b), the raw materials are moved by a pusher inside a pusher-type furnace.

7. The method according to claim 1 , wherein the monoxide gas release, formed as reaction output in the pusher-type furnace, is used again in the pusher-type furnace as fuel.

8. A product which is in boride or carbide structure and obtained by means of the method according to claim 1 , wherein said product is at least one of zirconium carbide, boron carbide, titanium carbide, titanium diboride and zirconium diboride.

9. The product according to claim 7, wherein the particle size is at most 50 pm.

10. The product according to claim 7, wherein the amount of impurity is at most 5%.