JPH0825729B2 - Combustion synthesis method of high-purity TiN - Google Patents

Description

TECHNICAL FIELD The present invention relates to a TiN combustion synthesis method using combustion of titanium powder and nitrogen, and uses liquid nitrogen as a nitrogen source to burn highly pure titanium nitride with high efficiency. It relates to a method of synthesizing. More specifically, the titanium powder compact is placed in a liquid nitrogen bath, the lower surface of the compact is heated and ignited to induce a reaction, and the gas phase component and heat are also moved upward as the reaction propagates to information. It relates to a method for producing a pure nitride.

BACKGROUND OF THE INVENTION Nitride is characterized by its high strength, wear resistance and corrosion resistance, and has a wide range of applications in the electrical engineering and chemical industries. One known method for the production of such nitrides consists of heating the initial components in a nitrogen or ammonia stream at a temperature of 1200-2000 ° C. As the starting component, pure elements and their compounds such as halides are used. The product resulting from the heat treatment is finely divided and the heat treatment is repeated in order to interact with the starting components. This process is carried out in several stages until the desired product reaches the required quality. This is because the nitriding reaction does not proceed completely because nitrogen is prevented from diffusing into the caked layer, and the caked nodule is discharged and crushed.
The nitriding is repeated again. As another method, there is a method of utilizing a combustion reaction, for example, as in the invention described in Japanese Patent Publication No. 56-27441, which uses a high-pressure nitrogen gas or liquid nitrogen to burn from the upper surface of a metal powder compact. It is a method of inducing a reaction to synthesize a nitride, and its purpose is to control the reaction propagation speed and improve the nitriding rate by changing the filling degree of the green compact.

(Problems to be solved by the invention) However, when liquid nitrogen is used, the reaction propagation direction is opposite to the reaction propagation heat and the migration direction of vaporized nitrogen in the downward reaction propagation due to ignition from the upper surface. However, the nitriding rate does not improve so much. That is, in the combustion of metal powder in liquid nitrogen, there is a vaporization process of liquid nitrogen as the first step, and the reaction between the vapor phase and the metal proceeds. Therefore, in the downward reaction propagation, the reaction propagation direction and the heat transfer direction are opposite, so the maintenance time of the high temperature region behind the reaction surface is short, and the nitrogen gas generated behind the high temperature region also moves upward, It is not effective for the continuous nitriding reaction on the surface of the high temperature region behind due to the propagation, and the impurity component (for example, oxygen gas) existing in the atmosphere is taken in downward in the process of moving nitrogen gas upward. It is not effective in purifying the obtained nitride.

(Means for Solving Problems) The present invention solves the problem that it is difficult to improve the nitriding rate in the above-described conventional combustion synthesis using liquid nitrogen, and realizes nitride synthesis with high purity and high conversion rate. In order to achieve this, a method for producing a nitride is adopted in which ignition is performed from the lower surface of a metal green compact placed in liquid nitrogen and the reaction is propagated upward.

In the present invention, a metal titanium powder green compact is placed in a reaction vessel filled with liquid nitrogen, a heat resistant conductor such as a tungsten wire is placed on the lower end face of the green compact, and this is connected to an external power source. , A part of the lower surface of the green compact is heated to 1700 ° C or more by energization to induce a combustion reaction between the green compact and nitrogen, and nitrogen in the constituent powder of the green compact following the combustion reaction The spontaneous nitridation reaction of titanium metal with diffusion is promoted, and the heat generated as a result of the initiated combustion process forms a high-temperature reaction layer of 2000 ° C or higher, and the reaction layer is successively advanced upward in layers. It is characterized by a combustion synthesis method of high-purity TiN.

(Operation) The feature of the present invention is that the transfer of heat generated by the exothermic reaction is controlled by igniting from the lower part of the sample with liquid nitrogen as the nitrogen source and setting the reaction propagation direction up and down By matching the direction, it is possible to achieve a higher conversion rate.

Liquid nitrogen has a higher nitrogen density per unit volume than nitrogen gas, and it is judged that the nitriding efficiency is high, but since the nitriding reaction proceeds in the gas phase, liquid nitrogen is disadvantageous by the amount equivalent to the heat of vaporization, The conversion rate is not higher than that of nitrogen gas.

For this reason, in the present invention, the reaction propagation is carried out in layers from the lower part to the upper part. That is, in the present invention, heat is also diffused upward as the reaction is propagated upward, but the reaction propagation speed is preferably equal to or higher than the propagation speed of heat in the powder compact, and if the powder compact state can induce the reaction Meets The induction of the reaction is achieved by locally heating, but the ignition temperature is preferably 1700 ° C or higher, and any method can be used as long as it is a means of producing such a temperature environment, but generally tungsten (W)
Electric heating using a wire can be used.

For general green compact, 40-60% of theoretical density is desirable. Further, since the nitrogen gas generated in the reaction propagation process also moves upward from the lower part, the purity of nitrogen in the high temperature region behind the reaction surface is high, and the obtained nitride has high purity. The nitriding reaction preferably proceeds at a temperature equal to or higher than the melting point of the reactive powder, and the temperature of the reaction system is preferably 2000 ° C. or higher even if part of the heat generated by the nitriding reaction is dissipated to the outside. During the reaction, it is desirable that liquid nitrogen is continuously supplied from the upper part so that the sample green compact is always kept in liquid nitrogen. When the reaction propagates upward, the heat transfer is also upward, and if the reaction propagation velocity is controlled to be higher than the heat conduction velocity in the reaction compact, steady combustion propagation is possible. In addition, the time for maintaining the high temperature state in the rear also becomes longer, and as a result, more efficient nitriding can be achieved. Further, when liquid nitrogen is used, the amount of impurities contained is small, and the nitrogen gas produced moves upward as the reaction propagates upward, so that the amount of impurities in the obtained nitride is small and a highly pure product can be obtained.

The reason why the reaction is carried out stepwise in layers is that when the reaction temperature rapidly rises to 4000 to 5000 ° C., the titanium powder is partially melted into a nodular solid solution, which is an unreacted substance that does not react with liquid nitrogen. Is generated and the conversion rate is lowered, which is not preferable. For this reason, the reaction is preferably performed by forming a high temperature reaction layer having a temperature of 2000 ° C. or more in a layered manner from the lower side to the upper side of the reaction layer.

The metal nitride obtained by the method of the present invention can be synthesized in a short time as compared with the conventional synthesis method in which an electric furnace is melted, and active elements are removed in the combustion process, so that high-purity synthesis with few impurities is performed. It becomes a nitride. Therefore, it is possible to supply a high-purity nitride that can be sufficiently used as a starting material such as titanium nitride, which is attracting attention as a diffusion blocking layer in the semiconductor field.

As described above, it has been found that a high conversion can be obtained by propagating the combustion reaction from the lower part and controlling the movement of heat and gas, and has led to the present invention.

Hereinafter, embodiments of the combustion synthesis method of high-purity titanium according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross section showing an example of a dewar used in the experiment, 1 is a transparent dewar (a thermos bottle used for a low temperature experiment as a liquefied gas container), 2 is liquid nitrogen stored in this container, 3 Indicates a refractory brick stored in a container,
In the present invention, the titanium powder compact sample 5 housed in the quartz tube 4 is provided with a tungsten wire 6 on the lower end surface of the compact sample for igniting the titanium powder compact sample and connected to an external power source (not shown). . Reference numeral 7 is a lid for a dewar. The upper part of the dewar should be open to the atmosphere but the heat flow should be blocked.
Reference numeral 8 is a transient recorder provided outside the container, which was connected to a sensor 10 provided on the sample inside or the quartz tube 4 holding the sample by a conductor 9 to record changes in reaction propagation velocity and temperature.

FIG. 2 shows an example of a reaction container other than the dewar, 11 is an aluminum container, 12 is a lid part screwed to the aluminum container 11, and 13 is a quartz tube. The sample green compact 14 is held. 15 is a refractory metal wire 15 such as tungsten for ignition disposed along the lower end surface of the sample green compact 14,
The container 11 is filled with liquid nitrogen 16. Reference numeral 17 is an electrode, and 18 is a liquid nitrogen supply port.

(Example) Example 1 A dewar bottle 1 filled with liquid nitrogen was formed by compacting 25 g of titanium powder into a cylinder having a diameter of 25 mm so that the filling degree was 58%.
The lower end surface of the powder compact sample 5 is ignited by electrically heating the tungsten wire 6 (diameter 0.5 mm) that is placed inside and brought into contact with the lower part of the powder compact sample 5, and the reaction is performed on the powder compact sample 13. By heating the local part of the lower end face to 1700 ° C. or higher, the combustion reaction between the green compact sample and nitrogen is induced, the interaction between the green compact sample and nitrogen, and the heat generated as a result of the initiated combustion reaction, 20
A high temperature reaction layer of 0 ° C. or higher was formed, and this reaction layer was successively advanced upward in layers.

The reaction spontaneously propagated in layers from the bottom to the top, and as a result, the conversion rate to nitride estimated from the volume change of the sample was 68%. The result was about 30% higher conversion rate than the case where the reaction between the same green compact sample and nitrogen was propagated downward from the upper part.

Example 2 25 g of a mixed powder of titanium powder and titanium nitride powder was filled at a filling degree of 5
The powder was compacted into a cylindrical shape having a diameter of 25 mm at 0%, placed in a dewar filled with liquid nitrogen, and ignited in the same manner as in Example 1 to induce and propagate the reaction. As a result, when the titanium nitride powder was added by 20%, the conversion rate was 90%. On the other hand, an attempt was made to ignite it from above, but it did not ignite.

Example 3 I. Objective: In the present study, in the combustion synthesis of TiN using combustion of Ti powder and nitrogen, the purpose was to investigate the possibility of high-efficiency combustion synthesis when the nitrogen source was liquid nitrogen. We investigated changes in reaction propagation characteristics and synthesis process by changing the reaction propagation direction upward or downward.

II. Experimental method: A commercially available Ti powder (40 μm or less) (50 g) was pressure-molded into a cylinder having a diameter of 25 mm at various packing degrees (ρ: 40% to 60%) to obtain a sample. A sample held in a quartz tube is placed in liquid nitrogen filled in a dewar, and a tungsten wire (0.5 mmφ) in contact with the upper or lower end of the sample is energized and ignited to cause a downward or upward reaction. Propagated. The time interval of temperature rise in the reaction process was measured by a thermocouple inserted at 25 mm intervals in the reaction propagation direction, and the propagation velocity (V) was obtained. The conversion (η) and properties of the obtained compound were investigated, and the influence of reaction propagation characteristics on the synthesis process was investigated.

III. Result: The heat of formation of about 340 kJ / mol is released in the nitriding reaction of Ti (Ti + 1 / 2N ₂ → TiN), so the amount of heat required in the process of gasification of liquid nitrogen (about 12 kJ / mol)
Can be fully compensated for, and the reaction will spontaneously propagate as long as it is ignited. However, in the combustion synthesis of TiN, it is considered that the high temperature state behind the propagating surface influences the conversion rate, and in consideration of the vaporization of liquid nitrogen and the temperature gradient between the sample and the surroundings through the vapor phase surface, the high conversion of liquid nitrogen is not always necessary. You can't expect a rate. Especially in reaction propagation from above, heat and vaporized nitrogen transfer at high temperature are in the opposite direction to reaction propagation,
High conversion rates are not expected. As a result of investigating the relationship between the propagation velocity and the conversion rate in the propagation from above and below and the filling rate, the tendency that the propagation rate decreases and the conversion rate increases with the increase of the filling degree is the same, but Propagation from below is reduced by about 10%. (Filling degree ρ: 40%, propagation velocity V during combustion from below
(Lower): 7 mm / s, filling degree ρ: 60%, propagation velocity V from lower side during combustion becomes V (lower side): 1 mm / s) Moreover, the conversion rate is particularly high at high filling degree and large propagation from lower side to combustion. (Filling degree ρ: 55%; Conversion rate η (downward): 60% or more from below, combustion conversion rate η (upper): 50% or less from above), combustion from below It was confirmed that a higher conversion rate is expected in the transmission of.

(Effects of the Invention) According to the present invention, high-speed nitride using liquid nitrogen,
In order to achieve high-purity and high-efficiency synthesis, the propagation direction of the reaction is set to the upper direction, so the heat of formation of combustion is effectively utilized and a high conversion rate is achieved. Since the manufacturing method according to the present invention is characterized in that the propagation direction of the conventional combustion method is changed, the apparatus for carrying out the method can be simplified and can be immediately implemented. As industrially valuable.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a dewar used for an experiment of the method of the present invention, and FIG. 2 is a cross-sectional view showing a schematic configuration of a reaction container used for carrying out the method of the present invention. 1 …… Dewar bottle 2 …… Liquid nitrogen 3 …… Refractory brick 4 …… Quartz tube 5 …… Powder compact sample 6 …… Ignition tungsten wire 7 …… Lid 8 …… Transient recorder 9 …… Conductor 10… … Thermoelectric stack 11 …… Aluminum reaction vessel 12 …… Lid 13 …… Quartz tube 14 …… Powder compact sample 15 …… Ignition tungsten wire 16 …… Liquid nitrogen 17 …… Electrode 18 …… Liquid nitrogen supply port 19 ...... Electrode insertion port 20 ...... Fluid for supplying liquid nitrogen

Claims (1)

[Claims] 1. A metal titanium powder green compact is placed in a reaction vessel filled with liquid nitrogen, and a heat resistant conductor such as a tungsten wire is placed on the lower end face of the green compact, which is used as an external power source. By connecting and energizing, a part of the lower surface of the green compact is heated to 1700 ° C. or more to induce a combustion reaction between the green compact and nitrogen, and the internal combustion of the powder inside the constituent powder of the green compact following the combustion reaction. It promotes the spontaneous nitriding reaction of titanium metal with the diffusion of nitrogen, and the heat generated as a result of the initiated combustion process forms a high temperature reaction layer of 2000 ° C or higher, and the reaction layer is successively advanced upward in layers. Combustion synthesis method of high-purity TiN characterized by the following.