JP5027024B2 - Oxygen concentration measurement method - Google Patents

Description

  The present invention relates to an oxygen concentration measurement method, and more particularly to an oxygen concentration measurement method capable of measuring the oxygen concentration in a high-temperature heat treatment furnace.

  In a heat treatment furnace for heat-treating an object to be processed in an inert atmosphere, it is necessary to measure the oxygen concentration in the furnace in order to perform heat treatment while keeping the oxygen concentration low. For example, when SiC is heat-treated as an object to be processed, a zirconia oxygen sensor has been conventionally used. However, the zirconia oxygen sensor cannot be used at a high temperature of 1400 ° C. or higher because zirconia is sintered at 1400 ° C. or higher and the oxygen concentration cannot be measured. For example, since SiC or the like needs to be heat-treated at a high temperature of 1400 ° C. or higher, there is a problem that the zirconia oxygen sensor cannot be used as an oxygen sensor when heat-treating the SiC or the like.

Conventional oxygen concentration sensors are usually used for measuring oxygen concentration in a relatively low temperature garbage incinerator or the like (for example, see Patent Document 1).
JP 2003-1114016 A

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide an oxygen concentration measurement method capable of measuring the oxygen concentration in a high-temperature heat treatment furnace. There is to do.

  In order to achieve the above object, the present invention provides the following oxygen concentration measurement method.

[1] In a heat treatment furnace in an inert atmosphere, an object to be treated is heat treated at a temperature of 1400 to 2450 ° C. in the presence of two or more types of silicon carbide having different porosities whose masses are measured in advance, and after the heat treatment, the carbonization is performed. An oxygen concentration measurement method for measuring a mass of each silicon, calculating a mass change before and after the heat treatment of the silicon carbide, and deriving an oxygen concentration when the object to be treated is heat-treated from the mass change of the silicon carbide.

[2] The oxygen concentration measuring method according to [1], wherein the two or more types of silicon carbide include dense silicon carbide having a porosity of 0 to 5% and porous silicon carbide having a porosity of 10 to 55%.

[3] The oxygen concentration measurement method according to [1] or [2], wherein the mass of the two or more types of silicon carbide in the heat treatment furnace is 0.5 to 5000 g, respectively.

[4] Any of [1] to [3], wherein the workpiece is at least one selected from the group consisting of sintered silicon carbide, recrystallized silicon carbide, oxide-bonded silicon carbide, and nitride-bonded silicon carbide. The method for measuring oxygen concentration according to claim 1.

  Thus, according to the oxygen concentration measurement method of the present invention, the mass change before and after heat treatment of two or more types of silicon carbide having different porosity is calculated, and the oxygen when the object to be treated is heat treated from the mass change of silicon carbide. The concentration can be derived. This is to measure the oxygen concentration in the heat treatment furnace after the fact that silicon carbide has the property that “the degree of mass change when heated to a high temperature varies depending on the difference in oxygen concentration”. . Moreover, since the mass change of silicon carbide occurs with high reproducibility even at a high temperature of 1400 to 2450 ° C., it can be used in a high-temperature heat treatment furnace.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments, and is within the scope of the present invention. Based on this knowledge, it should be understood that design changes, improvements, etc. can be made as appropriate.

  In one embodiment of the oxygen concentration measuring method of the present invention, the object to be processed is placed in a heat treatment furnace in an inert atmosphere in the presence of two or more types of silicon carbide having different porosities whose masses are measured in advance, and 1400 to 2450. Heat treatment at a temperature of ° C. After the heat treatment, each mass of silicon carbide is measured, the mass change before and after the heat treatment of silicon carbide is calculated, and the oxygen concentration when the workpiece is heat-treated is derived from the mass change of silicon carbide. Is the method. Here, the “inert atmosphere” refers to an atmosphere having an oxygen concentration of 500 ppm or less.

  Thus, the oxygen concentration measurement method of this embodiment calculates the mass change before and after heat treatment of two or more types of silicon carbide having different porosities, and the oxygen concentration when the object to be treated is heat treated from the mass change of silicon carbide. However, the relationship between the oxygen concentration in the heat treatment furnace and the change in the mass of silicon carbide will be described more specifically.

  FIG. 1 is a graph schematically showing the relationship between the oxygen concentration in the heat treatment furnace and the change in mass of silicon carbide when heat treatment is performed in the heat treatment furnace. The vertical axis (y-axis) indicates the mass change rate of silicon carbide, and the horizontal axis (x-axis) indicates the oxygen concentration in the heat treatment furnace. The mass change rate of silicon carbide is a value obtained by subtracting the mass of silicon carbide before heat treatment from the mass of silicon carbide after heat treatment and dividing the obtained value by the mass of silicon carbide before heat treatment to multiply by 100. . As silicon carbide, first silicon carbide having a porosity of 0.2% and second silicon carbide having a porosity of 17% are used. The first silicon carbide is dense silicon carbide, and the second silicon carbide is porous silicon carbide. The porosity of silicon carbide is a value measured by the Archimedes method. The graph of FIG. 1 schematically shows a change in mass when each silicon carbide is heat-treated under a nitrogen atmosphere at 1450 ° C. for 5 hours. On the graph, the data of the first silicon carbide is data 1 and the data of the second silicon carbide is data 2.

  As shown in FIG. 1, the relationship between the oxygen concentration of the first silicon carbide and the mass change of the silicon carbide is such that the mass of the silicon carbide first decreases as the oxygen concentration increases from 0 ppm, and the change in mass is a minimum value. Until the oxygen concentration reaches about 500 ppm, the degree of mass reduction of silicon carbide gradually increases as the oxygen concentration increases. When the oxygen concentration further increases from around 500 ppm (the point at which the mass change amount of silicon carbide becomes a minimum value), the degree of mass decrease decreases as the oxygen concentration increases. When the oxygen concentration is around 700 ppm, the change in the mass of silicon carbide disappears, and when the oxygen concentration is further increased from around 700 ppm, the mass of silicon carbide increases. Thus, since the mass change amount of silicon carbide before and after the heat treatment differs when the oxygen concentration is different, the oxygen concentration during the heat treatment can be measured later by calculating the mass change of the silicon carbide before and after the heat treatment. It becomes possible.

  However, since data 1 of the first silicon carbide in FIG. 1 has a minimum value between oxygen concentrations of 0 to 700 ppm (near 500 ppm), one mass change value (minimum) between oxygen concentrations of 0 to 700 ppm. Two oxygen concentrations correspond to (except the value). Usually, when heat treatment is performed in an inert atmosphere using SiC or the like as an object to be processed, it is preferable to perform an operation so as to reduce the oxygen concentration as much as possible so that the oxygen concentration is 100 ppm or less, but the first carbonization when the oxygen concentration is 0 to 100 ppm. Since the value of the mass change of silicon and the value of the mass change of the first silicon carbide when the oxygen concentration is 650 to 700 ppm are approximate, even if one mass change of silicon carbide is measured, These two possibilities (the oxygen concentration range of 0 to 100 ppm and the oxygen concentration range of 650 to 700 ppm) are included. Therefore, when heat treatment is performed in an atmosphere with an oxygen concentration of 100 ppm or less, the oxygen concentration cannot be specified as one value only with the first silicon carbide.

  On the other hand, the relationship (data 2) between the oxygen concentration and the change in mass of silicon carbide of the second silicon carbide having a porosity of 17% shown in FIG. 1 is the mass of silicon carbide within the range of the oxygen concentration of 100 to 200 ppm. Becomes a minimum value, and when the oxygen concentration exceeds 200 ppm, the mass of silicon carbide starts to increase. Thereby, when both the mass change of the 1st hydrocarbon and the mass change of the 2nd hydrocarbon are measured and these are combined, in the range where oxygen concentration is 200 ppm or less, the oxygen concentration corresponding to each combination is There will be only one. That is, for example, the mass change of the first silicon carbide is a value when the oxygen concentration is 100 ppm and the oxygen concentration is 650 ppm (assuming that the mass change of silicon carbide becomes the same value at the oxygen concentration of 100 ppm and the oxygen concentration of 650 ppm), If the mass change of silicon carbide is the value when the oxygen concentration is 100 ppm and the oxygen concentration is 180 ppm (assuming that the mass change of silicon carbide is the same at the oxygen concentration of 100 ppm and the oxygen concentration of 180 ppm), the oxygen during the heat treatment The concentration is specified to be 100 ppm, which is a common oxygen concentration when comparing two oxygen concentrations that can be read from the mass change of the first silicon carbide and two oxygen concentrations that can be read from the mass change of the second silicon carbide. Is possible.

  As described above, calibration of the relationship between the oxygen concentration and the change in mass of silicon carbide when heat treatment is performed in advance on two or more types of silicon carbide under the same heat treatment conditions as the heat treatment of the target object. By preparing the line, the oxygen concentration in the heat treatment furnace can be measured using those silicon carbides. For example, data 1 and data 2 in FIG. 1 can be referred to as calibration curves of the first silicon carbide having a porosity of 0.2% and the second silicon carbide having a porosity of 17%.

  Further, the first silicon carbide and the second silicon carbide are different from each other in the relationship between the oxygen concentration and the mass change of silicon carbide when heat-treated as shown in data 1 and data 2 of FIG. However, the relationship between the oxygen concentration when heat-treated and the mass change of silicon carbide varies depending on the porosity of silicon carbide. As a combination of the porosity of two or more types of silicon carbide used for oxygen concentration measurement, two or more types of silicon carbide are dense silicon carbide having a porosity of 0 to 5% and porous carbonization having a porosity of 10 to 55%. It is preferable to contain silicon. Furthermore, it is preferable to contain dense silicon carbide having a porosity of 0 to 1% and porous silicon carbide having a porosity of 15 to 55%. Silicon carbide having a porosity of 0 to 5% is referred to as dense silicon carbide, and silicon carbide having a porosity of 10% or more is referred to as porous silicon carbide. By measuring the oxygen concentration in combination with such silicon carbide, it is possible to easily and accurately measure the oxygen concentration in the high-temperature heat treatment furnace. Two or more types of silicon carbide may be used, but two types having different porosities are preferable, and three types may be used. This is because the oxygen concentration in the heat treatment furnace can be measured by using two or three types of silicon carbide. For example, it is preferably two kinds of the above-described dense silicon carbide having a porosity of 0 to 5% and porous silicon carbide having a porosity of 10 to 55%, and the dense silicon carbide having the porosity of 0 to 1%, and Two types of porous silicon carbide having a porosity of 15 to 20% are more preferable.

Here, when the oxygen concentration in the heat treatment furnace is lower than a predetermined value (about 700 ppm), the mass of silicon carbide decreases because silicon carbide and oxygen in an atmosphere having such an oxygen concentration are “SiC + O ₂ = This is because a chemical reaction represented by the chemical formula of “SiO + CO” occurs, and the generated SiO and CO are released as gas. Further, the mass of the silicon carbide increases when the oxygen concentration in the heat treatment furnace is higher than a predetermined value (about 700 ppm) is silicon carbide and the oxygen in the atmosphere of such oxygen concentration "2SiC + 3O 2 ₌ 2SiO _This is because the chemical reaction represented by the chemical formula of “ ₂ + 2CO” occurs and the generated SiO ₂ is heavier than the original SiC.

  The masses of the two or more types of silicon carbide used for measuring the oxygen concentration are preferably 0.5 to 5000 g, respectively. If it is lighter than 0.5 g, the accuracy of mass measurement may decrease, and if it is heavier than 5000 g, it becomes heavy and large, which may be inconvenient to handle. In addition, the shape of silicon carbide is not particularly limited, but a shape such as a quadrangular prism is preferable, and among these, a honeycomb shape is more preferable in view of excellent handling strength.

  The dense silicon carbide having a porosity of 0 to 5% is prepared by adding and mixing silicon carbide particles having an average particle size of 0.5 to 5 μm, a binder, and an auxiliary agent such as B4C. It can be obtained by firing under an inert atmosphere condition of 1700 to 2300 ° C. and vacuum to 100 MPa. As the binder, PVA (polyvinyl alcohol), PEG (polyethylene glycol), or the like can be used. As the auxiliary agent, carbon, B4C, or the like can be used. The porosity of such dense silicon carbide can be adjusted by the raw material particle size, the amount and type of the auxiliary agent, and further by the firing conditions. The average particle size of the silicon carbide particles is a value measured by a laser particle size distribution measuring method, and can be measured by an apparatus such as a laser particle size distribution measuring device (Mastersizer manufactured by MALVERN). The porous silicon carbide having a porosity of 10 to 55% is prepared by mixing, for example, two types of silicon carbide particles having an average particle diameter of 1 to 10 μm and an average particle diameter of 50 to 200 μm, a binder, and water. The molding raw material can be obtained by cast molding or extrusion molding, and then drying and firing in an inert gas atmosphere condition of 1500 to 2350 ° C. and vacuum to 100 MPa. Here, the term “vacuum” refers to a pressure of 100 hPa or less including a reduced pressure atmosphere. As the binder, PVA, PEG, or the like can be used as appropriate with a foamable resin. Thus, the porosity of porous silicon carbide can be adjusted by the water in the raw material, additives such as a binder, molding conditions, and firing conditions.

  Hereinafter, the oxygen concentration measurement method of the present embodiment will be described in the order of each operation.

  In the oxygen concentration measurement method of this embodiment, first, two or more types of silicon carbide having different porosities and an object to be processed are placed in a heat treatment furnace. The mass of silicon carbide is measured in advance. Moreover, about the silicon carbide to be used, the calibration curve regarding the relationship between the oxygen concentration and the change in mass of silicon carbide when heat treatment is performed at a predetermined temperature and time is prepared in advance. Although it does not specifically limit as a heat treatment furnace, The atmosphere control electric baking furnace in which heat processing temperature reaches 1400-2450 degreeC, a radiant tube heater heating atmosphere furnace, a carbon muffle furnace, etc. can be mentioned. Moreover, it is although it does not specifically limit as a to-be-processed object, It is what heat-processes by making process temperature reach 1400-2450 degreeC, and it is preferable to make it heat-process by reaching 1450-2350 degreeC. Examples of the object to be processed include SiC. Moreover, it is preferable to mount a to-be-processed object and silicon carbide in the near position in the range which does not contact. The distance between the workpiece and silicon carbide is preferably 1 to 100 cm. By setting it as such a range, it becomes possible to measure the oxygen concentration of the atmosphere around a to-be-processed object which the to-be-processed object is contacting directly. If the distance between the object to be processed and silicon carbide is shorter than 1 cm, the object to be processed and silicon carbide come into contact with each other or the influence of the gas released from the object to be processed makes it possible to accurately measure the oxygen concentration. When it is longer than 100 cm, it may be difficult to measure the oxygen concentration in the atmosphere around the object to be processed and in direct contact with the object to be processed.

  Next, the temperature in the heat treatment furnace is raised to 1400 to 2450 ° C., and the workpiece and each silicon carbide are heat treated. At this time, silicon carbide and oxygen react with each other to change the mass of silicon carbide. The heat treatment time is preferably 1 hour or longer in a state where the temperature in the heat treatment furnace is 1400 to 2450 ° C. If it is shorter than 1 hour, the mass change of silicon carbide is small and the measurement accuracy may be lowered.

Next, after the heat treatment, the mass of each silicon carbide is measured, and the change in the mass of each silicon carbide before and after the heat treatment is calculated. Then, the oxygen concentration is derived using a calibration curve that has been prepared in advance and is related to the relationship between the oxygen concentration and the mass change of silicon carbide. Here, it is natural that the indirect description of the oxygen concentration at the time of firing the SiC-based material includes CO concentration, CO ₂ concentration, SiO concentration, and SiO ₂ concentration.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
Using an inert gas atmosphere controlled electric furnace as the heat treatment furnace, heat treatment is performed using SiC as the workpiece in the presence of two types of silicon carbide, and the oxygen concentration in the heat treatment furnace is derived from the mass change of the two types of silicon carbide. It was. As the two types of silicon carbide, the above-described dense silicon carbide (silicon carbide 1) having a porosity of 0.2% and porous silicon carbide (silicon carbide 2) having a porosity of 17% were used. Silicon carbide 1 had a quadrangular prism shape and a mass of 1.5 g. The shape of silicon carbide 2 was a quadrangular prism shape, and its mass was 1.2 g. The calibration curves for silicon carbide 1 and silicon carbide 2 were represented by data 1 and data 2 shown in FIG. Silicon carbide 1 and silicon carbide 2 were each placed at a position 2 cm away from the workpiece.

  The heat treatment conditions were 1450 ° C. for 5 hours, and the atmosphere in the heat treatment furnace was an argon atmosphere.

  The mass change of silicon carbide 1 was +0.01 mass%, and the mass change of silicon carbide 2 was −1.0 mass%. When this was compared with a calibration curve, the oxygen concentration in the heat treatment furnace was 200 ppm.

(Example 2)
Using an inert gas atmosphere controlled electric furnace as the heat treatment furnace, one kind of silicon carbide is made into a dense SiC tube (diameter 10 mm, length 500 mm) with a porosity of 0.3%, and another kind of silicon carbide. Was subjected to heat treatment using a porous SiC honeycomb structure having a porosity of 50% as a workpiece, and the oxygen concentration in the heat treatment furnace was derived from the mass change of these two types of silicon carbide. Of the two types of silicon carbide, the mass of the above-described dense silicon carbide (silicon carbide 1) having a porosity of 0.3% was 200 g. The shape of silicon carbide 2 was a square pillar-shaped honeycomb structure, and its mass was 400 g. Silicon carbide 1 was placed at a position 20 cm away from the object to be treated, and silicon carbide 2 was placed at a position 2 cm away from the object to be treated.

  The heat treatment conditions were 2000 ° C. for 5 hours, and the atmosphere in the heat treatment furnace was an atmosphere containing a slight amount of CO in argon and nitrogen.

  The mass change of silicon carbide 1 was −0.01 mass%, and the mass change of silicon carbide 2 was −1.0 mass%. When this was compared with a calibration curve prepared separately, the oxygen concentration in the heat treatment furnace was 20 ppm.

  It can be used to measure the oxygen concentration in a high temperature heat treatment furnace.

It is the graph which showed typically the relationship between the oxygen concentration in a heat processing furnace, and the mass change of silicon carbide when heat-processing in the said heat processing furnace.

Explanation of symbols

1, 2: Data.

Claims (4)

  In a heat treatment furnace in an inert atmosphere, the object to be treated is heat treated at a temperature of 1400 to 2450 ° C. in the presence of two or more types of silicon carbide having different porosities whose masses are measured in advance. The oxygen concentration measuring method of measuring the mass of this, calculating the mass change before and behind the heat processing of the said silicon carbide, and deriving the oxygen concentration when the said to-be-processed object is heat-processed from the mass change of the said silicon carbide.   The oxygen concentration measuring method according to claim 1, wherein the two or more types of silicon carbide include dense silicon carbide having a porosity of 0 to 5% and porous silicon carbide having a porosity of 10 to 55%.   The oxygen concentration measuring method according to claim 1 or 2, wherein the masses of the two or more types of silicon carbide in the heat treatment furnace are 0.5 to 5000 g, respectively.   The oxygen according to any one of claims 1 to 3, wherein the object to be treated is at least one selected from the group consisting of sintered silicon carbide, recrystallized silicon carbide, oxide-bonded silicon carbide, and nitride-bonded silicon carbide. Concentration measurement method.

Images