JP7640261B2 - Heat and shock resistant materials - Google Patents

Description

This disclosure relates to thermal shock resistant components.

Traditionally, ceramics (ZTA) that are primarily composed of aluminum oxide and contain zirconium oxide have excellent mechanical strength and thermal shock resistance. For this reason, ZTA is used in firing jigs for firing electronic components such as dielectrics, multilayer capacitors, thermistors, varistors, and chip inductors, welding nozzles, furnace tubes for various electric furnaces, support tubes, radiant tubes, gas inlet tubes, gas sampling tubes, thermocouples for temperature measurement, protective tubes for various devices, and insulating materials for contact devices.

As such ZTA, Patent Document 1 describes an alumina-zirconia sintered body having a tetragonal or cubic zirconia crystal phase and a monoclinic zirconia crystal phase, and a porosity (open porosity) of 10 to 40%.

JP 2016-132577 A

The alumina-zirconia sintered body described in Patent Document 1 has a poor balance between the spacing between adjacent pores (open pores) and the spacing between adjacent zirconia. As a result, the alumina-zirconia sintered body described in Patent Document 1 cannot fully exhibit its inherent mechanical strength and thermal shock resistance.

The objective of this disclosure is to provide a thermal shock resistant component that can fully demonstrate the mechanical strength and thermal shock resistance of ZTA.

The thermal shock resistant member according to the present disclosure includes a ceramic that is mainly composed of aluminum oxide, contains zirconium oxide, and has an area ratio of closed pores of 10% to 20%. In the ceramic, the difference (A) between the average value of the distance between the centers of gravity of adjacent zirconium oxide crystal particles and the average value of the circle equivalent diameter of the zirconium oxide crystal particles is 0.7 to 1.3 times the difference (B) between the average value of the distance between the centers of gravity of adjacent closed pores and the average value of the circle equivalent diameter of the closed pores.

The welding and cutting or plasma cutting nozzle and the insulating member for the contact device according to the present disclosure include the above-mentioned thermal shock resistant member.

The thermal shock resistant member according to the present disclosure contains ZTA having an area ratio of closed pores of 10% to 20%, and the difference (A) is 0.7 to 1.3 times the difference (B). Therefore, the thermal shock resistant member according to the present disclosure can fully exhibit the mechanical strength and thermal shock resistance of ZTA.

The thermal shock resistant member according to one embodiment of the present disclosure includes ceramics that are primarily composed of aluminum oxide, contain zirconium oxide, and have an area ratio of closed pores of 10% to 20%. Ceramics with an area ratio of closed pores of 10% to 20% have properties intermediate between dense and porous.

In this specification, a thermal shock resistant component means a component containing ceramics having a thermal shock resistance temperature of 350°C or higher obtained according to the precision method specified in JIS R 1648:2002.

"Aluminum oxide as the main component" means that aluminum oxide accounts for 80% by mass or more of the total 100% by mass of the components that make up the ceramic. The components that make up the ceramic can be identified by an X-ray diffraction device using CuKα radiation. The content of each component can be determined, for example, by an ICP (Inductively Coupled Plasma) emission spectrometer or an X-ray fluorescence analyzer.

The area ratio of closed pores is measured by the following method. First, the cross section of the ceramic is mirror-polished, and the surface is thermally etched at a temperature of 1420° C. and observed at a magnification of 500 times. An average range is selected, and an area of, for example, 4.34×10 ⁴ μm ² (horizontal length 241 μm, vertical length 180 μm) is photographed with a scanning electron microscope to obtain an observation image. The area ratio of closed pores can be obtained by particle analysis using this observation image as the subject, using image analysis software "A-zo-kun (ver. 2.52)" (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.). Hereinafter, when the image analysis software "A-zo-kun" is written, it refers to the image analysis software manufactured by Asahi Kasei Engineering Co., Ltd.

The conditions for this method may be set, for example, as follows: a threshold value, which is an index showing the brightness of an image, is 91, the brightness is dark, the area of small figures removed is 1 ^μm2 , and a noise reduction filter is enabled. The threshold value may be adjusted according to the brightness of the observed image. With the brightness set to dark, the binarization method set to manual, the area of small figures removed is 1 ^μm2 , and a noise reduction filter enabled, the threshold value may be adjusted so that the markers appearing in the observed image match the shape of closed pores.

If the thermal shock resistant component is a cylindrical nozzle for welding and cutting or plasma cutting, the cross section perpendicular to the axial direction is mirror-polished and the area ratio of open pores is determined according to the method described above.

The thermal shock resistant member according to one embodiment has high fracture toughness due to the inclusion of zirconium oxide. As a result, even if the thermal shock resistant member according to one embodiment contains closed pores, it can maintain a certain degree of mechanical strength and absorb stress caused by temperature increases and decreases.

The content of zirconium oxide is not limited as long as it is an amount containing aluminum oxide as the main component. Zirconium oxide is contained in a proportion of 10 mass% or more and 15 mass% or less out of a total of 100 mass% of the components constituting the ceramic. When zirconium oxide is contained in a proportion of 10 mass% or more, the fracture toughness of the thermal shock resistant member according to one embodiment can be further increased. When zirconium oxide is contained in a proportion of 15 mass% or less, the decrease in thermal conductivity can be further suppressed.

The average particle size of the aluminum oxide crystal particles and the zirconium oxide crystal particles is not limited. For example, the average particle size of the aluminum oxide crystal particles should be larger than the average particle size of the zirconium oxide crystal particles. With such a configuration, it is more effective to suppress the decrease in the thermoelectric coefficient. The aluminum oxide crystal particles have an average particle size of, for example, about 6 μm or more and 12 μm or less. The zirconium oxide crystal particles have an average particle size of, for example, about 2 μm or more and 4 μm or less.

To determine the average particle size of aluminum oxide crystal particles, the area ratio of closed pores is calculated by drawing six lines of the same length, for example 100 μm, radially from an arbitrary point on the observation image. The average crystal grain size can be calculated by dividing the length of these six lines by the number of crystals present on each line.

The average particle size of the crystal grains of zirconium oxide may be determined by a method called particle analysis using the image analysis software "A-image-kun" for the above-mentioned observation image. The setting conditions for this method may be, for example, a threshold value, which is an index showing the brightness of the image, of 182, a brightness value of bright, a small figure removal area of 1 μm ² , and a noise removal filter. The threshold value may be adjusted according to the brightness of the observation image. The brightness may be set to bright, the binarization method may be set to manual, the small figure removal area may be set to 1 μm ² , and a noise removal filter may be set, and the threshold value may be adjusted so that the markers appearing in the observation image match the shape of the crystal grains of zirconium oxide.

In the ceramics contained in the thermal shock resistant member according to one embodiment, the difference (A) between the average value of the distance between the centers of gravity of adjacent zirconium oxide crystal particles and the average value of the equivalent circle diameter of the zirconium oxide crystal particles is 0.7 to 1.3 times the difference (B) between the average value of the distance between the centers of gravity of adjacent closed pores and the average value of the equivalent circle diameter of the closed pores.

The difference (A) between the average value of the distance between the centers of gravity of adjacent zirconium oxide crystal particles and the average value of the equivalent circle diameter of the zirconium oxide crystal particles is a value that indicates the distance between adjacent zirconium oxide crystal particles. The difference (B) between the average value of the distance between the centers of gravity of adjacent closed pores and the average value of the equivalent circle diameter of the closed pores is a value that indicates the distance between adjacent closed pores.

In this way, if the difference (A) is 0.7 to 1.3 times the difference (B), it can be said that there is a good balance between the spacing between adjacent zirconium oxide crystal particles and the spacing between adjacent closed pores. Therefore, even if a thermal shock is applied and microcracks originating from the zirconium oxide or closed pores occur, the microcracks are less likely to progress. Therefore, destruction due to cracks caused by thermal shock is suppressed. In order to further suppress destruction due to cracks caused by thermal shock, the difference (A) and the difference (B) may be made approximately the same, for example, the difference (A) may be made approximately 0.9 to 1.1 times the difference (B).

The average distance between the centers of gravity of zirconium oxide crystal particles can be measured by the following method. Using the image analysis software "A-Image-kun" for the above observation image, the average distance between the centers of gravity of zirconium oxide crystal particles can be calculated using the distance between the centers of gravity method for measuring dispersion.

The conditions for this method may be set, for example, as follows: a threshold value, which is an index showing the brightness of an image, is 182, a brightness value is bright, a small figure removal area is 1 ^μm2 , and a noise removal filter is not used. The threshold value may be adjusted according to the brightness of the observed image, and the brightness may be set to bright, the binarization method may be set to manual, a small figure removal area is set to 1 ^μm2 , and a noise removal filter is used, and then the threshold value may be adjusted so that the markers appearing in the observed image match the shape of the zirconium oxide crystal grains.

The equivalent circle diameter of zirconium oxide crystal particles can be determined by the following method. Using the above observation image as the subject, the equivalent circle diameter of zirconium oxide crystal particles can be determined by a method called particle analysis. The settings for this method should be the same as those used for the centroid distance method for measuring dispersion.

The average values of the distance between the centers of gravity of the closed pores and the equivalent circle diameter of the closed pores are measured in the same manner as the average values of the distance between the centers of gravity of the zirconium oxide crystal particles and the equivalent circle diameter of the zirconium oxide crystal particles. However, the set conditions are the same as those used to determine the area ratio of the closed pores.

The average spheroidization rate of the zirconium oxide crystal particles is not limited. The average spheroidization rate of the zirconium oxide crystal particles is preferably greater than the average spheroidization rate of the closed pores, in that it can reduce the stress generated at the grain boundaries of the zirconium oxide. The average spheroidization rate of the zirconium oxide crystal particles is preferably, for example, 10% or more, specifically, 14% to 20% greater than the average spheroidization rate of the closed pores. The average spheroidization rate of the zirconium oxide crystal particles may be, for example, 56% to 64%, and the average spheroidization rate of the closed pores may be, for example, 40% to 46%.

Here, the spheroidization rates of the crystal grains and closed pores of zirconium oxide are calculated by converting the ratios defined by the graphite area method, and are conceptually defined by the following formulas (1) and (2).
Spheroidization rate of zirconium oxide crystal particles (%) = (A/B) x 100 (1)
A: actual area of zirconium oxide crystal grain B: area of smallest circumscribed circle of zirconium oxide crystal grain Spheroidization rate of closed pores (%) = (C/D) x 100 ... (2)
C: Actual area of closed pore D: Area of minimum circumscribed circle of closed pore

Specifically, the average spheroidization rate of zirconium oxide crystal particles and closed pores can be determined by a technique called particle analysis using the above observation images. However, the set conditions for determining the average spheroidization rate of zirconium oxide crystal particles should be the same as the set conditions used for determining the average distance between the centers of gravity of zirconium oxide crystal particles. The set conditions for determining the average spheroidization rate of closed pores should be the same as the set conditions used for determining the area ratio of closed pores.

If the thermal shock resistant component is a cylindrical nozzle for welding and cutting or plasma cutting, the cross section perpendicular to the axial direction is mirror-polished. The surface is thermally etched at a temperature of 1420°C, and the average values of the distance between the centers of gravity of the closed pores and zirconium oxide and the circle equivalent diameter are determined according to the method described above.

The ceramics contained in the thermal shock resistant member according to an embodiment may further contain at least one selected from the group consisting of magnesium, calcium, _yttrium , and titanium. The oxides of these elements (MgO, CaO, _Y2O3 , and _TiO2 ) act as stabilizers for zirconium oxide. These elements may be contained in a total amount of, for example, 0.8% by mass or more _and 1.2% by mass or less in terms of oxides (MgO, CaO, _Y2O3 , and _TiO2 ).

When the total amount is 0.8% by mass or more, the proportion of tetragonal and cubic crystals, which are stable at room temperature, increases in the zirconium oxide crystals. As a result, the mechanical properties such as fracture toughness and mechanical strength of the thermal shock resistant component according to one embodiment can be further improved. When the total amount is 1.2% by mass or less, the occurrence of abnormal grain growth is suppressed. As a result, the above-mentioned mechanical properties can be maintained.

The ceramic contained in the thermal shock resistant member according to one embodiment may contain at least two types selected from the group consisting of lithium, sodium and potassium in a total amount of 0.08 mass% or less, calculated as oxide (Li ₂ O, Na ₂ O and K ₂ O).

If the total amount is 0.08 mass% or less, the increase in the dielectric tangent (tan δ) can be suppressed. As a result, even if the thermal shock resistant member is used in an environment where temperature variations occur depending on the distribution of plasma, such as a film-forming reaction vessel used in a plasma CVD device, the dielectric tangent (tan δ) is suppressed, so heat variations are unlikely to occur. Therefore, the occurrence of cracks is further suppressed.

The ceramics included in the thermal shock resistant member according to the embodiment may further include chromium. The amount of chromium is not limited, and may be, for example, 0.5% by mass to 2.5% by _mass in terms of _Cr2O3 .

The surface of the ceramics contained in _the thermal shock resistant member according to the embodiment has a pink color due to the chromium content of 0.5% by mass or more and 2.5% by mass or less calculated as _Cr2O3 , which can provide a sense of luxury, aesthetic satisfaction, and a soothing effect to consumers of the thermal shock resistant member according to the embodiment.

The components constituting the ceramics contained in the thermal shock resistant member may be identified by the JCPDS card based on the results of measurement using an X-ray diffraction device with CuKα radiation. The proportion of each component may be determined by first identifying the components, then calculating the content of the elements constituting the components using an X-ray fluorescence analyzer (XRF) or an ICP emission spectrometer, and converting the content into the identified components.

The heat-shock resistant component may be provided with characters, symbols, figures, logos, marks, QR codes (registered trademark of DENSO WAVE Inc.), etc. These characters, etc. can be obtained by irradiation with laser light. Characters, etc. irradiated with laser light will not disappear even when used at high temperatures (e.g., 500°C to 1200°C), and are therefore effective for product management.

The method for manufacturing the thermal shock resistant member according to one embodiment is not limited, and may be, for example, manufactured according to the following procedure.

First, aluminum oxide powder and zirconium oxide powder are prepared and mixed to obtain a mixed powder. The purity of these powders is not limited. These powders may have a purity of, for example, 99% by mass or more. The aluminum oxide powder is mixed in a ratio of, for example, 80% by mass or more, and the zirconium oxide powder is mixed in a ratio of, for example, 10% by mass or more and 15% by mass or less, out of 100% by mass of the mixed powder.

If necessary, chromium oxide powder, magnesium oxide powder, calcium oxide powder, yttrium oxide powder, titanium oxide powder, lithium oxide powder, sodium oxide powder, potassium oxide powder, etc. may be blended in a specific ratio. Specifically, chromium oxide powder may be blended in a ratio of 0.5 mass% to 2.5 mass% in 100 mass% of the blended powder, and at least one of magnesium oxide powder, calcium oxide powder, yttrium oxide powder, and titanium oxide powder may be blended in a total ratio of 0.8 mass% to 1.2 mass%. As for lithium oxide powder, sodium oxide powder, and potassium oxide powder, at least two of these powders may be blended in a total ratio of 0.08 mass% or less.

In addition to these powders, powders that are raw materials for ceramics may also be used. Examples of such powders include silica (silicon dioxide), hafnium oxide, and yttrium oxide.

Next, these powders and a solvent (e.g., ion-exchanged water, etc.) are put into a grinding mill. Next, the powder is ground until the average particle size (D50) of the powder is 1.5 μm or less, and then an organic binder and a dispersant for dispersing the powder are added and mixed to obtain a slurry. Examples of dispersants include acrylic acid ester copolymers and citric acid. Examples of organic binders include acrylic emulsions, polyvinyl alcohol, polyethylene glycol, and polyethylene oxide.

The obtained slurry is spray-granulated to obtain granules, which are then compressed at a molding pressure of 78 MPa to 160 MPa using a uniaxial press molding device or a cold isostatic press molding device to obtain a molded body that will serve as the base for the ceramics, and then machined as necessary. This molded body is fired in an air atmosphere at 1500°C to 1700°C for 4 hours to 6 hours to obtain ceramics. The obtained ceramics are processed into the desired shape to obtain a thermal shock resistant member according to one embodiment.

Alternatively, the obtained granules may be filled into a mold corresponding to the shape of the desired thermal shock resistant component to obtain a molded body, and the obtained molded body may be fired to produce a thermal shock resistant component according to one embodiment formed of ceramics. The pressure conditions for obtaining the molded body and the conditions for firing the molded body are as described above, and detailed explanations will be omitted.

Specifically, the ceramics contained in the thermal shock resistant member according to one embodiment were obtained by the following recipe. First, a mixed powder containing about 80.2 mass% aluminum oxide powder, about 12.2 mass% zirconium oxide powder, about 4.7 mass% silicon dioxide powder, about 1.53 mass% chromium oxide powder, about 0.57 mass% magnesium oxide powder, about 0.33 mass% calcium oxide powder, about 0.03 mass% yttrium oxide powder, about 0.06 mass% titanium oxide powder, about 0.05 mass% sodium oxide powder, about 0.01 mass% potassium oxide powder, and other trace components, and ion-exchanged water were charged into a grinding mill.

The powder was then pulverized until its average particle size (D50) was 1.5 μm or less, after which an organic binder (polyvinyl alcohol and polyethylene glycol) and a dispersant (acrylic acid ester copolymer) for dispersing the powder were added and mixed to obtain a slurry. The resulting slurry was spray-granulated to obtain granules, which were then pressurized to about 98 MPa using a uniaxial press molding device to obtain rectangular and cylindrical molded bodies that would become the basis of ceramics.

Then, the obtained molded body was fired in an air atmosphere at the temperature shown in Table 1 for 2 hours to obtain ceramic samples No. 1 to 6. For samples No. 1 to 6, the above-mentioned difference (A) and difference (B) were determined by the above-mentioned measurement method using cylindrical ceramic samples. The area ratio of closed pores for samples No. 1 to 6 was measured by the above-mentioned measurement method. The measurement results were all 12% or more and 16% or less.

For samples No. 1 to 6, the three-point bending strength, which indicates mechanical properties, was measured using samples made of rectangular columnar ceramics in accordance with JIS R 1601:2005. For samples No. 1 to 6, the thermal shock resistance temperature, which indicates thermal shock resistance, was measured using samples made of cylindrical ceramics in accordance with the precision method specified in JIS R 1648:2002.

For samples No. 1 to 6, the difference (A), difference (B), ratio value (A)/(B), three-point bending strength, and thermal shock resistance temperature are shown in Table 1.

As shown in Table 1, samples No. 2 to No. 5, in which the difference (A) is 0.7 to 1.3 times the difference (B), have both high mechanical properties and high thermal shock resistance. On the other hand, sample No. 1, in which the difference (A) is more than 1.3 times the difference (B), has good thermal shock resistance but poor mechanical properties. Sample No. 6, in which the difference (A) is less than 0.7 times the difference (B), has good mechanical properties but poor thermal shock resistance.

The thermal shock resistant member according to the present disclosure can fully exhibit the mechanical strength and thermal shock resistance of ZTA. Therefore, the thermal shock resistant member according to the present disclosure can be used, for example, as a material for nozzles for welding and cutting or plasma cutting, insulating materials for contact devices, jigs for heat treating electronic components, and the like.

Claims (8)

The ceramic material contains aluminum oxide as a main component, zirconium oxide, and an area ratio of closed pores is 12 % or more and 16 % or less,
The aluminum oxide crystal particles have an average particle size of 6 μm or more and 12 μm or less,
The zirconium oxide crystal particles have an average particle size of 2 μm or more and 4 μm or less,
In the ceramic, a difference (A) between an average value of the distance between the centers of gravity of adjacent zirconium oxide crystal grains and an average value of the equivalent circle diameter of the zirconium oxide crystal grains is 0.7 to 1.3 times a difference (B) between an average value of the distance between the centers of gravity of adjacent closed pores and an average value of the equivalent circle diameter of the closed pores.
Heat-shock resistant material. The thermal shock resistant member according to claim 1, wherein the average spheroidization rate of the zirconium oxide crystal particles is greater than the average spheroidization rate of the closed pores. The thermal shock resistant member according to claim 1 or 2, wherein the zirconium oxide is contained in the ceramic in a proportion of 10% by mass or more and 15% by mass or less. 4. The thermal shock resistant member according to claim 1, wherein the ceramic further contains chromium, the content of which calculated as Cr ₂ O ₃ is 0.5 mass % or more and 2.5 mass % or less. The thermal shock resistant member according to any one of claims 1 to ₄ , wherein the ceramic further contains at least one selected from the group consisting of magnesium, calcium, yttrium and titanium, and the total content calculated as MgO, CaO, Y ₂ O ₃ and TiO 2 is 0.8 mass% or more and 1.2 mass% or less. The thermal shock resistant member according to any one of claims 1 to 5, wherein the ceramic further contains at least two selected from the group consisting of lithium, sodium and potassium, and the total content calculated as Li ₂ O, Na ₂ O and K ₂ O is 0.08 mass% or less. A nozzle for welding and cutting or plasma cutting, comprising the thermal shock resistant member according to any one of claims 1 to 6. An insulating member for a contact device, comprising the thermal shock resistant member according to any one of claims 1 to 6.