JP3955901B2 - Conductive zirconia sintered body and manufacturing method thereof - Google Patents

Description

  The present invention relates to a conductive zirconia sintered body excellent in mechanical properties, heat resistance, corrosion resistance and the like, and a method for producing the same.

  Ceramic materials have corrosion resistance and heat resistance in addition to excellent mechanical properties such as wear resistance. Therefore, the use for the tray for a conveyance, the member for plasma etching, a hard disk bearing component, etc. in the manufacturing facility of a semiconductor and a liquid crystal device is expanding.

  Zirconia ceramics generally used for wear-resistant parts and the like have excellent characteristics such as high strength and high toughness. However, zirconia ceramics usually have high electrical insulation properties. For example, when used as a member for a semiconductor manufacturing apparatus or the like, it is inconvenient because the insulation property is too high and charging occurs. Sex is desired.

  In addition, ceramics are generally difficult to process, so the processing cost is high, and this is a bottleneck for expanding the use of ceramic materials. In order to improve this difficult workability, it is advantageous if an appropriate electrical conductivity is imparted to the material itself so that electric discharge machining used in a metal member or the like becomes possible.

  Usually, in order to convert an insulating ceramic material into a conductive material, approximately 15 to 40% by volume of a conductive material is dispersed and composited in the ceramic (for example, Patent Documents 1 to 5).

  However, because of the large amount of conductive material added as the second phase, the ceramic's original excellent characteristics (breaking strength, hardness, fracture toughness value, wear resistance, chemical resistance, heat resistance, creep resistance, etc.) May be damaged. In addition, there is a problem in that variations in characteristics are likely to occur because the technique for dispersing and combining conductive materials is not sufficient. Therefore, in order to impart conductivity without variation, the amount of conductive material added has to be increased.

In order to solve such a problem, the present inventors firstly made conductive zirconia sintered bodies containing 0.2 to 3% by weight of carbon conductive without sacrificing mechanical properties and the like. It has been reported that it can be expressed (Patent Document 6).
JP-A-10-297968 JP 2001-294479 A Japanese Patent Laid-Open No. 2001-294383 JP 2001-199764 A JP-A-9-221352 JP 2004-189509 A

However, it is more advantageous than the conductive zirconia sintered body of Patent Document 6 if the amount of conductive material added can be further reduced and desired conductivity can be imparted without impairing its excellent mechanical properties. Further, even with the conductive zirconia sintered body of Patent Document 6, the mechanical properties are not satisfactory, and in particular, the volume resistivity (about 5.0 × 10 ⁻¹ Ω · In the case where it has (cm or less), the mechanical properties still tend to be lowered, and there is much room for improvement.

  In view of the above-mentioned problems, the present invention is a zirconia that retains excellent mechanical properties (such as fracture strength and fracture toughness) by adding a smaller amount of a conductive material, and is provided with desired stable conductivity. It aims at providing a sintered compact and its manufacturing method.

As a result of intensive studies to solve the above-mentioned problems, the present inventor is a zirconia sintered body containing ZrO ₂ as a main component and Y ₂ O ₃ as a stabilizer, wherein Y ₂ O ₃ and ZrO _2. In the range of 1.5 / 98.5 to 3.5 / 96.5, the crystal phase of ZrO ₂ is mainly composed of tetragonal crystals, and the zirconia sintered body contains carbon nanotubes (hereinafter referred to as “CNT”). The zirconia sintered body having a volume resistivity of about 10 ⁻² to 10 ⁹ Ω · cm. It was found that can be solved. The present inventor has conducted further research based on such knowledge and has completed the present invention.

  In addition, although this invention relates to a zirconia sintered compact and its manufacturing method, let the following items 1-3 be a claim of this application among the said invention.

Item 1. A zirconia sintered body containing ZrO ₂ as a main component and containing a stabilizer, wherein the molar ratio of the stabilizer to ZrO ₂ is in the range of 1.5 / 98.5 to 3.5 / 96.5, ₂ crystal phase is mainly composed of tetragonal crystals, carbon nanotubes are contained in the zirconia sintered body in an amount of 1.35 to 3.0% by weight, and the volume resistivity of the zirconia sintered body is 1.0 × 10 ^−2. The zirconia sintered compact which is -9.21x10 < ^-2 > ohm * cm.

  Item 2. Item 2. The zirconia sintered body according to Item 1, wherein the carbon nanotube is at least one selected from the group consisting of a single-walled carbon nanotube, a multi-walled carbon nanotube, and the single-walled or multi-walled carbon nanotube containing a metal or carbon structure.

  Item 3. Item 3. The zirconia sintered body according to item 1 or 2, wherein the zirconia sintered body contains 0.05 to 15% by weight (0.1 to 20% by volume) of equiaxed particles having an average particle size of 300 nm or less. body.

The present invention is described in detail below.
I. Zirconia sintered body The zirconia sintered body of the present invention is a zirconia sintered body containing zirconia (ZrO ₂ ) as a main component and a stabilizer, and the molar ratio of the stabilizer to ZrO ₂ is 1.5. /98.5-3.5/96.5, the crystal phase of ZrO ₂ is mainly composed of tetragonal crystals, and the zirconia sintered body contains about 0.1 to 3.0% by weight of carbon nanotubes. The volume resistivity of the zirconia sintered body is about 10 ⁻² to 10 ⁹ Ω · cm.

  This zirconia sintered body retains excellent mechanical properties (breaking strength, fracture toughness, etc.) and imparts desired stable conductivity by adding a smaller amount of carbon nanotubes as a conductive material.

The zirconia sintered body of the present invention contains ZrO ₂ as a main component and contains a stabilizer. The molar ratio of stabilizer to ZrO ₂ (stabilizer / ZrO ₂ ) is in the range of 1.5 / 98.5 to 3.5 / 96.5, preferably in the range of 2/98 to 3/97. It is.

When the stabilizer / ZrO ₂ molar ratio is less than 1.5 / 98.5, the crystal phase tends to change, and the amount of monoclinic zirconia in the sintered body tends to increase. In addition, cracks are generated inside the sintered body, and if a load is applied to the sintered body or it is used for a long time, the crack develops and cracks and chips occur, resulting in a decrease in durability. It is not preferable.

On the other hand, if the molar ratio of the stabilizer / ZrO ₂ exceeds 3.5 / 96.5, the amount of tetragonal zirconia is lowered, and the mechanical properties are lowered.

Examples of the stabilizer contained in the zirconia sintered body of the present invention include Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO, CeO ₂ , Nd ₂ O ₃ , Yb ₂ O ₃ , Dy ₂ O ₃ , Examples thereof include metal oxides such as La ₂ O ₃ . Any one or a mixture of two or more of the above may be used as the stabilizer, and among them, Y ₂ O ₃ as a main component, particularly Y ₂ O ₃ is preferable.

In the zirconia sintered body of the present invention, the crystal phase of ZrO ₂ is mainly composed of tetragonal crystals. Specifically, a tetragonal volume fraction in the crystal phase of ZrO ₂ is recommended to be 90% by volume or more, preferably 95% by volume or more, particularly 97% by volume or more.

There are three crystal states of ZrO ₂ : tetragonal, cubic and monoclinic, and in particular tetragonal zirconia undergoes a stress-induced phase transformation with respect to external stress, and phase transforms to monoclinic zirconia, Due to the volume expansion that occurs at this time, fine microcracks can be formed around zirconia or compressive stress can be generated to prevent the progress of cracks caused by external stress. Therefore, in a zirconia sintered body mainly containing tetragonal zirconia, toughness and strength are increased.

On the other hand, if a large amount of monoclinic zirconia is contained in the zirconia sintered body, fine cracks are generated around the crystal. When stress is applied, micro-cracking occurs starting from the fine cracks, resulting in friction and impact. This is not preferable because resistance to crushing or the like is lowered. Therefore, monoclinic zirconia in the crystal phase of ZrO ₂ is 5% by volume or less, preferably 3% by volume or less.

In addition, when a large amount of cubic zirconia is contained, the crystal grain size becomes large, the mechanical properties are lowered, and the wear resistance and the like are lowered. Therefore, the cubic zirconia in the crystal phase of ZrO ₂ is 10% by volume or less, preferably 5% by volume or less.

  In the present invention, the content (volume%) of monoclinic zirconia (M), tetragonal zirconia (T) and cubic zirconia (C) in the crystal phase of zirconia is calculated by the following method using X-ray diffraction. Is done.

The surface of the zirconia sintered body and the processed sintered body product has been transformed from tetragonal zirconia to monoclinic zirconia by stress-induced phase transformation, and the true crystalline phase cannot be identified. The surface is polished to a mirror surface, and then measured by X-ray diffraction in a diffraction angle range of 27 to 34 degrees. The measured value is applied to the following formula to determine the presence and content of monoclinic zirconia.

Further, the presence and content of tetragonal zirconia and cubic zirconia are measured in the range of diffraction angles of 70 to 77 degrees by X-ray diffraction in the same manner as in the method of monoclinic zirconia, and obtained by applying the following equation.

The zirconia sintered body of the present invention may contain SiO ₂ in the sintered body, for example, about 0.1 to 3% by weight.

In the present invention, the average crystal grain size of ZrO ₂ is 0.1 to 0.8 μm, preferably 0.2 to 0.5 μm. When the average crystal grain size exceeds 0.8 μm, mechanical properties such as wear resistance and impact resistance are deteriorated, which is not preferable. On the other hand, an average crystal grain size of less than 0.1 μm is not preferable because phase transformation from tetragonal zirconia to monoclinic zirconia is reduced and mechanical properties are lowered.

  The average crystal grain size is determined as follows. That is, the surface of the sintered body is polished to a mirror surface, then subjected to thermal etching or chemical etching, then observed with a scanning electron microscope, measured at 10 points by the intercept method, and the average value is taken as the average crystal grain size. The calculation formula is as follows.

D = 1.5 × n / L
D: Average crystal grain size (μm)
n: Number of crystal grains per length L L: Measurement length (μm)
The relative density of the zirconia sintered body of the present invention may be 90% or more. If the relative density is 90% or more, the mechanical properties are maintained without lowering the conductivity. The relative density for maintaining excellent conductivity and mechanical properties is preferably 95% or more, more preferably 98% or more.

The relative density of the sintered body can be expressed as a ratio of the bulk density ρ actually measured in the sintered body to the theoretical density ρ _th of the sintered body. The theoretical density of the sintered body is derived from the theoretical density d (g / cm ³ ) of the material constituting the sintered body and its volume fraction V (%).

Theoretical density of sintered body ρ _th (g / cm ³ )
_{= D Z × V Z / 100} + d CNT × V CNT / 100
_{= D Z × (100-V} CNT) / 100 + d CNT × V CNT / 100
Relative density of sintered body (%) = ρ / ρ _th × 100
Here, d _CNT and d _Z are the theoretical densities of carbon nanotubes and zirconia, respectively, V _CNT and V _Z are the volume fractions of carbon nanotubes and zirconia, respectively, and V _Z + V _CNT = 100 (%) is there.

  The zirconia sintered body of the present invention is characterized in that it contains carbon nanotubes (CNT) as a conductive material. CNT is a hollow tube (tube) in which a carbon hexagonal network called graphene is rounded into a cylinder with a diameter of nanometer order, and the graphene constituting this tube is a single-walled nanotube (SWCNT), And multi-walled nanotubes (MWCNT) in which two or more layers are stacked in a nested cylinder. In addition, these CNT cylinders may include other components such as metals and carbon structures (for example, fullerene).

The diameter of CNT should just be about 0.5-50 nm. For example, in the case of SWCNT, the diameter is about 0.5 to 4 nm, and in the case of MWCNT, the diameter (outer diameter) is about 5 to 50 nm. Further, the aspect ratio of CNT is preferably 10 or more, more preferably 50 or more, and particularly preferably 100 or more from the viewpoint of effective conductivity imparting. Moreover, the electrical resistivity of CNT should just be about 10 ^{< -3} > ^-10 < ^-6 > (omega ^| ohm) cm (room temperature).

The zirconia sintered body of the present invention contains CNT in the range of 0.1 to 3.0% by weight (or 0.3 to 9.0% by volume). When the content of CNT is less than 0.1% by weight, the conductivity cannot be expressed significantly. When the content of CNT exceeds 3.0% by weight, the conductivity increases, but the sinterability decreases. This is not preferable because the amount of CNTs in the crystal grain boundary is excessively large and the mechanical properties are significantly deteriorated. In the present invention, the volume resistivity of the zirconia sintered body can be arbitrarily adjusted in the range of about 10 ⁻² to 10 ⁹ Ω · cm according to the amount of CNT added.

  In the present invention, by using CNTs having an anisotropic form with a high aspect ratio as the conductive material, high conductivity is imparted to the zirconia sintered body with a smaller amount of addition than in the conventional conductive material. be able to.

  For example, when the CNT-containing zirconia sintered body of the present invention is compared with the carbon-containing zirconia sintered body of Patent Document 6 described in the background art section, in obtaining a zirconia sintered body having an equivalent volume resistivity, When CNT is used as the conductive material, the addition amount (weight) can be reduced to about 1/10 to 1/1000 compared to when carbon is used. As a specific example, it can be easily understood by comparing Examples 1 to 5 with Comparative Example 2.

  Moreover, in the CNT-containing zirconia sintered body of the present invention, the critical volume fraction (Critical Volume Fraction) of electrical conductivity calculated by the effective medium theoretical formula (GEM formula) is 0.8 volume% or less, particularly 0.7-0. It has a low value of about .75% by volume (0.23-0.25% by weight). This also shows that the zirconia sintered body of the present invention is imparted with conductivity with a smaller volume of the conductive material as compared with the conventional case. For example, it can be easily understood by referring to FIG.

  The effective medium theoretical formula (GEM formula) is one theoretical formula that expresses the percolation theory. When a conductive substance is added to the non-conductive matrix, the resistivity, size, etc. It is a theoretical formula that expresses how the resistivity of the composite material changes according to the volume fraction of the added conductive material, and the calculated critical volume of conductivity expression is the value This is a characteristic value that changes the resistivity (conductivity) most abruptly before and after the addition of the conductive material, and means a threshold value that gives an added amount at which conductivity is developed.

Furthermore, in the zirconia sintered body of the present invention, if the content of CNT in the sintered body is 1.0% by weight or more, a volume resistivity (5.0 × 10 ⁻¹ Ωcm) that enables good electric discharge machining. Below). As a result, the electric discharge machining of the sintered body can be performed using a normal electric discharge machining apparatus.

In the zirconia sintered body of the present invention, the volume resistivity can be adjusted in the range of about 10 ⁻² to 10 ⁹ Ω · cm according to the CNT content. Specifically, when the zirconia sintered body of the present invention is used as an antistatic member (volume resistivity: about 10 ⁶ to 10 ⁹ Ω · cm), 0.1 to 0.1 CNT is contained in the zirconia sintered body. What is necessary is just to contain in 0.3 weight% (or 0.3-0.9 volume%). In particular, when MWCNT is used, 0.1 to 0.2% by weight (or 0.3 to 0.6% by volume) of MWCNT may be contained in the zirconia sintered body.

When the zirconia sintered body is used as a member that can be subjected to electric discharge machining (volume resistivity: about 10 ^{−2 to} 5.0 × 10 ⁻¹ Ω · cm), CNT is added to 1.0 to 3 in the zirconia sintered body. What is necessary is just to contain in the range of 0.0 weight% (or 3.0-5.8 volume%).

  In addition, the weight fraction (% by weight) and the volume fraction (% by volume) of CNT in the zirconia sintered body can be obtained by the method described in Example 1.

  In addition, the CNT-containing zirconia sintered body of the present invention is excellent in fracture toughness, and has a higher fracture toughness than a zirconia sintered body itself containing no CNT or a zirconia sintered body containing a conductive material other than CNT. ing.

  As described above, high conductivity and fracture toughness are exhibited in the zirconia sintered body of the present invention because CNTs having a high aspect ratio and an anisotropic shape are present in the zirconia crystal grains or at the crystal grain interfaces. This is considered to be because the three-dimensional conductive network (path) of CNTs is uniformly and effectively formed in the sintered body. As a specific example, see FIG. 5 of an electron micrograph of the sintered body obtained in Example 3, and CNTs are uniformly dispersed while maintaining the form in the crystal grains of the zirconia matrix particles or in the crystal grain boundaries. I can understand that.

  Furthermore, the dispersion of CNTs with a high aspect ratio causes a cross-linking effect that blocks the crack opening that propagates in the sintered body, and effectively suppresses chemical reactions at the interface between CNT and zirconia. The fact that a high toughness mechanism that effectively suppresses the generation and propagation of cracks, such as the effect of pulling out CNT generated at the crack opening portion caused by the action, works to achieve high fracture toughness. It can be easily understood from the electron micrograph shown in FIG.

  The zirconia sintered body of the present invention can be represented by a schematic diagram as shown in FIG. 3, for example. From FIG. 3, since CNT forms a conductive path three-dimensionally in zirconia and is uniformly dispersed, a conductive phase having an anisotropic structure is formed. For this reason, high conductivity is imparted by addition of a small amount of CNT, while the original characteristics of zirconia are maintained, and the conductivity becomes uniform.

  On the other hand, the conventional electroconductive ceramic which added the crystalline inorganic compound in patent documents 1-5 quoted by the term of background art can be typically represented like FIG. In this conductive ceramic, the conductive material is crystal particles, and the crystal particles need to be adjacent in order to exhibit conductivity. Therefore, it is necessary to add a large amount of a conductive material, and the mechanical characteristics of the ceramic itself are deteriorated.

  Moreover, the electroconductive ceramic which added the carbon of patent document 6 can be typically represented like FIG. In this case, although carbon has conductivity, it does not have a thin line shape, and therefore, it is necessary to connect it in a planar shape to form a conductive path necessary for developing conductivity. Therefore, a larger amount of conductive material needs to be added than in the present invention in order to develop conductivity, and as a result, the breaking strength is lowered.

In general, when a conductive substance is added to a zirconia sintered body, its breaking strength is lowered, and the addition of the CNT of the present invention is no exception. However, by adding nano-sized equiaxed particles in addition to CNT, the breaking strength of the zirconia sintered body can be dramatically improved. Here, the equiaxed particle means a particle having a spherical shape or a polyhedral shape close to a spherical shape and having an aspect ratio of about 1 to 1.5, specifically, silicon carbide (SiC), boron carbide (B ₄ C), boron nitride (BN), titanium nitride (TiN), titanium carbide (TiC), alumina (Al ₂ O ₃ ), monazite (LaPO ₄ ), zircon (ZrSiO ₄ ) and other ceramic particles, iron (Fe ), Cobalt (Co), nickel (Ni), copper (Cu), titanium (Ti), molybdenum (Mo), tungsten (W), etc., their intermetallic compounds, or alloys thereof. Of these equiaxed particles to be added, SiC is preferable from the viewpoint of being hard, stable without reacting with zirconia, and having semiconductivity. Note that the Si / C chemical composition ratio of SiC is not limited to 1.

The equiaxed particles to be added may be either crystalline or amorphous, and as long as the conductive path formed by the CNTs is not interrupted to impair the conductivity, good conductivity, semiconductivity, insulation Any of these may be used. The average particle diameter of the equiaxed particles to be added is preferably 300 nm or less, more preferably 200 nm or less, and particularly preferably about 150 to 30 nm. The average particle diameter is measured using a centered sedimentation type particle size distribution measuring apparatus. The addition amount of equiaxed particles to be added is about 0.05 to 15% by weight (or 0.1 to 20% by volume), particularly 1.0 to 6.0% by weight (or 2) in the zirconia sintered body. It is preferable to set so as to be about 10 to 10% by volume. As a specific example, it can be easily understood by looking at Example 4.
II. Manufacturing method of zirconia sintered body The manufacturing method of the electroconductive zirconia sintered body of this invention is demonstrated.

The conductive zirconia sintered body of the present invention can be manufactured using the following steps (1) to (4).
(1) A step of adding a carbon nanotube and a surfactant into a medium and sonicating to obtain a carbon nanotube dispersion, (2) a molar ratio of the stabilizer to ZrO ₂ is 1.5 / 98.5-3 A zirconia powder having a ZrO ₂ crystal phase mainly composed of tetragonal crystals in the range of .5 / 96.5 is added to the carbon nanotube dispersion obtained in the above (1) and subjected to ultrasonic treatment to obtain a mixed dispersion. (3) a step of distilling the medium from the mixed dispersion obtained in (2) above and drying to obtain a mixed powder; and (4) firing the mixed powder obtained in (3) above. A step of obtaining a zirconia sintered body by performing a ligation treatment.

In the present invention, the raw material zirconia powder is commercially available or can be produced by a known method. In particular, it is preferable to use zirconia powder purified by a liquid phase method. Specifically, for example, when the stabilizer is Y ₂ O ₃ , the content of Y ₂ O ₃ and ZrO ₂ is in the range of 1.5 / 98.5 to 3.5 / 96.5 (molar ratio). After uniformly mixing an aqueous solution of a zirconium compound (for example, zirconium oxychloride) and an aqueous solution of an yttrium compound (for example, yttrium chloride), hydrolyzing to obtain a hydrate, dehydrating and drying, It is calcined at 500 to 1000 ° C. to obtain zirconia powder. Here, the zirconia powder is preferably pulverized to an average particle size of about 0.05 to 0.2 μm. The average particle diameter is measured using a centered sedimentation type particle size distribution measuring apparatus.

As described above, the molar ratio of the stabilizer (for example, Y ₂ O ₃ ) to ZrO ₂ is in the range of 1.5 / 98.5 to 3.5 / 96.5, and the crystal phase of ZrO ₂ is mainly used. A zirconia powder composed of tetragonal crystals is obtained.

  Examples of the commercially available zirconia matrix include TZ-3YE manufactured by Tosoh Corporation.

  Separately, CNT is added to a (liquid) medium such as water or alcohol (for example, ethanol), a surfactant is added thereto, and ultrasonic irradiation is performed using an ultrasonic homogenizer. Thereby, a CNT dispersion liquid in which CNTs are uniformly dispersed in a medium is obtained. About 0.01 to 0.3 parts by weight of CNT and about 0.004 to 0.12 parts by weight of a surfactant as a surfactant component may be used with respect to 100 parts by weight of the medium. The surfactant may be any of nonionic, anionic, cationic or amphoteric surfactants, preferably nonionic surfactants such as polyoxyalkylene alkyl ether, polycarboxylic acid type polymer surfactants, etc. The anionic surfactant of these is mentioned.

  To this CNT dispersion, the zirconia powder obtained above was added so as to contain CNT in the range of 0.1 to 3.0% by weight with respect to the zirconia sintered body, and further subjected to ultrasonic dispersion treatment. A mixed dispersion (slurry) is obtained. Here, when the equiaxed particles (for example, SiC) are added, SiC weighed so as to be 0.05 to 15% by weight with respect to the total amount of the zirconia sintered body is added together with the zirconia powder, so What is necessary is just to carry out dispersion | distribution mixing by the sonic dispersion process.

Thus, by a combination of surfactant and an ultrasonic method, CNT is uniformly dispersible and will without aggregation in ZrO _2, 3-dimensional network (conductive uniform CNT to ZrO ₂ after sintering Path) is formed. As a result, a sintered body having a low resistivity can be obtained with a small amount of added CNT.

  Next, the medium is removed from the mixed dispersion (slurry) obtained by sufficiently mixing and dispersing to obtain a mixed powder. The medium may be removed by evaporating the medium using a rotary evaporator or the like and further drying in a heat dryer (45 to 55 ° C.). In addition, when water is used as a medium, it may be subjected to lyophilization. This mixed powder is mixed using a dry ball mill or the like to obtain a mixed powder.

  The obtained mixed powder is subjected to atmospheric pressure sintering, atmospheric pressure sintering, hot isostatic pressing (HIP) treatment, hot isostatic pressing (HIP) sintering, spark plasma sintering (SPS), etc. To sinter.

  In the normal pressure sintering method, the above-mentioned mixed powder is put into a mold and molded, and the removed molded body is heated and sintered at normal pressure. In the heat sintering process, for example, the temperature is increased to about 1400 to 1600 ° C. at about 20 ° C./min in an inert gas (Ar gas or the like) atmosphere using an atmosphere controlled electric furnace, and the temperature is about 3 to 5 hours. Just do it. The sintered body obtained by the normal pressure sintering method may be further subjected to a hot isostatic pressing (HIP) treatment. The HIP treatment may be performed at about 1300 to 1500 ° C. for about 1 to 3 hours in a pressure gas of about 180 to 200 MPa in an inert gas (Ar gas or the like) atmosphere. Thereby, the improvement of the relative density of a sintered compact is achieved, As a result, the resistance with respect to friction, an impact, crushing, etc. can be made high, and an improvement in mechanical property and also an improvement in durability can be performed.

  In the hot isostatic pressing (HIP) sintering method, the mixed powder is directly heated and sintered using the conditions of the above HIP treatment.

  In the spark plasma sintering (SPS) method, the mixed powder is directly heated and sintered using a discharge plasma sintering apparatus. Specifically, the mixed powder is filled into a graphite die, and heated to 1300 to 1550 ° C. at a temperature rising rate of 100 ° C./min in an inert gas (Ar gas or the like) atmosphere at a uniaxial pressure of about 25 to 35 MPa. And heat at the same temperature for about 3 to 10 minutes.

  The surface of the zirconia sintered body obtained by the above sintering method may be ground with a diamond grindstone or the like, if necessary.

  In the manufacturing method of the zirconia sintered body of the present invention, since CNT is used as the conductive material, generation of monoclinic zirconia which is weak mechanically in the sintering process and generation of unnecessary ZrC due to the reaction between carbon and zirconia. Can be suppressed. In particular, by adopting the pressure sintering method (SPS method) that allows rapid heating, it is possible to improve the relative density of the sintered body in a single hour, and the generation of ZrC by the chemical reaction between CNT and zirconia. It is possible to suppress the formation of monoclinic zirconia.

For example, in Comparative Example 1, in the case of a zirconia sintered body containing carbon powder, the production of monoclinic zirconia and ZrC, which are mechanically weak in the atmospheric pressure sintering process, is increased ( FIG. 8 ) . In the CNT-containing zirconia sintered body sintered by the SPS method of Example 3, ZrC is not generated, and monoclinic zirconia is hardly generated ( FIG. 7 ).

  The zirconia sintered body of the present invention thus obtained retains the original excellent mechanical properties (breaking strength, fracture toughness, etc.) of zirconia and has a stable conductivity.

  In the present invention, by using CNT as the conductive material, a zirconia sintered body having a low volume resistivity (high electrical conductivity) can be realized with a small amount of CNT added while maintaining mechanical properties.

When the added amount of CNT is 1.0% by weight or more (or 3% by volume or more), the volume resistivity is 5.0 × 10 ⁻¹ Ω · cm or less, which enables electric discharge machining. As a result, electric discharge machining of the sintered body becomes possible using a normal apparatus.

  Moreover, the fracture toughness value of the sintered body is improved by the addition of CNT, and the fracture strength is improved by the addition of silicon carbide nanoparticles.

Next, although this invention is demonstrated in detail using an Example, this invention is not limited to this Example.
A. The raw materials used in the raw material examples and comparative examples are shown below.
・ Zirconia: Tetragonal zirconia (3Y-TZP) powder stabilized by ₃ mol% yttrium oxide (Y ₂ O ₃ ) (Tosoh Corporation, TZ-3YE)
・ Multi-walled carbon nanotubes (MWCNT): Multi-walled carbon nanotubes with a diameter of 20-30 nm and a length of 1 μm or more (manufactured by Sigma-Aldrich Japan Co., Ltd.)
Single-walled carbon nanotubes (SWCNT): Single-walled carbon nanotubes with a diameter of 0.6-2 nm and a length of 0.5 μm or more (manufactured by Carbon Nanotechnologies Inc.)
・ Carbon particles: Hollow shell-like carbon powder (manufactured by Lion Corporation, EC600JD: primary particle diameter 34 nm, specific surface area 1270 m ² / g, aggregated particle size 230 nm)
・ Silicon carbide: β-SiC powder (Mitsui Toatsu Chemical Co., Ltd., primary particle size: 150 nm)
・ Surfactant: Carboxylic acid surfactant (oil-based) (Kao Corporation, Homogenol L-18, 40wt% concentration)
B. Evaluation of physical properties The following physical properties were evaluated for the zirconia sintered bodies obtained in Examples 1 to 7 and Comparative Example 1 described later.
(1) Resistance measurement Resistance measurement of the produced sintered body was performed at room temperature by Van der Pauw method (Resitest8308 type, manufactured by Toyo Technica Co., Ltd.). The sample was ground to a thickness of about 1 mm and polished. The shape of the sample was measured by circular sintering (diameter 13 mm) in normal pressure sintering and HIP processing, and the sintered body by the SPS method was processed into a square (10 mm square) and used for measurement.

The shape of the sample measured by the Van der Pauw method may be any shape as long as it is a sheet shape, and four small ohmic resistances are provided around the sample. If the resistance Rs of the sheet is known, the resistivity ρ (Ω · cm) can be known. Therefore, the resistance is calculated between the four terminals, and the sheet resistance Rs is calculated using this, and the volume resistivity is calculated using the thickness t:
ρ = Rs × t was calculated. The conductivity S (S / cm) was calculated by taking the reciprocal of the volume resistivity ρ.
(2) Fracture strength The fracture strength σ _f at room temperature of the sintered body was measured by a three-point bending test method. For measurement, an AG-C universal testing machine (Autograph) manufactured by Shimadzu Corporation was used, and a three-point bending test was performed under the conditions of a span length of 20 mm and a crosshead speed of 0.5 mm / min. The breaking strength was calculated by the following formula.

σ _f = 3P · L / (2b · d ² )
σ _f : Fracture strength (Pa)
P: Maximum load when the specimen breaks (N)
L: Distance between lower fulcrums (m)
b: Specimen width (m)
d: Test piece thickness (m)
(3) Fracture toughness The fracture toughness was measured using an AVK-M type Vickers hardness tester manufactured by Akashi Co., Ltd., and a Vickers indenter was driven into the polished sample surface with a holding time of 15 seconds and a load of 98 N. The crack length and the diagonal length of the resulting indentation were measured, and the fracture toughness was calculated using the following formula.

K1c = 0.203 ・ (c / a) ^-3/2・ HV ・ a ^1/2
KIC: Fracture toughness (Pa · m ^1/2 )
HV: Vickers hardness (Pa)
a: 1/2 (m) of diagonal length of indentation
c: Average crack radius (m)
(4) Relative Density The bulk density ρ of the produced sintered body was measured by the Archimedes method in toluene. The calculation formula shown below was used to calculate the density.

ρ (g / cm ³ ) = ρ1 × W1 / (W1−W2)
W1: Dry mass (g)
W2: Mass in toluene (g)
Density of toluene at temperature T (° C.) ρ1 (g / cm ³ ): ρ1 = 0.84812−0.00092248 × T
For composite materials, use the reported theoretical density of zirconia (3Y-ZrO ₂ = 6.05 g / cm ³ ) and the density of each carbon (carbon nanotubes 2.0 g / cm ³ , carbon powder EC600JD = 2.27 g / cm ³ ). The theoretical density was calculated from the added amount using the above formula, and the relative density (%) was calculated as the ratio of the bulk density of the sintered body to the theoretical density.
(5) Observation of microstructure of sintered body The microstructure of the sintered body was observed using a transmission electron microscope (TEM, Hitachi, H-8100, acceleration voltage 200 kV). The sintered body is thinly ground to a thickness of about 200μm, then polished with diamond slurry until it reaches about 100μm, then punched into a 3mm diameter circle with an ultrasonic machine, and the center thickness is about 20μm. I sharpened until. Thereafter, ion thinning with Ar ions was performed to obtain a TEM sample. Moreover, the fractured surface observation was performed using a scanning electron microscope (SEM, manufactured by Hitachi, Ltd., S-5000 type).
(6) X-ray diffraction measurement The phase of the sintered body was identified by the X-ray diffraction method (manufactured by Rigaku Corporation, RU-200B type). A CuKα ray (λ = 1.5418 mm) was used for the counter cathode, and the conditions were an applied voltage of 50 kV, an applied current of 150 mA, a scanning diffraction angle range of 2θ = 20 to 80 °, and a scanning speed of 4 ° / min.

(1) Preparation of mixed powder MWCNT weighed so as to be 0 to 2% by weight with respect to the weight (100 g) of the final zirconia sintered body was added to about 800 ml of ethyl alcohol (purity of 99.5% or more). Further, a surfactant was added so as to have the same weight as MWCNT (2/5 weight of MWCNT as a surfactant component). The mixture was subjected to dispersion treatment by ultrasonic irradiation at an output of 100 W for 1 to 3 hours using an ultrasonic homogenizer (manufactured by BRANSON, Sonifier S-450D type) to obtain a CNT dispersion.

Next, 100 to 98 g of zirconia powder was added to this CNT dispersion, and ultrasonic dispersion treatment was further performed for 1 hour. The mixed slurry obtained by sufficiently mixing and dispersing was dried by evaporating ethyl alcohol using a rotary evaporator, and then kept in a dryer at 50 ° C. for 24 hours to completely remove the solvent component. This mixed powder was subjected to dry ball mill mixing for 12 hours in a polyethylene pot using zirconia balls having a diameter of 5 mm as a mixing medium (bulk capacity: about 200 ml) to obtain a final mixed powder.
(2) Sintering process Use the mixed powder obtained in (1) above as a sample for evaluation of electrical properties in the form of a pellet with a diameter of 15 mm and a thickness of about 5 mm, or mechanical properties such as fracture strength. As a sample for use, it was molded at a pressure of 4 MPa so as to form a prism having a width of 5 mm, a thickness of 5 mm, and a length of 50 mm. Thereafter, molding was performed again at a pressure of 200 MPa using a cold isostatic press (CIP) apparatus. After burying it in graphite powder, using an atmosphere controlled electric furnace (manufactured by Marusho Denki Co., Ltd., SuperMini type), it was heated to 1500 ° C under an Ar gas atmosphere at a rate of temperature increase of 20 ° C / min for 4 hours. Sintering was performed to obtain a sintered body sample.
(3) Sample processing After the surface of the sintered body sample obtained in (2) above was ground with a diamond grindstone of particle size # 100, # 400 and # 800, diamond slurry of 9μm, 2μm and 0.5μm was prepared. The sample was used for mirror polishing to obtain samples for various evaluations. The final specimen shape and size is a disk-shaped sample with a diameter of 13 mm and a thickness of 1 mm (for electrical property evaluation), or a prismatic test piece with a width of 4 mm, a thickness of 3 mm and a length of 40 mm (for mechanical property evaluation). It was.

  Table 1 shows the physical property evaluation results of the obtained zirconia sintered body sample.

  In addition, the conversion formula of the volume fraction (vol%) and weight fraction (wt%) of zirconia and CNT in a zirconia sintered compact is as follows. same as below.

Zirconia CNT (or additive)
Density d _Z (6.02 g / cm ³ ) d _CNT (2.0 g / cm ³ )
Weight fraction (wt%) W _Z = 100−W _CNT W _CNT
Volume fraction (vol%) V _Z = 100−V _CNT V _CNT
V _CNT = 100 × (W _CNT / d _CNT ) / {(W _CNT / d _CNT ) + (W _Z / d _Z )}
= 100 × (W _CNT / d _CNT ) / {(W _CNT / d _CNT ) + ((100-W _CNT ) / d _Z )}
W _CNT = 100 × (V _CNT × d _CNT ) / {(V _CNT × d _CNT ) + (V _Z × d _Z )}
= 100 × (V _CNT × d _CNT ) / {(V _CNT × d _CNT ) + ((100−V _CNT ) × d _Z )}

(1) Preparation of mixed powder Mixed powder was obtained like Example 1 (1).
(2) Sintering process The sintered body sample obtained in Example 1 (2) was subjected to hot isostatic pressing (HIP) treatment at 1450 ° C. for 2 hours under Ar atmosphere (Kobe Steel Corporation, DrHIP type device) ) Was performed in the same manner as in Example 1.
(3) Sample processing A sample of the sintered body sample obtained in the above (2) was obtained in the same manner as in Example 1 (3).

  Table 2 shows the physical property evaluation results of the obtained zirconia sintered body sample.

  It was found that the fracture strength and the relative density of the sintered body of Example 2 subjected to HIP treatment are improved as compared with the sintered body obtained by only atmospheric pressure sintering of Example 1.

(1) Preparation of mixed powder Mixed powder in the same manner as in Example 1 (1) except that the amount of MWCNT added was varied from 0 to 3% by weight with respect to the weight of the final zirconia sintered body. Got.
(2) Sintering process The sintered compact sample was manufactured for the mixed powder obtained by said (1) using the discharge plasma sintering method (SPS method). After filling the mixed powder into a graphite die with a diameter of 15mm or 30mm and setting it in a discharge plasma sintering device (manufactured by Sumitomo Co., Ltd., SPS2080 type), uniaxial pressurizing pressure is set to 30MPa, heating rate is 100 under Ar After heating from 1300 to 1550 ° C. at a rate of 1 ° C./min, sintering was performed for 5 minutes to obtain an SPS sintered body sample.
(3) Sample processing Subsequently, the surface of the SPS sintered body sample obtained in (2) above was sequentially ground with a diamond grindstone of particle size # 100, # 400 and # 800, then 9 μm, 2 μm and 0.5 μm The diamond slurry was mirror-polished to obtain samples for various evaluations. The final specimen shape and size is a disk-shaped sample with a diameter of 15 mm and a thickness of 1 mm, and a disk-shaped test piece with a diameter of 30 mm is cut and polished into a prismatic shape with a diamond cutting machine. The specimen was subjected to the fracture strength test as a prismatic specimen having a length of 3 mm and a length of 25 mm.

  Table 3 shows the physical property evaluation results of the obtained zirconia sintered body sample.

When the addition amount is 1.35 wt% and 2.0 wt%, the obtained sintered body shows a volume resistivity (10 ⁻² order) to which electric discharge machining can be suitably applied. Further, it was found that the fracture strength and the relative density of the sintered body of Example 3 subjected to SPS sintering are dramatically improved as compared with the sintered body obtained only by atmospheric pressure sintering of Example 1.

For the zirconia sintered body obtained in Example 3, the volume resistivity (Ωcm) relative to the CNT content (vol%) was measured by the van der Pauw method. The result is shown in FIG. According to this, it turned out that the critical volume of electroconductivity expression is a very low value as 0.73 vol%. This means that the conductivity is imparted to the zirconia sintered body with a smaller amount of the conductive material added by using CNTs. The GEM theoretical formula and parameters used in FIG. 4 are shown below.

  Moreover, the transmission electron microscope (TEM) of the zirconia sintered compact obtained in Example 3 and the scanning electron microscope (SEM) photograph of a fracture surface are shown in FIG. According to this, the added MWCNT is uniformly distributed within the zirconia crystal particle interface (grain boundary) and inside the particles in the zirconia matrix, and the CNTs are also in contact with each other to form a three-dimensional conductive path. It can be seen that they are dispersed.

  Moreover, the measurement result of the X-ray diffraction of the zirconia sintered compact obtained in Example 3 is shown in FIG. According to this, since CNT is used as the conductive material and the short-time sintering method (SPS sintering method) is adopted, there is almost no formation of ZrC or monoclinic zirconia, and the sintering is excellent in fracture strength and fracture toughness. It can be seen that a ligation was obtained.

(1) Preparation of mixed powder MWCNT weighed to 1% by weight with respect to the weight (100 g) of the final zirconia sintered body was added to about 800 ml of ethyl alcohol (purity of 99.5% or more), and The surfactant was added so as to have the same weight as MWCNT (2/5 weight of MWCNT as a surfactant component). The mixture was subjected to ultrasonic irradiation at an output of 100 W for 1 to 3 hours using an ultrasonic homogenizer (manufactured by BRANSON, Sonifier S-450D type) to obtain a CNT dispersion.

Next, SiC was weighed so that silicon carbide (SiC) was 2.7 wt% or 11.5 wt% with respect to the final sintered body weight (100 g), and this was mixed with zirconia powder (about 96.3 g). Or 87.5 g) was simultaneously added to the CNT dispersion, followed by ultrasonic dispersion treatment for 1 hour. The mixed slurry obtained by sufficiently mixing and dispersing was dried by evaporating ethyl alcohol using a rotary evaporator, and then kept in a dryer at 50 ° C. for 24 hours to completely remove the solvent component. This mixed powder was subjected to dry ball mill mixing for 12 hours in a polyethylene pot using zirconia balls having a diameter of 5 mm as a mixing medium (bulk capacity: about 200 ml) to obtain a final mixed powder.
(2) Sintering process The sintered compact sample was manufactured for the mixed powder obtained by said (1) using the discharge plasma sintering method (SPS method).

The obtained mixed powder is filled into a graphite die with a diameter of 15 mm or 30 mm, set in a discharge plasma sintering apparatus (manufactured by Sumitomo Coal Industries, SPS2080 type), then uniaxially pressurized to 30 MPa and lifted in an Ar atmosphere. After heating from 1300 to 1550 ° C. at a temperature rate of 100 ° C./min, sintering was performed for 5 minutes to obtain an SPS sintered body sample.
(3) Sample processing The SPS sintered compact sample obtained by said (2) was obtained like Example 3 (3), and the test piece was obtained.

  Table 4 shows the physical property evaluation results of the obtained zirconia sintered body sample.

  When Example 4 is compared with Example 3, the fracture strength of Example 4 is dramatically improved over that of Example 3 (when the added amount of CNT is 1.0 wt%). This shows that the fracture strength of the sintered body is improved by adding silicon carbide (SiC).

  Moreover, the transmission electron microscope (TEM) photograph of the torn surface of the zirconia sintered compact obtained in Example 4 is shown in FIG. Thus, it can be seen that the added equiaxed particles are dispersed in a desirable form without breaking and breaking the conductive path formed by the CNTs.

(1) Preparation of mixed powder A mixed powder was obtained in the same manner as in Example 1 (1) except that SWCNT was used instead of MWCNT in Example 1 (1).
(2) Sintering step The SPS sintered compact sample was obtained for the mixed powder obtained in the above (1) in the same manner as in Example 3 (2).
(3) Sample processing The SPS sintered compact sample obtained by said (2) was obtained like Example 3 (3), and the test piece was obtained.

  Table 5 shows the physical property evaluation results of the obtained zirconia sintered body sample.

  Thus, it can be seen that any conductivity can be imparted by dispersing CNTs regardless of the difference in structure between the multilayer and single layer.

Comparative Example 1

(1) Preparation of mixed powder A mixed powder was obtained in the same manner as in Example 1 (1) except that carbon particles were used instead of MWCNT in Example 1 (1).
(2) Sintering process The sintered compact sample was obtained for the mixed powder obtained by said (1) like Example 1 (2).
(3) Sample processing A sample of the sintered body sample obtained in the above (2) was obtained in the same manner as in Example 1 (3).

  Table 6 shows the physical property evaluation results of the obtained zirconia sintered body sample.

  When the volume resistivity of Examples 1-5 and Comparative Example 1 in the case where the addition amount of the conductive material is the same, it can be seen that the volume resistivity of Comparative Example 1 is about 10 to 100 times larger. Further, it can be seen that the relative density is greatly reduced in Comparative Example 1.

  Moreover, the measurement result of the X-ray diffraction of the zirconia sintered compact obtained by the comparative example 1 is shown in FIG. According to this, it can be seen that a large amount of mechanically weak ZrC and monoclinic zirconia are produced.

Comparative Example 2

  Example 1 of JP-A-2004-189509 teaches a zirconia sintered body containing carbon derived from a phenol resin. For comparison with the present invention, an extract of the carbon content (wt%) and the volume resistance (Ωcm) in the zirconia sintered body is extracted from Table 1 described in Example 1 of JP-A-2004-189509. Table 7 shows.

  Table 8 below shows a comparison of volume resistivity in Japanese Patent Application Laid-Open No. 2004-189509 and Examples of the present invention in the case where the addition amount of the conductive material is the same.

  Thus, it can be seen that the volume resistivity of Example 1 of Japanese Patent Application Laid-Open No. 2004-189509 is about 3 to 700 times larger than that of the Example of the present invention when the amount of the conductive material added is the same.

Test example 1

  The zirconia sintered body obtained in Example 3 (addition amount 2.0 wt%) was subjected to electric discharge machining using a wire electric discharge machine (manufactured by Sodick Co., Ltd., AP200L type). An example of the electric discharge machining is shown in FIG. It was found that better electrical discharge machining can be performed than in FIG.

  The conditions for electrical discharge machining are shown below.

Wire: Zinc coated brass wire, 0.2mm diameter
Processing fluid: EDM oil Wire tension: 15N
Wire feed speed: 5mm / min
Processing time: 60 minutes

The schematic diagram of the conventional conductive ceramic is shown. The schematic diagram of the electroconductive zirconia sintered compact containing the conventional carbon is shown. The schematic diagram of the electroconductive zirconia sintered compact containing CNT of this invention is shown. 4 is a graph showing the relationship between the CNT content and the volume resistivity in the conductive zirconia sintered body obtained in Example 3. It is a transmission electron microscope (TEM) photograph (a, b) and a scanning electron microscope (SEM) photograph (c) of the electroconductive zirconia sintered compact obtained in Example 3. 4 is a transmission electron microscope (TEM) photograph of the zirconia sintered body obtained in Example 4. 4 is a graph showing X-ray diffraction results for each CNT content of the conductive zirconia sintered body obtained in Example 3. FIG. 5 is a graph showing X-ray diffraction results for each carbon particle content of the conductive zirconia sintered body obtained in Comparative Example 1. 6 is a diagram showing an example of electric discharge machining of the conductive zirconia sintered body obtained in Example 3. FIG.

Claims (3)

A zirconia sintered body containing ZrO ₂ as a main component and containing a stabilizer, wherein the molar ratio of the stabilizer to ZrO ₂ is in the range of 1.5 / 98.5 to 3.5 / 96.5, ₂ crystal phase is mainly composed of tetragonal crystals, carbon nanotubes are contained in the zirconia sintered body in an amount of 1.35 to 3.0% by weight, and the volume resistivity of the zirconia sintered body is 1.0 × 10 ^−2. The zirconia sintered compact which is -9.21x10 < ^-2 > ohm * cm. 2. The zirconia sintered body according to claim 1, wherein the carbon nanotube is at least one selected from the group consisting of a single-walled carbon nanotube, a multi-walled carbon nanotube, and the single-walled or multi-walled carbon nanotube containing a metal or a carbon structure. . The zirconia sintered body according to claim 1 or 2, wherein the zirconia sintered body contains 0.05 to 15% by weight (0.1 to 20% by volume) of equiaxed particles having an average particle size of 300 nm or less. Union.

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