JP2011219279A - Zirconia raw material, sintered zirconia compact, cutter, and hand cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zirconia raw material and a sintered zirconia compact, capable of suppressing reduction in strength in a hydrothermal degradation environment, and to provide a cutter and a hand cutting tool.SOLUTION: The zirconia raw material including zirconia as the main component and containing 1.5 to 3.5 mol% of yttria, 0.03 to 0.3 mass% of silica, 0.001 to 0.01 mass% of sodium oxide and 0.005 to 2.0 mass% of alumina, and the sintered zirconia compact, are provided. The zirconia raw material has a mean particle diameter of 0.4 to 1 μm, a maximum particle diameter of 1 to 3 μm, and a specific surface area of 4 to 16 m/g. This sintered zirconia compact has peak intensity ratios as described in the description as determined by EDS surface analysis of a surface crystal grain boundary. The cutter and the hand cutting tool have a blade made of the sintered zirconia compact.

Description

  The present invention relates to a zirconia raw material and a zirconia sintered body suitable for blades and the like, as well as a blade and a manual instrument.

A zirconia sintered body has a problem that its strength is lowered in a hydrothermal deterioration environment in which hot water, water vapor and the like are present. For example, Patent Document 1 describes a zirconia sintered body mainly composed of zirconia (ZrO ₂ ) and yttria (Y ₂ O ₃ ).

In this sintered body, the molar ratio of yttria / zirconia is 1.5 / 98.5 to 2.6 / 97.4, 0.005 to 4.5% by mass of alumina (Al ₂ O ₃ ), oxidation At least one of calcium (CaO) and magnesium oxide (MgO) is contained in a proportion of 1% by mass or less. In the sintered body, the total amount of silica (SiO ₂ ), sodium oxide (Na ₂ O) and potassium oxide (K ₂ O) is 0.3 mass% or less, and silica is 0.2 mass%. Hereinafter, sodium oxide is 0.05 mass% or less, potassium oxide is 0.05 mass% or less, and an average crystal grain size is 0.30 to 0.70 μm.

In Patent Document 1, this sintered body is used as a member for a zirconia-made dispersion / pulverizer, and it is described that the sintered body hardly undergoes phase transformation and has wear resistance even in warm water.
However, even in the case of this sintered body, the current situation is that the strength reduction in the hydrothermal deterioration environment cannot be suppressed. For this reason, development of the zirconia sintered compact which can suppress the strength reduction in a hydrothermal deterioration environment, and its raw material is desired.
JP-A-8-337473

  The subject of this invention is providing the zirconia raw material and zirconia sintered compact which can suppress the intensity | strength fall in a hydrothermal deterioration environment, a cutter, and a manual instrument.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found a solution means having the following constitution and have completed the present invention.
(1) Mainly composed of zirconia, yttria 1.5 to 3.5 mol%, silica 0.03 to 0.3 mass%, sodium oxide 0.001 to 0.01 mass%, and alumina 0 0.005 to 2.0% by mass, zirconia having an average particle size of 0.4 to ¹ μm, a maximum particle size of 1 to 3 μm, and a specific surface area of 4 to 16 m ² / g material.
(2) Mainly composed of zirconia, yttria 1.5 to 3.5 mol%, silica 0.03 to 0.3 mass%, sodium oxide 0.001 to 0.01 mass%, and alumina 0 0.005 to 2.0 mass%, and in the EDS surface analysis at the grain boundary of the surface, the maximum peak intensity of oxygen is 60 to 80% with respect to the maximum peak intensity of silicon, and the maximum of aluminum A zirconia sintered body comprising a silica compound having a peak intensity and a maximum peak intensity of zirconium of 20 to 80% of the maximum peak intensity of silicon.
(3) The zirconia sintered body according to the above (2), which has on its surface silica capable of forming the silica compound at a crystal grain boundary.
(4) The zirconia sintered body according to (2) or (3), wherein the silica compound is present more in the surface grain boundaries than in the internal crystal grain boundaries.
(5) A blade comprising a blade made of the zirconia sintered body according to any one of (2) to (4).
(6) A manual instrument comprising a blade made of the zirconia sintered body according to any one of (2) to (4).

  In general, under a hydrothermal deterioration environment, the zirconia crystal particles constituting the sintered body expand due to hydrothermal heat, and the entire sintered body has a compressive stress, and therefore the strength decreases. According to the present invention, the zirconia raw material and the zirconia sintered body were controlled to a specific composition. As a result, in a hydrothermal deterioration environment, the silica on the surface of the sintered body reacts with water to form a silica compound having a specific peak intensity ratio at the crystal grain boundary on the surface of the sintered body. Of the zirconia crystal particles to be processed, only the zirconia crystal particles on the surface of the sintered body can be expanded.

  That is, according to the present invention, the zirconia crystal particles on the surface of the sintered body can be expanded to form a compressive stress layer only on the surface of the sintered body. It is easy to improve the strength, and it is possible to suppress a decrease in strength under a hydrothermal deterioration environment.

<Zirconia raw material>
The zirconia raw material which is one embodiment of the present invention contains zirconia as a main component and contains yttria, silica, sodium oxide and alumina in a specific ratio. If it demonstrates concretely, the said yttria will be contained in the ratio of 1.5-3.5 mol%.

  When yttria is contained at a ratio of 1.5 mol% or more, it is possible to suppress an excessive ratio of the monoclinic phase in the zirconia sintered body described later. That is, it is possible to suppress the occurrence of cracks due to a large volume change due to the phase transition and the decrease in strength.

  Moreover, when yttria is contained at a ratio of 3.5 mol% or less, it is possible to suppress an excessive ratio of the cubic phase in the zirconia sintered body. That is, it is possible to suppress a decrease in strength due to a decrease in the effect of stress-induced transformation of the tetragonal phase. The stress-induced transformation means that the propagation of cracks that cause fracture is inhibited by phase transformation, and stress concentration at the crack tip is relaxed.

  The silica is contained in an amount of 0.03 to 0.3% by mass, preferably 0.05 to 0.2% by mass, more preferably 0.07 to 0.15% by mass. The sodium oxide is contained in an amount of 0.001 to 0.01% by mass, preferably 0.001 to 0.003% by mass. When silica and sodium oxide are contained in such a ratio, a silica compound is likely to be formed at a crystal grain boundary described later in a hydrothermal deterioration environment, and a decrease in strength in the environment can be suppressed. Moreover, when a silica is contained in the said ratio, it can also suppress that a sintered density falls.

  The said alumina is contained in the ratio of 0.005-2.0 mass%. Thereby, sinterability improves and it becomes easy to make a crystal structure uniform. Moreover, it can suppress that the fracture toughness of a zirconia sintered compact falls.

  The zirconia raw material which is an embodiment of the present invention is a specific particle size, maximum particle size and specific surface area after the zirconia, yttria, silica, sodium oxide and alumina are pulverized, mixed and dried, respectively, as shown below. Has a value.

  That is, the average particle size is 0.4-1 μm, and the maximum particle size is 1-3 μm. As described later, the dried zirconia raw material is sintered after being formed into a molded body, but if the average particle diameter and the maximum particle diameter are within the above ranges, the density of the molded body is suppressed from being lowered. Therefore, it becomes easy to obtain a dense sintered body. Moreover, it can suppress that sinterability and a sintering density fall.

  The average particle size and maximum particle size are measured with a laser diffraction particle size analyzer after a small amount of zirconia raw material is added to water, an appropriate dispersant is added and sufficiently dispersed with an ultrasonic cleaner. Is the value obtained.

The specific surface area is 4 to 16 m ² / g. Thereby, it can suppress that sinterability and a sintering density fall. Moreover, it can suppress that a molded object density falls. The specific surface area is a value obtained by measuring by a BET one-point method using a gas obtained by heating and drying a zirconia raw material at 200 ° C. and then mixing nitrogen and helium at a volume ratio of 3: 7.

  The zirconia raw material which is one embodiment of the present invention can be obtained through a first step of pulverizing and mixing the zirconia, yttria, silica, sodium oxide and alumina, and then a second step of drying.

  In the first step, the zirconia is not particularly limited in its production method, and can be obtained by employing a known method such as a coprecipitation method, a hydrolysis method, or a hydrothermal method. The yttria, silica, sodium oxide, and alumina may be pulverized and mixed in the form of an oxide, or may be contained as a component in zirconia, for example, yttria stabilized zirconia (YSZ: YTTRIA STABILIZED ZIRCONIA). Well this may be ground and mixed.

  The pulverization and mixing can be performed using, for example, a bead mill, a ball mill, a vibration mill, or the like. The pulverization and mixing time is suitably about 1 to 10 hours. In addition, wet pulverization may be performed using a solvent. Examples of the solvent include water and organic solvents, and examples of the organic solvent include ethanol, acetone, isopropyl alcohol, and the like. The solvent is preferably added in such a ratio that the solid content concentration of the slurry after wet pulverization is 40 to 60% by mass.

  Moreover, binders, such as polyvinyl alcohol and methylcellulose, can also be added to the slurry after wet pulverization according to the molding method. When the viscosity is high and the grindability is lowered, a dispersant may be added. Examples of the dispersant include polyethylene glycol, ammonium polyacrylate, ammonium polycarboxylate, sodium hexametaphosphate and the like.

  There is no limitation in particular as the drying method in the said 2nd process, A well-known drying method is employable. Specific examples thereof include a spray drying method (spray drying method) and the like in addition to drying with a dryer, and the spray drying method is preferable in order to obtain raw materials efficiently. When the spray drying method is employed, the hot air temperature of the spray dryer is preferably 150 to 250 ° C., and the dried powder after drying is preferably sized through a sieve of about 80 to 200 mesh.

  On the other hand, when using a dryer etc., about 100-200 degreeC is suitable for drying temperature, and it is preferable to crush the raw material after drying using a pin mill etc. In the zirconia raw material after drying, zirconia and yttria are usually in a solid solution state, and silica, sodium oxide, and alumina are in a mixed state.

<Zirconia sintered body>
The zirconia sintered body according to an embodiment of the present invention is mainly composed of zirconia, 1.5 to 3.5 mol% of yttria, 0.03 to 0.3 mass% of silica, and 0.001 of sodium oxide. -0.01 mass% and an alumina are contained in the ratio of 0.005-2.0 mass%.

  As shown in FIG. 1, the zirconia sintered body having such a composition can form a compressive stress layer 2 on the surface of the zirconia sintered body 1 in a hydrothermally deteriorated environment. The decrease can be suppressed.

  That is, the compressive stress layer 2 has a compressive stress in the arrow A direction. As shown in FIG. 2, when an external force is applied to one side of this compressive stress layer 2 from the direction of arrow B (vertical direction), a compressive stress is generated in the direction of arrow C in the peripheral area a where the external force is applied. To do. This compressive stress in the direction of arrow C can be offset by the compressive stress in the direction of arrow A that the compressive stress layer 2 has, and hence a decrease in strength in the environment can be suppressed.

  On the other hand, tensile stress is generated in the direction of arrow D on the other surface opposite to one surface of the compressive stress layer 2 to which the external force is applied, and in the region b facing the region a. Further, although compressive stress in the direction of arrow A of the compressive stress layer 2 is also applied to the region b, the volume of the region b increases due to the phase transformation of the zirconia crystal grains from tetragonal crystal to monoclinic crystal. (Stress-induced transformation).

  The compressive stress layer 2 is generated when the zirconia crystal particles expand due to hydrothermal heat, that is, when the zirconia crystal particles undergo a phase transformation from tetragonal to monoclinic. More specifically, the zirconia sintered body 1 has a plurality of zirconia crystal particles 10 as shown in FIG. The zirconia crystal particles 10 mean crystal particles mainly containing zirconia.

  The plurality of zirconia crystal particles 10 are adjacent to each other to form a crystal grain boundary 11. The sintered body 1 has silica on the surface that can react with water to form a silica compound 12 at the crystal grain boundaries 11. The silica is derived from the silica contained in the sintered body 1 in the above ratio, and is contained in a large amount in the crystal grain boundary 11 (particularly, the triple point grain boundary). As this reason, it is guessed that it originates in the sintered compact 1 containing a silica and sodium oxide in the said ratio.

  Under a hydrothermal degradation environment, hydrothermal degradation proceeds from the surface of the sintered body 1 toward the inside (in the direction of arrow E). In this process, the silica reacts with water, and a silica compound 12 is formed at the crystal grain boundary 11 on the surface of the sintered body 1. As a result, the zirconia crystal particles 10 undergo a phase transformation from tetragonal to monoclinic crystal only on the surface of the sintered body 1 and the volume increases by about 4%. As a result, the compressive stress layer 2 is easily formed.

  Since this compressive stress layer 2 is formed only on the surface of the sintered body 1, it can be suppressed that the entire sintered body 1 has a compressive stress and becomes brittle. The reason why the compressive stress layer 2 is formed only on the surface of the sintered body 1 is that when the silica compound 12 is formed at the crystal grain boundary 11 on the surface of the sintered body 1, this becomes a protective layer and the inside of the sintered body 1. It is presumed that the intrusion of water into the glass is easily prevented, and this is because the phase transformation of the zirconia crystal particles 10 inside the sintered body 1 is suppressed.

  The sintered body 1 has the silica that can react with water to form the silica compound 12 at the crystal grain boundaries 11 not only on the surface but also on the inside. As a result, the silica compound 12 usually tends to be present more in the crystal grain boundaries 11 on the surface than in the crystal grain boundaries 11 inside the sintered body 1.

  Processing conditions for appropriately forming the compressive stress layer 2 only on the surface of the sintered body 1 are not particularly limited. That is, while the sintered body 1 is polished or used, the phase spontaneously transforms from tetragonal to monoclinic and the compressive stress layer 2 is easily formed only on the surface of the sintered body 1.

  Here, the silica compound 12 has a specific peak intensity ratio. That is, in the EDS (energy dispersive X-ray spectroscopy) surface analysis at the grain boundary 11 on the surface of the sintered body 1, the silica compound 12 has a maximum peak intensity of oxygen of 60 to 80% with respect to the maximum peak intensity of silicon. In addition, the maximum peak intensity of aluminum and the maximum peak intensity of zirconium are both 20 to 80% with respect to the maximum peak intensity of silicon. When the silica compound 12 having such a specific peak intensity ratio is present at the crystal grain boundary 11 on the surface of the sintered body 1 and the compressive stress layer 2 including the silica compound 12 is formed on the surface of the sintered body 1 The folding strength of the sintered body 1 is increased, and it is possible to easily suppress the strength reduction in the hydrothermal deterioration environment. The silica compound 12 having such a peak intensity ratio can be easily formed by configuring the sintered body 1 with the above composition.

  In the EDS surface analysis, a transmission electron microscope (“JEM2010F” manufactured by JEOL) is set to an acceleration voltage of 200 kV, and an energy dispersive X-ray spectroscopic analysis (“Voyager IV” manufactured by Noran Instruments) is performed with a spot diameter of 1 nm and a measurement time. The measurement energy width is set to 0.12 to 20.48 keV for 50 seconds, and the determination amount calculation method is performed using a thin film approximation method.

  The composition analysis of the crystal grain boundary 11 is performed by structural observation with an SEM (scanning electron microscope). Specifically, SEM (“JSM-7001F” manufactured by JEOL Ltd.) is used under the conditions of Tilt 0 °, no evaporation, acceleration voltage 15 kV, magnification 2000 times, and reflected electron composition image. The composition analysis of the sintered body 1 itself can also be performed in the same manner as the composition analysis of the crystal grain boundaries 11.

  The zirconia sintered body which is one embodiment of the present invention can be obtained through a first step of producing a molded body from a zirconia raw material and a second step of sintering the molded body. In the first step, a known molded method such as cast molding, injection molding, extrusion molding, pressure molding, mold molding, or the like can be employed to produce a molded body from the zirconia raw material.

In particular, when pressure molding is employed, CIP molding is preferable in order to obtain a uniform and high-density molded body, and a molding pressure of about 0.5 to 2.0 t / cm ² is appropriate. In addition, before performing CIP shaping | molding, you may perform temporary shaping | molding using a uniaxial pressure molding machine etc. A molding pressure of about 0.5 to 1.0 t / cm ² is appropriate when employing mold molding.

  In the second step, the molded body is preferably fired at 1300 to 1600 ° C., preferably 1350 to 1450 ° C., for about 1 to 3 hours. When fired in this manner, it is possible to suppress the crystal grain boundary 11 from becoming large, and it is possible to suppress a decrease in strength in a hydrothermal deterioration environment.

  Moreover, when using the zirconia raw material which added the said binder, it is preferable to degrease at 350-600 degreeC. When degreasing is performed within this range, it is possible to prevent the binder from remaining or cracks due to abrupt degreasing from occurring in the molded body. As the firing atmosphere, in addition to the air, vacuum may be used in order to reduce pores in the sintered body.

  Since the zirconia sintered body which is one embodiment of the present invention can easily suppress a decrease in strength under a hydrothermal deterioration environment, it is suitable for blades such as blades and manual instruments. That is, the blade which is one Embodiment of this invention is equipped with the blade body which consists of the said zirconia sintered compact. Examples of the blade include a (cutter) knife and a knife.

  Moreover, the manual instrument which is one Embodiment of this invention is equipped with the blade body which consists of the said zirconia sintered compact. Examples of the manual instrument include scissors, peelers, spoons, forks, and frying. In these blades and manual instruments, it is possible to easily form a compressive stress layer on the surface of the sintered body even in the step of polishing the blade. In addition, the use of the zirconia sintered compact which is one Embodiment of this invention is not limited to these illustrated uses, It can be used also as various members used in a hydrothermal deterioration environment.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to a following example. In addition, the measuring method of each physical property is as follows.

(Average particle size / maximum particle size)
A small amount of zirconia raw material was added to water, a dispersant was added, and the mixture was sufficiently dispersed with an ultrasonic cleaner, and then measured with a laser diffraction particle size analyzer. In addition, sodium hexametaphosphate was used for the said dispersing agent, and the usage-amount was 80 weight part (solid content conversion) with respect to 100 weight part of zirconia raw materials.

(Specific surface area)
It measured by the above-mentioned BET one point method.

<Preparation of sintered zirconia>
First, YSZ having 2 mol% of yttria, 0.007 mass% of silica, 0.001 mass% of sodium oxide, 0.005 mass% of alumina, the remainder consisting of zirconia and having a specific surface area of 6.5 m ² / g was prepared. . Separately, alumina and silica were prepared.

  Subsequently, these were pulverized and mixed at the ratios shown in Table 1. In Table 1, the remaining composition excluding yttria, silica, sodium oxide and alumina is the composition of zirconia.

  The pulverization and mixing were performed by wet pulverization. That is, wet pulverization was performed using a vibration mill for 5 hours using water as a solvent. The water was added in such a ratio that the solid content concentration of the slurry after wet pulverization was 40% by mass.

  The slurry after wet pulverization was dried with a spray dryer (hot air temperature: 170 ° C.), and the obtained dry powder was sized through a 120-mesh sieve to obtain a powdery zirconia raw material (in Table 1). Sample numbers 1-41). About each obtained zirconia raw material, the average particle diameter, the maximum particle diameter, and the specific surface area were measured according to the above-mentioned method. The results are shown in Table 1.

Next, the powdery zirconia raw material thus obtained was temporarily molded using a uniaxial pressure molding machine (“HYDRALIC PRESS” manufactured by Marushichi Company), and then a CIP molding machine (“Dr. CIP” manufactured by Kobe Seisakusho). Was molded at a pressure of 1.0 t / cm ² . This molded body was sintered in the air at 1430 ° C. for 2 hours to obtain a zirconia sintered body (sample numbers 1 to 41 in Table 1). The composition analysis of each obtained sintered body was carried out by the analysis method using the SEM described above. As a result, the composition of each sintered body had the same composition as the composition shown in Table 1.

<Evaluation>
A hydrothermal deterioration test was performed on each of the obtained sintered bodies. First, the sintered body was cut and processed so as to comply with JIS 1601, and the surface was mirror-polished using a 3.0 μm diamond paste. Subsequently, this sintered body was placed in a 1000 ml pressure-resistant container so that the polishing surface was directed upward with respect to the bottom surface of the container.

  After slowly pouring 700 ml of pure water into the pressure vessel so that the sintered body does not move, the pressure vessel is set in an autoclave device ("TEM-V" manufactured by Pressure Glass Industrial Co., Ltd.), and 140 ° C. The hydrothermal deterioration test was conducted over 100 hours under the condition of 3.6 atm. And about the sintered compact after a hydrothermal deterioration test, the EDS surface analysis and the measurement of mine strength were implemented. The analysis method and measurement method are shown below, and the results are shown in Table 1.

(EDS surface analysis)
The EDS surface analysis was performed under the above-described conditions except that the measurement location was a triple point grain boundary on the surface of the sintered body. In Table 1, in the column of the peak intensity ratio, “oxygen” indicates the ratio of the maximum peak intensity of oxygen to the maximum peak intensity of silicon. Similarly, in this column, “aluminum” and “zirconium” indicate the ratio of the maximum peak intensity of aluminum and the maximum peak intensity of zirconium to the maximum peak intensity of silicon, respectively.

  As an example of the EDS surface analysis result, the observation result of the sample number 41 with a transmission electron microscope is shown in FIG. 4, and the EDS surface analysis result is shown in FIG. In addition, the EDS surface analysis was performed about the triple point grain boundary F in the sintered compact surface in FIG. In FIG. 5, “Si” represents silicon, “O” represents oxygen, “Al” represents aluminum, and “Zr” represents zirconium.

(Folding strength)
The mine strength was measured under the three-point bending strength measurement conditions based on JIS 1601 for the sintered body after the hydrothermal degradation test.

  As is apparent from Table 1, the zirconia sintered body within the scope of the present invention has a fold strength after the hydrothermal deterioration test of 1000 MPa or more, indicating a high value.

It is a schematic sectional explanatory drawing which shows the state which exposed the zirconia sintered compact which is one Embodiment of this invention to the hydrothermal deterioration environment. It is a schematic sectional explanatory drawing which shows the state in which the external force was added to the zirconia sintered compact which is one Embodiment of this invention. It is a schematic sectional explanatory drawing which shows the compressive-stress layer formed in the zirconia sintered compact which is one Embodiment of this invention. It is a microscope picture which shows the observation result by the transmission electron microscope of the sample number 41 in the Example which is one Embodiment of this invention. It is a graph which shows the EDS surface analysis result of the sample number 41 in the Example which is one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Zirconia sintered compact 2 Compression stress layer 10 Zirconia crystal grain 11 Grain boundary 12 Silica compound

Claims (6)

With zirconia as the main component,
1.5 to 3.5 mol% yttria,
0.03-0.3% by mass of silica,
0.001 to 0.01% by mass of sodium oxide,
And alumina in a proportion of 0.005 to 2.0 mass%,
A zirconia raw material having an average particle diameter of 0.4 to ¹ μm, a maximum particle diameter of 1 to 3 μm, and a specific surface area of 4 to 16 m ² / g. With zirconia as the main component,
1.5 to 3.5 mol% yttria,
0.03-0.3% by mass of silica,
0.001 to 0.01% by mass of sodium oxide,
And alumina in a proportion of 0.005 to 2.0 mass%,
In the EDS surface analysis at the surface grain boundary,
The maximum peak intensity of oxygen is 60-80% of the maximum peak intensity of silicon;
A zirconia sintered body having a silica compound in which the maximum peak intensity of aluminum and the maximum peak intensity of zirconium are both 20 to 80% of the maximum peak intensity of silicon.   The zirconia sintered body according to claim 2, which has silica capable of forming the silica compound at a grain boundary on a surface thereof.   4. The zirconia sintered body according to claim 2, wherein the silica compound is present more in the surface grain boundaries than in the internal crystal grain boundaries. 5.   A blade comprising the blade made of the zirconia sintered body according to any one of claims 2 to 4.   A manual instrument comprising a blade made of the zirconia sintered body according to any one of claims 2 to 4.