JP7392729B2 - Evaluation method and manufacturing method for ceramic articles - Google Patents

Description

The present invention relates to a method for evaluating and manufacturing a ceramic article.

Ceramic parts are molded using ceramic powder as the raw material, and various molding methods such as pressure molding, cold isostatic pressing (CIP), hot isostatic pressing (HIP), injection molding, cast molding, and extrusion molding are used. The method can be used to produce ceramic products of various shapes. Various efforts have also been made to improve the properties of the resulting ceramic parts. For example, a ceramic molded body containing a curable resin and a solvent is hardened by heat treatment, etc., to produce a ceramic with few cracks, high shape retention, excellent dimensional accuracy, and excellent physical properties when made into a sintered body. Methods of producing molded bodies are known.

Additionally, ceramic balls used in rolling bearings (ball bearings) are required to have high strength and extremely high sphericity. To manufacture such ceramic balls, there is generally a molding process in which ceramic raw material powder is compacted, a primary firing process in which it is fired at high temperatures, and high-temperature and high-pressure processes such as HIP (hot isostatic pressing) and gas pressure firing. A ceramic ball is produced through a secondary firing process, and then the resulting ceramic ball is polished to a high degree of sphericity by mechanical polishing or the like.

In order to control the quality of these spherical ceramic balls, their strength can be confirmed through a so-called crushing test, in which two product balls are lined up and crushed under a compressive load, as shown in Figure 7. (For example, see Patent Document 1 and Non-Patent Document 1). Here, conventionally, the testing apparatus 50 for crushing tests is composed of a lower member 51, an upper member 52, and an auxiliary member 53 that can hold two ceramic balls 100A, 100B in a stacked manner. The lower member 51 and the upper member 52 each have a conical recess so that the ceramic balls 100A, 100B can be stably held. Here, the test device 50 is shown in cross section.

Japanese Patent Application Publication No. 5-294728

Masahiro Ichikawa et al., "Sampling evaluation method for crushing strength of silicon nitride bearing balls", J. Soc. Mat. sci., Japan, Vol. 42, No480, pp. 1090-1095, Sep. 1993

In such a crushing test, one test data (n=1) is usually obtained from two test samples (hereinafter also referred to as ceramic specimens). Generally, strength data of at least n=5 is required, and in this case, at least 10 test samples are required. In addition, to evaluate dispersion, it is usually expressed using a Weibull distribution. Evaluation of Weibull distribution requires at least n=20, preferably n=30. In this case, the number of test samples used is as many as 60.

Preparing this many spherical samples for testing is labor-intensive. This is because, in the case of a spherical sample, if the shape accuracy is not good, it may be difficult to properly perform a crushing test, so a certain degree of shape accuracy is required to produce a spherical sample. If a test sample that requires a lower level of shape accuracy than a spherical sample and has a shape that can be easily manufactured can be used for easier evaluation and there is an alternative test method, it would reduce the cost of product manufacturing, etc. It is also preferable.

Furthermore, for the purpose of strength evaluation, there is a method of cutting out a plurality of three-point bending test pieces or four-point bending test pieces from the fired product and performing a bending test. However, in these bending tests, the part where the maximum stress occurs is the lower surface of the test piece, unlike the crushing test where the maximum stress occurs inside the test piece. Therefore, crushing tests can be considered to be able to evaluate the material itself of the test sample, but bending tests are affected by the processed state of the sample surface, so they cannot essentially replace crushing tests.

In addition, in order to produce a test sample for a bending test, the test sample must be processed from a product, which is a problem in that it requires a great deal of effort and cost.

In view of the above points, one aspect of the present invention aims to provide a novel evaluation method for ceramic articles that can replace a crushing test using a spherical sample in order to evaluate the strength of the ceramic article in manufacturing the ceramic article. . Another object of the present invention is to provide a method for manufacturing ceramic articles that efficiently manufactures ceramic articles having desired characteristics using such an evaluation method.

In order to solve the above problems, the inventors of the present invention conducted extensive studies and discovered that by using a cylindrical ceramic specimen as a test sample, the strength of a ceramic article can be evaluated instead of using a spherical sample. .

That is, a method for evaluating a ceramic article according to one aspect of the present invention involves producing a cylindrical ceramic specimen using a ceramic raw material for forming a ceramic article, and bringing two side surfaces of the ceramic specimen into contact with each other. The present invention is characterized in that a crushing test is carried out using the method, and the strength of the ceramic article is evaluated based on the results of the crushing test.

Further, in the method for manufacturing a ceramic article according to one aspect of the present invention, a raw material slurry in which a ceramic powder, a resin, a hardening agent, and a solvent are mixed is prepared as a ceramic raw material, the raw material slurry is injected into a mold, and the raw material slurry is injected into a mold. The resin in the raw material slurry injected into the raw material slurry is cured to produce a molded body having a desired shape, and after the molded body is removed from the mold, the molded body is subjected to drying, degreasing and Each firing process is performed in this order to produce a ceramic article, and the raw material slurry is injected into a mold for a specimen for forming a cylindrical ceramic specimen. After curing the resin in the raw material slurry to produce a cylindrical molded body, and removing the cylindrical molded body from the specimen mold, drying the cylindrical molded body. , degreasing, and firing in this order to produce a ceramic specimen, and the ceramic article evaluation method of the present invention is applied to the ceramic specimen to determine whether or not the production of the ceramic article can be continued. , is characterized by.

According to the method for evaluating ceramic articles according to one embodiment of the present invention, the maximum stress is generated internally, so the inherent strength of the material can be evaluated without being affected by surface processing quality, etc., as in evaluation samples for bending tests. It is possible to properly evaluate manufacturing processes and product characteristics.
In addition, in one aspect of the present invention, since the sample shape used is cylindrical, the required shape accuracy is less severe than that required for conventional spherical samples for crushing tests, and the labor required to prepare the same number of samples is reduced. Costs etc. can be significantly reduced compared to spherical samples. Therefore, the time and cost required for evaluation can be significantly reduced compared to conventional crushing tests.
Furthermore, since the cylindrical sample in one embodiment of the present invention is easy to produce, for example, in a ceramic manufacturing process that uses slurry, it is easy to produce a sample that reflects the process state during the process, and It can also be applied to determining whether the condition is good or bad.

According to the method for manufacturing a ceramic article of one embodiment of the present invention, the ceramic article can be manufactured by confirming whether the characteristics of the ceramic article to be manufactured are sufficient. Therefore, if the characteristics are not sufficient, the manufacturing conditions can be reviewed, and a product having the desired characteristics can be efficiently manufactured and shipped.

FIG. 1 is a perspective view showing an example of the arrangement of ceramic specimens in the ceramic article evaluation method of the present invention. FIG. 2 is a diagram showing an example of support for the ceramic specimen shown in FIG. 1. FIG. 3 is a diagram showing another example of supporting the ceramic specimen shown in FIG. 1. FIG. 4 is a diagram showing still another example of supporting the ceramic specimen shown in FIG. 1. FIG. 5 is a diagram showing still another example of support for the ceramic specimen shown in FIG. 1. FIG. 6 is a flowchart showing an example of the method for manufacturing a ceramic article of the present invention. FIG. 7 is a diagram showing an example of supporting a specimen (product) in a crushing test using conventional ceramic balls.

Hereinafter, a method for evaluating a ceramic article and a method for manufacturing a ceramic article, which are one embodiment of the present invention, will be described in detail.

[Evaluation method for ceramic articles]
A method for evaluating a ceramic article, which is an embodiment of the present invention, involves producing a cylindrical ceramic specimen using a ceramic raw material for forming a ceramic article, and bringing two side surfaces of the ceramic specimen into contact with each other. A crushing test is conducted and the strength of a ceramic article is evaluated based on the results of the crushing test.

Each of these steps will be explained below.

(Preparation of ceramic specimen)
The ceramic specimen in this embodiment is a cylindrical ceramic specimen. This ceramic specimen is a cylindrical ceramic body (sintered body) obtained by using the same ceramic raw material as the ceramic article to be evaluated and processing it under the same conditions.

The ceramic raw material used here includes ceramic powder and auxiliary materials suitable for ceramic molding that are used to give the shape. For example, those containing ceramic powder, additives such as organic substances, and solvents such as water are exemplified. In the present invention, the ceramic raw material is not particularly limited as long as it is suitable for a known ceramic molding method. For example, for press molding, ceramic powder to which an organic binder has been added may be made into powder form as it is, or may be granulated into granules. Further, for slip cast molding or gel cast molding, the ceramic powder may be made into a slurry together with a resin and a dispersant, or a curable resin and a hardening agent. For injection molding and extrusion molding, it may be in the form of a kneaded product in which ceramic powder is kneaded with a fluidity imparting material such as a resin.

Moreover, in order to form such a ceramic raw material into a cylindrical shape, there is no particular limitation, and the above-mentioned molding method may be appropriately adopted. As the cylindrical specimen mold, for example, a mold with a cylindrical cavity or a cylindrical syringe is used. A cylindrical molded body may be obtained by injecting a ceramic raw material into a cylindrical specimen mold. In a molding method using slurry such as a gel casting method, a part of the slurry conveying piping may be structured to be openable and closable, and may be used as it is as a mold for producing a cylindrical shape. Alternatively, a portion of the piping may be made of a disposable material such as resin, and that portion of the piping may be removed and used as a sample as it is. Alternatively, a part of the piping may be branched and a sample preparation jig or the like may be attached thereto. That is, in addition to general molds, any mold that can be shaped into a syringe, piping, jig, etc. can be used as the mold for the specimen of this embodiment.
Further, a cylindrical ceramic body (sintered body) can also be obtained by cutting out a molded body or a sintered body once produced in a block shape and processing such as grinding.

The size of the ceramic specimen used at this time is not particularly limited, but if it is large, the amount of raw material used to produce the ceramic specimen will be large, and processing such as molding and firing will take time. For example, the diameter of the ceramic specimen is preferably 2 mm to 50 mm, more preferably 5 mm to 20 mm, even more preferably 8 mm to 15 mm. The axial length of the ceramic specimen is preferably 5 mm to 100 mm, more preferably 10 mm to 50 mm, even more preferably 15 mm to 30 mm.

By doing so, it is possible to easily evaluate the combination and preparation of raw materials, in particular. For example, in the case of ceramic powder that is a mixture of nitride ceramics such as silicon nitride and oxide ceramics that are sintering agents for silicon nitride ceramics, it is necessary to evaluate the homogeneity of the mixture of nitride ceramics and oxide ceramics, and to Evaluation of the homogeneity of mixing ceramic powder in ceramic raw materials containing powder and additives such as resin, and evaluation of slurry when gel-casting ceramic powder, hardening resin, hardening agent, water, etc. in a slurry form into a mold. Examples include, but are not limited to, property evaluation.

Note that this method can be similarly applied to the evaluation of processing conditions at a later stage than raw material preparation. Examples of processing conditions include curing conditions, demolding conditions, drying conditions, degreasing conditions, and firing conditions. In addition, when evaluating the treatment conditions, the manufacturing conditions for the final ceramic article and the conditions for sufficiently treating the inside of the cylindrical ceramic specimen should be made equal (the deepest part of the ceramic article It is also possible to evaluate the processing conditions by adjusting the size of the ceramic specimen (so that firing near the axis of the ceramic specimen can be equally evaluated).

Here, in this evaluation method, as in the conventional crushing test described above, two specimens are required for one test, so prepare [number of tests (n) x 2] ceramic specimens. do.

(Crushing test)
Next, a crushing test is performed on the cylindrical ceramic specimen produced as described above. The crushing test can be carried out by using two ceramic specimens, bringing their side surfaces into contact with each other, and applying a compressive load until the ceramic specimens are crushed. In this respect, the only difference from the spherical ceramic specimen is the shape of the ceramic specimen used, and otherwise the same operations may be performed.

Further, in this crushing test, the side surfaces of the ceramic specimens are brought into contact with each other, and at that time, it is preferable that the ceramic specimens are brought into contact with each other so that the contact points are at one point. That is, by arranging the ceramic specimens so that their axes are not parallel, they can be brought into contact at one point. The ceramic specimens are preferably arranged so that their axes are perpendicular to each other. By doing so, the load during the test is concentrated on the contact point, so that appropriate strength evaluation can be performed. FIG. 1 shows a schematic diagram of ceramic specimens 1A and 1B stacked one above the other with their axes perpendicular to each other.

The crushing test will be described below with reference to the drawings.
FIG. 2 shows a schematic configuration of a crushing test apparatus capable of holding a ceramic specimen as shown in FIG. 1 above. The test apparatus 10 shown in FIG. 2 includes a lower member 11 that supports the lower ceramic specimen 1A from below, and compresses the upper ceramic specimen 1B from above to apply a compressive load to the ceramic specimens 1A and 1B. It is composed of an upper member 12 for arranging the ceramic specimens 1A and 1B, and an auxiliary member 13 for assisting the ceramic specimens 1A and 1B in a predetermined arrangement. In FIG. 2, (a) shows a front view of the test apparatus 10, and (b) shows a side view of the test apparatus 10. In addition, in these figures, in order to show the state in which the ceramic specimens 1A and 1B are held inside the test apparatus 10, only the auxiliary member 13 is shown in cross-sectional view.

Here, in order to perform appropriate strength evaluation as described above, the lower member 11 and the upper member 12 are designed to support (contact) each other by point contact at the contact portions with the ceramic specimens 1A and 1B. . FIG. 2 shows an example in which the pedestal forming this contact portion is a spherical pedestal. In addition, the spherical pedestal is designed to have a curvature larger than the curvature of the circle (cross section) of the ceramic specimens 1A and 1B so that the maximum stress occurs near the contact surfaces of the ceramic specimens in this test.

Further, the auxiliary member 13 has a support portion extending horizontally inside thereof so as to support the ceramic specimens 1A and 1B from the sides so that their axes are perpendicular to each other.

Moreover, the material of this test device 10 is not particularly limited as long as it can perform a crushing test well. It is preferable that the lower member 11 and the upper member 12, particularly the support portions that come into contact with the ceramic specimen, are made of a material having a Young's modulus smaller than that of the ceramic specimen. Thereby, the crushing test of the ceramic specimen can be properly performed and the strength of the ceramic article itself can be evaluated.

This crushing test can be performed in the same way as the conventional test using ceramic balls, with the only difference being that the specimen is different. That is, when using the test apparatus 10, the ceramic specimens 1A and 1B are held in the arrangement shown in FIG. The load is gradually increased until 1A and 1B are crushed, and the compressive load at the time of crushing can be evaluated as crushing strength.

In this test, as with conventional ceramic balls, the maximum tensile stress occurs inside the contact point of ceramic specimens 1A and 1B, causing a median crack, which becomes the starting point and causes macroscopic fracture. Conceivable. In fact, it was confirmed from the ceramic specimens 1A and 1B that were fractured after the test that the maximum tensile stress (the origin of fracture) was generated not on the surface but inside.

In addition, as a test device, instead of the test device 10 whose base is a ball base, the test device 20 shown in FIG. 3 whose base is an inclined cylindrical base, and the test device 20 shown in FIG. 4 whose base is a two-point ball base. The test apparatus 30 shown can also be replaced with the test apparatus 40 shown in FIG. 5, in which the pedestal is a cylindrical pedestal without inclination.

These test devices 20, 30, 40 basically consist of lower members 21, 31, 41, upper members 22, 32, 42, and auxiliary members 23, 33, 43, like the test device 10. Therefore, the ceramic specimens 1A and 1B can be held in contact with each other with their axes perpendicular to each other. Here, the only difference between the lower members 21, 31, 41 and the upper members 22, 32, 42 is the shape (shape of the pedestal) for holding the ceramic specimen. In the test device 20, two cylindrical support portions extend obliquely. In the test device 30, two spherical supports protrude. In the test device 40, one cylindrical support section extends without inclination. Each of the test apparatuses 20, 30, and 40 has a structure that supports the ceramic specimen from below and above. In these test devices 20 and 30, the contact portions between the support portion and the ceramic specimen are arranged at two locations in a direction perpendicular to the axis of the ceramic specimen.

This crushing test is carried out using a plurality of sets of ceramic specimens, and the crushing strength of the ceramic article obtained using the above ceramic raw material is measured. For this crushing strength, the load value when the ceramic specimen is crushed is directly used as the crushing strength. In addition, the Weibull distribution is taken into consideration in conjunction with the calculation of crushing strength. The Weibull distribution is understood as a failure model (weakest link model) for ceramic articles. Here, as an example, it is calculated by the Weibull statistical analysis method of strength data of JIS R 1625:2010 fine ceramics.

(Evaluation of strength)
Next, the ceramic article is evaluated based on the results obtained from the above crushing test. Ceramic articles can be evaluated based on whether they satisfy the strength required for ceramic articles. That is, when a ceramic article is produced using the ceramic raw material of the ceramic specimen used in the test, it can be confirmed whether the ceramic article has the required strength.

The criteria for this evaluation can be set arbitrarily from the viewpoint of usage, quality assurance, etc. For example, in the case of general industrial silicon nitride balls used in ceramic bearings, the crushing strength of a cylinder with a diameter of 10 mm may be set to 20 kN or more. In the case of silicon nitride balls for special purposes requiring high strength and high durability, the crushing strength may be set to 25 kN or more. Further, the Weibull coefficient is preferably 10 or more, more preferably 15 or more.

Ceramic specimens that meet this evaluation criterion can be evaluated as having good raw material slurry and ceramic bodies obtained through similar treatment as ceramic articles that satisfy the required quality. In addition to the raw material slurry being good, it can be evaluated that the subsequent steps of molding, demolding, drying, degreasing, and firing were also good.

[Method for manufacturing ceramic articles]
A method for manufacturing a ceramic article, which is an embodiment of the present invention, includes a ceramic article manufacturing step, a ceramic specimen manufacturing step, and a determination step. In both the ceramic article manufacturing process and the ceramic specimen manufacturing process, a ceramic raw material is prepared, this ceramic raw material is molded into a desired shape using a mold, and the resulting molded body is dried, degreased, and Each firing process is performed in this order (FIG. 6). Each of these operations will be explained in detail below.

(Raw material preparation process)
In the above operation, first, a ceramic raw material that is a raw material for a ceramic article and a ceramic specimen is prepared (S1).

The ceramic raw material used here is not particularly limited as long as it can produce a ceramic article. Specifically, the ceramic raw materials exemplified in the above-described evaluation method for ceramic articles may be mentioned.

Among the ceramic raw materials, a slurry-like ceramic raw material (hereinafter referred to as raw material slurry) obtained by mixing ceramic powder, a resin, a hardening agent, and a solvent is preferable. Ceramic raw materials obtained by containing resin in this way have a hardening effect during molding due to the function of the resin, so the size and shape of the molded object have little effect on the density of the molded object, so it can be molded. This is because there is little variation in body density, etc., and the characteristics between the product as a product and the specimen can be considered as they are. That is, even if the size of the ceramic specimen for testing is made small for a large-sized ceramic article (final product), the variation in the results is small. Since the size of the ceramic specimen can be reduced, the consumption of raw material slurry for crushing tests can be kept very low. In this case, the influence of the amount of raw materials used on cost can be reduced.

Hereinafter, a method for producing a ceramic article using this raw material slurry will be described as an example.

First, the ceramic powder used here is not particularly limited as long as it becomes ceramic by sintering, and examples thereof include known ceramic powders. Examples of the ceramic powder include oxide ceramics such as aluminum oxide (alumina), zirconium oxide (zirconia), silicon oxide (silica), cordierite, and nitrides such as silicon nitride, aluminum nitride, and SiAlON (also described as SiAlON). Examples include ceramics and carbide ceramics such as silicon carbide. These may be used alone or in combination of two or more.

Further, the ceramic powder preferably has a 50% particle size _D50 of less than 1.0 μm so that a stable sintered body can be obtained in the sintering process described later. When the 50% particle size D ₅₀ is 1.0 μm or more, particles settle in the slurry, resulting in poor molding, which may lead to a decrease in sintered density. The 50% particle size D ₅₀ is more preferably 0.8 μm or less, even more preferably 0.6 μm or less. Further, it is preferable that the particle size D ₅₀ of the ceramic powder is 0.1 μm or more, since scattering and clogging during handling can be prevented and procurement can be facilitated. In this specification, the 50% particle size _D50 refers to a value measured using a laser diffraction particle size distribution device.

In addition, when silicon nitride (component: Si ₃ N ₄ ) is used as a ceramic powder, the structure obtained by sintering is such that main phase crystal grains mainly composed of silicon nitride are combined with glassy and/or crystalline particles. It is in a form that is bonded in a phase.

At this time, the silicon nitride powder is preferably a powder in which the gelatinization rate of silicon nitride is 70% or more, more preferably 80% or more, and even more preferably 90% or more. If the powder has an alpha conversion rate of less than 70%, the effect of incorporating the acicular structure during the phase transition from alpha to beta during sintering will not be sufficiently achieved, resulting in a decrease in strength. If the powder has a gelatinization rate of 90% or more, a sufficient incorporation effect can be obtained and a sintered body with high strength, particularly toughness, can be obtained. The silicon nitride powder preferably contains 85% by mass or more of silicon nitride with a gelatinization rate of 70% or more, and more preferably 92% by mass or more.

In addition, as sintering aids, Group 2 (alkaline earth metals), Group 3 (rare earth metals (scandium group)), Group 4 (titanium group), Group 5 (earth metals (vanadium group)), A sintering aid containing at least one element selected from Group 13 (boron group (earth metals)) and Group 14 (carbon group) elements from 1% to 15% by mass on an oxide basis. The content is preferably 2% by mass to 8% by mass, more preferably 2% by mass to 8% by mass. In order to obtain a uniform and high-strength sintered body, it is preferable that the content of the sintering aid be small, but if it is less than 1% by mass, it may be difficult to obtain a sintered body.

The resin is a component for molding the ceramic raw material into a desired shape in the curing step described below, and includes known curable resins. The resin used in this embodiment is required to have good shape retention during the curing process, and a resin that forms a three-dimensional network structure through a polymerization reaction is used. At this time, it is preferable that the mixture is in a liquid state in that it increases the fluidity of the mixture and has good filling properties into a mold.

The resin is also required to be easy to remove from the ceramic molded body in a degreasing operation after curing and before sintering. Examples of such resins include epoxy resins, phenol resins, melamine resins, acrylic acid resins, and urethane resins. Among them, epoxy resins are preferably used because of their good shape retention properties. Examples of the epoxy resin include glycidyl ether type epoxy resins of bisphenols such as bisphenol A type and bisphenol F type, phenol novolak type epoxy resins, cresol novolak type epoxy resins, glycidylamine type epoxy resins, and aliphatic epoxy resins. Examples include ether type epoxy resin, glycidyl ester type epoxy resin, methyl glycidyl ether type epoxy resin, cyclohexene oxide type epoxy resin, rubber-modified epoxy resin, and the like.

The number average molecular weight of the epoxy resin is preferably 20 to 30,000. The number average molecular weight of the epoxy resin is preferably from 50 to 3,000, and even more preferably from 50 to 2,500, since it is easy to mix with powder and provides a certain level of mechanical strength.

The curing agent is for curing the resin, and is selected depending on the resin used. Examples of the curing agent include amine curing agents, acid anhydride curing agents, and polyamide curing agents. Amine-based curing agents are preferable because they react quickly, and acid anhydride-based curing agents are preferable because they yield cured products with excellent thermal shock resistance.

Examples of the amine curing agent include aliphatic amines, alicyclic amines, aromatic amines, and any of monoamines, diamines, triamines, and polyamines can be used. Examples of the acid anhydride curing agent include methyltetrahydrophthalic anhydride and dibasic acid polyanhydride.

The solvent adjusts the viscosity of the raw material mixture used to form a slurry, thereby facilitating filling of the raw material slurry into the mold. As the solvent used here, for example, water, alcohols, and other organic solvents can be used. Among these, water or an aqueous system containing water as a main component is preferable from the viewpoint of manufacturing cost and environmental burden.

At this time, in order to facilitate the removal of the resin in the degreasing operation described later, the combination of the resin and the solvent is selected to have good affinity. If the affinity is poor, the particles may separate and segregate inside the compact, which may cause defects such as pores during sintering.

The ceramic powder, resin, curing agent, and solvent described above are mixed to form a raw material slurry. At this time, the mixing may be carried out by a known method, such as a dissolver, homomixer, kneader, roll mill, sand mill, ball mill, bead mill, vibrator mill, high-speed impeller mill, ultrasonic homogenizer, shaker, planetary mill, or revolution. Examples include mixers, in-line mixers, and the like.

In addition, in the case of a reaction curing type, the reaction starts from the moment the resin and curing agent are mixed, so the slurry containing the resin and the slurry containing the curing agent must be prepared separately before use. Sometimes these may be mixed. Note that at this time, the ceramic powder may be mixed in either slurry, or both slurries, or a separate slurry containing the ceramic powder may be prepared. In particular, it is preferable to mix the ceramic powder into both slurries containing the resin and the hardening agent so that the concentrations are about the same, since there is little variation in concentration when mixed and stable operation is possible. .

First, the raw materials described above are mixed and stirred to prepare a raw material slurry.
The viscosity of the raw material slurry obtained here may be such that it can be easily filled in the slurry injection described later. For example, the viscosity at a shear rate of 10 [1/s] is preferably 50 Pa.s or less, and 20 Pa.s. The following are more preferred. Considering the handling property after filling, it is more preferable that the viscosity of the raw material slurry is in the range of 0.1 Pa·s to 10 Pa·s. This viscosity can be easily adjusted by adjusting the amount of solvent used and the amount of resin added in the raw materials used.

Note that air and the like may be drawn in during the mixing of the raw materials, and gas may be included in the obtained raw material slurry. Therefore, before the next slurry injection, it is preferable to perform a defoaming treatment to remove the gas contained in the raw material slurry. If gas is contained in the raw material slurry, there is a risk that pores due to air bubbles will be generated inside the slurry during the hardening process and may remain in the ceramic article obtained by firing.

This defoaming treatment can be carried out by defoaming the raw material slurry under reduced pressure, and a defoaming pump (vacuum pump), a defoaming mixer, or the like can be used. Defoaming may be performed, for example, for 1 minute to 5 minutes under reduced pressure of 0.6 kPa to 10 kPa. When using a defoaming mixer, the raw material mixing process and the defoaming process can be performed simultaneously. Examples of the defoaming mixer used here include a rotation/revolution mixer equipped with a vacuum pump, a planetary mixer, and the like.

Once the ceramic raw material is prepared, a ceramic article and a ceramic specimen are each manufactured. These manufacturing operations will be described in detail below.

<Ceramic article manufacturing process>
The above-mentioned raw material slurry is used to produce the ceramic article, and the steps of injecting the slurry into the mold, demolding, drying, degreasing, and firing may be carried out in order, as in the production of known ceramic articles.

(slurry injection)
Slurry injection is a step of injecting the raw material slurry obtained through the raw material mixing and defoaming into the mold (S2). The mold used here has a predetermined shape for producing the product shape, and a conventionally known mold or any mold can be used. As the mold, various types of molds such as metal molds, resin molds, styrofoam molds, rubber molds, and elastic containers can be used.

In order to inject slurry into such a mold, it is sufficient to use a device that can feed the raw material slurry and supply it into the mold. For example, pumps such as diaphragm pumps, tube pumps, and syringe pumps are commonly used. In particular, a rotary positive displacement diaphragm pump equipped with a precision constant velocity cam and having a structure that does not generate pulsation is preferable. In addition, an in-line mixer or the like that can feed the raw materials while preparing the raw material slurry can also be used. When using an in-line mixer, the raw material mixing step and the slurry injection step can be performed simultaneously. In addition, when molding is performed by preparing a slurry containing resin and a slurry containing a curing agent as raw material slurries as described above, the in-line mixer mixes both slurries and immediately sends the liquid to the mold for filling. Possible and preferred.

(hardening)
In the hardening process, after the raw material slurry is injected into the mold, the resin component in the raw material slurry is cured to give the ceramic raw material a desired shape (S3). In this curing treatment, desired curing conditions are appropriately selected and cured according to the characteristics of the raw material slurry.

For example, in the case of a reaction-curing type raw material slurry, the reaction starts from the moment the slurry containing the resin component and the slurry containing the curing agent component are mixed and the slurry is cured, so it may be left to stand for a predetermined period of time. At this time, the curing time is approximately 1 hour to 3 days, preferably 1 hour to 24 hours, and more preferably 1 hour to 12 hours from the viewpoint of manufacturing efficiency.

Furthermore, in the case of a heat-curable raw material slurry, it is sufficient to heat it to a desired temperature and ensure sufficient curing time. For example, heat curing may be performed at 80° C. to 150° C. for 5 minutes to 120 minutes. Considering production conditions, production efficiency, etc., the temperature is preferably 80°C to 100°C for 5 minutes to 90 minutes, and more preferably 5 minutes to 60 minutes at 80°C to 100°C.

(Demolding)
The demolding process is a process of taking out the molded body of the ceramic raw material that has been hardened in the curing process from the mold (S4). This demolding process may be carried out by conventionally known methods, such as disassembling the split mold, extruding the molded object from the mold, or, in some cases, destroying the mold. , the inner molded body may be taken out and demolded.

(dry)
The drying process is a process of removing water, volatile solvents, etc. from the molded body obtained by the demolding process and drying it (S5). In this drying process, the molded body is dried slowly so as not to cause cracks or the like. That is, the molded product is dried while preventing the occurrence of cracks or the like due to shrinkage stress caused by the difference in drying speed between the surface and the inside of the molded product.

The conditions for this drying treatment include, for example, relatively mild conditions such as 25°C to 30°C, relative humidity of 60% to 95%, and 48 hours to 7 days, so that moisture contained in the molded product can be removed over a long period of time. Conditions for removing . Here, the drying process is preferably performed such that the moisture content of the molded body is 20% or less based on the mass when completely dry.

(Degreasing)
The degreasing process is a process of removing resin, nonvolatile solvent, etc. from the molded article obtained by the drying process (S6). In this treatment, it is preferable to almost completely remove components that inhibit sintering in the next sintering treatment. If large amounts of these components remain, pores may occur within the sintered body during sintering, and carbides may be produced as by-products, making it impossible to obtain the desired properties of the final product. There is.

Conditions for this degreasing treatment include, for example, conditions in which the resin components contained in the molded article are removed at 400° C. to 800° C. over a relatively long period of time, such as 2 to 14 days. Here, especially in the degreasing treatment for silicon nitride, it is preferable that the amount of residual carbon in the molded article is 200 ppm or less. Note that this does not apply to carbides such as silicon carbide.

(Firing)
The firing process is a process in which the molded body that has undergone the degreasing process is fired to sinter the ceramic raw material into a ceramic article (S7). The firing in this firing process is to sinter the mixed powder to obtain ceramics, which may be manufactured by a known firing method.

The firing conditions in the firing process are not particularly limited as long as a ceramic body can be obtained by firing. For example, in the case of firing silicon nitride, a nitrogen atmosphere with an oxygen concentration of 50 ppm or less is preferable. At this time, the maximum firing temperature in this treatment is 1800°C or lower at which silicon nitride starts to thermally decompose, and this maximum temperature is preferably in the range of 1650°C to 1750°C. Further, the firing time is preferably in the range of 4 hours to 12 hours.

(Secondary firing treatment)
The fired body obtained by the firing process may be subjected to a secondary firing process in order to obtain a sintered body having desired characteristics. In this secondary firing process, the fired body obtained in the firing process (primary firing) is further subjected to high-pressure firing treatment to densify the structure of the fired body.

As the high-pressure firing treatment in this secondary firing treatment, hot isostatic pressing (HIP), gas pressure firing, hot pressing, etc. can be used. Generally, in order to obtain a high-strength sintered body, it is preferable to perform HIP treatment at 1500° C. to 1700° C. and 50 MPa to 200 MPa.

<Ceramic specimen preparation process>
The ceramic specimen can be manufactured by sequentially performing the steps of injecting slurry into a mold, demolding, drying, degreasing, and firing in the same manner as the ceramic article described above. Note that this step is the same as the above description except that the mold used is of a predetermined shape in order to produce a cylindrical specimen.

(slurry injection)
As described above, slurry injection is a step of injecting the raw material slurry obtained through the raw material mixing and defoaming into the mold (S8). The mold used here has a predetermined shape such as a cylindrical cavity in order to produce a cylindrical ceramic specimen, and this ceramic specimen is suitable for use in the above method for evaluating ceramic articles. This is a ceramic specimen. Therefore, any mold for obtaining the ceramic specimen described in the above evaluation method may be used. Note that the mold used here does not have to have the exact shape of the ceramic specimen, as in the case of processing the obtained molded body into a ceramic specimen.

The obtained molded body for the ceramic specimen is then subjected to the following treatments as described above: curing (S9), demolding (S10), drying (S11), degreasing (S12), and firing (S13). conduct. Each of these treatments has the same content as each treatment in the above-described ceramic article manufacturing process, so a description thereof will be omitted.

Preferably, the ceramic specimen is manufactured under the same conditions as the ceramic article is manufactured. That is, it is preferable that the processing conditions be the same in the ceramic article manufacturing process and the ceramic specimen manufacturing process. Further, the ceramic article manufacturing process and the ceramic specimen manufacturing process may be performed as separate processes, but it is more preferable to perform the same process in parallel, and the ceramic article and the ceramic specimen are processed in the same processing equipment. is most preferred.

Furthermore, it is preferable to make the volume of the ceramic specimen smaller than the volume of the ceramic article because the amount used as a test specimen relative to the total amount of raw materials used is small and the production efficiency of the ceramic article is improved. This is especially effective when the volume of the ceramic product is large or when the number of products produced is small. At this time, the volume of the ceramic specimen is preferably 1/4 or less, more preferably 1/15 or less, and even more preferably 1/100 or less of the volume of the ceramic article.

<Judgment process>
Next, the ceramic article evaluation method described at the beginning is performed on the ceramic specimen obtained by the above ceramic specimen manufacturing method (S14), and it is determined whether the obtained evaluation result is good or not. (S15).

If this evaluation result is good, the process of manufacturing the ceramic article is continued (S16). The produced ceramic article is then shipped as a final product.

On the other hand, if this evaluation result is not good, the process returns to raw material preparation (S1) and the method for manufacturing the ceramic article is repeated again. In this case, the cause is considered to be in any of the processes from raw material preparation (S1) to firing (S7), and at least one of the conditions is changed to obtain a good evaluation result. As an example, regarding defects in the raw material preparation stage, it is preferable to check and study the quality of the raw materials used, the composition of mixed raw materials, the mixing of raw materials, the defoaming conditions, etc., and change some of the conditions.

Note that the criteria for determining the quality may be set depending on the strength required of the product. As this criterion, the criterion described in the above-mentioned method for evaluating ceramic articles may be used.

Hereinafter, the present invention will be explained in more detail based on Examples and Comparative Examples, but the present invention should not be interpreted as being limited to these Examples. Note that although an example in which silicon nitride is used as the ceramic will be described here, ceramics other than silicon nitride can be used in the same manner.

[Example 1 (Example)]
(Preparation of slurry SN)
Silicon nitride powder (manufactured by Denka Co., Ltd., trade name SN-9FWS) 73.11 parts by mass, spinel powder 2.09 parts by mass as a sintering aid, water 23.19 parts by mass as a solvent, quaternary as a dispersant 1.61 parts by mass of ammonium salt (manufactured by Seichem) were mixed in a ball mill to prepare a silicon nitride slurry (slurry SN) that would serve as the base of the raw material slurry.
In the above ball mill, silicon nitride balls (manufactured by Nikkato Co., Ltd., diameter 5 mm) were used as the grinding media.

(Preparation and defoaming of slurry SN1)
90.10 parts by mass of the above slurry SN and 9.90 parts by mass of a water-soluble epoxy resin (manufactured by Nagase ChemteX Co., Ltd.) were mixed using a rotation-revolution mixer equipped with a vacuum pump to form an epoxy resin-containing silicon nitride slurry (slurry SN1). was prepared.
Note that the slurry SN1 was made free of air bubbles of 10 μm or more by reducing the pressure (0.6 kPa).

(Preparation and defoaming of slurry SN2)
98.4 parts by mass of the slurry SN, 1.6 parts by mass of the resin curing agent (a mixture of triethylenetetramine and 2,4,6-tris(dimethylaminomethyl)phenol at a mass ratio of 2:1), and vacuum A silicon nitride slurry containing a resin curing agent (slurry SN2) was prepared by mixing using a rotation-revolution mixer equipped with a pump.
Note that the slurry SN2 was made to contain no air bubbles of 10 μm or more by reducing the pressure (0.6 kPa).

(slurry injection)
Slurry SN1 and slurry SN2 were filled into slurry tank 1 and slurry tank 2 to the same volume, respectively. Next, slurry SN1 was pumped from slurry tank 1 and slurry tank 2 using two rotary positive displacement diaphragm pumps made by Takumina Co., Ltd. equipped with precision constant-velocity cams that do not generate pulsation or entrainment of air. and slurry SN2 were sucked and discharged. Slurry SN1 and slurry SN2 were sent to an in-line mixer (trade name: static mixer) manufactured by Noritake Company through a pipe that merged them.

They were mixed using an in-line mixer to obtain raw material slurry 1 containing an epoxy resin and a resin curing agent. At the same time as raw material slurry 1 was obtained, raw material slurry 1 was supplied to a product mold connected to the outlet side of the in-line mixer.

Subsequently, the raw material slurry 1 was supplied to a sample tube, Tygon Tube 2375 manufactured by Saint-Gobain (outer diameter 19.0 mm, inner diameter 12.7 mm). This was carried out by connecting the tube for the specimen to the outlet side of the in-line mixer after supplying it to the mold for the product.
(hardening)
The tube filled with raw material slurry 1 was left at room temperature of 25° C. overnight to cause the epoxy resin and the resin curing agent to react and to be cured.

(Demolding)
A cylindrical molded product was obtained by carefully cutting the tube and the molded product cured within the tube with a cutter. The length was cut to 25 mm. I got 40 pieces.

(dry)
The cylindrical molded body was allowed to stand for one week to dry in a constant temperature/humidity chamber controlled at a temperature of 25° C. and a relative humidity of 90%.

(Degreasing)
The dried cylindrical molded body was heated in an air atmosphere from room temperature to 700°C over a period of one week, and held at 700°C for one day to burn out the cured resin component and degrease it.

(Firing)
The degreased cylindrical molded body was fired at 1700° C. for 12 hours in a nitrogen atmosphere. After this firing, a cylindrical silicon nitride sintered body was obtained.

(HIP)
Further, the cylindrical silicon nitride sintered body was subjected to HIP (hot isostatic pressing) at 1700° C. under a pressure of 100 MPa using nitrogen gas as a pressure medium. After HIP, 40 dense cylindrical silicon nitride specimens 1 each having a diameter of about 10 mm and a length of 20 mm and having a density of 3.2 g/cm ³ were obtained.

Forty of the obtained cylindrical silicon nitride specimens 1 were stacked using the crushing test apparatus shown in Figure 2 so that their respective axes were perpendicular to each other, and a load was applied from above until crushing. The load during crushing (= crushing strength) was measured. This crushing test was conducted 20 times, and a crushing strength (average value) of 30 kN and a Weibull coefficient of 17 were obtained. The cylindrical silicon nitride specimen used here had a straightness of less than 2 mm and a circularity of less than 0.5 mm.

Further, the fracture surface after the crushing test was observed using an Olympus stereo microscope (trade name: SZX16) with an eyepiece magnification of 10 times and an objective lens magnification of 1 times to 2.5 times. As a result of the observation, it was confirmed that the fracture progressed from a depth of about 1 mm from the contact surface, that is, the maximum stress was generated inside the cylindrical silicon nitride specimen 1.

[Example 2 (comparative example)]
Using the same raw material slurry 1 as in Example 1, a cylindrical ceramic molded body with a diameter of 12 mm was obtained. Subsequently, the cylindrical ceramic molded body was processed into a spherical shape, degreased, and fired to obtain a spherical silicon nitride specimen with a diameter of about 10 mm.

The obtained spherical silicon nitride specimen was subjected to crushing load (= crushing strength) test 20 times using the conventional crushing test apparatus shown in FIG. As a result, the crushing strength (average value) was 16 kN and the Weibull coefficient was 16.

In addition, the fracture surface of the spherical silicon nitride specimen after the crushing test was observed using an Olympus stereomicroscope (trade name: SZX16) with an eyepiece magnification of 10x and an objective lens magnification of 1x to 2.5x. As a result of observation, it was confirmed that the fracture progressed from a depth of 1 mm to 2 mm from the contact surface, that is, the maximum stress was generated inside the spherical silicon nitride specimen.

A comparison between Example 1 and Example 2 revealed that the Weibull coefficient, which indicates the degree of strength variation, was large at 17 (Example 1) and 16 (Example 2), and the strength variation was small in both methods. Therefore, it was confirmed that the crushing test using the cylindrical silicon nitride specimen in this embodiment can be evaluated as equivalent to the crushing test using the conventional spherical silicon nitride specimen. Therefore, it was confirmed that the crushing test using the cylindrical specimen according to the present invention can be substituted for the conventional crushing test using the spherical specimen in the evaluation of ceramic articles.

[Example 3 (Example)]
The same as Example 1 except that in slurry SN of Example 1, 69.19 parts by mass of silicon nitride powder, 3.76 parts by mass of yttria powder and 2.25 parts by mass of alumina powder were used as sintering aids instead of spinel powder. Raw material slurry 2 was prepared.

A cylindrical silicon nitride specimen 2 was prepared under the same conditions as in Example 1, except that the obtained raw material slurry 2 was used, and a crushing test was conducted. As a result, the crushing strength (average value) was 25 kN, confirming the difference in strength due to different slurry raw materials.

[Example 4 (Example)]
A cylindrical silicon nitride specimen 3 was prepared under the same conditions as in Example 1 except for the firing conditions, and a crushing test was conducted. Here, the firing was carried out at normal pressure at 1700°C for 12 hours, and then under high pressure at 10 MPa and 1700°C. As a result of the crushing test, the crushing strength (average value) was 20 kN, confirming the difference in strength due to the difference in firing conditions.

[Example 5 (Example)]
Among the cylindrical silicon nitride specimens prepared in the same manner as in Example 1, those with a straightness of 2 mm or more and a roundness of less than 0.5 mm were selected to form a cylindrical silicon nitride specimen 4. A crushing test was conducted in the same manner as in Example 1 using the cylindrical silicon nitride specimen 4. As a result, results with no significant difference from Example 1 were obtained.

[Example 6 (Example)]
Among the cylindrical silicon nitride specimens prepared in the same manner as in Example 1, those with a straightness of less than 2 mm and a roundness of 0.5 mm or more were selected as cylindrical silicon nitride specimens 5. A crushing test was conducted in the same manner as in Example 1 using the cylindrical silicon nitride specimen 5. As a result, results with no significant difference from Example 1 were obtained.

[Example 7 (comparative example)]
Using the same raw material slurry 1 as in Example 1, a ceramic article was produced, from which a test piece for a three-point bending sample was cut out, and the four sides were processed to have a surface roughness Ra of 0.5 μm. Obtained. As a result of performing a three-point bending test using these test pieces, the average strength was 720 MPa. At this time, when we observed the fracture surface after the test, we found that in many specimens the fracture progressed from the defective parts of the surface and corners that were on the lower side at the time of the test, and that the maximum stress was It turned out that it was not inside the piece, but on the lower surface.

As described above, according to the method for evaluating a ceramic article and the method for manufacturing a ceramic article of the present invention, the inherent strength of the material of a ceramic article can be measured and evaluated instead of the conventional crushing test, and further, the ceramic article as a final product can be measured and evaluated. can be manufactured efficiently.
At this time, according to the evaluation method for ceramic articles of the present invention, the shape and surface roughness of the ceramic specimen can be evaluated without being influenced by the shape or surface roughness, and the evaluation can be carried out and evaluated without being limited by the processing conditions of the specimen. I found out that it can be done.

The method for evaluating a ceramic article and the method for manufacturing a ceramic article of the present invention can evaluate a ceramic article having a desired shape, and can efficiently manufacture the ceramic article while performing this evaluation. The ceramic article of interest here is not particularly limited and can be widely used as a raw material as long as it is a ceramic raw material.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications can be made to the embodiments described above without departing from the scope of the present invention. and substitutions can be added.
This application is based on Japanese Patent Application No. 2019-180093 filed on September 30, 2019, the contents of which are incorporated herein by reference.

1A, 1B...Ceramics specimen, 10,20,30,40...Testing device, 11,21,31,41...Lower member, 12,22,32,42...Upper member, 13,23,33,43...Auxiliary Element

Claims (9)

Using ceramic raw materials for forming ceramic articles, a cylindrical ceramic specimen was prepared,
Carrying out a crushing test by bringing the two sides of the ceramic specimen into contact with each other,
Evaluating the strength of the ceramic article based on the results of the crushing test,
A method for evaluating ceramic articles characterized by: 2. The method for evaluating a ceramic article according to claim 1, wherein in the crushing test, the two ceramic specimens are arranged so that their axes are perpendicular to each other. 3. The method for evaluating a ceramic article according to claim 1, wherein the ceramic specimen is supported by a spherical pedestal or a cylindrical pedestal in the crushing test. A raw material slurry containing ceramic powder, resin, curing agent, and solvent is prepared as a ceramic raw material.
Injecting the raw material slurry into a mold, curing the resin in the raw material slurry injected into the mold to produce a molded body having a desired shape, and demolding the molded body from the mold. After that, the molded body is subjected to drying, degreasing, and firing treatments in this order to produce a ceramic article,
The raw material slurry is injected into a mold for forming a cylindrical ceramic specimen, and the resin in the raw material slurry injected into the mold for the specimen is cured to form a cylindrical shape. After the cylindrical molded body is removed from the specimen mold, the cylindrical molded body is subjected to drying, degreasing, and firing treatments in this order to form a ceramic specimen. Fabricate and
Performing the ceramic article evaluation method according to any one of claims 1 to 3 on the ceramic specimen to determine whether or not the production of the ceramic article can be continued.
A method for manufacturing a ceramic article, characterized by: 5. The method of manufacturing a ceramic article according to claim 4, wherein the ceramic specimen is manufactured in the same process as the ceramic article except for the mold into which the raw material slurry is injected. 6. The method for manufacturing a ceramic article according to claim 5, wherein the ceramic specimen is manufactured under the same conditions as the manufacturing of the ceramic article. The method for manufacturing a ceramic article according to any one of claims 4 to 6, wherein the ceramic specimen is produced by injecting it into a cylindrical specimen mold. The method for manufacturing a ceramic article according to any one of claims 4 to 7, wherein the volume of the ceramic specimen is 1/4 or less of the volume of the ceramic article. The ceramic powder contains 85% by mass or more of silicon nitride with a gelatinization rate of 70% or more, and at least one element selected from Group 2, Group 3, Group 4, Group 5, Group 13, and Group 14. The method for producing a ceramic article according to any one of claims 4 to 8, wherein the sintering aid containing one type is contained in an amount of 1% to 15% by mass expressed as % by mass based on the oxide.

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