A ceramic powder, its preparation method and application

Abstract

This invention discloses a ceramic powder, its preparation method, and its application. The ceramic powder includes amino-modified alumina. The raw materials for preparing the amino-modified alumina include alumina and amine compounds. The mass ratio of the amine compounds to alumina is 1:(0.5-6). In this invention, the ceramic powder uses amine compounds to surface-modify alumina, giving it amino functional groups on its surface. When this ceramic powder is used to prepare ceramic structural parts, it can combine with hydroxyl-containing additives and undergo a condensation reaction, thereby enhancing the binding properties between the ceramic powder and the additives. This improves the stability of the feedstock for the prepared ceramic structural parts, reducing or even avoiding component segregation during injection molding. This results in ceramic structural green bodies with uniform density distribution and good shape retention, improved mechanical strength, and ultimately, high-quality, long-life ceramic structural parts, improving the quality and yield of finished ceramic structural parts.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials, specifically to a ceramic powder, its preparation method, and its application. Background Technology

[0002] Ceramic structural components, such as ceramic cleavers, have hollow, symmetrical, and complex pointed structures, playing an indispensable role in the semiconductor packaging field. To ensure circuit performance and reliable circuit connections, the manufactured ceramic cleavers must meet high performance requirements such as high hardness, high density, wear resistance, high temperature resistance, and corrosion resistance. Ceramic ferrules, as indispensable fiber optic connectors in the field of optical communication, are often used to connect different types of optical devices to obtain optical transmission channels. To ensure their transmission efficiency, the precision requirements for such precision ceramic components are also increasing.

[0003] In existing manufacturing processes, ceramic structural components such as ceramic cleavers, ceramic nozzles, and ceramic inserts have complex internal structures and high performance requirements. Injection molding is typically chosen to produce precision ceramic parts with high molding accuracy and quality requirements, achieving simultaneous improvement in production efficiency and quality. Injection molding generally uses alumina ceramic powder as the main raw material, adding various additives (binders, accelerators, and lubricants) to prepare a ceramic feedstock. The feedstock is then injection molded to obtain a green body, which is subsequently debinded, sintered, and machined to obtain the finished product. However, during the feedstock mixing and green body injection molding process, the poor compatibility between the ceramic powder and various additives makes it difficult to achieve a completely uniform combination. This leads to the easy occurrence of local segregation of one or more components during feedstock injection, resulting in uneven density distribution in the molded green body. This severely affects the shape stability of the molded green body, resulting in poor shape retention and low mechanical strength, directly impacting the finished quality, yield, and service life of the precision ceramic parts. Summary of the Invention

[0004] In order to overcome the problems existing in the prior art, one of the objectives of the present invention is to provide a ceramic powder.

[0005] The second objective of this invention is to provide a method for preparing the above-mentioned ceramic powder.

[0006] The third objective of this invention is to provide a ceramic structural component.

[0007] The fourth objective of this invention is to provide a method for preparing the above-mentioned ceramic structural component.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] The first aspect of the present invention provides a ceramic powder comprising amino-modified alumina; the raw materials for preparing the amino-modified alumina include alumina and an amine compound; the mass ratio of the amine compound to the alumina is 1:(0.5-6).

[0010] In this invention, if the mass ratio of amine compounds to alumina is too high (i.e., the mass of alumina powder is too low or the mass of amine compounds is too high), the amino content on the surface of the amino-modified alumina will be too high. This will result in excessively high feed viscosity after subsequent bonding with additives, leading to excessively high injection peak pressure during injection molding, incomplete injection into the ceramic green body, deformation, or even cracking. Conversely, if the mass ratio of amine compounds to alumina is too low (i.e., the mass of alumina powder is too high or the mass of amine compounds is too low), the modification effect will be poor, failing to achieve the minimum modification level on the alumina surface. The bonding stability between the amino-modified alumina and the additives will be poor, leading to localized segregation during injection and uneven density distribution in the ceramic green body.

[0011] This invention selects amine compounds as modifiers for alumina powder. These compounds possess amino functional groups, and the nitrogen atoms in these amino functional groups carry isolated electron pairs. The hydroxyl groups on the surface of the alumina powder can accept electron pairs, and the hydrogen atoms in these hydroxyl groups are easily substituted. Based on the Lewis acid-base theory, the amine compounds act as Lewis bases and can react with alumina, which acts as a Lewis acid. The amine compounds and the hydroxyl groups on the alumina surface form new chemical bonds through electron pair sharing, resulting in a coordination reaction as described in the Lewis acid-base theory. In the reaction, the hydroxyl functional group (-OH) reacts with the amino functional group (-NH2) to form an amino ether bond and simultaneously generate H2O, thus obtaining amino-modified alumina.

[0012] Preferably, the mass ratio of the amino group in the amine compound to the alumina is (0.07-0.9):1; more preferably, the mass ratio of the amino group in the amine compound to the alumina is (0.07-0.86):1; and even more preferably, the mass ratio of the amino group in the amine compound to the alumina is (0.29-0.47):1. If the amino content is too low (below the minimum modification degree), the effect of promoting the bonding between the amino-modified alumina powder and the additive will not be achieved, thereby affecting the stability of the prepared feedstock, causing segregation after injection, uneven density distribution, and affecting strength. If the amino content is too high (above the maximum modification degree), in addition to causing raw material waste and excessively high viscosity of the prepared feedstock during injection, it may also result in larger powder particle size or affect the density between molecules of the bonded ceramic green body, leading to a decrease in density and ceramic strength.

[0013] Preferably, the amine compound is selected from at least one of compounds containing one amino group, compounds containing two amino groups, and compounds containing three amino groups.

[0014] Preferably, the compound containing one amino group is selected from n-propylamine (C3H9N), isopropylamine (C3H9N), and 6-undecylamine (C3H9N). 11 H 25 At least one of N).

[0015] Preferably, the compound containing two amino groups is selected from 1,3-propanediamine (C3H4H4O3). 10 N2), 1,8-octanediamine (C8H) 20 At least one of N2).

[0016] Preferably, the compound containing three amino groups is selected from tris(2-aminoethyl)amine, 1,2,3-propanetriamine (C3H4H4O2), etc. 11 At least one of N3).

[0017] The second aspect of the present invention provides a method for preparing the ceramic powder provided in the first aspect of the present invention, comprising the following steps:

[0018] The raw materials, including amine compounds and alumina, are ball-milled at 40–50 °C for 20–30 h.

[0019] Preferably, the method for preparing the ceramic powder includes the following steps: ball milling a preparation raw material comprising alumina powder, an amine compound, and a solvent at a temperature of 40–50°C for 20–30 h, followed by drying. Ball milling at 40–50°C allows the modification reaction to proceed rapidly, achieving the surface amino modification process of alumina.

[0020] Preferably, the drying temperature is 150–200°C.

[0021] Preferably, the drying time is 3 to 5 hours.

[0022] Preferably, the ball milling speed is 150 to 450 rpm.

[0023] Preferably, the ball milling step uses ball milling beads for ball milling.

[0024] Preferably, the grinding balls are zirconia grinding balls.

[0025] Preferably, the mass ratio of the grinding beads to alumina is (0.83 to 2.34): 1.

[0026] Preferably, the particle size of the grinding beads is 5-15 mm.

[0027] Preferably, the solvent is selected from at least one of ethanol, methanol, acetone, and water.

[0028] Preferably, the ethanol is anhydrous ethanol.

[0029] Preferably, the water is deionized water.

[0030] A third aspect of the present invention provides a ceramic structural component comprising the following raw materials by weight percentage: 72-86% ceramic powder provided in the first aspect of the present invention, 4-8% zirconium oxide, and 10-20% additives; said additives include binders, accelerators, and lubricants.

[0031] In this invention, if the mass percentage of ceramic powder is low or the mass percentage of additives is high, the overall number of amino functional groups in the raw materials of the ceramic structural parts is low. This results in insufficient matching of corresponding functional groups when the ceramic powder and additives combine, leading to only partial binding of the additives with the ceramic powder, with some free additives remaining. The compatibility between the additives and the ceramic powder is generally poor, thus affecting the overall stability and shape retention of the resulting ceramic structural parts. Furthermore, after injection molding, the ceramic structural parts will exhibit larger and more numerous pores due to excessive organic matter volatilization and thermal decomposition after glue removal. The presence of additives can affect the density and mechanical strength of sintered ceramic structural parts, leading to product deformation and poor dimensional and quality uniformity. If the mass percentage of ceramic powder is high or the mass percentage of additives is low, the ceramic powder cannot fully react with the additives. Excessive remaining ceramic powder cannot play its role in modifying and promoting the combination with additives. The ceramic powder is in a free or non-agglomerated state, resulting in poor flowability and stability of the feed. Furthermore, excessively high viscosity can lead to excessively high injection peak pressure, which can easily cause problems such as incomplete injection and severe deformation of the ceramic structural parts. In addition, the shape retention is poor, resulting in a decrease in both the quality and yield of the finished product.

[0032] In this invention, amino-modified alumina has amino functional groups, which can undergo condensation reactions with hydroxyl groups in the additives to form amino ester bonds and encapsulate the ceramic powder, thereby improving the bonding stability between the ceramic powder and the additives. In contrast, the surface hydroxyl groups of traditional unmodified alumina powder cannot undergo the above-mentioned reaction with the additives, resulting in a lower bonding degree between the alumina powder and the additives, which affects the stability of the injection feeding of alumina powder and additives.

[0033] Preferably, the additive is a mixture of binder, accelerator and lubricant in a mass ratio of (3-26):1:(2-22); more preferably, the additive is a mixture of binder, accelerator and lubricant in a mass ratio of (5-13):1:(3-11).

[0034] Preferably, the adhesive is selected from ethylene-vinyl acetate copolymer ((C2H4)). x (C4H6O2) y EVA and polyvinyl alcohol (C2H4O)n PVA and polyethylene (C2H4) n PE), polypropylene (C3H6) n At least one of (PP). In this invention, the binder serves as the "skeleton" of the ceramic structural green body, providing it with a certain degree of support and shape retention. If its content is too low, it cannot completely encapsulate the powder, and component segregation is prone to occur during injection molding, resulting in uneven density distribution of the ceramic structural green body and generally poor dimensional stability of the finished ceramic. If the binder content is too high, the ceramic structural green body will have more pores and reduced strength after binder removal, affecting the density and strength of the sintered ceramic structural body.

[0035] Preferably, the accelerator is selected from polyacrylic acid (C3H4O2). n PAA), polyvinylpyrrolidone (C6H9NO) n PVP), polyethylene glycol (HO(C2H4O) n At least one of H, PEG). In this invention, the accelerator can act as a surfactant and flow aid to promote the reaction between the ceramic powder and the various components of the additives, thereby ensuring a stable bond between the ceramic powder and the additives. If the accelerator content is too high, it will increase the viscosity of the injection feed for the ceramic structural parts, potentially leading to incomplete injection, high residual stress, and other problems, affecting the stability and surface gloss of the green ceramic structural parts. If the accelerator content is too low, the compatibility between the ceramic powder and the additives, and between the various components of the additives, will be insufficient during the mixing process, resulting in poor stability and large deformation of the green ceramic structural parts obtained by injection feeding molding.

[0036] Preferably, the lubricant is selected from microcrystalline wax (C 21 H 17 NO3), ethyl stearate (C 20 H 40 O2), palmitic acid (C 16 H 32 At least one of O2). In this invention, the lubricant enables the injection feed of ceramic structural parts to have a certain fluidity. If the proportion of lubricant is too high, the stability of the green ceramic structural parts obtained by injection is poor, the deformation of the green ceramic structural parts is large, and the dimensional stability of the ceramic structural parts after sintering is generally poor. If the proportion of lubricant is too low, the viscosity of the injection feed of ceramic structural parts is too high, the frictional resistance between the feed and the equipment components during the injection process is too large, the injection peak pressure is too large, and in severe cases, it will lead to incomplete injection, large residual stress, and deformation of the ceramic structural parts.

[0037] Preferably, the ceramic structural component includes at least one of a ceramic chopping blade, a ceramic insert, a ceramic wire nozzle, a ceramic nozzle, and a ceramic suction nozzle. The ceramic powder provided in the first aspect of the present invention can be used to prepare ceramic structural components such as ceramic chopping blades, ceramic inserts, ceramic wire nozzles, ceramic nozzles, and ceramic suction nozzles.

[0038] A fourth aspect of the present invention provides a method for preparing the ceramic structural component provided in the third aspect of the present invention, comprising the following steps:

[0039] S1: Raw materials including ceramic powder, zirconium oxide and additives are mixed to obtain feedstock, and then injection molded to obtain green ceramic structural parts;

[0040] S2: The ceramic structural component green body is debonded and sintered to obtain the ceramic structural component;

[0041] The injection molding step is as follows: the feed material is granulated at 10-30 MPa to obtain feed particles, and then the feed particles are injected into the mold at 20-60 MPa.

[0042] Preferably, step S1 is as follows: preheating ceramic powder and zirconium oxide at 130-150°C for 2-3 hours, then mixing with additives at 170-180°C, and then injection molding to obtain a green ceramic structural component.

[0043] Preferably, the mixing time is 2 to 6 hours.

[0044] Preferably, the mixing speed is 5 to 30 r / min.

[0045] Preferably, the glue discharge temperature is 120–500°C.

[0046] Preferably, the glue removal time is 15 to 25 hours.

[0047] Preferably, the sintering temperature is 1200–1600°C.

[0048] Preferably, the sintering time is 15 to 32 hours.

[0049] The beneficial effects of this invention are as follows: The ceramic powder in this invention uses amine compounds to modify the surface of alumina, giving it amino functional groups. When this ceramic powder is used to prepare feedstock for ceramic structural parts, it can combine with hydroxyl-containing additives and undergo a condensation reaction, thereby enhancing the bonding between the ceramic powder and the additives and improving the stability of the prepared ceramic structural parts feedstock. This reduces or even avoids the occurrence of component segregation after injection molding, resulting in ceramic structural parts with uniform density distribution and good shape retention. The mechanical strength is improved, leading to high-quality ceramic structural parts with long service life, and improving the quality and yield of finished ceramic structural parts. Detailed Implementation

[0050] The following examples provide a more detailed description of the specific implementation of the present invention, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described below are methods that can be implemented or understood by those skilled in the art by referring to existing technology. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0051] Information on the amine compounds used in the present invention's 1-9 embodiments and comparative powders 1-3 is as follows:

[0052] n-Propylamine, with the molecular formula C3H9N, denoted as A1;

[0053] Isopropylamine, with the molecular formula C3H9N, is denoted as A2;

[0054] 6-Undecylamine, molecular formula: C 11 H 25 N is denoted as A3;

[0055] 1,3-Propanediamine, molecular formula: C3H 10 N2, denoted as B1;

[0056] 1,8-Octadiamine, molecular formula: C8H 20 N2, denoted as B2;

[0057] Tris(2-aminoethyl)amine, with the molecular formula: C6H 18 N4, denoted as C1;

[0058] 1,2,3-Propanetriamine, molecular formula: C3H 11 N3, denoted as C2.

[0059] Example 1

[0060] This example provides a ceramic chopping knife, the formula of which is shown in Table 1 below. It is prepared from the following raw materials by mass percentage: ceramic powder (powder 1) 80%, additives 14%, and zirconia powder 6%; the additives are EVA, PAA, and C in a mass ratio of 56:7:37. 21 H 17 A mixture of NO3. The ceramic powder (powder 1) is amino-modified Al2O3, and the formulation of its raw materials is shown in Table 2 below.

[0061] The ceramic chopping knife in this example can be prepared into a ceramic chopping knife green body using the following preparation method. Then, the ceramic chopping knife green body can be debonded at 120-500℃ for 20 hours, and then sintered at 1200-1600℃ for 25 hours to obtain the ceramic chopping knife.

[0062] The specific preparation steps for the ceramic cleaver green body in this example are as follows:

[0063] (1) Weigh out 23% by mass of alumina powder (commercially available, with hydroxyl groups on its surface) based on 100% of the total mass percentage of all materials used in the formulation (i.e., alumina, amine compounds, solvents, and zirconia grinding beads), and add the following materials by mass percentage in sequence: 25% of 1,3-propanediamine (C3H 10 N2, B1), 30% anhydrous ethanol solvent, and 22% zirconia grinding beads (approximately 3 mm in diameter) were added to a ball mill. The rotation speed was set to 300 rpm, and the ball milling time was 25 h. Circulating cooling water was used to maintain the ball milling temperature at 40℃~50℃ to ensure the smooth progress of the modification reaction. After ball milling, the resulting mixed liquid was transferred to an oven and dried at 180℃ for 4 h to obtain ceramic powder (powder 1).

[0064] (2) Weigh 80% of the implementation powder 1 and 6% of the zirconium oxide powder and mix them (the mixed powder is preheated at 140℃ for 3h). Then add 14% of the additive and mix further. Keep the mixing temperature at 170℃~180℃, set the rotation speed to 28r / min, and the mixing time to 5h to obtain the feed material for later use. The feed material is subjected to a pressure of 20MPa to obtain feed particles. The feed particles are then injection molded under a pressure of 50MPa to obtain the ceramic chopping green body.

[0065] Table 1. Formulations of the ceramic chopping knives in Examples 1-20 and Comparative Examples 1-8.

[0066]

[0067]

[0068] Table 2 shows the formulations of the raw materials for preparing ceramic powders in Implementation Powders 1-9 and Comparative Powders 1-3.

[0069]

[0070]

[0071] In Table 2, the mass percentages of Al2O3, amine compounds, and solvents are all calculated based on the mass percentages of all materials used in the formulation (i.e., alumina, amine compounds, solvents, and zirconia grinding beads) being 100%. The mass ratio of amino to Al2O3 refers to the mass ratio of amino groups in the amine compounds to Al2O3.

[0072] The mass of the amino group in amine compounds is calculated as follows: m 氨基 =m 胺类化合物 ×(M 氨基相对分子质量 ×n) / M胺类化合物相对分子质量 ×100%, where m 胺类化合物 M represents the mass of amine compounds. 氨基相对分子质量 M is the relative molecular mass of the amino group. 胺类化合物相对分子质量 denoted as α, where α is the relative molecular mass of the amine compound, and n is the number of amino groups in the chemical formula of the amine compound.

[0073] Examples 2-12

[0074] The formulations of the ceramic chopping knives in Examples 2 to 12 are shown in Table 1. All ceramic chopping knives in Examples 2 to 12 use the implementation powder 1 in Table 2.

[0075] The ceramic chopping knives in Examples 2 to 12 can all be prepared by referring to the preparation method in Example 1.

[0076] Examples 13-20

[0077] The formulations of the ceramic chopping knives in Examples 13-20 are shown in Table 1. The ceramic chopping knives in Examples 13-20 respectively use implementation powder 2 to implementation powder 9 in Table 2.

[0078] The ceramic chopping knives in Examples 13-20 can all be prepared by referring to the preparation method in Example 1.

[0079] Comparative Examples 1-3

[0080] The formulations of the ceramic chopping knives in Comparative Examples 1 to 3 are shown in Table 1. The ceramic chopping knives in Comparative Examples 1 to 3 use the comparative powders 1 to 3 in Table 2, respectively.

[0081] The ceramic chopping knives in Comparative Examples 1 to 3 can all be prepared by referring to the preparation method in Example 1.

[0082] Comparative Examples 4-8

[0083] The formulations of the ceramic chopping knives in Comparative Examples 4 to 8 are shown in Table 1. The ceramic chopping knives in Comparative Examples 4 to 8 respectively use the implementation powder 1 in Table 2.

[0084] The ceramic chopping knives in Comparative Examples 4 to 8 can all be prepared by referring to the preparation method in Example 1.

[0085] Performance testing

[0086] The amination degree of ceramic powders in the experimental powders 1-9 and control powders 1-3 were tested according to the test method for the mass ratio of amino groups recorded in Table 3 below. The specific test results are shown in Table 4 below.

[0087] The green density distribution (density properties), injection molding properties (shape retention), and mechanical strength properties (strength properties) of the ceramic chopping blades prepared in Examples 1-20 and Comparative Examples 1-8 were tested according to the test methods and test equipment recorded in Table 3 below. The specific test results are shown in Table 5 below.

[0088] Table 3 Test methods, test standards and test equipment

[0089]

[0090] Table 4. Test results of amino mass ratio of ceramic powders in implementation powders 1-9 and control powders 1-3.

[0091]

[0092]

[0093] In Table 4, the mass percentage of amino (NH2) refers to the mass percentage of amino functional groups contained in the amino-modified alumina ceramic powder.

[0094] Table 5 shows the performance test results of Examples 1-20 and Comparative Examples 1-8.

[0095]

[0096]

[0097] As shown in Table 4, ceramic powders 1 to 9 all used different types of amine compounds to modify alumina. When the mass ratio of amine compound to alumina was within the specified range, the mass ratio of amino to Al2O3 in the raw material formulation was 0.07 to 0.86, and ceramic powders with good amination modification effects could be obtained.

[0098] As shown in Table 5, when the amination-modified ceramic powders 1 to 9 were used for injection molding to prepare the ceramic green bodies and ceramic green bodies of Examples 1 to 20, tests revealed that the ceramic green bodies of Examples 1 to 20 exhibited excellent density uniformity, excellent shape retention, and high mechanical strength after sintering, specifically: density difference ≤ 0.13 g / cm³. 3The ceramic chopping blades produced exhibited good shape retention (≥99%) and strength (≥700N). Furthermore, it was found that when the mass ratio of binder, accelerator, and lubricant in the additives was (5-13):1:(3-11), the density uniformity, shape retention, and strength were significantly improved. This resulted in high-quality ceramic chopping blades with long service life, thus enhancing the overall quality and yield of ceramic chopping blades. However, in Comparative Examples 1-3, the type of ceramic powder was changed (raw material formulation), and in Comparative Examples 4-8, the amount of ceramic chopping blade formulation or the type and mass ratio of additives were changed. Consequently, the density uniformity and shape retention of the resulting ceramic chopping blade green bodies failed to meet the requirements, and the mechanical strength of the ceramic chopping blades was significantly reduced, severely impacting the subsequent quality and yield of ceramic chopping blades.

[0099] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A ceramic powder, characterized in that: The ceramic powder is amino-modified alumina; the raw materials for preparing the amino-modified alumina include alumina and amine compounds; the mass ratio of the amine compound to the alumina is 1:(0.5~6); the amine compound is selected from at least one of n-propylamine, isopropylamine, 6-undecylamine, 1,3-propanediamine, 1,8-octanediamine, tris(2-aminoethyl)amine, and 1,2,3-propanetriamine; the ceramic powder is prepared by ball milling the raw materials including the amine compound and alumina at 40~50℃ for 20~30h.

2. The ceramic powder according to claim 1, characterized in that: The mass ratio of the amino group in the amine compound to the aluminum oxide is (0.07~0.9):

1.

3. A ceramic structural component, characterized in that: The raw materials include the following percentages by mass: 72-86% ceramic powder as described in claim 1 or 2, 4-8% zirconium oxide, and 10-20% additives; the additives include binders, accelerators, and lubricants.

4. The ceramic structural component according to claim 3, characterized in that: The additive is a mixture of binder, accelerator and lubricant in a mass ratio of (3~26):1:(2~22).

5. The ceramic structural component according to claim 4, characterized in that: The adhesive is selected from at least one of ethylene-vinyl acetate copolymer, polyvinyl alcohol, polyethylene, and polypropylene; And / or, the accelerator is selected from at least one of polyacrylic acid, polyvinylpyrrolidone, and polyethylene glycol; And / or, the lubricant is selected from at least one of microcrystalline wax, ethyl stearate, and palmitic acid.

6. The ceramic structural component according to any one of claims 3 to 5, characterized in that: The ceramic structural component includes at least one of ceramic chopping blade, ceramic insert, ceramic wire nozzle, ceramic nozzle, and ceramic suction nozzle.

7. The method for preparing the ceramic structural component according to any one of claims 3 to 5, characterized in that: Includes the following steps: S1: Raw materials including ceramic powder, zirconium oxide and additives are mixed to obtain feedstock, and then injection molded to obtain green ceramic structural parts; S2: The ceramic structural component green body is debonded and sintered to obtain the ceramic structural component; The injection molding step is as follows: the feed material is granulated at 10~30MPa to obtain feed particles, and then the feed particles are injected into the mold at 20~60MPa.

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