High-processability silicon nitride ceramic composite and manufacturing method thereof

Abstract

The present invention relates to a high-processability silicon nitride ceramic composite and a manufacturing method thereof. More specifically, disclosed are a high-processability silicon nitride ceramic composite and a manufacturing method thereof, the high-processability silicon nitride ceramic composite comprising: silicon nitride particles having an average diameter of 0.1-10 ㎛; silicon nitride nanoparticles positioned in pores between the silicon nitride particles, and having an average diameter of 1-50 nm; and a sintering aid, wherein the silicon nitride particles, the silicon nitride nanoparticles, and the sintering aid are present at a molar ratio of 80-95:2-20:5-20, such that the silicon nitride particles and the silicon nitride nanoparticles form a dense structure and control surface roughness. According to the present invention, the size and molar ratio of the silicon nitride particles and the silicon nitride nanoparticles are adjusted to lower the roughness of a ceramic surface, thereby improving processability. In addition, since the silicon nitride particles and the silicon nitride nanoparticles form a dense structure to thereby increase the denseness of the ceramic composite, mechanical properties such as high-temperature flexural strength, thermal stability, and thermal expansion coefficient are improved.

Description

Highly processable silicon nitride ceramic composite and method for manufacturing the same

[0001] The present invention relates to a highly processable silicon nitride ceramic composite and a method for producing the same, and more particularly, to a highly processable ceramic composite in which silicon nitride particles and silicon nitride nanoparticles form a dense structure to provide high strength while improving surface roughness to enhance processability, and a method for producing the same.

[0002] Ceramics have lower fracture toughness than metals or polymers. Their mechanical properties are sensitive to micro-defects on the surface or within the material, leading to extreme fractures. They are also vulnerable to mechanical and thermal shocks and are difficult to process. Consequently, their various properties are highly dependent on the microstructure, which is governed by the manufacturing process. Therefore, improving or overcoming this brittle nature is essential for the widespread practical application of ceramics as structural materials.

[0003] In addition, it is necessary to remove large defects that are the origin of destruction in order to increase the strength and toughness values ​​of materials, and among these, the defects that must be removed first are surface defects. In this regard, surface roughness is an unevenness that occurs at very small angles and is mainly affected by the shape of the cutting tool edge and the feed rate. In addition, with the advancement of processing technology and the sophistication of products in industries such as semiconductors and aerospace, the influence of surface roughness on product quality is greatly increasing. This is because the machined surface is mostly formed through metal processing such as turning, milling, grinding, lapping, and honing, and the surface roughness is the most sensitive to any small change in the production process.

[0004] However, most ceramic materials are polycrystals composed of fine crystal grains obtained by molding and sintering powder. The mechanical properties of ceramic polycrystals, such as strength and toughness, are influenced by various variables, including microstructural elements such as crystal grains and pores, as well as the amount, shape, and distribution of the crystal grains and pores that make up the ceramic. Furthermore, most ceramics are composed of multiple components, and their microstructure can vary significantly depending on the characteristics of the raw powders or variables such as temperature, pressure, and atmosphere during the manufacturing process, making it very difficult to control the microstructure.

[0005]

[0006] Meanwhile, silicon nitride (Si3N4) ceramics possess high strength at high temperatures, as well as wear and corrosion resistance, making them suitable for use in high-temperature and harsh environments. Primary applications for silicon nitride ceramics include bearings, ceramic tools, and various wear-resistant components. Silicon nitride is used in various industries for wear, heat, and wear resistance. Industrial ceramic products used in these fields are categorized by application, such as steelmaking, molding, bearings, and welding.

[0007] In particular, silicon nitride ceramic bearings can maintain sufficient strength even at high temperatures exceeding 1,000℃, and have low density, high hardness, and excellent insulation. Ceramic bearing balls are classified into 11 grades from G3 to G200 according to the ISO international standard according to the precision of shape and surface roughness. G5 grade bearing balls require a shape precision and surface roughness of 0.13㎛ or less in ball diameter variation, 0.13㎛ in spherical deviation, and 0.014㎛Ra or less in surface roughness. Therefore, ceramic bearing balls require high shape precision and surface roughness, and therefore, a processing method suitable for these requirements is required.

[0008] In this regard, Korean Patent No. 10-1852040 (Processable Ceramic Composite and Manufacturing Method Thereof) describes a method for manufacturing a processable ceramic composite by further including boron nitride powder to improve the processability of silicon nitride and using yttrium oxide and alumina as sintering aids. However, boron nitride (BN) composite processable ceramics have the disadvantage of being difficult to sinter and not resolving the problems of ceramic processability caused by the inherent brittleness and hardness of ceramics.

[0009] Accordingly, the inventors of the present invention confirmed that a ceramic composite having a dense structure can be manufactured by controlling the size of the silicon nitride powder while manufacturing a silicon nitride ceramic composite by a sintering method of sintering Si3N4 powder, thereby controlling the surface roughness, and thus completed the present invention.

[0010] Accordingly, the present invention has as a technical solution a problem of providing a highly processable silicon nitride ceramic composite having a high strength and low surface roughness by forming a dense structure including silicon nitride particles, silicon nitride nanoparticles, and a sintering agent.

[0011] In addition, the present invention provides a method for manufacturing the highly processable silicon nitride ceramic composite as another technical solution.

[0012] In order to solve the above technical problem, the present invention,

[0013] It comprises: silicon nitride particles having an average diameter of 0.1 to 10 ㎛; silicon nitride nanoparticles located in the pores between the silicon nitride particles and having an average diameter of 1 to 50 nm; and a sintering aid;

[0014] The present invention relates to a highly processable silicon nitride ceramic composite characterized in that the silicon nitride particles, silicon nitride nanoparticles, and sintering aid are included in a molar ratio of 80 to 95: 2 to 20: 5 to 20, so that the silicon nitride particles and silicon nitride nanoparticles form a dense structure and control surface roughness.

[0015] In the present invention, the surface roughness is characterized by being at most 0.10 μm.

[0016]

[0017] In addition, in order to solve the above other technical problems, the present invention provides a method for manufacturing the above-described high-processability silicon nitride ceramic composite.

[0018] Preferably, the method for manufacturing the highly processable silicon nitride ceramic composite is as follows:

[0019] A step of preparing a ceramic raw material mixture by adding and stirring ceramic raw material powder into a dispersion solvent and mixing, and then further adding and stirring an organic binder;

[0020] A step of producing a ceramic raw material slurry by crushing and mixing the above ceramic raw material mixture through a ball milling process;

[0021] A step of manufacturing ceramic granules by spray drying the above ceramic raw material slurry;

[0022] A step of manufacturing a ceramic molded body by pressurizing and molding the above ceramic granules; and

[0023] It is characterized in that it is manufactured including a step of heat-treating the above ceramic molded body to remove the organic binder and then sintering it to manufacture a ceramic composite.

[0024] In addition, in the present invention, the step of manufacturing the ceramic granules comprises:

[0025] It is characterized in that the above ceramic raw material slurry is spray-dried at 100 to 200°C to produce ceramic granules.

[0026] In addition, in the present invention, in the step of manufacturing the ceramic composite, the sintering is characterized in that it is performed at 1500 to 2500°C for 2 to 24 hours.

[0027] The silicon nitride ceramic composite of the present invention has silicon nitride nanoparticles positioned in the pores of silicon nitride particles to form a dense structure, thereby increasing the surface area between particles, thereby increasing density and improving strength, and can significantly reduce surface roughness by densely controlling the surface of the composite during the molding and sintering process. Accordingly, by securing low surface roughness after ceramic processing, reliability can be increased in areas requiring precise control characteristics, such as leak control.

[0028] In addition, according to the present invention, there is an effect of being able to manufacture a highly processable silicon nitride ceramic composite having excellent mechanical properties and improved processability, including silicon nitride nanoparticles.

[0029] FIG. 1 conceptually illustrates the structure of a ceramic composite including silicon nitride nanoparticles and silicon nitride particles according to the present invention.

[0030] Figure 2 illustrates a manufacturing process of a high-processability ceramic composite according to the present invention.

[0031] Figure 3 is a photograph of a specimen according to an embodiment and comparative example of the present invention.

[0032] Figure 4 is a photograph showing the surface roughness of a specimen measured according to an example and comparative example of the present invention.

[0033] Figure 5 is a graph showing the test results of a ceramic composite manufactured by applying uniaxial pressing according to one embodiment of the present invention.

[0034] Figure 6 is a graph showing the test results of a ceramic composite manufactured by applying CIP pressurization after uniaxial pressurization according to one embodiment of the present invention.

[0035] The present invention is described in detail below.

[0036] Throughout the specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0037]

[0038] In one aspect, the present invention relates to a highly processable silicon nitride ceramic composite, comprising: silicon nitride particles having an average diameter of 0.1 to 10 μm; silicon nitride nanoparticles located in pores between the silicon nitride particles and having an average diameter of 1 to 50 nm; and a sintering aid; wherein the silicon nitride particles, silicon nitride nanoparticles, and sintering aid are included in a molar ratio of 80 to 95:2 to 20:5 to 20, so that the silicon nitride particles and silicon nitride nanoparticles form a dense structure and control surface roughness.

[0039] FIG. 1 is a conceptual diagram illustrating a process for manufacturing a highly processable ceramic composite using silicon nitride nanoparticles according to the present invention. Referring to this, the silicon nitride ceramic composite of the present invention is formed by press-molding and then sintering while silicon nitride nanoparticles are positioned in the pores between silicon nitride particles. Accordingly, the composite has a dense structure in which silicon nitride particles and silicon nitride nanoparticles fill the pores, thereby lowering the surface roughness and reducing surface defects, thereby improving processability.

[0040] At this time, the surface roughness is preferably at most 0.10 μm, and more preferably may be 0.08 μm or less. If the surface roughness exceeds the above range, the surface roughness is not improved, and it may be difficult to exhibit the effect of high processability.

[0041] In addition, the silicon nitride composite may have a flexural strength of at least 500 MPa and a Vickers hardness of 1700 to 1900 Hv. This is because the structure becomes dense due to the silicon nitride nanoparticles, and thus the composite of the present invention can improve both processability and mechanical properties by improving flexural strength and Vickers hardness while reducing surface roughness.

[0042] At this time, in the composite of the present invention formed by sintering while silicon nitride nanoparticles are positioned in the gaps between silicon nitride particles, it is important to control the molar ratio between the silicon nitride particles and the silicon nitride nanoparticles. Therefore, it is preferable that the silicon nitride particles, silicon nitride nanoparticles, and sintering aid are included in a molar ratio of 80 to 95 : 2 to 20 : 5 to 20. More preferably, the molar ratio may be 80 to 95 : 2 to 10 : 5 to 15, and most preferably, the molar ratio may be 85 to 95 : 2 to 7 : 5 to 10. If the silicon nitride nanoparticles are included in an amount less than the above range and the content of the silicon nitride particles increases, the effect of pore-filling by the silicon nitride nanoparticles is reduced, so that a dense structure cannot be formed, resulting in lowered structural stability and increased surface roughness. In addition, if the content of silicon nitride nanoparticles exceeds the above range, the content of silicon nitride nanoparticles may rather increase, which may result in an increase in surface roughness due to the nanoparticles or sintering agent during the sintering process, and may also result in increased difficulty and cost of the sintering process. In addition, if the content of the sintering agent is below the above range, the densification of the ceramic composite by sintering is insufficient, and if it exceeds the above range, the high temperature properties such as high temperature strength and oxidation resistance are significantly reduced, which is not desirable.

[0043] In addition, in the present invention, the silicon nitride particles may preferably be 0.1 to 10 μm, more preferably 0.1 to 3 μm, and most preferably 0.01 to 1 μm. This is because if the average diameter of the silicon nitride particles is too small, the driving force may decrease, thereby reducing the bonding force with the nanoparticles, and if the average diameter is too large, the pore-filling effect by the nanoparticles may be reduced, which may cause problems such as the generation of pores or surface defects.

[0044] In addition, in the present invention, it is preferable that the sintering aid is a metal belonging to the group of alkaline earth metals, rare earth metals, transition metals and typical metals or an oxide thereof. More preferably, it may be at least one selected from the group consisting of yttrium (Y), magnesium (Mg), zirconium (Zr), titanium (Ti), calcium (Ca), copper (Cu), gadolinium (Gd), lanthanum (La), neodymium (Nd), yttrium (Yb), scandium (Sc), silicon (Si), lutetium (Lu), erbium (Er), dysprosium (Dy), vanadium (V), chromium (Cr), manganese (Mn), hafnium (Hf), tantalum (Ta), bismuth (Bi), actinium (Ac) and oxides thereof, the group consisting of aluminum (Al) and nitrides thereof, and calcium carbonate and calcium fluoride. Preferably, it may be at least one selected from the group consisting of yttrium (Y), magnesium (Mg), zirconium (Zr), titanium (Ti), aluminum (Al) and oxides thereof. More preferably, it may be yttrium oxide (Y2O3) and magnesium oxide (MgO).

[0045] In this way, according to the present invention, by controlling the size and molar ratio of silicon nitride particles and silicon nitride nanoparticles, the surface roughness of the ceramic composite can be lowered and the processability can be improved, thereby improving the disadvantage of high brittleness of the ceramic composite during ceramic processing and increasing reliability in areas requiring precise control characteristics.

[0046] FIG. 2 illustrates a process for manufacturing the high-processability silicon nitride composite of the present invention, and in another aspect, the present invention provides a method for manufacturing the high-processability silicon nitride ceramic composite described above. The method for manufacturing the high-processability silicon nitride ceramic composite of the present invention is characterized by including the steps of: adding and stirring ceramic raw material powder to a dispersion solvent to mix, and then further adding and stirring an organic binder to manufacture a ceramic raw material mixture (S100); crushing and mixing the ceramic raw material mixture using a ball milling process to manufacture a ceramic raw material slurry (S200); spray-drying the ceramic raw material slurry to manufacture ceramic granules (S300); press-molding the ceramic granules to manufacture a ceramic molded body (S400); and heat-treating the ceramic molded body to remove the organic binder, and then sintering the ceramic molded body to manufacture a ceramic composite (S500).

[0047] First, the step (S100) of preparing a ceramic raw material mixture is a preliminary step for preparing a ceramic slurry, and is a step of mixing raw materials. This step is performed by adding and stirring ceramic raw material powder into a dispersion solvent and mixing, and then further adding and stirring an organic binder. It is important to first add the raw material powder to the dispersion solvent and mix so that the ceramic raw material powder can be uniformly mixed without agglomeration, and then further add the organic binder to ensure uniform mixing by the binder.

[0048] At this time, the ceramic raw material powder is characterized in that it contains silicon nitride particles having an average diameter of 0.1 to 10 ㎛, silicon nitride nanoparticles having an average diameter of 1 to 50 nm, and a sintering agent in a molar ratio of 80 to 95: 2 to 20: 5 to 20.

[0049] In addition, it is preferable to mix the dispersion solvent while maintaining a constant viscosity by additionally adding the dispersion solvent during the bead milling process to keep the viscosity of the slurry constant. The dispersion solvent may be an alcohol such as water (H2O), ethanol, or methanol.

[0050] In addition, examples of the organic binder include acrylic resins such as polyacrylic acid ester and polymethacrylic acid ester, cellulose-based resins such as methylcellulose, hydroxymethyl cellulose, nitrocellulose, and cellulose acetate butyrate, vinyl-containing resins such as polyvinyl butyraldehyde, polyvinyl alcohol, and polyvinyl chloride, hydrocarbon resins such as polyolefin, and oxygen-containing resins such as polyethylene oxide, and the like. One or two or more of these may be used in combination. By further adding the organic binder in this way, the raw material powder can be uniformly dispersed in the slurry. At this time, it is preferable to mix 0.01 to 3 parts by weight of the organic binder with respect to 100 parts by weight of the ceramic raw material powder. The organic binder may be polyvinyl alcohol, etc.

[0051] Next, the step of manufacturing a ceramic raw material slurry (S200) is a step of crushing and mixing the ceramic raw material mixture into a slurry through a milling process. In this step, the milling process may be any method, whether wet or dry, as long as it can uniformly mix silicon nitride particles, silicon nitride nanoparticles, and sintering aid in a solvent. Known methods such as a rotary mill, barrel mill, vibration mill, or ball mill can be used. A ball mill is preferably used.

[0052] Next, the step (S300) of manufacturing ceramic granules is performed by spray-drying the ceramic slurry. The factor that most significantly contributes to the volume shrinkage during sintering of silicon nitride is the density gradient of the molded body. In order to minimize the density gradient, it is important to control the composition or size of the initial particles. In this step, by spray-drying the ceramic raw material slurry containing silicon nitride nanoparticles at high temperature and high speed, granules are formed in a form in which silicon nitride nanoparticles fill the internal pores between silicon nitride particles, and the growth of the granule powder size is controlled, thereby manufacturing ceramic granules having a fine powder size. Preferably, the granule powder manufactured in this step has a diameter of 30 to 170 μm, and more preferably, 70 to 100 μm. Such granule powder has an agglomerated shape as silicon nitride nanoparticles fill the pores between silicon nitride particles.

[0053] Preferably, the spray drying is performed at a high temperature of 100 to 200°C, and more preferably, it is good to perform spray drying at a high temperature and high speed by setting the hot air temperature to 100 to 200°C, the exhaust air temperature to 60 to 100°C, the disk rotation speed to 5000 to 12,000 rpm, and the slurry input amount to 0.01 to 2 L / min.

[0054] Next, the step of manufacturing a ceramic molded body (S400) is a step of pressing and molding the ceramic granules. At this time, as the molding method of the pressurized molding, known methods such as press molding, injection molding, extrusion molding, injection molding, varnish molding, cold isostatic pressing (CIP) molding, and uniaxial press molding can be used.

[0055] Preferably, uniaxial pressing and CIP (cold isostatic pressing) pressing can be used. At this time, it is also possible to use one of the pressing processes or to sequentially use a two-stage pressing process. In the embodiment of the present invention, in both cases where uniaxial pressing or a two-stage pressing process of uniaxial pressing followed by CIP pressing was used, it was found that the surface roughness was 0.1㎛ or less, the bending strength was 500 MPa or more, and the Vickers hardness was 1700 to 1900 Hv. This means that the material properties such as surface roughness, bending strength, and hardness could be obtained because the structure became dense due to the composition of the composite including silicon nitride nanoparticles, and it means that it is important to apply an appropriate level of pressing pressure rather than the pressing method. This appropriate level of pressing pressure means a level at which the indicated forming defect (lamination) does not occur, and it is preferable to pressurize at 500 to 3000 kgf. More preferably, it is recommended to perform the process at 500 to 2000 kgf for single-axis press forming and at 1000 to 3000 kgf for CIP press forming.

[0056] Next, the step (S500) of manufacturing a ceramic composite is a step of heat-treating the ceramic molded body to remove the organic binder, and then sintering the ceramic molded body to manufacture a sintered body. In this step, the ceramic molded body is degreased by heat treatment to remove the organic binder, and then a debinding process is performed, and then the silicon nitride particles and silicon nitride nanoparticles are sintered to form a dense structure while controlling the surface of the sintered body to manufacture a silicon nitride sintered body with reduced surface roughness. By the sintering, the density is increased by increasing the surface area between the silicon nitride particles and silicon nitride nanoparticles, thereby improving strength, and the processability can be improved by forming fine β-Si3N4 particles.

[0057] Preferably, the debinding process by heat treatment can be performed in a vacuum at a temperature of 400 to 700°C for 7 to 15 hours.

[0058] In addition, as a sintering method of the above-mentioned molded body, any method known to a person skilled in the art may be used as long as the obtained sintered body becomes densified, but it is preferable to perform gas pressure sintering, pressureless sintering, or reaction sintering, and more preferably, gas pressure sintering can be used.

[0059] Specifically, the above gas pressure sintering can be used, and it is preferable to sinter the ceramic molded body from which the organic binder, etc. has been removed through the debinding process at 1500 to 2500°C for 2 to 24 hours. More preferably, it can be sintered at 1700 to 2000°C for 2 to 10 hours. The reason for sintering the molded body under gas pressure at a temperature in the above range is that a more complete densification effect of the molded body cannot be obtained at a temperature lower than or higher than the above range. At this time, the gas includes an inert gas such as argon (Ar), helium (He), or nitrogen (N2) gas.

[0060]

[0061] Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. However, these embodiments are intended to illustrate the present invention more specifically, and it will be apparent to those skilled in the art that the scope of the present invention is not limited thereby.

[0062] <Examples and Comparative Examples>

[0063] Manufacturing of ceramic composite granules

[0064] Silicon nitride (Si3N4) ceramic powder is used as the main raw material and sintering aids (Al2O3 / Y2O3 / MgO) are used to mix the powder. The mixing ratio is Si3N4 93 mol%, Y2O3 2 mol%, MgO 5 mol% as the basic mixing ratio. As a comparative example, the mixing ratio of alumina (Al2O3) is changed, and as an example, the mixing ratio of silicon nitride nanoparticles is changed, and the ceramic raw material is mixed so that the molar ratio of silicon nitride ceramic powder becomes 100 mol% in total. The particle sizes of the silicon nitride ceramic powder and ceramic nanoparticles used in the mixing of the raw materials are 0.7 μm (D50) and 20 nm (D50), respectively.

[0065] Ceramic raw materials were mixed in a solvent, a dispersant was added, and the mixture was then ball milled to produce a slurry in which the raw materials were homogeneously mixed in the solvent. The ball milling conditions were 200 rpm and mixing was performed for more than 12 hours.

[0066] Afterwards, the appearance of the slurry was examined and the viscosity was measured to confirm whether spray drying was possible, and then spray drying was performed to manufacture composite granules. Spray drying was performed at a high speed and high temperature of 180 ml / min, 1800 rpm of the atomizer, and 120°C during spray drying. The manufactured ceramic granules were visually examined for agglomerations and impurities, and the appearance and particle size were confirmed using a microscope.

[0067] All of the ceramic granules manufactured as a result above had a shape similar to that of commercially available ceramic granule powder, and no defects were observed in the particle shape.

[0068] Afterwards, molding and sintering were performed using the above-mentioned manufactured ceramic granules.

[0069]

[0070] Forming and sintering of ceramic granules

[0071] The above-mentioned granules were uniaxially pressed under a pressure of 800 to 1,500 kgf to produce ceramic molded bodies. Another molding method was used to produce ceramic molded bodies by performing a CIP molding process after uniaxial pressing. The CIP molding pressure was applied at 2,000 kgf for 5 minutes.

[0072] Afterwards, the manufactured molded body was heated at 600°C for 12 hours in a vacuum to perform a debinding process.

[0073] The molded body after the above debinding process was sintered using a GPS furnace to produce an α-Si3N4 composite. A photograph of the manufactured composite specimen is shown in Fig. 3.

[0074] The sintering conditions are as follows:

[0075] - Heating rate: Avg. 5℃ / min

[0076] - Peak Temperature: 1900℃

[0077] - Peak Temperature Holding Time: 4hr

[0078] - Gas: N2

[0079]

[0080] Physical property testing of ceramic composites

[0081] The surface roughness, Vickers hardness, flexural strength, and bulk density of the ceramic composite manufactured above were measured. Each measurement method is as follows.

[0082] - Surface Roughness: The surface roughness of a polished test piece using SiC Paper was measured. Polishing was performed in the following order: SiC Paper #230 → #500 → #1000 → #2400.

[0083] - Vickers hardness: Measured using a Micro-Vickers hardness tester under a 0.5 kgf indentation load condition (in accordance with KS L ISO 14705)

[0084] - Bending strength: Bending strength at room temperature is measured through a three-point bending strength test. The three-point bending strength is measured under conditions of a crosshead speed of 0.5 mm / min (in accordance with KS L ISO 17565).

[0085] - Bulk density: Measure the bulk density using the Archimedes test.

[0086]

[0087] The mixing ratios and property test results of the examples and comparative examples with different mixing compositions are shown in FIGS. 3 to 6, Tables 1 and 2. Specifically, FIG. 3 shows a photograph of each specimen, FIG. 4 shows a photograph measuring the surface roughness of each specimen, Tables 1 and 5 show the results of the examples and comparative examples when only the uniaxial pressing process was performed during press molding, and Table 2 and FIG. 6 show the results of the examples and comparative examples when uniaxial pressing and CIP pressing were performed.

[0088] Classification Preliminary Comparative Example 121234 Composition (molar ratio) Silicon nitride microparticles (㎛) 908793918987 Sintering aid Y2O3 222222 MgO5 55555 Al2O3 000246 Silicon nitride nanoparticles (nm) 360000 Physical properties Result Surface roughness (㎛) 0.048 0.03 0.56 10.25 60.39 60.419 Vickers hardness (HV0.5) 1875.31 819.5 1574.9 1336.110 73.110 90.7 Flexural strength (Mpa) 852786473682690373 Bulk density (g / cm 3 )3.173.182.542.892.922.74

[0089] Classification Preliminary Comparative Example 345468 Composition (molar ratio) Silicon nitride microparticles (㎛) 908793918987 Sintering aid Y2O3 2222222 MgO5 55555 Al2O3 000246 Silicon nitride nanoparticles (nm) 360000 Physical properties Result Surface roughness (㎛) 0.076 0.034 0.149 0.149 0.183 0.48 Vickers hardness (HV0.5) 1875.31 752.9 1373.31 424 1129.41 362.2 Flexural strength (Mpa) 760830 7758 036 19395 Bulk density (g / cm3 )3.183.163.082.952.962.68

[0090] Referring to Table 1, Figures 3 and 4 above, it can be seen that the surface roughness of Examples 1 and 2, which further include Si3N4 nanoparticle powder, is 0.048 ㎛ and 0.03 ㎛, respectively, and that the surface roughness is significantly lower than that of Comparative Examples 1 to 4.

[0091] Comparative Examples 1 to 4 showed that the surface roughness gradually increased as the mol% of alumina content increased. Compared to the surface roughness of 0.561 ㎛ of Comparative Example 1 with 0 mol% of alumina content, the surface roughness of 0.419 ㎛ of Comparative Example 4 with 6 mol% of alumina content was shown, confirming that the processability was somewhat improved by alumina.

[0092] However, when the above Comparative Example 4 is compared with Example 2, which contains 6 mol% of silicon nitride nanoparticles instead of alumina, the surface roughness is reduced to 1 / 13, confirming that processability can be improved. This means that, compared to Comparative Example 1, which does not contain alumina, the surface roughness is reduced to 1 / 18, indicating that the surface roughness can be significantly reduced in the composite composition containing the silicon nitride nanoparticles, thereby improving processability.

[0093] Also, in terms of bending strength, the examples showed a bending strength of 500 MPa or more, while comparative examples 1 and 4 could not satisfy this. The Vickers hardness also showed a value of 1800 Hv or more in the examples, but the comparative examples showed a significantly lower value compared to this. That is, when silicon nitride nanoparticles are further included and the composite is manufactured by press molding and sintering, the bending strength and Vickers hardness are higher, but the surface roughness after processing is better, so that a silicon nitride composite with excellent processability and mechanical properties can be manufactured. This is because the strength is improved due to the increase in density through the increase in the surface area between particles during molding and sintering, and β-Si3N4 is formed into fine particles.

[0094] In addition, when comparing the results of Table 2 and Table 1 above, which are cases where CIP pressing is applied after single-axis pressing and then molded and sintered, when comparing Examples 1 and 2 with Examples 3 and 4 having the same molar ratio composition, in Examples 1 and 3 where the content of silicon nitride nanoparticles is somewhat low, the surface roughness is somewhat increased in Example 3 where two-stage pressing is performed, but it can be confirmed that by lowering the surface roughness to less than 0.1㎛ and applying an appropriate pressing molding, a composite having excellent physical properties such as surface roughness, hardness, and strength can be manufactured by a composite composition including nanoparticles.

[0095] In this way, when comparing the examples and comparative examples from the results in Tables 1 and 2 above, the higher the Vickers hardness, the lower the surface roughness tended to be, and when more silicon nitride nanoparticles were included, the structure became denser and the volume density increased under the same sintering conditions compared to when they were not included.

[0096] That is, the silicon nitride ceramic composite of the present invention forms a dense structure by positioning silicon nitride nanoparticles in the pores of silicon nitride particles, thereby increasing the surface area between particles, thereby increasing the density and improving the strength, and significantly reducing the surface roughness by densely controlling the surface of the composite during the molding and sintering process. Accordingly, the present invention enables the manufacture of a highly processable silicon nitride ceramic composite having excellent mechanical properties and improved processability. Accordingly, by securing low surface roughness after ceramic processing, reliability can be increased in areas requiring precise control characteristics, such as leak control.

[0097]

[0098] The foregoing has broadly described the features and technical advantages of the present invention to better understand the scope of the claims that follow. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without changing the technical spirit or essential characteristics thereof. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims that follow rather than the detailed description above, and all changes or modifications derived from the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims

A silicon nitride particle having an average diameter of 0.1 to 10 ㎛; silicon nitride nanoparticles positioned in the gaps between the silicon nitride particles and having an average diameter of 1 to 50 nm; and a sintering aid; A highly processable silicon nitride ceramic composite characterized in that the silicon nitride particles, silicon nitride nanoparticles, and sintering aid are included in a molar ratio of 80 to 95: 2 to 20: 5 to 20, so that the silicon nitride particles and silicon nitride nanoparticles form a dense structure and control surface roughness.

2. In paragraph 1, A highly processable silicon nitride ceramic composite characterized by a surface roughness of up to 0.10 μm.

3. A step of preparing a ceramic raw material mixture by adding and stirring ceramic raw material powder into a dispersion solvent and then further adding and stirring organic binder; A step of producing a ceramic raw material slurry by crushing and mixing the above ceramic raw material mixture through a milling process; A step of manufacturing ceramic granules by spray drying the above ceramic raw material slurry; A step of manufacturing a ceramic molded body by pressurizing and molding the above ceramic granules; and It is manufactured including a step of heat-treating the ceramic molded body to remove the organic binder and then sintering it to manufacture a ceramic composite; The above-mentioned manufactured ceramic composite is characterized by being a highly processable silicon nitride ceramic composite according to claim 1 or claim 2. Method for manufacturing a highly processable silicon nitride ceramic composite.

4. In paragraph 3, The steps for manufacturing the above ceramic granules are: A method for producing a highly processable silicon nitride ceramic composite, characterized in that the above ceramic raw material slurry is spray-dried at 100 to 200°C to produce ceramic granules.

5. In paragraph 3, A method for manufacturing a highly processable silicon nitride ceramic composite, characterized in that in the step of manufacturing the ceramic composite, the sintering is performed at 1500 to 2500°C for 2 to 24 hours.

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