Black silicon nitride ceramic and method for producing the same

Abstract

The present application belongs to the technical field of nitride ceramics. The present application provides a black silicon nitride ceramic and a preparation method thereof. The preparation method comprises the following steps: mixing silicon nitride, niobium oxide, a dispersing agent and water to obtain a slurry; sequentially performing sand milling, drying and sieving on the slurry to obtain silicon nitride nano-powder; sequentially performing dry pressing pre-forming and cold isostatic pressing forming on the silicon nitride nano-powder to obtain a ceramic blank; and performing hot pressing sintering on the ceramic blank to obtain the black silicon nitride ceramic. The black silicon nitride ceramic prepared by the present application enriches the color of silicon nitride ceramic, has a dense structure, is a hexagonal crystal, has a hardness greater than 17.9 GPa, has a toughness greater than 11.0 MPa·m 1 / 2 , has excellent mechanical properties, and has a strength higher than 1830 MPa; compared with the zirconium oxide ceramic commonly used for the back plate of a mobile phone, the black silicon nitride ceramic has a smaller density, a lighter texture and a more smooth signal transmission; and the preparation method is simple and has a low cost.

Description

Technical Field

[0001] This invention relates to the field of nitride ceramics technology, and more particularly to a black silicon nitride ceramic and its preparation method. Background Technology

[0002] Silicon nitride ceramics possess advantages such as high strength, low density, good toughness, high thermal conductivity, good thermal shock resistance, corrosion resistance, and high-temperature resistance, making them widely used in metallurgy, machinery, aerospace, chemical engineering, electronics, and biomedicine. In recent years, with the advancement of communication technology, mobile phones and other electronic products have become necessities in our lives. To meet the requirements of future mobile phone 5G communication, wireless charging, and OLED displays, more ceramic products are needed to replace metal components. Currently, while the hardness and fracture toughness of silicon nitride ceramics are continuously improving, most silicon nitride ceramics are only available in a single color, typically gray or dark gray. Therefore, how to prepare silicon nitride ceramics with more colors has become a key research focus.

[0003] Furthermore, although most current mobile phone back panels use zirconia ceramic, zirconia ceramic has a high density, weak impact resistance, and high industrial production costs. Silicon nitride ceramic, on the other hand, not only has a lower density and lighter weight, making it easier to carry, but also has higher hardness, better impact resistance, and mechanical properties that are more suitable for practical use and better able to meet the requirements of future communication technology development. Therefore, researching and developing a black silicon nitride ceramic with low manufacturing cost, excellent mechanical properties, high hardness, low density, and the ability to meet the requirements of future communication technology development has promising application prospects. Summary of the Invention

[0004] The purpose of this invention is to provide a black silicon nitride ceramic and its preparation method, addressing the shortcomings of existing technologies.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing black silicon nitride ceramics, comprising the following steps:

[0007] 1) Mix silicon nitride, niobium oxide, dispersant, and water to obtain a slurry;

[0008] 2) The slurry is sequentially milled, dried and sieved to obtain silicon nitride nanopowder;

[0009] 3) The silicon nitride nanopowder is subjected to dry pressing preforming and cold isostatic pressing in sequence to obtain a ceramic body;

[0010] 4) The ceramic blank is hot-pressed and sintered to obtain black silicon nitride ceramic.

[0011] Preferably, the mass ratio of silicon nitride to niobium oxide in step 1) is 945–995:5–55.

[0012] Preferably, the dispersant in step 1) is one or more of polyammonium methacrylate, ammonium polyacrylate, sodium tripolyphosphate, polyethylene glycol, and sodium hexametaphosphate; the mass of the dispersant is 0.4-1% of the total mass of silicon nitride and niobium oxide.

[0013] Preferably, the solid content of the slurry in step 1) is 45-55%.

[0014] Preferably, the grinding time in step 2) is 3 to 6 hours, the grinding speed is 1600 to 2700 r / min, the grinding media in the grinding process is zirconia beads, the ball-to-material ratio is 1:1 to 2, and the particle size of the zirconia beads is 0.1 to 0.8 mm.

[0015] Preferably, the drying method in step 2) is spray drying, electric oven drying, or evaporator drying; the mesh size of the silicon nitride nanoparticles is 80-120 mesh.

[0016] Preferably, the pressure of the dry pressing preforming in step 3) is 5-15 MPa, and the time of the dry pressing preforming is 50-70 s; the pressure of the cold isostatic pressing is 150-250 MPa, and the time of the cold isostatic pressing is 180-220 s.

[0017] Preferably, the hot pressing sintering temperature in step 4) is 1600-1800℃, the hot pressing sintering pressure is 5-15MPa, and the hot pressing sintering time is 1-3h.

[0018] Preferably, the hot pressing sintering in step 4) is performed under vacuum conditions, with a vacuum degree of 6.5 × 10⁻⁶. -4 ~6.7×10 -4 Pa.

[0019] The present invention also provides a black silicon nitride ceramic prepared by the aforementioned preparation method.

[0020] The beneficial effects of this invention include the following:

[0021] 1) The sand milling technology of the present invention can refine the slurry, increase its activity, shorten the mass transfer distance between particles, and enable the colorant niobium oxide to be mixed evenly, thus overcoming the defects of the traditional solid-state reaction method, which easily causes uneven color distribution of ceramics, excessively high sintering temperature, and low production efficiency.

[0022] 2) The black silicon nitride ceramic prepared by this invention enriches the color of silicon nitride ceramics, has a dense structure, is a hexagonal crystal, has a hardness greater than 17.9 GPa, and a toughness greater than 11.0 MPa·m. 1 / 2 The ceramic exhibits excellent mechanical properties, with a strength exceeding 1830 MPa, indicating that the doping of niobium oxide as a colorant did not significantly reduce the mechanical properties of the ceramic.

[0023] 3) Compared with the zirconium oxide ceramic commonly used in mobile phone back panels, the black silicon nitride ceramic prepared by this invention has a lower density, lighter weight, and smoother signal transmission, thus having a larger application market.

[0024] 4) The method for preparing black silicon nitride ceramics in this invention is simple, has a short preparation cycle, low cost, is safe and pollution-free, and is suitable for mass production. Attached Figure Description

[0025] Figure 1 The ultraviolet-visible absorption spectrum of the black silicon nitride ceramic prepared in Example 5 of this invention is shown.

[0026] Figure 2 The image shows the XRD pattern of the black silicon nitride ceramic prepared in Example 5 of this invention.

[0027] Figure 3 This is a physical image of the black silicon nitride ceramic prepared in Example 5 of the present invention. Detailed Implementation

[0028] This invention provides a method for preparing black silicon nitride ceramics, comprising the following steps:

[0029] 1) Mix silicon nitride, niobium oxide, dispersant, and water to obtain a slurry;

[0030] 2) The slurry is sequentially milled, dried and sieved to obtain silicon nitride nanopowder;

[0031] 3) The silicon nitride nanopowder is subjected to dry pressing preforming and cold isostatic pressing in sequence to obtain a ceramic body;

[0032] 4) The ceramic blank is hot-pressed and sintered to obtain black silicon nitride ceramic.

[0033] In this invention, the mass ratio of silicon nitride to niobium oxide in step 1) is preferably 945-995:5-55, more preferably 955-985:15-45, and even more preferably 965-975:20-35.

[0034] In this invention, the dispersant in step 1) is preferably one or more of polyammonium methacrylate, ammonium polyacrylate, sodium tripolyphosphate, polyethylene glycol, and sodium hexametaphosphate; the mass of the dispersant is preferably 0.4-1% of the total mass of silicon nitride and niobium oxide, more preferably 0.5-0.8%, and even more preferably 0.6-0.7%.

[0035] In this invention, the solid content of the slurry in step 1) is preferably 45-55%, more preferably 48-52%, and even more preferably 50%.

[0036] In this invention, the grinding time in step 2) is preferably 3-6 hours, more preferably 3.5-5 hours, and even more preferably 4-4.5 hours; the grinding speed is preferably 1600-2700 r / min, more preferably 1800-2500 r / min, and even more preferably 2000-2200 r / min; the grinding media in the grinding process is preferably zirconia beads; the ball-to-material ratio is preferably 1:1-2, more preferably 1:1.5; the particle size of the zirconia beads is preferably 0.1-0.8 mm, more preferably 0.3-0.6 mm, and even more preferably 0.4-0.5 mm.

[0037] In this invention, the drying method in step 2) is preferably spray drying, electric oven drying, or evaporator drying; the temperature of the electric oven drying is preferably 85-100℃, more preferably 90-95℃, and the drying time is preferably 5-24h, more preferably 10-20h, and even more preferably 14-16h; the atomization frequency of the spray drying is preferably 40-60Hz, more preferably 50Hz, the inlet air temperature of the spray drying is preferably 220-270℃, more preferably 240-260℃, and even more preferably 250℃, the outlet air temperature of the spray drying is preferably 80-120℃, more preferably 90-110℃, and even more preferably 100℃, and the spray drying time is preferably 4-6h, more preferably 4.5-5.5h, and even more preferably 5h; the temperature of the evaporator drying is preferably 70-100℃, more preferably 80-90℃, and even more preferably 85℃, and the evaporator drying time is preferably 8-12h, more preferably 9-11h, and even more preferably 10h.

[0038] In this invention, centrifugal dehydration is preferably performed before drying in the electric heating oven in step 2).

[0039] In this invention, the mesh size of the silicon nitride nanopowder in step 2) is preferably 80-120 mesh, more preferably 90-110 mesh, and even more preferably 100 mesh.

[0040] In this invention, the pressure of dry pressing preforming in step 3) is preferably 5-15 MPa, more preferably 8-12 MPa, and even more preferably 10 MPa; the time of dry pressing preforming is preferably 50-70 s, more preferably 55-65 s, and even more preferably 60 s; the pressure of cold isostatic pressing is preferably 150-250 MPa, more preferably 180-220 MPa, and even more preferably 200 MPa; the time of cold isostatic pressing is preferably 180-220 s, more preferably 190-210 s, and even more preferably 200 s.

[0041] In this invention, the temperature of hot pressing sintering in step 4) is preferably 1600-1800℃, more preferably 1650-1750℃, and even more preferably 1700℃; the pressure of hot pressing sintering is preferably 5-15MPa, more preferably 8-12MPa, and even more preferably 10MPa; the time of hot pressing sintering is preferably 1-3h, more preferably 1.5-2.5h, and even more preferably 2h.

[0042] In this invention, the hot pressing sintering in step 4) is preferably performed under vacuum; the vacuum degree is preferably 6.5 × 10⁻⁶. -4 ~6.7×10 -4 Pa, more preferably 6.67 × 10 Pa. -4 Pa.

[0043] The present invention also provides a black silicon nitride ceramic prepared by the aforementioned preparation method.

[0044] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] 960g of silicon nitride, 40g of niobium oxide, 4g of ammonium polymethacrylate and deionized water were mixed to obtain a slurry with a solid content of 50%.

[0047] The slurry was milled for 3 hours in a sand mill with 0.5 mm zirconium oxide beads as grinding media, a ball-to-material ratio of 1:1, and a rotation speed of 2500 r / min. The milled slurry was then dried in an electric heating oven at 95℃ for 24 hours and then sieved to obtain silicon nitride nanopowder with a mesh size of 100.

[0048] Silicon nitride nanoparticles were dry-pressed for 50 seconds at 5 MPa, and then cold-isostatically pressed for 180 seconds at 150 MPa to obtain a ceramic preform.

[0049] The ceramic preform was placed under vacuum (vacuum degree 6.67 × 10⁻⁶). -4 Black silicon nitride ceramics were obtained by hot pressing and sintering at 1600℃ and 5MPa for 1 hour.

[0050] Example 2

[0051] 990g of silicon nitride, 10g of niobium oxide, 4.5g of ammonium polyacrylate and deionized water were mixed to obtain a slurry with a solid content of 45%.

[0052] The slurry was milled for 4 hours in a sand mill with zirconia beads of 0.8 mm in diameter as the grinding media, a ball-to-material ratio of 1:1.5, and a rotation speed of 2700 r / min. The milled slurry was then spray-dried for 5 hours at an atomization frequency of 50 Hz, an inlet air temperature of 250 ℃, and an outlet air temperature of 100 ℃. After that, it was sieved to obtain silicon nitride nanopowder with a mesh size of 80.

[0053] Silicon nitride nanopowder was dry-pressed for 60 seconds at 8 MPa, and then cold-isostatically pressed for 200 seconds at 180 MPa to obtain a ceramic preform.

[0054] The ceramic preform was placed under vacuum (vacuum degree 6.5 × 10⁻⁶). -4 Black silicon nitride ceramics were obtained by hot pressing and sintering at 1650℃ and 8MPa for 2 hours.

[0055] Example 3

[0056] 995g of silicon nitride, 5g of niobium oxide, 6g of sodium tripolyphosphate and deionized water were mixed to obtain a slurry with a solid content of 55%.

[0057] The slurry was milled for 3 hours in a sand mill with zirconia beads of 0.6 mm in diameter as the grinding media, a ball-to-material ratio of 1:2, and a rotation speed of 2300 r / min. The milled slurry was then dried in an evaporator at 80 °C for 10 hours and then sieved to obtain silicon nitride nanopowder with a mesh size of 120.

[0058] Silicon nitride nanoparticles were dry-pressed for 70 seconds at 5 MPa, and then cold-isostatically pressed for 220 seconds at 200 MPa to obtain a ceramic preform.

[0059] The ceramic preform was placed under vacuum (vacuum degree 6.7 × 10⁻⁶). -4 Black silicon nitride ceramics were obtained by hot pressing and sintering at 1700℃ and 10MPa for 3 hours.

[0060] Example 4

[0061] 945g of silicon nitride, 55g of niobium oxide, 8g of polyethylene glycol 2000 and deionized water were mixed to obtain a slurry with a solid content of 50%.

[0062] The slurry was milled for 6 hours in a sand mill with 0.6 mm zirconium oxide beads as grinding media, a ball-to-material ratio of 1:1.4, and a rotation speed of 1600 r / min. The milled slurry was then centrifuged and dehydrated (centrifugation speed of 10000 r / min for 20 min), and then dried in an electric heating oven at 90℃ for 8 hours. Finally, it was sieved to obtain silicon nitride nanopowder with a mesh size of 100.

[0063] Silicon nitride nanoparticles were dry-pressed for 55 seconds at 12 MPa and then cold-isostatically pressed for 190 seconds at 220 MPa to obtain a ceramic preform.

[0064] The ceramic preform was placed under vacuum (vacuum degree 6.67 × 10⁻⁶). -4 Black silicon nitride ceramics were obtained by hot pressing and sintering at 1750℃ and 15MPa for 2.5h.

[0065] Example 5

[0066] 950g of silicon nitride, 50g of niobium oxide, 10g of sodium hexametaphosphate and deionized water were mixed to obtain a slurry with a solid content of 50%.

[0067] The slurry was milled for 5 hours in a sand mill with zirconia beads of 0.3 mm in diameter as the grinding media, a ball-to-material ratio of 1:1.2, and a rotation speed of 2500 r / min. The milled slurry was then dried in an electric oven at 90 °C for 10 hours and then sieved to obtain silicon nitride nanopowder with a mesh size of 90 mesh.

[0068] Silicon nitride nanoparticles were dry-pressed at 15 MPa for 65 s and then cold-isostatically pressed at 250 MPa for 210 s to obtain a ceramic preform.

[0069] The ceramic preform was placed under vacuum (vacuum degree 6.7 × 10⁻⁶). -4 Black silicon nitride ceramics were obtained by hot pressing and sintering at 1800℃ and 10MPa for 2 hours.

[0070] Depend on Figures 1-3 It can be seen that the black silicon nitride ceramic prepared in this embodiment has a dense structure, uniform color, is a hexagonal crystal, and has low ultraviolet spectral reflectance.

[0071] The performance test results of the black silicon nitride ceramics prepared in Examples 1 to 5 are shown in Table 1.

[0072] Table 1. Performance test results of the black silicon nitride ceramics prepared in Examples 1-5

[0073] Example Hardness (GPa) <![CDATA[Toughness (MPa·m 1 / 2 )]]> Strength (MPa) Example 1 17.96 11.08 1832.64 Example 2 18.09 11.44 1845.90 Example 3 18.16 11.16 1853.05 Example 4 18.23 11.10 1860.19 Example 5 18.28 11.50 1860.19

[0074] As shown in Table 1, the black silicon nitride ceramic prepared by this invention has good hardness and toughness, excellent mechanical properties, and a strength higher than 1830 MPa, indicating that the doping of the colorant niobium oxide did not significantly reduce the mechanical properties of the ceramic.

[0075] The preparation method of this invention is simple, has a short preparation cycle, low cost, is safe and pollution-free, and is suitable for mass production.

[0076] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing black silicon nitride ceramic, characterized in that, It includes the following steps: 1) Mix silicon nitride, niobium oxide, dispersant, and water to obtain a slurry; 2) The slurry is sequentially milled, dried, and sieved to obtain silicon nitride nanopowder; 3) The silicon nitride nanopowder is subjected to dry pressing preforming and cold isostatic pressing in sequence to obtain a ceramic body; 4) The ceramic body is hot-pressed and sintered to obtain black silicon nitride ceramic; Step 4) The hot pressing sintering temperature is 1600-1800℃, the hot pressing sintering pressure is 5-15MPa, and the hot pressing sintering time is 1-3h. Step 4) The hot pressing sintering is performed under vacuum conditions, with a vacuum degree of 6.5 × 10⁻⁶. -4 ~6.7×10 -4 Pa.

2. The preparation method according to claim 1, characterized in that, In step 1), the mass ratio of silicon nitride to niobium oxide is 945–995:5–55.

3. The preparation method according to claim 1 or 2, characterized in that, The dispersant in step 1) is one or more of polyammonium methacrylate, ammonium polyacrylate, sodium tripolyphosphate, polyethylene glycol, and sodium hexametaphosphate; the mass of the dispersant is 0.4-1% of the total mass of silicon nitride and niobium oxide.

4. The preparation method according to claim 3, characterized in that, The solid content of the slurry in step 1) is 45-55%.

5. The preparation method according to claim 4, characterized in that, Step 2) The grinding time is 3 to 6 hours, and the grinding speed is 1600 to 2700 r / min. The grinding media in the grinding process is zirconia beads, the ball-to-material ratio is 1:1 to 2, and the particle size of the zirconia beads is 0.1 to 0.8 mm.

6. The preparation method according to claim 4 or 5, characterized in that, Step 2) The drying method is spray drying, electric oven drying or evaporator drying; the mesh size of the silicon nitride nanoparticles is 80-120 mesh.

7. The preparation method according to claim 6, characterized in that, Step 3) The pressure of dry pressing preforming is 5-15 MPa, and the time of dry pressing preforming is 50-70 s; the pressure of cold isostatic pressing is 150-250 MPa, and the time of cold isostatic pressing is 180-220 s.

8. The black silicon nitride ceramic prepared by the preparation method according to any one of claims 1 to 7.

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