A method for preparing silicon carbide / silicon nitride porous wave-absorbing ceramic by using lignite

Abstract

The application discloses a method for preparing silicon carbide / silicon nitride porous wave-absorbing ceramics by using lignite, and belongs to the field of wave-absorbing ceramics. The method aims at solving the problem that the prior art cannot prepare silicon carbide / silicon nitride porous wave-absorbing ceramics by using lignite. The preparation method comprises the following steps: firstly, uniformly mixing lignite, a silicon source and a foaming agent, and then performing compression molding; and secondly, performing carbonization reaction and nitridation reaction. The application is used for preparing silicon carbide / silicon nitride porous wave-absorbing ceramics by using lignite.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of wave-absorbing ceramics. BACKGROUND

[0002] Lignite is a kind of brown or dark brown coal with relatively high moisture content and low degree of coalification. China has abundant lignite reserves, which are widely distributed and have great development potential. However, in order to meet the needs of sustainable development in the future, it is necessary to liberate lignite from its traditional use as a fuel and shift to higher value-added utilization. Porous wave-absorbing ceramics have important application value in the fields of electromagnetic wave absorption and radio frequency shielding, and are crucial to the fields of electronic communication and military technology. They can effectively reduce the reflection and propagation of electromagnetic waves, and improve the performance and safety of systems. However, the high cost of raw materials and the complex preparation process have been important limiting factors for the large-scale production of porous wave-absorbing ceramics.

[0003] Therefore, using cheap lignite to manufacture silicon carbide / silicon nitride porous wave-absorbing ceramics can further promote the industrialization of porous wave-absorbing ceramics and realize the high value-added utilization of lignite. This is of great significance for promoting energy diversification, improving the stability of energy supply, and promoting sustainable economic development. However, the prior art cannot use lignite to manufacture silicon carbide / silicon nitride porous wave-absorbing ceramics. SUMMARY

[0004] The present application solves the problem that the prior art cannot use lignite to manufacture silicon carbide / silicon nitride porous wave-absorbing ceramics, and provides a method for preparing silicon carbide / silicon nitride porous wave-absorbing ceramics using lignite.

[0005] A method for preparing silicon carbide / silicon nitride porous wave-absorbing ceramics using lignite, which is completed according to the following steps:

[0006] I. Mix lignite, silicon source and foaming agent uniformly by ball milling, and then press into a shaped body to obtain a press-shaped body;

[0007] The mass ratio of lignite to silicon source is (1-3):1; the mass of the foaming agent is 1% to 10% of the total mass of lignite and silicon source;

[0008] II. Place the press-shaped body in a graphite crucible, then introduce N2 gas into the tube furnace, and sequentially perform carbonization reaction and nitridation reaction on the press-shaped body to obtain silicon carbide / silicon nitride porous wave-absorbing ceramics.

[0009] The present application has the following advantages:

[0010] The preparation method of the present application is simple, the process is easy to control, and is suitable for large-scale industrial production, the present application uses large lignite as raw material, reduces the cost, realizes the high value-added resource utilization of lignite to the maximum extent, and improves the comprehensive utilization ability of lignite in China.

[0011] The present application is used for a method for preparing silicon carbide / silicon nitride porous wave-absorbing ceramic by using lignite. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The XRD spectrum of the lignite described in step one of the embodiment;

[0013] Figure 2 The XRD spectrum of the silicon carbide / silicon nitride porous wave-absorbing ceramic prepared in example one;

[0014] Figure 3 The micro-morphology graph of the silicon carbide / silicon nitride porous wave-absorbing ceramic prepared in example one with a scale of 2 microns;

[0015] Figure 4 The micro-morphology graph of the silicon carbide / silicon nitride porous wave-absorbing ceramic prepared in example one with a scale of 1 micron;

[0016] Figure 5 The pore size distribution graph of the silicon carbide / silicon nitride porous wave-absorbing ceramic prepared in example one;

[0017] Figure 6 The wave-absorbing performance graph of the silicon carbide / silicon nitride porous wave-absorbing ceramic prepared in example one. DETAILED DESCRIPTION

[0018] Specific embodiment one: the present embodiment is a method for preparing silicon carbide / silicon nitride porous wave-absorbing ceramic by using lignite, which is completed according to the following steps:

[0019] I. The lignite, silicon source and foaming agent are ball-milled and uniformly mixed, and then are pressed into a shaped block;

[0020] The mass ratio of the lignite to the silicon source is (1-3):1; the mass of the foaming agent is 1% to 10% of the total mass of the lignite and the silicon source;

[0021] II. The shaped block is placed in a graphite crucible, and then N2 gas is introduced into a tube furnace, and the shaped block is subjected to carbonization reaction and nitridation reaction in sequence, to obtain silicon carbide / silicon nitride porous wave-absorbing ceramic.

[0022] The present embodiment has the following beneficial effects:

[0023] The preparation of the porous wave-absorbing ceramic of silicon carbide / nitride silicon is realized by introducing the interaction of the powder phase solid (silicon source and foaming agent) and the carbon component in the lignite in the high-temperature N2 gas.

[0024] Specific embodiment two: the difference between the embodiment and the specific embodiment one is that the silicon source in step one is one or a combination of several of waste silicon powder, fly ash, silicon dioxide and organosilicon.

[0025] Specific embodiment three: the difference between the embodiment and the specific embodiment one or two is that the foaming agent in step one is one or a combination of several of wood fiber, starch, aluminum oxide, silicate and aluminate.

[0026] Specific embodiment four: the difference between the embodiment and the specific embodiment one to three is that the ball milling in step one is specifically under the condition that the rotating speed is 200r / min-800r / min, the ball-to-material ratio is (2-6):1, and the ball milling time is 6h-24h.

[0027] Specific embodiment five: the difference between the embodiment and the specific embodiment one to four is that the diameter of the milling ball is 1.6mm-2mm, and the material is zirconium oxide.

[0028] Specific embodiment six: the difference between the embodiment and the specific embodiment one to five is that the pressing forming in step one is specifically under the condition that the pressure is 20MPa-200MPa.

[0029] Specific embodiment seven: the difference between the embodiment and the specific embodiment one to six is that the length of the pressing formed block in step one is 50mm-150mm, the width is 30mm-40mm, and the thickness is 10mm-20mm.

[0030] Specific embodiment eight: the difference between the embodiment and the specific embodiment one to seven is that the N2 gas is introduced into the tube furnace at a flow rate of 20mL / min-100mL / min for carbonization and nitridation in step two.

[0031] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the carbonization reaction in step two is specifically under the condition of nitrogen atmosphere and temperature of 1100-1300℃, and the holding time is 4-12h. The others are the same as specific embodiments one to eight.

[0032] Specific embodiment ten: the difference between this embodiment and one of the specific embodiments one to nine is that the nitridation reaction in step two is specifically under the condition of nitrogen atmosphere, first heated to 500-950℃ at a rate of 5-10℃ / min, then heated to 1100-1200℃ at a rate of 1-3℃ / min, then heated to 1250-1350℃ at a rate of 5-10℃ / min, and finally heated to 1400-1550℃ at a rate of 2.5-5℃ / min, and the holding time is 6-10h at the temperature of 1400-1550℃, and the cooling rate is 5-10℃ / min after sintering. The others are the same as specific embodiments one to nine.

[0033] The beneficial effects of the present application are verified by the following examples:

[0034] Example one:

[0035] A method for preparing silicon carbide / silicon nitride porous wave-absorbing ceramic by lignite is completed by the following steps:

[0036] I. The lignite, silicon source and foaming agent are ball-mixed uniformly, and then pressed into a shaped block;

[0037] The mass ratio of the lignite to the silicon source is 1.25:1; the mass of the foaming agent is 10% of the total mass of the lignite and the silicon source;

[0038] II. The shaped block is placed in a graphite crucible, and then N2 gas is introduced into the tube furnace to sequentially perform carbonization reaction and nitridation reaction on the shaped block to obtain silicon carbide / silicon nitride porous wave-absorbing ceramic.

[0039] The silicon source in step one is waste silicon powder, and the raw material source is Inner Mongolia Haitaihua Material Technology Co., Ltd. The lignite in step one is sourced from Zalainuoer Coal Industry Co., Ltd. The composition of the lignite is specifically 16% of water content, 12% of ash content, 60% of organic carbon content, and 12% of inorganic carbon content.

[0040] The foaming agent in step one is wood fiber.

[0041] The ball-milling in step one is specifically under the condition of rotation speed of 500r / min and ball-to-material ratio of 6:1 for 6h; the ball diameter is 2mm, and the material is zirconia.

[0042] The pressing forming in step one is specifically under the condition of a pressure of 200 MPa.

[0043] The pressing forming block in step one has a length of 50 mm, a width of 30 mm and a thickness of 10 mm.

[0044] In step two, the carbonization reaction and the nitridation reaction are carried out by introducing N2 into the tube furnace at a flow rate of 40 mL / min, and the purity of the N2 is ≥99.99%.

[0045] The carbonization reaction in step two is specifically carried out under the condition of a nitrogen atmosphere and a temperature of 1200℃ for 4 h.

[0046] The nitridation reaction in step two is specifically carried out under the condition of a nitrogen atmosphere, first by increasing the temperature to 950℃ at a rate of 5℃ / min, then by increasing the temperature to 1200℃ at a rate of 3℃ / min, then by increasing the temperature to 1350℃ at a rate of 5℃ / min, then by increasing the temperature to 1550℃ at a rate of 2.5℃ / min, and then by keeping the temperature at 1550℃ for 10 h, and then by decreasing the temperature to room temperature at a rate of 5℃ / min.

[0047] Figure 1 The XRD spectrum of the lignite in step one of the embodiment; as shown in the figure, the carbonaceous substance in the lignite is in an amorphous state, and such amorphous carbonaceous substance usually has high activity in chemical reactions.

[0048] Figure 2 The XRD spectrum of the SiC / Si3N4 porous wave-absorbing ceramic prepared in Example 1; as shown in the figure, strong diffraction peaks of SiC and Si3N4 are generated in the final product, which indicates that the SiC component is introduced by the method in the embodiment, and the SiC / Si3N4 porous ceramic is successfully prepared by the method in the embodiment.

[0049] Figure 3 The micro-morphology graph of the SiC / Si3N4 porous wave-absorbing ceramic prepared in Example 1, with a scale of 2 μm; Figure 4 The micro-morphology graph of the SiC / Si3N4 porous wave-absorbing ceramic prepared in Example 1, with a scale of 1 μm; as shown in the figure, the reaction product is porous under the N2 atmosphere.

[0050] Figure 5 The pore size distribution graph of the SiC / Si3N4 porous wave-absorbing ceramic prepared in Example 1; as shown in the figure, the porous wave-absorbing ceramic has three kinds of customized pore size structures, and the contents of the three kinds of pore size structures from high to low are 2.84 μm, 4.10 μm and 7.23 μm, and the three kinds of different pore size structures can significantly enhance the electromagnetic wave attenuation effect of the porous wave-absorbing ceramic.

[0051] The silicon carbide / silicon nitride porous wave-absorbing ceramic is prepared into a coaxial ring ceramic block with an outer diameter of 7.0 mm, an inner diameter of 3.0 mm and a thickness of 1.0 mm to 5.0 mm, and then wave-absorbing performance test is carried out; Figure 6 The wave-absorbing performance chart of the silicon carbide / silicon nitride porous wave-absorbing ceramic prepared for Example One is shown in the figure. As can be seen from the figure, when the ceramic thickness is 5 mm, the absorption effect on electromagnetic waves is best, the attenuation amount is -34.5 dB, and the center frequency is 6.74 GHz.

Claims

1. A method for preparing a porous SiC / SiN wave-absorbing ceramic using lignite, characterized in that It is completed according to the following steps: I. The lignite, silicon source and foaming agent are uniformly mixed by ball milling, and then are pressed to form a pressed block; The mass ratio of the lignite to the silicon source is 1.25:1; the mass of the foaming agent is 10% of the total mass of the lignite and the silicon source; II. The pressed block is placed in a graphite crucible, and then N2 gas is introduced into a tube furnace to sequentially perform carbonization reaction and nitridation reaction on the pressed block to obtain a porous SiC / Si3N4 wave-absorbing ceramic; the porous SiC / Si3N4 wave-absorbing ceramic has an attenuation of -34.5 dB at a center frequency of 6.74 GHz; The silicon source in step I is waste silicon powder; The foaming agent in step I is wood fiber; The ball milling in step I is specifically carried out at a rotation speed of 500 r / min and a ball-to-material ratio of 6:1 for 6 h; the diameter of the milling ball is 2 mm, and the material of the milling ball is zirconia; The pressing in step I is specifically carried out at a pressure of 200 MPa; The pressed block in step I has a length of 50 mm, a width of 30 mm and a thickness of 10 mm; In step II, the N2 gas is introduced into the tube furnace at a flow rate of 40 mL / min to perform the carbonization reaction and the nitridation reaction; the purity of the N2 gas is ≥99.99%; The carbonization reaction in step II is specifically carried out under a nitrogen atmosphere at a temperature of 1200℃ for 4 h; The nitridation reaction in step II is specifically carried out under a nitrogen atmosphere, first at a rate of 5℃ / min to 950℃, then at a rate of 3℃ / min to 1200℃, then at a rate of 5℃ / min to 1350℃, and finally at a rate of 2.5℃ / min to 1550℃; after the temperature is kept at 1550℃ for 10 h, the sintered product is cooled to room temperature at a rate of 5℃ / min.

Images