A method for preparing silicon carbide materials using coal gasification slag

Abstract

The invention discloses a method for preparing silicon carbide materials by using coal gasification slag, belonging to the field of solid waste recycling. The solution of the invention includes first pre-treating the coal gasification slag, then performing acid leaching, water washing, suction filtration and drying on the pre-treated coal gasification slag, and then performing Joule heating treatment. After calcination, silicon carbide is obtained; in the Joule heating treatment, the discharge voltage is set to 120V-150V, and the number of discharges is 1-5 times. By performing Joule heating treatment on the coal gasification slag, the reaction time of each Joule heating reaction is extremely short, greatly reducing the energy consumption, and sharply shortening the reaction time, solving the technical problem of high energy consumption caused by the long reaction time in the traditional carbothermal reduction for preparing silicon carbide materials in the prior art.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste recycling, and particularly relates to a method for preparing silicon carbide materials by using coal gasification slag. Background Art

[0002] Coal gasification, as the leading industry of coal chemical industry, plays an important role in the efficient and clean utilization of coal. It is a process in which solid fuels such as coal, coke or semi-coke react with gasifying agents under high temperature and high pressure to produce gaseous products and a certain amount of slag. However, at present, the treatment method of coal gasification slag is still mainly open-air stacking, resulting in waste of resources.

[0003] Traditional carbothermal reduction to prepare silicon carbide materials generally uses large resistance furnaces. Such devices have a long reaction time and high energy consumption. Chinese Patent CN104774023A discloses a lightweight ceramsite prepared by using fly ash and gasification slag, its preparation method and application. Although this preparation method also uses gasification slag as a raw material, the high-temperature reaction (i.e., the firing process) in its preparation process needs to go through heating and heat preservation at multiple temperature stages and needs to be completed in a resistance furnace or a kiln, resulting in an overly long reaction time for the entire reaction process, thus leading to an increase in energy consumption. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing silicon carbide materials by using coal gasification slag, and solve the technical problem of high energy consumption caused by long reaction time in the prior art when preparing silicon carbide materials by traditional carbothermal reduction.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for preparing silicon carbide materials by using coal gasification slag, which includes first pretreating the coal gasification slag, then performing acid leaching, water washing, suction filtration and drying on the pretreated coal gasification slag, and then performing Joule heating treatment. After calcination, silicon carbide is obtained; in the Joule heating treatment, the discharge voltage is set to 120V - 150V, and the number of discharges is 1 - 5 times.

[0007] Preferably, any one of hydrogen, helium or a mixed gas is introduced in the Joule heating treatment; the mixed gas is a mixed gas of hydrogen and helium.

[0008] Preferably, in the mixed gas, the mass ratio of hydrogen to helium is 1:1.

[0009] Preferably, the solution used in the acid leaching treatment includes an HCl solution with a molar concentration of 1 - 3mol / L, an H 2 SO 4 solution or an HCl and H 2 SO4 any one of the mixed solutions; the mixed solution is a mixed solution of HCl and H 2 SO 4 solution.

[0010] Preferably, in the mixed solution, the volume ratio of HCl and H 2 SO 4 solution is 1:1.

[0011] More preferably, the acid leaching treatment is to mix and react the pretreated coal gasification slag with any one of the above HCl solution, H 2 SO 4 solution or mixed solution at a dosage ratio of 1 g:20 mL, and the reaction conditions are: reacting at 85 - 95 °C for 2.5 - 3 hours.

[0012] Preferably, the coal gasification slag after acid leaching is washed with water until neutral.

[0013] Preferably, the drying temperature is 105 - 110 °C and the time is 8 - 12 h.

[0014] Preferably, the calcination treatment is to heat up to 650 - 700 °C and then keep warm for 30 - 40 min.

[0015] Preferably, the pretreatment includes soaking the coal gasification slag in hydrogen peroxide and then performing a drying treatment.

[0016] Preferably, the soaking time is 1 - 2 h, the drying temperature is 105 - 110 °C, and the drying time is 8 - 12 h.

[0017] More preferably, the coal gasification slag is filled in a quartz tube, both ends are blocked with conductive graphite blocks, electrodes are connected and placed in a reaction chamber, and any one of the above reaction gases is introduced.

[0018] More preferably, the quartz tube used for the Joule heating has a diameter of 12 mm, a wall thickness of 3 mm, and a length of 6 cm; the graphite block is a cylinder with a diameter smaller than the inner diameter of the quartz tube and a length of 5 mm.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides a method for preparing silicon carbide materials from coal gasification slag. By subjecting the coal gasification slag to Joule heating treatment, setting the discharge voltage to 120V - 150V and the number of discharges to 1 - 5 times, the Joule heating reaction time for each time is extremely short, only requiring less than 1 s, greatly reducing energy consumption and shortening the reaction time. In addition, in the preparation process of the present invention, the raw material is only coal gasification slag, and the carbon in the coal gasification slag acts as a reducing agent and a conductive phase. On the one hand, the role of the reducing agent reduces energy consumption, and on the other hand, no other additives need to be added, thus simplifying the entire preparation process and reducing production costs; the role of the conductive phase helps the reaction to proceed uniformly and the formation of silicon carbide crystals.

[0021] Further, introducing any one of hydrogen, helium or a mixed gas during the Joule heating treatment helps to promote the chemical reaction between carbon and silicon elements in the coal gasification slag during heating, promotes the reaction rate, and improves the formation efficiency and quality of silicon carbide.

[0022] Further, the mass ratio of hydrogen to helium is controlled at 1:1, which helps to optimize the reaction conditions, ensure the stability of the reaction process and obtain silicon carbide materials with a higher content.

[0023] Further, by setting specific discharge voltage and number of discharges, the energy input of the Joule heating treatment can be precisely controlled, thereby optimizing the formation conditions of silicon carbide and increasing the content of silicon carbide materials. Experimental data show that the relative content of the silicon carbide materials prepared by this preparation method is as high as 95.67%.

[0024] Further, acid leaching treatment can effectively remove impurities (such as iron, aluminum, calcium and other elements) in the coal gasification slag, improve the purity of the raw material, so that only SiO required for Joule heating 2 and carbon are retained in the coal gasification slag, creating favorable conditions for the subsequent formation of silicon carbide.

[0025] Further, the volume ratio of HCl and H in the mixed solution 2 SO 4 This helps to optimize the effect of acid leaching treatment and improve the removal efficiency of impurities.

[0026] Further, the coal gasification slag after acid leaching is washed with water until neutral, which can completely remove the residual acid solution and avoid affecting the subsequent processing process and product quality.

[0027] Further, specific drying temperature and time are set, which helps to ensure that the coal gasification slag can fully remove moisture during drying, while avoiding changes in the properties of the raw material caused by over-drying.

[0028] Furthermore, the heating temperature and holding time of the calcination treatment help to optimize the formation conditions of silicon carbide and increase the relative content of the silicon carbide material.

[0029] Furthermore, the pretreatment of coal gasification slag by soaking in hydrogen peroxide and drying can remove some impurities, improve the activity of the raw material, and create favorable conditions for the subsequent processing. At the same time, the pretreatment steps are simple and easy to implement, and are easy to be popularized and applied in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 XRD pattern of the silicon carbide material obtained in Example 1;

[0031] Figure 2 XRD pattern of the silicon carbide material obtained in Example 2;

[0032] Figure 3 XRD pattern of the silicon carbide material obtained in Example 3;

[0033] Figure 4 XRD pattern of the silicon carbide material obtained in Example 4;

[0034] Figure 5 XRD pattern of the silicon carbide material obtained in Example 5;

[0035] Figure 6 XRD pattern of the silicon carbide material obtained in Example 6;

[0036] Figure 7 XRD pattern of the silicon carbide material obtained in Example 7;

[0037] Figure 8 XRD pattern of the silicon carbide material obtained in Example 8;

[0038] Figure 9 XRD pattern of the silicon carbide material obtained in Example 9;

[0039] Figure 10 SEM image of the silicon carbide material obtained in Example 1;

[0040] Figure 11 SEM image of the silicon carbide material obtained in Example 9. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition only for the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning as understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0042] The theories or mechanisms described and disclosed herein, whether right or wrong, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0043] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0044] In this article, unless otherwise specified, the terms "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0045] In this article, for the sake of brevity of description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered to be within the scope described in this specification.

[0046] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0047] Conventional instruments and equipment in the art are used in the following examples. For the experimental methods without specific conditions noted in the following examples, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following examples. Unless otherwise stated, commercially available products are used, and their specifications are conventional specifications in the art.

[0048] The present invention uses Joule heating to treat gasification fine slag under different atmospheres, including the following steps:

[0049] (1) The gasification slag soaked in hydrogen peroxide is dried and then subjected to acid leaching. The acid leaching solutions used are 1 mol / L HCl solution, 1 mol / L H 2 SO 4 solution, and a mixed solution of 1 mol / L HCl and H 2 SO 4 (HCl:H 2 SO 4=1: (1), the samples obtained by acid leaching are washed with water, filtered by suction, and dried, and then the acid solution with the best effect is selected;

[0050] (2) Perform Joule heating treatment on it under different atmospheres, and obtain carbon-containing SiC after cooling;

[0051] (3) Finally, calcine to remove the unreacted carbon to obtain high-purity SiC. The discharge voltage of the Joule heating treatment is 120V, the number of treatment times is 1, 3, 5 times, and the reaction atmosphere is H 2 , CH 4 , mixed gas (H 2 : CH 4 = 1:1).

[0052] In the present invention, the prior acid leaching can remove most of the elements such as iron, aluminum, and calcium in the coal gasification slag, so that only SiO 2 and carbon required for Joule heating are retained in the coal gasification slag. Joule heating can raise the temperature to above 3000K in milliseconds, and the high temperature causes the residual carbon in the coal gasification slag to react with SiO 2 to occur a reduction reaction, converting SiO 2 into SiC, and different reaction atmospheres can promote the reaction rate. This provides a new research idea for the recovery of silicon resources in coal gasification slag, which is efficient, green, and low-carbon.

[0053] The principle of Flash Joule Heating (FJH) is that when an electric current passes through a sample, due to the internal resistance of the sample itself, Joule heat is generated under the action of the Joule effect, and the temperature will reach about 3000K in milliseconds. Such a high temperature and heating rate can meet many reactions with high temperature requirements.

[0054] The method for preparing a silicon carbide material using coal gasification slag provided by the present invention not only provides a new idea for treating coal gasification slag, but also the prepared SiC material has great application prospects in the fields of refractory materials, semiconductor materials, and wear-resistant materials.

[0055] The following further describes the present invention in detail with reference to the drawings and embodiments:

[0056] I. Optimization of the acid leaching solution:

[0057] The acid leaching treatment with an acid leaching solution with a molar concentration of 3mol / L includes the following steps:

[0058] 1) Immerse the coal gasification slag in hydrogen peroxide for 1h, and then dry it at 110°C for 12h;

[0059] 2) The dry coal gasification slag prepared in step 1) was mixed with HCl solution with a molar concentration of 3 mol / L, H 2 SO 4 solution and the mixed solution respectively according to the ratio of 1 g: 20 mL, and reacted at 85 °C for 3 hours to produce acid-leached slag.

[0060] The acid leaching treatment of the acid leaching solution with a molar concentration of 2 mol / L includes the following steps:

[0061] 1) Immerse the coal gasification slag in hydrogen peroxide for 1 h, and then dry it at 110 °C for 12 h;

[0062] 2) The dry coal gasification slag prepared in step 1) was mixed with HCl solution with a molar concentration of 2 mol / L, H 2 SO 4 solution and the mixed solution respectively according to the ratio of 1 g: 20 mL, and reacted at 85 °C for 3 hours to produce acid-leached slag.

[0063] The acid leaching treatment of the acid leaching solution with a molar concentration of 1 mol / L includes the following steps:

[0064] 1) Immerse the coal gasification slag in hydrogen peroxide for 1 h, and then dry it at 110 °C for 12 h;

[0065] 2) The dry coal gasification slag prepared in step 1) was mixed with HCl solution with a molar concentration of 1 mol / L, H 2 SO 4 solution and the mixed solution respectively according to the ratio of 1 g: 20 mL, and reacted at 85 °C for 3 hours to produce acid-leached slag.

[0066] The phase compositions of the acid-leached slag generated by the above 3 acid leaching treatments were analyzed by an X-ray fluorescence spectrometer, and the analysis results are shown in Tables 1, 2 and 3.

[0067] Table 1 Relative contents (%) of various phases of the acid-leached slag in the raw materials and 1 mol / L acid solution

[0068]

[0069] Table 2 Relative contents (%) of various phases of the acid-leached slag in the raw materials and 2 mol / L acid solution

[0070]

[0071] Table 3 Relative contents (%) of various phases of the acid-leached slag in the raw materials and 3 mol / L acid solution

[0072]

[0073] According to the obtained results, it is found that the concentration of the mixed acid solution has little effect on the removal effect of elements such as Fe and Al in the coal gasification slag, and the relative content of SiO 2 floats up and down at a relatively low level. Selecting a 1mol / L acid solution for acid leaching treatment of the coal gasification slag is a better choice from the perspective of test cost and economy. In addition, the mixed acid solution has a better removal effect on elements such as Fe and Al, because the relative content of SiO 2 in the coal gasification slag is relatively high after acid leaching, which is beneficial to the subsequent Joule heating of SiO 2 to react with carbon to form SiC. Therefore, a 1mol / L mixed acid solution is preferably selected to treat the coal gasification slag for the subsequent Joule heating treatment in Examples 1 to 9.

[0074] Example 1

[0075] A method for preparing silicon carbide materials using coal gasification slag according to the present invention is specifically implemented according to the following steps:

[0076] 1) Wash the acid-leached coal gasification slag to neutral, then filter it by suction, and finally dry it to constant weight in a drying oven at 110°C for 8 hours;

[0077] 2) Weigh 300 mg of the coal gasification slag prepared in step 2), fill it in a quartz tube, block both ends with conductive graphite blocks, connect the electrodes and put them into the reaction box, and introduce H 2 .

[0078] 3) Turn on the switch of the Joule heating instrument, set the discharge voltage to 120V, click to start charging, when the voltage reaches the set voltage, stop charging, and immediately click to start discharging, which is recorded as 1 time of Joule heating treatment.

[0079] 4) Keep it warm in a calcining furnace at 650°C for 30 minutes to remove the unreacted carbon and obtain silicon carbide.

[0080] In the preparation method of this Example 1, Joule heating is used to raise the temperature to 2734K within 0.8s. Under a hydrogen atmosphere, the reaction rate reaches 25.24 mg / s, and the relative content of the silicon carbide prepared by this method is 6.73%.

[0081] Example 2

[0082] A method for preparing silicon carbide materials using coal gasification slag according to the present invention is specifically implemented according to the following steps:

[0083] 1) Wash the acid-leached coal gasification slag to neutral, then filter it by suction, and finally dry it to constant weight in a drying oven at 107°C for 10 hours;

[0084] 2) Weigh 300 mg of the coal gasification slag prepared in step 1), fill it in a quartz tube, block both ends with conductive graphite blocks, connect the electrodes and place them in the reaction chamber, and introduce H 2 .

[0085] 3) Turn on the Joule heating instrument switch, set the discharge voltage to 135 V, click start charging, when the voltage reaches the set voltage, stop charging, and immediately click start discharging, which is recorded as 1 time of Joule heating treatment.

[0086] 4) Repeat step 3) 3 times.

[0087] 5) Keep it warm in a calcination furnace at 670 °C for 35 min to remove the unreacted carbon and obtain silicon carbide.

[0088] In the preparation method of this Example 2, the heating-up times of the 3 times of Joule heating are 0.8 s, 0.6 s, and 0.5 s respectively, the temperatures are increased to 2725 K, 3016 K, and 3229 K respectively. Under the hydrogen atmosphere, the reaction rate reaches 43.26 mg / s, and the relative content of the silicon carbide prepared by this method is 27.4%.

[0089] Example 3

[0090] A method for preparing silicon carbide materials by using coal gasification slag according to the present invention is specifically implemented according to the following steps:

[0091] 1) Wash the acid-leached coal gasification slag with water until it is neutral, then filter it by suction, and finally dry it in a drying oven at 110 °C until it reaches a constant weight, and the drying time is 12 h;

[0092] 2) Weigh 300 mg of the coal gasification slag prepared in step 1), fill it in a quartz tube, block both ends with conductive graphite blocks, connect the electrodes and place them in the reaction chamber, and introduce H 2 .

[0093] 3) Turn on the Joule heating instrument switch, set the discharge voltage to 150 V, click start charging, when the voltage reaches the set voltage, stop charging, and immediately click start discharging, which is recorded as 1 time of Joule heating treatment.

[0094] 4) Repeat step 3) 5 times.

[0095] 5) Keep it warm in a calcination furnace at 700 °C for 40 min to remove the unreacted carbon and obtain silicon carbide.

[0096] In the preparation method of this Example 3, the heating-up times of the 5 times of Joule heating are 0.8 s, 0.6 s, 0.6 s, 0.7 s, and 0.5 s respectively, the temperatures are increased to 2686 K, 3112 K, 3323 K, 3410 K, and 3394 K respectively. Under the hydrogen atmosphere, the reaction rate reaches 47.32 mg / s, and the relative content of the silicon carbide prepared by this method is 50.47%.

[0097] Example 4

[0098] A method for preparing silicon carbide materials using coal gasification slag according to the present invention is specifically implemented according to the following steps:

[0099] 1) Wash the acid-leached coal gasification slag with water until neutral, then perform suction filtration, and finally dry it to constant weight in a drying oven at 110 °C for 8 h;

[0100] 2) Weigh 300 mg of the coal gasification slag obtained in step 1), fill it in a quartz tube, block both ends with conductive graphite blocks, connect the electrodes and place them in the reaction chamber, and introduce He.

[0101] 3) Turn on the Joule heating instrument switch, set the discharge voltage to 120 V, click start charging, when the voltage reaches the set voltage, stop charging, and immediately click start discharging, which is recorded as 1 time of Joule heating treatment.

[0102] 4) Keep it warm in a calcining furnace at 650 °C for 30 min to remove the unreacted carbon and obtain silicon carbide.

[0103] In the preparation method of this Example 4, the temperature is raised to 2749 K in 0.8 s by Joule heating. Under the helium atmosphere, the reaction rate reaches 148.39 mg / s, and the relative content of the silicon carbide obtained by this method is 39.57%.

[0104] Example 5

[0105] A method for preparing silicon carbide materials using coal gasification slag according to the present invention is specifically implemented according to the following steps:

[0106] 1) Wash the acid-leached coal gasification slag with water until neutral, then perform suction filtration, and finally dry it to constant weight in a drying oven at 110 °C for 10 h;

[0107] 2) Weigh 300 mg of the coal gasification slag obtained in step 1), fill it in a quartz tube, block both ends with conductive graphite blocks, connect the electrodes and place them in the reaction chamber, and introduce He.

[0108] 3) Turn on the Joule heating instrument switch, set the discharge voltage to 135 V, click start charging, when the voltage reaches the set voltage, stop charging, and immediately click start discharging, which is recorded as 1 time of Joule heating treatment.

[0109] 4) Repeat step 3 three times.

[0110] 5) Keep it warm in a calcining furnace at 670 °C for 35 min to remove the unreacted carbon and obtain silicon carbide.

[0111] In the preparation method of Example 5, the heating-up times for the three Joule heating processes are 0.8 s, 0.7 s, and 0.5 s respectively, the temperatures are raised to 2802 K, 3278 K, and 3347 K respectively, the reaction rate reaches 65.7 mg / s under a helium atmosphere, and the relative content of silicon carbide obtained by this method is 43.8%.

[0112] Example 6

[0113] A method for preparing silicon carbide materials from coal gasification slag according to the present invention is specifically implemented according to the following steps:

[0114] 1) Wash the acid-leached coal gasification slag with water until it is neutral, then perform suction filtration, and finally dry it to a constant weight in a drying oven at 110 °C. The drying time is 12 h;

[0115] 2) Weigh 300 mg of the coal gasification slag obtained in step 1) and fill it into a quartz tube. Block both ends with conductive graphite blocks, connect the electrodes and place them in the reaction chamber, and introduce He.

[0116] 3) Turn on the switch of the Joule heating instrument, set the discharge voltage to 150 V, click to start charging, and when the voltage reaches the set voltage, stop charging, and immediately click to start discharging, which is recorded as one Joule heating treatment.

[0117] 4) Repeat step 3) five times.

[0118] 5) Keep it warm in a calcining furnace at 700 °C for 40 min to remove the unreacted carbon and obtain silicon carbide.

[0119] In the preparation method of Example 6, the heating-up times for the five Joule heating processes are 0.8 s, 0.7 s, 0.5 s, 0.5 s, and 0.6 s respectively, the temperatures are raised to 2913 K, 3168 K, 3162 K, 3245 K, and 3409 K respectively, the reaction rate reaches 79.35 mg / s under a helium atmosphere, and the relative content of silicon carbide obtained by this method is 82%.

[0120] Example 7

[0121] A method for preparing silicon carbide materials from coal gasification slag according to the present invention is specifically implemented according to the following steps:

[0122] 1) Wash the acid-leached coal gasification slag with water until it is neutral, then perform suction filtration, and finally dry it to a constant weight in a drying oven at 110 °C. The drying time is 8 h;

[0123] 2) Weigh 300 mg of the coal gasification slag obtained in step 1) and fill it into a quartz tube. Block both ends with conductive graphite blocks, connect the electrodes and place them in the reaction chamber, and introduce a mixed gas of H 2 and He, and the mass ratio of H 2 to He is 1:1;

[0124] 3) Turn on the switch of the Joule heating instrument, set the discharge voltage to 120 V, click "Start Charging", when the voltage reaches the set voltage, stop charging, and immediately click "Start Discharging", which is recorded as 1 time of Joule heating treatment;

[0125] 4) Keep it warm in a calcination furnace at 650 °C for 30 min to remove the unreacted carbon and obtain silicon carbide.

[0126] In the preparation method of Example 7, the temperature is raised to 3015 K in 0.8 s by Joule heating. Under the mixed gas atmosphere, the reaction rate reaches 151.99 mg / s, and the relative content of the silicon carbide obtained by this method is 40.53%.

[0127] Example 8

[0128] A method for preparing silicon carbide materials by using coal gasification slag according to the present invention is specifically implemented according to the following steps:

[0129] 1) Wash the acid-leached coal gasification slag with water until it is neutral, then filter it by suction, and finally dry it to constant weight in a drying oven at 110 °C, and the drying time is 8 h;

[0130] 2) Weigh 300 mg of the coal gasification slag in step 1) and fill it in a quartz tube, block both ends with conductive graphite blocks, connect the electrodes and put them into the reaction chamber, and introduce a mixed gas of H 2 and He, and the mass ratio of H 2 to He is 1:1;

[0131] 3) Turn on the switch of the Joule heating instrument, set the discharge voltage to 120 V, click "Start Charging", when the voltage reaches the set voltage, stop charging, and immediately click "Start Discharging", which is recorded as 1 time of Joule heating treatment;

[0132] 4) Repeat step 3) 3 times;

[0133] 5) Keep it warm in a calcination furnace at 650 °C for 30 min to remove the unreacted carbon and obtain silicon carbide.

[0134] In the preparation method of Example 8, the heating-up times of the 3 times of Joule heating are 0.7 s, 0.7 s, and 0.8 s respectively, the temperatures are raised to 2997 K, 3166 K, and 3367 K respectively. Under the mixed gas atmosphere, the reaction rate reaches 102.86 mg / s, and the relative content of the silicon carbide obtained by this method is 75.43%.

[0135] Example 9

[0136] A method for preparing silicon carbide materials by using coal gasification slag according to the present invention is specifically implemented according to the following steps:

[0137] 1) Wash the gasification slag after acid leaching with water until it is neutral, then filter it by suction, and finally dry it in an oven at 110 °C until it reaches a constant weight. The drying time is 8 h;

[0138] 2) Weigh 300 mg of the gasification slag obtained in step 1) and fill it in a quartz tube. Block both ends with conductive graphite blocks, connect the electrodes and place them in the reaction chamber, and introduce a mixed gas of H 2 and He. The mass ratio of H 2 to He is 1:1

[0139] 3) Turn on the switch of the Joule heating instrument, set the discharge voltage to 120 V, click start charging, and when the voltage reaches the set voltage, stop charging and immediately click start discharging, which is recorded as 1 time of Joule heating treatment;

[0140] 4) Repeat step 3) 5 times;

[0141] 5) Keep it warm in a calcination furnace at 650 °C for 30 min to remove the unreacted carbon and obtain silicon carbide.

[0142] In the preparation method of this Example 9, the heating-up times of the 5 times of Joule heating are 0.7 s, 0.8 s, 0.8 s, 0.6 s, and 0.6 s respectively, and the temperatures are increased to 2993 K, 3145 K, 3273 K, 3364 K, and 3446 K respectively. Under the mixed gas atmosphere, the reaction rate reaches 82 mg / s, and the relative content of the silicon carbide obtained by this method is 95.67%.

[0143] The following is a test and characterization of Examples 1 to 9:

[0144] Test Example 1

[0145] As Figures 1 to 9 shown, XRD diffraction tests were carried out on Examples 1 to 9. It can be seen that regardless of the reaction atmosphere, as the number of FJH (Joule heating) treatments increases, the diffraction peak intensity corresponding to SiC gradually increases, and the diffraction peak intensity of SiO 2 gradually decreases, but SiO 2 in H 2 still accounts for a large proportion. After FJH treatment under He gas, the SiC peak intensity is significantly higher. The group with the highest relative content of SiC is in Examples 7 to 9, that is, in the mixed gas of H 2 and He. After 5 times of FJH treatment, the peak of SiO 2 basically disappears.

[0146] Test Example 2

[0147] The relative content of carbon element in Examples 1 to 9 was obtained by using an inorganic carbon and sulfur analyzer, and according to the formula:

[0148]

[0149] In the formula ω(SiC) represents the relative content of SiC ω(C) represents the relative content of carbon element measured by a carbon and sulfur analyzer M(SiC) and M(C) represent the relative molecular masses of SiC and C respectively, and the calculation results are shown in Table 2

[0150] Table 2 Relative content of SiC in Examples 1 to 9

[0151]

[0152] Test Example 3

[0153] SEM analysis was performed on the silicon carbide materials prepared in Example 1 and Example 9. It was observed that most of the phases in Example 1 were still amorphous and spherical SiO 2 , because Joule heating treatment was carried out once at 120V voltage, and most of the SiO 2 did not undergo a reduction reaction with carbon; while dendritic SiC was observed in Example 9, which indicates that under the action of Joule heat, the reaction occurred, and high temperature and H 2 promoted the growth of grains

[0154] The above content is only to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention

Claims

1. A method for preparing silicon carbide material using coal gasification slag, characterized in that: The method comprises firstly pre-treating the coal gasification slag, then acid leaching, water washing, suction filtering and drying the pre-treated coal gasification slag, and then performing Joule heating treatment to obtain silicon carbide after calcination; In the Joule heating treatment, the discharge voltage is set to 120V-150V, the number of discharges is 1, 3 or 5 times, the heating time for each time is 0.5s, 0.6s, 0.7s or 0.8s, and the heating temperature for each time is 2686K, 2725K, 2734K, 2749K, 2802K, 2913K, 2993K, 2997K, 3015K, 3016K, 3112K, 3323K, 3145K, 3162K, 3166K, 3168K, 3229K, 3245K, 3273K, 3278K, 3347K, 3364K, 3367K, 3394K, 3409K, 3410K, 3411K, 3412K, 3413K, 3414K, 3415K, 3416K, 3417K, 3418K, 3419K, 3420K, 3421K, 3423K, 3424K, 3425K, 3426K, 3427K, 3428K, 3429K, 10K or 3446K, the reaction rate is 25.24mg / s, 43.26mg / s, 47.32mg / s, 65.7mg / s, 79.35mg / s, 82mg / s, 102.86mg / s, 148.39mg / s or 151.99mg / s; a mixed gas is introduced during the Joule heating treatment; the mixed gas is a mixed gas of hydrogen and helium, and the mass ratio of hydrogen to helium in the mixed gas is 1:1; the pretreatment comprises soaking the gasification slag in hydrogen peroxide and then drying it, the soaking time is 1-2h, the drying temperature is 105-110°C, and the drying time is 8-12h.

2. The method for preparing silicon carbide material using coal gasification slag according to claim 1, characterized in that: The solution used for the acid leaching treatment includes any one of a HCl solution, a H2SO4 solution or a mixed solution with a molar concentration of 1-3 mol / L.

3. The method for preparing silicon carbide material using coal gasification slag according to claim 2, characterized in that: The mixed solution is a mixed solution of HCl and H2SO4 solution.

4. The method for preparing silicon carbide material using coal gasification slag according to claim 3, characterized in that: In the mixed solution, the volume ratio of HCl and H2SO4 solution is 1:

1.

5. The method for preparing silicon carbide material using coal gasification slag according to claim 1, characterized in that: The coal gasification slag after acid leaching is washed with water to neutrality.

6. The method for preparing silicon carbide material using coal gasification slag according to claim 1, characterized in that: The drying temperature is 105-110°C and the time is 8-12h.

7. The method for preparing silicon carbide material using coal gasification slag according to claim 1, characterized in that: The calcination treatment is to heat the temperature to 650-700°C and then keep the temperature for 30-40 minutes.

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