CN101607821B - Method for utilizing gasifier slag to synthesize Ca-alpha-Sialon - Google Patents

Abstract

The invention discloses a method for utilizing gasifier slag to prepare Ca-alpha-Sialon. In the method, the gasifier slag is taken as main raw materials to prepare Ca-alpha-Sialon materials through carbon thermal reduction nitridation method, and the Ca-alpha-Sialon materials with higher purity can be obtained by controlling process parameters of burden, sintering temperature, thermal insulation time, nitrogen flow and the like in a preparation process. The invention has the advantage that regular hexagonal prism-shaped Ca-alpha-Sialon ceramic powders with higher purity (the quality percentage is 60 percent to 90 percent) can be obtained through lower cost to reasonably and fully utilize the gasifier slag.

Description

A method for synthesizing Ca-α-Sialon by utilizing gasification slag

technical field

The invention relates to the technical field of ceramics and refractory materials, and in particular provides a method for preparing Ca-α-Sialon material by using gasification slag, which has strong feasibility.

Background technique

Sialon retains the excellent properties of Si ₃ N ₄ such as high strength, high hardness, and high heat resistance, and is superior to Si ₃ N ₄ in terms of toughness, chemical stability, and oxidation resistance, so it is considered to be the most promising high-temperature One of structural ceramics. Ca-α-Sialon is a five-element sialon material of solid-solution alkaline earth metals. Because of its long columnar crystal shape, the ceramic material made of Ca-α-Sialon powder has great toughness. This opens up a new way of thinking for the development of tough ceramics. It has been widely used in blast furnace lining, mixed iron furnace (car) lining, ladle, sliding nozzle and heat exchanger components and other equipment.

Usually, Ca-α-Sialon is prepared by using nitrides (α-Si ₃ N ₄ , AlN) and CaO as raw materials under high-temperature hot-pressing conditions. The synthesis temperature is high (1700-1800 ° C), and the process is complicated. The high cost of preparation limits the large-scale industrial production of Ca-α-Sialon.

At present, there are few reports on gasification slag, and there are only a handful of researches on the application of gasification slag. Acosta (A.Acosta, I.Iglesias, M.Aineto, et al, Utilization of IGCC slag and clay steriles in soft mud bricks (by pressing) for use in building bricks manufacturing, Waste Management, 2002, 22: 887-89) utilizes gas Bricks for construction were prepared by using gasification slag and clay. The clay and gasification slag were mixed evenly in a certain proportion and then sintered at 900°C. The research showed that when the gasification slag content of the sample reached 50%, it could be prepared to meet the use requirements. Bricks for construction. However, the application of gasification slag in the synthesis of Ca-α-Sialon has not been involved. Therefore, the use of gasification slag to prepare Ca-α-Sialon materials has strong research value and technical significance for meeting the requirements of sustainable resource utilization.

Contents of the invention

For the defects existing in the above-mentioned background technology, the purpose of the present invention is to provide a method for synthesizing Ca-α-Sialon material from gasification slag, one is to realize the comprehensive utilization of gasification slag; the other is to design a method for preparing Ca - The α-Sialon material is cheap and the cost is reduced.

In order to realize the above technical tasks, the present invention takes the following technical solutions:

A kind of method utilizing gasification slag to prepare Ca-α-Sialon material is characterized in that, comprises the following steps:

a. Ingredients: Gasification slag is used as raw material, carbon black is used as reducing agent, and the mixture is formulated according to 6C+3SiO ₂ +2N ₂ →Si ₃ N ₄ +6CO, and the amount of carbon black added should exceed 7% of the theoretical amount -10%, the added amount of carbon black facilitates the carbothermal reduction nitriding reaction more fully.

b. Ball mill mixing: Put the prepared material into a ball mill tank, add 10% white dextrin as a binder, and dry ball mill for 10-20 hours to achieve the purpose of uniform mixing and fine powder.

c. Compression molding: the mixture is pressed into a cylindrical sample under a pressure of 120MPa.

e. Drying: Put the molded block into an oven and dry it at 70°C for 10-20 hours.

f. Carbothermal reduction and nitriding synthesis: Put the sample into a high-temperature controllable tubular atmosphere furnace, heat it to 800°C at a heating rate of 5-7 degrees per minute, and then rise to 1200°C after 2-3 hours for 1-3 hours Raise the temperature to 1300-1500°C, feed nitrogen at a flow rate of 0.5L/min, and keep the temperature at the highest temperature for 9 hours to achieve full sintering of the sample.

g. Decarbonization and iron removal: heat the sintered sample at 700-800°C for 6-7 hours to remove the carbon in the sample; grind the sample after carbon removal into powder, and place it in an iron remover for iron removal , finally get Ca-α-Sialon ceramic powder.

The composition of the gasification slag is: SiO ₂ 35-40%, Al ₂ O ₃ 7-12%, CaO 7-9%, MgO 0.5-1%, C 20-25%, Fe 3-5%, K ₂ O 1.2-1.8%, Na ₂ O 1-1.5%, others: balance.

The invention has the advantages of obtaining regular hexagonal columnar Ca-α-Sialon ceramic powder with relatively high purity (60-90% by mass) at relatively low cost, so that the gasification slag can be reasonably and fully utilized.

Description of drawings

Fig. 1 is the XRD spectrum of the gasification slag selected in the present invention.

The XRD pattern of Fig. 2 embodiment 1,2,3,4 product.

Fig. 3 embodiment 1,2,3, the phase composition content change diagram of the product of 4.

Figure 4 shows the microscopic morphology of Ca-α-Sialon in Example 4, wherein the magnification of Figure 4(a) is 50,000 times, and the magnification of Figure 4(b) is 200,000 times.

The present invention will be described in further detail below in conjunction with the accompanying drawings and the embodiments given by the inventor.

Detailed ways

The present invention uses gasification slag as the main raw material, and prepares Ca-α-Sialon material by carbothermal reduction and nitriding method. During the preparation process, the Ca-α-Sialon material with high purity can be obtained by controlling the process parameters such as sintering temperature, holding time, and nitrogen flow rate. Ca-α-Sialon material. Among them: the formation reaction principle of Ca-α-sialon is as follows:

mCaO+(24-2(m+n))SiO ₂ +(m+n)Al ₂ O ₃ +(16-n)N ₂ +(48-3n)C

→2Ca _(m/2) Si _(12-(m+n)) Al _m+n O _n N _16-n +(48-3n)CO

Follow above-mentioned reaction principle, the present invention takes the following steps:

a. Ingredients: Gasification slag is used as raw material, carbon black is used as reducing agent, and the mixture is formulated according to 6C+3SiO ₂ +2N ₂ →Si ₃ N ₄ +6CO, and the amount of carbon black added should exceed 7% of the theoretical amount -10%, the added amount of carbon black facilitates the carbothermal reduction nitriding reaction more fully.

b. Ball mill mixing: Put the prepared material into a ball mill tank, add 10% white dextrin as a binder, and dry ball mill for 10-20 hours to achieve the purpose of uniform mixing and fine powder.

c. Compression molding: the mixture is pressed into a cylindrical sample under a pressure of 120MPa.

e. Drying: Put the molded block into an oven and dry it at 70°C for 10-20 hours.

f. Carbothermal reduction and nitriding synthesis: Put the sample into a high-temperature controllable tubular atmosphere furnace, heat it to 800°C at a heating rate of 5-7 degrees per minute, and then rise to 1200°C after 2-3 hours for 1-3 hours Raise the temperature to 1300-1500°C, feed nitrogen at a flow rate of 0.5L/min, and keep the temperature at the highest temperature for 9 hours to achieve full sintering of the sample.

g. Decarbonization and iron removal: heat the sintered sample at 700-800°C for 6-7 hours to remove the carbon in the sample; grind the sample after carbon removal into powder, and place it in an iron remover for iron removal , finally get Ca-α-Sialon ceramic powder.

The invention has the advantages of obtaining regular hexagonal columnar Ca-α-Sialon ceramic powder with relatively high purity (60-90% by mass) at relatively low cost, so that the gasification slag can be reasonably and fully utilized.

The following are examples given by the inventors. The present invention is not limited to these examples. The applicant's experiments have proved that qualified Ca-α-Sialon materials can be prepared from gasification slag within the scope of the present invention. The gasification slags provided in the following examples are all selected from the Texaco gasification furnace slag of Shaanxi Shenmu Chemical Industry Co., Ltd. The main chemical composition of the gasification slag involved is SiO ₂ , Al ₂ O ₃ and CaO, and contains relatively high Residual carbon content, gasification slag composition: SiO ₂ : 35-40%, Al ₂ O ₃ : 7-12%, CaO: 7-9%, MgO: 0.5-1%, C: 20-25%, Fe : 3-5%, K ₂ O: 1.2-1.8%, Na ₂ O: 1-1.5%, others: balance. The X-ray diffraction pattern of gasification slag is shown in Fig. 1 . It can be seen from the figure that the content of glass phase and amorphous matter in gasification slag is very high, reaching over 90%, and the crystal phase is mainly quartz and calcite. Among them, quartz is obtained by crystallization of glass phase in the process of high-temperature liquid phase cooling. Calcite is a co-solvent introduced to adjust the melting point of ash and the properties of the melt. Due to the large particle size and short residence time in the gasifier, there is no It is completely decomposed and remains in the gasification slag.

Example 1:

Mix gasification slag and carbon black, wherein the amount of carbon black added exceeds 7% of the theoretical value, ball mill the mixture for 14 hours, press the ball milled mixture under a pressure of 120MPa, and dry it at 70-80°C for 10- After drying for 20 hours, the sample was calcined at 1300°C for 9 hours, and the nitrogen flow rate was controlled at 0.5L/min. The main crystal phase of the final product obtained was β-sialon, containing only a small amount of Ca-α-Sialon phase and mullite Stone phase, see Figure 2 and Figure 3.

Example 2:

Mix gasification slag and carbon black, wherein the amount of carbon black added exceeds 8% of the theoretical value, ball mill the mixture for 15 hours, press the ball milled mixture under a pressure of 120MPa, and dry it at 70-80°C for 10- After 20 hours, the sample was calcined at 1400°C for 9 hours after drying, and the nitrogen flow rate was controlled to 0.5L/min. The main crystal phase in the final product obtained was still β-sialon phase, but the content was reduced compared to Example 1 , Ca-α-Sialon phase content increased, see Figure 2 and Figure 3.

Example 3:

Mix gasification slag and carbon black, wherein the amount of carbon black added exceeds 9% of the theoretical value, ball mill the mixture for 18 hours, press the ball milled mixture under a pressure of 120MPa, and dry it at 70-80°C for 10- After 20 hours, the sample was calcined at 1450°C for 9 hours after drying, and the nitrogen flow rate was controlled at 0.5L/min. The main crystal phase of the final product obtained was Ca-α-Sialon phase, containing a small amount of β-sialon phase and mullite Stone phase, see Figure 2 and Figure 3.

Example 4:

The gasification slag and carbon black are mixed, and the amount of carbon black added exceeds 10% of the theoretical value. The mixture is ball milled for 20 hours. The mixture after ball milling is pressed at 120MPa and dried at 70-80°C for 10- After drying for 20 hours, the sample was calcined at 1500°C for 9 hours, and the nitrogen flow rate was controlled at 0.5L/min. The main crystal phase of the final product obtained was Ca-α-Sialon, and its mass fraction reached more than 80%, see Figure 2 and Figure 3. The main crystal phase Ca-α-Sialon is in the shape of a regular hexagonal column with a radial length of 3.5-5 μm, as shown in FIG. 4 .

Claims (2)

1. a method of utilizing gasifier slag to prepare Ca-α-Sialon material is characterized in that, may further comprise the steps:

A. prepare burden: as raw material, carbon black is as reductive agent, according to 6C+3SiO with gasifier slag ₂+ 2N ₂→ Si ₃N ₄+ 6CO is configured to compound, and wherein the carbon black add-on should surpass the 7%-10% of theoretical add-on, and it is more abundant that this carbon black add-on is convenient to the carbothermal reduction-nitridation reaction;

B. ball milling mixes: the material that will prepare is put into ball grinder, adds 10% white dextrin as wedding agent, and dry ball milling 10-20 hour, to reach the purpose that mixes with the refinement powder;

C. compression moulding: compound is pressed into cylindric sample under the pressure of 120MPa;

E. dry: as the moulding sample to be put into baking oven dried 10-20 hour down at 70 ℃;

F. carbothermal reduction-nitridation is synthetic: sample is put into the controlled tubular type atmosphere furnace of high temperature, with 5～7 the degree/minute heat-up rate be heated to 800 ℃, rise to 1200 ℃ behind 2～3h, 1～3h is warmed up to 1300～1500 ℃, the feeding nitrogen flow is 0.5L/min, top temperature insulation 9 hours, to realize the abundant sintering of sample;

G. carbon elimination deironing: sintered specimen is incubated 6-7h under 700-800 ℃ of condition, to remove the carbon in the sample; Sample behind the de-carbon is clayed into power, be positioned over and carry out deironing in the magnetic separator de-ironing, finally obtain Ca-α-Sialon ceramic powder.

2. the method for utilizing gasifier slag to prepare Ca-α-Sialon material as claimed in claim 1 is characterized in that described gasifier slag composition is: SiO ₂: 35～40%, Al ₂O ₃: 7～12%, CaO:7～9%, MgO:0.5～1%, C:20～25%, Fe:3～5%, K ₂O:1.2～1.8%, Na ₂O:1～1.5%, other: surplus.

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