CN100491251C - Method for preparing mullite from kaolin - Google Patents

Abstract

The invention relates to a method for preparing mullite by calcining kaolin. The method for preparing mullite from kaolin is characterized in that it comprises the following steps: 1) mixing the kaolin powder and an additive to obtain a batch, and the additive is a composite catalyst composed of KCl and _CeO , and the addition of KCl The amount is 1%-2% of the weight of the kaolin powder, and the amount of _CeO2 is 0.1%-0.5% of the weight of the kaolin powder; Calcined at 1300°C for 3 hours to obtain the product. The method has the characteristics of low energy consumption and low cost, and the prepared mullite does not contain cristobalite phase.

Description

Method for preparing mullite from kaolin

technical field

The invention relates to a method for preparing mullite by calcining kaolin.

technical background

Mullite is an aluminosilicate mineral with high refractoriness, good thermal shock resistance, chemical corrosion resistance, creep resistance, high softening temperature under load, good volume stability, and strong electrical insulation. Ideal high-grade refractory materials are widely used in industries such as metallurgy, glass, ceramics, chemistry, electric power, national defense, gas and cement. Mullite (mullite) is a natural mineral that is very rare in the earth's crust. It was named after it was first discovered on the Isle of Mull in Scotland in 1924. But artificial mullite is a common and widely used mineral. The chemical composition of mullite is not stable, and there are two common forms of 3Al ₂ O ₃ ·2SiO ₂ and 2Al ₂ O ₃ ·SiO ₂ . Mullite is quite similar to sillimanite group minerals. Its crystal structure can be seen as evolved from the sillimanite structure, each unit cell is composed of 4 sillimanite unit cells, and each sillimanite unit cell is composed of 4 Al ₂ O ₃ ·SiO ₂ Composition, therefore, the mullite unit cell is equivalent to composed of 16 Al ₂ O ₃ ·SiO ₂ .

At present, there are two main techniques for preparing mullite by calcining kaolin: 1. directly preparing mullite by calcining kaolin, the product name is M45, and the product requires no crystalline phase SiO ₂ (cristobalite) that seriously affects its performance; 2. Kaolin is calcined after adding industrial alumina to obtain mullite products with high aluminum content and high purity.

The current production process of M45 is as follows: kaolin is calcined at 1500°C and kept for 10 hours. There is only one patent report in China that directly prepares mullite from kaolin, and the product does not contain cristobalite phase that damages the performance of mullite. Calcining for more than 8 hours, and then at a constant temperature of 1300 ° C for 2 hours, or the coal series kaolinite is crushed to 40-250 mesh, adding 1% (weight) mineralizer, 1.5% (weight) flux and calcining at 1350 ° C for 8 hours hours, and then at 1150°C for 2 hours, the mineralizer is magnesium oxide, and the flux is calcium sulfate.

The main disadvantages of the above methods are high energy consumption and high cost input.

Contents of the invention

The object of the present invention is to provide a method for preparing mullite from kaolin, which has the characteristics of low energy consumption and low cost, and the prepared mullite does not contain cristobalite phase.

In order to achieve the above object, technical scheme of the present invention is: the method for preparing mullite from kaolin, is characterized in that it comprises the steps:

1), mix the kaolin powder and external additives evenly to obtain a batch, the additive is a composite catalyst composed of KCl and CeO ₂ , the amount of KCl added is 1%-2% of the weight of the kaolin powder, CeO ₂ The amount added is 0.1%-0.5% of the weight of kaolin powder;

2) Raise the temperature of the batch material to 1300°C at a rate of 2°C-10°C per minute, calcining at 1300°C for 3 hours to obtain a product with a mullite phase greater than 55% and no cristobalite phase.

The particle size of the kaolin powder is less than 200 mesh (0.074mm), and the Al ₂ O ₃ is greater than 36%.

The present invention adopts external additives (composite catalyst composed of KCl and CeO ₂ ) to enable kaolin to be converted into mullite as the main crystal phase at 1300° C. for 3 hours without cristobalite phase, thus greatly reducing energy consumption. Consumption, reduce production costs.

Compared with the prior art, the present invention has the following outstanding beneficial effects:

1. Reduce the calcination temperature from more than 1500°C in the current process to 1300°C.

2. Reduce the holding time from 10 hours to 3 hours.

3. At the same time, the prepared product does not contain cristobalite phase that damages the performance of mullite, and its composition is close to the Molochite sand produced by the famous British company ECC.

Description of drawings

Figure 1 is the XRD pattern obtained in Comparative Example 1 [Yunnan kaolin powder (less than 200 mesh) was calcined at 1300° C. for 3 hours without adding a phase change catalyst].

Fig. 2 is the XRD pattern obtained in Comparative Example 2 [Yunnan kaolin powder (less than 200 mesh) is added with 40% alumina, calcined at 1500° C. for 6 hours].

Fig. 3 is the XRD pattern obtained in Comparative Example 3 [Yunnan kaolin powder (less than 200 mesh) is added with 15‰ potassium chloride, 5‰ cerium oxide is calcined at 1300° C. for 3 hours].

Fig. 4 is the XRD pattern obtained in Example 1 of the present invention [Yunnan kaolin powder (less than 200 mesh) is added with 18‰ potassium chloride and 2‰ cerium oxide is calcined at 1300°C for 3 hours].

Fig. 5 is the XRD pattern obtained in Example 2 of the present invention [Yunnan kaolin powder (less than 200 mesh) is added with 16‰ potassium chloride and 4‰ cerium oxide is calcined at 1300°C for 3 hours].

Fig. 6 is the XRD pattern obtained in Example 3 of the present invention [Yunnan kaolin powder (less than 200 mesh) is added with 19‰ potassium chloride and 3‰ cerium oxide is calcined at 1300°C for 3 hours].

Fig. 7 is the XRD pattern obtained in Example 4 of the present invention [Yunnan kaolin powder (less than 200 mesh) is added with 20‰ potassium chloride and 5‰ cerium oxide is calcined at 1300°C for 3 hours].

Fig. 8 is the XRD pattern obtained in Example 5 of the present invention [Yunnan kaolin powder (less than 200 mesh) is added with 13‰ potassium chloride, and 5‰ cerium oxide is calcined at 1300°C for 3 hours].

In the figure: 口 is the characteristic peak of mullite, ○ is the characteristic peak of cristobalite, △ is the characteristic peak of corundum, and ▽ is the characteristic peak of quartz.

Detailed ways

In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

Embodiment one:

Get Yunnan kaolin powder (less than 200 mesh) 3.00g, add the potassium chloride powder of kaolin powder weight 18‰, add the cerium oxide powder of kaolin powder weight 2‰, mix evenly, put into corundum crucible, put Put the crucible in a silicon-molybdenum rod box-type resistance furnace, raise the temperature to 1300°C at a rate of 4°C per minute, and heat it at 1300°C for 3 hours to obtain the mullite product. The product is subjected to X powder crystal diffraction analysis to obtain XRD Atlas 4. It can be seen from Figure 4 that the mullite phase is about 55-60%, does not contain cristobalite, and the others are amorphous phases.

Embodiment two:

Get Yunnan kaolin powder (less than 200 mesh) 3.00g, add the potassium chloride powder of kaolin powder weight 16‰, add the cerium oxide powder of kaolin powder weight 4‰, mix evenly, put into corundum crucible, put Put the crucible in a silicon-molybdenum rod box-type resistance furnace, raise the temperature to 1300°C at a rate of 4°C per minute, and heat it at 1300°C for 3 hours to obtain the mullite product. The product is subjected to X powder crystal diffraction analysis to obtain XRD Atlas 5. It can be seen from Figure 5 that the mullite phase is about 55-60%, does not contain cristobalite, and the others are amorphous phases.

Embodiment three:

Get Yunnan kaolin powder (less than 200 mesh) 3.00g, add the potassium chloride powder of kaolin powder weight 19‰, add the cerium oxide powder of kaolin powder weight 3‰, mix well, put into corundum crucible, put Put the crucible in a silicon-molybdenum rod box-type resistance furnace, raise the temperature to 1300°C at a rate of 4°C per minute, and heat it at 1300°C for 3 hours to obtain the mullite product. The product is subjected to X powder crystal diffraction analysis to obtain XRD Atlas 6. It can be seen from Figure 6 that the mullite phase is about 55-60%, does not contain cristobalite, and the others are amorphous phases.

Embodiment four:

Get Yunnan kaolin powder (less than 200 mesh) 3.00g, add the potassium chloride powder of kaolin powder weight 20‰, add the cerium oxide powder of kaolin powder weight 5‰, mix evenly, put into corundum crucible, put Put the crucible in a silicon-molybdenum rod box-type resistance furnace, raise the temperature to 1300°C at a rate of 4°C per minute, and heat it at 1300°C for 3 hours to obtain the mullite product. The product is subjected to X powder crystal diffraction analysis to obtain XRD Atlas 7. It can be seen from Figure 7 that the mullite phase is about 55-60%, does not contain cristobalite, and the others are amorphous phases.

Embodiment five:

Get Yunnan kaolin powder (less than 200 mesh) 3.00g, add the potassium chloride powder of kaolin powder weight 13‰, add the cerium oxide powder of kaolin powder weight 5‰, mix evenly, put into corundum crucible, put Put the crucible in a silicon-molybdenum rod box-type resistance furnace, raise the temperature to 1300°C at a rate of 4°C per minute, and heat it at 1300°C for 3 hours to obtain the mullite product. The product is subjected to X powder crystal diffraction analysis to obtain XRD Atlas 8. It can be seen from Figure 8 that the mullite phase is about 55-60%, does not contain cristobalite, and the others are amorphous phases.

Embodiment six:

Get Yunnan kaolin powder (less than 200 mesh) 3.00g, add the potassium chloride powder of kaolin powder weight 10‰, add the cerium oxide powder of kaolin powder weight 1‰, mix well, put into corundum crucible, put Put the crucible in a silicon-molybdenum rod box-type resistance furnace, raise the temperature to 1300°C at a rate of 10°C per minute, and calcinate at 1300°C for 3 hours to obtain the mullite product.

Embodiment seven:

Get Yunnan kaolin powder (less than 200 mesh) 3.00g, add the potassium chloride powder of kaolin powder weight 20‰, add the cerium oxide powder of kaolin powder weight 5‰, mix evenly, put into corundum crucible, put Put the crucible in a silicon-molybdenum rod box-type resistance furnace, raise the temperature to 1300°C at a rate of 2°C per minute, and calcine at 1300°C for 3 hours to obtain the mullite product.

Comparative Example 1:

Take 5.00g of Yunnan kaolin powder (less than 200 mesh) and put it into a corundum crucible, put the crucible in a silicon-molybdenum rod box-type resistance furnace, raise the temperature to 1300°C at a rate of 4°C per minute, and keep it at 1300°C for 3 hours , the mullite product was obtained, and the product was subjected to X powder crystal diffraction analysis to obtain the XRD pattern 1. It can be seen from Figure 1 that the mullite phase is about 55%-60%, the cristobalite content is about 10%, and the others are amorphous phases. This figure shows that when kaolin is calcined at 1300 ° C without adding additives, the excess quartz will be partially transformed into cristobalite phase that damages the performance of mullite.

Comparative example 2:

Take 10.00g of Yunnan kaolin powder (less than 200 mesh), add 40% alumina by weight of the kaolin powder, mix well, put it into a corundum crucible, put the crucible into a silicon-molybdenum rod box-type resistance furnace, and The temperature was raised to 1500°C at a rate of 4°C, and calcined at 1500°C for 6 hours to obtain the mullite product. The product was subjected to X powder crystal diffraction analysis to obtain XRD pattern 2. It can be seen from Figure 2 that the mullite phase is about 60%, the corundum content is about 20%, the cristobalite content is about 10%, and the others are amorphous phases. The figure shows that even calcining kaolin at 1500°C cannot completely eliminate the cristobalite phase.

Comparative example 3:

Take 8.00g of Yunnan kaolin powder (less than 200 mesh), add potassium chloride with a weight of 15‰ of the kaolin powder, add cerium oxide with a weight of 5‰ of the kaolin powder, mix evenly, put it into a corundum crucible, and put the crucible in In the silicon-molybdenum rod box-type resistance furnace, the temperature was raised to 1300°C at a rate of 4°C per minute, and the mullite product was obtained by calcination at 1300°C for 3 hours. The XRD pattern 3 was obtained by X powder crystal diffraction analysis of the product. It can be seen from Figure 3 that the mullite phase is about 55-60%, does not contain cristobalite, and the others are amorphous phases. The prepared product does not contain cristobalite phase that damages the performance of mullite, and its composition is close to the Molochite sand produced by the famous British company ECC.

Claims (2)

1. kaolin prepares the method for mullite, is characterized in that it comprises the steps: 1), mix the kaolin powder and external additives evenly to obtain a batch, the additive is a composite catalyst composed of KCl and CeO ₂ , the amount of KCl added is 1%-2% of the weight of the kaolin powder, CeO ₂ The amount added is 0.1%-0.5% of the weight of kaolin powder; 2) Raise the temperature of the batch material to 1300°C at a rate of 2°C-10°C per minute, calcining at 1300°C for 3 hours to obtain the product. 2. The method for preparing mullite from kaolin according to claim 1, characterized in that: the particle size of the kaolin powder is less than 200 mesh, and the Al ₂ O ₃ is greater than 36%.

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