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Preparation of potassium cryolite
- Oct 30, 2018 -

Potassium cryolite is specially produced by chemical process, or it is a by-product of the production of certain products. The preparation process of the former type mainly includes a mixing method and a synthesis method, which may be referred to as a conventional process, and the latter type of product is a by-product of the production of an Al-Ti-B master alloy. The Al-Ti-B master alloy is a grain refiner for aluminum alloys, which must be added to produce aluminum to refine the grain and structure of the alloy and improve the properties of the material.

1.1 Conventional preparation process

1.1.1 Mixed research method

This method is prepared by mixing KF with AlF3 or K3AlF4 and KF or K3AlF6 and AlF3, or K3AlF6 and KAlF4 according to the specified composition ratio, mixing and grinding by different methods. Some processes also dispense a small amount of other fluorides based on these raw materials to further improve the performance of the braze. KF and AlF3 are mixed to prepare wet mixing method, dry and wet research method, melting

The method of research; KAlF4 and KF mixed preparation, generally anhydrous powder mixed research, the ratio is 80% ~ 99.8% KAlF4 and AlF3 mixed preparation, usually 60% ~ 70% K3AlF6, 27% ~ 33% AlF3, It is also possible to use this as a basic raw material, and add a small amount of other fluoride; K3AlF6 is mixed in a eutectic ratio, for example, 20% K3AlF6, 80% KAlF4. Corundum carbon

1.1.2 Synthesis method

The main disadvantages of preparing potassium cryolite by the mixed research method are as follows: The basic raw material is KF or KAlF4 or K3AlF6, which is high in price and difficult to prepare; the prepared product often contains free KF, which is easily soluble in water and absorbs moisture, causing welding. Corrosion. Although the research method does not have these shortcomings, it is cumbersome to operate, high in energy consumption, and requires high temperature melting and grinding. Therefore, a hybrid method has been developed, in which Al(OH)3, HF, KCl, KOH, K2CO3, KBr, etc. are used as raw materials, and some methods such as potassium metaaluminate method, potassium fluoride method, and potassium aluminum hydroxide method are formed. A commercial preparation process such as a potassium carbonate method or a potassium compound method. 

Taking the potassium metaaluminate method as an example to illustrate the main points and advantages of the synthesis method, Al(OH) 3 with known composition is reacted with a hot KOH solution to prepare a KAlO2 clear solution, in which K+ is abundant, so that K: Al in the solution The amount is exactly equal to the corresponding ratio of the eutectic point. Then, an excess of hydrofluoric acid is added, and a K3AlF6 and KAlF4 precipitation mixture is precipitated. It was evaporated to dryness and baked at 200 ° C to remove residual free acid. Reaction equation: just

Al( OH) 3 + KOH = KAlO2 + 2H2O

2KAlO2 + 2KF + 8HF = K3AlF6 + KAlF4 + 4H2O

The prepared K3AlF6, KAlF4 mixture is a white powder, very fine, particle size 0.1 ~ 5μm, melting point 560 ° C, is a good aluminum alloy brazing flux. Compared with the mixed research method, it does not need high temperature melting, no grinding, simple operation, good quality and low cost, and is suitable for mass production, and is suitable for the development of automobile aluminum parts brazing industry.

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