Preparation background and overview of synthetic mica
Mica is a general term for layered silicate minerals containing K, Al, Mg, Fe, Li and other metal elements. From the structure and composition point of view, it is mainly a hydroaluminosilicate of alkaline earth metals and alkali metals with a monoclinic complex network layered structure, with the general formula (natural X0.5-1Y2-3Z10(OH)2. Mica Due to its good elasticity, transparency, high-frequency insulation and chemical stability, it is widely used in aerospace, electrical appliances, machinery, pearlescent effect materials and other fields. At present, the main producing areas of natural mica in the world are concentrated in India, Canada, Brazil and a few other fields. Several countries. China’s high-quality natural mica resources are relatively scarce. With the continuous improvement of industrial level, the demand for high-quality mica is rising year by year. Imported natural mica is far from meeting the domestic market demand. And synthetic mica (mainly fluorphlogopite) Compared with natural mica, it is less restricted by natural resource conditions. Its structure is similar to natural mica, and its purity, transparency, insulation and high temperature resistance are better than natural mica. Therefore, it can completely replace or even replace natural mica in some industrial applications. Beyond natural mica.
Preparation of synthetic mica Characteristics of synthetic mica
The process of artificially synthesizing mica includes core processes such as weighing, mixing, furnace loading, electric fusion, cooling, unloading, crushing and peeling. The main principle is to use chemical raw materials to undergo high temperature, melting, and cooling under certain conditions. And crystallized monoclinic layered silicate, its chemical formula is KMg3 (AlSi3O10) F2. Compared with natural mica, it has the advantages of being more resistant to high temperatures (up to 1200°C), higher resistivity (1000 times higher), more acid and alkali resistant, transparent, peelable and elastic. It is a synthetic material used in spacecrafts. Core basic materials such as Yunu insulation sheets, synthetic mica insulation sheets for environmental monitoring satellites, and synthetic mica polarization sheets for radar phase shifters also have good application prospects in the medical and health fields. At present, China’s mica production is about 150,000 tons, of which 57,000 tons are synthetic mica, produced by only a few small manufacturers. They are all first-generation products. Their quality indicators do not meet the requirements of the high-end market and are only used for production. Low-end insulation, coatings and other products. At present, the annual demand for mica products in the world is nearly 500,000 tons, and the annual demand is growing at a rapid rate.
Preparation of synthetic mica
The main preparation principle of synthetic mica is to use an appropriate proportion of raw materials to mix and melt at high temperature to obtain a melt, and then cool the melt. When the melt temperature is lower than the freezing point, the atoms (molecules) in the melt will The disordered accumulation begins to change into an orderly arrangement and solids precipitate. Therefore, this process is a solid-liquid phase change process. The heating process, container, and raw material ratio in the mica synthesis process will all affect the state of solid precipitation, thus directly affecting the quality of the product. For example, when preparing fluorphlogopite, too fast a cooling rate may result in the product being stevensite instead of mica, while a slower cooling rate may be beneficial to the formation of larger crystals.
Preparation of synthetic mica 1. Preparation process of fluorphlogopite
Based on the above principles, the synthesis process of mica can be mainly divided into crucible descending seed method and internal heating method. Among them, although the crucible descending seed crystal method can prepare large book-shaped crystals, its production cost is high due to its high energy consumption, long cycle and the need to use expensive platinum crucibles, so it is rarely used in large-scale industrial production. The internal heating method mainly mixes the raw materials required for the synthesis of mica (mainly fused magnesia, quartz powder magnesium carbonate, potassium fluorosilicate, alumina powder and potassium carbonate, etc.) according to a certain ratio and then adds them to a high-temperature furnace made of refractory bricks. In the furnace, a heating electrode is used to melt part of the raw material. The molten melt can conduct electricity, thereby melting all the raw materials. Finally, the mica product is obtained by cooling and precipitating crystals. The internal heating method has the advantages of low energy consumption, high yield, low fluoride volatilization, and does not require a crucible. Therefore, this method has been extensively and in-depth researched as the main method for large-scale production of synthetic mica.
In the past 20 years, with the continuous improvement of mica synthesis technology, my country has grown large synthetic mica crystals through both internal heating and seeding methods, with a maximum area of 560cm2, which is the largest synthetic mica sheet in the world so far. Although my country’s research on synthetic mica started relatively late, it has now reached the world’s leading level of sodium perborate tetrahydrate in terms of growing large-size synthetic mica technology.
Preparation of synthetic mica 2. Other synthetic mica
Fluorphlogopite has the advantages of purity, high transparency, and high temperature resistance, but its biggest problem is that compared with natural mica, it is harder and less elastic. This hard and brittle characteristic makes processing The resulting synthetic mica powder has poor diameter and thickness, high bulk density, and poor adhesion, resulting in low color saturation of the pearlescent pigment produced from fluorphlogopite, which is particularly obvious in small particle sizes. This hard and brittle characteristic is mainly caused by the substitution of Mg for Al and F- for -OH, that is, the structure determines the properties. Therefore, the development of other types of synthetic mica is of great significance in improving the quality of pearlescent pigment products and expanding the application scope of synthetic mica.
