In China, mica waste residue after peeling in mica processing plants and mica waste after processing mica parts are partly used for papermaking and mica powder manufacturing, and some are discarded. Long-term accumulation wastes resources and pollutes the environment.
In mica industry, the so-called comprehensive utilization refers to making full use of all mined mica, including synthetic mica, in addition to using large mica, in order to improve the economic benefits of enterprises. There are many ways to comprehensively utilize mica, which can be summarized as follows: ① producing mica paper; (2) producing mica powder; ③ producing mica ceramics; (4) producing mica fused products; (5) producing mica pearlescent pigment; ⑥ Production of mica reinforced plastics.
Due to the expansion of comprehensive utilization and the increase of mica products, the product structure of mica enterprises has gradually changed from the product structure mainly producing large pieces of mica in the past to the product structure mainly processing broken mica now. For example, the mass production of mica paper has largely replaced mica sheet products in large motors. Another feature of product structure transformation is that the production of electrical materials has shifted to the production of non-electrical application materials.
Production of mica paper and its products
Mica has been an indispensable insulating material in the electrical industry for a long time. For example, 65438+1 00000 kw and10000 kv two-pole turbo-generators need1000 kg mica tape, of which mica accounts for about 450 kg. At present, although many new materials have appeared, none of them can replace mica. With the development of electrical industry, the demand for mica is increasing. However, it is difficult to mine mica, and the peeling and slicing of mica are all done by hand, so the output is extremely low. The effective way to solve this contradiction is the manufacture and utilization of mica paper.
Mica paper was first developed by France and put into production on 1947, and was patented. Mica paper manufacturing technology keeps pace with large-scale integrated circuits, high-temperature plastics and optical fibers, and is regarded as one of the four major technologies that have made important contributions to contemporary foreign electrical and electronic industries. It can be seen that the manufacture of mica paper plays an important role in modern science and technology.
Since 1960s, China has successfully developed mica powder paper by relying on its own technical strength, and since 1970s, new materials such as large-scale mica paper and synthetic mica paper have been developed one after another. At present, almost all large motors use mica paper as the main insulator.
(A) the production process of mica paper
Compared with other kinds of paper, the whole production process and equipment of mica paper are different in pulping process. The production process of mica paper is as follows:
Making mica pulp → making mica paper → finishing finished products → adhesive → reinforcing materials → mica paper products.
(2) Manufacture of mica slurry
Millimeter-thick broken mica is crushed into fine mica scales with a thickness below micron, and then the mica scales suitable for making mica paper are separated and mixed with a certain amount of water, which is the process of making mica slurry.
Mica paper is a combination of attraction (van der Waals force, etc.). ) between mica scales. Therefore, the larger the area, the thinner the mica scale and the better the performance of mica paper. In order to ensure the quality of mica paper, mica pulp scales should meet the following requirements: the thickness of scales is micron; The scale thickness ratio is above 50 ~ 100; The calibration area is uniform; Less surface defects; The surface is clean and pure, without pollution.
The manufacturing method of mica pulp generally adopts calcination chemical pulping method, hydraulic pulping method and so on.
1. Calcination chemical pulping method
The selected mica sheet is calcined at high temperature to remove the structural water in the mica structure, so that the mica sheet expands in the direction perpendicular to the cleavage plane, and the texture becomes soft. Then, the mica sheet is fully cleaved by chemical treatment, and then washed and stirred. This method is called calcination chemical manufacturing method, commonly known as cooking method. Copying mica paper is called cooked mica paper, also called mica powder paper. The process flow is as follows:
Processing, development and utilization of nonmetallic minerals
Chemical treatment methods are divided into:
(1) acid-base method
Without cooling, the calcined mica is soaked in Na2CO3 solution with a concentration of 2% ~ 10% for 5 ~ 30 minutes, and then 2% ~ 3% HCl or H2SO4 is added to make it undergo neutralization reaction, generating a large amount of CO2 gas to further expand and rupture mica sheets, and then mechanically stirring and washing to form mica slurry.
(2) Ammonium carbonate method
Soak the calcined mica clinker in ammonium carbonate solution, then heat the clinker soaked in ammonium carbonate solution to 100 ~ 400℃ in a reaction kettle to decompose (NH4)2CO3 into CO2 and NH3, and the mica layer is further expanded and broken, and stirred into slurry.
(3) acid treatment
Soak mica clinker in 2% ~ 5% dilute acid and heat it to form slurry. The treatment conditions are: solid: liquid 1: 8 ~ 1: 12, treatment temperature 90 ~ 100℃, and time 30 ~ 60 minutes.
2. Hydraulic pulping method
In a special cavity, mica flakes are stripped and broken into fine scales by high-pressure jet, and then mica scales suitable for papermaking are separated by mineral processing. The process is as follows:
Mica crushing → sorting → washing → hydraulic pulping → hydrocyclone classification → dehydration and concentration.
(3) The papermaking process of mica paper
Compared with other types of paper, the whole production process and equipment of mica paper are different in pulping process. Generally speaking, the papermaking technology and equipment of mica paper are the same as other kinds of paper and paperboard.
The composition of paper machine: wire section, press section, drying section, finishing section, winding section, transmission section, etc. 2% ~ 3% mica slurry in the slurry pool is diluted to 0.3% ~ 0.7% with water. Put into a downstream overflow net groove. As soon as the circular mesh cage turns into the mesh trough slurry, it starts to filter the slurry, that is, the slurry water leaks through the sieve, and the mica sheet is filtered on the mesh cage. When the speed of the slurry is consistent with the linear speed of the mesh cage, it can be uniformly sized to form a uniform mica paper embryo.
The mica paper blank is continuously formed with the continuous rotation of the round net cage in the net groove, and the formed paper blank is wrapped by the circular blanket under the action of the couch roll. Because the specific surface area of the blanket is much larger than that of the round cage, the wet embryonic paper is transferred to the blanket, supported by the blanket, and further dehydrated by the vacuum suction box and the press section. In the process of papermaking, the moisture removed from the wire is about 95% ~ 98%.
(4) mica paper products
Both calcined mica paper (cooked paper) and non-calcined mica paper (base paper) have low mechanical strength and cannot be used directly. Because mica scales are bonded by residual bonding force, and the fresh surface of mica scales is easy to absorb various ions or molecular gases such as moisture and hydroxyl, which affects the close bonding of mica. Therefore, mica paper needs to be made into various products, such as mica board, together with adhesives and reinforcing materials to meet the requirements of different uses.
1. Raw materials and requirements
1) mica paper tires: mica paper tires that have passed the inspection.
2) Adhesives: Adhesives with good electrical insulation, moisture resistance, water resistance, drug resistance, good thermal stability, excellent adhesion and high mechanical strength should be selected. Such as shellac, modified organic silica gel, modified organic titanium epoxy glue, polyester epoxy glue, phosphate, borate, etc.
3) Reinforcing materials: commonly used alkali-free glass cloth, mica tape paper (made of mulberry fiber, with high impregnation ability, good mechanical properties, thickness of 0.025~0.005mm, large tensile force and light weight), telephone paper (made of unbleached sulfuric acid pulp), polyester film, fully aromatic polyester ammonium fiber paper, etc.
2. Production technology
Cut mica paper and reinforcing materials into required sizes, match blanks according to the thickness of finished products, brush glue, bake at 100 ~ 130℃ for melting, press at 10 ~ 20kg/cm2 for 5 ~ 30min, cool to room temperature and discharge. The process flow is as follows:
Mica paper+reinforcing material+adhesive → hot pressing consolidation.
3. Ordinary mica paper products
According to the types, dosage and reinforcing materials of adhesives, mica paper products are divided into mica tape, soft mica board, plastic mica board, heat-resistant mica board and mica foil.
(1) mica powder band
Such as: multi-mica powder belt: with glue content above 35% and thickness of 0.14 ~ 0.16mm;
Mica tape with less rubber powder: the rubber content is about 5% and the thickness is 0.14 mm;
The thickness of three-in-one mica powder tape is 0.14 ~ 0.16mm;
Mica powder belt: the thickness is 0.1~ 0.15 mm;
Soft mica board: thickness 0.42 mm;
Mica paper: 0.04~0.08mm thick.
(2) molding mica plate
Plastic mica plate is a kind of hard plate at room temperature, which is slightly brittle, becomes soft and plastic after heating, and can be made into parts with different shapes under the action of external force, such as pipes.
Manufacturing method: firstly, lay the glass cloth flat on the workbench, evenly brush the prepared glue, and then brush the glue after laying the mica paper flat. According to the thickness of the product. If it is double-sided reinforcement, add a layer of glass fiber cloth, then put the molded mica board blank on the barbed wire and dry it at 140 ~ 150℃ for 2 hours. Stack the dried blanks into plates according to the thickness, arrange them in the same order as the soft mica plate, determine the number of plates according to the thickness requirements, and press them after leveling. The pressing conditions are 140 ~ 160℃ for 20 ~ 40 minutes, and then 15 ~ 20kg/cm2 for 20 minutes.
(3) Heat-resistant mica board
The improved heat-resistant mica board mainly relies on adhesive. Mica itself is heat-resistant above 600℃, and heat-resistant adhesives include inorganic adhesives, organic adhesives (special types) and organic-inorganic mixed adhesives. Such as heat-resistant silicone gel, ammonium phosphate, aluminum phosphate, borate and silicate.
(4) mica powder foil
It is made of mica powder paper, adhesive and reinforced glass fiber cloth or telephone paper through baking, melting and pressing. It is plastic at a certain temperature and can be used as insulation material for motors and electrical windings.
Second, mica ceramics
(1) Overview
Mica ceramics can be divided into natural mica ceramics and synthetic mica ceramics. Natural mica ceramics are also called mica glass (often called glass-bonded mica abroad), and synthetic mica ceramics are also called Erasmus-TIC (called supramica or Erasmus-TIC abroad). 19 18 years, the British first made molten glass-bonded mica into plates. 192 1 year, the United States obtained a patent for producing mica ceramics from natural mica. In the early 1960s, China began to study natural mica ceramics and produced them in small batches.
The production of mica ceramics is usually a composite material made by crushing mica, then mixing it with special glass powder or other inorganic powder in a certain proportion, pressing, roasting, hot pressing or injection molding, annealing and other processes.
(2) Production technology
1. Raw material requirements and formula
The raw materials of mica ceramics are mica powder, glass powder and a small amount of mineralizer or flux.
Mica powder: purity >; 98%, moisture
Glass powder: Lead glass with low softening point and good wettability (PbO=8 1.6%, B2O3= 18.4%) is selected, and the particle size is required to be -200 mesh, clarified and homogenized at 800℃, so that the structure of mica will not be destroyed at high temperature and the original properties of mica will not be lost.
Mineralizer: It can be used as flux to reduce sintering temperature. Mineralizers include K2CO3, Na2CO3, AlF3, PbF2, Na3AlF6 and K3AlF6. The addition amount is 1% ~ 3%.
Formula: glass powder accounts for 30% ~ 50%, mica powder accounts for 50% ~ 70%, and mineralizer accounts for 1% ~ 3%.
If the shape of hot-pressed products is complex, the amount of glass powder can be appropriately increased to ≥60% to increase the fineness of mica powder.
If the shape of hot-pressed products is simple, the dosage of mica powder can be appropriately increased, and the particle size of mica can be slightly coarse, so that the extruded products are ideal in electrical properties, strength, thermal stability and so on; In the process of injection molding, the amount of glass powder should be increased.
2. Hot-pressing molding process
Processing, development and utilization of nonmetallic minerals
After demoulding, annealing is needed to eliminate thermal stress. The demoulded product is put into a tunnel furnace, so that the inlet temperature is close to the demoulding temperature, and the cooling rate is 30℃/h, and when the outlet temperature is lower than 60℃, the mica ceramic finished product is obtained.
(3) Characteristics and uses of mica ceramics
Mica ceramics is a kind of composite material, which has the advantages of mica, ceramics and plastics, that is, it has the thermoplasticity of plastics, the excellent electrical insulation and machinability of mica, and the high temperature resistance of ceramics. It is a composite material with many properties.
Mica ceramic products are mainly used as insulating parts in electrical equipment, and are widely used in the fields of posts and telecommunications, radio and aerospace.
There are many kinds of mica ceramics, such as mica ceramics with molten glass as binder, phosphate bonded mica ceramics, hot-pressed pure mica ceramics and so on. And the production process is similar.
Three. Mica pearlescent pigment
(1) Overview
Since ancient times, pearls have been precious decorations like precious stones. Pearls can be used as decorations because they have pearl luster. People have been looking forward to making pearl luster decorations by artificial methods for a long time. As early as the middle of17th century (1650), the manufacturer of twisted beads in Paris extracted fine crystals of guanine from the scales of freshwater fish (obeitte), then dispersed them in gel, then poured the gel into hollow glass, cooled and solidified to form molded pearls.
Natural pearlescent pigment (alias fish scale) has two disadvantages: one is the shortage of raw materials, low quality and high price; Second, the brightness of the color is easy to change and the quality is unstable.
In the hundreds of years since then, while developing molded pearls, the synthetic production technology of pearlescent pigments has gradually developed. Synthetic pearlescent pigments mainly include lead compounds, such as basic lead carbonate 2pco3 Pb (OH) 2) 2, which are mainly used in ceramic glaze, art, cosmetics, antirust paint, outdoor paint and so on. Bismuth compounds, such as basic bismuth carbonate (bio-) 2CO3H2O, are used as additives for pearlescent plastics and adhesives for cosmetics. Because the compound of lead and bismuth is toxic, it cannot be used in food containers, cosmetics, toy coatings and so on. Therefore, it is urgent to find a non-toxic and cheap pearlescent pigment, so mica pearlescent pigment-mica titanium appears.
Decades ago, DuPont Company of the United States developed the technology of coating a titanium dioxide film on the surface of flaky mica. Compared with natural pearlescent pigments such as pearlescent pigments and lead-bismuth compounds, it has the advantages of wide source of raw materials, low price, non-toxicity, stable performance and wide application. At present, this kind of mica pearlescent pigment is in great demand internationally, and the domestic demand is also increasing, which is a new important aspect of mica comprehensive utilization.
(2) Preparation method of mica titanium pearlescent pigment-hydrolysis preparation method.
Preparation of pearlescent mica by hydrolysis;
Muscovite raw materials → wet crushing → classification → hydrolysis titanium plating → water washing → dehydration → drying → roasting → product.
Mica scale obtained by wet grinding is often used because of its smooth surface, few scratches, good performance and strong pearl luster. Classification is to obtain mica scales with appropriate size. When the particle size of flake mica is 5 ~ 27 microns, the pearlescent mica has strong luster and can emit uniform light. The gloss is uniform when it is & lt5μm, and strong when it is more than 40μm, but it can't emit uniform light. Titanium sulfate is a commonly used titanium plating material in industrial production. During the hydrolysis of titanium sulfate, a kind of metatitanic acid H2TiO _ 3 is generated, which precipitates and covers mica scales to form a uniform H2TiO _ 3 film. Then, the mica covered with H2TiO _ 3 film is calcined to crystallize the crystalline film of TiO _ 2. The reaction process is as follows:
Processing, development and utilization of nonmetallic minerals
The reaction is endothermic and accompanied by H+, so hydrolysis is affected by two aspects: temperature and pH value of hydrolysate. The effects of temperature and pH value on the hydrolysis process are as follows:
1. temperature
When the hydrolysis temperature is high, the hydrolysis rate of titanium salt water increases, the hydrolysis rate is fast, the hydrolysis product TiO _ 2 XH2O particles are coarse and the pearlescent effect is uniform. The hydrolysis temperature is low, the hydrolysis speed of titanium salt water is slow, and the generated TiO2 xH2O particles are fine and uniform, and the pearlescent effect is strong. But in industrial production, the hydrolysis rate of titanium sulfate is low at low temperature, which wastes chemicals and increases the cost. Considering the pearlescent effect and production cost, 95℃ is the best hydrolysis temperature, which can not only obtain a higher hydrolysis rate, but also ensure the pearlescent effect of pearlescent pigments.
2.pH
When pH >; 4. The hydrolysis speed is fast, and the generated TiO 2·XH2O has colloidal characteristics, so it is difficult to cover the surface of mica to form mica titanium. At the same time, due to the fast hydrolysis speed, the generated TiO 2·XH2O particles are coarse, and the gloss after roasting is poor. When ph
3. Hydrolysis time
Hydrolysis time usually takes 3 ~ 5 hours to reach hydrolysis equilibrium. If the reaction time is prolonged, fine metatitanic acid will condense to form coarse aggregate, which is difficult to be adsorbed on mica surface to form mica titanium.
The purpose of roasting is to remove colloidal water, SO42-,SO3 and other impurities in metatitanic acid, so as to crystallize titanium dioxide and enhance the pearlescent effect of mica titanium. The experiment shows that the crystallization and crystallization transformation of TiO2 _ 2 can be completed by melting sintering at 800℃ for 2 ~ 3 hours.
Most of the titanium dioxide on the surface of mica titanium produced by this method is anatase crystal film.
Wu Yishan, graduate department of Wuhan University of Technology, and others think that adding the crystal-transforming agent AB2 compound (with rutile structure) can promote the transformation of TiO _ 2-XH2O on mica surface into rutile TiO _ 2 during roasting, because rutile structure is more stable and its physical and optical properties are better, which is an ideal form of mica titanium.
(III) Main uses of mica pearlescent pigments
1) plastic filler: plastic filler for cosmetics and food containers, which makes the products have pearl luster.
2) decorative coatings filler: such as acrylic plastic button coating; Body coating filler; Fillers for cosmetics such as lipstick and nail polish.
Fourth, the production of mica powder
(A) the use of mica powder
& gt5 mesh mica powder is mainly used as oil drilling mud material;
8 ~ 20 mesh mica powder is used as anti-sticking layer, protective layer and cable wrapping layer in linoleum roofing materials;
40-60 mesh mica powder is used as the raw material of covered electrode coating;
60 ~ 120 mesh mica powder is used as the basic raw material of mica ceramics;
100 ~-325 mesh mica powder is used as filler in coatings, rubber, plastics and other industries.
Using mica powder in paint has the following advantages:
1) mica powder can reflect light and heat energy, which can reduce the damage of ultraviolet or visible light to paint film;
2) Enhance the acid resistance, alkali resistance and electrical insulation of the coating;
3) mica scales can reflect light, and pearl luster makes the coating beautiful;
4) Improve the weatherability, frost resistance, corrosion resistance, toughness and compactness of the coating;
5) It can replace some expensive pigment raw material titanium dioxide and reduce the cost.
(2) Production method of mica powder
1. Dry method
Dry-process mica powder generally adopts three-stage crushing process: coarse crushing, fine crushing and ultra-fine crushing.
Coarse grinding: discharging particle size
Fine grinding: discharging granularity
Ultrafine grinding: feeding
The characteristics of dry mica powder are: many scratches on the surface, serious sheet damage, 30% reduction in strength, but large output and low cost.
2. Wet production
Wet production of mica powder generally uses a roller mill. The roller mill is a circular steel cylinder with a diameter of 180 ~ 3000 cm and a height of 90 ~ 150 cm. The base is lined with wood blocks, and the drum radius is 50 ~ 76 cm. The surface of the drum is made of wood or other soft materials. Roller mills are divided into two types: double rollers and four rollers, and the rotating speed of the rollers is 15 ~ 30 rpm.
The production process is as follows: adding 30% ~ 45% water to the washed scale mica to form paste, putting it into a roller mill, rolling for a certain period of time, diluting and sieving the slurry in the roller mill, and then sending it to a settling tank for re-dilution. The settled coarse material returns to the roller mill for re-grinding, and the suspended particles of fine mica powder are pumped into another tank through a conveying pipe to settle for more than 36 hours, and clear water is sucked.
Characteristics of wet mica powder: mica sheet has few scratches and smooth surface, which has little influence on mechanical strength and strength loss is less than 5%, but the production process is complicated and the cost is high.
Five, mica reinforced plastics
1. Overview
Mica reinforced plastic is a composite material made of mica sheet with large diameter-thickness ratio treated by coupling agent and made of thermoplastic resin or thermosetting resin.
1972, Professor R.T.Woodham of the Department of Chemical Engineering of the University of Toronto used mica to make mica reinforced plastic composites for the first time.
Requirements for mica scales: The greater the diameter-thickness ratio, the higher the strength of its products.
Coupling agent: Because mica and plastic are two different substances, there is a great degree of incompatibility between them. In addition, the elastic modulus of mica and plastic is inconsistent, and shear stress is easy to occur at the interface, which affects the mechanical properties of their composites. Coupling agent, also known as surface treatment agent, combines two substances with different properties through chemical or physical action, that is, it can closely combine inorganic filler (mica) and organic polymer binder (plastic). Therefore, coupling agent is also a bridge between inorganic and organic materials. The surface of mica powder was modified by silane coupling agent.
2. Production technology
Mica powder → surface modification → adding resin for mixing → melting → injection molding → cooling → demoulding.
The diameter-thickness ratio of mica is required to be >; 100, with a narrow particle size distribution, accounting for 30% ~ 50% of engineering plastics, with a maximum of 70%. The dosage of coupling agent is 0.5% ~ 3% of the filler.
3. Properties and uses of mica reinforced plastics
1) mechanical properties: high strength, similar to FRP, which can strengthen plastics in two dimensions instead of glass fiber or asbestos in only one direction. The tensile strength and bending strength of mica reinforced plastics are almost the same as those of FRP, and the thermal deformation temperature is higher than that of FRP. The only disadvantage is that the notch impact strength is not as good as that of FRP, which can be overcome by adding a small amount of glass fiber.
2) Thermal performance: The thermal expansion coefficient and shrinkage of mica reinforced plastics decrease uniformly in all directions, unlike the shrinkage of FRP in different directions.
3) Electrical insulation performance: high breakdown voltage, coupled with the use of silane coupling agent, can still maintain its mechanical and electrical properties in humid environment.
4) Good chemical stability: resistant to acid and alkali and organic solvents, mica unsaturated resin and mica epoxy resin can be used as anticorrosive coatings.
5) Good radiation resistance: it can prevent plastics from aging.
6) Main uses: front bumper, dashboard of small cars, wings of light aircraft, and mica engineering plastics are mostly used in automobiles.
Six, synthetic mica casting products
1. concept
Synthetic mica melt-cast product is a new type of inorganic insulating material with high temperature resistance, machinability and corrosion resistance, which is made of synthetic mica flake as the main raw material through batching, melting, casting and crystallization annealing.
The research of synthetic mica casting products abroad began in the late 1960s, and in the early 1970s, the research and small batch production of synthetic mica casting products began in China.
2. Production process
(1) raw materials and requirements
Synthetic fluorophlogopite: crystal chemical formula is KMG3 [ALSI3O 10] Fe, using temperature is 1 100℃, melting temperature is1370℃; Additives: the dosage of ZnO, Cr2O3, Be2O3, PbO and CaF2 is 8%, and their main functions are to change the crystallization temperature of products, the size and shape of grains, and the chemical stability of materials.
(2) Production technology
Proportioning of raw materials → melting → pouring → crystallization → annealing → product.
The raw materials are melted at 65438 0420℃, homogenized for 2 ~ 3h, and then the flowing melt is injected into the mold for molding. Plate products are generally formed by gravity casting, and tubular and annular products are formed by centrifugal casting; In order to eliminate the internal stress caused by crystallization and cooling, annealing must be carried out. The annealing temperature of general products starts from 600℃.
Synthetic mica casting product is a mica microcrystalline polymer, and its structure is consistent with synthetic fluorophlogopite by X-ray diffraction analysis.
Step 3 perform
1) Good machinability: ordinary machining methods can be used for cutting, drilling, milling and polishing, and parts with complex shapes can be machined with accurate dimensions and smooth surfaces.
2) Good chemical stability: acid and alkali resistance, corrosion resistance of nonferrous metals and alkaline earth metals.
3) Good thermal stability: heat it to 800℃ and put it into cold water immediately, and repeat it for dozens of times without explosion. The long-term service temperature is 1 100℃.
4) Electrical insulation: It is a good electrical insulation material.
5) Mechanical strength: it has certain toughness, but it is still a brittle material.
4. Application
Metal heat treatment industry: the machinability, high temperature resistance, electrical insulation and mechanical strength of synthetic mica casting products are incomparable to those of general materials (ceramics and plastics), and are used as cathode insulation parts of ion nitriding furnaces in metal heat treatment equipment.
Non-ferrous metallurgy: used as pipeline material for transporting zinc and aluminum alloy melts.
Defense industry: used as throat lining material of missile nozzle.