The process of processing the mineral raw material after the processing and compounding is melted at a high temperature, and the transparent melt is clarified, homogenized at a high temperature, and then condensed to form a crystalline or amorphous material, which is called melt solidification.
Melting is the main process of synthesizing refractory materials, cast stone, artificial crystal, glass, ceramic glaze, glass fiber and other mineral materials. Melting is a process in which the batch material is heated at a high temperature to obtain various single-phase continuums having no solid particles and meeting the molding requirements. For example, a fused cast refractory material is generally melted at a high temperature in an electric furnace. The melting of the cast stone is to melt natural rock [ basalt , diabase, etc.) or industrial waste into a melt. The melting of the intraocular lens includes a zone melting method, a flame melting method, an internal resistance melting method, and the like. The melting of the glass is the melting of the glass batch into a uniform glass liquid that meets the molding requirements. The preparation of ceramic glaze frits is similar to the melting of glass. Melting of mineral materials is a very complex process. What they have in common is that the batch (powder or block) completes a series of physical, chemical and physicochemical processes through heat transfer, mass transfer and momentum transfer in a high temperature furnace, which can be summarized as Table 4. -9-12. The chemical bond inside the solid material is broken due to the high temperature, so that the original solid mixture becomes a melt having a certain atomic structure, a chemical bond and a uniform composition distribution.
The interaction of solid phase, liquid phase and gas phase in the melting process constitutes the transformation and balance of complex phases. That is, the transfer of heat from a high temperature portion to a low temperature portion at a high temperature causes a plurality of solid phase powders or bulk materials to reach a melting point or a low eutectic point, and is gradually converted into a single, uniform melt. Therefore, melting is a process of converting from a solid phase to a liquid phase without phase change, and the melt interacts with the gas phase to eliminate visible bubbles. Further, the diffusion of the different components in the melt without visible bubbles from a high concentration to a low concentration causes the melt to be chemically uniform, completing the mass transfer process. Mass transfer is accomplished by molecular diffusion and turbulent diffusion, and its density (concentration) gradient is the driving force for mass transfer.
Mass transfer, heat transfer, momentum transfer, referred to as "three pass." It is an indispensable process in the melting process of mineral materials. They follow the three most fundamental laws of physics, namely mass conservation, energy conservation, and momentum conservation. There are complex heat transfer, mass transfer and momentum transfer during the melting process. The three kinds of transmissions have their own laws, which are related to each other and conditions. How to organize the "three passes" in the melting process is the key to making various melts more, faster, better and more economically. The various reactions listed in Table 4-9-12 are all based on mass transfer, but they are all subject to a certain temperature. The speed of the process is closely related to the temperature, and also the various momentums. The transmission is inseparable. The difference in velocity between the fluid layers of the melt in the high temperature furnace results in the momentum transfer of the fluid, which makes the melt viscosity uniform for ease of forming. At the same time, the transfer of mass changes the state of matter and affects the transfer of heat and momentum.
If the melt is cooled to a certain temperature and crystallized and solidified, various polycrystalline or single crystal materials can be formed. These materials have excellent properties such as high density of fused cast refractories and excellent high temperature corrosion resistance; high hardness and excellent optical properties of artificial gemstones . The cast stone is formed by melting, casting and recrystallization of diabase, basalt and blast furnace slag, and has high wear resistance. Some artificial crystals, such as artificial gas mica , iron mica, polycrystalline, etc., are first made into a melt and then formed into crystals.
If a sufficiently clarified, homogenized melt at a high temperature is quenched and solidified under conventional conditions to avoid crystallization, a conventional amorphous solid-glass is formed; the glass block is reheated to a certain temperature to control crystallization, and Glass-ceramic, it has better quality than glass, such as small density, dense texture, no pores, impervious to water, airtight, high softening temperature, good chemical stability and thermal stability, high mechanical strength, high toughness, hardness Large, excellent electrical performance, etc. Therefore, it is widely used in many fields, see Table 4-9-13.
If the melt is directly drawn into a filament, various glass fibers can be obtained. Due to its high strength, high insulation and excellent thermal insulation properties, glass fiber has a wide range of applications, such as reinforcing materials for various matrix composites.
If refined, high-purity or synthetic raw materials are used, new processes are adopted, glass with special functions or special purposes synthesized under special conditions or strictly controlled in the glass state forming process, and the above-mentioned glass-ceramic obtained by conventional glass crystallization is also included. , called special glass. Special glass can be divided into optical functional glass (Table 4-9-14), electromagnetic functional glass (Table 4-9-15), thermal functional glass (Table 4 - 9 - 16), mechanical function according to its functional characteristics. Glass (Table 4 - 9 - 17), bio-functional glass and chemical functional glass (Table 4-9-18).
Special glass is an indispensable material in the field of high technology, especially the basic material developed by optoelectronic technology. Communication fiber has become the protagonist of the communication technology revolution, and plays a role that other materials cannot play in the current information highway. For example, optical glass fibers can be used for illumination light sources or light pipes with various optical sensing elements, industrial and medical endoscopes, "light knives" and the like. Compared with the microwave communication system of coaxial cable, it has the advantages of anti-electromagnetic interference, small size, light weight, radiation resistance and easy laying. Therefore, optical glass fiber has become the basis of modern optical communication. In the next few years, laser glass, functional fiber, optical memory glass, integrated circuit (IC) photomask, glass for optical integrated circuits, and electromagnetic, magneto-optical, optoelectronic, acousto-optic, piezoelectric, nonlinear optical glass, Functional glass such as high-strength glass and biochemistry will be greatly developed.
In order to obtain a glass with special functions, or to make certain characteristics of the glass more prominent, in addition to the conventional melting method, some special glass forming methods must be employed. For example, according to the different aggregate forms of materials to be classified into glass, representative glass forming methods are as follows.
(1) Vapor deposition method. There are several methods for producing a glass state by a vapor phase, such as a vacuum evaporation method, a cathode sputtering method, and a chemical vapor deposition method.
1 vacuum evaporation method. A small amount of sample is evaporated by heating or electron beam bombardment under vacuum
It is vaporized and then condensed onto an amorphous substrate to form an amorphous film. In general, the composition of the base material, vacuum evaporation system, substrate temperature and other factors will affect the structural composition of the film. The advantage of this method is non-polluting, more materials can be coated with a metal, oxide and the like.
2 cathode sputtering method. The method utilizes cathode electrons or inert gas atoms or ion beams to bombard the metal and oxide targets near the cathode, sputter it onto the substrate, and cool to form an amorphous material. In recent years, a reactive sputtering method has been developed on the basis of this method, that is, an oxide amorphous film (such as PbO-TeO2, PbO-SiO2 film, etc.) is formed on the substrate and reacted with oxygen after sputtering.
The energy of the sputtering method [10 eV) is higher than that of the vacuum evaporation method [energy is only 0.1 eV), so the adhesion of the film layer is strong and compact, and it is suitable for materials that are not easy to evaporate, and the disadvantage is that the efficiency is not high enough.
3 chemical vapor deposition (CVD). This method utilizes a gaseous species to chemically react on a solid surface to form a solid precipitate that condenses on the substrate as a reaction product while still maintaining a remote, disordered structural state. Of course, the reaction occurs close to or on the surface of the substrate and should not occur in the gas phase. The method is applied under the condition that the reactant has a high gas state or a high vapor pressure at room temperature or not high temperature, and has high purity; the desired deposition layer can be formed while other reaction products are volatile; the process reproducibility is good, low cost.
The coating prepared by the CVD method has good adhesion and small internal stress. Compared with the above method, the CVD process is simple, economical and practical. So far, the glassy materials prepared by the CVD method are glassy electrical insulating materials Si3N4 and conductive Si3N4-C, Si3N4-SiN, Si3N4-AIN and other composite glassy materials in the semiconductor industry; glass for boron diffusion sources The state BN and the glassy state boride having conductivity, chemical stability and hardness are Ti-B, Al-B, Zr-B, etc., and a phosphosilicate glass film (P2O5.SO2).
(2) Melt cooling method. The glassy substance is produced by melt cooling, and the remote disordered structure is obtained by heating and melting. Whether or not the remote disordered structure can be maintained depends on the tendency of the melt to reach a supercooled state, i.e., the ability of the melt to be subcooled below the melting point without causing nucleation and crystallization. Obviously, only those liquids that are too cold and not crystallization can become glass. Metals, alloys or some ionic compounds can be made into a glassy state by means of a high-speed cooling melt process. It has been studied to spray with a mechanical high-speed rotation and then impact the cooled surface. It is also possible to spray molten metal onto the cooled surface by centrifugal force. The cooling method can be cooled by conventional melt cooling. 20 to 30 times more. The piston-anvil method (or hammer-anvil method) drops molten metal between the rapidly moving piston (hammer) and the anvil, and the droplet is compressed; the compressed liquid is quickly transferred due to the copper pad. The drip can be quenched into glass. The glass piece obtained by the method can have a certain thickness (tens of micrometers) and its shape is regular, and the parallelism of the two sides is good. The cooling rate is 2 to 3 orders of magnitude higher than the conventional melt cooling method. Between the two rotating wheels It is poured into the melt, the melt is flattened, and quenched into a uniform long strip sample. This method is called roll quenching method. This method can be made into a continuous belt with a width of 5 ~ 10mm and a thickness of 0.02 ~ 0 ^ 12mm. There is also a certain value in practical use. The cooling rate of the roll quenching method can reach 108 KS -1 or higher. In short, some liquid cooling technologies developed in recent years will greatly increase the cooling rate of the melt cooling method.
Crystal energy pumping method.
1 irradiation method. This method is a method of bombarding a crystal material by a high-speed neutron beam or a particle beam to make it amorphous. The process is as follows:
Since neutrons or alpha particles can transfer a large amount of energy to the atoms in the crystal, so that the atoms leave their position in the crystal lattice, enter the void or collide to form defects, resulting in atomic spacing and chemical bonds in the crystal lattice. The angles change, causing the structure to transform into a remote state to form a glassy state.
2 shock wave method. Some crystalline materials are subjected to an explosion method or a transient shock wave in a splint to form a glassy state under extreme pressure and consequent high temperature. Phosphorus is formed of glass such as quartz crystals become amorphous when at pressures greater than 3.6 X 1010 Pa when the shock wave, and if crystalline white phosphorus at 250 deg.] C, a pressure of greater than 7 X 108 Pa.
3 ion implantation method. The surface of the crystal is bombarded with a high-energy ion beam (several tens of electron volts to several hundred keV), and the surface of the substrate can be amorphized when the implanted ions reach a high dose (generally not less than 10%). The hot peak generated during ion implantation and the extremely high pressure density and dislocation density when bombarding the surface cause the surface of the substrate to be remotely disordered. High-dose ion implantation can be used to make a variety of glass-state alloy systems. For example, Fe, Co A glassy alloy composed of Ni and B, P can be obtained by this method.
(4) Solid phase thermal decomposition method. Amorphous materials can also be obtained by solid phase thermal decomposition, but this method is of great significance in glass glass. It is made by heating carbonized phenolic resin and decyl alcohol. With carbonization, the pore surface area becomes larger at L111 °C ~ 800 °C, and the mass and volume decrease. At 500 ~ 1200T, the pores disappear one after another, and become a non-porous glassy carbon with a glassy appearance.
(5) Sol-gel method [Sol ~ gel method]. This method is also called solution low temperature synthesis. The sol-gel method has only been used for the preparation of glass for decades. Its principle is to form a gel by chemical reaction and polycondensation of a metal organic compound (metal alkoxide) of a suitable composition in a liquid state, dehydrated by heating and finally sintered. Glass material.
Compared with the high temperature melting method, the sol-gel method has the following advantages:
1 Based on this method is to use the chemical reaction in the solution, the raw materials can be uniformly mixed at the molecular level, so the product uniformity is high, especially for multi-component glass, this advantage is more prominent;
2 alkoxide raw materials are easy to purify, so the purity of the product is also high;
3 The sol-gel method heat treatment temperature is much lower than the melting temperature of the corresponding glass, thus saving energy and reducing volatilization loss and pollution;
4 Sol-gel method can obtain some glass obtained by the high viscosity and easy phase separation and crystallization composition which is difficult to obtain by the melting method.
The main disadvantage of the sol-gel method is that the raw material price is high, and the product is easily cracked during the drying and sintering stages, and the treatment time is relatively long.
Films, fibers, bulk glass, and hollow glass microspheres have been successfully produced by the sol-gel method.
In summary, although there are many methods for forming glass, new processes are continuously produced, but the total can be divided into two types: melt cooling method and non-melting method. Conventional melt cooling and solidification processes in melt cooling processes remain the primary method of synthesizing glass.
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