Say "crystal-shaved" powder material

Powder materials come in many forms, block, spherical, single-crystal rod, flaky, fibrous, wafer-like or irregular - in different forms, even the performance advantages of the same material vary. Among them, the wafer refers to the form of a single crystal growth similar to fiber or needle-like, the size is much smaller than the short fiber of the need-shaped single crystal.
Silica carbonized wafer
Because the atom structure is highly ordered at the time of crystallization, there is no greater defect that can weaken the crystal (e.g., holes, misaltation, structural incompleteness, etc.), and its strength is close to the theoretical strength of the perfect crystal, so the styre material Often has excellent high temperature resistance, high heat resistance, corrosion resistance, electrical insulation and other properties, but also has a very high mechanical performance, such as high strength, high elastic mod, high hardness, can be widely used as metal-based, ceramic-based, polymer-based modified reinforcing materials .
A method of preparation of inorgent wafers
because the form of "crystals" is relatively rare in nature, it is generally necessary to grow in the form of monocrystalline under artificial control conditions. At present, through the unremitting efforts of scientists, more than 100 kinds of wafer materials have been successfully developed, including metal monomorphism, various oxides, hydroxides, carbides, nitrides, halides, sulfates and so on.
1. Gas phase method
gas phase legal system inoranced crystal, according to the gasification method of raw materials can be divided into physical vapor deposition and chemical vapor deposition. Physical vapor deposition is an important material preparation technique, which refers to the use of physical methods under vacuum conditions, gasification of the material source surface into gaseous atoms, molecules or parts of ionization, and then the introduction of gas phase raw materials into the low temperature growth zone, in the low temperature zone, gas phase raw materials are low oversaturation, gas-phase condensed nuclei and grow into a wafer, mainly evaporation-condensation method. Physical vapor deposition is mainly used to prepare metal wafers with lower melting points, such as Zn, Ge, etc. Chemical vapor deposition is the chemical reaction of gas phase raw materials, the reaction products in the lower temperature areas to grow into a wafer. The method is often used to prepare ceramic wafers such as oxides, nitrides and carbides.
2. The method of growing the wafer in the solution
solution is similar to the method of growing the monocrystalline, the process is to make the solution oversaturated, so as to achieve the growth of crystals, but the growth of the wafer requires the introduction of some additives in the solution to promote the directional growth of crystals. Hydrothermal method is a research hot spot of the solution legal inorgeous wafer, which promotes the dissolution of raw material materials by artificially manufacturing the solution environment of high temperature and high pressure, or produces products that dissolve and water at high temperature and high pressure, and then forms temperature difference within the solution by controlling the local temperature of the autoclave, so that the solution is inflowing into a local oversaturated state, thus descrystalting and promoting crystal growth.
Hydrothermal method can be divided into hydrothermal redox method according to the reaction type (redox reaction in high temperature high pressure aqueous solution), hydrothermal precipitation (precipitation reaction in high temperature high-pressure aqueous solution), hydrothermal water dissolution (in high temperature high-pressure water solution, hydrolysing of raw materials), hydrothermal recrystation (recrystation in high temperature high-pressure water solution) and so on. The advantage of this method is that it can produce a single crystalline need with a single dispersion, but the output is low, the equipment and the process are more complex and the cost is higher.
3. Growth in a melt
The growth of a crystal in a melt must be the same as the growth of a crystal, the purpose of which is to make the reaction material in a melting state, form a melt, and then through a chemical reaction-shaped nucleation, continuous growth and preparation of the wafer material. The method includes direct melting method, fuse method and molten salt method, which is to heat the reaction material directly until the melt is formed, and then crystallize;
Because the low melting point salt is the reaction medium, the liquid phase appears in the synthesis process, and the reaction has a certain solubility in the liquid phase, which greatly accelerates the diffusion rate of the ions, so that the reactant is mixed at the atomic scale in the liquid phase. The method has the advantages of simple process, low synthetic temperature and short insulation time. The disadvantage is that the quality of the wafer is worse than that of the gas phase method and the solution method.
the classification of two wafer materials
inorderable wafers are divided into two categories: metal and non-metallic wafers. Metallic wafers are commonly found in metal-based composite materials and one-dimensional nano-functional materials such as precious metal nanowires and nanoarrays, and amorphous wafers include oxide and salt-based wafers, which are mainly used for the reinforcement of polymer-based composites, metal-based composites, ceramic-based composites, and a small number of one-dimensional nano-functional wafers with special physical and chemical properties, such as ZnO nanowires with special optical properties. The strength, elastic mould, heat resistance and other properties of amorphometlic wafers are better than metal wafers, widely used in a variety of substrate composite materials reinforcement and toughening, the following are some commonly used non-metallic wafers.
diagram of the principle of the crystalline crust toughening ceramic material
1. Silicon carbide
SiC wafer is a crystal internal defects are very few, with a certain length-to-diameter ratio of single crystal fiber, it has a considerable high temperature resistance and very high mechanical strength. SiC wafer is a cubic crystal, and diamond belongs to the same type of crystal, is currently all synthetic wafer in the largest hardness, the highest mould, the largest pull strength, the highest heat resistance temperature of the wafer products, according to structural differences in the α-type and β-type two forms, β-type performance is better than the α-type.The
β-type SiC whiste has a higher hardness than the α type (Mohs hardness of 9.5 or more), better conductivity, high temperature resistance, higher fracture toughness, mainly used in the need for high temperature and high-strength application material toughness occasions, such as aircraft, missile housing, engines, high-temperature turbine roors, special components and so on, has a very high performance price ratio.
2. Alumina crystal
alumina has many homogenous isoscrystals, research has reported more than 10 variants, of which α-Al2O3 is a three-way crystalline system, the most tight structure, low activity, stable at all temperatures, and the best electrical properties, with excellent mechanical and electrical properties, the most studied crystal type.
Alumina wafer
So the melting point of the α-Al2O3 wafer is as high as 2082 degrees C, showing white, with a needle-shaped or fibrous structure, the section is generally hexagonal, with high strength, high elasticity and other superior mechanical properties, high temperature conditions with antioxidant properties. Widely used in metals, ceramics and polymer composites, mainly play a role in strengthening toughening.
3. Calcium carbonate wafer
calcium carbonate wafer diameter is small, the plastic plays a micro-enhanced effect, with its enhanced plastic products surface finish is high, can be used for precision plastic products molded calcium carbonate crystals with high strength, high mould, heat resistance and good insulation and other excellent characteristics, is a high quality and low price environmental protection materials. With its enhanced polymer material, the rigidity, dimensional stability and thermal stability of the inorgic wafer can be combined with the toughness of the polymer material to produce high-performance polymer composite materials. Calcium carbonate as a coating adhesive in the coating, can significantly improve the viscosity of the coating, increase tentacles, improve the paint's resistance to cracking, adhesion, bonding strength and other properties. Calcium carbonate wafers are used for automotive brake linings and can replace asbestos products.
4. Potassium titanate
Potassium titanate wafer refers to a needle-shaped inorganic wafer chemically called K2O-nTiO2, and the structure and performance of potassium titanate wafers change with n changes. The preparation process of potassium titanate has been more mature and has been industrialized. Potassium titanate must have good insulation, chemical corrosion resistance, wear resistance, low thermal conductivity and high infrared reflectivity, can be widely used in high temperature insulation materials, insulation materials, catalyst carriers, filtration materials.
Potassium titanate crystal, molten quartz, alumina as raw materials to enhance ceramic-based honeycomb ceramic components, with precision size, good high temperature resistance and so on, can be used as automotive exhaust treatment, petroleum combustion gas purification catalyst carrier. Potassium titanate is required to enhance engineering plastics and can be used in the preparation of various polymer-based composite structural components, widely used in automotive, ship and computer fields.
5. Molestone
Molestone has the advantages of high temperature resistance, antioxidant, low coefficient of thermal expansion, high high temperature strength and good resistance to heat shock, and is an important engineering material. The addition of Molybon crystals can significantly improve the toughness of ceramics. For ordinary ceramics, when the quality score of the Mole stone staling is 30%, the toughening effect is the best, and for the mole stone stalve quality score is 10%, the toughening effect is the best. As a potential ceramic-based, metal-based, polymer-based composite materials to enhance toughening materials, the current Mole stone crystal must be widely used in high-temperature structural materials, friction materials and other fields.
the Mole stone
6. Silicon nitride
Compared with silicon carbide wafers, silicon nitride wafers have a high strength, usually up to 138 GPa, which is 5 times the silicon carbide wafer. It also has high elastic mod (390GPa), low expansion coefficient and good chemical stability.
When using silicon nitride as an enhancer, the properties and requirements of the wafer vary depending on the substate, such as the silicon nitride wafer and quartz glass have good physical compatible, its composite material has excellent properties of metal, and the silicon nitride crystal must be toughened in silicon carbide ceramics, both retain carbon The excellent high temperature, anti-creep and antioxidant properties of silicon nitride ceramics,has higher strength and toughness than silicon carbide ceramics, and the substation properties of silicon nitride crystals are improved to varying degrees when they are composite materials of other substations such as alumina ceramics, silicon nitride ceramics and glass.
nitride crystals are
7. Zinc oxide crystal
four-pin ZnO styrofox was discovered in the 1940s and was first developed by Panasonic Industries in Japan in 1989. The appearance of the wafer is white loose powder, the structure is four-pin three-dimensional structure, the crystal must have a core, from the core radial extension of four needle-like branches. Because of the unique three-dimensional structure, it is easy to achieve its uniform distribution in the substation material, added to the metal, resin, ceramic and other substation materials to form composite materials, can play a skeleton role, so that the pull strength significantly increased;
rod-shaped zinc oxide
8. Calcium sulfate
calcium sulfate crystal is based on gypsum as raw material, through artificial control, in the form of a single crystal, with a uniform cross-section, complete shape, perfect internal structure of the fibrous (must-shaped) single crystal, With high strength, high mould, high toughness, high insulation, wear resistance, high temperature, acid and alkali resistance, corrosion resistance, good infrared reflection, easy surface treatment, easy to compound with polymers, non-toxic and many other excellent chemical and chemical properties.
Calcium sulfate must combine the advantages of reinforced fibers and ultra-fine inorge inorge fillers, which can be used as reinforcements or functional fillers in polymeric materials, coatings, paints, friction and sealing materials, and can be used directly as a filter material, insulation material, refraction insulation material, infrared reflective material and highly insulated material covered wire.
source:
preparation, growth process and its application in ceramic toughening, Zhang Jinhua.
the performance of silicon nitride wafer structure and its application status, Li Fu.
research progress of alumina crystal, Li Jie, Nai Xueju, Bean Shaoju, Li Wu.
preparation and characteristics of different forms of low-dimensional ZnO wafers, Chen Erfan, Zhang Li.