Identification characteristics of brucite

It is characterized by its morphology, low hardness and (0001) very complete cleavage. Cubic system, A0 = 0.313nm, C0 = 0.474nm; Z=1。 Brucite type structure is one of the important layered structures. In the structure (OH) - it is approximately hexagonal close packing, Mg2 is filled in the octahedral gap one layer away from the stacking layer, each mg is surrounded by 6 Oh, and there are 3 mg on one side of each oh. The [Mg (OH) 6] octahedron ‖ {0001} is connected into layers in a common edge manner, and the layers are maintained by a very weak hydrogen oxygen bond to form a layered structure. Mg Oh is not a regular octahedral sheet, which is obviously flattened along the c-axis, and the sheet thickness changes from normal 0.247nm to 0.211nm. The structural characteristics of brucite make it have plate crystal shape, low hardness and very complete cleavage of ‖ {0001}.


Complex trigonal trigonohedral crystal class, d3d-3m (l33l33pc). The crystal is plate-shaped or leaf-shaped. Common simplex: parallel double-sided C {0001}, hexagonal column m {1120}, rhombohedron R {1011}, Q {0113} or {2021}. The crystals are usually plate-shaped, fine scaly, round and irregular granular aggregates; Sometimes there are parallel fibrous aggregates called fibrous brucite. There is structural distortion in wollastonite. White, grayish white, green, yellow or maroon when Fe and Mn are mixed; Fresh surface and fracture glass luster, cleavage surface pearl luster, fibrous brucite silk luster; Transparent. Cleavage {0001} is very complete. Hardness 2.5. The thin pieces are flexible and flexible. The relative density is 2.3 ~ 2.6. Thermoelectric. The whiteness of massive brucite can reach 95%.


Under polarizer: the abnormal interference color is reddish brown instead of normal primary yellow or orange. Under the influence of stress, ductility can be positive or negative. Uniaxial crystal (), but biaxial crystal, 2V ? 25 ?. Refractive index ne = 1.5705 ~ 1.5861, no = 1.5612 ~ 1.570, the difference between NE and no decreases after heating.


Mechanical properties: the tensile strength of brucite is 902mpa, which is a medium strength fiber material. Elastic modulus 13800mpa, with certain brittleness. Vickers hardness is 50.4 ~ 260.5 and has obvious anisotropy. Easy to grind into fine powder. Theoretical relative density 2.39.


Electromagnetic properties: the mass resistivity of wollastonite is 8.82 ? 106 Ω? g / cm2, the volume resistivity is 5.9 ? 106 Ω? cm, the surface resistivity is 3.6 ~ 4.5 ? 106 Ω, and the resistivity is anisotropic; The resistivity increases when heated. The dielectric constant is 4.7 ~ 5.4 (1MHz); At low frequency (50Hz) and intermediate frequency, the dielectric constant increases and has obvious directivity; The dielectric loss tangent is 0.105. The dielectric constant and dielectric loss tangent increased by 54% and 2.7 times respectively. The specific magnetic coefficient of wollastonite is 9.815 ~ 15.779 ? 10-6cm3 / g, which is a non-magnetic mineral; Heating increases the specific magnetic susceptibility, but there are valleys near 300 ℃, 500 ℃ and 600 ℃. When the temperature is higher than 700 ℃, it shows medium strong magnetism.


Thermal properties: the reliable service temperature of brucite is 400 ℃. The thermal conductivity of wollastonite is 0.46w / m · K and that of loose fiber is 0.131 ~ 0.213w / m · K (bulk density 0.47 g / cm3). The thermal expansion of wollastonite is 16.7 * 10-7 / ℃ in the longitudinal direction and 8.8 * 10-7 / ℃ in the transverse direction, and the thermal expansion behavior is basically linear. Wurtzite also has the properties of flame retardant, resistance to open fire and high temperature flame. The decomposition temperature of wollastonite is 450 ℃.


Chemical properties: wollastonite is the best alkali resistant natural inorganic fiber. However, it can be completely dissolved in strong acid, and can be dissolved at different speeds in oxalic acid, citric acid, acetic acid, mixed acid and Al (OH) 3 solution. In humid or rainy climate, brucite is easy to be eroded by CO2 and H2O in the atmosphere, so the surface of brucite products needs a waterproof protective layer.


Surface properties: the diameter of brucite fiber measured by transmission electron microscope is 0.54 ~ 0.86 μ m. The smallest is 0.086 μ m。 The electromotive potential of wurtzite can reach 36.3mv. The pH value of the zero potential point is 12.5. Brucite fiber has good splitting and dispersibility and long fiber. After mechanical beating or chemical dispersion, the beating degree can be significantly improved, which can be used for wet spinning and papermaking. It is formed by hydrolysis of soluble magnesium containing compounds in strong alkaline solution. It is the secondary change product of alkaline solution acting on magnesian silicate. The deposit is mainly related to serpentinite; It also occurs in contact metamorphic magnesite limestone and coexists with calcite, tremolite, serpentine, phlogopite, etc. Sometimes it occurs in dolomitized limestone and is associated with calcite, hydromagnesite and periclase. Brucite ore can be divided into three main types: spherical type, massive type and fibrous type:


Spherical type: it is formed by hydration of periclase and occurs in nodule shape, with a diameter of several millimeters to more than 20cm. The nodules are cemented by cryptocrystalline brucite and a small amount of calcite and serpentine. The ore is of good quality.


Massive type: it is the product of hydrothermal alteration of magnesium rich rocks. The ore is a crystalline granular massive aggregate, symbiotic with serpentine, calcite and magnesite, and the brucite content is about 30 ~ 40%.


Fiber type: it occurs in serpentinite in vein shape, and the content of fibrous brucite is generally 1 ~ 9%. The intercalated minerals are serpentine and magnetite. The purity of brucite is very high. Brucite is mainly used in the following industrial fields:


Extraction of Mg and MgO raw materials: Mg and MgO are extracted from brucite, which has high MgO content and less impurities; Low decomposition temperature; The volatiles produced during heating are non-toxic and harmless, so products such as Mg and MgO can be extracted from brucite.


Re fired magnesia: mainly used to produce magnesia refractories. Modern iron and steel industry needs a lot of magnesia carbon brick, magnesia chrome brick and so on. The amount of this kind of MgO has exceeded 1 / 2 of its output. The calcined magnesia prepared from brucite has the advantages of high density (> 3.55 g / cm3), high fire resistance (> 2800 ℃), high chemical inertia and high thermal shock stability.


Light magnesium oxide: the United States, Russia, Canada, Britain and other countries use chemical methods to extract light MgO from low-grade brucite rocks.


Fused periclase: it is a special pure product required by high-tech electronic products. Periclase aggregate made from brucite by electrofusion has high thermal conductivity and good electrical insulation, and the service life of the product is increased by 2 ~ 3 times.


Chemical pure magnesium reagent: metal magnesium can be extracted by electrothermal method to prepare MgCl2, MgSO4, Mg (NO3) 2 and other chemical pure reagents.


Reinforcing material: wollastonite can be used as a substitute for chrysotile asbestos in some fields. It is used in medium-grade thermal insulation materials such as microporous calcium silicate and calcium silicate board. The basic formula is: diatom earth rock mortar, water glass fiber brucite. The fiber content is 8 ~ 10%. The product has high whiteness, beautiful appearance and low bulk density.


Flame retardant: the test of flame retardant based on polypropylene shows that brucite has good flame retardant effect and is an ideal non-toxic, smokeless, pollution-free and high temperature flame retardant. At the same time, it can play the reinforcing effect of filler.


Papermaking filler: brucite has high whiteness, good peeling property, strong adhesion and poor water absorption. When it is used as papermaking filler with calcite, the papermaking process can be changed from acid method to alkali method, and the pollution of pulp water can be reduced.


Handicrafts: the dense block of brucite has rich and changeable colors, uniform texture, good transparency, fine and smooth; It often forms natural stripes and natural patterns with other minerals or varieties, which has ornamental value. Therefore, it can be carved into handicrafts.