Identification characteristics of brucite

It is characterized by its morphology, low hardness and (0001) very complete cleavage. Trilateral 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 each Oh side. [mg (OH) 6] octahedron ‖ {0001} is connected into layers in a common edge manner, and the interlayer is maintained by a very weak hydrogen oxygen bond to form a layered structure. Mg Oh is not a regular octahedral sheet, and it is obviously flattened along the c-axis. The thickness of the sheet changes from 0.247nm to 0.211nm. The structural characteristics of brucite make it have tabular crystal form, low hardness and ‖ {0001} very complete cleavage.
Complex trilateral trigonohedral bulk crystal class, d3d-3m (l33l33pc). The crystals are plate-shaped or leaf-shaped. Common simplex: parallel double-sided c{0001}, hexagonal column m{1120}, rhombohedral r{1011}, q{0113} or {2021}. The crystals are usually plate-shaped, fine scale like, round and irregular granular aggregates; Sometimes there are parallel fibrous aggregates, which are called fibrous brucite. There is structural distortion in wollastonite. White, grayish white, green, yellow or maroon when Fe and Mn are mixed; The fresh surface and fracture surface are of glass luster, the cleavage surface is of pearl luster, and the brucite is of silk luster; Transparency. Cleavage {0001} is extremely complete. Hardness 2.5. The thin piece is flexible and flexible. The relative density is 2.3~2.6. Thermoelectric. The whiteness of massive brucite can reach 95%.
Under the polarizer: the abnormal interference color red brown replaces the normal primary yellow or orange. Under the influence of stress, the 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 becomes smaller after heating.
Mechanical properties: the tensile strength of brucite is 902mpa, belonging to medium strength fiber material. The elastic modulus is 13800mpa, with certain brittleness. Vickers hardness is 50.4~260.5, with obvious anisotropy. Easy to grind into fine-grained powder. The theoretical relative density is 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 during heating. The dielectric constant is 4.7~5.4 (1MHz); At low frequency (50Hz) and intermediate frequency, the dielectric constant increases with 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, belonging to non-magnetic mineral; Heating makes the specific magnetization coefficient increase, but there is a trough near 300 ℃, 500 ℃ and 600 ℃. When the temperature is higher than 700 ℃, it shows medium strong magnetism.
Thermal performance: the reliable service temperature of brucite is 400 ℃. The thermal conductivity of wollastonite is 0.46w/m · K, and the bulk density of loose fiber is 0.131~0.213w/m · K (0.47 g/cm3). The thermal expansion of wollastonite is 16.7*10-7/ ℃ longitudinally and 8.8*10-7/ ℃ transversely, and the thermal expansion behavior is basically linear. It also has the properties of flame retardancy, resistance to open flame 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 rates 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. Thinnest 0.086 μ m。 The electromotive potential of wollastonite can reach 36.3mv. The pH value at the zero potential point is 12.5. Brucite fiber has good cleavage and dispersion, 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, and is the secondary change product of magnesium silicate under the action of alkaline solution. The deposit is mainly related to serpentinite; It also occurs in contact metamorphosed 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 ores can be divided into three main types: spherical, massive and fibrous:
Spherical type: it is formed by hydration of periclase and occurs in nodule shape. Its diameter ranges from 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.
Block type: it is the product of hydrothermal alteration of magnesium rich rocks. The ore is a crystalline granular massive aggregate, coexisting with serpentine, calcite, magnesite, etc., and the brucite content is about 30~40%.
Fibrous type: it occurs in serpentinite in vein shape, and the content of chrysotile is generally 1~9%. The intercalation minerals are serpentine and magnetite. The purity of chrysotile 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 few impurities; Low decomposition temperature; The volatiles produced during heating are non-toxic and harmless, so mg, MgO and other products can be extracted from brucite.
Heavy burned magnesia: mainly used to produce magnesia refractories. The modern iron and steel industry needs a lot of magnesia carbon bricks and magnesia chrome bricks. The consumption 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 inertness 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 method has high thermal conductivity and good electrical insulation, and the service life of the product is increased by 2~3 times.
Chemically pure magnesium reagent: the electrothermal method can be used to extract metallic magnesium and prepare MgCl2, MgSO4, Mg (NO3) 2 and other chemically 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 unit weight.
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 enhance the effect of filler.
Paper making filler: brucite has high whiteness, good peeling property, strong adhesion and poor water absorption. Using it with calcite as papermaking filler can change the papermaking process from acid method to alkali method and reduce the pollution of pulp water.
Crafts: the dense brucite block is rich in color, uniform in texture, good in transparency, fine and smooth; It often forms natural stripes and natural patterns with other minerals or varieties, and has ornamental value. Therefore, it can be carved into handicrafts.