Identification characteristics of brucite

Its morphology, low hardness and (0001) polar perfect cleavage are the identification features. Trilateral system, a0=0.313nm, c0=0.474nm；; Z=1。 Brucite type structure is one of the important layered structures. In the structure, (OH)- is approximately hexagonal and closely packed, and Mg2 is filled in octahedral gaps separated by one layer, each Mg is surrounded by 6 OH, and each OH side has 3 Mg. [Mg(OH)6] octahedron ∥{0001} is connected into layers in a prismatic way, and the layers are maintained by weak hydrogen-oxygen bonds, forming a layered structure. Mg-OH is not a regular octahedral sheet, but it is obviously flattened along the C axis, and the thickness of the sheet changes from normal 0.247nm to 0.211nm. The structural characteristics of brucite make it have tabular crystal form, low hardness and extremely perfect cleavage of ∥{0001}. Complex trigonal rhombohedral crystals, D3d-3m(L33L33PC). The crystals are plate-shaped or leaf-shaped. Common simplex: parallel double-sided c{0001}, hexagonal column m{1120}, rhomboid r{1011}, q{0113} or {2021}. Crystals are usually plate-shaped, fine scale-shaped, round and irregular granular aggregates; Sometimes parallel fibrous aggregate occurs, which is called brucite. There is structural distortion in brucite. White, off-white, green, yellow or maroon when Fe and Mn are mixed in; The fresh surface and fracture surface are glassy, the cleavage surface is pearly, and the brucite is silky. Transparent. Cleavage {0001} is extremely complete. Hardness 2.5. The thin sheet has flexibility and flexibility. The relative density is 2.3~2.6. It is pyroelectric. The whiteness of blocky 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 can show biaxial crystal, 2V?25?. The refractive index Ne=1.5705~1.5861 and No=1.5612 ~1.570, and the difference between Ne and No decreases after heating. Mechanical properties: the tensile strength of brucite is 902MPa, which belongs to medium strength fiber material. The elastic modulus is 13800MPa, which is brittle to some extent. Vickers hardness is 50.4~260.5, and it has obvious anisotropy. It is easy to grind into fine powder. The theoretical relative density is 2.39. Electromagnetic properties: the mass resistivity of brucite is 8.82?106Ω?g/cm2, the volume resistivity is 5.9?106Ω?cm, the surface resistivity is 3.6 ~ 4.5106ω, and the resistivity is anisotropic. The resistivity increases when heated. The dielectric constant is 4.7 ~ 5.4 (1 MHz); Under the conditions of low frequency (50Hz) and intermediate frequency, the dielectric constant increases and has obvious directivity; The tangent value of dielectric loss angle is 0.105. Heating increases the dielectric constant and dielectric loss tangent by 54% and 2.7 times respectively. The specific magnetization coefficient of brucite is 9.815 ~ 15.77910-6 cm3/g, which belongs to nonmagnetic mineral. Heating increases the specific magnetization coefficient, but there are valleys 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 brucite is 0.46 w/m k, and the bulk fiber is 0.131 ~ 0.213 w/m k (bulk density 0.47 g/cm3). The thermal expansion of brucite 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. Fibrobrucite also has the properties of flame retardancy, resistance to open flames and high temperature flames. The decomposition temperature of brucite is 450℃. Chemical properties: Fibrobrucite is the best alkali-resistant natural inorganic fiber. However, it can be completely dissolved in strong acid, and can be dissolved in oxalic acid, citric acid, acetic acid, mixed acid and Al(OH)3 solution at different speeds. In humid or rainy climate, brucite is easily 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 0.54~0.86μm, and the smallest one is 0.086 μ m. The electrodynamic potential of brucite can reach 36.3mV. The pH value of the zero potential point is 12.5. Brucite fiber has good cleavability and dispersibility, and is long. After mechanical beating or chemical dispersion, the beating degree can be obviously improved, which can be used for wet spinning and paper making. It is formed by hydrolysis of soluble magnesium-containing compounds in strong alkaline solution, which is the secondary change product of magnesium silicate acted by alkaline solution. The deposit is mainly related to serpentine. It also occurs in contact metamorphic magnesite limestone and coexists with calcite, tremolite, serpentine and phlogopite. Sometimes it occurs in dolomitized limestone and is associated with calcite, hydromagnesite and periclase. Brucite ore can be divided into three main types: spherical, massive and fibrous: Spherical type: it is hydrated by periclase, and it is nodule-shaped, with a diameter ranging from several millimeters to more than 20cm. Nodules are cemented by cryptocrystalline brucite and a small amount of calcite and serpentine. Good ore quality. Massive type: it is the hydrothermal alteration product of magnesium-rich rocks. The ore is a crystalline granular massive aggregate coexisting with serpentine, calcite, magnesite, etc. The brucite content is about 30~40%. Fiber type: it occurs in serpentine in vein shape, and the content of 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: Raw materials for extracting Mg and MgO: Mg and MgO are extracted with brucite, which has high MgO content and few impurities; Low decomposition temperature; Volatiles produced during heating are non-toxic and harmless, so products such as Mg and MgO can be extracted from brucite. Burned magnesia: mainly used to produce magnesia refractories. Modern iron and steel industry needs a large number of magnesia-carbon bricks and magnesia-chrome bricks. The amount of this kind of MgO has exceeded 1/2 of its output. The reburning magnesia made 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 MgO: America, Russia, Canada, Britain and other countries use chemical methods to extract light MgO from low-grade brucite rock. Fused periclase: an ultra-pure product required for high-tech electronic products. The 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. Chemically pure magnesium reagent: using electrothermal method, metal magnesium can be extracted to prepare chemically pure reagents such as MgCl2, MgSO4 and Mg(NO3)2. Reinforcing material: Fiberglass can be used as a substitute for chrysotile asbestos in some fields. Used in middle-grade thermal insulation materials such as microporous calcium silicate and calcium silicate board. The basic formula is diatomite lime slurry, sodium silicate fiber brucite. The fiber content is 8-10%. The product has high whiteness, beautiful appearance and low bulk density. Flame retardant: The experiment of making 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 filler. Paper filler: brucite has high whiteness, good stripping property, strong adhesion and poor water absorption. It can be used as paper-making filler with calcite, which can change the paper-making process from acid method to alkali method and reduce the pollution of pulp water. Arts and crafts: the dense block of brucite is rich in color, uniform in texture, good in transparency, delicate and smooth; It often forms natural stripes and patterns with other minerals or varieties, and has ornamental value. Therefore, it can be carved into handicrafts.