Identification characteristics of brucite

It is characterized by its morphology, low hardness and (0001) extremely 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, the (OH) - is approximately hexagonal and tightly packed, and Mg2 is filled in the octahedral voids separated by one layer. Each mg is surrounded by 6 Oh, and there are 3 mg on each Oh side. The [Mg (OH) 6] octahedron ‖ {0001} is connected into layers in a coplanar manner, and the layers are maintained by weak hydrogen oxygen bonds to form a layered structure. Mg Oh is not a regular octahedral sheet, and it is obviously flattened along the c-axis direction. The sheet thickness changes from 0.247nm to 0.211nm. The structural characteristics of brucite make it have plate-like crystal form, low hardness and ‖ {0001} extremely complete cleavage.


Complex trigonal trigonal crystal, d3d-3m (l33l33pc). The crystals are 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 scale, round and irregular granular aggregates; Sometimes there are parallel fibrous aggregates, called brucite. There is structural distortion in the brucite. White, off white, green, yellow or maroon when Fe and Mn are mixed; The fresh surface and fracture surface have glass luster, the cleavage surface has pearl luster, and the brucite has silk luster; Transparent. Cleavage {0001} is extremely 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 the normal primary yellow or orange. Under the influence of stress, the ductility can be positive or negative. Uniaxial crystal (), but can show 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 wollastonite is 902mpa, which is a medium strength fiber material. The elastic modulus is 13800mpa, with certain brittleness. Vickers hardness is 50.4 ~ 260.5, and has obvious anisotropy. It is 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 when heated. The dielectric constant is 4.7 ~ 5.4 (1MHz); Under the conditions of low frequency (50Hz) and intermediate frequency, the dielectric constant increases with obvious directionality; 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 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 0.46w/m · K, and the bulk density of loose fiber is 0.131 ~ 0.213w/m · K (volume density: 0.47 g / cm3). The thermal expansion property 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. Brucite also has the properties of flame retardancy, resistance to open fire and high temperature flame. The decomposition temperature of wollastonite is 450 ℃.


Chemical properties: brucite is the best alkali resistant natural inorganic fiber. But 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 easily eroded by CO2 and H2O in the atmosphere, so the surface of brucite products needs to be provided with a waterproof protective layer.


Surface property: the fiber diameter of brucite measured by transmission electron microscope is 0.54 ~ 0.86 μ m. Thinnest 0.086 μ m。 The electromotive potential of brucite can reach 36.3mv. The pH value of the zero potential point was 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, and it 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 serpentine; It is also produced in the contact metamorphic magnesite limestone and coexists with calcite, tremolite, serpentine and phlogopite. It is sometimes produced 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 fiber type:


Spherical type: it is formed by hydration of periclase and is produced 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, which coexists with serpentine, calcite, magnesite, etc. the brucite content is about 30-40%.


Fiber type: in vein form, it occurs in serpentine rock, 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: brucite is used to extract mg and MgO. The content of MgO in the ore is high and the impurities are small; 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.


Heavy burned magnesia: mainly used to produce magnesia refractory materials. The modern iron and steel industry needs a lot of magnesia carbon bricks and magnesia chrome bricks. The amount of such 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. The periclase aggregate refined from brucite by electrofusion has high thermal conductivity and good electrical insulation, and the product life is increased by 2-3 times.


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


Reinforcing material: wollastonite can be used as a substitute for chrysotile in some fields. Used in microporous calcium silicate, calcium silicate board and other medium-grade thermal insulation materials. 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 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 play the reinforcing effect of filler.


Papermaking filler: brucite has high whiteness, good peeling property, strong adhesion and poor water absorption. When it is combined with calcite as paper-making filler, the paper-making 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 varied colors, uniform texture, good transparency, fine and smooth; It often forms natural stripes and natural patterns with other minerals or varieties, and has ornamental value. So it can be carved into handicrafts.