The name wollastonite is no stranger to these years. After all, when a large number of "jade merchants" emphasized "Qinghai materials", they pointed out that the main component was wollastonite to confuse the market's cognitive status. During my investigation of the impurity content of Qinghai materials, some areas of Qinghai materials did contain a small amount of wollastonite, but more than 90% of the main components were still tremolite, actinite or iron actite. This rumor. But what kind of concept is wollastonite? Let me introduce you briefly this time

       Wollastonite is a calcium silicate mineral. It is a mineral formed by the reaction of calcite and quartz under certain temperature and pressure conditions to form acicular wollastonite powder. The formation of wollastonite is related to the ambient temperature and pressure, and also directly related to the pressure, water content, and parent rock composition of carbon dioxide needle-like wollastonite in the reaction system. The types of genesis mainly include skarn-type ore in contact with metamorphism, thermal metamorphism in contact, regional metamorphism, magma crystal type, volcanic blast, and meteorites.

       The chemical formula of wollastonite is CaSiO3 (or Ca3 [Si3O9]), the component content CaO; 48.3%, SiO; 51.7%. In the octahedral acicular wollastonite powder, Ca2 + is often replaced by a small amount of Fe2 +, Mn2 +, Mg2 +, etc., and in the tetrahedron, the acicular wollastonite powder Si4 + is also replaced by a small amount of Al3 +, Fe3 +, etc. The impurity composition of wollastonite from different places of origin is often directly related to the formation conditions, especially the parent rock composition related to mineralization. It can form a series of solid solutions in the CaSiO3 ~ FeSiO3 system.

       CaSiO3 has three homogeneous polymorphic variants, namely, wollastonite-Tc (the most common in nature) in triclinic system, wollastonite- 2M (mono-wollastonite, less in nature) in monoclinic system, and Triclinic system wollastonite (pseudo-wollastonite, extremely rare). The first two are low temperature variants (α-CaSiO3) and the third are high temperature variants (β-CaSiO3).

       The low-temperature variant is a single-chain structure silicate with three tetrahedral repeating units [Si3O9] consisting of alternating arrangements of single tetrahedral [SiO4] and double tetrahedral [Si2O5] bodies. This repeating unit extends along the b axis to form [ Si3O9] ∞ single-chain silicon backbone; [Si3O9] ∞ and [Si3O9] ∞ chains are arranged in parallel, and the gaps between the chains are filled with Ca ions to form a [CaO6] octahedron co-edge connected into a single chain parallel to the b-axis [CaO6 ] ∞. The [Si3O9] ∞ chain and the [CaO6] ∞ chain constitute the basic structural unit of the low temperature and low temperature variant (α-CaSiO3). Si is 4 coordinated and Ca is 6 coordinated. Chain length Si—O = 1.52 ~ 1.64Å, Ca—O = 2.32 ~ 2.40Å. The edge length of [CaO6] octahedron is 3.65Å, and the height of [Si2O7] double tetrahedron is about 4.1 ~ 4.2Å when Si—O—Si is a straight line.

       In the combination of a calcium-oxygen octahedron chain and a silicon-oxygen tetrahedron chain, in order to adapt 3 [SiO4] tetrahedrons to 2 [CaO6] octahedra, [Si2O7] double tetrahedral Si—O—Si was bent. Due to the different stacking methods of the basic units composed of [Si3O9] ∞ chain and [CaO6] ∞ chain, different types of wollastonite-Tc, 1T, 2M, 4M, 5T, 7T, and disorder can be produced. These They can be discriminated by X-ray diffraction analysis. Wollastonite-Tc is often said. Wollastonite-2M is rare, others are very rare.

       The high-temperature variant (β-CaSiO3) is a ring-shaped silicate. The [Si3O9] trigonal ring formed by three [SiO4] tetrahedrons and the [CaO6] octahedral joint formed by [CaO6] octahedrons are along the c. The axes are arranged alternately. The high-temperature variant (β-CaSiO3) forms jade above 1126 ° C and is only found in high-temperature metamorphic rocks.

       If the content of FeSO3 in the wollastonite solid solution is greater than 10%, it may have a calcareite structure. In wollastonite-Tc, Ca is disordered at M1, M2, and M3, while Fe and Ca are ordered in the calcareite structure. Ca and Fe are disordered in the less-iron wollastonite, and with the further iron-rich composition, the ordered structure gradually becomes dominant. Within a certain temperature and composition range, the wollastonite phase and the calcareite phase coexist.

       Wollastonite crystals are plate-column-shaped extending along the b-axis and develop a series of crystal planes parallel to the b-axis. Twin crystals can be formed according to (100) or (001). Single crystals are extremely rare in nature, and are mostly needle-like, fibrous, or radial aggregates.

       Under the microscope, wollastonite sections are often long, columnar, needle-like, with medium-positive protrusions, and the interference color is first-level gray to first-level yellow and white. The entry of iron and manganese into the lattice will lead to an increase in the refractive index and an increase in the optical axis angle. Wollastonite-Tc can be distinguished from wollastonite-2M according to the extinction, and false wollastonite can be distinguished according to the 2V value of the optical symbol and a high refolding rate.

       Wollastonite has a specific gravity of 2.75 to 3.10 g / cm³ and a Mohs hardness of 4.5 to 5.5. Cleavage {100} complete, {001}, {1¯02} medium, (100) ∧ (001) = 84 ° 30 ′, (100) ∧ (1¯02) = 70 °. Due to this unique cleavage, the fine particles of crushed and ground wollastonite are mostly needle-like and fibrous, and the ratio of fiber length to diameter is about (7 ~ 8): 1. However, I have naturally produced wollastonite fiber with an aspect ratio of 20: 1 to 30: 1. Most applications of wollastonite are based on this feature.

       Natural wollastonite is usually white, with a light gray or reddish white, and occasionally flesh red, yellow, green, and brown. Pure white wollastonite can sometimes turn cream, red or brown depending on the impurities it contains. Glass luster, cleavage pearl luster. Bright color is the main factor of wollastonite used in the coatings industry. The purity of 99%, wollastonite with a particle size of less than 325 mesh (see water sandpaper without understanding the number of eyes) and the guaranteed white magnesium oxide with a brightness of 100 are 92%. ~ 96%, ultraviolet light can emit yellow to orange or pink to orange fluorescence, some visible phosphorescence.

       Wollastonite has a melting point of 1540 ° C. Containing impurities will greatly reduce the melting point. It has the characteristics of linear expansion and small thermal expansion coefficient (6.32 x 10-6 / K [010] in the range of 25 ~ 650 ° C), which is transformed into pseudo wollastonite at 1126 ° C, and the thermal expansion coefficient increases accordingly.

       α-CaSiO3 has a large volume resistivity of 1.6 x 10-14 ~ 1.7 x 10-14Ω · cm, which is suitable for making low loss ceramics. Wollastonite has good chemical stability, and its solubility in neutral water at 25 ° C is 0.0095mg / 100ml. In general, it is resistant to acid, alkali, and chemical corrosion, but easily decomposes in concentrated hydrochloric acid to form flocs.

       Because wollastonite production and supply and demand vary, artificial wollastonite already exists in industrial raw materials. There are mainly synthetic methods such as melting method, sintering method, aqueous solution synthesis method, autoclave synthesis method, and phosphate slag transformation method. The sintering method wollastonite is mainly used in industry. It is made by using quartz powder and ground limestone as raw materials and adding co-solvent dolomite for baking. The composition, color, specific gravity, hardness, and melting point of synthetic wollastonite are similar to those of natural wollastonite, but the crystal form is approximately equiaxed and underdeveloped columnar, with a higher refraction rate than natural wollastonite.

       A large amount of wollastonite is used in the fields of building materials, ceramics, rubber, plastics and other industries. Wollastonite can reduce the firing temperature of ceramics, shorten the firing cycle, reduce embryo and glazed defects, reduce firing shrinkage and drying shrinkage, reduce hygroscopic expansion and thermal expansion, and at the same time, it is beneficial to molding and replaces it in hard mold casting The use of quartz sand and other materials greatly reduces the risk of silicosis.

       In the plastic industry, the use of wollastonite in almost all plastic systems is mainly to improve the mechanical properties, electrical properties, thermal properties and aging resistance of plastic products. It has a reinforcing effect. In the rubber industry, wollastonite powder can replace Lide powder and play a reinforcing and whitening role. In the coating industry, wollastonite is used in various types of light-colored oil-based or water-based emulsion coatings. Taking advantage of its ultraviolet and other fluorescence characteristics, there is now a wollastonite-containing fluorescent color enamel.

       In the manufacture of building materials, wollastonite can be used as a solvent in fired cement. Wollastonite white cement has high whiteness and good brightness, and is suitable for alpine regions. Wollastonite can also produce silicon calcium plates. In the metallurgical industry, wollastonite is a natural low-temperature melting material, which has excellent characteristics such as inherent fluxing performance, stable composition, high purity, and alkalinity tending to neutrality. The content of wollastonite is relatively small, which can enhance the ability of the produced metallurgical protective slag to adsorb harmful alumina in molten steel. It can replace lime as a soil conditioner in agriculture, can assimilate with phosphate fertilizer to facilitate absorption, and can also be used to make silicon fertilizer.