RU2806273C1 - Method for producing forsterite material - Google Patents

Abstract

FIELD: ceramic industry.

SUBSTANCE: invention relates to the production of forsterite ceramic and refractory materials used in converter linings, out-of-furnace steel processing units, steel-pouring ladles and non-ferrous metallurgy furnaces, as well as for ceramic dielectrics. To obtain forsterite ceramics, raw materials based on the magnesia-silicate group with a MgO/SiO₂ ratio corresponding to the theoretical composition of forsterite are first subjected to isothermal exposure, then mixed to obtain a composite charge. The charge is crushed to a fraction≤ 100 microns and carry out wet granulation to a fraction of 2-3 mm. The resulting agglomerated powder is poured into a plasma-chemical reactor, preheated to a temperature of at least 2050°C, where it melts under conditions of intense heat exchange at a temperature of 3500-4000°C. When the melting process is carried out at a given temperature, evaporation of impurity elements occurs that do not enter into the main reaction of the formation of forsterite material. The melt is drained at a temperature of at least 2150°C, then it crystallizes at a rate of 7°C/s with the formation of dense packing of rhombic-dodecahedral crystals with a size of 180-240 microns.

EFFECT: production of forsterite material of a homogeneous dense structure from common natural materials.

1 cl, 1 ex, 2 tbl, 1 dwg

Description

The invention relates to the ceramic industry, namely to the production of forsterite ceramic and refractory materials used in converter linings, out-of-furnace steel processing units, steel-pouring ladles and non-ferrous metallurgy furnaces, as well as for ceramic dielectrics.

The closest in technical essence (prototype) is a fused forsterite-containing material and a refractory based on it (variants) (patent No. 2149856 publ. 05/27/2000), including forsterite, periclase and glass phase in the following ratio of components, wt.%: forsterite 35-97 ; periclase 1-55 and glass phase 2-10 with a size of forsterite crystals in the form of prisms of at least 100 microns, obtained by additional grinding of Solovyovgorsk dunite (magnesial silicate material) to a fraction of less than 25 mm, was mixed with sintered periclase powder of a fraction of less than 6 mm. The charge was melted in an electric furnace at a current of 8-8.5 kA and a voltage of 225 V with a specific electricity consumption of 2200 kWh per 1 ton for 3.5-4.0 hours. Then the melt was poured into molds, where it crystallized and cooled at a rate of 3°C/min for 30-50 hours.

Significant disadvantages of the known method are the melting of the prepared charge under conditions of gradient heating in an electric furnace, which leads to the formation of a heterogeneous structure and a decrease in the physical and mechanical characteristics of the material, as well as the content of impurity elements in the composition of the material, since the temperature range in the electric furnace will not allow the formation of the required temperature for their evaporation.

The objective of the present invention is to obtain high-quality forsterite material from common natural and substandard materials of the magnesia-silicate group by plasma melting, eliminating the disadvantages of analogues.

To solve the problem and achieve the specified technical result, a method for producing forsterite material by plasma melting, including preliminary preparation of the charge and its melting, according to the proposed solution, raw materials based on the magnesia-silicate group are first subjected to isothermal exposure. Then they are mixed in a stoichiometric ratio, obtaining a composite mixture. The next step is to crush the mixture and then granulate it. The prepared mixture is poured into a preheated plasma-chemical reactor, where it is melted. The melting process is carried out at a temperature of 3500-4000°C, this promotes complete melting and homogenization of the melt. When the melting process is carried out at a given temperature, evaporation of impurity elements occurs that do not enter into the main reaction of the formation of forsterite material. The melt merges at a temperature of at least 2150°C, then it crystallizes at a rate of 7°C/s with the formation of a dense pack of rhombic-dodecahedral crystals with a size of 180-240 microns.

The method of obtaining forsterite material is carried out as follows. Raw materials based on the magnesium silicate group are preliminarily subjected to isothermal exposure. Then they are mixed in a stoichiometric ratio, obtaining a composite mixture. The next step, to obtain a powder, is to grind the mixture to a fraction of ≤100 microns and carry out wet granulation to a fraction of 2-3 mm. The resulting agglomerated powder is poured into a plasma-chemical reactor preheated to a temperature of at least 2050°C, where it is melted. The melting process is carried out at a temperature of 3500-4000°C, this promotes complete melting and homogenization of the melt. When the melting process is carried out at a given temperature, evaporation of impurity elements occurs that do not enter into the main reaction of the formation of forsterite material. The melt merges at a temperature of at least 2150°C, then it crystallizes at a rate of 7°C/s with the formation of a dense packing of rhombic-dodecahedral crystals with a size of 180-240 μm (Fig. 1).

As a result of synthesis by plasma melting, a forsterite material was obtained with a glass phase content of no more than 5%, a density of 3.56 g/cm ³ and a microhardness of up to 15 GPa with an elemental composition, wt.%: O = 38.28; Mg=32.49; Si=29.23 (Tables 1, 2) is characterized by dense packing of rhombic-dodecahedral crystals with a size of 180-240 microns.

Example.

To obtain forsterite material, magnesite MgCO ₃ and quartz sand SiO ₂ are used. In order to decompose MgCO ₃ into MgO and CO ₂ , magnesite is kept isothermally at 1000°C for 3 hours. After this, the materials are mixed in a stoichiometric ratio of MgO/SiO ₂ ~1.34, which corresponds to the theoretical composition of forsterite ceramics Mg ₂ SiO ₄ , obtaining a composite charge. Then the prepared mixture is crushed in a planetary ball mill to a fraction of less than 100 microns and wet granulation is carried out, to prevent it from being blown out of the plasma exposure zone, through a laboratory sieve with a mesh size of 2 mm. Polyvinyl alcohol grade 6/1 is used as a binder. The finished agglomerated powder weighing 100 g is poured into a plasma-chemical reactor preheated to a temperature of at least 2050°C and the melting process is carried out at a temperature of 3500-4000°C. Then the melt is cooled and poured by gravity into a graphite mold, where it crystallizes at a rate of 7°C/s.

The output, according to electron microscopy data, is a forsterite material from a chemically homogeneous melt with a dense packing of rhombic-dodecahedral crystals 180-240 microns in size and with a minimum level of impurity elements, and physical properties: the amount of glass phase is no more than 5%, density 3.56 g/cm ³ , microhardness up to 15 GPa, porosity less than 1% (Table 2).

Table 1. Elemental composition

Materials Elements, wt. % WITH O Mg Si Al Ca Fe Magnesite 20.71 50.76 26.73 0.16 - 0.48 1.16 Quartz sand - 46.25 - 51.21 02.54 - - The obtained material according to the stated methods - 38.28 32.49 29.23 - - -

Table 2. Characteristics of forsterite material

Density, g/cm ³ 3.56 Porosity, % ≤1 Microhardness, GPa up to 15 Amount of amorphous phase, wt.% up to 5 Crystal size, microns 180-240

Claims (1)

A method for producing forsterite material, including preparation of raw materials, mixing and melting of the charge and crystallization of the melt upon cooling, characterized in that the charge materials are mixed in the stoichiometric ratio MgO/SiO ₂ corresponding to the theoretical composition of forsterite ceramics, wet granulation of the crushed charge is carried out, and the charge is melted in a plasma-chemical reactor by plasma melting of components at a temperature of 3500-4000°C until complete melting and homogenization with the formation of a melt and evaporation of impurity elements; then, when the temperature reaches 2150°C, the melt is drained, followed by further cooling and crystallization at a rate of 7°C/s; wherein the resulting forsterite material with a glass phase content of 3-5%, a density of 3.56 g/cm ³ and a microhardness of up to 15 GPa with an elemental composition, wt.%: O=38.28; Mg=32.49; Si=29.23 is characterized by a dense packing of rhombic-dodecahedral crystals with a size of 180-240 microns.