Quartzite-carbon refractory

Abstract

1. Subject of the invention: A quartz-carbon refractory. 2. Field of the invention: The invention relates to refractory production and can be used for lining thermal and steel-making units. 3. Essence of the invention: A quartzite-carbon refractory containing a powdered graphite, a filler in the form of microcrystalline quartzite with a crystal size of 10 to 150 μm, a silicon dioxide (SiO2) content of not less than 97 % w / w, a bond in the form of a mixture of novolac phenol -formaldehyde resin (91 to 94 % w / w) and urotropin (6 to 9 % w / w), an antioxidant in the form of silicon and a bond solidification seed in the form of a dry phenol-formaldehyde resin at the following ratio of components, % w / w: Powdered graphite 8.0 to 20.0 Bond 2.5 to 5.0 Antioxidant 3.0 to 5.0 Bond solidification seed 1.0 to 3.0 Filler Q.S. to 100 4. The technical result of the proposed technical solution is the provision of the quartz-carbon refractory, the use whereof ensures the preservation of a dense bonding framework with the effective closure of the channel porosity this providing counteraction to shrinkage processes and reinforcement of the material structure in a wide temperature range.

Description

[0001] QUARTZITE-CARBON REFRACTORY

[0002] Field of the Invention

[0003] The invention relates to refractory production and can be used for lining thermal and steelmaking units, for example, in converter steelmaking.

[0004] Description of the Prior Art

[0005] Known from the state of the art is a carborundum-graphite refractory with a high content of silicon (Si) and carbon (C) [1], which contains a filler in the form of a mixture of polydisperse granular carborundum (SiC), a flake graphite; and crystalline silicon, and coal tar, pitch, bitumen, tar, etc. are used as a bond. The bond in combination with the filler provides an open porosity of up to 20% and a compressive strength of up to 15 MPa in products produced from the known refractory, such as bricks, blocks, crucibles, etc.

[0006] In the state-of-the-art carborundum-graphite refractory, dehardening and porosity growth occur under the influence of high temperatures, including during heat treatment or directly in service, which is associated with the removal of volatile components from the bond this being partially compensated by the formation of secondary beta-modified silicon carbide (0-SiC), which consolidates carborundum grains and graphite flakes as a result of the reaction of crystalline silicon with carbon components.

[0007] A disadvantage of the known carborundum-graphite refractory is the relatively high crumbliness and solubility of fine grains (SiC), especially when interacting with molten cast irons and steels.

[0008] Known from the state of the art is a quartzite-carbon refractory [2] comprising a powdered graphite, a filler, an aqueous solution of ethylene glycol, and a bond in the form of a powdered polymer mixture of a solid phenol-formaldehyde resin of the novolac type, urotropin, and an antioxidant -a powdered boric acid obtained in the process of simultaneous mechanical grinding of the components, and having not more than 5 % of a grain size ofmore than 0.1 mm, and crushed fine-grained crystalline quartzite is used as a filler at the following ratio of components, % w / w:

[0009] Filler 72.3 to 86.0 Powdered graphite 10.3 to 19.9 Bond 1.2 to 3.5 Aqueous solution of ethylene glycol 1.3 to 3.2 Antioxidant Q.S. to 100 The specified composition of the quartz-carbon refractory ensures a high density and mechanical strength of the product produced from the known refractory, both immediately after production due to bonding and in a high-temperature state due to the interaction of the refractory components with the creation of a ceramic structure.

[0010] Disadvantages of the known quartzite-carbon refractory include increased volumetric changes of the formed products in the low-temperature heat treatment range (200-600 °C), which is due to the removal of water vapor and other volatile decomposition products of the ethylene glycol aqueous solution, which leads to the formation of capillary porosity in the structure of the formed product, which reduces the corrosion resistance of the refractory in the operating environments of iron and steel making. In addition, a separate process step is required to produce the bond, which increases the cost of the material, limiting the operational suitability and feasibility of using the known quartz-carbon refractory in thermal metallurgical units, including in conditions of interaction with iron and steel melts.

[0011] The most similar in terms of its technical essence to the refractory according to the present invention is a silica-carbon refractory [3] containing a powdered graphite, a filler in the form of microcrystalline quartzite with a crystal size of 10 to 150 pm and a silicon dioxide (SiC ) content of at least 97 wt. % - the other components being a bond in the form of a mixture of novolac phenol-formaldehyde resin (91 to 94 % w / w) and urotropin (6 to 9 % w / w) at the following ratio of components, % w / w:Powdered graphite 8 to 20

[0012] Bond 2.5 to 5

[0013] Filler Q.S. to 100

[0014] The features of the known refractory include high heat resistance (up to 16 thermal cycles of 1300 °C - water) due to the irreversible hardening of the mixture of phenol-formaldehyde resin with urotropin and the formation of a branched binding frame of the formed product with good thermal conductivity, as well as an increased softening point of the produced refractory (not less than 1680 °C) due to the creation of beta-modified silicon carbide (0-SiC) during the operation of the refractory, including when interacting with molten cast irons and steels.

[0015] The disadvantages of the known refractory are associated with the oxidation of the thermolysis products of the solidified bond, which causes the loss of a coke residue in the structure of the refractory and an increase in an open porosity when exposed to high temperatures, especially in the melt of cast irons and steels. Also, a disadvantage of the known refractory is the impossibility of organizing spatially homogeneous solidification of the bond without the formation of zones of different density in the structure of the refractory, as well as fixing a dense bonding framework between the granular components. The physical and chemical reasons for these disadvantages include the uneven size and complex configuration of intergranular space cavities, which are filled to some extent with phenol-formaldehyde resin, which is retained in the structure of the formed product from the known refractory only due to the topological branching of the intergranular space and surface tension forces in the contact zones with the filler and graphite flakes. Precisely because there is no chemical affinity between the surfaces of the filler grains and graphite flakes with phenol-formaldehyde resin, the bond is pulled together at the initial stages of solidification until its clusters form due to capillary effects with violations of the integrity of thin films, limitations of the length and degree of branching of polymer chains in the solidified bond,and the development of mechanical stresses in local structural elements of products made of the known refractory.

[0016] The consequences of said disadvantages are manifested in the heterogeneous distribution of components in the volume of the refractory, which causes the formation of structural elements of different densities during the solidification of the bond, the frame continuity of which is disturbed and leads to the formation of a channel type of porosity and the volume changes during drying and heat treatment. Accordingly, large values of shrinkage of the refractory, an increase in its open porosity, and a decrease in the compressive strength are observed.

[0017] The disadvantages of the known refractory include a material deterioration of the refractory properties after heat treatment, since there are no obstacles to low-temperature oxidation of the thermolysis products of the solidified bond, which includes a newly synthesized phenol-formaldehyde resin. Moreover, the synthesis of silicon carbide (SiC) (capable of acting as an antioxidant in the high-temperature range) directly from silicon dioxide (SiC ) and carbon residue or graphite is possible at higher temperatures (> 1500 °C) compared to the synthesis of SiC (> 1250 °C) when using an antioxidant in the form of metallurgical silicon. Accordingly, at high-temperature heat treatment (> 650 °C) or under operating conditions, a progressive deterioration of the properties of the refractory of the known composition - the prototype - is manifested. Such degradation of the refractory properties is enhanced by the influence of cast iron and steel melts, while at the same time deteriorating their quality due to the penetration of the corresponding melts through open pores into the depth of the product and due to the course of complex corrosion processes involving the components of the melts and the formation of chemical compounds, the destruction of the weakened structure of the refractory and the ingress of corrosion products into the melts.Objects and Summary of the Invention

[0018] An object of the present invention is, therefore, to overcome said drawbacks of the prior art.

[0019] Another object of the present invention is to provide products from a refractory, the use of which ensures the preservation of a dense bonding framework with overlapping channel porosity, which counteracts shrinkage processes and reinforces the structure within a wide temperature range.

[0020] Yet another object of the present invention in eliminating said disadvantages is to increase the compressive strength, reduce the open porosity and shrinkage of refractory both after drying and after high-temperature treatment, as well as to reduce the penetration of cast iron and steel melts into the depth of the product and, as a result, to reduce the degradation of its structure.

[0021] The above-mentioned and other objects and advantages of the quartzite-carbon refractory will become more apparent by reference to the following description.

[0022] Accordingly, at least one employment of the present invention is a quartzite-carbon refractory containing a powdered graphite, a filler in the form of microcrystalline quartzite with a crystal size of 10 to 150 pm, a silicon dioxide (SiCh) content of not less than 97 % w / w, and a bond in the form of a mixture of novolac phenol-formaldehyde resin (91 to 94 % w / w) and urotropin (6 to 9 % w / w), characterized by that it contains additionally an antioxidant in the form of silicon and a bond solidification seed in the form of a dry phenolformaldehyde resin at the following ratio of components, % w / w:

[0023] Powdered graphite 8.0 to 20.0

[0024] Bond 2.5 to 5.0

[0025] Antioxidant 3.0 to 5.0

[0026] Bond solidification seed 1.0 to 3.0

[0027] Filler Q.S. to 100

[0028] The inclusion of the antioxidant in the form of silicon in the quartzite -carbon refractory ensures the preservation of a dense bonding framework fromthermolysis products of the solidified phenol-formaldehyde resin due to a higher reactivity to air oxygen and the possibility of synthesizing silicon carbide (SiC). New SiCh and SiC compounds produced by the reactions Si + O2 = SiCh and Si + C = SiC close the channel porosity, sinter with quartzite grains, give the material a constant volume, and reduce the degradation of refractory strength properties. The silicon content below the declared limit does not ensure an effective antioxidant role while exceeding the upper limit increases materially the cost of the refractory.

[0029] The inclusion of the bond solidification seed in the form of the dry phenol-formaldehyde resin in the quartzite-carbon refractory ensures a uniform distribution and a stronger fixation of the seed in the volume of the granular components of the mixture at the mixing and formation stages, while at the drying stage, due to its chemical affinity for a liquid phenol-formaldehyde resin, it promotes an active condensation and polymerization processes with the development of a continuous, with the equal chain length, framework of the solidified bond. At the same time, the channel porosity is closed as effectively as possible, shrinkage processes are counteracted, and the structure of the refractory is reinforced, including at high temperatures during the formation of coke residue based on the bond framework. The content of the dry phenol-formaldehyde resin below said lower limit does not sufficiently eliminate the possibility of forming zones of different densities in the refractory structure, which negatively affects the maintenance of a constant volume. The content of the seed above said upper limit increases the time required for mixing the components and worsens the formation properties of the mass for the refractory due to the intensification of structure formation.

[0030] The presence of the antioxidant in the quartz -carbon refractory and the bond solidification seed in said form and quantity ensures collectively the achievement of the objects of the present invention.

[0031] At the same time, the presence of the antioxidant and the bond solidification seed in the quartzite-carbon refractory of the invention not only ensures a positive effect on the structurally sensitive properties of productsmade of them (volume stability, reduction of open porosity, reinforcement and strengthening), but also exerts a superadditive effect in preserving these properties and widens the temperature range of functional capabilities to counteract thermal mechanical and corrosion loads of cast iron and steel melts due to the interaction of coke residue (including from the bond solidification seed) and silicon (C (coke residue) + Si (antioxidant) = SiC) with the formation of silicon carbide (SiC). The beta polymorphic modification of silicon carbide is a high-temperature antioxidant and additionally reinforces the microstructure by crystallizing in a needle-like form, which needles grow into the pore space, reduce the porosity of the quartzite-carbon refractory and, accordingly, the impregnation of products with cast iron and steel melts is reduced and their performance is improved.

[0032] Description of the Preferred Embodiment

[0033] Examples of mass compositions for the manufacture of the quartz -carbon refractor and the prototype are given in Table 1 hereinbelow.

[0034] Tablel Compositions of formation masses

[0035] Content, % w / w

[0036] Beyond the Formulation of Formulation

[0037] No. Components Prototype the invention of the

[0038] invention

[0039] 1 2 3 4 5 6

[0040] 1 Powdered graphite 8.0 15.0 20.0 7.0 21.0 15.0 2 Bond 2.5 4.0 5.0 2.0 6.0 5.0 3 Antioxidant 3.0 4.0 5.0 2.0 6.0 —

[0041] 4 Bond solidification seed 1.0 2.0 3.0 0.5 4.0 —

[0042] 5 Filler 85.5 75.0 67.0 88.5 63.0 80.0

[0043]

[0044] To obtain the refractory of the invention and that of the state of the art (prototype), identical materials were used: grade GE-1 powdered graphite (GOST 7478-75) (powder with the content of particles of more than 0.16 mm in size not more than 40 %, particles larger than 0.063 mm of not more than 25 %, ash content of not more than 10 %); bond: a mixture of Bakelite PF 9950 FL (Cofermin Rohstoffe, Germany) and urotropin (the content ofhexamethylene tetramine 99.7 %, Limited Liability Company “Expohim-Oltyg Group”, Dnipro), at the ratio, % w / w: phenol -formaldehyde resin - 93.0, urotropin - 7.0; silicon (Hengtai Alloy Materials Co, Ltd, China); make Bakelite PF 9950 FP powdered dry phenol-formaldehyde resin (Cofermin Rohstoffe, Germany); microcrystalline quartzite with a crystal size of 10-150 pm and a SiO2 content of 97 %, SCS-97 (Ukrainian Specifications TU U 23.2-00190503-382:2014, PJSC “KDZ”, Pokrovsk, Donetsk region). These components were dosed in the amounts indicated in the formulation of the invention (Specimen 1, 2, 3), beyond the formulation of the invention (Specimens 4, 5), and in the prototype composition formulation (Specimen 6).

[0045] The specimens were made by mixing polyfractional components (the powdered graphite, the antioxidant, the bond solidification seed, and the filler) with the bond, molding on a Lise 1600 press (specific pressure 100 MPa). The pressed specimens were dried and heat treated to final temperatures of 200 °C and 800 °C, respectively. The total drying time was 17 hours and the heat treatment time was 24 hours.

[0046] The properties of the obtained specimens of the quartz-carbon refractory of the invention and of that of state of the art (the prototype) were determined according to international standards: compressive strength (ISO 10059-1:1992), open porosity (DSTU ISO 5017:2014), shrinkage (ISO 2478:1987). The properties of the obtained specimens are presented in Table 2 hereinbelow.

[0047] Table 2 Properties of the obtained specimens

[0048] Beyond the Formulation of Formulation

[0049] Prototype No. Properties the invention of the

[0050] invention

[0051] 1 2 3 4 5 6 Compressive strength after

[0052] 1 43.5 45.0 42.8 41.3 40.0 33.1 drying, MPa

[0053] Compressive strength after

[0054] 2 35.6 40.1 37.0 35.5 30.9 17.2 heat treatment, MPa

[0055] 3 Open porosity after drying, % 7.5 7.0 7.5 8.0 8.0 8.0 Open porosity after heat

[0056] 4 12.1 11.9 12.3 14.2 16.4 17.1 treatment, %

[0057] 5 Shrinkage after drying, % 0.0 0.0 0.0 0.3 0.7 0.8 Shrinkage after heat

[0058] 6 0.0 0.0 0.0 0.5 1.1 1.4

[0059]

[0060] treatment, %For the quartzite-carbon refractory of the invention (Specimens 1, 2, 3), the property parameters exceed significantly those of the state of the art - the prototype (Specimen 6).

[0061] In the preceding detailed description, a specific embodiment of the present invention is shown by way of illustration, which explains its essence; it is to be understood, however, that the present invention is not limited to the specific embodiment described.

[0062] It is also understood that this description provides information that is necessary and sufficient for a clear understanding of the essence of the proposed technical solution. Information that is obvious to those skilled in the art and that does not contribute to a better understanding of the invention has not been provided in this description.

[0063] Technical Result

[0064] The technical result of the proposed technical solution is the provision of the quartz-carbon refractory, the use whereof ensures the preservation of a dense bonding framework with the effective closure of the channel porosity this providing counteraction to shrinkage processes and reinforcement of the material structure in a wide temperature range.

[0065] References:

[0066] 1. N.A. Golushko. Graphite-containing Refractories. - Moscow: State Scientific and Technical Publishers of Literature on Ferrous and Nonferrous Metallurgy, 1962. - pp. 63, 64

[0067] 2. Quartzite-carbon refractory: Patent RU2238253C2: International Patent Classification C04B 35 / 14, 35 / 6, 35 / 52. Application RU2002131112 / 03A; filed on 18.11.2002; published on 20.10.2004.

[0068] 3. Silica-carbon refractory: Patent RU2229455C1: International Patent Classification C04B 35 / 14, 35 / 6. Application RU2002126004 / 03A; filed on 30.09.2002; published on 27.05.2004.

Claims

What is Claimed is:A quartzite-carbon refractory containing a powdered graphite, a filler in the form of microcrystalline quartzite with a crystal size of 10 to 150 pm, a silicon dioxide (SiCh) content of not less than 97 % w / w, and a bond in the form of a mixture of novolac phenol-formaldehyde resin (91 to 94 % w / w) and urotropin (6 to 9 % w / w), characterized by that it contains additionally an antioxidant in the form of silicon and a bond solidification seed in the form of a dry phenol-formaldehyde resin at the following ratio of components, % w / w:Powdered graphite 8.0 to 20.0Bond 2.5 to 5.0Antioxidant 3.0 to 5.0Bond solidification seed 1.0 to 3.0Filler Q.S. to 100

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