RU2211200C1 - Fire-resistant mix and method for tempering thereof - Google Patents

Abstract

FIELD: refractory materials. SUBSTANCE: fire-resistant mix intended for lining and repair operations in high-temperature heat assemblies contains, wt %: silicon dioxide 32-45, aluminum 29-35, cement 10-20, fly ashes 0-16, aluminum oxide 0-10, and chamotte powder 0-18. Mix is tempered by stirring components in presence of water with liquid glass taken at ratio (1-1.5):1. EFFECT: expanded application areas and increased adhesion to refractory aluminosilicate surfaces. 3 cl, 3 tbl

Description

 The invention relates to the field of creating highly refractory mixtures that can be used in the form of solutions for masonry and coating in the manufacture of lining and repair work in high-temperature thermal units (furnaces, boilers, reactors, etc.), in ferrous and non-ferrous metallurgy, in chemical and by-product coke, thermal power and construction industries.

 The main purpose of refractory mixtures is the lining of the working surfaces of structures based on aluminosilicate products, concrete and other composite materials.

 Known lining mixtures are composed, as a rule, for reasons of similarity in the chemical composition of the mixture and the base refractory (see, for example, RU 2074152, class C 04 B 35/65, 35/66, 1997). This contributes to the compatibility and adhesion of the applied lining material and the base on which it is applied. However, even with such chemical compatibility, problems may arise with the adhesion of the lining or repair mixture to the base, especially in cases where it is necessary to ensure reliable adhesion during the long period of operation under high-temperature effects of a static or dynamic (including cyclic) nature . Often, under the influence of these factors, the lining is peeled off, it is chipped, or shells and burnouts are formed, which reduces the service life of a high-temperature thermal unit.

Known refractory mixture "GAMMA-3XP", which is intended to protect the surfaces of high-temperature furnaces made of chromite and chromite-periclase refractories, and the method of its mixing (see RF patent 2138464, CL 04 04 35/12, 35/65, 35 / 66 dated 1999). Known refractory mixture has the following composition, wt.%:
Chromite Ore - 40-65
Iron Oxide - 9-22
Magnesium Sulfate - 8-14
Aluminum or an alloy of aluminum and silicon - 10-14
Superplasticizer S-3 - 0.0-11.9
Initiator (NH ₄ Cl or a mixture of an ammonium-containing component with the halides of Ca, Mg, Al) - 0.1-0.9
Modifier (kyanite, sillimanite or a mixture thereof) - 2.0-20.0
The method of mixing this mixture is to mix the powdered components with the required amount of water.

The masonry solution obtained in this way is used in the lining of cement kilns, sintering furnaces, calcinations, etc. with a working temperature of 900-1800 ^o С. When the furnace heating temperature reaches about 900 ^o С, self-ignition occurs in the masonry joints and the SHS-combustion process begins (self-propagating high-temperature synthesis). The melt of materials formed in the SHS wave impregnates the surface layers of the adjacent chromite or chromite-periclase refractories to a depth of 0.1-0.5 mm and welds them into a monolith. The mortar fire resistance after firing in the SHS wave is 1780 ^o С, and heat resistance is up to 60 air heat exchangers.

 The disadvantages of the known refractory mixtures include the limited use of these mixtures only for chromite or chromite-periclase refractories, the lack of chemical resistance to the effects of molten metals and slags in direct contact, as well as the rather high complexity of the composition (multicomponent), which creates certain difficulties for its wide practical application.

 The closest to the claimed inventions in terms of technical nature and the achieved result are the refractory composition (mixture) and its mixing method described in patent 876353, 1961. The mixture includes powdered aluminum - a reducing agent and an oxidizing agent, for example silicon dioxide, and also (as a binder) alumina cement in an amount of 25-50% by weight of the composition. The method of mixing this known mixture is to mix the components with water containing 1.5 wt.h. gum arabic and 0.5 wt.h. tannic acid.

 The disadvantages of this known refractory mixture are low activity in exothermic synthesis and low adhesion to the surfaces of refractory materials treated with this mixture.

The objective of the invention is to create a simple and inexpensive mixture for use with aluminosilicate refractories, capable of high-temperature synthesis (SHS) when heated to 750-850 ^o C and providing the material after the SHS process with high performance characteristics: chemical and erosion resistance when in direct contact with aggressive high-temperature environments, wear resistance under mechanical (especially abrasive nature) influences.

 The objective of the invention is the creation of a multi-purpose refractory mixture, which allows the mixture to be used both for masonry, lining and repair work, and as a protective and hardening coating on the working surfaces of the linings of high-temperature units or individual piece and shaped refractory products with aluminosilicate base.

 The objective of the invention is the development of a method for mixing a refractory mixture, which allows to increase the adhesion of the refractory mixture to the machined surfaces of aluminosilicate refractories.

The solution to this problem is achieved by the fact that the proposed refractory mixture, including an oxidizing agent - silicon dioxide, a reducing agent - powdered aluminum, as well as alumina cement, contains alumina cement as a high alumina cement grade VHC in the following ratio, wt.h .:
Silicon Dioxide - 32-45
Aluminum - 29-35
VGC brand cement - 10-20
The proposed refractory mixture may additionally contain fly ash in an amount of 0-16 parts by weight, alumina in an amount of 0-10 parts by weight. and fireclay powder in an amount of 0-18 wt.h.

 The solution to this problem is also achieved by the proposed method of mixing a refractory mixture, including an oxidizing agent - silicon dioxide, a reducing agent - powdered aluminum, as well as alumina cement, by mixing it in the presence of water, in which the proposed refractory mixture is mixed with liquid glass in a mass ratio (1-1 , 5): 1.

The proposed method uses industrial liquid glass (GOST RF 13078-81) with a density of 1.45-1.47 g / cm ³ and composition by weight: SiO ₂ - 29.6-30.5%, Na ₂ O - 10, 6-11.0%, the rest is water.

In the proposed refractory mixture (mixture), substances with the following characteristics were used:
1. Silicon dioxide - fine sand (less than 100 microns) grade C-070-1 with a SiO ₂ content _of 98.3%. You can use other brands of ground sand.

 2. Aluminum powder with a particle size of less than 50 microns.

3. VHC brand cement with Al ₂ O ₃ content from 70 to 75%.

4. Fly ash with ultrafine dispersion (≤10 μm) and with the composition: SiO ₂ - 56.5%, Al ₂ O ₃ - 26.63%, Fe ₂ O ₃ - 10.47%, CaO - 2.5 %, MgO - 1.4%, etc. In our case, fly ash from TPP-22 (Moscow) was used.

5. Aluminum oxide (Al ₂ O ₃ ) of any brand with a dispersion of not more than 100 microns.

6. Fireclay powder (aluminosilicate with an Al ₂ O ₃ content of 28 to 45%).

The liquid-viscous slip-based composition obtained by mixing the mixture is applied in a thin layer (of the order of 1.5-3.0 mm) on the working surface of the base. With natural drying (about 1-2 hours), even before low-temperature firing in the SHS process mode, the used solution receives sufficient structural strength. The final operational properties of the material of the lining coating or the masonry seam acquire during heating of the thermal unit during its technological drying. Upon reaching the heating temperature of the lining of the thermal unit of the order of 750-850 ^o C in the coating material and / or in the joints of the masonry, a gas-free combustion process (SHS) is initiated, which propagates in the form of a directed combustion wave over the layer of the applied refractory mixture. The synthesis of new oxide-ceramic structures of the mullite type (3Al ₂ O ₃ • 2SiO ₂ ) occurs in the zone of the combustion wave at temperatures of 1600-1700 ^o C for times of the order of 10 ^-3 s. The synthesis is accompanied by the melting of fine aluminum powder, so that some of the melt penetrates into the surface layers of the base material, especially if it has open porosity. Due to this effect, the coating layer or masonry seam is welded with the aluminosilicate base material, which ensures their adhesion to the monolith. Of no small importance is the fact that the coefficients of linear and volume expansion of the materials of the refractory base and the oxide-ceramic coating formed in the SHS wave are almost identical, which ensures their long-term adhesion without stresses during the operation of the thermal unit.

 The experimentally obtained results showed that the addition of alumina to the mixture promotes the formation of mullite structures in the material during the SHS process and reduces the initiation temperature of this process.

The addition of fly ash to the composition of the mixture also lowers the initiation temperature of the SHS wave due to the metal oxides Al ₂ O ₃ , Fe ₂ O ₃ , MgO, etc. contained in the ash composition (up to the melting temperature of aluminum particles (660 ^o С)).

In addition to the described process of self-formation of a protective-hardening coating or ceramic material of the lining seam during the start of operation of thermal units, preliminary application of coatings on piece and shaped refractory products during their factory manufacturing or during the preparatory stage of the lining work in the heat generator itself can be widely used. In this case, the SHS process in the material applied to the product is ensured by low-temperature firing in any heating furnaces with a controlled heating mode (heating rate of 5-10 ^o C / min).

 The technical result of this invention is a significant increase (several times) in the life of the linings of thermal units operating under the influence of static and dynamic high-temperature loads. For piece and shaped refractory products, applying from the claimed mixture of protective and hardening coatings allows their properties to be transferred to the class of highly refractory materials.

 The possibility of implementing the invention is illustrated by examples of their specific practical applications, which are given in table. 1, 2 and 3.

 In addition to these examples, it can be pointed out that samples of cellular SHS concrete, coated on the outside with a layer of 2-3 mm thickness from the proposed refractory mixture (composition 4 in Table 1), placed in an aggressive chemical environment (acid-base nature), are not changed their physico-mechanical characteristics, despite a round-the-clock three-month stay in conditions of active chemical exposure to them.

 The above examples quite convincingly demonstrate the high performance of linings and coatings made from the proposed refractory mixture. The composition of the refractory mixture is simple to manufacture and is absolutely accessible to any consumer in the range of offered components.

Claims (2)

1. A refractory mixture comprising an oxidizing agent - silicon dioxide, a reducing agent - powdered aluminum, as well as alumina cement, characterized in that it contains high-alumina cement grade VHC as an alumina cement in the following ratio of components, wt. hours:
Silicon Dioxide - 32-45
Aluminum - 29-35
VGC brand cement - 10-20
2. The refractory mixture according to claim 1, characterized in that it further comprises fly ash of 0-16 wt. hours, alumina 0-10 wt. hours and chamotte powder 0-18 wt. h  3. The method of mixing a refractory mixture, including an oxidizing agent - silicon dioxide, a reducing agent - powdered aluminum, as well as alumina cement, by mixing the mixture in the presence of water, characterized in that the refractory mixture according to claim 1 or 2 is mixed with liquid glass in a mass ratio ( 1-1.5): 1.

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