CN1587189A - Process for preparing high strength corundum refractory material by low temperature sintering - Google Patents

Abstract

The present invention provides low temperature sintering process of preparing high strength refractory corundum material. On the basis of multiple stage grain compounding, silica fume of small granularity, high activity and low cost is added as sintering assistant; and after mixing and forming, high strength refractory corundum material is prepared through sintering at relatively low temperature. The said process can prepare high strength refractory corundum material product in low power consumption and low production cost. The high strength refractory corundum material may be used in high temperature furnace and kiln in various industry and in ceramic product.

Description

Preparation method of low-temperature sintered high-strength corundum refractory material

Field:

The invention belongs to the technical field of preparation of ceramics and refractory materials, and in particular relates to a method for preparing a low-temperature sintered high-strength corundum refractory material with fused white corundum aggregate and powder as main raw materials.

Background technique:

Corundum refractory material has excellent mechanical properties, high temperature resistance, corrosion resistance and wear resistance. It is a kind of high-grade refractory material with the earliest development and large production volume. It is mainly used in high-temperature kilns in the fields of steel, chemical industry, ceramics and machinery. The lining of key parts of the furnace, however, the sintering temperature of corundum refractory materials is high, usually above 1600 °C, and the production cost remains high, which affects the wide application of this material to a certain extent.

In order to reduce the firing temperature of corundum refractory materials, the methods usually used mainly include:

(1) Adding boric acid or B ₂ O ₃ method: After calcining at 1550°C, Na ₂ O is formed into sodium borate and volatilized. Adding B ₂ O ₃ is very effective in purifying alumina with high SiO ₂ content and perfect structure. However, due to the formation of coarse-grained structure of alumina, the density, mechanical properties and dielectric properties of special refractory materials are all reduced;

(2) MgCl ₂ can not only remove Na ₂ O in alumina, it is also a crystal transformation regulator required for firing corundum ceramic products, and no auxiliary process measures are required. This method is widely used to produce chemically pure and dense special corundum ceramic products under vacuum. The corundum clinker produced by this method can produce corundum products with particularly high chemical composition, mechanical properties and density. The sintering temperature is 1500 -1620°C. Adding an appropriate amount of MgO can also promote the sintering of corundum refractories and increase the strength of the fired materials.

(3) Although the calcination temperature of corundum refractories can be reduced to 1600°C by adding TiO ₂ or MnCO ₃ , both additives can make the grains grow and significantly reduce the mechanical strength of the material, and at the same time make the material color.

(4) The corundum refractory material added with Cr ₂ O ₃ or ZrO ₂ has excellent high temperature strength and thermal shock stability after firing at 1600 °C.

According to the records in China's scientific and technological achievements database, the corundum product project for heavy oil pressurized gasifier identified by Xinxiang Refractory Material Factory in 1993 is characterized by adding an appropriate amount of alumina micropowder to the ingredients and using a phosphate binder. Firing at 1610°C. The high-purity corundum brick identified by Luoyang Refractory Research Institute in 1992 is characterized by using two kinds of fused and sintered corundum that show different firing shrinkage at high temperature as the main raw material, and adding part of activated alumina powder, multi-level ingredients, double Surface pressure molding, high temperature firing in the system.

Patent application number 00123761.6 discloses a high-purity, low-silicon and low-iron corundum product, which is characterized in that a small amount of calcium-containing substances are added as sintering aids in addition to fused corundum, sintered alumina fine powder and binder in the ingredients. The sintering condition of the brick is improved, so that the brick can be sintered well at a lower firing temperature, and the high-purity corundum brick produced has a normal temperature compressive strength of about 110MPa.

In the patent application number 99123977.6, a relatively large amount of kaolin fine powder is added to the matrix to prepare corundum mullite products.

The patent application No. 88104671.X is characterized in that many sintered flaky corundum crystal particles with cleavage planes are molded in a prefabricated model, and then sintered at 1500 ° C to make the particles aggregate and bond together. The bonding mode makes the cleavage planes of these aggregated plate-like crystal grains substantially parallel to each other, thereby preparing sintered alumina products with high flexural strength.

The problems of the method for preparing corundum refractory materials recorded in the above documents are that the firing temperature is high, the energy consumption is large, and the cost is high, which affects the production of corundum refractory materials and their wide use in high-temperature industries to a certain extent.

Invention content:

The purpose of the present invention is to provide a method for preparing high-strength corundum refractory material at a relatively low temperature by using cheap silica fume as a sintering aid, so as to reduce the firing temperature, energy consumption and preparation cost, and is beneficial to industrial manufacturing.

The principle of the invention is to add an appropriate amount of silica fume to the corundum raw material, and utilize the sintering-promoting action of the silica fume with high sintering activity at high temperature to rapidly sinter the corundum material, thereby obtaining a low-temperature sintered high-strength corundum material. If the amount of silica fume added is too small, the material cannot reach a good sintered state within the temperature of the present invention, and the strength is low. However, if the amount of silica fume added is too large, there will be too much synthetic mullite phase in the material during the firing process, and the volume expansion will be large, which will affect the performance of the product. Therefore, the amount of silica fume added should be appropriate.

Realize the technical scheme of the object of the present invention is:

The preparation method of low-temperature sintered high-strength corundum refractory material mainly includes processes such as mixing raw materials, adding a binder, mixing, forming and drying, and firing, and is characterized in that:

a. Crushing or pulverizing the fused or sintered corundum raw materials into three particle sizes below 3-1mm, 1-0.088mm and 0.088mm;

b. Use silica fume or silicon oxide nanopowder as a sintering aid, and mix it evenly with corundum particles below 0.088mm in a mass fraction of 1-9% (additional) as a base material;

c. Mix 3-1mm and 1-0.088mm corundum pellets evenly;

d. Add a binder to the mixture in c, mix evenly, add the base material obtained in b, and mix evenly to make mud

e. Put the mud prepared in d into a press, press it into a green body under a pressure of 70-200MPa, dry it, and then burn it at a temperature of 1300-1550°C for 2-8 hours, cool it, and take it out of the furnace to obtain product.

In the above preparation method, the mixing ratio of three different corundum raw materials below 3-1mm, 1-0.088mm, and 0.088mm is 40-50%: 10-20%: 30-40%, preferably 45:15:40; The addition amount of the agent is 3-15% of the corundum raw material.

In the above preparation method, the corundum raw material used is one of fused white corundum, tabular corundum, brown corundum, gray corundum, bauxite corundum, and sintered corundum; the binder is sulfurous acid pulp waste liquid, polyvinyl alcohol, dextrin , One or more of lignin.

The corundum material prepared by the method of the present invention has phase composition: corundum ≥ 98%, physical and chemical properties: Al ₂ O ₃ ≥ 90%, bulk density 2.8-3.2g/cm ³ , apparent porosity ≤ 25%, room temperature resistance Bending strength ≥ 20MPa, compressive strength at room temperature ≥ 80MPa.

Compared with the prior art, the present invention has the advantages of:

1. Using silica fume as a sintering aid reduces the firing temperature of the material and reduces the preparation cost.

2. The prepared material has high strength, which is beneficial to improve the service life of the material.

3. The source of silica fume is abundant, the price is low, and the effect of promoting sintering is obvious.

Detailed ways

Example 1:

The main raw material used in this embodiment is:

(1) Fused white corundum: the chemical composition (mass fraction) is Al ₂ O ₃ ≥ 98%, and the particle size is 3-1mm, 1-0.088mm, and 0.088mm or less;

(2) Silica fume: choose SiO ₂ ≥ 91%.

Raw material of the present invention and silica fume ratio are shown in the following table:

                                                                 

Particle size 3-1mm 1-0.088mm ＜0.088mm 0.1μm

Proportion (weight fraction%) 45 15 40 4

Weigh various fused white corundum raw materials according to the proportions shown in the above table, wherein the added silica fume is 4%. First mix the fused white corundum particles below 0.088mm with silica fume evenly to obtain the base material; then put the premix of 3-1mm and 1-0.088mm particles and add 3% polyvinyl alcohol binder into the mixer Mix evenly in the medium, finally add the base material and mix in the mixer for 5 minutes until uniform to make mud; put the mud into the press and form a 25×25×125mm green body under 80MPa pressure; the green body is in 110 °C for 4 hours; then fired in an electric furnace at 1350 °C for 6 hours, lowered the temperature, and came out of the furnace to obtain a corundum material.

The properties of the prepared corundum material are as follows: Al ₂ O ₃ ≥ 90%, bulk density 2.9g/cm ³ , apparent porosity 25%, room temperature flexural strength 33.4MPa, room temperature compressive strength 105MPa.

Example 2:

Electric fused brown corundum is used as the granular material, the raw material ratio and preparation process are the same as in Example 1, and a 25×25×125mm green body is formed under a pressure of 120MPa; the green body is dried at 110°C for 4 hours; fired in an electric furnace at 1550°C ×6h. The properties of the prepared corundum material are as follows: the main crystal phase is corundum phase, Al ₂ O ₃ ≥ 90%, the bulk density is 3.0g/cm ³ , the apparent porosity is 23%, the flexural strength at room temperature is 35MPa, and the mineral phase composition of the material is relatively pure of corundum phase.

Example 3:

Add 9% silica fume in the batching, use sulfurous acid pulp waste liquid as the binder, other raw materials, proportioning and preparation process are the same as in Example 1, and form a green body of 25×25×125mm under a pressure of 120MPa; the green body is heated at 110°C Dry for 4 hours; burn in an electric furnace at 1350°C for 6h. The properties of the prepared corundum material are as follows: the main crystal phase is corundum phase, Al ₂ O ₃ ≥ 90%, the bulk density is 3.1g/cm ³ , the apparent porosity is 19%, the flexural strength at room temperature is 45MPa, and the mineral phase composition of the material is corundum phase and trace amounts of mullite phase.

Claims (6)

1, a kind of preparation method of low-temperature sintering high strength refractory corundum material comprises that mainly raw material mixes, adds wedding agent, moulding, drying, technological process such as burns till, and is characterized in that:

A. with electric smelting or alundum raw material crushing or be ground into 3-1mm, 1-0.088mm, the particle of three kinds of granularities below the 0.088mm;

B. make sintering aid with silicon ash or monox nanometer powder, mix in massfraction 1-9% ratio and the corundum in granules material below the 0.088mm, as the matrix material;

C. the corundum in granules material with 3-1mm, 1-0.088mm mixes;

D. in the compound of c, add wedding agent and mix, add the matrix material of b again, mix, make pug;

E. the pug that d is made is put into pressing machine, is pressed into base substrate under 70-200MPa pressure, and drying was burnt till 2-8 hour under 1300-1550 ℃ of temperature then, and cooling is come out of the stove, and promptly makes product.

2, according to the preparation method of the described low-temperature sintering high strength refractory corundum material of claim 1, it is characterized in that: the ratio of mixture of 3-1mm, 1-0.088mm, the following three kinds of different corundum raw materials of 0.088mm is 40-50%: 10-20%: 30-40%.

3, the ratio of mixture of 3-1mm, 1-0.088mm, the following three kinds of different corundum raw materials of 0.088mm is preferably 45%: 15%: 40%.

4, according to the preparation method of the described low-temperature sintering high strength refractory corundum material of claim 1, it is characterized in that: the add-on of wedding agent is the 3-15% of corundum raw material.

5, according to the preparation method of the described low-temperature sintering high strength refractory corundum material of claim 1, it is characterized in that: said corundum raw material is a kind of in fused white corundum, plate diamond spar, brown corundum, grey corundum, bauxite corundum, the alundum.

6, according to the preparation method of the described low-temperature sintering high strength refractory corundum material of claim 1, it is characterized in that: said wedding agent is one or more in lignosulfite, polyvinyl alcohol, dextrin, the xylogen.