JPS5833185B2 - Basic refractories - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refractory using a magnesia-chromium oxide based fused or sintered clinker.

Maguro bricks used in cement rotary kilns, special smelting furnaces (AOD Pitten furnaces) electric furnaces, molten steel degassing tanks, etc. As the furnaces are increasingly operated under harsh conditions, so-called direct bonds develop and the matrix Spinel bonded bricks are required.

For this purpose, direct bond bricks have been developed that use high-purity magnesia clinker and chromite with low 5i02 content and are fired at high temperatures.

Furthermore, magkuro ribboned bricks with developed direct bonding have been developed using high-density refractory raw materials such as so-called molten magkuro clinker and sintered magkuro clinker, which are made by pre-reacting magnesia and chromium ore.

Conventional Maguro direct bond bricks and bond bricks are MgOAZ20B-Cr203-Fe oxide-8i0
2-CaO brick, which is the main component of the liquid phase 5
i02 is taken in as a gangue mineral of chromite,
It is necessarily controlled by the type of chromite and the chromite content.

When these bricks are examined structurally, it is observed that the connective tissue is formed by spinel between periclase crystals, but a siliceous liquid phase is always observed around the spinel formed at high temperature, and is essentially a secondary phase from the liquid phase. (Mg, Fe
) 0, (Fe, Cr, Ag) 20a.

The solubility of spinel (MgO, R203) in a silicate liquid phase increases in the order of Cr203 (A1203) and Fe oxide.

Picrochromite (MgO-Cr203) is produced from magnesia-chromite (Mg,Fe)O
.

(Fe, CrA/) It has a higher melting point than spinel 203, and has excellent corrosion resistance, hot strength, and spalling resistance.

These conventional fused or sintered magnesia-chromium oxide clinkers are caused by dissolution between individual periclase crystals (chromium oxide that was solidly dissolved in periclase is precipitated on the surface of the periclase crystals, in this case heating and slow cooling). It is made up of an aggregate of picrochromite and periclase, which are precipitated on the surface.

Conventionally, the strength of bricks was given by sintering the picrochromites precipitated on the surface of clinker crystal particles to each other.

When manufacturing fired refractories using these clinkers, the temperature is 1800℃ to provide sufficient bond strength and corrosion resistance.
It was necessary to fire at a higher temperature.

For brick manufacturers, firing at high temperatures increases fuel costs and has to deal with air pollutants, especially nitrogen oxides, generated during the firing process. Reducing this is a major challenge.

In order to solve the above problems, the present invention uses specially treated fused or sintered magnesia-chromium oxide clinker (hereinafter referred to as clinker) to develop a matrix picrochromite bond even at low firing temperatures. It is related to making refractories.

That is, the present invention is a basic refractory constructed by eliminating the defects of the conventional clinker mentioned above, and which is composed of magnesia and Cr2O3.
Periclace obtained by heating a mixture of chromium oxide containing 90% by weight or more at a weight ratio of 9:1 to 4:6 to 1,800°C or higher and rapidly cooling it forms the skeleton, and chromium oxide is contained in the periclase. Using a clinker in which the periclase has a solid solution and the lattice constant of the periclase is 4.208 A or less, the chromium oxide dissolved in the periclase was precipitated by dissolution during brick firing, and a picrochromite bond in the matrix was developed. It is a basic refractory.

To make the fused or sintered clinker according to the present invention, magnesia raw material fine powder and chromium oxide raw material fine powder are used.

These fine powders should be crushed as much as possible due to their ease of reaction.
It is desirable to use one in which at least 50% passes through 44μ.

As the magnesia raw material that can be used in the present invention, it is preferable to use active powders that are more easily reactive, such as magnesium hydroxide or light calcined magnesia, but it is also possible to use pulverized products of general dead-burned clinker.

lI' as a chromium oxide raw material that can be used in the present invention
! , Cr2O3 content is required to be 90% by weight or more,
Refractory materials can be used.

The clinker according to the present invention is produced by mixing a chromium oxide raw material and a magnesia raw material in a desired ratio and melting or sintering the mixture at a high temperature.
This is obtained by rapidly cooling it from this high temperature.

The mixture must be heated at a temperature of 1800° C. or higher in order to form a solid solution of a large amount of chromium oxide in the clasp and to minimize the apparent porosity of the sintered clinker.

In the present invention, the proportion of magnesia and chromium oxide is limited to a weight ratio of 9 = 1 to 4:6.If the chromium oxide side is less than 10% by weight, the amount of periclase forming the skeleton is large compared to Cr2O3. -The amount of solid solution of chromium oxide in the space is small, and the lattice constant of periclase is 4.20.
This is because when the temperature exceeds s k, the amount of picrochromite separated and precipitated during brick firing is small, resulting in a decrease in sinterability.

When the chromium oxide side exceeds 60% by weight, picrochromite becomes the main component, and the sinterability of the clinker is poor.

In addition, the absolute amount of periclase decreases, and the amount of picrochromite that precipitates from periclase during brick firing decreases, resulting in a decrease in sinterability.

In the present invention, raw materials with a high Si02 content tend to form a liquid phase, that is, a low-melting glass phase around periclase, so it is desirable to have as little as possible.

In order to increase the density of the clinker, a sintering material can be added within a range that does not adversely affect the corrosion resistance of the brick.

The amounts added are TiO2, Al2O3, ZrO2゜Fe2O3
It is effective to limit one or more of these to 5% by weight or less of the total amount.

Molding m containing particles made of clinker according to the present invention
Finished product o Hot bending strength (kg/cII12) (1400℃
) and the periclase lattice constant (A) of the clinker is as shown in the drawing.

As is clear from the experimental results shown in the drawings, the product according to the present invention, which is formulated with the clinker of the present invention, molded, and fired at 1600°C, has a higher thermal resistance than the conventional product containing the conventional clinker, which has a lattice constant of 4.212A. The strength is about 2
．． It is recognized that there is a significant difference in effectiveness compared to 1x.

Although clinker can be rapidly cooled by air cooling outside the furnace, it is better to rapidly cool it in water, and it is also desirable to rapidly cool it by placing it in dry ice.

Clinker that has been sufficiently rapidly cooled has a large amount of chromium oxide dissolved in the periclase, and the periclase lattice constant of ordinary commercial magnesia clinker is 4.212±o, oo2A.
It has a much lower lattice constant compared to .

Even in formulations containing chromium oxide at a higher solubility in periclase at high temperatures, the same effect can be obtained by adding a quenching operation.

The periclase lattice constant of the quenched clinker is 4.2.
Those below 08A are effective, and those above that have little quenching effect, and the expected effect is poor because the amount of chromium oxide dissolved in periclase is small.

The clinker containing a large amount of chromium oxide as a solid solution in the periclase of the present invention is blended at a relatively low firing temperature of 1500°C to 1700°C when conventional brick manufacturing is carried out by crushing, adjusting particle size, kneading, molding, and firing. This method is extremely effective because picrochromite is separated and precipitated from the inside of the periclase of the clinker toward the surface, resulting in a sintered body in which the periclase is surrounded by picrochromite.

The present invention is not limited to fired products or unfired products, but can also be applied to molded products as well as monolithic refractories that are fired and hardened at the construction site.

Next, examples of the present invention will be shown together with comparative examples.

Table 1 shows typical chemical components of the magnesia raw material and chromium oxide raw material used in this invention.

Table 2 shows the blending ratio of the present invention using the refractory raw materials exemplified in Table 1 and the characteristics of the clinker of the product according to the present invention and comparative products obtained as follows.

Sintered clinker is made by mixing raw magnesia and chromium oxide raw materials finely pulverized to 74μ or less and forming them into 20 to 40 lumps.
The molten clinker was heated for 0 minutes, and the molten clinker was held at 2,500 C for 130 minutes in an arc-heating electric melting furnace, and the sintered or molten body was rapidly cooled in water (product of the present invention) and slowly cooled in the furnace. (comparison product).

Example 1 is a sintered product with a weight ratio of magnesia chromium dioxide of 8:2, and Examples 2, 3, and 4 are sintered products with a weight ratio of magnesia:chromium oxide of 7:3. Example 3 is a molten product, Example 4 is a sintered product with 3% by weight of ilmenite added as a sintering agent, and Example 5 is a sintered product with 5:5 weight ratio of magnesia chromium dioxide solidified in periclase of a rapidly cooled clinker. Chromium oxide is added in an amount higher than the solubility.

According to X-ray diffraction, the quenched clinkers of Examples 1, 2, 3, and 4 have one phase of periclase, and the lattice constant of periclase is 4.198 to 4.205A.

In addition, the rapidly cooled clinker of Example 5 consists of two phases, mainly periclase and picrochromite, and has a lattice constant of 4.20.
The apparent porosity of the rapidly cooled clinker, which is 1A, is slightly smaller than that of the slowly cooled surface (comparison product).

In order to investigate the sinterability of these rapidly cooled clinker and slowly cooled clinker (comparative products), the clinker of Example 2 was
Finely ground to 7μ or less and 20X10X12 at 500ky/d
Make a molded body between 0 and 1300**℃ for 2 hours, 1500℃
It was fired in a tunnel kiln at 1,600°C for 2 hours, at 1,600°C for 2 hours, and at 1,800°C, and the physical properties and hot bending strength at 1,400°C of the fired product were measured.

The results are shown in Table 3. As can be seen from Table 3, the use of rapidly cooled clinker improves the sintering properties and increases the hot bending strength.

In particular, extremely remarkable effects are achieved even at a firing temperature of 1500 to 1600°C.

In order to investigate the corrosion resistance and spalling resistance of the bricks of the present invention, the clinker of Example 2 was crushed, the particle size was adjusted, and kneaded.
1000kg/cIIL in the shape of 30x120x65
Table 4 shows the properties of electrofused ribbon bricks and direct bond bricks molded in Example 2 and tunnel-killed at 1600°C and having almost the same MgO content as Example 6 as comparative examples.

*1 *2 A 230 x 120 x 65 mm test piece was heated at 120 x 65 mm for 15 minutes at 1200°C in an electric furnace, then taken out of the furnace and rapidly cooled repeatedly.The 60 x 60 x 200 mm test piece was pasted together the number of times required for 5% peeling using a horizontal rotating arc type. Low basicity slag (CaO/S i
02=1.2), and the maximum erosion depth and penetration depth after the 1800° C. 4-hour test were compared with the direct bond brick as 1.0.

(The larger the number, the greater the corrosion resistance.

) As can be seen from Table 4, the spalling resistance of the bricks of the present invention is equivalent to that of direct bonded bricks, and when viewed structurally, the silicate liquid phase is small and the residual amount of picrochromite bonding makes it difficult to resist heating at 1500°C. In terms of mechanical strength and corrosion resistance, it is superior to conventional maguro bricks.

[Brief explanation of drawings]

The drawing is a curve diagram showing the relationship between the lattice constant of the clinker and the hot strength of the brick at 1400° C., obtained by blending the clinker according to the present invention in a simple manner and baking the brick. 1... 1800℃ firing of the wares, 2...
・Curve of product fired at 1600℃, 3...1300℃
Curve of fired product.

Claims (1)

[Claims] 1. The weight ratio of the magnesia raw material fine powder and the chromium oxide raw material fine powder with a Cr2O3 content of 90% by weight or more is 9:1 or more.
The periclase obtained by heating a 4:6 mixture to 1800°C or higher and rapidly cooling it forms the skeleton, chromium oxide is solidly dissolved in the periclase, and the lattice constant of the periclase is 4.2.
A basic refractory made using a clinker of 08'A or less.