JPS605556B2 - Method for preventing oxidation of graphite or silicon carbide refractories - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing oxidation of graphite or cinnamon carbide refractories by forming a uniform and dense molten coating layer on the surface of the refractories during high-temperature use.

Recently, graphite or graphite materials such as alumina-graphite, chamotte-graphite, zircon-graphite, magnesia-graphite, or silicon carbide-graphite have been used as refractories for blast furnaces, converters, electric furnaces, or continuous casting in steel plants. Silicon carbide refractories are widely used, and it is well known that their graphite or silicon carbide components are difficult to wet with slag and molten steel, and have excellent corrosion resistance, thermal conductivity, and spalling resistance. In normal air, that is, in an oxidizing atmosphere, this is 50
Na
0, K20, Ca○, Sj02, Fe203, P2Q,
SIC or a mixture that forms a glass phase at low temperatures, such as Si, Pb, Zn, AI, Si, or a reducing metal, is kneaded in advance into a clay pot and molded, or a cup ± molded body is mixed into a slip of the mixture. It has been attempted to impart oxidation resistance to refractories that have been soaked and fired, but this has the disadvantage that the corrosion and spalling properties of graphite or carbide refractories are impaired, and other oxidation As a prevention method, the refractory surface is coated with the above mixture (Si02-AI203 system) or Mg○ quality slip, but both have compositions that generate a glass phase at relatively low temperatures and cannot be heated to relatively high temperatures. If this is done, the coating tends to become uneven and there are accidents where insufficient coverage is damaged by oxidation, and there is still no satisfactory method for preventing oxidation.

Therefore, the present invention solves the drawbacks of such conventional oxidation prevention methods, and develops graphite that can reliably form an even and dense molten coating layer on the surface during high-temperature use without impairing the original properties of refractories. The purpose of the present invention is to provide a method for preventing oxidation of graphite or silicon carbide refractories, and its gist is to provide a method for preventing oxidation of graphite or silicon carbide refractories.
2 content is 95% or more, and the surface is further coated with S.
i〇250-80%, AI2〇35-30%, K2〇 and Na2〇3-15%, B2033-15%, and Fe
203, ZN0, P2Q or POO mixture 1-1
Thin coating layers containing 5% are laminated and the laminations are suitably heated to form a highly viscous, dense molten glass phase.

As a result of various studies on the shortcomings of the conventional oxidation prevention methods as described above, the present inventor has determined that when forming an oxidation-resistant coating layer, it is necessary to apply a coating layer on the surface of a refractory material that has a high degree of fire resistance during high-temperature heating. A thin coating layer (hereinafter referred to as the lower layer) with a high Sj02 composition that neither penetrates into the refractory nor flows down the surface, and a 70,000 mol of carbon dioxide on the surface that activates the oxidation reaction of the graphite or silicon carbide component of the refractory. A thin coating layer with a low Si02 composition (hereinafter referred to as the upper layer) that melts in the above temperature range and reacts with the lower layer components to form a delicate molten glass phase is laminated, and two layers with different compositions are laminated. They learned that scales can exhibit a remarkable antioxidant effect by coating them.

The process of studying the optimum composition ranges for the upper and lower layers of the coating material will be detailed below. First of all, the composition of the lower layer component Si02 is that it has a high degree of fire resistance in a high purity range of 95% or more, and has a high melting point and high density, so it exhibits an extremely stable coating effect when heated at high temperatures. Furthermore, a high viscosity, high density molten glass phase is generated by the reaction with the upper layer component, which will be described later.
If this is less than 95%, the effect of the coating layer as a base layer is reduced.

Next, regarding the composition of the upper layer coating material, the optimum composition differs depending on the composition of the graphite or cinnamon carbide refractory and the usage conditions, but according to the results of various studies on these refractories, the composition of Sj02 is as follows. In the range of 80% or more, the melting point of the upper layer material becomes relatively high, so 1000qo
Below this, it is not in a molten state and therefore glass is difficult to be produced by reaction with the lower layer components, and below 50%, the melting point will be low, but the glass produced will have a low viscosity and a stable coating layer will be obtained. There is no AI20
Regarding No. 3, if it is less than 5%, the viscosity of the melt of the upper layer material becomes high, and if it is more than 30%, the viscosity becomes small, and it tends to flow down from the surface of the refractory.

Next, regarding the amount of the mixture of K20 and Na20, if it is less than 3%, the amount of molten material is insufficient and it becomes difficult to form a uniform molten glass phase, and if it is more than 15%, the molten material becomes excessive, and the upper layer material is separated from the surface. Not only does it flow down, but it also reacts violently with the lower layer components, penetrating into the refractory and deteriorating its properties.Therefore, the composition of the mixture must be in the range of 3 to 15%. . Furthermore, for Ward 03, its composition is 3
% or less, the viscosity of the molten material of the upper layer material increases and a uniform and dense molten glass phase is not formed due to the reaction with the lower layer component.
If it exceeds 15%, the viscosity of the melt decreases and it tends to flow down the surface. Furthermore, a mixture of Fe2-Q, Zn○, P205 or POO is added from 1 to 15
%, it has the effect of improving properties such as adhesion with the lower layer component and density, but outside this range, the effect becomes small. In this way, the upper layer of the coating material contains 95% or more of Si02, and the lower layer contains 95% or more of Si02.
80%, AI2Q5~30%, K20 and Na20 3~
15%, B2033~15%, and Fe203, Zn
By coating a slip prepared by suitably mixing a mixture of ○, P2Q, or Pb○ within a composition range of 1 to 15%, the melt will not flow down during high-temperature heating, and will not penetrate into the refractory. A uniform and delicate molten glass phase with high viscosity and high density is formed, which can exhibit excellent antioxidant effects. Then, above,
To explain in detail the raw materials used for the coating material of each lower layer and their preparation method, the lower layer contains Si0
2. Use a single or a mixture of silica slip with a composition of 95% or more, but if necessary, use a small amount of clay, chamot,
Add 20 to 35 parts by weight of water to 100 parts by weight of a mixture containing alumina etc. together with a binder and wet-pulverize the mixture using a ball mill or the like, and reduce the viscosity to 100 mesh or less, preferably 3.25 mesh or less to a slip containing 85% or more. If so, coating construction will be easy.

Further, as raw materials for the upper layer, a powder mixture of Keisuke, Rouseki, Chamotte, clay or glass powder SIC, Si, Pb, and Zn○ is mixed with sodium carbonate, Tanasa, Textlin, P.I. V.
A, or within the above composition range using rubber or the like as a binder,
And the melting point is 700 depending on the components of the refractory, that is, the conditions of use.
It is mixed appropriately so that the ratio is 1400 to 0.
Depending on its components, the upper layer material may shrink in volume or generate pyrolysis gas when heated, causing it to peel off from the surface of the lower layer, or create a large number of pores. Therefore, frit obtained by baking the upper layer material in advance is recommended. The particle size should be 48 mesh or less and 200 mesh or less should be 50% or more from the viewpoint of coating construction and antioxidant effect.
-8 parts by weight are added and kneaded to form a slip.
To coat refractories with the slip prepared in this way, first coat the lower layer slip by brush coating, cough spray coating, or bonding current coating method, but the moisture content of the slip at this time is 25% by brush coating. ~40%, 30-50% for fogged and immersed coatings, and 50-90% for dense energized coatings.
% range, the adhesion to the refractory surface and workability are good, and when applying with a brush, by adjusting the pH value of the slip to 1 to 3 using hydrochloric acid, the brush spread and adhesion are even better. Therefore, it is easy to apply the coating, and if the spot value is adjusted to 5 to 8 in the case of immersion current coating, when the refractory is immersed in this and energized (direct current), the surface of the refractory (which becomes the anode) is A uniform and dense underlayer can be formed.

Next, the upper layer slip is coated on the surface of the lower layer by forming an even thin layer by brushing, spraying, or immersion coating. is used. Examples of the antioxidant method of the present invention and their effects will be listed below. Example 1 A slip was prepared by adding 2 parts by weight of water to 10 parts by weight of fused silica containing 80% or more of fused silica with a Si02 content of 98.5% and a particle size of 325 mesh or less, and further added 20% to 100 parts by weight of this slip. Add 20 parts by weight of hydrochloric acid aqueous solution to make a spot of 2.0
Coating material (1) prepared in were mixed in a ball mill for 3 hours to form Si026.
0.2%, N20313.7%, K20 and Na208.
A coating material (0) was prepared by adding 65 parts by weight of water to 100 parts by weight of a mixture consisting of 7%, &038.1% and 9.1% of others, and kneading the mixture.
%, Sj0215%, other 5% composition, porosity 21
%, a compressive strength of 200k9/c is used for continuous casting nozzles, and a number of specimens (cubes of 3 square meters) are cut out, and the above coating material (1) is evenly applied with a brush to several of the specimens. The lower layer was coated by drying at room temperature for 1 hour, and then the above coating material (B) was applied with a brush to the surface, and this was dried for 1 day at 10°C to form multiple samples in which two layers with different compositions were laminated (
Covering material (1) was applied to group A) and two sets of multiple specimens.
Samples (B) group and (C) in which the coating material (B) was coated on the top and bottom two layers in the same manner and in the same thickness.
A coating material (Machi) prepared by crushing Rouseki containing 270% Si, 20324% AI, and 6% other to a size of 200 mesh or less was applied to multiple specimens with a brush, then dried, and the above coating material ( Sample (A) by brushing 0),
Group (D) samples, which were made in the same machine as Groups (B) and (C) and coated with the upper two layers under the same thickness, were heated in a silicon carbide heating element electric furnace at a temperature within the range of 500°C to 1200qo. Individual samples (A), (B), (C) at heating temperature
And (D), the oxidation loss depending on the heating time was measured.

The results are as shown in the diagram for each sample (A), (B), (C
There is a clear difference in the oxidation loss between groups ) and (D), and this difference is particularly noticeable in the temperature range of 70 mm or higher, where the oxidation reaction becomes active. The sample (A) group coated with two layers showed a superior antioxidant effect than the sample (B) group or (C) group coated with only the lower layer or the upper layer slip. Furthermore, in the sample (D) group in which the Si02 component in the lower layer is 70% outside the composition range of the present invention, it is particularly 700% lower than the core sample (A) group.
The oxidation loss clearly increases at temperatures above .degree. C., and the influence of the Si02 composition of the lower layer component on the antioxidant effect is clearly seen. Furthermore, the results of observing the cut surfaces of these sample groups showed that in the sample (A) group, a uniform glass phase was formed in the coating layer, and this completely covered the specimen, but on the other hand, in the sample (B) group. In the sample (C) group, the coating material (1) had penetrated into the specimen and the surface was partially exposed, which had been oxidized and worn away, and in the sample (C) group, the desired glass phase had not been formed in the coating layer at all. However, the degree of oxidation damage on the surface of the specimen was the most significant. Furthermore, the sample (D
) group, contrary to expectations, a uniform coating layer was not formed and the molten material penetrated into the donor body in some places. Example 2 A large number of specimens (cubes on the 40 side) were cut out from a graphite electrode product made of 95% C, and coating materials (1) and (b) of Example 1 were applied as a lower layer to each of 4 sets of 2 specimens. 0
．． 5 skin, sample coated with a brush to a thickness of 0.5 on the upper layer side (B)
2 pieces, 2 samples (F) with coating material (0) brushed on the bottom and top layers to a thickness of 0.5 skin each, and coating material (1) coated with a brush on the bottom and top layers each at a thickness of 0.5 skin. 2 samples (G) and 5 parts by weight of water glass were mixed with 10 parts by weight of Rouseki powder of 200 mesh or less to obtain 1.7% Si02 and 1.7% AI2.
0324.1%, K201.7%, Na200.7% was mixed with 4 parts by weight of water, and a coating material (m) of Rouseki slip was applied to the surface of the body with a brush to a thickness of 0.5 skin. Then, a total of 8 samples, 2 samples (H) on which the above coating material (0) was applied with a brush only on the 0.5 side, were coated with 10000
After drying for several days, each sample (B), (F), (G), and (H) was heated at 100,000 and 120,000, respectively, and the oxidation loss was measured.

The results are shown in Table 1, as shown in Table 1.
), there is almost no difference between heating temperatures of 1000°C and 1200°C, but for other samples (F), (G) and (H)
The difference is seen in sample (E) and sample (F).
), (G) and (H), the oxidation loss is approximately 1'5 to 1'7 at 100 picoC, and approximately the same amount at 1200QO, and the upper and lower 2 The anti-oxidation effect of the coating layer was significant.
Table 1 Example 3 A silicate carbide-graphite type brick consisting of 83% SIC, 12% C (graphite), and 5% other materials (65 legs x 12 bricks x 23
A coating material of kamelite slip (W ) for 6 minutes, the surface was coated with a 0.5 willow-thick bottom layer, and after air drying, this was further mixed with 40% Rouseki, 45% glass powder, 5% clay, and 10% terra sand. TeS
i0261.2%, AI20311.3%, K20 and N
a209.8%, B2037.3% and others 10.
60 parts by weight of water and 3 parts by weight of valve waste liquid were added to 10 parts by weight of a 4% mixture, and wet milled for 3 hours in a ball mill.
Two samples (J) were immersed in the coating material (V) with a grain size of 325 mesh or less and covered with an upper layer of 0.5 rib thickness, and the coating material (W) and (
Two samples (K) were obtained by coating V) on the lower layer and upper layer by 0.5 ribs each, which were further immersed in the coating material (N) to form a three-layer coating layer. Two samples (L) were prepared by immersing them in immersion solution V) to form a coating layer of 0.5 side thickness on the lower and upper layers, and each sample (J) (K
) and (L) were heated at 100,000 and 1,200 q0 for 5 hours, respectively, and the oxidation loss of each sample was measured.

The results are shown in Table 2, including a sample (J) according to the present invention with different compositions and two lower layers, and a sample (J) in which a lower layer material was further laminated to form a three-layer coating layer. There is almost no difference between sample (J) and sample (K), and the oxidation loss of sample (J) and sample (K) is approximately 1 at each temperature compared to sample (L).
/3. Table 2 Example 4 The coating material (1) used in Example 1 was applied with a brush to a thickness of 0.5 on the entire surface of a specimen (hollow cylinder) of an alumina-graphite continuous casting immersion nozzle, After drying, a sample (M
) and the specimen with the above-mentioned coating material (b) on the bottom, and the sample (M
) and the sample (N), which was applied with a brush to each 0.5 side, were actually used as bonding nozzles, and the inner diameter dimensions were measured. As shown in Table 3, both samples (M) and ( N)
There was a noticeable difference in the degree of wear and tear.

Table 3 Furthermore, as mentioned above, in the present invention, the coating layer on the surface of the refractory has two lower layers of different compositions, but the upper and lower two layers are laminated multiple times, Of course, a more complete oxidation-preventing effect can be exerted by coating with a thicker oxidation-resistant molten glass phase.

As described above, according to the method for preventing oxidation of a graphite or silicon carbide refractory of the present invention, by coating the surface of the refractory with an upper layer and a lower layer having different compositions in advance, high viscosity can be prevented when used at high temperatures. , a high-density molten coating layer is reliably formed, and unlike conventional oxidation prevention methods, it has become possible to exhibit an excellent oxidation prevention effect, so the industrial application effect in the steel industry is said to be revolutionary. It's possible.

[Brief explanation of drawings]

Samples (A), (B), (C) and (
It is a graph which shows the change of oxidation weight loss with respect to heating temperature of D).

Claims (1)

[Claims] 1 SiO_2 on the surface of graphite or silicon carbide refractories
A thin coating layer with a content of 95% or more and a SiO layer on the surface.
_250-80%, Al_2O_35-30%, K_2
O and Na_2O3~15%, B_2O_33~15%,
and Fe_2O_3, ZnO, P_2O_5 or
Thin coating layers containing 1 to 15% of a mixture of PbO are laminated and then dried, and a high-density, high-viscosity molten glass phase covering the refractory is formed in the lamination at an appropriate high temperature. A method for preventing oxidation of graphite or silicon carbide refractories, characterized by: