JPH02315B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an antioxidant for carbonaceous materials. Carbonaceous materials generally have extremely stable physical properties against heat, and are widely used in many applications. However, such carbonaceous materials cannot be used in an oxidizing atmosphere.
If used at temperatures above 600℃, the material will oxidize and wear out. For this reason, much research has been conducted to improve the oxidation resistance of carbonaceous materials, using the PVD method (Physical
Vapor Deposit method), CVD method (Chemical
A method of coating the surface of carbonaceous materials using the vapor deposit method is being considered. Of these,
The PVD method and the CVD method are difficult to control the atmosphere and process large products, require a long processing time because the coating layer thickness per processing time is thin, have poor reproducibility, are expensive, and are not industrially practical. On the other hand, the method of infiltrating and filling various inorganic salts is inexpensive and widely used, but in order to impart water resistance to the phosphate coating layer,
It requires heat treatment at 500℃ or higher, and if a product coated with this process is used in a high-temperature atmosphere, carbon reduces the phosphate, even with aluminum phosphate, which is said to be stable up to 1600℃. _{P2O5 _}
evaporates and contaminates the product and surrounding equipment. In recent years, as product materials have become more highly purified, P ₂ O ₅
Contamination with is particularly disliked. In addition, alkaline earth metal salts, which are relatively reactive with phosphates, are used as hardening agents to prevent water resistance and moisture absorption, and to omit the heat treatment process at temperatures above 500°C. Workability is poor due to high reactivity with carbonaceous materials, and phosphates do not penetrate into carbonaceous materials due to increased viscosity due to curing action, resulting in the coating layer falling off during use and contaminating the molten product. It's becoming a problem. In view of the shortcomings of the conventional methods, the present invention has been made through intensive research to develop an antioxidant with excellent antioxidant properties, and as a result, basic aluminum lactate or basic aluminum glycolate has excellent antioxidant properties. Furthermore, by using these in combination with boric acid, silica sol, or alumina sol, or in combination with metal silicon and carbon black, basic aluminum lactate or basic aluminum glycolate, The present invention was completed based on the discovery that the antioxidant performance was further improved compared to the use of a single ingredient. The basic aluminum lactate and basic glycol aluminum used in the present invention have a composition of _{Al2O3 /} lactic acid (molar ratio) of 0.2 _to 2.0 and _Al2O3 /glycolic acid (molar ratio) of 0.2 to 1.0. As described in Japanese Patent Application No. 56-161867, the manufacturing method is to react a water-soluble aluminum salt with an alkali metal, ammonium carbonate, heavy carbonate, etc., or to react an alkali aluminate with carbon dioxide gas. It can be produced by dissolving the precipitated alumina hydrate in lactic acid or glycolic acid. Also, in place of the above carbonate, ammonium hydroxide,
Sodium hydroxide can also be used. Furthermore, it can also be produced by adding a compound that forms a water-insoluble sulfate, such as a calcium compound or a barium compound, to a mixed solution of aluminum sulfate and lactic acid, or aluminum lactate, or glycolic acid or aluminum glycolate. . Another manufacturing method is to combine lactic acid or glycolic acid A with a concentration of 10 to 30% by weight and metal aluminum B with a specific surface area of 3.0 x 10 ^-4 m ² /g or more, as described in Japanese Patent Application No. 155951/1982. It can also be produced by reacting with /A (molar ratio) of 3.0 or more. In the present invention, basic aluminum lactate or aluminum glycolate is used. However, with aluminum lactate or a normal salt of aluminum glycolate, the coating film after application is uneven and cracks occur in the coating film when heated. The anti-oxidation effect of the carbonaceous material mentioned above can hardly be expected. Other aluminum salts include normal salts and basic salts such as aluminum chloride, aluminum acetate, aluminum malate, aluminum citrate, and aluminum tartrate, but these also have weak coating film strength and are prone to cracking. Aluminum chloride has almost no antioxidant effect and damages the furnace by generating chlorine gas during heating, and aluminum oxalate is not suitable for use because its decomposition gas is harmful. Furthermore, aluminum acetate has a strong acetic acid odor, which worsens the working environment, and higher aliphatic carboxylic acids and aromatic carboxylic acids have poor thermal decomposition properties, producing complex gas decomposition products, which worsens the working environment.
On the other hand, with aluminum malate, aluminum citrate, and aluminum tartrate, it is difficult to obtain a highly basic salt, and the Al ₂ O ₃ concentration is too low, resulting in a low coating film strength and a reduced antioxidant effect. The carbonaceous material used in the present invention is not particularly limited, but carbonaceous products obtained by kneading and molding carbon materials such as coke and graphite with an organic binder, or Graphite products made of cast graphite and natural (scaly) graphite, which are made by graphitizing this fired product at a higher temperature,
Alternatively, there are composite products made by mixing magnesia or alumina with graphite, or flexible graphite materials with emphasis on functionality, liquid level sensors, graphite jigs, rocket nozzle inserts, etc. Although it is sufficient to coat such carbonaceous material products with the antioxidant of the present invention, it can also be used as a substitute for an organic binder during molding. The coating method is not particularly limited, but methods include brushing or spraying an aluminum lactate solution onto the surface of the carbonaceous material product;
Or a method of impregnating it by immersing it in the aqueous solution,
Alternatively, there is a method of reducing the pressure in a closed container. Simply drying it at a low temperature of around 110°C creates an antioxidant film with low moisture absorption. However, if higher water resistance is desired, it is desirable to perform heat treatment at 300°C or higher. When using basic aluminum lactate or basic aluminum glycolate of the present invention, the Al ₂ O ₃ concentration thereof is in the range of 6.0 to 15.0% by weight. That is, below the lower limit, the Al ₂ O ₃ concentration is too low and the antioxidant effect of the carbonaceous material of the present invention cannot be expected.
Further, a concentration exceeding the upper limit is undesirable because it increases the viscosity of the solution, resulting in non-uniformity of the coating film during coating and the formation of cracks. Incidentally, the above-mentioned powdered aluminum salt may be used after being dissolved in water. The first invention uses basic aluminum lactate or basic aluminum glycolate alone as an antioxidant for carbonaceous materials. The prevention effect is further improved. The second invention is one in which one or more selected from boric acid, silica sol, and alumina sol is added to the first invention, and it particularly improves the film strength of the coating film, and thereby improves the strength of the carbonaceous material. Its purpose is to enhance the antioxidant effect of. In other words, when applying an antioxidant to a carbonaceous material, depending on the type of carbonaceous material, cracks may form in the film during use if only basic aluminum lactate or basic aluminum glycolate is used. . As a result of investigating the cause of this, the present inventors found that the membrane strength was still insufficient. Therefore, as a result of researching ways to improve the strength, the inventors discovered that the use of the above compound would avoid the occurrence of cracks, and as a result, the antioxidant effect would be further improved, thus completing the present second invention. . As the boric acid, silica sol, and alumina sol used in the present invention, commercially available ones may be used, and the amount used (as solid content) is that of basic aluminum lactate and basic aluminum glycolate.
30 to 140% by weight based on Al ₂ O ₃ is suitable. Below the lower limit, no improvement in crack prevention effect, ie, improvement in the antioxidant effect, can be expected, while above the upper limit, the sol will gel, the coating will become uneven, and the antioxidant effect will decrease. Although the amount of boric acid added may be in an undissolved state, it is more preferable to dissolve the boric acid so that the boric acid is uniformly contained during drying. Dissolving boric acid in basic aluminum lactate, or basic aluminum glycolate, produces aluminum borate, or aluminum borate, by adding an amount much greater than the solubility of boric acid in water. The condition can be maintained, and the film is also strengthened to provide even better antioxidant effects. The best way to use these is to mix them with the aluminum salt, but they may also be added and mixed to the carbonaceous material in advance. The third invention relates to an antioxidant for a carbonaceous material consisting of basic aluminum lactate or basic aluminum glycolate, metal silicon, and carbon black. When used at high temperatures above, it exhibits extremely good antioxidant effects. When using basic aluminum lactate or basic aluminum glycolate alone, the antioxidant effect gradually decreases when carbonaceous material products are used at high temperatures. This tendency is especially remarkable at temperatures above about 1000°C. When such carbonaceous material products are used at high temperatures, the use of metallic silicon and carbon black significantly improves the antioxidant effect compared to the use of aluminum salt alone. Moreover, the use of both imparts high conductivity, which is particularly preferred when the carbonaceous product is an electrode or the like. The ratio of metal silicon and carbon black to be used is the total amount of Al ₂ O ₃ of the above aluminum salt.
100 to 500% by weight, and the ratio of metal silicon to carbon black may be in the range of 1/0.38 to 1/0.60 in terms of weight ratio. That is, in this range, the high-temperature oxidation prevention effect is best exhibited, and it is also the best from the viewpoint of electrical conductivity. Regarding the types of carbon black, acetylene black, SAF of furnace black,
HAF is suitable for use. In the present invention, by using a combination of these compounds and basic aluminum lactate, it has an excellent effect of preventing oxidation of carbonaceous materials, but in addition to these compounds, borax, alumina,
Silicon carbide, zircon, titanium metal, tungsten metal, aluminum phosphate, sodium hexametaphosphate, etc., aluminum stabilizers such as organic acids, sodium silicate, sodium aluminate, etc. can also be used in combination. In addition to the above-mentioned carbonaceous materials, the antioxidant of the present invention can be used as an antioxidant coating agent for magnesia carbon bricks and a caking agent for pencils. The present invention will be further explained below with reference to Examples, but the present invention is not limited thereto. In this example, unless otherwise specified, all percentages are by weight. Example 1 A carbon product prepared by kneading and molding 60 parts of coke, 20 parts of graphite, and 20 parts of organic resin, calcined at 900°C, and graphitized at 2400°C was used as a test product. This is 25×25×
Cut to 25m/m (hereinafter referred to as carbon specimen)
Then, the air in the carbon specimen was degassed at 1×10 ^-3 mmHg or less in an autoclave, and then a basic aluminum lactate aqueous solution (Al ₂ O ₃ 12%, Al ₂ O ₃ /
lactic acid molar ratio 0.6) was added and the carbon specimen was immersed. This was pressurized with _N2 gas 10Kg/ ^cm2 for 30 minutes in an autoclave, and after being removed from the autoclave,
Dry at °C. The amount of treatment agent impregnated was determined from the weight increase of the carbon specimen before immersion and after drying. Separately, replace the basic aluminum lactate aqueous solution with a basic aluminum glycolate aqueous solution (Al ₂ O ₃ 12%, Al ₂ O ₃ /glycolic acid molar ratio 0.5).
The test was conducted in the same manner as above. These were heated in a tubular heating furnace at 800° C. for 1 hour in air at a flow rate of 500 ml/min, and the weight loss rate was determined from the weight change of the carbon specimens before and after heating. Furthermore, as a comparative example, the weight loss rate was determined in the same manner for a carbon test piece that was not treated with the antioxidant of the present invention. These results are shown in Table 1.

[Table] Example 2 The same carbon specimen used in Example 1 (25×25×
25 m/m) and basic aluminum lactate aqueous solutions (Al ₂ O ₃ /lactic acid molar ratio) with various concentrations shown in Table 2.
0.6), the carbon specimen was immersed in the same manner as in Example 1. In addition, these were heated in the same manner, and the weight loss rate of the carbon specimens was determined, and the results are shown in Table 2.

[Table] Example 3 Basic aluminum lactate aqueous solution (Al ₂ O ₃ 15%,
Silica sol (SiO ₂ 30%, manufactured by Catalysts Kasei Co., Ltd., trade name Cataloid) was added to 100 parts of Al ₂ O ₃ /lactic acid molar ratio 0.33).
SiC fine powder was added to a mixed solution of 25 parts of SA) and 25 parts of water and kneaded to prepare a paste liquid of approximately 2000 cps. Similarly, 100 parts of the above basic aluminum lactate, 4.5 parts of boric acid, and silica sol (30% SiO ₂ ) were added.
SiC fine powder was added to a mixed solution of 25 parts of SiC and 20.5 parts of water and kneaded to prepare a paste liquid of approximately 2000 cps. Furthermore, the above basic aluminum lactate
Add an appropriate amount to a mixed solution of 100 parts, 30 parts of alumina sol (Al ₂ O ₃ 25%), 4.5 parts of boric acid, and 15.5 parts of water.
A paste liquid of approximately 2000 cps was prepared by adding SiC fine powder. These were connected to a graphite electrode of 50 x 50 x 50 m/m (approximately
210 g) was brushed to a coating amount of approximately 230 g/m ² . These were heated in a tubular heating furnace at 800°C and 1200°C for 1 hour while passing air at a flow rate of 500ml/min, and the weight loss rate was determined from the change in weight of the graphite electrode before and after heating. In addition, the surface condition was also observed.
These results are shown in Table 3.

[Table] Example 4 Basic aluminum glycolate (Al ₂ O ₃ 12
%, Al ₂ O ₃ / glycolic acid molar ratio 0.33) solution 100
per part, boric acid, silica sol (SiO ₂ 30%)
were mixed and dissolved in the proportions shown in Table 4. The autoclave containing the carbon specimen (25 x 25 x 25 m/m) was depressurized to 1 x 10 ^-3 mmHg or less and degassed. Then, the above solution was added from the inlet tube, and the autoclave was heated to 10 kg/m under an N ₂ gas atmosphere. The carbon specimen was sufficiently immersed in the solution under pressure of cm ² . This carbon specimen was taken out, dried at 110℃, the amount of treatment agent impregnated was determined from the increase in weight, and heated at 800℃ for 3 hours in air at a flow rate of 500ml/min in a tubular heating furnace. The weight reduction rate was determined from the change in weight of the carbon specimen before and after. These results are shown in Table 4. In addition, in the comparative example, the treatment solution thickened or gelled,
It was very difficult to impregnate carbon specimens.

[Table] Example 5 Basic aluminum lactate solution (Al ₂ O ₃ 10%,
To 100 parts (Al ₂ O ₃ /lactic acid molar ratio 0.69 g), 7.8 parts of carbon black (manufactured by Tokai Carbon Co., Ltd., trade name: SEAST 600) and 18.2 parts of metal silicon fine powder were added and kneaded, and this was mixed into carbon specimens. (25×25×25m/m),
It was brushed, dried at 110°C, and the amount of treatment agent applied was determined. In addition, this was placed in a tubular heating furnace at a rate of 500ml/
Heating was performed at 1000°C and 1300°C for 1 hour each in air at a flow rate of min, and the weight loss rate was determined from the weight change of the carbon specimen before and after heating. Furthermore, the conductivity of this was measured. The conductivity was measured by holding the carbon specimen heat-treated at 500° C. between copper electrodes at a contact pressure of 40 kg/cm ² and measuring the contact resistance. Similar tests were conducted for each composition of treatment agents, and the results are shown in Table 5.

【table】

Claims (1)

[Scope of Claims] 1. An antioxidant made of carbonaceous material consisting of basic aluminum lactate or basic aluminum glycolate. 2. A carbonaceous material antioxidant comprising basic aluminum lactate or basic aluminum glycolate and one or more selected from boric acid, silica sol, or alumina sol. 3. An antioxidant made of carbonaceous material consisting of basic aluminum lactate or basic aluminum glycolate, metal silicon, and carbon black.