【Abstract】Phenolic resin is an important binder of refractory materials. Compared with asphalt, phenolic resin has good wetting properties for refractory materials and graphite, high residual carbon rate, good adhesion, and can be mixed and molded at room temperature. The green body has the advantages of high strength, low content of harmful substances, and can improve the working environment. It has been widely used as a binder for carbon-containing refractories. This article starts with phenolic resin, analyzes and discusses the application of phenolic resin in magnesia-carbon bricks, aluminum-carbon bricks and other carbon composite shaped refractories, as well as in tundish dry materials, blast furnace anhydrous gun mud and other amorphous refractories.
The research of phenolic resin used in refractories mainly focuses on the modification of resin. Among them, the use of catalytic reactions to improve the structure and performance of resin residual carbon is a major trend in future research. Binder is an indispensable component in refractory materials, it plays the role of cementing the refractory material particles and powder together. The synthesis of a new type of network interpenetrating high-performance phenolic resin is another trend in future research. This method mainly focuses on changing the structure of the resin itself so that it has a more complex network structure than ordinary phenolic resin after curing. Improve the low-temperature baking strength and medium-temperature strength of the material, while reducing the amount of phenol and reducing the cost of phenolic resin.
1Phenolic Resin
Phenolic resins (Phenolicresins) are a large class of synthetic resins prepared by polycondensation of phenolic compounds and aldehyde compounds. The aldehyde compound used is mainly formaldehyde, and other aldehydes such as acetaldehyde, formaldehyde, furfural or a mixture of several aldehydes are commonly used. Phenolic resin's unique chemical structure and macromolecular cross-linked network structure endow it with excellent properties such as excellent adhesion, excellent heat resistance, unique ablation resistance and good flame retardancy. Therefore, phenolic resins are widely used in glass fiber reinforced plastics, molding materials, adhesives, thermal and electrical insulation materials, coatings, etc.
Phenolic resins can be divided into two types: thermosetting phenolic resins and novolac phenolic resins according to their structure and heating shape. Thermosetting phenolic resin is produced by using alkali, such as potassium hydroxide, sodium hydroxide, barium hydroxide or calcium hydroxide as a catalyst, with a molar ratio of formaldehyde/phenol>1, controlling pH>7, and reacting for a period of time at a certain temperature. A resin containing reactive methylol groups that can be further reacted. Thermoplastic phenolic resin is usually called novolac or novolac resin. It is a phenolic resin produced by the reaction of formaldehyde (F) and excess phenol (P) under the action of acidic catalysts such as oxalic acid, hydrochloric acid, sulfuric acid and formic acid, among which moles Ratio (F/P)=0.6-0.9). Regardless of whether it is a thermosetting resin or a thermoplastic resin, the final cured structure is the same, which is a three-dimensional network structure. Residual carbon obtained from resin carbonization at high temperature is an important structure that supports the work of refractories and ensures their life.
2Application of phenolic resin in carbon composite shaped refractory
At present, due to the development of the metal smelting industry, especially the iron and steel industry, the demand for refractory materials has greatly increased, resulting in an increase in the application of phenolic resin in the refractory industry. Refractory materials are widely used in the metal smelting industry, cement industry, and ceramic industry. The binder is an indispensable component in the production of refractory materials, and plays a role in binding the refractory particles and powder together. Moreover, in the production practice of refractory materials, people realize that the quality and stability of phenolic resins are one of the main factors affecting the performance of carbon-containing refractories, and the importance of phenolic resins has become increasingly prominent.
2.1 Application in magnesia carbon brick
Magnesia-carbon brick is a high-temperature carbon complex composite material fired with fused magnesia, graphite and binder. It has a relatively long service life, and the furnace age can reach more than 1600 furnaces. Therefore, it has achieved rapid development in recent years. Magnesia carbon bricks are widely used in the iron and steel metallurgy industry mainly because of their good properties, but the properties of the binder phenolic resin can affect the performance of the magnesia carbon bricks. Phenolic resin used for magnesia carbon bricks should have the characteristics of high solid content, low relative molecular weight, high residual carbon rate and low water content.
By studying the relationship between the various properties of the resin and its raw material ratio and synthesis process, it is concluded that the best raw material ratio of phenolic resin for the synthesis of magnesia carbon bricks is m(F)/m(P)=1.0~1.3; the catalyst is w (NaOH)=50% NaOH solution, the added amount is 1%~1.5% of the mass of phenol; the best synthesis process is: first react at 60~70℃ for 1h, then heat up to 80~90℃ for 1~2h . The phenolic resin synthesized under the best raw material ratio and process conditions has a relative molecular weight of 300~400, a viscosity of 15~20Pa·s, a solid content of 77.0%~82.0%(w), and a residual carbon rate of 43.0%~ 49.0% (w), which can meet the performance requirements of phenolic resin for magnesia carbon bricks.
Since the performance of magnesia carbon bricks depends to a large extent on the carbon structure formed by the bonding system, phenolic resin pyrolysis forms a disordered brittle homogeneous glass-carbon structure, which is very sensitive to oxidation and stress, so magnesia carbon bricks Resins are often combined with other binders such as asphalt to improve oxidation resistance and mechanical properties.
2.2 Application in aluminum carbon brick
Aluminum-carbon bricks are made of graphite and corundum as raw materials, and a certain amount of binder and additives are added to the mixer and pressed. Since Al2O3 and C do not undergo a solid phase reaction at the firing temperature of the product, the bonding strength of aluminum-carbon bricks mainly comes from additives and binders. Phenolic resin is widely used in aluminum carbon bricks due to its excellent properties. At present, aluminum-carbon refractories widely use phenolic resin as a bonding agent. The bonding principle is mainly to improve the bonding force between the bonding agent and the material by cross-linking the phenolic resin molecular segments during the curing process to form a network structure.
3Application of Phenolic Resin in Unshaped Refractories
Phenolic resin is mainly used as a binding agent in carbon-containing shaped refractory products. In recent years, its application field has been continuously expanded, and it has been used as a binder in unshaped refractories.
3.1 Application in anhydrous blast furnace mud
Compared with other unshaped refractories, phenolic resin is the most widely used in gun clay. Early gun mud was used as a binder, mainly using tar and pitch, but in the process of use, tar pitch would produce carcinogens and black smoke, which caused great harm to the environment, and it was also difficult to sinter and hardened slowly. . As a binder for anhydrous gun mud, phenolic resin not only avoids the pollution problem caused by tar as a binder, but also improves the corrosion resistance, sinterability and wear resistance of the gun mud.
3.2 Application in tundish dry materials
There are more and more applications of dry tundish materials. The most widely used binder in tundish dry work at home and abroad is phenolic resin, which has good construction and use properties. However, phenolic resin has the disadvantages of increasing carbon and hydrogenation of molten steel, high cost and low strength at medium and high temperatures, which makes the application of phenolic resin in tundish dry materials to a certain extent hindered greatly.
In general, this article analyzes the application of phenolic resin in different types of refractory materials such as magnesia carbon bricks, aluminum carbon bricks, tundish dry materials, and blast furnace waterless gun mud. As the earliest synthetic resin, phenolic resin has the advantages of thermosetting, high dry strength and high high temperature strength, and is widely used. It is used as a better binder in the field of refractory materials in the preparation of carbon composite refractories. However, phenolic resin has two major shortcomings: high cost and its pyrolysis charcoal is glass charcoal, which affects its application in refractories to a certain extent.
