Aluminum Chromium Refractory Castable

Aluminum-chromium castables are castable refractory materials with AL2O3 and Cr2O3 as the main components, and are neutral refractory castables.

Aluminum-chromium castables are composed of coarse aggregate, fine aggregate, and powder in a certain proportion, and a certain amount of binder and admixture are added. The material is suitable for casting and molding. During construction, binders, coagulants and appropriate amounts of water are added, and aluminum-chromium castables with good fluidity can be made by stirring and mixing.

Chromium is hard and is often mixed into steel to make alloys that are both hard and corrosion-resistant. It is mainly used to refine stainless steel, heat-resistant steel and various electric heating element materials. When stainless steel encounters corrosive substances, a fine and solid chromium oxide film will form on its surface to protect the metal inside from further corrosion.

 

Aluminum-chromium castables have the characteristics of high refractoriness, high physical strength, good thermal shock stability, and strong corrosion resistance. In industrial use, they are resistant to erosion, corrosion, wear and peeling. It is widely used in nonferrous metallurgy, glass, petrochemical, carbon black and waste incineration industries.

When the melting furnace is lined with a corundum refractory castable mixed with chromium oxide powder and alumina powder, it is believed that the aluminum-chromium castable with a high chromium oxide content in the matrix material will also have high durability.

The aluminum-chromium castable was tested under erosion conditions (1750℃) using a rotary erosion test furnace, and the following conclusions were drawn from the slag resistance test:

(1) The fact that the concentration of chromium oxide near the working surface of the aluminum-chromium refractory castable decreased confirmed that the chromium oxide had transferred to the slag. The slag contained chromium oxide and increased its viscosity, which inhibited the further penetration and erosion of the aluminum-chromium refractory castable by the slag.

(2) At high temperatures, chromium oxide reacts with alumina to form a solid solution, which improves the high-temperature performance of the material while also improving the material's erosion resistance.

(3) Since the slag containing chromium oxide has a high viscosity, it also improves the slag resistance (erosion and penetration resistance) of the aluminum-chromium refractory castable.

This shows that aluminum-chromium refractory castables with higher chromium oxide content have higher slag resistance. Therefore, the main body of the industrial melting furnace is mainly made of refractory materials containing chromium oxide, among which the most typical aluminum-chromium castable is widely used.

Aluminum-chromium castables are widely selected as refractory materials for waste melting furnaces because they have excellent corrosion resistance to high-temperature slag, and the higher the chromium oxide content, the stronger the corrosion resistance. Therefore, in order to obtain a long life, the chromium oxide content in aluminum-chromium castables for waste melting furnaces tends to be 50% to 70% aluminum-chromium castables. However, in order to reduce the cost of the furnace lining and to obtain a refractory with both corrosion resistance and thermal shock resistance, it tends to be low chromium. In this case, it should be noted that reducing the chromium oxide content in aluminum-chromium refractory castables will reduce the service life of the melting furnace lining. If the service life of the material is not reduced while significantly reducing the chromium oxide content (<50% chromium oxide), it is necessary to enrich the chromium oxide in the matrix of the aluminum-chromium castable. Because the refractory reacts with the slag and produces corrosion from the matrix, the durability of the material can be improved by increasing the chromium oxide content in the matrix. When the chromium oxide/(aluminum oxide + chromium oxide) of the matrix composition of aluminum-chromium refractory castable is ≥40% (equivalent to 15% to 20% chromium oxide in the total ingredients), its erosion rate is significantly reduced. For aluminum-chromium refractory castables with corundum as aggregate and aluminum-chromium powder as matrix, when the chromium oxide content in the material is 15% to 20%, and the particle distribution in the material is optimized, a high service life can be obtained.

When aluminum-chromium refractory castables with low chromium oxide content are used for lining in thermal decomposition gasification melting furnaces, there is also a tendency that the higher the chromium oxide content, the better the slag resistance.

According to the analysis of the damage of aluminum-chromium lining in gasification melting furnace, this damage is mainly caused by diffusion rate type melting reaction. The slag penetration is very small, only a few millimeters, and there is no damage caused by the generation of low-melting materials. In addition, due to the reduction of chromium oxide on the working surface, it melts into the slag, increasing the viscosity of the slag and inhibiting the further reaction of the material with the slag.

The main reasons for the damage of aluminum-chromium refractory materials for gasification melting furnaces are:

(1) Diffusion reaction (the components of the lining refractory material diffuse into the slag and melt out). At this time, the use of refractory materials containing chromium oxide is a better choice for gasification melting furnace lining refractory materials.

(2) Damage caused by the reaction to generate low-melting materials and the melting of refractory materials in the slag.

(3) Damage caused by the structural peeling of the metamorphic layer on the working surface.

(4) Damage caused by thermal shock caused by heating and cooling.

(5) Fracture damage caused by thermal expansion stress.

(6) Damage caused by corrosive gases.

The lining of the waste melting furnace can obtain a long life as long as aluminum-chromium refractory materials are used. At the same time, it is believed that the use of aluminum-chromium refractory materials for lining the most demanding parts of the melting furnace is also a good choice.

In fact, many melting furnaces (including incineration ash melting furnaces and gasification melting furnaces), especially melting furnaces with oxidizing atmosphere in the furnace, generally use refractory castables containing chromium oxide.

Among the aluminum-chromium refractory castable products of melting furnaces, aluminum-chromium (10%) refractory castables are used for parts with less erosion; aluminum-chromium (20% to 30%) refractory castables are used for parts with severe erosion; aluminum-chromium-zirconium (ZrO2) refractory castables with a chromium oxide content of 60% can be used for slag mouth parts with particularly severe erosion.

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