The Application of Silicon Nitride in Metallurgical Industry

image_pdfimage_print

With the development of science and technology, metallurgical industry is developing towards the direction of large-scale, continuity, automation, no (little) pollution, low consumption, etc. day by day. Therefore, metallurgical industry has to adopt new technology, new equipment, and new material. Among the numerous materials, silicon nitride and silicon nitride composite sialon ceramic material is continuously adopted by the metallurgical enterprises of various countries in the world. Its application field in metallurgical industry is gradually widening.

Application in Aluminum Metallurgy, Copper Smelting, Zinc Smelting and Other Industries

Free from the corrosion of molten aluminum and excellent thermal properties of silicon nitride ceramics give full play to its talent in the aluminum industry. In the production line of aluminum tandem rolling casting, aluminum metallurgy, and aluminum melting operations, temperature-measuring thermocouple bushing, furnace lining of aluminum metallurgy forge, liner of molten aluminum container, and aluminum crucible mould, all of which can be made by silicon nitride ceramics. Combined with silicon nitride and sialon brick, high quality silicon carbide is used in aluminum reduction cell, and have made obvious effectiveness in taking place of the traditional carbon material. It has been gradually popularized in Europe and America. For example, it has been used in 110kVA aluminum reduction cell for three years and still in good status. Its advantages are: a. Extend service life. Due to its great ability to be free from the corrosion of cryolite and so on, its oxidation resistance ability is also great; b. Increase output. Its high mechanical strength can reduce liner thickness and increase the working volume of reduction cell, electrode energy is correspondingly increased; c. Reduce unit power consumption. It has high conductivity, so the corresponding electric loss is less. This kind of product has also already been adopted in steel industry, such as blast furnace liner, burner, chute, copper residues separator, and fire-proof components of continuous copper casting.

Presently, silicon nitride ceramics thermowell used to measure the temperature of molten aluminum has been popularized in China. The operational performance of this kind of bushing is better than the commonly-used stainless steel and corundum ceramic bushings. Stainless steel is susceptible to the corrosion of molten aluminum. It breaks down after continuous use of 20 hours. Corundum can not withstand thermal shock. However, silicon nitride ceramics can remain long-term stability in molten aluminum. Interval temperature measurement for over 20 times will not lead to cracks. Silicon nitride ceramics thermowell is also of great use in the measurement of molten zinc temperature.

Application in Steel-making and Steel Rolling Industry

The application of new steel-making technology and crafts places greater demands on fire-proof material for steel ladle. The liner of steel ladle is shifted from the original predominated high-alumina brick, etc. into better anti-corrosion material. In recent 10 years, combined with silicon carbide, silicon nitride has been applied in steel ladle in Europe and America one after another and has achieved obvious economic benefit. While in China, it began to be used in recent two years. A steel mill in Shanghai indicated through experiment that silicon nitride and silicon carbide combined brick used in steel ladle can achieve following effects: a. Extend the service life of steel ladle. The original wall of steel ladle is constructed of high-alumina brick. Under the repeated washout of molten steel, the wall is severely damaged and the using effects are not ideal, with the average service life of only 37 furnaces. After adopting silicon nitride and silicon carbide combining brick, the usage counters reach 156, 4 times of the service life of the original steel ladle; b. Reduce the cost of fire-proof material consumption and masonry. The original steel ladle masonry needs 608kg fire-proof material, and the masonry cost is RMB 498.8 Yuan. Steel-making total quantity is 81.4 tons, the fire-proof material consumption per ton is 7.47kg, and the steel masonry cost per ton is RMB 6.13 Yuan. After adopting silicon nitride and silicon carbide combining brick, the fire-proof material needed is 830kg, the masonry cost is RMB 1696.6 Yuan, the steel-making total quantity is 342.2 tons, the fire-proof material consumption per ton is 2.41kg, and the masonry cost per ton is RMB 4.98 Yuan. Compared with the original steel ladle, the fire-proof material consumption per ton decreased 5.06kg, the masonry cost per ton decreased RMB 1.19 Yuan; c. Improve the quality of steel. After adopting silicon nitride and silicon carbide combining brick, there is little damage in the fire-proof material, slag inclusion of steel decreased.

As the fire-proof material in the steel industry, the most important function of silicon nitride is its usage as the separating ring of horizontal continuous casting. In horizontal continuous casting, the separating ring divides the molten steel flow into molten steel area and the molten steel solidification beginning area, separating the steel’s liquid and solid interface. It plays a great role in stabilizing the solidification starting point of molten steel and the quality of casting base. As the key component of horizontal continuous casting technology, separating ring has strict requirement about the fire-proof material: precise size, easy machining, good thermal conductivity, and resistance to high thermal stress and thermal shock; resistance to the corrosion and damage of molten steel for long time; long service life.