Effect of α-Al2O3 on the Properties of Aluminum-Chrome Bricks Made of Chromium-Containing Slag

Aluminum-chrome bricks containing chromium slag. The aluminum-chrome bricks with an aluminum-chrome slag addition amount (wt) of 30% were used as reference samples, and the formula was set as the basic formula. On this basis, 1wt%, 2wt%, 3wt%, and 4wt% of α-Al2O3 were added respectively, and the increased amount replaced the brown corundum fine powder, keeping the Cr2O3 content unchanged, and exploring the effect of α-Al2O3 on the performance of aluminum-chrome bricks containing chromium slag.

Performance of Aluminum-Chrome Bricks

After the raw aggregates were dry-mixed in a small wet mill for 3 minutes, about 3% of the binder (aluminum dihydrogen phosphate solution) was added. After mixing for 1 minute, the machine was stopped, and fine powder was added to continue mixing. Continue to add binder until the mud is suitable, and the total amount of binder added is about 3.5%. After fully mixing, the material is discharged and loaded into a woven bag lined with a plastic bag. Then the trapped material was sealed for 12 hours and formed on a 630-ton electric press. The molded blank sample is a standard brick (230×114×65mm). The formed wet bricks enter the tunnel drying kiln and are kept warm and dried at 110℃~120℃ (>12 hours). After drying, they are loaded with the loading method with the width direction as the pressure direction. They are heat treated in a 111m long ultra-high temperature tunnel kiln fueled by natural gas. The firing system is 1600℃×4.5h.

According to relevant standards, the bulk density, apparent porosity, compressive strength, linear change rate after firing, load softening temperature and thermal shock stability (1100℃ water cooling) of the samples are tested, and the performance indicators of each experimental brick are tested.

Effect of α-Al2O3 on the performance of aluminum-chrome bricks containing chromium slag

The effect of α-Al2O3 micropowder addition (wt.%) on the volume density, apparent porosity, compressive strength and post-firing linear change rate of aluminum-chrome bricks containing aluminum-chrome slag. With the increase of α-Al2O3 micropowder addition, the apparent porosity decreased, the volume density increased, but the amplitude was not large; the compressive strength tended to increase, but the amplitude was not large. The post-firing linear change rate is gradually decreasing, and the comprehensive effect is better when the α-Al2O3 micropowder is added at 3wt%. This is because the basic mechanism of micropowder is ST filling. Appropriate micropowder is filled in the micropores of refractory aggregate and fine powder, which can increase its volume density and reduce apparent porosity. In corundum products, adding α-Al2O3 micropowder can promote sintering and reduce the sintering temperature.

Since the brown corundum and aluminum-chromium slag used in the raw materials are both electro-melting materials, and the South African chromium ore are both raw materials with high volume density and low apparent porosity, the change rate of the product during the sintering process is very limited. Although the addition of α-Al2O3 micropowder has a certain improvement on the conventional performance, the impact is relatively small. When the addition amount is 3wt%, the filling effect is more obvious, and the performance will be reduced if the addition amount is further increased. This has a certain relationship with the overall particle grading of the product.

Effect of α-Al2O3 on load softening temperature. The addition amount of α-Al2O3 micropowder has almost no effect on the load softening temperature, which is due to the high grade of the raw materials of the product itself. The load softening temperature of the reference sample itself is ≥1700℃. The addition of α-Al2O3 micropowder has the effect of promoting sintering. After sintering, it mainly forms high-melting-point mineral phases such as corundum or aluminum-chromium solid solution. Therefore, it will not reduce the load softening temperature of the product.

Effect of α-Al2O3 addition amount (wt.%) on thermal shock stability As the amount of α-Al2O3 powder added increases, the thermal shock stability of the product is not greatly affected. However, when the amount added is 4wt%, the thermal shock stability decreases. This is because as the volume density of the product increases, the apparent porosity decreases, and the denser structure reduces the thermal shock stability of the product. Therefore, it is more appropriate to add α-Al2O3 powder within 3wt%.