Effect of boric acid on properties of high-alumina phosphate-bonded plastic refractory materials

The effect of boric acid on the properties of high-alumina phosphate-bonded plastic refractory materials at medium temperature is investigated in this work. Powder X-ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TG/DTA), and scanning electron microscopy (SEM) techniques are used to investigate the compositions and microstructures of the Al2O3-H3BO3 sintering products, in order to study the influence of the generated aluminum borate on the high-aluminum refractories. Additionally, the effect of the addition of H3BO3 on the densification and mechanical strength of high-aluminum phosphate-bonded plastic refractories is studied by the permanent linear change, apparent porosity, cold compressive strength, flexural strength, and scanning electron microscopy pattern. The densification and mechanical strength of the refractories can be improved significantly by the optimal addition of H3BO3. However, excess H3BO3 will bring about a large amount of bound water into the refractories, and superabundant aluminum borate whiskers will be generated by the excess addition of H3BO3, both of them resulting in the reduction of the densification and mechanical strength of the refractory. In conclusion, the optimum dosages of H3BO3 in the powder system of highalumina phosphate-bonded plastic refractories are 5, 4, and 3 wt%, sintered at 700, 900, and 1100 degrees C, respectively.