Development and Properties of New Mullite Based Refractory Grog

The presented study is focused on optimization and characterization of a high-alumina refractory aggregate based on natural raw materials—kaolins, claystone, and mullite dust by-product (used to increase the alumina and mullite contents, respectively). In total, four individual formulas with the Al2O3 contents between 45 and 50 wt.% were designed; the samples were subsequently fired, both in a laboratory oven and an industrial tunnel furnace. The effects of repeated firing were examined during industrial pilot tests. Mineral and chemical compositions and microstructures, of both the raw materials and designed aggregates, were thoroughly investigated by the means of X-ray fluorescence spectroscopy, powder X-ray diffraction, and optical and scanning electron microscopies. Porosity, mineral composition, and mullite crystal-size development during the firing process were also studied. Based on the acquired results, the formula with the perspective to be used as a new mullite grog, featuring similar properties as the available commercial products, however, with reduced production expenses, was selected. The quality of grog determines to a large extent the properties of the final product. Hence, optimization of aggregates for specific refractories is of a great importance. The production of engineered aggregates provides the opportunity to utilize industrial by-products.

High alumina refractory concretes bonded with calcium aluminate phosphate binder

For many industries, further progress is possible provided that more efficient refractories of new types are created. The refractory concretes bonded by calcium aluminate phosphate binders in comparison with conventional refractories continue to gain in popularity because of the following advantages: quick installation and low construction costs; reduced and simplified furnace maintenance; good thermal-shock resistance; monolithic (no joints); linings of the units done need not be cured to develop initial strength. The longevity of refractory is essentially increasing provided structure is forming under conditions of the service site. That is why developing of new refractory materials must be carried out by means of its structure design. These principles have been realizing in the refractory concretes technology under the limited conditions of refractory lining installation and industrial unit final heat up. The present paper identifies the phosphate phases responsible for developing mechanical-strength properties of high alumina concretes bonded with calcium aluminate phosphate binders. It sets out the colloid and crystalline phases resulted from interphase interaction that provides the basis for calcium aluminate phosphate binders (suspensions) useful to the refractory industry. The concretes obtained retain their volume integrity after 30 cycles of heating and cooling; can be used for refractory applications > 1700 °С; exhibit sufficient strength of lining 40 MPa.