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After a general introduction, the working process for the industrial production of the saggers for sintering and baking dye oxides is described. All the technological properties which those materials must have are then shown. The refractory saggers behaviour during the baking cycle is afterwards explained and some examples about the consumption mechanism of these products are given. Finally some consideration about these saggers are provided.
Two types of natural dead burned magnesia with different C/S ratios were doped with different amounts of Zr02. The phase development in bodies fired at 1750°C was studied by XRD and SEM/EDX. It was found that in magnesia with C/S ratio smaller than 1, Ca0-bearing silicate phases based on monticellite react with Zr02 and formed calcium-stabilized zirconia. In magnesia with C/S>4, zirconia reacts with Ca0-bearing phases forming calcium-stabilized zirconia and calcium zirconate. In both types of magnesias, addition of Zr02 helps the growth of periclase grains.
Refractory MgAl204 is normally produced by pressing a mixture of MgO and Al2O3 powders to form green briquettes and making them react at elevated temperatures. The problems involved in the laboratory and industrial production of synthetic spinels to meet the requirements of the refractory industry are presented. The raw materials used, the stoichiometry, the impurities, the particle size and the production process influence the properties of the final product. The surface potential of alumina also affects the manufacturing process. The use of periclase as MgO source increases the density of spinel compared to natural magnesite (MgCO3). The packing density of the green magnesia and alumina mixture favors the production of a dense spinel. However the best product is obtained after regrinding the so formed spinel, making briquettes of spinel powder and firing again. The resistance of spinel to corrosion decreases as the alumina content increases.
Studying the characteristics and evaluating the condition of bricks and plasters of the external masonry, belonging to historical buildings known as Fabbrica Vecchia and Marchesato, located in Marina di Ravenna at the entrance of the ship canal which links Ravenna to the Adriatic Sea, the problem of the determination of the soluble salts content has been tackled. A cause of deterioration of bricks and plasters is the presence of soluble salts, originated from air pollution, capillary raising of solutions and marine aerosol. In the examined case, the soluble salts are composed mainly of halite and gypsum. It has been observed that the differential thermal analysis (DTA) and the themogravimetric analysis (TGA), besides giving information about alteration and deterioration of the above said materials, point out well the presence of gypsum and halite and allow their quantitative assessment, through data obtained from TGA. The comparison with a chemical method of analysis (ion chromatography) of such soluble salts has lead to the conclusion that the determination of their content through TGA is preferred because it is a direct method, with a good precision level.
The effect of moulding pressure on the physico-mechanical properties of lime-rich clay building bricks made by firing and subsequently cured in water was investigated from 75 up to 600 kg/cm2. The bricks were pre-fired at 850°C for one hour with a heating rate of 5°C/min, then cured in tap water for 90 days. The results show the good improvement of water curing on the compressive strength of the product up to a moulding pression of 450 kg/cm2. Increasing the moulding pressure from 450 up to 600 kg/cm2 leads to a lesser effect of water curing on the strength. The optimum compressive strength is attained at 300 kg/cm2 moulding pressure and a water curing of 90 days, and amounts almost 370 kg/cm2.
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