Improving the hydration resistance of lime-based refractory materials

Abstract

Studies to improve the hydration resistance of lime-based materials are reviewed. The methods described include densification of the lime aggregate by addition of sintering aids and surface treatment. Methods for assessing hydration resistance are also reviewed. Additions of ZrO 2 , TiO 2 (including Ti chelating compounds) and rare earth oxides can improve the hydration resistance of CaO aggregate by, it is believed, enhancing solid state sintering without sacrificing refractoriness via formation of hydration resistant solid solutions. Fe 2 O 3 , Al 2 O 3 (as well as Al chelating compounds and Al metal), CuO and V 2 O 5 , act as liquid forming aids. These additives improve the sintering of lime and subsequently the hydration-resistance via formation of liquids at high temperature which cool to produce hydration-resistant solids surrounding the lime polycrystals. However, the liquids formed may significantly reduce the refractoriness of lime materials, thus eroding their particular advantage. The same problem is thought to arise on addition of salts such as CaCl 2 and NaF. The hydration resistance of CaO aggregates can also be improved by surface carbonation and surface treatment using acids, phosphates, machine oils, silicones and fluxes. Surface carbonation of CaO aggregate is proving to be a promising experimental method, but practical problems currently limit its application on an industrial scale. A combination of the two methods mentioned above should therefore be even more effective in improving the hydration resistance of CaO refractory materials.

Effect of chopped ZrO2 fiber content on the microstructure and properties of CaO-based integral ceramic mold

“…CaO has long been considered as an attractive refractory for application in metallurgical and ceramics industries because of the global abundant sources of high-purity limestone, as well as its advantages of high melting temperature, low vapor pressure, and excellent thermodynamic stability [1][2][3][4][5]. In recent years, CaO was studied as a potential ceramic core material for investment casting due to the reactionresistance to molten active alloy [6][7][8], easy dissolution compared to common ceramic core materials, such as fused silica or alumina [9][10][11], and approximating the thermal expansion coe cient of superalloys [12].…”

“…In recent years, CaO was studied as a potential ceramic core material for investment casting due to the reactionresistance to molten active alloy [6][7][8], easy dissolution compared to common ceramic core materials, such as fused silica or alumina [9][10][11], and approximating the thermal expansion coe cient of superalloys [12]. However, in spite of these primary advantageous properties, the application of CaO is inhibited due to its hydration susceptibility in atmospheric moisture [2][3][4][5][13][14], which increased the di cultly of fabricating CaO ceramics as well. Most existing methods for forming CaO ceramic, such as hot-pressing [1], cold-pressing [3][4][5], can only fabricate simple architectures, which makes them untenable for generating complex ceramic structures.…”

Wettability between molten slag and dolomitic refractory

“…The dolomitic refractory is widely used for containment of steel melts during steelmaking and refining, especially in the production of special steels and clean steels [1][2][3] , due to its excellent high temperature stability, slag erosion resistance and peeling resistance [4] . Compared with MgO-C refractory, dolomitic refractory will not cause the increase of carbon in molten steel.…”

“…Based on the previous advantages, the dolomitic refractory plays an important role in the production of stainless steels. However, the application of dolomitic refractory is restricted to the hydration of free CaO [4,8] at room temperature and the low erosion resistance of low basicity slag [1] . In MgO-based refractory, MgO was proved to be less reactive during the manufacture of refractory [5,6,9,10] as well as -2 -during the erosion of refractory.…”

Defect Study of MgO-CaO Material Doped with CeO2

“…MgO-CaO refractories have been widely used in metallurgy industry [1] and cement rotary kilns [2] owing to their excellent properties such as high melting points, excellent thermal shock resistance, and slag corrosion resistance [3]. They have also been considered as one type of chromefree refractories that are suitable for substituting the MgO-Cr 2 O 3 refractories [4].…”