Low Temperature Synthesis of High Alumina Cements by Gel‐Trapped Co‐Precipitation Process and Their Implementation as Castables

Abstract

Use of high alumina cement (HAC) as low cement castables (LCC) and ultra-cement castables (ULCC) has increased for refractories applications over the last few years. HAC is being prepared commercially, by fusing or sintering a mixture of argillaceous and calcareous materials above 1500°C and subsequent grinding to obtain a fine powder. Powders produced by this method have low specific surface area. Therefore, the present work was aimed to prepare nano structured HAC powders at lower temperatures than the conventional one. The powder process adopted here was modified gel-trapped precipitation method as described earlier. Two compositions of calcium aluminate powders containing 70 and 80 wt% Al 2 O 3 , respectively, were selected. The remaining material was CaO in both mixtures. The gel powders obtained by the abovementioned process were calcined at different temperatures with varying soaking periods. The prepared cements were characterized for structural, mechanical, and cementing properties. Finally, the calcination temperature and time were optimized to obtain the desired phases in HAC. The prime cementing phases observed were CA, CA 2 , CA 6 , C 3 A 5 , and C 4 A 3 SO 4 . These cements were then used with bauxite of different grain sizes to prepare LCC and then their physical properties were studied. The XRD patterns of the bauxite-based castables indicated the formation of the corundum phase along with a mullite phase in all samples. Castable containing HAC and 10 wt% zirconia substituted for bauxite improved physico-mechanical and refractory properties. Mullite formed at high temperature acts as a bonding phase and is accounted for high CCS values. These excellent properties of such castables may enable their use in various applications such as refractory lining for fabrication of steel, aluminum,

Low Temperature Synthesis of High Alumina Cements by Novel Co‐Melt Precursors and Their Implementation as Castables with Some Micro Fine Additives

“…It is measured as the amount of water required as to a particular wt% of dry cement which permits the Vicat's plunger of 10 mm diameter to penetrate to a point 5–7 mm from the bottom of Vicat's mold with gauging time 3–5 min. Calcined HAC powder having 70% alumina and 80% alumina content samples were tested for their consistency by Vicat's apparatus …”

“…This procedure is repeated until the paste starts losing its plasticity, and the penetration is limited only to 5–7 mm depth. This duration of setting it counted and termed as initial setting time …”

“…To get rid of such environmental concerns a novel process is required which could not only bring down the cost of production but could also chain up the pollution norms. Low temperature synthesis of HACs by gel trapped co‐precipitation process is described earlier . CA, CA 2 , CA 6 , C 12 A 7 are the main constituents of HAC.…”

“…Low temperature synthesis of HACs by gel trapped co-precipitation process is described earlier. 1 CA, CA 2 , CA 6 , C 12 A 7 are the main constituents of HAC. Sometimes, it also contains some minor amount of un-reacted alumina.…”

Mechanochemically synthesized high alumina cement and their implementation as low cement castables with some micro-fine additives

“…It has been reported by many researchers that the mechanochemical synthesis processing can be designed in such a way as to synthesize nano-crystalline particles dispersed within a soluble salt matrix. The chemical precursors react, either during milling or in the subsequent heat treatment stage [22][23][24][25][26][27][28][29]. In the present work, a high-energy ball milling process has been applied to the mixtures of Al 2 O 3 and CaCO 3 .…”