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

Abstract

a b s t r a c tHigh-energy ball milling viz. mechanochemical process is being utilized to mechanically activate ceramic powders for low temperature solid state reactions. The process can help to select low-cost commercially available oxides and can produce powders with nanometer size granules. On the other hand, high alumina cement provides high service temperature when used as refractory castable. Therefore, the effects of highenergy ball milling and subsequent calcinations on the formation of high alumina cementing phases using mixtures of Al 2 O 3 and CaCO 3 were investigated. Nano-meter sized high alumina cement (HAC) powders were synthesized by mechanochemical treatment of Al 2 O 3 and CaCO 3 in weight ratios 7:3 and 8:2. This paper compares the calcined high alumina cement obtained by mechanically activated precursor mix for 1, 2 and 3 h. Low cement castables were prepared from calcined Chinese bauxite as aggregate matrix, prepared HAC acting as hydraulic binder and micro-fine additives as pore filling agents. The bonding of high alumina cement as well as sinterability in these castable was studied with ZrO 2 , ␣-Al 2 O 3 and SiC as micro-fine additives. Castables formulated by prepared high alumina cement demonstrate remarkably improved bulk density and apparent porosity as when compared with those prepared by commercially available cement. Casting water demand was also reduced, as a result quick setting behavior was observed. The addition of mechanochemically processed cements in refractory castables improved the thermo-mechanical properties to a significant extent.

Effects of Post-Treatment to Improve the Surface Quality of 3D Printing Cement Mold Casting

“…The increase in strength during the 200 • C heat treatment can be attributed to the increase in the role of the cement binder due to the evaporation of the remaining water, similar to the result of Salomão et al [10]. The subsequent decrease in strength was due to the dehydration characteristics of alumina cement [9], and the increase in strength above 800 • C was confirmed in the complete dehydration reaction [11,12]. Therefore, the printed sample (G sample) was obtained by drying at 200 • C for 30 min.…”

De-Powdering Effect of Foundry Sand for Cement Casting

“…Up to their lowest strengths, the S + C, M + C, and A + C samples show a reduction in strength of 88.9% (6.43 MPa to 0.71 MPa), 37.7% (14.49 MPa to 8.31 MPa), and 35.6% (12.23 MPa to 7.23 MPa), respectively. This affects the characteristics of CAC owing to the different sand types; CAC cement showed the same trend as a result of strength reduction in the temperature range 600-1200 °C [16,[22][23][24]. In comparison, the strength of silica significantly decreased at 600 °C, and the strength recovery was slow at higher heating temperatures [22].…”

Effect of zircon surface coating on alumina grog and its influences on the properties of low‐cement castables

“…The better performance of the castables resulted in the addition of alumina aggregates, fumed silica, calcium aluminate cement, and additives. [26][27][28] Ghasemi-kahrizsangia et al 29 synthesized bauxite-based LCC with the addition of nanoalumina particles to promote the formation of needle mullite, which led to good physical, thermal, and microstructural characteristics. [29][30] Zawrah et al 31 prepared ultralow-and low-cement castables containing 90% weight aggregates and fines as a combination of 2%, 4%, 6%, and 8% zircon and 8%, 6%, 4%, and 2% alumina cement, respectively; they reported the formation of an in situ mullite-zircon composite microstructure with good physical and thermal properties.…”

“…The HMOR and creep resistance were lower at 1500°C owing to the formation of a liquid phase. The better performance of the castables resulted in the addition of alumina aggregates, fumed silica, calcium aluminate cement, and additives 26–28 . Ghasemi‐kahrizsangia et al 29 .…”