Abhinav Srivastava

Implementation of industrial waste ferrochrome slag in conventional and low cement castables: Effect of calcined alumina

Abstract A new class of conventional and low-cement ferrochrome slag-based castables were prepared from 40 wt.% ferrochrome slag and 45 wt.% calcined bauxite. Rest fraction varied between high alumina cement (HAC) acting as hydraulic binder and calcined alumina as pore filling additive. Standard ASTM size briquettes were prepared for crushing and bending strengths evaluation, and the samples were then subjected to firing at 800, 1100 and 1300 °C for a soaking period of 3 h. The microstructure and refractory properties of the prepared castables have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), cold crushing strength, modulus of rupture and permanent linear changes (PLCs) test. Castables show good volume stability (linear change <0.7%) at 1300 °C. The outcomes of these investigations were efficacious and in accordance with previously reported data of similar compositions. High thermo-mechanical and physico-chemical properties were attained pointing out an outstanding potential to increase the refractory lining working life of non-recovery coke oven and reheating furnaces.

Implementation of industrial waste ferrochrome slag in conventional and low cement castables: Effect of microsilica addition

Abstract Ferrochrome slag is a waste material obtained from the manufacturing of high carbon ferrochromium alloy. This slag is formed as a liquid at 1700 °C and its main components are SiO2, Al2O3 and MgO. Additionally it consists of chrome, ferrous/ferric oxides and CaO. Present work outlines a novel approach in formulating castables with this industrial waste.

Role of CaF2 on mechanochemically synthesized leucite as dental veneering glass ceramics

Abstract Leucite based glass ceramic is widely used in dental ceramics as porcelain fused to metals for veneering applications. Main properties considered here are high coefficient of thermal expansion and good mechanical properties. Owing to these requirements, high expansion phase such as leucite is incorporated in these glass ceramics. The present work was aimed to synthesise leucite using its stoichiometric batch compositions and subsequent high energy ball milling. CaF2 was also added in another mix to study its role on leucite formation. Further prepared, leucite phase was added in separately prepared low temperature glass frit powders to control amount of glass and leucite content. X-ray diffraction results displayed that high energy ball milling and additive promoted the formation of leucite as a major crystalline phase. Furthermore, CaF2 also suppressed the subsidiary crystallisation of kalsilite phase. Evaluated average coefficient of thermal expansion in the temperature range of 20–500°C was very close to the theoretical value of pure leucite.

Role of MgF 2 addition on high energy ball milled kalsilite: Implementation as dental porcelain with low temperature frit

Porcelain fused to metal (PFM) has received great attention over the last few years due to its importance in the dentistry. Kalsilite (K2O·Al2O3·SiO2) is a high thermal expansion porcelain, suitable for bonding to metals. However, kalsilite is a metastable phase which gets converted into crystalline leucite upon heating. In the current work feasibility of developing stable kalsilite phase, dispersion of MgF2 in it as an additive and using mechanochemical synthesis are studied. Micro fine dental material has been formulated by mixing prepared kalsilite with low temperature frit (LTF) in different ratio. The crystalline phases evolved in fired powders are characterized by powder X-ray diffraction (XRD) technique. Kalsilite with different ratio of LTF has been cold pressed and heat treated to examine its coefficient of thermal expansion (CTE), flexural strength, apparent porosity (AP), bulk density (BD) and microstructure. Results indicate that MgF2 addition and high milling duration help in kalsilite stabilization. Temperature also plays an important role in this stabilization, and at 1100°C single phase kalsilite formation is observed. Present outcomes demonstrate that it is easily possible to synthesize a stable single phase kalsilite with desirable properties.

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

Abstract High-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 high-energy ball milling and subsequent calcinations on the formation of high alumina cementing phases using mixtures of Al2O3 and CaCO3 were investigated. Nano-meter sized high alumina cement (HAC) powders were synthesized by mechanochemical treatment of Al2O3 and CaCO3 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 ZrO2, α-Al2O3 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.