The Corex process has been developed as an alternative to the blast furnace where 80-85% noncoking coal and 15-20% coke is used as fuel for heat generation, production of reduction gases and to maintain adequate char bed permeability in the melter-gasifier. Non-coking coals, which can be used in Corex, have to meet certain physical, chemical and high temperature properties for stable process and to attain high performance levels. JSW Steel operates largest Corex based integrated steel plant with two modules each of 0 . 8 Mtpa capacity where several coals have been used so far and the type of coal used significantly influenced operation. Statistical analysis shows that the significant parameters affecting fuel rate are moisture, volatile matter, slag rate and melting rate. It was observed that at high rate of production, stability and permeability of char bed becomes critical hence coals producing char of high strength after reaction are required.
The presence of large oversize particles (>0.5 μm) in the slurry is known to cause polishing defects during chemical mechanical planarization/polishing (CMP) process. One of the reasons for presence of large particles in the slurry is due to usage of pumps during slurry delivery. The shear rate of pumps is known to cause agglomeration problem in CMP slurries, with increasing shear rate leading to increase in agglomeration in the slurries. However, till now all the work on shear-induced agglomeration has been qualitative or at best semi-quantitative in nature. In the present work, a novel technique to study agglomeration behavior as a function of quantified shear rates has been developed. A rheometer was used as a means to subject slurry to different shear rates for various times. The resulting change in oversize particle distribution was measured using a single particle optical sensing (SPOS) system. It was observed that the behavior of silica slurry when subjected to different shear rates falls into three regions namely de-agglomeration, transition region and agglomeration region. This technique provides a deterministic way for slurry stability and can be used as a guide for design of slurry, slurry selection and design of slurry delivery systems.
Increasing exacting requirements for defectivity during chemical mechanical planarization/polishing (CMP) process has led to an increased demand of highly stable CMP slurries. Herein, we describe a novel method to obtain values of stability ratio (SR) denoted as 'W', a parameter which defines the ability of slurry particles to resist agglomeration. We found that SR is independent of shear rates, is constant for a given slurry and higher the value of SR, lesser is the inclination of the slurry particles to agglomerate even under intense shear stress conditions. We conclude that for determining slurry stability, evaluation of the SR value is a much better metric than traditional methods such as zeta potential, particle size measurements etc. For a 10 wt% silica slurry depending upon conditions such as pH, addition of salts, particle size; values of SR were in the range 1.26-16.53. Based on comparison with CMP defects data, we concluded that (among the slurry samples studied) 10wt% solids, 35 nm basic pH silica slurry with no salt, having SR value 16.53 is most stable and 35 nm acidic pH silica slurry with KCl salt and 135 nm basic pH slurry having SR value 1.26 are relatively most unstable.
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