A Study of the Production of Soederberg Paste from Indian Raw Materials

CONTINUOUS self-baking electrodes of the Soederberg type are used in electrolytic extraction of metals such as aluminium and in electric smelting of pig iron and certain Ferro -alloys. These electrodes are made of carbon paste tamped in situ in hollow sheet metal colum- ns that travel downward as the electrodes get consumed in the furnace. The descending paste gets baked by heat of the furnace and thereby becomes it fairly rigid and dense conductor when it contacts the electric bus-bars. Below this point there is virtually no difference between this and prebaked amorphous carbon electrodes

Mineralogy of some Indian Kaolinitic clays and crystalline of Kaolinite

The three kaolinite clays viz. Travancore, Rajmahal China clays and a Ball clay were examined for their mineralogical composition by different technique such as chemical analysis, differential thermal analysis, X-ray diffraction and electron microscopy. X-ray, d. t. a., base exchange electron microscope studies indicated that Travancore China clay is a relatively well crystallized kaolinite. Rajmahal China clay ranks next to Travancore in crystallinity but the hexagonal morphology of kaolinite could not be clearly seen in a electron micrographs. This may be due to intimate association of fine mica and hence difficulty in having good resolution. Ball clay shows smaller crystals of kaolinite and the morphology of kaolinite is clearly manifested. From X-ray, d. t. a.., and base exchange studies, it appears to be b/3 disordered type

The Role Monovalent and divalent cations in the Dehydroxylation of Kaolinite

Homo-ionic forms of kaolinite exhibit difference in peak shapes of dehydroxylation reaction in differential thermal analysis. H-forms are found to give higher amplitudes, A/w and slope ratios of dehydroxylation peak than divalent cations in general. Na+- forms tend more towards hydrogen forms in their behavior. The peak temperatures of the various homo-ionic forms are not much affected when the furnace is controlled and temperature measured with a thermocouple in the centre of the sample while the furnace temperature is raised according to a predetermined heating cycle by changing the input energy. The difference in the dehydroxylation peaks of homo-ionic forms are consideration to be due to change in the rate of dehydroxylation. The divalent cations though not in an orderly way are found to decrease the rate of dehydroxylation and this is considered to be the formation of oxide linkages which bring down the interparticle porosity and obstruct the easy escape of water vapour. Slight pressure due to entrapped water vapour is considered to cause retardation of the forward reaction. No rigid order of cations regarding dehydroxylation is to be found and perhaps work with close sized fractions may throw greater light on this aspect

Consideration of surface area and crystallinity of Kaolinite as factors in its base exchange capacity

With a view to study the influence of surface area and crystallinity of kaolinitic on its 'bec', the base exchange capacities of three kaolinitic clays were compared with their surface areas as determined by low temperature argon adsorption and crystallinity as indicated by their X-ray difractograms in the region 16°C-43°C 2q using CmKa radiation coupled with their differential thermal curves. The results indicate that even though there is correlation between 'bec' and crystallinity of kaolinite in the different clays, no relation is observed between surface area and 'bec' of the different clays. It is considered that correlation may exist with surface area and base exchange due to broken bonds within the same clay but it may not hold with different clays due to some changes in the mineralogical composition and presence of minerals like tubular halloysite which can permit argon entry within the tubes and contribute to internal surface area also. (Dr. P. Prabhakaram, Scientist, National Metallurgical Laboratory, Jamshedpur

Thermo- gravimetric studies on the low-temperature pyrolysis of bituminous coal

Studies on the thermal decomposition of washed bituminous coal from Raniganj coal fields were carried out at steady temperatures ranging from 410¬-o-456oC by means of a thermal balance .this study is part of the project related to the preparation of dens carbon aggregates from bituminous coals for incorporating in the soederbergpaste

Thermo-gravimetric studies on the low temperature pyrolysis of bituminous coal

Studies on the thermal decomposition of a washed bituminous coal from Raniganj coalfields were carried out at steady temperatures ranging from 410°-456°C by means of a thermal balance. The experiment percentage loss versus time curves follow equation of the type,where Y = percentage loss in weight, X= time in minutes, C = the intercept on Y-axis at the assumed zero time and "a" and "b" are constants. The limiting losses at various temperatures, calculated from the horizontal asymptote of the curves, when plotted versus temperature fall on a straight line whose equation is L = mt + C where L = the maximum or limiting loss at any temperature, t=the temperature in degrees centrigrade and "m" and "C" have the usual significance. From this equation, the maximum loss at any intermediate temperature can be found by intrapolation within the experimental range. The activation energy of the thermal decomposition of this coal is found to be 50 K./cals/gm mole and the frequency factor is 1.15 x 1013. (Mr. P. Prabhakaram, Junior Scientific Officer; Mr. H.P.S. Murthy, Senior Scientific Officer, National Metallurgical Laboratory

Production of dense carbon aggregates from carbonaceous materials for varied volatile contents for use in carbon products in general and soderberg paste in particular

The paper describes the various process details of preparing dense carbon aggregates from indigenous raw materials and production of Soederberg paste from the carbon aggregates. The properties of dense carbon aggregates obtained under optimum conditions have been furnished. The detailed study of the green and fired properties of the imported electrode pastes and the compositions developed at the National Metallurgical Laboratory has shown that the NML made products are well comparable with the French and Norwegian pastes. (Messrs P. Prabhakaran, Junior Scientific Officer and H.P.S. Murthy, Senior Scientific Officer, National Metallurgical Laboratory

Diffusion coatings on steel

In the present work, the authors carried out siliconizing, chromizing, aluminizing and chrome-aluminizing of mild steel in a pack cementation process with a view to evaluate the optimum experimental conditions to obtain satisfactory coatings which possess high resistance to oxidation. It is visualised to adopt some of the experimental conditions in later experiments where diffusion coating treatments are carried out using pastes containing the various diffusion elements. Some of the findings of the authors in siliconizing, chromizing, aluminizing and chrome-aluminizing of mild steel in pack process are reported. It was observed that there is excess grain growth during siliconizing by the pack process and the coatings are porous and lack good oxidation resistance compared to coatings in the gas phase carried out by other workers. Chromized, aluminized and chrome-aluminized samples are superior to 18/8 stainless steel and even Inconel in their oxidation resistance. Chromizing followed by aluminizing makes the coating layer less brittle as observed by the micro hardness measurements across the layer and hence chrome-aluminizing will improve the spoiling resistance of the coatings

Diffusion coating of saddle castings and spacers for boiler applications

The most commonly used method for obtaining diffusion coating of aluminium on mild steel, stainless steel and nimonic alloys is pack cementation process, known commonly as `calorising'. In the present work, the authors have attempted to study some parameters for opti-mizing the conditions for obtaining uniform Alliffusion coatings having good oxidation resistance using low alloy steel specimens from spacers, saddle castings and tubes used in boilers, as the basis material

Performance evaluation of zinc rich primer based on soluble silicates

Zinc rich primers are now a par of the most effective corrosion protective systems for steel under different environmental conditions. There are three types of inorganic vehicles (1) which are currently used in countries abroad for zinc rich primers and they are (i) inorganic post curing vehicles which are water based such as alkali silicates (ii) inorganic self curing vehicles which include soluble alkali silicates, quaternary silicates, polymeric modifications of these silicates, titanates etc. Work was carried at NML on the development and evaluation of zinc rich primer based on soluble silicate and the results presented here encompass the laboratory investigations carried during developmental work and evaluation studies made by atmospheric exposure of the primer at three different places viz. Jamshedpur, Digha and Madras. Other published data on some protective systems exposed under similar conditions are included here for comparison. It is concluded from the laboratory and atmospheric exposure studies that the zinc rich primer developed at NML has proved its performance in protection of steel and it can be an extremely good sacrificial primer steel protection under aggressive environment. (Dr. P. Prabhakaram, Shri A.K. Dey, S. Rao Addanki and D.K. Khan, National Metallurgical Laboratory