Papers by Balakrishna Palanki
Indian Journal of Engineering and Materials Sciences, Oct 1, 1996
196-200<span style="font-size:11.0pt;line-height:115%; font-family:" calibri",&... more 196-200<span style="font-size:11.0pt;line-height:115%; font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:="" "times="" new="" roman";mso-fareast-theme-font:minor-fareast;mso-hansi-theme-font:="" minor-latin;mso-bidi-font-family:"times="" roman";mso-ansi-language:en-us;="" mso-fareast-language:en-us;mso-bidi-language:ar-sa"="">End-capping defect is one of the causes of rejection in pressed and sintered ceramic compacts. The causes of its occurrence lie both in the quality of the powder and that of pressing. In this paper, end-capping and other defects have been described and their relationship to powder characteristics and pressing parameters has been brought out. It is found that soft powders that are free from agglomerates, and well finished suitably tapered hard material dies and moderate compaction pressures tend to minimize end-capping and other defects.</span
On a tente d'etudier les effets des differents parametres sur les procedes de preparation des... more On a tente d'etudier les effets des differents parametres sur les procedes de preparation des poudres ainsi que sur le compactage, le frittage et la qualite de ceramiques frittees de type oxyde. En particulier, on a discute des causes de fissuration et de defauts d'encapuchonnement dans les produits frittes, et on a suggere des mesures de prevention. Bien que les resultats experimentaux aient ete obtenus a partir d'essais portant sur UO 2 et ThO 2 , les conclusions qui en sont tirees peuvent etre de portee generale pour les processus ceramiques.
Transactions of the Indian Ceramic Society, 1987
UO2 is one of the most commonly used nuclear power reactor fuels today. The sintering process of ... more UO2 is one of the most commonly used nuclear power reactor fuels today. The sintering process of UO2 presented in this article brings out the special features of UO2 including the effect of nonstoichiometry and dependence of its defect structure on the sintering atmosphere. A theoretical basis for UO2 sintering has been developed in the first part of the paper and subsequently its relevance to industrial practice has been brought out. The effect of variables such as oxygen to uranium ratio, specific surface area of UO2 powder, sintering temperature and additions on the sinterability of UO2 have been discussed and the optimum conditions for the production of UO2 fuel have been brought out.
Lo qualite finale d'une ceramique frittee depend des caracteristiques des poudres de depart a... more Lo qualite finale d'une ceramique frittee depend des caracteristiques des poudres de depart ainsi que des conditions de mise en forme et de cuisson. Les caracteristiques des poudres, elles, sont fonction des caracteristiques des precurseurs dont la decomposition thermique a permis leur obtention. Le precurseur (precipite de diuranate d'ammonium) est seche, calcine et reduit a des temperatures et a des vitesses de chauffe adaptees a la production de poudre d'UO 2 . L'acceptabilite du produit final d'UO 2 fritte a ete obtenue en combinant une basse temperature de precipitation, un revenu intermediaire du precipite, et un lavage et une decomposition thermique susceptibles non seulement de preserver la morphologie du precurseur mais aussi de permettre le developpement d'une porosite suffisante. Ces conditions de preparatior menent a des poudres exemptes d'agglomerats et qui ne reclament ni broyage ni ajout de liant avant le compactage. Apres granulation, les poudres ont un comportement au compactage favorable et conduisent a une microstructure des frittes homogene et dense.
Journal of Nuclear Materials, 1988
Calcination of thorium oxalate in hydrogen is found to yield black powder-a mixture of carbon and... more Calcination of thorium oxalate in hydrogen is found to yield black powder-a mixture of carbon and thorium oxide. Reheating in air eliminated the carbon and resulted in white ThO, powder. Optimum compaction pressure has been suggested to be that at which axial and diametral sintering shrinkages of a cylindrical pellet are equal. The effects of the additives MgO and Nb,O, and the effect of furnace atmosphere on the sinterability of ThO, have been investigated and the interdependence of additive and atmosphere has been brought out. 0.25 mol% of Nb,O, in ThO, lowers the sintering temperature in air from 1600-1700 o C to 1150-l 200 o C. Air sintering of niobia added thoria thus provides an economical alternative to conventional hydrogen sintering. A novel thermal etching technique has been used to reveal the microstructure of sintered thoria.
Journal of Engineering Education Transformations, 2021
The college teachers have been aware of the industry requirements of students such as knowledge o... more The college teachers have been aware of the industry requirements of students such as knowledge of latest engineering developments, ethical practices, good communication and team play, flexible and lifelong learning and multitasking. However, a neglected aspect by the teachers, but essential for the industry, is their role in the development of critical thinking skills in the students. In particular, the students need to be made aware of numerous errors of the intellect while still at the college. Published literature on Engineering Education has missed this important aspect. The author recollects what his teacher taught him fifty five years ago at the Indian Institute of Technology, Bombay where he was a student. The memories are supplemented with information and examples from a later period.
The role of the educational technologist is deemed to span over a major part of life, involving s... more The role of the educational technologist is deemed to span over a major part of life, involving school education, university education, on the job training and retraining while in service. Each individual has a tremendous potential to do things. It is for the educational technologist to facilitate its utilization by the individual through creative exertion. Education is not to be restricted to one class of people. For example, in a manufacturing industry, the education plans includes not only its managers, supervisors and workmen, but also its suppliers and customers. In this paper, the authors recollect their experiences concerning motivated learning at teaching institutions and in industry and plead for innovative methods. The availability of a disciplined, committed and affectionate teacher possessing a fund of knowledge (be he a professor or a manager) can be highly motivating to the student or employee. An academic or corporate environment that actively supports such a teacher ...
Journal of Materials Science and Chemical Engineering, 2016
The burnable poison Gadolinium oxide was incorporated into UO2 in two of the 36 elements of the f... more The burnable poison Gadolinium oxide was incorporated into UO2 in two of the 36 elements of the fuel assembly in the reload fuel of BWR Units I & II of Tarapur Atomic Power Station. This enabled loading of higher quantities of fuel and achieving a more flattened neutron flux distribution over a longer period of time in the nuclear reactor core. The UO2-Gd2O3 pellets are made by powder pressing and sintering. In the early days of this author's experience of the 1970s, the processing of UO2-Gd2O3 turned out to be more complex than that of UO2 alone. The small proportion of Gd2O3 in the powder mixture (1.5%) is to be uniformly distributed in the UO2 before and after sintering and substitutional solid solution formation must be complete prior to densification. The inadequacy of homogeneity in the powder and pressed pellets leads to severe defects in the sintering process. In this paper, the processing of UO2-Gd2O3 has been revisited. The defects in the product such as "free gadolinia", low sintered density and bloating, caused by improper processing, have been brought out. The structural defect chemistry aspects of UO2-Gd2O3 and diffusion processes relevant to sintering have also been discussed.
Natural Science, 2012
India is one of the few countries committed to expansion of nuclear power. In view of the abundan... more India is one of the few countries committed to expansion of nuclear power. In view of the abundance of thorium relative to uranium, thorium cycle is under serious development and implementation. Both ThO 2 and (U,Th)O 2 are used. Fine powders of the same are mostly prepared through the aqueous chemical route, pressed and sintered. Extrusion and hot impact densification are also being used. Sol-gel method and other alternatives are also being pursued with the advantage of automation and remote operation. Relevant papers on the thorium cycle with emphasis on processing methods and related aspects are reviewed here.
Journal of Nuclear Materials, 2001
ABSTRACT The concept of coarsening–densification transition temperature (CDTT) has been proposed ... more ABSTRACT The concept of coarsening–densification transition temperature (CDTT) has been proposed to explain the experimental observations of the study of sintering undoped uranium dioxide and niobia-doped uranium dioxide powder compacts in argon atmosphere in a laboratory tubular furnace. The general method for deducing CDTT for a given material under the prevailing conditions of sintering and the likely variables that influence the CDTT are described. Though the present work is specific in nature for uranium dioxide sintering in argon atmosphere, the concept of CDTT is fairly general and must be applicable to sintering of any material and has immense potential to offer advantages in designing and/or optimizing the profile of a sintering furnace, in the diagnosis of the fault in the process conditions of sintering, and so on. The problems of viewing the effect of heating rate only in terms of densification are brought out in the light of observing the undesirable phenomena of coring and bloating and causes were identified and remedial measures suggested.
Journal of Materials Science Letters, 1988
Journal of Materials Science Letters, 1994
... AV ... 87 Page 3. References 1. P. BALAKRISHNA, BP VARMA, TS KRISHNAN, TRR MOHAN and P. RAMAK... more ... AV ... 87 Page 3. References 1. P. BALAKRISHNA, BP VARMA, TS KRISHNAN, TRR MOHAN and P. RAMAKRISHNAN, J. Mater. Sci. ... Tech. J. 37 (1958) 711. 4. DS PATIL, SB MENON, N. VENKATARAMANI and VK ROHATGI, Babha Atomic Research Centre BARC/I-933 (1988). ...
Indian Journal of Engineering and Materials Sciences, 1998
Admixed lubricants are used to bring down compaction and ejection pressures, and to increase pack... more Admixed lubricants are used to bring down compaction and ejection pressures, and to increase packing efficiency in ceramic powder pressing. Admixed binders are used for increasing green strength of the compact. The stronger and denser green compacts so obtained, sinter to high densities without defects and with minimal shrinkage, leading to very high acceptance rates in large scale production. Zinc behenate powder has been used as a lubricant cum binder for uranium dioxide with very good results. Green density versus compaction pressure has been obtained. Weight loss with temperature of free and admixed zinc behenate and carbon and zinc loss in admixed compact and other data are presented. On the other hand, the use of zinc behenate could lead to bloating and high nitrogen values in sintered uranium dioxide under some conditions of processing, which have been identified.
Natural Science, 2015
Thorium based nuclear fuel is of immense interest to India by virtue of the abundance of Thorium ... more Thorium based nuclear fuel is of immense interest to India by virtue of the abundance of Thorium and relative shortage of Uranium. Thorium metal tubes were being cold drawn using copper as cladding to prevent die seizure. After cold drawing, the copper was removed by dissolution in nitric acid. Thorium does not dissolve being passivated by nitric acid. Initially the copper cladding was carried out by inserting copper tubes inside and outside the thorium metal tube. In an innovative development, the mechanical cladding with copper was replaced by electroplated copper with a remarkable improvement in thorium tube acceptance rates. Oxalate derived thoria powder was found to require lower compaction pressures compared to ammonium diuranate derived urania powders to attain the same green compact density. However, the green pellets of thoria were fragile and chipped during handling. The strength improved after introducing a ball milling step before compaction and maintaining the green density above the specified value. Alternatively, binders were used later for greater handling strength. Magnesia was conventionally being used as dopant to enhance the sinterability of thoria. The normal sintering temperature for magnesia doped thoria was 1600˚C-1700˚C, which was achieved in electrically heated molybdenum element sintering furnaces with reducing atmosphere. 0.25 mole percent addition of niobia to the thoria was found to bring down the sintering temperature to 1150˚C. Sintering could be done in ordinary furnaces in air atmosphere using silicon carbide or Kanthal heating elements. Electrical conductivity was measured for both magnesia and niobia doped sintered thoria and used in interpreting differences in sintering behavior.
Journal of Engineering Education Transformations, 2021
The college teachers have been aware of the industry requirements of students such as knowledge o... more The college teachers have been aware of the industry requirements of students such as knowledge of latest engineering developments, ethical practices, good communication and team play, flexible and lifelong learning and multitasking. However, a neglected aspect by the teachers, but essential for the industry, is their role in the development of critical thinking skills in the students. In particular, the students need to be made aware of numerous errors of the intellect while still at the college. Published literature on Engineering Education has missed this important aspect. The author recollects what his teacher taught him fifty five years ago at the Indian Institute of Technology, Bombay where he was a student. The memories are supplemented with information and examples from a later period.
Journal of Nuclear Materials
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Papers by Balakrishna Palanki