Sudhir Sen

Study of the Physico-Chemical Properties of Some Indian Bentonites—Part I: General Properties

Physico-chemical properties of some Indian bentonites were systematically studied in view of their wide application in recent years in ceramic industries as plasticizer, in glazes etc. The study includes the general properties of bentonites e.g. colour, fracture, sp. gr., hardness, plasticity, pH, sp conductivity, particle size, soapy touch, swelling, thixotropy and settling behaviour. The bentonites studied were Bihar, Jaipur, Akli, Hathi-ki-dhani, Rajula and Karauli. Of the bentonites studied Akli showed maximum fineness, swelling and dry linear shrinkage. Akli and Hati-ki-dhani appeared to be Na-based bentonite, and Bihar appeared to be a Ca-based. Jaipur and Karauli did not exhibit the characteristic properties of bentonite.

Mineralogical characterisation of some Indian Bentonites based on IL: MA ratios

The ratio of ignition loss (IL) to the moisture absorption (MA) at a particular relative humidity of a clay mineral has been used as a technique for clay mineral identification. This technique has been employed for studying the mineral components present in some Indian Bentonites. It has been found that if the three main groups of clay minerals are lined up in the order of increasing of particle fineness as kaolinite, illite and montmorillonite, the IL values increased in the reverse order MA, however, followed the same order and increased from Kaolinite to Montmorillonite. Bihar, Rajula, Akli and Hathi-ki-Dhani Bentonites were found to be typically montmorillonitic. Jaipur and Karauli were predominantly illitic.

Zircon Opacifiers: Their Preparation and Performance in Glazes

Zircon sand obtained from Kerala was studied with a view to evaluate its suitability in the manufacture of opacifiers. Mineralogical data include petrography, DTA, X-ray, and chemical analysis.Different types of opacifiers including zirconium silicate, spinel, double silicates were successfully prepared using indigenous zircon sand and their performance as opacifiers was tested with four types of base glazes. Larger batches of some of the opacifiers were also tried in ceramic factories, the results of which indicated that indigenous zircon sand is quite suitable for the manufacture of zircon base opacifiers used in ceramic industry.

A Study of the Physico-Chemical Properties of Bihar Bentonite

The physical and chemical properties of Bihar bentonite in comparison to those of a widely used and well known bentonite, Wyoming have been studied. Mineralogically the clay was montmorillonitic with some kaolinite. Gypsum, rutile and iron minerals were found to be present in the clay as impurities. The clay was predominantly a calcium-magnesium base bentonite. Due to contamination with gypsum and to the presence of Ca and Mg as exchangeable cations, Bihar bentonite showed very poor physical properties related to its utilisation in ceramic industries. Preliminary experiments showed that considerable improvement is likely to be effected by suitable treatments.

Effect of Iron Oxide and Titania on the Fired Colour of Clays and Whiteware Bodies

Six near white china clays were examined for their colour, following the I.C.I. trichromatic colorimetric co-ordinate system after being fired to come 7 and 13 and the results were correlated with their Fe2O3, and TiO2 contents, determined polarographically. The yellowness factor giving a measure of the off-whiteness of the samples was also calculated. The clay having the minimum purity, maximum brightness and lowest yellowness factor was selected for incorporation in a porcelain composition. Different amounts of Fe2O3 and TiO2 were added to this composition and fired to cone 7 and 13. The fired colour of the samples were similarly examined. It was observed that Fe2O3 imparts colour to porcelain body and its effect becomes prominent in presence of TiO2. In samples comparatively free from Fe2O3, TiO2 has little effect on colour.

Glass Electrodes for the Direct Measurement of Sodium Ion Activity: Part II

Five Lithia Alumina Silicate glasses having different proportions of additives were melted and studied for their suitability as sodium electrodes. A particular composition was found to be the best so far as the sodium ion specificity was concerned. The effect of interfering ions like K+, Ca2+, Mg2+, Al3+, Fe3+ and SO42- was studied and it was found that only Al3+ and Fe3+ had interference which also could be completely suppressed by using triethanol-amine. The results of Na2O determinations made with sodium electrode were compared with those determined by flame spectrophotometry and they were analysed statistically.

A Study of the Sedimentation Volume of Clays

AbstractSedimentation rate characteristic and final sedimentation volume of four Indian china clays were studied. The clays could be grouped as flocculated and deflocculated. When the phenomenon was observed after adding some electrolyte, clear indications regarding the degree of base saturation and the degree of deflocculation were obtained. The results also provided a direct measure of the amount of alkali needed to obtain a deflocculated slip from those clays. The sedimentation volume method was found to be useful for the determination of b.e.c. of clays.

X-ray and Differential Thermal Analysis of Some Indian Bentonites

With a view to determine their mineralogical nature, X-ray and differential thermal studies were carried out on six Indian bentonites from Bihar, Rajula, Akli, Hathi-ki-dhani, Jaipur and Karauli. All the deposits were found to contain montmorillonite in addition to other minerals. The DTA curves showed the presence of kaolinite in Bihar, Akli and Hathi-ki-dhani bentonites. Jaipur and Karauli bentonites were found to contain clay minerals in which illtie and montmorillonite were found to be interstratified.

Zircon Sand from Kerala Beach, Its Mineralogy, Metamictization and Suitability as a Raw-Material for Glaze Opacification

Mineralogical studies of zircon sand from Kerala beach revealed that about 97% of the grains were unaltered, but they appeared to have a lower degree of crystallinity. About 2% of the grains were found to be partly metamicted. Huttonite (ThSiO4) was found as one of the impurities responsible for the radio activity of the sample.Calcination improved the crystallinity and colour of zircon grains, making them more suitable for use as opacifiers in porcelain glazes. The behaviour of raw and calcined zircon in various types of glazes have been explained.

Chemical Decolourisation of Some Indian Clays

Dissolution of Fe2O3 from clay suspension by various reducing agents at different pH and temperature was systematically studied. Based on these observations a procedure was worked out for decolourisation of clays by reducing-their Fe2O3 content. The method developed involved dispersion of the clay suspension, addition of Na2S2O5 in presence of zinc at controlled pH and after completion of the reactions washing the decolourised clay free of excess salts, filtering and drying. An important feature of the process was that no external heating was necessary and it could as such be adopted as an adjunct to a clay washing plant.Clays from different regions were studied. In most cases substantial increase in brightness factor was obtained without showing any deterioration in the other properties.