K Subba Rao
Articles written in Proceedings – Section A
Volume 25 Issue 2 February 1947 pp 162-173
The effect of variation of the temperature of precipitation of gels of hydrous oxides of silica, titania and alumina on the hysteresis effect in the sorption of water vapour has been studied at 30°C. Gels have been obtained by precipitating the hydrous oxides at 25°C. and 100°C. with previous boiling of the silicate solution.
In all the systems studied, permanent hysteresis loops have been obtained. With increase in the temperature of precipitation, there has been a diminution in the sorptive capacity of gels for water at different partial pressures and in most of the systems the hysteresis loop suffers a diminution in size with a change in the shape and position of the loop. But in none of these systems, is any complete elimination of the loop noticeable. Gels precipitated at 100°C. are less porous than the gels precipitated at 25°C. and appear to have fewer cavities that are responsible for the phenomenon of hysteresis.
Volume 25 Issue 2 February 1947 pp 174-180
The effect of the activation temperature of silica gel on the hysteresis effect has been studied. Sorption and desorption of water vapour at 30°C. have been conducted on gels activated at 35° C., 70° C., 140° C., 300° C., 500° C. and 1000° C.
All the gels gave permanent and reproducible hysteresis loops. A marked variation however, was noticed in the total sorptive capacity and the area of the loop.
The results indicate that from 35° C. to 140° C., there is a decrease in the capillary space in the gel but from 140° C. to 500° C., the capillary space remains practically unaltered. Whereas, above 500° C., the gel suffers structural change, the capillaries collapse and there is a marked decrease in the total capillary volume.
Volume 25 Issue 2 February 1947 pp 181-185
By employing the quartz fibre spring technique, the hysteresis in sorption has been studied, of water vapour at 30° C. on precipitated silicic acid gel. A comparative study has been made with regard to the shape and size of the hysteresis loops of precipitated silica gel with that of the adsorbent obtained from silicic jelly.
The mode of preparation of the gel was found to greatly influence the shape and size of the hysteresis loop.
Volume 25 Issue 2 February 1947 pp 186-189
The effect of variation of activation temperature on the hysteresis effect has been studied for titania gel. Sorption and desorption of water vapour at 30°C. on titania gels activated at 30°C., 97°C., 214°C, 400°C., 600°C. and 1000°C. have been measured.
At different temperatures of activation, permanent and reproducible hysteresis loops have been obtained. There is however, a marked variation in the total sorptive capacity, the area of the hysteresis loops and the relative vapour pressures corresponding to the tail end of the hysteresis loops.
The results indicate that with an increase in the temperature of activation from 30°C. to 97°C., there is a small increase in the total capillary space and in the total cavity volume. Above 97°C., the gel suffers a structural change with a diminution in capillary space and in cavity volume. There is also a collapse of the smaller cavity necks. At 1000°C., there is a breakdown of the gel structure and a complete collapse of the capillary space.
Volume 25 Issue 3 March 1947 pp 221-228
A series of sorptions and desorptions of water vapour at 30° C., on gelatin, casein, egg albumin, denatured casein, denatured egg albumin have been conducted and in these systems either there is no hysteresis loop at all or the loop initially exhibited disappears on successive sorptions and desorptions.
These results indicate that the swelling of the adsorbent on imbibing the solvating liquid is responsible for the disappearance of the hysteresis effect.
Experiments on the sorption of ethyl alcohol at saturation pressure on the above proteins at 30°C. show that the nonsolvating liquid is either not adsorbed at all or taken up to a very small extent.
With casein and egg albumin, the sorptive capacities for water are lower in the denatured forms of the proteins. These results indicate a decrease in hydrophilic character of the proteins on denaturation.
Volume 25 Issue 3 March 1947 pp 229-234
Studies in sorption and desorption of water vapour at 30° C. on red laterite soil and black cotton soil and their fractions—fine sand, silt and clay have been carried out. Sorptive capacity of fine sand is found to be very small. That of silt is higher. Clay fractions have the highest sorptive capacity. Removal of organic matter lessens the sorptive capacity of the soil.
The soils and their fractions have all yielded permanent and reproducible hysteresis loops. There is thus evidence that in soils we are dealing with rigid systems having cavities with constricted ends. The practical importance of the hysteresis effect in soils in nature is indicated.
Volume 37 Issue 1 January 1953 pp 68-80
Volume 39 Issue 3 March 1954 pp 132-136
The principle and the experimental details of the new method of determining ultrasonic velocities in transparent liquids along with a brief description of the crystal holder designed to suit this method are given. Ultrasonic velocities determined for about ten common liquids are tabulated along with those obtained previously by different methods. The main features of this method are briefly discussed.
Volume 70 Issue 1 July 1969 pp 18-28
By employing the quartz fibre spring technique, sorption-desorption hysteresis at 35° has been studied of Iso-propyl, Iso-Butyl, Sec-Butyl, Tert-Butyl, Active Amyl and Iso-Amyl alcohols on fibrous silica gel (Santocel C) activated at 250°. The isotherms of all the alcohols have clearly defined “knees”. By the application of BET theory, the monolayer capacities are determined. Knowing the specific surface area of fibrous silica gel, assuming oriented sorption of the isomeric alcohols with the OH group attached to surface; the cross-sections of the alcohol molecules are calculated. Excepting Iso-Propyl and Sec-Butyl alcohols, all others have cross-sections greater than that of normal aliphatic alcohols. These higher values are to be expected in view of the side CH3 groups. The exceptional behaviour of Iso-Propyl and Sec-Butyl alcohols is not clear.
Permanent and reproducible hysteresis loops have been obtained in all the cases. Cohan’s theory of hysteresis cannot explain the observations satisfactorily. Cavity theory however explains all the cases of hysteresis. The shapes of the isotherms of the different alcohols in the high relative vapour pressure region indicate a variation in contact angles of the alcohols.