An apparatus for the measurement of thermal expansion of solids at low temperatures

A dilatometer, using the three terminal capacitance technique, suitable for measurement of linear thermal expansion of solids in the temperature range 1.3–300 K is described. The dialtometer is designed such that the mounting system for the specimen does not undergo any significant changes in dimensions when the specimen is heated. The apparatus, therefore, yields in principle absolute values of α, the coefficient of linear thermal expansion. The performance of the apparatus has been checked by measurements on copper in the temperature range of 77–300 K. Some preliminary results on the behaviour of α for Y₁Ba₂Cu₃O_6.9 compound in the vicinity of superconducting transition temperature,T _c are also described. The system can detect relative changes in length Δl/l ₀ of about 10⁻⁸. Attempts are being made to improve the sensitivity.     

Thermal expansion of orthorhombic and tetragonal phases of the highT c superconductors RE1Ba2Cu3O y (RE=Y,Gd, Dy)

Measurements of the coefficient of linear thermal expansion α have been carried out for the orthorhombic and tetragonal phases of RE₁Ba₂Cu₃O _y (RE=Y, Gd, Dy) compounds using a high resolution capacitance dilatometer in the temperature range 77–300 K. All the superconducting samples exhibit a jump Δα at their respective transition temperatures,T _c. Evidences of, sample-to-sample variation in α values and dependence of Δα on the sample preparation conditions, have been obtained. The non-superconducting samples, in general, exhibit lower values of α possibly because of lowering of oxygen content.     

A Comparative Evaluation of Nitrogen Compounds in Petroleum Distillates

Although the concentration of nitrogen compounds in crude oil is relatively low, they can become more concentrated in petroleum distillates and poison the catalysts used in refining processes. They cause undesirable deposits, color formation and odor in products; they also contribute to air pollution and some are highly carcinogenic. The poisoned catalyst becomes deactivated for hydrodesulfurization and unable to remove sulfur from middle distillates. In order to understand the effect on catalytic processes, it is desirable to identify the nitrogen compounds in various petroleum distillates. This paper compares the nitrogen species profiles in different petroleum distillates using a nitrogen chemiluminescence detector. In addition, four different petroleum distillate samples from different refineries were analyzed to find the variation in their nitrogen profiles. The nitrogen compounds in petroleum distillate samples were identified as anilines, quinolines, indoles, and carbazoles and their alkyl derivatives. Quantitation was carried out against known reference standards. The quantitative data were compared to the total nitrogen content determined by elemental analysis.     

Excess conductivity of thin superconducting films of tin above the transition temperature

The excess conductivity of thin superconducting Sn films has been measured. These films have been grown at room temperature and ～ 77 K on glass substrates. The results show that the pair breaking parameter is not simply and solely related to the normal state sheet resistance but depends also on the substrate temperature.     

Stimulated Raman spectra of H2O and D2O

SRS of the valence band of liquid H₂O and D₂O are obtained using a nanosecond pulse from a Q-switched ruby laser. The SRS contours obtained are in overall agreement with those of earlier workers using picosecond pulses and help clarify the results of one of the published works. The broad SRS bands are less likely to be attributed to self-focusing in water, but to the stimulation of overlapping components.