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| Abstract: | In this communication, we discuss the details of fabricating an off-line fibre optic sensor (FOS) based on evanescent wave absorption for detecting trace amounts of Fe3+ in water. Two types of FOS are developed; one type uses the unclad portion of a multimode silica fibre as the sensing region whereas the other employs the microbent portion of a multimode plastic fibre as the sensing region. Sensing is performed by measuring the absorption of the evanescent wave in a reagent medium surrounding the sensing region. To evaluate the relative merits of the two types of FOS in Fe3+ sensing, a comparative study of the sensors is made, which reveals the superiority of the latter in many respects, such as smaller sensing length, use of a double detection scheme (for detecting both core and cladding modes) and higher sensitivity of cladding mode detection at an intermediate range of concentration along with the added advantage that plastic fibres are inexpensive. A detection limit of 1 ppb is observed in both types of fibre and the range of detection can be as large as 1 ppb–50 ppm. All the measurements are carried out using a LabVIEW set-up. |
| URI: | http://dyuthi.cusat.ac.in/purl/602 |
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| Dyuthi-P0251.pdf | (176.4Kb) |
| Abstract: | The effect of the chemisorbed hydroxyl groups on the thermal diffusivity of gama alumina is determined by evaluating the thermal diffusivity at various degassing temperatures and by doping it with rare earth oxide using photoacoustic technique. The thermal diffusivity is found to decrease with the increase in degassing temperature as well as with the increase in the doping concentration of rare earth oxide. This decrease has been attributed to the loss of hydroxyl ion from the y-Al2O3. |
| URI: | http://dyuthi.cusat.ac.in/purl/2656 |
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| Dyuthi-P0337.pdf | (665.8Kb) |
| Abstract: | Thermal diffusivity (TD) measurements were performed on some industrially important dyes – auramine O (AO), malachite green and methylene blue (MB) – adsorbed K-10 montmorillonites using photoacoustic method. The TD value for the dye-adsorbed clay mineral was observed to change with a variation in dye concentration. The contribution of the dye towards TD was also determined. The repeatedly adsorbed samples with MB and AO exhibited a lower TD than the single-adsorbed samples. TD values of sintered MB samples were also obtained experimentally. These sintered samples exhibit a higher TD, although they show a trend similar to that of non-sintered pellets. A variation in dye concentration and sintering temperature can be used for tuning the TD value of the clay mineral to the desired level. |
| URI: | http://dyuthi.cusat.ac.in/purl/2621 |
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| Dyuthi-P0182.pdf | (398.5Kb) |
| Abstract: | Thermal diffusivity (TD) measurement on commercial K-10 and KSF montmorillonites was carried out by photoacoustic technique. The TD of the montmorillonites after methylene blue adsorption changed with the dye concentration. The repeatedly adsorbed samples showed a lesser TD than the single adsorbed samples. After methylene blue adsorption the acid leached K-10 samples showed well defined changes in TD when compared to the ordered KSF samples. |
| URI: | http://dyuthi.cusat.ac.in/purl/1756 |
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| pdf 3.pdf | (325.8Kb) |
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