DR A Sobha

Varying the ratios of citric acid and urea during the synthesis of carbon dots (CDs) provides a strategy to modulate their fluorescence properties. The impact of different precursor ratios on the resulting CDs' size, surface chemistry, and structure was investigated using X-ray diffraction (XRD) analysis and confirmed through transmission electron microscopy (TEM). Fourier transform infrared spectroscopy (FTIR) was employed to study the influence of precursor ratios on the types and densities of surface functional groups. The optical properties of the CDs were examined using a UV-visible absorption spectrometer, photoluminescence excitation (PLE) spectra, and photoluminescence spectroscopy (PL). Smaller CDs generally exhibit higher energy emissions, resulting in bluer light, while larger CDs tend to emit lower energy light, appearing redder. By adjusting the precursor ratios, it is possible to induce shifts in fluorescence emission, leading to CDs with different fluorescence colours. Furthermore, the antimicrobial activity of CDs against bacterial pathogens was assessed, and their potential for promoting plant growth was explored by coating seeds with concentrated and diluted CDs solutions.

Different synthesis routes and different starting precursors can have different effects upon the properties of materials. In this paper, two different methods: solid state method, sol-gel method has been used to prepare BaTiO3 powders. BaCO3, Ba(OH)2.8H2O and [CH3COO]2Ba were used as barium precursor and TiO2, Ti[OCH[CH3]2]4] as titanium precursor. With the help of thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscope (SEM), the powder characterization has been compared. The results show that sol-gel derived powders are having larger grain growth compared to solid state powders irrespective of starting precursors. It is also evident that dielectric constant value is a function of grain size. Another important findings are starting precursor also plays a major role especially for the grain size and dielectric constant value. The barium hydroxide octahydrate precursor was showing better result than barium acetate precursor.

... ed U Balachandran et al (Pennsylvania: TMS) pp 147–56 [26] Motowidlo LR, Haldar P, Jin S and Spencer ND 1993 IEEE Trans. Appl. Supercond. 3 942 [27] King C, Herd K, Laskaris T and Mantone A 1996 Adv. Cryogenic Eng. 42 855–61 [28] Sobha A, Aloysius RP ...

... U Syamaprasad, RP Aloysius, A Sobha, P Guruswamy and KGK Warrier ... et al (Pittsburgh, PA: The Minerals, Metals and Materials Society) [7] Riley GN Jr, Parker DR, Christopherson CJ ... 3 195 [10] Perin A, Grass G, Daumling M, Hensel B, Walker E and Flukiger R 1993 Physica C ...

ABSTRACT (Bi, Pb)-2223/Ag sheathed tapes were prepared using precursor powders with different particle size distributions which were obtained by grinding the calcined powder for different durations. DTA results revealed that the reaction temperature of the precursor powder depends on the particle size and is at a minimum for the finest powder. Phase evolution studies, transport current measurement at 77 K with and without the application of an external field, microstuctural examination etc, were carried out in order to evaluate the relative performance of the tapes. The results showed that the particle size has significant effects on the reaction kinetics, ultimate phase fraction, microstructure and transport critical current density. For the tapes fabricated using coarser powder, the reaction kinetics were found to be slower and the microstructure contained smaller grains with many misalignments and voids. On the other hand use of extremely fine precursors yielded tapes with a large fraction of secondary phases due to the degradation of the crystallinity of the precursor and a consequent change in the reaction sequence. The tape prepared using a precursor with an average particle size of 3-4 µm showed the best results with respect to JC, high-TC phase fraction, microstructure and JC-B characteristics.

ABSTRACT The dependence of Ic on the bend strain and tensile stress characteristics of (Bi, Pb)-2223/Ag-Cu alloy sheathed tapes with varying Cu composition in the sheath has been studied in both mono- and multifilamentary configurations. The irreversible stain (εr) and the critical stress (σc) were found to improve as the level of Cu doping in the sheath increases. εr and σc were found to be about twice as large for the 9 at% Cu doped sample in both mono- and multifilamentary cases compared to the corresponding pure samples. The multifilamentary tapes were found to endure more strains and stresses due to their fine filament structure and low fill factor of the superconductor core. The degradation of Ic above σc was found to be rapid, while that for strains above εr was gradual, retaining a significant amount of Ic even after high values of applied strain.

A systematic study on the effect of Ag powder, Ag2O and AgNO3 (0–25 wt.% Ag) on the phase evolution in (Bi,Pb)–Sr–Ca–Cu–O (BPSCCO) system has shown that the kinetics of (Bi,Pb)-2223 formation depends strongly on the form of Ag additive. All the three additives, in general, accelerate the (Bi,Pb)-2223 formation with widely varying rates during the first 100–150 h of heat

ABSTRACT The influence of starting packing density (SPD) and tape width on the final core density and Jc of PIT processed (Bi,Pb)-2223/Ag tapes was studied. Twelve sets of tapes with varying SPD (2.3 to 3.3 g cm−3) and wire diameter prior to flat rolling (1 to 3 mm) were fabricated using silver tubes of OD 10.0 mm and ID 7.5 mm keeping the other parameters identical. The highly packed samples (SPD 3.3 g cm−3, i.e., powder fraction 40 wt.%) yielded punctured tapes with significantly low values of core density (84–89% of ϱth) and Jc (4.6–10.5 kA cm−2). SPD in the range 2.3–2.8 g cm−3 (i.e., powder fraction 27–33.5 wt.%) yielded good quality tapes with core density varying from 92.5–97% of ϱth and Jc from 8.1 to 18.7 kA cm−2 depending on their width. Best results were obtained for tapes with SPD around 2.8 g cm−3 and width around 4.2 mm corresponding to a wire diameter of 2 mm. Possible reasons for the observed variations of core density and Jc are explained.

This paper outlines preliminary results from a combined XRD, TEM and APFIM investigation of a rapidly solidified Al94V4Fe2 alloy that had been produced by melt spinning. The microstructure produced consists of a high volume fraction (≈50%) of 20 nm icosahedral particles in an f.c.c. matrix. Three-dimensional atom probe analysis shows that this second phase is enriched in iron and vanadium