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- Author or Editor: A. Hussain x
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Abstract
The present investigation has been revealed that homogeneous silver-tungsten (Ag–W) composite powders doped with cobalt as sinter aid can be produced by the two-stage reduction of co-precipitated tungstate. The sintering of the powders has been studied using dilatometry and the results showed that the critical level for activated sintering is of the order of 0.3 mass percent cobalt with respect to the tungsten content of the compact powder. This critical level is equivalent to approximately six to seven atomic layer coverage of the tungsten particles by cobalt. The levels of cobalt addition above the critical amount leads to the formation of cobalt tungsten (CoW3) intermetallic compound precipitates, which become trapped within the silver phase in the sintered composite material. Microstructural evaluation of sintered specimens has been carried out using optical and electron microscopy. Transmission electron microscopy results revealed the neck formation between adjacent tungsten particles along with the presence of silver around the tungsten particles. Energy dispersive X-ray (EDX) analysis also confirmed that amounts of cobalt was 0.3 mass percent, in the region containing the silver at the tungsten particle interface which agreed with the level of activated sintering.
Abstract
The use of locally available mineral clay for the removal of radionuclides from the low and intermediate level liquid waste has been studied. Adsorption behavior of this naturally available inorganic adsorbent is reported. The factors such as contact time, nature of the waste, pH and adsorption capacity have been considered. These optional physico-chemical conditions suggest an effective use of this locally available adsorbent for the decontamination of the liquid radioactive waste at Pakistan Institute of Nuclear Science and Technology (PINSTECH), Islamabad.
Studies of basic zirconium carbonate, oxalate, nitrate and sulphate using TG, DTA and DTG methods, combined with isothermal gaseous product analyses, IR spectroscopy and X-ray diffraction techniques, have shown that the ease of ligand removal from such salts follows the sequence: ‘loosely bound’ H2O>CO3 2−≈ C2O4 2−>NO3 −>OH− (or ‘ tightly bound’ H2O)>SO4 2−.
Abstract
Yttrium aluminum garnet (YAG) and neodymium-doped yttrium aluminum garnet (Nd-YAG) nano-crystalline powders were successfully grown using cost effective sol spray process without the addition of any chelating agent or organic templates. Thermal decomposition behavior was studied by thermogravimetry (TG) and differential thermal analysis (DTA). Results revealed that crystallization of YAG started around 920 °C. The shrinkage/expansion behavior of synthesized powder was examined by dilatometer and revealing that sintering kinetics of these materials can be related to the evaporation of binder and formation of crystalline phases. Nano-crystallinity and garnet structure of YAG and Nd-YAG specimens were analyzed by Raman, fourier transform infra red (FTIR), and X-ray diffraction (XRD) techniques. XRD patterns were indexed using Rietveld refinement method. Smaller lattice parameter and a small change in atomic position of oxygen were found in Nd-YAG when compared with YAG structure. Scanning electron microscope (SEM) results indicated that particle size of Nd-YAG was <150 nm. The morphology of Nd-YAG nanosized powder was rounded in shape.
Xanthones are well recognized as chemotaxonomic markers for the plants belonging to the genus Garcinia. Xanthones have many interesting pharmacological properties. Efficient extraction and rapid liquid chromatography methods are essentially required for qualitative and quantitative determination of xanthones in their natural sources. In the present investigation, fruit rinds extracts of 8 Garcinia species from India, were prepared with solvents of varying polarity. Identification and quantification of 3 xanthones, namely, α-mangostin, β-mangostin, and γ-mangostin in these extracts were carried out using a rapid and validated ultra-high-performance liquid chromatography–photodiode array detection (UHPLC–PDA) method at 254 nm. γ-Mangostin (3.97 ± 0.05 min) was first eluted, and it was followed by α-mangostin (4.68 ± 0.03 min) and β-mangostin (5.60 ± 0.04 min). The calibration curve for α-mangostin, β-mangostin, and γ- mangostin was linear in the concentration range 0.781–100 μg/mL. α-Mangostin was quantified in all 4 extracts of Garcinia mangostana. Its content (%) in hexane, chloroform, ethyl acetate, and methanol extracts of G. mangostana was 10.36 ± 0.10, 4.88 ± 0.01, 3.98 ± 0.004, and 0.044 ± 0.002, respectively. However, the content of α-mangostin was below the limit of detection or limit of quantification in the extracts of other Garcinia species. Similarly, β-mangostin was quantified only in hexane (1.17 ± 0.01%), chloroform (0.39 ± 0.07%), and ethyl acetate (0.28 ± 0.03%) extracts of G. mangostana. γ-Mangostin was quantified in all 4 extracts of G. mangostana. Its content (%) in hexane, chloroform, ethyl acetate, and methanol extracts of G. mangostana was 0.84 ± 0.01, 1.04 ± 0.01, 0.63 ± 0.04, and 0.15 ± 0.01, respectively. γ-Mangostin was also quantified in hexane (0.09 ± 0.01), chloroform (0.05 ± 0.01), and ethyl acetate (0.03 ± 0.01) extracts of G. cowa, ethyl acetate extract of G. cambogia (0.02 ± 0.01), G. indica (0.03 ± 0.01), and G. loniceroides (0.07 ± 0.01). Similarly, γ-mangostin was quantified in 3 extracts of G. morella, namely, hexane (0.03 ± 0.01), chloroform (0.04 ± 0.01), and methanol (0.03 ± 0.01). In the case of G. xanthochymus, γ-mangostin was quantified in chloroform (0.03 ± 0.001) extract only. α-Mangostin and β-mangostin were not detected in any of 4 extracts of G. pedunculata.
