Influence of Cr-doping on structural, magnetic and dielectric properties of M-type hexaferrites synthesized using microwave digestion technique

M-type hexaferrite SrCrxFe12-xO19 compounds doped with Cr (x=0, 1, 2, 3 and 4 at.%) were prepared by microwave digestion system. X-ray diffraction was used to study the structure and crystallization of the samples. The samples are found to have a hexagonal phase, SrFe12O19, as a main phase at 2Θ ≈ 33.144° and 35.618° for x = 0 and 1 respectively, and 32.451° and 34.295° for x ≥ 2. The Rietveld refined parameters such as the lattice parameters (a=b, c), direct and indirect cell volume, crystallite size and microstrain were investigated. TEM and SEM results showed that the samples have hexagonal shape and grain sizes range from 126 nm to 379 nm. Magnetization, M, as a function of the applied magnetic field, H, was obtained from the hysteresis loop. The coercive field, HC , saturation, Ms and remnant, Mr , magnetization and squareness ration, Mr/Ms , were extracted from the hysteresis loop results. These results revealed that HC is inversely proportional with the grains size of the samples but directly proportional with Cr-doping values candidating these compounds to be used in computer hard disk memories applications. M values are inversely proportional with Cr-doping values. The variation of conductivity, σ, impedance, Z, dielectric constant, ε, dielectric loss factor, tan δ and dissipation factor as functions of both AC frequency, F(Hz) and Cr-doping, x, were investigated. The maximum value of the dissipation factor was at x=2 which equals 8.05x109 m/F when F = 2x105 Hz. The impedance of the samples behaved as a capacitor reactance that makes our compounds candidate for many crucial dielectric applications.

Investigation of Heavy Metal Contamination in Fishes from Passur River near the Sundarbans Mangroves of Bangladesh

The study was conducted to investigate the heavy metal contamination in fishes and shrimps from the Passur River near the world famous Sundarban mangroves located in the southwestern part of Bangladesh, during the period from January to June 2013. The fish (Liza parse) and shrimp (Penaeus monodon) samples were collected from two stations as St-1 (Katakhali-1 km upper from port area- upstream) and St-2 (Amtola-1 km lower from port area- downstream) monthly for three months in January (winter), March (pre monsoon) and May (Monsoon). Before analysis, a bit of muscle, the whole liver and two gill arches from each fish and shrimp were removed. Samples of tissues from each fish and shrimp were removed, weighed and dried. A microwave digestion system was used to prepare the samples for analysis. After digestion residue diluted with 25 ml 2.5% HNO3. The water used was deionized and distilled. The metal analyses of samples (Cd, Cr, Cu, Pb and Zn) were carried out by using UNICAM-929 atomic absorption spectrophotometer (AAS) in SGS Bangladesh Limited, Dhaka-1205, Bangladesh. Among the heavy metals studied Cd, Cr, Cu, Pb and Zn were detected in fish and shrimp species were within acceptable limits by FAO standards. The results of this study indicated that a general absence of serious pollution in the Passur River is due to heavy metals; whereas the concentrations of elements found could mainly be attributed to geological sources. In this regard, to maintain the water and sediment qualities as well as the sound and safe aquatic life of the river need proper monitoring and management by the relevant authorities of the Government of Bangladesh.J. Environ. Sci. & Natural Resources, 10(1): 21-24 2017

BIOMONITORING OF AIR POLLUTION WITH ZINC IN CROATIA STUDIED BY MOSS SAMPLES AND ICP-AES

A b s t r a c t: Samples from different moss species were collected from 121 sampling sites evenly distributed over the territory of Croatia, during the summer and autumn of 2010. Moss samples were totally digested by using microwave digestion system and analysed by using atomic emission spectrometry with inductively coupled plasma (ICP-AES). Descriptive statistics were made from analyses of zinc in all moss samples. The content of Zn varies between 11.6 mg kg–1 and 77.1 mg kg–1. The median value of Zn content is 24.8 mg kg–1 which is similar to the median value obtained in investigation in 2005 (29.0 mg kg–1). Map of distribution of zinc shows the sites of the country with higher levels of this element. High contents of Zn were found in moss samples collected from the vicinity of Sisak, region of Podravina and Rijeka as a result of anthropogenic pollution. By the comparison of median value found in moss samples from neighboring and Balkan countries as well as Norway, it can be noted that the median for Zn in Croatia has the lowest value.

Hardwood pulping kinetics of bulk and residual phases

The kinetics of the bulk and residual delignification phases of Eucalyptus nitens, E. globulus, E. benthamii, acacia, maple, and loblolly pine were determined in an effort to improve the use of various hardwoods. Kinetic experiments were performed using a microwave digestion system for fast heating of the kraft liquor. Delignification rates were obtained for three different temperatures (150°C, 160°C, and 170°C) and correlated with the wood’s syringyl-to-guaiacyl ratio. A linear correlation between the kraft delignification rate and the syringyl-toguaiacyl ratio was found to exist.