Band 115, Heft 8

The dependence between stimulated-emission cross-sections and polarizability volumes has been studied for laser transitions of Nd 3+ , Ho 3+ , Er 3+ , and Tm 3+ ions doped in dielectric crystals: complex oxides, simple and complex fluorides. The overall polarizability of each crystal containing Ln 3+ ions has been calculated by inclusion of the dopant polarizability in respective concentration. The applied method has revealed distinctly different positions of Nd 3+ ions in the mentioned dependence in a series of crystals, e.g. Y 3 Al 5 O 12 , YAlO 3 , LiYF 4 , compared to the other Ln 3+ ions doped in the same lattices.

This paper reports the photoluminescence studies of pure polycrystalline nano-sized gadolinium gallium garnet (Gd 3 Ga 5 O 12 , GGG) powders synthesized by the method of co-precipitation using ammonium hydrogen carbonate (NH 4 HCO 3 , AHC) as the precipitant. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared, ultraviolet, visible, near-infrared (UV–Vis–NIR) spectroscopy and photoluminescence studies. The X-ray diffraction analysis confirms the formation of cubic structure of gadolinium gallium garnet (Gd 3 Ga 5 O 12 ) . The average particle sizes are found to be in the range of approximately 19 nm–88 nm, for different calcining temperatures. The formation of gadolinium gallium garnet is also confirmed by Fourier transform infrared studies. Scanning electron microscopy image measurement confirms the formation of nanosized particles. The photoluminescence studies of the pure gadolinium gallium garnet sample shows emission peaks around at 441 nm for an excitation wavelength of 350 nm for the sample calcined at 1,100 °C.

In this research, a three-component composite was synthesized by using carbon nanotube as the background phase. Iron oxide phase with high magnetization and low coercivity (with particle size of 200 nm) has been coated on the carbon nanotubes. Then, the silver nanoparticles were coated on a conductive and magnetized substrate by an ultrasonic method. Semiconductor photocatalys is a favorable route for the degradation of organic pollutants. Ultraviolet–visible spectrophotometry has been used to investigate the photocatalytic properties of synthesized nanocomposite and control of their dye degradation on methyl blue, methyl orange and methyl red. The obtained nanocomposite is easily collected due to its magnetic property and does not pose a risk to environmental waters. The dye degradation degree has been compared for the produced nanocomposite. The experimental results confirmed that methyl red shows the greatest amount of degradation within 1 h, which was about 90 %, methyl orange shows about 80 %, and methyl blue shows the lowest degradation, around 60 %.

Antibiotic overuse has caused a variety of bacterial pathogens to develop new resistance mechanisms. As a result, discovering an appropriate replacement for the standard antibiotics has become an immediate concern. The present work demonstrates a facile, eco-friendly and economical method for the synthesis of hexagonal wurtzite zinc oxide nanoparticles (ω-ZONPs) using the ethanolic extract of triphala. Gas chromatography–mass spectrometry analysis of the triphala extract proved the presence of certain secondary metabolites, which aids in the formation of ω-ZONPs. The influence of annealing temperature on the antibacterial action of as-synthesized ω-ZONPs was studied for three different annealing temperatures. X-ray diffraction, dynamic light scattering, field emission electron microscopy and energy dispersive X-ray spectroscopy analyses were used to examine the impact of annealing temperature on the structure, particle size and morphology of ω-ZONPs. Fourier transform infrared spectra revealed the change in intensity of the characteristic peaks in ω-ZONPs with different annealing temperatures. From UV–Visible diffuse reflectance spectroscopy, variation in the band gap of ω-ZONPs with increasing annealing temperature was detected. Kirby Bauer disc diffusion was adopted to examine the antibacterial potential of ω-ZONPs against bacterial strains such as Staphylococcus aureus, Enterococcus faecium, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa . The ω-ZONPs annealed at 200 °C inhibited the growth of three bacterial pathogens, E. coli , B. subtilis and P. aeruginosa and exhibited effective antibacterial activity in comparison with ω-ZONPs annealed at relatively high temperatures. Thus, the antibacterial potential of ω-ZONPs could be further explored as disease controlling agents and such prototypes could be made available for commercial mass production.

We have examined the behavior of CoFe 2− x Al x O 4 ( x = 1.0 and 1.2) ferrite close to the transition from ferromagnetic to paramagnetic phases ( T C ). The findings indicate that at a temperature of T C = 314 K ( x = 1.0) and T C = 224 K ( x = 1.2), there is a second order magnetic phase transition. We used various methods, including modified Arrott plot, Kouvel–Fisher method, and critical isotherm analysis, to determine the critical exponents which were found to be similar to those expected for the Tricritical Mean-field model ( β = 0.288, γ = 1.057, and δ = 4.665) for the x = 1.0 sample. The critical exponents for the x = 1.2 sample ( β = 0.771, γ = 1.081, and δ = 2.403) belonged to a different universality class. These results suggest that the replacement of Fe ions with non-magnetic Al ions decreases the Co–Fe, Fe–Fe, Co–Co interaction sites in the CoFe 2 O 4 spinel ferrite, increasing magnetic disorder.

Wood ceramics using biomass materials as templates possess the benefits of facile fabrication and versatile applicability. To investigate the physical properties, chemical properties and microstructure of wood ceramics prepared from biomass materials, the basic properties and potential applications of wood ceramics were expounded. In this paper, wood powder wood ceramics (WPWC) and wood fiber wood ceramics (WFWC) were prepared through the vacuum carbonization method, utilizing pine powder and pine fiber as raw materials. The impact of phenolic resin concentration and mixture filling mass on various properties of wood ceramics, including mass loss rate (MLR), volume shrinkage rate (VSR), apparent porosity (AP), and bending strength (BS) were investigated on this basis. The microtopography and pore structure of wood ceramics were also analyzed. The test results show that an increase in the concentration of phenolic resin led to a decrease in the MLR, VSR, and AP of WPWC and WFWC, while their BS exhibited an increase. When the concentration of phenolic resin was 60 %, the phenolic resin yielded a BS of 8.70 MPa and 9.20 MPa for WPWC and WFWC, respectively. Furthermore, the microstructures of both WPFC and WFWC reveal hierarchical porous structures. The difference is that WPFC has a dispersed three-dimensional network topology in its overall morphology, which is mainly formed by filamentous or long linear glass carbon in wood ceramics dominated by carbon. The natural and consistent pore structure of WFWC is comparable to a three-dimensional honeycomb structure, the primary mesoporous size was around 40.28 nm and the main macropore size was more than 10,000 nm. It elucidates the pore structure of WPWC and WFWC, characterized by “hierarchical porosity”, the differences and relationships between porous wood ceramics derived from powdery and fibrous biomass as raw materials were analyzed, which contributes to the advancement of the fundamental principles of wood ceramics and establishes a theoretical basis for the practical exploration and development of biomass materials.

Wild silk varieties are less explored in the field of biomaterials than cultivated mulberry silk ( Bombyx Mori ). In the present work, an electrospun scaffold was produced from wild silk, muga ( Antheraea assamensis ), and it was assessed for the properties required for biomaterials. Scanning electron microscopy images showed that the electrospun fibers were formed without beads, and the majority of the fibers had diameters in the range of 500–900 nm. The scaffold started to decompose at 210 °C, which is higher than the temperature used for sterilization of the scaffold. The PBS uptake percentage was found to be 400 %, which is sufficient for the absorption of the medium used during cell culture. The scaffold had a hemolysis value of less than 5 %, which indicates that the scaffold exhibits good blood compatibility. The MTT assay showed cell viability of more than 80 % after 24 h and 48 h, and fluorescence microscopy showed that cells adhered and spread on the surface of the scaffold. The results show that muga silk electrospun mat can be used as an ideal biomaterial.

Site preference, structural stability and mechanical properties of Mg 2 Si doped by ternary elements were studied by first-principles calculation. Formation enthalpies show that light element impurity Al and rare earth elements Sc and Y tend to occupy the Mg site, while transition element Cu has a preference for the Si site. Shear modulus to bulk modulus ratio ( G / B ), Poisson’s ratio ν and Cauchy pressure show that the ductility of Mg 2 Si is improved for ternary element addition. The introduced parameter of ductility factor D indicates that the enhanced dislocation emission but suppressed micro-crack propagation is the key to enhancing ductility. Electronic structure indicates the brittleness is due to the strong covalent interaction between Mg-2p and Si-3p (Mg-3s and Si-3p/3s). While, with the incorporation of alloying elements, abundant electrons are injected into the matrix Mg 2 Si. Thereby, the covalent interaction is effectively suppressed and the ductility is improved.

The study investigates how Zr additions and process annealing affect mechanical and corrosion properties of AA5083 Al–Mg alloys by microstructural examination, tensile strength, hardness testing and ASTM G67 nitric acid mass loss test. In the present work, process annealing temperatures were set to 220 °C and 250 °C. The results show that the hardness and tensile properties of Zr-containing cold rolled alloy were superior to that of Zr-free cold rolled alloy before and after process annealing treatment and sensitization heat treatment. Unfortunately, adding Zr to AA5383 alloy significantly degraded the corrosion resistance of the Zr-containing cold rolled alloy annealed at 220 °C. For improving corrosion resistance of Zr-containing alloy, annealing temperature could be increased to 250 °C to avoid a marked drop in the corrosion resistance.

The micro-arc oxidation of TC4 titanium alloy was carried out by adding LuCl 3 . The effect of LuCl 3 addition on the properties of the micro-arc oxidized coatings, and the rate of weight loss by erosion under simulated oil field conditions, were analysed. The results show that the increase of oxidation voltage after the addition of LuCl 3 makes the surface structure of the coatings denser. The coating is mainly composed of Rutile TiO 2 , Anatase TiO 2 , and a small amount of Lu 2 O 3 phase. The kinetic potential polarization curves showed that the addition of LuCl 3 can increase the corrosion potential and decrease the corrosion current density of TC4 titanium alloy, and at the same time reduce the rate of erosion weight loss of micro-arc oxidized coatings under simulated oilfield conditions. The overall performance of the coatings is best when the concentration of LuCl 3 is 0.3 g L −1 .