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Open access

Ishu Sharma and Sruthi Sunder

Abstract

Glass forming ability of lone-pair semiconductors was analyzed for (x = 0, 2, 4, 6, 8, 10) system. Values of lone pair electrons L were calculated using average coordination number of valence electrons. These values were found to decrease, as the system was moving towards the rigid region. L > 3 values showed vitreous state. Deviation of the stoichiometry confirmed the chalcogen-rich region. A linear correlation was found between the mean bond energy and glass transition temperature. Chemical Bond Approach model was applied to calculate the cohesive energy of the system. A linear relationship was found to exist between the cohesive energy and the theoretical band gap, calculated using Shimakawa relation. A decrease in both parameters was explained on the basis of average stabilization energy and electronegativity of the system. The density values were found to increase and may account for higher refractive index of the system. Large Bohr radius of the Bi atom accounted for an increase in the polarizability. Other parameters viz. degree of covalency, packing density, compactness, molar volume, free volume percentage, excess volume and polaron radius were also calculated. An effort was made to correlate the effect of Bi addition to Ge12Se76 - xAs12Bixlone-pair semiconductor on the basis of the structure of the glassy matrix or the connectedness of the material.

Open access

A. Katunin

Abstract

Since self-heating effect may significantly intensify structural degradation, it is essential to investigate its criticality, i.e. the temperature value at which fatigue fracture is initiated. In this paper, a new and sensitive criticality indicator based on evaluation of evolution of surface temperature distribution was proposed and experimentally validated. It was shown that comparing to other measurement techniques the presented approach allows for precise evaluation of the critical value of the self-heating temperature. The properly determined critical value may be helpful both during design and operation of elements made of polymers and polymeric composite.

Open access

Shuiping Li, Qisheng Wu, Chun Zhang, Huajun Zhu, Changsen Zhang, Xin Wang and Cancan Kong

Abstract

LiNiO2 was prepared through two-step solid-state reaction by mechanochemical method and heat treatment, using LiOH (Li2CO3) and Ni(OH)2 as starting materials. The influence of grinding speed and time, heat treatment time, and starting materials on the structure of LiNiO2 was studied. The as-milled samples and products were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that uniform as-milled samples can be obtained at grinding speed of 580 rpm for 0.5 h, using LiOH and Ni(OH)2 as raw materials. Perfect crystal LiNiO2 has been prepared by calcining the as-milled samples at 700 °C for 15 h. Composite material powders consisting of Li2Ni8O10 and LiNiO2 have been obtained using Li2CO3 as lithium source.

Open access

P. T. Beyli, M. Doğan, Z. Gündüz, M. Alkan and Y. Turhan

Abstract

Boron oxide (B2O3)/Poly(acrylic acid) (PAA) nanocomposites were synthesized by solution intercalation method, and characterized by Fourier transform infrared spectroscopy (FTIR-ATR), transmission electron microscopy (TEM), X-ray diffraction and thermogravimetric analysis (DTA/TG). The effect of boron oxide amount on the thermal stability of nanocomposites was investigated. Moreover, the antimicrobial activities of them were also determined by the serial dilution method against E. coli and S. aureus. XRD analysis showed that boron oxide was homogenously dispersed in polymer matrix; FTIR-ATR that there was interaction between PAA and boron oxide; and TEM that boron oxide particles had spherical structure, and dispersed in nano size in polymer matrix; DTA/TG that the thermal stability of polymers increased with the adding of boron oxide into polymer matrix, and changed the decomposition mechanism of PAA. B2O3/PAA nanocomposites exhibited higher decomposition temperature. The decomposition mechanisms of PAA and its nanocomposites occurred through three decomposition steps; dehydration, decarboxylation and chain scission. B2O3/PAA nanocomposites showed greater antimicrobial activity with increasing B2O3 amount.

Open access

Izabela Stępińska, Elżbieta Czerwosz, Mirosław Kozłowski, Halina Wronka and Piotr Dłużewski

Abstract

Field emission from materials at high electric fields can be associated with unfavorable or even destructive effect on the surface of the investigated cathode. The impact of high voltage electric power supply causes locally very strong electric fields focusing on the cathode surface. It causes a number of phenomena, which can adversely affect the morphology and the structure of the cathode material. Such a phenomenon is, for example, peeling of an emissive layer from the substrate or its burnout. It results in tearing of the layer and a decrease or loss of its ability to electrons emission. The cold cathodes in a form of CNT films with various CNTs superficial distribution are obtained by physical vapor deposition followed by chemical vapor deposition. CNTs are catalyzed in pyrolytic process with xylene (CVD), by Ni in a form of nanograins (few nm in size) placed in carbonaceous matrix. These films are built of emissive CNTs - carbonaceous film deposited on different substrates. In this work, the morphology and topography of superficial changes resulting from external electric field in such films were investigated.

Open access

K. Pańcikiewicz

Abstract

Gas Tungsten Arc butt welded joints of tubes of 7CrMoVTiB10-10 made using bainitic-martensitic P 24-IG filler metal were found to be susceptible to root cracking. This was avoided by using the CMS-IG filler metal and austenitic EPRI P87 filler metal. Detailed coefficient of thermal expansion analysis for both filler metals was performed. Unfortunately, CMS-IG filler metal is characterized by a lower creep rupture strength than P 24-IG. For this reason, the joints were produced by the 141 method with using two filler metals: P 24- IG and EPRI P87. All the welded joints was characterized by the B quality level. Macrostructural, microstructural and hardness data for both welded joints are presented. The standard requirement, < 350 HV10, was marginally not met and was achieved through post weld heat treatment.

Open access

K. Selvarani, R. Mahalakshmi and B. Thanuja

Abstract

Co-crystals of L-phenylalanine hydrochloride (LPAHCl) were grown by slow evaporation technique in the presence of manganese sulphate and cadmium chloride. Crystallinity of the grown crystals was confirmed by single crystal X-ray diffraction. Optical transmission spectra showed very high transmittance in the entire visible region. The cut-off wavelength was observed at 250 nm for both the crystals. The optical band gap energy was found to be 4.37 eV and 4.31 eV for the grown co-crystals of LPAHCl with MnSO4 and CdCl2, respectively. The second harmonic generation of the grown crystals was confirmed by Kurtz and Perry powder SHG method and compared with KDP. The frequency dependent dielectric properties of the co-crystals were studied at different temperatures.

Open access

Y. Madhava Kumar, K. Bhyagyasree, N.O. Gopal and Ch. Ramu

Abstract

Pure and VO2+ doped methacrylic acid ethylacrylate (MAA:EA) copolymer films were prepared by using a solution casting method. Various techniques including X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, scanning electron microscopy and electron paramagnetic resonance were employed for characterization of the samples. XRD patterns showed some degree of crystallinity of the doped polymer films due to interaction of the MAA:EA copolymer with VO2+. FT-IR spectral studies of pure and VO2+ doped MAA:EA copolymer films displayed significant structural changes within the doped copolymer film indicating the complexation. The optical absorbance of the pure and VO2+ doped films were measured in the 200 nm to 800 nm wavelength range. The values of the absorption edge and indirect band gaps were calculated. The optical band gap decreased with the increase of mol% of VO2+. From the EPR spectra, the spin- Hamiltonian parameters (g and A) were evaluated. The values of the spin-Hamiltonian parameters confirmed that the vanadyl ions were present in MAA:EA copolymer films as VO2+ molecular ions in an octahedral site with a tetragonal compression (C4v). The morphology of the copolymer samples was examined by scanning electron microscopy. The enhanced crystalline nature of the doped copolymer was identified from SEM analysis.

Open access

H. Menasra, Z. Necira, K. Bounabe, M. Abba, A. Meklid and A. Boutarfaia

Abstract

Pb(1-x)Lax [(Zr0.6Ti0.4)(1-x)(Mn1/3Sb2/3)x]O3 ceramics with x = 0.02, 0.03, 0.04, and 0.05 were synthesized by using a conventional solid state reaction route. The influence of La, Mn, and Sb contents on phase structure, microstructure, and electric properties were investigated. The results of X-ray diffraction (XRD) show that the phase structure of the ceramics transforms from rhombohedral phase to tetragonal phase. However, the minority pyrochlore phase appears on the micrographs of XRD and SEM if the doping concentration is greater than 2 mol%. The grain size of the ceramics gradually increases (from 1.36 μm to 1.57 μm) with increasing doping. The dielectric properties of the ceramics have been measured as a function of temperature in the range of 20 °C to 430 °C at 1 kHz. The results indicate that the transition temperature and the maximum dielectric constant decrease with increasing PL-PMS content in the system. These results clearly show the significance of PL-PMS in controlling the dielectric behavior of the PL-PMS-PZT system.

Open access

D. Siva Kumar, K. Chandra Babu Naidu, M. Mohamed Rafi, K. Prem Nazeer, A. Ayisha Begam and G. Ramesh Kumar

Abstract

Superparamagnetic iron oxide nanoparticles (SPIONs) have been synthesized using co-precipitation method. Their microstructure and dielectric properties were studied. The sugar solutions like glucose, fructose and sucrose were used as stabilizers to control the size of the SPIONs. The crystal structure and grain size of the particles were determined by X-ray diffraction. The magnetic studies of the samples were carried out using the vibrating sample magnetometer and their surface morphology was studied by HRTEM, FE-SEM and zeta potential. The dielectric properties of glucose-SPIONs (GF), fructose-SPIONs (FF) and sucrose-SPIONs (SF) were investigated in the frequency range of 10 Hz to 5 MHz at selected temperatures. The FF showed a high dielectric constant of 62 at 1 MHz and the dielectric properties of SPIONs were found to have been significantly improved, especially in the low frequency regime according to the Maxwell-Wagner interfacial polarization. The AC conductivity measurements revealed that the electrical conduction depends on both frequency and temperature. Impedance analysis was carried out using Cole-Cole plot and the conduction mechanism of the studied compounds was explained. R and C values were further calculated using RC-circuit.