• Volume 26, Issue 4

June 2003,   pages  365-460

• Electrical properties of Ta2O5 films deposited on ZnO

High dielectric constant (high-𝑘) Ta2O5 films have been deposited on ZnO/𝑝-Si substrate by microwave plasma at 150°C. Structure and composition of the ZnO/𝑝-Si films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) for chemical composition. The electrical properties of the Ta2O5/ZnO/𝑝-Si metal insulator semiconductor (MIS) structures were studied using high frequency capacitance–voltage (𝐶–𝑉), conductance–voltage (𝐺–𝑉) and current–voltage (𝐼–𝑉) characteristics. Charged trapping properties have been studied by measuring the gate voltage shift due to trapped charge generation under Fowler–Nordheim (𝐹–𝑁) constant current stressing.

• Influence of N atomic percentages on cell attachment for CN$_x$ coatings

Carbon film is an excellent candidate for use as a biocompatible coating due to its excellent properties. However, considerable attention has just been focused on the biocompatibility of diamond-like carbon (DLC) in recent years. It is difficult to find reports on the investigations of the biocompatibility of CN$_x$ so far. It is well known that CN$_x$ has similar structural characteristics as that of DLC. Its excellent mechanical and tribological properties are comparable to that of DLC. In addition, it is probable that the presence of nitrogen leads to a positive effect on biocompatibility. So, this work focusses on cell attachment of CN$_x$ coating and the relation between nitrogen atomic percentage and cell attachment.

CN$_x$ coatings were prepared using magnetron sputtering under two N2 partial pressures for the evaluation of relation between nitrogen atomic percentage and cell attachment. Cell culture tests using human endothelial cells and mouse fibroblasts were performed. Both coatings resulted in no adverse effects on the cells in culture. Compared with CN$_x$ (𝑥 = 0.088), CN$_x$ (𝑥 = 0.149) film provided a better surface for normal cellular attachment, spreading and proliferation without apparent impairment of cell physiology. At the same time, the coatings exhibited excellent tribological and corrosion performance. XPS and AES analyses showed that higher nitrogen atomic percentage might lead to a positive effect on the cell attachment.

• Preparation and characterization of Eu3+ activated CaSiO3, (CaA)SiO3 [A = Ba or Sr] phosphors

Eu3+ activated CaSiO3, (Ca, Ba) SiO3 and (Ca, Sr) SiO3 have been prepared by sol–gel technique. Residual solvent and organic contents in the gel were removed by firing at 100°C for 3–4 h at 300 and 600°C for 2 h. Small exothermic shoulder around 850 to 875°C, as observed in DTA curve, corresponds to crystallization temperature of the doped calcium silicate. Influence of firing temperature on the luminescence of Eu3+ shows the maximum emission intensity in gel fired at 850°C. Photoluminescence emission peak is observed at 614 nm due to ${}^{5}D_{0} \rightarrow {}^{7}F_{2}$ transition of Eu3+ ion in (Ca, Ba) SiO3 and (Ca, Sr) SiO3 phosphors, when excited by 254 nm. The (Ca, Ba) SiO3 material is proposed as an efficient red phosphor.

• Photoconductivity and dielectric studies of potassium pentaborate crystal (KB5)

Single crystal of potassium pentaborate (KB5) has been grown by solution growth technique. FTIR and laser Raman measurements are carried out to make a qualitative analysis on KB5 crystal. Dielectric behaviour of the KB5 crystal has been studied in the microwave region using K-band microwave bench equipped with the Gunn Oscillator guided with rectangular wave-guide. To confirm the suitability of this crystal as electro optic device, its dielectric behaviour with the change of frequency has also been investigated. Photoconductivity studies were also carried out on this material. It was interesting to observe that the KB5 crystal exhibited negative photoconductivity.

• Band gap determination of Ni–Zn ferrites

Nanocomposites of Ni–Zn with copolymer matrix of aniline and formaldehyde in presence of varying concentrations of zinc ions have been studied at room temperature and normal pressure. The energy band gap of these materials are determined by reflection spectra in the wavelength range 400–850 nm by spectrophotometer at room temperature. From the analysis of reflection spectra, nanocomposites of copolymer of aniline and formaldehyde with Ni$_{1–x}$Zn$_x$Fe2O4 (𝑥 = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been found to have direct band gaps ranging from 1.50–1.66 eV.

• Dielectric, electrical and infrared studies of 𝛾-Fe2O3 prepared by combustion method

This paper reports the electrical and spectroscopic investigation of the gamma ferrite synthesized through combustion route. The electrical study and dielectric behaviour showed a typical ferrite nature for the samples. The $\gamma \rightarrow \alpha$ transition is observed from the electrical conductivity data. Infrared spectral study showed the transition of a typical ferrite. The effect of the presence of 𝛼-impurities in 𝛾-Fe2O3 is also explained here.

• Dielectric and piezoelectric properties of neodymium oxide doped lead zirconate titanate ceramics

The dielectric and electromechanical properties of lead zirconate titanate [Pb(Zr, Ti)O3] ceramic added with neodymium oxide have been systematically studied employing the vector impedance spectroscopic (VIS) technique. The specimens were prepared using the mixed oxide route by adding different mol% of Nd2O3 (0.1 to 7 mol%) in [Pb(Zr, Ti)O3] near morphotropic phase boundary. Piezoelectric equivalent circuit parameters 𝑅, 𝐿, $C_a$ in series and $C_b$ in parallel have been determined by simulating /Z/ and 𝛩 plots. Electromechanical coupling coefficients and strain constants for the radial modes show a peak at about 3 mol%, the dielectric constant peaks at about 1 mol% and voltage constants peak at about 0.75 mol% of Nd2O3.

• Development of hardened PVF : PMMA polyblend: effect of gamma and electron irradiation

Specimens of poly(vinyl formal) (PVF) : poly(methyl methacrylate) (PMMA) polyblends with different weight percentage ratios were subjected to gamma irradiation (1 to 50 Mrad) and electron irradiation (1 to 20 Mrad). The effect of irradiation on the strength of the blend specimens was studied by measuring the surface microhardness using a Vickers microhardness tester attached to a Carl Zeiss NU 2 Universal research microscope. Significant changes were observed in the Vickers microhardness number, $H_v$. The $H_v$ values of gamma irradiated specimens are found to be higher than the unirradiated specimens indicating an occurrence of radiational crosslinking. The maximum value of $H_v$ is obtained at the gamma radiation dose of 15 Mrad. In case of electron irradiation the radiational crosslinking is found to take place for the blend specimens having lower wt% content of PMMA (0 and 1 wt%) in PVF matrix. On the other hand degradation of polymeric system is observed for the blends having PMMA content more than 1 wt%. The maximum value of $H_v$ is obtained for all the blend specimens at the electron irradiation dose of 8 Mrad. The degree of crosslinking in polyblends due to gamma irradiation is found to be more than electron irradiation. The scissioning mechanism is found to predominate in the polyblend system in case of electron irradiation.

• Conductivity studies in SnO–NaPO3 glasses

Na+ ion conductivity has been studied in SnO.NaPO3 glasses, which have been prepared over a wide range of compositions using a microwave melting technique. D.c. activation barriers seem to reflect the structural changes in system. A.c. conductivity analysis has revealed that while the power law exponent, 𝑠, seem to bear correlation to the structural changes, the exponent 𝛽 of the stretched exponential function describing the dielectric relaxation is largely insensitive to the structure. Possible importance of the correlation of transport property to the variation of available non-bridging oxygen (NBO) atoms in the structure is discussed.

• Development of a fully injectable calcium phosphate cement for orthopedic and dental applications

A study on the development of a fully injectable calcium phosphate cement for orthopedic and dental applications is presented. The paper describes its characteristic properties including results of bio- compatibility studies.

A conventional two-component calcium phosphate cement formulation (having a powder part containing dry mixture of acidic and basic calcium phosphate particles and a liquid part containing phosphate solution) is modified with a biocompatible gelling agent, to induce flow properties and cohesion. The quantity of the gelling agent is optimized to get a viscous paste, which is smoothly injectable through an 18-gauge needle, with clinically relevant setting parameters.

The new formulation has a setting time of 20 min and a compressive strength of 11 MPa. The X-ray diffraction, Fourier transform infrared spectrometry, and energy dispersive electron microprobe analyses showed the phase to be hydroxyapatite, the basic bone mineral. Scanning electron microscopy revealed a porous structure with particle sizes of a few micrometers. The cement did not show any appreciable dimensional or thermal change during setting. The injectability is estimated by extruding through needle and the cohesive property is assessed by water contact method. The cement passed the in vitro biocompatibility screening (cytotoxicity and haemolysis) tests.

• Existence domains for invariant reactions in binary regular solution phase diagrams exhibiting two phases

The thermodynamic origin of various types of phase diagrams in simple binary systems exhibiting two phases (e.g. a liquid and a solid phase) has been examined using the regular solution model. The necessary conditions for the occurrence of each of these types are identified in terms of the appropriate intersections of the miscibility gap boundaries (in solid/liquid phases) and the liquidus/solidus/iso-𝐺 curves. Thus, the regions of occurrence of the different types of possible phase diagrams in the space of the regular solution interchange energy parameters (𝑊𝛼, 𝑊𝛽) are clearly delineated. This analysis makes it easier to make intelligent initial selections of model (energy) parameters for their optimization in the calculation of phase diagrams using thermodynamic models such as CALPHAD/CVM.

• Effect of Cl on the corrosive wear of AISI 321 stainless steel in H2SO4 solution

The effect of Cl on the corrosive wear behaviour of AISI 321 stainless steel in H2SO4 solution was studied via the corrosive wear rate, the load bearing capacity of passive film and the relationship between pitting and corrosive wear. There is a critical load at natural potential, below which the corrosive wear rate is slightly lowered by Cl, while above which is increased. At natural potential there are more pits at low load than that at a higher one in the wear tracks and the pits are also deeper. The load bearing capacity is lowered by Cl at passive region and then the corrosive wear rate increased.

• Effect of heat treatments on the hydrogen embrittlement susceptibility of API X-65 grade line-pipe steel

Delayed failure tests were carried out on hydrogen charged API X-65 grade line-pipe steel in as received (controlled rolled), normalized, and quenched and tempered conditions. The resistance to hydrogen embrittlement was found in the order of controlled rolled $\gt$ quenched and tempered $\gt$ normalized. The fracture mode in the hydrogen embrittled steel was ductile.

• Aging of a copper bearing HSLA-100 steel

Investigations were carried out on aging of a HSLA-100 steel after varying amounts of cold deformation. Mechanical properties (hardness, tensile properties and toughness) were measured and structural changes were studied using optical, TEM and SEM techniques. As a result of various treatments, the hardness and UTS could be significantly improved, but with drastic fall in ductility and impact strength, especially in peak aged conditions. The parameters affecting impact strength were examined and it was concluded that various microstructural features affected toughness through their influence on tensile properties. In this steel the impact strength could be improved by lowering the UTS and increasing the ductility (pct elongation). The improvement in hardness and UTS was attributed to formation of thick precipitate-dislocation tangles. The aging process caused a slow transformation of lath martensite into acicular ferrite due to occurrence of in situ recrystallization. The concentration of Cu in particles precipitating on aging was followed using EDAX technique.

• Thermogravimetry-evolved gas analysis–mass spectrometry system for materials research

Thermal analysis is a widely used analytical technique for materials research. However, thermal analysis with simultaneous evolved gas analysis describes the thermal event more precisely and completely. Among various gas analytical techniques, mass spectrometry has many advantages. Hence, an ultra high vacuum (UHV) compatible mass spectrometry based evolved gas analysis (EGA–MS) system has been developed. This system consists of a measurement chamber housing a mass spectrometer, spinning rotor gauge and vacuum gauges coupled to a high vacuum, high temperature reaction chamber. A commercial thermogravimetric analyser (TGA: TG + DTA) is interfaced to it. Additional mass flow based gas/vapour delivery system and calibration gas inlets have been added to make it a versatile TGA–EGA–MS facility. This system which gives complete information on weight change, heat change, nature and content of evolved gases is being used for

1. temperature programmed decomposition (TPD),

2. synthesis of nanocrystalline materials,

3. gas–solid interactions and

4. analysis of gas mixtures.

The TPD of various inorganic oxyanion solids are studied and reaction intermediates/products are analysed off-line. The dynamic operating conditions are found to yield nanocrystalline products in many cases. This paper essentially describes design features involved in coupling the existing EGA–MS system to TGA, associated fluid handling systems, the system calibration procedures and results on temperature programmed decomposition. In addition, synthesis of a few nanocrystalline oxides by vacuum thermal decomposition, gas analysis and potential use of this facility as controlled atmosphere exposure facility for studying gas–solid interactions are also described.

• Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• Editorial Note on Continuous Article Publication

Posted on July 25, 2019