Bulletin of Materials Science

The aim of this paper is to study the influence of curing time on the microstructure and mechanical strength development of alkali activated binders based on vitreous calcium aluminosilicate (VCAS). Mechanical strength of alkali activated mortars cured at 65 °C was assessed for different curing times (4–168 h) using 10 molal NaOH solution as alkaline activator. Compressive strength values around 77 MPa after three days of curing at 65 °C were obtained. 1·68 MPa/h compressive strength gain rate was observed in the first 12 h, decreasing to 0·95 MPa/h for the period of 12–72 h. The progress of geopolymeric reaction was monitored by means of TGA and, electrical conductivity and pH measurements in an aqueous suspension. Significant decrease in pH and electrical conductivity were observed in the 4–72 h period, demonstrating the geopolymerization process. Furthermore, SEM images showed an important amount of (N, C)ASH gel and low porosity of the developed matrix.

Using the conventional phonon-exchange mechanism of superconductivity we have succeeded in reproducing the transition temperatureT c of a large number of newly discovered highT c superconductors by introducing a certain modification to the well-known BCS-formula forT c .

Cu-doped forsterite Mg2−xCuxSiO4 (0.1 ≤ x ≤ 0.6) and Mn-doped forsterite Mg2−xMnxSiO4 (0.2 ≤ x ≤ 1) powders have been prepared by sol–gel method and characterized by XRD, SEM–EDS mapping, UV–Vis–NIR spectroscopy and CIE L*a*b* colour measurements to be explored as powdered ceramic pigments. The use of a sol–gel method based on silicic acid (H2Si2O5)aq and mineralizers (KCl and NaCl) along with a thermal treatment at 1200°C for 3 h, led to the formation of highly pure materials. The presence of Cu and Mn ions in the M1 and M2 sites was the main origin of the pigments colour. The latter was mostly affected by the chromophore’s valence state and concentration, and some formed minor phases. Besides that, the pigments with low doping levels showed very nice and attractive blue (Cu) and purple (Mn), making them interesting less toxic and less expensive ceramic pigment candidates.

The purpose of this paper is to evaluate the radiation resistance of gamma irradiated ethylene propylene diene monomer (EPDM) and to identify the pattern discriminating abilities of the surface tracking patterns. Simple objects can be described by the ideal shape primitives such as cubes, cones and cylinders. But most of the natural objects are so complex that cannot be described in terms of simple primitives. Fractals have been very successfully used to address the problem of modeling and to provide a description of naturally occurring phenomena and shapes, wherein conventional and existing mathematical models were found to be inadequate. The geometrical patterns of dielectric breakdown like electrical trees, surface discharges, and lightning are known to be of fractal in nature. These fractal patterns can be analysed numerically using fractal dimensions and lacunarity. Surface tracking occurring in HV insulation systems is a very complex phenomenon and more so are the shapes of tracking patterns. It has been fairly well established that the shapes and the underlying parameters causing tracking have a 1 : 1 correspondence and therefore, methods to describe and quantify these patterns must be explored. This paper reports preliminary results of such a study wherein2-d tracking patterns of gamma irradiated ethylene propylene diene monomer were analysed and found to possess fairly reasonable pattern discriminating abilities. This approach appears promising and further research is essential before any long-term predictions can be made

The compositions of lead lanthanum zirconate titanate PLZT [Pb(Zr0.57Ti0.43)O3 + x at% of La, where x = 3, 5, 6, 10 and 12] have been synthesized using mixed oxide route. The temperature dependent electromechanical parameters have been determined using vector impedance spectroscopy (VIS). The charge constant d 31 and elastic compliance s 11 show a peak in all the samples at a temperature T mt much below the ferroelectric — paraelectric transition temperature, whereas the series resonance frequency f s shows a dip at these temperatures. The Poisson’s ratio σ E increases with temperature T showing a broad peak at a temperature higher than T mt . The voltage constant g 31 decreases and the planar coupling coefficient K p remains constant up to half of the T mt and then falls sharply with T. Half of the T mt can, therefore, be used for specifying the working temperature limit of the piezoceramics for the device applications.

A simple cost-effective wet synthesis route has been proposed for synthesis of Na2Ti6O13, which is an efficient anode material that can be used for 1–3 volt batteries. The material has been synthesized by sonochemical route, which offers two distinct features: (1) energy-savvy (green) synthesis by significantly lowering the final calcination temperature and duration, and (2) formation of uniform and nano-scale particles suitable for battery application. The sonochemical synthesis was carried out at 20 kHz–500 W by applying sonication for 30 min at 25°C, using precursors (NaOH:TiO2) in a molar ratio of 6:1 followed by calcination at 750°C for 1 h in air. This material showed excellent reversible electrochemical performance (up to 93% retention) and offers reversible capacity around 40 mAh g−1 acting to be 0.82 V anode for Na-ion battery.

SnO2 nanowires and nanobelts have been grown by the thermal evaporation of Sn powders. The growth of nanowires and nanobelts has been investigated at different temperatures (750–1000°C). The field emission scanning electron microscopic and transmission electron microscopic studies revealed the growth of nanowires and nano-belts at different growth temperatures. The growth mechanisms of the formation of the nanostructures have also been discussed. X-ray diffraction patterns showed that the nanowires and nanobelts are highly crystalline with tetragonal rutile phase. UV-visible absorption spectrum showed the bulk bandgap value (∼ 3–6 eV) of SnO2. Photoluminescence spectra demonstrated a Stokes-shifted emission in the wavelength range 558–588 nm. The Raman and Fourier transform infrared spectra revealed the formation of stoichiometric SnO2 at different growth temperatures.

Two coal samples collected from Makum coal field, Assam, India were studied by XRD and FT-IR techniques. The X-ray diffractogram shows the existence of some crystalline carbons in Assam coals as proven by the appearance of peaks. The radial distribution functional (RDF) method was applied for the determination of structural aspects of the coals. The study indicates that the coals are lignite in type and there is no evidence of graphite-like structures. The maximum in the G(r) plots of function of radial distribution of atoms (FRDA) relates to different distances between carbon atoms of aliphatic chains. The first significant maximum relates to the C-C bond (type C-CH=CH-C), the second maximum relates to the distance between carbon atoms of aliphatic chains that are located across one carbon atom. The curve intensity profiles obtained from FRDA show quite regular molecular packets for this coal. The coals were found to be lignite in nature. FT-IR study shows the presence of aliphatic carbon, C=O and C-O stretching associated with -OH and -NH stretching vibrations. Kaolinite and quartz were also found to be major minerals in Assam coals by FTIR spectroscopy. The difference in intensities of carbonyl groups of the coal samples is likely to relate with the rank.

Yttrium iron garnet thin films have been prepared by low pressure metallo-organic chemical vapour deposition method (MOCVD). Dipivaloyl methanates of yttrium and iron have been used as the precursors in the MOCVD growth of the garnet films. Post deposition O2 annealing at 900°C is required to form a garnet phase which also shows orthoferrite and component Y2O3 and α-Fe2O3 phases. We show that a partial H2 reduction treatment minimizes secondary phases and stabilizes the garnet phase. These treatments also enhance the magnetic properties considerably.