High Performance ZnO Varistors Prepared From Nanocrystalline Precursors for Miniaturised Electronic Devices

An industrially viable solution-based processing route using minimal amounts of solvent has been used to prepare bulk quantity nanopowders (average particle size 15.3 nm) for the fabrication of ZnO varistors. The xerogels, calcined powders and sintered materials were fully characterised. The preparation of varistors from nanopowders has been optimised by studying the effect of temperature on grain growth, densification and breakdown voltage. The varistors are prepared by sintering at 1050 C for 2 hours, a temperature that is significantly lower than that used in the current industrial process. Highly dense varistor discs prepared from the sintered material produce devices, with a breakdown voltage 85% higher than that of commercial varistors, making them suitable for use in miniaturised electronic circuitry. Improved performance of these materials has been attributed to the small grain size and better dispersion of additives on ZnO grains

Self-assembled arrays of ZnO nanoparticles and their application as varistor materials

Linear arrays of ZnO nanoparticles have been successfully prepared by a simple sol–gel condensation reaction involving chemical modifiers, followed by drying (80oC) and calcination (500 oC). The calcined material (nanoarray ZnO) is composed of approximately spherical nanoparticles of average diameter 21+/-3 nm, selfassembled to form arrays extending in length to 2–4 mm. The morphology of the ZnO is found to depend sensitively on the amounts of chemical modifiers present. In their absence the ZnO produced (nano-ZnO) is an unstructured agglomerate of nanoparticles. The mechanism for formation of these linear arrays has been investigated by examining the intermediates formed at 80 oC and 250 oC using XRD and TEM and by following the decomposition reactions using TGA and DSC. Varistors prepared from the nano-array ZnO by sintering (1050 oC) with ppropriate mixtures of metal oxides showed a breakdown voltage of 786 +/- 30 Vmm-1, which is substantially higher than that of samples prepared under similar conditions from either micronsized commercial ZnO (507 +/-30 V mm-1) or from nano-ZnO (683 +/-30 V mm-1)

Self-assembled arrays of ZnO nanoparticles and their application as varistor materials

Linear arrays of ZnO nanoparticles have been successfully prepared by a simple sol–gel condensation reaction involving chemical modifiers, followed by drying (80oC) and calcination (500 oC). The calcined material (nanoarray ZnO) is composed of approximately spherical nanoparticles of average diameter 21+/-3 nm, selfassembled to form arrays extending in length to 2–4 mm. The morphology of the ZnO is found to depend sensitively on the amounts of chemical modifiers present. In their absence the ZnO produced (nano-ZnO) is an unstructured agglomerate of nanoparticles. The mechanism for formation of these linear arrays has been investigated by examining the intermediates formed at 80 oC and 250 oC using XRD and TEM and by following the decomposition reactions using TGA and DSC. Varistors prepared from the nano-array ZnO by sintering (1050 oC) with ppropriate mixtures of metal oxides showed a breakdown voltage of 786 +/- 30 Vmm-1, which is substantially higher than that of samples prepared under similar conditions from either micronsized commercial ZnO (507 +/-30 V mm-1) or from nano-ZnO (683 +/-30 V mm-1)

Pressure dependence of the chlorine NQR in three solid chloro anisoles

The 35Cl Nuclear Quadrupole Resonance (NQR) frequency (νQ) and spin lattice relaxation time (T1) in the three anisoles 2,3,4-trichloroanisole, 2,3,6-trichloroanisole and 3,5-dichloroanisole have been measured as a function of pressure upto 5.1 kbar at 300 K, and the data have been analysed to estimate the temperature coefficients of the NQR frequency at constant volume. All the three compounds show a non linear variation of the NQR frequency with pressure, the rate of which is positive and decreases with increasing pressure. In case of 3,5-dichloroanisole the value becomes negative in the higher range of pressure studied. The spin lattice relaxation time T1 in all the three compounds shows a weak dependence on pressure, indicating that the relaxation is mainly due to the torsional motions

An investigation of co-fired varistor-ferrite materials

The purpose of this work was to co-fire crack-free varistor-ferrite ceramic multilayers fabricated via a dry pressing route. Multilayers were sintered using a standard industrial grade varistor sintering regime. Sinter shrinkages of both varistor and ferrite materials were measured using dilatometry and showed that the varistor shrunk significantly more than the ferrite material. X-ray diffraction analysis indicated that no significant phase changes occurred in the materials under investigation as a result of the sintering process. Scanning electron microscopy observations of the dry-pressed co-fired varistor-ferrite revealed vertical cracking in the ferrite due to thermal expansion mismatch between the materials. By pressing a mixed composition interlayer in the ratio 50:50, between the varistor and ferrite materials, a crack-free multilayer structure could be obtained. Energy dispersive X-ray analysis of the co-fired ferrite and varistor confirmed diffusion of Fe and Ni components from the ferrite into the varistor material. The degree of diffusion was reduced by using 50:50 ratio mixed composition interlayers

Comparison and analysis of audible sound energy emissions during single point machining of HSTS with PVD TiCN cutter insert across full tool life

In precision engineering, tool wear affects the dimensional accuracy and surface finish of machined components. Currently, errors associated with tool wear remain uncompensated for and are usually only detected at the end of the machine cycle, by which time the product may be scrap. If real-time, accurate monitoring were available, machine parameters could be adjusted to compensate for tool wear thereby minimising waste. Experienced machinists in the corresponding author׳s organisation, a precision engineering CNC machining manufacturing organisation, have been able to detect a poorly performing cutting operation through the sound emitted from the machining centre during the various phases of the cutting cycle and, although not a precise science, appear capable of informally differentiating between a good process and a degraded one. In this article experimental work was undertaken on a single point machining operation whereby the sound energy emissions from the machine were logged and analysed for the full life of the tools. The experiments demonstrated consistent acoustic signatures, which are specific to the tool in a known good cutting state, and distinct, but also consistent sound energy signatures, in a known bad cutting state. The experimental measurements replicated the audible range of human hearing and sought to determine what encouraged experienced machinists to declare a machining process to be in a state of degradation. The experimentation was undertaken at Schivo Precision, Waterford, Ireland

In Silico Prediction of 3D Structure of Pectatelyase from Fusarium oxysporum f. sp. lycopersici

In Silico Prediction of 3D Structure of Pectatelyase from Fusarium oxysporum f. sp. lycopersic

Biochemical Changes during Plantlet Regeneration in Two Accessions of Mucuna pruriens

The genus Mucuna is an important medicinal herb and is extensively used in traditional Indian systems of medicine for various ailments. In vitro culture technique provides an alternative to plant propagation and germplasm conservation. Our aim was to study the biochemical changes occurring during regeneration of shoots (plantlets) from explants of two accessions of Mucuna pruriens, by monitoring the efficiency of nitrogen utilization and changes in levels of some hydrolytic enzymes. A rapid micropropagation system was developed using Murashige and Skoog's (MS) medium supplemented with BAP and IAA combined. In both the accessions, 3.0mg l-1 6-BAP, in combination with 0.2mg l-1 IAA, induced shoot buds and shoot elongation; however for multiple-shoot induction, a slightly higher concentration of cytokinin, i.e., 3.5mg l-16-BAP, in combination with 0.2mg l-1 IAA, was required. Results of the present study confirm an active growth of explants revealed by nitrate assimilation enzymes and hydrolytic enzymes. It is concluded that medium composition, growth regulator combination and culture incubation conditions are all vital in both the accessions of Mucuna pruriens for induction of in vitro plant regeneration