Phase transitions in lithium ammonium sulfate below room temperature: An ultrasonic study

A detailed ultrasonic study of the elastic properties of lithium ammonium sulfate ~LiNH4SO4! or LAS has been carried out below room temperature. The elastic constants of LAS at room temperature are reported. The discrepancy present in earlier elastic constant data associated with the different choice of axes for this orthorhombic system are clarified. The results of the temperature variation study down to 220 K confirm the ferroelastic phase transition at 285 K and establish a thermal hysteresis of about 2.5 K between the cooling and heating cycles. Results of the investigation on the suspected weak phase transition at 256 K suggest that this transition occurs at 242 K on cooling and at 256 K on heating, thus having a thermal hysteresis of about 14 K. However, since the observed elastic anomaly for this transition is very small, the nature of this transition still remains unclear

Near fifty percent sodium substituted lanthanum manganites—A potential magnetic refrigerant for room temperature applications

Nearly half of lanthanum sites in lanthanum manganites were substituted with monovalent ion-sodium and the compound possessed distorted orthorhombic structure. Ferromagnetic ordering at 300K and the magnetic isotherms at different temperature ranges were analyzed for estimating magnetic entropy variation. Magnetic entropy change of 1.5 J kg 1 K 1 was observed near 300 K. An appreciable magnetocaloric effect was also observed for a wide range of temperatures near 300K for small magnetic field variation. Heat capacity was measured for temperatures lower than 300K and the adiabatic temperature change increases with increase in temperature with a maximum of 0.62K at 280 K

Mn2þ-induced room-temperature ferromagnetism and spin-glass behavior in hydrothermally grown Mn-doped ZnO nanorods

The magnetic properties of Mn-doped ZnO (ZnO:Mn) nanorods grown by hydrothermal process at a temperature of 200 8C and a growth time of 3 h have been studied. The samples were characterized by using powder X-ray diffraction with Rietveld refinement, scanning electron microscopy, energy-dispersive X-ray analysis and SQUID magnetometry. Mn (3 wt%) and (5 wt%)-doped ZnO samples exhibit paramagnetic and ferromagnetic behavior, respectively, at room temperature. The spin-glass behavior is observed from the samples with respect to the decrease of temperature. At 10 K, both samples exhibit a hysteresis loop with relatively low coercivity. The room-temperature ferromagnetism in 5 wt% Mn-doped ZnO nanorods is attributed to the increase in the specific area of grain boundaries, interaction between dopant Mn2þ ions substituted at Zn2þ site and the interaction between Mn2þ ions and Zn2þ ions from the ZnO host lattice

Effect of Substrate Temperature on the Structural and Luminescent Characteristics of RF-Magnetron-Sputtered ZnGa2O4:Dy3+ Thin Films

ZnGa2O4:Dy3+ phosphor thin films were deposited on quartz substrates by radio frequency rf magnetron sputtering and the effect of substrate temperature on its structural and luminescent properties was investigated. Polycrystalline film could be deposited even at room temperature. The crystalline behavior, Zn/Ga ratio, and surface morphology of the films were found to be highly sensitive to substrate temperature. Under UV illumination, the as-deposited films at and above 300°C gave white luminescence even without any postdeposition treatments. The photoluminescent PL emission can be attributed to the combined effect of multicolor emissions from the single luminescence center Dy3+ via host-sensitization. Maximum PL emission intensity was observed for the film deposited at 600°C, and the CIE chromaticity coordinates of the emission were determined to be x,y = 0.34, 0.31 .

Xanthate Accelerators for Low Temperature Curing of Natural Rubber

ABSTRACT: Zinc salts of ethyl, isopropyl, and butyl xanthates were prepared in the laboratory. They were purified by reprecipitation and were characterized by IR, NMR, and thermogravimetric analysis techniques. The melting points were also determined. The rubber compounds with different xanthate accelerators were cured at temperatures from 30 to 150°C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density, elongation at break, and modulus at 300% elongation were evaluated. The properties showed that all three xanthate accelerators are effective for room temperature curing.

New accelerator system for low temperature curing of elastomers with special reference to NR, NBR and NR/BR blends

The primary objective of this work is to develop an efficient accelerator system for low temperature vulcanization of rubbers. Although xanthates are known to act as accelerators for low temperature vulcanization, a systematic study on the mechanism of vulcanization, the mechanical properties of the vulcanizates at varying temperatures of vulcanization, cure characteristics etc are not reported. Further. xanthate based curing systems are not commonly used because of their chance for premature vulcanization during processing. The proposed study is to develop a novel accelerator system for the low temperature vulcanization of rubbers having enough processing safely. lt is also proposed to develop a method for the prevulcanisation of natural rubber latex at room temperature. As already mentioned the manufacture of rubber products at low temperature will improve its quality and appearance. Also, energy consumption can be reduced by low temperature vulcanization. in addition, low temperature vulcanization will be extremely useful in the area of repair of defective products, since subjecting finished products to high temperatures during the process of repair will adversely affect the quality of the product. Further. room temperature curing accelerator systems will find extensive applications in surface coating industries.

Studies On Preparation And Characterization Of Hts Current Leads Using Multifilamentary Ag And Ag-Alloy Sheathed (Bi,Pb)-2223 Superconducting Tapes

The application vistas of superconductors have widened very much since the discovery of high TC superconductors (HTS) as many of the applications can be realised at 77 K rather than going down to 4.2 K, the liquid He temperature. One such application is the HTS current lead which is used to connect a superconducting system with a room temperature power source. Minimising heat leak to the cryogenic environment is the main advantage of introducing current leads into superconducting systems. The properties of HTSS likes zero resistance (avoiding joule heating) and very low thermal conductivity (minimized conductive heat transfer) make them ideal candidates to be used as current leads. There are two forms of HTS current leads. (i) bulk form (tube or rod) prepared either from YBCO or BSCCO and (ii) tape form prepared from Bi-2223 multifilamentary tapes. The tape form of current leads has many advantages with respect to the mechanical and thermal stability related criteria. Crucial information on various aspects of HTS current lead development are not available in the literature as those are kept proprietary by various companies around the world. The present work has been undertaken to tailor the properties of multifilamentary tapes for the current lead application and to optimise the processing parameters of the same for enhanced critical current density and field tolerance. Also it is the aim of the present investigation is to prepare prototype current leads engineered for operation in conduction cooled mode and test them for operational stability

Temperature dependent polarized Raman spectra of nonaaqualanthanoid (Pr) single crystal

Polarized Raman spectral changes with respect to temperature were investigated for Pr(BrO3)3·9H2O single crystals. FTIR spectra of hydrated and deuterated analogues were also recorded and analysed. Temperature dependent Raman spectral variation have been explained with the help of the thermograms recorded for the crystal. Factor group analysis could propose the appearance ofBrO3 ions at sites corresponding to C3v (4) and D3h (2). Analysis of the vibrational bands at room temperature confirms a distorted C3v symmetry for the BrO3 ion in the crystal. From the vibrations of water molecules, hydrogen bonds of varying strengths have also been identified in the crystal. The appearance υ1 mode of BrO3− anion at lower wavenumber region is attributed to the attachment of hydrogen atoms to the BrO3− anion. At high temperatures, structural rearrangement is taking place for bothH2Omolecule and BrO3 ions leading to the loss ofwater molecules and structural reorientation of bromate ions causing phase transition of the crystal at the temperature of 447 K.