Thermal expansion of irradiated nylon-6 from 10 K to 340 K

Thermal expansion of irradiated nylon-6 has been studied in the temperature range 10 to 340 K using a three-terminal capacitance bridge technique. Irradiation is carried out using cobalt-60 gamma-rays up to 500 Mrad dosage. Radiation enhances chain scission over crosslinking. alpha increases from 0 to 250 Mrad between 10 to 340 K and not much variation is observed between 250 to 500 Mrad for samples from 10 to 250 K.

Thermal expansion of irradiated polyvinyl chloride from 10 K to 340 K

The coefficient of thermal expansion is measured for irradiated Polyvinyl Chloride (PVC) from 10K to 340K. The samples of PVC are irradiated, up to 500 Mrad in steps of 100 Mrad, in air at room temperature by using Co gamma rays with a dose rate of 0.3 Mrad/h. The PVC is an amorphous sample which is confirmed by X-ray diffraction. The coefficient of thermal expansion is found to decrease with radiation dose from 10K to 110K and it increaseswith radiation dose from 110K to 340K. The results are explained on the basis of radiation induced degradation of the sample.

Thermal expansion studies of substituted CTP derivatives

Several new Na, Y and Zr substituted derivatives of Ca-0.5 Ti-2(PO4)(3) (CTP) have been synthesized. These derivatives retain the hexagonal structure of the parent (CTP) compound with minor changes in lattice parameters. Linear thermal expansion coefficients (alpha) have been obtained using a high sensitivity dilatometer.

Thermal expansion of LaBa2Cu2CoO7+delta

In this paper, we report high-temperature X-ray diffraction (HTXRD) and dilatometric studies on LaBa2Cu2CoO7+delta. Bulk and volume thermal expansion studies, along with a study of its phase transition, were carried out. The linear and volume thermal expansion coefficients were found to be 11.7 X 10(-6) K-1 and 42.3 X 10(-6) K-1, respectively. (C) 2000 Elsevier Science Ltd.

Crystal structure, thermal expansion and electrical conductivity of Nd0.7Sr0.3Fe1-xCoxO3 (0 <= x <= 0.8)

The crystal structure, thermal expansion and electrical conductivity of the solid solution Nd0.7Sr0.3Fe1-xCoxO3 for 0 less than or equal to x less than or equal to 0.8 were investigated. All compositions had the GdFeO3-type orthorhombic perovskite structure. The lattice parameters were determined at room temperature by X-ray powder diffraction (XRPD). The pseudo-cubic lattice constant decreased continuously with x. The average linear thermal expansion coefficient (TEC) in the temperature range from 573 to 973 K was found to increase with x. The thermal expansion curves for all values of x displayed rapid increase in slope at high temperatures. The electrical conductivity increased with x for the entire temperature range of measurement. The calculated activation energy values indicate that electrical conduction takes place primarily by the small polaron hopping mechanism. The charge compensation for the divalent ion on the A-site is provided by the formation of Fe4+ ions on the B-site (in preference to Co4+ ions) and vacancies on the oxygen sublattice for low values of x. The large increase in the conductivity with x in the range from 0.6 to 0.8 is attributed to the substitution of Fe4+ ions by Co4+ ions. The Fe site has a lower small polaron site energy than Co and hence behaves like a carrier trap, thereby drastically reducing the conductivity. The non-linear behaviour in the dependence of log sigmaT with reciprocal temperature can be attributed to the generation of additional charge carriers with increasing temperature by the charge disproportionation of Co3+ ions. (C) 2002 Elsevier Science B.V. All rights reserved.

Synthesis, Structure, Negative Thermal Expansion, and Photocatalytic Property of Mo Doped ZrV(2)O(7)

A new series of compounds identified in the phase diagram of ZrO(2)-V(2)O(8)-MoO(3) have been synthesized via the solution combustion method. Single crystals of one of the compounds in the series, ZrV(1.50)Mo(0.50)O(7.25), were grown by the melt-cool technique from the starting materials with double the MoO(3) quantity. The room temperature average crystal structure of the grown crystals was solved using the single crystal X-ray diffraction technique. The crystals belong to the cubic crystal system, space group Pa (3) over bar (No. 205) with a = 8.8969 (4) angstrom, V = 704.24 (6) angstrom(3), and Z = 4. The final R(1) value of 0.0213 was achieved for 288 independent reflections during the structure refinement. The Zr(4+) occupies the special position (4a) whereas V(5+) and Mo(6+) occupy two unique (8c) Wyckoff positions. Two fully occupied O atoms, (24d) and (4b), one partially occupied 0 atom (8c) have been identified for this molybdovanadate, which is a unique feature for these crystals. The structure is related to both ZrV(2)O(7) and cubic ZrMo(2)O(8). The temperature dependent single crystal studies show negative thermal expansion above 370 K. The compounds have been characterized by powder X-ray diffraction, solid-state UV-vis diffuse reflectance spectra, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic activity of these compounds has been investigated for the degradation of various dyes, and these compounds show specificity toward the degradation of non-azoic dyes.

Crystal Structure, Thermal Expansion and ElectricaH Conductivity of Yo.sCao.2Fel-x Mnx03+o (0 < x < 1.0)

The crystal structure, thennal expansion and electrical conductivity of the solid solutions YOgCao.2Fel-x MnxOJ+c5 (0 ~ x ~ 1.0) were investigated. All compositions had the GdFeOrtype orthorhombic perovskite structure with trace amounts of a second phase present in case of x = 0.8 and 1.0. The lattice parameters were detennined at room tempe'rature by using X-ray powder diffraction (XRPD). The pseudocubic lattice constant decreased with increasing x. The average I inear thermal expansion coefficient (anv) in the temperature range from 673 to 973 K showed negligible change with x up to x = 0.4. The thennal expansion curve for x = I had a slope approaching zero in the temperature range from 648 to 948 K. The calculated activation energy values for electrical conduction indicate that conduction occurs primarily by the small polaron hopping mechanism. The drastic drop in electrical conductivity for a small addition of Mn (0 ~ x ~ 0.2) is caused by the preferential fonnation of Mn4t ion~ (rather than Fe4 +) which act as carrier traps. This continues till the charge compensation for the divalent ions on the A-site is complete. The results indicate that with further increase in manganese content (beyond x =0.4) in the solid solutions, there is an increase in exc :::ss oxygen and consequently, a small increase in Mn'll il>I1~, which are charge compensated by the formation of cation vancancies.

Thermal diffusivity measurements on ternary Ge-Te-Tl glasses using Photo-thermal Deflection method: Effect of thallium addition

Photo-thermal Deflection (PTD) technique is used to investigate the thermal diffusivity (alpha) of Ge17Te83 - xTlx (0 <= x <= 13) glasses as a function of composition. The thermal diffusivity of these glasses is found to lie in the range 0.020 to 0.048 cm(2)/s, which is consistent with the memory type of electrical switching exhibited by these samples. Further, it is found that alpha shows an initial increase with Tl addition, followed by a decrease. The observed composition dependence of thermal diffusivity has been understood on the basis that the thallium atoms are incorporated as a covalent species for lower values of x, increasing the network rigidity; however, they enter as ionic species for higher x values, fragmenting the network. The initial increase in a is due to the increasing network rigidity and the subsequent decrease is because of the fragmentation of the network. Also, there is a strong correlation between the composition dependence of switching voltages observed earlier and the variation with composition of electrical resistivity and thermal diffusivity of Ge17Te83 - xTlx glasses obtained in the present study. (C) 2012 Elsevier B.V. All rights reserved.

Synthesis, microstructure and thermal expansion studies on Ca0 center dot 5+x/2Sr0 center dot 5+x/2Zr4P6-2x Si-2x O-24 system prepared by co-precipitation method

We report on the synthesis, microstructure and thermal expansion studies on Ca0 center dot 5 + x/2Sr0 center dot 5 + x/2Zr4P6 -aEuro parts per thousand 2x Si-2x O-24 (x = 0 center dot 00 to 1 center dot 00) system which belongs to NZP family of low thermal expansion ceramics. The ceramics synthesized by co-precipitation method at lower calcination and the sintering temperatures were in pure NZP phase up to x = 0 center dot 37. For x a parts per thousand yen 0 center dot 5, in addition to NZP phase, ZrSiO4 and Ca2P2O7 form as secondary phases after sintering. The bulk thermal expansion behaviour of the members of this system was studied from 30 to 850 A degrees C. The thermal expansion coefficient increases from a negative value to a positive value with the silicon substitution in place of phosphorous and a near zero thermal expansion was observed at x = 0 center dot 75. The amount of hysteresis between heating and cooling curves increases progressively from x = 0 center dot 00 to 0 center dot 37 and then decreases for x > 0 center dot 37. The results were analysed on the basis of formation of the silicon based glassy phase and increase in thermal expansion anisotropy with silicon substitution.

Temperature variation of the grüneisen parameter in magnesium oxide

The thermal expansion of magnesium oxide has been measured below room temperature from 140°K to 284.5°K, using an interferometric method. The accuracy of measurement is better than 3% in the temperature range studied. The agreement of these results with Durand's is quite good, but consistently higher over most of the range by 2 or 3%, for the most part within the estimated experimental error. The Grüneisen parameter remains constant at about 1.51 over the present experimental range; but an isolated measurement of Durand at 85°K suggests that at lower temperatures it rises quite sharply above this value. This possibility is therefore investigated theoretically. With a non-central force model to represent MgO, γ(−3) and γ(2) are calculated and it is found that γ(−3) > γ(2), again suggesting that the Grüneisen parameter increases with falling temperature. Of the two reported experimental values for the infra-red absorption frequency, correlation with the heat capacity strongly indicates a wavelength of 25.26μm rather than 17.3μm. Thermal expansion measurements at still lower temperatures must be carried out to confirm definitely the rise in the Grüneisen parameter.

Structural, thermal, and electrical properties of CrSi2

Stoichiometric CrSi2 was prepared by arc melting and compacted by uniaxial hot pressing for property measurements. The crystal structure of CrSi2 was investigated using the powder x-ray diffraction method. From the Rietveld refinement, the lattice parameters were found to be a = 4.427 57 (7) and c = 6.368 04 (11) Å, respectively. The thermal expansion measurement revealed an anisotropic expansion in the temperature range from room temperature 800 K with αa = 14.58×10−6/K, αc = 7.51×10−6/K, and αV = 12.05×10−6/K. The volumetric thermal expansion coefficient shows an anomalous decrease in the temperature range of 450–600 K. The measured electrical resistivity ρ and thermoelectric power S have similar trends with a maxima around 550 K. Thermal conductivity measurements show a monotonic decrease with increasing temperature from a room temperature value of 10 W m−1 K−1. The ZT values increase with temperature and have a maximum value of 0.18 in the temperature range studied. An analysis of the electronic band structure is provided.

Anomalous thermal dynamics of Bragg gratings inscribed in germanosilicate optical fiber

An interesting, periodic appearance of a new peak has been observed in the reflected spectrum of a Fiber Bragg Grating (FBG) inscribed in a germanosilicate fiber during thermal treatment. The new peak occurs on the longer wavelength side of the spectrum during heating and on the shorter wavelength side during cooling, following an identical reverse dynamics. Comparison with a commercial grating with 99.9% reflectivity shows a similar decay dynamics. It is proposed that the distortion due to simultaneous erasure and thermal expansion of the index modulation profile may be responsible for the observed anomaly. The reported results help us in understanding the thermal behavior of FBGs and provide additional insights into the mechanisms responsible for the photosensitivity in germanosilicate fibers.

Thermal properties of MOSi2 with minor aluminum substitutions

Mo(Si1-xAlx)(2) compositions (x = 0-0.1) have been prepared by a modified SHS route under uniaxial hydrostatic pressure. Oxidation studies carried out by thermal analysis and sheet resistivity indicate an improvement in the low temperature (700-900 K) oxidation resistance with increasing aluminum addition. Dilatometric results show a decrease in the a value up to x = 0.05 substitution. With the aluminum substitution, both thermal expansion coefficient and thermal conductivity show decrease in their values except in the biphasic region. The x = 0.05 composition containing both C11(b) and C40 phases is a promising material for high temperature thermal barrier coating as it shows higher oxidation resistance and a similar K/alpha value as compared to pure MoSi, (c) 2006 Elsevier Ltd. All rights reserved.