Thermal Stability Range Research Articles

Contributions to the radiation chemistry of octasilsesquioxanes:: unique traps for atomic hydrogen and free radicals at ambient temperature

Evidence was given for trapping of H-atoms in fluid solutions of octasilsesquioxanes. Use was made of the positive effect of scavengers on the yield of trapped H-atoms. Carbon and silicon-centered radicals formed simultaneously through radiation chemical processes were detected. Most of the radical species were identified by the simulation of the corresponding ESR spectra. A wide range of thermal stability is covered by the radicals depending on the chemical nature of the substitutents of the cages and the precursors.

Formation of Bimetallic Pt-Rh Surface with Nanosize Metal Domains

An approach to produce a bimetallic Pt-Rh model catalyst has been developed. It includes vacuum deposition of platinum on a Rh2O3 film, followed by the oxide reduction with hydrogen. The thermal stability range of the resulting bimetallic structure has been determined.

The effect of molecular structure on the thermal properties of ferroelectric liquid crystalline cyclic siloxane tetramers

A series of liquid crystalline cyclic siloxane tetramers was prepared to investigate, in a systematic manner, the role of molecular structure of (a) the spacer group, (b) the mesogenic side group and (c) the chiral end group, on the liquid crystalline behaviour of these novel tetramers. The results from this systematic structure/property correlation study clearly showed the effects of the structure of the chiral end group and the mesogenic side group on the thermal stability and temperature range of the SmC* phase (ferroelectric) exhibited by these materials. For a given chiral end group, the effect of the length of the spacer group on the thermal stability and temperature range of the SmC* phases depended greatly on the structure of the mesogenic side group. By appropriate choice of spacer group, mesogenic side group and chiral end group, a number of tetramers exhibiting wide SmC* ranges (ferroelectricity) from below room temperature were synthesized.

Spin-stand characterization of thermal stability in high density disk media

An experimental technique has been developed to characterize the thermal stability of recording media. We measured the remanent magnetization decay in a significant range under various reverse fields in a short time scale. By directly fitting the experimental data with an Arrhenius-Neel type model, the effective energy barrier distribution has been estimated. Unlike other previously reported techniques, this new technique enables more accurate analysis of energy barrier distribution and reliable evaluation of long-term stability for media with a wide range of thermal stability.

Thermal and spectroscopic studies of polymorphic transitions of zirconia during calcination of sulfated and phosphated Zr(OH) 4 precursors of solid acid catalysts

Zirconia, ZrO 2, was synthesized by calcination of pure, sulfate-impregnated, and phosphate-impregnated Zr(OH) 4 at different temperatures in the range from 600 to 1100°C for 5 h. Weight variant and invariant processes involved were monitored by thermogravimetry, differential thermal analysis and differential scanning calorimetry. The bulk structure and phase composition of the zirconias thus produced were characterized by X-ray powder diffractometry, infrared absorption spectroscopy and Raman scattering spectroscopy. The results have been correlated, so as to reveal the influence of the sulfate and phosphate additives on the zirconia polymorphic transitions as a function of temperature. Accordingly, phosphate species have been revealed to stabilize or influence stabilization of cubic-structured zirconia at temperatures as low as 600–900°C, where it is otherwise unstable. IR- and LRa-observed formation of Zr 2P 2O 7 species (cubic-structured) is suggested to act as seed species for the stabilized cubic structure of zirconia. An analogous stabilizing influence was revealed for sulfate species, however, toward cubic and/or tetragonal zirconia, and functions within the thermal stability range of the sulfate (i.e. up to 720°C).

Present status and future avenues of source region discrimination and characterization using fission track analysis

Amongst the various dating methods available for use in sediment provenance studies there exists a wide range (∼60–900°C) of temperature stability fields that can be used to record different geological processes. The adoption of a particular geochronological method for use in the study of provenance requires selecting a technique and mineral phase that have a thermal stability range suited to the type of provenance information required. This paper describes the unique provenance applications of the low temperature (∼60–320°C) fission track (FT) method. Apatite fission track data can monitor changes in the thermal regime of the upper 3–5 km of crust and are therefore particularly sensitive to cycles of burial, tectonic and erosive denudation. Provenance applications include dating source, estimating source denudation rates, detecting changes in tectonic processes, constraining models of thermal evolution at the depositional site and reconstructing eroded sections. Future detrital apatite FT applications should concentrate on improving resolution of the temporal relationships between source evolution and sedimentation in adjacent basins. A small study from the Hebrides Basin, western Scotland is used to demonstrate the effectiveness of adopting such an approach. The range of applications for detrital zircon FT data is more restricted due primarily to difficulties interpreting a detrital zircon age because of possible metamorphic resetting. Common applications that avoid these uncertainties include dating source, determination of source denudation rates and constraining the age of biostratigraphically barren sediments. In the future, interpretative difficulties may be overcome by adopting a dual approach to zircon dating using both U–Pb and FT methods.

Gas chromatographic characteristics and application studies of the stationary phase of CH-B-15-C-5

In this paper, separations of organic compounds, such as, n-alkanes, alcohols, ethyl asters of C 1–C 8 carboxylic acid, halogen derivatives, position-isomers of the replacement aromatic hydrocarbon, optical isomers of ethyl lactate and isoamyl alcohol, etc. were studied using 4′-cholestenoxycarbonyl-benzo-15-crown-5 liquid crystal crown ether (CH-B-15-C-5) as stationary phase in gas-solid chromatography (GSC), general gas-liquid chromatography (GLC) and crown ether liquid crystal gas-liquid chromatography (CL-GLC). Also, the chromatographic characteristics, such as the chemical stability, thermal stability, selectivity, polarity and operating temperature range, of the CH-B-15-C-5 as stationary phase for GSC, GLC and CL-GLC systems were studied. The results showed that the polarity of this chromatographic column is mean-weak; the chemical and thermal stabilities and the selectivity are good and the operating temperature range is wide. The results of separations of organic compounds are satisfactory.

Effects of Temperature on Formation of Insolubles in Aviation Fuels

Ten aviation turbine fuels (five Jet-A fuels, three JP-5, one JP-8, and one JPTS) were stressed at 185 and 225°C in a single-pass heat exchanger. On the basis of several criteria applied at 185°C, these fuels cover a broad thermal-stability range from lesser-quality fuels to the most stable JPTS fuel. Three of these fuels contain significant concentrations of dissolved metal (copper, >30 ppb). The surface and bulk insolubles formed from each fuel have been quantified using surface-carbon burnoff of tubing sections and of in-line filters. The total insolubles measured at 185 and 225°C fall in the range 0.3–7.5 μg/mL, and 0.1–2 μg/mL, respectively. In general, the greater the quantity of insolubles formed at 185°C, the greater its reduction at 225°C. Possible explanations for this effect are offered, and implications relative to understanding surface fouling are discussed.

On X-Ray Diffraction and X-Ray Absorption Spectroscopy Characterization of Ball Milled Iron Copper Solid Solution

Present paper is mainly aimed at reporting on X-Ray Diffraction (XRD) and X-ray Absorption Spectroscopy (XAS) characterization of Fe/Cu metastable solid solution of different stoichiometries prepared by ball milling. Special attention is devoted to thermal stability and eventual short range ordering. The wide reciprocal solubility is confirmed with slight variation in the solubility gap which is related to the peculiar milling conditions. X-ray information and differential scanning calorimetry suggest an atomic level solubility. Near edge absorption measurements performed during heating process provide evidence of precursor segregation at grain boundaries for Fe80Cu20 composition. Such effect dominates over in-grain nucleation. Samples of lower Cu contents do not exhibit the same behavior.

Structural Disorder in Mechanosynthesized Zinc Ferrite

The character of the mechanically induced structural disorder and nature of the metastability of mechanosynthesized zinc ferrite are elucidated by investigation of its structure. Attention is concentrated on the explanation of an origin of mechanically induced changes in magnetic properties of the nanoscale mechanosynthesized ferrite. The range of thermal stability of mechanically induced metastable states is determined by studying the response of the metastable mechanosynthesized zinc ferrite to changes in temperature.

Positional Preferences of Ionizable Residues in Gly-X-YTriplets of the Collagen Triple-helix

Collagens contain a high amount of charged residues involved in triple-helix stability, fibril formation, and ligand binding. The contribution of charged residues to stability was analyzed utilizing a host-guest peptide system with a single Gly-X-Y triplet embedded within Ac(Gly-Pro-Hyp)3-Gly-X-Y-(Gly-Pro-Hyp)4-Gly-Gly-NH2. The ionizable residues Arg, Lys, Glu, and Asp were incorporated into the X position of Gly-X-Hyp; in the Y position of Gly-Pro-Y; or as pairs of oppositely charged residues occupying X and Y positions. The Gly-X-Hyp peptides had similar thermal stabilities, only marginally less stable than Gly-Pro-Hyp, whereas Gly-Pro-Y peptides showed a wide thermal stability range (Tm = 30-45 degrees C). The stability of peptides with oppositely charged residues in the X and Y positions appears to reflect simple additivity of the individual residues, except when X is occupied by a basic residue and Y = Asp. The side chains of Glu, Lys, and Arg have the potential to form hydrogen bonds with available peptide backbone carbonyl groups within the triple-helix, whereas the shorter Asp side chain does not. This may relate to the unique involvement of Asp residues in energetically favorable ion pair formation. These studies clarify the dependence of triple-helix stability on the identity, position, and ionization state of charged residues.

Thermal stability of thin CoSi 2 layers grown on amorphous silicon

The thermal stability of thin cobalt silicide layers grown on amorphous silicon deposited by chemical vapor deposition has been studied in the temperature range between 950 and 1100°C. The relation between the agglomeration process and the increase of the sheet resistance has been evidenced. The range of thermal stability of the silicide is reduced if the CVD amorphous silicon is previously implanted with Si ions. The occurrence of some epitaxial CoSi 2 grains in the case of CVD amorphous Si can account for this difference.

Low-threshold injection lasers based on vertically coupled quantum dots

We have fabricated and studied injection lasers based on vertically coupled quantum dots (VECODs). VECODs are self-organized during successive deposition of several sheets of (In,Ga)As quantum dots separated by thin GaAs spacers. VECODs are introduced in the active region of a GaAs-A1GaAs GRIN SCH lasers. Increasing the number of periods (N) in the VECOD leads to a remarkable decrease in threshold current density ( ~ 100 A/cm 2 at 300 K for N = 10). Lasing proceeds via the ground state of the quantum dots (QD) up to room temperature. Placing the QD array into an external AIGaAs--GaAs quantum well allows us to extend the range of thermal stability of threshold current density (To = 350 K) up to room temperature. Using (In,Ga)As-(A1,Ga)As VECODs in combination with high temperature growth of emitter and waveguide layers results in further reduction of threshold current density (60-80 A/cm 2, 300 K) and increase in internal quantum efficiency (70%). Room temperature continuous wave operation (light output 160 mW per mirror) and lasing via the states of QDs up to I = (6-7) Ith have been demonstrated.

Stabilization and induction of discotic mesophases by trifluoroacetic acid

It is shown that trifluoroacetic acid (TFA) can form 1 1 molar complexes with alkyloxy discotic compounds, thereby enhancing their mesomorphic properties. In particular, when hexaalkyloxytriphenylenes (THEn) (n being the number of carbons per side chain) are crystallized from, or mixed with, TFA, complexes are formed which exhibit the Dho(Colho) mesophase, as do the neat THEn's, but with a broader range of thermal stability and a higher degree of order. The mesophases of these complexes are completely miscible with those of the neat compounds. Likewise, 1 1 mixtures of hexa-alkyloxytribenzocyclononene (TBCEn) and TFA yield complexes showing enhanced mesomorphic properties for the mesogenic homologues of this series and induced mesomorphism for the lower homologues, which in the neat form are not mesogenic. The mesomorphic properties of these TFA complexes with THEn (n=3-6) and with TBCEn (n=4-6) are investigated by means of optical microscopy, differential scanning calorimetry, X-ray diffraction and NMR spectroscopy. It is suggested that the enhancement of the mesomorphic properties is due to formation of oxonium ion complexes.

A comparative study on the thermal decomposition of lanthanide biscitrato chromate(III) hydrates, Ln[CrC6(H5O7)2]·nH2O

The thermal decomposition of lanthanide biscitrato chromate (III) hydrates, [Ln(Cr(C6H5O7)2] nH2O whereLn=Pr, Nd, Dy and Ho have been carried out in static air and flowing argon atmospheres and thereby compared the decomposition nature with that of the lanthanum biscitrato chromate(III) dihydrate reported earlier. The precursor complexes decompose in four major steps. Stable oxycarbonates and chromates(V) have been isolated as intermediates. It has been found that for heavier lanthanide complexes all the decomposition steps are pushed to ‘higher temperature’ ranges. Moreover, the thermal stability range of chromates(V) is much lesser compared to that of LaCrO4. Based on the observed experimental results a general scheme for the decomposition of lanthanide biscitrato chromate(III) hydrates is proposed.

Quantum dot injection heterolaser with ultrahigh thermal stability of the threshold current up to 50 °C

Gaseous phase epitaxy from metal organic compounds is used to obtain a low-temperature injection laser with an active region based on In0.5Ga0.5As/GaAs quantum dots. Optimizing the growth conditions and geometric parameters of the structure has made it possible to increase the range of ultrahigh thermal stability in the threshold current (the characteristic temperature is T0=385 K) up to 50 °C.

Effect of nickel content on the formation and properties of amorphous Al100-xRE5Nix alloys

The thermal stability and formation range of amorphous Al(100-x)Ln(5)Ni(x) (x = 3, 5, 9, 13, 17, 21, 23) alloys were studied by differential scanning calorimetry and X-ray diffraction techniques. The microhardness, H-v, of these Al-RE-Ni alloys was measured. The experimental results show that toughness was adversely affected by increase in the nickel content. The atomic size factor was applied to explain the formation mechanism of aluminium-based amorphous alloys by the atomic clusters model. The minimum concentration of nickel in Al-RE-Ni alloys results from the effective atomic volume difference of the nickel and aluminium atoms.

Polarized electroluminescence of light emitting liquid crystalline polymers

Abstract Smectic liquid crystalline arylenevinylene main chain polymers were used in light emitting diodes (LEDs) to produce linearly polarized electroluminescence. The degree of orientational order induced by a rubbed polyimide layer amounted to S = 0.64, as extracted from the electroluminescence spectra. The great advantages of these LC polymers are their good thermal stability, processability and broad mesophase range, and the possibility of applying established orientation techniques in order to achieve a macroscopic orientation.

DTA study of rare earth doped ZBYA‐type fluoride glasses

AbstractIn the present study the effect of the rare earth elements Ho and Eu on the crystallization behavior of ZBYA‐type fluoride glasses was investigated by means of DTA. Stability criteria like thermal stability range, weighted thermal stability range, crystallization range and Saad and Poulain's criterion were calculated. Furthermore a kinetic analysis was carried out in terms of the Kissinger method and the apparent activation energy of crystallization was evaluated to characterize the crystallization trends as a function of type and concentration of dopants.

Influence of processing parameters on the scattering properties of fluorozirconate glasses prepared by the gas film levitation technique

Fluoride glasses for optical fibre applications were prepared using a containerless processing technique (the gas film levitation technique) to prevent the contamination of the glass melts by the crucible. Bulk glass samples of high optical quality were obtained by starting directly from a powder mixture of the different fluoride precursors. Differential scanning calorimetry, laser scanning tomography and light scattering measurements were used to measure the properties of the levitated glasses as compared to crucible-made glasses prepared in the same conditions. The bulk levitated glasses had an extended thermal stability range along with improved optical properties over the crucible-made glasses.