Influence Of Crystallization Temperature Research Articles

Titanium dioxide thin films for high temperature gas sensors

Titanium dioxide (TiO 2) thin film gas sensors were fabricated via the sol–gel method from a starting solution of titanium isopropoxide dissolved in methoxyethanol. Spin coating was used to deposit the sol on electroded aluminum oxide (Al 2O 3) substrates forming a film 1 μm thick. The influence of crystallization temperature and operating temperature on crystalline phase, grain size, electronic conduction activation energy, and gas sensing response toward carbon monoxide (CO) and methane (CH 4) was studied. Pure anatase phase was found with crystallization temperatures up to 800 °C, however, rutile began to form by 900 °C. Grain size increased with increasing calcination temperature. Activation energy was dependent on crystallite size and phase. Sensing response toward CO and CH 4 was dependent on both calcination and operating temperatures. Films crystallized at 650 °C and operated at 450 °C showed the best selectivity toward CO.

Optical bistability performance of laser-diode end-pumped Tm, Ho: YLF laser

The bistable output of a 792 nm laser-diode end pumped continuous wave Tm, Ho: YLF laser is reported for the first time. When the temperature of the Tm, Ho: YLF crystal is 283 K, the width of bistable section is 100 mW, and the jump power at the turning point is 15 mW. The influence of crystal temperature on the bistable performance of 2 μm laser is studied in the experiment. The width of bistable section was reduced from 100 mW to 60 mW and the jump power at the turning point reduced from 15mW to 6 mW respectively, when the temperature of laser crystal is increased from 283 K to 298 K. The bistable output in the continuous wave Tm, Ho: YLF laser comes from the co-effect of the energy transfer upconversion, excited state absoption and lower level reabsorption of 2 μm laser light.

Optical bistability effects in a Tm,Ho:YLF laser at room temperature

We demonstrate strong optical bistability in a 2 microm continuous-wave Tm,Ho:YLF laser pumped by a 792 nm laser diode near room temperature. The bistable region is as much as 100 mW wide at 283 K and can be controlled by the temperature of the laser crystal. The influence of crystal temperature on the characteristics of optical bistability is obtained. The influence of the pump-to-mode ratio on the bistable characteristics of the laser is also discussed. To our knowledge this is the first report of optical bistability effects in Tm,Ho:YLF lasers.

The influence of crystallization temperature and boron concentration in growth environment on its distribution in growth sectors of type IIb diamond

Type IIb diamond single crystals of size up to 8 mm were grown using the temperature-gradient method at high static pressure and temperature in Fe–Al–C system with added boron. The influence of crystallization temperature and boron concentration in growth environment on its distribution in growth sectors has been investigated using optical techniques. Variation from cubo-octahedral to octahedral habit with an increasing added amount of boron has been noted and explained.

Morphology – Property Correlations of PP Materials by Means of Microhardness

AbstractThe present work deals with the influence of crystallization temperature, cooling rate and annealing conditions on microhardness, indentation modulus and creep behaviour of ethylene/propylene (E/P) random copolymers with 4, 6 and 8 mol% ethylene as well as α‐ and β‐spherulites in a homopolymer and an E/P random copolymer. The materials are unnucleated, the formation of β‐spherulites occurs sporadically. Additionally the indentation creep behaviour of α‐ and β‐nucleated PP is investigated.A nearly linear correlation between hardness as well as indentation modulus and crystallintity of the E/P copolymers can be proved. An increasing cooling rate leads to decreasing hardness and modulus values due to the hindered crystallization.For the investigation of the α‐ and β‐phases different crystallization and annealing temperatures are used. Independent of these conditions, microhardness and modulus determined by indentation testing are lower for the β‐phase in both materials. Increasing crystallization temperature and annealing lead to an increasing hardness and modulus in both phases. However, an effective annealing effect takes place only at short times and elevated temperatures above 100 °C. The increasing of microhardness and modulus is correlated with an increasing in lamellae thicknesses. Additionally, indentation creep experiments were carried out on nucleated materials that show the stronger creep tendency of the β‐phase PP and the stronger influence of annealing on this phase.

Effects of crystallization temperature on the polymorphic behavior of syndiotactic polystyrene

The influence of crystallization temperature on formation of the α- and β-form crystals of syndiotactic polystyrene (sPS) was investigated by X-ray diffraction and non-isothermal differential scanning calorimetry analysis. For sPS samples without any thermal history, the crystallization temperature must be the intrinsic factor controlling the formation the α and β-form crystals. Being crystallized at different cooling rate from the melt, sPS forms the β-form crystal until the temperature cooled down to about 230°C, and α-form crystal can only be obtained when the temperature was below about 230°C.

Morphology and melting behaviour of poly(vinylidene fluoride) crystallized from the melt

AbstractThe influence of crystallization temperature on the melting behaviour and the morphology of poly(vinylidene fluoride) (PVF2) has been investigated. The DSC endotherms of PVF2 crystallized from the melt show at least two peaks. The peak areas depend on the thermal history of the samples and the heating scan rate. The area of the first peak was found to increase as the crystallization temperature or the scan rate increased. The double peak configuration was attributed to a melting–recrystallization process. Electron microscopy supports these results, for which only one type of lamella was found in the spherulitic structure.

Progress in monitoring thin film thickness by use of quartz crystals

The sensor function of high-accuracy quartz crystal thin film thickness monitors is determined by the properties of the unloaded crystal and the acoustic impedance z F of the film material. This material constant z F is often not precisely known, but it can be determined by the introduced two-frequency or Auto-Z-Match ® technique which uses the frequencies of two different quasiharmonic modes of the crystal. In comparison with standard crystal thickness measurement techniques as well as with atomic absorption spectrometry and the conventional microbalance, the superiority of the Auto-Z-Match ® technique is demonstrated for the evaporation materials copper, titanium, aluminium and lead. As the two-frequency technique allows the determination of the effective acoustic impedance of the film and thus thickness, determinations with higher accuracy are possible in the case of poorly known or unknown z-values. Other contributions to the practical performance and accuracy of quartz crystal thin film thickness monitors, such as the influence of crystal temperature, thin films stresses and the relaxation phenomenon, as well as the occurrence of frequency jumps, are discussed on the basis of the most recent research results.

538. The influence of crystallization temperature on growth and doping of gallium arsenide autoepitaxial films. I

538. The influence of crystallization temperature on growth and doping of gallium arsenide autoepitaxial films. I

Influence of crystallization temperature, molecular weight, and additives on the crystallization kinetics of poly(ethylene terephthalate)

AbstractThe spherulite growth rate, the maximum spherulite radius, and the overall rate of crystallization of poly(ethylene terephthalate) (PETP) were measured by means of scattering and transmission of depolarized light. The influence of crystallization temperature, molecular weight, and additives on the above‐mentioned quantities was investigated. An expression has been derived for the spherulite growth rate of PETP as a function of crystallization temperature and the number‐average molecular weight for M̄n in the range of 19,000 to 39,000.

The influence of crystallization temperature on the deformation of polypropylene spherulites

The influence of crystallization temperature on the deformation of polypropylene spherulites

Influence of crystallization temperature on degree of doping of gallium arsenide films and the impurity distribution: L G Lavrenteva et al, Izv VUZ Fiz, No 12, 1971, 144–146 ( in Russian)

Influence of crystallization temperature on degree of doping of gallium arsenide films and the impurity distribution: L G Lavrenteva et al, Izv VUZ Fiz, No 12, 1971, 144–146 ( in Russian)

Influence of crystal temperature on anomalous absorption of electrons in Si single crystals

The normal and anomalous absorption parameters μ o and μ h of Si have been determined from filtered intensities of the primary beam and some reflections at two temperatures. It is concluded that μ o and μ h contain contributions of thermal scattering.

Etude de la structure lamellaire des gels des copolymères séquencés polystyrolène‐polyoxyéthylène

AbstractIf a block‐copolymer of styrene and ethyleneoxide is mixed with a solvent which exhibits preferential affinity for the polystyrene block, birefringent gels are obtained. The structure of these gels is lamellar and the layers of unsolvated polyethyleneoxide are crystalline. In the present work, the influence of crystallization temperature, of concentration and of the nature of the solvent on the thickness of the crystalline sheets has been discussed. An interpretation for the observed experimental features is put forward.

Morphology of polyethylene single crystals

AbstractAn electron microscope study of polyethylene single crystals is reported. The following points have been investigated: (1) influence of crystallization temperature on crystal shape; (2) effect of solvent etching on already formed crystals. Crystals were deposited from very dilute solutions at temperature ranging between 80 and 120°C. Solvents like xylene, butyl acetate, isoamyl acetate, and diphenyl ether were used. Besides the already reported true and truncated lozenges, hexagonal crystals have been obtained with tendency to regularity as the temperature of crystallization increases. The melting point of hexagonal crystals is somewhat lower than that of lozenges. Their structure, as revealed by electron diffraction, is orthorhombic, similar to that of lozenges. Diamond‐shaped crystals etched with solvent under strictly controlled conditions display unexpected morphology. The peripheral region of the crystal of the sectors composing the crystals is characterized by a lower solubility and a lower density.

A Thermochemical Study of High Molecular Weight Compounds

Abstract Among the classical methods which have found application in research on high-molecular compounds, the method of Calorimetry is noteworthy. It is sufficient to mention the investigations into heat capacity, which, along with other measurements, helped to establish the second-order transition points, as well as the influence of crystallization temperature on the liquefaction of high polymers. The determination of the heat capacity of isoprene and of natural rubber, in combination with data on their heats of combustion, permitted a calculation of the change of free energy of formation of natural rubber. According to the data of Hock and Schmidt, the heat of swelling of natural rubber in various solvents ranges from +1.36 to −3.0 cal./gram. These data agree with those obtained from osmotic measurements. Thus the change of free energy when natural rubber goes into solution is approximately determined by the entropy term; i.e., ΔF=−TΔS. Bearing in mind that the heats of solution of rubber are of the same order of magnitude as the heats of mixing for two liquids, and are considerably lower than the heats of solution of solid bodies in liquids, we may conclude that the rubberlike state has more in common with liquid than with solid substances as regards solubility.