Function Of Treatment Temperature Research Articles

Influence of Parameters in Vapor Transport Equilibration Treatment on Composition and Homogeneity of LiTaO3 Single Crystals

The effect of key parameters such as time, temperature, and equilibration powder concentration in vapor transport equilibration (VTE) treatment on the Li2O content of initially congruent X‐, Y‐, and Z‐cut LiTaO3 crystals is experimentally investigated. The Li2O content across the thickness of the crystal is estimated by Raman spectroscopy with accuracy of 0.05–0.15 mol%. The Li2O loss from equilibration powders has been monitored as a function of treatment temperature and duration. The results show that the Li2O content in the crystal nonlinearly depends on the equilibration powder composition and that homogeneous stoichiometric LiTaO3 crystals can be obtained by treatment for at least 36h at 1250°C in Li2O‐rich atmosphere, created by powders containing >54 mol% of Li2O. The anisotropic Li+ diffusion coefficients and its activation energy are also experimentally estimated. Finally, the VTE conditions are defined for the production of different cuts of LiTaO3 crystals with controlled homogeneous Li2O nonstoichiometry in the range from subcongruent to stoichiometric compositions.

Additive manufactured parts surface treatment through impinged hot air jet technique the theoretical and experimental evaluation

PurposeMaterial extrusion-based additive manufacturing is a prominent manufacturing technique to fabricate complex geometrical three-dimensional (3D) parts. Despite the indisputable advantages of material extrusion-based technique, the poor surface and subsurface integrity hinder the industrial application of this technology. The purpose of this study is introducing the hot air jet treatment (HAJ) technique for surface treatment of additive manufactured parts.Design/methodology/approachIn the presented research, novel theoretical formulation and finite element models are developed to study and model the polishing mechanism of printed parts surface through the HAJ technique. The model correlates reflow material volume, layer width and layer height. The reflow material volume is a function of treatment temperature, treatment velocity and HAJ velocity. The values of reflow material volume are obtained through the finite element modeling model due to the complexity of the interactions between thermal and mechanical phenomena. The theoretical model presumptions are validated through experiments, and the results show that the treatment parameters have a significant impact on the surface characteristics, hardness and dimensional variations of the treated surface.FindingsThe results demonstrate that the average value of error between the calculated theoretical results and experimental results is 14.3%. Meanwhile, the 3D plots of Ra and Rq revealed that the maximum values of Ra and Rq reduction percentages at 255°C, 270°C, 285°C and 300°C treatment temperatures are (35.9%, 33.9%), (77.6%,76.4%), (94%, 93.8%) and (85.1%, 84%), respectively. The scanning electron microscope results illustrate three different treatment zones and the treatment-induced and manufacturing-induced entrapped air relief phenomenon. The measured results of hardness variation percentages and dimensional deviation percentages at different regimes are (8.33%, 0.19%), (10.55%, 0.31%) and (−0.27%, 0.34%), respectively.Originality/valueWhile some studies have investigated the effect of the HAJ process on the structural integrity of manufactured items, there is a dearth of research on the underlying treatment mechanism, the integrity of the treated surface and the subsurface characteristics of the treated surface.

Comparison between nitriding behavior of Mo-Ti and Mo-V alloys

Internal nitriding behavior of Mo-15 at.% Ti and Mo- 5/15 at.% V alloys were compared in a temperature range from 700 °C to 1100 °C using Forming gas (95% N2 and 5% H2) for nitriding times of 10 h and 15 h. The variations of specimen weight, microstructure and hardness of nitrided layer as well as the developed nitriding products were investigated as a function of treatment temperature and time. VN and TiN nitrides with a minor amount of TiO2 oxide are formed on the surface of Mo-V and Mo-Ti alloys, respectively. The maximum nitrided depths of around 14 μm are achieved for both Mo-15 Ti/V alloys after nitriding at 1100 °C for 10 h. Larger hardness values are measured on nitrided layer of Mo-Ti in comparison to that of Mo-V at the same treatment temperature. According to X-ray diffraction assessment, at moderate temperature of 900 °C, the diffraction of Mo matrix and VN nitrides is recognized as an incoherent diffraction, whereas coherent diffraction by matrix and nitrides is realized for Mo and TiN. In general, higher affinity of nitride formation for V is observed at lower temperature of 700 °C as compared to Ti in a Mo matrix, which is attributed to the stronger interaction of V and N in Mo matrix given by calculating corresponding interaction parameters. The difference in stress relieving and coarsening behavior were also observed in matrices containing VN and TiN, which is argued with regards to the dissimilar impacts of VN and TiN on precipitation hardening of Mo matrix at investigated temperatures. These results imply that the previously reported brittleness of Mo-based alloys containing Ti can be improved at moderate temperatures by replacing Ti with other nitride forming elements such as V, regardless of N concertation in Mo matrix.

Behavior of wood during the thermal transition between torrefaction and pyrolysis: chemical and physical modifications.

ABSTRACT Despite the wealth of physical and chemical information available about wood torrefaction and pyrolysis, very few studies to date have focused on the transition between these two processes. It has been experimentally determined, however, that torrefaction and pyrolysis lead to very different products, indicating a change in their degradation chemistry. There exists, therefore, a need to investigate this transition between torrefaction and pyrolysis from a chemical perspective, very useful for the development of kinetic models. This study focuses on investigating thermogravimetric analysis, shrinkage, flexural strength, total weight loss, of two common industrial European wood species treated at temperatures ranging from 250°C to 400°C. A comparison reveals an obvious change in the degradation of cellulose as a function of treatment temperature that can be correlated with the yield of the main thermal treatment products, such as acetic acid, furfural, CO, H2, etc. At temperatures higher than 350°C, all wood components are extensively degraded. In conclusion, this study indicates a deep modification during the transition between torrefaction and pyrolysis. The results obtained in this study help establish specific temperature ranges, based on wood component degradation, that can be used in the refinement of kinetic models for wood thermal treatment. It is envisioned that, due to the sudden change in behavior at temperatures covering a range between torrefaction and soft pyrolysis, an adequate model with distinct stages is required. Ultimately, this study aims at defining, based on TGA, DTG, mechanical testing, color/appearance, and dimensional change results, the appropriate temperature ranges to be used in the refinement of unique kinetic models that contemplate the degradation of wood components.

Preparation of crack-free, non-notched, flattened bamboo board and its physical and mechanical properties

Bamboo flattening technology can increase the utilization of bamboo, flattening half or third bamboo tube sections into flattened bamboo strips through steam softening, roller flattening and drying. Compared with earlier notched flattening technology, newer non-notched flattening technology does not incise or damage the culm inner surface. In this paper, we introduce a non-notched flattening method and assess the macro-and micro-mechanical properties of the flattened bamboo. Results showed that the parenchyma cells shrank and distorted and the hygroscopicity of bamboo decreased and the hygroscopicity of bamboo decreased due to the decomposition of hemicelluloses. The modulus of elasticity (MOE) and hardness were increased as a function of treatment temperature and time. The MOE increased by 25% and the hardness significantly increased by 34% after the flattening process due to the tissue densification and increased crystallinity index. The improved micromechanical properties of cell walls and increased density positively contributed to the macro-mechanical properties.

Low temperature thermal treatment of gas-phase fluorotelomer alcohols by calcium oxide

Given the extent to which per- and polyfluoroalkyl substances (PFAS) are used in commercial and industrial applications, the need to evaluate treatment options that reduce environmental emissions and human and ecological exposures of PFAS is becoming more necessary. One specific chemical class of PFAS, fluorotelomer alcohols (FTOHs), have vapor pressures such that a significant fraction is expected to be present in the gas-phase even at ambient temperatures. FTOHs are used in a variety of PFAS applications, including synthesis and material coatings. Using two complementary mass spectrometric methods, the use of calcium oxide (CaO) was examined as a low temperature and potentially low-cost thermal treatment media for removal and destruction of four gas-phase FTOHs of varying molecular weights. This was accomplished by assessing the removal/destruction efficiency of the FTOHs and the formation of fluorinated byproducts as a function of treatment temperature (200–800 °C) in the presence of CaO compared to thermal-only destruction. During the treatment process, there is evidence that other PFAS compounds are produced at low temperatures (200–600 °C) as the primary FTOH partially degrades. At temperatures above 600 °C, thermal treatment with CaO prevented the formation or removed nearly all these secondary products.

Temperature effects on light yield and pulse shape discrimination capability of siloxane based scintillators

In this work, we report the study of temperature effects on light yield of siloxane-based scintillators and on n/gamma discrimination capability, in terms of pulse shape discrimination (PSD). The solid scintillators are composed of phenyl containing polysiloxane (PMPS100), as a base polymer, loaded with moderate amounts (6 wt%) of 2,5-diphenyloxazole (PPO) as a primary dye and Lumogen Violet (LV) as waveshifter. The samples were heated in the range of 60–150 ^circ hbox {C} and scintillation performance were tested both after annealing for 24 h and in real time during heating. Light yield of siloxane-based scintillators containing 6 wt% PPO heated at 100 ^circ hbox {C} is very close to the room-temperature value, while heating at 120 ^circ hbox {C} causes a decrease of light yield (LY) of 17%. In addition, the figure of merit (FoM) for n/gamma discrimination of the scintillator shows a sensible worsening of the discrimination performances in case of prolonged treatment at 120 ^circ hbox {C}. Similar tests are made using the commercial plastic scintillator EJ-299 (currently named EJ-276), based on polyvinyltoluene (PVT). In this case, the light yield undergoes a much more rapid deterioration with annealing temperature, and at 70 ^circ hbox {C} it is reduced to 60% of the original value. The discrimination capability of EJ-299 decreases upon heating at 70 ^circ hbox {C} as well, with a 20% reduction of FoM; meanwhile for T > 70 ^circ hbox {C} the mechanical and optical features are remarkably degraded. The mass loss of primary dye PPO from the siloxane scintillator as a function of treatment temperature and initial dye concentration has been evaluated and compared to the behaviour of EJ-299. This measurement allows to single out and characterize a series of processes occurring during heating, which are relevant to the whole performance of the system under study, such as sublimation at the interface, thermally induced photooxidation of components, diffusion of fluorophores from the polymer bulk to the surface. The variation in luminescence characteristics have been analyzed by excitation/fluorescence spectroscopy and time-resolved fluorescence spectroscopy, in order to correlate the annealing treatment with the primary dye loss by sublimation, formation of superficial aggregates and/or degradation of the scintillator components in the synthesized siloxane scintillator.

Evaluation of Energy Consumption in the Mercury Treatment of Phosphor Powder from Spent Fluorescent Lamps Using a Thermal Process

In a pilot-plant-scale thermal mercury treatment of phosphor powder from spent fluorescent lamps, energy consumption was estimated to control mercury content by the consideration of reaction kinetics. Mercury content was analyzed as a function of treatment temperature and time. The initial mercury content of the phosphor powder used in the thermal process was approximately 3500 mg/kg. The target mercury content in the phosphor powder thermal process of the phosphor powder was 5 mg/kg or less at 400 °C or higher because the target mercury content was recommended by Minamata Convention and Basel Convention. During thermal processing, the reaction rate was represented by a first order reaction with the Arrhenius equation. The reaction rate constant increased with temperature from 0.0112 min−1 at 350 °C to 0.0558 min−1 at 600 °C. The frequency factor was 2.51 min−1, and the activation energy was 6509.11 kcal/kg. Reaction rate constants were used to evaluate the treatment time required to reduce mercury content in phosphor powder to be less than 5 mg/kg. The total energy consumption in a pilot-plant-scale thermal process was evaluated to determine the optimal temperature for removing mercury in phosphor powder.

Microstructural and Diffusion Analysis of Au-Sn Diffusion Couple Layer Undergoing Heat Treatment at Near Eutectic Temperatures

Diffusion couples of pure gold and pure tin were created by mechanical cold rolling method. The couples were isothermally treated at temperatures slightly above and below the eutectic temperature near tin-rich region of the equilibrium phase diagram. Differences in the diffusion behaviors were observed as a function of treatment temperatures below (473 K) and above (498 K) the eutectic temperature. At the boundary, it was found that first solid state inter-diffusion was initiated which resulted in local compositional change and solid-state formation of intermetallic compounds. As the composition shifts away towards mixing, the growth of the intermetallic phases was monitored as a function of temperature and time. At temperature above the eutectic, there may be a liquid fraction as the interface isothermally melted. The kinetic involves dissolution of Au atoms into locallized tin-rich liquid. At below eutectic temperature, the formation and growth kinetic of phases follows a solid state diffusion mechanism. By investigation the exponent n values in the growth equation l=k(t/t0)n, the values were found to be in between 0.62 - 0.77 which implies that the kinetics of IMC formations experiment are controlled by both diffusion and intermetallic reaction. The bonding temperature was found to be faster and more reliable at bonding temperature slightly above the eutectic.

The impact of the synthesis conditions on SrAl2O4:Eu, Dy formation for a persistent afterglow

The design of phosphorescent materials, highly crystalline, with a submicron particle size is a challenge for industrial applications. Based on molten salt assisted process, the effects of salt/SrAl2O4 molar ratio on the phase evolution are studied. A significant influence of salt/SrAl2O4 molar ratio on synthesis and final properties has been observed. Moreover, the phase evolution has been explored as a function of treatment temperature. To remove the salt from the powder, the wash step is carried out with glycerin avoiding hydrolysis reaction due to the sensitivity of strontium aluminates to water. The salt/SrAl2O4 molar ratio of 3:1 and the thermal treatment at 1000°C are preferred, avoiding extra wash step. Here, we have obtained highly crystalline SrAl2O4:Eu2+, Dy3+ powder with a particle size ≤0.5μm after a 2h treatment at 1000°C employing the molten salt approach. As a result, we believe that the general strategy described in this study opens the possibility of obtaining technologically relevant phosphors with enhanced properties, expanding their application range to radiation detection.

Direct acid activation of kaolinite and its effects on the adsorption of methylene blue

Coal-bearing kaolinite was directly treated with concentrated sulfuric acid to improve its surface properties and adsorption ability. Acid treatment was carried out at various temperatures (i.e., room temperature −250°C), by varying time of treatment from 0 to 120min. The samples were characterized by X-ray diffraction analysis, elemental analyses, thermogravimetric analysis, N2 adsorption-desorption analysis, high-resolution transmission electron microscopy, and Fourier transformed infrared spectroscopy. The activation of kaolinite strongly depended on the acid treatment including treatment temperature and time. Acid treatment at room temperature did not cause significant alterations either in the chemical composition or in the structure of the kaolinite. On the other hand, treatment at increased temperature led to the removal of Al3+ ions and thus increased the porosity of the material. The surface area and the pore volume of original kaolinite could be greatly changed as a function of treatment temperature and time of treatment, and they increased from 13.6 to 257.8m2g−1 and from 0.045 to 0.25cm3g−1, respectively, when the kaolinite was treated at 200°C for 30min. The adsorption ability of acid-activated kaolinite (AAK) was investigated using methylene blue (MB) as a typical pollutant. For this, the effects of contact time, pH, initial MB concentration and temperature were studied in batch mode. Gibb's free energy (ΔG0), entropy (ΔS0) and enthalpy (ΔH0) changes for MB adsorption were calculated. Owing to its high surface area, the AAK showed higher removal efficiency for MB than for original kaolinite, with a maximum adsorption capacity of 101.5mgg−1.

Dielectric and thermal studies of segmental dynamics in silica/PDMS and silica/titania/PDMS nanocomposites

ABSTRACTEffects of silica and silica/titania nanoparticles on glass transition and segmental dynamics of poly(dimethylsiloxane) (PDMS) were studied for composites of a core–shell type using differential scanning calorimetry, thermally stimulated depolarization current, and dielectric relaxation spectroscopy techniques. Strong interactions between the filler and the polymer suppress crystallinity (Tc, Xc) and affect significantly the evolution of the glass transition in the nanocomposites. The segmental relaxation associated with the glass transition consists of three contributions, arising, in the order of decreasing mobility, from the bulk (unaffected) amorphous polymer fraction (α relaxation), from polymer chains restricted between condensed crystal regions (αc relaxation), and from the semi‐bound polymers in an interfacial layer with strongly reduced mobility due to interactions with surface hydroxyls of silica and silica/titania nanoparticles (α′ relaxation). The evolution of surface affected CH3 groups, as well as the degree of interaction of PDMS molecules with surface hydroxyl groups as a function of treatment temperature, was assessed by Fourier transform infrared spectroscopy, thermogravimetry and differential thermal analysis. The effectiveness of silica/PDMS and silica/titania/PDMS nanocomposites as hydrophobic coatings was investigated by static contact angle measurements. It was shown that the presence of titania nanoparticles and adsorbed PDMS promotes the hydrophobic properties of the PDMS coating after treatment in the 80–650°C range. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41154.

Formation of three-dimensional Parylene C structures via thermoforming

The thermoplastic nature of Parylene C is leveraged to enable the formation of three-dimensional structures using a thermal forming (thermoforming) technique. Thermoforming involves the heating of Parylene films above its glass transition temperature while they are physically confined in the final desired conformation. Micro and macro scale three-dimensional structures composed of Parylene thin films were developed using the thermoforming process, and the resulting chemical and mechanical changes to the films were characterized. No large changes to the surface and bulk chemistries of the polymer were observed following the thermoforming process conducted in vacuum. Heat treated structures exhibited increased stiffness by a maximum of 37% depending on the treatment temperature, due to an increase in crystallinity of the Parylene polymer. This study revealed important property changes resulting from the process, namely (1) the development of high strains in thermoformed areas of small radii of curvature (30–90 µm) and (2) ∼1.5% bulk material shrinkage in thermoformed multilayered Parylene–Parylene and Parylene–metal–Parylene films. Thermoforming is a simple process whereby three-dimensional structures can be achieved from Parylene C-based thin film structures with tunable mechanical properties as a function of treatment temperature.

Response Surface Modeling of Hydrothermal Treatment Conditions on Color Changes, Strength, and Durability Properties of Rubberwood

The effect of hydrothermal treatment at various temperatures (100 to 160 °C) and treatment times (30 to 720 minutes) on color changes (ΔE*), equilibrium moisture content (EMC), tensile strength (TS), shear strength (SS), brown-rot fungal decay mass loss (FML), and termite attack score (TAS) of rubberwood was examined. Response surface methodology (RSM) with a two-factor, four level (42) full factorial was employed. The mathematical models describing those properties as functions of treatment temperature and logarithm of treatment time were obtained. Hydrothermal treatment adversely and positively influenced mechanical properties (TS and SS) and durability (FML and TAS), respectively, of rubberwood. Strong correlations between ΔE*, TS, SS, and FML of hydrothermally treated rubberwood, proposed to be a consequence of degradation of hemicelluloses, were observed. Finally, ΔE* proved to be a good indicator of TS, SS, and FML but not that of EMC and TAS of hydrothermally treated rubberwood.

Effect of heat curing on antifungal activities of anise oil and garlic oil against Aspergillus niger on rubberwood

The effect of heat curing (30–100 °C) on the antifungal activity of rubberwood impregnated with anise oil and garlic oil (10–100 μl ml−1) against Aspergillus niger was examined. Essential oil constituents left within the rubberwood after the heat curing and after incubation were analyzed by GC–MS. Response surface methodology (RSM) with a central composite face-centered (CCF) design was employed to evaluate the time needed for initiation of mold growth. The mathematical models containing only significant parameters (p ≤ 0.05) as functions of treatment temperature and essential oil concentration were obtained. Heat curing adversely and positively influenced the antifungal activities of anise oil and garlic oil, respectively. Such thermal effect was more pronounced at a higher concentration of essential oil. Decomposition of trans-anethole and estragole in anise oil and formation of diallyl disulfide in garlic oil by heat was proposed as the agent responsible for temperature dependencies of the essential oil antifungal activities observed.

An investigation on the microstructure, tribological and corrosion performance of AISI 321 stainless steel carbonitrided by RF plasma process

An anticorrosive and wear-resistant superficial top layer was distinctly produced in AISI 321 austenitic stainless steel by rf plasma carbonitriding. Details about the elemental distribution profiles and the microstructure of the carbonitrided samples, as a function of treatment temperature, were characterized by glow discharge optical spectroscopy (GDOS), grazing incidence X-ray diffraction (GIXRD) and optical microscopy (OM). The tribological behavior was investigated using a ball-on-disc tribometer. Further the corrosion performance of the treated samples compared to the untreated one was examined using electrochemical tests with potentiodynamic anodic polarization curves. Glow discharge optical spectroscopy indicated that, the nitrogen and carbon contents diffused into the surface during carbonitriding were found to be treatment temperature dependent. The lowest friction coefficient and superior wear resistance in the presence of excellent corrosion resistance were observed for the samples carbonitrided at treatment temperature of 818–863 K. According to Arrhenius plot analysis, the activation energy was 4 eV/atom while the effective diffusion coefficient was found to be 199.3 × 10 2 μm 2/h.

Staphylococcus aureus Enriched in Ordered Lipids Present Resistance Towards the Antibacterial Agent sPLA2-IIA: An Unusual Mechanism to Survive

Bacterial membranes present solid-ordered/liquid-disordered (so/ld) cooperative melting event close to physiological temperature. The cellular advantage of this thermotropic melting event is yet to be determined. We show that this thermal behavior provides resistance towards a membrane active antibacterial agent. Phospholipase A2 type IIA (sPLA2-IIA) is a hydrolytic enzyme which presents antibacterial properties towards Gram positive bacteria. The enzyme has higher activity in ld phase compared to so phase in anionic membranes. We show that the lipid phase behavior of Staphylococcus aureus (S.aureus) membranes as measured by FTIR modulates sPLA2-IIA by inducing a sharp drop in activity below the melting temperature of the membrane (centered at 15.3°C). The effects of sPLA2-IIA treatment on cell viability are also investigated. While above the main melting event viability drops to 20% of the initial CFU after treatment, below the main melting event cell viability only drops to 60% under the same treatment. This strongly suggests that cells in the solid-ordered phase are better adapted to survive the enzymatic insult. These results led us to explore if a subpopulation of S.aureus enriched in ordered lipids can be selected after repeated treatment with sPLA2-IIA at 37°C. After selecting for resistance at 37°C we measured growth curves, membrane order, and cell viability as a function of treatment temperature. The results suggest that at 37°C there is a bacterial subpopulation with increased membrane rigidity that insures survival of the colony to an insult by sPLA2-IIA. This subpopulation also presents a longer latency period which can be explained by the increased presence in ordered lipids, which are known to inhibit cell division. Even if the growth conditions are not optimal, the presence of this subpopulation ensures survival from the antibacterial insult.

IMPACT OF KEROGEN HETEROGENEITY ON SORPTION OF ORGANIC POLLUTANTS. 1. SORBENT CHARACTERIZATION

The overall goal of the present study was to establish correlations between organic pollutant sorption and physicochemical properties of kerogen materials. Three coal samples, each representing a typical kerogen type, were used as the starting materials. A thermal technique was employed to treat the kerogen materials under seven different temperatures ranging from 200 to 500 degrees C to simulate different diagenetic history. These samples were systematically characterized for their chemical compositions, functionalities, physical rigidity, and optical properties. The results showed that the chemical, spectroscopic, and optical microscopic properties of each kerogen series changed consistently as a function of treatment temperature or kerogen maturation. The oxygen-to-carbon atomic ratio decreased from 0.29, 0.12, and 0.07 for the original lignite (XF0), fusinite (HZ0), and lopinite (LP0) samples, respectively, to 0.07, 0.06, and 0.04 for XF7, HZ7, and LP7, respectively, that underwent the highest temperature treatment. The hydrogen-to-carbon atomic ratio exhibited similar reducing trend, which is consistent with the aromaticity increasing from 45 to 58% of the original samples to 76 to 81% of highly mature samples. Under the fluorescence microscope, the organic matrix changed from yellow (original lignite sample) and red-brown (original lopinite sample) to colorless for the samples of higher maturation. The measured reflecting index increased from the original samples to the highly mature samples. Moreover, the original and the slightly matured samples exhibited very different chemical compositions and structural units among the three types due to the difference in their source materials. As the kerogen maturation increased, such differences decreased, indicating highly mature kerogen became homogenized regardless of the source material.

Structural and optoelectronic characterization of TiO2 films prepared using the sol–gel technique

TiO2 is a versatile material that makes for fascinating study in any of its several physical forms: monocrystal, polycrystal, powder or thin film. Its enhanced photosensitivity to UV radiation and excellent chemical stability in acidic and aqueous media point to its excellent potential for use in a variety of applications, such as solar cells, electronic devices, chemical sensors and photocatalysts. Of late, thin films of TiO2 have permitted the study of physical and chemical properties that are almost impossible to examine in powders. Using the sol–gel technique, it was possible to prepare TiO2 films, and to specifically modify their characteristic properties by means of annealing treatments. Optical measurements carried out on sol–gel derived films produced results similar to those found in films prepared using the sputtering technique. The use of TiO2 films facilitates the study of the behaviour of crystalline structure, grain size, photoresponse, electrical conductivity in both darkness and light and energy band gap (Eg) as a function of treatment temperature. For the first time, it has been demonstrated that the photoconductivity of TiO2 becomes apparent at a treatment temperature of 350 °C, which means that below this temperature the material is not photosensitive. The photosensitivity (S) of TiO2 films prepared by the sol–gel technique reaches values between 100 and 104, surpassing by more than two orders of magnitude the photosensitivity of TiO2 in powder form. In addition, it was possible to study the surface crystalline structure, where TEM studies clearly revealed both the polycrystalline order and the atomic arrangements of the TiO2 films. Our findings will afford us an opportunity to better study the nature of TiO2 and to enhance its performance with respect to the above-mentioned applications.

Polydimethylsiloxane at the interfaces of fumed silica and zirconia/fumed silica

Polydimethylsiloxane (PDMS)/fumed silica A-300 and PDMS/ZrO 2/A-300 were studied using adsorption, thermogravimetry, temperature-programmed desorption (TPD) mass-spectrometry, infrared spectroscopy, XRD, and broadband dielectric relaxation spectroscopy. ZrO 2 was synthesized on fumed silica with zirconium acetylacetonate in CCl 4 at 350 K for 1 h and calcinated at 773 K for 1 h (1–4 reaction cycles). PDMS (5–40 wt.%) was adsorbed onto silica and zirconia/silica from hexane solution and then dried. Grafted zirconia changes the chemistry of the surface (because of its catalytic capability) and the topology of secondary particles (because of occupation of voids in aggregates of primary silica particles by zirconia nanoparticles) responsible for the textural porosity of the powders. Therefore, many properties (such as structural characteristics of the composites, reactions on heating in air and vacuum, interfacial relaxation phenomena, hydrophobicity as a function of treatment temperature, etc.) of PDMS/zirconia/silica strongly differ from those of PDMS/A-300. Broadening of the α-relaxation of PDMS at the interfaces of disperse oxides suggests both weakening of the PDMS–PDMS interaction and strengthening of the PDMS–oxide interaction.