Use of bomb calorimetry to assess recovery of waste industrial mineral oils through regeneration

Emanation thermal analysis (ETA), based on the measurement of the release of radon previously incorporated into the sample, was used to characterize the differences in the thermal behavior porous titania film (thickness 200 nm),when heated in argon and in oxygen, respectively, in the range from 20 to 800°C. It was observed that the annealing of porosity and structure defects in the near surface layers of the porous titania film (anatase) was enhanced on heating in oxygen in comparison to the heating in argon. ETA results were compared with SEM micrographs and XRD patterns of the titania film samples heated to 500 and 800°C, respectively. A mathematical model was used for the evaluation of the temperature dependence of the titania films microstructure development.This revised version was published online in November 2005 with corrections to the Cover Date.     

Stress and Cracks in Gel-Derived Ceramic Coatings and Thick Film Formation

Residual stress was evaluated by measuring the substrate curvature for alkoxide-derived silica and titania films deposited on silica glass substrates. The residual stress was tensile, increasing with increasing heat-treatment temperature. The stress in fired films was affected greatly by water/alkoxide ratio and chelating agents in starting solutions. Secondly, in situ observation was made on cracking of gel films subjected to heat-treatment. Silica and titania gel films deposited on silicon wafers were cracked in the heating-up stage at temperatures of 100°–400°C, depending on the film thickness and heating rate. Larger thickness and lower heating rates were found to lower the cracking onset temperature. Finally, organic polymers with amide groups were demonstrated to increase the uncracking critical thickness. The polymers include polyvinylpyrrolidone and polyvinylacetamide, allowing single layer ceramic coating films over 1 m in thickness to be formed without cracking.     

Effect of Incorporation of Silver on the Electrical Properties of Sol-Gel-Derived Titania Film

Metallic Ag nanoparticles-incorporating titania films were prepared using the sol-gel method. X-ray diffraction (XRD) patterns, UV/Vis optical spectra and transmission electron microscopy (TEM) images were recorded to characterize the Ag/titania composite films. Electrometer was used to estimate the resistance of Ag/titania composite film to understand the effect of the incorporation of metallic Ag nanoparticles on the electrical properties of titania film. The results showed that metallic Ag nanoparticles distributed randomly in titania film and most metallic Ag particles size was in the range of 5–15 nm. The agglomeration of a small quantity of metallic Ag particles occurred and when the amount of Ag species was increased the agglomeration was enhanced. The resistance of Ag/titania composite films decreased greatly compared with pure titania film.     

Thermal Behaviour of Titania Based Materials: Mathematical modeling of emanation thermal analysis results

Emanation thermal analysis (ETA) was used in the characterization of microstructure changes during heating ofprecursors for the titania based materials: hydrous titania, TiO₂nH₂O (n=0.58) and hydrous titania containing 10% ruthenia,(TiO₂)_0.9(RuO₂)_0.1nH₂O (n=1.5). The precursors were heated at the constant rate 6 K min^–1 in argon flow in the range 20–1000°C. ETA results were compared with the theoretical curves simulating the temperature dependences of radon release rate, E(T). Two mathematical models were used in the simulation. The models considered either subsequent or simultaneous solid state processes (i.e. dehydration, crystallization orphase transition, resp.) during thermal treatment of titania based materials. A good agreement was found between experimental and the simulated ETA curves. The results of ETA were confirmed by XRD patterns of intermediate products of thermal treatment of the precursors.This revised version was published online in November 2005 with corrections to the Cover Date.     

Sol–gel titania coating on unmodified and surface-modified polyimide films

Sol–gel coating of metal oxides on polymer substrates is a useful process to fabricate various organic–inorganic hybrid materials under mild conditions. However, this process is hardly applicable to pristine polyimide (PI) films because their surfaces do not display effective functional groups for metal oxide coatings. In this study, we firstly examined direct sol–gel coating of titania thin layers on unmodified PI film surfaces. The results confirmed homogeneous, ultrathin titania layer coating and showed that the thickness and microscopic morphology of the titania layers were affected by titanium alkoxide concentrations in the spin coating solutions. We next investigated titania layer coating on surface-modified PI films that prepared using alkaline hydrolysis, which generated carboxylic acid groups on the film surfaces. Optimal hydrolysis time was determined using FT-IR spectroscopy and contact angle measurements. After sol–gel titania coating on the hydrolyzed PI film surfaces, the Scotch tape test was conducted to evaluate adhesion strength between the titania layers and PI film surfaces. Morphological observations of the sample surfaces after the tests clearly showed that surface modification of PI films increased titania layer adhesions. Effect of hydrothermal treatments on film formability and adhesion strength between titania-PI film interfaces was also evaluated.     

Preparation and phase transition characterization of VO2 thin film on single crystal Si (100) substrate by sol–gel process

Vanadium dioxide (VO₂) thin films were fabricated on single crystal Si (100) substrates by sol–gel method, including a process of annealing a vanadium pentoxide (V₂O₅) gel precursor at different temperatures. The crystalline structure and morphology of the films were investigated by XRD, FE-SEM and AFM, indicating that the films underwent the grain growth, agglomeration and grain refinement process with increased annealing temperatures. The film annealed at 500 °C exhibits the formation of VO₂ phase with a strong (011) preferred orientation and high crystallinity, the surface of the film is uniform and compact with a grain size of about 120 nm. Meanwhile, the film exhibits excellent phase transition properties, with a decrease of transmittance from 35.5 to 2.5% at λ = 25 μm and more than 3 orders of resistivity magnitude variation bellow and above the phase transition temperature. The phase transition temperature is evaluated at 60.4 °C in the heating transition and 55.8 °C in the cooling transition. Furthermore, the phase transition property of the VO₂ film appears to be able to remain stable over repetitive cycles 100 times.     

Theory of Emanation Thermal Analysis: XI. Radon diffusion as the probe of microstructure changes in solids

The theoretical background for the use of radon diffusion as a probe of microstructure changes in solids is given. The high sensitivity of the emanation thermal analysis (ETA) in the study of solid state processes especially interactions taking place on surfaces and in the near surface layers is described. The increasing sensitivity of the method towards bulk processes with rising temperature is theoretically shown. The background considerations to be used in the mathematical modeling of temperature dependences of the radon release from solids on heating (i.e. simulated ETA curves) are presented. Various models for radon diffusion and various functions describing the annealing of structure irregularities, which served as diffusion paths for radon, were used in the modeling. It was shown, that ETA is able to characterize microstructure changes in the surface layers of the thickness from several nanometers to several micrometers.This revised version was published online in November 2005 with corrections to the Cover Date.     

Unusual crystallization behaviors of anatase nanocrystallites from a molecularly thin titania nanosheet and its stacked forms: increase in nucleation temperature and oriented growth

Crystallization behaviors of anatase nanocrystallites from an ultrathin two-dimensional reactant composed of exfoliated titania nanosheets have been studied by monitoring the heating process of their well-organized films, with which the film thickness can be controlled from a molecularly thin monolayer to a stacked multilayer structure with a stepwise increment of approximately 1 nm. The heated products were identified by means of total reflection fluorescence X-ray absorption near-edge structure analysis and in-plane X-ray diffraction measurements using a synchrotron radiation source. The films composed of five or more layers of stacked nanosheets were transformed into anatase at 400-500 degrees C, which is a normal crystallization temperature of anatase from bulk reactants. As the film became thinner by decreasing the number of nanosheet layers to five or less, the crystallization temperature was found to increase and finally reached 800 degrees C for the monolayer film. Interestingly, preferential growth of anatase along the c-axis was strongly promoted for these ultrathin films. These unusual behaviors may be understood in terms of crystallization from the two-dimensional system of scarcely distributed reactants. The titania nanosheet crystallite is much thinner than the unit cell dimensions of anatase, and therefore, extensive atomic diffusion is required for the transformation particularly for the ultrathin films with a critical number (2-3) of stacked nanosheet layers. There is some structural similarity between anatase and titania nanosheet, which may account for the oriented growth of anatase nanocrystallites.     

Temperature programmed desorption analysis of sol-gel-derived titania films

Sol-gel-derived titania films were analyzed by temperature programmed desorption (TPD) and X-ray diffraction (XRD) techniques. The relationship between the TPD curves measured for two types of titania gel films and their crystal structures was investigated. On the basis of the analyses, a preparation process for a titania sol solution containing anatase nanocrystals was designed and developed. Using this process, a colloidal anatase titania sol solution was prepared by heating aqueous titanium hydroxide containing HCl at 60°C for 2 h. The nanocrystal structure of the titania films obtained by coating the sol on glass substrates was confirmed by TPD and XRD measurements.     

Annealing Temperature Dependence of the Size of C60 Clusters in C60-Doped Silicon Oxide Films

C₆₀-doped silicon oxide thin films were prepared by spin-coating a viscous solution formed upon soaking at 40°C an acidic toluene/ethanol solution of C₆₀, phenyltriethoxysilane, and tetraethoxysilane with a C₆₀–to–Si molar ratio of 2.5 × 10^–3. The films were submitted to annealing at 300–500°C in Ar to investigate variation in the size of C₆₀ clusters embedded in the films by photoluminescence spectroscopy. The film before annealing was found to contain the clusters consisting of ca. 60 C₆₀ molecules, suggesting that C₆₀ is present well-dispersed in the film. The molecules in the film aggregated to increase the size with increasing annealing temperature, indicating that the molecules diffuse easily in the film upon heating and therefore the size of the clusters is controllable with the annealing temperature.     

The effects of oxygen concentration on ultraviolet luminescence of ZnO films by sol–gel technology and annealing

ZnO thin films were successfully deposited on SiO₂/Si substrate using the sol–gel technique and annealed in various annealing atmospheres at 900 °C by rapid thermal annealing (RTA). X-ray diffraction revealed the (002) texture of ZnO thin films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that the grains of the ZnO thin film were enlarged and its surface was smoothed upon annealing in oxygen. PL measurement revealed two ultraviolet (UV) luminescence bands at 375 and 380 nm. The intensity of the emission peak at 380 nm became stronger as the concentration of oxygen in the annealing atmosphere increased. The X-ray photoelectron spectrum (XPS) demonstrated that a more stoichiometric ZnO thin film was obtained upon annealing in oxygen and more excitons were generated from the radiative recombination carriers consistently. Additionally, the UV intensity increased with the thickness of ZnO thin film.     

Kinetics of latex formation of PBMA latex in the presence of alkali soluble resin using atomic force microscopy

 The effect of alkali-soluble resin (ASR), poly(ethylene-co-acrylic acid), EAA, postadded to emulsifier-free monodisperse poly(butyl methacrylate) (PBMA) latexes on the kinetics of film formation was investigated using atomic force microscopy (AFM). Corrugation height of latex particles in films was monitored at various annealing temperatures as a function of annealing time. Enhanced polymer diffusion was found in a latex film containing ASR regardless of anneal-ing temperature. With increasing annealing temperature, a much higher rate of polymer diffusion was found in latex films containing ASR. These results can be interpreted that the low molecular weight and low Tg EAA resin adsorbed at the particle surface is more susceptible to diffusion than that of the PBMA in the film formation stage, thus it enhances the mobility of PBMA polymer. Received: 30 October 1997 Accepted: 20 March 1998     

Photocatalytic properties of titania nanostructured films fabricated from Titania nanosheets

We examined the photochemical properties of well-ordered multilayer films of titania nanosheets prepared on quartz-glass substrate using the layer-by-layer deposition method. The photocatalytic decomposition of gaseous 2-propanol and bleaching of Methylene Blue dye under UV light illumination were measured to evaluate the photocatalytic oxidation ability. Photoinduced hydrophilicity was also studied by measuring the contact angle of water droplets on the film. The results indicated that titania nanosheets had good photoinduced hydrophilicity. The monolayer film of titania nanosheets showed almost identical activity compared with well investigated sol-gel derived anatase TiO(2) film, while its photocatalytic oxidation activity was low by more than an order of magnitude. This fact suggests that photoinduced hydrophilicity could not be explained simply in terms of the photocatalytic removal of hydrophobic organic species adsorbed on the surface. The photocatalytic oxidation activity and the photoinduced hydrophilic conversion rate decreased with increasing number of nanosheet layers, suggesting that photogenerated carriers produced in the internal part of the multilayer films can hardly diffuse to the surface layer. Photochemical properties of ultrathin anatase films obtained simply by heating the titania nanosheet films were evaluated as well, and also revealed high photoinduced hydrophilicity.     

Structure and dielectric properties of HfO<Subscript>2</Subscript> films prepared by a sol–gel route

Mono- and multilayer HfO₂ sol–gel thin films have been deposited on silicon wafers by dip-coating technique using a solution based on hafnium ethoxide as precursor. The densification/crystallization process was achieved by classical annealing between 400 and 600 °C for 0.5 h (after drying at 100 °C). Systematic TEM studies were performed to observe the evolution of the thin film structure depending on the annealing temperature. The overall density of the films was determined from RBS spectrometry correlated with cross section (XTEM) thickness measurements. After annealing at 450 °C the films are amorphous with a nanoporous structure showing also some incipient crystallization. After annealing at 550 °C the films are totally crystallized. The HfO₂ grains grow in colonies having the same crystalline orientation with respect to the film plane, including faceted nanopores. During annealing a nanometric SiO₂ layer is formed at the interface with the silicon substrate; the thickness of this layer increases with the annealing temperature. Capacitive measurements allowed determining the value of the dielectric constant as 25 for four layer films, i.e. very close to the value for the bulk material.     

TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> hard coating on polycarbonate substrate by microwave assisted sol–gel technique

To enhance the poor scratch resistance of polycarbonate, a silica (SiO₂) and titania (TiO₂) transparent inorganic coatings was designed and synthesized using a microwave assisted sol–gel heating. Due to the transparency of PC to microwave, the idea was to obtain a localized heating only on the coating film. The obtained films were fully characterized to mainly evaluate the effect of titania content, added both as nanoparticles and from tetraethyl orthotitanate, TEOT, on scratch resistance and surface morphology. Particular attention was paid to preserve the transparency of the final product. The results allowed to define that TEOT addition enhances the adhesion between coating and polycarbonate, even if the optimized quantity have to be defined in order to avoid a decrease of coating mechanical resistance. In this work optimized TEOT level results to be the associated to 5 wt% of TiO₂, which enable the better balancing between adhesion and mechanical resistance performances.     

The Influence of Heat Treatment Mode on the Properties of Bi4Ti3O12 Thin Films by Chemical Solution Deposition Technique

Bi₄Ti₃O₁₂ thin films were prepared by chemical solution deposition technique on n-Si(lOO). Bismuth nitrate and titanium butoxide were used as starting materials. In this paper, we used this technique to prepare Bi₄Ti₃O₁₂ thin films heat treated by both rapid annealing for 30 seconds in a rapid annealing heater and annealing in a furnace for 30 minutes, and found that the heat treat mode greatly influences the properties of the films. The crystallization temperature of the film made from rapid annealing is about 500℃, while that of the film prepared by heating in a furnace is about 550℃. X-ray diffraction pattern of the film heat treated by the former has stronger (004), (006), (008), (0010) peaks than that of the film heat treated by the latter, which suggests that the rapid annealing heat treat mode favors preferential c-oriental film. The grain size of the film obtained by rapid annealing is smaller than that of the film prepared by heating in a furnace. When the films were both annealed at 600℃,the coercive field of the film heat treated by the former is 45 kV/cm, while that of the film heat treated by the latter is 87 kV/cm.     

Influence of surfactant and annealing temperature on optical properties of sol–gel derived nano-crystalline TiO2 thin films

Titanium dioxide thin films have been synthesized by sol–gel spin coating technique on glass and silicon substrates with and without surfactant polyethylene glycol (PEG). XRD and SEM results confirm the presence of nano-crystalline (anatase) phase at an annealing temperature of 300 °C. The influence of surfactant and annealing temperature on optical properties of TiO₂ thin films has been studied. Optical constants and film thickness were estimated by Swanepoel's (envelope) method and by ellipsometric measurements in the visible spectral range. The optical transmittance and reflectance were found to decrease with an increase in PEG percentage. Refractive index of the films decreased and film thickness increased with the increase in percentage of surfactant. The refractive index of the un-doped TiO₂ films was estimated at different annealing temperatures and it has increased with the increasing annealing temperature. The optical band gap of pure TiO₂ films was estimated by Tauc's method at different annealing temperature.     

Corrosion protection enhancement effect by mixed silica nanoparticles of different sizes incorporated in a sol–gel silica film

We demonstrate an enhancement of corrosion protection by sol–gel silica film including mixed silica nanoparticles of 10 and 50 nm. Low-temperature silica films were prepared by sol–gel dip-coating method, followed by a thermal annealing at 200 °C. Importantly, film with mixed particles exhibits lower corrosion current density and slower loss of film resistance during the immersion in electrolyte solution, showing an improved corrosion protection over the film with 50 nm particles. The improved corrosion protectability of the mixed particles comes from the suppressed diffusion of ionic species by a close packing of 10 nm particles.     

Emanation thermal analysis study of N-doped titania photoactive powders

Thermal behaviour of N-doped titania powders prepared by heat treatment of anatase in gaseous ammonia at 550 and 575°C, respectively, was characterized by emanation thermal analysis (ETA). The ETA results were used to assess transport properties of the samples subsurface using the mobility data of radon atoms previously incorporated into the samples to the depth of 60 nm. It was demonstrated that the radon permeability of anatase in the temperature range 50–500°C was enhanced for the N-doped titania as compared to the non-doped titania powder. Microstructure changes accompanying the anatase-rutile transition were pointed out from the decrease of the radon release rate in the temperature range 850–1000°C. The results of surface area and porosity measurements, DTA results as well XRD patterns supported the ETA results.     

Elimination of porosity in heavily rare-earth doped sol–gel derived silicate glass films

The combination of spin-coating and rapid thermal annealing is a very important sol–gel technique to prepare high quality silicate glass films, widely used in the fabrication of waveguides, photonic bandgap structures and other film-based optical devices. This work found that high rare-earth concentrations will seriously affect the optical quality of the films prepared by the spin-coating/rapid thermal annealing process, with pores with hundreds of nanometres in size being found in heavily rare-earth doped aluminosilicate glass films, causing significant light scattering. However, it was also found that a new recipe using acetylacetone was able to dramatically eliminate these pores and to improve the film optical quality, even for rare-earth concentrations as high as 15 mol%. This result will be useful for the fabrication of sol–gel derived devices based on rare-earth doped silicate glass films like active waveguides, functional films and photonic bandgap structures.