Preparation and characterization of nanocrystalline and mesoporous strontium titanate thin films at room temperature

The low temperature perovskite-type strontium titanate (SrTiO₃) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol–gel route. The prepared sol had a narrow particle size distribution with hydrodynamic diameter of about 17 nm. X-ray diffraction (XRD) revealed that the synthesized powders had a perovskite-SrTiO₃ structure with preferable orientation growth along the (1 0 0) direction. TEM images showed that the average crystallite size of the powders annealed in the range 300–800°C was around 8 nm. FE-SEM analysis and AFM images revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 25 nm at 600°C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure with BET surface area in the range 92–75 m²/g at 400–600°C. One of the smallest crystallite sizes and one of the highest surface areas reported in the literature were obtained, which can be used in many applications, such as photocatalysts.     

Temperature-Dependent Site Control of InAs/GaAs (001) Quantum Dots Using a Scanning Tunneling Microscopy Tip During Growth

Site-controlled InAs nano dots were successfully fabricated by a STMBE system (in situ scanning tunneling microscopy during molecular beam epitaxy growth) at substrate temperatures from 50 to 430°C. After 1.5 ML of the InAs wetting layer (WL) growth by ordinal Stranski–Krastanov dot fabrication procedures, we applied voltage at particular sites on the InAs WL, creating the site where In atoms, which were migrating on the WL, favored to congregate. At 240°C, InAs nano dots (width: 20–40 nm, height: 1.5–2.0 nm) were fabricated. At 430°C, InAs nano dots (width: 16–20 nm, height: 0.75–1.5 nm) were also fabricated. However, these dots were remained at least 40 s and collapsed less than 1000 s. Then, we fabricated InAs nano dots (width: 24–150 nm, height: 2.8–28 nm) at 300°C under In and As₄ irradiations. These were not collapsed and considered to high crystalline dots.     

Optical and mechanical characterization of transparent α-alumina fabricated by spark plasma sintering

The aim of this work was the analysis of the experimental results of a transparent alumina (BMA15) ceramic which was fabricated by Spark Plasma Sintering (SPS) from nanopowder (BMA15, Baikowski Chimie, France), at different temperatures (1200°C, 1250°C, 1300°C). With the application of a maximum uniaxial pressure of 73 MPa during all the fabrication-cycle (more than 3 hours). We sought an optimal sintering temperature combining better optical and mechanical properties of our pellets. The sintered alumina (BMA15) has a crystalline and dense microstructure. The samples sintered at 1200°C exhibit the best optical properties, in particular: good real inline transmission (RIT) and an optical gap greater than those of the samples sintered at 1250°C and 1300°C. Due to their low density, the Young modulus of alumina sintered at 1200 °C, deduced by ultrasound, has a low value which is about 385 GPa. Similarly, its small grain size gives it a better Vickers hardness ~ 21 GPa. Therefore, the value of the coefficient of friction μ stabilizes around the mean value of 0.21.     

Synthesis and characterization of soluble polyamides from bis-[(4′-aminobenzyl)-4-benzamide] ether and various diacids

New aromatic diamine containing preformed amide, ether, and methylene; bis-[(4′-aminobenzyl)-4-benzamide] ether (BABE), was synthesized and characterized by FT-IR, NMR, and mass spectrometry. Aromatic–aliphatic polyamides were prepared from BABE with aliphatic/aromatic diacids via Yamazaki’s polymerization. The polyamides were characterized by FT-IR, ¹H NMR, inherent viscosity [η_inh], solubility tests, differential scanning calorimetry [DSC], thermogravimetric analysis [TGA], and X-ray diffraction [XRD]. Polyamides had inherent viscosities 0.35–0.84 dL/g, soluble in aprotic polar solvents like N-methyl-2-pyrrolidone, N, N-dimethyl acetamide and dimethyl sulphoxide containing LiCl due to an amorphous to partially crystalline morphology; as XRD patterns indicated. DSC analysis of polyamides showed glass transition temperatures 166–268 °C. Polyamides showed high thermal stability as they did not degrade below 300 °C, had 10% weight loss temperature higher than 375 °C, and the char yields at 900 °C were 22–55%; indicating potential applications as engineering materials.     

Synthesis and characterization of thermosensitive core–shell polymeric nanoparticles

Thermosensitive core–shell nanoparticles were synthesized by semicontinuous heterophase polymerization of styrene, followed by a seeded polymerization for forming a shell of poly(N-isopropyl acrylamide) (PNIPAM). Nanoparticles characterization by scanning transmission electronic microscopy showed core–shell morphology with average particle diameters around 40 nm. An inverse dependence of the particle size with temperature in the range 20–55 °C was identified by quasielastic light scattering measurements. As was expected for core–shell particles with PNIPAM as the shell, a volume phase transition near 32 °C was detected. In spite of thermosensitive properties of core–shell nanoparticles synthesized here, the volume percentage loss values were not so high, probably due to their relatively low content of PNIPAM.     

Polymerization of propylene with Ziegler–Natta catalyst: optimization of operating conditions by response surface methodology (RSM)

Optimization of operational conditions for the polymerization of propylene with Ziegler–Natta catalyst was carried out via RSM. Response surface methodology (RSM) based on a three-level, four-variable Box–Behnken design was used to evaluate the interactive effects of reaction conditions such as reaction temperature (60–80 °C), monomer pressure (5–8 bar), hydrogen volume (130–170 mL), and cocatalyst to catalyst ratio (Al/Ti, 340–500) on the catalyst activity and melt flow rate (MFR). The optimum reaction conditions derived via RSM were: temperature 70 °C, pressure 8 bar, hydrogen volume 151 mL, and cocatalyst to catalyst ratio 390. The experimental catalyst activity and MFR were 8 g polypropylene/mg catalyst and 10.9 g/10 min, respectively, under optimum conditions. Optimum values were determined from process cost point of view and offered better operational conditions.     

Synthesis and characterization of thioether-containing polyimides with high refractive indices

Colorless and transparent polymers with high refractive indices and high temperature resistance have aroused great interest in the industrial community. Here, a series of polyimides (PIs) were prepared from a newly synthesized thioether-containing dianhydride, 1,4-bis(3,4-dicarboxy-phenylenesulfanyl)-benzene dianhydride, and various diamines by a two-step polycondensation reaction. Some flexible and tough films were obtained by casting solutions of them in poly(amic acid) (PAA). The tensile strengths and elongations at break of these PI films were greater than 58 MPa and 10%, respectively. All of them were thermally stable up to 500 °C in both air and nitrogen. Their glass transition temperatures were in the range from 204.5 to 265.8 °C. PI films with a thickness of 10–20 μm showed good optical transparency in the visible light region. Their cutoff wavelengths were lower than 400 nm and their transmittance was higher than 80% at 460 nm. The thioether linkages in the PIs endowed them with high average refractive indices (n _AV) of 1.68–1.74 and low birefringence values (Δn) of 0.0085–0.0120.     

In situ X-ray diffraction study of a TiO2 nanopowder Spark Plasma Sintering under very high pressure

We investigated the effect of very high pressure on the sintering temperature, phase transition and the grain growth during Spark Plasma Sintering (SPS) of a 15 nm TiO₂ nanopowder. Using in situ synchrotron X-ray diffraction during sintering at 1.5 and 3.5 GPa, we followed the evolution of the crystalline phases and the crystallite size as a function of temperature. In comparison, in the laboratory, SPS experiments were performed on two original facilities: A Paris-Edinburgh press and a high-pressure module adapted to standard SPS equipment. We studied the effect of the pressure on the sintering in the range 76 MPa to 3.5 GPa. We have shown that highly dense nanostructured ceramics can be prepared under very high pressure at low sintering temperatures. At 1 GPa, we limited the grain growth to an average size of 233 nm by heating at only 560 °C, and achieved a relative density of 98 %.     

Optically transparent and colorless poly(ether-imide)s derived from a phenylhydroquinone bis(ether anhydride) and various trifluoromethyl-substituted bis(ether amine)s

A series of colorless and organosoluble poly(ether-imide)s (PEIs) were prepared from a phenylhydroquinone bis(ether anhydride), i.e., 2,5-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, and seven trifluoromethyl-containing bis(ether amine)s by the conventional two-stage process via the thermal or chemical imidization of the precursor poly(amic acid)s. The fluorinated PEIs prepared via the chemical imidization procedure had inherent viscosities of 0.46–1.27 dL/g and weight-average molecular weights of 68,000–87,500. The PEIs exhibited good solubility in a variety of organic solvents; they were readily soluble in amide-type polar solvents and chlorinated hydrocarbons on a concentration higher than 10%. The solution-cast films showed a high optical transparency and low color intensity, with an ultraviolet-visible absorption edge of 368–375 nm and a yellowness index of 5.9–9.9. These films were flexible and tough with tensile strengths of 89–114 MPa. They exhibited glass-tranisition temperatures of 198–250°C and 10% weight loss temperatures higher than 488°C in air or nitrogen. In addition, these PEI films also displayed low dielectric constants (3.22–3.52 at 1 MHz) and low moisture absorptions (0.22–0.73 wt%).     

Optical and electrical properties of ITO film on flexible fluorphlogopite substrate

Indium Tin Oxide (ITO) films were prepared, at room temperature, on a fluorphlogopite substrate using magnetron sputtering technology. At various temperatures of 500 °C, 600 °C, 700 °C, 800 °C, and 900 °C, the samples were (had) annealed for 2 h (a 2-h duration). The results showed improvement in the crystalline performance of ITO film at selected annealing temperatures, with a significant reduction in resistivity at 800 °C. The lowest resistivity is 4.08 × 10^?4 Ω-cm, which is nearly an order of magnitude lower than the unannealed sample. All samples have an average light transmittance above 85% in the visible light range (400–800 nm), and with increasing annealing temperature, the average light transmittance tends to decrease. Besides, at the sensitive wavelength of 550 nm, the light transmittance is as high as 93.74%. The sheet resistance testing of the sample was through the number of bending times, which revealed that with the increase of the number of bending, the sheet resistance increases. However, after 1200 bending times, the change rate of the sheet resistance remains below 5%. Thus, the ITO film prepared on the flexible fluorphlogopite substrate revealed excellent optical and electrical properties, good flexibility, and improved stability after high-temperature annealing, which guarantees successful application in flexible electronic devices.     

Synthesis of nanocrystalline solid solutions based on zirconia and hafnia

Nanosized (2–8 nm) amorphous powders of the solid solution based on zirconia and hafnia are synthesized through back coprecipitation upon treatment of gels at temperatures from +20 to −77°C. Heat treatment of these powders at temperatures up to 1000 and above 1100°C leads to the formation of cubic (fluorite type, O _h ⁵ = Fm3m) and tetragonal phases of the Zr₈₂Hf₁₀Y₃Ce₅O _x composition, respectively. It is revealed that a decrease in the synthesis temperature (from +20°C to −6°C) results in a decrease in the size of gel agglomerates from 30 to 1 μm. Recrystallization processes in the gels prepared using cryochemical treatment are developed very slowly in the temperature range 500–1200°C (the crystallite size does not exceed 25 nm). Original Russian Text ? T.I. Panova, V.B. Glushkova, A.E. Lapshin, 2008, published in Fizika i Khimiya Stekla.     

Crystallization Behavior of Diacylglycerol-Rich Oils Produced from Rapeseed Oil

We examined the crystallization behavior of high-melting fractions in liquid oil containing high concentrations of diacylglycerols (DAG >80%) (hereafter referred to as DAG-rich oil). By differential scanning calorimetry and optical microscopy at moderate cooling rates, crystallization in the DAG-rich oil was detected at around 6 °C. It was found that the crystallization extent increased with decreasing temperatures of crystallization below 0 °C. A gas chromatographic analysis was performed on the crystallized fractions, which were separated by filtration at different periods of isothermal crystallization at 3 °C. The results indicated that at earlier crystallization periods, the concentrations of 1,3-disaturated DAG such as palmitic and stearic acid moieties (15 min) and 1,3-saturated–unsaturated mixed-acid DAG including oleic acid, palmitic, and stearic acid moieties (15 min–3 h) were predominant. However, the concentrations of 1,3-diunsaturated DAG including oleic acid moiety increased after a crystallization period of 6 h. To clarify the sequential crystallization process of DAG, we examined the binary mixing behavior of principal DAG components occurring in the rapeseed-based DAG-rich oil. It was evident that 1,3-disaturated DAG, 1,3-saturated–unsaturated mixed-acid DAG, and 1,3-diunsaturated DAG exhibited immiscible behavior. From these data, basic information on the precipitation processes in DAG-rich oils at chilled temperatures was obtained.     

Viscoelastic Properties of Montmorillonite Clay/Polyimide Composite Membranes and Thin Films

Montmorillonite clay, cloisite 30B (nanoclay), was successfully dispersed in a polyimide (PI) matrix by in situ condensation polymerization followed by solution casting and thermal imidization. Wide angle X-ray diffraction, WAXD, test was used to study the structure of cloisite 30B clay powder and nanoclay/polyimide composites. The WAXD spectra of nanoclay powder and the composites show one major diffraction peak at 4.76° and 6°, respectively, suggesting that the d-spacing of nanoclay was decreased by about 26% after composite film processing. The viscoelastic property of polyimide and nanoclay/polyimide composite was studied by using dynamic mechanical spectrometer. The storage modulus and glass–rubber transition temperature of nanoclay/polyimide composites increases with increasing volume fraction of clay. The storage modulus of the composites in the rubbery plateau region, (T > 400 °C) increased remarkably with increasing volume fraction of clay. A modulus enhancement, (E_C/E_M) of about three orders of magnitude, (E_C/E_M ~1,440) was obtained for nanoclay/polyimide composite containing 6.8 vol% of nanoclay. The tangent of the loss angle (tan δ) for the composites, decreased with increasing volume fraction of nanoclay. The observed decrease in tan δ with increasing volume fraction of clay is consistent with the established trend of increasing storage modulus and glass–rubber transition temperature with increasing volume fraction of nanoclay. The phenomenal increase in the rubbery plateau storage modulus and glass–rubber transition temperature with increasing volume fraction of clay is believed to be due to increased restriction of chain motion with increasing nanoclay volume fraction.     

In situ HTXRD formation of magnesium titanates

Coprecipitated xerogel precursors of nanocrystalline magnesium titanates, with a Mg:Ti stoichiometric ratio of 2:1, were subjected to thermal treatment in air at constant temperature, from 100 to 1300°C, using a hot‐stage X‐ray powder diffractometer. The phase sequences, the kinetics of phase evolution and crystallite size were studied during the first hour of the process at different temperatures. Until 500°C no diffraction peaks were observed. Between 550 and 800°C the structure was a mixture of two cubic nanocrystalline coherent structures: qandilite‐like and periclase‐like forms. At 900 and 1000°C, after 15 minutes, geikielite and periclase appear in small amounts but the qandilite‐like phase remains predominant; at 1100°C and above, qandilite is formed again as a single phase. The diffraction lines were substantially broadened for all crystalline phases formed at low temperatures, becoming sharper with increasing temperature and time. The phase evolution is interpreted as a consequence of the decrease in the surface area to volume ratio with increasing temperature and time, thus decreasing the significance of the surface energy. Linear thermal expansion coefficients were derived for qandilite.     

Nitrogen and oxygen annealing effects on properties of aluminum-gallium oxide films grown by pulsed laser deposition

Aluminum-gallium oxide (AGO) films on c-plane sapphire substrates by pulsed laser deposition are described. Both nitrogen and oxygen annealing effects on the structural and optical properties of AGO films are investigated. The AGO film shows an amorphous structure when deposited at low temperatures (≤400 °C) while a crystalline structure at 800 °C. After post annealing at 900 °C, an amorphous-to-crystalline phase transformation for the 400°C-deposited film occurs and shows the preferred β phase. The corresponding optical bandgap also increases from 5.14 eV to 5.41–5.46 eV depending on the annealing ambience. From Raman measurements, the 800°C-deposited AGO sample possesses a more stable O–Ga–O bonding compared to that of the 400°C-deposited one after annealing. Unusually, an evident increase in the nitrogen content is observed for the samples after post annealing at 900 °C in nitrogen atmosphere. The rapid dissociation of oxygen atoms may accelerate the disintegration of crystals and rearrangement, which makes the AGO film adsorb nitrogen atoms and cause the grain size to be significantly reduced. However, the extent of the nitrogen incorporation seems to have no apparent effect on the optical properties. All the AGO films show the optical transmittance over 80% in the ultraviolet–visible region with the calculated bandgaps more than 5.4 eV. Details of the mechanism about the nitrogen incorporation into the annealed AGO films via the oxygen vacancies or micro-pores will be discussed.     

Micro-tubular solid oxide fuel cells fabricated from hollow fibres

Recent literature is reviewed on a phase inversion process followed by sintering, used to fabricate ceramic hollow fibres (HFs) as precursors to micro-tubular solid oxide fuel cells (MT-SOFCs) with sub-millimetre inner diameters. These aimed to address the outstanding technological and economic issues that have delayed mass production of SOFCs, by increasing electrode surface areas per unit volume relative to planar structures, increasing power outputs per unit volume/mass, facilitating sealing at high temperatures, and decreasing fabrication costs per kW. Some recent experimental results are presented of the effects of temperature, hydrogen flow rate, thermal cycling and time of NiO reduction with H₂ on the subsequent performance of 25 mm long H₂|Ni–CGO|CGO|LSCF|air MT-SOFCs, incorporating cerium–gadolinium oxide (CGO) electrolyte, nickel anodes and lanthanum strontium cobalt ferrite–CGO (LSCF–CGO) cermet cathodes, designed to operate at 500–600 °C. Maximum power densities of 3–5.5 kW m⁻² were achieved as the temperature was increased from 550–600 °C. The co-extruded MT-SOFCs were resilient to three thermal cycles when heated to operating temperature in ca. 5 min. Their performance was intimately related to the reduction time, suggesting slow conversion of the NiO to Ni within the fabricated anodes. At constant cell voltage, mass transport limited current densities increased from ca. 11 to ca. 13.5 kA m⁻² as hydrogen flow rates were increased from 15 to 60 cm³ min⁻¹, though had residual NiO in the anode been fully reduced, current densities would have been significantly greater.     

Polymeric semiconducting carbon from fullerene by pulsed laser ablation

The polymeric semiconducting carbon films are grown on silicon and quartz substrates by excimer (XeCl) pulsed laser deposition (PLD) technique using fullerene C₆₀ precursor. The substrate temperature is varied up to 300 °C. The structure and optical properties of the films strongly depend on the substrate temperature. The grain size is increased and uniform polymeric film with improved morphology at higher temperature is observed. The Tauc gap is about 1.35 eV for the film deposited at 100°C and with temperature the gap is decreased upto 1.1 eV for the film deposited at 250 °C and increased to about 1.4 eV for the film deposited at 300 °C. The optical absorption properties are improved with substrate temperature. Raman spectra show the presence of both G peak and D peak and are peaked at about 1590 cm^− 1 and 1360 cm^− 1, respectively for the film deposited at 100 °C. The G peak position remains almost unchanged while D peak has changed only a little with temperature might be due to its better crystalline structure compared to the typical amorphous carbon films and might show interesting in device such as, optoelectronic applications.     

Simplified synthesis of isomorphously nickel substituted ZSM-5

Isomorphously nickel-substituted nano-crystalline ZSM-5 is synthesized in the absence of acidic aqueous fluoride medium incorporating simple and low-cost metal inorganic salt precursor NiCl₂.6H₂O instead of large organic cationic salt like bis (tetraethyl ammonium) tetrachloronickelate (II) with less water quantity to minimize the synthesis waste. PXRD, FT-IR, TG/DTG, XPS, UV–Vis DRS, SEM, TEM, ICP and N₂ adsorption-desorption techniques were used to confirm the presence of nano-crystalline material having a MFI structure and heteroatom substitution. The unit cell dimensions increase with increasing levels of nickel substitution. The crystallite size of as synthesized samples was in the range of 60–75 nm, which increased to 60–160 nm after calcination at 550°C. Percentage crystallinity and crystallite size increases with increasing nickel substitution level up to 0.17 mol and beyond that the material becomes amorphous.     

Synthesis and characterization of nanometric gadolinia powders by room temperature solid-state displacement reaction and low temperature calcination

Nanometric-sized gadolinia (Gd₂O₃) powders were obtained by applying solid-state displacement reaction at room temperature and low temperature calcination. The XRD analysis revealed that the room temperature product was gadolinium hydroxide, Gd(OH)₃. In order to induce crystallization of Gd₂O₃, the subsequent calcination at 600 ∼ 1200 °C of the room temperature reaction products was studied. Calculation of average crystallite size (D) as well as separation of the effect of crystallite size and strain of nanocrystals was performed on the basic of Williamson-Hall plots. The morphologies of powders calcined at different temperatures were followed by scanning electron microscopy. The pure cubic Gd₂O₃ phase was made at 600 °C which converted to monoclinic Gd₂O₃ phase between 1400° and 1600 °C. High-density (96% of theoretical density) ceramic pellet free of any additives was obtained after pressureless sintering at 1600 °C for 4 h in air, using calcined powder at 600 °C.     

Fabrication and Optical Behaviors of Core–Shell ZnS Nanostructures

Novel core–shell nanostructures comprised of cubic sphalerite and hexagonal wurtzite ZnS have been synthesized at 150°C by a simple hydrothermal method. The results of HR-TEM and SAED investigation reveal that the cores of hexagonal wurtzite ZnS (ca. 200 nm in average diameter) are encapsulated by a shell of cubic sphalerite ZnS. The FE-SEM image of the nanomaterials shows a surface tightly packed with nanoparticles (<10 nm in size). The optical properties of the fabricated material have been studied in terms of ultraviolet–visible absorption and photoluminescence. Furthermore, a possible mechanism for the fabrication of the core–shell nanostructures has been presented.