Evidence Of Preferred Orientation Research Articles

Gold nanoparticles on metal oxide surfaces derived from n-alkanethiolate-stabilized gold nanoparticles; investigations of the adsorption mechanism and sulfate formation during subsequent thermolysis

n-Alkanethiolate-stabilized gold (n-CnSAu) nanoparticles (n=6, 12, 16) have been studied as the source of gold nanoparticles supported on the metal oxides NiO, TiO2 (anatase and rutile), CeO2, and γ-Al2O3 following adsorption from n-hexane and thermolysis in air at 340°C. Adsorption times increase with an increase in length of the carbon chain and vary with the metal oxide, particularly with specific surface area. Evidence of oxidation of some of the thiolate sulfur to give sulfoxide- and sulfone-type species has been established. TG/DTA studies and FT-IR (attenuated total reflectance) spectroscopy show that the adsorbed n-CnSAu nanoparticles thermally decompose at about 210–340°C depending on the metal oxide, with some decomposition products, particularly those containing sulfur, adsorbing onto the metal oxide surface. Following thermolysis at 340°C, XPS and the FT-IR studies, combined with laser-ablation mass spectrometry, show that all organic material decomposition products are generally lost, and that the residual sulfur exists as sulfate at about 0.2wt% or lower. TEM/STEM studies have shown that the n-CnSAu nanoparticles, originally about 2nm in diameter, produce gold nanoparticles with a range of 2–4nm in size on the oxide surface following thermolysis at 340°C. The final average size of the gold nanoparticles depends on the metal oxide. For NiO, HRSTEM images shows little evidence of preferred orientation following immediate adsorption of n-C6SAu nanoparticles, indicating weak interaction with the oxide surface, while a preferred orientation occurs on thermolysis at 340°C, indicating a much stronger interaction. The total oxidation of a representative alkane, isobutane, over TiO2 (both anatase and rutile) and NiO, together with the addition of 5wt% Au nanoparticles has been studied. Anatase and rutile are initially inactive but addition of the gold nanoparticles generates active oxidation catalysts, with anatase slightly more active than rutile. For NiO and 5wt% Au/NiO reaction begins at 205–215°C and complete oxidation occurs by 430–440°C. The presence of the gold nanoparticles reduces the apparent activation energy from 89 to 51kJ/mol. All active catalysts show formation of CO as well as CO2 at about 20% conversion of isobutane, but at 100% oxidation the main product is almost exclusively CO2 (>99.0%). The presence of the sulfate from the decomposition of the n-CnS− ligands has minimal apparent poisoning effect on the oxidation of isobutane for anatase, rutile, or NiO.

STRUCTURE CHARACTERISTICS AND MECHANICAL PROPERTIES OF COLD ROLLED AUSTEMPERED DUCTILE IRON ALLOYED WITH NICKEL

Effect of nickel additions on structure characteristics and mechanical properties of ductile iron austempered at 400°C for 60 minutes was investigated. TRIP effect more significantly occurred in 0.95% Ni ADI leading to the optimum tensile properties and impact toughness. Increasing Ni-content to 1.90% resulted in the increase of retained austenite and martensite formed on cooling. This led to the decrease of tensile strength and impact toughness. Cold rolled 0.95% Ni ADI showed the optimum tensile and impact properties whereas 1.90% Ni ADI exhibited an anomalous decrease in the yield and tensile strengths under cold reductions < 19% due to the initiation of microcracks in the brittle martensite. The highest increasing rate of internal microstrain with deformation was shown in 1.90% Ni ADI. Crystallographic preferred orientation in ADI was remarkable only in the martensite and enhanced by cold deformation in the austenite. There was no evidence of preferred orientation in ferrite.On a étudié l’effet d’additions de nickel sur les caractéristiques de la structure et sur les propriétés mécaniques de la fonte ductile à trempe étagée bainitique (ADI) à 400 °C pendant 60 minutes. L’effet TRIP s’est manifesté de façon plus importante pour l’ADI à 0.95% de Ni, menant à des propriétés optimales de résistance à la traction et de résistance à l’impact. L’augmentation de la teneur en Ni à 1.90% conduit en une augmentation de l’austénite résiduelle et de la martensite formée lors du refroidissement. Ceci mène à une diminution de la résistance à la traction et de la résistance à l’impact. L’ADI à 0.95% de Ni, laminée à froid, a montré des propriétés optimales de résistance à la traction et de résistance à l’impact alors que l’ADI à 1.90% de Ni a exhibé une diminution anormale de la limite d’élasticité et de la résistance à la traction lors du laminage à froid 19% due à l’initiation de microfissures dans la martensite fragile. Le taux d’augmentation le plus élevé de microcontrainte interne avec déformation a été démontré pour l’ADI à 1.90% de Ni. L’orientation cristallographique préférée de l’ADI était remarquable seulement pour la martensite et accentuée par la déformation à froid pour l’austénite. Il n’y avait pas d’évidence d’orientation préférée pour la ferrite.

Transmission electron microscopy studies of atomic layer deposition TiO 2 films grown on silicon

Transmission electron microscopy techniques have been used to characterise atomic layer deposition TiO 2 films grown on silicon substrates after RCA and HF treatment. The influence of deposition temperature (250–350 °C) and substrate type on the film microstructure have been determined. The major influence of substrate type is to control nucleation of crystallisation. HF treated silicon, which was devoid of the native oxide layer, promoted a crystalline, island growth mode. The nucleation of crystalline particles at the onset of deposition resulted in films with very fine grain sizes (≈20 nm). The RCA treated silicon, which was coated with amorphous native oxide, caused the growth of an initially amorphous TiO 2 film, which crystallised once a critical film thickness had been exceeded. The major influence of temperature on the films grown on RCA treated silicon was to control nucleation of crystallisation within the amorphous layers, resulting in grain size refinement at higher deposition temperatures. Under the processing conditions used, other than the transient amorphous films formed on RCA treated silicon, anatase was the only phase formed. No evidence for preferred orientation was found.

Analysis of in vitro reaction layers formed on Bioglass using thin-film X-ray diffraction and ATR-FTIR microspectroscopy.

Fourier transform infrared spectroscopy and thin-film X-ray diffraction (TF-XRD) techniques were used to analyze the inorganic carbonate apatite (CA) layer developed on a bioactive glass (45S5 type Bioglass) in an in vitro environment. The C-O and P-O vibrational modes appeared on the bioactive glass surface following immersion in the simulated body fluid solution. Initially, the C-O and P-O peaks increased with immersion time as crystallization of CA phase progressed. The TF-XRD confirmed that the deposited layer was apatite, crystallographically. Furthermore, evidence of preferred orientation in the 001 direction was seen, indicated by very strong 002 reflection. With time, the crystal growth became more random and the intensity of the 002 reflection decreased.

The murundus of the cerrado region of Central Brazil

ABSTRACTCampos de murundus (earthmound fields) are common throughout the cerrado (savanna) in Brazil. They have a clearly defined distribution particularly where they are associated with ground water. There is a distinctive woody vegetation on the discrete mounds contrasting with surrounding grass-covered depressions.After a reconnaissance ground and air-photograph survey of the nature and distribution of mounds within the Federal District, four one-hectare plots were chosen for detailed study within the ecological reserve of the University of Brasília. Measurements were made of the size, shape and frequency of mounds. Numbers varied from 26 to 61 ha-1 with a uniform distribution occupying 10–50% of the plots. Heights ranged from 0.05 to over 2 m. The generally semi-elliptical shape in ground plan had an average size of 7 by 5.5 m with no evidence of preferred orientation although water scouring from runoff partly influences the morphology. Volumes varied from 0.01 m3 to 141.5 m3. The soils of the murundus differed from those of surrounding depressions by being better drained, with bright colours and strong cohesive structures; they were more argillic with lower base saturation and pH values. Such sites favour colonization both by cerrado plants and by termites. A classification of the murundus is postulated. Although this paper does not consider the origins of murundus, they appear to relate more closely to drainage and differential erosion than to termite activity.

A statistical study of phenocryst orientation fabrics in a dacite ignimbrite

Preferred orientation of phenocrysts is common in oriented thin sections of Bonanza Tuff, an early Oligocene composite ignimbrite sheet of dacite composition in the San Juan Mountains, Colorado. The phenocryst fabric is considered the result of primary laminar flow during the final stages of ignimbrite emplacement. A detailed statistical analysis of eight samples of Bonanza Tuff shows the progressive development of preferred orientation with increasing sample size and suggests that approximately 100 measurements of the long axes of phenocrysts are required to yield a statistically significant fabric if it exists. Approximately 100 measurements are also needed to calculate a reproducible vector mean regardless of the strength of the fabric. Accumulation of a much larger population of data strengthens the evidence of preferred orientation, as shown by Tukey Chi-square and probability tests, but does not significantly alter the resulting vector mean. Samples which yield statistically random fabrics with 100 measurements remain random despite accumulation of a large data base.