The Leidenfrost effect during spray pyrolysis of nickel oxide-gadolinia doped ceria composite thin films

NiO-Ce_0.8Gd_0.2O_1.9 − x (CGO) thin films were prepared by air blast spray pyrolysis with precursors containing nickel nitrate, cerium nitrate and gadolinium chloride in ethanol and a high boiling point organic solvent. Precursors containing solvents with boiling points between 120 and 314 °C were sprayed on sapphire, silicon, Foturan^®, yttria stabilized zirconia and CGO at different substrate surface temperatures.A maximum deposition temperature, above which film deposition ceased completely, was observed. The limiting temperature for film formation was correlated with the Leidenfrost phenomenon. At temperatures above the Leidenfrost point of the precursor, the sprayed droplets do not impact and spread on the substrate surface but levitate on a vapour cushion above the substrate and are swept away by the air stream. The Leidenfrost point of a precursor was found to depend on the solvent boiling point, the metal salt concentration and the thermal properties of the substrate expressed as the product of density, thermal conductivity and heat capacity. The maximum deposition temperature increased with increasing solvent boiling point or metal salt concentration and with decreasing product of density, thermal conductivity and heat capacity of the substrate.     

Densification and phase formation in seeded, reactively sintered Sr0.53Ba0.47Nb2O6 ceramics

Sr_0.53Ba_0.47Nb₂O₆ (SBN53) ceramics were reactively sintered from SrNb₂O₆ and BaNb₂O₆ powders. The formation temperature decreased from 1260°C for unseeded samples to 1130°C for the samples with 15.4 wt% seeds plus 0.85 mol% V₂O₅ at a heating rate of 4°C/min. For the V₂O₅-free samples, the activation energy was lowered from 554 ± 15 kJ/mol for unseeded samples to 241 ± 17 kJ/mol for the samples with 15.4 wt% seeds. In the V₂O₅-containing samples, densification and phase formation occurred simultaneously. In the V₂O₅-free samples, however, phase formation was completed before densification. In both cases, ceramics with 95% relative density were obtained. In all cases, SBN53 formed directly, rather than via a variety of intermediate SBN solid solutions. The microstructure evolution was also studied.     

Grain Boundaries in Titania-Doped α-Alumina with Anisotropic Microstructure

The microstructure of sol-gel-derived alpha-alumina (Al₂O₃) doped with 0.6 wt% titania, sintered at 1450°C for 1 h, consisted of thin platelets with (0001) faces in a matrix of equiaxed grains. Short facets at the edges of the platelets developed primarily parallel to the {10     2} planes, while some were parallel to the {11     3} planes; other edges showed irregular, curved boundaries. The basal surfaces of the platelets were coated with thin layers (0.5-6 nm) of an amorphous titanium-containing aluminosilicate phase, which also was present at triple points. No amorphous phase was found on the short faceted boundaries, on curved boundaries at platelet edges, or at grain boundaries of equiaxed, matrix grains. However, titanium enrichment was observed at all examined boundaries, suggesting that titanium segregation alone did not account for the development of anisotropic microstructure. Curved incursions on basal facets were associated with occasional particles of aluminum titanate (Al₂TiO₅).     

Texture Development by Templated Grain Growth in Liquid-Phase-Sintered α-Alumina

The distribution and orientation of platelet-shaped particles of α-alumina in a fine-grained alumina matrix is shown to template texture development via anisotropic grain growth. The textured microstructure ranges from 4 wt% oriented platelet particles in calcined samples to nearly 100% oriented α-Al₂O₃ grains after sintering at 1400°C. A CaO + SiO₂ liquid phase creates favorable thermodynamic and kinetic conditions for anisotropic grain growth and grain reorientation during sintering. Important criteria for templated grain growth include (1) anisotropic crystal structure and growth, (2) high thermodynamic driving force for template grain growth, and (3) modification of diffusion in the system to continuously provide material to the anisotropically growing template grains.     

(Reactive) Templated Grain Growth of Textured Sodium Bismuth Titanate (Na1/2Bi1/2TiO3-BaTiO3) Ceramics—II Dielectric and Piezoelectric Properties

(Na_1/2Bi_1/2)TiO₃-BaTiO₃ (<6.5% BaTiO₃) ceramics with <001>_pc orientation were fabricated by Templated Grain Growth (TGG) or Reactive Templated Grain Growth (RTGG) using tabular SrTiO₃ template particles. The maximum electrically-induced strain was 0.26% at 70 kV/cm. d₃₃ coefficients over 500 pC/N were obtained for highly textured samples (f 90%) when driven at high electric fields. Under these conditions, the materials show considerable hysteresis in the strain—field response, even after poling. Berlincourt piezoelectric coefficients for the same samples gave d₃₃ of 200 pC/N.     

The formation of α-Al2O3 from θ-Al2O3: The relevance of a “critical size” and: Diffusional nucleation or “synchro-shear”?

The coarsening of -Al₂O₃ crystals to a 'critical size' is often interpreted as the first step in the shear nucleation of -Al₂O₃. The existence of this so-called critical size has also been used to explain the observation that -Al₂O₃ nuclei are generally twice as large as the crystals in the -Al₂O₃ matrix. This paper discusses the important issues in the nucleation of -Al₂O₃ from -Al₂O₃. A few key experiments are also presented to clarify the nucleation process. It is concluded that a critical -Al₂O₃ crystal size is not a prerequisite for -Al₂O₃ nucleation, but is primarily a result of the incubation time required to produce -Al₂O₃ nuclei by diffusional nucleation. It is proposed that the large observed -Al₂O₃ crystal size also does not result from a shear nucleation event in a 'critical size' -Al₂O₃ crystal, but is due to the intrinsically low -Al₂O₃ nucleation density, together with rapid growth of -Al₂O₃ after nucleation.w     

Women's occupational health: a critical review and discussion of current issues

Action to improve women's occupational health has been slowed by a notion that women's jobs are safe and that any health problems identified among women workers can be attributed to unfitness for the job or unnecessary complaining. With increasing numbers of women in the labor force, the effects of work on women's health have recently started to interest health care providers, health and safety representatives and researchers. We begin our summary of their discoveries with a discussion of women's place in the workplace and its implications for occupational health, followed by a brief review of some gender-insensitive data-gathering techniques. We have then chosen to concentrate on the following four areas: methods and data collection; directing attention to women's occupational health problems; musculoskeletal disease; mental and emotional stress. We conclude by pointing out some neglected occupational groups and health issues.     

Importance of anchor genomes for any plant genome project

Progress in agricultural and environmental technologies is hampered by a slower rate of gene discovery in plants than animals. The vast pool of genes in plants, however, will be an important resource for insertion of genes, via biotechnological procedures, into an array of plants, generating unique germ plasms not achievable by conventional breeding. It just became clear that genomes of grasses have evolved in a manner analogous to Lego blocks. Large chromosome segments have been reshuffled and stuffer pieces added between genes. Although some genomes have become very large, the genome with the fewest stuffer pieces, the rice genome, is the Rosetta Stone of all the bigger grass genomes. This means that sequencing the rice genome as anchor genome of the grasses will provide instantaneous access to the same genes in the same relative physical position in other grasses (e.g., corn and wheat), without the need to sequence each of these genomes independently. (i) The sequencing of the entire genome of rice as anchor genome for the grasses will accelerate plant gene discovery in many important crops (e.g., corn, wheat, and rice) by several orders of magnitudes and reduce research and development costs for government and industry at a faster pace. (ii) Costs for sequencing entire genomes have come down significantly. Because of its size, rice is only 12% of the human or the corn genome, and technology improvements by the human genome project are completely transferable, translating in another 50% reduction of the costs. (iii) The physical mapping of the rice genome by a group of Japanese researchers provides a jump start for sequencing the genome and forming an international consortium. Otherwise, other countries would do it alone and own proprietary positions.     

Metal Organic Resin Derived Barium Titanate: I, Formation of Barium Titanium Oxycarbonate Intermediate

Crystallization of BaTiO₃ from an X-ray amorphous, metal organic precursor was investigated by comparing samples heated in O₂, air, argon, and CO₂. It is evident that an intermediate barium titanium oxycarbonate phase forms between 500° and 620°C and that BaTiO₃ forms directly by the endothermic decomposition of this phase between 635° and 700°C. From thermodynamic calculations, thermal analysis, X-ray diffraction, and Raman spectroscopy, it is concluded that the intermediate oxycarbonate is a highly disordered, metastable, and weakly crystalline phase with a stoichiometry close to Ba₂Ti₂O₅CO₃.