Templated Grain Growth of Textured Bismuth Titanate

Textured bismuth titanate, Bi₄Ti₃O₁₂ (BiT), was produced by templated grain growth (TGG). Molten-salt-synthesized BiT platelets were dispersed in a matrix of 200 nm BiT powder and aligned by tape casting. Highly textured BiT was obtained with the use of only 5 vol% template particles by sintering at 1000°C for 1 h. The uniformity of the through-thickness texture is much higher than reported in the literature for BiT tapes cast with 100% platelets. Initial platelet alignment is shown to increase because of frequent interaction with the fine powder particles during tape casting. By avoiding pressure densification techniques and using only a small portion of anisometric particles, TGG is a low-cost option for fabricating textured ceramics.     

Hybrid Gels for Homoepitactic Nucleation of Mullite

Hybrid gels, defined as gels from mixtures of polymerically and colloidally derived sols, offer many opportunities for crystalline microstructure development upon heating. In this study, hybrid mullite gels are formed by mixing a colloidal boehmite—silica sol with a polymeric aluminum nitrate—tetraethoxysilane-derived sol. The polymeric gel crystallizes in situ to form mullite that acts as seed crystals for homoepitactic nucleation during the subsequent transformation of the colloidal component of the hybrid gel. Compared with the entirely colloidal gel, the introduction of a 30 wt% polymeric gel fraction results in an increase in apparent nucleation frequency from ∼5x10¹¹ to ∼1x10¹⁴ nuclei / cm³ at 1375°C, a reduction in high-temperature grain size from 1.4 to 0.4 μm at 1550°C, and an increase in the degree of microstructural homogeneity, as evidenced by intragranular pore removal.     

Gender, women's work and ergonomics

A submaximal test for estimating the physical work capacity has been developed and compared with a more complicated bicycle test. The testing procedure is a modified Harvard step test which in its original form is a maximal test The pulse rate was counted during work.

The step height was 40 cm for young males and 27 cm for the older ones and for the females 33 cm; the stepping rate was 22·5 steps per min.

The average values for ‘ step test 40 cm ’, and ‘ bicycle test 900 kgm/min ’ for male subjects were: oxygen intake 2·11 ±0·04 and 2·15±0·02 l./min ; pulse rate during work 130±1·5 and 132± 1·9 beats/mm respectively. The average values for ‘ step test 33 cm ’ and ‘ bicycle test 600 kgm/min ’ for female subjects were : oxygen intake 1·56±0·03 and 1·48±0·02 l./min ; pulse rate during work 140±1·6 and 138 ±2·2 beats/min respectively. The mechanical efficiency did not vary with the body height or weight.

As the aerobic capacity for trained individuals without excessive fat is closely correlated to the body weight the light ones will be tested at a relatively higher intensity than the heavy ones, when the bicycle test is used with a fixed load. In the step test the load varies with the body weight but the oxygen intake per kilogram body weight is constant.     

SiC-Whisker-Reinforced Cellular SiO2 Composites

Fabrication of lighweight, cellular ceramic composites by foaming sol–gels is presented. Foams of 20-vol%-SiC-whisker-reinforced SiO₂ can be tailored with relative densities as low as 10%, with either open or closed cell structures. In addition to reducing drying shrinkage and thus gel cracking, whisker reinforcement significantly increases the strength of the composite foams relative to pure silica foams.     

Constrained Densification of Alumina/Zirconia Hybrid Laminates, I: Experimental Observations of Processing Defects

Various forms of damage were observed in pressure-less-sintered Al₂O₃/ZrO₂symmetric laminates and asymmetric laminates (bilayers) fabricated by tape casting and lamination. These defects included channel cracks in the ZrO₂ layers, Al₂O₃ edge-effect cracks parallel to the layers, delamination in the Al₂O₃layers, and debonding between the Al₂O₃and ZrO₂layers. Based on detailed microscopic observations, the defects were attributed to sintering rate and thermal expansion mismatch between the layers. Cracks or cracklike defects were formed in the early stages of densification, and these cracks either opened during sintering or acted as preexisting flaws for thermal expansion mismatch cracks. Consequently, the extent of cracking could be reduced or even eliminated by decreasing mismatch stresses during the sintering and cooling stages. This can be accomplished by reducing the heating and/or cooling rates or by adding Al₂O₃in the ZrO₂layers. The sintering mismatch stresses were estimated from the degree of curling in asymmetric laminates and from layer viscosities that were obtained by cyclic loading dilatometry. The measured curvature was an indication of the mismatch in sintering strain between Al₂O₃and ZrO₂and were consistent with the dilatometric data that were obtained for the component layers.     

Transformation, Microstructure Development, and Densification in α-Fe2O3-Seeded Boehmite-Derived Alumina

Addition of α-Fe₂O₃ seed particles to alkoxide-derived boehmite sols resulted in a 10-fold increase in isothermal rate constants for the transformation of γ- to α-Al₂O₃. Changes in porosity and surface area with sintering temperature showed no effect of seeding on coarsening of the transition alumina gels, but the 200-fold decrease in surface area associated with transformation to α-Al₂O₃ occurred ∼ 100°C lower in seeded gels compared with unseeded materials. As a result of high nucleation frequency and reduced microstructure coarsening, fully transformed seeded alumina retained specific surface areas >22 m²/g and exhibited narrow pore size distributions, permitting development of fully dense, submicrometer α-Al₂O₃ at ∼ 1200°C.     

Erratum to: In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

Nano Research - The article In situ observation of synthesized nanoparticles in ultradilute aerosols via X-ray scattering, written by Sarah R. McKibbin, Sofie Yngman, Olivier Balmes, Bengt O....     

Texture Development and Microstructure Evolution in Liquid-Phase-Sintered α-Alumina Ceramics Prepared by Templated Grain Growth

Texture development in alumina that contains calcia and silica and has been templated with platelet-shaped α-Al₂O₃ particles has been evaluated. The texture fraction is shown to be related directly to template growth. Texture quality is controlled by the template concentration, decreasing at template concentrations of >10%, as a result of template–template interactions during tape casting. Almost fully textured alumina has been obtained at template concentrations of ≥20%. The growth of template grains is much more rapid in the radial direction and is shown to be inversely related to the thickness of the grain-boundary liquid. The activation energy for growth (376 kJ/mol) and the inverse relation with the grain-boundary thickness indicate that template growth in the radial direction is controlled by Al³⁺ diffusion.     

A description of agricultural releases of anhydrous ammonia in Minnesota

Anhydrous ammonia releases were reviewed during a three-year period (1995 to 1997) by the Minnesota Hazardous Substances Emergency Events Surveillance Program. Of the 800 hazardous substances emergency events recorded, 97 (12.1%) involved anhydrous ammonia. This review found that 51% of the total quantity of anhydrous ammonia released in emergency events came from agriculture (92% excluding one train car event). Emergency events involving anhydrous ammonia were almost twice as likely to involve victims than other events. However, nonagricultural and agricultural anhydrous ammonia emergency events had similar probabilities for victims. Nonagricultural anhydrous ammonia events were more likely to result in evacuations than agricultural anhydrous ammonia events. Given the large amount of agricultural anhydrous ammonia used every year in Minnesota, an average of 690 million pounds per year, the tiny fraction (0.005%) of agricultural ammonia released in emergency events, and the small number of victims and evacuations, agricultural ammonia is being handled relatively safely. Nevertheless, most accidents involving agricultural ammonia could be prevented if operators would practice relatively simple safety precautions.