Deformation-induced localized solid-state amorphization in nanocrystalline nickel

Although amorphous structures have been widely obtained in various multi-component metallic alloys, amorphization in pure metals has seldom been observed and remains a long-standing scientific curiosity and technological interest. Here we present experimental evidence of localized solid-state amorphization in bulk nanocrystalline nickel introduced by quasi-static compression at room temperature. High-resolution electron microscope observations illustrate that nano-scale amorphous structures present at the regions where severe deformation occurred, e.g. along crack paths or surrounding nano-voids. These findings have indicated that nanocrystalline structures are highly desirable for promoting solid-state amorphization, which may provide new insights for understanding the nature of the crystalline-to-amorphous transformation and suggested a potential method to produce elemental metallic glasses that have hardly been available hitherto through rapid solidification

Ion homeostasis in the Chloroplast

peer reviewedThe chloroplast is an organelle of high demand for macro- and micro-nutrient ions, which are required for the maintenance of the photosynthetic process. To avoid deficiency while preventing excess, homeostasis mechanisms must be tightly regulated. Here, we describe the needs for nutrient ions in the chloroplast and briefly highlight their functions in the chloroplastidial metabolism. We further discuss the impact of nutrient deficiency on chloroplasts and the acclimation mechanisms that evolved to preserve the photosynthetic apparatus. We finally present what is known about import and export mechanisms for these ions. Whenever possible, a comparison between cyanobacteria, algae and plants is provided to add an evolutionary perspective to the description of ion homeostasis mechanisms in photosynthesis

The re-entry of disordered phases in a crystalline polymer poly-4-methyl-pentene-1

In situ x-ray expts. are reported on a cryst. polymer, poly(4-methylpentene-1) (I) as a function of pressure (P) and temp. (T) carried out under isothermal and isobaric conditions. At room temp., when the cryst. tetragonal phase (Ct) of I is subjected to pressure, it passes through a range of mesomorphic phases leading to complete amorphization. The melting temp. (Tm) gradually increases with P up to 3Kb where the trend reverses on further increase in P leading to a decrease in Tm. This, combined with the pressure-induced amorphization at room temp. raises the possibility of reentrant of 2 widely sepd. regions of disordered phases (along the T axis) in the P-T phase diagram. This effect, namely a reentrant of disordered phases, i.e. disordering setting in on isobaric cooling, at appropriately elevated P, was in fact obsd. exptl. In the course of the above expts. a new hexagonal crystal (Ch) phase was identified lying between Ct and the low T disordered phase along the T axis of P-T phase diagram. This Ch phase is attainable along 2 routes with basically different characteristics. Also, there is a triple point where the liq., Ct, and Ch phases are in equil. Recently similar observations were reported for inorg. materials such as silicates, phosphates, sulfates, and ice-water (the latter at low T and high P), so that the newly recognized behavior pattern seems to be of wider generality beyond the subject of polymers. [on SciFinder (R)