Synthesis of Convex Hexoctahedral Pt Micro/Nanocrystals with High-Index Facets and Electrochemistry-Mediated Shape Evolution
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Systematic manipulation of nanocrystal shapes is prerequisite for revealing their shape-dependent physical and chemical properties. Here we successfully prepared a complex shape of Pt micro/nanocrystals: convex hexoctahedron (HOH) enclosed with 48 {15 5 3} high-index facets by electrochemical square-wave-potential (SWP) method. This shape is the last crystal single form that had not been achieved previously for face-centered-cubic (fcc) metals. We further realized the shape evolution of Pt nanocrystals with high-index facets from tetrahexahedron (THH) to the HOH, and finally to trapezohedron (TPH) by increasing either the upper (EU) or lower potential (EL). The shape evolution, accompanied by the decrease of low-coordinated kink atoms, can be correlated with the competitive interactions between preferentially oxidative dissolution of kink atoms at high EU and the redeposition of Pt atoms at the EL.Suspension
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'Disintegration' and 'dissolution' of solid drug dosage forms are considered as partial processes of drug liberation. Besides the (apparent) disintegration time that is determined in the official disintegration tester, there is a second (intrinsic) disintegration time which can be deduced from the experimental dissolution data, but shows only limited correlation with the former. Various methods for the graphical resolution of dissolution data and the calculation of the intrinsic disintegration time therefrom are discussed. For the simultaneous determination of disintegration and dissolution, the approved rotating flask method is recommended.
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Abstract Thorium oxide is poorly soluble: unlike uranium oxide, concentrated nitric acid medium is not sufficient to get quantitative dissolution. Addition of small amounts of fluoride is required to achieve thorium oxide total dissolution. The effect of several parameters on thorium oxide dissolution in order to optimize the dissolution conditions is reported in this paper. Thus the influence of solid characteristics, dissolution method, temperature and composition of dissolution medium on ThO 2 dissolution rate has been studied. No complexing agents tested other than fluoride allows total dissolution. Beyond a given HF concentration a decrease of the dissolution rate is observed due to the formation of a precipitate at the solid/solution interface. It was demonstrated by XPS measurements that this precipitate is constituted of thorium fluoride (ThF 4 ) formed during the ThO 2 dissolution. The low concentration of HF required to achieve a total dissolution and the activation energy value measured tends to show a catalytic effect of HF on the dissolution process.
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In this paper the theoretical background of dissolution determining the oral administration, the physicochemical and physiological factors influencing the rate of dissolution, the relation between solubility and dissolution, the most important pharmacopoeial and miniaturized dissolution measurements and finally the dissolution in biorelevant media are reviewed.
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