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121.
A pH‐sensitive detector for flow‐through potentiometry based on a graphite/quinhydrone/silicone composite electrode was applied to determine calcium and magnesium in aqueous solutions. The determinations are performed by FIA titrations with EDTA as the carrier solution. The method was applied to the analysis of mineral water, drinking water, and river water. The results were compared with those obtained by batch complexometric titration. The proposed new method is suitable for the simple, rapid and automated determination of water hardness in small sample volumes of aqueous solutions. The detection limit for both ions is about 1×10?5 mol L?1, the standard deviation is less than 2%. The sampling frequency is 60 determinations per hour. 相似文献
122.
123.
Bin Duan 《Polymer Degradation and Stability》2010,95(9):1655-3700
This study focused on the fabrication of calcium phosphate (Ca-P)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposite scaffolds loaded with biomolecules using the selective laser sintering (SLS) technique and their evaluation. Ca-P/PHBV nanocomposite microspheres loaded with bovine serum albumin (BSA) as the model protein were fabricated using the double emulsion solvent evaporation method. The encapsulation efficiency of BSA in PHBV polymer microspheres and Ca-P/PHBV nanocomposite microspheres were 18.06 ± 0.86% and 24.51 ± 0.60%, respectively. The BSA loaded Ca-P/PHBV nanocomposite microspheres were successfully produced into three-dimensional porous scaffolds with good dimensional accuracy using the SLS technique. The nanocomposite microspheres served as protective carriers and maintained the bioactivity of BSA during SLS. The effects of SLS parameters such as laser power and scan spacing on the encapsulation efficiency of BSA in the scaffolds and in vitro BSA release were studied. An initial burst release was observed, which was followed by a slow release of BSA. After 28-day release, The PHBV matrix was slightly degraded after 28-day in vitro release study. It was shown that nanocomposite scaffolds with controlled architecture obtained via SLS could be incorporated with biomolecules, enhancing them with more functions for bone tissue engineering application or making them suitable for localized delivery of therapeutics. 相似文献
124.
Jianyun Wang Dongming Zhang Xixun Yu Changsheng Zhao 《Polymer Degradation and Stability》2010,95(7):1205-1012
Organic and inorganic composite material is becoming a solution on making the mechanical and degradation properties of biomaterial more suited. Porous calcium polyphosphate was immersed into different concentrations of carboxymethyl chitosan before immersing 10% alginate dialdegyde. After freeze-drying, the scaffolds were performed in physiologic saline. At stated day, the weightloss, Ca2+ concentration, pH value and morphology were measured. The biocompatibility of the composite was demonstrated by extract and direct contact tests. As the results showed, the degradation rates of composites were faster, and the compressive strength became bigger because of the cross-linked network formed by Carboxymethyl chitosan (CMC) and alginate dialdehyde (ADA). The pH value of composite was higher than that of calcium polyphosphate (CPP) due to the organic part of composite’s pH was in slight alkaline. From the SEM, the cross-linked network structure could be observed clearly. Because the glycosaminoglycans-like chains in CMC molecules, which are typically presented in extracellular matrix (ECM), extractions of composite material gave the cells good adhesion and growth condition. All the results testified the composite scaffold was a good candidate for bone repair. 相似文献
125.
Emily Asenath-Smith 《Journal of solid state chemistry》2010,183(7):1670-14
Brownmillerite calcium ferrite was synthesized in air at 1573 K and thermoelectric properties (direct current electrical conductivity σ, Seebeck coefficient α, thermal conductivity κ, thermal expansion αL) were measured from 373 to 1050 K in air. Seebeck coefficient was positive over all temperatures indicating conduction by holes, and electrical properties were continuous through the Pnma-Imma phase transition. Based on the thermopower and conductivity activation energies as well as estimated mobility, polaron hopping conduction was found to dominate charge transport. The low electrical conductivity, <1 S/cm, limits the power factor (α2σ), and thus the figure of merit for thermoelectric applications. The thermal conductivity values of ∼2 W/mK and their similarity to Ruddlesden-Popper phase implies the potential of the alternating tetrahedral and octahedral layers to limit phonon propagation through brownmillerite structures. Bulk linear coefficient of thermal expansion (∼14×10−6 K−1) was calculated from volume data based on high-temperature in situ X-ray powder diffraction, and shows the greatest expansion perpendicular to the alternating layers. 相似文献
126.
Vitalie Stavila Jae-Hyuk Her Wei Zhou Son-Jong Hwang Leigh Anna M. Ottley 《Journal of solid state chemistry》2010,183(5):1133-1140
Calcium borohydride can reversibly store up to 9.6 wt% hydrogen; however, the material displays poor cyclability, generally associated with the formation of stable intermediate species. In an effort to understand the role of such intermediates on the hydrogen storage properties of Ca(BH4)2, calcium dodecahydro-closo-dodecaborate was isolated and characterized by diffraction and spectroscopic techniques. The crystal structure of CaB12H12 was determined from powder XRD data and confirmed by DFT and neutron vibrational spectroscopy studies. Attempts to dehydrogenate/hydrogenate mixtures of CaB12H12 and CaH2 were made under conditions known to favor partial reversibility in calcium borohydride. However, up to 670 K no notable formation of Ca(BH4)2 (during hydrogenation) or CaB6 (during dehydrogenation) occurred. It was demonstrated that the stability of CaB12H12 can be significantly altered using CaH2 as a destabilizing agent to favor the hydrogen release. 相似文献
127.
Athanassios Panagiotopoulos Spyros P. Perlepes Evangelos G. Bakalbassis Aris Terzis Catherine P. Raptopoulou 《Polyhedron》2010
A bioinorganic approach into the problem of the isomorphous substitution of calcium(II) by lanthanide(III) ions in biological systems is discussed. Reactions of malonamic acid (H2malm) with CaII and NdIII sources under similar conditions yielded the compounds [Ca(Hmalm)2]n (1), [Nd(Hmalm)2(H2O)2]n(NO3)n (2) and [Nd(Hmalm)2(H2O)2]nCln·2nH2O (3·2nH2O). Their X-ray crystal structure data show that the malonamate(-1) ligand presents two different ligation modes and coordinates through the two carboxylate and the amide-O atoms, thus bridging three CaII ions in 1 and two NdIII ions in 2 and 3·2nH2O. Complex 1 is a 3D coordination polymer based on neutral repeating units, whereas 2 and 3·2nH2O are 1D coordination polymers based on the same cationic repeating unit. Hydrogen bonding interactions further stabilize the 3D framework structure of 1 and assemble the 1D chains of 2 and 3·2nH2O into 3D networks. The three complexes were characterized spectroscopically (IR, far-IR, and Raman) and the thermal decomposition of 2 and 3·2nH2O was monitored by TG/DTA and TG/DTG measurements. Variable-temperature magnetic susceptibility data for 2 are also reported. The bioinorganic chemistry relevance of our results is discussed. 相似文献
128.
<正>The effect ofαphase nucleating agent(NA) 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol(DMDBS) on crystallization and physical properties of polypropylene/calcium carbonate(PP/CaCO_3) composites has been comparatively investigated.Compared with binary PP/CaCO_3 composites,in which CaCO_3 exhibits weak heterogeneous nucleation, inconspicuous reinforcement and toughening effects for PP,the introduction of a few amounts of DMDBS induces a great increase of the degree of crystallinity.Largely improved tensile properties,fracture toughness at relatively higher temperature and heat deformation temperature(HDT) are observed for DMDBS nucleated PP/CaCO_3 composites. 相似文献
129.
对近年来国内火焰原子吸收光谱法测定钙的样品预处理方法的进展进行了评述,内容包括干灰化法、酸消解法、微波消解和其他方法。 相似文献
130.
Rare earth doped BaZrO3 is one of most promising proton conducting oxides as it has high proton conductivity and sound chemical stability. Sintering aids such as ZnO, however, should be incorporated in order to improve poor sinterability. In this study, the effects of adding ZnO on proton conductivity of Yb-doped BaZrO3 (BZYb) were investigated. From the electrical conductivities measured under various water vapor pressures, concentration and mobility of the proton were obtained. Proton mobility of BZYb with ZnO (BZYb-Zn) was smaller than that of BZYb while hydration enthalpy of BZYb-Zn was more negative than that of BZYb. 相似文献