Analytical characterization of municipal solid waste incinerator fly ash. Part II

The synergy of the micro FT-IR (Fourier Transform-Infrared) and SEM-EDX (Scanning Electron Microscopy-Energy Dispersive X-ray) techniques has been shown to be particularly helpful and effective for the characterization of inorganic compounds in fly ashes. The experimental data obtained by these techniques have been interpreted in comparison with those of other techniques. The presence of calcium carbonate, some sulfates, ammonium nitrate, calcium hydrogen phosphate, some chlorides, some oxides and aluminium silicates have been verified.     

Thermal stability and degradation mechanisms of poly(acrylic acid) and its salts: Part 3—Magnesium and calcium salts

The magnesium and calcium salts of acrylic acid have been polymerised in aqueous solution using ammonium persulphate as initiator. Both polymers were also prepared by the neutralisation of poly(acrylic acid) with metal oxide in the same medium.

The thermal degradation behaviour of magnesium and calcium polyacrylate was studied using thermogravimetry (TG), differential thermal analysis (DTA) and thermal volatilisation analysis (TVA). Degradation products were investigated by IR spectroscopy, mass spectrometry and GC-MS techniques, the volatile product fraction having first been separated by subambient TVA.

The decompositions of these materials show some similarities to the behaviour of the alkali metal salts of poly(acrylic acid) and to that of the alkaline earth metal salts of poly(methacrylic acid), but there are also important differences. Acetone and carbon dioxide are the most important volatile products and, in addition, there are various other carbonyl containing products. More carbon dioxide, resulting from side group scission, is evolved from magnesium polyacrylate than from calcium polyacrylate, because of the lower thermal stability of magnesium carbonate.     

Purity control of aluminium metal

As a contribution to the neutron activation assay of the reactor grade aluminium, a number of elements have been investigated by a developed analytical scheme. With the performance of ion-exchange chromatography combined with the precipitation techniques, ppm concentration (or even less) of arsenic, antimony, calcium, copper, mercury, selenium and strontium contaminants were demonstrated with good reproducibility. Whenever possible, some of the elements analyzed by radioactivation and proved to be present in high concentration levels were assayed by other standard analytical methods.     

Calcium carbonate phase transformations during the carbonation reaction of calcium heavy alkylbenzene sulfonate overbased nanodetergents preparation

The preparation and application of overbased nanodetergents with excess alkaline calcium carbonate is a good example of nanotechnology in practice. The phase transformation of calcium carbonate is of extensive concern since CaCO(3) serves both as an important industrial filling material and as the most abundant biomineral in nature. Industrially valuable overbased nanodetergents have been prepared based on calcium salts of heavy alkylbenzene sulfonate by a one-step process under ambient pressure, the carbonation reaction has been monitored by the instantaneous temperature changes and total base number (TBN). A number of analytical techniques such as TGA, DLS, SLS, TEM, FTIR, and XRD have been utilized to explore the carbonation reaction process and phase transformation mechanism of calcium carbonate. An enhanced understanding on the phase transformation of calcium carbonate involved in calcium sulfonate nanodetergents has been achieved and it has been unambiguously demonstrated that amorphous calcium carbonate (ACC) transforms into the vaterite polymorph rather than calcite, which would be of crucial importance for the preparation and quality control of lubricant additives and greases. Our results also show that a certain amount of residual Ca(OH)(2) prevents the phase transformation from ACC to crystalline polymorphs. Moreover, a vaterite nanodetergent has been prepared for the first time with low viscosity, high base number, and uniform particle size, nevertheless a notable improvement on its thermal stability is required for potential applications.     

Computational and analytical chemistry: Methodology to study chemical reactions between sodium,calcium, and aluminum fluorides in molten cryolite

Reaction constants and composition profiles in molten cryolite have been theoretically investigated. Hartree-Fock and density functional calculations were applied to determine the exact nature (structure and energetic) of complexes existing in molten cryolite. The aim of this work was thus the understanding of chemical processes occurring in the electrowinning of aluminum and was a demonstration of how computational chemistry (based on density functional theory) can help us to determine structures and reaction energies in particularly complex medium such as cryolite. An analytical study, based on mass balance and equilibrium constants has been undertaken. This was performed on molecular liquid entities taking into account the four-, five- and sixfold coordinated aluminum complexes of the AlF₃-3NaF melt system. Moreover, the effect of calcium has been studied by substituting two sodium atoms with one calcium atom, thus leading to the CaNaA1F₆ system. Two conformers (instead of three for Na) were obtained for this system. They can be described as representing the four- and fivefold coordinated aluminum complexes in molten cryolite. The structurizing effect of calcium was clearly illustrated by the resulting optimized structures, showing that calcium stabilizes the IV and V coordinations of aluminum. By computing reaction constants, we have obtained composition profiles that are presented with those based on experimental data. Comparisons point out that computational chemistry techniques match with experimental results, especially in the case of pure cryolitic melts. For the presence of the fivefold coordinated aluminum complex in cryolite, and the predominance of the fourfold coordinated complex with calcium, it is clear that these computational techniques show us correct trends in predicting the main species in molten media. © 1997 John Wiley & Sons, Inc.     

Quantum chemical study on the interaction of some bisphosphonates and Ca2+: The role of molecular electrostatic potentials in the prediction of binding geometry

Summary Molecular electrostatic potentials have been used to model the calcium binding properties of some bisphosphonate drugs, which are used to treat various bone diseases. The mechanism of action involves the binding of bisphosphonates to the bone surface, where calcium plays an important role. Electrostatic potential maps derived from ab initio partial charges have been compared with both the crystal structure and the fully optimized ab initio structure of (dichloro)methylenebisphosphonate-calcium ion complex. Molecular electrostatic potentials can correctly predict the calcium binding geometry of bisphosphonate-type compounds and this type of information can be used in the practical drug design work.     

Note sur quelques complexes entre nicéthamide (N,N-diéthyl-nicotamide) et/ou de la pémoline (phényl-5-imino-2-oxazolidone-4) et divers sels,particulièrement de sels calciques de monoesters aminoalkylphosphoriques

Note on some complexes between nikethamide and/or pemoline with various salts, especially calcium aminoalkylphosphates A number of binary and ternary complexes of nikethamide and/or pemoline with various calcium salts, particularly calcium aminoalkylphosphates, have been prepared in order to assess their pharmacological properties. The formation of such complexes has been established by IR. spectroscopy.     

Etude par analyse thermique des sels de calcium de quelques acides alcanesulfoniques

Calcium salts of some alkanesulphonic acids have been prepared. Most of them are new. Their dehydration and the decomposition of anhydrous salts have been studied by thermogravimetric analysis (TG) and by thermal differential analysis (DTA) under ordinary pressure. In an inert atmosphere the sulphides formed indicate that carbon-sulphur and oxygen-sulphur bonds have been broken. The mechanism of decomposition of the calcium alkanesulphonates seems to be more complicated than that of the corresponding carboxylates.     

The photo-stabilising action of metal chelates in polypropylene: Part IX—Practical synergism with other commercial systems and the importance of calcium stearate

The photo-stabilising action of three metal chelates (Cyasorb UV 1084, Irganox 1425 and Irgastab 2002) in a number of synergistic formulations with three commercial stabilising systems (Weston 618, Cyasorb UV 531 and Tinuvin 770), in polypropylene films has been examined. The results show that, although antagonistic effects are observed at some mass ratios, synergistic effects prevail at others. The effects are a function of the particular formulation.The addition of calcium stearate to the stabilising mixture can have marked effects on the observed behaviour. Thus, an antagonistic effect can become synergistic if calcium stearate is used in the formulation. The results have scientific and technological implications as calcium stearate is often used as a processing aid in the stabilisation of polypropylene.     

A radiometric investigation of the precipitation of calcium fluoride

Errors arising from solubility losses and co-precipitation in the gravimetric determination of fluoride by precipitation of calcium fluoride by classical and homogeneous methods have been investigated by radiometric techniques. It is shown that co-precipitation of chloride is the larger source of error and least in the homogeneous method. Distribution of chloride in the calcium fluoride precipitate is shown to follow the Doerner-Hoskins distribution law.     

REMOVAL AND RECOVERY OF DYESTUFFS FROM DYEING WASTEWATERS

The toxic nature of some dyestuffs (DSs) has long been recognized. Accordingly, dyeing wastewaters represent a source of water contamination, and should be treated in some way so as to reduce the concentration of the polluting DSs to permissible limits, prior to dumping its wastewater. In addition, some DSs can be recovered for reuse, a point which should represent saving in the overall cost of the dyeing process. Extensive publications on the removal of DSs from dye house wastewaters have been cited in the literature in which many techniques have been applied, biological treatment being the method most widely used as a primary treatment. However, only few publications have been concerned with recovery of DSs from their wastewaters. In the present paper, numerous techniques, if not all, that are presently used for either removal or recovery of DSs have been reviewed, evaluated and compared.     

Effect of acid on morphology of calcite during acid enhanced defluoridation

Fluoride removal from water by lime materials is a promising defluoridation process. Acid enhanced limestone defluoridation (AELD) technique involves precipitation of CaF₂ as well as adsorption of fluoride on the surface of limestone which is capable of reducing fluoride concentration to below the WHO guideline value of 1.5 mg/L. Acids such as acetic acid and citric acid are added to the fluoride water before filtration through limestone column to enhance the Ca²⁺ activity in solution for precipitation of fluoride as CaF₂. This paper describes the effects of these acids on the quality of the limestone during the AELD process, which has been studied to evaluate the reusability of the limestone. The reaction products that formed during the AELD process have also been analyzed. The detail study of the morphology of the limestone before and after use have been done using various analytical techniques, viz., X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy combined with energy dispersive X-ray spectroscopy. The study reveals that the limestone degrades to some extent in the process due to dissolution of calcium carbonate by the acids and adsorption of fluoride by the limestone. While appreciable quantity of the citrate salt of calcium was formed in the column, the acetate salt mostly remained dissolved in the water. Since mainly the surface of the limestone particles take part in the reaction, the limestone particles can be reused for the defluoridation process after cleaning the outer surface. The limestone after use remains also suitable as raw material for cement.     

Fabrication and Properties of Polycaprolactone Composites Containing Calcium Phosphate-Based Ceramics and Bioactive Glasses in Bone Tissue Engineering: A Review

Polycaprolactone (PCL) is a bioresorbable and biocompatible polymer that has been widely used in long-term implants and controlled drug release applications. However, when it comes to tissue engineering, PCL suffers from some shortcomings such as slow degradation rate, poor mechanical properties, and low cell adhesion. The incorporation of calcium phosphate-based ceramics and bioactive glasses into PCL has yielded a class of hybrid biomaterials with remarkably improved mechanical properties, controllable degradation rates, and enhanced bioactivity that are suitable for bone tissue engineering. This review presents a comprehensive study on recent advances in the fabrication and properties of PCL-based composite scaffolds containing calcium phosphate-based ceramics and bioglasses in terms of porosity, degradation rate, mechanical properties, in vitro and in vivo biocompatibility and bioactivity for bone regeneration applications. The fabrication routes range from traditional methods such as solvent casting and particulate leaching to novel approaches including solid free-form techniques.     

The suitability of various calcium electrodes based on metal salts of di-(n-octylphenyl)phosphoric acid and some derivatives for the measurement of calcium in sea water

The calcium salts of di-(n-octylphenyl)-phosphoric acid, di-(p-n-octyl-o-nitrophenyl)-phosphoric acid and di-(p-n-octyl-o-bromophenyl)-phosphoric acid have been investigated as calcium sensors in membrane electrodes. The electrodes have been used for potentiometric titrations of calcium in sea water. The effect of varying the membrane solvent and the chelate metal has been studied.     

Studies towards understanding the mechanism of organic reagent enhancement in flame and plasma atomic absorption spectrometry

A series of organic reagents have been tested in atomic absorption measurement for signal enhancement of metal elements. Organic reagents like tetrabutylammonium bromide are demonstrated to enhance the absorption sensitivity to some specific elements such as calcium and chromium. A group of amines were found to have significant enhancement for chromium and calcium measurements. The function of organic reagents in flame and plasma atomic absorption spectrometry (AAS) was investigated in this work with emphases on mechanism of signal enhancement and interference suppression. An alternative mechanism of organic reagent enhancement in flame and plasma AAS has been suggested based on the experimental results obtained in this work. The reduction environments in flame and plasma produced by the organic reagents are considered as major reason for the signal enhancement.     

Classification of Cm I energy levels using PCA-BPN and PCA-NLM

Two pattern recognition (PR) techniques, principal component analysis-back propagation networks (PCA-BPN) and principal component analysis-nonlinear mapping (PCA-NLM), have been applied to the problem of classifying unknown energy levels of the first spectrum of curium (Cm I) according to their configurations. In comparison, with those reported by early PR techniques and counter propagation neural networks (CPN's), PCA-BPN has been demonstrated to possess much more prediction accuracy as to its performance on test sets. Obtained results further confirm the most previous assignments with these energy levels given by some early PR techniques and CPN. Moreover, the obtained results definitely reassign some energy levels' electronic configurations which were ambiguously conjectured in previous work.     

荧光寿命测定的现代方法与应用

介绍了时间相关单光子计算、相调制和频闪等三种现代荧光寿命测定方法的工作原理,指出了各种方法的优点和局限性;介绍了时间相关单光子计数实验数据的处理方法;概述了时间分辨荧光技术在化学和生命科学中的应用。     

Non-destructive in situ determination of pigments in 15th century wall paintings by Raman microscopy

Raman microscopy has been applied to the study of 15th century wall paintings in a chapel of St. Orso Priory palace (Aosta, Italy) in view of their restoration. The use of a transportable instrument has made it possible to work non-destructively in situ without sampling. The main inorganic pigments used by the unknown artist, namely mercury sulphide, azurite, white lead, red and yellow ochre, carbon black and lead tin yellow type I have been identified, and the presence of organic substances and of some decay products (calcium sulphate and oxalate) has been observed.     

Characterization of oxide coatings on glass

Some representative characteristics of oxide films deposited on glass by different techniques have been briefly described as well as several relevant methods of thin-film analysis to determine these quantities. The most powerful information obtained by some analytical techniques have been given, and some typical problems that may occur during the analysis of oxidic thin films have been discussed. With a few selected results, the potential of some modern methods has been demonstrated.     

Constituents of the roots of Boerhaavia diffusa L. III. Identification of Ca2+ channel antagonistic compound from the methanol extract

Two known lignans, liriodendrin and syringaresinol mono-beta-D-glucoside, have been isolated from the methanol extract of the roots of Boerhaavia diffusa L. (Nyctaginaceae), and the former compound was found to exhibit a significant calcium (Ca2+) channel antagonistic effect in frog heart single cells using the whole-cell voltage clamp method. Reexamination of the carbon-13 nuclear magnetic resonance (13C-NMR) spectra of these compounds was also carried out by the use of two-dimensional NMR techniques including a 1H-detected heteronuclear multiple bond connectivity (HMBC) experiment, and it was found that the previous signal assignments for C-1' and C-4' have to be revised.