Hairdressing shish-kebabs; comprehensive survey and theoretical discussion of overgrowth crystallization

The platelet component of shish-kebabs crystallizes after the core, during cooling or storage below the formation temperature of the core. Three basic platelet morphologies were previously identified which were mutually interconvertible, a process we have termed “hairdressing”. In this paper we show that these three categories are special cases of a continuous range of overgrowth spacings. Crystallization at high temperatures gives widely spaced overgrowths and, as the crystallization temperature is reduced, so the overgrowth spacing decreases gradually. In the extreme case (only obtainable by quenching) the overgrowths become so close as to overlap and appear continuous. We also report a variety of further effects which were caused by exposing the shish-kebabs, while in solvent, to temperatures above their initial formation temperature. A new theoretical approach is described which considers the depletion of material available to form new overgrowths during crystallization. Two versions of this theory are presented (one a computer simulation and one analytic); interpreting our results on the basis of this theory we show that shish-kebabs crystallize at high temperatures even when quenched (90°C and above except in a few exceptional circumstances) and we are able to explain all the features of shish-kebab crystallization that we have observed.     

A database for QA/QC in neutron activation analysis and gamma-ray spectrometry

A database has been designed for storing, retrieving and analyzing information about samples, experimental conditions and results obtained by neutron activation analysis and gamma-ray spectrometry. It has been created using Microsoft ACCESS 2002 under a Windows operating system. The database has been designed not only for saving information but also for quality assurance and quality control purposes. The structure of the relational design has been discussed and demonstrated with a new graphical feature of ACCESS 2002 called PIVOTCHART.     

Retention of alkali,alkaline earth and transition metals on an itaconic acid cation-exchange column. Eluent pH,ionic strength and temperature effects upon selectivity

The unusual selectivity of a methylene succinic (itaconic) acid modified polymeric column was investigated for the separation of alkali, alkaline earth, transition and heavy metals employing non-chelating inorganic eluents. The retention of selected metal ions on the column was investigated with simple HNO3 eluents and eluents prepared from KNO3 and KCl salts of varying pH (adjusted using HNO3). From these studies both the effect of eluent ionic strength and pH upon retention was evaluated for the itaconic acid stationary phase. The results obtained showed that despite slow exchange kinetics causing poor efficiencies, acceptable baseline separations of selected alkaline earth and transitions could be obtained under optimum conditions (the baseline separation of Mg(II), Ca(II), Mn(II), Cd(II), Zn(II) and Co(II) was possible using a 15 mM KNO3-5 mM KCl eluent at pH 3.50 in under 25 min). The use of an simple ionic strength step gradient was shown that facilitated the addition of Pb(II) to the above group of metal ions. An investigation into the effect of temperature upon peak efficiency and retention showed increased column temperature could be used to improve the resolution of closely eluting metal ions such as Ca(II) and Sr(II) and Ca(II) and Mn(II).     

Synergistic extraction of Ce(III), Eu(III) and Tm(III) with a mixture of picrolonic acid and benzo-15-crown-5 in chloroform

Summary The synergistic mixture comprising picrolonic acid (HPA) and benzo-15-crown-5 (B15C5) in chloroform has been used for the extraction of Ce(III), Eu(III) and Tm(III) as representatives of lanthanide(III) ions from pH 1-2 solutions having ionic strength of 0.1 mol^. dm^-3(K⁺/H⁺, Cl^-). The composition of the extracted species has been determined as M(PA)₃^. nB15C5 where M is Ce, Eu and Tm and n=1 or 2. The influence of various anions and cations on the extraction of these ions has also been studied and only oxalate, cyanide and tartrate have some deleterious effect. The extraction equilibrium constants have been evaluated and discussed.     

The system K2SO4-K2S

A new experimental technique has been developed to determine the phase equilibrium diagram for the system K₂SO₄-K₂S.The technique involves isothermal thermogravimetry of potassium sulphate during reduction to potassium sulphide at elevated temperatures in a stream of dry oxygen-free hydrogen gas. Several abrupt changes in the rate of weight loss occur in each curve and these can be related to phase changes in the phase diagram for the system.On the basis of such results the liquidus and solidus (solid solution) boundaries can be located.Simple thermal analysis is used to confirm the eutectic temperature and various liquidus temperatures.The diagram K₂SO₄-K₂S is a simple eutectic system with the eutectic at 610 and 23 mole % K₂S. The limits of solid solubility of K₂S in K₂SO₄ and K₂SO₄ in K₂S at the eutectic temperature are 11 % and 36 mole% respectively.The odd shape of the liquidus curves on each side of the eutectic suggests the possibility of phase changes in both K₂SO₄ and K₂S solid solutions. No evidence for this was obtained from thermal analysis.

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Zusammenfassung Eine neue experimentelle Technik wurde zur Bestimmung des Phasengleichgewichtsdiagramms des Systems K₂SO₄-K₂S entwickelt.Die Technik umfasst die isotherme Gravimetrie von Kaliumsulfat wÄhrend der Reduktion zu Kaliumsulfid bei erhöhten Temperaturen in strömenden trockenen und Sauerstoff-freien Wasserstoff. Verschiedene plötzliche Änderungen der Geschwindigkeit des Gewichtsverlustes treten bei jeder Kurve auf und können mit den PhasenÄnderungen im Phasendiagramm des Systems in Zusammenhang gebracht werden.Durch diese Ergebnisse können die GrenzflÄchen der flüssigen und der Festphasenlösung festgestellt werden.Die einfache Thermoanalyse wird zur BestÄtigung der eutektischen Temperatur und verschiedener Liquidus-Temperaturen herangezogen.Das Diagramm K₂SO₄-K₂S ist ein einfaches eutektisches System mit dem Eutektikum bei 610 und 23 Mol % K₂S. Die Grenzwerte einer festen Lösung von K₂S in K₂SO₄ und K₂SO₄ in K₂S betragen bei der eutektischen Temperatur 11% bzw. 36 Mol %.Die aussergewöhnliche Form der Liquidus-Kurven zu beiden Seiten des Eutektikums lÄsst auf die Möglichkeit von PhasenÄnderungen in den Festlösungen von sowohl K₂SO₄ wie auch von K₂S schliessen Hierzu ergab jedoch die Thermoanalyse keine BestÄtigung.

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Résumé Une nouvelle technique expérimentale a été développée afin de déterminer le diagramme d'équilibre des phases dans le système K₂SO₄-K₂S.La technique fait appel à la thermogravimétrie isotherme du sulfate de potassium lors de sa réduction en sulfure de potassium à températures élevées dans un courant de gaz hydrogène sec exempt d'oxygène. Plusieurs changements abrupts de vitesse de perte de poids ont lieu sur chaque courbe et ces changements peuvent Être rapportés aux changements de phases dans le diagramme de phases du système.A partir de tels résultats on peut déterminer les limites du liquidus et du solidus (solution solide).L'analyse thermique simple a été utilisée pour confirmer la température eutectique etdiverses températures du liquidus.Le diagramme K₂SO₄-K₂S forme un système eutectique simple à 610 et 23 p.c. molaires de K₂S. Les limites de la solubilité en phase solide de K₂S dans K₂SO₄ et de K₂SO₄ dans K₂S sont, à la température eutectique, respectivement de 11 et 36 mol %.La forme particulière des courbes du liquidus de chaque cÔté de l'eutectique fait penser à la possibilité de changements de phases dans les solutions solides tant de K₂SO₄ que de K₂S, mais l'analyse thermique n'en a pas donné de preuve.

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K₂SO₄-K₂S . , . , . ( ). . K₂SO₄-K₂S 610 23% K₂S. K₂S K₂SO₄ K₂SO₄ K₂S , , 11 36 . K₂SO₄ K₂S . , .

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The authors would like to thank the National Research Council of Canada for their financial support.     

Performance evaluation of k 0-instrumental neutron activation analysis and flame atomic absorption spectrophotometry in the characterization of various types of alloys

Certified alloys of Ni–Cu based, Fe based and Cu–Sn based were analysed by semi-absolute, standardless k ₀-instrumental neutron activation analysis (k ₀-INAA) and flame atomic absorption spectrophotometry (FAAS) aiming at evaluating their comparative performances. In k ₀-INAA measurements, the irradiations were performed at miniaturized neutron source reactor having thermal neutron flux of about 1 × 10¹² cm^?2 s^?1. The experimentally optimized parameters for INAA suggested a maximum of three irradiations for the quantification of 21 elements within 5 days. The same experiments also produced quantitative results of 13 elements not reported in the certificates of the reference materials. AAS was, however, unable to determine any of those elements. Accuracy of the two techniques was assessed by comparing their average root mean squared errors. The data analysis concluded that k ₀-INAA had better sensitivity and accuracy than FAAS.     

Synthesis and biological evaluation of benzimidazole pendant cyanopyrimidine derivatives as anticancer agents

Thirteen new benzimidazole pendant cyanopyrimidine derivatives were synthesized. The compounds were synthesized through multistep reaction protocol. The structures of synthesized derivatives were studied by EI-MS, ¹H NMR, FT-IR and elemental analysis. All the compounds were studied for their anticancer activity at National Cancer Institute. Except compound 7j , all the compounds unveiled cytotoxicity against cancer cells. The most active compound 7a had shown highest value of growth inhibition of 88.44% and 84.19% against HOP-92 and T-47D cancer cell lines.     

Gelation and the production of surface grown polyethylene fibres

Summary In the course of examining the limiting conditions for growth of polyethylene fibres by the surface growth method (1, 2) an unexpected gelation effect was observed. Accordingly a solution, after having been stirred at such elevated temperatures where no visible crystallization can take place, is found to set as a gel after cooling under quiescent conditions. It is established that the ability to form this gel is a necessary condition for fibre production byPennings andZwijnenburg's surface growth method which by the new findings essentially should consist of the stretching of such gels. We verified that material indeed accumulates at the surface of the rotor used in the surface growth method as was originally envisaged, but we now infer that this material consists of gel particles formed during the preceding treatments. This adhesion of the gel to a rotating surface enables it to be readily stretched by an externally introduced fibre as done in the surface growth method. The gel precursor is of interest in its own right. We find that it is a transient structure but with long, up to several hours, persistence time during which the solution `remembers' that it has been stirred. The structure itself is presumably an incipient network forming crystallization induced by localised chain stretching, where the crystal junctions are likely to provide the nuclei for the more permanent fibrous crystals which arise on cooling causing the gel to set. Electron microscopy indeed identified smooth fibres in the gel which could develop into shish-kebabs on appropriate treatment, while the bulk of the gel consists of large single crystal platelets which arise within the network on final cooling to room temperature. Finally we suggest, that many, if not all, shishkebab structures conventionally observed on stirring arise by the stretching of the gel network formed at a preceding stage of the preparation procedure.