Effect of magnetic field on sodium arsenate metastable zone width and crystal nucleation kinetics for crystallization

Sodium arsenate, the main component of arsenic-containing solid waste pollutants, causes serious environmental health threats. Crystallization is one of the effective methods for separating and purifying sodium arsenate from arsenic-alkali residue lixivium. However, the crystallization process is limited for its low observability and the lack of separation and purification data. In this work, a laser detection system with a magnetic field generator was designed, and the solubility, metastable zone width, interfacial tension, interfacial entropy factor, crystal nucleation, and growth rate of sodium arsenate were investigated in a constant composition environment. The results showed that the solubility, metastable zone width, interfacial tension, and interfacial entropy factor decreases with the presence of a magnetic field. The magnetic field shortened the crystallization induction time and changed the nucleation and growth rate of sodium arsenate. Under the magnetic field, the nucleation rate increased from 2.43 × 10¹⁶ to 8.98 × 10¹⁷ (s m³)⁻¹, and the growth rate decreased from 4.94 × 10⁻⁸ to 2.73 × 10⁻⁸ (s m³)⁻¹, the growth mechanism of sodium arsenate as a continuous growth mode was unchanged. In addition, the X-ray diffraction and infrared showed that the crystal structure of sodium arsenate is unaffected by the magnetic field, indicating that the enhancement of the crystallization process of sodium arsenate with the magnetic field could be a feasible method in engineering application.     

A fully automatic apparatus for stripping voltammetry Application to the determination of triphenyltin compounds

An apparatus for automatic stripping voltammetry is described. The polarograph unit (sweep generator, potentiostat, and current read-out) is constructed from operational amplifier modules and the various operations of sample injection, pre-electrolysis, stripping, etc are controlled by a cam cycle-timer. Application to the determination of submicrogram concentrations of triphenyltin acetate and hydroxide is described.     

Nucleation parameters for polymer crystallization from non-isothermal thermal analysis

Differential scanning calorimetry (DSC) has been used to obtain kinetic and nucleation parameters for polymer crystallization under a non-isothermal mode of operation. The available isothermal nucleation growth-rate equation has been modified for non-isothermal kinetic analysis. The values of the nucleation constant (K _g ) and surface free energies (, _e ) have been obtained for i-polybutene-1, i-polypropylene, poly(L-lactic acid), and polyoxymethylene and are compared with those obtained from isothermal kinetic analysis; a good agreement in both is seen.     

A new apparatus for simultaneous differential thermal analysis and gas evolution analysis

A new apparatus is described which permits the simultaneous recording of the differential thermal analysis and gas evolution curves for a given sample from ambient to 900°. The sample is pyrolyzed in a dynamic helium gas atmosphere using a conventional DTA furnace and sample holder assembly. The evolved decomposition products are detected in the helium gas stream by means of a thermistor thermal conductivity cell. From a knowledge of the GE curve and an analysis of the decomposition products, a more accurate interpretation of the DTA curve can be made.     

A high pressure differential thermal analysis apparatus

A high pressure differential thermal analysis apparatus is described which is capable of operation in the pressure range from 1-600 atm of nitrogen gas and at temperatures from 25 to 500°C. Use of the apparatus is illustrated by the deaquation reactions of CuCl₂·2H₂0 and CoSO₄·7H₂O at pressures from 1 to 69 atm.     

Hydration breaking and chemical ordering in a levitated NaCl solution droplet beyond the metastable zone width limit: evidence for the early stage of two-step nucleation

For over two decades, NaCl nucleation from a supersaturated aqueous solution has been predicted to occur via a two-step nucleation (TSN) mechanism, i.e., two sequential events, the formation of locally dense liquid regions followed by structural ordering. However, the formation of dense liquid regions in the very early stage of TSN has never been experimentally observed. By using a state-of-the-art technique, a combination of electrostatic levitation (ESL) and in situ synchrotron X-ray and Raman scatterings, we find experimental evidence that indicates the formation of dense liquid regions in NaCl bulk solution at an unprecedentedly high level of supersaturation (S = 2.31). As supersaturation increases, evolution of ion clusters leads to chemical ordering, but no topological ordering, which is a precursor for forming the dense disordered regions of ion clusters at the early stage of TSN. Moreover, as the ion clusters proceed to evolve under highly supersaturated conditions, we observe the breakage of the water hydration structure indicating the stability limit of the dense liquid regions, and thus leading to nucleation. The evolution of solute clusters and breakage of hydration in highly supersaturated NaCl bulk solution will provide new insights into the detailed mechanism of TSN for many other aqueous solutions.

This work provides evidence for two-step nucleation in highly supersaturated bulk NaCl solution, using electrostatic levitation combined with Raman/X-ray scatterings.     

Effects of different temperatures and additives on the metastable zone width precipitation kinetics of NaBO2

In this study, the sodium metaborate, which is applicable in various industrial areas, and its metastable zone width that is very important for its production by crystallization, and its nucleation are investigated to obtain the necessary thermodynamic parameters. The polythermal and isothermal method has been used for the measurement of metastable zone width. Metastable zone width of NaBO₂ has found at 9°C at average and cooling rate do not have any effect on it. In addition, the effect of sodium metaborate on the hydrogen storage capacity of sodium borohyride solutions that is known as one of the best hydrogen sources today is investigated at the various concentrations of sodium borohyride in the medium. Results have shown that three different areas emerged as the percentage of NaBH4 in the solution increased.     

Activation energy determinations from dielectric thermal analysis of reacting polymeric systems

Methods were developed for calculating reaction activation energies from dielectric property measurements during isothermal and nonisothermal cure of thermosetting polymers. These methods were derived by assuming that features of the dielectric response occurred at unique extent of reaction values. Activation energy results were obtained through dielectric analysis for two thermosetting resin systems: a model epoxy system — tetraglycidyl-4, 4-diaminodiphenylmethane cured with 25 parts per hundred of 4,4-diaminiphenylsulfone hardener; and a model dicyanate blend resin, 55% (by weight) of bisphenol A dicyanate and 45% of tetrao-methyl bisphenol F dicyanate. Results were in excellent agreement with activation energies determined from differential scanning calorimetry measurements.

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Zusammenfassung Es wurden Verfahren zur Berechnung der Aktivierungsenergien aus dielektrischen Messungen der isothermen bzw. nichtisothermen Aushärtung von Duroplasten entwickelt. Dabei wurde angenommen, daß die dielektrische Antwort bei einem einzelnen Wert der Reaktionswerte erfolgt. Die Aktivierungsenergie-Ergebnisse wurden für zwei Duroplast-Harze ermittelt: ein Epoxysystem — Tetraglycidyl-4,4-diamonidiphenylmethan, gehärtet mit 25% 4,4-Diaminodiphenylsulfonhärter; und ein Dicyanatmischharz aus 55 Gew.% Bisphenol A Dicyanat und aus 45 Gew.% Tetra-o-methylbisphenol F Dicyanat. Die Ergebnisse stehen in guter Übereinstimmung mit den aus DSC-Messungen erhaltenen Werten.

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The authors would like to thank Dr. M. A. Bachmann of ICI, Dr. R. B. Prime of IBM, and Dr. E. M. Woo of the Polymeric Composites Laboratory and currently with Boeing Commercial Airplane Group, for helpful discussions in the development of this technique. In addition, the expert coordination for the project provided by Ms. Louise Peterson and Dr. Kyujong Ahn, as well as Shangying Zeng in analyzing the dicyanate data at the Polymeric Composites Laboratory, is gratefully acknowledged. Equipment support for this project was provided by Tetrahedron Associates and TA Instruments (formerly DuPont Instruments), through their participation at the Polymeric Composites Laboratory consortium at the University of Washington. Financial assistance for this work was provided by ICI, and the National Science Foundation Grant # MSM 8352414.     

Solution crystallization analysis of poly(lactic acid) by Scalls: A facile approach for thermal analysis of polymers in solution

Non-isothermal solution crystallization and dissolution behaviour of both enantiomers (D and L) of poly(lactic acid) (PLA) and their blends were studied by the unique Solution Crystallization Analysis by Laser Light Scattering (Scalls) method. For the first time, we have investigated the crystallization of this biopolymer in solution, as well as the subsequent dissolution or “solution melting”. It was found that addition of the D-enantiomer (PDLA) to the L-enantiomer (PLLA) in solution resulted in the formation of stereocomplex crystals (SC), and the nucleation-effect of the crystals was intensified with increase in PDLA content, leading to an earlier onset of crystallization and increased crystallization peak area. Differential Scanning Calorimetry (DSC) analysis confirmed the formation of SC during solution crystallization. Large re-crystallization events were seen for the pristine polymers, indicative of their low crystallization rates. Overall, results obtained by Scalls provided promising information regarding PLA crystallization kinetics, which significantly influences practical applications of this biopolymer.     

A comparison of two techniques for inducing fibrous crystallization from solution

Experimental results are presented and discussed comparing two techniques for inducing fibrous growth of polyethylene crystals from flowing solutions: a plunging cone device and a standard rotating cylinder (Couette) device. Comparison of crystal “overgrowth” diameter to spacing ratios for the several experiments with predictions based on an earlier postulated model lead to conclusions regarding the model inadequacy. A detailed comparison is made of the melting behavior of crystals produced by both flow fields and those results are discussed in light of a modified model for the growth process presented elsewhere. The conclusion is reached that differences in melting behavior may be attributed to differences in extension of the high molecular weight chains involved in the growth processes occurring in the two different flow fields.     

A simultaneous electrical conductivity—differential thermal analysis apparatus

A highly sensitive simultaneous electrical conductivity—differential thermal analysis apparatus is described. The apparatus can simultaneously record both the electrical conductivity and differential thermal analysis curves of a sample under the same conditions of furnace heating rate and atmosphere. Application of the apparatus is illustrated by curves of CuSO₄·5H₂O, [Co(NH₃)₅H₂0]Br₃ and Cu₂HgI₄.     

Rate-constants for diffusion-controlled crystallization of barium tungstate from sodium tungstate melts by differential thermal analysis

Variations of rate constants in diffusion-controlled crystal growth of barium tungstate from solutions in sodium tungstate melts in platinum crucibles were studied by continuous cooling from crystallization temperaturesT ₀=800 to 1000 to below the eutectic temperature at cooling ratesR _T=0.67 to 3.37 min^–1. During the induction periods (¯t) heterogeneous nuclei slowly formed in the solution; the main crystal growth started only after the development of some excess solute concentrations (AC) at the endoil. The diffusion rate-constants for the growth increased withT ₀ andR _T. These were much smaller than the real diffusion rate-constants but higher than those for diffusion-controlled crystal growth of barium tungstate from sodium tungstate melts in alumina crucibles.

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Zusammenfassung Die Änderung der Geschwindigkeitskonstanten bei dem diffusionsbedingten Kristallwachtum von Bariumwolframat aus Lösungen von Natriumwolframatschmelzen in Platintiegeln wurde durch kontinuierliches Kühlen von den KristallisierungstemperaturenT ₀=800 bis 1000 bis zur eutektischen Temperatur unter Anwendung von Kühlgeschwindigkeiten vonR _T=0.67 bis 3.37 C min^–1 untersucht. WÄhrend der Induktionsperioden (¯t) bildeten sich in der Lösung langsam heterogene Keime; das Hauptkristallwachstum begann nur bei etwas übersÄttigter Konzentrationen der gelösten Substanz (¯C) am Ende von¯t. Die Diffusionsgeschwindigkeitskonstanten ( ) des Wachstums nahmen mitT ₀ undR _T zu. Diese waren viel niedriger als die wirklichen Diffusionsgeschwindigkeitskonstanten , jedoch höher als die des diffusionsbedingten Kristallwachstums von Bariumwolframat aus Natriumwolframatschmelzen in Aluminiumtiegeln.

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Résumé On a étudié les variations des constantes de vitesse lors de la croissance, contrÔlée par le diffusion, des cristaux de tungstate de baryum, en solution dans le tungstate de sodium fondu en creusets de platine. Le refroidissement en continu a été effectué depuis la température de cristallisationT ₀=800 à 1000 jusqu'au-dessous de la température eutectique à des vitesses de refroidissementR _T=0.67 à 3.37 C.min^–1. Pendant les périodes d'induction (¯t) des noyaux hétérogènes se forment lentement dans la solution; la croissance principale des cristaux ne commence qu'après le développement de concentrations quelque peu supérieures à la sursaturation de la substance en solution (¯C), à la fin de¯t. Les constantes de vitesse de diffusion ( ) correspondant à la croissance augmentent avec T₀ et R_T. Elles sont bien plus petites que les constantes de vitesse réelles de la diffusion _réel, mais plus élevées que celles de la croissance des cristaux, contrÔlée par la diffusion, du tungstate de baryum dans le tungstate de sodium fondu en creusets d'alumine.

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- T₀=800 1000 R _f 0.67 3.37 . (¯t) . () ¯t. T ₀ R _T. , ., , .

     

Hydrodynamically induced crystallization of polymers from solution

Summary This paper primarily describes an investigation into the origin of persistent lamellar overgrowth of fibrillar crystals with a Shish-kebab morphology. Fibers grown from stirred p-xylene solutions of high molecular weight polyethylene at 108 °C exhibited an average spacing of 1 x 10³ Å between the lamellae when cooled down to room temperature in a normal way. Fibers quenched in liquid nitrogen displaved smaller lamellae with a periodicity of 0.4 x 10³ Å.It was found that the lamellae could be dissolved at 108 °C and recrystallized isothermally on the backbones at temperatures up to 94.6 °C. The spacing between the lamellae increased strongly with temperature in the range between 90.0 °C and 94.6 °C.The temperature dependence of this periodicity could be accounted for by the theory of secondary nucleation in polymer crystallization. The Poisson distribution of the numbers of lamellae along the backbones also suggests that lamellar growth is essentially controlled by the crystallization kinetics.The fibrillar polyethylene crystals grown at elevated temperatures from flowing solutions may be visualized as backbones constituted by partially crystallized polymer molecules and dangling ends extending from the backbones into the surrounding solution resembling centipedes.

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Zusammenfassung Dieser Bericht befaßt sich mit einer Untersuchung des Ursprungs von persistenter lamellarer Überwachsung von Faser-Kristallen mit Schaschlik-Morphologie.Faser-Kristalle, gewachsen aus geruhrten Xylol-Lösungen von hochmolekularem Polyäthylen bei 108 °C, zeigen ein mittleres Intervall zwischen den Lamellen von 1 x 10³ Å, wenn auf normae Weise abgekühlt zur Zimmertemperatur. Fasern, abgeschreckt im flüssigen Stickstoff, zeigen kleinere Lamellen mit einem Zwischenraum von etwa 0.4 x 10³ Å. Es wurde festgestellt, daß die Lamellen bei 108 °C gelöst werden können und von neuem auf den Faserkernen bis zu 94.7 °C kristallisieren. Die Temperaturabhangigkeit dieser Periodizität kann erklärt werden auf Grund der Theorie der sekundären Keimbildung bei polymerer Kristallisation. Wie sich zeigt, gruppiert sich die lamellare Überwachsung um den Kern entsprechend einer Poisson-Verteilung, was darauf hinweist, daß die lamellare Überwachsung wesentlich durch die Kristallisationskinetik bedingt wird.Die faserigen Polyathylenkristalle, bei erhöhter Temperatur hergestellt aus gerührten Lösungen, kann man sich als teilweise kristallisierte Moleküle, im Faserkerne aufgenommen, vorstellen mit langen Kettenenden im umgebenden Lösungsmittel, so ziemlich als einen Tausendfüßler.

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With 12 figures     

Hydrodynamically induced crystallization of polymers from solution

Summary This paper primarily describes the large diversity in morphology of fibrillar polyethylene crystals precipitated from stirred solutions at elevated temperatures. Shish-kebabs crystallized at 112°C from stirred xylene solutions of linear polyethylene exhibit lamellar overgrowths having thicknesses of the order of 150 Å from which it was concluded i. a. that at crystallization temperatures above 100°C only backbones are formed and that the surrounding polymer molecules deposit epitaxially on the substrate at lower temperatures. The variation in the appearance of the overgrowth and the inhomogeneity of the samples can be traced back to irregular stacking and to differences in washability of the fibrillar crystals, these differences being largely due to the non-uniform flow pattern along the various stirrer parts. Unusual lamellar shapes, interconnections, sheets between lamellae, the veil on the Shish-kebab noted byKeller andMachin, may well be explained byKeith, Padden andVadimskys mechanism of crystallization-induced orientation of macromolecules between the lamellae and the consequent formation of extendedchain crystals. The lamellar overgrowth appears to be arranged along the backbone according to a logarithmic normal distribution, and the average diameter of the lamellar crystals increases with the average spacing, both being approximately equal in size. The fibrillar crystals end in smooth tapered tails having lengths varying between 5 and 8 .These observed fibre ends agree best with the unroll model proposed for fibrillar crystal growth in flow fields if on the average each molecule introduces one chain fold and the chain ends are randomly assimilated by the crystal lattice. Linear polyethylene below molecular weight of 50×10³ and low density polyethylene did not crystallize in fibrillar habit. whereas copolymers of ethylene and slight amounts of propylene and butylene proved capable of forming fibrillar crystals and isotactic polypropylene yielded smooth and overgrown fibres.

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Zusammenfassung Der Bericht befaßt sich zuerst mit der großen morphologischen Mannigfaltigkeit faseriger, bei erhöhter Temperatur aus gerührten Lösungen gefällter Polyäthylenkristalle. Bei 112°C aus gerührten Xylollösungen von linearem Polyäthylen herauskristallisierte Schaschlik-Strukturen zeigen eine lamellare Überwachsung mit einer Dicke von etwa 150 Å, woraus u. a. geschlossen wird, daß sich bei Kristallisations-temperaturen über 100°C nur Faserkerne bilden und daß die umringenden polymeren Moleküle sich bei niedrigeren Temperaturen epitaxial auf dem Substrat ablagern. Die Verschiedenheit in der Form der Überwachsung und die Inhomogenität der Proben lassen sich erklären durch eine unregelmäßige Ablagerung auf dem Rührer und durch Unterschiede in der Auswaschbarkeit der faserigen Kristalle, welche Unterschiede weitgehend auf das nicht einheitliche Strömungsbild längs der verschiedenen Rührerteile zurückzuführen sind. Ungewöhnliche lamellenartige Formen, interlamellare Verbindungen, Häutchen zwischen den Lamellen und die vonKeller undMachin festgestellte Verschleierung der Schaschlikgebilde lassen sich sehr gut durch denKeith-, Padden- undVadimsky-Mechanismus einer durch die Kristallisation verursachten Orientierung von Makromolekülen zwischen den Lamellen und durch die anschließende Bildung von extended-chain Kristallen erklären. Wie sich zeigt, gruppiert sich die lamellare Überwachsung um den Kern entsprechend einer logarithmischen Normalverteilung; der mittlere Durchmesser der lamellaren Kristalle nimmt zu mit der mittleren Größe der Zwischenabstände, wobei beide ungefähr gleich groß sind. Die faserigen Kristalle enden in allmählich spitz auslaufenden Gebilden mit Längen von etwa 5 bis 8 . Diese Faserenden stimmen gut überein mit dem für das Wachsen faseriger Kristalle in Strömungsgebieten vorgeschlagenen unroll-Modell, falls im Durchschnitt jedes Molekül eine Kettenfaltung einleitet und die Kettenenden willkürlich in das Kristallgitter aufgenommen werden. Lineares Polyäthylen mit einem Molekulargewicht unter 50×10³ und Hochdruckpolyäthylen kristallisieren nicht in der faserigen Form, während —wie sich zeigt—Copolymere von Äthylen und geringen Propylen- und Butylenmengen in der Lage sind, faserige Kristalle zu bilden und isotaktisches Propylen schöne und überwachsene Fibrillen ergibt.

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With 25 figures in 28 details     

The kinetics of flow-induced crystallization from solution

In situ birefringence measurements of the seeded growth in a tubular flow geometry of 0.01 wt% solution of a polyethylene fraction in xylene have been used to determine the flowinduced crystallization kinetics as a function of temperature and flow rate. In contrast to earlier reports on higher molecular weight polyethylene and polypropylene systems, orientational properties of the crystallized fibers do not show a clear correlation with growth conditions (i.e., temperature and flow rate). The combined kinetic data from these experiments and our earlier studies of higher molecular weight polyethylene—xylene and polypropylene—tetralin systems are analyzed in terms of a modified from of the Avrami equation which provides a basis for separately correlating temperature and flow rate effects. The observed temperature dependency of the crystallization process can be interpreted in terms of nucleation and growth models while the flow rate dependency can be interpreted on the basis of entanglement formation arguments. Results showing liquid phase precursor formation in an atactic polystyrene system are also presented to further document the liquidphase separation which can be induced in polymers under flow.     

Fluorinated liquid-enabled protein handling and surfactant-aided crystallization for fully in situ digital microfluidic MALDI-MS analysis

A droplet (digital) microfluidic device has been developed that enables complete protein sample preparation for MALDI-MS analysis. Protein solution dispensing, disulfide bond reduction and alkylation, tryptic digestion, sample crystallization, and mass spectrometric analysis are all performed on a single device without the need for any ex situ sample purification. Fluorinated solvents are used as an alternative to surfactants to facilitate droplet movement and limit protein adsorption onto the device surface. The fluorinated solvent is removed by evaporation and so does not interfere with the MALDI-MS analysis. Adding a small amount of perfluorooctanoic acid to the MALDI matrix solution improves the yield, quality and consistency of the protein-matrix co-crystals, reducing the need for extensive 'sweet spot' searching and improving the spectral signal-to-noise ratio. These innovations are demonstrated in the complete processing and MALDI-MS analysis of lysozyme and cytochrome c. Because all of the sample processing steps and analysis can be performed on a single digital microfluidic device without the need for ex situ sample handling, higher throughput can be obtained in proteomics applications. More generally, the results presented here suggest that fluorinated liquids could also be used to minimize protein adsorption and improve crystallization in other types of lab-on-a-chip devices and applications.     

Thermal analysis and crystallization from melts

The growth of atenolol, pindolol and betaxolol hydrochloride from melt was investigated by differential scanning calorimetry (DSC) and polarized light thermal microscopy (PLTM). Phase transitions occurring on cooling and subsequent reheating runs performed between −160 °C and a temperature above the respective melting points were studied by DSC. The thermal cycles were also followed by PLTM. Details about the dynamic of the crystallization front taken from microscopic observations are given. An explanation of the results on the basis of molecular supramolecular recognition is advanced.