The abnormal changes of electrical resistivity in liquid Pb–In alloys

Electrical resistivity of liquid lead and indium (Pb–In) alloys with different compositions has been measured using the four-probe method in a large temperature range. Marked turning points on each resistivity–temperature (ρ–T) curve of the liquid Pb–In alloys can be observed far above the liquidus. The unusual variation of the resistivity of Pb–In melts suggests a structural transition of these melts, for resistivity is a sensitive parameter to the structure. Moreover, the DSC experiment of Pb–In melts supports the existence of a liquid–liquid (L–L) structure transition in Pb–In melts. Such a L–L structural transition can be described in terms of the gradual disappearance of atomic bonds corresponding to the crystal structure and/or to a reduction of the size of pre-formed atomic clusters. This implies an increase of disorder in the high temperature melts. The transition temperatures depend on the composition of Pb–In melts and the onset transition temperatures of the intermediate phase (α) Pb–63%In and Pb–70.6%In melts are higher than that of other compositions.     

Kinetic and equilibrium factors affecting saturation of chromium oxide in soda-silicate melts

Factors controlling the rate at which chromium oxide reaches saturation in Na₂O-xSiO₂ liquids have been studied as a function of melt composition and oxygen fugacity. Under an oxidizing atmosphere, liquid Na₂CrO₄ or Cr₂O₃ crystals can be in equilibrium with soda-silicate melts, depending on the concentration of sodium in the studied system. Under reducing conditions, NaCrSi₂O₆ is stabilized in silica-rich melts when T is lower than 1160 °C, while Cr₂O₃ is in equilibrium with the sodium-rich melts when T is above 1160 °C. The chromium oxide (Cr₂O₃) to pyroxene (NaCrSi₂O₆) transformation is described in terms of the time required to reach chemical and textural equilibrium. Na₂CrO₄, NaCrSi₂O₆, and Cr₂O₃ phase stability domains are reported as well as the Na₂O-SiO₂-Cr₂O₃ phase diagram in the studied temperature and fO₂ range.     

The state space of short-range Ising spin glasses: the density of states

The correlations between the segments of a semidilute polymer solution are found to induce correlations in the positions of small particles added to the solution. Small means a diameter much less than the polymer's correlation length. In the presence of polymer the particles behave as if they attracted each other. It is shown how the polymer's correlation length may be determined from a scattering experiment performed on the spheres. Received: 7 July 1997 / Received in final form: 12 November 1997 / Accepted: 19 November 1997     

Birefringence measurements in extensional flow of polyisobutylene around an expanding bubble

Birefringence in liquid polymers offers the possibility of obtaining information about stress in complex flows. In this work, this is done for extensional flows of polyisobutylene in a “breathing bubble” rheometer. In this type of rheometer, a bubble consisting of an incompressible, low-viscosity fluid (usually water) is injected into the sample with a nozzle. Expanding or collapsing the bubble by adding or removing water induces biaxial or uniaxial extension in the surrounding sample. The pressure difference between the bubble and the surroundings can be measured and compared to the predictions of constitutive equations. This measurement only gives one integral value for a complex flow history. In this paper, the birefringence around the bubble is measured in order to learn more about the flow. This is done by comparing pressure and birefringence results to those of standard constitutive equations for a polyisobutylene sample. A good agreement between the pressure and optical measurements and the theory is found with a single value of the stress-optical constant. Received: 25 June 1997 Accepted: 12 November 1997     

聚合物熔体注模流变学：Ⅳ,熔体的弹性及其表征

本文论述了聚合物熔体注模过程中弹性特性的几种重要的表现。对于国内外学者在熔体弹性行为的表征及过程机理的解释等方面的研究进展作了简要的述评,并综述了作者及其同事近年来在这方面所做的工作。     

The adsorption theory of electrolytes and the volumetric properties of some nitrate-water systems. From fused salts to dilute solutions

Summary On the basis of theBrunauer-Emmet-Teller adsorption model extended byStokes andRobinson to concentrated electrolyte solutions, from theStokes-Robinson equation for water activity, and from theAbraham equation for electrolyte activity,Ally andBraunstein have derived equations for the partial excess molar volumes of salt and water in salt-water systems. In their equations, only oneBET parameter is considered to be pressure dependent. In the present publication, complete equations are proposed, taking into account the dependence of bothBET constants on pressure. These equations are tested successfully with nitrate-water systems containing mono and divalent cations over a concentration range from fused salts to water: [0.500 LiNO₃–0.500 KNO₃+H₂O], [0.467 TlNO₃–0.214 CsNO₃–0.319 Cd (NO₃)₂+H₂O], [N(C₂H₅)₄NO₃+H₂O], [0.515 AgNO₃–0.485 TlNO₃+H₂O], and [AgNO₃–TlNO₃–M(NO₃) _n +H₂O] (M=Na, K, Cs, Cd, Ca;x(AgNO₃)/x(TlNO₃) as in the preceding systemx(M) being varied from 0.025 to 0.125 depending on the cation). Additivity rules which involve the partial derivatives of theBET constants with respect to pressure are also proposed.

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Adsorptionstheorie der Elektrolyte und volumetrische Eigenschaften einiger Nitrat-Wasser-Systeme. Von Salzschmelzen zu verdünnten Lösungen

Zusammenfassung Auf der Basis desBrunauer-Emmet-Teller-Modells, vonStokes undRobinson für konzentrierte Elektrolytlösungen erweitert, sowie ausgehend von den Gleichungen nachStokes-Robinson für die Aktivität von Wasser und nachAbraham für dieAktivität von Elektrolyten, leitetenAlly undBraunstein Beziehungen für die partiellen molaren Zusatzvolumina von Salz und Wasser in Salz-Wasser-Systemen her, in denen nur einBET-Parameter als druckabhängig behandelt wird. In der vorliegenden Publikation werden vollständige Gleichungen vorgestellt, die die Druckabhängigkeit beiderBET-Konstanten berücksichtigen und die erfolgreich an Nitrat-Wasser-Systemen getestet wurden, die mono- und divalente Kationen enthalten und deren Konzentrationsbereich von Salzschmelzen bis zu reinem Wasser reicht: [0.500 LiNO₃–0.500 KNO₃+H₂O], [0.467 TlNO₃–0.214 CsNO₃–0.319 Cd(NO₃)₂+H₂O], [N(C₂H₅)₄NO₃+H₂O], [0.515 AgNO₃–0.485 TlNO₃+H₂O] und [AgNO₃-TlNO₃-M(NO₃) _n +H₂O] (M=Na, K, Cs, Cd, Ca;x(AgNO₃)/x(TlNO₃) wie im vorhergehenden System:x(M) je nach Kation zwischen 0.025 und 0.125). Zusätzlich werden Additivitätsregeln, die sich auf partielle Ableitungen derBET-Parameter bezüglich des Drucks beziehen, vorgestellt.

     

线型与支化聚烯烃熔体高速挤出时的不稳定扰动源

采用恒速型双毛细管流变仪对比研究线型与支化聚烯烃熔体在高速流场中的流动曲线、挤出畸变、挤出压力变化及粘弹性的特征,分析讨论了引发熔体不稳定流动的扰动源位置及扰动性质.结果表明,高速流场中的扰动源有:口模入口区的扰动、口模壁处的扰动、口模出口区的扰动.支化聚合物易受入口区的扰动干扰,造成挤出物无规破裂;线型聚合物易受口模壁处的扰动干扰,造成挤出压力振荡和挤出物有规畸变;鲨鱼皮畸变主要由于口模出口区的振荡扰动造成.     

Falling sphere viscometry in gravitational and magnetic fields

The classical falling sphere method based onStokes' law is well known. Using gravitational forces, however, restricts the range of measurements considerably. This advantage can be overcome by applying iron spheres in a magnetic field, which allows to measure polymer melts with viscosities up to ₀=10⁹ Pa s (with very strong magnets available even more). A special measuring cell designed for application in the magnetic field is tested with several silicon oils in the gravitational field too. In both cases wall and end corrections toStokes' law have to be considered and are of main concern. Another important point is a reliable temperature measurement. Results especially for the high viscosity region of polymer melts are given.Herrn Prof. Dr.K. Komarek zum 60. Geburtstag gewidmet.     

Enthalpy of mixing of hydrated melts. II. Evidence for an endothermic step in the chlorocomplex formation of zinc

The enthalpies of mixing measured for the systems x(ZnCl₂+RH₂O)-(1–x)(LiCl+RH₂O) are reported. In contrast to the exothermic effects for R=4, the mixing processes at R=6 are considerably endothermic. For R=5, the sign of H _M depends on the composition. The mixing enthalpies of these hydrated melts are controlled by an endothermic step in the chlorocomplex formation of zinc and the exothermic hydration of lithium cations.     

NIR FT Raman Spectroscopy–a Rapid Analytical Tool for Detecting the Transformation of Cellulose Polymorphs

This is a report of the combined use of NIR FT Raman spectroscopy and X-ray diffraction measurements (WAXS) to investigate the polymorphic transformation of cellulose I into cellulose II. For this reason samples of cellulose I were swelled in different concentrations of NaOH and dissolved in different molten inorganic salts hydrates (LiCl·2ZnCl₂·6H₂O, LiClO₄·3H₂O, LiSCN·2,5H₂O and ZnCl₂·4H₂O). NIR FT Raman spectra of the alkali treated samples were recorded. They characterize the pure modifications cellulose I and II as well as mixtures of the two polymorphic phases. The results of the Raman measurements were confirmed by X-ray scattering. The paper demonstrates that FT Raman vibrational spectroscopy is a powerful, rapid analytical method which may be used to follow the polymorphic transformation of cellulose I into cellulose II.