Liquidus Curves of AgNO3(aq) Calculated from the Modified Adsorption Isotherm Model for Aqueous Electrolytes

Summary. The Brunauer-Emmett-Teller (BET) adsorption isotherm as modified by Robinson and Stokes is used to calculate the liquidus curve of AgNO₃(aq) including the eutectic point and metastable phases. The simplified approach described here predicts the liquidus curves by using sparse data and readily available constants.     

Eutectic Type Liquidus Curves in Compound Forming Systems

Abstract

The thermodynamics of eutectic type liquidus curves in compound forming systems is developed for the case when a single compound A_μ B_μ is formed. The liquidus curves are considered in three regions: (i) A-rich (ii) B-rich and that in which equilibrium conditions involve the compound (iii). In region (iii) the slope of the liquidus curve in the presence of the compound A_μ B_μ has a multiplying factor μ-(μ+v)c and hence changes sign at c = μ/μ+v, in agreement with observation.

To illustrate the formalism we have considered numerically the limiting case when there is a strong tendency to form compounds and results thus obtained for Mg-Bi and Mg-Sn are briefly referred to.     

Synthesis and Characterization of New Unsymmetrically Substituted Phthalocyanines

Summary.  Unsymmetric metallophthalocyanines (M=Zn, Co, Ni) carrying alkylthio and acetyloxyethylthio groups on peripheral positions were prepared from 4,5-bis-alkylthio-phthalonitrile, 4,5-bis-(acetyloxyethylthio)-phthalonitrile, and the corresponding anhydrous metal salts Zn(CH₃COO)₂, NiCl₂, and CoCl₂. The extremely soluble compounds were characterized by their IR, ¹H NMR, and UV/Vis spectra. Their long wavelength absorption band was found to be bathochromically shifted; their solubility is superior to that of symmetrical phthalocyanines. Received July 27, 1999. Accepted (revised) September 30, 1999     

A Method for the Synthesis of 2,3-Disubstituted 2,3-Dihydrobenzofurans

Summary.  The synthesis of 2,3-disubstituted 2,3-dihydrobenzofuran diastereomers is described. The key step in the reaction sequence is the chemoselective reduction of a tert. alcohole with tert.-butylamine-borane/AlCl₃. The relative configuration of the substituents on the dihydrofurane moiety was assigned via NMR spectroscopy. Received September 7, 1999. Accepted November 9, 1999     

The phase diagram and supercooling conditions for the Ca(NO3)2−CaCl2−H2O system

The liquidus temperature and induction periods were measured for crystallization in a system of calcium nitrate, calcium chloride, and water over a concentration range of 5–20 mole% Ca(II), i.e., R=4–18 [R=moles H₂O/moles Ca(II)] and y_cl=0–1 [y_cl=moles Cl^–/moles (NO ₃ ^– +Cl^–)]. A ternary phase diagram was constructed, and qualitative dependences of the supercooling at which the solution began to crystallize on the system composition were found. A wide range of stability toward crystallization was found for solutions withR=4–10 and y_cl=0–0.7 The relationships between the system stability toward crystallization and the viscosity, glass-transition temperature, and the liquidus temperature are discussed.     

On the structure of melt in the BaO-CuO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (50.0–80.0 mol % CuO) system at <Emphasis Type="Italic">p</Emphasis>(O<Subscript>2</Subscript>) = 21 kPa

The composition of melt from the crystallization and liquidus regions of the BaO-CuO _x phase diagram was studied within the range 50.0–80.0 mol % CuO at p(O₂) = 21 kPa. At 900–1050°C, melt in the range of the compositions studied is structured and consists of oxides having cubic structure BaCuO₂; (Ba/Cu = 0.80−0.96), tetragonal structure BaCu₂O₂; (Ba/Cu = 0.50−0.62), and monoclinic structure (CuO). The off-stoichiometry of BaCu₂O₂ manifests itself in electron diffraction (ED) patterns taken in a transmission electron micro-scope (TEM) as diffuse scattering streaks extending in the [100] and [010] directions. These data find explanation in the existence of clusters having a suggested composition of Ba₂Cu₃O_{3.5 + x} which are produced by BaCu₂O_{2 + x} disproportionation and are integrated into the BaCu₂O₂ structure. Thermal effects observed in the liquidus region, which are accompanied with a change in oxygen content, are associated with the cluster structure of the melt and its evolution in response to varying temperature.     

Phase Equilibrium in the SeO2–Bi2O3 System

The subject of the present study is the system SeO₂-Bi₂O₃ that comprises two oxides with low melting points. All batches are thermal treatment in quartz ampoules, which are evacuated and sealed at a pressure P=0.1 Pa. On the basis of DTA (differential thermal analysis) and X-ray data, the most probable liquidus line of the system has been plotted. The eutectic composition lies about 90 mol% SeO₂,with on eutectic temperature at 230°C. Above 20 mol% Bi₂O₃ the liquidus temperature extremely increases. The formation of three compounds is proved:Bi₂Se₃O₉ and Bi₂Se₄O₁₁ are melting incongruently at 540 and 350°C respectively and Bi₂SeO₅ congruently at 915°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

The structure changes in Sn1− x Ti x alloys at transition from liquid to solid state

The structures of Sn_{1– x} Ti _x (x = 0.00; 0.02, 0.05, 0.15, 0.25; 0.35; 0.45) alloys were studied by X-ray diffraction at different temperatures. The structure factors, pair correlation functions, and parameters obtained were analysed. It is shown that the structures of the liquid alloys are inhomogeneous in the pre-crystallisation temperature region. The solidified phases are in agreement with the equilibrium phase diagram. The X-ray diffraction data were used for the specification of the liquidus line position.     

Lattice parameters,magnetic properties,and melting behavior of the ternary NiAs-phase in the Ni-Sb-Te system

Lattice parameter, magnetic, and DTA-measurements were performed in the range of the ternary NiAs-phase in the nickel-antimony-tellurium system which exhibits a continuous range of homogeneity. Lattice parameter and susceptibility values are reported for three sections with constant ratios ofx _Sb/x _Te=4.00, 1.00, and 0.25. The ternary liquidus projection is given between about 35 and 60 at % Ni.Dedicated to Prof.K. L. Komarek on the occasion of his 60th birthday.     

Supramolecular Ribbons. Crystal Structure and Spectroscopic Properties of 2,2′-Bipyrroyl

Summary.  A crystal structure determination of 2,2′-bipyrroyl (1; 2,2′-dipyrryl-diketone, bis (2-pyrrolyl)ethanedione) and its spectroscopic properties in solution are reported. In the crystal, 1 self-assembles via hydrogen bonding into supramolecular ribbons that extend indefinitely through the crystal lattice. The observed molecular conformation is one where each pyrrole ring and adjacent carbonyl group are co-planar (torsion angle ∼ 0.9°), with the N-H pointing in the same direction as the C=O. The two carbonyls have a transoid but not co-planar geometry with a torsion angle of ∼128°. Adjacent molecules in the crystal are linked by pairs of intermolecular hydrogen bonds, pyrrole NH to carbonyl oxygen, to form a matrix of polymeric chains that lie like neatly stacked, parallel streams of ribbons. Molecular mechanics calculations on the monomer indicate an intra-molecularly hydrogen bonded planar conformation (sp, ap, sp) at the global energy minimum. In CHCl₃, 1 is monomeric according to vapor pressure osmometry (MW _obs=179±10 vsċMW _calc=188). In THF, the measured molecular weight is 340±15, which corresponds best to one molecule of 1 solvated by two THF molecules (MW=322 for C₁₀H₈N₂O₄ċ2 C₄H₈O) rather than to a dimer. Received October 21, 1999. Accepted November 2, 1999     

An Unexpected Synthesis of Novel Oxygen-Bridged 1,5-Benzothiazepine Derivatives and their Reductive Five-Membered-Ring Opening

Summary.  A convenient procedure is reported for the preparation of benzofuro-annelated 2-phenyl-1,5-benzothiazepine derivatives by oxidative cyclocondensation of phenolic β-diketones with o-aminothiophenol in DMSO. The regiochemistry of these compounds is proven by HMBC signals and the existence of a five-bond ¹⁹F,¹³C-2 coupling. Surprisingly, treatment with LiAlH₄ at room temperature led to a double reduction under opening of the five-membered ring. Refluxing such solutions with a higher amount of LiAlH₄ gave rise to a further reduced derivative possessing the trans-configuration. All structures (regio- and stereochemistry) were assigned on the basis of NMR spectroscopic data. Received November 22, 1999. Accepted December 21, 1999     

Immobilization of Rhodococcus AJ270 and Useof Entrapped Biocatalyst for the Productionof Acrylic Acid

Summary.  Rhodococcus AJ270 is adsorbed by Dowex 1 at 15.4  mg dry weight per g resin with maximum amidase specific activity observed at lower loadings. Bacteria form a monolayer on the resin surface, and adsorption is complete within 2 min. AJ270 can be entrapped in agar and agarose gels (optimum loading: 20 mg dry weight bacteria per cm³ gel). Adsorption and entrapment improve amidase thermal stability 3–4 fold, and entrapment shifts the pH optimum from 8 to 7. Adsorbed and free bacteria show similar values for K _m and V _max, but entrapped bacteria have higher K _m values. Compared with bacteria adsorbed to Dowex, the activity per cm³ of matrix of agar-entrapped AJ270 is eight-fold higher. In stirred-tank reactors, exposure to acrylic acid reduces the amidase activity of the biocatalyst in the hydrolysis of acrylamide. In column reactors, entrapped AJ270 suffers little reduction in amidase activity against 0.25 M acrylamide over 22 h continuous operation. Received November 18, 1999. Accepted December 14, 1999     

Atomic distributions in liquid copper-tin alloys

Abstract

Molten copper-tin alloys have been studied by X-ray diffraction, using a focusing theta-theta diffraetometer and Mo-Kα radiation (monochromator in the diffracted beam). Five alloys with 20, 35, 45, 55 and 78 atomic percent Sn, and pure Cu and Sn were measured at temperatures about 20 °C above the liquidus, and at 1100 °C. The total interference functions I(K), where K = 4π sin θ/δ, were obtained from the observed scattered intensities I_a(K) per atom and the theoretical atomic scattering factors. Splitting of the first peak in I(K) has been observed in the Cu-55 at% Sn alloy at the liquidus temperature.

The partial interference functions I_tj(K) at the liquidus temperature and at 1100°C were evaluated (assuming that they are independent of atomic concentration) using the five total I(K) of the alloys. The functions I_ij(K) are in reasonable agreement with those obtained by Enderby, North and Egelstaff from neutron diffraction data of a Cu-45 at % Sn alloy.

The reduced partial distribution functions G_ij(r) = 4πρ₀ r{g_ij(r) ? 1} and the probability functions g_ij(r) = ρ _ij(r)/c_j ρ₀, where ρ _ij(r) is the number of j-type atoms per unit volume at the distance r from an i-type atom, c_j is the atomic fraction of j-type atoms and ρ₀ is the average atomic density, have been evaluated by Fourier transformation of {I_ij(K) ? 1} K.

The electrical resistivities ρ _R of the alloys, calculated with the Faber-Ziman equation using the measured I_ij(K) and Animalu-Heine pseudo-potential elements U_i(K), are in good agreement with the experimental values of Roll and Motz. Assuming that U_i (2k _F) is independent of the values of the Fermi diameter 2k _F of the alloys, the concentration dependence of (3 - X)ρR, where X is the thermoelectric parameter measured by Enderby and Howe, is well reproduced when using the X-ray values of I_ij (2k _F).     

Tree of phases of the Li,Na,Ba‖F,Br quaternary reciprocal system and study of the LiF-NaBr-BaFBr stable triangle

The Li,Ba‖F,Br ternary reciprocal system was investigated by differential thermal analysis. The T-x diagrams of the polythermal sections studied and the liquidus of the system were constructed. It was deter-mined that the system is of the adiagonal section type with a subordinate diagonal (according to Bergman’s classification). The characteristics and enthalpies of melting of the alloys corresponding to invariant equilibrium points were found. The Li,Na,Ba‖F,Br quaternary reciprocal system was partitioned, and the tree of phases was constructed. The LiF-NaBr-D₁(BaFBr) stable triangle was experimentally studied, the liquidus was constructed, and the characteristics of the alloy corresponding to a ternary eutectic were determined.     

Oxo Peroxo Glycolato Complexesof Vanadium (V). Crystal Structureof (NBu4)2[V2O2(O2)2(C2H2O3)2]ċH2O

Summary.  Oxo peroxo glycolato complexes of vanadium(V) (M ₂[V₂O₂(O₂)₂(C₂H₂O₃)₂]ċnH₂O (n=0, 1; M=NBu₄ ⁺ (1), K⁺ (2), NH₄ ⁺ (3), Cs⁺ (4), NPr₄ ⁺ (5)) as well as (NBu₄)₂[V₂O₄(C₂H₂O₃)₂]ċ H₂O (6) have been prepared and characterized by spectroscopic methods. X-Ray structure analysis of 1 revealed the presence of dinuclear [V₂O₂(O₂)₂(C₂H₂O₃)₂]²⁻ anions with a (chemical structure) bridging core and six coordinated vanadium(V) atoms in a distorted pentagonal pyramidal array. Received July 12, 1999. Accepted (revised) October 28, 1999     

Synthesis and Properties of Complexes of Lead(II), Cadmium(II), and Zinc(II) with N-Phosphonomethylglycine

Summary.  Sparingly water soluble complexes of lead(II), cadmium(II), and zinc(II) with N-phosphonomethylglycine (glyphosate, NPMG) of the general formulae C₃H₆O₅NPPb, C₃H₆O₅NPCdċ2H₂O, and C₃H₆O₅NPZn were synthesized. The complexes were also precipited from a dilute Roundup solution, and their solubility in water was determined. Thermal, diffractometric, and IR spectrophotometric analyses were carried out. It was found that the metal is bonded to glyphosate through the oxygen atoms of the carboxylic and phosphonate groups; metal-nitrogen binding is absent in the above compounds. Studying the complexing behaviour in solution by UV spectrophotometry pointed out that a complex of the composition Pb(II) : NPMG=1:1 with an absorption band at 232 nm is formed. Its stability constant as determined by Job’s method is logK=5.9±0.1. Using potentiometric techniques, the dissociation constant of N-phosphonomethylglycine and the stability constants of its complexes with cadmium (II) and zinc (II) were determined. Received June 30, 1999/Accepted July 21, 1999.     

Monovariant eutectic reaction in the Fe-Ni-S system as studied by directional solidification

The reaction of binary eutectic formation from (Fe_{1 − y} Ni _y )S_{1 − z} and γ-(Fe _y Ni_{1 − y} ) solid solutions was studied using directional solidification of a three-component melt in a quasi-equilibrium mode. An experiment was carried out to obtain a sample comprising a single-phase region and a two-phase region. Component distribution curves for this sample were constructed; a change in the melt composition was calculated. These data were used to determine the change in phase compositions during solidification, construct the relevant dependences on the triangular diagram, and determine the transformation of tie-lines along monovariant curves on liquidus and solidus surfaces.     

Calculation of salt activities in molten salt hydrates applying the modified BET equation,I: Binary systems

Summary On the basis of the modified BET model according to Stokes and Robinson, an equation for the calculation of salt activities in molten salt hydrates has been derived. The equation is used to describe successfully the liquidus curves of the hydrates of MgCl₂, Mg(NO₃)₂ and CaCl₂ inT-x diagrams. A promissing feature of the model is the small number of adjustable parameters and its extrapolative power.Dedicated to o. Univ._Prof. Dipl.-Ing. Dr. mont. Heinz Gamsjäger on the occasion of his 60th birthday     

Synthesis of polypropylene-co-p-methylstyrene copolymers by metallocene and Ziegler–Natta catalysts

This paper discusses the copolymerization reaction of propylene and p-methylstyrene (p-MS) via four of the best-known isospecific catalysts, including two homogeneous metallocene catalysts, namely, {SiMe₂[2-Me-4-Ph(Ind)]₂}ZrCl₂ and Et(Ind)₂ZrCl₂, and two heterogeneous Ziegler–Natta catalysts, namely, MgCl₂/TiCl₄/electron donor (ED)/AlEt₃ and TiCl₃. AA/Et₂AlCl. By comparing the experimental results, metallocene catalysts show no advantage over Ziegler–Natta catalysts. The combination of steric jamming during the consective insertion of 2,1-inserted p-MS and 1,2-inserted propylene (k₂₁ reaction) and the lack of p-MS homopolymerization (k₂₂ reaction) in the metallocene coordination mechanism drastically reduces catalyst activity and polymer molecular weight. On the other hand, the Ziegler–Natta heterogeneous catalyst proceeding with 1,2-specific insertion manner for both monomers shows no retardation because of the p-MS comonomer. Specifically, the supported MgCl₂/TiCl₄/ED/AlEt₃ catalyst, which contains an internal ED, produces copolymers with high molecular weight, high melting point, and no p-MS homopolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2795–2802, 1999     

LiF-K2WO4-BaWO4-CaWO4 four-component system

The LiF-K₂WO₄-BaWO₄-CaWO₄ four-component system was studied by physicochemical methods. A priori prediction of the phase composition of this system revealed its phase tree and crystallization tree, which were experimentally verified by topological modeling of the phase diagram. Equations of the general liquidus formation law were used to verify the validity and adequacy of the geometrical liquidus model. The density and electrical conductivity of a eutectic alloy sample of the title system were studied experimentally.