EXTRACTION OF CADMIUM FROM PHOSPHORIC ACID WITH DIORGANYLDITHIOPHOSPHINIC ACIDS. Part I: Equilibrium Data.

Liquid-liquid extraction of cadmium ions from 55-65 w% “black” phosphoric acid from a Nissan H process with diphenyldithio-phosphinic acid (DPP) or dicyclohexyldithiophosphinic acid (DCP) dissolved in an alkane (C₁₂ or C₁₆) at 90°C was investigated. The cadmium concentration could be reduced from 25 ppm to below 2 ppm at a ligand/(Cd+Cu) ratio of 6 (mol/mol). Cd and Cu were removed with a high selectivity. At lower ligand/(Cd+Cu) ratios Cu is removed more selectively than Cd. DPP forms precipitates with Cd, Ni, Zn and Cu, whereas the Cd and Zn complexes of DCP are soluble in the organic phase.

For DCP the equilibrium constant K_e =[CdL₂] / ( [Cd] [L¯]²) in 55 w% c.p. H₃Po₄ (90°C) has a value of 5?10⁵l²/mol². K_e decreases slightly with decreasing % H₃PO₄ A fast decomposition of DPP was observed in “black” phosphoric acid at 90°C.     

Polymerization of methyl methacrylate by imidazole–carbon tetrachloride charge-transfer system

The kinetics of charge-transfer (CT) polymerization of methyl methacrylate (MMA) in the presence of imidazole (Imy) and CCl₄ was studied in dimethyl sulfoxide (DMSO) at 60°C. The rate of polymerization (R_p) is sensitive to the [CCl₄] up to a concentration of 0.60 mol L⁻¹, but at a higher concentration, it is practically independent of the [CCl₄]. When [CCl₄] > [Imy], R_p is proportional, to [MMA]^1.45±0.15 and [Imy]^0.53±0.04 and the average rate constant for the polymerization of MMA is 3.25±0.41 × 10⁻⁶ L mol⁻¹ s⁻¹. This article also reports the polymerization of MMA initiated by Imy and CCl₄ and accelerated by hexakis (dimethyl sulfoxide) iron (III) perchlorate, [Fe(DMSO)₆] (CIO₄)₃ (A), at 60°C. The presence of Fe(Imy)³⁺₃ in the polymerization system produced well-defined induction periods. The rate constant at 60°C for the interaction of the poly(MMA) radical toward Fe(Imy)³⁺₃ is 7.19 × 10⁴ L mol⁻¹ s⁻¹. A probable reaction mechanism for the polymerization system has been postulated to explain the observed results. © 1996 John Wiley & Sons, Inc.     

Elektrochemische synthesen—XXI. Cyclovoltammetrische und epr-spektroskopische untersuchung des redoxverhaltens des [S4N5]−-ions

Whilst the anodic oxidation of (Bu₄N) [S₄N₅] in 0,15 M (Bu₄N) [BF₄]/CH₂Cl₂ yielded no detectable radical species, the cathodic reduction at ?40°C and at room temperature leads to epr spectra, which can be assigned to [S₄N₅]^2? and [SN₂]^? plus a species containing one N atom—possibly NS^.₂.     

Low Temperature‐Based Flexural Properties of Carbon Fiber/Epoxy Composite Laminates Incorporated with Carbon Nanotube Sheets

This study introduces carbon nanotube buckypaper (CNTBP) into the easily fractured sites of [0°]₁₆ and [0°/90°]_4S composite laminates, and comparatively explores how the CNTBP affects the flexural properties of the laminates at 25, ?15, and ?55 °C. Compared to the base [0°]₁₆ and [0°/90°]_4S laminates at the same temperature, improvements of the flexural strengths in the order of 4.0–15.3% and 6.5–31.0% are respectively obtained from the corresponding CNTBP‐reinforced [0°]₁₆ and [0°/90°]_4S laminates. Importantly, the lower the temperature is, the higher the strength improves. In fact, the CNTBP has little effect on the flexural moduli of the studied laminates, although there is an increasing trend with decreased temperature. Moreover, the introduced CNTBP would significantly change the fracture mechanism of the laminates at low temperature. The present work reveals that the CNTBP exhibits more positive reinforcing capability to the polymer matrix‐based composite laminates at relatively low temperatures.     

Effect of tris(bathophenanthroline)iron(III) on the polymerization of styrene

The polymerization of styrene at 60°C initiated by 2,2′-azobisisobutyronitrile (AIBN) was studied in N,N-dimethylformamide (DMF) in the presence of tris-(bathophenanthroline)iron(III) complex, [Fe(bathophen)₃]³⁺. The complex was prepared in situ by mixing hexakis(N,N-dimethylformamide)iron(III) perchlorate with bathophen-anthroline (systematic IUPAC nomenclature: 4,7-diphenyl-1,10-phenanthroline) in the molar ratio of 1 : 3. The equilibrium constant for was 3.12×10³ L³ mol⁻³. The transfer constant for bathophenanthroline was found to be 0.38 ± 0.01 for the styrene/DMF system at 60°C. Mean velocity constant at 60°C for interaction of polystyryl radical with [Fe(bathophen)₃]³⁺ was 3.73× 10⁴ L mol⁻¹ s⁻¹. © 1996 John Wiley & Sons, Inc.     

The activation mechanism of oxalic acid on γ-alumina and the formation of α-alumina

Converting the γ phase into the α phase completely is necessary in the presintering stage of industrial alumina (Al₂O₃), which requires high temperature and energy consumption. To reduce the presintering temperature, γ-Al₂O₃ was activated by oxalic acid. XRD, ²⁷Al-MAS-NMR and TG-DSC were used to characterize the γ - alumina before and after activation, and the phase transformation was studied. The formation temperature of α-Al₂O₃ decreased to 1029 °C for oxalic acid activated γ-Al₂O₃, and the α-fraction was 100% for activated γ-Al₂O₃ at 1300 °C. After oxalic acid activation, the diffraction peak intensity of γ-Al₂O₃ decreased significantly; the results of ²⁷Al-MAS-NMR suggested that octahedral [AlO₆] in γ-Al₂O₃ was easier than tetrahedral [AlO₄] to be attacked by oxalic acid, and the formation of pentavalent [AlO₅] with higher reaction activity, which was in favour of the lowering formation temperature of α-Al₂O₃. The dissolution concentration of Al increased after oxalic acid activation, and the dissolution process was controlled by surface reactions. Oxalic acid mainly attacked the octahedral aluminium in γ-Al₂O₃ and extracted Al as three complexes of [Al(C₂O₄)]⁺, [Al(C₂O₄)₂]^- and [Al(C₂O₄)₃]^3-. Oxalic acid activated γ - Al₂O₃ with a lower phase transformation temperature has broad application prospects in the alumina industry.     

Nitrogen-containing apatite

Two commercial hydroxyapatites were treated in dry ammonia at temperatures between 800 and 1300°C for different times up to 30 h. Nitrogen was incorporated with a maximum content of 3·7 wt% in presence of graphite. X-ray diffraction studies show no important phase transformation by the incorporation of nitrogen up to 1200°C. Treatments at temperatures above 1200°C resulted in the formation of CaO or Ca(OH)₂. ³¹P NMR studies indicate no direct bonding of nitrogen and phosphorous. Infrared spectra show increasing intensities of four new bands at 3250, 2016, 1966 and 700 cm⁻¹ with increasing nitrogen contents, while the OH-bands at 3570 and 630 cm⁻¹ vanish. Taking into account results of the carbon content, XRD, NMR and IR spectra it is suggested that nitrogen enters into the structure as [CN₂]²⁻ ion, substituting [OH]⁻ groups, and forming cyanamidapatite Ca₁₀(PO₄)₆(CN₂). ©     

Diels-Alder-Reaktionen. VII. Über die Isomerisierung von 2-Vinylbicyclo[2,2,1]hepten-(5)

Diels-Alder Reactions. VII. The Isomerization of 2-Vinylbicyclo[2,2,1]hept-5-ene The isomerization of exo/endo-2-vinylbicyclo[2,2,1]-hept-5-ene in the presence of Na/Al₂O₃ rapidly gives the thermodynamic equilibrium between exo- and endo-2-vinylbicyclo-[2,2,1]hept-5-ene and cis- and trans-2-ethylidenbicyclo[2,2,1]-hept-5-ene. Far more slowly vinylnortricyclene is formed, which enriches to an equilibrium concentration of about 75% at 60°C. The dependence of equilibrium constants of isomerization on temperature allows the calculation of enthalpies and entropies of isomerization.     

LAMELLAR INORGANIC ION-EXCHANGERS.BEHAVIOUR OF γ-TITANIUM PHOSPHATE IN THE H+/Na+ION-EXCHANGE

H⁺/Na⁺ ion-exchange in Ti(HP0₄) ₂.2H₂0 (γ TiP) was studied. The exchange isotherm, titration and hydrolysis curves at 25°C were obtained. In initially acidic or neutral solutions the 25% of the material exchange capacity was reached. The half-exchanged phase was obtained by additions of stoichiometric amounts of NaOH, with hydrolysis lower than 3% and at acidic equilibrium pH. For additions of NaOH over 4.0 me/g Y-TiP conversions higher than 50% were reached with an increase in the values of the equilibrium pH and the hydrolysis. The evolution of the solid was followed by X-ray diffraction. The substituted phases of samples dried in air at room temperature showed the following hydration degrees: ----H N ----------------------- conversion phase stored over P205 was dehydrated originating H1-5Na0.5 When i t is heated at 80°C-200°C i t transformed i n t o mixtures o f iTFi ( 9. 1 A ) and HNa (10.1 Å ).     

Polymerization of methyl methacrylate by charge-transfer mechanism with 2,2′-bipyridine and iron (III) complex

Polymerization of methyl methacrylate (MMA) by the charge-transfer complex formed by the interaction of 2,2′-bipyridine (bpy), MMA, and carbon tetrachloride (CCl₄) was studied in dimethylsulfoxide (DMSO) at 60°C. The rate of polymerization (R_p) is sensitive to the [CCl₄] at low concentration of CCl₄, but at a higher concentration it is practically independent of [CCl₄]. R_p is proportional to [MMA]^1.45±0.04 and [bpy]^0.52±0.04 when [CCl₄] > [bpy], and the average rate constant, k, at 60°C for the polymerization of MMA was 7.14 ± 0.40 × 10⁻⁶ L mol⁻¹s⁻¹. Kinetic studies showed that the polymerization proceeds through free radical intermediates. This article also reports the polymerization of MMA initiated by bpy and CCl₄ and accelerated by Lewis acid, hexakis (dimethylsulfoxide)iron(III) perchlorate [Fe(DMSO)₆](ClO₄)₃ at 60°C. The glass transition temperature and molecular weights of the samples were investigated by using differential scanning calorimetry and gel permeation chromatography techniques, respectively. Probable reaction mechanisms are proposed to explain the observed results. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2097–2103, 1997     

The characterization of mixed titanate Ba1−xSrxTiO3 phase formation from oxalate coprecipitated precursor

Mixed titanates Ba_1−xSr_xTiO₃ were synthesized via calcination of oxalate coprecipitated precursors. On heating there were three thermal event occurred: T<250°C corresponds to the evaporation of trapped water and dehydration, T=250°C–450°C corresponds to the decomposition of oxalate and the formation of an intermediate phase where the composition is close to [Ba_1−xSr_x]₂Ti₂O₅.CO₃ and T=600°C–700°C corresponds to the carbonate decomposition and the formation of Ba_1−xSr_xTiO₃ phase. Powders calcined at T=700°C for 2 h are single phase, have grain size ranges of 0.2–2 μm and elongated morphology. Rietveld refinements of the XRD data showed single phase of perovskite structure in which their tetragonality decreased with increasing concentration of Sr²⁺ incorporated in Ba²⁺ site. The transition temperature showed strong correlation with the tetragonality.     

Synthesis of Ti3SiC2 Phase from Polycarbosilane Precursor

Ti₃SiC₂ phase was synthesized by reactive pyrolysis of three different polycarbosilane, [Si(H)₂CH₂]_m·[(H)Si(Vi)CH₂]_n·[(H)Si(Me)CH₂]_p (AHPCS), [Si(CH₃)₂CH₂]_x·[Si(H)(CH₃)CH₂]_y (PCS), and [Me(H)SiC≡C]_n, filled with metal Ti powder. The pyrolysis was carried out in argon atmosphere between 1200°C and 1400°C. The metal–precursor reactions and phase evolution during the pyrolysis were studied by means of X-ray diffraction and scanning electron microscopy. The results indicated that PCS/Ti system was more beneficial for the synthesis of Ti₃SiC₂. In addition, the high-purity Ti₃SiC₂ could be synthesized through the pyrolysis of green compact of the PCS/Ti system with CaF₂ at 1400°C.     

Ionization equilibria in solutions of nickel(II) chloride in dimethyl-sulphoxide

Visible absorption spectra and the molar conductance curve of NiCl₂ dissolved in dimethyl-sulphoxide (DMSO) have been determined at 25°C. The results indicate the formation of the [NiCl(DMSO)₅]⁺ inner-sphere complex followed by the formation of the {NiCl(DMSO)₅]⁺Cl^?} outersphere ion-pair as the concentration of NiCl₂ increases. The [NiCl₂(DMSO)₄] inner-sphere complex in pure dimethyl sulphoxide at 25°C is formed to but a small extent, but its relative content increases upon addition of the non-coordinating diluent, chlorobenzene. Dilutions with chlorobenzene also enhance coordination disproportionation producing the [NiCl₃ DMSO]^? tetrahedral complex. The stability constant of the monochloro complex derived from the conductometric data has the value of 297 (^±10)M^?2 at 25°C, and the estimated value of the association constant of the [NiCl (DMSO)₅]⁺Cl^? complex electrolyte, dominating in moderately concentrated solutions at room temperature, is 7(±3)M^?1.     

Crystal structure,dielectric properties,and lattice vibrational characteristics of LiNiPO4 ceramics sintered at different temperatures

LiNiPO₄ (LNP) ceramics were synthesized using a conventional solid-state reaction method and different sintering temperatures. Differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, and X-ray diffraction (XRD) measurements indicated that single- phase olivine (Pnma, No. 62) was formed above 750°C, and dense LNP ceramic with a theoretical density of more than 95% was obtained at 825°C. Raman and far-infrared (IR) vibrational modes were assigned and discussed in detail. The intrinsic dielectric properties of the samples were calculated using the four-parameter semi-quantum (FPSQ) model based on far-IR reflectance spectroscopy and were in good agreement with the measured values. A positive relationship existed between the Raman shift of the υ₁ mode (attributed to the symmetric vibration of [PO₄]³⁻) and the corrected permittivity, and the opposite correlation was observed between the quality factor (Q × f) and the damping of the υ_s mode as well as the distortion of the [NiO₆] octahedra. The optimized microwave dielectric properties of the LNP ceramics sintered at 825°C include an ultralow dielectric constant (5.18) and a good quality factor (24 076 GHz, f = 17.2 GHz).     

Synthesis and Structure Determination of the Adducts of Dibenzo[a,l]pyrene Diol Epoxides and Deoxyadenosine or Deoxyguanosine

Abstract

(±)?Syn?dibenzo[a,l]pyrene diol epoxide (DB[a,l]PDE) and (±)?anti?DB[a,l]PDE were reacted with deoxyadenosine (dA) or deoxyguanosine (dG) in dimethylformamide at 100 °C for 30 min. The crude products were purified by reverse phase HPLC under gradient and isocratic conditions. The structure of each adduct was assigned by 1D and 2D NMR spectra and by fast atom bombardment mass spectrometry. Five adducts were isolated from the reaction of (±)?syn?DB[a,l]PDE and dA: syn?DB[a,l]PDE?N⁶dA?1, syn?DB[a,l]PDE?N⁶dA?2, syn?DB[a,l]PDE?N⁶dA?3, syn?DB[a,l]PDE?N⁶dA?4 and syn?DB[a,l]PDE?N7Ade. Four adducts were isolated from the reaction of (±)?anti?DB[a,l]PDE and dA: anti?DB[a,l]PDE?N⁶dA?1, anti?DB[a,l]PDE?N⁶dA?2, anti?DB[a,l]PDE?N⁶dA?3 and anti?DB[a,l]PDE?N⁶dA?4. Two adducts were isolated from the reaction of (±)?syn?DB[a,l]PDE and dG: (±)?11,12,13?trihydroxy?tetrahydroDB[a,l]P?14?N²dG and (±)?11,12,13?trihydroxy?tetrahydroDB[a,l]P?14?N7Gua. Two adducts were isolated from the reaction of (±)?anti?DB[a,l]PDE and dG: (±)?11,12,13?trihydroxy?tetrahydroDB[a,l]P?14?N²dG and (±)?11,12,13?trihydroxy?tetrahydroDB[a,l]P?14?N7Gua.     

Electrical conductivity measurements as a microprobe for structure transitions in polysiloxane derived Si–O–C ceramics

Polysiloxanes [RSiO_1.5]_n with R=CH₃ (PMS) and C₆H₅ (PPS), respectively, were transformed to Si–O–C ceramics of variable composition and structure upon pyrolysis in inert atmosphere at 800–1500°C. The electrical conductivities of the Si–O–C ceramics in air were measured at room temperature by using a shielded two point configuration. In situ measurements of the dc-conductivity during the pyrolytic conversion from the polymer to the ceramic phase were carried out up to 1500°C with four point contacted carbon electrodes in inert atmosphere. During polymer-ceramic conversion excess carbon precipitates above 400°C (PPS)–700°C (PMS). At temperatures above 800°C (PPS) and 1400°C (PMS) coagulation and growth of the carbon clusters results in a percolation network formation. While below the percolation threshold electrical conductivity can be described according to Motts mechanism by variable-range-hopping of localized charge carriers, regular electron band conduction due to the instrinsic conductivity of turbostratic carbon (8×10⁻⁴ (Ωcm)⁻¹) predominates above. Thus, the in situ measurement of non-linear electrical property changes can be used as a microprobe of high sensivity to detect microstructural transformations during the pyrolysis of preceramic polymers.     

Solubility of potassium ferrate in 12 M alkaline solutions between 20°C and 60°C

The solubility of potassium ferrate (K₂FeO₄) was measured in aqueous solutions of NaOH and KOH of total concentration 12 M containing various molar ratios of KOH:NaOH in the range 12:0 to 3:9. Several analytical methods were tested for the determination of ferrate concentration. The final method chosen consisted of potentiometric titration of the ferrate sample with an alkaline solution of As₂O₃. The assumption was made that ferrate dissociates in concentrated KOH solutions predominantly to KFeO₄⁻. The solubility constant, S, defined as the product of the molar concentration of the potassium ion, K⁺, and the ferrate anion, KFeO₄⁻, was found to be 0·044 ± 0·006 mol² dm⁻⁶ for 20°C, 0·093 ± 0·004 mol² dm⁻⁶ for 40°C and 0·15 ± 0·09 mol² dm⁻⁶ for 60°C. From these results the heat of dissolution of K₂FeO₄ was calculated as −14·3 kJ mol⁻¹. At 60°C the enhanced decomposition of the ferrate at the higher temperature led to a greater deviation in solubility values compared with data for either 20°C or 40°C.     

Ring-opening polymerization of ϵ-caprolactone initiated by rare earth complex catalysts

The polymerization of caprolactone (ϵ-CL) was initiated by yttrium triisopropoxide {Y(OPⁱ_r)₃}, bimetallic isopropoxide of yttrium and aluminum {Y[Al(OPⁱ_s)₄]₃}, yttrium and tin(II) {Y[Sn(OPⁱ_r)₃]₃}, and tin(II) and yttrium {Sn[Y(OPⁱ_r)₄]₂}, respectively. The polymerization was carried out through coordinative insertion of a monomer into the free metal-oxygen bond. The molecular weight and yield of poly(ϵ-caprolactone) (PCL) were affected drastically by the mol % of the initiator to the monomer (C_o/M_o). The results showed that Y(OPⁱ_r)₃ and Sn[Y(OPⁱ_r)₄]₂ were more effective than were {Y[Al(OPⁱ_r)₄]₃} and {Y[Sn(OPⁱ_r)₃]₃} for the polymerization of ϵ-CL. When polymerization was conducted at 5°C using Y(OPⁱ_r)₃ as the initiator or at 10°C using Sn[Y(OPⁱ_r)₄]₄ as the initiator, polymers with a molecular weight of 45.9 × 10³ or 54.0 × 10³ and high yield resulted in 30 or 5 min, respectively. The polymer was characterized by FTIR, H-NMR, and GPC. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1295–1299, 1997     

A Facile Route to BaSiF6:Mn4+ Phosphor with Intense Red Emission and Its Humidity Stability

Red phosphor BaSiF₆:Mn⁴⁺ has been synthesized by a hydrothermal method at 120°C for 24 h, in which either Si or SiO₂ is used as silicon source. HF as weak acid performs a complex agent for the formation of anion groups [SiF₆]^2? and [MnF₆]^2?. The luminescence properties of undoped BaSiF₆ have been firstly observed. The dependence of luminescence intensities of BaSiF₆:Mn⁴⁺ on the concentrations of HF and KMnO₄ in precursory solution has been investigated. The as‐prepared BaSiF₆:Mn⁴⁺ exhibits high chemical stability even in deionized water.     

Phase formation,microstructure development,and mechanical properties of kaolin-based mullite ceramics added with Fe2O3

The effects of Fe₂O₃ on phase evolution, density, microstructural development, and mechanical properties of mullite ceramics from kaolin and alumina were systematically studied. X-ray diffraction results suggested that the ceramics consisted of mullite, sillimanite, and corundum, in the sintering range of 1450°C–1580°C. However, as the sintering was raised to 1580°C, mullite is the main phase with a content of 94%, and the corundum phase content is 5.9%. Simultaneously, high-temperature sintering had a positive effect on the densification of the mullite ceramics, where both the bulk density and flexural strength could be optimized by adjusting the content of Fe₂O₃. It was found that 6 wt% Fe₂O₃ was optimal for the formation of rod-shaped mullite after sintering at 1550°C for 3 h. The sample's maximum bulk density was 2.84 g/cm³, with a flexural strength of 112 MPa. Meanwhile, rod-shaped mullite grains with an aspect ratio of ~9 were formed. As a result, a dense network structure was developed, thus leading to mullite ceramics with excellent mechanical properties. The effect of Fe₂O₃ on the properties might be attributed to the fact that Al³⁺ ions in the [AlO₆] octahedron were replaced by Fe³⁺ ions, resulting in lattice distortion.