Thermal analysis studies on electrochemically oxidized carbon fibers

The results are presented of studies on the effect of electrochemical oxidation of carbon fibers (CFs) in 1 mol·dm^–3 H₂SO₄ on their thermal decomposition in air.The resistance to oxidation of the as-received fibers increases with increasing ordering of their internal structure, characterized by the interlayer spacing¯d ₀₀₂ of the graphite crystallites.After anodic oxidation, the resistance to oxidation of CFs in air is markedly decreased. It is shown that in the course of anodic polarization of CFs with a current density of more than 5 A·m^–2, the regions of the material with highest ordering convert to graphite oxide, which is hydrophilic and thermally unstable.

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Zusammenfassung Es werden die Ergebnisse einer Untersuchung über den Einfluß der elektrochemischen Oxydation von Kohlefiber (CF) in 1 molarer H₂SO₄ auf dessen thermische Zersetzung in Luft dargelegt. Ihre Oxydationsbeständigkeit wächst mit steigender innerer Strukturordnung, charakterisiert durch den Zwischenschichtabstand¯d ₀₀₂ zwischen den Graphitkristalliten. Nach anodischer Oxydation ist die Oxydationsbeständigkeit von CF in Luft deutlich niedriger. Es wurde gezeigt, daß sich die Materialregionen mit der geordnetsten Struktur im Verlauf der anodischen Polarisation von CF mit einer Stromdichte von mehr als 5 A·m^–2 in hydrophiles und thermisch instabiles Graphitoxid umwandeln.

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1 M . , d ₀₀₂ . . , 5 · ^–2, , .

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The author is indebted to Miss Lucyna Hrynczyszyn for experimental assistance during the derivatographic measurements. This study was carried out with support from Government Research Programme 01. 15.     

Top soil environmental radioactivity in Akwa Ibom State of Nigeria

A survey of top soil environmental radioactivity in Akwa Ibom State of Nigeria has bean investigated. The results vary considerably from one environment to another ranging between a minimum of 161 mBq·g^–1 and a maximum value of 648 mBq·g^–1 -activity. The work reveals that hospitals and health centres lead in top soil radioactivity with the highest mean values of (378 mBq·g^–1) and (294 mBq·g^–1) followed closely by industrial areas with mean values of (372 mBq·g^–1) and (283 mBq· g^–1) trailing beaches and recreation centres having average values of (364 mBq·g^–1) and (273 mBq·g^–1). Lower levels of top soil radioactivity were observed mostly in environments with high level human interaction activity such as schools, offices, environments and recreation centres. An overall top soil mean of 342 mBq·g^–1 -activity, 271 mBq·g^–1 -activity and 71 mBq·g^–1 -activity were observed in the State.     

The electronic spectrum of acrylonitrile

The vapor absorption spectrum of acrylonitrile CH₂CHCN has been measured in the vacuum ultraviolet region. In addition, an all-valence-electron molecular orbital calculation has been used to calculate the electronic structure and spectrum of the molecule. On the basis of the MO calculation, as well as a vibrational analysis of the observed spectrum, several electronic transitions are assigned. The lowest energy absorption band (2107Å, = 150) is assigned as an n ^* transition. Absorption bands at 2030Å (=1600), 1725Å ( = 2100), and 1570Å ( = 1920) are assigned as 0–0 bands associated with transitions that are, respectively, ^*,^*, and ^* in character.

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Zusammenfassung Das UV-Absorptionsspektrum von dampfförmigen Acrylnitril wurde gemessen und eine CNDO/2-Rechnung für die Elektronenstruktur durchgeführt. Auf dieser Basis konnten unter Zuhilfenahme der Analyse der Schwingungsstruktur im beobachteten Spektrum mehrere Banden zugeordnet werden: die 2107-Å-Bande ( = 150) einem n^*-Übergang, die drei Banden bei 2030Å ( = 1600), 1725Å ( = 2100) und 1570 Å ( = 1920)0-0-Übergängen von ^*-, ^*- bzw. ^*-Banden.

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Résumé Mesure du spectre d'absorption en phase vapeur de l'acrilonitrile CH₂CHCN dans la région de l'ultraviolet. Par ailleurs, la structure électronique et le spectre de la molécule ont été calculés à l'aide d'une méthode des orbitales moléculaires semi-empirique pour tous les électrons de valence. Sur cette base, ainsi que sur une analyse vibrationnelle du spectre expérimental, on procède à l'attribution de plusieurs transitions électroniques. La bande d'absorption de plus basse énergie (2107 Å, = 150) est attribuée à une transition n ^*. Les bandes d'absorption à 2030Å ( = 1600), 1275Å ( = 2100) et 1570Å ( = 1920) sont considérées comme des bandes 0 - 0 associées à des transitions ^*, ^* et ^* respectivement.

     

VUV-Photolyse von Methanol bei 1236 Å

Zusammenfassung Es wird über die indirekte und die direkte VUV-Photolyse von luftfreiem Methanol in flüssiger Phase bei 1236 Å berichtet. Bei der Bestrahlung von wäßr. 0,01m-Methanol wurden folgende Produkte und Ausbeuten erhalten: (H₂)=1,00, (HCHO)=0,27, (CH₂OH)₂=0,12, (CH₂OH·CHO)=0,04 und (HCOOH)=0,02. Die Photolyse von flüssigem Methanol lieferte die gleichen Produkte, jedoch mit höheren Ausbeuten: (H₂)=1,50, (HCHO)=0,98, (CH₂OH)₂=0,28 und (CH₂OH·CHO)=0,06. Unter Anwendung von Methanol als Radikalfänger konnte auch die Quantenausbeute der Wasserphotolyse bei 1236 Å, (H,OH)=1,025 verifiziert werden. Wahrscheinliche Reaktionsmechanismen werden diskutiert.

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V.U.V.-Photolysis of methanol at 1236 Å

The indirect and the direct v.u.v.-photolysis of air free methanol in liquid phase at 1236 Å is reported. After irradiation of aqueous 0.01M-methanol the following products were obtained: (H₂)=1.00, (HCHO)=0.27, (CH₂OH)₂=0.12, (CH₂OH·CHO)=0.04 and (HCOOH)=0.02. The photolysis of liquid methanol yielded the same compounds, however with higher amount as follows: (H₂)=1.50, (HCHO)=0.98, (CH₂OH)₂=0.28 and (CH₂OH·CHO)=0.06. Using methanol as a scavenger for the H and OH radicals the quantum yield of the water photolysis at 1236 Å could be verified to be (H,OH)=1.025. Probable reaction mechanisms are discussed.

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Mit 3 Abbildungen

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Herrn Prof. Dr.E. Broda zum 60. Geburtstag gewidmet.     

ESR characteristics of paramagnetic species on Pd/La2O3 catalysts

Reduction of Pd/La₂O₃ catalysts by H₂ and CO at room temperature leads to the formation of Pd⁺ ions stabilized in bulk and the subsurface layer. Hydrogen spillover seems to enhance the process. O ₂ ^– and (CO) ₂ ^– radicals are formed after adsorption of CO and O₂ at 295 K.

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Pd/La₂O₃ CO Pd⁺ . . CO O₂ (CO) ₂ ^– O ₂ ^– La₂O₃.

     

Energetic and kinetic investigation of thermally induced molecular rearrangements of esters of (hydroxymethyl) hydridosilanes by DSC

Silanes of the type R¹R²Si(H)CH₂OEl(O)_xR _y ³ [R=organyl; El=C (x=y=1), S (x=2,y=1), P (x=1y=2)] undergo a thermally induced rearrangement to give silanes of the type R¹R²Si (CH₃)OEl(O)_xR _y ³ . The energetic (reaction enthalpy) and kinetic data (reaction order, enthalpy and entropy of activation) of this reaction were determined by means of differential scanning calorimetry. The results obtained are discussed in terms of mechanistic aspects.

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Zusammenfassung Silane des Typs R¹R²Si(H)CH₂OE10_xR _y ³ mit R=organyl; E1=C (x=y=1), S(x=2, y=1) oder P (x=1,y=2) zeigen eine thermisch induzierte Umlagerung zu Silanen des Typs R¹R²Si(CH₃)OE10_xR _y ³ . Energetische (Reaktionsenthalpie) und kinetische Daten (Reaktionsordnung, Aktivierungsenthalpie und -entropie) dieser Umlagerungsreaktion wurden mittels DSC ermittelt. Die mechanistischen Aspekte der Ergebnisse werden diskutiert.

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R¹R²Si(H)OE1(O)_xR _y ³ , R= , E1=C (x=y=1), S (x=2,y=1), P (x=1,y=2), R¹R²Si(CH₃)OE1(O)_xR _y ³ . ( ) ( , ) . .

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Thermal decomposition of Cu(I) phosphine complexes

The thermal decomposition of Cu(I) phosphine complexes of the general types (CuXPPh₃)₄, [CuX(PPh₃)₂] and [CuX(PPh₃)₃] was investigated.The thermal decomposition of (CuXPPh₃)₄, where X denotes Cl^–, Br^–, I^–, NO ₃ ^– and PPh₃=P(C₆H₅)₃, occurs with formation of a phosphine oxide intermediate. For the remaining complexes this intermediate was not proved in the thermal decomposition.

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Zusammenfassung Die thermische Zersetzung der Cu(I)-Phosphinkomplexe vom allgemeinen Typ (CuXPPh₃)₄ und [CuX(PPh₃)₂], wie auch [CuX(PPh₃)₃] wurde untersucht. Die thermische Zersetzung von (CuXPPh₃)₄, wobei X=Cl^–, Br^–, I^– und NO ₃ ^– bedeutet und PPh₃=P(C₆H₅)₃, verläuft unter Bildung eines Phosphinoxid Zwischenproduktes, bei den übrigen Komplexen konnte dieses im Laufe der thermischen Zersetzung nicht nachgewiesen werden.

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Résumé On a étudié la décomposition thermique des complexes phosphine-Cu(I) de formule générale (CuXPPh₃)₄, [CuX(PPh₃)₂], [CuX(PPh₃)₃]. La décomposition thermique de (CuXPPh₃)₄, où X désigne Cl^–, Br^–, I^– et NO ₃ ^– , et PPh₃=P(C₆H₅)₃, s'effectue avec formation d'un oxyde de phosphine intermédiaire; avec les autres complexes, cet intermédiaire n'a pas été mis en évidence au cours de la décomposition thermique.

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(CuXPPb₃)₄ [CuX(PPh₃)₂] [CuX(PPh₃)₃]. (CuXPPh₃)₄, X=Cl^–, Br^–, I^–, NO ₃ ^– , PPh₃=(₆₅)₃ . .

     

Quantum chemical calculations on the catalytic dehydration of 2-propanol

The charge on atoms and the bond strengths in CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– and CH₃ CH₃...O(H)CH(CH₃)₂ have been calculated by the CNDO/2 method. The results are in agreement with published experimental observations on catalytic dehydration. A modified mechanism of anti-elimination on solid catalysts is proposed.

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CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– CH₃ CH₃...O(H)CH(CH₃)₂, CNDO/2. . .

     

Photometrische Bestimmung von Bor in hochreinen Chemikalien

Zusammenfassung Bor reagiert in Form des Tetrafluoroboratkomplexes mit dem basischen Farbstoff Methylenblau unter Bildung eines mit 1,2-Dichlorethan extrahierbaren Ionenassoziatkomplexes. Die optimalen Bedingungen für die photometrische Bestimmung von Mikromengen Bor werden ermittelt und das vorgestellte Verfahren hinsichtlich Empfindlichkeit, Genauigkeit und kleinster bestimmbarer Menge charakterisiert.Die Borbestimmung ist im Bereich von 0,25–2,5 g Bor mit einer relativen Standardabweichung von 3,8% für 1,0 g Bor möglich. Der molare Extinktionskoeffizient beträgt ₆₆₅=8,2·10⁴1·mol^–1·cm^–1, die Nachweisgrenze nach Kaiser 0,125 g Bor.Das Verfahren wurde zur Bestimmung von 10^–6 bis 10^–5% Bor in folgenden hochreinen Chemikalien eingesetzt: Methanol, Ethanol, Isopropanol, Aceton, Mineralsäuren, Essigsäure, Ammoniak und Wasserstoffperoxid.

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Photometric determination of boron in high-purity chemicals

Summary Boron reacts with fluoride to form borofluoride which itself reacts with the basic dye methylene blue forming a complex which can be extracted into 1,2-dichloroethane. Optimum conditions were established for the determination of microamounts of boron by an extraction-photometric method. The procedure presented has been characterized with regard to sensitivity, precision and detection limit.Boron can be determined within a range from 0.25 to 2.5 g with a relative standard deviation s _rel=3.8% for 1 g B. The absorptivity is ₆₆₅=8.2·10⁴1·mol^–1·cm^–1, the detection limit according to Kaiser was found to be 0.125 g B.The procedure was used to analyse high-purity chemicals (10^–6–10^–5% B) such as organic solvents, mineral acids, acetic acid, ammonia, hydrogen peroxide etc.

     

Thermal and related studies of some basic zirconium salts

Studies of basic zirconium carbonate, oxalate, nitrate and sulphate using TG, DTA and DTG methods, combined with isothermal gaseous product analyses, IR spectroscopy and X-ray diffraction techniques, have shown that the ease of ligand removal from such salts follows the sequence: loosely bound H₂O>CO ₃ ^2– C₂O ₄ ^2– >NO ₃ ^– >OH^– (or tightly bound H₂O)>SO ₄ ^2– .With the exception of the basic sulphate where the high temperature necessary for complete removal of the sulphato groups resulted in direct formation of crystalline monoclinic zirconia, such ligand removal generally led to generation of the cubic crystalline variety.

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Zusammenfassung Auf Grund von TG-, DTA- und DTG-Untersuchungen, verbunden mit einer isothermen Gasprodukteanalyse, sowie IR-spektsoskopischen und Röntgendiffraktionsuntersuchungen von basischen Zirkoniumkarbonaten, -oxalaten, -nitraten und -sulfaten wurde festgestellt, dass die relative Abspaltbarkeit eines Liganden solcher Salze der folgenden Reihenfolge entspricht: locker gebundenes H₂O>CO ₃ ^2– >C₂O ₄ ^2– >NO ₃ ^– >OH^– (bzw. stark gebundenes H₂O)>SO ₄ ^2– . Mit Ausnahme des basischen Sulfates, bei dem zur vollständigen Abspaltung der Sulfatogruppen eioe hohe Temperatur notwendig ist und sich die direkte Bildung von kristallinem, monoklinem Zirkoniumdioxid abspielt, führen solche Ligandenabspaltungen im allgemeinen zu einer kubischen Kristallmodifikation.

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, , , , , , , , : ₂> ₃ ^2– C₂Ol ₄ ^2– > N ₃ ^– > ^– — H₂O>SO ₄ ^2– . , , .

     

Extraction of Polonium from Aqueous α-Hydroxyisobutyric Acid Solutions Using Dioctyl Sulphide, Cyanex 272, Cyanex 301 or Cyanex 302 in Toluene

A study of the extraction of polonium from aqueous solutions containing -hydroxyisobutyric acid (-HIBA) was performed with four different extractants, di-n-octyl sulphide (DOS), Cyanex 272, Cyanex 301 and Cyanex 302, dissolved in toluene. The extracted complex for DOS at low -HIBA concentrations is most likely PoO(-HIB)₂·2DOS, while at higher -HIBA concentrations there seems to be a solvating effect implicating an extracted complex of the type PoO(-HIB)₂(-HIBA)₂·2DOS. For the extraction of polonium with Cyanex 272 the results are inconclusive. The extracted complex is either PoOA₂ or PoO(-HIB)₂·2HA. For extraction with Cyanex 301 or Cyanex 302 the major extracted species does not contain any -HIBA molecules. The neutral species in both cases is PoOA₂, extracted at low extractant concentrations, while at higher extractant concentrations a complex of the type PoOA₂·xHA is extracted. The extraction of polonium increases in the order Cyanex 272 < DOS < Cyanex 302 < Cyanex 301.     

Polymorphism of Crystalline Inclusion Complexes and Unsolvated Hosts. Part 8

Crystallization of cyclotriveratrylene (CTV) from solutions in acetone at 40°C gave a new 4:1 host-guest complex instead of the conventional 2:1 clathrate (-phase) whose X-ray crystal structure was determined. Data for 2(C₂₇H₃₀O₆) · 0.5(CO(CH₃)₂): monoclinic, P2₁/c, a = 18.942(4), b = 24.697(5), c = 10.508(2) Å, = 91.10(2)°, V = 4915(2) ų, Z = 8, D _x = 1.257 g/cm³, T = 293 K, R = 0.077 (for 2694 reflections). One of the two crystallographically independent CTV molecules (molecule A) is stacked into columns characteristic of the CTV - or -phase complexes. Molecules B face each other enclathrating inside around the inversion center disordered acetone molecules giving rise to the molecular capsule. The acetone molecule is H-bonded simultaneously to both host molecules by C(H₂)--H ··· O type bonds forming centrosymmetric dimers. Dimers are incorporated together with two A molecules into centrosymmetric units also by C(H₂)--H ··· O type H-bonds. Packing of these units gives rise to the crystal structure of the clathrate.     

Phase equilibria in the system La2O3-Na2O-P2O5: Binary phase diagram La(PO3)3-NaPO3

In the ternary system La₂O₃-Na₂O-P₂O₅, the binary system La(PO₃)₃-NaPO₃ was examined by means of thermal (heating and cooling), dilatometric, X-ray powder diffraction and microscopic analyses. The occurrence of the phosphate NaLaP₄O₁₂ was confirmed and its temperature of congruent melting was determined to be 1174 C. The powder data indicate a monoclinic system with the lattice constantsa=12.36(6);b=13.45(0);c=6.57(4) å; =109.48;V=1030.97 å³. The investigations were carried out on monocrystals.

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Zusammenfassung Das binäre Teilsystem La(PO₃)₃-NaPO₃ des ternären Systemes La₂O₃-Na₂O-P₂O₅ wurde mittels thermischer, dilatometrischer, Röntgendiffraktions- und mikroskopischen Methoden untersucht. Es wurde die Existenz des Phosphates NaLaP₄O₁₂ und dessen kongruenter Schmelzpunkt von 1174 C festgestellt. Die Röntgendiffraktionsaufnahmen lassen auf ein monoklines System mit den Gitterkonstantena=12,36(6),b=13,45(0),c=6,57(4) å,=109,48 undV=1030,87 å³ schliessen. Die Untersuchungen wurden an Einkristallen durchgeführt.

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( ), , La(PO₃)₃-NaPO₃, La₂O₃-Na₂O-P₂O₅. NaLaP₄O₁₂, 1174. -, - - , , 350, 750 840. NaLaP₄O₁₂ a=12,36 å,b=13,45 å,=6,57 å,=109,48 V=1030,97 å³. 500 820. La(PO₃)₃ 1050, 820 — -, - . 2–2,5 % .

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The author thank Dr. T. Znamierowska and Dr. J. Matuszewski for helpful discussions and G. Orczykowska for translation of the text. This work was supported by grant CPBP-01.18.     

Broadening and shift of Ν(AH)IR bands in a series of H complexes of one base with various acids

The parameters of the IR bands for the (AH) stretching vibration (the frequencies, the widths, and partly the intensities) were measured in a series of AH ... B H complexes between one base B (ethylene oxide) and 17 various OH, NH, and CH acids in carbon tetrachloride solutions. The width _1/2 and shift =₀ ⁰– (from the frequency ₀ ⁰ of the gaseous AH) of the investigated bands amount to 530 and 740 cm^–1. A relationship close to direct proportionality between the broadening and the shift of the band for the H bond was found for all the H complexes. The relationship was insensitive to the medium and was preserved for the gaseous complex and in the undiluted ethylene oxide; it did not change greatly when was calculated from the free AH in carbon tetrachloride. This partial (with constant B) proportionality is not observed in the traditional series of acids (phenol, alcohol) with various bases, where agreement is only observed for _1/2 and . cThe electric-donating power of ethylene oxide (0.79±0.03) on the E scale (with reference to diethyl ether, E=1) was determined from the increase and shift of (AH).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 461–466, July–August, 1988.     

Influence of polarity of medium on the nature of charge transfer complex,kinetics, and mechanism of reaction with a one-electron transfer in a tetracyanoethylene-n-alkyl-substituted aniline system

The influence of the polarity of the medium (B, ) on the thermodynamic characteristics of the formation of a charge transfer complex (CTC) and one electron transfer from a donor D to and acceptor A was studied in N-alkyl-substituted aniline (D) — tetracyanoethylene (A) systems. It was shown that in systems with CTC in which [B]/[D] 1, the limiting step in the reaction with one electron transfer in weakly polar solvents (<20) is the formation of molecular (AD), and in strongly polar sovents (>20), of ionic (AD) CTC. A correlation was established between the spectral (VCT) characteristics of the formation of the CTC and the kinetic parameters (k_eff) of one electron transfer reaction and degrees of charge transfer in molecular and ionic CTC were determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 167–173, March–April, 1989.     

Kinetic Spectrophotometric Determination of Chromium (VI) by Oxidation of Sodium Pyrogallol-5-sulphonate by Hydrogen Peroxide

Summary. A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437nm within 1min after addition of H₂O₂. The optimum reaction conditions are PS (1.32·10^–3mol·dm^–3), H₂O₂ (0.32mol·dm^–3), HClO₄ (2.6·10^–3mol·dm^–3) at 25°C. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25ng·cm^–3 and a detection limit of 0.024ng·cm^–3, based on the 3 criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples.     

Transition State Geometry and a Polar Effect in the Reactions of Peroxy Radicals with Oxygen-Containing Compounds

The reactions of structurally different peroxy radicals with the C–H bonds of oxygen-containing compounds (ketones, aldehydes, ethers, and esters) were analyzed in terms of a parabolic model. The enthalpies of these reactions and the activation energies of equienthalpic reactions of peroxy radicals with hydrocarbons were calculated, and the contribution of the polar interaction E to the activation energy was evaluated. The geometry parameters of the transition state were calculated with the use of an algorithm developed based on quantum-chemical calculations in combination with the intersecting parabolas method. It was found that the polar interaction resulted in a change in the configuration of the C···H···O reaction center in the transition state from linear to angular. A different angle (C···H···O) from 180° appeared in this case. The following linear correlation between E (kJ/mol) and cos (180° – ) was obeyed: cos (180° – ) = 1 + 6.76 × 10^–3E .     

Reactivity of coordinated O2? towards. One-electron oxidants

Ion-radical complexes Ti(IV) (O ₂ ^– ) are unreactive towards most oxidants except Ce(IV) and Cr₂O ₇ ^2– . The one-electron redox potential for the O_{2 coord.}/O _{2 coord.} ^– couple lies between 1 and 1.6 V.

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- O ₂ ^– Ti(IV) , Ce(IV) Cr₂ O ₇ ^2– . - O_{2 .}/O ₂ ^– . 1 1,6 .

     

Kinetics of isotope exchange of dioxygen with a powdered high-temperature superconducting material Ba2YCu3O7?x

It has been found that the rate of isotope exchange in Ba₂YCu₃O_7–x–O₂ system is high. Its kinetics is exponential, first order with respect to dioxygen and the exchange is of the mixed first/third type.

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Ba₂YCu₃O_7–x–O₂ . -, -, - .