Thermal behaviour of cobaltic and cobaltous oxides as influenced by doping with some alkali metal oxides

The role of Na₂O- and Li₂O-doping on the thermal decomposition of Co₃O₄ to CoO and the re-oxidation of cobaltous to cobaltic oxide has been investigated using DTA, with controlled rates of heating and cooling, IR and X-ray diffraction spectrometry techniques.

The DTA investigation revealed that both Li₂O and Na₂O increased the thermal stability of Co₃O₄. However, the effect was much more pronounced in the case of lithium oxide. Doping Co₃O₄ with 1.5 mole% Li₂O was found to prevent any thermal decomposition of cobaltic oxide even by heating at 1100°C. The maximum thermal stabilization effect induced by doping with sodium oxide (4.5 mole%) was 30%. The sodium oxide- and lithium oxide-doping enhanced the reactivity of the produced CoO towards the re-oxidation by O₂ yielding Co₃O₄.

The X-ray diffraction and IR spectrometric investigations showed that part of Li₂O and Na₂O was effectively incorporated in the Co₃O₄ lattice, affecting the thermal stabilization of the solid, and another part of the dopant oxide interacted with the produced CoO and also with Co₃O₄ giving a new sodium cobalt compound, and with Co₃O₄ producing, also, a new lithium cobalt oxide phase. However, the amount of Li₂O dissolved in the Co₃O₄ lattice was greater than that of Na₂O. The sudden cooling of doped solids, from 1000°C to room temperature, favoured the formation of the new sodium cobalt oxide compound, and exerted no effect on the production of the new lithium cobalt oxide phase. The characteristic d spacings and IR absorption bands of these new compounds have been determined.

The possible mechanisms of dissolution of Li₂O and Na₂O in cobaltic oxide lattice are discussed.     

Polarographic activity of the arylhydrazones of α-cyanoketones as a criterion of their acidity

The polarographic behaviour of phenylhydrazonomesoxalonitrile (2) and ethyl phenylhydrazonomesoxalonitrile (3) as well as pK′ and pK_a values are reported for a series of arylhydrazones of α-cyanoketones.     

Gamma irradiation induced photochemical reactions in V-doped borate glasses

Glasses of the composition XNa₂O · 4Al₂O₃ (96-X) B₂O₃ (mole%) where X = 10, 20, 30 to which 0.03 g V₂O₅ per 100 g glass was added, were prepared by normal melting. Their absorption characteristics together with the corresponding V-free base glasses were determined before and after gamma irradiation. The characteristic spectra of the unirradiated glasses show absorption bands at 315, 470, 560–580, 610–650, 700–870, and 860–1000 nm, indicating the presence of vanadium ions in more than one oxidation state, viz, V⁵⁺, V⁴⁺, and V³⁺. Gamma irradation of V-containing glasses causes the formation of color centers in the glass matrices, with absorption bands at 330, 500, and 610 nm, and photoreduced [V³⁺] and [V²⁺] ions with absorption bands at 350–355 and 530–570 and 520 nm, respectively. Photoreduced [V⁴⁺] may also be formed, giving rise to absorptions at 690–700 and 750–800 nm. The induced vanadium ions are found to absorb at shorter wavelengths than the intrinsic ones. An explanation based on the difference in the field energy of the two states is given.     

Chemical and nanomechanical analysis of rice husk modified by ATRP-grafted oligomer

Rice husk (RH), an abundant agricultural residue, was reacted with 2-bromoisobutyryl bromide, to convert it to a heterogeneous polyfunctional macroinitiator for Atom Transfer Radical Polymerization (ATRP). The number of active sites placed on the RH surface was small, but they were ATRP active. Non-polar methyl methacrylate (MMA) and polar acrylonitrile (AN) were polymerized from the RH, and a sequential monomer addition was used to prepare an amphiphilic PMMA-b-PAN copolymer on RH surface. FTIR qualitatively confirmed the grafting. Gravimetric and XPS analysis of the different RH surface compositions indicated thin layers of oligomeric PMMA, PAN, and PMMA-b-PAN. The modified surfaces were mapped by nanomechanical AFM to measure surface roughness, and adhesion and moduli using the Derjaguin-Muller-Toropov model. RH grafted with MMA possessed a roughness value of 7.92, and a hard and weakly adhering surface (13.1 GPa and 16.7 nN respectively) while RH grafted with AN yielded a roughness value of 29 with hardness and adhesion values of 4.0 GPa and 23.5 nN. The PMMA-b-PAN modification afforded a surface with a roughness value of 51.5 nm, with hardness and adhesion values of 3.0 GPa and 75.3 nN.     

Mixed integer linear models for the optimization of dynamical transport networks

We introduce a mixed integer linear modeling approach for the optimization of dynamic transport networks based on the piecewise linearization of nonlinear constraints and we show how to apply this method by two examples, transient gas and water supply network optimization. We state the mixed integer linear programs for both cases and provide numerical evidence for their suitability.     

Copolymerisation von Acrylnitril mit ?thylmethacrylat. 2. Mitt

Ohne Zusammenfassung     

Determination of principal characteristics of turbulent swirling flow along annuli: Part 2: Measurement of turbulence components

Turbulence data for swirling flows along the annulus formed between two co-axial tubes are presented. The swirl was generated by a set of inlet guide vanes which produced, after settling and removal of wall boundary layers, a nominally free vortex flow over the complete entry plane of the test section. The work complements that described in Part 1 of the paper which considered the behaviour of time mean values under the same entry conditions¹. A hot wire anemometer was used to detect turbulence quantities and techniques have been developed for the measurement of these using the minimum number of simple probe geometries. The theory leading to the derivation of the separate turbulence parameters from hot wire measurements is described. A series of radial profiles are given as representative examples of the extensive data collected in addition to longitudinal variations of friction factor and shear stress. A brief discussion is given on the determination of eddy diffusivity as a function of radial and axial location.     

Interactions of gamma rays with undoped and Mn-doped sodium phosphate glasses

Ultraviolet and visible spectroscopic measurements were used to investigate prepared undoped and Mn-doped sodium phosphate glasses before and after successive gamma irradiation. The effects of both glass composition and MnO₂ content on the generation of radiation-induced defects were investigated. Undoped sodium phosphate glass shows strong UV absorption, which is attributed to the presence of trace iron impurities present in the raw materials. Mn-doped glasses reveal an additional visible broad band centered at about 500 nm due to Mn³⁺, which has recently been related to the ⁵E_g →⁵T_2g transition. The radiation-induced bands are correlated with the generation of liberated electron–hole pairs during the process of gamma irradiation and the possibility of photochemical reactions especially with trace iron impurities and manganese ions. The intensity and the position of the induced bands are observed to depend on the type and composition of glass, concentration of the dopant and also on the irradiation dose. Manganese ions when present in relatively higher content have been found to show a shielding behavior towards the effects of progressive gamma irradiation causing a retardation of the growth of the induced defects. Infrared and Raman spectra of the undoped and Mn-doped glasses were measured to investigate the structural phosphate groups present and the effect of MnO₂ on the network structure. An ESR investigation was carried out to confirm the state of manganese ions in the prepared sodium phosphate glasses.     

Isothermal dimensional changes of some dental materials

The isothermal dimensional changes of four types of dental amalgams during the setting and for the next 24 hours after condensation have been studied by means of a Heraeus TA 500 thermal analysis system. The four types of dental amalgams were the lathe-cut conventional lowcopper amalgam (Amalcap), the spherical conventional low-copper amalgam (Spheralloy), the ternary unicomposition high-copper amalgam (Sybralloy) and the admixed high-copper (Dispersalloy) amalgam.The dimensional changes of the four types of amalgams are explained on the basis of their particle sizes and shapes and their constitutions.

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Zusammenfassung Mittels eines Heraeus TA 500 Thermoanalysensystemes wurden isotherme Größenveränderungen von Dentalamalgamen während des Setting und der 24 Stunden nach der Kondensation untersucht. Die Größenveränderungen der vier Amalgamgrundtypen (am Beispiel von Amalcap, Spheralloy, Sybralloy und Dispersalloy) wurden auf der Grundlage ihrer Teilchengröße und -form sowie auf der Grundlage ihrer Zusammensetzung erklärt.

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