Thermoanalytical studies of 2,2,6,6-tetramethyl-4-oxy-4-ethynylpiperidin-1-oxyl polymerization

The structure transition temperature, monomer melting point and critical temperatures of polymerization and decomposition of 2,2,6,6-tetramethyl-4-oxy-4-ethynylpiperidin-1-oxyl were determined by means of thermal analysis. Some features of the polymerization of the acetylenic monomer were studied via thermal analysis, and IR and ESR spectroscopy.It was shown that, during non-isothermal temperature increase, the mass loss of the sample associated with the exothermic effect of polymerization occurred at the expense of the monoacetylene sublimation process (42%), a reagent explosion and decomposition of the reaction products formed (15%).

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Zusammenfassung Mittels Thermoanalyse wurde die Strukturumwandlungstemperatur, der Monomerschmelzpunkt und die kritischen Temperaturen für Polymerisierung und Zersetzung von 2,2,6,6-Tetramethyl-4-oxy-4-ethynylpiperidin-1-oxyl bestimmt. Mit Hilfe von Thermo-analyse, IR- und ESR-Spektroskopie wurden einige Eigenschaften der Polymerisierung des Acethylen-Monomers untersucht.Es wurde gezeigt, daß bei einem nichtisothermen Temperaturanstieg der Massenverlust der Probe zunimmt, verbunden mit einem exothermen Effekt der eingetretenen Polymerisierung auf Kosten des Monoacetylen-Sublimierungsprozesses [42%], der Explosion und der Zersetzung der gebildeten Reaktionsprodukte [15%].

     

Über den Einfluß von Temperatur und Fremdionen auf Eigenschaften und Bau der Natriumwasserglaslösungen

The Influence of Temperature and Impurities Addition on the Properties and the Constitution of Sodium Water Glass Solutions Sodium water glass (NaWG-)solutions of constant composition (SiO₂/Na₂O = 3,3; C_SiO2 = 6,2 M) and different concentration of impurities (Fe, Al, Ti, Cu, chloride, sulfate) were investigated in dependence on temperature by means of the dye absorption method, ¹H- and ²³Na-NMR spectroscopy. It is shown, that the differences in the dye absorption spectra of normalized technical NaWG-solutions, mainly depend on the Fe-concentration in the solutions and their thermal history. From the results follow a crosslinking of polymeric silicate species by Fe? O? Si bonds and/or hydrogen bridges and a fully or partially degradation of these bonds at higher temperatures (150°C).     

Hydrothermal synthesis, structure, Raman spectroscopy, and self-irradiation studies of Cm(IO3)3

The study of curium iodate, Cm(IO₃)₃, was undertaken as part of a systematic investigation of the 4f- and 5f-elements’ iodates. The reaction of ²⁴⁸CmCl₃ with aqueous H₅IO₆ under mild hydrothermal conditions results in the reduction of IO₆⁵⁻ to IO₃⁻ anions, and the subsequent formation of Cm(IO₃)₃ single crystals. Crystallographic data are: (193 K, MoKα, ): monoclinic, space group P2₁/c, , , , β=100.142(2)°, V=811.76(14), Z=4, R(F)=2.11%, for 119 parameters with 1917 reflections with I>2σ(I). The structure consists of Cm³⁺ cations bound by iodate anions to form [Cm(IO₃)₈] units, where the local coordination environment around the curium centers can be described as a distorted dodecahedron. There are three crystallographically unique iodate anions within the structure; two iodates bridge between three Cm centers, and one iodate bridges between two Cm centers and has a terminal oxygen atom. The bridging of the curium centers by the iodate anions creates a three-dimensional structure. Three strong Raman bands with comparable intensities were observed at 846, 804, and 760 cm⁻¹ and correspond to the I-O symmetric stretching of the three crystallographically distinct iodate ions. The Raman profile suggests a lack of inter-ionic vibrational coupling of the I-O stretching, while intra-ionic coupling provides symmetric and asymmetric components that correspond to each iodate site. Repeated collection of X-ray diffraction data for a crystal of Cm(IO₃)₃ over a period of time revealed a gradual expansion of the unit cell from self-irradiation. After 71 days, the new parameters were: , , , β=100.021(2)°, V=818.3(2).     

Ag／Al2O3选择性催化丙烯还原氮氧化物表面反应机理的原位红外光谱研究

 在富氧条件下Ag／Al2O3对以丙烯为还原剂选择性催化还原NOx的反应有很高的催化活性．本实验成功地利用原位红外光谱分析手段,在真实的催化反应条件下,探讨了丙烯选择性还原NOx的反应机理,证实了催化剂表面反应中间体Al－NCO和Ag－NCO虽在真空中稳定,但在实际反应条件下极为活泼．催化剂表面上R－ONO和R－NO2分解成NCO是整个反应的速度控制步骤．这一结论与在真空系统条件下对其反应机理的研究结果一致,证明了在这一反应体系中两种研究方法的相关性．同时本实验还从反应机理上探讨了催化剂的水蒸气中毒现象．水蒸气的存在阻碍了催化剂表面R－ONO和R－NO2的生成,并进一步阻碍了反应的速度控 制步骤,即R－ONO和R－NO2向Al－NCO和Ag－NCO的转化,但这是一种完全可逆的暂时中毒现象．结合相应的催化剂活性评价结果对表面反应机理进行了讨论．     

低能离子散射谱分析中的荷电效应及中和作用

用低能离子散射谱（ISS）对比分析了与样品托有良好电接触的和与样品托绝比的金属银片，观察到荷电效应对ISS分析有严重影响。实验还表明在ISS分析时使用低能电子中和枪可以有效地消除荷电效应，还发现电子中和枪的使用对于惰性气体离子的中和作用无明显影响。     

用XPS研究兖州煤各显微组分中有机硫存在形态

应用ＸＰＳ（Ｘ射线光电子能谱）法研究了兖州煤显微组有机硫的存在形态。按密度不同分离出的兖州煤中各显微且分内的有机硫存在形态是有差异的。据ＸＰＳ分析，稳定组中含有大量的硫砜、硫醚含硫化合物，噻吩型硫闪之；镜质组中硫、硫醚与脂肪族硫化物含量相当；惰性组中噻吩型硫与硫醚和硫醇型硫各占有机硫的一半。噻吩型硫在充州煤各显微组分中，随密度增加。含量有所减少，硫醚、硫醇及二硫化物的含量也有类似的趋势。这些结果将     

Behavior of rifampicin in association with<Emphasis Type="Italic"> β</Emphasis>-cyclodextrin in aqueous media: a spectroscopic and conductometric study

The behavior of rifampicin (D) with -cyclodextrin (-CyD) in aqueous media (W) has been examined by means of UV-vis spectroscopy and conductivity measurements over the temperature range 15–30 °C. The UV-vis study has been used to characterize the systems. The estimated molar absorption coefficient for D/CyD/W system was 10757±280 M^–1 cm^–1 in comparison to the value of 6133±99 M^–1 cm^–1 for D/W system. The conductivity was measured (i) as a function of [D] for binary D/W systems, (ii) as a function of [CyD], keeping the concentration of drug constant, for D/CyD/W system, and (iii) as a function of [D] in the presence of a constant cyclodextrin concentration. Two transition points were observed for D/CyD/W system at constant [CyD], which were assigned as cac-1 and cac-2. The stoichiometry of the association was estimated from the conductivity data. This was obtained from [drug] value at which the change in slope of occurs. The standard free energy change, of aggregation was also calculated from the critical concentration data. An attempt has also been made to estimate the stoichiometry of -cyclodextrin:rifampicin association.     

Brightness Reversion of Mechanical Pulps. Part XVII: Diffuse Reflectance Study on Brightness Stabilization by Additives Under Various Atmospheres

Brightness reversion of softwood (SW) and hardwood (HW) bleached chemithermomechanical pulps (BCTMP) with a 300–400nm light source under argon, oxygen, and air were studied in the absence and presence of UV-screens using UV–Vis reflectance difference spectroscopy. The UV-Vis difference absorption spectra of control SW and HW BCTMP testsheets indicate that as the concentration of atmospheric oxygen is increased, the absorption at max 360nm increases and a blue shift occurs. In all of the cases studied, brightness reversion was observed to occur under an argon atmosphere. The addition of benzophenone and benzotriazole additives to BCTMP testsheets resulted in a significant decrease in formation of chromophores absorbed at 400nm and 360nm. The possible mechanisms contributing to these effects are discussed in terms of the photoformation of lignin chromophoric structures.     

Analysis of powdered tungsten carbide hard-metal precursors and cemented compact tungsten carbides using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been applied to the direct analysis of powdered tungsten carbide hard-metal precursors and cemented tungsten carbides. The aim of this work was to examine the possibility of quantitative determination of the niobium, titanium, tantalum and cobalt. The investigated samples were in the form of pellets, pressed with and without binder (powdered silver) and in the form of cemented tungsten carbides. The pellets were prepared by pressing the powdered material in a hydraulic press. Cemented tungsten carbides were embedded in resin for easier manipulation.

Several lasers and detection systems were utilized. The Nd:YAG laser working at a basic wavelength of 1064 nm and fourth-harmonic frequency of 266 nm with a gated photomultiplier or ICCD detector HORIBA JY was used for the determination of niobium which was chosen as a model element. Different types of surrounding gases (air, He, Ar) were investigated for analysis. The ICCD detector DICAM PRO with Mechelle 7500 spectrometer with ArF laser (193 nm) and KrF laser (248 nm) were employed for the determination of niobium, titanium, tantalum and cobalt in samples under air atmosphere. Good calibration curves were obtained for Nb, Ti, and Ta (coefficients of determination r² > 0.96). Acceptable calibration curves were acquired for the determination of cobalt (coefficient of determination r² = 0.7994) but only for the cemented samples. In the case of powdered carbide precursors, the calibration for cobalt was found to be problematic.     

Physical properties and electrochemical performance of LiMn2O4 cathode materials prepared by a precipitation method

LiMn₂O₄ powder for lithium-ion batteries was prepared by a precipitation method, and the effects of calcination temperature on the physical properties and electrochemical performance of the samples were investigated by various methods. The results of X-ray diffraction (XRD) showed that the lattice parameter (a) and the unit cell volume (v) decrease with the increasing calcination temperature, and the LiMn₂O₄ sample calcined at 750°C has smaller particle size and higher crystallinity than other samples. The results of the electrochemical experiments showed that the sample calcined at 750°C has larger peak currents, higher initial capacity, and better cycling capability, because of its lower charge-transfer resistance and larger diffusion coefficient of Li⁺ ions than those of other samples.