Etude par resonance paramagnetique electronique de noirs de carbone traites par l'azodiisobutyronitrile en absence d'oxygene

Various carbon blacks were treated in absence of oxygen with azobisisobutyronitrile (AIBN). Samples of non-graphitized carbon blacks (Spheron 6, P33, Sterling FT) and graphitized carbon blacks (Graphon, P33 (HTT)) were studied by ESR before and after the AIBN treatment. The line width, g-factor, and the contributions of localized and conduction carrier spins were determined. The results obtained lead the authors to conclude that in the process of fixation of the products of the thermolysis of the AIBN no radicals are involved.     

Etude a 4,2° K de quelques proprietes galvanomagnetiques de pyrocarbones

Hall effect and magnetoresistance of pyrocarbons and of boronated pyrocarbons, heat treated up to 3000°C were measured at 4.2°K in high magnetic field. The positive Hall coefficient of all the boronated (even heat treated) pyrocarbons is field and temperature independant. It goes through a negative minimum, as a function of the magnetic field, for heat heated unboronated pyrocarbons. The negative magnetoresistance of the 2100°C pyrocarbon presents a minimum, whereas the heat treated boronated pyrocarbons have a magnetoresistance starting small and negative, at small magnetic field and becoming positive and linear at higher fields. The magnetoresistance of heat treated pyrocarbons is positive and fairly linear with increasing field. It is impossible to explain quantitively the results using well-known electronics models. De Haas-van Alphen and Shubnikov-De Haas effects were found for a specimen prepared by hot pressing and stress recrystallisation of pyrolitic material.     

Observation directe au microscope electronique par transmission de la liaison pate de ciment-granulats dans des mortiers de calcite et de quartz

A component mainly composed of hydrated silicate of calcium or of a by-product, making very close binding, exists at the proximate contact between the aggregates of calcite or quartz surrounded by a hardened cement paste or C₃S. This component, observed by electron microscopy, doesn't offer the same appearance close to two minerals which leads one to think that chemical binding strength does exist, above all with calcite.     

Application de la microscopie electronique,des mesures d'impedance et des: Radiotraceurs a l'etude du comportement de l'interface Ag+/Ag monocristallin

The interface Ag/Ag⁺ has been studied using several techniques: radiotracers, current—voltage curves and impedance measurements over a wide frequency range. Surfaces of the specimen are observed after the electrodeposition or anodic dissolution by means of transmission and scanning electron microscopy. The silver (100), (110) and (111) surfaces were previously chemically polished. The silver—silver ion exchange has been shown to be dependent on anions adsorption. The behaviour of silver electrodes in AgNO₃ solutions is described by an appropriate model.     

Etude de polymères thermostables en vue de leurs applications en electronique

Heat resistant polymer are more and more needed for structural applications in aerospace and for electrical applications in electronics. Thermostable dielectric coatings are used as intermetallic layers in wafer fabrication or for interconnection processes and dielectric films find their main applications for the production of flexible circuits. On the other hand, for the development of surface mount technology, heat resistant films are required, due to the severe thermal stresses encountered by the components during the wave soldering. Among the heat resistant polymers, polyimides are the most popular. In spite of all the works performed on polyimides, these materials still exhibit certain shortcomings such as good processability. An approach to improve the processability involves the synthesis of fully cyclized linear polymers with a good solubility. For this we can introduce in the main chain flexible linkages (ether, carbonyl, sulfone), lateral groups with large steric hindrance or polar groups giving strong interactions with solvent. We will discuss in this paper the synthesis and the thermal and dielectric properties of various heterocyclic polymers fully cyclized and soluble. Additionally, new applications of polyimides can be relevant regarding the properties which are obtained under irradiation with ion-beams. We will present some results on the effect of irradiation and the induced conductive character of such materials.     

Realisation de lames ultra-minces de mortier pour observation directe au microscope electronique par transmission

The bond between the aggregate and the hydrated cement paste is an essential factor of the mechanical strength of concretes. Previous work has shown the need of a small-scale study; it was decided to use transmission electron microscopy to prepare ultra-thin slides of a few hundreds of Å of thickness by ionic bombardment. This technique is described and is shown to be well fitted to the heterogeneous nature of the material: the main stages of the paste are undamaged and their identification by microdiffraction is possible. Moreover, it is shown that the contact between the calcite and the paste was very close.     

香气共振理论

把各种香料按蒸气压大小分为＂头香香料＂、＂体香香料＂和＂基香香料＂三组,计算香精和香水中三组香料的总蒸气压。如果以＂头香香料＂与＂体香香料＂蒸气压之比为A,＂体香香料＂与＂基香香料＂蒸气压之比为B,＂基香香料＂总蒸气压为C,当A∶B∶C=m2∶m∶1时,则认为该香精或香水符合共振结构。具有共振结构的香精香气比较和谐、稳定。香水香精的m值一般为4～6,m值小的留香时间较长;香水的m值一般为500～2 000。     

La résonance paramagnétique électronique dans les carbones partiellement graphites: Exemple d'étude sur une série de pyrocarbones irradies

The EPR of graphite and well organised carbons is reviewed. The effects of motional averaging, anisotropy, and skin-effect on the EPR of bulk and powdered samples are discussed with the heat-treatment and neutron irradiation dependences of the g-factor and the linewidth.As an illustration, the paramagnetic susceptibility, the g-factor and linewidth anisotropies of a series of neutron irradiated graphites measured in the temperature range 42-300 K are given. They are shown to be consistent with previous studies, the existence of a Curie like component of the paramagnetism is evidenced.A model involving the interaction between localized spins and free charge carriers, reminiscent of these used for interpreting the EPR of diluted alloys, is described. Assuming the adiabatic approximation to hold, it is shown to account for the only single line always observed and for the empirical relation proposed far ago for the g-factor of carbons. It predicts a similar relation for the line width. Assuming the g-factor and linewidth anisotropies of free carriers to have the same behavior as in graphite single crystals, we show that these relations fit fairly well with experimental data. Incidentally such a model allows us to explain the decrease of the g-factor anisotropy of the non irradiated PGCCL at low temperature by assuming the existence of a small number of localized spin centers at defects.The values of the parameters provided by the fitting are discussed. Their behavior under irradiation is found to be similar to the ones evidenced by previous studies on carbon blacks and neutron irradiated carbon blacks. The “degraphitization” effect of neutron irradiation is seen to be of limited extend.From the three sets of results, we can infer that a linear relationship between the g-factor Δg₀ and linewidth ΔS₀ anisotropies at zero temperature holds wlthm experimental and fitting errors.Finally, although the degeneracy temperatures T′₀ and T″₀ are empirical parameters in those non crystalline carbons, they must be related to the degeneracy temperature T₀ of the free electron gas model for they have the same behavior as the structural disorder increases.     

Resonance in periodically forced processes

The interaction of an external periodic forcing with the natural frequencies of chemically reacting systems gives rise to interesting qualitative dynamic behavior. This behavior is centered around the creation and breaking of resonances and invariant tori. We present a numerical study of the high forcing amplitude region of the excitation diagram and through this an explanation for the shapes of entrainment regions. The algorithms constructed for this purpose are also discussed.     

Adsorption des cations a des potentiels anodiques

As is known from the literature, the nature of the cation has a marked influence upon the kinetics of the anodic process of the formation of persulphuric acid at a platinum electrode, occurring at such potentials where the adsorption of cations would not seem to be of essential importance. The study of the dependence of the rate of evolution of oxygen in HClO₄ solutions on the concentration and radius of the cation has shown that the adsorption of cations is connected with the covering of the electrode surface with chemisorbed oxygen resulting in a discontinuous rise of oxygen overvoltage. This adsorption effect can be explained by the dipole nature of the platinum/oxygen bond.

The phenomena observed during a change in the properties of surface oxides in the region of considerable anodic polarization are somewhat similar to those found in the initial stage of the oxidation of platinum, which was shown to impart to the electrode the ability to adsorb cations.

The absorption of organic cations at positively charged metal/solution interfaces depends to a large extent on the presence of primarily adsorbed surface active anions and on the interaction of the π-electrons of the aromatic nuclei with the metal surface. The latter effect is demonstrated by the difference of the adsorbabilities of anilinium and cyclohexylammonium cations on positively charged mercury.

Some inorganic cations, for instance thallium on mercury, or thallium and cadmium on platinum, display a specific adsorbability similar to the adsorbability of bromide or iodide anions.     

Magnetic Resonance Imaging of fluidized beds

This paper reviews recent developments in Magnetic Resonance Imaging (MRI) which enable it to follow particle motion in fluidized beds. Imaging with a spatial resolution of 400 μm and a temporal resolution of 1 ms is now feasible; particle velocities of order 1 m/s can be measured with good accuracy. The technique provides voidage fractions on a motion-picture basis and particle velocity fields. Limitations are: (i) the particles must contain appropriate atoms e.g. C or H; and (ii) currently the fluidized bed diameter cannot exceed 50 mm, though measurements from larger units will doubtless become available. MR studies on fluidized beds are described: results are reported for (i) air jets entering the bed (ii) bubbling and slugging beds and (iii) dispersion in a bubbling bed. The data are consistent with published measurements. Study (i) helps to resolve the longstanding puzzle about the behaviour of an air jet entering a fluidized or partly-fluidized bed, answering the question: does the entering air form bubbles or a continuous jet?     

核磁共振(NMR)测试技术进展及应用

介绍了核磁共振（NMR）测试技术进展，着重介绍固体高分辨核磁共振和二维核磁共振技术的进展及它们在高分子材料领域的主要应用举例。     

电子顺磁共振技术

<正> 电子顺磁共振(EPR)又叫做电子自旋共振(ESR),是近二、三十年才迅速发展起来的一门新兴学科。它是利用具有未成对电子的物质在静磁场作用下对电磁波的共振吸收特性来进行分析的技术。这一研究手段具有深入物质内部,进行细致分析而不破坏样品;对化学反应过程无影响;灵敏度高和信息丰富等优点。目前已广泛地应用于物理、化学、生物学、医学以及各种材料科学领域。EPR 技术仅适用于含有未成对电子的物质,EPR 手段却能更多地研究那些以微量杂质、吸附中心、活性中心、缺陷、色心及自由基等微量顺磁中心的形式,广泛地散布在反磁性材料中的体系,即使在样品中不含有不成对电子,也可采用人工的方法在材料中形成不成对电子,然后用EPR 技术加以研究。例如吸     

Topological Resonance Energies of Conjugated Structures

The graph-theoretical backbone of the topological resonance energy (TRE) concept is outlined and the connection with the Dewar resonance energy (DRE) approach is described. It appears that the TRE is not a new aromaticity index, but an optimal DRE-like quantity of great practical value for understanding and predicting the aromatic stability of conjugated structures. In the TRE concept the most important result is the introduction of the acyclic polynomial which closely approximates the acyclic-polyene reference structure. The rules for the construction of the acyclic (reference) polynomial are presented. Application of TRE to monocyclic systems, to polycyclic molecules and their radicals and ions, to homoaromatic systems, and to excited states is discussed. In most cases the agreement between the theory and experimental findings is good. However, in some examples the predictions appear to be inconsistent with reported data. The reasons for the occasional anomalies in the TRE are investigated. In addition, the problem of normalization of the TRE is considered.     

Electrochimie des composes organometalliques des metaux de transition

Electrochemical results obtained on transition metals organomettalic compounds during the period 1950–1976 are presented with 290 references. Attempt is made to put together the known mechanistic informations on the electrolytic processes both for oxidation and reduction. This review shows that most of the experimental studies have been carried out on the electrochemical reductions and that there is a lack of anodic studies in the promising field of unstable low oxidation state of transition metals. The reviewed electrochemical studies were generally undertaken to elucidate the redox mechanisms, and to obtain kinetic informations on the different steps of the overall process. The problem of determining the molecular orbital involved in the electron transfer is in most cases not solved. Metallocenes, carbonyl metal are the subject of numerous papers, but only few publications are devoted to electrochemistry of metallocarborans, carbyns, ylids and clusters. In a second part of this review is developed a very important application of the electrochemistry, the electrosynthesis of metal complexes. Examples are chosen to illustrate the specific possibilities offered by this method and special attention is given to in situ electrochemical generation of orgnanomettalic catalysts, a route to polymerization and oligomerization in organic synthesis.     

Utilisation des techniques impulsionnelles dans l'etude des piles

Determinations of double-layer capacitance for electrodes in known conditions have been performed; they allow us to deduce specific surfaces of porous electrodes. Influence of surface-active agents or amalgamation can also be studied.