Etude de noirs de carbone par resonance paramagnetique electronique

The spin resonance of H.A.F. and M.P.C. carbon blacks oxidized by ozone or nitric acid has been studied by means of a 9 kMc/s EPR spectrometer. The oxidation treatments create new paramagnetic centers in addition to those already present in these carbon blacks. Since the corresponding spin absorption χ₂ increases with oxidation time one can conclude that the oxidizer (oxygen, or O₃, or HNO₃) is responsible for the creation of these new spin centers. The thermal variation of χ₂ obeys the Curie-Weiss law with a Curie temperature θ = 60°K independent of the oxidation time and of the type of oxidation process.     

Etude de quelques composes lamellaires des pyrocarbones

Pyrolytic carbons constitute a group of graphitizable carbons. Similarly, as in the case of soft carbons, their graphitizability can be quite well established using several intercalation reactions such as Brodie's reaction, insertion of the alkali metals, and formation of acid salts. Intercalation of other reagents, such as bromine and ferric chloride is more difficult in case of pyrolytic carbons than in soft carbons, especially when the material is composed of large lumps. Intercalation of chromic anhydride is impossible, except in case of pyrographite rendered monocrystalline by annealing under pressure. The existence of barriers preventing the ingress of the reagent between the layers can be attributed to the structure of pyrolytic carbons, these barriers being eliminated by grinding or annealing under pressure.     

Preparation en lit fluidise de pyrocarbones massifs proprietes physiques de ces pyrocarbones

Massive pyrolytic carbons have been deposited on substrates submerged in a fluidised bed at temperatures of about 1200°C, using acetylene nitrogen mixtures at atmospheric pressure. The density, microstructure, preferential orientation of the crystallites and deposition rate of these pyrocarbons depend on the experimental conditions, the most important parameters being the temperature, partial pressure of acetylene, gas flow rates, position of the substrate in the fluidised bed and grain size of the bed. Two types of pyrocarbon were prepared by the methods described: One, of density greater than 2, has a very fine microstructure (of the order of lμ) and there is very little preferential orientation of the crystallites. The thermal expansion of this substance is effectively isotropic and its mechanical properties are good. The other, of density between 1 and 1.3, has a granular microstructure, a very narrow pore spectrum and an exceptionally high deposition rate, of the order of 7 mm h⁻¹. The thermal properties (expansion and conductivity coefficients) of this pyrocarbon are also only slightly anisotropic.     

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.     

Cinetique d'hydratation des ciments alumineux en CAH10 et C2AH8 etude en microscopie electronique

The kinetics of hydration of high alumina cement have been investigated by electron microscopy. At low temperature CAH₁₀ develops from seed formed during the dormant period, then crystallizes with time, in the voids, as “pencil-like” crystals. At 50°C, C₂AH₈ is the first hydrated material to be formed, then the C₃AH₆ appears by direct hydration of CA, and at last C₂AH₈ converts slowly into C₃AH₆.     

Etude magnetique de la graphitisation de pyrocarbones dopes au bore

Pyrocarbons deposited at 2100°C, with a total boron content of 0·04, 0·056 and 0·10% were isothermally graphitized at 2300, 2500 and 2700°C. The diamagnetic anisotropy was studied as a function of residence time at each heat-treatment temperature, up to 66 hr. The behavior of the diamagnetic anisotropy of all the samples between 77 and 1500°K may be quantitatively explained with the help of a two-dimensional electronic band model, slightly different from the one previously used for non-graphitized pyrocarbons. Effective masses of the holes in the valence band are thus obtained. The concentration of holes is found to decrease rapidly at the beginning of the graphitization process, and to remain constant during the later stages. The corresponding shifts of the Fermi level can only be explained assuming a density of states decreasing during the earlier stages of the graphitization process: such an assumption could also explain the minimum of diamagnetism observed during the graphitization of nonboronated pyrocarbons. The catalytic action of boron may account for the quite low value (150–170 kcal) of the apparent activation energy of graphitization. Some measurements, were also performed of pyrocarbons with a very low boron content (50 ppm).     

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。     

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.     

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?     

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.     

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     

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。     

Sur l'etude des impedances des electrodes polarographiques

We present methods that permit the study of electrode impedance from about 100 kc/s to a few c/s, with good precision and a distinct improvement in reproducibility. We give examples of their application to the determination of the impedance of mercury dropping electrodes. Results so far obtained show that the methods may be generalized for other studies in electrode kinetics, in particular for the examination of phenomena at the metal/solution interface and for the study of electrode reaction rates.