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Low–angle grain boundaries have been analyzed by transmission electron microscopy (TEM) and electron team induced current (EBIC). Diffusion length and interface recombination velocity have been calculated by measuring the area and the variance of the contrast profile by applying the model of Donolato.

Coke-oven workers are exposed to dust and irritant gases. Therefore they are at risk of developing lung diseases including chronic bronchitis. Nonspecific bronchial hyperresponsiveness (BHR) has been advocated as a potential risk factor predisposing to the development of chronic bronchitis. In a previous study, we showed that prevalence of BHR was higher in retired coke-oven workers than in retired blast furnace workers. The present study was carried out to determine the prevalence of BHR in active steelworkers. Thus, 137 coke-oven workers and 150 blast furnace workers underwent clinical examination, a standardized questionnaire for the study of respiratory symptoms, pulmonary function testing and methacholine aerosol challenge. The study demonstrates a higher prevalence and degree of BHR [provocative concentration of methacholine causing a 20% fall in forced expiratory volume in one second (PC20) < or = 8 mg x mL(-1)] in coke-oven workers than in blast furnace workers (31.4 versus 6.7%; p

Some polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene and benzo(a)anthracene are well-established genotoxic agents. Long-term exposure to PAHs may lead to proliferative cell disorders in humans, predominantly in the skin, lung, and bladder. The concentration of several tumor markers in serum, of polyamines and modified nucleosides in urine, and of cytogenetic endpoints in peripheral lymphocytes (sister-chromatid exchanges, high frequency cells [HFC], and micronuclei) were measured in 149 male workers exposed to PAHs in two coke oven and one graphite electrode plants, and in 137 controls. We have assessed whether these biomarkers were related to several parameters reflecting exposure to PAHs, i.e., the sum of the airborne concentration of 13 PAHs, 1-hydroxypyrene (1-OHP) concentration in postshift urine, benzo(a)pyrene-diolepoxide adducts to hemoglobin (BPDE-Hb adducts), and duration of exposure, taking also into account several possible confounding factors. HFC was the biomarker most consistently associated with the intensity of current exposure to PAHs. Smoking exerts an independent effect on the same parameter. On the basis of the logistic regression between the prevalence of abnormal HFC values and PAHs in air and 1-OHP in postshift urine found in nonsmokers, it is suggested that the latter should be kept below 6.4 mug/m3 and 2.7 mug/g creatinine, respectively. No relationship was found between the cytogenetic effects and BPDE-Hb adducts although both parameters are statistically correlated with the airborne PAH level. Some tumor markers in serum (carcinoembryonic antigen, tissue polypeptide antigen, sialic acid) and the urinary concentration of some polyamines were correlated with either PAHs in air or 1-OHP in urine. The associations, however, were very weak which suggests that these biomarkers have limited practical value for the health surveillance of groups of workers exposed to genotoxic PAHs. (C) 1995 Wiley-Liss, Inc.

A cross-sectional epidemiological study was performed on 286 workers from two coke oven and one graphite electrode plants. The aim was to evaluate the usefulness of monitoring 1-hydroxypyrene (1-HOP) in urine for assessing exposure to polycyclic aromatic hydrocarbons (PAHs), and that of the urinary excretion of thioethers and D-glucaric acid, and the mutagenic activity of urine as indicators or biological effects of PAHs. The results confirm that 1-HOP determination in urine probably reflects exposure to PAHs by all routes and is not significantly influenced by the smoking habit. In comparison with the total PAHs in the air and 1-hydroxypyrene in urine, taken as reference exposure parameters, the results indicate that urinary D-glucaric acid excretion is not positively influenced by PAHs exposure; thioethers determination in urine is of poor value, since the smoking habit is a strong confounding factor. The determination of urinary mutagenicity might contribute to the detection of groups of workers exposed to potentially genotoxic PAHs.

Triple junctions in polycrystalline silicon for solar cell applications have been studied by TEM (transmission electron microscopy). The typical characteristic of these junctions is the existence of high-symmetry interfaces, i.e. twins of different order. Whenever the triple junction contains two such interfaces, the intersection axis is a CSL (coincidence site lattice) symmetry axis. In this case the mutual relation of the grain boundaries of the triple junctions is revealed by symmetry rules, since the boundaries are described by symmetry elements of the corresponding CSL which do not belong to the symmetry group of the parent lattice. Therefore, the different variant orientations of these CSL symmetry elements, implied by the symmetry of the lattice, are used for the study of triple junctions. A junction is geometrically characterized by the point-group-symmetry properties. The observations concern symmetrically different triple junctions of the same type of macroscopically stable grain boundaries and faceted and microfaceted interfaces. It is shown that in silicon the thermodynamically favored twins are combined by specific symmetry rules. The results are discussed in accordance with the possible growth mechanisms.

The effects of high temperature creep on the microstructure and the grain boundaries of the oxide-dispersion-strengthened superalloy MA6000 are investigated by means of transmission electron microscopy. Rafting of the γ′ phase is observed in the elongated grains, whereas in the small non-recrystallized grains γ′ rafting does not occur. Dislocations form networks around γ′ precipitates only in particular areas of the coarse grains where the oxide particles are absent. In the rest of the areas, where oxide dispersion is homogeneous, dislocations are pinned to the hard oxide particles instead of accumulating at γ-γ′ interfaces. Dislocation networks around the γ′ phase are not observed in the small grains. There is no detectable influence of high temperature creep on the grain boundaries of the material. The majority of them are of the small angle type and exhibit a very disordered morphology. Large angle grain boundaries are randomly oriented and they are mainly decorated by chromium carbides.

High‐precision characterization of grain boundaries with a deviation from the ideal coincidence is presented. The analysis is based on the shift of Kikuchi lines at grain boundaries. The accuracy was controlled using Frank's relationship applied to intrinsic secondary dislocations which accommodate the orientation deviation. An application is presented to coincidences with Σ = 25 and 3 observed in polycrystalline silicon. 1990 Blackwell Science Ltd

The purpose of this study is to determine the metal content of alveolar macrophages by PIXE from 94 subjects divided into two groups as follows: group (1) — subjects with non-occupational exposure to industrial dust: 30 healthy volunteers (controls), 16 patients suffering from lung cancer; group (2) — 48 healthy steel workers from the Liege area (blast-furnace [n=29] and coke oven [n=19]). We hope to define more precisely the influence of carcinoma, smoking habit, pathology and occupational exposure in the steel industry on the macrophage metal content. This study has shown: (a) an Fe and Sr increase and a Br decrease in the macrophages of smokers (especially in heavy smokers): (b) a significant Fe, Ti, Br and Cu increase and a trend to Pb, Cr, As and Sr increase in macrophages of healthy steel workers (especially blast-furnace workers) in comparison with non-exposed controls; (c) a significant Fe, Br, Cu and Zn increase and a trend to Pb, As and Ni increase in macrophages of non-exposed patients with lung cancer by comparison with non-exposed controls. The mechanism of metal change could be explained by professional exposure and endogenous changes (protein synthesis, inflammation, bronchial bleeding, …)

Steelworkers are exposed to many pollutants, and they are at risk for developing lung cancer. We demonstrated previously that steelworkers may be subject to an occult exposure to amphiboles in the plant environment. In the current study, we further analyzed bronchoalveolar lavage fluid of steelworkers by measuring intramacrophagic trace-metal content and nonfibrous mineral particles, using the particle-induced x-ray emission method and electron microscopy, respectively. Forty-seven blast-furnace workers and 45 healthy white-collar workers volunteered for this study. Significantly increased levels of iron, titanium, zinc, and bromine were found in the steelworkers, and levels of lead, chromium, arsenic, and strontium tended to increase in the macrophages and bronchoalveolar lavage fluid of the steelworkers. Nonfibrous particles, including illite, kaolinite, talc, chlorite, amorphous silica, quartz, iron (compounds), and titanium hydroxide, were found in both groups, but the particle number per ml bronchoalveolar lavage fluid (particularly iron hydroxides and silicates) was more pronounced in blast-furnace workers. These elements and particles may act synergistically with other occupational carcinogens and cigarette smoke, the result of which may be an increased incidence of lung cancer in the ironsteel industry.

OBJECTIVES--Characterisation of the airborne concentration of 13 polycyclic aromatic hydrocarbons (PAHs) at various workplaces in a graphite electrode and a coke production plant. Validation of the urinary excretion of 1-hydroxypyrene (hydroxypyrene) as a biological marker of exposure to PAH. DESIGN--Cross sectional study of workers exposed to PAHs (106 in the graphite electrode producing plant and 16 in the coke works). METHODS--Personal air sampling during at least six hours per workshift using a glass fibre filter and a Chromosorb 102 solid sorbent tube and analysis of PAHs by high performance liquid chromatography (HPLC) and spectrofluorometric detection (SFD). Collection of spot urine samples before and after the shift and analysis of 1-hydroxypyrene by HPLC and SFD. RESULTS--The workers most exposed to PAHs were those occupied at the topside area of the coke oven plant and those working in the blending and impregnation areas of the graphite electrode producing plant (mean airborne concentration of total PAHs: 199 and 223 micrograms/m3 respectively). Except for naphthalene and perylene, the relative proportion of the different PAHs did not differ between the plants. Pyrene concentration in air was highly correlated with the total airborne PAH concentration (r = 0.83, p < 0.0001) and the correlation coefficients between hydroxypyrene concentration in postshift urine samples and pyrene or total PAHs in air were 0.67 (p < 0.0001) and 0.72 (p < 0.0001) respectively. Excretion of hydroxypyrene doubled when the exposure to pyrene in air increased 10-fold. The half life for the urinary excretion of hydroxypyrene was around 18 hours (95% confidence interval 16.1-19.8). Smoking habits only explained 2.3% of the variance in hydroxypyrene excretion compared with 45% for the pyrene concentration in air. CONCLUSION--The determination of the urinary excretion of hydroxypyrene in postshift urine samples can be used as a suitable biomarker to assess individual exposure to PAHs in coke ovens and in graphite electrode manufacturing plants.

The O-lattice is a mathematical tool for the determination of CSL. It is modified in order to allow an analytical determination of the vectors of a CSL as well as the DSC lattice. This concept can be applied to all crystal systems. It is more specially developed to the hexagonal system. Since the CSL (or a multiple of the CSL) unit cell is a known multiple of the modified O-lattice unit cell, the CSL can be determined. An identical procedure is also developed for the DSC lattice. Le reseau O de Bollmann, utilise comme instrument mathematique pour la determination des reseaux de sites en coincidence, a ete modifie afin de permettre une determination analytique des vecteurs de ce reseau (CSL) ainsi que du reseau des translations laissant le bireseau invariant (DSC). La methode, applicable a tous les systemes cristallins, a ete plus particulierement developpee pour le systeme hexagonal. La maille primitive du reseau de sites en coincidence (ou un de ses sous-multiples) etant un multiple connu de la maille primitive du reseau O modifie, cette premiere (ou un de ses sous-multiples) peut etre determinee. Un raisonnement identique est egalement applique a la determination du reseau des translations laissant le bireseau invariant.

A method for the characterization of coincidence cells is proposed for hexagonal crystals. It is based on a simple formulation of the orientation relationships for coincidence site lattices. Therefore tables of coincidence orientation are established for different axial ratios with rational values of (c/a)2. Possible practical cases of coincidence are characterized by their comparison with these tables. This comparison is preferably performed using the description given by a rotation angle of 180°.

The early stages of ordering in Ni3Mo have been studied by electron diffraction and microscopy. A long period superlattice of 13.9 A is observed which can be attributed to a periodic array of non-conservative antiphase boundaries in the Ni3Mo-structure. This superlattice disappears by coarsening of the array after longer annealing times. From the shift of the superlattice reflections the displacement vector associated with the antiphase boundaries could unambigeously be determined as [102] using a method developed earlier for shear structures. This result is in agreement with the structural model and with the displacement vector as derived from image extinctions. Direct evidence is found for the shear transformation from the f.c.c. high temperature phase to the ordered Ni3Mo-structure, which is a superstructure of the h.c.p. structure. Die fruhen Ordnungszustande in Ni3Mo wurden mit Elektronenmikroskopie und Elektronenbeugung untersucht. Es wird ein lang-periodisches Ubergitter von 13,9 A beobachtet, das einer periodischen Anordnung von nicht-konservativen Antiphasengrenzen in der Ni3Mo-Struktur zugeordnet werden kann. Dieses Ubergitter verschwindet durch Vergroberung der Anordnung nach langerer Temperungsdauer. Aus der Verschiebung der Ubergitter-Reflexionen last sich der Verschiebungsvektor, der mit den Antiphasengrenzen verknupft ist, eindeutig als [102] mit einer Methode bestimmen, die schon fruher fur Scherstrukturen entwickelt wurde. Dieses Ergebnis befindet sich in Ubereinstimmung mit dem Strukturmodell und mit dem aus der Bildextinktion bestimmten Verschiebungsvektor. Es wurde ein direkter Hinweis fur die Schertransformation von der k.f.z.-Hochtemperatur-phase zu der geordneten Ni3Mo-Struktur gefunden, die eine Uberstruktur der h.d.p.-Struktur ist.

The dislocation dissociation in the DO23 structure of Al3Zr is performed by contrast experiment in TEM, and confirmed by a precision analysis of low angle grain boundary characteristics. In particular, the precision determination of the angle of rotation at subgrain boundaries allows a determination of amplitudes of Burgers vectors. The type of dissociation is interpreted in terms of the characteristics of the ordered lattice. La dissociation des dislocations dans Al3Zr de structure DO23 a ete determinee a l'aide du contraste au microscope electronique; les resultats sont confirmes par une analyse a haute precision des caracteristiques des joints de grains a faible desorientation. La mesure precise de l'angle de rotation aux sous-joints de grains permet, en particulier, une determination de la longueur des vecteurs de Burgers. Le type de dissociation observe est interprete a partir des caracteristiques du reseau de l'alliage ordonne.

A combination of analytical expressions and a knowledge of symmetry is employed for the displacement shift complete lattice (DSCL) base computation. The method is of general use and its application to cubic and hexagonal systems is given. Tables containing all the symmetrically equivalent descriptions of one and the same coincidence site lattice (CSL) as a function of one description are given for both cubic and hexagonal systems.

The identification of a bicrystal with possible approximate CSL's is performed using the matrix product of their rotation matrices. The approximation is expressed by a small angle rotation matrix of the form of a sum of a unitary matrix and a skew symmetric matrix. This supplementary rotation may only be determined after appropriate treatment of the symmetrically equivalent descriptions. It is also, based on the comparison of an experimental case with tables of CSL's given in their description using the greatest rotation angle, generally 180°. That deviation expressed by a small angle rotation may easily be presented in terms of a small angle twist component and a small angle tilt component. L'identification de la relation d'orientation d'un bicristal a une relation en coincidence est realisee a l'aide du produit de leurs matrices de rotation. L'approximation est exprimee par une matrice de rotation d'un petit angle ayant la forme d'une somme d'une matrice unitaire et une matrice antisymetrique. Cette rotation supplementaire ne peut ětre determinee qu'apres traitement approprie de leurs descriptions symetriquement equivalentes. Elle est egalement basee sur la comparaison d'un cas experimental avec des tables de coincidences decrites a l'aide du plus grand angle de rotation possible, generalement 180°. Cette deviation exprimee par une rotation d'un petit angle peut directement ětre exprimee en termes d'une petite composante angulaire de torsion et d'une petite composante angulaire de flexion.

The dehydration reaction accompanying the goethite-hematite transformation was observed by high resolution electron microscopy. The origin of the satellites which appear during the transformation is discussed from the point of view of structure factor and shape factor. Details of the transformation mechanism have been clarified through these results and from the considerations based on the observations. The transformation goes directly from goethite to hematite in such a way that the dehydration reaction is completed within a small volume of about 60 A width in such a manner that practically only local rearrangement into the product structure takes place, growth of hematite being very limited. After surface transformation is completed, bulk transformation develops spatially by the repeated generation of units composed of voids and hematite, until the whole volume is occupied by such units. The role of the voids and the changes of their morphology are also discussed in comparison with other interpretations of the transformation sequences.

A method is presented allowing a high precision in the determination of all the elements characterizing a subgrain boundary. These elementes are: the rotation axis and its small angle, the boundary plane, the directions of the dislocation lines, the equidistances of the different dislocation families. These informations allow the determination of the length of Burgers vectors of the boundary dislocations. The precision of the method is controlled by Burgers vectors determinations obtained from their contrast analysis in transmission electron microscopy. Une methode de determination a haute precision de tous les elements qui caracterisent un joint a faible desorientation est presentee. Ces elements sont: l'axe de rotation ainsi que son angle (petit), le plan du joint, les directions des lignes de dislocations, les equidistances des differentes familles de dislocations. Ces informations conduisent a la determination de la longueur des vecteurs de Burgers des dislocations du joint. La precision de la methode a ete contrǒlee par la determination des vecteurs de Burgers des dislocations a l'aide de l'analyse de leur contraste au microscope electronique en transmission.

Energy dispersive analysis of X-rays as an accessory to a transmission electron microscope has been used to investigate local compositional changes associated with the presence of periodic non-conservative antiphase boundaries in the initial stages of ordering in Ni3Mo. It is shown how a relative quantitative elemental analysis of the local alloy composition can be performed to a precision of better than 5%. A detailed analysis is described for 13.9 A spaced periodic antiphase boundaries in Ni3Mo where a local excess in Ni could be determined, leading to a composition of Ni3.4Mo. The measurements confirm the proposed structural model. Es wird die Energiedispersionsanalyse von Rontgenstrahlen als Zusatz zu einem Transmissionselektronenmikroskop benutzt, um lokale Anderungen der Zusammensetzung zu untersuchen, die mit periodischen nicht-konservativen Antiphasengrenzen im anfanglichen Ordnungszustand von Ni3Mo verbunden sind. Es wird gezeigt, wie eine relative, quantitative Elementanalyse der lokalen Legierungszusammensetzung bis zu einer Genauigkeit von besser als 5% durchgefuhrt werden kann. Es wird eine detaillierte Analyse fur periodische Antiphasengrenzen mit 13,9 A Abstand in Ni3Mo beschrieben, wobei ein lokaler Uber schus von Ni bestimmt werden konnte, der zu einer Zusammensetzung von Ni3,4Mo fuhrt. Die Messungen bestatigten das vorgeschlagene Strukturmodell.

X-ray diffraction peaks recorded from hematite derived from goethite by a dehydration reaction and its isostructural system corundum from diaspore exhibit systematic peak broadening for l ≠ 3n, which corresponds to the reflections belonging to either the obverse or reverse variant of hematite. The peak width of l = 3n lines, which are common to both twin components remains as sharp as that of goethite. Estimation of the size of the scatterer from half peak widths shows that the product of the topotactic transformation from an individual particle behaves like a single crystal to common reflections and like an agglomerate of hematite crystallite pieces to non-common reflections. This implies a markedly good coherence at the twin boundaries. A decrease in peak width of non-common reflections with dehydration temperature is observed. It is due to an increase of crystallite size in the grain growth process by surface diffusion and coalescence following transformation. The difference in peak broadening is interpreted in terms of the fact that the structure of the scatterer is the same, i.e. the final reaction product hematite, but the shape factor is different for common and non-common reflections and after dehydration at different temperatures. The different sensitivity of X-rays and electrons to the incoherency at twin boundaries is also considered in relation to their wavelengths. Die Rontgenbeugungsmaxima, die von Hamatit aufgezeichnet werden, das aus Goethit durch Dehydrationsreaktion abgeleitet wird, und von seinem isostrukturellen System Korund von Diaspor zeigen eine systematische Maximumverbreiterung fur l = 3n, die mit den Reflexen uber-einstimmen, die entweder zu der Vorder- oder Ruckseitenvariante von Hamatit gehoren. Die Maximumbreite von l = 3n-Linien, die beiden Zwillingskomponenten gemeinsam sind, bleiben so scharf wie die von Goethit. Berechnungen der Grose der Streuer aus den Halbwertsbreiten zeigen, das das Produkt der topotaktischen Transformation von einem individuellen Teilchen sich wie ein Einkristall gegenuber gemeinsamen Reflexionen und wie ein Agglomerat von Hamatitkristalliten gegenuber nicht gemeinsamen Reflexionen verhalt. Dies schliest eine bemerkenswerte gute Koharenz an der Zwillingsgrenze ein. Eine Abnahme der Breite der Maxima der nichtgemeinsamen Reflexionen mit der Dehydrationstemperatur wird beobachtet. Sie wird verursacht durch eine Zunahme der Kristallitgrose im Kornwachstumsprozes durch Oberflachendiffusion und Koaleszenz nach dem Ubergang. Der Unterschied der Maximumverbreiterung wird mit der Tatsache erklart, das die Struktur des Streuers dieselbe' ist, z. B. das Endprodukt Hamatit, jedoeh ist der Formfaktor fur gemeinsame und nichtgemeinsame Reflexionen und nach Dehydration bei unterschiedlichen Temperaturen verschieden. Die unterschiedliche Empfindlichkeit von Rontgenstrahlen und Elektronen gegenuber der Inkoharenz an Zwillingsgrenzen wird ebenfalls hinsichtlich ihrer Wellenlangen untersucht.

Different structures of the intermetallic compound Ni3±xTe2 are known. An electron microscopy study reveals the existence of a quasi-continuous series of superstructures between the monoclinic low temperature phase and a new orthorhombic phase. A possible interpretation of this series is based on the concept of partially ordered intermediate phases. The most significant characteristic of these phases is the presence along the [h00]* row of a pair of irrational superlattice reflections shifting continuously in position as a function of the degree of order. The proposed model is based in agreement with the relative intensities of the superlattice reflections. Differentes structures du compose intermetallique Ni3±xTe2 sont connues. La microscopie electronique a revele l'existence d'une serie quasi continue de surstructures entre la phase monoclinique basse temperature et une nouvelle phase orthorhombique. Cette serie peut s'interpreter sur la base de phases intermediaires partiellement ordonnees. Ces phases sont essentiellement caracterisees par la presence le long de la rangee des reflexions [h00]* de paires de reflexions en position irrationnelle et derivant de maniere continue en fonction du degre d'ordre. Les intensites relatives calcules pour les reflexions de surstructure apportent une confirmation au modele propose.

Solution annealed samples of the MnCr austenitic steel Nitronic 32 are uniformly implanted at 310 K with 500 atppm He corresponding to a dose of ≈ 0.1 dpa. Specimens are subsequently aged, one set at 773 K and another set at 1023 K; the evolution of the dislocation structure and the related segregation and precipitation phenomena are examined by TEM, EELS, and electron diffraction. Short annealing (2 h) at 1023 K lead to the formation of Frank interstitial dislocation loops which are found enriched in N and Cr. After longer annealing (25 h) at 1023 K, Cr2N precipitated on the loops, small He bubbles becomes visible in the matrix, whereas no lamellar precipitation is observed in contrast to unirradiated specimens. Losungsgegluhte Proben von austenitischem MnCr-Stahl Nitronic 32 werden bei 310 K mit 500 atppm He implantiert. Die entsprechenden Strahlungsschaden betragen ≈ 0,1 dpa. Die Proben werden anschliesend bei 773 und 1023 K warmebehandelt. Die Entwicklung der Versetzungsstruktur und die damit zusammenhangenden Segregations- und Ausscheidungsphanomene werden mittels TEM, EELS und Elektronenbeugung untersucht. Kurze Anlaszeiten (2 h) bei 1023 K fuhren zur Bildung von Frankschen Zwischengitterversetzungsringen, in denen N und Cr angereichert sind. Bei langerem Anlassen (25 h) bei 1023 K scheidet sich Cr2N an den Versetzungsringen aus und kleine He-Blasen werden in der Matrix sichtbar. Im Gegensatz zu unbestrahlten Proben wird keine lamellare Ausscheidung beobachtet.

The {110}and {321}composition planes are analysed by electron microscopy in a {211}twin in the b.c.c. vanadium. Fringe systems of the α-type in the boundary planes reveal the presence of a rigid body translation between both elements of the twin. For the {321}planes the displacement vector is close to 1/36 or close to 1/36 , whilst for the {110}twin boundary a displacement vector close to 1/36 is proposed. These calculated vectors are in good agreement with the observations. A curved boundary presenting α-fringe with varying contrast is also analysed and a translation vector varying with the fault orientation is proposed. Les plans de composition {110}et {321}d'une macle {211}dans le vanadium cubique centre ont ete examines en microscopie electronique. La presence de franges α dans le joint est consecutive a une translation de l'une des deux parties de la macle. Pour le plan {321}le vecteur translation est voisin de 1/36 ou de 1/36 alors que pour le plan {110}il est voisin de 1/36 . Ces vecteurs calcules sont en bon accord avec les observations. Un joint courbe presentant des franges α au contraste variable a egalement ete observe; il est montre que le vecteur de translation de la paroi varie avec l'orientation de celle-ci.

The microstructural characteristics of polycrystalline pure zirconium are studied by means of transmission electron microscopy (TEM), following several thermo-mechanical treatments and internal friction measurements. Dislocations with Burgers vectors (a/3) 〈1120〉 arranged in tilt or twist boundary configurations are observed in annealed specimens and following prestraining at room temperature. This type of microstructure is also found following elongations not exceeding 6% at 8 K, whereas larger amounts of deformation (up to 17%) cause heavily twinned structures. Analysis of those twins reveals the presence of primarily the {1012} type and also of the {1012} type. Moreover, other twinning modes, not usually observed in zirconium, are also detected in specimens cold rolled at room temperature. Les caracteristiques microstructurelles d'echantillons de zirconium pure polycrystallin ont ete etudiees par microscopie electronique a transmission, apres des traitements thermo-mecaniques et des mesures de frottement interne. Des dislocations (a/3) 〈1120〉, formant des parois de flexion ou de torsion, ont ete observees dans des echantillons recuits ou deformes a temperature ambiante. Ce type de microstructure est observe aussi apres des elongations inferieures a 6% executees a 8 K, tandis que des deformations plus grandes donnent lieu a des structures forte-ment mǎclees. Ces mǎcles sont essentiellement du type {1012}, parfois du type {1012}. De plus, dans des echantillons ecrouis a temperature ambiante on a pu mettre en evidence aussi d'autres types de mǎcles qui ne sont pas observes generallement dans le zirconium.

A theoretical analysis for the computation of the coincidence site lattice (CSL) symmetry is presented. It is shown that three types of symmetry elements can exist and each one can be found by properly using the CSL's rotation matrix of the smallest-angle description. Thus, from the existence of the subgroup H1, the order of which is directly connected with the number of the different orientations that the sublattice Λ11 can have, a low-symmetry H1 group implies more possibilities for the formation of the corresponding CSL. From the existence of the symmetry elements of the second type, the smallest-angle rotation matrix can be a symmetry element but only of the fourth or sixth order. From the third type of elements a connection between CSLs of different Σvalues can exist. Since the analytical form of this smallest-angle rotation matrix can be deduced for every crystallographic system, the procedure described here is of general use. Thus a new classification of the different CSLs is possible according to their symmetry group. This allows the study of the CSL model from the symmetry point of view.

Transmission electron microscopy is used to carry out a number of observation on crystal defects and on alteration reactions in a natural porous diopside mineral. Dislocations as well as stacking faults and grain boundaries are observed. The observations confirm the Burgers and translation vectors found by other authors for diopside i.e. b = [001], and R ‖ [100]. A Burgers vector b = [101], not mentioned in the literature is also determined here. Moreover a topotactic phase transformation is observed and analyzed in the same mineral. This phase is of the amphibole type. The amphibole phase resulted from the diopside phase following an alteration reaction indicating that diopside acted as an open chemical system free to exchange material with its surroundings. The amphibole phase grew on diopside in an orientation corresponding to the prevailing deformation twin orientation of diopside: K1 = (100), n1 = [001]. Transmissionselektronenmikroskopie wird benutzt, um eine Zahl von Beobachtungen an Kristalldefekten und Reaktionsanderung in einem naturlichen porosen Diopsidmineral durchzufuhren. Sowohl Versetzungen als auch Stapelfehler und Korngrenzen werden beobachtet. Die Beobachtungen bestatigen die Burgers- und Translationsvektoren, die von anderen Autoren fur Diopsid gefunden werden, d. h. b = [001] und R ‖ [100]. Ein Burgersvektor b = [101] der in der Literatur nicht erwahnt wird, wird hier ebenfalls bestimmt. Daruberhinaus wird ein topotaktischer Phasenubergang in demselben Mineral beobachtet und analysiert. Diese Phase ist vom amphibolen Typ. Die amphibole Phase ruhrt von der Diopsidphase her, die der anderungsreaktion folgt und zeigt, das Diopsid als ein offenes chemisches System wirkt, das frei ist fur Materialaustausch mit seiner Umgebung. Die amphibole Phase wachst auf Diopsid mit einer Orientierung, die der vorherrschen-den Deformationszwillingsorientierung von Diopsid: K1 = (100), n1 = [001] entspricht.

A study by means of electron microscopy at high resolution has enabled the analysis of the microstructure of hematite as produced by dehydration from goethite. The apparently “polycrystalline” structure is found to consist of aggregates of well-oriented twin-related hematite crystals, separated by regularly spaced H(001) walls of voids resulting from the loss of water. The material is thus broken up into blocks with sizes smaller than 50 A. The crystallography of the twinned structure can be analyzed by electron diffraction data and dark-field imaging. These aggregates of hematite crystals provide an ideal mosaic structure. In particular the effect of this mosaic structure on the individual reflections of the diffraction patterns has been analyzed and discussed.

The generation of tables of CSL's in the cubic system is presented with three parameters giving easy and rapid access to all the significant data characterizing a CSL: it is given by the rotation matrix from which the rotation axis and the rotation angle are easily determined. A method for the experimental determination of a CSL is presented, based on this new formulation.

It is shown that the satellites observed in the diffraction pattern of the dehydrated single crystal of the mineral goethite, which were previously attributed to a “superstructure,” are better interpreted in terms of small angle scattering by a “texture” of the dehydration product hematite. This texture consists of rows of cavities parallel to the H(003) = G(100) planes with an average distance of 30–50 A, depending on the stage of the transformation, in a highly twinned hematite matrix. In corundum resulting from the dehydration of diaspore a more isotropic texture is formed and the diffraction pattern exhibits “halos” instead of rows of satellite spots.

The order-Disorder transformation in CuPt has been investigated by means of electrical resistance measurements, transmission electron microscopy, and electron diffraction. Upon heating disordered CuPt, short range order is developing in the temperature range 20 to 190 °C by the formation of microdomains which grow into long range order domains upon further heating. This development of short range order gives rise to an electrical resistance increase, followed by a decrease due to the formation of long range order. The electrical measurements are correlated with electron microscopic observations. Der Ordnungs-Fehlordnungsubergang in CuPt wurde mit Hilfe von Messungen des elektrischen Widerstandes, von Transmissionselektronenmikroskopie und Elektronenbeugung untersucht. Beim Tempern von fehlgeordnetem CuPt entwickelt sich im Temperaturbereich 20 bis 190 °C Nahordnung durch die Bildung von Mikrodomanen, die bei weiterer Temperung zu Fernordnungsdomanen wachsen. Diese Entwicklung von Nahordnung gibt Anlas zu einem Ansteigen des elektrischen Widerstands, dem ein Abfall infolge der Ausbildung von Fernordnung folgt. Die elektrischen Messungen werden mit elektronenmikroskopischen Beobachtungen korreliert.

Inversion domains are revealed in dark field images by a difference in background intensity. The inversion boundaries show an α-like fringe contrast i.e. a symmetrical fringe pattern in bright field and an asymmetrical pattern in the dark field image. Experimental evidence for these contrast features are obtained from the non-centrosymmetrical α-GeTe. A theoretical analysis of the contrast characteristics is presented which is based on the logical assumption that for a non-centro-symmetrical crystal, the phases of extinction distance and of the absorption length are different. A very good agreement is found between theory and experiment for the contrast between the domains as well as for the fringe patterns at the boundaries. Also a particular multiple beam situation is treated. Durch eine Differenz in der Untergrundintensitat werden Inversionsdomanen in Dunkelfeld-diagrammen beobachtet. Die Inversionsgrenzen zeigen α-ahnlichen Streifenkontrast, d. h. ein symmetrisches Streifenmuster im Hellfeld- und ein asymmetrisches Muster im Dunkelfelddiagramm. Experimentelle Hinweise fur diese Kontrastbilder werden am nichtzentrosymmetrischen α-GeTe beobachtet. Es wird eine theoretische Analyse der Kontrastcharakteristiken gegeben, die auf der logischen Annahme beruht, das fur einen nichtzentrosymmetrischen Kristall die Phasen der Extinktionsabstande und Absorptionslangen unterschiedlich sind. Es wird sehr gute Ubereinstimmung zwischen Theorie und Experiment sowohl fur Kontrast zwischen den Domanen als auch fur die Streifenmuster an den Grenzen erhalten. Ein spezieller Vielstrahlfall wird behandelt.

The system V–N is investigated by X-rays, electron diffraction, and electron microscopy in the composition range 0 up to 25 at% N. The solid solubility of nitrogen is determined in the temperature range 500 up to 1200 °C. Two phases are formed upon quenching. The first is the V8N tetragonal phase. A supercell of the vanadium cell is proposed (a = b = 2ao √2, c = co). The transformation b.c.c. b.c.t. gives rise to a particular twinned configuration. The domains are related by a reflection twin (101)t, taking into account a supplementary rotation due to the tetragonal deformation. A new pseudo-orthorhombic phase V4N is analysed. This phase is isomorphous to Ta4N. The domain structure is described using a reflection twin (110)o and a rotation twin (130)o. Le systeme vanadium-azote a ete etudie dans le domaine de composition 0 a 25% atomique d'azote par rayons X, microscopie et diffraction electronique. La limite de solubilite a ete determinee pour les temperatures comprises entre 500 et 1200 °C. Deux phases se forment par trempe. L'une d'entre elles, V8N, est quadratique et une maille multiple de celle du vanadium est proposee (a = b = 2ao √2, c = co). La transformation cubique centre quadratique centre s'accompagne d'une configuration de macle particuliere. Les domaines sont relies par une operation de macle (101)t et une rotation supplementaire consecutive a la deformation quadratique. Une nouvelle phase pseudo-orthorhombique, V4N, a ete obseree et analysee. Cette phase est isomorphe de la phase Ta4N. La structure en domaines est expliquee au moyen de deux operations de macle: une macle de reflexion (110)o et une macle de rotation (130)o.

A new orthorhombic (possibly monoclinic) phase has been observed and analysed in the TaN system around the composition Ta4N with lattice parameters a = 5.16 A, b = 9.33 A, c = 4.94 A. Peculiar domain configurations as a consequence of the hexagonal to orthorhombic phase transformation have been analysed in detail. The coexistence of coherent reflection twins and rotation twins has been justified on the basis of minimization of the strain energy in complex domain boundary configurations. The particular domain boundary intersections formed by the phase transformation in this system are not a particular effect but have also been observed in other systems. Es wurde im TaN-System nahe der Zusammensetzung Ta4N mit den Gitterparametern a = 5,16 A, b = 9,33 A, c = 4,94 A eine neue orthorhombische (moglicherweise monokline) Phase beobachtet und analysiert. Besondere Domanenkonfigurationen infolge der Phasenumwandlung hexagonal orthorhombisch wurden genau untersucht. Es konnte die Koexistenz von koharenten Reflexions- und Rotationszwillingen mit der Minimierung der Zugspannungsenergie in komplizierten Domanengrenzen-Konfigurationen begrundet werden. Die durch die Phasenumwandlung gebildeten besonderen Domanengrenzenuberschneidungen sind nicht nur an diesem, sondern auch an anderen Systemen beobachtet worden.

A study by means of electron microscopy and electron diffraction of synthetic digenite reveals the existence of a series of closely related structures with basic spacings 2a o , 3a o , 4a o , 5a o and 6a o , where a o is the (111) spacing of the cubic close packed sulphur sublattice. In all these structures copper atoms occupy tetrahedral interstices in a cubic close packed matrix of sulphur atoms. By means of high resolution microscopy non-rational spacings are shown to be the result of a mixture of spacings. It is shown that the particular set of systematic extinctions in the diffraction pattern discussed in previous papers, is related to a particular state of disorder and does not imply the presence of twinning.

The electron diffraction patterns of Cu3—xTe2 are characterized by the occurrence of “incommensurate” superlattice reflections of which the positions with respect to the “basic” reflection, shift in a systematic manner with composition and/or degree of order. Similar effects were described previously with reference to Ni3±xTe2. Such diffraction patterns are interpreted in terms of “shear structures” derived from a simple hypothetical reference phase, for which a structure could be proposed. The incommensurability results from the occurrence of a mixture of spacings between shear planes. The model is consistent with high-resolution images. Optical diffraction experiments from two-dimensional gratings representing the structure also support the models. Fur die Elektronenbeugungsdiagramme von Cu3—xTe2 ist das Auftreten von “linkommensurablen” Ubergitterreflexionen charakteristisch, deren Positionen bezuglich der “Basis”-Reflexionen sich in systematischer Weise mit der Zusammensetzung und/oder dem Grad der Ordnung verschieben. Ahnliche Effekte wurden bereits fur Ni3±xTe2 beschrieben. Derartige Beugungsbilder werden mit einer “Scherstruktur” interpretiert, die aus einer einfachen hypothetischen Bezugsphase abgeleitet wird. fur die eine Struktur angegeben werden konnte. Die Inkommensurabilitat ruhrt von dem Auftreten einer Mischung der Abstande zwischen Scherungsebenen her. Das Modell ist konsistent mit Hochauflosungsdiagrammen. Optische Beugungsexperimente an zweidimensionalen Gittern, die die Struktur reprasentieren, unterstutzen ebenfalls diese Modellvorstellungen.