bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of aluminophosphates: Identification of 18-member ring structure in AlPO4-8
Authors: Ulan J. , Szostak R. , Gronsky R. 
Published: June 2020

The first claim in 1987 of an aluminophosphate (VPI-5) with a pore diameter greater than 7 Å regenerated interest in ultra-large pore molecular sieves for which theoretical models have existed since 1969. Large micropore materials are needed, especially in the oil industry, as catalysts which have the high acidity of zeolites, are thermally stable at high temperatures and pressures, and have significant porosity to allow diffusion of heavier feedstocks currently being seen in refineries.The aluminophosphate VPI-5 is reported to be the first molecular sieve to contain an 18-member ring structure with a pore diameter greater than 12 Å based on X-ray powder diffraction and adsorption data. Researchers at Mobil laboratories have crystallized the silicoaluminophosphate molecular sieve MCM-9 an its X-ray powder diffraction pattern has been shown to match a mixture of VPI-5 and AIPO4-11.
Recent applications of TEM to the study of interfaces
Authors: Barry Carter C. 
Published: June 2020

This paper will review the current state of understanding of interface structure and highlight some of the future needs and problems which must be overcome. The study of this subject can be separated into three different topics: 1) the fundamental electron microscopy aspects, 2) material-specific features of the study and 3) the characteristics of the particular interfaces. The two topics which are relevant to most studies are the choice of imaging techniques and sample preparation. The techniques used to study interfaces in the TEM include high-resolution imaging, conventional diffraction-contrast imaging, and phase-contrast imaging (Fresnel fringe images, diffuse scattering). The material studied affects not only the characteristics of the interfaces (through changes in bonding, etc.) but also the method used for sample preparation which may in turn have a significant affect on the resulting image. Finally, the actual nature and geometry of the interface must be considered. For example, it has become increasingly clear that the plane of the interface is particularly important whenever at least one of the adjoining grains is crystalline.A particularly productive approach to the study of interfaces is to combine different imaging techniques as illustrated in the study of grain boundaries in alumina. In this case, the conventional imaging approach showed that most grain boundaries in ion-thinned samples are grooved at the grain boundary although the extent of this grooving clearly depends on the crystallography of the surface. The use of diffuse scattering (from amorphous regions) gives invaluable information here since it can be used to confirm directly that surface grooving does occur and that the grooves can fill with amorphous material during sample preparation (see Fig. 1). Extensive use of image simulation has shown that, although information concerning the interface can be obtained from Fresnel-fringe images, the introduction of artifacts through sample preparation cannot be lightly ignored. The Fresnel-fringe simulation has been carried out using a commercial multislice program (TEMPAS) which was intended for simulation of high-resolution images.
HREM of the interface between CVD Si3N4 and single-crystal SiC
Authors: Unal O. , Mitchell T. E. 
Published: June 2020

Ceramic/ceramic composites are of interest because of their potential structural applications, especially at high temperature. The interface between the components is especially important in influencing the mechanical properties. As part of a program to investigate Si3N4 matrix/SiC whiskers composites, macroscopic Si3N4/SiC interfaces have also been prepared in order to study their mechanical behavior, particularly with regard to crack propagation. These interfaces have also been studied by HREM.Transparent single crystals of SiC a few mm in size were obtained as a by-product of the Acheson process. They were mounted on graphite pillars and coated with 5mm of Si3N4 deposited by CVD using a mixture of ammonia, trichorosilane and hydrogen at 1500°C. Cross-sectional specimens were made by the sandwich technique with the final ion-milling at liquid nitrogen temperatures. HREM was performed on a Philips CM3OT.
The role of Electron Microscopy in the study of grain boundaries
Authors: Clark William A. T. 
Published: June 2020

Our understanding the nature of interfaces in polycrystalline materials has depended critically on observations obtained in the transmission electron microscope. This is especially true in the case of interfacial structure, where developments in models of atomic and defect structures in interfaces have closely paralleled advances in techniques available for their study. The general acceptance that the crystallography and relative misorientation of the two crystals forming an interface dictate the interfacial structure, and many of its properties, results in large part from direct TEM studies of interfaces.Grain boundaries were originally considered structureless, amorphous, films, because optical microscopy could not provide information at the necessary resolution, and inferences about the nature of boundaries had to be made from measurements of mechanical properties. However, the development of X-ray methods in the 1920's quickly showed that the crystalline structure of the grains was preserved right up to an interface, and that the boundary could be thought of as a “transition lattice” from one crystal to the other, a concept remarkably similar to many of those still current today. Although there was some earlier optical microscopy of decorated low-angle boundaries in Si, it was not until 1956 that the development of the TEM provided the first detailed picture of dislocations and grain boundaries in opaque materials.
Structure of Nb/Al2O3 interfaces produced by molecular beam epitaxy
Authors: Mayer J. , Flynn C. P. , Rühle M. 
Published: June 2020

HREM Studies of the atomistic structure of idealized metal/ceramic interfaces are important for both fundamental and applied reasons. Epitaxial growth by molecular beams allows to produce such interfaces under controlled conditions. Nb/Al2O3 has been chosen as a model system because of the absence of any chemical reactions between the metallic overlayer and the ceramic substrate and since both components possess nearly the same thermal expansion coefficient. Results of x-ray diffraction studies indicate that a unique three-dimensional orientation relationship exists between niobium and sapphire which is established for different choices of surface plane of the sapphire substrate. Aim of the present investigations was to study the orientation relationships and the atomic arrangement at the interface by conventional TEM and HREM.During MBE growth the sapphire substrates were heated to 1123 K and a vacuum in the 10-7Pa range was maintained. Typical growth rates of 1 monolayer/sec were obtained. Cross-section TEM samples were prepared by a special technique involving cylindrical alumina holders with a diameter of 3mm. Shielding was applied during ion-milling to reduce the effect of the different milling rate of Nb and Al2O3.
Coincidence-site-lattice-pattern (CSL-pattern) of 70.5°/[110] boundary of the 6H-type layer structure
Authors: Kitano Yasuyuki , Takata Masaki 
Published: June 2020

The most useful and intuitive model may be a CSL-model to analyze boundary structures. In order to apply the CSL-model to layer structures, we have proposed to use ‘lattice point’ in a wide sence and to add extra lattice points to the Bravais lattice points when interpenetrating(IP)-lattices are drawn. These lattice points will be called ‘extended lattice points’. It is well known that a layer structure is built up with (almost) identical layers stacking on the top of the others with a cirtain amount of shift in a direction perpendicular to the stacking. Each layer consists of one or more atomic planes and has almost (or exactly) the same atomic configuration. The extended lattice points can be defined as the origins in each layer in crystal. The number of such points depends upon the number of layers in a unit cell.To draw IP-lattices we have adopted all the extended lattice points in addition to the Bravais lattice points. There are three important advantages of doing this extension. First is that the Coincidence-Sites in the IP-lattices drawn do not scatter homogeneously, but gather in a region and make a cluster. They exibit a characteristic pattern of Coincidence-Sites. This pattern is called a CSL-pattern. Second is that the DSC-lattice (Displacement Shift Complete Lattice) provides a set of basic vectors smaller than predicted before extention.
Diffraction contrast images of interphase boundaries in cobalt
Authors: Cheng S.C. , Sheinin S. 
Published: June 2020

The boundaries between HCP and FCC phases in cobalt are generally expected to be of the type {111}FCC ‖ {001}HCP. Observations carried out by the authors indicate that the contrast exhibited by this type of boundary is very similar to the contrast exhibited by twin boundaries, as discussed by Sheinin and Corbett. These authors showed that images of twin boundaries consist of two intersecting sets of fringes with the possibility that one set is suppressed under certain diffraction conditions. The purpose of the work presented in this paper is to investigate the contrast exhibited by boundaries between the same two phases but which lie in a different habit plane.Experimental observations were carried out on boundaries in wedge crystals of cobalt, as shown schematically in Fig.1. The orientations of the crystals on either side of the boundary were obtained from selected area diffraction. For the bright and dark field images in Figs. 3a and 4a the orientations were found to be (12
)FCC on the left of the boundary and (100)HCP on the right. The boundary was found to be of the {111}FCC ‖ {312}HCP type. In the diffraction pattern obtained from the region containing the boundary shown in Fig. 2, the reflections (111)FCC and (002)HCP are identified.
The role of interfaces in the creep-deformation of a Sic whisker-reinforced Si3N4 composite
Authors: More K.L. , Koester D.A. , Davis R.F. 
Published: June 2020

The high temperature mechanical properties of a SiC whisker-reinforced composite are currently being investigated. The deformation characteristics of the composite are controlled not only by the distribution of the constituent phases, but also by the interfaces between phases. The material is a hot pressed 30 vol.% SiC whisker-reinforced Si3N4 containing sintering aids of 1.5 wt.% A12O3 and 6.0 wt.% Y2O3. Constant compressive stress creep experiments were conducted in a continuously purified 0.11 MPa nitrogen atmosphere in a system described elsewhere. This work focussed on two creep experiments conducted at temperatures of 1470 K and 1620 K, both in the stress range 50-350 MPa. Figure 1 shows the stress exponent, n, for creep of the composite at both 1470 K and 1620 K. At 1620 K, n exhibited a bi-linear behavior. However, this behavior was not observed for creep at 1470 K.In the as-hot pressed state, the composite had an amorphous grain boundary phase containing N, O, Al, Si, and Y as determined by energy dispersive spectroscopy. Prior to loading, the specimens were annealed for 4 hr at the creep temperature. During the anneal, the grain boundary phase crystallized and underwent a change in composition as determined by X-ray diffraction and transmission electron microscopy (TEM).
The staining of carboxylated latex with cesium hydroxide
Authors: Shaffer O.L. , Stanislawczyk V. , El-Aasser M.S. 
Published: June 2020

Various staining techniques of polymers have been developed for transmission electron microscopy. The ability to diferentiate polymer phases is crucial in the understanding latex particle morphology. A new technique has been developed to study the acidic groups on the surface as well as in the interior of acrylic latex particles.A 2% aqueous solution of cesium hydroxide(CsOH) is used as a swelling and staining agent. The alkali metal hydroxides are the most basic of all the hydroxides and CsOH is the strongest base in the group. A drop of latex is diluted in 1 to 2 cc of freshly prepared 2% aqueous CsOH. A drop of the dispersion is placed on a 200 mesh formvar-carbon coated copper TEM grid. Most of the drop is removed with filter paper leaving a thin film of the dispersion. The grid is then positioned in a Philips cold stage which is filled with liquid nitrogen after placement in a Philips 400 TEM.
Measurement of microscopic displacements in graphite/epoxy composite materials using a SEM-generated surface map
Authors: Burghardt R.C. , Ehrman J.M. , Stephens T.C. , Hibbs M.F. 
Published: June 2020

Graphite fiber-reinforced resin composite materials have a wide use in aerospace, automotive and sporting goods applications where high strength to weight ratios are requisite. Many of these materials use highly cross-linked epoxy resins as the matrix material. Unfortunately these resins have a low resistance to crack propagation and as a result research efforts have been directed towards reducing this tendency.The ability to measure microscopic displacements and calculate strain fields in the vicinity of a fracture crack tip under experimental conditions was needed in order to help predict the fracture resistance of various composite materials being tested. A technique was developed that made it possible to derive displacement measurements on a micrometer scale in the region of a crack tip from observations of epoxy-based composites being fractured using a tensile stage equipped scanning electron microscope (SEM). Samples were polished on the surface to be observed and sputter coated with 5 to 10 nanometers of either gold or 60:40 gold-palladium prior to mounting on the TS-2 tensile stage of a JEOL JSM-35CF. This instrument was also equipped with a Krisel beam interceptor, a beam current meter, a Tracor Northern TN-2000 x-ray analyzer and a TN-1310 digital beam control system. Using the digital beam and x-ray mapping capabilities a matrix of small dots was “written” onto the surface of the sample as shown in figure 1.
Shear structures in the Al5CuLi3 frank-fasper phase
Authors: Zhou D. S. 
Published: June 2020

Stacking faults and shear structures are often observed in the Frank—Kasper phases, especially in those composed of juxtaposed pentagonal antiprisms (or icosahedral chains) and/or juxtaposed hexagonal antiprisms. Their relationship with the quasicrystals has been extensively studied and leads to some structural models for quasicrystals. Recently, the transformation from icosahedral quasicrystals to crystalline (Frank—Kasper) phases has been studied upon heating. The current paper focuses on the defect structures of the Frank—Kasper phase, which is believed to have the same basic building units as quasicrystals.The alloy used in the present investigation was made from high purity (>99.99 at%) constituent elements. They were melted in an induction furnace in a graphite crucible under partial argon atmosphere and then were poured into a stainless steel mold. Rapid solidification was carried out by a melt spinner in a helium atmosphere. X-ray diffraction only revealed the presence of icosahedral quasicrystals. Heat treatment was done by encapsulating the samples in quartz tubes and transforming at 397°C for 20 seconds to obtain crystalline phases. The heat treated samples were first examined in a Philips EM400T microscope and then in a JEOL-4000EX microscope for atomic imaging.
Dislocation microstructures in boron-doped Ni3Al
Authors: H.F. Yu , Jones I.P. , Smallman R.E. 
Published: June 2020

Despite its relative engineering eclipse (at least in aeronautical terms), Ni3Al is still a rewarding area for scientific research, primarily because so much is already known about it. Many of its mechanical properties, however, are still not understood in terms of secondary defect populations and behaviour. For example, the fundamental Kear-Wilsdorf mechanism, wherein cross slip from {111} to {100} planes provides an increase in strength with temperature, has received intensive microscopic scrutiny recently, and it now appears that the movement of the superpartials on {100} is far more than the atom spacing or so envisaged in Paidar et al. Whether delocking occurs, however, and if so how often, is still not clear. Examples of other problems which remain are:a) What are the relative contributions to work hardening of the Kear-Wilsdorf mechanism, APB tube formation and SISF formation?b) Although the yield stress increases with temperature it also increases slightly with strain rate, whereas a negative strain rate dependence might have been expected.
In-situ studies in the high-voltage Electron Microscope
Authors: Westmacott K.H. 
Published: June 2020

The principal advantages of high voltage electron microscopes are the ability to 1) attain higher resolution by virtue of the shorter wavelength, and 2) penetrate thicker specimens to observe dynamic behavior representative of bulk material. Some recent examples of in-situ HVEM research, representing the latter category, will be summarized in this contribution, and future directions discussed. Included in the most active research areas are phase transitions, deformation, high temperature reactions and environmental cell studies.Irradiation with high energy electrons in an HVEM provides a convenient alternative to thermal treatments for inducing phase transitions in alloys. An illustration of how ordering or disordering of the same material can occur under electron irradiation is shown in Figure 1. In this example, a Pt7C ordered phase was formed in a Pt-C alloy at 500°C with a defocused beam (outer region) and subsequently disordered at 30°C with a focussed beam (inner spot).
In-situ high-voltage Electron Microscopy of defect ordering under high-dose irradiation
Authors: Jin N.Y. , Phillipp F. , Seeger A. 
Published: June 2020

High-dose irradiation of metals employing dpa values (= displacements per atom) substantially larger than unity may lead to ordered arrangements of defects at temperatures well below the temperature of void formation. We report on a systematic study of defect-ordering phenomena in three fcc metals with markedly different stacking-fault energies, viz. Cu, Ag, and Ni.5N-pure foils of Cu, Ag and Ni were prepared for in-situ electron microscopy in the conventional way. They were irradiated in an AEI-EM7 high-voltage electron microscope (HVEM) with lMeV electrons (e-) at various temperatures (Tirr) between 20 and 500K (Ag and Cu) or between 300 and 600K (Ni). The electron flux density and the total dose, Φ, were typically 7×l023e-m-2s-1 and 1x1027e-m-2, respectively. The development of the defect patter was investigated in the HVEM during the irradiation.In all three metals a temperature regime has been found in which visible defects are regularly arranged along <100> directions after a minimum dose of ∼1026 e-m-2 (Fig.l).
The evolution of damage structures under simultaneous dual beam irradiation by ions and electrons in a HVEM
Authors: Takahashi Heishichiro , Ohnuki Soumei , Suzuki Takashi , Hidaka Yasuyoshi , Hishinuma Akimichi 
Published: June 2020

It is well-kncwn that the materials for fusion reactor are damaged by high energy neutrons and other energy particles , and that due to nuclear reaction of (n,α) and (n,p) helium and hydrogen are introduced in the materials. Therefore, it is inportant to see the simultaneous effects of these fission productes and damage defects in materials to develope the fusion materials. To simulate the behaviors of damage structure in fusion reactor, the simultaneous dual beam irradiation is the most convenient method.In order to investigate the effects of hydrogen and helium on the behaviors of defect clustering and void (cavity) formation under the dual beam irradiation, i. e. the simultaneous irradiation with hydrogen or helium ions and electrons was carried out using a high voltage electron microscope with 1000 KeV in the temperature range of 673 k and 823 K for the cold worked and annealed 316 stainless steels. Also, to see the effect of the ratio of hydrogen per dpa,H+ (or He+)/dpa ratio was changed between 0 and 300 appm H+ or He.
“In Situ” observation by Transmission Electron Microscope of the deformation and fracture micromechanisms in 7050 aluminum alloy
Authors: Monteiro W.A. , Alarcon O.E. , Nazar A.M.M. 
Published: June 2020

During the last ten years the "in situ" deformation experiments by transmission electron microscopy have been used in metals to study the micromechanism of plastic deformation and fracture propagation mode occuring from the crack tip.These studies were performed in mono and policrystals metals with the aim to investigate the dislocation emission from crack tip phenomena relating it with the ductil versus brittle behavior of materials.The material used in this experiment was a high strength aluminum alloy 7050 contained recrystal1ized and unrecrystal1ized microstructures, as the obtained by thermomechanical treatment in previous work .Due to the small dimensions of the miniature tensile specimens (2.7 × 6.8 × 0.02 mm ) and the requisite to obtain a lot of samples without introduction of strain during manufacture, the specimens was performed using a lithographic process.
The threshold energy for atom displacement in fcc metals
Authors: Sigle Wilfried , Hohenstein Matthias , Seeger Alfred 
Published: June 2020

Prolonged electron irradiation of metals at elevated temperatures usually leads to the formation of large interstitial-type dislocation loops. The growth rate of the loops is proportional to the total cross-section for atom displacement,which is implicitly connected with the threshold energy for atom displacement, Ed . Thus, by measuring the growth rate as a function of the electron energy and the orientation of the specimen with respect to the electron beam, the anisotropy of Ed can be determined rather precisely. We have performed such experiments in situ in high-voltage electron microscopes on Ag and Au at 473K as a function of the orientation and on Au as a function of temperature at several fixed orientations.Whereas in Ag minima of Ed are found close to <100>,<110>, and <210> (13-18eV), (Fig.1) atom displacement in Au requires least energy along <100>(15-19eV) (Fig.2). Au is thus the first fcc metal in which the absolute minimum of the threshold energy has been established not to lie in or close to the <110> direction.
Crystallization of amorphous ceramics during electron irradiation in high voltage microscope
Authors: Ohnuki S. , Takahashi H. , Kanamura R. , Nakaoka T. , Kinoshita H. 
Published: June 2020

Transmission electron microscopy (TEM) has been a conventional method for studying for ceramics materials, therefore, the structural change induced by electron beam is a serious subject. It is well known that some ceramics with covalent bonding are able to change to amorphous structure during the charged particle-irradiation, and also Al2O3 has three structures of alpha, amorphous and gamma. Unfortunately, we have no detailed information on the effect of charged particle irradiation on structure of ceramics. The authors have found that Al2O3 amorphous changes easily to gamma crystalline during TEM observation. The aim of this study is to clarify the effect of some factors on the crystallization process, such as accelerating voltage and irradiation temperature.Amorphous Al2O3 was prepared by 200 keV Ar+ ion implantation to 5×1016 cm−2 at 170K - room temperature (RT). High voltage and conventional TEMs of 1000 and 200 keV were used in this investigation of crystallization behavior of the amorphous which was produced on [0001] single crystal.