A structural investigation of the Cape York meteorite by transmission electron microscopy

Examination of the kamacite phase of the Cape York meteorite by TEM revealed the following principal microstructural features: subgrains, Neumann bands, slip traces, dislocation networks, dislocation loops and precipitate particles. Quantitative data on many of these features have been collected. The significance of a pre-terrestrial shock event in explaining the origin of several of these features is discussed and microstructural evidence is presented showing that the maximum shock pressure encountered by the meteorite was in the range 70 to 120 kbar. This result is at variance with that claimed by other workers.     

Transmission electron microscopy observations of the lamellar structure in the Arispe iron meteorite

The Arispe iron meteorite contains approximately 7 at.% Ni. The structure consists of coarse ferrite plate-like crystals with a Widmanstätten pattern. In between some of these plates is retained austenite, some of which has decomposed to a variety of structures (e.g., martensite, spheroidized structure, etc.). One of these structures is a lamellar arrangement of alternating plates of a low-Ni and a high-Ni phase. The structure has been identified using transmission electron microscopy. The low-Ni phase is ferrite and contains approximately 6 at.% Ni. The high-Ni phase contains approximately 48 at.% Ni and has the ordered NiFe (L1_o) structure. The Fe–Ni phase diagram indicates that the lamellar structure formed by a monotectoid reaction of austenite decomposing to ferrite and disordered austenite containing approximately 48 at.% Ni. Upon further cooling, the austenite ordered to form NiFe.     

A transmission electron microscopy study of microscopic causes for localized-corrosion morphology variations in the AA7055 Al alloy

By Using (scanning) transmission electron microscopy, localized-corrosion morphology variations of the AA7055 AlZn(Cu)Mg alloy with different thermal processes and their underlying microscopic causes were investigated systematically. Our study shows that the corrosion resistance of the nanoscale precipitates varies with their structure type and Cu-content. Just like the Al-matrix, the early-stage precipitates are corrosion resistant, as compared with the η_p/η-precipitates without high Cu-content. With a high Cu-content, however, the η-precipitates become most corrosion resistant among all phases involved. Hence, tailoring the precipitate microstructure and chemistry though thermal processes may change the overall corrosion morphology and improve corrosion resistance property of the alloy.     

A transmission electron microscope study of glass-ceramics

A technique for preparing thin foils of glass-ceramics for transmission electron microscopy has been developed, using a combination of chemical, abrasion and ion-beam machining. This has permitted a study of the microstructural development in a number of glasses of different chemical compositions subjected to various heat-treatments. Results are presented and discussed for materials based on the Li₂O-SiO₂ system and on a more complex Li₂O-K₂O-ZnO-SiO₂ material employing phosphorus pentoxide as a nucleation catalyst.     

Scanning electron microscopic fractography of permanent moulded cast iron

The fracture susceptibility of chill-free permanent moulded cast iron is discussed in terms of graphite configuration. The details of fracture surface topography as revealed by scanning electron microscope examination on areas of slow crack growth and fast fracture are presented and the usefulness of these SEM fractographs in categorizing the fracture modes is demonstrated.     

A transmission electron microscopy study of hexagonal ice

The morphologies of fast-frozen, thin-film samples of pure and dilute solutions of salts and surfactants in hexagonal ice are investigated with transmission electron microscopy. The cold-stage microscopy technique is described briefly and limitations imposed by the equipment and the sample itself are discussed. Ice grains, grain boundaries, dislocations, and stacking faults are imaged before radiolysis from the electron beam can alter their structures. The technique shows that screw dislocations in the ice basal plane are common, in accord with observations from X-ray topography and etch-replication microscopy. It also makes visible nonbasal dislocations in hexagonal ice, including dislocations in first prismatic planes, nonprismatic dislocation loops, and stacking faults on first pyramidal planes; heretofore, these defects have not been confirmed experimentally. Implications of the work for cold-stage microscopy of microstructured fluids are mentioned.     

A scanning electron microscopic study of hybrid composite impact response

Scanning electron micrographs of fracture surfaces of various hybrid composite materials subjected to Charpy impact tests are presented. Macrophotographs of the failed specimens which indicate the gross failure modes, and actual impact load-time traces obtained using an instrumented tup impact test technique are also included. These data permit a direct comparison between observed microfailure modes and the gross response of each composite to failure. An all-graphite/epoxy control configuration and three hybrid configurations are considered. The third-phase fibre additions in these hybrids include glass, Kevlar 49, and Nomex nylon. Longitudinal and transverse impact tests of both notched and unnotched standard Charpy specimens are included, for both a basic unidirectional graphite/epoxy composite and a quasi-isotropic laminate orientation.     

A transmission electron microscope study of the structure of electrolytic nickel

Conclusions In conclusion, during the electrolysis of nickel from acid sulphate solutions, the coverage of the cathode by a possible colloidal film of nickel hydroxide is the decisive factor. In its presence, the cathode exhibits a very fine-grained, randomly oriented structure. If the film is removed, the structure consists at these current densities of relatively large grains with a very strong texture [100] perpendicular to cathode. The large grains are often twinned, but no individual stacking faults are found.The inhibitive action of the hydroxide film can be eliminated by chloride ions [2], or it can be replaced by an organic additive [3].     

A transmission electron microscopy study of the electrochemical process of lithium-oxygen cells

The electrochemical reaction of a lithium-oxygen cell using a tetraethylene glycol dimethyl ether-lithium triflate, TEGDME-LiCF(3)SO(3) electrolyte, is investigated by a detailed transmission electron microscopy analysis. The results confirm the reversibility of the process by showing the formation-dissolution of lithium peroxide, Li(2)O(2), upon repeating cell charge and discharge cycles.     

A transmission electron microscopy study of polymer-stabilised liquid crystal structure

A method has been established for observing the internal structure of the network component of polymer-stabilised liquid crystals. In situ photopolymerisation of a mesogenic diacrylate monomer using ultraviolet light leads to a sparse network (1 wt%) within a nematic host. Following polymerisation, the host was removed through dissolution in heptane, revealing the network. In order to observe a cross-section through the network, it was embedded in a resin and then sectioned using an ultramicrotome. However, imaging of the network was not possible due to poor contrast. To improve this, several reagents were used for network staining, but only one was successful: bromine. The use of a Melinex-resin composite for sectioning was also found to be advantageous. Imaging of the network using transmission electron microscopy revealed solid droplets of width 0.07–0.20 m, possessing an open, yet homogeneous structure, with no evidence for any large-scale internal structures.     

Transmission electron microscopic study of multiwalled carbon nanotubes

Multiwalled carbon nanotubes have been studied by transmission electron microscopy, selectedarea electron diffraction, and transmission electron energy loss spectroscopy (EELS). The results demonstrate that the walls of carbon nanotubes consist of graphite-like layers with an increased interlayer spacing compared to graphite. The local density distribution in the CNTs has been evaluated from EELS scans over the nanotubes.     

A high resolution electron microscopic study of the microstructure in rapidly solidified Al-Li-Cu-Mg-Zr alloys

The microstructure in rapidly solidified Al-Li-Cu-Mg-Zr alloys has been reexamined by transmission electron microscopy (TEM). The results show that the weakening intermetallic phases, e.g. hexagonal, Z, face centred cubic (f.c.c), T, and tetragonal, H, (new phase) phases, exist in alloys with relatively high contents of Mg besides the strengthening phases. The sizes of these weakening intermetallic phases are on the scale of micrometres. The newly found tetragonal H phase, having parameters of a = 2.8 nm and c = 2.4 nm, was observed to coexist with the Z phase, and has a defined orientation relationship with the Z phase. High resolution images reveal that there are planar defects and 90 ° domains in the Z phase, multiple twins in the T phase, and two well defined crystallographic orientation relationships between the Z and T phases.     

A high-resolution transmission electron microscope study of a zinc oxide varistor

Investigations were made of varistor microstructure, the morphology of Bi₂O₃ at multiple ZnO grain junctions, Bi₂O₃/ZnO grain boundaries and ZnO/ZnO grain boundaries (especially whether Bi₂O₃ is present or not at the ZnO/ZnO grain boundary) by means of high-resolution transmission electron microscopy and X-ray microanalysis in the scanning transmission electron microscope. Bi₂O₃ at multiple ZnO grain junctions consists of small particles of 0.1m in diameter, and they are vitrified to some extent. It is suggested that bismuth ions dissolve into ZnO grains over a 30 nm range from a Bi₂O₃/ZnO grain boundary; however, there is no bismuth at ZnO/ZnO grain boundaries.     

An electron microscopic study on MnBi thin films

The structure and orientation of MnBi thin films prepared by sequential evaporation of bismuth and manganese on glass substrates were studied by transmission electron microscopy and electron diffraction. Results indicate that these films develop a preferred orientation with thec-axis perpendicular to the film plane. This preferred orientation is due to the formation of MnBi from a highly oriented bismuth layer, i.e., a layer with thec-axis perpendicular to the film plane. Trace amounts of elemental bismuth, manganese and MnO are found in these MnBi films. There is evidence of close parallel alignment between the MnBi and the bismuth lattices.     

An electron microscopic study of the morphology of cured epoxy resin

An electron microscropic study of fracture surfaces and microtomed sections of a cured epoxy resin based on a difunctional bisphenol A type resin cured with different amounts ofm-phenylenediamine is presented. Heterogeneities in the range 5 to 100 nm are seen to be present and have relatively higher crosslink density compared to the surrounding matrix. It is observed that the fracture path is around the heterogeneity and not through it. The size of the heterogeneity is a function of curing agent concentration and also of cure cycle. The stoichiometric sample, which has the highest crosslink density and the highest glass transition temperature, has the smallest heterogeneities. On either side of stoichiometry, the heterogeneity size increases. Samples subjected to a more severe post-curing cycle have much larger heterogeneities. The possible physical basis for these differences is discussed.On leave from the Indian Institute of Technology, New Delhi 110016, India.     

A study of evaporated gold-tin films using transmission electron microscopy: II

Using transmission electron microscopy the time development at room temperature of the different Au-Sn phases present in evaporated gold-tin films was studied. An interaction was found to take place which resulted in the formation of AuSn and AuSn₄ at early stages and a subsequent transformation into other Au-Sn phases depending on the overall composition.     

A transmission electron microscopy study of particulate concentrations in seven individual snowflakes

An electron microscope analysis of seven individual snowflakes, which were collected over a six-hour period and allowed to dry upon collodion support films, showed the particle concentration to increase with elapsed time of snowfall, reach a maximum at $\text{3}\text{4}$ of the duration, and to essentially stabilize thereafter. The size of the particles ranged from less than 0.01 μm to 4.5 μm in diameter, with average particle size first increasing then decreasing with elapsed time of snowfall. The particle concentration in individual snowflakes was observed to be roughly 5 times greater than that observed previously in individual raindrops in the same geographic area, and there was no evidence of asbestiform fibers.     

Scanning electron microscopic study of acacia and eucalyptus wood chars

SEM studies of acacia and eucalyptus wood chars, prepared under different carbonization conditions, were undertaken to provide information on what happens in the transformation of wood to chars. The material normally lost as volatiles contributes totally to the formation of pores, cracks and pyrolytic carbon. Both woods exhibited similar devolatilization behaviour in pore structure development, crack formation and pyrolytic carbon deposition, showing a decrease in pore size with an increase in carbonization temperature and cracks/voids formation during rapid carbonization at higher temperatures (i.e. 800–1050 °C). Slow carbonization led to pyrolytic carbon deposition in resulting wood char structures and did not disturb the fibrous nature and cell structures of the wood, even at a high carbonization temperature of 1200 °C. Prolonged heating at carbonization (slow) temperatures of 800 and 1000 °C caused sintering of the adjacent fibres resulting in the formation of compacted mass.