High resolution and high efficiency planar display, one of the national priorities for advanced technologies and commercial applications, require highly efficient phosphor materials with crystalline monodispersive fine particles [1,2]. Europium oxide activated yttrium oxide (Y2O3:Eu) is a potential red-emission phosphor powders to be used in high efficiency electroluminescence and field emission displays. In this paper, a novel hydrolysis technique is employed to prepare phosphor particles of Y2O3: Eu, and the structure characterization is reported.

In this synthesis technique, urea reacts with water to release OH−, cations of Y3+ and Eu3+ combine with OH− to form (Y1−xEux)(OH)3 precipitates. Y2O3 particles doped with Eu are formed after the precipitates being fired at a given temperature [3]. The particles prepared by this method are nearly spherical, and have an average diameter of ∼200 nm (Fig. 1). The distribution of particle sizes is narrow, and almost no agglomeration among particles is observed. The particle sizes remain approximately the same before (Fig. 1a) and after (Fig. 1b) being fired at 1200°C.

In the last decade, new in-situ processing techniques, such as DIMOX™, XD™, VLS and SHS, for fabricating metal and intermetallic matrix composites have emerged. It is expected that the in-situ formed composites may reveal not only excellent dispersion of fine reinforcing particles, but high thermodynamical stability and high temperature performance. The fully dense Al2O3-Al3Ti-57Vol%Al composite was in-situ processed by combing combustion synthesis with squeeze casting utilizing the reaction between TiO2 powder (with average diameter of 0.6μm and volume fraction of 14%) and pure Al (99.5%). First, the 14Vol%TiO2/Al bulk materials were fabricated via squeeze casting method, subsequently, the TiO2/Al materials were heat treated to form final in-situ composites. Using XRD, SEM, TEM and HRTEM techniques, the microstructure and its evolution were investigated.

The X-ray diffraction pattern of the composite is shown in Fig.1 which indicates that the composite is composed of A12O3, Al3Ti and Al. According to the reaction formula between TiO2 and Al the volume fraction of Al in the composite is about 57%. Fig.2 is a typical scanning electron micrograph of the composite.

The mechanical reliability of ceramic matrix composites (CMCs) at elevated temperatures in oxidative environments is primarily dependent upon the chemical and structural stability of the fiber/matrix interface. Graphitic carbon coatings have traditionally been used to control the interfacial properties in CMCs, however, their use is limited in high temperature oxidative environments due to the loss of carbon and subsequent oxidation of the fiber and matrix. Thus, BN is being investigated as an alternative interfacial coating since it has comparable room temperature properties to carbon with improved oxidation resistance. The stability of BN interfaces in SiC/SiC composites is being investigated at elevated temperatures in either flowing oxygen or environments containing water vapor. The effect of several factors on BN stability, including crystallographic structure, extent of BN crystallization, and impurity content, are being evaluated.

Nicalon™ fiber preforms were coated with ≈ 0.4 μm of BN by CVD using BCl3, NH3, and H2 at 1373 K. The coated preforms were densified using a forced-flow chemical vapor infiltration (FCVI) technique developed at ORNL.

Si3N4-based materials exhibit attractive mechanical properties for high-temperature applications. These properties are influenced strongly by the size and morphology of the grain boundaries and grain-boundary phase. An amorphous intergranular film (IGF) commonly exists at two grain junctions. The thickness of these IGFs sensitively depend on the chemical composition of the intergranular phase.In this work, our studies on the grain boundary microstructure of Si3N44 ceramics made by Hot Isostatically Pressing (HIPing).

Si3N44 materials were densified by HIPing Si3N4 powders (UBE E-10) at 1950°C at 200 MPa for 1 hour, with sintering aids of either Y2O3 or Y2O3 + A12O3. Two materials were made: material A consisting of 2 wt% Y2O3; material B consisting of 5 wt% Y2O3 and 1 wt% A12O3. Both as-HIPed and oxided samples were investigated. TEM specimens were prepared by conventional procedures. The microstructure and chemical composition were studied on a JEOL 2000FX.

Silicon carbide (SiC) composites are receiving much attention for structural use at high temperatures. One class of composites are those reinforced with SiC fibers. The SiC fibers are coated with boron nitride (BN) which is weakly bonded to the fiber. During fracture, the coating deflects cracks causing pull-out of the fibers (Fig. 1). This process of fiber pull-out consumes energy and increases the toughness of the composite. Although much work has been done on characterizing these materials by SEM, not much has been done using TEM due to difficulties in specimen preparation. The purpose of this study is to characterize these fibers and composites using conventional and analytical TEM.

In this study, TEM specimens were prepared by dimpling and ion milling. Careful control of the preparation was needed to ensure the integrity of the SiC-BN interface. Figure 2a is a TEM image of the fiber showing delamination at the SiC-BN interface.

Silicon nitride-based or SiAlON ceramics are increasingly being considered for many engineering applications due to their low density, high strength, and high modulus. For many engineering applications SiAlON ceramics are required to have, among many other properties, both high fracture toughness and good tribological properties. Typically, an interlocking microstructure consisted of β-Si3N4 and/or β'-SiAlON grains is produced, by sintering Si3N4 with desirable additive(s), with a residual glassy or partly crystalline grain boundary phase. The fracture process in such a microstructure is predominantly intergranular, the cracks tend to follow a tortuous path. However, the presence of an intergranular glassy phase causes rapid deterioration of properties at temperature above the glass transition temperature. Therefore, in order to improve high-temperature properties of these ceramics it is desirable to minimize, and if possible to eliminate, the intergranular glassy phase. Particle coating techniques are receiving increasing attention as they are convenient ways of incorporating sintering aids/dopants more uniformly than conventional powder blending method.

After the discovery of C fullerenes and C nanotubes grown in the vapor phase, the formation of carbon onions [1] in the condensed phase from the irradiation of graphitic polyhedral particles with an intense electron beam gave further evidence that spherical carbon network can be favored under high temperature and strong irradiation regimes. Recently, BN and B-C-N hybrid nanotubes were synthetized. In spite of theoretical predictions, so far there has been no experimental evidence for the stability of B-N and B-C-N analogs of buckminster fullerenes. We exposed turbostratic BC2N and turbostratic BN samples to intense electron irradiation to study the ability of the honey comb network to include non hexagonal member rings and form curved structures.

In the experiments described here, the BC2N starting materials were synthesized from vapor phase reaction (CVD) of BC13 and CH3CN. Such samples were then exposed to high temperature-high pressure (HT-HP) conditions at 7.7.

Nickel ferrite (NiFe2O4) thin films are of potential interest for magnetic applications. In the present study, the production of NiFe2O4 by solid-state reaction between thin films of hematite (α-Fe2O3) and nickel oxide (NiO) on (0001) sapphire (α-Fe2O3) substrates has been examined. The NiFe2O4 thin films were prepared by two different methods. In the first case the NiFe2O4film was grown in situ in the deposition system, while in the second case the NiFe2O4 film was formed ex situ by reacting at elevated temperatures in air. These two methods of reaction lead to interesting morphological differences in the ferrite layers.

Epilayers of α-Fe2O3 followed by NiO were deposited onto (0001) α-Al2O3 by pulsed-laser deposition (PLD) in 6 mTorr O2. NiFe2O4 films were obtained by reacting the starting films in two different ways: in situ (during film growth) and ex situ.. In both cases, the α-Fe2O3 films were grown under the same conditions while those for the deposition of the NiO layers were different.

The {001} surface of magnesium oxide (MgO) has been the focus of numerous studies, which were prompted by the importance of MgO for its use as a substrate for thin film growth and also as a chemical catalyst. In the present work, atomic force microscopy (AFM) was used for studying the dynamics of surface processes of MgO which occur at elevated temperatures. AFM was chosen, in part, because it allows for imaging of topographical details at the atomic level with minimal sample preparation. Additionally, because the surface morphology of the same area was traced through a series of heat treatments, scanning electron microscopy analysis would be difficult because no conductive coating could be used (such a coating may have altered the surface between subsequent heat treatments).

AFM images were recorded in contact mode, in air, on a Nanoscope III (Digital instruments, Santa Barbara, CA) using Si3N4 cantilevers (Ultralevers, Park Inst., Sunnyvale, CA) with a nominal applied force of 10-15 nN.

SiC fibers fabricated by chemical vapor deposition (CVD) methods are being used as reinforcement for metal and ceramic matrix materials because of their high modulus, high strength and good corrosion resistance. These fibers have a complex composite microstructure consisting of a pyrolytic-carbon coated graphite core and a SiC sheath which is often protected by a single or a double layer of carbon-rich coating. Commercially available SCS-6 SiC fibers with a diameter of ˜ 140 μm have been most widely in use for composite fabrication. However, with an ever increasing demand for thinner and stronger fibers, an experimental SiC fiber with a diameter of ˜ 50 μm and having a C-rich SiC sheath was developed by Textron Specialty Materials. The as-fabricated tensile strength of this fiber was found to be ˜ 6 GPa, which is ˜ 50 % higher than that of the SCS-6 fiber.While the room temperature tensile strengths of these fibers heat treated for 1 h in Ar to temperatures ≤ 1600° C were better than those of the SCS-6 fiber, strength of the 2000° C heated fibers decreased to < 1 GPa.

Mixed-conducting oxides with appropriate values of electronic and ionic conductivity have the potential to be used as ceramic “membranes” for the separation of oxygen from other gases. The separation is based on oxygen transport from an O2-rich, and hence oxidizing, gas reservoir on one side of the membrane to an O2-lean, and hence reducing, take-up reservoir on the membrane's other side. The oxide Sr(Co1-xFex)O3-δ (SCFO), which has a cubic perovskite structure, is one such potential membrane material. Although the permeation flux of oxygen through SCFO membranes has been mea-sured, the microstructural evolution of SCFO membranes during permeation has been little studied in comparison to other potential membrane oxides. Several of these other systems do show segregation and/or decomposition phenomena that potentially may affect membrane properties. Here we report preliminary results of a systematic microanalytical study of SCFO membranes using scanning electron microscopy and microanalysis in an electron probe microanalyzer (EPMA), as well as transmission electron microscopy in an analytical TEM.

A titanate-based ceramic waste form, rich in phases structurally related to zirconolite (CaZrTi2O7), is being developed as a possible candidate for immobilizing excess plutonium from dismantled nuclear weapons. The waste form is made by cold pressing and sintering of CaO, TiO2, ZrO2, A12O3, BaO, and Gd and Pu oxides. A prototype Pu-loaded ceramic that is being tested contains Pu,Gd-zirconolite-(3T), Pu-bearing brannerite, Gd-zirconolite-(4M), zirconolite-(2M) (see Figure 1), rutile (TiO2), Gd-bearing perovskites, various aluminotitanate phases, and undissolved plutonium oxide. Evidence from laboratory testing and natural analogues of titanates suggests that these phases are extremely corrosion resistant. Zirconolite-rich ceramics have also been considered for the disposal of actinide-bearing waste streams, because zirconolite and related polytypes are able to incorporate at least 20 wt% of actinides. However, since each phase in the multiphase ceramic corrodes at a different rate, the release of any one component or the corrosion of the bulk waste form is difficult to predict

Cathodoluminescence (CL) is the luminescent emission from a material which has been irradiated with electrons. Cathodoluminescence microanalysis (spectroscopy and microscopy) in an electron microscope complements the average defect structure information available from complementary techniques (e.g. Photoluminescence, Electron Spin Resonance spectroscopy). CL microanalysis enables both pre-existing and irradiation induced local variations in the bulk and surface defect structure to be characterized with high spatial (lateral and depth) resolution and sensitivity. This is possible as electron beam parameters such as the beam energy, may be varied to finely control the penetration depth of the incident electrons and hence the local volume of specimen probed.

Irradiation with charged and neutral energetic radiation produces defects in radiation sensitive materials. The energetic electron beam in an electron microscope may also induce defects in the specimen. Cazaux has characterized the electric field produced by electron irradiation of a insulator with a conductive surface coating

Cathodoluminescence (CL) Microscopy (imaging) and Spectroscopy in a Scanning Electron Microscope enables high spatial resolution, high sensitivity detection of defect centers in materials. Cathodoluminescence microanalysis has been used to investigate the irradiation sensitive defect structure of Types I, II, III and IV amorphous silicon dioxide SiO2 (quartz and silica glasses). The CL experiments were performed in a JEOL JSM 35C SEM equipped with Oxford Instruments liquid N and liquid He cryogenic stages, and an Oxford Instruments MonoCL cathodoluminescence imaging and spectral analysis system. The observed CL emissions, were excited with a stationary electron beam at normal incidence and corrected for total instrument response. The corrected CL spectra were fitted with a multiparameter Gaussian function using a non linear least squares curve fitting algorithm and were identified with particular defect structures. The CL emission from high quality pure amorphous silica and quartz glasses is dominated by intrinsic processes (associated with the host lattice). See Table 1.

The research in biological hard tissues offers lessons for biomimetic (structure and processing) strategies, such as for the synthesis of hierarchical architectures tailored for specific engineering applications. These biocomposites, i.e., biogenic materials in which the major phase is an inorganic component associated with macromolecules (proteins and polysaccharides), include bones, dentin, sea-urchin skeletal units, bacterial and algal particles and molluscan shells. Here, a summary is given from a recent TEM study of the interfacial region of nacreous and prismatic sections of red abalone shell to understand the morphological and crystallographic correlations across this transition region.

Many mollusk species have shells made of CaCO3 in various architectures that have evolved under different ecological conditions to produce structures that best protect the organism. The shells of many species contain both aragonite (orthorhombic, Pmnc) and calcite (Rhombohedral, R3m). In red abalone (Haliotis rufescens), the outer section, prismatic (P), is composed of columnar crystallites of calcite (1-5 μm base, 5-10 μm height), and the inner section, nacre (N), is composed of pseudo-hexagonal platelets of aragonite (side 2-5 μm), stacked as 0.25 μm layers, separated by a few nm-thick organic layer (Fig. 1).

Since the early 1980s, Se toxicity in wildlife has created a great deal of interest and concern. Reservoirs, marshes, and wetlands in which excessive amounts of Se have been found are considered to be the source of their toxicity problems. Thus, an effective and inexpensive treatment of Se-contaminated waters which significantly lowers the concentration of this element is needed. One such method for removing selenites and selenates from water utilizes iron (II) hydroxide as a reducing agent. In this work, the reduction products are analyzed in the transmission electron microscope (TEM) using electron diffraction and energy-dispersive spectroscopy (EDS) to determine the presence of Se.

A “standard” aqueous solution was prepared by the addition of KOH to distilled water to pH 8.8. Sufficient quantities of Na2SeO3 or Na2SeO4 were weighed and dissolved in the “standard” solution to yield SeO3-2 or SeO4-2 ions. A weighed quantity of Fe(NH4)2(SO4)2 was then added to the SeO3-2 or SeO4-2 “standard” solution to form a precipitate of iron hydroxide.

Chromite mined from the Great Dyke in Zimbabwe is used for the production of about 180 000 tonnes of ferroalloy per annum, equivalent to about 6% of the world’s supply. The chemical and physical characteristics of the ores, which vary even within the same seam, affect the carbon content of the ferroalloys and hence their commercial value. The purpose of this study is to examine some of the differences between two extremes of chromitites, sheared and unsheared, used in the ferroalloy industry in Zimbabwe to provide a better understanding of the factors that influence the composition of the alloys as a basis for process mineralogy.

The ores consist of chromium spinels (MgAlCrFe)3O4 with a lattice of alternating non-equivalent planes of tetrahedrally coordinated A sites and octahedrally coordinated B sites. The distribution of five major cations (Mg2+, Al3+, Fe2+, Fe3+ and Cr3+) was examined by the technique of electron channelling.

A high water to cement ratio in concrete produces excessive porosity in the paste, thereby increasing the concrete’s susceptibility to sulfate attack and subsequent premature deterioration. Widely used as a building material, concrete experiences physical and chemical deterioration whose extent and nature may be determined by polarized light microscopy (PLM) and scanning electron microscopy (SEM). New software innovations allow exact image relocation in PLM and SEM, thereby producing complementary information which aids in analyst recognition and increases the effectiveness of each analytical technique.

Although overlapping information may be derived using both PLM and SEM, each technique has inherent advantages and disadvantages which complement the other. The advantages of PLM include a color image, good low magnification resolution providing a bridge between macro/micro analysis, and the ability to distinguish polymorphs and materials of nearly identical composition (e.g., solid-solution series components). Disadvantages of PLM include limited high magnification potential, mineralogical identification based on the analyst’s knowledge of optics, and the need for photographic attachments.

The objective of this study was to simulate the aqueous corrosion of the nuclear waste glass over extended periods of time using vapor phase alteration by which reaction progress of glass corrosion is accelerated to form a characteristic suite of secondary alteration phases. In this study, extensive SEM/EDS, AEM, and HRTEM have been performed on the French SON68 waste glasses which were reacted in saturated water vapor at 200 °C for 908, 1013, and 1021 days, respectively. In order to study chemistry and microstructure of surface layers, TEM specimens were prepared in cross-section using the ultramicrotomy slicing technique. In this process, small chunks containing the surface layer and a thin layer of unaltered glass were broken off from the sample surface and each of these chunks was then embedded in resin to form a block. Finally, thin sections, approximately 50-90 nm thick, were microtomed from these blocks and were transferred to holey carbon coated copper grids.

Previous TEM study of natural Amelia albite (Ab99.3An0.1Or0.6) isothermally annealed at 1073°C for various periods revealed distinct tweed microstructures from the intermediately disordered albite samples (intermediate albite), but not from both the natural sample (low albite) and the highly disordered samples (high albite).1 These tweed microstructures seemed to correlate well with the degree of peak broadening and distortion in corresponding conventional powder X-ray diffractograms. Previous XRD, synchrotron radiation and TEM studies on the annealed albite samples at 1080°C for various periods gave rise to similar results.

Reinvestigation of the annealed albite samples with distinct tweed microstructures by TEM confirmed their existence in wide areas, giving two-directional streaking in the corresponding SADP’s (Fig. 1 and 2). Tweed directions are roughly perpendicular to and parallel to the trace of albite twin plane, {010}, as shown in Fig. 3. This tweed microstructure is apparently unaffected by the twinning and probably formed after it.