A nanoscale and pure, olivine-structured LiFePO4 was synthesized at ∼300 °C using an organic–inorganic steric entrapment method. Normally, when calcined and crystallized in air, this method leads to the synthesis of compounds where the cations are in their highest oxidation state. However, in this study, we found a way to produce compounds having lower oxidation states (e.g., compounds containing Fe2+), which may have wider applications in the synthesis of other compounds with complex chemistry that have variable oxidation states and, therefore, potential applications in electronic ceramics. The resulting LiFePO4 or (Li2O·2FeO·P2O5) was characterized by thermogravimetric analysis/differential thermal analysis, x-ray diffractometry, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma emission spectroscopy, specific surface area by Brunauer–Emmett–Teller nitrogen absorption, and particle size analysis.

Fine grained, three-phase ceramic composites that exhibit favorable toughness, hardness, and high room-temperature strength were evaluated for high-temperature mechanical stability. A 50vol%Al2O3–25vol%NiAl2O4–25vol%3 mol%yttria-stabilized tetragonal zirconia polycrystal (3Y–TZP) and a 33vol%Al2O3–33vol%NiAl2O4–33vol%3Y-TZP composite were compression creep tested at temperatures between 1350 and 1450 °C under constant stresses of 20–45 MPa. The three-phase microstructure effectively limited grain growth (average d0 = 1.3 μm, average df = 1.6 μm after 65% true strain). True strain rates were 10−4 to 10−6 s−1 with stress exponents n = 1.7 to 1.8 and a grain-size exponent p = 1.3. A method for compensating for grain growth is presented using stress jump tests. The apparent activation energy for high-temperature deformation for 50vol%Al2O3–25vol%NiAl2O4–25vol%3Y–TZP was found to be 373 kJ/mol-K.

The high-temperature indentation fracture and microstructures of dysprosium niobate (DyNbO4) were investigated by optical, scanning, and transmission electron microscopy (OM, SEM, and TEM). Polycrystalline samples were sintered at 1350 °C for 3 h and cut into 3 mm disks for TEM. The disks were indented in a Nikon QM (Tokyo, Japan) hot hardness indenter at room temperature up to 1000 °C. Many lamellar twins having different widths were observed by TEM as well as intergranular microcracks. The room temperature hardness was relatively low at 5.64 GPa and decreased with elevated temperatures. Crack lengths were short, showing a typical micro-cracking effect. In the sample indented at 1000 °C, dislocations in periodic arrays were evident, and their density increased markedly due to heavy plastic deformation.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Nanoscale ceramic particles, such as layered double hydroxides (LDHs), have been developed to deliver drugs or genes into biological cells. In this article, we describe the controlled-release properties of LDHs as drug delivery carriers, the formation of bio-LDH nanohybrids, their in vivo and in vitro cytotoxicity tests, and their potential as anticancer gene delivery carriers. Unstable biomolecules can be intercalated into LDHs, displacing the interlayer anions; the drug or gene's negative charge is thus shielded, enabling penetration into the cell. In the slightly acidic environment of the cell, ceramic nanoplatelets of ∼100 nm diameter dissolve, thus releasing the intercalates in a controlled manner.

Phase transformations in synthetic hexacelsian were investigated by hot-stage transmission electron microscopy. A second phase transformation from an orthorhombic to hexagonal structure was identified in the synthetic hexacelsian at approximately 700 °C. The hexacelsian was found to exhibit a sequence of phase transformations on heating of hexagonal (P63/mcm)–orthorhombic (Immm)–hexagonal (P6/mmm). Antiphase domain boundaries, which were observed in P63/mcm and Immm phases, were absent in the P6/mmm phase. Crystal symmetries of the three phases were determined by convergent beam electron diffraction, and space group symmetries were derived by comparison of experimental selected area electron diffraction patterns with computer-simulated patterns.

Mullite (3Al2O3•2SiO2) exists in a solid solution field (∼57-63 mol% Al2O3) as the only stable compound in the Al2O3•SiO2 phase diagram at ambient pressures. Equilibrium 3:2 mullite has an orthorhombic structure with b>a (o-mullite). However, when initially crystallized from molecularly mixed, 3:2 precursors at temperatures < 1200°C, the first phase that forms has lattice parameters with a ≈b. This structure is often termed pseudotetragonal mullite (pt-mullite), since even when the ‘a’ and ‘b’ lattice parameters are identical, they are symmetrically independent. Pseudotetragonal mullite has been shown to contain approx. 70 mol% Al2O3. with increasing time and temperature, the structure gradually assimilates the residual SiO2, and the lattice parameters change, such that by 1400°C, the material has attained its equilibrium structure and composition.

TEM was used to determine the spatial relationship between the crystalline phase and the residual, amorphous, SiO2-rich phase in pt-mullite. The starting materials were quenched, 3:2 mullite beads and fibers (made by containerless processing).

The kinetics and pathways for crystallization of solid, amorphous, yttrium aluminum garnet (YAG) were studied using isothermal differential thermal analysis, x-ray diffraction, and transmission electron microscopy. The activation energy for crystallization was 437 KJ/mol and the measured Avrami exponent was 2.74, which corresponded to three-dimensional crystal growth with a constant number of nuclei. Time–temperature–transformation (T–T–T) curves were developed from the data to predict crystallization rates as a function of temperature. The crystallization pathway for YAG in this system is compared to others reported in the literature.

Recent progress in the crystallization of amorphous mullite (3Al2O3•2SiO2) and yttrium aluminate (Y3Al5O12, 5Al2O3•3Y2O3 or “YAG”) beads and fibers is reviewed. Studies were made by differential thermal analyses, (DTA, DSC), synchrotron X-ray diffraction and Rietveld profile fitting, HREM, EDS and SEM. Crystallization kinetics, activation energies and microstructures were determined, leading to temperature-time-transformation (T-T-T) curves. The crystallization of mullite from the solid state proceeds by formation of large-grained, pseudo-tetragonal mullite of composition 70 mol% Al2O3, which is highly strained and which contains <10 nm silica-containing inclusions. During further heat treatments, the inclusions react with the first-formed mullite yielding single phase, orthorhombic mullite of 60 mol% Al2O3. Recrystallization also occurs on further heating with a significant reduction of grain size, in a manner similar to recrystallization in brass. These observations (using more modern and sensitive characterization techniques) suggest the presence of a peritectic-like, syntectic or syntectoidal invariant reaction in the Al2O3-SiO2 phase diagram. Further work needs to be done to ascertain whether the reaction is an equilibrium or non-equilibrium phenomenon.

A polymerized organic–inorganic complexion route is introduced for the synthesis of yttrium aluminum garnet, YAG (Y3Al5O12) and cordierite (Mg2Al4Si5O18) powders. Long-chain polymers such as polyvinyl alcohol (–[CH2–CHOH]-n or PVA) or polyethylene glycol (H[O–CH2–CH2]nOH or PEG) were used as the organic carriers for a precursor ceramic gel. Calcined powders were very porous and homogeneous in distribution of components. Experimental studies by differential thermal analysis and thermogravimetric analysis, x-ray diffraction, solid-state nuclear magnetic resonance, and Fourier transform infrared spectrometry indicated that metal-ion chelation is not the primary mechanism for obtaining molecularly homogeneous precursor powders. Water-soluble cations of mixed oxides in the PVA or PEG process were sterically entrapped in the entangled network and resulted in fine and pure, mixed oxide powders.

The crystallography, microstructures, and phase transformation mechanisms in dysprosia (Dy2O3) have been studied. The lattice parameters of B and C phases were refined by x-ray diffraction (XRD). The modulated structures and decomposed structures in the CaO-doped samples were characterized by transmission electron spectroscopy (TEM). A new twin was observed in the modulated B phase. Contrary to the previous studies, the B to C transformation was induced by grinding. The A to B transformation was considered to be ferroelastic and the spontaneous strain was calculated. The major driving force for the B (monoclinic) to C (cubic) transformation is suggested to be the release of lattice strains and cation charge repulsions in the B structure, which is analogous to the β (monoclinic) to γ (orthorhombic) transformation in Ca2SiO4. This transformation can be displacive, if some conditions are provided to overcome the bonding energy of the interlayer oxygens in the B structure.

The adhesion strength between a low-firing substrate consisting of an alumina/glass composite and a copper thick film was affected by the addition of cupric oxide and glass frit to the copper paste in a new co-firing process. An interlayer, 3–4 μm in thickness, was produced in the metal-ceramic interface during the new co-firing process due to the diffusion of copper. At the same time, the adhesion strength was improved by controlling the cupric oxide content. The addition of about 3 wt.% glass frit (softening point = 670 °C, based on the calcium-barium borosilicate glass composition) to the metal paste resulted in highest adhesion strength of 3 kg/mm2 with a shift of the debonding site toward the ceramic substrate within the interlayer. The shift of the debonding site could be observed by comparing the ratios of Al2O3/Cu and Ca concentration at the test pad areas on the substrate after debonding. The shift of the debonding site is attributed to the migration of glass frit into the interfacial region. The migration of glass frit occurred easily when the softening point of the glass frit was compatible with the new co-firing process, regardless of how much frit was used.

The response of ferroelastic crystals on an applied stress is considered, and a distinction is seen between the reorganization of the domain structure within a grain at low stress and the reorientation of whole grains at high stress. The procedures are modeled in the framework of defect theory, i.e., by twinning dislocations and deformation twinning. The reorganization is controlled by the motion of pre-existing twinning dislocations. Since the Peierls stress of the twinning dislocations is very small, domain reorganization occurs under a very small load. The process of grain reorientation involves the nucleation of dislocations and, therefore, it requires a much higher stress. This concept is confirmed by comparison with experiments.

The decomposition mechanism of hillebrandite (Ca2SiO4 · H2O) to larnite (β-Ca2SiO4) was studied by conventional and in situ hot-stage TEM methods. The hillebrandite structure is suggested to be a composition of parawollastonite (CaSiO3) and portlandite [Ca(OH)2] adjoining on {001} planes. The larnite fibers showed occasional bending and kinking as well as internal defects such as dislocations and domains. No transformation-related microstructures such as twinning were observed. The preferred orientations in the larnite fibers were not distinct. The decomposition mechanism of hillebrandite in air and in a vacuum may be different. In air, the CaO from the decomposed portlandite layer directly participates in the process of SiO4 chain breaking to form larnite. In the TEM this CaO is removed and apparently reprecipitated, so that hillebrandite converts directly to parawollastonite, A possible lattice correspondence between hillebrandite (C2SH) and larnite (β-C2S), based on crystallographic considerations, is proposed to be bC2SH ¶bβ-c2s, αC2SH ¶ ≍[102]β-C2S, and CC2SH ¶ ≍ [401]β-C2S.

Chemical interactions between polyvinyl alcohol (PVA) and triethanol amine titanate chelate were studied using x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The titanate chelate cross coupled the PVA solution and produced a viscous gel. The gel had a three-dimensional network structure containing -CPVA-O-Ti-O-CPVA- organic complexes. A new C(ls) signature at 285.7 eV and an O(ls) signature at 531.25 eV were associated with the formation of these complexes. The water of the PVA solution was physically retained in the gelled structure and was readily available for chemical reactions. The removal of this entrapped water was irreversible and led to a collapsed film of Ti-cross-linked PVA.

Processing of multi-phase ceramic composite materials using chemically bonded ceramics as a binding agent appears to be a promising route for fabricating complex-shaped structures. In a zirconia-calcium aluminate ceramic matrix composite, the hydraulic property of fine, monocalcium aluminate (CaAl2O4) powders was used to prepare strong prefired bodies.

The changes in the physical characteristics of the composite during the conversion from a chemically bonded compact into a sintered composite were studied using thermogravimetric analyses (TGA), X-ray diffraction and scanning electron microscopy. The density and the hardness of the chemically bonded and sintered composite were measured.

Chemically bonded ceramics appear to be a promising alternative route for near-net shape fabrication of multi-phase ceramic matrix composites (CMC's). The hydraulic (and refractory) properties of fine mono-calcium aluminate (CaAl2O4) powders were used as the chemically bonding matrix phase, while calcia stabilized zirconia powders were the second phase material. Samples containing up to 70 wt% (55 vol%) zirconia have been successfully compacted and sintered.

Various processing techniques were evaluated. Processing was optimized based on material properties, dilatometry and simultaneous thermal analysis (DTA'TGA ). The physical characteristics of this novel CMC were characterized by hardness, density, and fracture toughness testing. Microstructures were evaluated by SEM and phase identification was verified using XRD.

Hillebrandite (dicalcium silicate hydrate) was produced by a hydrothermal process. Its crystal structure and microstructures were investigated by conventional TEM and HREM. Most hillebrandite fibers showed their elongation to be parallel to the b axis and tended to lie on the {001} cleavage planes. Selected area diffraction patterns frequently displayed continuous streaking, and corresponding dark-field images revealed stacking disorders perpendicular to the fiber axis. The morphology, stacking disorders, and extinction conditions of {hkO} reflections and hillebrandite resembled those of the minerals wollastonite (CaSiO3) and pectolite (Ca2NaH[SiO3]3). Periodic (100) faulting with a displacement vector 1/2 b is suggested to be the major origin of the streaking and the systematic absences in hillebrandite.

The term “macro-defect-free” refers to the absence of relatively large voids (or defects) that are normally present in conventional cement pastes due to entrapped air or inadequate mixing. A decade ago, Birchall and co-workers developed a novel processing method that avoids the formation of these strength-limiting defects. This method, outlined schematically in Figure 1, consists of mixing hydraulic cement powder, a water-soluble polymer, and a minimal amount of water under high shear to produce a macro-defect-free (MDF) cement composite. Several cement/polymer systems can be processed by this flexible technique, although the calcium aluminate cement/polyvinyl alcohol-acetate (PVA) copolymer system is most common: MDF cements display unique properties relative to conventional cement pastes. For example, the flexural strength of MDF cement is more than 200 MPa as compared to values on the order of 10 MPa for conventional pastes. One can view MDF cements as a type of “inorganic plastic.” As is the case with plastic processing, fillers such as alumina, silicon carbide, or metal powders can be added to MDF cement to modify its performance properties (e.g., abrasion resistance, thermal or electrical conductivity, and hardness). The combined attractiveness of inexpensive raw materials and flexible, low-temperature processing has generated great interest in this new class of advanced cement-based materials.