The reaction kinetics for the formation of mullite (3Al2O3 · 2SiO2) from sol-gel derived precursors were studied using dynamic x-ray diffraction (DXRD) and differential thermal analysis (DTA). The reaction kinetics of diphasic and single phase gels are compared and different reaction mechanisms are found for each gel. Mullite formation in the diphasic gel exhibits an Avrami type, diffusion-controlled growth mechanism with initial mullite formation temperatures of about 1250 °C and an activation energy on the order 103 kJ/mole. On the other hand, mullite formation from the single phase gel is a nucleation-controlled process with an initial formation temperature of 940 °C and a much lower activation energy of about 300 kJ/mole.

We review our field investigations of construction materials which were initiated after the 1985 Mexico City earthquakes. We report observations on reinforcing steel samples collected in the ruins of collapsed buildings and describe the experiences in the production and testing of HSLA steel reinforcing bars with mechanical and metallurgical properties suitable for earthquake resistant construction. We review some aspects of the cement and concrete industries of Mexico before 1985 and present a description of the properties of polymer modified cements considering the potential not only for construction but for many other applications.

The local structure of barium-aluminofluorophosphate (Ba–Al–P–O–F) glasses was investigated using high resolution magic-angle sample spinning nuclear magnetic resonance (MASS-NMR) spectroscopy. The 27Al spectra show three different aluminum environments [Al(4), Al(5), and Al(6)] in these glasses. Changes were observed due to the addition of fluorine and nitrogen. 31P results indicate only one type of phosphorus environment which shifts with fluorine additions. The 19F spectra suggest that fluorine has both Ba and Al as nearest neighbors.

Compressive behavior of an open cell, porous ceramic has been examined and compared to a prior theoretical model. The study involved (i) microstructural characterization, (ii) crushing strength and Young's modulus measurements, and (iii) construction of a deformation-mode map. Initially, the crushing behavior was found to be different than predicted theoretically. Weaker struts throughout the material fractured during the loading and this damage was accumulated until a macroscopic crack or cracks propagated through the material at the crushing stress. Further work showed the discrepancy was related to the uniformity of loading in these porous materials. The use of compliant faces on the loading rams improved the loading uniformity, leading to a substantial reduction in the experimental scatter and increasing the likelihood of unstable crack propagation events rather than damage accumulation. Both crushing strength and Young's modulus were found to be dependent on cell size, but this was considered to be a result of strut cracking at the smallest cell size. A deformation-mode map was constructed using the average stress/strain values at critical points such as the onset of crushing, the minimum crushing stress, and the densification stress. Although some of the details of the deformation map were different from that expected theoretically, the map did appear to be a useful guide to the compressive behavior.

The structural and magnetic properties of the stage 2 CocNi1−cCl2- and COcFe1−cCl2-graphite intercalation compounds (GICs) for 0 ≤ c ≤ 1 have been studied by x-ray scattering and dc magnetic susceptibility. The stage 2 CocNi1−cCl2-GICs approximate two-dimensional randomly-mixed ferromagnets with XY spin symmetry. The average effective magnetic moment Peff, the Curie-Weiss temperature θ, and the paramagnetic-to-ferromagnetic phase transition temperature Tc have been determined as continuously varying functions of Co concentration c. They indicate that the Co2+ and Ni2+ spins are randomly distributed on the triangular lattice sites of each intercalate layer. They also show that the intraplanar exchange interaction J(Co–Ni) between the Co2+ and Ni2+ spins is enhanced and is larger than the interaction J(Co–Co) between two Co2+ spins and J(Ni–Ni) between two Ni2+ spins. This enhanced interaction, J(Co–Ni), can be expressed as J(Co–Ni) = 1.28 [J(Co–Co) · J(Ni–Ni)]1/2. The stage 2 CocFc1−cCl2-GICs approximate two-dimensional randomly mixed ferromagnets with competing spin anisotropy. The dc magnetic susceptibility results suggest that Co2+, Fe3+ rather than Fe2+ are distributed in the intercalate layer. The repeat distance along the c-axis (d-spacing) versus Co concentration deviates from Vegard's law which states that the d-spacing is proportional to Co concentration. The broad peak of d-spacing observed at c = 0.75 is discussed in terms of the double layer model developed by Jin and Mahanti.

Since the characteristics of the electrode made from Ag paste greatly affect the dielectric properties of (Nb, Ba) doped TiO2 ceramics, the processing condition, i.e., baking temperature, was investigated. Low melting glass binder contained in Ag paste reacted with TiO2 ceramics to form an interface layer between Ag electrode and TiO2 ceramics during baking. The interface layer was identified as Bi2Ti2O7 by x-ray diffraction (XRD), and the thickness of the Bi2Ti2O7 layer was estimated from line profiles of EPMA and dielectric properties. The interface layers were found to increase with baking temperature. Increased baking temperature lowered the relative dielectric constant and dielectric dissipation factor of TiO2 ceramics, while it raised the resistivity. Controlling the baking condition of the Ag paste electrode on TiO2 ceramics resulted in reasonably good dielectric properties and excellent temperature stability.

Amorphous fluoride powder in the ZrF4-BaF2-LaF3-AlF3 (ZBLA) system has been prepared by a direct chemical route from metal alkoxides by reaction with bromine trifluoride. The potential of bromine trifluoride as a solvent for use in sol-gel synthesis of fluoride glass is discussed.

Single shot pulses from a Nd:YAG laser have been used to generate different sized holes and patterns in unfired ceramic sheets for electronic packaging applications. The single shot laser pulses were targeted using a computer controlled deflection system and a programmed pattern. With changes in pulse energy level and profile, the laser beam was also used to sinter line patterns in deposited thin and thick films. The surface radial temperature profile resulting from the laser pulse interaction was also directly mapped using a lacquer thermocoat. Effects of the laser pulse energy and beam spot size on laser/ceramic interactions, morphology, and structure of the drilled holes before and after sintering were examined by SEM. High quality hole patterns (of ∼100 μm hole size) were produced in unfired 100 μm thick ceramic sheets up to 100 μm thick using single shot of laser irradiation with 8 mJ pulse energy and 18 nsec pulse duration.

Results of crack growth observations on mica in water-containing environments are described. The study focuses on equilibrium crack states for reversed loading cycles, i.e., for initial propagation through virgin solid and subsequent retraction-repropagation through healed or misoriented-healed interfaces. Departures from these equilibrium states are manifest as steady-state forward or backward crack velocities at specific applied loads. The equilibria are thereby interpreted as quiescent, threshold configurations G = WE, with G the Griffith mechanical-energy-release rate and WE the Dupré work of adhesion, on crack velocity (v-G) diagrams. Generally, WE is found to decrease with concentration of water, in accordance with a Gibbs formalism. Hysteresis is observed in the forward-backward-forward crack propagation cycle, signifying a reduction in the adhesion energy on exposure of the open interface to environmental species prior to healing. This hysteresis is especially marked for those interfaces that are misoriented before healing, indicating that the structure of the underlying solid substrate as well as of the intervening fluid is an important consideration in the interface energetics. The equilibrium states for different environments can be represented on a simple energy-level diagram, as differences between thermodynamic end-point states: initial, closed-interface states refer to crystallographic bonding configurations ahead of the crack-tip adhesion zone; final, open interface states refer to configurations behind the crack-tip zone. The significance of this diagram in relation to the fundamental atomic structure of interfaces in fracture and other adhesion geometries, including implications concerning kinetics, is discussed.

Precipitation of calcium carbonate from hydroxyethyl cellulose (HEC) containing aqueous solutions of CaCl2 and Na2CO3 resulted in an uncommon polymorph, vaterite. In contrast to precipitations without HEC, crystallization in the presence of HEC led to a shell-shaped body consisting of organized vaterite platelets. The artificial shell is a composite of stacks of vaterite and about 2% HEC. In the experimental arrangement used, HEC controlled both nucleation and crystal growth of vaterite. Concentration of HEC also affected the platelet's thickness which in turn influenced the shell's morphology as well. These results demonstrate the importance of organic-inorganic interface in controlling crystallization.

The crystal structure of Na2Al2Ti6O16 was refined by the Rietveld method using synchrotron radiation and conventional x-ray powder data, and the agreement factors were Rp = 3.35%, Rwp = 4.30%, and RBragg = 6.39% for synchrotron data. The formula based on the chemical analysis and 16 O atoms is Na1.97Al1.82Ti6.15O16. The crystal data are monoclinic, C2/m, a = 12.1239(3) Å, b = 3.7749(1) Å, c = 6.4180(2) Å, β = 107.59(1)°, V = 280.00(4) Å3, Z = 1, and Dx = 3.82 g cm−3. The site occupancy refinement showed a partial ordering of Al3+ and Ti4+ ions in the two-crystallographically independent octahedral sites.

Three series of cordierite powders were prepared by the sol-gel route: a single phase (monophasic) gel prepared from alkoxides, a nominally triphasic nanocomposite gel made with two nanosized powders and one solution phase, and a truly compositionally triphasic nanocomposite gel prepared from three nanosized powders. Crystalline α-cordierite seeds were also incorporated with the gels and their effectiveness as nucleating agents was investigated and found to lower the crystallization temperature of α-cordierite by 125–150°C. The densification behavior of powder compacts was examined and alterations made to the heat treatment until optimum conditions were found. The truly triphasic compact sintered at 1300°C for 2 h resulted in 100% of theoretical density whereas the nominally triphasic and monophasis pellets densified to 96% and 80%, respectively. The enhanced densification achieved with powder compacct prepared for triphasic nanocomposite gels is due to part to the excess free energy of the three components.

Alkali-metal-graphite intercalation compounds (alkali-metal-GIC's) absorb hydrogen in two ways: physisorption and chemisorption. Hydrogen uptake through the physisorption process occurs at low temperatures below about 200 K in higher stage alkali-metal-GIC's, where hydrogen molecules are stabilized to form a two-dimensional condensed phase in the galleries of the graphite sheets. The concentration of absorbed hydrogen molecules is saturated at a rate of H2/alkali metal atom ∼2. The hydrogen physisorption shows a strong isotope effect and a swelling effect on c-axis lattice expansion. In the case of hydrogen uptake through the chemisorption process, dissociated hydrogen species are stabilized in the intercalate spaces. The activity of the chemisorption increases in the order Cs < Rb < K. The introduction of hydrogen generates a charge transfer from the host alkali metal GIC's to the hydrogen since hydrogen has strong electron affinity. The hydrogenated potassium-GIC's have intercalates consisting of K+-H−-K+ triple atomic layer sandwiches which are inserted between metallic graphite sheets. The inserted two-dimensional hydrogen layer is suggested to consist of H ions with a weakly metallic nature. The superconductivity of the hydrogenated potassium-GIC is also discussed in terms of the change in the electronic and lattice dynamical properties by hydrogen uptake. The hydrogen-absorption in alkali-metal-GIC's is an interesting phenomenon in comparison with that in transition metal hydrides from the point of hydrogen storage. The hydrogen-alkali-metal-ternary GIC's obtained from hydrogen absorption have novel electronic properties and lattice structures which provide attractive problems for GIC research. The studies of hydrogen-alkali-metal ternary GIC's are reviewed in this article.

The evolution of atomic composition, atomic depth distribution, and structural states of La(OH)3/Cu bilayers prepared by electron gun evaporation and submitted to ion beam irradiation is described. Chemical reactivity of La with O and H is evidenced in the initially deposited La/Cu bilayer, despite the fact that the pure La layer is coated with a thick Cu layer. Ion beam mixing with energetic Au ions, at 300 K and 700 K, results in breaking down the La–O–H bonds, while Cu atoms are knocked into the layer. There is a depth redistribution of the different atomic species, with formation of nonidentified phases.

Raman spectra were taken of 48 polycrystalline diamond films grown by hot-filament and microwave-plasma chemical vapor deposition (CVD), and one gem-quality diamond, and characterized by fitting the spectra to a model line shape function. The line shape function contains three components: a narrow symmetric line at ∼1333 cm−1, the Raman line of diamond; a band centered at ∼1525 cm−1 ascribed to sp2-bonded carbon; and a broad background due to photoluminescence (PL). Four spectral parameters were observed to change from one specimen to another in an interrelated manner: (1) the linewidth of the diamond Raman line, which varies from ∼3 to ∼25 cm−1; (2) the intensity in the tails of the diamond Raman line, several halfwidths away from the peak; (3) the peak intensity ratio of the sp2-bonded carbon band to the diamond Raman line, which varies from ∼0 to ∼1; and (4) the intensity ratio of the PL background to the diamond Raman peak, which varies from ∼0.03 to ∼9. We suggest that the interrelated changes in the Raman spectra are due to changes in the abundance of sp2-bonded defect structures within the diamond crystallites. Polynuclear aromatic clusters are a possible model for these defect structures. Differences in film morphology, which were observed by SEM imaging, appear to be correlated with the changes in the Raman spectra. The peak position of the diamond Raman line is shifted to higher wave number in the CVD-grown films than in the gem, by as much as 3 cm−1, but this shift is not correlated with the other changes in the Raman spectra. As a function of deposition conditions, the defect-related features of the Raman spectra generally increase with increasing methane concentration or substrate temperature, and decrease with increasing oxygen concentration. A cyclic dependence of the defect-related features on deposition time is observed for one set of films grown by hot-filament CVD.

The adhesion forces and interaction potentials between two mica surfaces as a function of the orientation (twist angle) of their surface lattices are reported. The forces were measured in air, in water, and in an aqueous KCl solution where oscillatory structural forces are present. In air, the adhesion is relatively independent of the twist angle θ in the range −10° < θ < +10° due to a 0.4 nm thick amorphous layer at the interface. In water, apart from a relatively angle-independent baseline adhesion, a sharp adhesion peak (energy minimum) occurs at θ = 0°, corresponding to maximum alignment of the surface lattices. As little as ±1° away from this peak the energy decreases by 50%. In aqueous KCl solution, due to potassium ion adsorption the water between the surfaces becomes ordered, resulting in an oscillatory structural force where the adhesive minima occur at discrete separations corresponding to an integral number of water layers. The adhesion energies corresponding to the first three potential minima were angle dependent near θ = 0° (again decreasing by 50% at ±1° away from θ = 0°). The repulsive maxima were also affected near θ = 0°. The results show that the whole interaction potential between two surfaces in liquids depends on the orientation of the surface lattices, and that these effects can extend at least four molecular layers. We discuss the consequences of these findings for material properties such as grain boundary energies, cracks, and friction.

The applicability of models based on fractal geometry to length scales of nanometers is confirmed by Fourier analysis of scanning tunneling microscopy images of a sputter deposited gold film, a copper fatigue fracture surface, and a single crystal silicon fracture surface. Surfaces are characterized in terms of fractal geometry with a Fourier profile analysis, the calculations yielding fractal dimensions with high precision. Fractal models are shown to apply at length scales to 12 Å, at which point the STM tip geometry influences the information. Directionality and spatial variation of the topographic structures are measured. For the directions investigated, the gold and silicon appeared isotropic, while the copper fracture surface exhibited large differences in structure. The influences of noise in the images and of intrinsic mathematical scatter in the calculations are tested with profiles generated from fractal Brownian motion and the Weierstrass-Mandelbrot function. Accurate estimates of the fractal dimension of surfaces from STM data result only when images consist of at least 1000–2000 points per line and 1/f-type noise has amplitudes two orders of magnitude lower than the image signal. Analysis of computer generated ideal profiles from the Weierstrass-Mandelbrot function and fractional Brownian motion also illustrates that the Fourier analysis is useful only in determining the local fractal dimension. This requirement of high spatial resolution (vertical information density) is met by STM data. The fact that fractal models can be used at lengths as small as nanometers implies that continued topographic structural analyses may be used to study atomistic processes such as those occurring during fracture of elastic solids.

The single crystal growth of boron phosphide (BP) by employing the high pressure flux method and chemical vapor deposition (CVD) process is described together with characterization of the prepared BP and its electrical, thermal, semiconducting, and electrochemical properties. BP single crystals prepared by the high pressure flux method contain copper used as the flux, but they are promising for photocathode materials. BP single crystalline wafers prepared by the CVD process using Si wafer substrate contained autodoped silicon with the concentration of 1018−1020 atoms·cm−3, depending on the growth temperature and the substrate plane. The Si atoms which act as acceptors are incorporated at phosphorus sites in BP. The lattice constants determined by the Bond method explain the conduction type of BP. Some electronic transport properties such as donor and acceptor levels and lattice scattering process before and after thermal neutron experiments are clarified. The thermal conduction is limited by three-phonon processes. The formation of defects by thermal neutron irradiation and that of structural disorder by ion-irradiation are mentioned. Schottky diodes consisting of n–BP and Sb or n–BP and Au, which are denoted as n–BP–Sb and –Au, respectively, show excellent characteristics, and their barrier heights are independent of metals and two-thirds of energy bandgap, expected from the surface-state model. Finally, recent results on thermoelectric properties of sintered specimens are mentioned.

A conventional microhardness tester has been instrumented with a piezoelectric load cell and capacitance displacement gages to measure load and displacement during indentation. As in other recently-developed load and displacing sensing indentation instruments, the new device can be used to measure a variety of mechanical properties, but has the advantage of being relatively inexpensive to assemble since many of its components are standard equipment. Tests were performed on soda-lime glass and an aluminum alloy, demonstrating the diversity of material elastic-plastic responses under indentation, particularly in the unloading cycle. The data suggest that models of elastic unloading based on invariant indenter-surface contact area may not be general, and may lead to underestimates of hardness and modulus.