The structure and physical properties of sodium antimony germanate glasses with compositions 10Na2O − xSb2O3 − (90 − x)GeO2, x = 10−30 mol%, prepared by the melt-quenched route have been studied. It is observed from x-ray diffraction, SEM, density and oxygen molar volume, infrared (IR), differential thermal analysis (DTA), and optical absorption that single phase homogeneous glasses with a random network structure can be obtained in this system. The strength and connectivity of the glass network increase with GeO2 content. The main Ge−O stretching vibration also shifts to higher wavelength side. Two oxidation states of antimony, Sb3+ and Sb5+, are present, while the so-called “germanate anomaly” is absent in these glasses. This study discusses the probable structural reasons behind this type of behavior of these glasses.

Polymeric carbon artifacts are particularly difficult to make in thick section. Heating rate, temperature, and sample thickness determine the outcome of carbonization of resin leading to a glassy polymeric carbon ware. Using wedge-shaped samples, we found the maximum thickness for various heating rates during gelling (300 K–360 K), curing (360 K–400 K), postcuring (400 K–500 K), and precarbonization (500 K–875 K). Excessive heating rate causes failure. In postcuring the critical heating rate varies inversely as the fifth power of thickness; in precarbonization this varies inversely as the third power of thickness. From thermogravimetric evidence we attribute such failure to low rates of diffusion of gaseous products of reactions occurring within the solid during pyrolysis. Mass spectrometry shows the main gaseous product is water vapor; some carboniferous gases are also evolved during precarbonization. We discuss a diffusion model applicable to any heat-treatment process in which volatile products are removed from solid bodies.

Glass microballoons (GB) of about 1 μm in diameter were prepared by ultrasonic spray pyrolysis from sodium silicate solution. A silica-rich type of glass microballoons (SB) was prepared by acid treatment of GB. The structural changes of both microballoons with thermal treatment up to 973 K were examined. Both GB and SB showed properties similar to hydrated sodium silicate glass, to some extent. SB was more thermally stable than GB, but the spherical structures of both microballoons were collapsed by heating at 973 K; cristobalite was observed in samples heated at 973 K. The loosely and tightly incorporated water molecules evolved up to 573 K and near 850 K, respectively. The crystallization of cristobalite caused tightly incorporated water molecules to develop. The ultramicropores accessible only to H2O molecules in SB gradually decreased by heating and disappeared by heating at 773 K.

A recently proposed method for measuring decohesion energy of ductile films on substrates is discussed. The loading mechanism that causes the decohesion of the ductile film is that of gradually depositing an additional layer, with large residual tensile stresses, on top of the film. Hence, the method involves the decohesion of a bilayer film on a substrate. The suggested method assumes that the unloading of the film is controlled entirely by elasticity. This assumption is a prerequisite for the suggested linear elastic analysis, from which the interfacial debond energy is derived in closed form. However, as is shown in the present comment, large scale yielding can occur in the wake of the crack tip and is prohibitive to the suggested linear elastic analysis. A sufficient condition for the occurrence of said large scale yielding is outlined in the present comment. Indeed it is shown that large scale plasticity must have occurred in the experiments described by Bagchi et al.1

Three important polymers: polystyrene (PS), poly ether ether ketone (PEEK), and polyimide Kapton, were irradiated separately with 1 MeV He+, 1 MeV Ar+, and 1 MeV He+ followed by 1 MeV Ar+ sequentially, to a fluence of 3 × 1019 ions/m2 for each ion. The specimens were characterized for changes in surface hardness using a nanoindentation technique, and wear resistance using a reciprocating sliding wear apparatus with a steel ball counterface. Results indicated that while all polymers showed higher hardness values after ion irradiation, the dual irradiation resulted in the largest hardness increase, greater than for the single ion-irradiated specimens. Wear test results also indicated that the dual He+ + Ar+ irradiation resulted in the best improvement in wear resistance of the polymers. These improvements in properties are a consequence of cross-linking of the polymer material caused by the ion irradiation. Linear energy transfer considerations showed that the dual He+ + Ar+ implantation was better because it combined a deeper implant, in the form of He, along with Ar irradiation which resulted in a shallower but more highly cross-linked layer at the near surface. Thus a deeper and graded cross-linked surface region was formed. The study shows that there is greater flexibility for tailoring surface properties of polymers by using a judicious combination of ion species, ion energies, and fluences.

A very high vacuum compatible microwave plasma chemical vapor deposition system has been fabricated for the growth of diamond thin films. Microcrystalline diamond thin films have been grown on silicon substrates from the CH4−H2 gas mixture. Scanning electron microscopy and x-ray diffraction have been used to study the surface morphology and the crystallographic structure of the films. Optical emission spectroscopy has been used for the detection of chemical species present in the plasma. The strong dependence of the film microstructure on the intensity of CH emission line has been observed.

The linear thermal expansion of the bulk amorphous Zr4.12Ti13.8Cu12 5Ni10Be22.5 (atomic percent) alloy has been measured from 80 K to 773 K. The data for T, Tg were fitted by a model based on the Grüneisen relation and a Debye expression for the heat capacity. From the fit, we deduced the Grüneisen parameter, g = 1.25, and the Debye temperature, QD = 400 K. Annealing the amorphous alloy at 663 K, which is between the glass transition temperature Tg = 623 K and the crystallization temperature Tx = 693 K, causes viscous flow in the sample. This is due to the small viscosity in the undercooled liquid.

We present the derivation of the elastic Green's function for an anisotropic bimaterial in a state of plane strain. A Fourier transform method is used to calculate the Green's function. A discontinuity in displacement is permitted across the interface between the two solids. This provides a useful functional form for parameterizing damage along an interface. We show several examples for the form of the displacement discontinuity and calculate the displacement Green's function for each. The Green's function derived here is applicable to a variety of interface problems between two different anisotropic solids or for two similar solids at different orientations.

We have grown Nb-doped TiO2 epitaxial films on (100) and (110)-oriented TiO2 rutile substrates by molecular beam epitaxy. Nb substitutionally incorporates at cation sites in the rutile lattice, forming NbxTi1−xO2 solid solutions. However, the crystal quality and surface roughness of the films depend strongly on the substrate orientation. Surface roughening and defect formation occur at lower values of x on (100) than on (110). This result is due to anisotropic changes in the metal-oxygen bond lengths within the rutile structure in going from TiO2 to NbO2; there are 1% and 12% changes in the metal atom to octahedron-base oxygen and metal atom to octahedron-vertex oxygen bond lengths, respectively. Every metal atom in the (100) growth surface has in-plane components of the 12% mismatch. However, only half of the metal atoms in the (110) growth plane have such components. Thus, there is substantially larger in-plane lattice mismatch when the growth surface is (100) compared to (110), resulting in surface roughening and formation of defects at a lower doping level for (100)-oriented NbxTi1−xO2 epitaxial films.

Silane-coated glass microspheres randomly embedded in an epoxy polymer matrix have been employed as a model system to investigate the degradation of disordered composite materials by water, and to test various models of deformation and fracture. Numerous composites containing sodalime (A) glass in the range 0 to 25% by volume were tested dry and immersed in saturated NaCl at 40 °C for periods up to 70 days before testing. Enhanced osmotic water uptake due to percolating interface damage was observed for composites containing more than 15% glass. The electrical resistance of similar composites filled with conducting spheres confirmed the existence of a percolation transition, though with high resistance values implying no direct contact of the spheres. Tensile measurements conducted on dry material at a nominal strain rate of about 10−3 s−1 showed an increase in elastic modulus and a decrease in the fracture strength with increasing glass content. New detail was apparent in these curves and confirmed by statistical analyses. For wet specimens, in addition to a general embrittlement effect of water absorption, there was a distinct plateau or small peak in fracture strength in the range 9 to 12% glass, and an abrupt drop between 12 and 15%. The plateau can be related to favorable crack interaction effects between disconnected clusters of interfaces just below the percolation threshold. The steep increase in elastic modulus with glass content seen in the dry material vanished entirely in wet material, which behaved like a porous polymer above 6% glass, owing to osmotic interface damage within particle clusters.

Large scale yielding (LSY), in general, has a profound influence on the fracture toughness of metal/dielectric interfaces. For thin metal film/dielectric systems exhibiting “weak” bonding, small-scale yielding (SSY) prevails due to local plastic dissipation intrinsic to crack growth and the high yield strength of metal thin films. For systems involving low yield strength materials and strong interfaces, a more detailed LSY methodology needs to be developed.

When a melt seeded with droplets of a volatile liquid is rapidly decompressed, the droplets explosively vaporize, taking their latent heat of vaporization from the melt and, therefore, homogeneously cooling and expanding it. The possibility of using this dynamic decompression and cooling (DDC) technique for producing an amorphous metallic foam is theoretically investigated. To test the premises of this theoretical model, preliminary experiments with an organic melt (p-terphenyl) seeded with water drops were performed. Results of these experiments demonstrate the potential of this novel approach to materials processing.

The crystallization of amorphous oxides synthesized by pyrolytic decomposition of mixed Li and Ta 2-ethylhexanoates and alkoxides has been investigated. The study was motivated by thermodynamic considerations that, in the light of experience in other systems, suggest the potential for metastable extension of the LiTaO3 homogeneity range. Materials investigated are described by the general stoichiometry Li1–5xTa1+xO3 and include Li2O contents from 0 to 70 mol% (20.18 ≤ x ≤ 0.2). The samples were prepyrolyzed at 400 °C and subsequently crystallized by heat treatments in air at 550–700 °C for 0.1–100 h. The first product of crystallization for compositions from 30 to 65% Li2O is always the LiTaO3 phase. Extensive characterization by x-ray and neutron diffraction, as well as 7Li-NMR spectroscopy, revealed that this phase evolves with a structure and stoichiometry close to equilibrium. For Li+-deficient compositions, excess Ta5+ is rejected to the amorphous constituent during crystallization and eventually gives rise to the evolution of Ta2O5, with the LiTa3O8 phase suppressed in all cases. Similar observations were made for the Li+-rich compositions, but the evolving second phase is the equilibrium Li3TaO4. The absence of solubility extension in LiTaO3, which appears feasible from a thermodynamic viewpoint, is ascribed to the large differences in mobilities of the Li and Ta species in the parent amorphous oxide resulting from pyrolysis.

A vacuum deposition method is presented in which copolymer films are grown from a vinylic monomer chosen for desirable properties and paraxylylene. The concentration of paraxylylene in the final copolymer can be negligibly small if proper deposition conditions, presented here for the first time, are employed. Films of paraxylylene with N-phenyl maleimide deposited at 40 °C, for example, showed thermal stability and FTIR spectra nearly identical with homopolymers of poly(N-phenyl maleimide). Different rate-limiting steps are proposed to explain film composition; paraxylylene is under surface reaction control, while the comonomer obeys mass flow control. This results in a deposition environment extremely rich in comonomer. Growth rates and compositions were consistent with predictions. The initiation reaction did not appear different from homopolymerization of paraxylylene. The general method presented here allows fabrication of vapor-deposited thin films with properties limited primarily by the comonomer employed.

Two materials of α-type manganese dioxide were synthesized and examined. They were prepared by the pyrolysis of mixtures of MnCO3 and (CH3)3COK. An ill-ordered material was obtained when prepared at large (CH3)3COK content. Both samples behave as acids, but their apparent capacities are obviously different: about 0.9 meq/g for a well-ordered sample and about 2.6 meq/g for an ill-ordered sample. Ion-exchange properties were examined on Kielland's plot. Zero intersections of the two samples are almost the same but slopes are different (about −50 for a well-ordered sample and about −10 for an ill-ordered sample). The difference in slope is likely caused by the flexibility. An evidence of the flexibility can be seen by x-ray diffractometry.

Coexistent amorphous and nanoscale bcc-Mg7Li3 phases were found in slowly quenched alloys of the Mg65–xLixCu25Y10 system containing 3 to 15 at. % Li. The crystallization behavior of these alloys has been studied. The grain size of the nanocrystalline bcc phase which is formed ranges from 2 to 20 nm. The volume fraction of nanocrystalline phases as well as the grain size of the nanocrystals increase as the Li composition increases. Transmission electron microscopy studies suggest that the alloy exhibits phase separation in the undercooled liquid state and that the nucleation and growth of the bcc-nanocrystals is related to the phase separation. Some characteristic thermal properties of the glassy phase are presented, and the composition dependence of Tg and Tx is discussed. It is concluded that the addition of a small amount of Li is essential for the production of a bcc nanocrystalline phase in the Mg–Li–Cu–Y system.

We are developing techniques to isolate and characterize grain boundary defects with controlled geometries in 1,6-di(N-carbazolyl)-2,4 hexadiyne (DCHD) diacetylene polymer bicrystals. To be successful in this endeavor, it is important to determine the influence of processing variables such as evaporation rate, solution concentration, and environment on DCHD diacetylene crystal morphology. We have found that large, high quality DCHD diacetylene single crystals can be grown from solution under a controlled atmosphere. The quality of the DCHD crystals can be evaluated by optical microscopy and quantitative digital image analysis. Defect structures in DCHD diacetylene crystals have been studied by transmission electron microscopy (TEM). Two single-crystal textured structures have been found in porous DCHD crystals precipitated from solution: (1) a microfibrillar structure and (2) a “cross-hatched” structure. The porous DCHD crystals show localized shear deformation zones (twins and kinks), but only in those regions where the density is greater than 95% that of the perfect crystal. Lateral chain invariant (LCI) small-angle grain boundaries have been identified in DCHD by HREM.

The process of complex formation has been studied during milling a powder mixture of metallic Al and titania hydrogel, TiO2 · H2O. Solid state 27Al NMR and ESR are employed together with conventional x-ray diffractometry and thermal analyses. Al atoms partly changed from metallic to oxide state. 27Al NMR analyses indicate that two metallic Al states are allotted to distorted and undistorted lattices, while the other to AlOx units in the oxide state, where x is 4, 5, or 6. As detected by ESR, Ti4+ was partly reduced to Ti31, suggesting a redox reaction during milling. A vigorous thermit reaction was detected during subsequent heating of the mixture after prolonged milling. These results indicate the formation of Al–O–Ti bonds during milling, leading to Al2TiO5 on subsequent heating.

Rapid, spontaneous infiltration can be achieved by dipping a SiC preform that contains pyrolyzed carbon into an Al–Si alloy bath in an open air environment. The mechanism for infiltration is investigated in the present work by studying the effects of several relevant parameters on the infiltration process. Experimental results have shown that the requirements for rapid spontaneous infiltration are an infiltration temperature higher than 1400 °C, the presence of a pyrolyzed carbon, and the presence of SiC particle in the preforms. The concentration of Si in the alloy does not have significant influence on the infiltration rate, but it strongly affects the resulting microstructures in the infiltrated composites.

Ion irradiation with various oxygen flow rates has been carried out to improve the wettability of polymethylmethacrylate (PMMA) to water and to enhance the adhesion between Al and the polymer. Ar+ ion and oxygen ion were irradiated on the polymer, and amounts of ions were changed from 5 × 1014 Ar+/cm2 to 5 × 1016 Ar+/cm2 by a broad ion beam source. Oxygen gas from 0 ml/min to 7 ml/min was flowed near the polymer surface during the ion irradiation, and the energy of ions was changed from 500 eV to 1500 eV. The wetting angle was reduced from 68° to 49° with the Ar+ ion irradiation only at 1 keV energy, to 43° with the oxygen ion irradiation, and dropped to 8° with Ar+ ion irradiation with flowing 4 ml/min oxygen gas near the polymer surface. Changes of wetting angle with oxygen gas and Ar+ ion irradiation were explained by a two-step chemical reaction among polymer matrix, energetic ions, and oxygen gas. The effects of Ar+ ion and oxygen ion irradiation were explained by considering formation of hydrophilic groups due to a reaction between irradiated polymer chain by energetic ion irradiation and blown oxygen gas, and enhanced adhesion between Al and PMMA was explained by the formation of electron acceptor groups in polymer and electron donors in metal, and by the chemical reaction in the interface between irradiated polymer surface and deposited metal.