This paper presents a method for determining diffusivities in solids where the diffusing species desorbs or reacts at the external surfaces, and where the diffusivity does not vary appreciably with concentration. The method involves measuring the flux of the diffusive species out of the solid under the influence of a temperature program. A general model is developed, based on nonisothermal Fickian diffusion, which is applicable to solid particles with slab or spherical geometry. The solution is presented both as an analytical expression and as correlation charts of experimentally observable quantities. These charts are contour diagrams of the temperatures of peak diffusion rate with ln(E/R) and ln(D0/h2) as the axes, where E and D0 are the activation energy and pre-exponential terms of the diffusivity expression D = D0 exp(−E/RT), where R is the gas constant, and h the size of the particles. This paper deals exclusively with the case of oxygen diffusion in the vanadium oxide system. In this case, vanadium oxide was reduced in a reactive ammonia stream at conditions in which the surface reaction was fast compared to the diffusive transport process. Using this method the diffusion parameters were found to be D0 = 1.9 × 10−5 cm2 s−1 and E = 101 kJ/mol. The method was checked by varying the crystallite size of the vanadium oxide sample in the range 2h = 0.14−0.29 μm.

The magnetic properties and crystallographic alignment for Fe–Nd–B–Al magnets having different Nd contents were studied. It was found that higher Nd concentration (above 18 at. %) resulted in deterioration of the alignment. Also, extended ball milling of the powder particles resulted in poorer alignment of the grains in the final sintered magnet. This behavior was attributed to the cold welding of the small particles of the Fe14Nd2B phase by a mechanically soft Nd-rich phase in the course of ball milling.

The recent novel temperature-modulated differential scanning calorimetry (DSC) (MDSCTM TA Instruments) technique has been applied to characterize the thermal properties of Ge–Se chalcogenide glasses in the glass transition region. All samples in this work were given the same thermal history by heating to a temperature above the glass transition, equilibrating, and then cooling at a rate of 5 °C/min to a temperature of 20 °C. The reversing and nonreversing heat flows through the glass transformation region during both heating and cooling schedules were measured, and the values of the parameters Tg, ΔH, Cp, and ΔCp, which characterize the thermal events in the glass transition region, were determined. The ability of determining the reversible heat flow in MDSC enables an accurate measurement of the true heat capacity (that normally associated with reversible heat flow), which could not be done hitherto in conventional thermal analysis where the detected heat flow is the total heat flow, the sum of reversing and nonreversing heat flows. The structurally controlled parameters Tg, ΔH, Cp, and ΔCp reveal extrema when the Ge–Se glass system reaches the average coordination number 〈r〉 = 2.67 at 33.3 at.% Ge which corresponds to the stoichiometric composition GeSe2. We also observed extrema in the composition dependence of the above thermal parameters at 20.0 and 40.0 at.% Ge which correspond to stoichiometric compositions GeSe4 and Ge2Se3 with average coordination numbers 2.40 and 2.80, respectively. No such clear local maxima below and above the 33.3 at.% Ge composition could be observed previously in thermal analysis. We compare our MDSC results with previously published works on glass transition in Ge–Se glasses and discuss the results in terms of recent structural models for chalcogenide glasses.

Protection of glass substrates by direct ion beam deposited diamond-like carbon (DLC) coatings was observed using a commercial pin-on-disk instrument at ambient conditions without lubrication. Ion beam sputter-deposited titanium carbide and boron carbide coatings reduced sliding friction, and provided tribological protection of silicon substrates, but the improvement factor was less than that found for DLC. Observations of unlubricated sliding of hemispherical glass pins at ambient conditions on uncoated glass and silicon substrates, and ion beam deposited coatings showed decreased wear in the order: uncoated glass > uncoated silicon > boron carbide > titanium carbide > DLC > uncoated sapphire. Failure mechanisms varied widely and are discussed. Generally, the amount of wear decreased as the sliding friction decreased, with the exception of uncoated sapphire substrates, for which the wear was low despite very high friction. There is clear evidence that DLC coatings continue to protect the underlying substrate long after the damage first penetrates through the coating. The test results correlate with field use data on commercial products which have shown that the DLC coatings provide substantial extension of the useful lifetime of glass and other substrates.

Copper particles of sizes in the range 3.1 to 11.4 nm have been grown within gel compositions of the system CuO–SiO2 by an electrodeposition process applying voltages varying from 5 to 15 V. Composite films of these metal particles dispersed in a polystyrene matrix have been prepared on Corning No. 7059 glass slides by a dip-coating technique and their optical absorption characteristics have been delineated. The spectra show maxima at wavelengths in the range 380 to 470 nm, depending on the particle size. The results have been analyzed using the Mie theory. The electrical conductivity as extracted from this analysis is found to have reasonable correspondence with data reported earlier for copper nanoparticles in glass-ceramic systems.

We have developed a new technique for measuring the adhesion of brittle films to ductile substrates. In this technique, a wedge indenter is driven through the brittle coating and into the underlying substrate. Plastic deformation of the substrate causes the coating to delaminate from the substrate. The width of the delaminated area can be directly related to the interface toughness. We present a simple analysis of this technique and apply it to diamond-coated titanium. The toughness of the diamond-titanium interface as measured with this wedge delamination technique is approximately 51 ± 11 J/m2. XPS measurements reveal that a reaction layer of titanium carbide forms between the diamond coating and the titanium substrate. Delamination of the coating occurs by crack propagation in this reaction layer and in the diamond film itself. These observations agree well with nanoindentation measurements performed in the delaminated area of the substrate.

This study addresses the correlation of the macroscopic and microscopic characteristics of synthetic diamond crystals produced by high pressure, high temperature conditions. Microscopic properties were characterized using Raman spectroscopy, birefringence, and photoluminescence (PL). Macroscopic properties characterized included inclusion content and crush force. Raman measurements detected measurable stress shifts in only two samples. The PL measurements indicated an increased presence of the H3 center in areas of high strain. The absence of the H3 center and the presence of the N-V PL center was correlated to lower average crush force. A hierarchy has been developed that relates microscopic properties to average crush force.

TiN/Pt multilayers with individual thicknesses between 1 and 8 nm were prepared by ion beam sputtering deposition to simulate the micro-laminated architecture of nacre. Multilayer hardness and the laminated structure were investigated. It was found that sharp but incoherent interfaces were formed between individual layers. The multilayer hardness had strong dependence on layer arrangement. The range of layer thickness appropriate for high hardness was experimentally determined. Hardness enhancement of 30–70% was generally observed. With the layer thickness properly adjusted, the multilayer can even be harder than the hard component (TiN). Annealing experiments indicated that the hardness enhancement was an intrinsic property of the TiN/Pt multilayers.

Transmission of acoustic waves in two-dimensional composite media composed of arrays of Duralumin cylindrical inclusions embedded in a poly vinyl chloride (PVC) matrix is studied. Experimental and theoretical results for the transmission spectrum of a periodic array of cylinders organized on a square lattice are reported. Local gaps in the first two-dimensional Brillouin zone are predicted and observed. The experimental measurements of power spectra for a random array of inclusions show a weak correlation between disorder and acoustic absorptions up to a high degree of disorder. Only in the case of highly random arrangements does the transmission spectrum diverge from the one obtained with a periodic array of inclusions.

This paper presents a new form of linear free energy (LFE) relationship for diffusive mass transport in oxides and other binary compounds. The relationship applies to a family of related compounds. For a given substance, i, solid-state diffusivity is related to the equilibrium constant Ki or the free energy of transformation, , via a transfer coefficient γ, through the expression ln Di = γ ln Ki + constant . The system investigated here is the series of suboxide intermediates of vanadium pentoxide formed during temperature-programmed synthesis of vanadium nitride. The value of γ for this series is 0.27. The diffusivity values are determined by fitting a mathematical model to the experimental data. Diffusivity data are presented graphically in contour diagrams which correlate pre-exponential values, activation energies, particle sizes, and heating rates used in the temperature-programmed syntheses. An Evans–Polanyi linear relation, , relating activation energy, Ei, to enthalpy change of transformation, , via a transfer coefficient α = 0.53, is also shown to exist for the above system. The discrepancy between α and γ is resolved by using the Horiuti concept of the stoichiometric number of the rate-determining step.

The amount and defect type of substitutional nitrogen in synthetic diamond strongly influences crystal strength. There is an optimum amount of nitrogen that yields the highest compressive fracture strength for crystals derived from common growth conditions. It is postulated that the role of nitrogen is to charge-balance vacancies created during growth. If too little nitrogen exists in the diamond, vacancies are not charge-balanced and may serve as crack initiation and/or propagation sites. Excess nitrogen above that required to charge-balance vacancies may weaken the lattice by adding local strain to the crystal. IR microscopy indicates that most of the substitutional nitrogen in synthetic diamond is increased in the vicinity of the intersections of growth sectors on the crystal surface. Most surface IR-visible nitrogen is biased toward the (111)–(100) intersection. The bias in incorporation of substitutional nitrogen at external growth sector intersections (i.e., edges and corners) of an industrial high-grade saw diamond crystal influences the progression of fatigue by microfracture during cutting of hard stone.

In situ growth of SrBi2Ta2O9 (SBT) films as a function of Bi concentration in the target, substrate temperature, oxygen pressure, and the thickness of bottom Pt electrode by pulsed laser deposition was studied. The SBT phase initially formed at a temperature of 500–520 °C. The SBT films grown from the stoichiometric target generally showed Bi deficiency. A well-crystallized and stoichiometric SBT film could be grown at a temperature of 550–580 °C in 300 mTorr of O2 from the surplus Bi targets, which showed c-axis preferred orientation. The formation temperature of SrTa4O11 (ST) phase was above 600 °C, depending on the Bi concentration in the target. Higher oxygen pressure raised the formation temperatures of the SBT and ST phases and concomitantly enriched the Bi concentration of the SBT films. For the bottom Pt electrode 1200 Å thick, the voids were not observed in the SBT overlayer until the deposition temperatures were above 590 °C. Annealing at temperatures above 700 °C in an atmosphere of O2 was required to improve the contact between Pt electrode and the SBT film and hence the ferroelectric properties of the SBT film. In the present study, a smooth, stoichiometric, and c-axis oriented SBT film, about 350 nm thick, could be grown on Pt (1200 Å)/Ti/SiO2/Si at a temperature of 550–580 °C in 300 mTorr of O2 from the Bi surplus targets, which showed remnant polarization (Pr) of 3.0–3.5 μC/cm2 and coercive field (Ec) of 30–40 kV/cm at 4 V. No fatigue was observed up to 109. switching cycles

A liquid source metal-organic chemical vapor deposition system was installed to deposit SrBi2Ta2O9 (SBT) thin films on sapphire and Pt/Ti/SiO2/Si substrates. The process parameters such as deposition temperature and pressure, and ratio of Sr: Bi: Ta in the precursor solutions were optimized to achieve stoichiometric films with good reproducible ferroelectric properties. It was found that the nucleation of SBT started at a deposition temperature close to 500 °C and grain growth dominated at 700 °C and higher temperatures. With increasing deposition temperatures, the grain size of SBT thin films increased from 0.01 μm to 0.2 μm; however, the surface roughness and porosity of the films also increased. To fabricate specular SBT films, the films had to be deposited at lower temperature and annealed at higher temperature for grain growth. A two-step deposition process was developed which resulted in high quality films in terms of uniformity, surface morphology, and ferroelectric properties. The key to the success of this process was the homogeneous nucleation sites at lower deposition temperature during the first step and subsequent dense film growth at higher temperature. The two-step deposition process resulted in dense, homogeneous films with less surface roughness and improved ferroelectric properties. SBT thin films with a grain size of about 0.1 μm exhibited the following properties: thickness: 0.16–0.19 μm; 2Pr: 7.8–11.4 μC/cm2 at 5 V; Ec: 50–65 kV/cm; Ileakage: 8.0–9.5 × 10−9 Acm−2 at 150 kV/cm; dielectric constant: 100–200; and fatigue rate: 0.94–0.98 after 1010 cycles at 5 V.

The thermal stresses in carbon-coated optical fibers at low temperature have been analyzed. The thermally induced lateral pressure in the glass fiber would produce microbending loss. In order to minimize such a microbending loss, the thickness, Young's modulus, and Poisson's ratio of the carbon coating should be decreased. On the other hand, the maximum thermal stress is the tangential stress in the carbon coating that occurs at the interface of the carbon coating and glass fiber. It was experimentally observed that if the maximum thermal stress is larger than the tensile strength of the carbon coating, the carbon coating will be broken along the axial direction. In order to minimize such a maximum thermal stress, the thickness of the carbon coating should be increased, but Young's modulus, thermal expansion coefficient, and Poisson's ratio of the carbon coating should be decreased. Finally, an optimal selection of the carbon coating for optical fiber is discussed.

Submicrometer-sized SiC coated with SiO2 of 0.4–1.8 wt.% and α–Al2O3 powder of median size 0.2 μm were mixed in aqueous solutions in the pH range 3.0–10.0. The SiC/Al2O3 (4.3–6.9 wt. %) powders were consolidated by filtration through gypsum molds and hot-pressed at 1600°–2040 °C under a pressure of 39 MPa. These compacts were densified to near the theoretical density at 1700°–1800 °C. The sintering mechanisms are discussed based on the analysis of shrinkage curves of SiC/Al2O3 compacts during hot-pressing. The equiaxed SiC grains grew with low aspect ratios below 1800 °C and changed to plate-like grains at 1900 °C. The fracture toughness of SiC as a function of average grain size reached a maximum of 5 Mpa · m0.5 at 2.5 μm grains of low aspect ratios of 1–2. The flexural strengths at room temperature were 230–430 MPa in the SiC above 98% of the theoretical density and showed a similar grain size dependence.

The deformation behavior of fine-grained, α-phase rich silicon nitride materials has been studied between 1823 and 1923 K, both in compression and in tension. It is first shown that the higher the α-phase content, the better the superplastic forming ability. A large tension-compression flow asymmetry was evidenced. For instance, shear-thickening flow shows up in compression whereas shear-thinning is observed in tension. Furthermore, much higher flow stresses and hardening rates are reported in compression than in tension. Elongations of more than 80% were achieved for strain rates between 2.5 and 5 × 10−5 s−1. In the light of our results and of the abundant literature dealing with the high temperature deformation in silicon nitride, a sketch of the different deformation stages is proposed, which emphasizes the tension-compression asymmetry. Starting from the promising results obtained at the laboratory scale, the feasibility for net-shaping of a real part was demonstrated by hot-forging of a parabolic shell.

Thin films of Ti–W–O were prepared from a W–Ti alloy target by rf magnetron sputtering in reactive atmosphere. Analysis devoted to investigate the microstructural properties of this material was carried out in order to explain the origin for the high sensing performance of a W–Ti-oxide gas sensor. Scanning and transmission electron microscopy techniques showed that after annealing the film consists of a polycrystalline layer, isostructural to tetragonal WO3, over which crystallites of pure WO3 are dispersed. The WO3 crystallites are insulated from each other and do not enter into the process of conduction of the layer. It was shown that Ti is soluted in the tetragonal WO3 lattice of the underlying layer. This layer exhibits fine granularity, which is an optimal feature for materials suited to gas sensing.

We demonstrate the method of x-ray diffraction at shallow angles of incidence, using the intrinsically highly collimated x-ray beam generated by a synchrotron source, to study the atomic-scale structure of amorphous thin films and coatings in their as-deposited (i.e., on-substrate) state. As the incident angle is decreased, scattering from the film/coating can be isolated as contributions from the substrate are reduced. Systems studied include chemical vapor deposition (CVD) diamond films deposited onto both silicon and steel substrates, where evidence of an interfacial region between the film and silicon wafer has been observed, but we focus on a range of amorphous films/coatings (mixed TiO2 : SiO2 sol-gel spun films, hydrogenated carbon films and “glassy” carbon coatings, silicon: germanium semiconducting films and alumina coatings). The data are used both to comment upon the systems studied and to elucidate the potential, and the limitations, of the experimental method.

We report the results of a study on the deposition and characterization of partially oriented BaTiO3 thin films on MgO-buffered Si(100) by radio-frequency magnetron sputtering. The structural and morphological characteristics of the MgO buffer layer were investigated as a function of substrate temperature. The x-ray θ-2θ, φ scans, and observation of surface morphology revealed that MgO grew with a tendency of (001) orientation. Partially (00l) or (h00) textured BaTiO3 thin films were obtained on Si(100) with the MgO buffer layer while randomly oriented BaTiO3 thin films with large-scale cracks on the surface were made without the MgO layer. Pt/BaTiO3/Pt multistructures were formed on Si(100), MgO/Si(100), and MgO(100) single crystal substrates to conduct preliminary electrical measurements for metal-insulator-metal type capacitor. Comparison of the crystallographic orientation, morphology, and electrical properties between the BaTiO3 films on Si(100) with and without the MgO buffer layer supported the favorable role of the MgO layer as a buffer for the growth of BaTiO3 films on Si(100).

Photothermal radiometry has been used to obtain thermal wave images in the vicinity of indentations in WC–6% Ni coated with chemical vapor deposited (CVD) diamond. Features in the magnitude and phase of the thermal signal profile are consistent with a one-dimensional thermal wave theory that assumes (i) an air gap extending well beyond the visibly observable indented region, and (ii) a thermal resistance interface between the diamond film and the substrate over the entire coated surface. The theory allows us to estimate the air gap thickness, which decreases as the distance from the indented region increases. Air gap variations of tens of nanometers appear to be easily detectable.