bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interfacial Adhesion: Theory and Experiment
Authors: Ferrante John , Bozzolo Guillermo H. , Finley Clarence W. , Banerjea Amitava 
Published: March 2011

AbstractAdhesion, the binding of different materials at an interface, is of general interest to many branches of technology, e.g., micro-electronics, tribology, manufacturing, construction, etc. However, there is a lack of fundamental understanding of such diverse interfaces. In addition, experimental techniques generally have practical objectives, such as the achievement of sufficient strength to sustain mechanical or thermal effects and/or have the proper electronic properties. In addition, the theoretical description of binding at interfaces is quite limited, and a proper data base for such theoretical analysis does not exist.This presentation will review both experimental and theoretical aspects of adhesion in nonpolymer materials. The objective will be to delineate the critical parameters needed, governing adhesion testing along with an outline of testing objectives. A distinction will be made between practical and fundamental objectives. Examples will be given where interfacial bonding may govern experimental consideration. The present status of theory will be presented along with some recommendations for future progress and needs.
The Role of Fracture Mechanics in Adhesion
Authors: Thouless M. D. 
Published: March 2011

AbstractThe problem of adhesion cannot be completely comprehended by consideration of interfacial properties alone. Other parameters such as geometry, applied and residual stresses, and the interfacial flaw population are equally important. The well-established field of fracture mechanics permits these aspects to be considered. One of the most important features of fracture mechanics is that it can provide a means of characterizing interfacial properties which does not depend upon the method of testing. It may also allow a predictive ability in determining failure and a rational explanation of what is known as “adhesive” or “cohesive” failure. These issues are addressed in conjunction with a discussion of the current limitations in the application of fracture mechanics to the topic of adhesion.
Enhancement of Thin-Film Adhesion by MeV-ION and keV Electron Bombardment
Authors: Tombrello T. A. 
Published: March 2011

AbstractSince the discovery in 1981 that the electronic excitation produced by MeV ions can enhance thin film adhesion to a substrate, there have been many investigations to determine the origin of the effect and to apply it to problems of technological interest. As we approach the seventh anniversary of its discovery, I shall use this opportunity to review our progress toward these goals. In general, we have discovered that although the electronic excitation provided by the incident beam is responsible for the improvement in adhesion, it is certain that there are quite a number of separate effects involved. These have been shown to include: surface cracking of the substrate; the breakup of contaminant or oxide layers on the substrate by the beam; and the relaxation of surface strain in the substrate. The recent use of a variety of new techniques seems to offer the hope that we are beginning to make progress in untangling these phenomena.
A Correlation Law for Steady State Creep and Stress Relaxation Tests on the Al-Al2Cu Composite
Authors: Ignat M. , Bonnet R. , Durand F. 
Published: March 2011

ABSTRACTDeformation by creep or by stress-relaxation involve similar thermally activated phenomena. In particular our microstructural observations on the Al-Al2Cu lamellar composite illustrated the importance of the interphase accommodation mechanisms, specially movements of linear defects at the phase boundaries.Our experimental results have shown that the asymptotic stress measured in stress-relaxation tests takes the same value as the threshold stress limiting the steady state creep domain. From this finding we develop a simple Bingham rheological model in which a temperature dependent threshold stress is combined with a generalized Dorn viscosity law. The model correlates satisfactorily the results of both steady state creep tests and the results of stress-relaxation tests.The calculated activation energy and stress exponent are compared with the values deduced from physical models of deformation accommodation through grain boundary sliding. The preexponential factor of the viscosity law is discussed with reference to its dependence on the dislocation substructure.
The Role of Solidification Rate on Fiber Distribution and Mechanical Properties of a Directionally Solidified Nickel Base-Tac Eutectic
Authors: Walter John L. 
Published: March 2011

ABSTRACTA nickel base-TaC eutectic alloy consisting of 53 wt % Ni, 11 W, 3 Re, 5 Co, 3 Mo, 2 Al, 21.67 Ta and 1.33 C was directionally solidified at rates from 0.32 to 3.8 cm/hr. Samples were taken from the regions of aligned TaC fibers and tested in tension at 1000°C and in stress-rupture. The fiber density increased from 1×106 fibers/cm2 at 0.32 cm/hr to 27×106 fibers/cm2 at 3.8 cm/hr. The stress-rupture life at 927°C and 275.6 MPa ranged from 4 hrs for samples solidified at 0.32 cm/hr to 4187 hrs for the sample solidified at 2.54 cm/hr at which time the test was terminated. Examination, by transmission electron microscopy, of the samples tested at 1000°C in tension, to just the beginning of fiber breakage, revealed a change in the mode of deformation of the nickel-base alloy matrix with increasing fiber density. It was also seen that the TaC fibers deformed by two mechanisms; by slip and by the formation of stacking faults.It appears that tailoring the alloy composition to allow for higher solidification rates may be a more effective strengthener than alloying the matrix for high strength.
Thermal, Viscoplastic Analysis of Composite Laminates
Authors: Krempl E. , Lee K. D. 
Published: March 2011

AbstractFor the modeling of ply deformation behavior the orthotropic, thermal viscoplasticity theory based on overstress is used. It can represent creep, relaxation and rate sensitivity as well as monotonic and cyclic loadings. The theory is “unified” since creep and plasticity are not separately modeled. No yield surfaces and loading/unloading conditions are employed. The laminate theory for in-plane loading maintains the geometric assumptions of classical laminate theory. The elasticity law, however, is replaced by the thermal, orthotropic viscoplasticity law. Numerical experiments illustrate the predictions of the theory for an angle-ply and a cross-ply laminate subjected to a temperature increase, temperature hold and subsequent return to the original temperature. The ply and laminate stresses are calculated as a function of time for unconstrained and constrained conditions using postulated properties close to a real metal matrix composite. Redistribution of ply stresses and relaxation are found. In some cases, nearly permanent residual ply stresses are present after completion of the temperature cycle.
Fibers and Grids by Integrated Circuit Technology
Authors: Steinwall James E. , Johnson H. H. 
Published: March 2011

AbstractCeramic fibers and grids of controlled geometry and composition were fabricated by electron beam evaporation of Al2O3 onto substrates patterned by optical lithography. The fibers were 4 and 5μm wide by 1μm thick. In addition, mixed metal oxide films from 0 to 10at% Ti, Zr, or Cr were produced by coevaporation with Al2O3. The compositions of the films were determined by Rutherford Backscattering Spectroscopy. TEM and electron diffraction examination showed all the films to be amorphous in structure.The Al2O3 fibers had tensile strengths between 143 and 168 ksi and the Al2O3 film had a microindentation hardness of 8.4 GPa. Films with ≈ 1at% additions of Zr, Ti, and Cr had hardnesses of 11.0, 9.7, and 8.8 GPa respectively. The hardness then decreased with higher Zr, Ti, and Cr concentrations
XD™ Titanium Aluminide Composites
Authors: Christodoulou L. , Parrish P. A. , Crowe C. R. 
Published: March 2011

AbstractThe advantages of reinforcing metals with ceramic particles to produce metal matrix composites are well known. The behavior of discontinuously reinforced intermetallic compounds, however, has not been extensively studied. Martin Marietta Laboratories has produced a new generation of discontinuously reinforced titanium aluminide composites using a proprietary casting process known as XD™ technology. These new materials possess enhanced properties at room and elevated temperatures and may be cast, extruded, or forged. The effects of matrix composition, reinforcing phase, and thermal mechanical processing on properties have been studied using optical and various electron microscopy and mechanical and physical property measurement techniques to characterize the alloys. To date, most work has been done on a two-phased lamellar Ti-45 a/o Al alloy reinforced with TiB2 ceramic having an equiaxed morphology. Data on temperature dependence of the dynamic Young's modulus, coefficient of thermal expansion, deformation and fracture behavior, and microstructure are presented.
Hrem Characterisation of The Interface in A Sic Fibers/Ti Matrix Composite
Authors: Lancin M. , Bour J. S. , Thibault-Desseaux J. 
Published: March 2011

AbstractThe microstructure of the interfacial zone in a SCS6 filaments/Ti-6A1–4V matrix composite was determined using TEM and HREM. The interfacial zone (e ∼5 μm) consists of microstructurally distinct layers. The fiber/matrix interaction resulted in two layers respectively crystallized in grains of about 20 nm and 100 nm. The reaction zones are mainly made of brittle TiC. They are separated from the SiC reinforcement by five layers which form the coating of the SCS6 filament. These five layers may be described as SiC-C composites with either an equiaxe fine grain structure or a distorted lamellar structure. The structure of these layers can explain the toughning of the alloy by the SCS6 filaments despite of the brittle F/M reaction products formed during the processing.
Crack-Tip Shielding in Metal-Matrix Composites: Modelling Of Crack Bridging by Uncracked Ligaments
Authors: Shang Jian Ku , Ritchie R. O. 
Published: March 2011

AbstractAs part of an investigation into the micro-mechanisms of crack-tip shielding associated with the growth of fatigue cracks in metal-matrix composites, simple models are developed for the role of crack bridging in high-strength aluminum alloys reinforced with SiC particulate (AI/SiCp). Based on experimental observations of crack growth, crack-tip shielding and crack-path morphology in these alloys, the bridges are found to be associated with uncracked ligaments in the wake of the crack tip, and are modelled in terms of approaches based on a critical crack-opening displacement or critical tensile strain in the ligament.
Growth and Structure of Alumino-Silicate Polymers
Authors: Boilot J. P. , Pouxviel J. C. , Dauger A. , Wright A. 
Published: March 2011

ABSTRACTGels have been prepared in the H2O, HOiPr, (BuO)2Al-O-Si(OEt)3 ternary phase diagram in a large range of oxide concentrations. The gelation time is governed by the initial water concentration, showing that the hydrolysis of Si-OR groups is the rate-determining process for the gelation.The structure of clusters and the kinetics of aggregation have been studied by SANS. We observe mass-fractal particles characterized by a fractal dimension of 1.9, in agreement with the existence of a cluster-cluster aggregation mechanism during the gelation. The scattering curves exhibit a maximum intensity corresponding to interparticle correlations due to purely excluded-volume effects.
Correlations Between Processing Parameters, Ultrastructure, and Strength of Gel-Silica
Authors: West Jon K. , Nikles Randy , Latorre Guy 
Published: March 2011

ABSTRACTThe effect of various processing parameters during the aging of sol-gel derived silica are evaluated. Improvement in the physical properties of the wet gel-silica are shown to be well correlated to their aging temperatures and time. Changes in the pore structure also show correlations with aging process parameters.
Sol-Gel Kinetics: 29Si NMR and a Statistical Reaction Model
Authors: Assitik Roger A. , Kay Bruce D. 
Published: March 2011

ABSTRACTThe early time behavior of an acid catalyzed Si(OCH3),4 (TMOS) sol-gel was studied by high resolution 29Si nuclear magnetic resonance (NMR). Both the water producing and the alcohol producing condensation reactions were found to contribute significantly to the overall condensation rate. A general theoretical kinetic formalism which specifically treats the temporal evolution of the various chemical function groups about a specific silicon atom was developed. The experimentally observed functional group distribution was in agreement with the distribution predicted by a simplified statistical reaction model. The mathematical framework for the study of chemical speciation at the next-to-nearest functional group level was developed. This framework was used to assign several fine structure resonances, and to show that the formation of various dimeric species is also largely statistical in nature.
Preparation of Stoichiometric M'TiO3, Powders (M' = Ba, Sr, Ca) from Catecholate Complexes
Authors: Ali N. J. , Bultitude J. , Xue L. A. , Milne S. J. 
Published: March 2011

ABSTRACTPowders of BaTiO3, SrTiO3, and CaTiO3, were prepared from intermediate catecholate complexes, M'[Ti(C6H4O2], M' = Ba, Sr, Ca. Conversion to oxide was accomplished by heating at 600°C to produce stoichiometric powders of crystallite size, < 0.1 μm, with relatively weak agglomeration. Ultrasonic treatment of aqueous suspensions of the powders resulted in measured agglomerate sizes of less than 2–3 μm. Chemical and physical properties of the new powders are reported, together with information on sintering behaviour.
Light Scattering of SiO Monodisperse Microspheres Prepared by the Sol-Gel Route
Authors: Ziemath E. , Aegerter M. A. , Moreira J. , Figueiredo M. , Zarzycki J. 
Published: March 2011

ABSTRACTSiO microspheres have been prepared from TMOS/Methanol/water sols in basic condition (pH ≃ 12) by the Stöber method and studied by TEM static and dynamic light scattering techniques in order to determine the mean size Ṝ size distribution, hydrodynamic radius RH, radius of gyration RG and translational diffusion coefficient Dt; the ratio RH/RG was found less than 0.55 and the aggregates have a fractal geometry with df ∼ 2.3 ± 0.05. The results are compared to previous work on colloidal silica aggregates prepared by other techniques and discussed.
Dielectric Relaxation Analysis of Water Adsorption in Sol Gel Derived Silica Gel Monoliths
Authors: Wallace S. , Hench L. L. 
Published: March 2011

ABSTRACTThe polarization mechanism of the low frequency dielectric relaxation (R1) observed in water adsorbed in porous silica gel is investigated using monolithic samples. It is attributed to electrode polarization involving proton hopping conduction. The influence of the thickness of the adsorbed water layer on the relaxation mechanism is discussed.
Low Temperature Direct Reactions Between Elemental Silicon and Liquid Ammonia or Amines for Ceramics and Chemical Intermediates
Authors: Pugar Eloise A. , Morgan Peter E.D. 
Published: March 2011

ABSTRACTDirect processes that may be used to manufacture high purity silicon nitride or silicon carbide are described. Elemental silicon has been found to react directly with liquid ammonia and amines at low temperature to yield compounds for both the ceramic and chemical industries. Silicon-amine direct reactions, previously thought not to occur, were investigated by using 29Si NMR, IR, UV, Raman, XRD, ICP, EDS and TGA methods to detect and characterize product formation. The [Si,N,H] and [Si,C,N,H] products transform to silicon nitride or silicon carbide respectively when heated above 1300°C.
The Synthesis of Boron-Containing Ceramics by Pyrolysis of Polymeric Lewis Base Adducts of Decaborane(14)
Authors: Seyferth Dietmar , Rees William Smith 
Published: March 2011

ABSTRACTPolymeric adducts, [B10H12L∼∼L]x, have been prepared by reaction of B10H14 with diphosphines and diamines. These show good promise as precursors whose pyrolysis can give either boron carbide (in the case of the diphosphine polymers) or boron carbonitride and boron nitride (in the case of the diamine polymers).
Aminoborane Polymers as Precursors of Ceramic Materials
Authors: Maya L. 
Published: March 2011

ABSTRACTA series of polymeric materials was prepared through the condensation of t ri ethyl borane or tris(dimethylamino)borane with polyfunctional amines. The amines examined and the ceramic yields of the corresponding condensation products after pyrolysis under vacuum at 800°C were as follows: Methylene dipyrazole – 52%, o-phenylenediamine – 85%, 3,3’ diaminobenzidine – 59% and diethylenetriamine – 12%. Volatile products evolved in the pyrolyses were identified and the solid residues characterized by chemical analyses and spectroscopie means.
Synthesis of Ain and AlN/SiC Ceramics from Polymeric Molecular Precursors
Authors: Paine Robert T. , Janik Jerzey FR. , Narula Chaitanya 
Published: March 2011

ABSTRACTReactions of (Me3Si)3 AI·Et2O with NH3 in different stoichiometric ratios have been studied in search of useful precursors to AIN. Two molecular condensation-elimination compounds and an insoluble oligomer have been obtained from these reactions, and pyrolysis of the compounds leads to the convenient formation of AlN/SiC solid solutions.
Studies on Organoaluminum Precursors OP Aluminum Nitride Fibers
Authors: Thomas Baker R. , Bolt John D. , Rbddy Gade S. , Christopher Roe D. , Staley Ralph H. , Tebbe Pred N. , Vega Alexander J. 
Published: March 2011

ABSTRACTA melt-spinnable precursor of aluminum nitride fibers derived from triethylaluminum and ammonia contains AlNH, AlNH2 groups, and a small number of AlN units characteristic of aluminum nitride. The molecular weight of a spinnable composition is 070, corresponding to an average molecular weight of 13 organoaluminum groups. Ammonia, a curing agent for the fibers, accelerates elimination of ethane from the material, and decreases its solubility in toluene.
Sol-Gel Processed BaTiO3
Authors: Della Nelcy , Mohallem Santina , Aegerter Michel André 
Published: March 2011

ABSTRACTBaTiO. thin films deposited on pyrex supportsby dip-coating technique and powders have been prepared by the sol-gel route from sols containing a mixture of tetraisopropyl orthotitanate, iso propanol, barium acetate and glacial acetic acid. The thickness of the films is proportional to the first power of the withdrawal speed. Gelled sols have been dried hypercritically and by natural evaporation. Films and powders have been characterized by X-ray diffraction during their heat treatment. Tetragonal BaTiO structure is observed for T ≥ 600°C.
The Structures of Tantalum Pentoxide Film Formed by Reactive DC Magnetron Sputter-Deposition of Ta
Authors: Chang P.-H. , Bohlman J. G. , Liu H. Y. , Keenan J. A. , Shen B. W. , Chen I.-C. 
Published: March 2011

ABSTRACTTantalum pentoxide (Ta2O5) films are candidates for application as storage capacitors in high density memory cells and as gate insulators in MOS devices because of their large dielectric constant. Thin Ta2O5 films deposited by reactive DC magnetron sputtering of a pure Ta target using an argon/oxygen mixture have been characterized using TEM, glancing angle X-ray diffraction and RBS. The films are amorphous in the as-deposited condition but crystallize after high temperature (> 600 °C) annealing. Numerous pores and significant grain boundary grooving were observed in the crystallized film. A high level (∼2 at. %) of argon was detected in both as-deposited and annealed films formed by Ar/O2 sputtering. The effects of sputtering and annealing conditions on the structure of the films were investigated.
Planarization of Metal Substrates for Solar Mirrors
Authors: Ashley Carol S. , Reed Scott T. , Roderick Mahoney A. 
Published: March 2011

ABSTRACTThe planarizing ability of sol-gel films was investigated on several as-rolled stainless steel substrates. The smoothing effect afforded by the films was evaluated, using optical techniques, following deposition of silver over the planarized substrates. The specular reflectance of various substrates, initially ranging from 0.36 to 0.90, could be improved to final reflectance values of -0.93 with sol-gel processing. This process is being used to prepare prototype foil mirrors for evaluation in the next generation of solar concentrators.
In Situ NMR Study of Gel Pore Structure During Aging and Drying
Authors: Smith Douglas M. , Glaves Christopher L. , Davis Pamela J. , Jeffrey Brinker C. 
Published: March 2011

ABSTRACTLow field NMR spin-lattice relaxation measurements of pore fluid were used to study pore structure during aging and drying of two silica gels. The NMR method provides in situ information concerning pore size, size distribution and surface area which is impossible to obtain by other techniques. Surface areas measured for a sol-gel sample aged in a potassium hydroxide solution were compared to similar measurements made on an ethanol aged sample during drying. Surface area and pore size distributions of the corresponding final dried gels were measured by both NMR and nitrogen adsorption/condensation. The measurements for a given sample were in good agreement. The surface area of samples before drying were much higher than after drying and the base-aged sample had a higher initial surface area than the ethanol-aged sample although after drying, this trend was reversed.
Process Considerations in Monolithic Aerogels
Authors: Hunt Arlon J. , Lofftus Kevin D. 
Published: March 2011

ABSTRACTThis paper describes important process considerations in the preparation of super-critically evacuated alcogels called aerogels. Aerogels are fine grained, open pore, low density materials that possess a variety of unusual properties and have a number of diverse applications. Factors influencing the microstructure and uniformity of alcogel monoliths are discussed. The effects of hydrolysis rate, diffusion, condensation, dispersion medium, and electrostatic interactions on particle formation and gelling are outlined. These effects are illustrated with the preparation of zirconia, mullite precursors, and silica alcogels. A theoretical model of particle interaction based on the combination of van der Waals and electrostatic double layer forces is used to interpret gelation and homogeneity. Solvent substitution and supercritical drying processes are discussed.
Film Preparation by Inorganic-Organic Sol-Gel Synthesis
Authors: Schmidt H. , Rinn G. , Naβ R. , Sporn D. 
Published: March 2011

ABSTRACTFilm formation by sol-gel techniques is an advantageous method to obtain inorganic coatings. The sol-gel process allows the preparation of prepolymers with suitable viscosities to use various coating techniques like dipping, spraying and spin-on coating. The main disadvantage is the shrinkage of the gel layer during drying or sintering which leads to cracks with layer thicknesses more than some micrometers.The introduction of organics, causing a decrease of the network connectivity and increasing relaxation ability can help to overcome densification problems. Moreover, in some cases, hardness or abrasion resistance are not too much affected by organics. In these cases, the organics can be left within the inorganic network. The possibilities of inorganic-organic processing techniques will be discussed and examples for film formations will be given.