bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and Chemistry of Metal/Ceramic Interfaces
Authors: Rühle M. , Evans A. G.
Published: March 2011

In this paper, the present state of knowledge is reviewed concerning the structure and chemistry of metal/ceramic interfaces. Experimental observations are described for several model systems and open problems concerning different aspects of structure and properties of heterophase boundaries are discussed.
Interfacial Chemistry-Structure and Fracture of Ceramic Composites
Authors: Schoenlein L. H. , Jones R. H. , Henager C. H. , Schilling C. H. , Gac F.
Published: March 2011

The interfacial chemistry and phases of SiC-reinforced Si3N4 composites have been evaluated by transmission electron microscopy (TEM) with associated x-ray energy dispersive spectroscopy (EDS) microanalysis, and Auger electron spectroscopy (AES). Hot-pressed Si3N4 (HPSN) composites reinforced with Nicalon™ SiC fibers or Tateho SiC wiskers and reaction-bonded Si3N4 (RBSN) composites reinforced with uncoated or coated VLS SiC whiskers have been evaluated. In the Nicalon™ fiber-reinforced HPSN, an interfacial phase composed of a layer of amorphous carbon and an adjacent layer of graphitic carbon was observed and is believed to assist fiber pullout during fracture of the composite. However, the fracture strength and toughness of these composites were considerably less than those of unreinforced HPSN. HPSN composites reinforced with Tateho SiC whiskers contained an interfacial phase believed to be similar to the intergranular phase found in the HPSN matrix. In RBSN composites fabricated with an Fe2O3 sintering aid, the VLS SiC whiskers were severely faceted by a reactive iron silicide phase despite C, BN, or SiO2 coatings on the whiskers. When no sintering aid was used, the uncoated whiskers were not degraded and appeared to be strongly bonded to the RBSN matrix. The composites reinforced with SiO2-coated whiskers possessed the highest fracture strength and toughness, and the composites reinforced with the BN-coated whiskers possessed the lowest fracture strength and toughness.
Thermal Oxidation of Al2O3-SiC Whisker Composites: Mechanisms and Kinetics
Authors: Lin F. , Marieb T. , Morrone A. , Nutt S.
Published: March 2011

It has been shown that SiC whisker-reinforced Al2O3 is susceptible to thermal oxidation because of a series of reactions in which SiC is oxidized and then reacts with Al2O3 to form a whisker-free layer of mullite and silica glass. In this paper, the kinetics of the reaction are analyzed as a function of the composition and whisker content of the composite. The mechanism of the reaction is described in terms of the evolution of phases within the reaction layer on the basis of transmission electron microscope observations and concentration profiles determined by electron microprobe analyses. The reaction is initiated by oxidation of SiC, forming silica glass and graphitic carbon. The silica glass penetrates the Al2O3 matrix along grain boundaries, and reacts to form mullite. As the reaction proceeds, Al2O3 is consumed, leaving residual intragranular Al2O3 islands, and a population of transgranular microcracks in the mullite. It has also been shown that Al2O3-SiC composites are susceptible to crack nucleation and growth under cyclic compressive loads. The presence of the mullite reaction layer on the surface of the composite reduces its resistance to crack initiation under these conditions. The threshold for crack initiation in cyclic compression is measured as a function of reaction layer thickness.
Ultrasonic Propagation at Cylindrical Metal-Ceramic Interfaces in Composites
Authors: Wadley H. N. G. , Simmons J. A. , Drescher-Krasicka E.
Published: March 2011

The nature of ultrasonic propagation at cylindrical interfaces is being explored as a potential method for inferring the modulus of the interface in metal matrix composites. In many metal matrix composite systems leaky interface waves have been found to propagate along the interface. The velocity of these waves depends sensitively upon the local moduli and provides a potential basis for measuring these quantities. The opportunity exists to exploit the leaky character of these waves for microscopic imaging at the interface.
High Temperature Intermetallic Composites
Authors: Anton D. L.
Published: March 2011

Many intermetallic compounds possess properties which make them excellent candidates for high temperature use in advanced gas turbine and aerospace applications. One method proposed for increasing damage tolerance in these brittle materials is to artificially composite them with high temperature fibers as utilized in both ceramic and glass composites. Fabrication of these composites is a formidable problem. One method of fabricating these structures, termed here Transient Liquid Phase Consolidation, TLPC, is demonstrated for a number of intermetallic/reinforcing fiber combinations. Thermal stability of the fibers in the intermetallic matrices was observed with FP Alumina being the most stable. Ambient temperature tensile property evaluations were made on monolithic, chopped and aligned FP fiber reinforced Al3 Ta with the aligned structure having the highest ultimate strength and the chopped fiber composite the greatest pseudo plastic response.
Mechanisms and Models of High Temperature Deformation of Composites
Authors: McLean Malcolm
Published: March 2011

The deformation mechanisms that can occur in advanced composites at high temperature are reviewed and the implications of different deformation modes in the constituent phases for the creep behaviour of the composite are considered. A generalised description of creep of composites in terms of internal state variables that have clear physical significance is presented.
Molecular Growth Pathways in Silica Sol-Gel Polymerization
Authors: Klemperer W. G. , Ramamurthi S. D.
Published: March 2011

Capillary gas chromatography has been used to monitor the stoichi-ometries, structures, and abundances of low molecular weight polysilicate esters formed by partial hydrolysis of methanolic tetramethylorthosili-cate and redistribution of methanolie hexamethyoxydisiloxane under acidic (HC1) and basic (KOH) conditions. The polysilicate molecular size distributions, expressed in terms of mole percent of total silicon present as a function of degree of polymerization, show maxima near the number average degree of polymerization under acidic conditions. Under basic conditions, the distribution has its maximum at the monomer percent and extends to very high molecular weights, yielding a distribution far broader than the one observed under acidic conditions. These features are in agreement with covalent network theories of silica gelation, as opposed to particle aggregation theories. Weight fraction distributions of the type observed under acidic conditions are characteristic of linear polymers with a low degree of crosslinking and weight fraction distributions of the type observed under basic conditions are characteristic of branched polymers with high degree of crosslinking. The low degree of crosslinking obtained under acidic conditions is observed to arise from steric crowding that discourages branching in polysilicate structures.
Raman and NMR Studies of Hydrous Sodium Titanates
Authors: Bunker B. C. , Peden C.H.F. , Tallant D. R. , Martinez S. L. , Turner G. L.
Published: March 2011

Raman and solid state 17O NMR spectroscopies have been used to determine the molecular structure of amorphous hydrous sodium titanate catalyst support materials prepared by hydrolysis of titanium isopropoxide. Three types of oxygens have been identified: oxygens bridging three titanium atoms, oxygens bridging two titaniums, and non-bridging oxygens. Changes in the relative populations of the different oxygen types have been used to help understand the ion-exchange and polymerization properties of hydrous titanates.
Mathematical Modeling of the Structures and Bulk Moduli of TX2 Quartz and Cristobalite Structure-Types, T = C,Si,Ge and X = O,S
Authors: Gibbs G. V. , Boisen M. B. , Downs R. T. , Lasaga A. C.
Published: March 2011

Models of the oxide and sulfide structure-types of quartz and cristobalite have been made using potential energy surfaces derived from MO calculations on small molecules. The bond length and angle and the volume compressibility data calculated for quartz match those observed for pressures up to 40 kbars. An analysis of the force constants that define the potential energy surface indicates that the bulk modulus of the mineral is governed primarily by the bending force constant of the bridging angle. Similar calculations were completed for the GeO2 form of quartz, but the agreement with the observed data is somewhat poorer. A modeling of the CO2 form of quartz predicts that it would be significantly harder, more incompressible and show less expansibility than the SiO2 form.
Syneresis in Silica Gel
Authors: Scherer George W.
Published: March 2011

The driving force for syneresis is generally attributed to the same chemical reactions that produce gelation, but it has also been proposed that shrinkage could be driven by interracial energy. The latter possibility is explored and discounted. The kinetics of syneresis depend on the driving force, the mobility of the gel network, and the rate of fluid flow through the contracting gel. A model that allows for viscoelastic behavior of the gel and fluid flow according to Darcy's law is shown to provide a quantitatively accurate representation of the shape of the shrinkage curves and the dependence of the shrinkage rate on sample size.
Adhesion of Hydrated Silicate Films
Authors: Michalské Terry A. , Keefer Keith D.
Published: March 2011

We used fracture mechanics test techniques to measure the adhesive bond energy formed between hydrated silica glass surfaces and silicate species deposited from solution. In the case of silicate surfaces hydrated in room temperature water vapor, intermolecular bonding between hydrated surfaces can be attributed to either hydrogen bonding interactions between adsorbed water molecules (0.15 J/m2) or electrostatic bonds formed between adsorbed cations and anionie-nonbridging surface oxygen groups (2.0 J/m2). The bonding interaction observed at room temperature depends upon the glass surface composition and the degree of surface hydration. When hydrated silicate solution species are added to the interface and heat treated, adhesion energies as large as the cohesive energy of silica glass can be obtained with heat treatments as low as 200 C. The adhesion of the silicate interfacial film produced by the addition of solution species is greatest for silicate precursors showing a low degree of molecular crosslinking. In addition, the presence of alkali in the silicate solution greatly enhances interface adhesion for heat treatments below 200 C.
Comparison Between the Sol-Gel Processes of Zirconia and those of Alumina
Authors: Pierre Alain C. , Uhlmann Donald R.
Published: March 2011

Zirconia gels have been synthesized from zirconium butoxide in excess water with HNO3. The structure and characteristics of the gels have been studied as a function of the acid content, and the transformation during heat treatment has been followed up to 1150°C.

From the results of a previous similar study on aluminum hydroxide gels, a comparison is made between the sol-gel processes of zirconia and those of alumina. A discussion of the differences of the aqueous media chemistry of Al and Zr, and gelation mechanisms, is presented.
Alumina Powders from Aluminum Alkoxide.
Authors: Ayral A. , Phalippou J. , Droguet J. C.
Published: March 2011

A new way of producing alumina powder from the alkoxide is reported. Aluminum basic acetate is first synthesized by reactions which allow controlled precipitation. The chemical reactions are followed using IR spectroscopy. Alumina powder is obtained by subsequent thermal decomposition.
Preparation of BaTiO3 by Sol-Gel-Processing
Authors: Tomandl G. G. , Rösch H. , Stiegelschmitt A.
Published: March 2011

Barium acetate, titanium ethoxide, and the acetates of calcium and magnesium and zirconium-n-propoxide as additives, were dissolved in an acetic acid methanol mixture. By adding water, this sol was converted to a gel.

Extended investigations of the calcination result in a crystalline barium tita-nate without other titanate phases, with a very small amount of carbonate and a negligible contents of free carbon. Aggregates could not be destroyed totally by the milling process. Therefore, the green density of the green bodies reaches only 60 to 65 %. Thus, a minimum sintering temperature of 1200° C was necessary to obtain a density of at least 95 %. In future work, a special treatment to destroy the aggregates must be developed to lower the sintering temperature.
Characterisation of Colloids and Gels
Authors: Ramsay John D.F.
Published: March 2011

Sol-gel processes can provide a route to oxide ceramics with controlled microstructure and homogeneity. This feature can be exploited from an understanding of the inter-relationship between the characteristics of concentrated sols and the microstructure of the resultant gels produced on dehydration. Among several characterisation techniques employed (light scattering, incoherent neutron scattering, viscoelastic behaviour) neutron small angle scattering (SANS) has proved particularly powerful in the study of the mechanism of the sol to gel conversion process. Applications of SANS in the characterisation of sols containing (a) discrete particles (charge stabilised), (b) mixed oxide systems, and (c) particle aggregates, with fractal properties are illustrated.
Characterization of the Surface Area and Porosity of Sol-Gel Films Using Saw Devices
Authors: Frye Gregory C. , Ricco Antonio J. , Martin Stephen J. , Jeffrey Brinker C.
Published: March 2011

A novel technique for accurately obtaining nitrogen adsorption isotherms on thin porous films has been developed. These isotherms are useful for characterizing the surface area and pore size distribution of porous samples. The sensitivity to adsorbed nitrogen is increased by several orders of magnitude over conventional techniques by forming the test film on the substrate of a surface acoustic wave (SAW) device. This device functions as a microbalance able to detect less than 100 pg/cm2 of film. Surface areas and pore size distributions calculated from adsorption isotherms obtained with this technique on silicate sol-gel films are compared to those for bulk samples prepared from similar sol-gel solutions.
Structural Evolution During the Sol to Gel Transition of Silicon-Alkoxide Based Sols Observed by Cryogenic Transmission Electron Microscopy (CRYO-TEM)
Authors: Bailey Joseph K. , Mecartney Martha L.
Published: March 2011

The gelation reaction for tetraethoxysilane in both acid and base catalyzed environments was studied using cryogenic transmission electron microscopy. The evolution of the gel structure was observed in wet samples by the technique of fast-freeze vitrification, in which the three dimensional gel structure is preserved in vitreous solvent. The sample is then observed in the electron microscope using a cold stage. Samples were prepared and allowed to react until a specific point of gelation was reached, then were vitrified at that point. Results from this technique show a coarse network structure for base catalyzed gels. This network is composed of silica clusters ≈40Å in size. The acid catalyzed gels show an extremely fine texture (<10Å) at end point of gelation. The structures at intermediate stages of gelation were also determined.
Conventional and Chemical Processing of High Tc Superconductors
Authors: Yan M. F. , Ling H. C. , O'Bryan H. M. , Gallagher P. K. , Rhodes W. W.
Published: March 2011

Conventional and chemical processing of the superconducting YBa2Cu3Ox ceramic powders are reviewed. Conditions for calcination, sintering and microstructural development are shown to be important considerations for the superconducting properties of YBa2Cu3Ox ceramics. We examine different forming techniques, e.g. dry pressing, hot pressing, tape casting and screen printing, to prepare superconducting components with different sizes, shapes and configurations. We also identify and discuss problem areas related to incomplete decomposition of BaCo3 precursor; oxidation of YBa2Cu3Ox ceramics; sensitivity of the YBa2Cu3Ox phase to water; reactivity of the YBa2Cu3Ox phase with substrates and co-firing materials; low critical current density in bulk ceramics of YBa2Cu3Ox and low mechanical strength of YBa2Cu3Ox ceramics.
Synthesis of Superconducting Powders by Freeze-Drying
Authors: Johnson Sylvia M. , Gusman Michael I. , Hildenbrand Donald L. , Eom C. B.
Published: March 2011

The freeze-drying method of synthesizing powders of the superconducting oxide YBa2Cu3O7-δ is described. This process produces homogeneous, submicron powders of high purity. The effects of salt selection, solution concentration and pH on the process are described. Some evaluation of the sintering behavior and the effects on critical current density are included.
Tailored Organometallics as Low-Temperature CVD Precursors to Thin Films
Authors: Girolami Gregory S. , Jensen James A. , Gozum John E. , Pollina Deborah M.
Published: March 2011

We have been investigating the use of “tailored” organo-metallic precursors for the chemical vapor deposition (CVD) of thin films in an effort to open up new approaches to the low-temperature synthesis of ceramic, electronic, and optical materials that contain transition metals. Following our approach to the successful deposition of high-quality titanium carbide thin films at 150–250°C from tetraneopentyltitanium, we have extended this technique to the preparation of other carbides, such as ZrC, HfC, TaC, and WC, at temperatures some 1000°C lower than previous CVD methods from the metal halides and methane. The details of the thermolysis of the organometálico precursors are most consistent with a mechanism involving homolysis of M-C bonds to give alkyl radicals followed by C-C and C-H bond activation steps. Metal diboride thin films such as TiB2, ZrB2, and HfB2 can be prepared at ca. 250 °C by CVD of suitable tetrahydroborate precursors: Ti(BH4)3-(MeOCH2CH2OMe), Zr(BH4)4, and Hf(BH4)4. In these cases, the principal byproducts are hydrogen and diborane. Mirror-bright, adhesive thin films up to 2 μm thick can be grown on a variety of substrates including glass, steel, aluminum, copper, silicon, and graphite. Despite the amorphous nature of the films, their electrical resistivities are essentially identical with those of the bulk polycrystalline material.
An Investigation Into the Preparation, Properties, and Processing of SiC/AIN and Si3N4/AIN Solid Solutions from Organometallic Precursors.
Authors: Interrante Leonard V. , Czekaj Corinna L. , Hackney Micheal L.J. , Sigel Gary A. , Schields Paul J. , Slack Glen A.
Published: March 2011

Solid solutions of SiC and AIN have been prepared by the co-pyrolysis of polysilanes and organoaluminum amides. In the presence of ammonia. Si3N4and AIN are formed. These materials are fully characterized by TEM, SAD, SEM, XRPD, and elemental analyses. The influence of reaction conditions, as well as precursor properties and reactivity, on the composition and morphology of these materials is addressed.
A Novel Route to Aluminum Nitride Ceramics Using a Polyaminoalane Precursor
Authors: Seibold M. , Rüssel C.
Published: March 2011

Metallic Aluminum is dissolved anodically in an electrolyte, containing a primary amine, an aprotic solvent and a tetraalkylammonium salt. Removal of the solvent and subsequent heating lead to a polymer network. Initial drying causes a more viscous liquid, further drying up to 150°C accelerates the polymerization process and a gel-like consistency is obtained. Pyrolysis is carried out under NH3 or inert gas atmosphere. X-ray diffraction data show amorphous products up to 800°C, treatment above 800°C leads to the desired ceramic product aluminum nitride. Peak broadening indicates extremely small crystallite sizes. Pressureless sintering without additives gives a compact product, having densities up to nearly 100% of the theoretical density.
Molecular Building Blocks in Low PH Silicon Sol-Gels: A Silicon-29 NMR Study
Authors: Kelts Larry W. , Armstrong Nancy J.
Published: March 2011

High field Silicon-29 NMR is used to study the structural intermediates in tetramethyl and tetraethyl orthosilicate (TMOS and TEOS) low pH sol-gel reactions. Linear oligomers as well as ring components of various sizes are identified and their evolution in the sols is followed. Differences in the number of compact ring structures are related to differences in gel times. Reactions are followed for various silicon alkoxide:water:acid molar ratios.
Preparation of Titanium Nitride (TiN1-x-yCxOy) from Ti(OPri)4-Triethanolamine Condensation Product by Pyrolysis
Authors: Kuroda Kazuyuki , Tanaka Yuji , Sugahara Yoshiyuki , Kato Chuzo
Published: March 2011

In order to develop new precursors for the preparation of titanium nitride, a Ti alkoxide-nitrogen containing polyol condensation product was prepared and heat-treated. A stoichiometric mixture of titanium tetra-isopropoxide (Ti(OC3H7)4) and triethanolamine (N(CHM2H4OH)3) was heated at ca. 200°C under reduced pressure. The distilled liquid was isopropyl alcohol and its amount indicated that the transesterification reaction proceeded almost quantitatively.

The condensation product was a transparent glassy solid on cooling to room temperature. Thermal treatment of the condensation product at 1600°C in a nitrogen flow yielded titanium nitride (TiN1-x-yCxOy) as the main phase with a small amount of Ti3O5. The thermal treatment for a longer time reduced the amount of the oxide. The heat treatment of the product in an Ar flow also yielded nitrogen containing ceramics, which indicated the effectiveness of nitrogen in the condensation product during the conversion.
The Use of Organometallic Precursors to Silicon Nitride as Binders
Authors: Schwab Stuart T. , Blanchard-Ardid Cheryl R.
Published: March 2011

Current techniques of advanced ceramic component fabrication are based on pressureless green body consolidation technology in which voids often remain in the final microstructure. Much of this residual porosity is created when the organic binder used to consolidate the ceramic powder burns off on sintering. A new concept in the field of ceramic processing is the use of an organometallic binder material which will pyrolyze on sintering and convert into a predetermined ceramic. Silicon nitride (Si3N4) is a ceramic material in great demand for elevated temperature applications because of its excellent high temperature properties. At the present time, silicon nitride cannot be successfully processed without the use of costly pressure sintering (e.g., hot pressing), or the addition of a glassy phase, which degrades the high temperature properties.

Various preceramic polymers to be used as binders for cold pressing operations have been synthesized and studied. It has been demonstrated that these polymers may be dissolved in an appropriate organic solvent and mixed with a powder. Removal of the solvent yields homogeneous mixtures which may be consolidated into highly dense (> 66% of theoretical) green bodies. The ceramic yields of these polymers have also been determined.
Synthesis and Properties of YBaSrCu3O6.9 Prepared from Soluble Precursors
Authors: Nigrey Paul J. , Kwak J. F. , Venturini E. L. , Eatough M. O. , Baughman R. J.
Published: March 2011

Solution chemistry routes have been used to prepare single-phased superconducting ceramics of YBaSrCu3O6.9 (1113). Resistivity measurements on air annealed samples showed a superconducting onset temperature of 85 K with zero resistance at 78 K which improves to 81 K upon oxygen annealing. Magnetization data show ca. 78% flux exclusion at 5 K for 1113. X-ray diffraction experiments revealed that an orthorhombic to tetragonal transition occurs near 590°C when 1113 was heated in air. This work has demonstrated that such techniques can be utilized to prepare solid solution material with properties similar to those observed in YBa2Cu3Ox (123).
Partially Hydrolyzed Alkoxysilanes as Precursors for Silica Aerogels
Authors: Tillotson T. M. , Hrubesh L. W. , Thomas I. M.
Published: March 2011

The classical sol-gel process for synthesizing SiO2 aerogels involves the hydrolysis/condensation of tetraethyoxysilane (TEOS) and/or teramethyoxysilane (TMOS) to produce a gel which can then be super-critically extracted to a low density, highly porous aerogel glass. Controlled hydrolysis of TEOS and TMOS leads to partially hydrolyzed compounds that can be subsequently water processed to form silica aerogels in the density range from .020 to .500 gms/cc. The partially hydrolyzed compounds are stable when sealed from moist air and can be stored for future use.

We discuss the controlled conditions used to obtain these compounds and present data that characterize their structure. We detail the procedures for preparing the wide range of aerogel densities. We also report on their use as an adhesive.
Precursor Chemistry and the Structure of Silica Aerogels
Authors: Schaefer D. W. , Brinker C. J. , Wilcoxon J. P. , Wu D.-Q. , Phillips J. C. , Chu B.
Published: March 2011

Small-angle X-ray scattering is used to characterize the structure of aerogels prepared by two-stage polymerization processes. Second-stage catalysis controls the resistance to collapse during drying with the base-catalyzed system being most resistant. Base catalysis in the second stage leads to compaction of the polymer network on short length scales. This short-scale rigidity makes the networks sufficiently robust to withstand the surface tension forces present during solvent extraction and re-exposure to the atmosphere. Aging in solution also improves aerogel quality. In this case, a dissolution-repolymerization process leads to short length scale circuits and improved rigidity.
Supercritical Fluid Applications in Advanced Materials Processing
Authors: Wagner Richard A. , Krukonis Val J. , Coffey Michael P.
Published: March 2011

The feasibility of using supercritical fluids to impregnate carbon/carbon composites with a ceramic precursor was successfully demonstrated. Improvements in mechanical properties and oxidation resistance were correlated with the distribution of silicon within the microstructure of the composites. In addition, supercritical fluids were also used to fractionate silicon carbide precursors and thereby control the physical properties and char yield.
Physics and Applications of DIP Coating and Spin Coating
Authors: Scriven L. E.
Published: March 2011

Dip coating is a simple old way of depositing onto a substrate, especially small slabs and cylinders, a uniform thin film of liquid for solidification into a coating. The basic flow is steady, and in it film thickness is set by the competition among viscous force, capillary (surface tension) force and gravity. Thickness and uniformity can be sensitive to flow conditions in the liquid bath and gas overhead. The faster the substrate is withdrawn, the thicker the film deposited. This can be countered by using volatile solutes and combining rapid enough drying with the basic liquid flow. Then the physics grows more complicated, theoretical prediction of process performance more difficult, and control of the process more demanding. Outside product R&D labs it is far less often used in precision coating manufacture than a variety of premetered coating methods.

Spin coating is a more recently developed way of getting onto piecemeal substrates, especially small flat disks, a uniform thin liquid film for the same end. The basic flow is unsteady radial drainage in which centrifugal and viscous forces so compete that ordinary (Newtonian) liquid of constant viscosity tends toward a uniform film that grows ever thinner ever more slowly. Volatile solvents are commonly used because conditions can often be found that adequately separate thinning by spin-off from later thinning and solidification by drying. Thickness and uniformity, today theoretically predictable, are sensitive to speed, gas conditions, and rheology of concentrating, solidifying liquid. For the rheology of photoresist coating in microelectronics, spin coating works well. For that of suspension coatings in magnetic disk technology the process demands more careful control; actually it is often modified.
Ellipsometric Imaging of Drying Sol-Gel Films
Authors: Hurd Alan J. , Jeffrey Brinker C.
Published: March 2011

Although controlled dip-coating is an established way to apply high quality uniform coatings, the details of the coating and drying process have not been deeply studied. Depending on the physical and chemical state of the sol and the parameters of dipping (dipping angle and speed), a variety of thicknesses and porosities can be achieved [1]. For optical coatings, the refractive index and optical thickness can thereby be controlled.

We have developed a method to view the drying front of a dip-coated film using broad beam ellipsometry [2], or “ellipsometric imaging.” In dip-coated films we take full advantage of the fact that a steady state is quickly reached where the drying line velocity matches the withdrawal velocity; however, the technique might also be used in unsteady situations such as spin coating. Imaging ellipsometry makes it possible to measure the refractive index and thickness profiles of both wet and dry films point-by-point in an entire image at once. These profiles provide important clues as to the relative importance of gravity, evaporation and other phenomena.
Poly [Benzobis Thiazole] (PBT)/SOL-GEL Microcomposites
Authors: Ross Haghighat R. , Kovar Robert F. , Lusignea Ricahrd W.
Published: March 2011

The objective of this Small-Bus i ness Innovative Research (SBIR) effort is to expand on work reported previously [1] and further develop a new class of microcomposite materials which combine the outstanding properties of ordered polymers and the excellent compressive strength of glass. In Phase I we demonstrated adverse property changes in poly(p-phenylene benzobisthiazole) (PBT) ordered polymer films by infiltrating sol-gel glass reagents. During Phase II we have addressed the following areas: sol-gel infiltration process; effect of sol-gel glass composition; tensile strength characterization, microcomposite UV resistance, lamination process, compressive strength determination. The following subsections present the work conducted to date.
Sol-Gel Processing of Lithium Niobate Thin-Layers on Silicon
Authors: Eichorst Dennis J. , Payne D. A.
Published: March 2011

Sol-gel processing was used for the fabrication of LiNbO3 thin-layers on semiconductors. Two different alkoxide systems were investigated (i.e., ethoxide vs. methoxyethoxide) to determine the role of solution chemistry on the evolution of structure in LiNbO3 layers. An alcohol exchange reaction, which produced lithium niobium methoxyethoxide, proved advantageous with respect to the amount of hydrolysis water content which could be added to give stable solutions. Spin-casting was used for the deposition of thin-layers which crystallized at 500 C on Si. The refractive index of sol-gel derived LiNbO3 was determined to be similar to sputtered or epitaxially grown films. Data are reported for the processing route and the material characteristics. Methoxyethanol based systems appeared to be more forgiving than ethanol based solutions for the fabrication of high-quality thin-layer devices.
Structure and Physical Properties of TiO2-V2O5 Gel Coatings
Authors: Hirashima Hiroshi , Kamimura Seiji
Published: March 2011

Semiconducting V2O5 gels containing up to 30 mol% of TiO2 were prepared through simultaneous hydrolysis of alkoxides in ethanol solution. Coatings of these gels about 5 nm to 20 μm,in thickness were made by dip coating. The coatings were yellowish green and transparent. The fiber-like structure of the gels was observed by TEM. The gels were about 10 nm or less in diameter, and the diameter decreased with increasing TiO2 content. The refractive indices, n, and the thickness, d, of the coatings were determined by ellipsometry. d was approximately proportional to the square root of the pulling rate. When d was less than 10 nm, the refractive indices parallel to the pulling direction were lower than those perpendicular to the pulling direction. The dc conductivity parallel to the surface of the coatings, σ//, of V2O5 gel coating was higher than that of crystalline V2O5. The dc conductivity perpendicular to the surface of the coatings, σ/, was about 3 to 4 orders of magnitude lower than σ//. With increasing Tio2 content, both σ// and σ/ decreased.
Synthesis of Inorganic Films from Organosilicon Polymers
Authors: Yu Yuan-FU , Heng Sangvavann , Patrizio Diane B. , McCormick Anthony W.
Published: March 2011

Multicomponents silicon based ceramic thin films were prepared by ion beam irradiation of organosilicon polymer films. Our approach involved dissolving organosilicon polymers in toluene and using spinning technique to deposit the polymer films. Four organosilicon polymers were used to prepare polymer films with various thickness (2000 Å to 5000 Å). These polymer films were then irradiated with high energy ion beams, 6.0 MeV F beam, 2.0 MeV He beam, 1.0 MeV Au beam, and 50 KeV N beam. Amorphous, crack-free, hard ceramic films of up to 4000 Å may be produced in this manner. The presence and concentrations of each elememt were monitored with proton recoil detection and Auger analysis. The in-situ loss of gases was monitored by quadrupole mass spectrometry. Cross-sectional TEM was used to determine the overall homogeneity and thickness of these films. These ceramic films provide significant protection of silicon substrates from high temperature surface oxidation and chemical corrosion.
Characterization of Baria-Alumina-Silica Glasses and Yba2Cu3O7−x Superconducting Films Prepared by the Sol-Gel-Process
Authors: Strehlow P. , Schmidt H. , Birkhahn M.
Published: March 2011

The preparation of eutectics in the system BaO-Al2O3-SiO2 by the conventional technique is carried out by fusions with intermittent crushing and grinding. Hydrolysis and polycondensa-tion of alkoxides in a suitable solvent provide a simple way to obtain the homogeneous baria-alumina-silica glasses. The physical and chemical changes which occur during the gel-to-glass conversion were investigated on gel powders by thermal gravimetric analyses, differential thermal analyses, mass spectroscopy, nitrogen sorption analyses, and dilatometry.

By means of the sol-gel route it is also possible to prepare coating solutions in the Y-Ba-Cu-system. Coatings of composition YBa2Cu3O7−x were deposited on substrates using dip coating and characterized by scanning electron microscopy and measurements of superconducting temperature.
Electrical Properties of Metal-Oxide-Silicon Structures Wrm Sol-Gel Oxides
Authors: Warren W. L. , Lenahan P. M. , Brinker C. J.
Published: March 2011

We have investigated the electronic properties of sol-gel derived films on silicon substrates. Our investigation involves SiO2, aluminosilicate and borosili cate oxides on silicon. Seme sol-gel oxides are excellait insulators; seme sol-gel films on silicon also exhibit quite low oxide/silicon interface trap densities. We have also subjected sol-gel films on silicon to 4 Mrad(SiO2) of radiation and have found that these structures appear to be radiation hard (very little radiation induced oxide space charge or interface trap generation). Our results strongly suggest that sol-gel processing could provide insulating films for a variety of microelectronic device applications.
Ceramic Technoindgy and Problems of Social Evolution in Southwestern Iran
Authors: Blackman M. James
Published: March 2011

The use of the technology of manufacture of a class of artifacts as data to address questions of culture process {social evolution} is fraught with pitfalls. This is especially true with ceramic technology. The study of this type of artifact begins with a basic circularity for most prehistoric periods in most areas of the world. Many prehistoric chronologies are based on the most abundant and durable artifact, ceramics. Periods or phases are, to a large extent, defined by similarities in form, style, and production methods of these ceramics. Therefore using more refined assessments of the technology of production to assess changes occurring between periods or phases and to infer cultural change is merely reaffirming the cornequences, and reinforcing an image of abrupt step wise progression. This image is of little help in understanding the inner causes and dynamics of social or technological evolution. The use of more refined ceramic technological data to test the validity of a chronology based on ceramic data must be used with great caution.
Working of Gem Materials: Consequences of the Indian and Sri Lankan Sea Trade
Authors: Foster Giraud V.
Published: March 2011

The major events that promoted gemstone jewelry production in ancient Rome included: the separation of gold from silver, the expansion of land trade routes to the east, and presentations of treasure during Roman triumphs that popularized eastern jewelry. In this paper a fourth event is studied, namely the development of the sea trade to India and Sri Lanka that made possible the importation of sapphires and diamond technology. Classical references were reviewed, methods of identifying Sri Lankan sapphires were explored, and experimental studies were undertaken to test various bow drills, abrasives, and methods of securing stones and abrasive onto solid surfaces. From these studies it is concluded that (1) opaque dark blue sapphires were imported from central India around the first or second century A.D. and pale blue transparent stones from Sri Lanka by the fourth century A.D., (2) with the importation of sapphires, industrial diamonds and lac technology was also brought to the west, and (3) a wide variety of bow drills were probably employed, however, for hard stones, the horizontal bow driven lathe was probably preferred because of the relative ease with which stones could be worked against it.
Tapping the Memory in Archaeological Materials
Authors: Notis Michael R. , Lyman Charles E. , Moyer Heidi , Cowen Christopher
Published: March 2011

In the areas of archaeology, archaeometry, museum management and conservation science conflict often exists between the desire to preserve, and the desire to understand an artifact. This conflict exists because much laboratory analysis can be destructive. However, conservation can best be done when the materials and techniques that were used for making the object originally are understood. Thus there is a constant drive to develop non-destructive and/or microsample analysis procedures that are meaningful in terms of the statistical accuracy of the results and the added understanding that they provide. In addition to the availability of new microanalytical techniques, the scientific approach developed in materials science is of great value to the fields of archaeometry and conservation science. The ‘materials science approach’ involves the determination of structure and chemistry at various levels in the microstructural hierarchy, and includes the relationship between this structure and chemistry and the material's properties. On the other hand, the study of archaeological materials can be of great value to the materials scientist because these objects exist in a time frame not reproduceable in typical laboratory experiments.
The Soldering of Gold in Antiquity
Authors: Demortier G.
Published: March 2011

Results of non-destructive analyses of solders on gold jewelry artefacts involving the irradiation of the material with protons and the prompt detection of X-ray signals allow us to understand the joining procedures used by ancient goldsmiths.

A non conventional interpretation of the Natural History (33th Book) of Elder Pliny (1st cent. A.D.) concerning chrysocolla (or goldsolder) sheds some light on the present debate around the possible use (in antiquity) of greenockite (natural CdS) as an alloyed element with gold to achieve low melting point brazing.
Obsidian Hydration Dating - Field, Laboratory, and Modeling Results
Authors: Mcgrail B.P. , Pederson L.R. , Strachan D.M. , Ewing R.C. , Cordell L.S.
Published: March 2011

Hydration rind thicknesses found on obsidian artifacts provide one means of estimating the age of an archaeological site. The model used in the method usually assumes a diffusion-controlled reaction of the glass with water. However, results using this model are not always in agreement with other dating methods. Observations of secondary mineral formation on glasses in contact with water vapor suggests that other rate-controlling mechanisms may be operative. In this paper, we apply the glass dissolution code GLASSOL, coupled with the geochemical code PHREEQE to model the reaction of Glass Mountain obsidian in water. The results show the importance of accounting for the effects of solution chemistry on the time-dependence of the hydration reaction.
Induced Obsidian Hydration Experiments: An Investigation in Relative Dating
Authors: Tremaine KIM J. , Fredrickson David A.
Published: March 2011

Induced obsidian hydration experiments have been conducted over the last six months at Sonoma State University. Our initial focus has been to assess the influence of experimental conditions on hydration development within a thermally controlled pressure reaction vessel. Although an ultimate goal is to calculate source-specific rates for local obsidians, given current uncertainties regarding the ability to reliably express hydration widths as calendar years, a more immediate goal is to develop a means to compare hydration rim measurements of samples from one obsidian source relative to another so that archaeological assemblages containing obsidians from two or more sources can be placed into a time series. Induced hydration experiments are expected to provide data that illustrate the relationship between hydration measurements of different obsidians with temporal equivalency. Results and implications of initial experiments are discussed.
The Fading of Some Traditional Pigments as A Function of Relative Humidity
Authors: Bailie C. W. , Johnston-Feller R. M. , Feller R. L.
Published: March 2011

As part of a project sponsored by the Getty Conservation Institute to investigate the effects of humidity and temperature on photochemicallyinduced deterioration, the influence of relative humidity on the rates of fading of four traditional artists' pigments has been investigated -- carmine lake, gamboge, alizarin lake and Vandyke brown.
Lead Isotope Analysis for Provenance Studies in the Aegean Region: A Re-Evaluation
Authors: Reedy Chandra L. , Reedy Terry J.
Published: March 2011

For more than a decade lead isotope analyses have been used in attempts to identify ore sources for silver and lead artifacts from the Aegean region. These regional provenance studies have been used to formulate statements on archaeological issues in the Aegean. Methods of data analysis and presentation used to interpret lead isotope analyses have been borrowed directly from the field of geology, where this technique was developed and originally applied. However, the goals of geologists and those of archaeologists are not the same.
Use of FTIR-Microspectrometry in Examinations of Artistic and Historic Works
Authors: Baker Mary T. , endt David W. Von
Published: March 2011

Infrared Spectroscopy (IR) has traditionally been considered a “non-destructive” analysis method because it causes no chemical change to the sample, and the sample can be recovered for further analysis. However, physical changes are generally necessary for the sample to be introduced into the spectrometer: slicing, crushing, dissolving, melting, etc. In an art object or historical artifact, these sampling methods can be considered somewhat “destructive.”
Reconstructing and Interpreting the Technologies of Ancient Ceramics.
Authors: Vandiver Pamela B.
Published: March 2011

The application of modern methods and strategies of materials science has allowed study of the technology of ancient ceramics to enter a new era. Ceramics include refractories, plasters and cements, some pigments, glasses, pottery, porcelain, bricks, tiles and enamels. Some of the questions necessary to understand and interpret ancient ceramics are given below.
Environmentally Enhanced Fracture of Ceramics
Authors: Freiman Stephen W.
Published: March 2011

This paper presents a review of our current understanding of environmentally induced crack growth in glasses, single crystal ceramics, and polycrystalline ceramics. It is shown that the rate of crack growth is controlled by the chemical activity of the active species in the environment as well as by the crack tip stress. A molecular model of a stress-induced chemical reaction between vitreous silica and water is described, and the implications of this model for predicting the effects of other chemical species on crack growth are discussed. Effects of chemical bonding in the solid as well as in the reacting solutions, on the crack growth mechanism are elucidated. Finally, the complicating effects of multigrain arrays on crack extension in polycrystalline ceramics are pointed out.
Electron Interaction with Alkali Chromium Fluorides in the High-Resolution Electron Microscope
Authors: Sharma Renu , Eyring LeRoy
Published: March 2011

Different structure types related to the hexagonal tungsten bronze structure have been observed in the AxCrF3 sytem (A= K, Rb) by electron diffraction and high resolution electron microscopy. These structures decomposed into alkali metal and CrF3 in the electron beam. The former evaporates, leaving the original structure highly unstable. CrF3 crystallizes via a highly disordered phase to a distorted ReO3–type structure.
Lifetime Prediction of Organic Coatings on Steel
Authors: Kendig M. , Mansfeld F.
Published: March 2011

A review of methods for predicting the lifetime of protective organic coatings on steel is presented in terms of a model which includes the steps of defect formation, transport of corrodents, loss of adhesion, and corrosion. Electrochemical impedance methods and acoustic techniques have played important roles in characterizing how the four processes interact and depend on coating processes and environmental effects. A major result of this work has been the observation that both the anodic and cathodic partial processes of the corrosion reaction limit adhesion of organic coatings on steel by generating tensile stresses and polymer degradation, thereby limiting the life of the protective system.
Phthalocyanine and Polyphthalocyanine Coatings for Corrosion Protection of Metals
Authors: Hettiarachchi S. , Chan Y.W. , Wilson R.B. , Agarwala V.S.
Published: March 2011

The effectiveness of phthalocyanines and polyphthalocyanines as corrosion inhibiting coatings for protection of steel have been studied. The metallo-phthalocyanines studied included phthalocyanine tetracarboxylates of Fe(III), Co(II), VO(IV), Cr(III), Si(IV) and Zn(II). Polymeric phthalocyanine coatings based on Fe(III) polyphthalocyanines gave the highest inhibitor efficiency of 82%, as confirmed by AC impedance analysis. The polymerization was achieved by simple dip coating followed by heat treatment of the coated surface at 450°C in an inert atmosphere. The resulting coating is adherent and electrically conducting when appropriately doped. Our recent findings indicate that the inhibition efficiencies can be further improved by introducing a long alkyl chain into the phthalocyanine molecule.