bluuebunny/crossref_metadata_2025 huggingface dataset:
Porosity/Diffusivity And Alkali-Silica Reaction
Authors: Moranville-Resocurd Micheline
Published: March 2011

Physical and chemical processes are responsible for the alkali-silica reaction in concrete. Physical processes include (i) migration of hydroxyl and alkali ions (ii) swelling by water imbibition of the alkali-silica gel produced, (iii) development of cracks. Chemical processes involve (i) neutralisation of acidic silanol groups and attack of siloxane bridges, both by OH- ions (ii) formation of an alkali silicate. These reactions result in a breakdown in the silica structure and diffusion of some silicate and impregnate the cement paste filling the capillary pores. The increase in permeability due to the opening and progression of cracks facilitates secondary chemical deteriorations like the formation of ettrinqite, carbonation and corrosion of steel reinforcement. Recent studies have emphasized the role of Ca(OH)2 preventing the dissolution or miqration of freed silica out of the structure. Only the removal of Ca(OH)2 is able to stop the expansion of concrete.

The paper will present some new interpretations of alkali-silica reaction related to the diffusivity of various ions from the pore solution.
Pore Structure And Its Relationship To Properties Of Materials
Authors: Pereira C. J. , Rice R. W. , Skalny J. P.
Published: March 2011

Pore structure affects almost all the physical properties of materials and, thus, is important in engineering practice. Engineering desired physical properties by microstructural modification of the porosity and/or the solid phases has practical importance and, therefore, there is considerable research activity in developing relationships between the desired physical properties and the pore structure. The ability to vary the level of porosity, the pore size distribution, pore shape, and pore connectivity opens new opportunities for developing materials not only for conventional uses but also for novel applications such as electronics.
The Porosity and Pore Structure of Hydrated Cement Pastes as Revealed by Electron Micrsocopy Techniques
Authors: Richardson Ian G. , Groves Geoffrey W. , Rodger Sally A.
Published: March 2011

The application of transmission electron microscope techniques to the study of cement hydration can reveal the nature of the fine pore structure present in dried cement pastes. Studies of OPC cement pastes and OPC/fly ash or blast-furnace slag blends are presented and compared. Preliminary results of a technique which allows effective imaging of the porosity which is important in permeation, and which is involved in mercury porosimetry measurements, are presented.
Corrosion of Hardened Cement Paste by NH4NO3and Acetic and Formic Acids
Authors: Bajza Adolf
Published: March 2011

Effects of NH4NO3, CH3COOH and HCOOH solutions on the pore structure and other properties of hardened cement pastes made out of portland, slag, and fly ash cements at different water-to-cement ratios are discussed.

Total porosity and the volume of pores detectable by mercury intrusion porosimetry (MIP) increased with increasing water-to-cement ratio, concentration of aggressive solution, and time of immersion. The weight, bulk density, and compressive strenath of the samples decreased at the same time. Use of blended cements did not result in improvement of the long-term durability of the samples. The degradation of the cement pastes increased from NH4NO3to CH3COOH to HCOOH.
Studies Of Cement Grouts And Grouting Techniques For Sealing A Nuclear Fuel Waste Disposal Vault
Authors: Onofreic Maria , Gray Malcolm N. , Keil L. Douglas , Pusch Roland
Published: March 2011

A cement-based grout (90% Type 50, 10% silica fume, 0.4 < water-to-cement ratio, w/c < 0.6) has been used in field trials at AECL's Underground Research Laboratory in Canada and at the OECD/NEA Stripa Mine in Sweden, to evaluate suitable grouts and grouting techniques that could be used for sealing a nuclear fuel waste disposal vault mined deep in granite. Laboratory studies have been carried out to determine the following grout properties: hydraulic conductivity (k); resistance to piping and erosion during setting; influence of grout on the pH and chemical composition of water permeating grouted rock; and the ability of the grout to self-seal after fracturing.

Laboratory tests have confirmed the low intrinsic k of these cement mixtures (10−14 m/s). Using a specially developed cone-in-cone apparatus, we have studied the effect of fracture dilation and temperature changes on the k of thin films of cement. If fractured, the grout has an ability to self-seal and the rate of self-sealing increases with increasing temperature.

The pH and ionic composition of the water permeating grouted fractured granite rock were found to vary with grouted fracture aperture and grout/rock volume ratio. The field tests demonstrated that grout can penetrate and seal very fine fissures (apertures less than 50 μm).
Seawater Leachability Of Cement Solidified Heavy Metal Wastes
Authors: Elkorchi Tahar , Campbell Kristine , Gress David
Published: March 2011

The seawater leachability of portland cement solidified cadmium and lead wastes is investigated. The synthetic seawater leachates were analyzed for metals content using atomic absorption spectrophotometry. The pH and alkalinity of the leachate was also measured. The cumulative cadmium release after 46 days of leaching was approximately 1.0 percent of the initial total amount added to the portland cement mixture. Lead was not detected in the leachate. The pH was initially higher and the alkalinity lower and subsequently approached the pH and alkalinity values for seawater after 30 days of leaching.

The microstructure of the solidified waste was investigated using the SEM, XRD, MIP and helium pycnometry. Cadmium was detected as cadmium hydroxide while lead was not detected in crystalline form. The total porosity of cadmium and lead wastes were similar however the cadmium waste had a higher volume of pores larger than 0.2 microns.

During the leaching process the surficial microstructure of the solidified waste exhibited a dynamic layer of calcite, aragonite and brucite while the internal structure showed large amounts of ettringite crystals in the cadmium waste only which caused excessive expansion and cracking. A proposed leaching mechanism experienced by the solidified waste is related to the microstructural characteristics of the matrix.
Relationships Between Permeability And Microstructural Characteristics Of Fly Ash Mortars
Authors: Day Robert L. , Konecny Ladislav
Published: March 2011

The paper describes research to evaluate permeability and the microstructure of mortars containing fly ash as a partial replacement for cement. The replacement levels of cement by fly ash were 35 and 50% by volume and 50% by weight; effectiveness of mortars made with four types of fly ash at two water/cement ratios, 0.47 and 0.65, were assessed. Three types of permeability measurements were made: (a) water permeability, (b) oxygen permeability and (c) permeability to chloride ion by the 6-hour rapid permeability test. Measurements were performed at 7, 28 and 160 days age. Strength gain in the mortar mixes was also monitored. In an attempt to explain trends observed in permeability, the pore structures of oven-dried and solventexchanged specimens were examined by mercury porosimetry. Mortars manufactured with fly ash displayed superior engineering properties when compared to the control mortars. Significant correlations were found among measurements of permeability by water, oxygen and chloride ion. Relationships were also observed between permeability and some microstructural indicators, especially the volume of mercury intruded up to a pressure of 41 MPa (6000 psi).
Pore Structure, Permeability, And Chloride Diffusion In Fly Ash-And Slag-Containing Pastes And Mortars
Authors: Malek R. I. A. , Roy D. M. , Fang Y.
Published: March 2011

The transport of ions through cement pastes and mortars with variable contents of fly ashes and granulated blast-furnace slag from different sources and with variable composition has been investigated. The research included the determination of chloride diffusion rate and chloride permeability in relation to microstructure development. The median pore size generally was much diminished in mature blended material compared with Portland cement (PC) pastes and mortars. It appears that, at the same age, a finer microstructure is generally developed in blended specimens compared to PC specimens. Also, it was found that the microstructure approaches a limiting value at longer ages of hydration. That limiting value may be reached at earlier ages with the blends. The chloride diffusion rates and permeabilities in the blends were significantly lower than PC mixes. A comparison between the blends containing fly ashes and those containing slag was made.
Chloride Permeability Of Concrete Containing A Flyash And A Blastfurnace Slag
Authors: Kawamura Mitsunori , Torii Kazuyuki
Published: March 2011

The effects of curing conditions on the chloride permeability of concrete with various replacements of Portland cement by a flyash and a blastfurnace slag was investigated. In order to relate the porosity and pore size distribution of concretes to their chloride permeability, mercury intrusion porosimetry measurements were also conducted. The results showed that exposure of concretes to a relatively low humidity at early ages increased their chloride permeability. It was also found that the chloride permeability of concrete increased proportionally with increasing volume of pores larger than 0.1 μm in diameter.
Densification And Migration Of Ions In Blast Furnace Slag-Portland Cement Pastes
Authors: Feng Q. L. , Lachowski E. E. , Glasser F. P.
Published: March 2011

Well-cured slag cement blends are known to give rise to paste matrices of low permeability. Electron microscopy has been used to follow microstructural development in slag cement pastes. An initially dense layer of hydrated product develops around the slag grains. Its chemistry and microstructure are not constant but evolve with time. These variations have been explored by analytical electron microscopy, X-ray diffraction, etc. Mg is concentrated in this zone and serves as a useful chemical marker. However an outer matrix of mixed hydration products also develops, to which slag and cement both contribute. The additional contribution of Ca, Al and Si derived from slag to this matrix is considered to explain its gradual densification and resultant low permeability.
The Porosity And Pore Structure Of Hydrated Portland Cement Paste
Authors: Feldman R. F.
Published: March 2011

Pore structure and the surface area of the pores are the most important characteristics controlling the properties of porous materials. Many techniques, based largely on nitrogen or water vapour isotherms or mercury porosimetry, have been used to determine the pore structure of solids. Values obtained from these methods have been relatively reliable for materials with pore structures that remain stable on removal or addition of water.
As Review Of Conventional And Non-Conventional Pore Characterization Techniques
Authors: Gerhardt Rosario
Published: March 2011

A series of techniqu1es were employed to characterize the pore microstructure of a group of colloidal silica-alkali silicate gels. Methods used included mercury penetration porosimetry, nitrogen desorption measurements, transmission electron microscopy, single and multiple small angle neutron scattering, nuclear magnetic resonance relaxation measurements, x-ray tomography and dielectric constant measurements. Comparison of results of pore volume, pore size and size distribution as well as homogeneity of the pore structure are presented.
Methodologies Of PSD Measurements In HCP : Postulates, Peculiarities, And Problems
Authors: Diamond Sidney
Published: March 2011

A brief discussion is presented of some of the characteristics of hardened cement paste (hcp) and hcp in concrete that bear on the measurement of pore size distribution. The postulates underlying several present and potential measurements are discussed individually, and an attempt is made to assess the applicability of each in light of the peculiar characteristics of hcp. Some of the problems inherent in each procedure are briefly described.
Formation of Interstitial Defects in High Concentration Shallow Phosphorous Diffusions in Si.
Authors: Jaccodine Ralph
Published: March 2011

An experimental study of high concentration (1019 –1021 /cm3 shallow diffusion was undertaken using TEM to investigate the nature of these diffusion-related defects. Phosphorous from a wide variety of sources (PBr3, POCl3, etc.) other than ion implantation was used in temperature range from 950°– 1100°C and for times of 15 minutes to 1 hour. Care was taken in surface preparation and material selection to avoid extraneous defects from sources other than the diffusions.

A high concentration of small dislocation loops (1012/ cm2) was present in the top few microns of the wafers. Diffraction contrast on the loops revealed that they are of edge character with Burger's vector b = ½<110>. Identification of the nature of these loops by tilting method [(g·b)·s] and anomalous dark-faced black-white lobes show they are of the interstitial type, i.e. the observed defects place the surrounding matrix in a compressive state.
Infrared-Absorption of Thermal Donors in Silicon
Authors: Oeder Robert , Wagner Peter
Published: March 2011

Thermal donors generated in CZ-silicon by annealing at 450° C are investigated by infrared absorption spectroscopy.Up to nine double-donors can be distinguished due to their line spectra characteristic for effective-mass-like donors.Their number and their concentrations depend on the duration of the thermal treatment. The formation of the different donors is ruled by complicated kinetics.
Correlation of Oxygen and Recombination Centers on a Microscale in Asgrown Czochralski Silicon Crystals
Authors: Nauka K. , Gatos H. C. , Lagowski J.
Published: March 2011

Quantitative microprofiles of the interstitial oxygen concentration and of the excess carrier lifetime, with a spacial resolution of about 20 μm, were obtained in as-grown dislocationfree CZ-Si crystals employing a double laser absorption technique. It was found that maxima (minima) in oxygen concentration along the crystal growth direction coincide with minima (maxima) of the lifetime. It was further found that the relation between changes in oxygen concentration and in lifetime varies in the radial direction indicating that “as-grown” oxygen precipitates are involved in lifetime limiting processes.
Oxygen Precipitation in Silicon - Its Effects on Minority Carrier Recombination and Generation Lifetime
Authors: Varker C. J. , Whitfield J. D. , Fejes P. L.
Published: March 2011

The effects of oxygen precipitation on the minority carrier recombination lifetime (TR) and the carrier generation lifetime (TG) have been characterized for a ‘typical’ silicon crystal grown with the Czochralski method. Infrared (IR) absorption measurements were obtained on polished wafers, before and after 2 step thermal anneals at 800°C and 1050°C to characterize the axial distribution of interstitial and precipitated oxygen in the ingot. Computerized measurements on NMOS diode and capacitor arrays were used to characterize the axial and radial distributions of carrier lifetime. The results indicate that oxygen precipitation is the dominant mechanism contributing to the degradation of both minority carrier recombination andgeneration lifetime.
Crystalline Particles in Thermally Grown Silicon Dioxide
Authors: Ponce F. A. , Yamashita T.
Published: March 2011

Small crystalline particles in the vicinity of the Si/SiO2 interface have been directly observed by high resolution transmission electron microscopy. These crystallites have typical diameters between 20 and 120 Å. Based on the observed interplanar spacings and angles in lattice images, the structure of these particles has been found to match those of cristobalite. Some orientation relationships also appear to exist between these particles and the silicon layer.
Deep Radiative Transitions in InP
Authors: Temkin H. , Dutt B. V.
Published: March 2011

Results of a detailed photoluminescence study of deep radiative transitions in InP crystals prepared by bulk and epitaxial techniques with a variety of dopants are reported. In order. to understand the origin of the photoluminescence spectra, bulk samples were subjected to isothermal anneals at different partial pressures of phosphorus. Similarly, the LPE wafers were grown with and without phosphorus in the gas stream. The electrical nature of some of the species responsible for the PL emission was inferred by a study of Cddiffused bulk samples.

Based on these experiments the following tentative assignments are proposed. The photoluminescence band at 0.99 eV, common to all samples, is due to emission from a donor-like level related to the P-vacancy-impurity complex. Bands at 1.21 eV and 1.15 eV appear to be due to emission to native acceptor levels associated with the In-vacancy. The 1.08 eV band is attributed to emission to a level involving the complex of the donor (0.99 eV) and acceptor (1.21 eV) species. The relationship between these bands and residual impurities is discussed. A comparison with the work of other investigators tends to support these assignments.
Analysis of Defects in Heavily-Doped MBE-GaAs
Authors: Carter C.B. , Desimone D.M. , Griem H.T. , Wood C.E.C.
Published: March 2011

GaAs Has Been Grown By Molecular-Beam Epitaxy (MBE) With Large Concentrations (∼1018CM−2) Of Sn, Si, Ge, And Mn As Dopants. The Heavily-Doped N-Type Material Has Been Found To Contain Regions Of A Very High Dislocation Density. An Analysis Of The Less Complex Defect Areas Shows That The Dislocations Originate In The MBE-Grown Layer. These Observations And Others On More Complex Defect Clusters Are Compared With Recent Studies Of Defects In Material Grown By Liquid Phase Epitaxy (LPE). The More Heavily Doped P-Type Material Contains Discs Of Mn-Rich Material At The Surface Of The MBEgrown Epilayer. Both The Structure And Composition Of These Regions Have Been Examined.
Process-Induced Defects in High-Purity GaAs
Authors: Campbell P. H. , Aina O. , Baliga B. J. , Ehle R.
Published: March 2011

High temperature annealing of Si 3 N4 and SiO2 capped high purity LPE GaAs is shown to result in a reduction in the surface carrier concentration by about an order of magnitude. Au Schottky contacts made on the annealed samples were found to have severely degraded breakdown characteristics. Using deep level transient spectroscopy, deep levels at EC–.58eV, EC–.785eV were detected in the SiO2, capped samples and EC–.62eV, EC–.728eV in the Si3N4 capped Samples while none was detected in the unannealed samples.The electrical degradations are explained in terms of compensation mechanisns and depletion layer recombination-generation currents due to the deep levels.
Interaction of Dislocations with Impurities and its Influence on the Mechanical Properties of Silicon Crystals
Authors: Sumino Koji
Published: March 2011

A review is presented of the work on the influence of impurities on the dynamic behavior of dislocations in silicon crystals and also on the resulting effects in the mechanical strength performed by the author's group. Special emphasis is laid on the effects of light element impurities such as oxygen, nitrogen and carbon. Although all of these impurities do not affect the velocities of dislocations moving under relatively high stresses, oxygen and nitrogen atoms are found to lock slowly moving dislocations and dislocations at rest very effectively. Such locking of dislocations results in the decreases in the activities of generation and multiplication centers for dislocations, leading to the strengthening of the crystals. The high strength of silicon crystals brought about by the impurities is lost when the crystals are subjected to the heat treatments which allow the precipitation of the impurities on a macroscopic scale. This softening is shown to be caused by dislocations punched out from precipitates and by the exhaustion of the impurities dissolved in the matrix crystal.
Shear Force Effects on Sidewall Penetration of Extended Dislocations in Phosphorus Implanted Emitters
Authors: Tseng W. F. , Davis G. E.
Published: March 2011

Phosphorus implanted emitters are known to have a dislocation network formed to relieve the strain caused by the lattice contraction of solute phosphorus ir, silicon. The extension of the dislocation network into the emitter-base regior, has also been related to the degradation of leakage current and the generatiol, of excess noise in an NPN bipolar transistor. The penetration of the extendeot dislocation network is shown in this paper to be related to a shear force. The shear force is the resultant of the compressive force generated from the solute phosphorus and an induced surface force generated from the thick oxide layer over the emitter formed during high temperature heat treatments. This shear force can pull the dislocation network through the junction sidewall.
Photoplastic Effects in II-VI Crystals
Authors: Takeuchi Shin , Maeda Koji , Nakagawa Kiyokazu
Published: March 2011

A reversible change in the flow stress with the illumination of a band gap light (photoplastic effect: PPE) is observed commonly in II-VI semiconducting compounds both with the zincblende and the wurtzite structures. After reviewing the experimental results accumulated so far concerning the usually observed PPE, detailed microscopic experiments on CdTe (partly on CdS) single crystals are described. In-situ TEM straining experiments with a laser illumination system clarified that the dislocation mobility, evidently controlled by the Peierls mechanism, is not affected by light illumination.The investigation of the dislocation glide behavior over a longer range using the etch pit method and the cathodoluminescence microscopy with a SEM revealed that the dislocations are apt to become immobilized after traveling a certain distance from the sources with a high velocity.The dislocation loops and cusps observed by TEM suggest that the immobilization is caused by jog formation along screw segments. Those results suggest that the positive PPE is caused by the decrease in the mean free path of multiplied dislocations due to the enhanced jog formation by illumination. This viewpoint is supported by the high density of dislocation debris left in specimens deformed under illumination, the enhanced work hardening rate under illumination and the reduction of the PPE when the dislocation mean free path becomes determined by other photoinsensitive factors such as forest dislocation cutting and specimen size. The microscopic mechanism of the enhanced jog formation is discussed in terms of electrostatic interaction between charged point defects and dislocation charge which is increased with the illumination.
Quenched-in Defects in CW Laser Irradiated Virgin Silicon.
Authors: Chantre A. , Kechouane M. , Bois D.
Published: March 2011

Quenched-in defects in cw laser irradiated silicon have been identified using deep level transient spectroscopy. Four among the five dominant defect states arise from transition metal impurities (iron, chromium) present in precipitates in the as-grown material and dispersed into the crystal upon heat treatment. Native defects are involved in the form of phosphorous-vacancy complexes, which account for the remaining level.
Combined Oxygen - Nitrogen Ion Implants into Ti6Al4V
Authors: Greenwald Anton , Daly James , Meroth John , Oliver Richard , Sioshansi Piran , Clayton Clive
Published: March 2011

The alloy preferred for medical protheses, Ti6Al4V, was ion implanted with oxygen and nitrogen alone and in combination at varying energies, 25 to 120 keV, and varying dose levels, 1017 to 1018 ions/cm2. Measurements were made of microhardness, corrosion resistance, chemical bonding of implanted species, and (with UHMpWol yethylene) pin-on-disk wear and friction. The addition of oxygen to nitrogen implants now used in production was found to have little effect on wear or any other parameter.
A Review of European Trends in Space Tribology and its Application to Spacecraft Mechanism Design
Authors: Rowntree Robert A. , Todd Michael J.
Published: March 2011

The development of space tribology and its application in the design of spacecraft moving mechanical assemblies (MMA's) in Europe has followed a different course from that in the USA. This is probably because of the distinct preponderance of 3-axis stabilised space vehicles - used for communications and for earth observation over Europe - together with the preference for solid lubricants in such devices as solar array drives and some types of scanner and de-spin mechanism. The paper reviews the current status and discernible future trends in European space tribology. Examples of current MMA types are given where evolved lubricants and lubrication techniques have been applied.
MoS2 Interactions with 1.5 eV Atomic Oxygen
Authors: Martin J.A. , Cross J.B. , Pope L.E.
Published: March 2011

Exposures of MoS2 to 1.5 eV atomic oxygen in an anhydrous environment reveal that the degree of oxidation is essentially independent of crystallite orientation and thesurface adsorbed reaction products are MoO3 and MoO2. A mixture ofoxides and sulfide exist over a depth of about 90 Å and this layer has a low diffusion rate for oxygen. It is concluded that a protective oxide layer will form on MoS2 upon exposure to the atomic-oxygen-rich environment of low earth orbit.
Reduction in Wear Rate of α-Alumina and Silicon Nitride by Diffusional Surface Modification
Authors: Gangopadhyay A.K. , Fine M.E. , Cheng H.S.
Published: March 2011

The surface regions of α-alumina and hot pressed silicon nitride were modified by suitable alloying in order to improve their wear resistance. The surface modification in polycrystalline α-alumina was done by diffusing chromia into the surface region which resulted in the formation of a thin layer of A12O3 - Cr9O3 solid solution which has a lower thermal expansion coefficient than pure α-alumina. Also Cr2O3 has a larger lattice parameter than α-alumina thus during cooling the surface was put into compression. The surface region of hot pressed silicon nitride was modified by diffusing α-alumina into the surface which resulted in the formation of a thin sialon layer. A surface compressive stress was again introduced due to the lower thermal expansion coefficient and larger latticeparameter of sialon compared to silicon nitride.

Wear tests were conducted against 52100 steel under both lubricated and unlubricated sliding contact using a block on ring apparatus. The wear resistance of chromia surface alloyed α-alumina was improved considerably over unalloyed α-alumina under both lubricated and unlubricated conditions. The wear resistance of alumina surface alloyed silicon nitride was also improved over unalloyed silicon nitride under both lubricated and unlubricated conditions.

Different wear modes were identified by examining the worn surfaces under the scanning electron microscope.
Surface and Bulk Oxidizing Species for Self Lubricating Ceramics
Authors: Blanchard-Ardid C. R. , Lankford J. , Page R. A.
Published: March 2011

The use of ceramic materials for high temperature engine applications has prompted interest in the friction and wear characteristics of ceramicceramic pairs in mating contact. This interest has led to both surface and bulk material modifications aimed at improving the lubricity and wear resistance of these materials. This paper will discuss two basic systems developed to allow self-lubrication at high temperatures in ceramic materials through the formation of a lubricious oxide film. Both methods operate under the assumption that the oxide chemistry of the system controls the lubricity and wear properties. Relevant issues for each system will be presented and discussed.
Fluorinated Diamond Films, Slabs, and Grit
Authors: Patterson Donald E. , Hauge Robert H. , Margrave John L.
Published: March 2011

Diamond powders, single crystal diamonds (slabs and naturally occurring stones), and CVD diamond films have been fluorinated via direct fluorination and plasma techniques at a variety of temperatures and reaction times. Infrared, ESCA, and mass spectrometric studies verify that the diamond surfaces are altered by fluorination and that fluorine is attached to the surface to some degree in most instances. Based on spectra obtained using the FT-IR techniques of DRIFTS and ATR, the fluorine appears to have an effect on the diamond surfaces at relatively low temperatures in short reaction times by the removal of surface contaminants. A relatively high temperature (600ºC) or long reaction time at slightly lower temperatures is needed to attach a significant number of fluorine atoms onto the diamond surface. Once fluorinated, the diamonds show enhanced resistance to further oxidation. The outward appearance of the diamonds remains unchanged even at fluorination temperatures nearing 800ºC.
Thin Diamond Films for Tribological Applications
Authors: Wong M.S. , Meilunas R. , Ong T.P. , Chang R.P.H.
Published: March 2011

Diamond films have been deposited on Si, Mo and many other substrates by microwave and radio frequency plasma enhanced chemical vapor deposition. Although the adhesion between the diamond film and most of the metal substrates is poor due to residual thermal stress from the mismatch of thermal expansion coefficients, we have developed processes to promote the growth of uniform and continuous diamond films with enhanced adhesion to metal substratesfor tribological applications. The tribological properties of these films are measured using a ring-on-block tribotester. The coefficients of friction of diamond films sliding against a 52100 steel ring under the same experimental conditions are found to be significantly different depending on the morphology, grain size and roughness of the diamond films. However, under all cases tested, it is found that for uniform and continuous diamond films with small grain size of 1-3 micrometers, the coefficient of friction of thediamond film sliding against a steel ring under lubrication of a jet of mineral oil is about 0.04.
Comparative Wear Tests of Different Types of Coatings on Steels
Authors: Habig Karl-Heinz
Published: March 2011

Different coatings were formed by galvanical deposition, thermochemical treatment, CVD, PVD or plasma spraying. Their wear behaviour was tested under various conditions so that adhesive and abrasive wear mechanisms predominated. The resistance of the coatings to adhesive failure and wear was examined with the pin and disc system under conditions of boundary lubrication. The discs were protected by different coatings while the pins were made of tool steel or alumina. For abrasive wear tests a grinding apparatus with grinding papers of flint, alumina or silicon carbide was used. From the resultsthe following conclusions can be drawn: -Thermochemically treated steels and nickel-phosphorus coatings have a high resistance to galling if the counterbody consists of steel or alumina. The couples plasma sprayed molybdenum against steel and tungsten carbide against alumina also have a high resistance against galling.

-The wear of most coatings is low if the counterbody is made of steel. By analumina counterbody the wear of the coatings isincreased. Alumina is worn less by the coatings than steel.

-The hard CVD- and PVD-coatings, the thermochemically formed iron boride andvanadium carbide coatings and the electroless nickel-phosphorus-diamond coatings have a high abrasive wear resistance.
What Part do Adhesion and Deformation Play in Fine-Scale Static and Sliding Contact?
Authors: Guo Q. , Ross J.D.J. , Pollock H.M.
Published: March 2011

We describe experiments involving the static or sliding contact of a 'single asperity' and a flat surface. Plastic deformation and possibly junction growth can occur even at zero applied load, as a consequence of surface forces. The conditions for this to occur, and the different modes of separation of an adhesive contact, are clarified with the help of 'maps': use of the macroscopic concepts involved, such as yield stress and work of adhesion, is sometimes questionable and evidence of the importance of nanometre-scale stepped topography is presented. Strong adhesion between hard non-metals can required thermal activation. Sliding contacts at the sub-micrometre level have shown behaviour ranging from 'unstable ploughing' to adhesive peeling, but the frictional mechanisms involved are often unclear.
Measurements of Static and Dynamic Interactions of Molecularly Thin Liquid Films Between Solid Surfaces
Authors: McGuiggan Patricia M. , Israelachvili Jacob N. , Gee Michelle L. , Homola Andrew M.
Published: March 2011

New experimental techniques are described for measuring both the static and dynamic interactions of very thin liquid films between two molecularly smooth surfaces as they are moved normally or laterally relative to each other. Film thickness can be measured and controlled to IA. Results are presented of how the properties of liquid films only one, two, or three molecular layers thick differ from those of bulk liquids. When close together, two molecularly smooth surfaces slide (shear) past each other while separated by a discrete number of liquid layers. The critical shear stress required to initiate motion for simple spherical molecules is “quantized” with the number of layers. Another important characteristic of molecular thin liquid films undergoing shear is the phenomenon of “stick-slip” or “intermit-tent” motion. Both of these phenomena have been studied as a function of driving velocity, area of contact, and number of molecular layers.
Assessment of the Tribological Requirements of Advanced Spacecraft Mechanisms
Authors: Fleischauer Paul D. , Hilton Michael R.
Published: March 2011

A survey was conducted of existing technologies for moving mechanical assemblies used in spacecraft applications. The purpose was to identify areas where future requirements for lifetimes in excess of ten years with anticipated speeds, loads, and temperatures might not be satisfied. Some specific mechanisms, such as momentum/reaction wheels, high-speed turbines, pointing and tracking mechanisms, despin mechanisms, and gimbal mechanisms, were identified as areas for potential application of existing but unused technologies. Two major problem areas identified involve boundary-regime lubrication and lubricant supply (active or passive) for long life. Areas where substantial, near-term improvements appear practical include the use of hybrid bearings, new synthetic fluid lubricants, new bearing retainer materials, and properly designed solid-film lubricants.
NDT-Techniques for Monitoring Material Degradation
Authors: Höller Paul , Dobmann Gerd
Published: March 2011

The early detection of material degradation by NDT is of basic importance for safe and economic operation of many industrial components. Depending on the type of component as well as on service exposure conditions, NDT-techniques, which are sensitive to deformation, erosion, wear, porosity, microcracks and so on, are required. At present, only very few techniques are available for monitoring early stages of degradation. An overview of NDT-techniques already in use as well as under development in Germany for this problem is given. Special emphasis will be laid on the presentation of recent advances towards better detectability and objectivity.
Nondestructive Detection of Material Degradation Caused by Creep and Hydrogen Attack
Authors: Birring A. S.
Published: March 2011

Hydrogen attack and creep damage may reduce the fracture toughness as well as the strength of steels. This reduction is caused partially by the presence of cavities and microcracks at the grain boundaries. A large reduction in fracture toughness can make some components unsafe for operation. Ultrasonic tests performed on damaged samples showed a decrease in wave velocity and an increase in backscatter. The longitudinal-wave velocity decreased more than shear-wave velocity. Where the fracture toughness was reduced by 43 percent, samples with hydrogen attack showed a tenfold increase in backscatter. Such results demonstrate the potential for ultrasonic nondestructive testing to quantify damage and assess the component's remaining life.
Ultrasonic Non Destructive Evaluation of Microstructural Changes and Degradation of Ceramics at High Temperature
Authors: Gault Christian
Published: March 2011

This paper deals with the use of pulsed ultrasonic waves to monitor microstructural changes and degradation of ceramics in the field of high temperature. Two types of devices are described. One is a low frequency system for the measurement of Young's modulus at temperatures up to 1800°C. The second is an ultrasonic spectroscopy system for the evaluation of damage in structural ceramics during thermal fatigue experiments. Applications concern phase changes, porosity evolution or microcracking induced by thermal stresses when heating monolithic or composite ceramics.
Ultrasonic Characterization of SOL/GEL Processing
Authors: Chiou S. , Hahna H. T.
Published: March 2011

The sol/gel process has recently received attention because it enables the production of pure and homogeneous glass without external heating, eliminating the high processing temperatures needed in conventional methods. A disadvantage of the process is that if the rate of evaporation during syneresis is too high, cracking due to mechanical shrinkage can be extensive. A slower evaporation rate produces less cracking, but results in a longer processing time. The key to decreasing processing time while simultaneously eliminating shrinkage cracks lies in monitoring the change of the mechanical properties during the evaporation process. Ultrasonic techniques are ideal for this purpose.

To monitor the process, an ultrasonic signal was passed through the material. Spectrum changes were measured and then converted to changes in modulus and viscosity, while shrinkage and density changes were monitored using an air-type transducer and an electronic balance. The results show no observable change up to the beginning of the gelation process, followed by rapid increase in the modulus and viscosity after the onset of shrinkage. This finding was confirmed using a viscometer and laser light scattering measurements. Because of the effectiveness of this ultrasonic technique in detecting changes in the material, such as the onset of cracking, it may be used in controlling and improving the process.
Anomalous Scattering of Polarized X-Rays
Authors: Templeton David H. , Templeton Lieselotte K.
Published: March 2011

Some elements in some chemical states exhibit strong dichroism and birefringence near x-ray absorption edges. The atomic scattering factor is a complex tensor. This polarization anisotropy has profound effects on the transmission and scattering of x-rays even when the incident radiation is unpolarized. The linear polarization of synchrotron radiation makes it easier to study the effects and to use them for new methods of structure determination. Several of these anomalous scattering tensors have been measured by absorption spectroscopy and in diffraction experiments. New polarization terms enter the calculation of diffraction intensities, with interesting consequences. Reflections forbidden by a screw-axis rule are observed in sodium bromate near the Br K edge and permit direct observation of the structure factor phases of their second order reflections. This technique is a method of selective diffraction in which atoms of single element in a single chemical state contribute to the signal, and it can reveal their positions with precision. These effects can be a handicap for some applications of near-edge anomalous scattering in the study structures of crystals and amorphous materials.
Polycrystalline Diffraction and Synchrotron Radiation
Authors: Hart Michael , Parrish William
Published: March 2011

Synchrotron radiation sources allow a new generation of parallel beam instruments to be developed for polycrystalline xray diffraction. Spectroscopy can be combined with diffraction in either angle or energy scanning modes. The high intensity narrow instrument profile and freedom from aberrations make possible a wide range of measurements; of anomalous dispersion, of peak-shape analysis to determine particle size and strain, of preferred orientation and structure as a function of depth and of lattice parameters with a precision approaching 1 part per million. The parallel beam instrument which we have developed is now to be installed on a regular basis at SSRL and at Daresbury.
Near Surface Structure of Ion Implanted Si Studied by Grazing Incidence X-Ray Scattering
Authors: Wallner G. , Burkel E. , Metzger H. , Peisl J. , Rugel S.
Published: March 2011

X-rays incident on a surface under grazing angle may undergo total external reflection and excite an interior wave field damped exponentially into the bulk. These evanescent waves are a sensitive probe for the study the real structure in the near surface region. We report results on the influence of implantation defects on Bragg diffracted and on diffuse intensities. By detailed comparison of Bragg intensities with predictions of dynamical scattering theory we detect the presence of amorphous layers and determine their thickness. For the first time defect induced diffuse scattering underconditions of grazing incidence andexit is observed and compared to recent theoretical results. Strength and symmetry of implantation induced defects can be determined as well as their depth distribution which is compared to results of a TRIM simulation: the defect distribution is found to agree with that of the deposited collisional energy.
Time-Resolved Small Angle X-Ray Scattering and Dynamic Light Scattering Studies of Sol-Gel Transition in Gelatin
Authors: Wu Dan Q. , Chu Benjamin
Published: March 2011

Structural and dynamical properties of an aqueous gelatin solution (5 wt%, 0.1M NaCi, pH=7) in a sol-gel transition were studied by time-resolved small angle x-ray scattering (SAXS) and dynamic light scattering (DLS) after quenching the gelatin sol at ∼45”C to 11°C. SAXS intensity measurements suggested the presence of gel fibrils which grew initially in cross-section. The average cross-section of the gel fibrils reached a constant value after an initial growth period of ∼800 sec. Further increase in SAXS intensity could be attributed to the increase in the length of the gel fibrils. Photon correlation, on the other hand, clearly showed two relaxation modes in both the sol and the gel (∼1 hr after the quenching process) states: a fast cooperative diffusion mode which remained constant from the sol to the gel state after correction for the temperature dependence of solvent viscosity; and a slow mode that could be attributed to the self-diffusion of the “free” gelatin chains and aggregates. The slow mode contribution to the time correlation function was reduced from ∼40% in sol to ∼20% in gel signaling a decrease but not the elimination of “free” particles in the gel network. The decrease in the intensity contribution by the slow mode is, however, accompanied by a large increase in the characteristic line-width distribution.
Investigation of Grain Boundary Migration in Situ by Synchrotron X-Ray Topography
Authors: Bauer C. L. , Gastaldi J. , Jourdan C. , Grange G.
Published: March 2011

Grain boundary migration has been investigated in prestrained monocrystalline specimens of aluminum in situ, continuously and at temperatures ranging from 415 to 610°C by synchrotron (polychromatic) x-ray topography (SXRT). In general, new (recrystallized) grains nucleate at prepositioned surface indentations and expand into the prestrained matrix, revealing complex evolution of crystallographic facets and occasional generation of (screw) dislocations in the wake of the moving boundaries. Analysis of corresponding migration rates for several faceted grain boundaries yields activation energies ranging from 56 to 125 kCal/mole, depending on grain boundary character. it is concluded that grain boundary mobility is a sensitive function of grain boundary inclination, resulting in ultimate survival of low-mobility (faceted) inclinations as a natural consequence of growth selection. Advantages and disadvantages associated with measurement of grain boundary migration by SXRT are enumerated and corresponding results are interpreted in terms of fundamental relationships between grain boundary structure and corresponding migration kinetics.
Synchrotron Microtomography of Composites
Authors: Stock S. R. , Kinney J. H. , Breunig T. M. , Bonse U. , Antolovich S. D. , Johnson Q. C. , Nichols M. C.
Published: March 2011

X-ray computed tomography (CT) uses absorption profiles from many different viewing directions to reconstruct the two-dimensional distribution of x-ray absorptivity within a slice of the sample. The tunability, high brightness and parallelism of synchrotron radiation are critical to high resolution (0.001mm), high contrast (1%) CT or microtomography. In situ study of samples multiple times during the course of an experiment is exciting to consider.

Continuous fiber SiC/Al composites were deformed under three-point bending, and the resulting damage and fiber arrangement were revealed with synchrotron microtomography. Several hundred slices of 0.012 mm thickness were recorded simultaneously using 25 key radiation and a phosphor screen/charge coupled device (CCD) detector. Reconstruction was with the filtered back projection method. Low density regions were observed in the matrix in regions of highest stress where cracking is expected.
X-Ray Fluorescence Microprobe Imaging with Undulator Radiation
Authors: Rivers Mark L. , Sutton Stephen R. , Gordon Barry M.
Published: March 2011

Synchrotron x-ray fluorescence experiments were performed using a prototype undulator for the Advanced Photon Source installed on the CESR storage ring at Cornell University during a run in May, 1988. Fluorescence spectra were collected from a number of standard references and unknowns. Thick target minimum detectable limits (MDL) were about a factor of two higher than those obtained using white bending magnet radiation at the NSLS. The higher MDLs could be due to lower polarization and/or imperfect alignment of the Si(Li) detector. Thin target MDLs were about 10 times lower than the NSLS since the undulator produced a usable spot size which was also 10 times smaller. Several one dimensional multi-elemental scans and two dimensional images were made with 10 μm resolution and 30 ppm MDL. These experiments demonstrate that undulators on the proposed Advanced Photon Source will be ideal for a trace element x-ray fluorescence microprobe with excellent elemental sensitivity and spatial resolution.
Multilayer Monochromators for the Soft X-Ray and Extreme Ultraviolet
Authors: Barbee Troy W. , Pianetta Piero
Published: March 2011

Simple multilayer structures and multilayer diffraction gratings are now of sufficient quality to be used as optical elements in synchrotron radiation source instrumentation. In this paper results obtained with a multilayer two element monochromator will be presented. Three specific types of results will be discussed. First, transmission measurements of the absorption cross-sections of elemental thin films in the energy range 50 to 2000 eV will be presented and used to demonstrate the performance of the monochromator. Second, application of this monochromator in x-ray lithography research will be described and the advantages of the broad bandpass of multilayer optics demonstrated. Third, use of this monochromator in scattering studies of long period structures will be discussed. The potential for the use of multilayer diffraction gratings in high resolution monochromator applications will also be considered.