bluuebunny/crossref_metadata_2025_split huggingface dataset:
Germanium Loaded Zeolite Y: Preparation and Characterization
Authors: Tomiya S. , Petroff P.M. , Margolese D. , Srdanov V. I. , Stucky G. D. , Zhang Y. H. 
Published: March 2011

ABSTRACTThe cavities of molecular sieves offer an opportunity for synthesis of periodically ordered semiconductor nanoclusters. Ge clusters were synthesized in zeolite Y by thermal decomposition of GeH4 absorbed in the zeolite cages. Upon inclusion of germanium in proton exchanged zeolite Y (HY), the X-ray diffraction (XRD) pattern shows a small change in line positions and considerable change in intensities. No extra reflections were detected in either XRD or transmission electron diffraction (TED) for the samples synthesized at 300°C. These observations are in accordance with the energy dispersive X-ray (EDX) spectroscopy data which reveal the presence of germanium within the HY in concentrations higher than 5x1019 cm-3. At annealing temperatures higher than 500°C, small Ge crystallites (∼0.2μm) form on the exterior surface of the HY, as documented by TED, TEM and absorption spectroscopy. The results from the absorption and photoluminescence spectroscopy of the Ge loaded HY will be discussed.
Deposition of Diamond/ Tin Composite Film on Tool Steel Substrate
Authors: Chen X. , Narayan J. 
Published: March 2011

ABSTRACTTiN/Diamond/TiN composite film has been deposited on tool steel substrate by CVD and laser ablation technique. A TiN film of about 0.5µm thick was first deposited as a buffer layer by laser ablation and then diamond was deposited with proper number density by CVD. After this the diamond layer was covered by a second layer of TiN. It was found that the TiN buffer layer was stable during CVD process of diamond and can chemically isolate the depositing surface from steel substrate. This prevents the reaction between the diamond and the substrate and makes it possible to deposit high quality diamond films on steel. The second TiN layer embeds the diamond particles to form a TiN/diamond composite film and therefore greatly enhances adhesion of the deposited diamond. SEM, Raman. adhesion and hardness measurements show that an extremely hard. adherent and thermalshock-resistant diamond/TiN composite film can be deposited on steel.
Nanocomposites For magnetic Refrigeration
Authors: Shull R.D. , Mcmichael R.D. , Ritter J.J. , Bennett L.H. 
Published: March 2011

ABSTRACTUpon the application of an external magnetic field, the magnetic spins in a material partially align with the field, thereby reducing the magnetic entropy of the spin system. When performed adiabatically, the specimen's temperature will rise. This temperature rise, δT, related to the entropy change by the heat capacity, is known as the magnetocaloric effect. Upon cycling the magnetic field, this effect can be used for transferring heat from one thermal reservoir to another, forming the basis for a magnetic refrigerator. Recently, NIST scientists predicted composite magnetic materials containing nanometer-size magnetic species could possess enhanced magnetocaloric effects [1-2], especially at high temperatures or low magnetic fields. Magnetic nanocomposites may be prepared in many different ways, and recent magnetocaloric effect data measured on Fe-doped gadolinium gallium garnets are presented to show both the effect of processing and a methodology for optimizing δT.
Evaluation of The Catalytic Activity of A High Surface Area, Regular, Porous Solid Formed From The Clusters of Clusters, MII4O[(CO)9Co3CCO2]6, M = Co, Zn
Authors: Cen Wei , Fehlner Thomas P. , Kalenik Zbigniew , Wolf Eduardo E. 
Published: March 2011

ABSTRACTThe discrete molecular clusters of clusters, M1140[(CO)9Co3CCO2]6, M = Co, Zn undergo thermolysis with the production of highly porous solid materials. Evaluation of the catalytic properties of these materials has been investigated using the hydrogenation of 1,3- butadiene as a test reaction. These experiments suggest it is the unique structure of the porous materials that is responsible for the high activities and the selectivities observed.
Mechano-Chemical Effects of High-Energy Attrition Milling On The Bi2Sr2CaCu2Ox Superconductor
Authors: Luo J. S. , Lee H. G. , Sinha S. 
Published: March 2011

ABSTRACTThe mechano-chemical effects of high-energy attrition milling on the microstructure evolution and superconducting properties of Bi2Sr2CaCu2Ox oxide powder were investigated by a combination of x-ray diffraction, scanning electron microscopy, and magnetization techniques. The powder was attrition-milled under an argon atmosphere, using a standard laboratory attritor with yittria-stabilized ZrO2 balls having a ball-to-powder weight ratio of ∼10:1. After selected time increments the mechanical attrition was interrupted and a small quantity of the milled powder was removed for analysis. The results indicate that (1) the crystal size decreases, (2) this decrease in crystal size is accompanied by degradation of crystallinity of the powder and accumulation of atomic-level strain, (3) the Bi-2212 phase decomposes under conditions of excessive deformation, and (4) the superconducting transition is depressed from 70 K to 60 K in the early stages of milling and completely vanishes upon prolonged deformation. The influence of defects (created during cold work) on the current carrying capacity is also presented and discussed.
Phase Characterization and Grain Size Effects of Nanophase Y2O3, ZrO2 and Y2O3-ZrO2 Composites Produced by the Gas-Phase Condensation Technique
Authors: Foster C. M. , Bai G. R. , Parker J. C. , Ali M. N. 
Published: March 2011

ABSTRACTNanophase (n-) ZrO2 was produced in its pure and partially stabilized form by the gas-phase condensation method. The material was examined by x-ray diffraction and Raman scattering to obtain information on the structural evolution of the material during sintering. Two types of Y2O3 doped ZrO2 nanophase materials were made one by co-deposition of n-Y2O3 and n-ZrO2 in a consecutive manner and the second by mechanically mixing n-Y2O3 and n-ZrO2. We have determined that the co-deposition process is the most effect means of doping the n-ZrO2.
Surface Effects on the Properties of Cadmium Selenide Quantum Dots
Authors: Carter A. C. , Majetich S. A. 
Published: March 2011

ABSTRACTThe surface chemistry of 35 Å diameter CdSe quantum crystallites is varied by bonding different molecules to the surface of the crystallites. There are two main variables. The steric hindrance of the molecule is altered to control the density of dangling bonds at the surface. In addition, different bond types between the ligand and surface atoms were used to control the surface electron density. Nanosecond hole burning experiments were used to compare ground state recovery times. Luminescence revealed information on excited state recombination pathways. Analysis suggests that increased surface passivation reduces the fast nonradiative recombination.
Sialons and Silicon Nitrides; Microstructural Design and Performance
Authors: Lewis M.H. 
Published: March 2011

ABSTRACTsurvey is presented of developments in silicon nitride and sialon ceramic microstructures designed for application in differing temperature regimes.For low temperature (< 1000°C) application, pressureless-sinterable sialons with moderate (10-15%) intergranular glass, anisotropic β′ grains and high values of MOR and Kc (1 GPa and 6-10MPa| m respectively) are preferred.Improved hardness and high temperature capability may be achieved by tailoring intergranularp hases for crystallisation and further enhanced by the introduction of mixed α′/β′ Sialon microstructures. Examples are given of microstructural evolution in β′- Y3Al5O12(garnet), β′-Nd3Si3Al3O12N2 and α′/β′/garnet ceramics and a comparison of their mechanical behaviour.Novel Sialon ceramics containing dispersed transition metal compounds (TiN, TiB2) may be formed by in-situ redox reaction, utilising the α′ Sialon phase as an oxygen receptor. The dispersed phase may enhance hardness and toughness and confer electro-discharge machinability.Oxidation instability of Sialon compositions dictates the use of diphasic Si3N4/M2Si2O7 microstructures for application above 1300°C. The thermal cycle during pressurised sintering of these non-sialon compositions is critical in avoiding crystallisation of mixed polymorphs of the intergranular disilicate, with consequent microcracking.
Applications of Silicon Nitride Based Ceramics in the U.S.
Authors: Katz R. Nathan 
Published: March 2011

ABSTRACTSilicon nitride based ceramics have unique combinations of mechanical, thermal-physical and electrical properties. Additionally, silicon nitride based materials can be fabricated into near net shape components by several processing routes. This unique combination of properties and processing versatility have encouraged the use of silicon nitride based ceramics in a variety of demanding commercial applications over the past decade. In the U.S., these applications currently include cutting tools, bearings, and selected components for diesel engines. Projected future applications include a broader range of reciprocating and gas turbine engine components, and electronic components. For each of these applications examples of use and the key properties of silicon nitride which enable enhanced systems performance will be discussed. Several materials developments which may broaden the range of applicability of silicon nitride based ceramics will be described.
Mg-Si-AI-O-N Glasses Prepared By Nitriding Cordierite Powders Derived from Polymer Precursors
Authors: Laine Richard M. , Bickmore Clint R. , Waldner Kurt F. , Mueller Brian L. , Estry Hal W. 
Published: March 2011

ABSTRACTWe have previously reported the synthesis of cordierite polymer precursors directly from MgO, SiO2 and alumina.1 Removal of organics at 400°C in air and/or in oxygen gave amorphous, atomically mixed, oxide powders with surface areas of 250-400 m2/g. It is possible to convert these high surface area oxide powders to Mg-Si-Al-O-N powders by heating in a flowing NH3 atmosphere. The effects of selected processing conditions on nitrogen incorporation, in a set of well defined oxide powders, were examined. The powders are nitrided in flowing NH3, at temperatures of 700-1200°C, to obtain N contents of up to 5 atomic percent.
Elemental Analysis of Matrix Grain Boundaries in Sic Whisker Reinforced Si3N4 Based Composites
Authors: Liu J. , Chowdhury K. Das , Carpenter R. W. , Braue W. 
Published: March 2011

ABSTRACTThe structures of SiC/Si3N4 interfaces and Si3N4 matrix grain boundaries in Ceramic Matrix Composites (CMC) were investigated by high resolution electron microscopy. The light element chemistry of the interfaces was analyzed by high spatial resolution (∼3 nm) position resolved EELS in a field emission TEM and by high spatial resolution EDS in a dedicated scanning transmission electron microscope (STEM). High-angle annular dark-field (HAADF) imaging (resolution < 1 nm) technique was used to determine the distribution of yttrium atoms at matrix grain boundaries and at SiC/Si3N4 interfaces. HAADF images suggest that yttrium might diffuse into Si3N4 crystals bounding the interfacial and grain boundary regions.
Reaction Sintering of β-Si3N4/α'-Sialon Ceramics
Authors: Boskovic S. , Lee K.J. , Tien T.Y. 
Published: March 2011

ABSTRACTCompositions in the α'-SiAlON-√-Si3N4 solid solution region in the system Si,Al,Y/N,O which contained a third phase as a sintering aid were prepared. Mixtures of starting materials were reaction sintered to full densities without applied pressure. Phases were identified and lattice parameters of β' and √ph ases were measured and compared with standards. The results were used to construct β'-SiAION-√-Si3N4 solidsolution tie lines in the two phase region. As expected, the specimens with a higher β'-SiAION content showed higher hardness and lower toughness values.
Phase Relationship Studies of Silicon Nitride System—A Key to Materials Design
Authors: Yen T.S. , Sun W.Y. 
Published: March 2011

ABSTRACTAdditions and revisions to several of the most important phase diagrams and phase behavior diagrams in the silicon nitride field are reviewed in this work, with emphasis on the Y-Si-A1-O-N system. This information is further used to make observations on the promising silicon nitride systems containing either highly refractory grain boundary phases or compatible matrix phases of desirable properties. Examples are provided to illustrate the advantage of such a basic approach to materials design. Hardness, toughness, strength at room temperature and elevated temperature and even sinterability can all be improved by adopting such an approach.
The Effect of Glass Chemistry on the Microstructub and Properties of Self Reinforced Silicon Nitride
Authors: Pyzik Aleksander J. , Carroll Daniel F. , Hwang C. James 
Published: March 2011

ABSTRACTThe advantage of self-reinforced silicon nitride is the in-situ control of the microstructure. This control is provided in large degree by the chemistry of glassy phase which can be adjusted to tailor the morphology of silicon nitride grains as well as the matrix - reinforcement interface. The presence of high aspect ratio silicon nitride grains is necessary but not sufficient condition to produce materials with optimum properties. For maximum flexure strength and fracture toughness an optimized glass matrix is required.
Characterization of Hot-Pressed Silicon Nitride Ceramics with Alkoxide-Derived Oxide Mixtures As the Sintering Aid
Authors: Sato Y. , Sakurai C. , Ueki M. , Sugita K. 
Published: March 2011

ABSTRACTA homogeneous mixture of Y2O3, CeO2 and MgO with a final weight ratio of 3:1: 2 was prepared by the alkoxide method. The powder mixture was then added into Si3N4 powder in amounts ranging from 4 to 12 wt%, andconsolidated by hot-pressing. Microstructure and mechanical properties of the sintered bodies were determined and compared to those of materials prepared by the conventional route of mixing the oxide powders as sintering aids individually in essentially same composition. The β-fraction (modification ratio) in same composition was higher in thesintered bodies made through the alkoxide method than those made through the conventional one. The room temperature flexural strength was maximized with 6wt% addition of the alkoxide derived oxide, whereas, 12wt% addition of the total oxide was required to maximize the strength by conventional processing.
Direct Observation of Microstructure Change During Densification of Silicon Nitride Ceramics with A Novel Characterization Method
Authors: Iwamoto Y. , Nomura H. , Sugiura I. , Tsubaki J. , Takahashi H. , Ishikawa K. , Shinohara N. , Okumiya M. , Yamada Y. , Kamiya H. , Uematsu K. 
Published: March 2011

ABSTRACTA novel characterization method is applied to study the evolution of microstructures during densification of silicon nitride ceramics. This characterization method involves an immersion liquid for making green and sintered bodies transparent, and a subsequent direct optical microscopic examination. Granules were prepared with the spray drying processand formed into green bodies by CIP. After sintering at various temperatures, the specimens were examined for microstructural evolution. Large pores were located at the center and boundary regions of granules left in the green bodies; they were not removed by densification and resulted in large pores in the sintered body, possibly forming fracture origin in ceramics.
Acoustic Emission Study of Si3N4
Authors: Subbarao E. C. , Srikanth V. , Walck J. C. , Tarry C. A. 
Published: March 2011

ABSTRACTSintered Si3N4 (with 2 w/o A12O3 and 6 w/o Y2O3) was studied by acoustic emission method during indentation testing and during heating to and cooling from 920ºC in air. The acoustic emission activity was discontinous and its magnitude and duration increased with load applied during indentation testing. Intense acoustic emission signals were detected on cooling Si3N4 ceramics to temperatures below 590ºC, particularly below 450ºC. X-ray diffraction studies showed the presence of SiO2 (Quartz) after heating the sample to 920ºC during acoustic emission study, compared to single phase β Si3N4 before the heat treatment.
High Temperature Fatigue Properties of Silicon Nitride in Nitrogen Atmosphere
Authors: Shigegaki Yasuhiro , Inamura Takashi , Suzuki Akihiko , Sasa Tadashi 
Published: March 2011

ABSTRACTCyclic and static fatigue properties of pressure-less sintered silicon nitride were evaluated at 1000° C in air and in nitrogen using four-point bending mode. The data of cyclic fatigue tests or static fatigue tests and the morphology of the fractured surfaces in nitrogen were compared with those in air. The cyclic fatigue behavior was remarkably influenced by the atmosphere, while the static fatigue was less influenced. Crack healing effect due to the oxidation around the crack are thought to be the most probable mechanism to affect the cyclic fatigue rate in air.
Studies on Si3N4 Ceramic Cutting Tool Materials and their Applications
Authors: Miao He-Zhuo , Qi Long-Hao , Ma De-Jin , Jiang Zuo-Zhao 
Published: March 2011

ABSTRACTSi3N4 ceramics are excellent metal cutting materials. The cutting behavior can be improved by hard particle dispersion phase hardening and heat treatment so as to reduce glass phase in the grain boundaries. Compared with cemented carbide tools, the cutting life of the composite Si3N4 cutting tool is about 10-100 times longer, and the optimum cutting speed is about 3-10 times faster. It performs well in cutting hardened tools, nickel based alloys, and other hard materials and can sustain shock loads in operations such as milling, planing and other types of interrupted cutting. Applications in various fields show that machining efficiency can be increased by 3-10 times resulting in savings of time, electricity, and machining of 30-70% or even more.
Development of Advanced Silicon Nitride Valves for Combustion Engines and Some Practical Experience on the Road
Authors: Hamminger Rainer , Heinrich Juergen 
Published: March 2011

ABSTRACTOne major goal of automotive engineers actually is to reduce fuel consumption and emissions of present internal combustion engines. First promissing results have been achieved by the substitution of conventional by silicon nitride valves. The weight reduction of about 60 % per valve is corresponding with lower inertia and spring forces, which lead to improved emissions, reduced fuel consumptions as well as high performances of the engines. Applying statistical methods, two advanced silicon nitride materials have been developed, concerning their application as “cool” inlet valves and “hot” exhaust valves, respectively. Using high quality powders and combined optimum processing parameters, 4-point-bending strength of more than 1200 MPa (room temperature) and 870 MPa (1000 °C), resp., have been realized. Weibull moduli of more than 30 have been reproduced. Grinding of valves produced from these materials has economically been demonstrated by drastically reducing the machining times. Some results of road tests as well as of simulated engine tests from cooperations with different automotive companies are presented in detail.
Structure and Corrosion Properties of Pvd Coatings in the System Si-AL-O-N
Authors: Knotek Otto , LÖffler Frank , Beele Wolfram 
Published: March 2011

ABSTRACTSi-Al-O-N ceramics, especially β′-Sialon, are well known as a material offering a very good resistance against aggressive media combined with a good thermal shock behaviour. This combination recommends the Si-Al-O-N ceramics also as coating for products used in applications with high thermal gradients plus corrosion attack.Therefore this paper presents new developments in the deposition of Si-Al-ON, especially in combination with the aircraft alloy TiAl6V4 as substrate. Investigations of the coating structure in dependence on the deposition parameters were done and the resistance against oxidation and attack of H2SO4 containing media were examined.
Microstructure and Flow Behaviior of Fresh Cement Paste
Authors: Jiang W. , Roy D.M. 
Published: March 2011

AbstractCharacteristics of aqueous cement suspensions and the packing nature during setting were investigated as keys controlling the microstructure and density of a cement paste. The theological properties of the paste were studied as functions of hydration and setting; these properties are influenced by a variety of external factors, which are discussed. The objective of this paper is to sketch a new atomistic approach to a group of rheological phenomena which are as interesting from a scientific viewpoint as they are important for technology. The experiments were carried out by a HAAKE rheometer and an acoustic ultrasonic system. At different flow state, the acoustic emission signal generated from micro-structure is transformed due to wave propagation and due to the transducer response. The scientific information obtained through this study is expected to contribute the establishment of concept of setting processing. The measurements of flow properties relating to flocculation and coagulation were evaluated with respect to the effects of processing conditions on structure development in cement paste.
Cement Viscosity As A Function Of Concentration
Authors: Struble Leslie J. , Sun Guo-Kuang 
Published: March 2011

AbstractThe Krieger-Dougherty equation allows calculation of viscosity as a function of volume fraction for suspensions of noninteracting particles. For model suspensions (of spherical, monosized particles), it has been shown to provide excellent agreement between calculated and measured viscosities. In the present study, this equation was applied to portland cement pastes, also with good correlations between calculated and measured viscosities. Because cement has a broad particle size distribution and its particles are angular and elongated, the two constants in this equation (the maximum volume fraction and the intrinsic viscosity) were estimated using nonlinear optimization techniques. The equation provides an excellent fit to measured viscosity data. However, the nature of the equation makes the estimation somewhat difficult, and the solutions are not well-defined.
Effect of Superplasticizers on the Workability of Concrete as Evident from Apparent Viscosity, Yield Stress and Zeta-Potential
Authors: Malek R.I.A. , Roy D.M. 
Published: March 2011

AbstractModem concrete technology projections indicate a great expansion in low-cost and time efficient construction. Mixture designers will likely be more concerned with the developments in concrete making materials. Among those is the effective use of chemical admixtures and superplasticizers which will lower the water to cement ratio but will still give a dense workable concrete. An investigation of the workability of fresh concrete and the effect of superplasticizers should, therefore, constitute an essential part of modem concrete durability studies.In this paper we report part of the work on rheological properties of fresh concrete. Various concrete samples covering a range of compositions that are commonly used for highway pavements are prepared. The proportioning parameters are: cement content, aggregate size, gradation and sphericity-roundness, and water and superplasticizer contents. The individual solid ingredients were characterized and the fresh concrete properties were assessed by the slump, two-point workability (Tattersall's) apparatus, air pressure and unit weight methods. The effects of superplasticizer on the apparent viscosity and yield stress of concrete are discussed and the relevance of the findings for field applications (handling of fresh concrete) are discussed. Also discussed are the implications for microstructural development.