Properties Of Related Materials Research Articles

Molecular Modelling of Ground- and Excited-States Vibrations in Organic Conducting Devices: Hexakis(n-hexyloxy)triphenylene (HAT6) as Case Study

In order to gain insight into fundamental aspects of organic photocell materials, we have calculated ground and excited electronic-state structures and molecular vibrations for an isolated HAT6 molecule (hexakis(n-hexyloxy)triphenylene). Excited-state calculations are carried out using time-dependent density functional theory and frequencies are evaluated analytically using coupled perturbed Kohn–Sham equations. These model calculations have been validated against new infrared and ultraviolet data on HAT6 in solution. The main allowed valence excitation, having the largest oscillator strength, is chosen for the structural and vibrational investigations. Comparison with the ground-state vibrational dynamics reveals surprisingly large spectral differences. In addition, the alkoxy tails, which are usually considered to play only a structural role, are clearly involved in the molecular vibrations and the structural distortion of the excited electronic state compared with the ground state. The tails may play a more important role in charge separation, transport and excited-state relaxation than was previously thought. In this case, chemical modification of the tails would allow vibrational and related properties of organic photocell materials to be tailored.

Structural Insight into Germanium-Containing Silicate Species by Electrospray Ionization Mass Spectrometry (ESI-MS) and ESI-MS/MS

The properties of zeolitic and related materials highly depend on their pore dimensions and topology as well as the presence and nature of framework heteroelements. Here, we present detailed insights into prenucleating solutions of zeolitic materials using two different organic structure-directing agents (SDAs) in the presence of fluoride ions. The silicate speciation was analyzed by means of electrospray ionization mass spectrometry (ESI-MS), wherein the structures of the occurring species were proven to depend on the nature of the used organic SDA. In addition, MS/MS experiments were revealed as a powerful tool to obtain detailed structural insight into the occurring silicate oligomers. With this information, we were able to locate heteroelements, namely, germanium, within these species and, furthermore, to determine the structure-directing effects of the used organic SDAs.

The incommensurately modulated crystal structure of β-Pb2BiVO6: interpretation of the phase transition α → β → δ and conduction properties of related materials

A new polymorph of Pb(2)BiVO(6) was prepared under ambient conditions and its crystal structure was determined by single-crystal X-ray diffraction. The phase transitions alpha --> beta and beta --> delta were identified in the mother phase; the high-temperature form delta-Pb(2)BiVO(6) eventually decomposes at 753 K to a mixture of Pb(4)BiVO(8) and the high-temperature form of PbBiVO(5) before showing recombination at 923 K. beta-Pb(2)BiVO(6) has an incommensurate monoclinic modulated structure. This crystal structure is twinned and complementary structural investigations of a powder sample of beta-Pb(2)BiVO(6) by TEM diffraction studies confirmed the lattice and incommensurate modulation character. Log sigma = f(T(-1)) dependences for Pb(2)BiVO(6)-related materials (6% M-for-V-substituted compositions; M = Cr, Mn, P) are reported, which allow the characterization (E(a) and isothermal sigma values) of the beta- as well as the delta- and alpha-Pb(2)BiVO(6) varieties.

Exciton Trapping in π-Conjugated Materials: A Quantum-Chemistry-Based Protocol Applied to Perylene Bisimide Dye Aggregates

Access to excited-state structures and dynamics of pi-chromophor aggregates is needed to understand their fluorescence behavior and the properties of related materials. A quantum-chemistry-based protocol that provides quantitative and qualitative insight into fluorescence spectra has been applied to perylene bisimide dimers and provides excellent agreement with measured fluorescence spectra. Both dispersion and dipol-dipole interactions determine the preferred relative arrangements of the chromophores in ground and excited states of the dimer. An exciton trapping mechanism is identified, which may limit the energy transfer properties of perylene bisimide and other dye materials.

Nonpolar and Semipolar Orientations: Material Growth and Properties

Nitride-based optoelectronic devices prepared in the c orientation have been successfully introduced to the global marketplace and are changing the way we think about lighting. A part of the research interest has shifted toward nonpolar and semipolar orientations, which has the potential to broaden the scope and impact of this technology. This is because quantum-well structures prepared in nonpolar and semipolar orientations are able to suppress the quantum-confinement Stark effect, which has a negative impact on optoelectronic device performance. The lower crystal symmetry of such orientations provides spontaneously polarized light emission. Despite these attractive properties of nonpolar and semipolar orientations, the corresponding materials growth is not trivial. The present chapter discusses our efforts on growth of III-nitride materials in nonpolar and semipolar orientations and the related material properties.

Fatigue crack growth of a double fillet weld

The welded structures have a broad applicability, steel constructions, car industry, aeronautical, marine, pipelines, etc. These structures are generally subjected to cyclic requests. A simple existing defect after welding can generate a catastrophic fracture. This work studies the fatigue crack growth of a double fillet weld with the existence of a semi-elliptical crack. Two types of aluminum alloys are studied with knowing the alloy 2024 T351 and the 7075 T6. Crack growth analysis uses linear elastic fracture mechanics and related crack growth material properties to determine how fast a crack or crack-like defect will grow. Fracture mechanics is based on the concept of stress intensity ( K) that describes the magnitude of both the stress and strain fields around a crack. It is computed from the stress range (Δ σ), and crack size ( a) and crack shape ( β). The effect on the fatigue life of the geometrical parameters of the crack ( a/ c ratio), the angle of inclination of the weld bead and the level of loading are studied. In order to predict the fatigue behavior of the welded structure, a constant amplitude loading is applied where the influence of the load ratio over the fatigue life is presented. A comparative study of fatigue crack growth of the cited aluminum alloys are detailed in order to show the effect of several parameters.

A Physical Model of Solenoid Inductors on Silicon Substrates

In this paper, a physical model is presented to predict the frequency-dependent characteristics of solenoid-type inductors on standard silicon substrates. The model considers the skin-depth effect in the conductor, interwinding capacitance, parasitic capacitance between the conductor and substrate, substrate resistance, and substrate capacitance of a solenoid inductor on the silicon substrate, which are all computed based on the inductor's geometric dimensions and related material properties. Surface-micromachined inductors of various geometries have been tested to validate the physical model and found a satisfactory consistency between the measured results and the theoretical predictions in the multigigahertz frequency range. It is also suggested that the increase of the solenoid aspect ratio is beneficial in enhancing quality factors of solenoid inductors on the silicon substrate at a high frequency.

A graph-based parameterization concept for global laminate optimization

A new graph-based parameterization concept aimed at the global optimization of laminated structures by the means of evolutionary algorithms and finite element analysis is introduced. The motivation to develop this novel parameterization concept is twofold. First, the entire design space is accessible to optimi zation down to the smallest entity, which is a single finite element, and secondly, this concept guarantees greatest flexibility in terms of laminate layer shape and placement. The finite element mesh of a structure is represented as a mathematical graph. Substructures of this graph form fiber reinforced and possibly overlapping patches and are affiliated to virtual graph vertices representing their properties. Adapted genetic variation operators are directly applied on this graph. The method allows for concurrent optimization of number, size, shape, and position of the patches and an arbitrary number of material related properties for each of them. The novel concept overcomes the limits of traditional geometry-based approaches, as it is able to represent almost arbitrary patch shapes even on curved surfaces. Two numerical examples demonstrate the efficiency of the method.

Failure Modes in Ceramic‐Based Layer Structures: A Basis for Materials Design of Dental Crowns

A research program on failure modes induced by spherical indenters in brittle layer structures bonded to polymeric substrates, in simulation of occlusal function in all‐ceramic dental crowns, is surveyed. Tests are made on model flat and curved layers bonded onto a dentin‐like polymer base, in bilayer (ceramic/polymer) and trilayer (ceramic/ceramic/polymer) configurations. All‐transparent systems using glass as a porcelain‐like outer or veneer layer and sapphire as a stiff and strong core support layer enable in situ observation of the entire evolution of fracture modes in the brittle layers, from initiation through to failure. With the fracture modes identified, tests are readily extended to systems with opaque polycrystalline dental core ceramics, notably alumina and zirconia. A variety of principal failure modes is identified: outer and inner cone cracks developing in the near‐contact region at the top surface; radial cracks developing at the bottom surface along the loading axis; margin cracks from the edges of dome‐like structures. All of these modes are exacerbated in cyclic loading by time‐cumulative slow crack growth, but inner cones are subject to especially severe mechanical fatigue from hydraulic pumping of water into the crack fissures. Conditions under which each mode may be expected to dominate, particularly in relation to geometrical variables (layer thickness, contact radius) and relative material properties, are outlined. Clinical issues such as crown geometry, overload versus fatigue failure, role of residual stresses in fabrication, etc. are addressed.

Processing and Property of Net-Shaped Fe-Based Nanoparticulate Material

This paper overviews our recent investigations on the processing of net-shaped Fe-based nanoparticulate materials and their related material properties such as mechanical and corrosion properties. The key-process for fabricating fully densified net-shaped nanopowder by pressureless sintering is an optimal control of agglomerate size of nanopowder. Enhanced mechanical property of powder injection molded Fe-Ni nanopowder could be explained by grain refinement and uniformity of microstructure.

Modeling of curvature in multilayered epitaxially grown films

A model was developed to calculate the radius of curvature produced by stresses in lattice-mismatched multilayers grown epitaxially on a planar substrate. The analysis was done for any number (N) of layers using beam bending theory and strain partitioning theory introduced by our group earlier. This model is reduced to a limiting case of a two-layer structure (film-substrate). The variation of the radius of curvature with the relative thicknesses and other material properties of the layers was determined and compared to finite element calculations. The analytical model was further verified by applying it to a symmetric tri-laminate structure.

Modified embedded-atom method interatomic potentials for Ti and Zr

Semiempirical interatomic potentials for hcp elements, Ti and Zr, have been developed based on the MEAM (modified embedded-atom method) formalism. The new potentials do not cause the stability problem previously reported in MEAM for hcp elements, and describe wide range of physical properties (bulk properties, point defect properties, planar defect properties, and thermal properties) of pure Ti and Zr, in good agreement with experimental information. The applicability of the potentials to atomistic approaches for investigation of various materials behavior (slip, irradiation, amorphous behavior, etc.) in Ti or Zr-based alloys is demonstrated by showing that the related material properties are correctly reproduced using the present potentials and that the potentials can be easily extended to multicomponent systems.

Through Process Modelling

A new approach to improve existing and develop new simulation models and apply them in a sequence to simulate the complete production processes of Aluminium semi-finished products is described. The development has been a joint effort of academic and industrial partners developed in the frame of the VIR* European projects. It integrated advanced material models with industrial fabrication process models to predict the microstructures and properties in the complete production chain processes of Al sheet and profiles, i.e. by DC ingot casting, rolling and extrusion and analyze complex interactions of critical process parameters with the corresponding metallurgical mechanisms and predict the related material response and properties. The principles are discussed and examples are given for their successful application to simulate industrial fabrication processes.

RELATIVE MECHANICAL PROPERTIES OF SURGICAL WIRES AND CABLES USED IN SPINAL FIXATION AND THE GRIPPING TECHNIQUES USED FOR THEIR TENSILE TESTS

Surgical wires and cables have been extensively used for spinal fixation. They are used in conjunction with spinal instrumentation to stabilize the spine. This paper seeks to explore the best method for clamping stainless steel wire and stainless steel cable for tensile test and to compare the relative mechanical material properties of Sofamor Danek Axis (SDA) stainless steel wire with SDA stainless steel cable using the most suitable gripping method found, in order to determine which is mechanically more superior/effective for spinal fixation. Utilization of mechanical grips with sandpaper lining has been found to be an effective method for clamping wires for tensile test. For cables, the problem of stress concentration and premature failure during tensile test has been overcome by embedding both ends of the cable in carbon fibre.

Processing of Net-shaped Fe-Ni Nanomaterials by Powder Injection Molding

This paper provides an overview on our recent investigations on the processing of net-shaped Fe-Ni nanoalloy powder and related material properties. The key-process for fabricating fully densified net-shaped nanopowder by pressureless sintering is an optimal control of agglomerate size of nanopowder. Especially, the pressureless sintering process is inevitable for consolidation of the Powder Injection Molded nanopowder. The mechanical- and corrosion properties of the PIMed Fe-Ni nanopowder are discussed in association with the microstructure of sintered nanoagglomerate powder.

Multi-Dimensional Crystal Structures and Unique Solid-State Properties of Heterocyclic Thiazyl Radicals and Related Materials

Abstract The crystal structures and magnetic properties of heterocyclic thiazyl radicals and related materials have been examined. TTTA (=1,3,5-trithia-2,4,6-triazapentalenyl) exhibited a first-order phase transition between a paramagnetic high-temperature (HT) phase and a diamagnetic low-temperature (LT) phase, with a wide thermal hysteresis loop over the temperature range 230–305 K. The phase control of TTTA was achieved by pressure and by light irradiation. BDTA (=1,3,2-benzodithiazolyl) also exhibited a diamagnetic–paramagnetic phase transition above room temperature. However, fresh samples always exhibited a superheating of the LT phase that resulted in a double melting (melt–recrystallization–melt process) and supercooling of the HT phase, which in turn led to an antiferromagnetic ordering at 11 K. The molecular compounds of thiazyl radicals were prepared; TTTA formed a coordination polymer structure in the TTTA·[Cu(hfac)2 (=bis(hexafluoroacetylacetonato)–copper(II))] crystal, where a ferromagnetic coupling was found between the organic and inorganic species. The cation radical salts, [BBDTA (=benzo[1,2-d:4,5-d′]bis[1,3,2]dithiazole)]·MCl4 (M = Ga and Fe), exhibited ferromagnetic ordering at 7 K and ferrimagnetic ordering at 44 K after evaporation of crystal solvents. We also grew crystals of M–TTDPz (TTDPz = tetrakis(thiadiazole)porphyrazine and M = H2, Fe, Co, Ni, Cu, and Zn) and performed their structural analyses. Their crystal structures were found to depend strongly on the central metal ion and could be classified into three forms: α, β, and γ.

Pavement Design Analysis with 2002 Design Guide Software

There has been a continuous evolutionary process in hot-mix asphalt (HMA) pavement design. In the beginning it was primarily based on past experience. Through research, empirical methods were developed on the basis of the materials' response to specific loading in the AASHO Road Test. Today pavement design has progressed to a mechanistic-empirical method. This methodology takes into account the mechanical properties of the individual layers and uses empirical relationships to relate material properties to performance. The mechanical tests that are used as part of the current methodology include dynamic modulus and flow number, which have been shown to correlate with field pavement performance. The use of the dynamic modulus test and its impact on pavement design with the current design guide (2002) and its associated software are examined here. The three pavement structures that are examined were derived from the 1972 AASHTO design guide approach and were constructed in Wisconsin during the 2004 construct...

Ecological Impact and Economic Aspects of Advanced Concrete Technologies

Reinforced concrete structures are often conceived for a certain time span of serviceability. Due to the superposition of different kinds of loads and particularly due to the presence of aggressive substances the resistance of construction materials is insufficient in numerous cases. Hence, many structures have to be repaired before the end of their designed life span. In case of reinforced concrete structures these repair measures are not only very expensive but they also consume high amounts of energy and materials which causes strong environmental impacts. The main challenge in developing reliable concrete technologies is the capability to enhance the life span of new and already repaired structures to a reasonable maximum. When aiming this objective not only durability related material properties have to be accomplished but their environmental impact has to be minimized simultaneously. This paper evaluates different concrete technologies and materials from diverse perspectives: Durability (simulating expected life span using numerical analyses), ecology (product life cycle and environmental impact assessments) and economy (estimating life cycle costs by investment appraisals). This kind of combined analysis facilitates the efficient design of structural elements and repair measures and provides the possibility to significantly increase the life span of new and repaired concrete structures.

Pavement Design Analysis with 2002 Design Guide Software

There has been a continuous evolutionary process in hot-mix asphalt (HMA) pavement design. In the beginning it was primarily based on past experience. Through research, empirical methods were developed on the basis of the materials’ response to specific loading in the AASHO Road Test. Today pavement design has progressed to a mechanistic-empirical method. This methodology takes into account the mechanical properties of the individual layers and uses empirical relationships to relate material properties to performance. The mechanical tests that are used as part of the current methodology include dynamic modulus and flow number, which have been shown to correlate with field pavement performance. The use of the dynamic modulus test and its impact on pavement design with the current design guide (2002) and its associated software are examined here. The three pavement structures that are examined were derived from the 1972 AASHTO design guide approach and were constructed in Wisconsin during the 2004 construction season. Through iterative changes in the HMA layer thickness, the major distresses of permanent deformation and fatigue were examined. Included in the examination were changes in air voids and asphalt binder content over ranges that were believed to be typical of HMA production and paving. All three pavements were predicted to perform well in terms of permanent deformation for the as-designed layer thicknesses. The 2002 design guide software, however, indicates that two of the three pavements considered may be prone to fatigue cracking, specifically at higher air void contents (+7.0%).

Modeling Radiative Properties of Silicon with Coatings and Comparison with Reflectance Measurements

Achieving high-accuracy temperature measurements in rapid thermal processing using radiation thermometry requires knowledge of the optical properties of silicon and related materials, such as silicon dioxide, silicon nitride, and polysilicon. However, available optical property models lack consistency and are not fully validated by experiments at the wavelength and temperature ranges critical to radiation thermometry. A critical survey is given of the existing optical models, with emphasis on the need for extrapolation and validation. Also described is an algorithm for calculating the radiative properties of lightly doped silicon with coatings. The effect of coatings covering one or both sides of a smooth silicon wafer is theoretically studied at room temperature, as well as at elevated temperatures. A spectrophotometer was used to measure the reflectance for selected samples in the wavelength region from (1.5 to 1 μm at room temperature. The measurements agree well with the predicted reflectance for bare silicon, a silicon wafer with a nitride coating, and wafers with an oxide coating of different thicknesses, whereas a larger deviation of as much as twice the measurement uncertainty is observed for a silicon wafer coated with polysilicon and oxide films.