Relief Of Strain Energy Research Articles

Understanding Anisotropic Growth of Au Penta-Twinned Nanorods by Liquid Cell Transmission Electron Microscopy.

Morphology control of anisotropic nanocrystals is important for tuning shape-dependent physicochemical properties, but the anisotropic growth mechanism remains unclear. Here we investigate the formation of the Au penta-twinned nanorod by liquid cell transmission electron microscopy. It is found that a truncated decahedron forms in the absence of cetyltrimethylammonium bromide (CTAB), whereas in the presence of CTAB, a penta-twinned nanorod forms by producing {100} facets via the reentrant groove and selectively inhibiting atom addition to {100} facets. Density functional theory simulations show that the partial relief of strain energy of the decahedron is caused by the adsorption of Br- ions. Moreover, the selective adsorption of CTAB lowers the surface energy of {100} facets, thus enhancing the nanorod growth. Our work points out the importance of the synergy of strain and surface energy, which provide an in-depth insight into the anisotropic growth of nanorods and lay foundations for the controlled synthesis of nanomaterials.

Cleaving carbon–carbon bonds by inserting tungsten into unstrained aromatic rings

The cleavage of C-H and C-C bonds by transition metal centres is of fundamental interest and plays an important role in the synthesis of complex organic molecules from petroleum feedstocks. But while there are many examples for the oxidative addition of C-H bonds to a metal centre, transformations that feature oxidative addition of C-C bonds are rare. The paucity of transformations that involve the cleavage of C-C rather than C-H bonds is usually attributed to kinetic factors arising from the greater steric hindrance and the directional nature of the sp(n) hybrids that form the C-C bond, and to thermodynamic factors arising from the fact that M-C bonds are weaker than M-H bonds. Not surprisingly, therefore, most examples of C-C bond cleavage either avoid the kinetic limitations by using metal compounds in which the C-C bond is held in close proximity to the metal centre, or avoid the thermodynamic limitations by using organic substrates in which the cleavage is accompanied by either a relief of strain energy or the formation of an aromatic system. Here, we show that a tungsten centre can be used to cleave a strong C-C bond that is a component of an unstrained 6-membered aromatic ring. The cleavage is enabled by the formation of an unusual chelating di(isocyanide) ligand, which suggests that other metal centres with suitable ancillary ligands could also accomplish the cleavage of strong C-C bonds of aromatic substrates and thereby provide new ways of functionalizing such molecules.

Towards a Fully Conjugated, Double‐Stranded Cycle: A Mass Spectrometric and Theoretical Study

The two compounds, 1 and 5, are investigated by means of collision-induced dissociation experiments by using ion cyclotron resonance mass spectrometry and other mass spectrometric techniques as to their ability to act as precursors for the fully unsaturated double-stranded target compound 2. These experiments are complemented by flask-type pyrolyses of 5, the products of which are analyzed by mass spectrometry. For 1, no conditions were found under which the expected molecular ion of 2 at m/z 932 appeared, however, for its derivative 5 this was possible. This interesting finding is not in contradiction with the chemical structure of the long sought for compound 2 but calculations suggest that this compound may have isomerized into one where the conjugation is interrupted by hydrogen shift from the solubilizing alkyl chains into the cycle's perimeter. The key driving force for such an isomerization would be the considerable relief of strain energy.

Lifetime modeling for stress-induced voiding in integrated circuit interconnections

By considering the stress-induced voiding (SIV) as a result of strain energy relief in the presence of flaws, an analytical lifetime model for SIV is derived from the energy perspective. The SIV lifetime is strongly dependent on the passivation integrity of the cap layer, effective bulk modulus of the interconnect system, diffusivities of the interconnect atoms in the dominant diffusion paths, stress free temperature, and temperature of the interconnection. The calculated SIV lifetime and the critical temperature are found to be consistent with the experimental values.

Transformation of Self-Assembled InAs/InP Quantum Dots into Quantum Rings without Capping

Transformation of self-assembled InAs quantum dots (QDs) on InP(100) into quantum rings (QRs) is studied. In contrast to the typical approach to III--V semiconductor QR growth, the QDs are not capped to form rings. Atomic force micrographs reveal a drastic change from InAs QDs into rings after a growth interruption in tertiarybutylphosphine ambient. Strain energy relief in the InAs QD is discussed and a mechanism for dot-to-ring transformation by As/P exchange reactions is proposed.

Crystallinity changes and melting behavior of the uniaxially oriented iPP exposed to high doses of gamma radiation

Samples of isotactic polypropylene (iPP) oriented via solid-state stretching at elevated temperature (draw ratios of 1, 3, 5, 7.5, 10, 12.5 and 15) were analyzed. Gel content measurements, wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) were used to study the effects of high absorbed doses of gamma irradiation, up to 700 kGy. Conclusions derived according to the different methods are compared. The results indicate that the changes in the structure of pristine iPP due to orientation also significantly affect the radiation induced changes in crystallinity, melting behavior and gel production. The role of highly strained tie molecules in radiation-induced increase in crystallinity at doses lower than 250 kGy, for oriented iPP is discussed in terms of the scission and strain-energy relief process on the crystals followed by the growth of new, thin-crystal, lamellae. At higher doses (300, 500 and 700 kGy) radiation-induced decrease in crystallinity is explained in terms of the effect of crosslinking. Orientation induced supermolecular structural changes are related to the decrease in the gel production with draw ratio.

Self-assembled SiGe quantum rings grown on Si(001) by molecular beam epitaxy

SiGe quantum rings (QRs) were grown by partially capping on Ge quantum dots (QDs) on Si(001). Atomic force microscopy images show the shape transformation from QDs to QRs. Initial capping, with a Si layer thickness less than 2 nm, will result in the decrease of height of QDs and increase of base diameter of QDs. Capped with a Si layer, QDs will change into QRs. The mechanism of transformation from QDs to QRs is discussed. The strain will redistribute after capping, thus the strain energy relief, together with high Ge surface diffusion and Ge surface segregation at a relative high temperature of 680 °C, play the dominant role.

DSC melting behavior of drawn and gamma-irradiated low-density polyethylene

Differential scanning calorimetry measurements (DSC) were used to study the effect of gamma irradiation on the melting behavior of drawn low-density polyethylene (LDPE). The drawing, to various draw ratios (5, 6, 9, 10 and 11), was performed via solid-state stretching at 80 °C. It was found that for the lower doses (50kGy) there is an increase in melting temperature with increasing draw ratio, λ. For the higher doses, the melting temperatures decrease slightly. The increase in heat of fusion with absorbed dose is explained in terms of the strain-energy relief process on the crystals by the scission of tie-molecules and the growth of new thin lamellae.

Cooperative cavitation in rubber-toughened polycarbonate

Particle cavitation in the stress-whitened zone ahead of a semicircular notch in polycarbonate blended with a core-shell rubber was characterized by transmission electron microscopy. Cavitation of rubber particles at five locations in the stress-whitened zone was correlated with the local stress and strain history. It was found that cavitation initiated some distance ahead of the notch when a mean stress condition was met. Initially, only a fraction of the particles cavitated and these were randomly distributed. Single cavitated particles grew into cavitated domains by cooperative cavitation of nearby particles until cavitation was arrested when shear yielding of the matrix provided an alternative mechanism for relief of strain energy. Far from the notch, where the stress state approached uniaxial tension, cavitated domains grew into linear arrays of cavitated particles. A mechanism of cooperative crazing in microlayer composites of polycarbonate and styrene/acrylonitrile copolymer was adapted to cooperative cavitation of core-shell rubber particles. It was proposed that cooperative cavitation of nearby particles occurred by impingement of a small plastic zone that formed at the equator of a cavitated particle.

The Bishop's Castle (UK) Earthquake of 2 April 1990

ABSTRACTA large earthquake, by British standards, occurred near Bishop's Castle in the Welsh Borders on 2 April 1990 at 13:46 GMT. This magnitude 5.1 ML event was felt over a wide area of Britain, from Ayrshire in the north to Cornwall in the south, Kent in the east and Dublin in the west. The epicentre was near the village of Clun, 7 km SSW of Bishop's Castle. Damage was minor and limited to the epicentral area, north to Wrexham and in particular Shrewsbury, which suffered most. Results from a macroseismic survey by BGS revealed that the maximum intensity in the epicentral area was 6 MSK.The mainshock had a focal depth of 14.3±4.7 km; however, better located aftershocks further constrained the mid‐crustal seismicity to 15±0.2 km in the best cases. The marked lack of aftershocks contrasts with some previous similar magnitude events for intraplate earthquakes in Britain and throughout the world and may represent a large stress drop due to almost total relief of strain energy by the mainshock. The aftershock epicentral distribution shows a preference for an approximately N‐S orientation which is consistent with one of the focal planes of the mainshock focal mechanism and suggests that this is the fault plane. Movement on this plane was predominantly strike‐slip with a component of thrust and was consistent with a maximum compressive stress axis orientated NW‐SE. The NE striking Welsh Borderland Fault System dominates the epicentral area; however, there is no surface fault which can clearly be related to the seismicity.

1.1.1]Propellane: Reaction with free radicals

[1.1.1]Propellane is more reactive towards free radicals than bicyclo[1.1.0]butane, and much more reactive than bicyclo[2.1.0]pentane. Therefore, the reactivity is not determined by strain energy relief or the HOMO energy. The addition of acetaldehyde is unique in that a 1:2 adduct is formed. A number of other additions are described, and provide convenient routes to 1,3-disubstituted bicyclo[1.1.1]pentanes.

Solidification of droplets

The response of a crystallite to the thermal fields developing during the solidification of a droplet and the mode of growth on a S−L interface are discussed. Stresses are relieved by causing the crystallite to deform plastically. The dislocations and/or twins that arise alter the morphology of the S−L interface and can enhance its growth rate. The analysis concentrates on crystallites growing in the bulk or at the surface of a droplet. For the hexagonal metals Cd, Mg and Zn, when the temperature varies only through the thickness of a thin floating raft, the growth helixes arise mainly as a result of the relief of strain energy due to the action of surface tension forces. Their calculated height is lower than the height measured on spherical particles of Cd.

Pressure solution and hydrothermal recrystallization of carbonate sediments — an experimental study — reply

Abstract The extent of calcite recrystallization was determined in pressure-solution and hydrothermal experiments which were conducted on deep-sea carbonates of low-Mg calcite, Iceland spar, and reagent-grade calcite powder. In the pressure-solution experiments, wet sediments were subjected to confining pressures of 500–1500 bars and pore pressures of 150–500 bars, at temperatures between 22° and 180°C, for 21–240 h. The hydrothermal experiments were performed in sealed teflon-coated bombs at 200°C, zero effective stress, in sulfate-free sea water, for two weeks. The hydrothermal system was solution-dominated. The extent of calcite recrystallization was determined by measuring the oxygen isotopic compositions of the pore fluids and solids before and after each experiment. Scanning Electron Microscope observations, porosity and specific surface-area measurements were performed. In fine-grained carbonate samples subjected to high effective stresses, the mechanism for recrystallization apparently involves both relief of strain energy at grain-to-grain contacts and decrease in surface free energy by decreasing the surface area, while in coarse-grained carbonates, relief of strain energy appears to be the most important control of recrystallization. In the hydrothermal experiments, however, decrease in surface free energy is the only driving force for recrystallization. Effective stress increased the rate of calcite recrystallization. In both pressure-solution and hydrothermal experiments, clay minerals retarded the reaction. The effects of diatomite and basaltic glass on the extent of calcite recrystallization was investigated only in the hydrothermal experiments. Both admixed non-carbonate materials retarded the reaction, diatomite being the most effective inhibitor. Surface chemical reactions seem to be responsible for the observed inhibitions of calcite recrystallization. Increases in the extent of calcite recrystallization with increasing ionic strength were observed in hydrothermal experiments in NaCl solutions of five different ionic strengths.

Pressure solution and hydrothermal recrystallization of carbonate sediments — An experimental study

The extent of calcite recrystallization was determined in pressure-solution and hydrothermal experiments which were conducted on deep-sea carbonates of low-Mg calcite, Iceland spar, and reagent-grade calcite powder. In the pressure-solution experiments, wet sediments were subjected to confining pressures of 500–1500 bars and pore pressures of 150–500 bars, at temperatures between 22° and 180°C, for 21–240 h. The hydrothermal experiments were performed in sealed teflon-coated bombs at 200°C, zero effective stress, in sulfate-free sea water, for two weeks. The hydrothermal system was solution-dominated. The extent of calcite recrystallization was determined by measuring the oxygen isotopic compositions of the pore fluids and solids before and after each experiment. Scanning Electron Microscope observations, porosity and specific surface-area measurements were performed. In fine-grained carbonate samples subjected to high effective stresses, the mechanism for recrystallization apparently involves both relief of strain energy at grain-to-grain contacts and decrease in surface free energy by decreasing the surface area, while in coarse-grained carbonates, relief of strain energy appears to be the most important control of recrystallization. In the hydrothermal experiments, however, decrease in surface free energy is the only driving force for recrystallization. Effective stress increased the rate of calcite recrystallization. In both pressure-solution and hydrothermal experiments, clay minerals retarded the reaction. The effects of diatomite and basaltic glass on the extent of calcite recrystallization was investigated only in the hydrothermal experiments. Both admixed non-carbonate materials retarded the reaction, diatomite being the most effective inhibitor. Surface chemical reactions seem to be responsible for the observed inhibitions of calcite recrystallization. Increases in the extent of calcite recrystallization with increasing ionic strength were observed in hydrothermal experiments in NaCl solutions of five different ionic strengths.

Anti-bredt monomers

1-Aza-6-oxabicyclo [3.2.1]octan-7-one 3 polymerized in bulk to polyurethane at 112–131°C with opening of the 5-membered urethane ring. Organometallic, cationic, anionic and organophosphoric initiators polymerized the strained bicyclic urethane to the polyurethane. In solution the monomer was shown to polymerize slowly under the influence of phosphoric acid. The driving force for the polymerization may be the relief of strain energy in the monomer caused by a boat conformation of the 6-membered ring.

Hardness and Recrystallization Behavior of Ag-Ni Sintered Two Phase Alloys Prepared by Cold Drawing

The purpose of this paper is to discuss the hardening mechanisms of Ag-Ni sintered two phase alloys containing fibrous Ni prepared by cold drawing. Deformation behavior during cold drawing and softening behavior during isochronal annealing were studied by hardness measurements.The results are summerized as follows:(1) Ag-Ni alloys containing fibrous Ni were obtained by cold drawing of sintered alloys. The hardness of these alloys was higher than that calculated by the mixing rule based on the hardness of Ag and Ni.(2) In the region of low Ni volume fractions and low reduction, the matrix and secondary phases were deformed with different strain. Deformation in the matrix was larger than that in the secondary phase.(3) Hardening by fine structure and strain hardening were distingusihed. Structural hardening was represented by the Hall-Petch type relation.(4) Ag-Ni alloys containing fibrous Ni had a higher recrystallization temperature than that of Ni. The main cause of this behavior was the inhibition of the strain energy relief due to the fine structure.

Factors that Predict Fracture Orientation In a Gas Storage Reservoir

The data presented here indicate that surface joints and lineaments as revealed by aerial photographs are related to the maximum horizontal stress in a region and to the orientation of induced vertical wellbore fractures. This information could help engineers to make the optimum choice of wells for fracturing, thus enhancing reservoir performance. Introduction The natural state of earth stresses, in which the vertical stress generally exceeds the horizontal stress, is a condition favoring the formation of vertical fractures. Petroleum-producing reservoirs have vertical fractures Petroleum-producing reservoirs have vertical fractures along a preferred azimuthal direction. The orientation of vertical fractures in areas of flat or gently dipping rocks may be ascertained both quickly and accurately from regional surface features. In certain areas where no apparent relationship exists between jointing and present folding or stress orientation, the jointing may be due to failure planes or directions inherited from deep-seated basement rocks. In relating surface joint trends to hydraulically induced wellbore fractures, we hypothesized that one direction of jointing in surface rocks could be related to the orientation of the maximum horizontal stress in that locality. This hypothesis, in conjunction with the presently accepted theory that hydraulically induced vertical fractures will be oriented parallel to the maximum horizontal stress and nominal to the minimum horizontal stress direction, allows us to infer the orientation of the stress field by comparing surface-orientation data with subsurface-orientation data. In some tectonic provinces, the stress-field orientation can be inferred from the structural geometry; however, stress history must be examined or great errors arise from this method. In a reservoir study at microscopic scale, investigators have detected permeability to be directional in samples from various oilfields and have indicated that the idea is applicable in primary- and secondary-recovery development. Relative primary- and secondary-recovery development. Relative to the preferred direction of fracturing, higher permeabilities were found parallel to the wellbore permeabilities were found parallel to the wellbore fracture in one Appalachian oilfield, indicating a relationship between directional permeability and fracture orientation. In a noteworthy laboratory investigation on the relationship between directional characteristics and the induced fracture orientation in sedimentary rocks, it was shown that fracture propagation was parallel to the direction defined by greatest strain-energy relief in relaxation during overcoring of strain gauges mounted in boreholes. In an effort to determine the preferred direction of fracturing in an established gas-storage reservoir, the Petroleum Div. of the Morgantown Energy Research Center initiated a program to relate microscopic rock properties with observed macroscopic reservoir fractures. properties with observed macroscopic reservoir fractures. We believe that an interdisciplinary study involving both laboratory and field experiments is the proper approach to understanding the factors influencing fracture orientation. Therefore, we have directed our research toward relating basic rock properties to present and past geologic stresses. present and past geologic stresses. JPT P. 546

Crystal and molecular structure of racemic 5,7,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradeca-4,14-dienenickel(II) perchlorate

The structure of 5,7,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradeca-4,14-dienenickel(II) perchlorate has been determined and refined to R 0·062 for approximately 1000 reflections measured on a linear diffractometer. The complex crystallises in the orthorhombic space group Pbcn with a= 10·60, b= 11·11, c= 19·16 A, Z= 4. A crystallographic two-fold axis passes through the cation which, as a consequence of the asymmetric nitrogen centres, is chiral; the space group ensures that the crystal is a racemate. The chiral isomer is more stable than the analogous meso-isomer because the C2 symmetry allows greater freedom in the torsion angles for relief of strain energy than does the alternative Cs symmetry. Conformational analysis is used to point out the strong dependence of molecular geometry and, in particular, of metal–ligand-atom distances on geometrical constraints imposed by the cyclic ligand.