Anisotropic Expansion Behavior Research Articles

Anisotropic expansion behavior and crack orientation of reinforced concrete due to the alkali–silica reaction

In this study, the expansion behavior, surface and internal crack developments due to the alkali–silica reaction in two types of reinforced concrete prisms with and without stirrups are investigated. Longitudinal and transverse expansions are continuously monitored at various positions on the prism surfaces. Image analysis is employed to determine the densities of surface and internal cracks. Crack orientations for several groups of crack angles are measured to characterize the dominant crack pattern. The findings indicate that longitudinal expansion was transferred to the transverse direction at the middle region in both prisms, regardless of the presence of stirrups. However, average longitudinal, transverse, and volumetric expansions are reduced in prisms with stirrups. The anisotropy coefficient of expansion exhibits a strong proportional relationship with the surface and internal crack densities of each crack angle group. Therefore, the trend of internal crack orientations and expansion anisotropy can be estimated based on surface crack information.

Effect of vertical aligned carbon nanofiber/carbon nanotube on the mechanical, electrical and electromagnetic interference shielding properties of epoxy foams

In this study, one-dimensional (1D) carbonaceous blends containing multi-walled carbon nanotube (MWCNT) and carbon nanofiber (CNF) were added into epoxy resin (EP) to obtain hybrid powder though ball milling. Limited foam with vertically aligned nanofillers was fabricated through limited-foaming epoxy hybrid in a mold and Two-step foam was prepared by further freely foaming a preformed Limited foam in an oven. The cellular structure, compressive, electrically conductive and EMI shielding properties of these two kinds of epoxy composite foams were carefully investigated. Limited foam showed an isotropic electrical resistivity while the electrical anisotropy started to emerge after the second-step foaming. This result was ascribed to the twisty MWCNT bridged the aligned CNF to build conductive pathways in horizontal direction, thus eliminating the electrical anisotropy of Limited foam. However, these loose interconnections between MWCNT and CNF in horizontal direction were more seriously destroyed by the further growth of bubbles, consequently endowing the Two-step foam with electrical anisotropy. Adding CNF into EP/MWCNT foams not only improved the electromagnetic interference (EMI) shielding effectiveness (SE), which was due to the synergistic effect between hybrid nanofillers in enhancing the electrical conductivity, but also enlarged the anisotropy in EMI SE of both Limited foam and Two-step foam. As compared to anisotropic bubbles, the vertically aligned MWCNT/CNF in composite foams exhibited a weak effect on anisotropy in compressive strength. Moreover, a remarkably anisotropic expansion behavior of preformed foam during the second-step foaming was observed and this behavior can be tuned by the ball milling time and the content of vertically aligned nanofillers.

Non-axisymmetric droplet irradiation effects on ion and extreme ultraviolet light emission of laser-produced plasma light sources

Extreme ultraviolet (EUV) light emission and ion emissions in the lateral direction generated by Nd:YAG irradiated droplet targets were studied experimentally under non-axisymmetric droplet irradiation. EUV energy monitors and ion electrostatic probes were positioned symmetrically at fixed positions around the plasma. Bulk ion kinetic energy Ekin and bulk ion density ni were characterized for angles of γ=31° to γ=90° from the laser axis in a low-pressure nitrogen atmosphere of 1×10−2mbar. The EUV light emission reached a maximum level, with an increase of 5%, at γ=60° through a shift of the droplet by around 18% of the droplet diameter. The ion bulk kinetic energies at 31° and 75° also increased by 9% and 15%, respectively, with a small increase in ion density of around 3%. Intentional offset of the droplet target can, therefore, potentially result in higher EUV light output for non-axisymmetric mirror configurations, at the expense of a higher ion load but a decreased droplet fragment load. The ion kinetic energy showed a strongly anisotropic expansion behavior when offsetting the droplet relative to the laser focus, with kinetic energies increasing up to 60% in the lateral direction by offsetting the droplet by more than 0.5 droplet diameters for a lateral range of 31°–90°. The ion density showed a more isotropic change with droplet offset, while maintaining a forward-peaked distribution.

Thermal Behavior and Micro Structure of TKX‐50

AbstractThe thermal behaviour of TKX‐50 was reinvestigated in an extended temperature range by means of temperature resolved X‐ray diffraction. TKX‐50, synthesized at the Fraunhofer ICT, was identified using Rietveld‐analysis and reference data from the CCDC. Monitoring the refined crystal data versus temperature verified a highly anisotropic expansion behavior connected to a layer structure. However, the coefficients of thermal expansion (CTEs) were found at an order of magnitude higher than reported, and a slight bent of lattice parameter a was found near room temperature. At temperatures between 180 and 200 °C the decomposition of TKX‐50 started with the formation of 1 to 5 wt.% diammonium 5,5’‐bistetrazole‐1,1’‐diolate (ABTOX). Moreover, the micro structure was investigated by means of size/strain analysis and so called indexed Williamson‐Hall plot. The analysis revealed moderate micro strain and absence of size broadening. The results give rise to the hypothesis that the (010) layer structure supports a low sensitivity of TKX‐50 without impairment of the mechanical stability. The results provide a base for future quality assessment and the development of advanced products.

Elastic strain induced abnormal grain growth in graphene nanosheets (GNSs) reinforced copper (Cu) matrix composites

Orientation related grain growth stimuli during primary and secondary recrystallization of the metal matrix in laminated metal/non-metal composites demonstrate unique effect on orientation evolution but has rarely been investigated. In this work, the recrystallization and grain growth of Cu in a graphene nanosheets (GNSs) reinforced laminated Cu matrix composite during sintering was thoroughly investigated. The microstructure, texture and lattice strain evolution of the Cu/GNS composite was examined referenced to the Cu stack without GNSs by ex-situ and in-situ orientation characterization techniques (SEM-EBSD, neutron diffraction and synchrotron radiation) from mesoscale to macroscopic scale. The results evidenced that a strong Cube orientation was produced in the Cu/GNS composite instead of the individual non-Cube orientations in the pure Cu stack without GNSs. Detailed strain-state analysis of the Cu foils in the Cu/GNS composite revealed that the anisotropic expansion behavior of the GNS that is incompatible with that of the Cu foils imposed multiple elastic constraints to the foils during the sintering process, resulting in a biaxial isostrain state in the surface layers and a uniaxial compressive strain state in the central layer of each Cu foil. The elastic anisotropy of Cu favors the growth of the Cube oriented grains to minimize the total strain energy. This work clarified the thermal strain induced abnormal grain growth of selected orientations. The mechanism revealed can be useful for analysing abnormal grain growth in elastically strained materials and can also be applied to fabrication process for texturization or even monocrystallization.

Growth of large size SnSe crystal via directional solidification and evaluation of its properties

SnSe crystal is an attractive Ⅳ-Ⅵ thermoelectric (TE) material. In this work, a Ø25 × 50 mm3 SnSe crystal was prepared using a directional solidification method. The as-grown crystal has standard Pnma structure at room temperature. The band gap Eg is determined to be 0.96 eV which agrees well with the theoretical value. Thermal expansion measurements show that SnSe crystal has significant anisotropic expansion behaviors. The linear thermal expansion along <010> and <100> directions are positive but is negative in <001> direction. Pnma-Cmcm phase transition has remarkable influence on thermal expansion performance. The electronic and thermal transport properties of SnSe crystal along (100) plane are investigated. It is found the highest power factor PF = 6.20 μWcm−1K−2 and the lowest total thermal conductivity ktot = 0.46 W/m-K both occur near Pnma-Cmcm phase transition temperature. Finally, the maximum ZT = 1.05 appears around 800 K suggesting SnSe crystal is a candidate for middle-temperature TE material.

Thermal Expansion of Carbamazepine: Systematic Crystallographic Measurements Challenge Quantum Chemical Calculations.

We report systematic temperature-dependent X-ray measurements on the most stable carbamazepine polymorph. This active pharmaceutical ingredient is used to demonstrate how the thermal expansion can probe certain intermolecular interactions resulting in anisotropic expansion behavior. We show that most structural features can be captured by electronic structure calculations at the quasi-harmonic approximation (QHA) provided a dispersion-corrected density functional based method is employed. The impact of thermal expansion on the phonon modes and hence free energy contributions is large enough to impact the relative stability of different polymorphs.

Enhanced lithiation and fracture behavior of silicon mesoscale pillars via atomic layer coatings and geometry design

Crystalline silicon nanostructures are commonly known to exhibit anisotropic expansion behavior during the lithiation that leads to grooving and fracture. Here we report surprisingly relatively uniform volume expansion behavior of large aspect-ratio (∼25), well-patterned, n-type (100) silicon micropillars (∼2 μm diameter) during the initial lithiation. The comparison results with and without atomic layer metal oxides (Al2O3 and TiO2) coatings reveal drastically enhanced solid electrolyte interphase (SEI) formation, higher volume expansion, and increased anisotropy. Square-pillars are found to exhibit nearly twice volume expansion without fracture compared to circular-pillars. Models are invoked to qualitatively address these beneficial or detrimental properties of silicon for lithium ion battery. Our experiments and computer simulations point at the critical relevance of SEI and pristine geometry in regulating volume expansion and failure. ALD-coated ultrathin metal oxides can act as an ion channel gate that helps promote fast Li+ transport into the bulk by changing the surface kinetics, suggesting new ways of designing electrodes for high-performance lithium ion battery applications.

Anisotropic thermal expansion and anharmonic phonon behavior of mullite-type Bi2Ga4O9

We report the lattice thermal expansion and the temperature-dependent phonon behavior of the mullite-type Bi2Ga4O9 complex oxide. The thermal expansion was studied using composite data collected from powder and single crystal X-ray diffraction between 100K and 1273K. The lattice expansion occurred in the order of a<c<b. The anisotropic expansion behavior was monitored with respect to thermal expansion coefficients and the anisotropy factor. The volume thermal expansion was expressed using an extended Grüneisen first-order approximation to the zero-pressure equation of state; the model includes harmonic, quasi-harmonic and intrinsic anharmonic contributions to the internal energy as a function of temperature. The temperature dependent Raman spectra were collected from a single crystal between 78K and 1273K. The shift of the frequencies and the broadening of the line-widths with increasing temperature helped to analyze the anharmonicity and the thermal behavior of some phonons.

Pressure and Temperature Dependent Structure Of Zircon Type ThGeO4

Herein we report the results of high pressure diffraction studies of zircon type ThGeO4. ThGeO4 exhibits anisotropic compressibility with the average compressibility along a-axis (20.8 × 10−4/GPa) larger than that along c-axis (9.98 × 10−4/GPa). Fitting the pressure dependence unit cell volume to 3rd order Birch-Murnaghan equation of states, the zero pressure bulk modulus (Ko) and volume (Vo) of 166(5) GPa and 341.6(3) Å3, respectively have been obtained. Preliminary studies on temperature dependent neutron and x-ray diffraction studies on ThGeO4 revealed anisotropic expansion behaviour with larger expansion coefficient along c-axis compared to a-axis. No structural transition under temperature or pressure is observed in between ambient pressure to 10 GPa and in the temperature range of 25 to 1273K.

Anisotropic Thermal Expansion Coefficients of Y2O3‐Stabilized Tetragonal Zirconia

The transformability of the grains in tetragonal zirconia polycrystals is determined by thermal stresses (eigenstresses) which develop because of anisotropic expansion behavior of the tetragonal grains on cooling. Anisotropic thermal expansion coefficients based on lattice parameter determinations at room temperature and 600° and 800°C are presented for tetragonal zirconia containing 2 and 3 mol% Y2O3. The sources of errors in these data are discussed.