Oxide scale stresses in polycrystalline Ni200

An X-ray diffraction (sin² ψ) method has been successfully used to measure the oxidation stresses at room temperature in annealed and electropolished samples of polycrystalline Ni200 coupons oxidized in the temperature range 760 to 982° C for 4 h. The stresses on the free surface of the oxide (σ ₁₁ andσ ²²) were compressive and the average stress through the thickness normal to the oxide layer was found to be tensile. Surface stresses on the oxides formed at temperatures up to 927° C were found to be isotropic and both surface stresses and the average normal stress increased with increasing temperature of oxidation. At 982° C, the surface stresses were lower and this was attributed to the deformation and fracture of oxide layer resulting in stress relaxation.     

Barrier characteristics of Pt/Ru Schottky contacts on <Emphasis Type="Italic">n</Emphasis>-type GaN based on <Emphasis Type="Italic">I–V–T</Emphasis> and <Emphasis Type="Italic">C–V–T</Emphasis> measurements

We have investigated the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Ru/Pt/n-GaN Schottky diodes in the temperature range 100–420 K. The calculated values of barrier height and ideality factor for the Ru/Pt/n-GaN Schottky diode are 0·73 eV and 1·4 at 420 K, 0·18 eV and 4·2 at 100 K, respectively. The zero-bias barrier height (Φ_b0) calculated from I–V characteristics is found to be increased and the ideality factor (n) decreased with increasing temperature. Such a behaviour of Φ_b0 and n is attributed to Schottky barrier (SB) inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs) at the metal/semiconductor interface. The current–voltage–temperature (I–V–T) characteristics of the Ru/Pt/n-GaN Schottky diode have shown a double Gaussian distribution having mean barrier heights ( [`(F)]<sub>\textb0</sub> {\bar{{\Phi}}_{\text{b}0}} ) of 1·001 eV and 0·4701 eV and standard deviations (σ <sub>0</sub>) of 0·1491 V and 0·0708 V, respectively. The modified ln (J<sub>0</sub> /T<sup>2</sup> )-( q<sup>2</sup>s <sub>0</sub><sup>2</sup>/2k<sup>2</sup>T<sup>2</sup> ){ln} ({{J}_{0} /{T}^{2}} )-( {{q}^{2}{\sigma} _{0}^{2}/{2}{k}^{2}{T}^{2}} ) vs 10<sup>3</sup>/T plot gives [`(F)]_\textb0 \bar{{\Phi}}_{\text{b}0} and Richardson constant values as 0·99 eV and 0·47 eV, and 27·83 and 10·29 A/cm²K², respectively without using the temperature coefficient of the barrier height. The difference between the apparent barrier heights (BHs) evaluated from the I–V and C–V methods has been attributed to the existence of Schottky barrier height inhomogeneities.     

Synthesis,growth, optical,mechanical and electrical properties of <Emphasis Type="Italic">L</Emphasis>-lysine <Emphasis Type="Italic">L</Emphasis>-lysinium dichloride nitrate (<Emphasis Type="Italic">L</Emphasis>-LLDN) single crystal

Semi-organic nonlinear optical material, L-lysine L-lysinium dichloride nitrate (2C₆H₁₅N₂O₂⁺_{2}^{+} · H⁺ · NO₃^-_{3}^{-} · 2Cl⁻) was synthesized at room temperature. Single crystals of L-LLDN were grown by slow cooling solution growth technique. The grown crystal was confirmed by powder X-ray diffraction analysis. The crystalline perfection of the grown single crystal was characterized by high-resolution X-ray diffraction (HRXRD) studies. The cut-off wavelength was determined by UV-vis transmission spectral analysis. The frequency doubling of the grown crystal was confirmed by powder second harmonic generation (SHG) measurement. The refractive index and birefringence of the crystal were determined using He–Ne laser source. Mechanical property of the crystal was determined by Vickers hardness tester. The frequency and temperature dependence of dielectric constant (ε _r), dielectric loss (tan δ) and a.c. conductivity (σ _ac) were also measured.     

High-<Emphasis Type="Italic">T</Emphasis><Subscript>C</Subscript> phase transition in K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> lead-free ceramic synthesised using solid-state reaction

Solid-state reaction synthesised K₂Ti₆O₁₃ lead-free ceramic was characterized using XRD, SEM, and X-band EPR, at room temperature. EPR-spectra showed the presence of ( \textFe_\textTi^￠ - V_\textO ^·· ) \left( {{\text{Fe}}_{\text{Ti}}^{\prime } - V_{\text{O}}^{ \bullet \bullet } } \right) defect associate dipoles, in orthorhombic phase, responsible for the broadening of the dielectric anomaly identified in the ε _r (T) plots at T _C  ~ 300 °C. This anomaly resembled a ferroelectric–paraelectric type phase transition following Curie–Weiss type trend. Besides, dielectric loss mechanism jointly represented electrical conduction, dipole orientation, and space charge polarization.     

Effect of fibre concentration,temperature and mould thickness on weldline integrity of short glass-fibre-reinforced polypropylene copolymer composites

The effect of fibre concentration, temperature and mould thickness on tensile strength of single- and double-gated injection-moulded polypropylene copolymer reinforced with 0, 10, 20, 30 and 40 wt% short glass fibre was studied at a fixed strain-rate of 7.58 × 10⁻³ s⁻¹ between 23 and 100 °C. It was found that tensile strength of single-gated mouldings, σ_c, increased with increasing volume fraction of fibres, ϕ_f in a nonlinear manner and decreased with increasing temperature in a linear manner. However, for ϕ_f values in the range 0–10% a simple additive rule-of-mixtures adequately described the variation of σ_c with ϕ_f over the entire temperature range 23–100 °C studied here. Tensile strength of double-gated mouldings like their single-gated counterparts decreased linearly with increasing temperature. The presence of weldlines significantly reduced tensile strength of double-gated composite mouldings but had little effect on tensile strength of the matrix. Weldline integrity factor, F _σ, defined as weldline strength divided by unweld strength, decreased with increasing ϕ_f but increased with increasing temperature. A linear dependence was found between F _σ and temperature. Mould thickness had no significant effect upon weld and unweld tensile strengths and consequently had no significant effect upon weldline integrity factor.     

Acoustic investigations on PbO-Al2O3-B2O3 glasses doped with certain rare earth ions

Elastic moduli (Y, η), Poisson’s ratio (σ), microhardness (H) and some thermodynamical parameters such as Debye temperature (θ_D), diffusion constant (D _i),latent heat of melting (ΔH _m) etc of PbO-Al₂O₃-B₂O₃ glasses doped with rare earth ions viz. Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺ and Yb³⁺, are studied as functions of temperatures (in the temperature range 30–200°C) by ultrasonic techniques. All these parameters are found to increase with increasing atomic numberZ of the rare earth ions and found to decrease with increasing temperature of measurement. From these results (together with IR spectra of these glasses), an attempt is made to throw some light on the mechanical strength of these glasses.     

Ultimate tensile strength of loblolly pine strands using stochastic finite element method

The purpose of the study was to predict the failure strength of different orientation of wood strands from different growth ring positions under tension loading. Stochastic models were constructed to account for the uncertainty of material properties. The Tsai–Hill criteria were used to predict the ultimate tensile strength (UTS). The UTS results from experimental testing were used to validate the results from models. The difference of UTS between experimental and SFEM ranged from 0.09 to 11.09%. Different stress distributions were found for different orientation strand models, whereas uniform stress distribution was found for homogeneous models. The magnitude of the stress distribution was greater for strands from the growth ring number 11–20. Sensitivity analysis showed that grain orientation and growth ring number influenced the UTS of strands. UTS of strands from growth ring number 1–10 showed strength indexes (X _t, Y _t, and S) as dominant factor, whereas UTS of strands from growth ring number 11–20 showed both strength indexes and stress components (σ ₁, σ ₂, and τ ₁₂) as dominant factors.     

Elastic,piezoelectric, and dielectric properties of lanthanum-gallium tantalate crystals at temperatures of 20–600°C

Measurements of the temperature variations in the relative dielectric constants e₃₃^T/e₀ \varepsilon_{33}^T/{\varepsilon_0} , e₁₁^T/e₀ \varepsilon_{11}^T/{\varepsilon_0} ,and e₂₂^T/e₀ \varepsilon_{22}^T/\varepsilon {}_0 , conductivities g₁₁, g₂₂, and g₃₃, elastic constants C₁₁^D C_{11}^D , C₆₆^D C_{66}^D , and S₂₂^E S_{22}^E , and electromechanical coupling constants k_t, k₂₆, and k₁₂ of lanthanum-gallium tantalate over temperatures of 20–600°C are reported. Data are presented on the effect of lifetime (breakdown) testing on these characteristics of the piezoelectric crystals after retention at a temperature of 625°C for 250 h.     

Predicting long-term creep failure of bimodal polyethylene pipe from short-term fatigue tests

Short-term fatigue testing was used to predict long-term creep failure of a bimodal polyethylene (BMPE) pipe with superior creep resistance. The stepwise crack propagation was studied by increasing the R-ratio (defined as the ratio of the minimum to the maximum stress intensity factor in the fatigue loading cycle) at 50 °C from 0.1 approaching creep (R = 1). Crack growth rate (da/dt) was related to the maximum stress intensity factor K _I,max and R-ratio by a power law relationship \frac\textda\textdt = B^￠ K_\textI,max⁴ (1 + R) ^{- 8.5} {\frac{{{\text{d}}a}}{{{\text{d}}t}}} = B^{\prime } K_{{{\text{I}},\max }}^{4} (1 + R)^{ - 8.5} . The correlation in crack growth kinetics allowed for extrapolation to creep fracture from short-term fatigue testing. The temperature dependence of crack growth rate was contained in the prefactor B′. A change in slope of the Arrhenius plot of B′ at 67 °C indicated that at least two mechanisms contributed to crack propagation, each dominating in a different temperature region. This implied that a simple extrapolation to ambient temperature creep fracture from elevated temperature tests might not be reliable.     

Effect of grain boundaries on dynamic recrystallization behaviour of copper isoaxial bicrystals with 〈001〉 tilt boundaries

Dynamic recrystallization behaviour of copper isoaxial bicrystals with various 〈001〉 tilt boundaries was investigated at 1023 and 1073 K at an initial strain rate of 3.33×10⁻⁴sec⁻¹, with special attention paid to the effect of grain boundaries on the recrystallization stress (strain) and the substructure developed during deformation. The grain boundaries in the bicrystals have almost no effect on the stress-strain curves. Flow stress was found to fall abruptly and significantly during deformation, being similar to the flow stress in the single crystals. The stressσ _R (ɛ _R), just before the stress fall indicates the stress (strain) at which dynamic recrystallization occurs. The growth of recrystallized grains is markedly fast in these bicrystals, suggesting that dynamic recrystallization is controlled by a nucleation process. The value ofσ _R in bicrystals with a tilt boundary of 9°,θ9 bicrystals, is almost equal to that in single crystals, but is larger thanσ _R inθ23,θ36 andθ43 bicrystals. These results indicate that theθ9 boundary has no effect on the dynamic recrystallization of bicrystals, whereas grain boundaries with tilt angles above 23° accelerate the dynamic recrystallization of these bicrystals. Theθ-dependence ofσ _R orɛ _R is discussed in connection with the stress concentration near the grain boundary.     

Effect of soil moisture on microwave scattering for remote sensing

The main objective of remote sensing is to design space borne microwave sensors to sense a target and derive useful geophysical parameters. For this purpose, the knowledge of the target characteristics must be obtained through ground based remote sensing. In this paper, soil has been taken as the target. Various percentages of gravimetric soil moisture (m _g) have been taken for establishing its relation with the scattering coefficient (σ ₀) for both like polarizations at X-band frequencies. A linear model has been developed for correlating these two variables (i.e.m _g andσ ₀). Using this model, regression analysis has been done for obtaining different regression parameters and predicted values. Treating measurements from bare smooth soil fields with different soil moistures, the data were analysed to examine the effect of soil moisture on scattering co-efficient (σ ₀) at 9.50 GHz frequency in X-band. The scattering coefficient increases with increase in soil moisture content. Different regression parameters have been obtained, which show that the best look-angle is at 25° for HH-pol and 60° for VV-pol for observingσ ₀ from bare moist soil. Data analysis indicated that the basic cause and effect relationship between the sensor measurements and soil moisture can be extrapolated from theory and small-scale tests to larger resolution elements observed by the sensing aircraft. These results indirectly provide reference data for a satellite-borne remote sensor. From the results, the look angles suitable for operation with radar antennas can be suggested.     

The characteristics of granular-bright facet in hydrogen pre-charged and uncharged high strength steels in the very high cycle fatigue regime

In this study, the effect of hydrogen on fatigue strength of high strength steels in the very high cycle fatigue regime was further discussed. It is found that the calculated results of fatigue strength by modified Murakami’s expression are in good accordance with the experimental results in ±15% error band. The relationship between fatigue life (N _f) and the ratio of granular-bright facet (GBF) to inclusion size (\frac?{A_\textGBF } ?{A_\textinc } ) \left({\frac{{\sqrt {A_{\text{GBF}} } }}{{\sqrt {A_{\text{inc}} } }}}\right) for quenching and tempering (QT) specimens and pre-charged specimens by soaking (SK) and cathodic (CD) charging can be approximately expressed by \frac?{A_\textGBF } ?{A_\textinc } = \fracR_\textGBF R_\textinc = 0. 2 5N_\textf ^{0. 1 2 5} {\frac{{\sqrt {A_{\text{GBF}} } }}{{\sqrt {A_{\text{inc}} } }}} = {\frac{{R_{\text{GBF}} }}{{R_{\text{inc}} }}} = 0. 2 5N_{\text{f}}^{ 0. 1 2 5} ; however, the value of \frac?{A_\textGBF } ?{A_\textinc } {\frac{{\sqrt {A_{\text{GBF}} } }}{{\sqrt {A_{\text{inc}} } }}} for specimens pre-charged by high-pressure thermal hydrogen charging is obviously greater than that for QT specimens and pre-charged specimens by SK and CD charging at an identical N _f. The stress intensity factor range at the periphery of the GBF, ΔK _GBF, was calculated in this work. It is found that the value of ΔK _GBF is not a constant but approximately proportional to (?{A_\textGBF } ) ^{1/ 3} (\sqrt {A_{\text{GBF}} } )^{ 1/ 3} . Besides it is also found that ΔK _GBF decreases with the increase of hydrogen content.     

Effect of drawing on the dielectric properties and polarization of pressed solution cast β-PVDF films

Poly(vinylidene fluoride), PVDF, samples containing exclusively the polar β phase were obtained by crystallization from N,N-dimethylformamide (DMF) solution at 60 °C and subsequent pressing. Some of these samples were uniaxially drawn at 120 °C at draw ratio of 4, resulting in oriented films. Oriented and unoriented samples were characterized as to relative fraction of β phase, degree of crystallinity and orientation by infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). The dependence on frequency of the real ( e_\textr^￠ \varepsilon_{\text{r}}^{\prime} ) and imaginary ( e_\textr^￠￠ \varepsilon_{\text{r}}^{\prime\prime} ) components of the relative permittivity of the samples was determined between 10⁴ and 1.7 × 10⁷ Hz. The coercive field and stable and metastable remanent ferroelectric polarization were determined from the hysteresis loop obtained by the ramp voltage technique, described in detail in this work. The results allowed verification of the effect of drawing on structure and of the resulting structure on the dielectric properties, remanent polarization, and coercive field of β-PVDF. A possible effect of the crystal–amorphous interphase region on the metastable remanent polarization is suggested. The results obtained with the oriented and unoriented samples were compared with those obtained for films commercialized by Piezotech S.A.     

A New Method for Modeling of Initiation and Propagation of Delamination Between [0/θ<Superscript>o</Superscript>] Layers of Laminated Composites

In this article, initiation and propagation of delamination of a double cantilevered beam (DCB) is studied. The delamination of DCB specimen occurs between 0 ^o and θ ⁰ layers. Due to damage induced, during the loading, in the matrix of θ ⁰ layer, virtual crack closure technique (VCCT) as a well known method for simulation of initiation and propagation of the delamination for DCB is not able to model the propagation of delamination properly. To overcome this shortcoming, the stiffness of the damaged θ ⁰ layer is decreased with a developed technique in this study. The stiffness reduction technique (SR) is introduced in this paper to model the induced cracks in the matrix of the θ ⁰ layer. Then the stiffness reduction technique is coupled with the critical length parameter. The presented method is called stiffness reduction—critical length (SR-CL) method. By using SR-CL method, initiation and propagation of delamination for a [ ( 0₂^o/90^o )₆/0₂^o//q^o/( 0₂^o/90^o )₆/0₂^o ] \left[ {{{\left( {0_2^o/{{90}^o}} \right)}_6}/0_2^o//{\theta^o}/{{\left( {0_2^o/{{90}^o}} \right)}_6}/0_2^o} \right] configuration in which θ = 0^o, 22.5^o, 45^o, 67.5^o, 90^o and for a cross ply laminate (0°/90°) ₁₂ are modeled. The obtained results are in very good agreements with experimental data.     

Electrical conductivity of modified poly(vinyl chloride)

Chemical modification of poly(vinyl chloride) (PVC) by dehydrochlorination with ethanolic KOH is found to yield modified PVC with conjugated polyene sequence. The semiconducting nature of ethoxide-modified PVC is illustrated with temperature dependence of conductivity (σ). The relative ratios (r) of conductivity,σ _modifiedpvc /σ _{unmodifiedpvc} , are greater than unity in the temperature range 50° to 180°C,r being maximum in the vicinity of glass-transition temperature (T _g).T _g inferred from conductivity-temperature profiles is found to be greater for modified PVC relative to unmodified PVC, which is explicable in terms of restricted free rotation limiting segmental motion. For comparison with the conductivity andT _g of ethoxide-modified PVC, LiCl-modified PVC and (aniline + S₂O ₈ ²⁻ )-modified PVC have also been studied.     

Assembly and Study of Different Mercury Cells with Known Impurity Content and Isotopic Composition

The “Centro Español de Metrología” is carrying out a project to improve the knowledge of the influence of impurities and isotopic composition on the temperature of the mercury triple point. High-purity mercury from the Almaden mine (stated purity of 99.9998%) was further purified by vacuum distillation. Three mercury fractions, the original mercury from Almaden and two distilled fractions, were characterized in terms of both impurities and isotopic composition and used to measure the mercury triple point. The original mercury sample contained silver at 560 ng · g^?1 as the main impurity while the impurity levels were much lower (silver < 1 ng · g^?1) in the two distilled fractions. The isotopic composition of the distilled fractions showed delta values, expressed as $1,000\times(^{198/202}{\rm Hg}_{\rm sample}-^{198/202}\,{\rm Hg}_{\rm reference})/^{198/202}{\rm Hg}_{\rm reference}The “Centro Espa?ol de Metrología” is carrying out a project to improve the knowledge of the influence of impurities and isotopic composition on the temperature of the mercury triple point. High-purity mercury from the Almaden mine (stated purity of 99.9998%) was further purified by vacuum distillation. Three mercury fractions, the original mercury from Almaden and two distilled fractions, were characterized in terms of both impurities and isotopic composition and used to measure the mercury triple point. The original mercury sample contained silver at 560 ng · g⁻¹ as the main impurity while the impurity levels were much lower (silver < 1 ng · g⁻¹) in the two distilled fractions. The isotopic composition of the distilled fractions showed delta values, expressed as , of 1.37±0.07 (1σ) for the first distilled sample and −1.55±0.03 (1σ) for the second distilled sample with reference to the original Almaden mercury. For the measurement of the mercury triple point, an alcohol stirred bath was used that allowed two cells to be compared nearly simultaneously. It was observed that the presence of the silver impurities in the high-purity mercury modified slightly the mercury triple point while the effect of variations in the isotopic composition can be considered negligible.     

Measurement of Gibbs energies of formation of CoF2 and MnF2 using a new composite dispersed solid electrolyte

Gibbs energies of formation of CoF₂ and MnF₂ have been measured in the temperature range from 700 to 1100 K using Al₂O₃-dispersed CaF₂ solid electrolyte and Ni+NiF₂ as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF₂ thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al₂O₃ in the solid electrolyte and NiF₂ (or CoF₂) at the electrode, the dispersed solid electrolyte was coated with pure CaF₂, thus creating a composite structure. The free energies of formation of CoF₂ and MnF₂ are (± 1700) J mol⁻¹; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF₂ as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol⁻¹, which compares with a value of −671·5 (± 4) kJ mol⁻¹ given in Janaf tables. For solid MnF₂, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol⁻¹, which is significantly different from a value of −803·3 kJ mol⁻¹ given in the compilation by Barinet al.     

Influence of different deformation processing on the AZ31 magnesium alloy sheets

AZ31 magnesium alloy sheets were processed by normal rolling (NR), one-pass equal channel angular rolling (1P-ECAR), and cross equal channel angular rolling (C-ECAR) at 400 °C on a die with 105 ° channel angle. The microstructure, texture, and tensile properties of sheets were measured. The results show that ECAR processing can weaken the basal plane texture, thus obviously improve the mechanical properties. The yield ratio σ_s/σ_b decreases and strain hardening exponent n increases along rolling direction (RD) during ECAR, which means that the uniform plastic formability is enhanced. After C-ECAR, the mechanical properties along both the RD and transverse direction (TD) are improved. Different twinning types, fine contraction twinning in the NRed sheets and coarse extension twinning in the ECARed sheets, were observed. The easier activation of twinning and basal 〈a〉 slip leads to the lower yield strength of the ECARed sheets. Dynamic recrystallization (DRX) during the rolling process has great effect on the microstructure of the as-deformed and annealed sheets. The annealed C-ECARed sheets have significant finer and homogenous grains than the annealed NRed sheets, which is attributed to the rarely DRX process during ECAR. The average grain sizes of the annealed C-ECARed samples and NRed samples are 14 and 24 μm, respectively.     

Effects of oxygen partial pressure control on the microstructure and PTCR properties of Ho doped BaTiO<Subscript>3</Subscript>

Effects of oxygen partial pressure ( ) control on the electrical properties and microstructural development of (Ba_1-xHo_x)_0.997TiO₃ were studied. An oxidation condition ( ∼ 1.0 atm) was maintained during the heating process, and then the specimen was sintered in a reducing atmosphere ( < 10⁻⁹ atm) at 1350 °C, followed by the annealing process at 1000 °C and = 1 atm. The switching temperature (T_S) from the oxidation atmosphere to the reducing condition was changed from 1100 to 1350 °C. A significant decrease in the room-temperature resisitivity (ρ₂₅) was observed as T_S was increased. The temperature coefficient of resistance (TCR) was independent of the change in T_S, and closed pores decreased with increasing T_S.     

HRXRD Analysis for YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">x</Emphasis></Subscript> Deposited on {001} SrTiO<Subscript>3</Subscript>

YBa₂Cu₃O_7−x (YBCO) film was deposited on {001} SrTiO₃ (STO) substrate by pulse laser deposition (PLD). The microstructure of YBCO and STO was analyzed by High resolution X-ray diffraction (HRXRD). The results showed that the YBCO film alignment was C-axis coexisting with about 1 vol.% a-axis, and the spreading of YBCO’s out-plane alignment is anisotropic inherited from STO’s. In addition, there was 90° 〈110〉 twin domain with in-plane distort angle ±0.85° distort angle in the film, which was caused by T-O phase transition.