Virial coefficients of normal fluids

The force constants of the square-well potential for normal fluids were correlated in terms of the critical properties P_c, T_c, and the acentric factor ω, by means of a non-linear regression technique. The second virial coefficients, a total fo 100 points chosen uniformly with respect to P_r and ω from the compilation of Dymond, together with the compressibility factors, taken from the generalized tables of Pitzer. were employed in the correlation. The valid ranges of the correlation are 0.5 ?T_r ? 2·0 and 0 ? ρ_r ? 1·0. The calculated results for the second virial coefficients compare favourably with the generalized correlation of Pitzer and Curl. The calculated third virial and cross third virial coefficients, and the compressibility factors also agree well with the literature values.     

In-situ investigation of martensitic transformation toughening with electron backscatter diffraction and nano-indentation

Quantitative and direct evidence for tetragonal to monoclinic martensitic transformation toughening was revealed by electron backscatter diffraction (EBSD) and in-situ nanoindentation, using plasma-sprayed 3?mol% Y₂O₃–ZrO₂ coatings. On the basis of EBSD phase distribution, four zooms with different phase compositions and microstructure were selected. The tetragonal grains, which were surrounded by large pores, completely transformed into a monoclinic phase, but were then crushed when subjected to a loading of 10 mN. Moreover, the critical excitation stress σ_c for the martensitic transformation was estimated to be about 4.2?GPa. According to the displacement curves, the ratio of reduced modulus to hardness (E_r/H), which directly indicates the toughness of a material, was quantitively calculated. This experimentally demonstrated that both the elastic and plastic deformation capacity of the partially transformed grain were significantly improved, compared with the untransformed tetragonal grains. These findings will provide a fundamental insight into martensitic transformation toughening.     

Application of critical state to uniaxial compaction

From the radial stress σ_R and the normal stress σ_A, measured continuously during uniaxial loading and unloading on three compactable (sodium chloride, polyethylene and tartaric acid) and two non-compactable (polypropylene and polystyrene plastics) materials, characteristic compaction profiles of (σ_A ? σ_R) versus (σ_A + σ_R) can be observed. The uniaxial loading stress pathways for both compactable and non-compactable materials validated the assumption that the Coulomb yield criterion, which is usually applicable for the shear testing of soils, can be applied to the uniaxial compression of particulate materials. In addition, the unloading stress profiles for the compactable materials produced two characteristic parameters: a normal stress value at zero shear (σ_A + σ_R)_o and a minimum shear stress value (σ_A ? σ_R)_min. Correlation of (σ_A + σ_R)_o and (σ_A ? σ_R)_min values with either the tensile strength f_c or the Vickers hardness number H_V from the resultant compacts showed a linear logarithmic relationship. No such relationship was found, however, with non-compactable materials.     

Indices of tableting performance

Indentation hardness P and tensile strength σ_T measurements are used to formulate three dimensionless parameters, indices, that characterize the relative tableting performance of individual components and mixtures. The Strain Index P/E′ is obtained from the dynamic indentation hardness experiment. E′ is the reduced Young's Modulus. P/E′ may be interpreted as indicating the relative strain during the elastic recovery that follows plastic deformation or as the relative potential for strain energy to develop at the tip of a defect. The Bonding Index σ_T/p is interpreted as indicating the relative survival during decompression of the areas of true contact that formed at maximum compression. The Brittle Fracture Index is obtained by comparing the tensile strength of tablets with and without a hole at their center. The rationale for all three indices is given. This includes a discussion of processes at the ‘isthmus’ regions between contacting particles. It is concluded that plastic deformation in these regions during decompression is necessary to produce significant bond strength. The use of the indices as formulation guides is discussed.     

Uniaxial compaction behaviour and elasticity of cohesive powders

The compression and compaction behaviour of bentonite, limestone and microcrystalline cellulose (MCC) — three cohesive powders widely used in industry were studied. Uniaxial compression was performed in a cylindrical die, 40 mm in diameter and 70 mm high, for three selected cohesive powder samples. The initial density, instantaneous density and tablet density were determined. The influence of maximum pressure and deformation rate was examined. The secant modulus of elasticity E_sec was calculated as a function of deformation rate v, maximum pressure p and powder sample. After compaction experiments in hydraulic press at three pressures - p = 30, 45 and 60 MPa - and two different deformation rates, the strength of the produced tablets was examined in a material strength testing machine.From uniaxial compression tests performed on the universal testing machine for loading and unloading, the modulus of elasticity E was calculated on the basis of the first linear phase of unloading. The total elastic recovery of tablets was also obtained.     

Radiofrequency and microwave (10 kHz–8 GHz) electrical properties of polypyrrole and polypyrrole–poly(methyl methacrylate) composites

The complex permittivity ? = ?′ ?j ?″ of polypyrrole (PPY) samples and polypyrrole–poly(methyl methacrylate) (PPY‐PMMA) composites is calculated from measurements in the radiofrequency and microwave range (F = 10³–8 × 10⁹ Hz) at room temperature. A relaxation phenomenon is observed in PPY‐PMMA composites with polypyrrole concentration p = 6–12% by weight. The frequency F_max corresponding to the maximum of ?″ appears in the radiofrequency domain and increases with the PPY concentration from 10⁴ to 2 × 10⁶ Hz. This relaxation is caused by space charge moving into the conductive clusters of PPY. At low frequency F ? F_max, the real part of the permittivity ?′ becomes very high. For F ? F_max, PPY‐PMMA composites have a percolative behaviour, the percolation threshold p_c being 3.85%. For F ? F_max, in the microwave domain, an ac component of the conductivity σ_ac appears. σ_ac varies as a power function of the frequency, σ_ac ∝ ω ^x; with x < 1, x independent of p. © 2001 Society of Chemical Industry     

Ferroelectric properties and large electric field-induced strain of Eu3+-doped Na0.5Bi0.5TiO3–BaTiO3 lead-free ceramics

Eu³⁺-doped lead-free piezoelectric ceramics, 0.937Na_0.5Bi_0.5?xEu_xTiO₃-0.063BaTiO₃ (abbreviated as NBE_xT-BT, where x = 0, 0.003, 0.005, 0.01, 0.013, 0.015, 0.017, and 0.02), were synthesized using a conventional solid-state synthesis method. All the component samples were crystallized in a pure perovskite structure without a secondary phase. The introduction of Eu³⁺ caused the evident variation of the dielectric, ferroelectric and luminescence properties. The remanent polarization and coercive field of the pure NBT-BT are P_r ～29.24 μC/cm², E_c～39.33 kV/cm, respectively. The maximum of the remanent polarization P_r of ～38.02 μC/cm² at room temperature and the highest dielectric constant of 6899 with a frequency of 1 kHz were obtained for NBE_0.003T-BT. The maximum bipolar strain S_max of ～0.91% and the minimum of coercive field E_c ～18.45 kV/cm were achieved by the NBE_0.015T-BT, resulting from the formation of a double hysteresis loop. For all the components, Eu³⁺ doping stabilized the antiferroelectric phenomenon at high temperature. Furthermore, the polarized NBE_0.015T-BT had the strongest fluorescence luminescence intensity as well as a fluorescence lifetime reaching 785.98 μs.     

Effect of hydrostatic pressure on the deformation behavior of polyethylene and polycarbonate in tension and in compression

The stress-strain response of crystalline high density polyethylene and of amorphous polycarbonate has been determined in tension and in compression at superimposed pressures up to 1104 MPa(160 ksi). Strain softening occurred in the polycarbonate at low pressures but was inhibited by pressure. Tensile necking occurred in both materials, but was promoted by pressure in polyethylene and inhibited in polycarbonate. The initial modulus, E, and the flow stress, σ, at a given offset strain varied linearly with the mean pressure, P, with essentially the same pressure coefficient, α. Thus, E = (1+αP)E₀ and σ = (1+αP)σ₀, where E₀ and σ₀ are values at zero mean pressure. In polyethylene, the coefficient, σ₀, was the same in tension and compression, indicating that the strength differential between tension and compression was a simple manifestation of pressure-dependent yielding. In polycarbonate the coefficient, σ₀, was different in tension and in compression, implying an effect due to the third stress invariant or to anisotropy. The results suggest a constitutive model for polymers in which the flow stress is linearly dependent on mean pressure, but in which inelastic volume change is negligible. The results also suggest that the pressure dependence of flow stress in polymers is the same as that of the initial modulus.     

Influence of calcium substitution on structural and electrical properties of substituted barium titanate

Ba_0.80−xCa_xPb_0.20Ti_0.90Zr_0.10O₃ ceramics (x = 0, 0.10 and 0.20) were synthesized by solid state reaction. Samples microstructure and dielectric, ferroelectric and piezoelectric properties were studied. Dielectric constant (?), coercive field (E_c), remanent polarization (P_r) and ratio of remanent to spontaneous polarization (P_r/P_s) were studied at different temperatures. Sample with x = 0.10 was found to have maximum and comparatively more stable P_r/P_s ratio over a wide temperature range. Dielectric loss was found to improve with increase in x whereas piezoelectric charge coefficient d₃₃ was found to decrease with increase in x.     

Relationship between the maximum and the random reflectance of vitrinite for coal from the Upper Silesian Coal Basin (Poland)

The relationship between the maximum and random reflectance of vitrinite, R_max and R_r, for Upper Silesian coal is represented by the equation: R_max=1.090R_r−0.052. When the random reflectance is higher than 0.90%, the difference between R_max and R_r values becomes significant. R_max is a more precise rank indicator, the standard deviation is much smaller than the standard deviation of the random reflectance value, which is larger due to the optical anisotropy of vitrinite.     

An application of scattered-light photoelasticity in the determination of the side pressure distribution of the pressed powder bed

Improved photoelastic measurements were applied for the determination of the side pressure distribution of the pressed powder bed on the basis of the principle given in the previous paper. Absolute values of stress components σ_r, σ_θ, σ_z and τ_rz in the container wall were determined from the measurements of three different directions of incidence of the laser beam. By extrapolating the values of σ_r and τ_rz to the inner surface of the container, side pressure components of the powder bed, normal and tangential to the wall respectively, were obtained. Indirect confirmations for the validity of the results were given.     

Phosphorus Fractionation and Sorption in P-enriched Soils of Norway

Phosphorus (P) enrichment can lead to imbalance in nutrient availability and pollution of terrestrial and aquatic ecosystems. Hence studies were carried out to investigate fractionation and sorption of P in eleven P-enriched soils collected from different agro-climatic sites in Norway. Different P fractions viz. total, organic, inorganic (easily soluble P, Fe-P, Al-P, Ca-P and occluded P), P_w (water extractable), and NH₄-lactate extractable P (P_AL) at the beginning and after the completion of the experiments varied widely among the soils studied, indicating a wide variability of P supplying capacity of these soils. Soluble P was positively correlated to Ca-P (r = 0.94; P < 0.001), P_w (r = 0.87; P < 0.001), pH (r = 0.79; P < 0.01) and P_AL (r = 0.79; P < 0.01), whereas it was negatively correlated with ammonium oxalate-extractable Al (Al_ox) (r = ?0.68; P < 0.05). Iron-P was only moderately related to Al_ox(r = 0.64; P < 0.05) and P_ox(r = 0.70; P < 0.05), whereas it was not related to any of the other parameters tested. The α [α = P_ox/(Fe_ox + Al_ox)] was highly correlated with P_AL (r = 0.93; P < 0.001), pH (r = 0.87; P < 0.001), inorganic P (r = 0.80; P < 0.01) and P_w(r = 0.77; P < 0.01) but moderately to total P (r = 0.71; P < 0.05). Adsorption data fitted well to the Langmuir equation for most soils. The P affinity constant (k), adsorption maximum (b) and thus maximum buffering capacity (mbc) and adsorption isotherm of P were highest in the sandy clay soil from Øsaker, which also contained high amounts of Fe, Al and clay particles and the lowest in sandy soil from Vestrålen, which contained very high initial P_ALand the lowest content of Fe, Al, silt and clay among all the soils studied. The P affinity constant (k) was correlated positively and significantly to clay content (r = 0.66; P < 0.05), whereas mbc was correlated positively and significantly to clay content (r = 0.63; P < 0.05) and ammonium oxalate-extractable Fe (Fe_ox) (r = 0.63; P < 0.05). Phosphorus desorption of the soils varied widely depending on the initial P status and texture of the soils. Phosphorus desorbed by NH₄-lactate was many fold higher as compared to CaCl₂ in most soils.     

Enhanced piezoelectricity and energy storage performances of Fe-doped BNT–BKT–ST thin films

Fe-doping is an effective way to improve physical performances of piezoelectric and ferroelectric materials. Under such circumstances, x mol% (x?=?0.0, 1.0, 1.5, 2.5) Fe-doped 0.72Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃–0.10SrTiO₃ (BNT–BKT–ST–xFe) thin films were prepared by sol-gel method and the relationships between the content of Fe and electromechanical properties of the films were studied. The BNT–BKT–ST–1.0Fe thin films exhibit the best electromechanical properties, whose S_max/E_max, W_rec, η, P_max, P_rem and ε_r of are 68.00?pm/V, 20.34?J/cm³, 65.17%, 71.5?μC/cm², 14.8?μC/cm², 868 respectively. These results indicate that BNT–BKT–ST–1.0Fe thin films are promising for applications for advanced piezoelectric materials and capacitors with high energy-storage density.     

Correspondence Between CIELAB and CIELUV Color Differences

The CIE presently recommends two uniform color spaces, the CIE 1976 (L*u*v*)-space (CIELUV) and the CIE 1976 (L*a*b*)-space (CIELAB). With each of these spaces is associated a color-difference formula. Color differences calculated by one formula cannot readily be converted to color differences calculated by the other formula. A conversion factor such as ρ = ΔE_uv*/ΔE_ab* cannot be determined uniquely. However, for any given location in color space, it is possible to determine a range, ρ_min ? ρ ? ρ_max, within which ρ must lie. Lines of constant ρ_min and ρ_max can be plotted in (L*a*b*)-space which indicate the range of ρ in (L*u*v*)-space.     

MOCVD-derived GdYBCO tapes with smooth surface and low Rs based on a new self-heating technology

The metal organic chemical vapor deposition (MOCVD) method was used to prepare GdYBCO films on LaMnO₃/ homo epitaxial-MgO/ ion-beam-assisted-deposition-MgO/ solution-deposition-planarization-Y₂O₃ buffered Hastelloy tapes. By adopting a simple self-heating technique, the substrates were heated by the joule effect after applying a heating current (I_h) through Hastelloy metal tapes. The effects of substrate temperature and (Gd, Y)/Ba ratio (r_c) in the precursor on the biaxial texture, surface morphology and superconducting performance of GdYBCO films were systematically investigated by varying the values of I_h and r_c. Needle-like outgrowths formed on the substrate surface were characterized using a scanning electron microscope, energy dispersive spectrometer and X-ray diffraction system. The results show that a high I_h or r_c leads to the formation of needle-like outgrowths. Therefore, I_h and r_c are crucial process parameters that control the growth of needle-like outgrowths on the surface of GdYBCO films. Three hundred nanometer thick GdYBCO films were prepared at different I_h and r_c by the MOCVD process. At an I_h of 27.0?A and an r_c of 0.6, the surface of the GdYBCO film was very smooth and dense, which can provide a good template for multiple depositions of GdYBCO films. The critical current density of the deposited 300?nm-thick GdYBCO film was 4.4 MA/cm² (77?K, 0?T), which is attributed to good biaxial texture and appropriate film composition. Furthermore, the microwave surface resistance (77?K, 10?GHz) of the GdYBCO film was merely 0.581?mΩ.     

Reduced leakage current,enhanced energy storage and dielectric properties in (Ce,Mn)-codoped Ba0.6Sr0.4TiO3 thin film

Ba_0.6Sr_0.4TiO₃, Ce-doped Ba_0.6Sr_0.4TiO₃, Mn-doped Ba_0.6Sr_0.4TiO₃, (Ce,Mn) co-doped Ba_0.6Sr_0.4TiO₃ (abbreviated as BST, BSTCe, BSTMn, BSTCeMn) thin films were deposited on LaNiO₃(LNO)/Si substrates. The effects of ion doping on the microstructure and electrical properties of BST-based thin film have been researched and discussed. The X-ray diffraction pattern shows that each sample has pure perovskite phase structure with high (l00) peaks. The microstructure of each film is quite dense with uniform size. Compared with pure BST, improved insulating properties can be found in ion-doped BST thin films. For all the films, Ohmic conduction, space charge limited conduction and interface-limited Fowler-Nordheim tunneling should be the main conduction mechanisms within different electric field regions. For the case of BSTCeMn thin film, it possesses enhanced energy storage performance with a recoverable energy storage density (18.01?J/cm³) and a energy storage efficiency (75.1%) under 2000?kV/cm. This can be closely related to the small remanent polarization value (P_r=?1.89 μC/cm²), large maximum polarization value (P_max=?28.08?μC/cm²) as well as big maximum electric field (2000?kV/cm). Also, it exhibits a large dielectric constant of 405 and a small dissipation factor of 0.075 at 500?kHz.     

Structural,electrical and magnetic properties of (110)-oriented BF-BZT-ST Films

Highly (110)-oriented BiFeO₃-Bi(Zn/Ti)O₃-SrTiO₃ thin films were prepared on conductive Nb doped SrTiO₃ substrates by pulsed laser deposition. The results demonstrate that the films show a pure perovskite phase with R3c symmetry. The films have a low dielectric loss, and a typical multiferroics character, possessing both of ferroelectric and ferromagnetic properties. The reduced dielectric loss is attributed to thermodynamic stabilization and charge compensation mechanisms in the BiFeO₃ system. The remnant polarization (P_r) and the remnant magnetization (M_r) are ~ 46.2?μC/cm² and ~ 4.6?emu/cm³ respectively.     

Excellent energy storage performance of paraelectric Ba0.4Sr0.6TiO3 based ceramics through induction of polar nano-regions

Dielectric energy storage materials with congenitally high power densities and ultrafast discharge rates have been extensively studied for emergent applications. As a typical and traditional dielectric material, paraelectric Ba_0.4Sr_0.6TiO₃ (BST) ceramic exhibits a moderate dielectric constant (ε_r), low dielectric loss and slightly nonlinear P–E hysteresis. However, its energy storage density (W) is extremely low because of its low maximum polarisation (P_max) and weak breakdown strength (BDS). In this study, ferroelectric Na_0.5Bi_0.5TiO₃ (NBT) was introduced into paraelectric BST to enhance energy storage performance. The results show that the introduction of NBT induced polar nano-regions (PNRs) in the paraelectric matrix, resulting in a slim hysteresis loop with low remnant polarisation (P_r) and high P_max simultaneously. Furthermore, owing to a decrease in the oxygen vacancy concentration and an increase in the band gap energy, the BDS of the BST ceramic also significantly increased. As a consequence, a remarkable energy storage density (W_rec = 3.89 J/cm³) and a high energy storage efficiency (η = 83.8%) were realised in the 0.75Ba_0.4Sr_0.6TiO₃-0.25Bi_0.5Na_0.5TiO₃ (0.75BST–0.25NBT) ceramic under a practical electric field of 360 kV/cm. Moreover, the ceramic also exhibited an excellent current density (～1029.7 A/cm²) and ultrahigh power density (～128.7 MW/cm²). The attained energy storage performances indicate that the NBT-modified BST ceramics are promising materials for high energy storage capacitor applications field.     

Fabrication and ferroelectric/dielectric properties of La-doped PMN-PT ceramics with high optical transmittance

Relaxor ferroelectric 0.75(Pb_1–3x/2La_x)(Mg_1/3Nb_2/3)O₃-0.25(Pb_1–3x/2La_x)TiO₃ (La³⁺:PMN-PT x/75/25, where x=2.8, 3.0, 3.5, and 4.0 mol% of La³⁺) transparent ceramics were fabricated by the combination of oxygen atmosphere pressureless sintering and hot-pressing sintering process. The optical transmittances of above four ceramics are higher than 60% at the wavelength of 500–900 nm. La³⁺:PMN-PT 3.0/75/25 exhibits the highest transparency around 70% at 900 nm which is very close to the theoretical transmittance 71%. Each of the four ceramics exhibits the pure perovskite phases. They show fully dense microstructures and their relative densities are higher than 99.8%. The ferroelectric and dielectric measurements indicate that these four ceramics exhibit relaxation characteristics. With increasing La³⁺ content, (200) peak in XRD patterns shifts to higher angles and the average grain size increases, while the temperature Tε_max corresponding to the maximum ε_r, the remanent polarizations P_r and coercive fields E_c decrease gradually.