Fracture Mechanics of aV-peel Adhesion Test - Transition from a Bending Plate to a Stretching Membrane

A linear elastic solution is proposed for a “V-peel” adhesion test for a thin film adhered to a rigid substrate. The mechanical responses of a stiff plate-like coating under pure bending, a semi-flexible film under mixed bending and stretching, and a flexible membrane-like film under pure stretching are discussed. For delamination to occur, the mechanical energy release rate is shown to be G = χ(Fw₀/2bl) with χ a numerical constant varying from 3/2 for a plate-like disc to 3/4 for a thin flexible membrane.     

Free convection mass transfer at horizontal electrodes

The free convection mass-transfer behaviour of upward-facing horizontal surfaces has been investigated experimentally using an electrochemical technique involving the measurement of limiting currents for the deposition of copper on copper electrodes from acidified cupric sulphate solutions. The data are well correlated by the equations

Sh = 0·64(Sc . Gr)^0·25 for 3 × 10⁴ < ScGr < 2·5 × 10⁷ and

Sh = 0·16(Sc . Gr)^0·33 for 2·5 × 10⁷ < ScGr < 10¹². Electrode diameters varied between 0·1 and 12 cm and cupric sulphate concentrations between 0·01 and 0·3 M.

The data compare favourably with previous experimental results for the corresponding heat-transfer case.     

Sintering behavior and microwave dielectric properties of Bi2O3–ZnO–Nb2O5-based ceramics sintered under air and N2 atmosphere

The sintering behavior and dielectric properties of the monoclinic zirconolite-like structure compound Bi₂(Zn_1/3Nb_2/3)₂O₇ (BZN) and Bi₂(Zn_1/3Nb_2/3−xV_x)₂O₇ (BZNV, x = 0.001) sintered under air and N₂ atmosphere were investigated. The pure phase were obtained between 810 and 990 °C both for BZN and BZNV ceramics. The substitution of V₂O₅ and N₂ atmosphere accelerated the densification of ceramics slightly. The influences on microwave dielectric properties from different atmosphere were discussed in this work. The best microwave properties of BZN ceramics were obtained at 900 °C under N₂ atmosphere with _r = 76.1, Q = 850 and Q_f = 3260 GHz while the best properties of BZNV ceramics were got at 930 °C under air atmosphere with _r = 76.7, Q = 890 and Q_f = 3580 GHz. The temperature coefficient of resonant frequency τ_f was not obviously influenced by the different atmospheres. For BZN ceramics the τ_f was −79.8 ppm/°C while τ_f is −87.5 ppm/°C for BZNV ceramics.     

Mass transfer by free convection at horizontal electrodes

Limiting currents were measured in an unstirred cell at horizontal cathodes facing upward. Electrolyte composition ranged from 0·01 to 0·7 M CuSO₄ in 1·5 M H₂SO₄. Cathode sizes varied from 0.1–30 by 10 cm, and the free height above the electrode from 1–16 cm. Limiting currents for deposition of copper ranged from 0·68–129 mA/cm². For electrode width larger than 20 mm the data is well represented by the general correlation

Nu′ = 0.19 (Sc. Gr) , where Nu′, Sc, and Gr are the Nusselt number for mass transfer, the Schmidt, and Grashof numbers, respectively. The experimental range used in the correlation included 10⁸ < (Sc. Gr) < 1·4 × 10¹² The results indicate that the boundary layer is turbulent, as it is in the case of the analogous heat-transfer model.     

Aerosol measurement by laser doppler spectroscopy—II. Operational limits, effects of polydispersity, and applications

The theoretical basis and the results of a computer simulation are presented which describe the operational limits of size and concentration for aerosol sizing by laser Doppler spectroscopy LDS,. This analysis suggests that a state of the art LDS system has the capability of sizing 0·03 μm diameter particles when the number concentration is 10⁸ cm⁻³ or greater and 0·2 μm diameter for coocentrations as low as 100 particles cm⁻³. An evaluation of the effect on the laser Doppler spectroscopy measurements of a polydisperse aerosol having a log normal size distribution is presented and methods for combining these measurements with other averaged measurements to determine both count median diameter (CMD) and geometric standard deviation (δ_g) are proposed. For aerosols having log normal distributions with 0·3 < CMD < 3 μm and 1·0 < δ_g < 2·0, laser Doppler spectroscopy is able to measure the surface area median diameter within ± 15 per cent, independent of polydispersity. Applications of LDS to aerosol sizing are evaluated and its advantages and disadvantages relative to other sizing methods are discussed.     

Estimation of particle size distribution parameters in animal lungs

A constant of specific solubility of 2·5 × 10⁻⁸ g cm⁻²day⁻¹ was determined for fused aluminosilicate particles, by observing in vivo retention kinetics after intravenous injection into rats. Studies over the past years in this laboratory, in which dogs and rats have inhaled labeled aerosols of these particles, have shown retention half-lives in the lung of 460 and 285 days, respectively. By applying these values for solubility and half-life to Mercer's theory of dissolution from the deep lung, the initial distribution of particles deposited in the pulmonary regions of dogs and rats following inhalation was calculated. From an inhaled aerosol with a mass median diameter, D_m, of 1·0 μm and σ_o = 1·7, a distribution described by D_m = 0·51 μm and σ_o's ranging from 1·16–1·48 was estimated to have been deposited in the Beagle dog lung. and a D_m =< 0·32 μm and σ_o's ranging from 1·18–1·29 was similarly calculated for rats.     

Investigation of some niobate-based dielectrics in view of base metal co-sintering

Bearing in mind the excellent dielectric properties at high frequency of some niobates like ZnNb₂O₆, Zn₃Nb₂O₈, BaNb₂O₆, Ba₅Nb₄O₁₅ (_r 20–45, tan δ < 10 × 10⁻⁴ and ρ_i > 10¹⁰ Ω cm), synthesis, sintering and properties of these oxides are reported. The lowering of their sintering temperature has been investigated for these four ceramics using sintering aids. Using appropriate additive, it is possible to densify these ceramics at a temperature for which base metal electrodes, e.g. Cu and Ag can be employed. Two formulations were found to be sinterable at 1000 °C (lower than the copper melting point) whereas a third formulation is co-sinterable with silver electrodes. For this later, the dielectric properties are globally maintained in comparison with the pure compound sintered at 1200 °C. This result makes this formulation suitable for silver based passive components devices manufacturing.     

NMF effect on photosensitized charge separation using partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes

The solvent effects on the photosensitized charge separation using partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes (RuQPIm), in which bis(2,2′-bipyridine)ruthenium(II) complexes are coordinated to the imidazolyl residues on the poly(1-vinylimidazole) partially quaternized by 1-bromohexadecane and the degree of quaternization is 19 (RuQPIm-19) and 44 (RuQPIm-44) molar percentage, have been investigated in methanol and methanol–NMF (NMF: N-methylformamide). These systems consist of RuQPIm-19 and RuQPIm-44 as photosensitizers, 1,1′-dimethyl-4,4′-bipyridinium dication (MV²⁺) and 1,1′-didodecyl-4,4′-bipyridinium dication (C₁₂V²⁺) as electron acceptors, and triethanolamine (TEOA) as a sacrificial donor. The addition of NMF mainly affect the forward and back reactions in the charge separation reactions. In RuQPIm-19 systems, the reaction proceeds through an interactive process, which is through the viologen having π–π interaction for MV²⁺ and van der Waals interaction for C₁₂V²⁺. In contrast, the reaction proceeds through a direct process by MV²⁺ having no interaction and through an interactive process by C₁₂V²⁺ undergoing van der Waals interaction with the polymer for RuQPIm-44 systems. For MV²⁺, the rates of MV^·+ formation increased, although the quenching efficiency decreased with increasing NMF content for RuQPIm-19 and RuQPIm-44. These results are attributed to stabilization of MV^·+ species by π–π interaction for RuQPIm-19 and steric repulsion between MV^·+ species and RuQPIm-44; namely, the restriction of the back reactions by these effects. In contrast, for C₁₂V²⁺, the rates of C₁₂V^·+ formation decreased and the quenching efficiency increased with the addition of NMF. These are attributed to that the addition of NMF increases the van der Waals interaction of the C₁₂V²⁺ with these polymers and the diffusion of the C₁₂V^·+ species into the bulk solution; namely, the back reaction is accelerated. Furthermore, it is suggested that the conformational changes in these polymers contribute to the charge separation reaction.     

Dilute solution properties of carboxymethylchitins in high ionic-strength solvent

The hydrodynamic characteristics in aqueous solution at ionic strength I=0.2  of carboxymethylchitins of different degrees of chemical substitution have been determined. Experimental values varied over the following ranges: the translational diffusion coefficient (at 25.0°C), 1.1<10⁷×D<2.9 cm² s⁻¹; the sedimentation coefficient, 2.4<s<5.0 S; the Gralen coefficient (sedimentation concentration-dependence parameter), 130<k_s<680 mL g⁻¹; the intrinsic viscosity, 130<[η]<550 mL g⁻¹. Combination of s with D using the Svedberg equation yielded ‘sedimentation–diffusion' molecular weights in the range 40 000<M<240 000 g mol⁻¹. The corresponding Mark–Houwink–Kuhn–Sakurada (MHKS) relationships between the molecular weight and s, D and [η] were: [η]=5.58×10⁻³ M^0.94; D=1.87×10⁻⁴ M^−0.60; s=4.10×10⁻¹⁵ M^0.39. The equilibrium rigidity and hydrodynamic diameter of the carboxymethylchitin polymer chain is also investigated on the basis of wormlike coil theory without excluded volume effects. The significance of the Gralen k_s values for these substances is discussed.     

Kinetics of the selective catalytic reduction of NO by NH3 on a Cu-faujasite catalyst

The kinetics of the selective catalytic reduction (SCR) of NO by NH₃ in the presence of O₂ has been studied on a 5.5% Cu-faujasite (Cu-FAU) catalyst. Cu-FAU was composed of cationic and oxocationic Cu species. The SCR was studied in a gas phase-flowing reactor operating at atmospheric pressure. The reaction conditions explored were: 458<T_R<513 K, 2503 (ppm) < 4000, 12 (%) < 4. The kinetic orders were 0.8–1 with respect to NO, 0.5–1 with respect to O₂, and essentially 0 with respect to NH₃. Based on these kinetic partial orders of reactions and elementary chemistry, a wide variety of mechanisms were explored, and different rate laws were derived. The best fit between the measured and calculated rates for the SCR of NO by NH₃ was obtained with a rate law derived from a redox Mars and van Krevelen mechanism. The catalytic cycle is described by a sequence of three reactions: (i) Cu^I is oxidized by O₂ to “Cu^II-oxo”, (ii) “Cu^II-oxo” reacts with NO to yield “Cu^II-N_xO_y”, and (iii) finally “Cu^II-N_xO_y” is reduced by NH₃ to give N₂, H₂O, and the regeneration of Cu^I (closing of the catalytic cycle). The rate constants of the three steps have been determined at 458, 483, and 513 K. It is shown that Cu^I or “Cu^II-oxo” species constitute the rate-determining active center.     

Micromechanics of domain switching in rhombohedral PZT ceramics

The lattice strain {2 0 0} and diffraction peak intensity ratio R{1 1 1} have been determined in soft rhombohedral PZT ceramics during the application of an electric field up to 2.5 MV m⁻¹ and as a function of the grain orientation ψ, using high energy synchtron X-ray diffraction. The magnitude of both {2 0 0} and R{1 1 1} increased sharply beyond a field level of 1 MV m⁻¹ due to the onset of ferroelectric domain switching. {2 0 0} exhibited a near linear dependence on cos² ψ, in agreement with previous studies of the remanent-poled state. In contrast, the R{1 1 1}–cos² ψ plot showed evidence of saturation in ferroelectric domain switching, particularly for ψ > 60°. The development of lattice strain during poling is discussed in terms of contributions from the intrinsic piezoelectric effect and from residual stress caused by differences in the poling strain of a grain, and the piezoelectric strain of a grain relative to its surroundings.     

The homogeneity range and the microwave dielectric properties of the BaZn2Ti4O11 ceramics

Ceramics with a composition close to BaZn₂Ti₄O₁₁ were synthesized according to various substitutional mechanisms in order to verify an existence of a homogeneity range in the vicinity of this composition. Structural and microstructural investigations showed that the crystal structure of BaZn₂Ti₄O₁₁ was formed in the homogeneity range corresponding to the formula BaZn_2 − xTi₄O_11 − x (0 < x < 0.1). Densely sintered BaZn_2 − xTi₄O_11 − x (0 < x < 0.1) ceramics exhibited a dielectric constant around 30, τ_f = −30 ppm/K and high Q × f values, which increased from 68,000 GHz at x = 0 to 83,000 GHz at x = 0.05. Structurally, the deficiency of Zn in BaZn_2 − xTi₄O_11 − x (0 < x < 0.1) resulted in a slight decrease in the unit-cell volume. The influence of secondary phases in the BaZn₂Ti₄O₁₁-based materials on the microwave dielectric properties was also investigated. A presence of small amounts of ZnO, BaTiO₃, hollandite-type solid solutions (Ba_xZn_xTi_8 − xO₁₆) and BaTi₄O₉ caused a decrease in Q × f values.     

Raman spectroscopic studies on the sulfation of cerium oxide

In the present study, we have examined sulfation of cerium oxide via impregnation of (NH₄)₂SO₄, followed by heating in the temperature range of 220–720°C, using Raman Spectroscopy. Based on the SO and SO stretching frequencies in the range of 900–1400 cm⁻¹, a wide range of surface oxysulfur species and bulk cerium-oxy-sulfur species are identified. At 220°C, a mixture of (NH₄)₂SO₄ crystals, SO²⁻_4(aq) and HSO¹⁻_r(aq) is found to have formed on ceria's surface, whereas complete conversion of (NH₄)₂SO₄ to SO²⁻_4(aq) and HSO¹⁻_4(aq) occurs at 280°C. At 350°C, formation of a mixture of surface pyrosulfate S₂O²⁻_7(surf.0, consisting of two SO oscillators and a bulk type compound identified as Ce(IV)(SO₄)_x(SO₃)_2−x (0 < x < 2) have been observed. Upon introduction of moisture, the former transforms to HSO¹⁻_4(surf.), whereas the latter remains unchanged. At 400°C, only the bulk type compound can be observed. At 450°C, only Ce₂(SO₄)₃ is generated and remains stable until 650°C. Further increase in the temperature to 720°C results in the formation of CeOSO₄. The present study not only provides a more thorough understanding of the sulfation of cerium oxide at a molecular level, but also demonstrates that Raman spectroscopy is a highly effective technique to characterize sulfation of metal oxides.     

Synthesis of platelike CaTiO3 particles by a topochemical microcrystal conversion method and fabrication of textured microwave dielectric ceramics

Platelike CaTiO₃ particles with an orthorhombic perovskite structure have been synthesized by topochemical microcrystal conversion (TMC) from platelike precursor particles of the layer-structured CaBi₄Ti₄O₁₅ at 950 °C. The CaTiO₃ particles inherited and retained the shape of the precursor particles with a thickness of approximately 0.3 μm, and a width of 2–6 μm. XRD analysis showed that in the TMC reaction, the crystallographic {0 0 1} plane of CaBi₄Ti₄O₁₅ is converted into the {1 0 0} plane of CaTiO₃. Using the platelike CaTiO₃ particles as templates in the templated grain growth method, dense {1 0 0} grain-oriented CaTiO₃ ceramics having a {1 0 0} orientation could be fabricated at sintering temperatures between 1350 and 1500 °C. The maximum orientation factor reached 99.7% at 10% of template. It was found that texturing improves microwave dielectric low-loss properties, providing a 1.55 times higher Q_f value of 9310 GHz in textured ceramics compared to that of 6005 GHz in non-textured ceramics.     

Crystal lattice defects in di-calcium silicate

It is well documented that the impurity content of C₂S has a marked effect on its hydration properties. It is also a fact that pure C₂S at room temperature exists in a crystal configuration, γ, which is completely different from the clinker C₂S. Incorporation of impurity ions into pure C₂S inhibits the β → γ transition on cooling, even at impurity levels as low as 0.1%. Currently, there is no fully accepted model for the mechanism of the stabilization of the β phase over the γ phase by impurities. The presence of these trace impurities naturally raises the question of the location and role of the impurities in producing this marked stabilizing effect. A quantitative solution to this problem requires that the lattice defect disorder of C₂S be defined and related to the phase stabilization properties of the impurities. Definition of crystal defect disorder can be achieved through detailed measurements of the electrical conductance of the solid with the data being interpreted in terms of solid state physics. Data for the electrical conductance of pure and “intentionally” impure (doped) C₂S over the temperature range 300 to 1100°C is presented. These data are interpreted in terms of crystal defects, their formation, location and kinetics. Models are presented to account for the stabilizing action of impurity ions within the crystal lattice of C₂S.     

Conductivity of Na5+xYAlxSi4-xO12 ceramics

A series of ceramics samples, Na_5+xYAl_xSi_4-xO₁₂, has been prepared by a solid state reaction with the starting materials of SiO₂, Y₂O₃, Al₂O₃ and Na₂CO₃. Their crystalline structure and morphology have been studied by the determination of XRD, IR, TG, DTA and SEM. Their conductivity has been measured by means of the complex impedance method. The dependence of the conductivity and density of the samples on the amount of the added Al₂O₃ and the reaction between the conductivity and the temperature have been discussed. When x = 0, the density of the sintering sample is 90% T.D., and the conductivity is 1·48 x 10⁻¹ (ωcm)⁻¹ at 300°C; when x = 0·1, the density is up to 97% T.D., and the conductivity up to 1·74 x 10⁻¹ (ω cm)⁻¹ at 300°C.     

Ceria-based oxides as supports for LaCoO3 perovskite; catalysts for total oxidation of VOC

Supported LaCoO₃ perovskites with 10 and 20 wt.% loading were obtained by wet impregnation of different Ce_1−xZr_xO₂ (x = 0–0.3) supports with a solution prepared from La and Co nitrates, and citric acid. Supports were also prepared using the “citrate method”. All materials were calcined at 700 °C for 6 h and investigated by N₂ adsorption at −196 °C, XRD and XPS. XRD patterns and XPS measurements evidenced the formation of a pure perovskite phase, preferentially accumulated at the outer surface. These materials were comparatively tested in benzene and toluene total oxidation in the temperature range 100–500 °C. All catalysts showed a lower T₅₀ than the corresponding Ce_1−xZr_xO₂ supports. Twenty weight percent LaCoO₃ catalysts presented lower T₅₀ than bulk LaCoO₃. In terms of reaction rates per mass unit of perovskite calculated at 300 °C, two facts should be noted (i) the activity order is more than 10 times higher for toluene and (ii) the reverse variation with the loading as a function of the reactant, a better activity being observed for low loadings in the case of benzene. For the same loading, the support composition influences drastically the oxidative abilities of LaCoO₃ by the surface area and the oxygen mobility.     

Die abhängigkeit der Ah-Kapazität von Leclanché-trockenbatterien von der Zellenbelastung und Zellengeometrie

An attempt is made to show that a definite relation exists between the ampere-hours capacity of Leclanché cells, their discharge current strength and their cell geometry which is satisfactorily represented by the formula

Ah = Ah_max{1 - exp [-K₀(4πhRa)^1/2]}

Résumé

On essaye de démontrer qu'une relation simple existe entre la capacité en Ah d'éléments Lechlanché et du courant de décharge ainsi que de la géométrie de la cellule, qui est représentée d'une manière satisfaisante par la formule

Ah = Ah_max{1 - exp [-K₀(4πhRa)^1/2]}     

Effect of different templates on microstructure of textured Na0.5Bi0.5TiO3–BaTiO3 ceramics with RTGG method

One-dimensional needle-like KSr₂Nb₅O₁₅ (KSN) and two-dimensional plate-like Bi_2.5Na_3.5Nb₅O₁₈ (BNN) particles were used as templates to fabricate grain-oriented Na_0.5Bi_0.5TiO₃–BaTiO₃ (NBTBT) ceramics by reactive-templated grain growth. The effects of the template concentration on the microstructure and orientation of NBTBT ceramics were investigated, and the mechanism of grain growth was discussed. The results show that NBTBT textured ceramics cannot be obtained with KSN template, since the needle-like KSN particles were aligned randomly along the tape casting direction. Ceramics contain perovskite NBTBT and tungsten–bronze-type KSN phase. Some cucurbit-like KSN grains resulted from the defects of needle-like KSN templates were detected. Textured ceramics with orientation factor more than 60% were obtained successfully when the plate-like BNN was used as templates. The results show that the texture fraction of NBTBT textured ceramics increase with increasing the content of BNN. The textured ceramics exhibited {h 0 0} preferred orientation have brick wall microstructure with strip-like grains aligning in the same plane as the casting plane. The reaction and crystal formation of textured NBTBT ceramics with plate-like BNN templates are by diffusion–recrystallization process. Finally the selecting rules of suitable templates are proposed.     

TRANSITION TO ANNULAR FLOW IN TWO-PHASE, TWO-COMPONENT VERTICAL FLOW: EXAMINATION OF CORRELATIONS

The available empirical, semi-empirical and analytical correlations and flow pattern maps for predicting the transition to annular flow in upward, two-phase, gas-liquid flow in a vertical tube were tested against a large set of experimental data. These experimental data were taken on the same rig through an observation section (i.d. = 11.7 mm, L = 30.5 cm), preceded by a heated test section ( L/D≃ 52) and a calming length (L/D = 130), all having the same inside diameter as that of the observation section. The total range of variables covered by these data is: 2≤Re_SL≤ 1.3 × 10⁵, 5.6 ≤Pr_L≤ 7000, 0.01 V_SG/V_SL ≤ 7900, 2 × 10^-4≤ρ_G/ρ_Ls0.01, and 19.7 × 10^-3≤ σ ≤72× 10^-3N/m. In total, fifteen correlations and flow-pattern maps were tested with eight liquid-gas combinations covering a very wide range of fluid properties and mass flow rates of both phases. Using the Kutateladze number as the criterion for the transition appears to provide an excellent separation particularly when a lower value than 3.1, as suggested in the model of Taitel et al. (1980) is used (between 1.5 and 2.0). Also using the Weisman and Kang (1981) correlation, the Wallis parameter and the void fraction criteria of Mishima and Ishii (1984) were quite successful in correlating the data.