Breakage behaviour of spherical granulates by compression

This paper describes the deformation and breakage behaviour of granulates in single particle compression test. Three industrial spherical granulates—γ-Al₂O₃, the synthetic zeolite Köstrolith^® and sodium benzoate (C₆H₅COONa) were used as model materials to study the mechanical behaviour from elastic to plastic range. The elastic compression behaviour of granulates is described by means of force-displacement curves, by application of Hertz-Huber contact theory and continuum mechanics. An elastic-plastic contact model was proposed to describe the deformation behaviour of elastic-plastic granules. The effects of granulate size and stressing velocity on the breakage force and contact stiffness during elastic and elastic-plastic displacement are examined. It is shown that the zeolite granulates with elastic-plastic behaviour have viscous properties as well. Breakage mechanisms of granulates during elastic, elastic-plastic and plastic deformation are also explained. The breakage probability is approximated by Weibull distribution function. The behaviour of the granulate during compression under the repeated loading-unloading conditions was investigated.     

Understanding the Behavior of Native Point Defects in ZrC by First‐Principles Calculations

Phase stability and macroscopic performances of ZrC are closely related to the behavior of native point defects. In this study, structures and stabilities of native point defects in ZrC as well as diffusion of C‐related defects are investigated by first‐principles calculations. It is shown that the carbon vacancy (V_C) and interstitials (C_is) are the dominant native point defects in ZrC. Six types of C_i configurations: two C‐trimers, one C‐tetrahedron, and three C‐dimers are identified with low defect formation energies. The V_C has a high migration energy (4.39 eV) which suggests its low mobility in ZrC. The C_is have low diffusion energy barriers (from 0.26 to 1.29 eV) which lead to their high mobility. In addition, the impact of defects (V_C, V_Zr, Zr_C, and C_Zr) on bonding strengths of neighboring Zr–C bonds is discussed. Especially near V_C, the 1NN (nearest neighboring) and 2NN Zr–C bonds are strengthened but 4NN Zr–C bonds are weakened. Interestingly, the 3NN Zr–C bonds are almost not affected by the presence of V_C. These results may be closely related to the short‐range interactions and ordering of V_C in nonstoichiometric ZrC.     

On the fluid dynamics of shaken bioreactors— flow characterization and transition

Phase‐resolved PIV measurements were carried out to provide a thorough characterization of the flow and mixing dynamics occurring in a cylindrical shaken bioreactor when operating conditions such as medium height h, shaking rotational speed N, orbital shaking diameter d_o, and cylinder inner diameter d_i, are varied. A scaling law based on the aspect ratio h/d_i, on the orbital to cylinder diameter ratio d_o/d_i, and on the Froude number Fr = 2(πN)²d_o/g, is derived to predict the incipience of flow transition occurring when the free surface orientation starts to exhibit a phase delay to the shaker table position along its orbit; depending on the combination of Fr, d_o/d_i and h/d_i the transport phenomena in the bioreactor are controlled by a horizontal toroidal vortex, or by a vertical one precessing around the cylinder axis. The free surface interfacial area was directly measured by image analysis to assess oxygen transfer potential and compared to an analytical solution valid for low Fr. © 2012 American Institute of Chemical Engineers AIChE J, 59: 334–344, 2013     

Large Bubble Sizes and Rise Velocities in a Bubble Column Slurry Reactor

The results are reported of an experimental study of the gas holdup, ?_G, large bubble diameter, d_Lb, and large bubble rise velocity, V_Lb, in a 0.1 m wide, 0.02 m deep and 0.95 m high rectangular slurry bubble column operated at ambient temperature and pressure conditions. The superficial gas velocity U was varied in the range of 0–0.2 m/s, spanning both the homogeneous and heterogeneous flow regimes. Air was used as the gas phase. The liquid phase used was C₉‐C₁₁ paraffin oil containing varying volume fractions (?_S = 0, 0.05, 0.10, 0.15, 0.20 and 0.25) of porous catalyst (alumina catalyst support, 10 % < 10 μm; 50 % < 16 μm; 90 % < 39 μm). With increasing slurry concentrations, ?_G is significantly reduced due to enhanced bubble coalescence and for high slurry concentrations the “small” bubbles are significantly reduced in number. By the use of video imaging techniques, it was shown that the large bubble diameter is practically independent of the gas velocity for ?_S > 0.05 and U > 0.1 m/s. The measured large bubble rise velocity V_Lb agrees with the predictions of a modified Davis‐Taylor relationship.     

Substituierte Alkinyle als axiale Liganden an häminähnlich gebundenem Eisen(III) - Einordnung in eine spektrochemische Serie

Substituted Alkinyles as Axial Ligands at Hemine Like Bound Iron(III) - Incorporation into a Spectrochemical Series . Substituted lithium alkynyles Li CC R (R = ^tBu, Ph, p-Cl C₆H₄, Me₃Si, ⁱPr₃Si, Ph₃Si) react with the hemine like macrocyclic iron(III) complex 6,13-di(ethoxycarbonyl)-5, 14-dimethyl-1, 4, 8, 11-tetraazatetradeca-4,6,12,14-tetraenato[2⁻]iron(III)-iodide (formula 2 ;) in tetrahydrofuran to form anionic low-spin di-adducts [fe(CC R)₂]⁻. The incorporation of the alkynyles into a spectrochemical series of the axial ligands (studied by the sharp equatorial-ligand-to-metal CT absorption band) results in the wavelength-sequence (nm): OH⁻ (≈︁ 510) « N₃⁻ (≈︁ 625) < ^tBu CC⁻ (664) < NH₃ (666) < Ph CC⁻ (692) < Ph NH₂ (695) < Me₃Si CC⁻ (698) < SCN⁻ (713) < Ph₃Si C  C⁻ (716) < CN⁻ (739) < 4-picoline (759) < pyridine (765) < nicotinamide (776) < methylnicotinat (788) < pyrazine (798) and points to a significant π-acceptor ability of the silyl substituents.     

Titanium complexes with β-ketoiminate chelate ligands for ethylene polymerization: The significant influence of substituents on structures and catalytic activities

Four titanium complexes having β-ketoiminate chelate ligands with fluorine or alkyl groups [(Ar)NC(CH₃)C(H)C(CH₃)O]₂TiCl₂ (3a: Ar = 2.6-F₂C₆H₃; 3b: Ar = C₆F₅; 3c: Ar = 2.6-Me₂C₆H₃; 3d: Ar = 2.6-ⁱPr₂C₆H₃) have been synthesized and characterized by ¹H NMR and EA. Complexes 3a, 3c and 3d were further characterized by X-ray diffraction analysis and demonstrated distorted octahedral coordination structure around the titanium center. The substituents in ligands greatly affect the coordination mode, resulting in three different isomeric structures. These complexes are active catalysts for polymerization of ethylene with MMAO as cocatalyst. The substituents in ligands have also great influences on catalytic activity. The complexes with alkyl groups have lower activity, while the complexes with fluorine atoms have middle or high catalytic activity.     

Etude de mecanismes ec sur electrode a pate de graphite

A theoretical analysis of EC mechanisms on graphite paste electrode (GPE) in linear sweep voltammetry is proposed for the following E_iC_j mechanisms. reversible electrochemical reactions E_i: Ox + ne ? Red (E₁), or: Ox + e ? S, S + e ? Red, 2S ? Ox + red (E₂); irreversible chemical reaction C_j: p Ox → A (C₁), or: p Ox → A + m Red (C₂), or: p Ox + m Red → A (C₃).Current—potential relationships are similar to those obtained by Laviron for both layer electrodes and film covered electrodes when the differential capacitance C and the circuit and electrode resistance R are negligible. For large values of the kinetic contants, it is possible to establish a set of relationships between the mechanism parameters and the experimental characteristics of the voltammograms.On a practical point of view, two types of mathematical analysis are proposed.     

Electrochemical wall mass transfer in liquid particulate systems

Ionic mass transfer coefficients between the wall of a 2.081 inch tube and liquid fluidized beds of lead glass, soda glass and lucite spheres have been measured using the diffusion-controlled reduction of ferricyanide ion at a nickel cathode for porosities 0.90 to 0.45 and Schmidt numbers 580 to 2100. The developed fluidization mass transfer coefficient for 41 < D_T/d_p < 105 were correlated by i_D E = 0.274 Re_H^?0.38 for 10 < Re_H <1600 and by J_D E = 0.455 Re_H^?0.44 for 16.7 < D_T/d_p < 27 and 50 < Re_H < 3500. Re_H is the hydraulic Reynolds number = d_H up/μ_E and d_H is D_T E/[1 + (3/2) ((1–E)) (D_T/d_p)). The distinct effect of D_T/d_p ratio is attributed to wall effects and the non-particulate behaviour of the fluidized bed for D_T/d_p < 27. Measurements in the open pipe and packed bed agreed very well with literature values. The packed bed gives highest mass transfer coefficients at given Re_H.     

Drag coefficients of irregularly shaped particles

The steady-state free-fall conditions of isolated groups of ordered packed spheres moving through Newtonian fluids have been studied experimentally. Measurements of the drag coefficients are reported in this paper for six different geometrical shapes, including isometric, axisymmetric, orthotropic, plane and elongated conglomerates of spheres. From these measurements, a new and accurate empirical correlation for the drag coefficient, C_D, of variously shaped particles has been developed. This correlation has been formulated in terms of the Reynolds number based on the particle nominal diameter, Re, the ratio of the surface-equivalent-sphere to the nominal diameters, d_A/d_n, and the particle circularity, c. The predictions have been tested against both the experimental data for C_D collected in this study and the ones reported in previous works for cubes, rectangular parallelepipeds, tetrahedrons, cylinders and other shapes. A good agreement has been observed for the variously shaped agglomerates of spheres as well as for the regularly shape particles, over the ranges 0.15<Re<1500, 0.80<d_A/d_n<1.50 and 0.4<c<1.0.     

Thermogravimetry of Thermoplastic Polyimide Powders under Four Different Atmospheres

Thermal degradation of a thermoplastic polyimide ( TPI ) fine powder was studied in nitrogen, helium, argon, and air, from room temperature to 790°C by a high‐resolution thermogravimetry (TG) at a variable heating rate in response to changes in the weight‐loss rate of the sample and also by traditional TG. In the three inert atmospheres, the high‐resolution TG found a two‐step degradation process with higher resolution for the TPI , which was hardly ever revealed by a traditional TG for the TPI and other similar polyimides. On the contrary, only a traditional TG in air observed a two‐step degradation process for the TPI . The initial thermal degradation temperature T_d, the temperatures at the maximum weight‐loss rate T_dm1 and T_dm2, the first maximum weight‐loss rate (dα/dT)_m1, as well as the degradation activation energy of the TPI all increase with the variation of testing atmosphere in the following order: in nitrogen < in helium < in argon < in air, but the char yield at 700°C appears to increase in a different order: in air < in helium < in argon < in nitrogen.     

Effect of FA chain length on normal- and reversed-phase HPLC of phospholipids

Forty-seven saturated synthetic diacyl PA, PC, PE, PG, and PS and five unsaturated diacyl phospholipids (PL) underwent normal- and reversed-phase (RP) HPLC with isocratic isopropanol/hexane/water (5∶4∶1) and methanol/chloroform/acetonitrile/water (79.5∶9∶8∶3.5) mobile phases, respectively. For normal-phase HPLC, capacity factors (k′ _i ) decrease with chain length (n) of the two identical PL FA residues, whereas the opposite occurs with RP (C₁₈)-HPLC. Plots of In k′ _i vs. n for individual PL classes are in general curved, violating the linear free-energy relationship. For PL of the same n but with different head groups, k′ _i with normal-phase HPLC varies as PE<PG<PA<PS<PC, except when n≥16, when the order is PE<PS≈PA≈PG<PC. For RP-HPLC, the order of k′ _i values is PG<_A≈PS≤PC≈PE until n≥16, when it is PA≈PG<PS≪PC≈PE. With normal-phase HPLC, k′ _i values of PL with unsaturated FA of n=18 are ordered as PE<PA<PC. Increasing degrees of unsaturation lead to increasing k′ _i .     

A proposed universal homogeneity and mixing index

The word “homogeneous” is generally used qualitatively. A simple numerical homogeneity index is proposed suitable for expressing varying degrees of homogeneity quantitatively, namely, the negative log of the sample weight (9) required to obtain a standard deviation of 1%. The scale is universal in that a homogeneity index can be computed for heterogeneities observable only on the atomic scale (e.g. sodium chloride crystals and air) and for homogeneities observable only on the stellar scale. Values of the index, H_i, are computed for certain defined and certain theoretical mixture arrangements as follow: (a) pure hydrogen (maximum and limiting value of H_i), 23.5; (b) sodium chloride, 22.0 < H_i < 22.2; (c) air, 19.1; (d) 10% oil in water emulsion, 9.4 < H_i < 12.4; (e) a 1-g medical pill composed of 15% A and 85% B homogenized so that 99.99% of the 1-g pills are within the limits (15±1)%A, 1.2; (f) some arbitrarily defined, partially mixed industrial materials, considered as equivalent to random segregations of 1 lb., ?6.1; 1 ton, ?9.4; and (g) an approximate, order of magnitude, figure for the universe according to available scanty astronomical data, ?46.3. The index (and even more directly, its antilog) should be a useful measurement of the degree of mixing, since homogeneity is measured directly rather than indirectly as have previously used indices of degree of mixing.     

Thermal degradation of cellulose and cellulose esters

Cellulose, cellulose diacetate (CDA), cellulose triacetate (CTA), cellulose nitrate (CN), and cellulose phosphate (CP) were subjected to dynamic thermogravimetry in nitrogen and air. The thermostability of the cellulose and its esters was estimated, taking into account the values of initial thermal degradation temperature T_d, the temperature at the maximum degradation rate T_dm, and char yield at 400°C. The results show that these polymers may be arranged in the following order of increasing thermostability: CN < CP < regenerated cellulose < filter cotton < CDA < CTA. The activation energy (E), order (n), and frequency factor (Z) of their degradation reactions were obtained following the Friedman, Chang, Coats–Redfern, Freeman–Carroll, and Kissinger methods. The dependence of T_d, T_dm, E, n, Ln Z, and char yield at 400°C on molecular weight and test atmosphere is also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:293–304, 1998     

Synthesis,Structure and Thermal Properties of Copper and Silver Polyynides and Acetylides

Polyynes or oligoynes having general formula H–(C≡C)_n–H with n = 1,2,3,4,…, are a class of molecules that has become easily accessible in recent years due to new synthetic approaches. These molecules form copper and silver salts, which have been called, respectively, Cu-polyynides and Ag-polyynides. Here we show the synthesis of these salts and discuss their FT-IR spectra and thermal behaviour, which is studied by Differential Scanning Calorimetry (DSC). These properties are compared to the spectra and thermal behaviour of Cu₂C₂ and Ag₂C₂. It is shown that Cu₂C₂ can be oxidized to Cu-polyynides thereby loosing its original structure and becoming a polymeric coordinative structure. The structural changes make Cu-polyynides no more explosive than the parent Cu₂C_2. Similarly, Ag-polyynides, which decompose exothermally when heated, are not explosive compared to Ag₂C₂. The explosive decomposition of Cu₂C₂ occurs at 127 °C (DSC) whereas Ag₂C₂ decomposes explosively at 169 °C under the same conditions. Conversely, Cu-polyynides, when heated in the DSC, show a broad exothermal peak at about 243 °C. Ag-polyynides decompose near 94 °C and the release of energy is sufficiently gradual that no explosion is detected.     

Achieving single domain in rhombohedral and tetragonal Mn-doped Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)-PbTiO3 crystals for infrared detecting applications

The [111]-oriented rhombohedral Mn-doped 0.15Pb(In_1/2Nb_1/2)-0.55Pb(Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ (Mn:PIMNT(15/55/30)) crystal and the [001]-oriented tetragonal Mn-doped 0.29Pb(In_1/2Nb_1/2)-0.29Pb(Mg_1/3Nb_2/3)O₃-0.42PbTiO₃ (Mn:PIMNT(29/29/42)) crystal were poled under different conditions. The pyroelectric performance of the two crystals as a function of poling temperature, as well as the relationship with ferroelectric domain configuration and phase structure was investigated systematically. The pyroelectric properties of the two crystals enhance with rising the poling temperature, which can be attributed to the improvement of the single state. And for the rhombohedral Mn:PIMNT(15/55/30) crystal locating near morphotropic phase boundary (MPB), the increase of tetragonal phase induces the deterioration of pyroelectric properties. Due to more residual tetragonal phase, the pyroelectric coefficient of the Mn:PIMNT(15/55/30) crystal poled at 150°C is lower than that poled at 100°C. In general, both the crystals poled above T_C achieve nearly single state, exhibiting the best pyroelectric properties with relatively high Curie temperature (T_C), where P = 9.71 × 10⁻⁴ C m⁻² K⁻¹, F_i = 3.88 × 10⁻¹⁰ m V⁻¹, F_v = 0.068 m² C⁻¹ and F_d = 29.7 × 10⁻⁵ Pa^−1/2 for the rhombohedral Mn:PIMNT(15/55/30) crystal (T_C = 171°C) and P = 6.78 × 10⁻⁴ C m⁻² K⁻¹, F_i = 2.71 ×10⁻¹⁰ mV⁻¹, F_v = 0.1 m² C⁻¹, F_d = 23.54 × 10⁻⁵ Pa^−1/2 for the tetragonal Mn:PIMNT(29/29/42) single crystal (T_C = 251°C), meeting the stable operation of infrared detector at relatively high environmental temperatures.     

Oscillatory behavior in catalytic systems: Effect of a non-diagonal capacity matrix

The mechanism presented is modelled as a second order system

d$\text{x}$/dt = $\text{F}$($\text{x}$) with a non-diagonal capacity matrix. The model admits oscillatory solutions due to the interaction between the chemisorption capacities of the dynamic variables, even though no positive feedback is incorporated in the kinetic terms, that is ?F_i/?x_i < 0.The model is investigated for regions of characteristic behavior and its stable and oscillatory solutions are compared to experimental observations.     

Dynamic Kerr-effect and dielectric relaxation studies of a poly(methylphenyl siloxane)

Dynamic Kerr-effect and dielectric relaxation studies have been for a poly(methylphenyl siloxane) fluid in the region of its α relaxation process. The relaxations are broader than a single relaxation-time process and we find τ_K,r < τ_K,d < τ_? and β_K,r ? β_K,d < β_?, where K, r; K, d and ? refer to Kerr-effect rise, decay and dielectric, respectively; τ and β are the relaxation time and the Williams-Watts relaxation parameter, respectively. It is suggested that the observed Kerr-effect relaxation is largely due to the motions of the phenyl group and that a substantial part of this process is due to motions about the bond joining the silicon atom to the aromatic ring.     

Synthesis and rapid expansion in supercritical carbon dioxide through porous sintered metal plate of poly(1,1,2,2‐tetrahydroperfluorodecyl acrylate)

Poly(1,1,2,2‐tetrahydroperfluorodecyl acrylate) [poly(TA‐N)] was synthesized in dry benzene using AIBN as an initiator at 60°C. The effects of the monomer concentration (C_m), initiator concentration (C_i), and reaction time on the polymerization were investigated. The results of DSC and TGA showed that when the C_i remains constant, the higher the C_m value is, the better the thermal character for the product in the range of experiments. When the reaction was conducted for 30 h, polymerization is almost completed. The C_i should remain lower than 0.25 g/100 g monomer when the C_m is lower than 15 g/L. When the C_m is higher than 15 g/L, the C_i should be increased slightly. When the C_m remains constant, it was observed that an increase in the C_i increases the yield (mass of polymer after reaction/mass of monomer before reaction). On the other hand, the melting (T_m) and decomposition (T_d) temperatures of the reaction product decrease, except when the C_m reaches 20 g/L and the reaction time is 30 h. High purity CO₂ was continuously pumped using a high pressure syringe pump. Rapid expansion of poly(TA‐N) in supercritical CO₂ happened under control through a porous sintered metal plate. The poly(TA‐N) morphology was analyzed with a scanning electron microscope. An amorphous polymer was formed at a preexpansion temperature of 45°C. Fibers were formed at temperatures of around 60–80°C. An increase of the temperature slightly increases the particle size. At 105°C, most of the particles are spheres and dendrites. The corresponding CO₂ flow rate upon expansion was 2.5–5.0 ± 0.3 L/min (STP) and the pressure drop was 2 MPa. At the higher CO₂ flow rate, the spheres and dendrites became smaller. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2763–2768, 2003     

Effect of oriented defect-dipoles on the ferroelectric and piezoelectric properties of CuO-doped (K0.48Na0.52)0.96Li0.04Nb0.805Ta0.075Sb0.12O3 ceramics

The orientation characteristics of the defect dipoles formed by acceptor ions (${\mathrm{Cu}}_{\mathrm{Nb}}^{″\prime }$) and oxygen vacancies ($V_{\mathrm{O}}^{??}$) in CuO-doped (K_0.48Na_0.52)_0.96Li_0.04Nb_0.805Ta_0.075Sb_0.12O₃ piezoceramics were investigated. The ferroelectric and piezoelectric properties of the ceramics were obviously affected by the defect dipoles which are oriented along with the domains when poled under a dc electrical field of 3.5?kV/mm at the temperature near T_C. The poled ceramics with 1.0–3.0?mol% CuO displayed strong asymmetric P-E loops and a large internal bias field (E_i), 3.89–4.57?kV/cm, when polarized at the temperature near T_C. The enhanced piezoelectric coefficient d₃₃, 186–192?pC/N, was obtained for the ceramics poled near T_C when 0.02?≤?x?≤?0.03. The ceramics with oriented defect dipoles showed a relatively good thermal stability of d₃₃ until 180?°C.     

Supersaturation of oxygen in acidic solution in the vicinity of an oxygen-evolving platinum anode

The concentration of O₂ in 1 M H₂SO₄ solution in the vicinity of the O₂-evolving smooth Pt anode was measured as a function of anodic cdi_a using the galvanostatic potential—transient method.The solution near the O₂-evolving anode was supersaturated with O₂. When the anodic current was interrupted, supersaturated concentration C^* decreased at a rate proportional to C^*  C₀, where C₀ is the solubility of O₂ in the electrolyte at 1 atm. The rate constant of the decay of the supersaturation under the open circuit condition was measured to be 0.069 sec^?1 at 25°C.At i_a < 40 mA/cm² there was a linear relation between log(C^*  C₀) and log i_a. At i_a > 200 mA/cm², however, the supersaturation exhibited a limiting value of 9.0 × 10^?2 mol/l.