A Halomanganates(II) with P,P’-Diprotonated Bis(2-Diphenylphosphinophenyl)ether: Wavelength-Excitation Dependence of the Quantum Yield and Role of the Non-Covalent Interactions

A [H₂DPEphos][MnX₄] [X = Br, Cl] tetrahalomanganates(II) with P,P’-diprotonated bis[2-(diphenylphosphino)phenyl]ether cation has been designed and investigated in photophysics and EPR terms. The complexes exhibit a green luminescence resulted from the Mn(II) d–d transitions (⁴T₁→⁶A₁) with the wavelength-excitation dependence of the quantum yield. The solid [H₂DPEphos][MnBr₄] complex exhibits a bright green phosphorescence (λ_max = 515 nm) with the high luminescence quantum yield depending on the excitation energy whereas the solid [H₂DPEphos][MnCl₄] complex exhibits a very weak phosphorescence (λ_max = 523 nm). The unexpected shorter luminescence lifetime for the [H₂DPEphos][MnCl₄] than for the [H₂DPEphos][MnBr₄] at 300 K can be a result of the higher non-radiative relaxation contribution. On the one hand, the non-covalent PH…X(Mn) interactions quench the manganese(II) luminescence. On the other hand, the PH…X(Mn) interactions are a pathway of the excitation transfer from [H₂DPEphos]²⁺ to [MnX₄]²⁻.     

The influence of the tunnel probability on the anodic oxygen evolution and other redox reactions at oxide covered platinum electrodes

Potentiostatic and galvanostatic pulse measurements were carried out to investigate the anodic oxygen evolution at platinum electrodes in 1N H₂SO₄ in dependence on the oxide layer thickness d and the electrode potential ε. The thickness d (1·5–10 Å) was obtained from cathodic charging curves. Further, the temperature dependence (0°–81°C) was evaluated from Bowden's measurements. Summarizing, the current i_o2 follows the relation, log i = A - (E⁰_a - αFη)/2·3 RT - d/d_o. The experimental activation energy E_o = E^o_a = αFη decreases linearly with increasing overvoltage η. The linear decrease of log i with increasing d, which is given by the term d/d_o, is correlated to the probability of the quantum mechanical tunnel transition of the electron from adsorbed ions, OH^?_ad or O^2?_ad respectively, through the oxide layer to the metal. Similar effects of the oxide layer thickness on the current density were observed in the case of the oxygen evolution at iridium, the CO-oxidation on platinum, and the reduction of Cl^? and Ce⁴⁺ at platinum. In these cases a rate determining electron transfer through the oxide layer is also assumed.     

Initiation of the explosive decomposition of pentaerythritol tetranitrate with ultradispersed particle additives by laser pulses

The explosive decomposition threshold of pentaerythritol tetranitrate was studied depending on the concentrations of ultradispersed Al particles and Ni-C and Al-C mechanocomposites in the samples. It was found that the critical pulse energy density W _0.5, which corresponds to a 50% probability of explosion, reached a minimum value at additive concentrations of 0.1?C0.3 wt %: W _0.5 = 1.4, 5, or 4 J/cm² for Al, Ni-C, or Al-C, respectively.     

Burning of liquid fuels: effect of burner diameter on burning rate and measurements of quenching diameter

Laminar pool flames of four straight-chain alcohols were studied in uncooled glass and copper burners and water-cooled glass burners. The mass burning rate $\text{m}\text{?}$ increased with the burner diameter d decreasing as $\text{m}\text{?}$ ∝ d^?n, where n ≈ 1.2 for uncooled glass burners. The values of $\text{m}\text{?}$ in copper burners were lower by a factor of 1.5–2 than those in glass burners of the same diameter. Vigorous boiling of the subsurface layer of liquid occurred in sufficiently narrow uncooled glass burners, and numerous burning droplets were observed to traverse the flame. The quenching diameter d_c was measured. For uncooled copper burners d_c increased with increasing molecular weight M_r of the alcohol, from ≈ 2 mm for propanol to ≈ 20 mm for decanol. For uncooled glass burners d_c was much lower (1–2 mm) and less dependent on molecular weight. The product of d_c and the critical mass burning rate is assumed to have a characteristic value for the stability of diffusion burning, in accordance with the Zel'dovich criterion (Pe) = (Pe)_c = const. for flame stability in gas mixtures. However, the stability of diffusion burning increased with increasing heat losses from the burner wall. Two possible interpretations of this paradoxical effect are suggested.     

Self-assembly of an organometallic silver(I) 1D architecture supported by three different types of bonding interactions

The new ligand o-C₆H₄[CH₂OCH₂C(3-Phpz)₃]₂ (pz=pyrazolyl ring) reacts with AgBF₄ to yield the coordination polymer {o-C₆H₄[CH₂OCH₂C(3-Phpz)₃]₂Ag₂(BF₄)₂}_n. The organometallic supramolecular architecture contains two different types of silver(I) cations arranged in bimetallic units forming a 1D coordination polymer. The bimetallic units show three different types of bridging interactions, including a μ-κ¹,κ²-tris(3-Ph-pyrazolyl)methane unit, a silver η²-bonded to a phenyl group and π–π stacking interactions.     

A model for transitional breakage probability of droplets in agitated lean liquid-liquid dispersions

A model for transitional breakage probability of droplets in agitated lean fiquid-liquid dispersions is proposed based on the mechanism of breakage of droplets due to their oscillations resulting from relative velocity fluctuations. A universal transitional breakage probability in terms of non-dimensionalized drop diameter is derived for all dispersed phases whose density and viscosity are almost the same as that of continuous phase. The maximum stable drop diameter d_s derived from the model, shows a dependence of N_We^?0.6. It is shown that a “power law” approximation Kvⁿ is valid for transitional breakage probability for d/d_s up to 2. The exponent 2.67, predicted by this model corresponds rather well with an estimate of 2, obtained from experimental observations. A functional relation for the rate constant K in terms of the parameters and physical properties of the system is derived. A universal non-dimensionalized equilibrium drop-size distribution for agitated lean liquid-liquid dispersions is derived by analytical solution of a population balance equation simplified by order of magnitude estimates. Interestingly enough, this analytical solution is the same as the Gaussian distribution suggested empirically by Chen and Middleman.     

Determination of the collision frequency between bubbles and particles in flotation

Collision efficiency for a spherical bubble rising in a uniform concentration of small non-inertial particles is studied by direct numerical simulations (DNS). The Stokes number of the particles is negligibly small so that the particle trajectories follow the streamlines. The effect of the bubble interface contamination is studied for the flow surrounding the bubble using the spherical cap model. Numerical results are obtained for a wide range of bubble Reynolds number (based on bubble diameter d_b) ranging from 0.01 to 1000 and for different angles of contamination ranging from 0^° to 180^°. The collision efficiency is found to be increased with the Reynolds number and significantly decreased with the level of contamination. Correlations of the numerical results are proposed for efficiencies versus d_p/d_b (d_p being the particle diameter), bubble Reynolds number and interface contamination degree. For clean (respectively, fully contaminated) spherical bubbles, the efficiency evolves as d_p/d_b (respectively (d_p/d_b)²) whatever the bubble Reynolds number and the particle size. For partially contaminated bubbles, efficiency can be scaled with d_p/d_b or (d_p/d_b)² depending on both the level of contamination and the particle size.     

Studies on the mechanism of the hydrogen electrode reaction by means of deuterium tracer—III. The stoichiometric number

The stoichiometric number of the hydrogen electrode reaction on Rh, Ni, Pt, Au, Ag, and Ir was determined by means of deuterium tracer at the reversible potential. It is shown that, along with the change of the rate-determining step in the reaction route, H₂ ? 2H(a) followed by H(a) + B ? H⁺B + e, where B = H₂O or OH^?, the stoichiometric number v? experimentally observed should change by the relation, v? = (m + 2)/(m + 1), where m = v_d/2v_c and v_c and v_d are the exchange rates of these steps. The experimental v?vs m relation observed on these metals qualitatively satisfied this relation. Disagreement which existed were quantitatively explained by taking the isotope effect into account. The isotope effect of the individual steps, which were needed to interpret the disagreements, were found to be of reasonable magnitude.     

Determination du courant limite d'electrodialyse par conductivite pour les faibles nombres de reynolds. Cas des solutions de tartrate acide de potassium

In the case of an electrodialysis operation, it is possible to obtain the limiting current by measuring the conductivity of the solution undergoing dilution. Starting from the equation of the constant flux of matter, when the concentration at the membrane falls to zero, (i/σ_d)_crit = δ relates the current density i and the conductivity of the diluate σ_d. The critical value of (i/σ_d) is easily obtained from the drawing of σ _dvs the potential applied to the apparatus. Experiments carried on aqueous solutions of KHC₄H₄O₆ at 8 g/l show that (i/σ_d)_crit) is well related to the Reynold's number by the relation αRe^β. It is then possible to calculate the thickness δ of the diffusion layer as a function of the Reynold's number.     

The influence of chloride ions on the kinetics of iron dissolution

The anodic dissolution of pure iron was studied in oxygen-free solutions at high concentrations of chloride and hydrogen ions at 25°C under potentiostatic steady-state conditions. In the range c_H⁺ ? 1 M the following kinetic data were obtained: Tafel slope b₊ ? +100 mV, electrochemical reaction order related to C_H⁺, n_+.H⁺ = +1·1, and electrochemical reaction order related to the chloride ion concentration, n_+,Cl^? = +0·6. These values cannot be correlated to the currently proposed mechanisms of iron dissolution, another mechanism is suggested for the described conditions. The correlations to known mechanisms are discussed.     

Effect of blend ratio on rheological properties of aqueous SiC suspensions

The relationship between blend ratio and rheological properties of concentrated suspensions is of great importance since it is the key to get high solid suspensions. The rheological properties of bidisperse aqueous suspensions made of two SiC powders with different particle size [d_(0.5)=1.63 and 18.43 μm, respectively] has been studied as a function of blend ratio ξ (the volume fraction of larger particle size). The results showed that the value of critical blend ratio ξ, at which the viscosity is minimized, is in close relation to the shear rate applied. At shear rates below 10 S⁻¹, the critical ξ was greater than 70%. But at shear rates from 10 to 500 S⁻¹, ξ turned to be 50%. The change of shear region from shear-thinning behavior to shear-thickening behavior may be used to account for the variation of critical ξ. Dynamic oscillatory tests showed that the moduli and the linear viscoelastic region of suspensions with higher ξ are smaller than those with low ξ and the increment of blend ratio ξ leads to the change of suspension from nearly an elastic response to a liquid like response.     

Fluorescence studies of associative behavior of cationic surfactant moieties covalently linked to poly(acrylamide) at the surfactant head or tail

Association properties of hydrophobically modified water-soluble polymers bearing the same (or similar) hydrophobic and charged groups at different relative positions (with respect to the polymer main chain) were compared. Two types of surfactant monomers (surfmers) were synthesized; a cationic surfactant was linked to the p-position of styrene at the surfactant charged head (dimethyldodecyl-4-vinylbenzylammonium chloride (St-QC₁₂)) or at the tail end (13-(4-vinylphenyl)tridecyltrimethylammonium bromide (St-C₁₃Q)). These surfmers were copolymerized with acrylamide (AAm), and the association behavior of the copolymers in water was characterized using different fluorescence techniques. The surfmer contents in the AAm/St-QC₁₂ and AAm/St-C₁₃Q copolymers were fixed to more or less 10 mol%. The surfmer units in the copolymers self-associate to form multipolymer aggregates. An apparent critical micelle concentration (cmc) (i.e. a polymer concentration for the onset of interpolymer association of the surfmer units) estimated from excitation spectra of pyrene probes for AAm/St-QC₁₂ (cmc=2.6×10⁻⁴ g/l) was several times lower than that for AAm/St-C₁₃Q (cmc=1.3×10⁻³ g/l), surfmer units in AAm/St-QC₁₂ showing a stronger tendency for interpolymer association than those in AAm/St-C₁₃Q. The presence of excimer emissions in steady-state fluorescence spectra for the p-substituted styrene residues (phenylene groups) in AAm/St-C₁₃Q indicated that the benzene rings are in close proximity to one another in the polymer aggregates. Steady-state fluorescence spectra and fluorescence quenching by thallium nitrate and 1-nitrohexane indicated that the phenylene groups in AAm/St-C₁₃Q were incorporated in hydrophobic microdomains formed from surfactant hydrocarbon chains, whereas the phenylene groups in AAm/St-QC₁₂ are located near the surface of polymer aggregates in a way that they are sufficiently apart from each other and hence no excimer is formed.     

Dynamics of Order Reconstruction in a Nanoconfined Nematic Liquid Crystal with a Topological Defect

At the wall in a hybrid nematic cell with strong anchoring, the nematic director is parallel to one wall and perpendicular to the other. Within the Landau-de Gennes theory, we have investigated the dynamics of s = ±1/2 wedge disclinations in such a cell, using the two-dimensional finite-difference iterative method. Our results show that with the cell gap decreasing, the core of the defect explodes, and the biaxiality propagates inside the cell. At a critical value of d_c* ≈ 9ξ (where ξ is the characteristic length for order-parameter changes), the exchange solution is stable, while the defect core solution becomes metastable. Comparing to the case with no initial disclination, the value at which the exchange solution becomes stable increases relatively. At a critical separation of d_c ≈ 6ξ, the system undergoes a structural transition, and the defect core merges into a biaxial layer with large biaxiality. For weak anchoring boundary conditions, a similar structural transition takes place at a relative lower critical value. Because of the weakened frustration, the asymmetric boundary conditions repel the defect to the weak anchoring boundary and have a relatively lower critical value of d_a, where the shape of the defect deforms. Further, the response time between two very close cell gaps is about tens of microseconds, and the response becomes slower as the defect explodes.     

Pressure dependence of upper critical solution temperatures in the polystyrene - cyclohexane system

The pressure dependence of the upper critical solution temperature $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ in the polystyrene-cyclohexane system has been measured over the pressure range of 1 to 50 atm. The value of $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ determined over the molecular weight (M_w) range of 3.7 × 10⁴ to ～145 × 10⁴ greatly depends on the molecular weight of polystyrene. The value of $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ for a polystyrene solution of low molecular weight (M_w = 3.7 × 10⁴) is positive (3.14 × 10^?3 degree atm^?1), while the values are negative (?0.52 × 10^?3～?5.64 × 10^?3 degree atm^?) for solutions of polystyrene over the high molecular weight range of 11 × 10⁴ to ～145 × 10⁴. The Patterson-Delmas theory of the corresponding state and the newer Flory theory have been used to explain this behaviour.     

Fluorescence studies on local density change in supercritical CO2 mixtures using the order parameter model

Supercritical CO₂ has many unusual physicochemical properties in or near the critical region, which is mostly due to the local density enhancements and specific molecular interactions. Compared to pure CO₂, the study on CO₂ mixed with co-solvent is attractive in wide applications but it is hard to quantitatively describe the local density change and intermolecular clusters in CO₂ mixtures. The fluorescence response of a sensitive pyrene probe, empirical Py scale, was determined in CO₂ mixed with pentane at 323.15 K in different phase regions. A variable called the order parameter was introduced to account for possible correlations in the first derivative of Py scale and fluid pressure (dPy/(d(P/P₀ − 1))). This model, avoiding the hard choice of the reference line in CO₂ mixtures, was effective in calculating the local density change and it showed the specific molecular interaction in the critical region. The behaviors of the local density change and the isothermal compressibility of supercritical CO₂ mixtures correlated well with microscopic and macroscopic observations.     

Kinetics of ligand exchange reaction of Cu(II)-ammine complex with poly(vinyl alcohol) in aqueous solution

The kinetics of the ligand exchange reaction of the Cu(II)-ammine complex with poly(vinyl alcohol) (PVA) has been studied by a stopped-flow method at pH 9–10, at μ=0.1 (NH₄Cl) and at 25°C. The reaction is initiated by the formation of unstable [Cu(NH₃)₃]²⁺ by the attack of H⁺ on Cu(II)-ammine complex, and proceeds through the mixed complex {[Cu(NH₃)₃(O?PVA)]²⁺}. This step may be rate-determining, followed by a rapid reaction. Finally, the Cu(II) ion is taken up by PVA. The rate is given by d[Cu(II)?PVA]/dt=k[H⁺]{[Cu(NH₃)₄]²⁺}[PVA]/[NH₄Cl], where k=k₁ + k′₂[H⁺], k₁=4.25× 10s^?1 and k′₂=5.20× 10¹¹l mol^?1s^?1.     

Megalopolis lignite drying kinetics based on TGA experimental results

Lignite drying kinetic data are of critical importance for the design of drying and occasionally gasification process equipment because of the particularly high (55–60%) moisture content held in the lignite particles. A lumped kinetic model, R_d(t) = ηk_d(T)(W^* - W(t))^n_d(T), describing the dependence of the drying rate upon the residual moisture content (dry basis) of lignite single-particle systems is proposed in this paper. The mathematical analysis is based on data obtained from TGA experimental studies carried out on lumps or on samples of pulverized Greek (Megalopolis) lignite in a nitrogen atmosphere under transient temperature conditions. (A rate of temperature rise 20°C/min, up to 100°C, was applied.) The temperature dependence of both the relevant rate constant and the kinetic order was determined by the best fit of the theoretical model to the relevant experimental data. Megalopolis lignite drying can be described satisfactorily by the kinetic equation

η = f(d_p) and T = f′(t) are described graphically in the text.     

The effect of ball size on mill performance

The specific rates of breakage of particles in a tumbling ball mill are described by the equation S_i = ax^α_i(Q(z), where Q(z) is the probability function which ranges from 1 to 0 as particle size increases. This equation produces a maximum in S, and the particle size of the maximum is related to ball diameter by x_m = k₁d². The variation of a with ball diameter was found to be of the form a = k₂/d^1.5. Both k₁ and k₂ vary with mill diameter, and simple power laws have been assumed, k₁ ∝ D^0.1, k₂ ∝ D^0.6. If it is also assumed that the mean overall values of S_i for a mixture of balls is the weighted mean of S_i values for each ball size, equations are derived for calculating this mean value. As an example, the results are used in a mill simulation to show the quantitative effect of different ball mixes in a two-compartment cement mill versus a uniform mix over the whole mill.     

Power numbers,Taylor numbers and Taylor vortices in viscous newtonian and non-newtonian fluids

Power numbers (Po) as a function of Taylor numbers (Ta) have been investigated for the flow between concentric cylinders with the inner cylinder rotating and the outer cylinder stationary. Both Newtonian and non-Newtonian fluids were used and torque measurement was done by strain gauges. Flow visualization enabled Taylor vortices to be studied too. Three pairs of cylinders were used: two plain and one where the outer cylinder had vertical strip baffles. The nominal outer dimensions were 0.1 m diameter × 0.2 m high. The maximum values of Ta measured were 90 for width of gap (d)/inner cylinder radius (R_i) ratio = 0.9 and approximately 400 for d/R_i = 0.7.Experimental data for all the systems used agreed well with theory in the laminar region (Ta<Ta_c), giving Po ∝ Ta⁻¹. For the laminar Taylor vortex region (Ta>Ta_c),

. In the latter case, the laminar shear rate was used to calculate the Taylor number for the non-Newtonian fluids. Critical Taylor number Ta_c for non-Newtonian fluids was found to be greater than the Newtonian one.The results are useful for estimating the power consumption of potential industrial devices utilizing the advantages of laminar Taylor vortex flow.     

Dynamic flow rates of granular particles

Flow rates (W) of powder and granules are usually measured by letting the particulate solid pass through a stationary orifice. This is not a physical duplication of the event in, for instance, a rotary tablet machine, where the dies move in relation to the powder bed. An apparatus is described by which dynamic flow rates (i.e. flow into a moving orifice) can be measured. These dynamic flow rates (W₂ g/sec) differ from static flow rates. They are subject to the same dependence on particle diameter, d, as static flow rate, i.e.: W₂ ? W_m = ? k(d ? d_m)^s, where “m” refers to maximum and k and s are constants. They also exhibit the same type dependence on orifice opening (P cm) as static flow rates, i.e.W₂ = qPⁿ, where q and n are constants. The values for _n are 3 – 3.25, which is somewhat higher than for static flow where n = 2.3 – 2.6.