New kinetic aspects on the mechanism of thermal oxidative degradation of polypropylenes with various tacticities

Thermal oxidative degradation behavior of polypropylene (PP) with different tacticities was studied based on the activation energy (ΔE) data obtained by thermogravimetric analysis (TGA). The ΔE value showed a negative proportion to the content of meso pentad fraction (mmmm) in all of isotactic PP (iPP) samples, and that of syndiotactic PP sample considerably deviated from this negative proportion relationship. Since the value of mmmm was directly related to polymer chain conformation, the ΔE value was thought to have close connection with the concentration of 3₁ helix conformation in the iPPs. The ΔE changes would be caused by the competition between uni- and bimolecular hydroperoxide decomposition, which was controlled by concentration and character of conformations of PPs.     

The Rule of Interfacial Equilibrium

The detailed analysis of the well-known relation γ₁₂ = γ₁ -γ₂ has been done (γ₁₂, γ₁ and γ₂ are interfacial and surface tensions of phases 1 and 2). The analysis of equilibrium of a liquid drop at the interface with another liquid allowed us to prove that this relation should be modified by including in it the value γ₂* which is considered as the result of all interactions at the interface and is accepted depending on γ₁. The value γ₂* represents the surface tension of a phase in the ternary point solid-liquid-gas, i.e. in the zone of interfacial nonuniformity. The modified form of the relation, called the rule of interfacial equilibrium, allows us to show that thermodynamic work of adhesion is equal to the cohesion energy of the interphase formed by phase 2.     

Analysis of the thermal hysteresis in partially deuterated tryglicine selenate

Dielectric constant data on partially deuterated triglycine selenate (TGSe)_1-x, (DTGSe)_x for x = 0, 0.35, 0.80 show a steady increase of thermal hysteresis ΔT(x) with deuteration, in agreement with previous data by Gesi. In this work we correlate this observed thermal hysteresis with the parameter g(x) = (γ/β)N²μ² obtained from hysteresis loops data, in order to characterize the ferroelectric transition. For x = 0, the transition is close to a tricritical point (g ≌ 1/3) and we see that cooling very slowly through T_c under these quasitricritical conditions results in a very large residual contribution to the dielectric constant at the ferroelectric phase.     

Solvation of ions—XX. The ferrocene—ferricinium couple and its role in the estimation of free energies of transfer of single ions

The ferrocene-ferricinium electrode (Pt/Foc, Fic⁺) was investigated in water, acetonitrile, ethanol, DMSO and DMF using single scan cyclic voltammetry and phase sensitive ac polarography. The oxidation-reduction is pseudo-reversible in all five solvents with an electrochemical rate constant of approximately 10⁻² cm/s. In all solvents a slow irreversible chemical step involving the ferricinium cation follows electron transfer, so that slow cyclic voltammetry or polarography rather than potentiometry is preferred if ferrocene is to be used as a reference electrode in non-aqueous solvents.

The Strehlow assumption, ΔG_tr(Foc) = ΔG_tr(Fic⁺ gives very different free energies of transfer of single ions from non-aqueous solvents to water when compared with the TATB assumption that ΔG_tr(Ph₄As⁺) = ΔG_tr(Ph₄B⁻). This discrepancy is likely to be because ferricinium is only a moderately large cation, so that ΔG_tr(Fic⁺) is less positive than ΔG_tr(Foc) for transfer to water. The discrepancy is not because of abnormal electrochemical behavior of the Pt/Foc, Fic⁺ electrode in water or other solvents. Values of E° vs nhe, H₂O in a variety of solvents based on the TATB assumption are presented.     

Effect of macromolecular length on anisotropic scattering of light in an electric field

Light scattering by monodisperse solutions of rigid rod-like anisotropic macromolecules, with linear dimensions l of the order of incident wavelength λ, oriented in an external d.c. electric field, →E has been analysed. The relative variations δV^E_v, δH^E_v, δV^E_h, δH^E_h of the scattered light components are discussed for the three values [l/λ] = 1, 0·5, 2, and various reorientation parameters, p = [μE/kT] of the permanent dipole moment μ and q = [(₃ − ₁)E²/2kT] of the moment induced by the principal polarizabilities ₁ = ₂ ≠ ₃. The saturation orientation field strength has been calculated for certain macromolecules with the aim of determining their optical anisotropy numerically.     

A theoretical study on Brønsted acidity of WO3 clusters supported on metal oxide supports by “paired interacting orbitals” (PIO) analysis

Ammonia adsorption on Brønsted acid sites of WO₃ cluster supported on metal oxide supports: SnO₂, ZrO₂, and TiO₂, is analyzed by PIO analysis. We employed (HO)(WO₃)₄(H) and (HO)(WO₃)₉(H) on (SnO₂)₁₂, (ZrO₂)₁₂, and (TiO₂)₁₂, respectively, as supported Brønsted acid models and examined two types of Brønsted acid sites, an edge type and a face type. We estimated ammonia adsorption strength by total overlap population (∑OP) of all PIOs between the Brønsted acid site and NH₃. The order of acidity (∑OP) of each model is as follows: edge type: SnO₂, 0.0096 > ZrO₂, 0.0048 > TiO₂, −0.0001  face type: ZrO₂, −0.0759 > TiO₂, −0.0761 > SnO₂, −0.0867. The edge type adsorption is far stronger than the face type one. This order in the edge type coincides with the experimental results. The reason of these results is explained by the difference of the influence of oxygen atoms sitting near the N atom of NH₃.     

Supported MoO3 catalysts: preparation by the new “slurry impregnation” method and activity in hydrodesulphurization

A new preparation of supported MoO₃ is described. Slurry MoO₃/water is used instead of the solution (NH₄)₆Mo₇O₂₄. Preparation and HDS activity are illustrated for MoO₃ supported over Al₂O₃, active carbon and ZrO₂. Another application of the new principle is the preparation of high surface area MoO₃/MgO by the reaction of MgO with slurry (NH₄)₆Mo₇O₂₄/methanol. Texture of MgO that is deteriorated in aqueous solution of (NH₄)₆Mo₇O₂₄ is stable in that slurry. “Slurry impregnation” is a special case of equilibrium adsorption impregnation. It is simple and it provides monolayer dispersion of molybdena.     

Electrosorption and inhibition properties of p-norborn2-yl phenolate ions at the mercury/solution interface

The electrosorption properties of p-norborn-2-yl phenolate ions in alkaline solutions were investigated by ac polarographic and electrocapillary measurements.

Two adsorption regions were found. At low bulk surfactant concentrations the adsorption at the positively charged electrode (−0.2 E −0.6 V) is predominant while at higher surfactant concentrations the adsorption at the negatively charged electrode (−0.6 E −1.0 V) is more pronounced. At E = −0.40 V the adsorption parameters were determined (a ≈ 2; ΔG°_A = −32.5 ± 1 kJ mol⁻¹. Between −0.6 E −1.0 V one potential of maximum adsorption for all concentrations does not exist and therefore the adsorption parameters could not be calculated.

At E = −0.40 V progressive two-dimensional nucleation with a nucleation order of 3 was observed which corresponds well with the high attraction constant.

The electrode reaction S₂O²⁻₈ + 2e⁻ → 2 SO²⁻₄ is inhibited by norborn-2-yl phenolate ions in the potential range −0.2 E −0.6 V. In the second potential range of capacity decrease the electrode process is much less retarded. At E = −0.40 V, in a similar manner as described for neutral molecules, a linear dependence of the log k_s (k_s apparent rate constant) on ln c_A and π (π = surface film pressure), respectively, has been found.     

A study on chloride-induced depassivation of mild steel in simulated concrete pore solution

The effect of chloride ions on passivity breakdown of steel in simulated concrete pore (SCP) solution was studied using electrochemical techniques. In this regards, the sensitivity of cyclic potentiodynamic parameters such as ΔE (difference between E_pit and E_rep), i_peak and AC-impedance parameters like R_ct, R_f, C_i, R_ad and C_ad to chloride ion concentration was investigated. Adsorption of OH⁻ ions on the metal surface in free chloride SCP solution and also displacement of those ions by Cl⁻ ions were demonstrated in high frequency part of Nyquist plots. In addition, a severe decrease in resistance of interfacial reaction (R_f+R_ct) was observed through breakdown of passive film in the [Cl⁻]/[OH⁻] ratio of 0.6. The interfacial capacitance, C_i, was abruptly raised when localized corrosion changed to general one.     

磁场对(C4H9NH3)2(CH3NH3)Pb2I7钙钛矿发光特性调控的研究

(C₄H₉NH₃)₂(CH₃NH₃)Pb₂I₇是一种Ruddlesden-Popper相钙钛矿材料，具有层状结构，层间通过van der Waals力结合，因此可以通过机械剥离的方法，获得其二维薄层。二维(C₄H₉NH₃)₂(CH₃NH₃)Pb₂I₇内束缚激子会自发复合从而表现出强的荧光，其圆极化率、峰位均受磁场调控。在外磁场中，荧光圆极化率与磁场呈线性关系，激子中电子和空穴之间的朗德因子差Δg约为0.43。束缚激子在磁场中受抗磁效应影响，致使其发光峰随磁场增加而红移。     

The electrochemistry of organotellurium compounds—I. The class of aryltellurium trichlorides

The electrochemical behaviour of various classes of organotellurium compounds in methylene chloride containing tetrabutylammonium perchlorate (TBAP) as supporting electrolyte was studied. It was found that the half-wave potentials of the reduction waves of the p-substituent ArTeCl₃ are linearly proportional to the corresponding substituent constants (ΔE_1/2/Δδp = 0.73 V).

Artyltellurium trichlorides were found to be reduced in a one-electron pathway to the corresponding ditellurides followed by disproportionation of the ditellurides to tellurides. In some cases, as in the reduction of PhTeCl₃, metallic tellurium was deposited on the electrode at a very low faradaic efficiency.     

Polarographic studies of copper(II) in aqueous dimethylsulphoxide and aqueous acetone and free energy of transfer of copper(I) and copper(II) from water to dimethyl-sulphoxide-water mixtures

Polarographic studies of Cu(ClO₄)₂ in aqueous dimethylsulphoxide (DMSO) mixtures have identified compositions in which Cu(I) is stable. The half-wave potentials E_1/2, of Cu(II)/Cu(I) and Cu(I)/Cu(Hg) decrease in DMSO-water mixtures and values of free energies of transfer, ΔG_tr, of Cu(II) and Cu(I) from water to aqueous DMSO are reported. Similar measurement in aqueous acetone mixtures show that ΔG_tr Cu(II) increases upon addition of acetone.     

Phase transformations in mesostructured vanadium–phosphorus-oxides

Mesostructured lamellar, hexagonal and cubic vanadium–phosphorus-oxide (VPO) phases were prepared employing cationic, anionic and alkylamine surfactants under mild conditions and low pH. The obtained mesophases displayed desirable vanadium oxidation states (+3.8 to +4.3) and P/V molar ratios 1.0 for the partial oxidation of n-butane to maleic anhydride. As-synthesized mesostructured VPO underwent phase transformations to various mesostructured and dense VPO phases depending on the post-synthesis treatment. The phase transformations of mesostructured VPO during Soxhlet extraction and thermal treatment in N₂ have been observed for the first time. These transformations were explained by the changes in the surfactant packing parameter, g. Calcination in air produced more disordered mesostructures and dense VPO phases such as γ-VOPO₄ and (VO)₂P₂O₇.     

Deformation kinetics of ageing materials

A constitutive equation of time-dependent, chemically stable materials, which stems from the basic ideas of the irreversible thermodynamics of an internal variable and Eyring's absolute reaction rate theory, has been extended to chemically unstable materials. This formulation is quite general and, in principle, can be applied to many types of materials. In this paper, the ageing behaviour of time-dependent network polymers undergoing chain scission is considered. In the network scission process, we postulate that the energy barrier is affected by a changing of the chemical crosslink density. An explicit equation to account for the energy barrier change, which influences the relaxation process, is formulated. For the purpose of illustration, the effect of different chemical crosslink density, ν, on the relaxation rate has been considered, from which the following theoretical expression of relaxation modulus ΔE(t) is obtained:

ΔE = ΔE[t exp (γv/kT)]

It can be seen that a change in v leads to an effective change in the time scale, usually denoted by a_x. Here the analytical expression a_x = exp(γν/kT) correlates quite well with the experimental data.     

Radiation graft-copolymerization kinetics of poly(ethylene terephthalate) fibres

A theoretical analysis of radiation grafting kinetics has been made in terms of the quantitative interrelationship between the degree of grafting (G_f), the grafting periods (t) grafting temperature (T) and the monomer content in the polymeric system (M). Poly(ethylene terephthalate) fibres and a number of hydrophilic monomers have been employed for these experiments. The grafting reactions were initiated by trapped radicals produced by irradiation of the polymeric system under vacuum at room temperature. Experimental results showed that the monomer content in the fibres obeyed the Arrhenius relationship. The overall activation energy of the grafting reaction has been calculated. Grafting reactions can proceed only if ΔE_t > ΔE_p + ΔE_M. This termination activation energy ΔE_t is a function of the state of polymeric system.     

KBaB5O9的两步法制备及其过程动力学研究

本文利用溶液法制备了K₂Ba[B₄O₅(OH)₄]₂·8H₂O,并将其进行热处理制备得到了KBaB₅O₉,利用XRD、FT-IR、TG-DTA-DTG对样品进行了表征。分析研究了由K₂Ba[B₄O₅(OH)₄]₂·8H₂O热处理制备KBaB₅O₉过程中的物相变化过程,其物相变化经历脱结晶水、脱羟基、重结晶、再分解、熔融再结晶5个阶段,其中结晶水的脱失分两步进行。运用Kissinger法、Flynn-Wall-Ozawa法、Šatava-Šesták法对K₂Ba[B₄O₅(OH)₄]₂·8H₂O结晶水第二步脱失过程的动力学参数进行了计算,可知K₂Ba[B₄O₅(OH)₄]₂·8H₂O结晶水第二步脱失过程的活化能E_s为151.94 kJ/mol,指前因子的对数值lg A_s为21.25 min^-1,机理函数G(α)=(1-2α/3)-(1-α)^2/3(其中α为转化率)。     

Stress measurements in high-shear granulators using calibrated “test” particles: application to scale-up

Granulation is a process by which fine powders are agglomerated into larger particles using a liquid binder. In high-shear granulation the powder–binder mix experiences intense agitation inside a mixing vessel as binder is dispersed and granules form and strengthen under the influence of shear and compacting forces in the device.

It is an implicit assumption that in a “high shear” mixer, large forces are transmitted to the powder and this results in a short and efficient granulation process. Owing to these desirable characteristics, high-shear granulation was adopted by several industries including pharmaceuticals and detergents where the process is used almost exclusively. In the work reported here, we attempt to measure shear forces in a moving powder inside a mixer-granulator. The method is based on previous numerical simulations [Powder Technology 110 (2000) 59] and experiments [Journal of Fluid Mechanism 347 (1997) 347] where we showed that at equilibrium between stresses in the mixer and the yield strength of the particles, granules attain a characteristic elongated shape. The measuring method adopted is indirect in the sense that pellets with well-defined mechanical properties were used to interrogate forces inside the granulating vessel at the point where they attain their characteristic elongated shape. We subsequently used the condition of equal shear forces in the device as a scale-up criterion so as to preserve the magnitude of stresses at both scales and thereby to expose forming granules to similar forces in both the small- and large-scale machines.

We found that shear forces in a “High-Shear” mixer-granulator with a vertical axis (Fielder) are actually not always high. The mixer has the potential to produce high shear forces but these forces are transmitted to the powder mass only if the powder is sufficiently cohesive or becomes cohesive due to binder addition. Shear forces in the granulator are strongly wet-mass-dependent and they increase rapidly as soon as a “granulation limit” is achieved, i.e., at the point where granules start to form in the shearing powder mass. We found that granulators with geometrically similar bowls can be scaled to generate comparable shear forces by decreasing the impeller rotational speed of the large machine by the factor (D/d)ⁿ, where D and d are the impeller diameters of the large and small machine, respectively, and n is a scaling index that depends on impeller geometry but not on wet mass properties. For the equipment studied in this work, the coefficient n was obtained as 0.80<n<0.85. We also propose an improved granulation process in which dry powders are pre-wetted before introduction into the main granulating device. This scheme has the potential to produce larger shear forces during wetting and binder introduction and thereby improve homogeneity and consequently final granule properties.     

Microwave dielectric properties of rutile (Zn1/3Nb2/3)0.40(Ti1−xSnx)0.60O2 (0.15 ≤ x ≤ 0.30) ceramics

Microwave dielectric properties of (Zn_1/3Nb_2/3)_0.40(Ti_1−xSn_x)_0.60O₂ ceramics were investigated as a function of SnO₂ content (0.15 ≤ x ≤ 0.30). A single phase with tetragonal rutile structure was obtained through the entire composition. The unit-cell volume of the specimens was increased with SnO₂ content, due to the larger ionic radius of Sn⁴⁺ (0.69 Å) than that of Ti⁴⁺ (0.605 Å) for octahedral site. Dielectric constant (K) of the sintered specimens was affected by the dielectric polarizability. Quality factor (Qf) was dependent on the degree of reduction of Ti⁴⁺ ion. With an increase of SnO₂ content, the temperature coefficient of resonant frequency (TCF) of the specimens decreased due to the decrease of the octahedral distortion of rutile structure.     

Physico-Chemical Criteria for Maximum Adhesion. Part II: A New Comprehensive Thermodynamic Analysis

In this paper, two parameters defined as the relative work of adhesion [W_A/γ_L] and the relative interfacial energy [γ_SL/γ_L] have been examined for their assumed usefulness in correlating the thermodynamic properties of the components of the system substrate/ adhesive with its practical performance (strength). It is shown that the minimum value of [γ_SL/γ_L] relevant to conditions for the maximum adhesion becomes zero only for those systems (relatively rare) for which interaction factor Φ₀ is equal to 1.0.

Several transition points were identified for boundary conditions acquired at θ = 0° and θ = 90° which can be used to predict the properties and performance of an adhesive joint. These transition points are: a_MIN—energy modulus of the system (E. M. S.), relevant to the minimum interfacial energy; a_S—E. M. S. where self-spreading of adhesive occurs; a_CRIT—E. M. S. relevant to conditions under which the thermodynamic work of adhesion becomes negative and the system exhibits a tendency for self-delaminating or has “zero-strength”; a_CF—E. M. S. beyond which the geometry of the interface at any interfacial void or boundary of the joint may be regarded as a crack tip.

It is shown that only in those systems for which Φ₀ = 1.0 can a minimum contact angle of 0° indicate a condition for the maximum strength. If Φ₀ is known, the optimum contact angle can be estimated and hence the optimum surface energy of the substrate (adjusted by surface treatment, etc.) for the maximum adhesion.