Thermal runaway prediction for impregnated activated carbons from isothermal DSC measurements

Isothermal DSC measurements are used to extract the kinetics of the reaction between activated carbon, which has been impregnated with K₂CO₃, and air at elevated temperature. For the carbon studied here, the reaction takes place in two apparently independent processes. In the first process, the surface functional groups react with the carbon and with air, and in the second process the remaining carbon reacts with air. The impregnate causes the dramatic acceleration of the reaction compared to the reactivity of the pure base carbon in air. The reaction of the surface functional groups with air obeys the following reaction for the fractional degree of conversion, dα₁/dt=γ₁ exp(−E_a1/k_BT) α₁^m (1−α₁)ⁿ, with m and n approximately equal to −0.95 and 0.5, respectively. The reaction of the remaining carbon with air follows zero-order reaction kinetics. The obtained reaction kinetics can fit the results of isothermal DSC measurements over a wide range of temperature and scanning DSC measurements over a wide range of sweep rates, without any adjustment of parameters. The reaction kinetics, among other experimentally-derived parameters, were then used to calculate the temperature-time profiles for samples of carbon held in stainless steel mesh cylinders of various diameters within a heated constant-temperature oven. These calculations are shown to agree well with experiments at numerous temperatures for two cylinder radii using the same set of kinetic parameters used to fit the DSC results. Some of the temperatures and radii were selected such that thermal runaway of the carbon sample would occur, and the simulations modeled the time and temperature of this runaway accurately. Therefore, it should now be possible to simulate the temperature-time response of this particular impregnated carbon to conditions of high-temperature storage, such as those of the IATA oven exposure test or to storage within a shipping container exposed to a particular thermal history.     

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.     

Application of [001]-textured (K,Na)(Nb,Sb)O3-CaZrO3 thick films to piezoelectric energy harvesters

A (K, Na)NbO₃ (KNN)-based lead-free piezoceramic for a piezoelectric energy harvester (PEH) should exhibit a large k_ij, Q_m, d_ij, and a small ε^T₃₃ to generate a large power output. Texturing was used to enhance the piezoelectricity of KNN-related piezoceramics. In particular, the k_ij and d_ij values of the KNN-based piezoceramics were considerably improved after texturing along the [001] direction, with a small change in the ε^T₃₃/ε₀ value, indicating that the [001]-textured KNN-based thick films are good candidates for use in PEHs. The 0.97(K_0.5Na_0.5)(Nb_0.93Sb_0.07)O₃-0.03CaZrO₃ [KN(N_0.93S_0.07)-CZ] thick film was textured along the [001] direction, and this thick film exhibited a large k_p (0.57) and d₃₃ × g₃₃ (25.7 pm²/N), which is the largest d₃₃ × g₃₃ of the KNN-based piezoceramics reported to date. A cantilever PEH fabricated using the textured KN(N_0.93S_0.07)-CZ thick film exhibited a power density of 21.4 μW/mm³ at the resonance frequency. This is the highest power density observed for PEHs fabricated using lead-free piezoceramics. The PEH also exhibited a power density of 0.023 μW/mm³ at the off-resonance frequency. Therefore, the textured KN(N_0.93S_0.07)–CZ thick film is a good candidate for use in PEHs.     

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.     

NO2 inhibits the catalytic reaction of NO and O2 over Pt

The rate equation for the overall reaction of NO and O₂ over Pt/Al₂O₃ was determined to be r=k_f[NO] ^1.05±0.08[O₂]^1.03±0.08[NO₂]^0.92±0.07(1-), with k_f as the forward rate constant, =([NO₂]/K[NO][O₂]^1/2), and K as the equilibrium constant for the overall reaction. An apparent activation energy of 82 kJ mol^–1 ± 9 kJ mol^–1 was observed. The inhibition by the product NO₂ makes it imperative to include the influence of NO₂ concentration in any analysis of the kinetics of this reaction. The reaction mechanism that fits our observed orders consists of the equilibrated dissociation of NO₂ to produce a surface mostly covered by oxygen, thereby inhibiting the equilibrium adsorption of NO, and the non-dissociative adsorption of O₂, which is the proposed rate determining step.     

Fabrication and electrical properties of textured (Na,K)0.5Bi0.5TiO3 ceramics by reactive-templated grain growth

Textured (Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (NKBT) ceramics with a relative density of >94% were fabricated by reactive-templated grain growth. Plated-like Bi₄Ti₃O₁₂ template particles synthesized by the NaCl–KCl molten salt process were aligned by tape casting in a mixture of original oxide powders. The effect of sintering temperature on the grain orientation and electrical properties of textured NKBT ceramics were investigated. The results show that the textured ceramics have a microstructure with plated-like grains aligning in the direction parallel to the casting plane. The degree of grain orientation increased at increasing sintering temperature. The textured ceramics show anisotropic electrical properties in the directions parallel and perpendicular to the casting plane. The dielectric constant parallel to {h 0 0} plane is three times higher than that of the perpendicular direction in textured NKBT ceramics. The optimized sintering temperature is 1150 °C where the maximum dielectric constant is 2041, the remnant polarization is 68.7 μC/cm², the electromechanical coupling factor (k₃₁) and the piezoelectric constant (d₃₃) amount to 0.31 and 134 pC/N, respectively.     

Shrinking-core model for systems with facile heterogeneous and homogeneous reactions

The shrinking-core equation for pore diffusion control has been extended to the case of a facile heterogeneous reaction coupled to a facile homogeneous reaction occurring within the pores of the product layer and in the bulk solution. The model considered is very general in that the simultaneous transport of all reacting species is included. The resulting equation is identical to the standard one for diffusional control by a single species except that the parabolic rate constant k_d is considerably more complex and contains useful information concerning the system. Analysis of its dependence on the system parameters yields important criteria that determine the identity of the rate-controlling species and the direction of the heterogeneous reaction. Depending upon the relative values of the equilibrium constants of the two reactions, the dependence of k_d on the bulk reactant concentration can vary significantly from the linearity expected from the standard model.     

Phase-formation,microstructure, and piezoelectric/dielectric properties of BiYO3-doped Pb(Zr0.53Ti0.47)O3 for piezoelectric energy harvesting devices

This paper proposes a method for the composition and synthesis of lead zirconate titanate (PZT) piezoelectric ceramic for use in energy harvesting systems. The proposed material consists of (1?x)Pb(Zr_0.53Ti_0.47)O₃–xBiYO₃ [PZT–BY(x)] (x=0, 0.01, 0.02, 0.03, 0.04, and 0.05 mol) ceramics near the morphotropic phase boundary (MPB) region, prepared by a solid-state mixed-oxide method. The optimum sintering temperature was found to be 1160 °C, which produced high relative density for all specimens (96% of the theoretical density). Second phases were found to precipitate in the composition containing x≥0.01 mol of BY. It is shown that the addition of BY inhibits grain growth, and exhibits a denser and finer microstructure than those in the un-doped state. Fracture surface observation revealed predominant intergranular fracture for x=0 and x=0.01, while a mixed mode of transgranular and intergranular fracture appeared for x≥0.02. The optimal doping level was found to be x=0.01, for which a dielectric constant (K₃₃^T) of 750, a Curie temperature (T_C) of 373 °C, a remnant polarization (P_r) of 50 µC/cm², a piezoelectric constant (d₃₃) of 350 pC/N, and an electro-mechanical coupling factor (k_p) of 65% were obtained. In addition, the piezoelectric voltage constant (g₃₃), and transduction coefficient (d₃₃×g₃₃) of PZT–BY(x) ceramics have been calculated. The ceramic PZT–BY(0.01) shows a considerably lower K₃₃^T value, but higher d₃₃ and k_p. Therefore, the maximum transduction coefficient (d₃₃×g₃₃) of 18,549×10^?15 m²/N was obtained for PZT–BY(0.01). The large (d₃₃×g₃₃) indicates that the PZT–BY(0.01) ceramic is a good candidate material for energy harvesting devices.     

Modelling the post treatment process of model implants prepared by in situ polymerized poly(ε-caprolactone) using a BF3-glycerol catalyst system

The post treatment process of a poly(ε-caprolactone) (PCL) model implant prepared using a boron trifluoride (BF₃) catalyst and glycerol initiator by in situ polymerisation process for craniofacial and maxillofacial treatment is modelled using a ‘moving-boundary’ diffusion model. A numerical method was used to solve a system of diffusion equations of the model. The variable diffusion coefficient (D) was correlated with crystallinity (x_c) of the polymer which is a function of its molecular weight (M_w) and its degradation rate constant (k_d), D=f(x_c(M_w,k_d)). The post treatment time and the molecular weight retained after post treatment can be obtained using this model. The modelling results show that the process is potentially suitable for manufacturing thin model implants of complex shape.     

Preparation and characterization of a macroporous agarose monolith as a stationary phase in IMAC chromatography

A macroporous monolith used as stationary phase for the separation of biomolecules by immobilized metal ion affinity chromatography (IMAC), based on D5 agarose (D5) chemically modified was proposed. The characterization of physical properties was studied. Pressure drop was <0.4?MPa, being a very low value compared to other similar chromatographic supports. The adsorption/desorption process was carried out using bovine serum albumin (BSA) at pH 7.4 as a target protein. The monolith was re-used for 20 adsorption/desorption cycles and it was possible to verify that the average percentage of adsorption in all cycles was 89.65%. It was also possible to apply a model in order to obtain the kinetic adsorption constant (k_a), desorption constant (k_d) and equilibrium constant (K_e) by the proposed system. These results indicate that this system is governed by the adsorption process.     

The kinetics of enzyme catalyzed synthesis of sterol ester

The production of sterol ester by transesterification of β‐sitosterol with fish oil (TAG) catalyzed by Thermomyces lanuginosus immobilized lipase enzyme with varied reaction parameters such as temperature, substrate molar ratio, concentration of enzyme to deduce the enzyme kinetics for the reaction was investigated. For this transesterification reaction, the kinetic model was derived by using Ping Pong Bi Bi Mechanism. The K_m value from the first plot containing fish oil as substrate was 1.31 ± 0.05, while K_m from the second plot containing β‐sitosterol as substrate was 1.01 ± 0.04; identical V_max (0.213 ± 0.06) values were obtained by keeping one of the substrate concentration constant and varying the other. Practical applications : Deduction of reaction kinetics is an important criterion to ascertain the viability of any chemical process. Enzymatic processes need special attention to set model reaction parameters which could help in optimization or design of the actual process. In the present study we have derived the enzyme kinetics for the production sterol ester, an important nutraceutical, and calculated its K_m and V_max values along with the Arhenius activation energy to establish the viability of the reaction.     

活性焦汞吸附特性及动力学机理分析

通过固态吸附剂汞吸附效能测定系统进行了太西活性焦吸附单质汞的实验,考察单质汞Hg⁰入口浓度和温度对太西活性焦脱汞性能的影响并探讨了吸附机理。结果表明:在CO₂/N₂/O₂/NO/Hg⁰体系中,不同Hg⁰入口浓度获得的汞脱除效率曲线相似,脱除效率随Hg⁰入口浓度增大而增加;变入口浓度工况下,汞的吸附全过程遵循准二级动力学反应模型,该吸附过程以化学吸附为主;在反应温度从403 K升高到423 K的过程中,系统发生了化学吸附或者化学反应,423 K可作为活性焦的最佳除汞温度;Bangham方程可对变温工况下活性焦脱除单质汞的吸附过程进行准确描述,并获得不同温度下活性焦脱汞的吸附速率常数存在k_423K>k_463K>k_403K的关系。     

Investigation of flue-gas treatment with O3 injection using NO and NO2 planar laser-induced fluorescence

Direct ozone (O₃) injection is a promising flue-gas treatment technology based on oxidation of NO and Hg into soluble species like NO₂, NO₃, N₂O₅, oxidized mercury, etc. These product gases are then effectively removed from the flue gases with the wet flue gas desulfurization system for SO₂. The kinetics and mixing behaviors of the oxidation process are important phenomena in development of practical applications. In this work, planar laser-induced fluorescence (PLIF) of NO and NO₂ was utilized to investigate the reaction structures between a turbulent O₃ jet (dry air with 2000 ppm O₃) and a laminar co-flow of simulated flue gas (containing 200 ppm NO), prepared in co-axial tubes. The shape of the reaction zone and the NO conversion rate along with the downstream length were determined from the NO-PLIF measurements. About 62% of NO was oxidized at 15d (d, jet orifice diameter) by a 30 m/s O₃ jet with an influence width of about 6d in radius. The NO₂ PLIF results support the conclusions deduced from the NO-PLIF measurements.     

Kinetics for free radical solution polymerization of heptadecafluorodecyl (meth)acrylate in supercritical carbon dioxide

Free radical solution polymerization of heptadecafluorodecyl acrylate (HDFDA) and heptadecafluorodecyl methacrylate (HDFDMA) was carried out by using 2,2′-azobisisobutyronitrile (AIBN) as the initiator in supercritical carbon dioxide (scCO₂). We performed solution polymerization with changing initiator concentration, temperature and polymerization time to study the polymerization kinetics. A nonlinear least square method and dead-end theory were used to determine the constant, K (K=(k _p √f)/√k _d k _d ) and initiator decomposition rate constant (k _d ) from experimental data. k _d was measured as 3.77 × 10⁻⁵ s⁻¹ at 62.7°C for poly(HDFDA) and 2.71 × 10⁻⁵ s⁻¹ at 62.5 °C for poly(HDFDMA), respectively, by nonlinear least square method.     

Kinetics of the metal exchange reaction of a Cu(II)-poly(vinyl alcohol) complex with Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid in aqueous solution

The kinetics of the metal exchange reaction between Cu(II)-poly(vinyl alcohol) [Cu(II)-PVA] and Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid [Zn(II)-EDTA] has been studied by mixing both solutions in a spectrophotometer at pH 10.0 to 11.0, ionic strength μ=0.10(KNO₃), and 15 to 35°C. The reaction is initiated by the formation of unstable Cu(II)-H-PVA through attack of H⁺ ion on the Cu(II)-PVA complex, and both reactions, ligand exchange and metal exchange, proceed simultaneously. The metal exchange step may be rate determining. The rate equation and rate constants of this reaction were determined as follows: ?d[Cu(II)-PVA]/dt=k _0(H)[PVA^?][Cu(II)-PVA] [Zn(II)-EDTA], wherek _0(H)=k ₁+(k′₂+k′₃)[H⁺],k ₁=5.98±1.64M ^?1 s^?1, andk ₂+k ₃=k′₂ K _Cu(II)-H-PVA ^?H +k′₃ K _Zn(II)-EDTA ^H =(5.91±0.89)×10⁷ M ^?2 s^?1.     

Kinetics of the metal exchange reaction of a Cu(II)-poly(vinyl alcohol) complex with Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid in aqueous solution

The kinetics of the metal exchange reaction between Cu(II)-poly(vinyl alcohol) [Cu(II)-PVA] and Zn(II)-ethylenediamine-N,N,N,N-tetraacetic acid [Zn(II)-EDTA] has been studied by mixing both solutions in a spectrophotometer at pH 10.0 to 11.0, ionic strength =0.10(KNO₃), and 15 to 35°C. The reaction is initiated by the formation of unstable Cu(II)-H-PVA through attack of H⁺ ion on the Cu(II)-PVA complex, and both reactions, ligand exchange and metal exchange, proceed simultaneously. The metal exchange step may be rate determining. The rate equation and rate constants of this reaction were determined as follows: –d[Cu(II)-PVA]/dt=k _0(H)[PVA^–][Cu(II)-PVA] [Zn(II)-EDTA], wherek _0(H)=k ₁+(k₂+k₃)[H⁺],k ₁=5.98±1.64M ^–1 s^–1, andk ₂+k ₃=k₂ K _Cu(II)-H-PVA ^–H +k₃ K _Zn(II)-EDTA ^H =(5.91±0.89)×10⁷ M ^–2 s^–1.     

Physical properties, crystallization kinetics, and spherulitic growth of well-defined poly(ε-caprolactone)s with different arms

Both well defined star-shaped poly(ε-caprolactone) having four arms (4sPCL) and six arms (6sPCL) and linear PCL having one arm (LPCL) and two arms (2LPCL) were synthesized and then used for the investigation of physical properties, isothermal and nonisothermal crystallization kinetics, and spherulitic growth. The maximal melting point, the cold crystallization temperature, and the degree of crystallinity of these PCL polymers decrease with the increasing number of polymer arms, and they have similar crystalline structure. The isothermal crystallization rate constant (K) of these PCL polymers is in the order of K_2LPCL>K_LPCL>K_4sPCL>K_6sPCL. Notably, the K of linear PCL decreases with the increasing molecular weight of polymer while that of star-shaped PCL inversely increases. The variation trend of K over the number of polymer arms or the molecular weight of polymer is consistent with the analyses of both nonisothermal crystallization kinetics and the spherulitic growth rate. These results indicate that both the number of polymer arms and the molecular weight of polymer mainly controlled the isothermal and nonisothermal crystallization rate constants, the spherulitic growth rate, and the spherulitic morphology of these PCL polymers.     

Determination of initiator decomposition constant in a heterogeneous polymerisation system

A new method for determination of initiator decomposition constant k_d is described based on the use of instantaneous polymerisation rates for two similar experiments run with different initiator concentrations. The constant found will be specific for the polymerisation system used. If the propagation and termination rate constants for the monomer are known from other studies the initiator efficiency factor f can then be obtained. To verify the validity of the method, poly(vinyl chloride) latexes were prepared by potassium persulphate (K₂S₂O₈) initiated polymerisation of submicron-sized monomer droplets. The monomer droplets were obtained by diffusion of vinyl chloride monomer into a preformed emulsion of water-insoluble oil droplets. The polymerisation was performed in an isothermal calorimeter. From the measured heat evolution, the instantaneous polymerisation rates were calculated. The thermal decomposition constant of potassium persulphate k_d was determined to be 2·5×10^-6s^-1 at 51°C. In the same system the order of reaction with respect to the initiator concentration was found to be 0·50. © 1998 SCI.