Thermodynamic functions of the grain-like ZnO nanostructures

Grain-like ZnO nanostructures were prepared by a simple microemulsion-mediated hydrothermal route, and were characterized by X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). In order to associate thermodynamic functions of nano ZnO with bulk ZnO, a novel thermochemical cycle was designed. Combined with in situ microcalorimetry, the standard molar enthalpy of formation, standard molar Gibbs free energy of formation and standard molar entropy of the obtained products at 298.15 K were successfully acquired as (? 322.36 ± 0.42) kJ mol^? 1, (? 318.74 ± 0.03) kJ mol^? 1 and (44.61 ± 1.02) J mol^? 1 K^? 1, respectively.     

Removal of Congo Red from aqueous solution by cattail root

In this study, cattail root was used to remove Congo Red (CR) from aqueous solution. The effects of operation variables, such as cattail root dosage, contact time, initial pH, ionic strength and temperature on the removal of CR were investigated using batch adsorption technique. Removal efficiency increased with increase of cattail root dosage and ionic strength, but decreased with increase of temperature. The equilibrium data fitted well to the Langmuir model (R² > 0.98) and the adsorption kinetic followed the pseudo-second-order equation (R² > 0.99). Thermodynamics parameters such as standard free energy change (ΔG°), standard enthalpy change (ΔH°), and standard entropy change (ΔS°) were analyzed. The values of ΔG° were between ?7.871 and ?4.702 kJ mol^?1, of ΔH° was ?54.116 kJ mol^?1, and of ΔS° was ?0.157 kJ mol^?1 K^?1, revealing that the removal of CR from aqueous solution by cattail root was a spontaneous and exothermic adsorption process. The maximum adsorption capacities of CR on cattail root were 38.79, 34.59 and 30.61 mg g^?1 at 20, 30 and 40 °C, respectively. These results suggest that cattail root is a potential low-cost adsorbent for the dye removal from industrial wastewater.     

Solid-phase crystallization of spray-dried glucose powders: A perspective and comparison with lactose and sucrose

The solid-phase crystallization growth kinetics of spray-dried sugar powders, including glucose, lactose and sucrose, have been studied from water-induced crystallization experiments at a relative humidity of 75% and temperatures from 15 to 40 °C on amorphous powders of these sugars produced in a laboratory-scale spray dryer (Buchi B290). All results have shown that the enthalpies and Gibbs Free Energies of activation of the sugars studied here increase during the crystallization process, suggesting that the binding energy needed for the formation of an activated complex increases as the moisture content decreases. The enthalpies of activation for glucose, lactose and sucrose crystallization have been compared by the Activated Rate equation and found to be 58 ± 8 kJ mol⁻¹, 39 ± 2 kJ mol⁻¹ and 68 ± 4 kJ mol⁻¹, for glucose, lactose and sucrose, respectively, Similarly, the entropies of activation have been calculated as −92 ± 27 J mol⁻¹ K⁻¹, −156 ± 6 J mol⁻¹ K⁻¹ and −60 ± 5 J mol⁻¹ K⁻¹ for glucose, lactose and sucrose, respectively. These different numerical values may be expected from the different structures of the sugars.     

Effect of heat treatment on morphology and thermal decomposition kinetics of multiwalled carbon nanotubes

High temperature treatment in inert atmosphere proved to be an effective way to improve high temperature stability of MWNTs in ambient condition. TEM analysis of heat-treated MWNTs confirmed successful removal of impurities and formation of ordered graphene layers and internal bamboo structure. TG–DTG curves indicated that decomposition range and rate of as-received MWNTs were narrow and notably higher, respectively, than heat-treated MWNTs mainly due to presence of impurities like metal nanoparticles in the former. Non-isothermal kinetic analysis revealed that the rate determining mechanism for as-received MWNTs was random nucleation and growth of active species. However, for heat-treated MWNTs, rate controlling mechanism was chemical reaction. Higher activation energies (～203 kJ mol^?1 and 280 kJ mol^?1) and reaction orders (3 and 4) of MWNTs heat-treated at 1200 °C and 1800 °C in inert, respectively, indicated delayed thermal decomposition than as-received MWNTs (E_a ≈ 178 kJ mol^?1; n = 1) even in oxidative atmosphere.     

Thermal behavior of some organic/inorganic composites based on epoxy resin and calcium carbonate obtained from conch shell of Rapana thomasiana

Thermal behavior of some diglycidyl ether of bisphenol A/p-aminobenzoic acid systems with calcium carbonate as a filler were studied. The kinetics parameters of the curing reactions were estimated using the variable peak exotherm method of Kissinger and Ozawa. The most probable kinetic model and the kinetic parameters of the degradation process were also estimated. The energies of crosslinking reactions are situated in the range of 46–57 kJ mol^?1 for the first exotherm and between 68 and 72 kJ mol^?1 for the second exotherm. The cured resins have a good thermal stability and the activation energies of degradation reactions are situated in the range of 178–218 kJ mol^?1.     

Thermal conductivity and Kapitza resistance of cyanate ester epoxy mix and tri-functional epoxy electrical insulations at superfluid helium temperature

In the framework of the European Union FP7 project EuCARD, two composite insulation systems made of cyanate ester epoxy mix and tri-functional epoxy (TGPAP-DETDA) with S-glass fiber have been thermally tested as possible candidates to be the electrical insulation of 13 T Nb₃Sn high field magnets under development for this program. Since it is expected to be operated in pressurized superfluid helium at 1.9 K and 1 atm, the thermal conductivity and the Kapitza resistance are the most important input parameters for the thermal design of this type of magnet and have been determined in this study. For determining these thermal properties, three sheets of each material with different thicknesses varying from 245 to 598 μm have been tested in steady-state condition in the temperature range of 1.6–2.0 K. The thermal conductivity for the tri-functional epoxy (TGPAP-DETDA) epoxy resin insulation is found to be k = [(34.2 ± 5.5)?T ? (16.4 ± 8.2)] × 10^?3 Wm^?1 K^?1 and for the cyanate ester epoxy k = [(26.8 ± 4.8)?T ? (9.6 ± 5.2)] × 10^?3 Wm^?1 K^?1. For the Kapitza resistance, R_k, the best curve fitting the experimental data is described by R_k = (3057 ± 593) × 10^?6?T (?1.79 ± 0.34) m² KW^?1 for the TGPAP-DETDA insulation and R_k = (4114 ± 971) × 10^?6?T (?1.73 ± 0.41) m² KW^?1 for the cyanate ester epoxy insulation. Our results are compared with other epoxy based composite electrical insulation found in the literature.     

Kinetics of aluminum dross dissolution in sec-butyl alcohol for aluminum sec-butoxide

Al sec-butoxide (ASB) has been used as a precursor for activated aluminas but its cost is higher than any other type of precursor. This study was carried out on the dissolution kinetics for synthesis of the ASB from Al dross waste. The reaction was performed under the molar ratio of Al dross and sec-butyl alcohol (SBA) of 3 mol SBA/mol Al with a catalyst of 10^?3 mol HgI₂/mol Al and three different dissolution temperatures of 80, 90 and 100 °C. The Al reactant was used with Al dross of 3–5 mm size range. As a result of the experiment, the dissolution reaction gave a 65% yield after 24 h. The dissolution mechanism was determined by the shrinking core model assumed by the shape of spherical particles. Especially, the kinetic data were well fitted by a chemical reaction in the model. By the Arrhenius equation, the apparent activation energy was determined to be 40.9 kJ mol^?1 at the given reaction temperatures.     

Preparation of biomorphic porous calcium titanate and its application for preconcentration of nickel in water and food samples

Biomorphic porous nanocrystalline-calcium titanate (SPCTO) was successfully prepared using the sol–gel method and with sorghum straw as the template. Characterization was conducted through XRD, SEM and FTIR. The ability of SPCTO to adsorb nickel ion in water was assessed. Elution and regeneration conditions, as well as the thermodynamics and kinetics of nickel adsorption, were also investigated. The result showed that the sorbent by the sol–gel template method was porous and has a perovskite structure with an average particle diameter of 26 nm. The nickel ion could be quantitatively retained at a pH value range of 4–8, but the adsorbed nickel ion could be completely eluted using 2 mol L^? 1 HNO₃. The adsorption capacity of SPCTO for nickel was found to be 51.814 mg g^? 1 and the adsorption behavior followed a Langmuir adsorption isotherm and a pseudo-second-order kinetic model. The enthalpy change (ΔH) of the adsorption process was 33.520 kJ mol^? 1. At various temperatures, Gibbs free energy changes (ΔG) were negative, and entropy changes (ΔS) were positive. The activation energy (E_a) was 25.291 kJ mol^? 1 for the adsorption. These results demonstrate that the adsorption was an endothermic and spontaneous physical process. This same method has been successfully applied in the preconcentration and determination of nickel in water and food samples with good results.     

A capric–palmitic–stearic acid ternary eutectic mixture/expanded graphite composite phase change material for thermal energy storage

This paper demonstrated a capric acid–palmitic acid–stearic acid ternary eutectic mixture/expanded graphite (CA–PA–SA/EG) composite phase change material (PCM) for low-temperature heat storage. The CA–PA–SA ternary eutectic mixture with a mass ratio of CA:PA:SA = 79.3:14.7:6.0 was prepared firstly, and its mass ratio in the CA–PA–SA/EG composite can reach as high as 90%. The melting and freezing temperatures of CA–PA–SA/EG composite were 21.33 °C and 19.01 °C, and the corresponding latent heat were 131.7 kJ kg⁻¹ and 127.2 kJ kg⁻¹. The CA–PA–SA/EG composite powders can be formed into round blocks by dry pressing easily, with much higher thermal conductivity than CA–PA–SA. Thermal performance test showed that the increasing thermal conductivity of CA–PA–SA could obviously decrease the melting/cooling time. Thermal property characterizations after 500 heating/cooling cycles test indicated that CA–PA–SA/EG composite PCM had excellent thermal reliability. Based on all these results, CA–PA–SA/EG composite PCM is a promising material for low-temperature thermal energy storage applications.     

Measurement and correlation of frictional pressure drop of refrigerant-based nanofluid flow boiling inside a horizontal smooth tube

The objective of this paper is to investigate the effect of nanoparticle on the frictional pressure drop characteristics of refrigerant-based nanofluid flow boiling inside a horizontal smooth tube, and to present a correlation for predicting the frictional pressure drop of refrigerant-based nanofluid. R113 refrigerant and CuO nanoparticle were used for preparing refrigerant-based nanofluid. Experimental conditions include mass fluxes from 100 to 200 kg m^?2 s^?1, heat fluxes from 3.08 to 6.16 kW m^?2, inlet vapor qualities from 0.2 to 0.7, and mass fractions of nanoparticles from 0 to 0.5 wt%. The experimental results show that the frictional pressured drop of refrigerant-based nanofluid increases with the increase of the mass fraction of nanoparticles, and the maximum enhancement of frictional pressure drop is 20.8% under above conditions. A frictional pressure drop correlation for refrigerant-based nanofluid is proposed, and the predictions agree with 92% of the experimental data within the deviation of ±15%.     

Immobilization of Bacillus sp. in mesoporous activated carbon for degradation of sulphonated phenolic compound in wastewater

Xenobiotic compounds are used in considerable quantities in leather industries besides natural organic and inorganic compounds. These compounds resist biological degradation and thus they remain in the treated wastewater in the unaltered molecular configurations. Immobilization of organisms in carrier matrices protects them from shock load application and from the toxicity of chemicals in bulk liquid phase. Mesoporous activated carbon (MAC) has been considered in the present study as the carrier matrix for the immobilization of Bacillus sp. isolated from Effluent Treatment Plant (ETP) employed for the treatment of wastewater containing sulphonated phenolic (SP) compounds. Temperature, pH, concentration, particle size and mass of MAC were observed to influence the immobilization behavior of Bacillus sp. The percentage immobilization of Bacillus sp. was the maximum at pH 7.0, temperature 20 °C and at particle size 300 μm. Enthalpy, free energy and entropy of immobilization were ? 46.9 kJ mol^? 1, ? 1.19 kJ mol^? 1 and ? 161.36 J K^? 1 mol^? 1 respectively at pH 7.0, temperature 20 °C and particle size 300 μm. Higher values of ΔH⁰ indicate the firm bonding of the Bacillus sp. in MAC. Degradation of aqueous sulphonated phenolic compound by Bacillus sp. immobilized in MAC followed pseudo first order rate kinetics with rate constant 1.12 × 10^? 2 min^? 1.     

Iodide selective membrane electrodes based on a Molybdenum–Salen as a neutral carrier

A new polymeric membrane electrode (PME) and a coated platinum disk electrode (CPtE) based on Schiff base complex of Mo(VI) as a suitable carrier for I^? ion were described. The influence of membrane composition, pH and possible interfering anions were investigated on the response properties of the electrodes. The electrodes exhibited a Nernstian slope of 63.0 ± 0.5 (CPtE) and 60.3 ± 0.4 (PME) mV decade^? 1 in I^? ion over a wide concentration range from 7.9 × 10^? 7 to 1.0 × 10^? 1 M for CPtE and 9.1 × 10^? 6 to 1.0 × 10^? 1 M I^? for PME. The potentiometric response of the electrodes was independent of the pH of the test solution in the pH range 2.0–8.5 with a fast response time (< 10 s). The process of transfer of iodide across the membrane interface was investigated by use of the AC impedance technique. The proposed sensors were successfully applied to direct determination of iodide in samples containing interfering anions, waste water and as indicator electrodes in precipitation titrations.     

Selective electrodes for [PF6]− and [BF4]− anions based on the associates formed by ionic liquid and cationic dyes

The feasibility of the newly synthesized ionic associates L1 and L2 formed by ionic liquid [C₄mim][PF₆] and cationic dyes (malachite green and methylene blue) has been tested as a novel ionophore for the preparation of anion-selective polymeric membrane electrodes. The electrode exhibits Nernstian response and enhanced potentiometric selectivity towards [PF₆]^? compared to many other anions. The influence of some experimental parameters such as membrane composition, nature of plasticizer and amount of additive on the potential response of the [PF₆]^? sensor are investigated. Under the optimized conditions, the response slopes of the membrane electrodes towards [PF₆]^? are 59.7 ± 0.5 and 58.1 ± 0.5 mV/decade based on ionophore L1 and L2, respectively, in 1.0 × 10^? 5–1.0 × 10^? 1 or 1.0 × 10^? 6–1.0 × 10^? 1 mol/L concentration range. Interestingly, the optimized electrodes based on ionophores L1 and L2 also exhibit Nernstian response characteristics (60.3 ± 0.5 and 56.0 ± 0.5 mV/decade) for tetrafluoroborate anion [BF₄]^? in a wide concentration range. Thus, the proposed sensor has been used for the determination of [PF₆]^? and [BF₄]^? in aqueous ionic liquids samples and the solubility of the [PF₆]^? and [BF₄]^? based ionic liquids in water. The satisfactory results are obtained.     

Depressing effect of 0.1 wt.% Cr addition into Sn–9Zn solder alloy on the intermetallic growth with Cu substrate during isothermal aging

In this paper, the effect of 0.1 wt.% Cr addition into Sn–9Zn lead-free solder alloys on the growth of intermetallic compound (IMC) with Cu substrate during soldering and subsequent isothermal aging was investigated. During soldering, it was found that 0.1 wt.% Cr addition did not contribute to forming the IMC, which was verified as the same phase structure as the IMC for Sn–9Zn/Cu. However, during solid-state isothermal aging, the IMC growth was remarkably depressed by 0.1 wt.% Cr addition in the Sn–9Zn solder, and this effect tended to be more prominent at higher aging temperature. The activation energy for IMC growth was determined as 21.2 kJ mol^? 1 and 42.9 kJ mol^? 1 for Sn–9Zn/Cu and Sn–9Zn–Cr/Cu, respectively. The reduced diffusion coefficient was confirmed for the 0.1Cr-containing solder/Cu. Energy-dispersive X-ray mapping and point analysis also showed ZnCr phase existing in solder matrix, which can reduce diffusion rate of Zn atoms.     

Potentiometric determination of ketoprofen and piroxicam at a new PVC electrode based on ion associates of Rhodamine 6G

The characteristics, performance and application of ion-selective electrodes for ketoprofen and piroxicam ions based on Rhodamine 6G as electrode-active substances are described. These electrodes respond with sensitivities of (58.0 ± 1.0) and (57.0 ± 2.0) mV/decade over the range 1.0 × 10^? 4–1.0 × 10^? 1 and 1.0 × 10^? 4–5.0 × 10^? 2 mol/l at pH 5–9 and 6–10 and a detection limit of 6.3 × 10^? 5 and 3.2 × 10^? 5 mol/l for ketoprofen and piroxicam, respectively. The electrodes are easily constructed at a relatively low cost, have a fast response time and can be used for a period of 5 months without any considerable divergence in potential. The proposed sensor displayed good selectivity for ketoprofen and piroxicam in the presence of several substances and inorganic anions. It was used for the direct assay of ketoprofen and piroxicam in commercial pharmaceutical preparations.     

Identification of diffusive transport properties of poly(vinyl alcohol) hydrogels from reservoir test

In this paper the identification of diffusion coefficient, retardation factor and surface distribution coefficient for selected salts in poly(vinyl alcohol) hydrogels is performed. The identification of the transport parameters is based on the previously developed inverse problem technique using experimental data from the reservoir test and the solution of the diffusive transport equation with linear equilibrium sorption. The estimated values of diffusion coefficient are: for physiological fluid (6.30 ± 0.10) × 10^? 10 m²/s, for 1 M NaCl (6.42 ± 0.39) × 10^? 10 m²/s, and for 1 M KCl (7.94 ± 0.38) × 10^? 10 m²/s. The retardation factor for all tested materials and salts is equal or close to one. The average value of the effective surface distribution coefficient is equal to 0.5.     

High-precision CTE measurement of hybrid C/SiC composite for cryogenic space telescopes

This paper presents highly precise measurements of thermal expansion of a “hybrid” carbon-fiber reinforced silicon carbide composite, HB-Cesic® – a trademark of ECM, in the temperature region of ～310–10 K. Whilst C/SiC composites have been considered to be promising for the mirrors and other structures of space-borne cryogenic telescopes, the anisotropic thermal expansion has been a potential disadvantage of this material. HB-Cesic® is a newly developed composite using a mixture of different types of chopped, short carbon-fiber, in which one of the important aims of the development was to reduce the anisotropy. The measurements indicate that the anisotropy was much reduced down to 4% as a result of hybridization. The thermal expansion data obtained are presented as functions of temperature using eighth-order polynomials separately for the horizontal (XY-) and vertical (Z-) directions of the fabrication process. The average CTEs and their dispersion (1σ) in the range 293–10 K derived from the data for the XY- and Z-directions were 0.805 ± 0.003 × 10^?6 K^?1 and 0.837 ± 0.001 × 10^?6 K^?1, respectively. The absolute accuracy and the reproducibility of the present measurements are suggested to be better than 0.01 × 10^?6 K^?1 and 0.001 × 10^?6 K^?1, respectively. The residual anisotropy of the thermal expansion was consistent with our previous speculation regarding carbon-fiber, in which the residual anisotropy tended to lie mainly in the horizontal plane.     

Impact of functional monomers,cross-linkers and porogens on morphology and recognition properties of 2-(3,4-dimethoxyphenyl)ethylamine imprinted polymers

The main objective of this paper was to examined the impact of synthetic reagents on morphology and recognition properties of 2-(3,4-dimethoxyphenyl)ethylamine imprinted polymers. The effect of nine different functional monomers, five porogens and four cross-linkers on the binding capacity of particles was analyzed. The results revealed that the highest imprinting factor (1.81) showed the polymer obtained from methacrylic acid and ethylene glycol dimethacrylate in toluene. The binding capacities of imprinted (MIP1) and non-imprinted (NIP1) materials were 135.3 ± 9.8 and 74.8 ± 7.8 μmol g^? 1, respectively. The specific surface areas were 55.05 ± 3.89 for MIP1 and 38.72 ± 2.40 m² g^? 1 for NIP1. The SEM analysis confirmed that the surface of MIP1 is rougher and denser than NIP1. Structural analysis supported by ¹³C CP/MAS NMR spectra was also performed. The binding abilities of homoveratrylamine and eight structurally related compounds to MIP1 showed that strong interactions between carboxylic group in the polymer and amine group in the analyte together with its molecular volume govern the recognition mechanism.     

Kinetics of thermal gradient chemical vapor infiltration of large-size carbon/carbon composites with vaporized kerosene

Large-size samples of carbon/carbon composites were prepared using thermal gradient chemical vapor infiltration with kerosene precursor at 950, 1020, 1100, 1180 and 1250 °C. The temperature gradient, kinetics and density distribution of these samples were studied and the microstructure of pyrolytic carbon was examined by polarized light microscopy. The results show that the initial infiltration rate increased from 5.81 to 21.32 g min^?1 by increasing deposition temperature from 950 to 1250 °C. The densification kinetics relied on deposition temperature and competition between reaction and diffusion, and the diffusion mechanism transformed from bulk to Knudsen diffusion regime. The calculated apparent activation energy is about 68.2 kJ mol^?1. The temperature range 1020–1100 °C is appropriate for fabricating composites with high final bulk density due to high degree of pore filling and the density of sample S3 infiltrated at 1100 °C is the highest among all investigated samples.     

Application of 1-ethyl-3-(2,5-dihydro-4-(3,5-dimethyl-1H-pyrazol-4-yl)-5-oxo-1H-pyrazol-3-yl)thiourea as sensing material for construction of Tm3+-PVC membrane sensor

A thulium(III) membrane sensor was made using 2% sodium tetraphenyl borate (NaTPB), 65% dibutylphthalate (DBP), 30% poly(vinyl chloride) (PVC) and 3% 1-ethyl-3-(2,5-dihydro-4-(3,5-dimethyl-1H-pyrazol-4-yl)-5-oxo-1H-pyrazol-3-yl)thiourea (ET) as an ionophore. Conductometric study shows selectivity of the Et toward Tm³⁺ ions. Nernstian response of 19.6 ± 0.4 mV per decade of thulium concentration was observed, and the electrode worked well in concentration range of 1.0 × 10^? 6 to 1.0 × 10^? 2 mol L^? 1 with a lower detection limit (LDL) of 7.2 × 10^? 7 mol L^? 1, in a pH range of 4.3–10.4. The selectivity of the sensor over alkaline, alkaline earth, transition and heavy metal ions was also found to be in a satisfactory range. To check the analytical applicability of the proposed Tm³⁺ sensor, it was successfully used as an indicator electrode in analysis of thulium in certified reference materials.