Differential Method Of Analysis Research Articles

Thermal analysis and modeling of phase equilibria in the NaCl–NaBr–Na2WO4 system

The phase complex of a three-component system of sodium chlorides, bromides and tungstates was studied for the first time using experimental and theoretical methods. It was found that the liquidus surface of the system consists of the crystallization fields of NaBr, Na2WO4, Na3ClWO4 compounds and NaClxBr1–x solid solutions. The differential thermal method of physico-chemical analysis (DTA) revealed the compositions and melting points of eutectic in the quasi–binary and three–component systems NaBr–Na3ClWO4 and NaCl–NaBr–Na2WO4, respectively. To establish the nature of the physico-chemical interaction in the system, three compositions were studied in the secondary triangle NaCl–NaBr–Na3ClWO4 by the DTA method, thermal effects of tertiary crystallization were not recorded on the DTA curves of these compositions, which is proof of the absence of a non-invariant composition in the NaCl–NaBr–Na3ClWO4 simplex. To determine the composition and melting point of the nonvariant composition located in the NaBr–Na2WO4–Na3ClWO4 simplex, a polythermal section located in the field of crystallization of sodium bromide and a nonvariant section emerging from the crystallization pole of sodium bromide passing through the point of joint crystallization of sodium chloride and the compound, with a constant decrease in the content of sodium bromide in the studied compositions before the onset of non-invariant crystallization process. The composition of the three-component eutectic of ED in molar percentages, crystallizing at 560оC with the following component content, has been determined: 7.5% NaCl; 38.5% NaBr; 54% Na2WO4. Based on data on the melting temperatures of the initial salts, compositions and crystallization temperatures of two- and three-component systems, a 3D-model of the “composition–temperature” phase complex in the temperature range 500–700оC was formed using theoretical methods. On the basis of the model, the isotherms of the liquidus surface and the T–x diagram of the polythermal section for which experimental studies were conducted was constructed. Also, as an example of using a 3D-model, the composition of the equilibrium phases released during cooling of an arbitrarily selected figurative point in the temperature range from 700 to 500оC. was calculated.

The significant impact colloidal nanothermite particles (Fe2O3/Al) on HMX kinetic decomposition

ABSTRACT HMX is one of the most powerful energetic materials; however, HMX experience low sensitivity and high activation energy. Whereas ferric oxide particles can act as catalyst for HMX decomposition with change in its decomposition kinetics from C-N bond cleavage to hydrogen atom abstraction; ferric oxide can induce vigorous thermite reaction with aluminum particles. Consequently, thermite particles can catalyze HMX decomposition, and enhance its decomposition enthalpy. This study reports on the fabrication and of ferric oxide nanoparticles of 5 nm particle size. Ferric oxide NPs and aluminum nanoplates of 100 nm were effectively integrated into HMX via co-precipitation technique. Elemental mapping was performed using EDAX detector; uniform dispersion of nanothermite particles was confirmed. Nanothermite particles experienced enhanced HMX decomposition enthalpy by 53%, with decrease in decomposition temperature by 13°C. The impact of nanothermite particles on HMX kinetic decomposition was evaluated using two different analysis models including differential isoconversional method of model-free Friedman analysis, and integral isoconversional method of Ozawa. Thermite nanoparticles demonstrated drastic decrease in HMX activation energy by 24 and 30% using Friedman and Ozawa models, respectively. The developed colloidal nanothermite particles demonstrated superior catalytic effect with enhanced decomposition enthalpy.

Particle size distribution modeling and kinetic study for coagulation treatment of tannery industry wastewater at response surface optimized condition

The presence of considerable amounts of Total Suspended Solids (TSS) in wastewater streams can pose a severe threat to aquatic and human life. A high level of TSS will increase water temperature at an alarming rate and decrease dissolved oxygen levels. This study aims to remove TSS from raw tannery wastewater using an active coagulating protein extracted from Moringa oleifera (MO) seeds. The process variables such as, coagulant dosage and pH are varied to test the potential of the coagulant extracted using NaCl and KCl salt solutions, for TSS removal from tannery wastewater. The results show that the NaCl extracted coagulant could effectively remove 89.87% of TSS whereas the KCl extracted coagulant eliminated 76.23% of TSS, at the optimum condition of 40 mL coagulant dosage and 7 pH. The assessment of coagulation rate parameters using differential method of analysis reveals that at optimum condition, the TSS reduction process obeys second order kinetics with a rate constant 3.556 × 10– 5 (mg/L)– 1 min– 1. The volume distribution of suspended solids in raw wastewater is fitted with a log-normal distribution model and Gaussian distribution model. From the magnitude of the coefficient of determination (R2) and Akaike information criterion (AIC) of the Gaussian model (R2 = 0.6864 and AIC = 3.89), it is concluded that the Gaussian model is better than the log-normal distribution model (R2 = 0.4708 and AIC = 6.31) for explaining the volumetric distribution of suspended particles. The numeric distribution of suspended solids in raw wastewater is explained well by the variable β model (R2 = 0.668) rather than the power law model (R2 = 0.196). The 3D response surface plot indicates that maximum TSS removal can be achieved at an optimal condition of 40 mL coagulant dose and 7 pH. The quadratic model developed for the treatment process utilizing the NaCl extracted coagulant shows better response prediction ability (R2 = 0.8118) when compared to the model built for the KCl extracted coagulant (R2 = 0.7911). Both the model equations have a p-value less than 0.05 which indicates that the proposed models are statistically significant. The elliptical contours for TSS removal using NaCl extracted coagulant demonstrate the significant interactions between the process variables. This study exhibited the applicability of MO seed extract for real-time tannery wastewater treatment.

Studying and Modeling of the Extraction Properties of the Natural Deep Eutectic Solvent and Sorbitol-Based Solvents in Regard to Biologically Active Substances from Glycyrrhizae Roots.

The purpose of this work was the studying and modeling of the extraction properties of the sorbitol-based natural deep eutectic solvent (NADES) and sorbitol-based solvents in regard to biologically-active substances (BASs) from Glycyrrhizae roots using theoretical fundamentals based on the laws of statistical physics, thermodynamics, and physical chemistry previously developed by us. In our studies, we used Glycyrrhizae roots, simple maceration, plant raw material:solvent ratio 1:10 w/v, temperature 25 °C, extraction time 24 h; standards of licuroside and glycyram; RP HPLC, differential scanning calorimetry, integral dielectric, impedance and conductivity spectroscopy method of analysis; the following solvents: sorbitol-based NADES sorbitol:malic acid:water (1:1:3 in molar ratio), a modified solvent based on NADES sorbitol:malic acid:water:glycerin (1:1:1:1 in molar ratio) and sorbitol-based solvents sorbitol:ethanol:water at different ratios. It has been found that regression equations for sorbitol-based solvents in coordinates predicted by the theory have a high value of determination coefficient that equals to R2e = 0.993 for glycyram and R2e = 0.976 for licuroside. It has been found that the extraction properties of sorbitol-based NADES with a dielectric constant (ε) equal to 33 ± 2 units are equivalent to those of the sorbitol:ethanol:water solvent with ε = 34 units, and the extraction properties of modified solvent based on NADES with ε = 41 ± 2 units are inferior to those of the sorbitol-ethanol-water solvents with maximum value of BASs yield with the dielectric constant range 40 ÷ 50 units. The theoretical fundamentals suggested provide a possibility for an explanation of the mechanism, quantitative description of the extraction properties of the solvent, and target search of the optimal solvent by its dielectric constant.

Catalytic dehydrogenation of formic acid-triethanolamine mixture using copper nanoparticles

In a bid to complement the lost reserves from fossils, recent advances in research are tailored towards producing hydrogen as an alternative source of fuel which is aimed at fostering a globally sustainable and reliable energy-economy. In this work, hydrogen was produced from formic acid (FA) using a new technology that involves the use of copper nanoparticles (CuNPs) supported on triethanolamine. The CuNP-catalysts of variant concentrations (i.e. 0.6–1.2 M) were synthesized using the conventional chemical deposition method. Also, a novel approach that bothers on the application of the Differential Method of Analysis (DMA) was used in determining the kinetic parameters for the FA-dehydrogenation. Based on the results, the volume of H2 produced varied with time, pH, concentration and catalyst-size. At 6 h, the 1 M CuNPs gave the highest volume (815 mL) of hydrogen with corresponding pH, particle size and approximate conversion of 3.19, 1.5 nm and 100% respectively, whereas, over extended periods i.e. over 6 h, the approximate volume-conversions of FA increased insignificantly for all catalysts. According to the investigation, the optimum CuNP-catalyst concentration required to produce 815 mL H2 in 6 h is 1 M. The decomposition was a first-order-type with a rate constant (k-value) of 1.0041 s−1.

PHASE EQUILIBRIUM IN SYSTEM (LiF)2 – Li2CO3 – Li2SO4

The liquidus surface of the system (LiF)2-Li2SO4-Li2CO3 was studied by the calculated and differential thermal method of physicochemical analysis. An analysis of the systems of lower dimensionality of the facets of the investigated object showed that the most informative, for the experimental study, is the sections located in the crystallization field of lithium fluoride. A study of the DTA of a number of compositions located at the initially chosen polythermal section in the lithium fluoride crystallization field, the ratios of lithium sulfate and carbonate in the eutectic are determined. The composition of the triple eutectic was revealed by studying a non-invariant cut from the vertex of the triangle (LiF), through a point showing a constant ratio of sulfate and lithium carbonate in the eutectic, to the fusion of the thermal effects of the primary and tertiary crystallizations. The complexity of the study was that lithium carbonate is the most fusible component in the system, and according to the literature, after the melting of lithium carbonate, decomposition begins, which greatly complicates the interpretation of research results. In order to avoid the decomposition of lithium carbonate, each experimentally studied composition was heated to the melting temperature of lithium carbonate and kept in isothermal mode, at a temperature below its melting. Thus, the theoretical melting calculations and the region of location of the non-invariant composition have been extrapolated, allowing to limit the number of experimentally studied samples, and the subsequent experimental investigation of DTA of two polythermal sections revealed a eutectic composition crystallizing at 476 ° C and containing LiF-20 eq.%, Li2SO4 - 51 eq.%, Li2CO3 – 29 eq.%. The discrepancies between theoretical calculations and experimental studies are 8.3% in temperature and 5.05% in composition.

Pd-Ag/Al2O3 catalyst: Stages of deactivation in tail-end acetylene selective hydrogenation

The deactivation of a Pd-Ag/α-Al2O3 catalyst (2.5mm in diameter, containing 0.03wt.% Pd and 0.18wt.% Ag) with egg-shell distribution was studied for acetylene selective hydrogenation. The reaction was performed in a fixed bed reactor using C2H2/C2H4/H2 feed mixture (1:67.5:1.5 molar ratio). The long-term deactivation behaviour of the catalyst was studied by differential method of analysis using appropriate power law kinetics for the main reaction and catalyst decay. Based on the analysis of model results, it was proposed that the catalyst deactivation proceeded in two stages. The initial stage (Stage I) was relatively short (<20h) and characterized by rapid catalyst deactivation, followed by second stage (Stage II) of much slower deactivation rate exhibiting a deactivation rate constant one order of magnitude smaller than Stage I. It was attributed to the dual role of carbonaceous deposits on catalyst that exhibited sequential activation and deactivation effects. The TG and FT-IR analysis of the spent catalyst revealed formation of aliphatic (soft) coke after about 100h on stream.

Parameter evaluation, kinetics, and energy consumption for Cr(VI) photocatalytic reduction under mild conditions

Photocatalytic reduction of hexavalent chromium, Cr(VI), ions in aqueous solutions was studied using remarkably low doses of commercial titania nanoparticles at conventional temperature range of 15–45 °C. A direct imposed irradiation photo-reactor, equipped with ultrasonic source was utilized. Design of experiments, correlating and process optimization were performed using central composite design of response surface methodology. Accordingly, a reduced quadratic expression was developed to predict the reduction efficiency as a function of involved parameters. Analysis of variance shows the agreement of the provided model with experimental data. At the found optimum conditions of titania concentration: 33.1 mg/L, pH: 2.50, temperature: 36 °C and reaction time: 120 min; 81 % efficiency was achieved for reduction of initial 5 mg/L of Cr(VI). The process revealed proceeding through parallel branches of photolysis and photocatalysis, and only UV irradiation was promising for reaction progress. Based on differential method of analysis, the relevant kinetic model, jointed with the Arrhenius equation, was introduced. Energy (electrical and thermal) consumption evaluations revealed that treatment at higher temperatures provides a significant cost reduction. Meantime, a criterion was proposed for a more valid assessment of photocatalytic processes.

EXAFS and kinetic study of MnOx/γ-alumina in gas phase catalytic oxidation of toluene by ozone

This work addresses characterization of Mn2O3 materials by EXAFS technique and the mechanism of toluene oxidation by ozone over MnOx/γ-alumina (10%) catalyst. Bond Valence Model was used to model EXAFS signal of bulk and nano-particles of Mn2O3. The Bond Valence Model relates formal oxidation state of Mn atoms to the coordination number of oxygen atoms at the first Mn shell, adding restraints to the EXAFS theoretical models. Use of the Bond Valence Model resulted in distinguishing closely located oxygen atoms around each Mn site without any simplifying assumption on the structure of Mn2O3. Kinetic study of catalytic oxidation of toluene by ozone using MnOx/γ-alumina (10%) was performed at constant toluene or ozone partial pressures by varying the reactor space time in the range of 0–1212kgcat.moltol.−1s. Differential method of analysis was used to estimate the initial reaction rates. Apparent activation energy of the reaction was determined to be 31kJmol−1, obtained by a power law model. The power law model also determined the reaction orders with respect to toluene and ozone as −1 and 2, respectively. To explain the initial reaction rates, two Langmuir–Hinshelwood mechanisms based on different toluene activation steps were examined. The first mechanism was based on activation of adsorbed toluene molecule by atomic oxygen while the second model was based on activation of toluene molecule via abstraction of hydrogen from the methyl group. The second Langmuir–Hinshelwood mechanism led to the same rate equation as the power law model, explaining the effect of toluene and ozone partial pressures on toluene oxidation rate.

Kinetic study of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al2O3 catalyst

The kinetics of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al2O3 catalyst were studied. Performance test runs were carried out in a fixed-bed integral reactor. Using a power-law rate expression for the surface reaction kinetics and independent law for deactivation kinetics, the experimental data were analyzed both by integral and a novel differential method of analysis and the results were compared. To avoid fluctuation of time-derivatives of conversion required for differential analysis, the conversion-time data were first fitted with appropriate functions. While the time-zero and rate constant of reaction were largely insensitive to the function employed, the rate constant of deactivation was much more sensitive to the function form. The advantage of the proposed differential method, however, is that the integration of the rate expression is not necessary which otherwise could be complicated or impossible. It was also found that the reaction is not limited by external and internal mass transfer limitations, implying that the employed kinetics could be considered as intrinsic ones.

A wavelet-analysis-based differential method for engine wear monitoring via on-line visual ferrograph

Wear over time affects engine’s reliability and efficiency. On-line wear monitoring could provide timely information about engine health condition. In the current study, on-line monitoring of engine wear via an on-line visual ferrograph was performed in reliability tests of gasoline engines, and a wavelet-analysis-based differential method of data analysis for wear condition estimation was proposed. The tests were designed for 220 h, which consist of a running-in stage of 20 h and a thermal shock cycle test stage of 200 h. One of the tests was terminated because of failures in the main bearings and crankshaft journal at 146th hour of thermal shock cycle test, while the other two completed successfully without failures. Index of particle coverage area, which represents wear-debris concentration in lube oil, was studied, and piecewise trend-extraction of index of particle coverage area was achieved by wavelet decomposition and reconstruction. The first-order differential of the index of particle coverage area trend was used to represent the wear rate or the generation rate of debris for health condition assessment of engines. Off-line oil analyses were performed in laboratory via an analytical ferrograph, and engine disassembly results of the engines were given to determine the causes of engine failures if it happened. It is found that favorable trend extraction from index of particle coverage area could be achieved by the segmented wavelet de-noising. Moreover, on-line visual ferrograph monitoring estimated the engine wear at macro-levels effectively, and it provided an advance warning for the failures after the continued deterioration of the engine wear. The study and application of this method can make early failure prediction of engine and avoid serious fault.

Modelling of an annular photocatalytic reactor

This work deals with the photocatalytic oxidation of toluene at room temperature and atmospheric pressure in the gas phase. The differential equations of the reactor model are solved numerically with simultaneous estimation of the model parameters. Estimation of the kinetic data is performed using a modified differential method of data analysis and a Nelder–Mead method of nonlinear optimization for parameter estimation. The reaction is performed in an annular photoreactor using UVA black light blue fluorescent lamp. The experiments are carried out at different total flow rates of the reaction feed (20–160 cm3 min−1), two different inlet concentrations of toluene (2.67 and 5.24 g m−3) and at constant relative humidity (25%). A good agreement between the experimental data and theoretical predictions is obtained, supporting the applicability of the proposed models to describe the investigated process performed in laboratory annular photoreactor.

Differential method of analysis of luminescence spectra of semiconductors

A method for analyzing the luminescence spectra of semiconductors is suggested. The method is based on differentiation of the spectra. The potentialities of the method are demonstrated for luminescence in the region of the fundamental absorption edge of Si and SiGe alloy single crystals. The method is superior in accuracy to previously known luminescence methods of determining the band gap of indirect-gap semiconductors and practically insensitive to different conditions of outputting radiation from the sample.

Cellular associations and the differential spermiogram: Making sense of stallion spermatozoal morphology

Morphologic assessment of spermatozoa is one of the most objective measures in a Breeding Soundness Examination of a stallion. There are different systems for morphologic assessment of spermatozoa. The objectives of this article are to review spermatogenesis, describe clinical sample preparation, discuss previous methods of morphologic classification and explain the use of a differential spermiogram. The advantages of the differential spermiogram method of analysis are discussed, along with its use in delineating intrinsic and extrinsic disturbances in spermatogenesis. Case examples of specific cellular associations and their diagnostic relevance are discussed.

Special features of charge transport in PbGa2Se4 crystals

The current-voltage (I-V) characteristics of PbGa2Se4 single crystals grown by the Bridgman-Stockbarger method with a resistivity of 1010–1012 Ω cm were measured. The value of the majority carrier mobility μ=14 cm2 V−1 s−1, calculated by the differential method of analysis of I-V characteristics, makes it possible to evaluate a number of parameters: the carrier concentration at the cathode (nc0=2.48 cm−3), the width of the contact barrier dc=5.4×10−8 cm, the cathode transparency D c * =10−5–10−4 eV, and the quasi-Fermi level EF=0.38 eV. It is found that a high electric field provides the charge transport through PbGa2Se4 crystals in accordance with the Pool-Frenkel effect. The value of the dielectric constant calculated from the Frenkel factor is found to be equal to 8.4.

Rapid biocatalytic polytransesterification: reaction kinetics in an exothermic reaction

Biocatalytic polytransesterification at high concentrations of monomers proceeds rapidly and is accompanied by an increase in the temperature of the reaction mixture due to liberation of heat of reaction during the initial phase. We have used principles of reaction calorimetry to monitor the kinetics of polymerization during this initial phase, thus relating the temperature to the extent of polymerization. Rate of polymerization increases with the concentration of monomers. This is also reflected by the increase in the temperature of the reaction mixture. Using time-temperature-conversion contours, a differential method of kinetic analysis was used to calculate the energy of activation ( approximately 15.1 Kcal/mol). Copyright 1998 John Wiley & Sons, Inc.

Catalytic effect of some inorganic ligands on a ligand substitution reaction involving mercury(II) and its application as a differential kinetic method of analysis

To design a sensitive and selective kinetic method for determining a catalyst, the kinetics of the ligand substitution reaction between the mercury(II)-4-(2-pyridylazo)resorcinol complex and 1,2-cyclohexanediamine- N, N, N′, N′-tetraacetic acid together with the catalytic effect of some inorganic ligands on this reaction were studied. The rate constant for a catalyzed reaction path was found to be linearly correlated with the electron donor constant of the catalyst. From this correlation, the difference in reactivity between sulfite or thiosulfate and sulfate was established. Under the selected conditions, sulfite up to 1.5 × 10 −6 M and thiosulfate up to 7 × 10 −7 M could be determined with detection limits of 3 × 10 −8 and 2 × 10 −8 M in the presence of 10 000 and 25 000-fold molar amounts of sulfate, respectively. The tolerance level in the determination of 1 × 10 −6 M of sulfite and 4 × 10 −7 M of thiosulfate was studied for 15 inorganic anions and 44 metal ions.

Measurement and differential kinetic analysis of wall temperatures in monolith converters—I kinetic analysis

It is possible to measure axial wall temperature profiles in adiabatic monolith converters under actual reaction conditions. By applying a differential method of kinetic analysis, axial profiles of concentrations at the wall as well as of reaction rates can be derived with proper computation methods. The data thus obtained may serve for further kinetic evaluation, that is for model building and parameter estimation by proven and well-known methods. The whole procedure looks also promising for performing activity tests on fresh and partly deactivated monolith converters. The slightly greater effort of measuring wall temperatures compared with the usual method only to record inlet and outlet temperatures and integral conversions might more than pay off. In the present first part of the paper the differential method of kinetic analysis is developed and tested by some simulation studies. The second part will deal with actual experiments.

The trap parameters in polycrystalline tetracene layers from measurements of thermally stimulated currents and space charge limited currents

The trap parameters in thin polycrystalline tetracene films are investigated. The thermally stimulated current technique determining parameters of shallow traps and a differential method of analysis of steady-state isothermal current-voltage characteristics for estimating energies and density of deep traps are used.

Thermogravimetric investigation of the pyrolysis of pitch materials. A compensation effect and variation in kinetic parameters with heating rate

Thermogravimetric measurements of weight loss accompanying the pyrolysis of four pitches have been made over a range of linear heating rates. For three of the samples, the data at each heating rate could be described by an integral and a differential method of analysis, assuming a simple order function for f(α), with the result that the apparent activation energy increased with heating rate. The data for all four samples could also be satisfactorily described by the Ozawa or Friedman multiple heating rate methods, and these resulted in apparent activation energies ( E a) which increased with the value of β at which they were determined. It is suggested that this tendency for the apparent activation energy to increase, as the temperature is raised, is due to a change in the relative importance of the different reactions which lead to weight loss in this system. The apparent kinetic parameters all fall on a common compensation plot which is used to explain the relative magnitude of E a values from Ozawa and Doyle methods of analysis. The higher values of E a from Friedman than from Ozawa analyses are also explained.