جستجوی مقالات مرتبط با کلیدواژه "activation energy" در نشریات گروه "شیمی"
تکرار جستجوی کلیدواژه «activation energy» در نشریات گروه «علوم پایه»-
Woolen yarns are the main material for the fabrication of nanocomposite blended yarns, multilayer fabrics and nanostructure nonwovens for the textiles and garments. This study was started in an effort to search the kinetic and thermodynamic characteristics of CI Acid Blue 106 (A leveling acid dye) on woolen yarns. Various models (zero order, first order, second order, Parabolic, cegarra–Puente, and modified cegarra–puente models) were used to recognize an appropriate dyeing apparatus. It was established that the modified cegarra-puente model top fitted to the studied information with the maximum correlation (R2≥0.999). The dyeing-rate constant, the half dyeing times, rise time and fixation time were then considered. Also, thermodynamic parameters, such as the activation energy (Ea), were considered.Keywords: CI Acid Blue 106, Wool, Nanocomposite Yarns, Activation Energy, Modified Cegarra-Puente
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In this work, the dielectric properties of intercalated 1-(4-nitrophenyl)-N-(p-tolyl) methanimine into bentonite interlayers were investigated in the frequency range 102 to 106 Hz at five different temperatures between 24oC and 60oC. The impedance of the composite decreased with increasing the temperature from 24oC to 60oC, as it drops 7*103 Ω at 100 Hz and 1.5*103 Ω at 1 MHz. The composite showed a very low conductivity with little effect of increasing temperature in the low frequencies, yet the high frequencies make the effect of maximizing the temperature more obvious. The imaginary dielectric permittivity exhibited peaks of energy losses which reached the highest magnitude with 60oC, whereas the dielectric breakdowns were shifted toward higher frequencies with increasing temperature. Moreover, the activation energy of relaxation time was obtained by using Arrhenius equation from the slope of ln(τ) vs. (KT)-1 curve and the value was (965.24 J). In the same approach, the activation energies of charge carriers were estimated in three different frequency regions; high, moderate, and low regions and the values were 529.31, 698.09, and 541.98 J, respectively.Keywords: Dielectric permittivity, organo-clay composite, Bentonite, Schiff base, conductivity, activation energy, relaxation time
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Inverse spinel nickel ferrite (NiFe2O4 (or) NiO.Fe2O3) like- broccoli shape was manufactured as a brown nanoparticle. The NiFe2O4 preparation is done in the presence of the mixture of precursor salts in a ratio (2:1) of the iron ion with nickel ion prior to the presence of a nonpolar surfactant (hexamine). Hexamine acts as a capping agent before adding ammonia to solution; template and stabilizer via growth and storage of its powder. The solvothermal technique aided the precipitation route by using ethanol solvent at 180°C for 90 minutes to depress the defect in the prepared nanoparticle. The XRD data revealed that the NiFe2O4 peaks were wide and had a modest mean crystal size (20.13 nm). The broccoli-like NiFe2O4 nanoparticles with homogenous agglomerations were investigated using SEM- EDX analysis. The particle size is found to be 30.67 nm composing 100% of Ni, Fe, and O atoms. The - FT-IR analysis exhibited the positions of the tetrahedral site for (Fe3+-O2-) and octahedral site peaks for (Ni2+- O2-), and proved the type of NiFe2O4 is an inverse spinal structure. The NiFe2O4 has been owned as an excellent optical property with a small indirect band gap value (2.05 eV). Following this fact, this spinal can be used as a photocatalyst. The best photo-decolorization of this dye took place at pH 7 as a pseudo-first order with efficiency (98 %). This photoreaction is fast, endothermic and non-spontaneous. Negative entropy value refers to the products in this dye decolorization being more regular than the reactant (dye) structure.Keywords: Nickel ferrite, inverse spinel Nickel ferrite, activation energy, non- ionic surfactant, alkali blue 4B dye, solvothermal method
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در این پژوهش، سینتیک حذف رنگدانه اسید آبی 260 که یک رنگدانه اسیدی است، از محلول آبی با استفاده از نانولوله کربنی چند دیواره در شرایط بهینه pH که برابر 6.5 است و در دمای K298 مورد بررسی قرار گرفت. شش مدل سینتیکی که شامل مدل شبه درجه اول، شبه درجه دوم، نفوذ درون ذره ای، الویچ، بنگهام و فروندلیج اصلاح شده استفاده شد. داده های سینتیکی با استفاده از مدل های یاد شده و روش برازش خطی و برازش غیرخطی مورد برازش قرار گرفتند. نتیجه های آنالیز داده ها نشان داد که مدل سینتیکی شبه درجه دوم در هر دو روش برازش خطی و غیرخطی، بیش ترین سازگاری را داشت. این نتیجه نشان داد که مرحله کنترل کننده سرعت، جذب روی سطح است. مقدار ظرفیت جذب تعادلی محاسبه شده در مدل شبه درجه دوم در برازش خطی و غیرخطی بین 73 تا 75 میلی گرم جذب شونده بر گرم جاذب، به مقدار تجربی (mg/g99) نزدیک است. ترتیب تطابق داده هاب ا مدل های دیگر در برازش غیرخطی به ترتیب مدل شبه درجه اول، بنگهام، فروندلیچ اصلاح شده، الوویچ و مدل نفود درون ذره ای و در برازش خطی، بنگهام، الوویچ، فروندلیچ اصلاح شده، نفود درون ذره ای و مدل شبه درجه اول است. انرژی فعال سازی آرنیوسی دیده شده از داده های تجربی برابر kJ/mol61.63- محاسبه شد که نشان دهنده این واقعیت است که سد انرژی در فرایند جذب وجود ندارد و واکنش گرمازا است.کلید واژگان: سینتیک, جذب سطحی, رنگدانه اسید آبی 206, نانولوله کربنی چند دیواره, انرژی فعال سازی, برازش خطی, برازش غیر خطیIn this research, the kinetics of removal of acidic blue 206, an acidic dye, from aqueous solution by multi-wall carbon nanotube at optimized pH of 6.5 and 298K has been investigated. Six kinetics models contain pseudo-first-order, pseudo-second-order, intra-particle, Elovich, Bingham, and modified Freundlich model used. Kinetic data were fitted by these six models using linear and nonlinear regression. The results showed that the pseudo-second-order model was best fitted in both linear and nonlinear regression methods. The rate-determining step was the surface adsorption. The calculated qe at pseudo-first-order and pseudo-second-order models, (73mg/g and 75mg/g, respectively) are near the experimental value (99 mg/g). The order of compatibility of data with other models at nonlinear regression is pseudo-first order> Bingham> modified Freundlich> Elovich> intra-particle diffusion models. For leaner regression the order of compatibility of data are Bingham> elovich> modified freundlich> intra-particle diffusion> pseudo-first-order models. The calculated Arrhenius activation energy was -61.63kJ/mol. The negative activation energy, Ea, means that there is no barrier energy on surface adsorption and the adsorption is exothermic.Keywords: Kinetics, Surface adsorption, acidic blue 206 dye, Multi-wall carbon nanotube, Activation Energy, linear regression, nonlinear regression
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امروزه تغییرهای آب و هوایی به وجود آمده از انتشار گازهای گلخانه ای یکی از مهم ترین چالش های زیست محیطی بشر است. در این مطالعه، با استفاده از محاسبه های نظریه ی تابعیت چگالی، مکانیسم های محتمل کاهش کربن دی اکسید به وسیله مولکول هیدروژن بر روی بسترگرافنی دوپه شده با اتم های نیتروژن ونیکل مورد بررسی قرارگرفت. نتیجه های به دست آمده نشان دادند که اتم نیکل می تواند به طور موثری با اتم های نیتروژن دوپه شدهدر بستر گرافنی برهمکنش دهد. بر اساس نتیجه های به دست آمده، فعالیت کاتالیزگری سطح یادشده به طور عمده از هیبریداسیون قوی بین اوربیتال سیگمای مولکول هیدروژن و اوربیتال های -d3 اتم نیکل ناشی می شود. انرژی های فعال سازی به دست آمده نشان داد که در کاهش کربن دی اکسید با هیدروژن تشکیل حدواسط کربوکسیل نسبت به تشکیل فرمات بسیارمساعدتر است.کلید واژگان: کاهش, CO2, انرژی فعال سازی, دوپه کردن, نظریه ی تابعیت چگالیToday, climate change caused by the emission of greenhouse gasses is one of the most important environmental challenges facing humankind. In this work, using density functional theory calculations, the probable reaction mechanisms for the reduction of CO2 by H2 molecule were investigated over a Ni atom incorporated nitrogen-doped graphene. Our results indicated that the Ni atom can be efficiently adsorbed over the monovacancy site in the nitrogen-doped graphene. According to the obtained results, the catalytic activity of the mentioned surface is mainly originated from the strong hybridization between the σ orbital of the hydrogen molecule and 3d orbitals of nickel. The activation energies indicated that for the reduction of CO2, the formation of carboxylate is energetically more favorable than that of the formate intermediate.Keywords: Reduction, CO2, Activation Energy, Doping, density functional theory
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The wet peroxide oxidation (CWPO) of phenol in the polluted water on Mg-Al nano mixed oxide was investigated and the optimization and kinetic of the process were studied. The nanocatalyst was characterized by XRD, FESEM, EDS and BET. The average crystallite size of 25 nm was estimated using Scherrer formula.FESEM images approved the catalyst comprised of spherical nanoparticles in the range of 94-130 nm. BET results indicated the mesoporous nanocatalyst (dpore=21 nm) has a specific surface area of 86.3 m2.g-1. The optimized conditions of the process resulted at initial concentration of phenol, reaction temperature, reaction time and hydrogen peroxide volume of 100 ppm, 60ºC, 55 min and 3 mL, respectively. The phenol degradation under the optimal conditions reached 85%. The result of the kinetic study indicated that the oxidation of phenol over Mg-Al nano mixed oxide follows the pseudo-first-order kinetics with a correlation factor of 0.94. The activation energy of phenol oxidation over the catalyst was determined to be 19.07 kJ.mol-1. The Mg-Al mixed oxide is a cheap and green catalyst and could be prove to promising for the CWPO process.Keywords: Wet peroxide oxidation, phenol, Mg-Al mixed nanooxide, Kinetic studies, activation energy
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Magnetic behavior of Co/Al2O3 catalyst in Fischer-Tropsch (FT) synthesis is performed using a magnetically fixed bed reactor. X-ray diffraction (XRD) spectroscopy, scanning electron microscope (SEM) method, Brunauer-Emmett-Teller (BET) method, and vibrating sample magnetometer (VSM) method are used to analyze the catalyst. Magnetic field of 0.015 T is suggested for CO hydrogenation on Co/Al2O3 catalyst with fixed bed reactor. Significant effects of magnetic fields are observed in the FT reaction of CO hydrogenation over Co/Al2O3 catalyst. The CO conversion value increases from 78% to 86% at 250 oC with external magnetic field. The apparent activation energy of FT reaction (102.33kJ/mol without external magnetic field) is reduced (96.45 kJ/mol with applying external magnetic field), and the catalytic activity of Co/Al2O3 catalyst is improved by applying the external magnetic fields during FT process at low temperatures (200-250 oC). The results indicated that the external magnetic fields improved both the rate of reaction and catalytic selectivity to desired hydrocarbons on Co/Al2O3 catalyst.Keywords: Magnetic field effect, Fixed-bed Reactor, CO hydrogenation, activation energy
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Oils of vegetable origin are of great importance in food, soap, and cosmetic industries and they may also be used as lubricants and raw materials for biodiesel production depending on their viscosity and thermal stability. This work provides insight into the fatty acid components, physicochemical properties and thermal stability of some refined vegetable oils. The Saponification values, peroxide values, acid values, iodine values and refractive index of these oils range from 185.38 to 209.26 mg/g KOH, 2.00 to 37.00 meq O2/ kg, 2.50 to 5.50 mg KOH/ g, 31.09 to 89.46 g / 100g and 1.441 to 1.488 respectively The activation energies obtained from Arrhenius-type equation range from 11.32 to 3.85 kJ mol-1, while the enthalpy (∆H҂) and entropy (∆S҂) of activation obtained from Eyring-type equation range from 6.852 to 14.317 kJ mol-1 and -31.85 to -29.06 J mol-1 K-1 respectively. The Gibbs free energy of activation (∆G҂) ranges from 15.51 to 23.81 k J mol-1. The Pw oil brand has the highest thermal stability and resistance to shear stress due to its high activation energy and a low degree of unsaturation. The heat was absorbed during the process, the reaction mechanism was associative and the entire process was non-spontaneous.
Keywords: Viscosity, fatty acids, Eyring-type equation, Arrhenius-type equation, activation energy -
Aluminosilicate gel precursor having mullite composition was synthesized from inorganic salts of aluminum and silicon by employing the sol-gel method. Chemical analysis, surface area, and bulk density measurements were performed to characterize the dried gel. The course of the palletization was examined by FT-IR analysis which confirmed the diphasic nature of the gel. SEM and XRD analysis were performed to study microstructure and phase development. ThermoGravimetric (TG) analysis of the dried gel was performed at multiple heating rates and from the results obtained; kinetics of thermal dehydration was studied by applying Friedman differential and Kissinger-Akahira-Sunose integral isoconversional procedures. It was observed that the total dehydration process of the gel was accomplished by two different stages and both the stages followed second-order rate kinetics. The first stage was assigned to the dehydration of silicon hydroxide gel whereas the second stage was associated with aluminum hydroxide gel dehydration.Keywords: Sol-gel process, Dehydration kinetics, Activation Energy, Friedman method, Kissinger-Akahira-Sunose approximation
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Iranian Journal of Chemistry and Chemical Engineering, Volume:38 Issue: 3, May-Jun 2019, PP 283 -292
Acetic acid was separated from a dilute mixture using a commercial polyvinyl alcohol (PVA) membrane. Intrinsic separation characteristics of the membrane were studied as a function of temperature. The degree of membrane swelling decreased marginally with increase in feed temperature. At 25o</sup>C the maximum degree of swelling was found out to be 46.3%, which reduced to 39.5% at 65o</sup>C. Although the pervaporation flux increased with increasing temperature of the liquid feed mixture, the separation factor decreased. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters for water permeation were estimated. Diffusion and partition coefficient for water and acid were found to increase with temperature, but the diffusion coefficient of water was substantially higher than that of acetic acid at a constant feed concentration. The membrane used in the present study could tolerate highly concentrated corrosive acetic acid, thus may be useful for dehydration of other organics.
Keywords: Pervaporation, Acetic acid, PVA, Swelling, flux, Activation energy -
Nanocomposites films of (polymer blend-ceramics) were prepared from (PVA-PAA) blend and (PVA-PAA) blend doped with niobium carbide nanoparticles for humidity sensors have low cost, easy fabrication, high sensitivity, lightweight and high corrosion resistance. The structural, electrical and optical properties of (PVA-PAA-NbC) nanocomposites have been studied. The D.C electrical properties of (PVA-PAA-NbC) nanocomposites were studied with different temperature range. The results showed that the D.C electrical conductivity (PVA-PAA) blend increases with increase in niobium carbide nanoparticles concentrations and temperatures. The activation energy of (PVA-PAA) blend decreases with increase in niobium carbide nanoparticles concentrations. The results of optical properties showed that the transmittance of (PVA-PAA) blend decreases with increase in niobium carbide nanoparticles concentrations. The (PVA-PAA-NbC) nanocomposites tested for humidity sensors and the results showed that the (PVA-PAA-NbC) nanocomposites have high sensitivity for humidity sensors. Keywords: niobium carbide, nanocomposites, humidity sensors, activation energy.Keywords: activation energy, Humidity sensors, Nanocomposites, Niobium Carbide
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This paper presents a novel microwave-assisted hydrothermal technique for synthesizing tin(II) oxide nanoparticles. This technique can be used for producing large quantities of homogeneous nanoparticles in a short time. The effect of the solution molarity, final pH, hydrothermal processing time and microwave power were studied. The tin(II) oxide structure verified from XRD and the mean crystallite size was evaluated to be about 5 nm using the Debye-Scherrer formula on the most intense peak. The particle size was measured from STM pictures in the range between 4-5 nm. For different samples, UV-Vis spectroscopy showed the absorption peak due to tin(II) oxide at about 240 nm and an exitonian peak at about 280 nm that shifted with respect to solution molarity, final pH, hydrothermal processing time and microwave power. The photoluminescence spectroscopy (PL) results showed the emission peaks in the visible spectrum range. The results showed that synthesized SnO nanoparticles have a direct bandgap equal to about 2.5 eV, an Urbach energy of about 2.7 eV and activation energy of 47.75kJ/mol.Keywords: Tin(II) oxide nanoparticles, Microwave-assisted hydrothermal technique, Urbach energy, Activation Energy
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امروزه آلودگی هوا یکی از مهم ترین مشکل های زیست محیطی است که بیش تر کشورهای در حال توسعه با آن روبرو هستند. در این مطالعه، با استفاده از محاسبه های نظریه ی تابعیت چگالی، مکانیسم احیای گاز NO بر روی بسترهای B12N12 و B11N12C بررسی می شود. مسیر پیشنهادی برای این مکانیسم به صورت 2NO → N2O + Oads و Oads + N2O → N2 +O2می باشد. نتیجه ها نشان می دهد دوپه کردن نانوقفس B12N12 با اتم کربن باعث افزایش واکنش پذیری سطح آن می شود. مقدارهای انرژی فعال سازی و پارامترهای ترمودینامیکی محاسبه شده نشان می دهد که نانوقفس B11N12C فعالیت کاتالیستی بهتری نسبت به B12N12 دارد که به دلیل حضور اتم کربن دوپه شده در این نانوساختار باشد.کلید واژگان: احیای NO, انرژی فعال سازی, دوپه کردن, نانو قفس بور نیتریدی, نظریه ی تابعیت چگالیToday, air pollution is one of the important environmental problems in most developing countries. In this paper, using density functional theory calculations, the mechanism of NO reduction is investigated over B12N12 and B11N12C nanocages. The proposed pathway for this reaction is as 2NO → N2O + Oads and Oads + N2O → N2 + O2. The results indicate that C-doping increases the surface reactivity of B12N12 nanocage. The activation energies and calculated thermodynamic parameters show that the B11N12C nanocage has a better catalytic activity than B12N12, which could be due to the presence of doped carbon atom in this structure.Keywords: NO reduction, Activation Energy, Doping, boron-nitride nanocage, density functional theory
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ماده منفجره A4، که حاوی 5/96% سیکلونیت (RDX) و 5/3% واکس پارافینی است، یکی از اجزای اصلی انواع مهمات و سرجنگی انواع راکت ها و موشک های دفاعی است. در این تحقیق، رفتار حرارتی و سینتیک تجزیه این ماده با استفاده از روش های آنالیز حرارتی غیرهمدمای دیفرانسیلی (DTA) و وزن سنجی حرارتی (TG) در سرعت های حرارتی مختلف °C/min 2 تا 8 موردمطالعه قرارگرفته است. پارامترهای سینتیکی از قبیل انرژی فعال سازی، فاکتور پیش نمایی و دمای بحرانی تجزیه حرارتی این ماده منفجره با استفاده از روش های برازش مدل و مستقل از مدل که توسط کنفدراسیون بین المللی آنالیز حرارتی (ICTAK) برای تجزیه وتحلیل ترموگرام ها پیشنهاد شده است، ارزیابی شدند. نتایج برازش مدل، مقدار میانگین انرژی فعال سازی و فاکتور پیش نمایی را به ترتیب kJ/mol 397/190 و 1/min 22+E89/1 و مدل واکنش تفکیک حرارتی ماده منفجره را به صورت تابع انتگرالی اتوکاتالیستی A3 با رابطه [-Ln(1-α)]1/3پیشنهاد می نماید. همچنین، جهت تخمین طول عمر A4 در دماهای بالا، روند کاهش وزن ماده با زمان به روش مستقل از مدل با استفاده از ترموگرام های آنالیز حرارتی تخمین زده شد و نتایج محاسبات، با داده های تجربی آزمون های کهولت تسریع یافته در دمای °C 140 مقایسه و با آزمون آماری t تائید شدند. استفاده از این روش، امکان تخمین سریع طول عمر مواد منفجره در دماهای نزدیک به تفکیک حرارتی ماده را فراهم میآورد.کلید واژگان: ماده منفجره, RDX غیر حساس شده, آنالیز حرارتی DTA-TG, ترموسینتیک, انرژی فعال سازیA4 explosive, containing 96.5 wt. % RDX and 3.5 wt. % paraffin wax, is one of the main components in the ammunitions, and warheads of military rockets and missiles. In this work, the thermal behavior and the decomposition kinetics of this explosive has been studied experimentally by non-isothermal differential thermal analysis technique (DTA) and thermal gravimetric (TG) methods, under various heating rates (2.0-8.0 °C/min). Kinetic parameters such as activation energy and frequency factor and critical ignition temperatures for thermal decomposition of these explosives have been evaluated via the fitting-model and free-model methods, proposed by International Confederation for Thermal Analysis and Calorimetry (ICTAC). The results show a single thermal decomposition process for A4, with the integral fitting- model of [-Ln(1-α)]1/3, indicating an autocatalytic degradation with 3-dimensional diffusion mechanism. The mean kinetic parameters of activation energy (Ea) and A of exothermic decomposition of these explosives, calculated by Kissinger, Ozawa, Friedman and KAS methods, are near to 190.397 kJ/mol and 1.89E min-1. The kinetics results were used for the estimation of mass loss prediction of mentioned explosives and were statistically compared to experimental accelerated ageing consequences. By using this method, it is possible to be predicted the lifetime of explosives in the temperatures near to decompositions regions.Keywords: Explosive, Desensitized RDX, DTA-TG thermal analysis, Thermokinetics, Activation energy
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Composite solid propellants were prepared with and without nano-alloys (Ti-Co, Ti-Ni, Ti-Zn), where nano-alloys used as catalyst. These nano-alloys are prepared by hydrazine reduction method. Catalytic properties of these nanomaterials were measured on Ammonium perchorate/hydroxyterminatedpolybutadiene propellant by thermogravimetery analysis and differential thermal analysis. Both experimental results show enhance in the thermal decomposition of propellants in presence of nano-alloys. In this differential thermal analysis method experiments had done in 3 heating rate â1=5, â2=10, â3=15 degree on minute. Independent to model free; calculation of activation energy of high temperature decomposition step was done by using following kissinger equation. Burning rate of propellants is also calculated.Keywords: Activation energy, Ammonium perchlorate, Burning rate, Propellants, Thermal decomposition
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در چند دهه گذشته علاقمندی به پژوهش و استفاده از نانوفیبر سلولزی به طور چشمگیری افزایش یافته است. بنابراین اصلاح سطح نانوفیبر سلولزی به صورت شیمیایی می تواند با ایجاد ویژگی جدید و یا بهبود ویژگی های آنبا حفظ ویژگی های ذاتی نانوفیبر کاربردهای جدیدی را برای آن معرفی کند. در این پژوهش به منظور افزایش پایداری گرمایی نانوفیبر سلولزی، سیانواتیلاسیون توسط پیوندزنی با آکریلونیتریل در دمای °C60 و در شرایط قلیایی انجام شد. پس از تعیین میزان نیتروژن با روش کجدال درجه استخلاف نمونه های سیانو اتیل دار محاسبه شد. افزون بر این ساختار شیمیایی نانوفیبر سلولزی اصلاح شده توسط پرتو بینی FT-IR و آنالیز پراش پرتو ایکس (XRD) شناسایی شد. سپس پایداری گرمایی نانوفیبر سلولزی اصلاح شده با استفاده از آنالیز گرمایی وزن سنجی (TGA) در سه رژیم دمایی °C/min 10، °C/min 15 و °C/min 20 در جو نیتروژن ارزیابی شد. منحنی های مشتق (DTG)TG با استفاده از داده هایTGA رسم شدند و با توجه به داده های تجربی، انرژی فعال سازی محاسبه شد. نتیجه های اندازه گیری میزان نیتروژن، دستیابی به درجه استخلاف 87/0 را در شرایط واکنش نشان دادند. همچنین سیانواتیلاسیون نمونه ها با تحلیل پرتوهای FT-IR و مقایسه آن با پرتو نمونه شاهد و آشکارسازی نوار جذب در 1-cm 2250 منتسب به گروه های نیتریل تایید شد. بررسی ساختار نانو فیبر سلولزی سیانواتیل دار شده با روش پراش پرتو ایکس، کاهش بلورینگی آن را در اثر سیانواتیلاسیون تایید کرد. نتیجه های مطالعه های TGAنیز پایداری گرمایی بیش تر نانوفیبر سلولزی سیانواتیل دار شده را در مقایسه با نمونه اصلاح نشده نشان دادند. همچنین تجزیه گرمایی نمونه های اصلاح نشده و سیانواتیل دار شده هر دو طی یک مرحله رخ داد و با زیاد شدن نرخ گرما دهی افزایش پیدا کرد. همچنین انرژی فعال سازی کمتری برای نانوفیبر سلولزی سیانواتیل دار شده در مقایسه با نانوفیبر سلولزی اصلاح نشده دیده شد. به طور کلی به نظر می رسد که پیوند زنی آکریلونیتریل به نانوفیبر سلولزی می تواند به واسطه بهبود پایداری گرمایی و ایفاینقش به عنوان نرم کننده درونی و بهبود ویژگی های ترموپلاستیکی، استفاده از آن را در کاربردهای خاص توسعه دهد.کلید واژگان: نانوفیبر سلولزی, سیانواتیلاسیون, درجه استخلاف, پایداری گرمایی, انرژی فعال سازیInterest in research and development as well as utilization of Cellulose NanoFiber (CNF) has increased drastically over last decades. Therefore, surface chemical modification and improvement of CNF properties can open up new applications with giving new property while keeping its inherent properties. In this research, in order to enhance thermal stability of CNF cyanoethylation was carried out by acrylonitrile grafting at 60°C under alkaline condition. Degree of Substitution (DS) of cyanoethylated samples was calculated after determination of nitrogen content by Kjeldahl method. Moreover, the chemical structure of modified CNF was characterized with FT-IR spectroscopy and X-Ray Diffraction (XRD) pattern analyses. Thermal stability of modified CNF was then assessed by ThermoGravimetric Analysis (TGA) at three heating rate of 10ºC/min, 15ºC/min, and 20ºC/min under nitrogen atmosphere. Differential ThermoGravimetry (DTG) curves were plotted using TGA data and activation energies were calculated from experimental data. Results of nitrogen content measurements demonstrated DS=0.87 achievement. In addition, cyanoethylation of CNF was confirmed by FT-IR spectra analyses in comparison with control samples and detection of absorption band at 2250 cm-1 which is attributed to nitrile groups. Decrease in CNF crystalinity due to cyanoethylation was demonstrated by XRD analyses. Results of TGA also indicated high thermal stability of cyanoethylated CNF in comparison with unmodified CNF. Moreover, thermal decomposition of both untreated and cyanoethylated CNF occurred in one stage and increased with increasing heating rate. Also low activation energy was observed in cyanoethylated CNF than unmodified CNF. It seems that grafting of acrylonitrile to CNF can increase its utilization in special applications due to improving thermal stability and giving thermoplasticity because of playing role as internal plasticizer.Keywords: Cellulose nanofiber, Cyanoethylation, Degree of substitution, Thermal stability, Activation energy
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In the present research work, the kinetics of sunflower oil transesterification reaction in the presence of Ba-Sr/ZSM-5 nanocatalyst which prepared using incipient wetness impregnation method was investigated. The 10wt.%Ba-Sr/ZSM-5 (Sr/Ba=3/2) nanocatalyst was calcined at 600 °C for 6 h with a heating rate of 3 ºC/min. The experimental conditions were the methanol/oil 9/1molar ratio, reaction time (0-180 min) and reaction temperature (323–333 K) with mechanical stirring of 500 rpm. An irreversible pseudo-second order kinetics was considered for triglyceride conversion from the best modeling of experimental data. From the kinetic study, Ea=67.03 kJ/mol and A=9.29×108 1/min were obtained. The yield of the methyl ester products (86.69%) were determined using gas chromatography–mass spectrometry. characterization of the catalysts and precursors was performed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-Ray diffraction (XRD), Transmission electron microscopy (TEM), and N2 adsorption-desorption measurement methods.Keywords: Biodiesel, Kinetics, Activation energy, Characterization, Operational conditions, Pseudo, second order
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Poly(ethylene adipte) and poly(ethylene adipate)/silica nanocomposite (PEAd/SiO2) containing 3 wt. % SiO2 were prepared by an in situ method. The examinations on the nonisothermal crystallization kinetic behavior have been conducted by means of differential scanning calorimeter (DSC). The Avrami, Ozawa, and combined Avrami and Ozawa equations were applied to describe the crystallization kinetics and to determine the crystallization parameters of the prepared PEAd/SiO2 nanocomposites. It is found that the inclusion of the silica nanoparticles can accelerate the nucleation rate due to heterogeneous nucleation effect of silica on the polymer matrix. According to the obtained results, the combined Avrami and Ozawa equation shown that the better model for examination of this system.Keywords: Nanocomposite, Non, isothermal crystallization, Activation energy, Silica
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We report on the synthesis, morphology, chemically and structurally of TiO2-NiO-SiO2 nanostructure. The TiO2-NiO-SiO2 nanostructure was synthesized by a method based on the sol-gel method, by the simultaneous gelation of all cations. The coatings were deposited on dried soda-lime glass slides by spin coating. Composite powders and coating on glass have been characterized by XRD, SEM, EDAX, and FTIR. X-ray diffraction showed the formation of nano crystalline, anatase, TiO, NiO and NiTiO3 phases. Scanning electron microscopy revealed that nanostructure formed by increasing the calcinations temperatures. EDX spectroscopy confirmed the composition of the ternary powders and coating, which were formed during the gelation process. The effects of chemical compositions and calcinations temperature on the surface topography and the crystallization of phases were studied. The activation energy (E) of nanoparticles formation during thermal treatment was calculated.Keywords: Nanostructure, Poly, component, TiO2, NiO, SiO2, Activation energy, Sol, Gel method
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In continuation to our previous work with composite polyaniline-zirconium (IV)- arsenate (PZA), we further extended with the conductivity measurements in this report. All the calculations reported in here were extracted from the experiments carried out in the temperature range of (25-50)±0.1°C and at different concentrations (0.01C(M)1) of KCl, NaCl and LiCl 1-1 electrolyte solutions. The diffusion coefficient for 1-1 electrolyte solutions was found to decrease in the order K+> Na+> Li+, which is in accordance with a decrease in the size of cation. The resistance is decreasing with increasing time in the order Li+> Na+> K+, and is due to an increased size of the cation for the chosen electrolytes. From the results, the conductivity values for 1-1 electrolytes in the membrane phase were found to be higher at the lower concentration for all the electrolytes in the order of Li+> Na+> K+. It was observed that the conductivity found to be increased with an increase of temperature and obeyed the Arrhenius equation. The activation energy increased with an increased concentration of electrolyte solution and the sequence for the energy of activation is Li+> Na+> K+. The Gibbs free energy, enthalpy and entropy for the ions were calculated at different concentrations and temperatures. All the values of G, H, and S were found to be positive in nature and are following the order K+> Na+> Li+.Keywords: Ionic Conductivity, Alkali Halides, Composite Polyaniline Zirconium (IV) Arsenate Membrane, Gibbs Free Energy, Membrane Conductivity, Diffusion Coefficient, Activation Energy
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