Enthalpy

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1 - Calculation of energy lost by radiation and convection during laser welding of TA6V titanium alloy
Soumaya Lemkeddem Fethi Khelfaoui Oumelkheir Babahani

10.1007/s40094-018-0288-x

AbstractLaser welding is being used more frequently in industrial processes because of its advantages; therefore, energy loss in welding is an important issue during planning and operation. We calculated the energy losses expected during the laser welding of TA6V titani چکیده کامل

AbstractLaser welding is being used more frequently in industrial processes because of its advantages; therefore, energy loss in welding is an important issue during planning and operation. We calculated the energy losses expected during the laser welding of TA6V titanium alloy. We used the heat equation to describe the energy distribution of solid and liquid TA6V. The solid-to-liquid phase change was taken into account by comparing the accumulated energies and enthalpy of fusion. A numerical model was used to calculate the energy lost by convection and radiation. Finite difference calculations were performed using a FORTRAN-based computer program to solve the heat equation. The numerical results suggested that the appropriate laser welding velocity and power were in good agreement with the experimental data published elsewhere in the literature. The results showed the importance of the influence of the energy lost by radiation and convection in the welding area on welding energies and temperatures. پرونده مقاله

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2 - Determination of thermodynamic parameters of produced materials from (ATTZ) with boron nitride nano-cages in different conditions of temperature, with DFT method
Roya Ahmadi Elahe Sadat Mirkamali

6-Amino-1,2,4-triazolo[4,3-b][1,2,4,5]tetrazine (ATTz)is an explosive material, that has been synthesized from the reaction of 3,6-diaminotetrazine , with nitrous acid and then sodium azide. In the simplest terms, an explosive is defined as a substance, which on initiat چکیده کامل

6-Amino-1,2,4-triazolo[4,3-b][1,2,4,5]tetrazine (ATTz)is an explosive material, that has been synthesized from the reaction of 3,6-diaminotetrazine , with nitrous acid and then sodium azide. In the simplest terms, an explosive is defined as a substance, which on initiation by friction, impact, shock, spark, flame, heating, or any simple application of an energy pulse, undergoes a rapid chemical reaction evolving a large amount of heat and so exerting a high pressure on its surroundings. The vast majority of explosives release gaseous products on explosion. In this study the reaction of 6-Amino-1,2,4-triazolo[4,3-b][1,2,4,5]tetrazine (ATTz) with boron nitride Nano- cages in different conditions of temperature, by density functional theory methods was investigated. For this purpose, the material on both sides of reaction was geometrically optimized, and then the calculation of the thermodynamic parameters was performed on all of them. The values of ΔH, ΔG, ΔS for this reaction at different temperatures were obtained, and finally, the best temperature for the synthesis of explosives nano derivatives, according to the results of thermodynamic parameters were evaluated. پرونده مقاله

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3 - A Theoretical Study on the Aromaticity of 5-methylcytosine tautomers in the gas phase
H. Aghaie K. Zare E. Zahedi S.R. Emamian

The armaticity of 5 methylcytosine tautomers in the gas phase has been studied and the chemical structures of related tautomers are investigated . The electronic energy, enthalpy and free energy of each tautomer are also estimated at the B3LYP/6-31 G* // B3LYP/6-31 G* a چکیده کامل

The armaticity of 5 methylcytosine tautomers in the gas phase has been studied and the chemical structures of related tautomers are investigated . The electronic energy, enthalpy and free energy of each tautomer are also estimated at the B3LYP/6-31 G* // B3LYP/6-31 G* and MP2 / 6-31 G* // MP2 / 6-31 G* Levels پرونده مقاله

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4 - Adsorption of Bis(1,4-dinitro toprop-2-yl) Nitramine on Boron Nitride Nano-cages Surfaces: DFT Studies
Roya Ahmadi Maryam Ebrahimikia Elham Pournamdar

In this study Bis(1,4-dinitro toprop-2-yl) Nitramine, BNA, was attached to boron nitride nano- cages (B12N12). , thermodynamic parameters of BNA with B12N12 have been computed using one of the methods of density functional theory (B3LYP) In the temperature variety 300 t چکیده کامل

In this study Bis(1,4-dinitro toprop-2-yl) Nitramine, BNA, was attached to boron nitride nano- cages (B12N12). , thermodynamic parameters of BNA with B12N12 have been computed using one of the methods of density functional theory (B3LYP) In the temperature variety 300 to 400 K each 10 degree one times, were calculated. So these materials were geometrically optimized. After that thermodynamic parameters were calculated. Enthalpy values (ΔH), Specific heat capacity (Cv) and Gibbs free energy (ΔG) were computed for these reactions. Finally, the effect of nano structures on explosion properties and other chemical attributes of BNA were evaluated. پرونده مقاله

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5 - بررسی امکان اندازه‌گیری ترکیبات فنولی حلقوی در شکر قهوه‌ای به روش DFT
پرستو مسگران کریمی مسعود هنرور

مقدمه: گیاه نیشکر و شکر حاصل از آن حاوی انواع ترکیبات فنولی است که خواص آنتی اکسیدانی مطلوبی نیز دارند. از این رو پژوهش حاضر به بررسی امکان اندازه گیری این ترکیبات فنولی در شکر قهوه ای با استفاده از روش DFT می پردازد. مواد و روش‌ها: در این پژوهش از دو نوع شکر پخت (II) چکیده کامل

مقدمه: گیاه نیشکر و شکر حاصل از آن حاوی انواع ترکیبات فنولی است که خواص آنتی اکسیدانی مطلوبی نیز دارند. از این رو پژوهش حاضر به بررسی امکان اندازه گیری این ترکیبات فنولی در شکر قهوه ای با استفاده از روش DFT می پردازد. مواد و روش‌ها: در این پژوهش از دو نوع شکر پخت (II) و پخت (III) در فرایند تولید شکر نمونه گیری شد و در ابتدا با استفاده از دستگاه کروماتوگرافی مایع با کارایی بالا (HPLC) نوع و نسبت ترکیبات فنولی حلقوی در دو نوع شکر پخت (II) و پخت (III) شناسایی و تعیین شد. در گام بعدی و برای اولین بار، با استفاده از روش محاسباتی پیشرفته نظریه تابعیت چگالی DFT و براساس محاسبه انتالپی تفکیک پیوند BDE)) و پتانسیل یونیزاسیون (IP) خاصیت آنتی اکسیدانی این نوع از ترکیبات محاسبه شد. یافته‌ها: با مقایسه میزان BDE و IP ترکیبات شناسایی شده مشخص شد کنیفرول الکل بیشترین و بنزوئیک اسید کمترین خاصیت آنتی‌اکسیدانی را در دو نمونه شکر پخت (II) و شکر پخت (III) دارا است. نتیجه‌گیری: استفاده از روش های محاسباتی به منظور تعیین میزان ترکیبات فنولی به خوبی می تواند کارآمد باشد. پرونده مقاله

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6 - First Principles calculation High Spin to Low Spin transition in the SrMnO3 and the CaMnO3 compound
Narges Saki Azadeh Aezami

In this research, structural, electronic, magnetic, and electrical properties of SrMnO3 and CaMnO3 have been investigated using calculations based on density-functional theory from scratch and Quantum-Espresso calculation code. The Hubbard parameter has been calculated چکیده کامل

In this research, structural, electronic, magnetic, and electrical properties of SrMnO3 and CaMnO3 have been investigated using calculations based on density-functional theory from scratch and Quantum-Espresso calculation code. The Hubbard parameter has been calculated for the Mn atom using a linear response approach and LDA+U approximation for both compounds. This parameter is 3.5 eV for CaMnO3 and it is 3.1 eV for SrMnO3. The calculations showed that even though both compounds are insulator and G-type antiferromagnetic materials. Both samples have a cubic perovskite structure in which the Mn atom is located at the center of an octagon surrounded by oxygen atoms, and the vertices of a cube are the place for Sr and Ca atoms. The effect of pressure on these two compounds has been studied from %5 to %20 in tensile pressure (TP) and compressive pressure (CP) directions along the z-axis. The transition from High Spin (HS) to Low Spin (LS) of both compounds has been searched through the results of enthalpy calculations in terms of pressure. Results reveal that both materials are in stable HS and LS states in pressures higher and lower than -10 GPa and -20 GPa, respectively. Moreover, the magnetic moment of CaMnO3 in the pressure of -20.51 GPa decreases from 3.41µB in a stable HS state to 1.44 µB in an LS state, and that of SrMnO3 in the pressure of -26.87 GPa declines from 4.37 µB in HS state to 1.55 µB in LS state. پرونده مقاله

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7 - Structure-radical scavenging activity relationships of hydroxytoluene derivatives
Adnan Bekhit Baye Akele Ariaya Hymete

Research works proposed that radical scavenging activity of flavonoids is due to ring B, andthe remaining part of the molecule can be disregarded. Thus the objective of this work is toobserve whether hydroxytoluenes account the radical scavenging activity of flavonoid a چکیده کامل

Research works proposed that radical scavenging activity of flavonoids is due to ring B, andthe remaining part of the molecule can be disregarded. Thus the objective of this work is toobserve whether hydroxytoluenes account the radical scavenging activity of flavonoid and toestablish structural requirements for their activity (as they showed appreciable activity) andelucidate a comprehensive mechanism that can explain their activity and termination. Thus, theradical-scavenging activity of nine hydroxytoluene derivatives against 2,2-diphenyl-1-picrylhydrazyl, DPPH was determined. The relative change in energy (ΔHf) associated with theformation of phenolic radicals and the spin distributions in these radicals were determined usingcomputational programs (Density function theory and Hartree Fock). By correlatingexperimental data with ΔHf, the most active compounds and structural features that areresponsible for their activities were identified. Reaction product of 4-methyl catechol with 2,2-diphenyl-1-picrylhydrazyl, DPPH was isolated and characterized in order to unravel themechanism of termination of most active hydroxytoluenes. Termination enthalpy (ΔH2) ofmethyl-catechols and methyl-hydroquinone, once the termination mechanism explained, wascalculated to understand its role in the radical scavenging activity. پرونده مقاله

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8 - بررسی نقش اربیم بر رفتار ترمودینامیکی آلیاژهای آلومینیوم – روی
رضا امینی نجف آبادی محمد رزازی بروجنی عزت الله غنی‌اف ضیادالله ابیداف

ضریب هدایت حرارتی، ظرفیت گرمای ویژه، آنتالپی، آنتروپی و انرژی آزاد گیپس آلیاژهایZn5Al و Zn55Al که اربیم به آن اضافه شده است با استفاده از قانون سرد شدن نیوتن در یک دستگاه جدید مورد مطالعه قرار گرفت. مشاهده شد که با افزایش دما، ظرفیت گرمای ویژه، آنتالپی و آنتروپی این آلی چکیده کامل

ضریب هدایت حرارتی، ظرفیت گرمای ویژه، آنتالپی، آنتروپی و انرژی آزاد گیپس آلیاژهایZn5Al و Zn55Al که اربیم به آن اضافه شده است با استفاده از قانون سرد شدن نیوتن در یک دستگاه جدید مورد مطالعه قرار گرفت. مشاهده شد که با افزایش دما، ظرفیت گرمای ویژه، آنتالپی و آنتروپی این آلیاژها افزایش می یابد. در حدود دمای 520 تا 530 درجه کلوین، کاهش شدید ضریب هدایت حرارتی و ظرفیت گرمای ویژه نشان داد که در تمام این سیستم ها شامل تغییر فاز درجه دوم می باشد. در نهایت فاکتورهای ترمودینامیکی ذکر شده محاسبه گردید. پرونده مقاله

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