Study of dynamic features of highly energetic reactions by DSC and High-Speed Temperature Scanner (HSTS)

2013 ◽  
Vol 1521 ◽  
Author(s):  
M.A. Hobosyan ◽  
Kh.G. Kirakosyan ◽  
S.L. Kharatyan ◽  
K.S. Martirosyan
Keyword(s):  
High Speed ◽  
Initial Period ◽  
Exothermic Reaction ◽  
Dynamic Features ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Dsc Measurements ◽  
High Heating ◽  
Mechanism And Kinetics ◽  
Conventional Dsc

ABSTRACTThe dynamic features of Al2O3 - polytetrafluoroethylene (PTFE) and Al - PTFE reactions in non-isothermal conditions are presented. The Differential Scanning Calorimetry (DSC) and High-Speed Temperature Scanner (HSTS) were used to characterize the Al2O3/Al – PTFE reactions at different heating rates. The study shows that the HSTS instrument can give more information about the reaction mechanism and kinetics than the conventional DSC measurements. In this work we show that high heating rates may reveal exothermic reaction between Al2O3 and PTFE that were previously unidentified. The PTFE can potentially remove the oxide layer from aluminum in the initial period of the reaction and increase the direct contact area between oxygen and aluminum, which increases the reaction velocity and improves the energy release abilities of the system.

Safe Conditions for Conducting Tests Using Ballistic Facilities

2019 ◽  
pp. 105-114
Author(s):  
S.I. Gerasimov ◽  
I.A. Odzeriho ◽  
R.V. Gerasimova ◽  
A.V. Salnikov ◽  
A.P. Kalmykov ◽  
...  
Keyword(s):  
High Speed ◽  
Practical Implication ◽  
Structure Change ◽  
Heating Rates ◽  
Significant Challenge ◽  
Modern Engineering ◽  
High Heating ◽  
Compressed Gas ◽  
Strong Compression ◽  
Exterior Ballistics

Understanding the physical and thermomechanical response of materials subjected to intense dynamic loading is a significant challenge that has a practical implication for modern engineering. Shock compression followed by expansion precipitates both reversible and irreversible physical and mechanical processes in the material. These processes include strong compression in solids, high heating rates, phase transformations, electronic structure change, work hardening, spalling. Methods and devices for producing intense shock loads can be subdivided into several groups. Presently, in worldwide practice, gun type launchers have gained the widest acceptance in studying dynamic compressibility, strength characteristics, and spallatation phenomena in laboratory conditions. In this type of facility, the launched body moves in a tube under the force of a compressed gas. The facilities differ depending on the gas used and the method of its compression. Specific features of the facilities impose certain limitations on the registration and format of the tests. Examples of determining the boundary between the interior and exterior ballistics, the influence of the launched body supporting elements and the conditions of safe testing at high-speed entry in fuel are considered in this work.

scholarly journals Study of poly(L-lactide) using Fast Scanning Calorimetry

2020 ◽  
Vol 6 (3) ◽  
pp. 422-425
Author(s):  
Daniela Arbeiter ◽  
Stefan Oschatz ◽  
Sabine Illner ◽  
Niels Grabow
Keyword(s):  
Thermal Properties ◽  
Quantitative Analysis ◽  
Small Sample ◽  
Analytical Tool ◽  
Solution Casting ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Dsc Measurements ◽  
Fast Scanning Calorimetry ◽  
Small Sample Sizes

AbstractFast scanning calorimetry (FSC) is an effective analytical tool to characterize the thermal properties of polymers. Heating rates up to 100 000 K/s allow studies at time scales inaccessible with conventional calorimeters, whose rates are typically less than about 0.5 K/s. Recent studies have successfully demonstrated methods for obtaining quantitative analysis of thermal properties of polymer samples using chip-based FSC. Therefore very small sample sizes, such as particles or nonwovens, can be characterized. In this study, we investigated the thermal properties of poly(L-lactide) PLLA with FSC compared to the results from standard DSC methods. PLLA specimens were fabricated via solution casting and needle electrospinning. The results suggest a significant influence of heating rates on the melting temperature of PLLA. The results show that different fabrication methods lead to changes in crystallinity and that FSC results are not completely comparable with standard DSC measurements.

scholarly journals Scanning Rate Extension of Conventional DSCs through Indirect Measurements

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1085 ◽  
Author(s):  
Hannes Fröck ◽  
Michael Reich ◽  
Benjamin Milkereit ◽  
Olaf Kessler
Keyword(s):  
Aluminum Alloys ◽  
Indirect Measurement ◽  
Heat Treatments ◽  
Dissolution Behavior ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Heating And Cooling ◽  
Heat Treated ◽  
Conventional Dsc

In this work, a method is presented which allows the determination of calorimetric information, and thus, information about the precipitation and dissolution behavior of aluminum alloys during heating rates that could not be previously measured. Differential scanning calorimetry (DSC) is an established method for in-situ recording of dissolution and precipitation reactions in various aluminum alloys. Diverse types of DSC devices are suitable for different ranges of scanning rates. A combination of the various available commercial devices enables heating and cooling rates from 10−4 to 5 Ks−1 to be covered. However, in some manufacturing steps of aluminum alloys, heating rates up to several 100 Ks−1 are important. Currently, conventional DSC cannot achieve these high heating rates and they are still too slow for the chip-sensor based fast scanning calorimetry. In order to fill the gap, an indirect measurement method has been developed, which allows the determination of qualitative information, regarding the precipitation state, at various points of any heat treatment. Different rapid heat treatments were carried out on samples of an alloy EN AW-6082 in a quenching dilatometer and terminated at defined temperatures. Subsequent reheating of the samples in the DSC enables analysis of the precipitation state of the heat-treated samples. This method allows for previously un-measurable heat treatments to get information about the occurring precipitation and dissolution reactions during short-term heat treatments.

scholarly journals Joint Reduction of NiO/WO3 Pair and NiWO4 by Mg + C Combined Reducer at High Heating Rates

Metals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1351
Author(s):  
Marieta Zakaryan ◽  
Khachik Nazaretyan ◽  
Sofiya Aydinyan ◽  
Suren Kharatyan
Keyword(s):  
Composite Materials ◽  
High Speed ◽  
Synergetic Effect ◽  
Isoconversional Method ◽  
Heating Rates ◽  
Formation Pathway ◽  
High Heating ◽  
Functional Features ◽  
Maximum Temperatures ◽  
Solid Liquid

Functional features of Ni-W composite materials combined with successful performance enabled a breakthrough in their broad application. To disclose the formation pathway of Ni-W composite materials at extreme conditions of combustion synthesis in the NiO-WO3-Mg-C and NiWO4-Mg-C systems for the optimization of the synthesis procedure, the process was modeled under programmed linear heating conditions by thermal analysis methods. The reduction kinetics of tungsten and nickel oxides mixture and nickel tungstate by Mg + C combined reducer at non-isothermal conditions was studied at high heating rates (100–1200 °C min−1) by high-speed temperature scanner techniques. It was shown that when moving from low heating to high heating rates, the mechanism of both the magnesiothermic and magnesio-carbothermic reductions of the initial mixtures changes; that is, the transition from a solid-solid scheme to a solid-liquid scheme is observed. The strong influence of the heating rate on the reduction degree and kinetic parameters of the systems under study was affirmed. The simultaneous utilization of magnesium and carbon as reducers allowed the lowering of the starting and maximum temperatures of reduction processes, as evidenced by the synergetic effect at the utilization of a combined reducer. The effective values of activation energy (Ea) for the reactions proceeding in the mixtures NiO + WO3 + 4Mg, NiO + WO3 + 2.5Mg + 1.5C, NiWO4 + 4Mg and NiWO4 + 2Mg + 2C were estimated by Kissinger isoconversional method and were 146 ± 10, 141 ± 10, 216 ± 15 and 148 ± 15 kJ mol−1, respectively.

scholarly journals Curing kinetics of two commercial urea-formaldehyde adhesives studied by isoconversional method

2011 ◽  
Vol 65 (6) ◽  
pp. 717-726 ◽  
Author(s):  
Mladjan Popovic ◽  
Jaroslava Budinski-Simendic ◽  
Mirjana Jovicic ◽  
Joszef Mursics ◽  
Milanka Djiporovic-Momcilovic ◽  
...  
Keyword(s):  
Activation Energy ◽  
Urea Formaldehyde ◽  
Curing Kinetics ◽  
Isoconversional Methods ◽  
Isoconversional Method ◽  
Reaction Enthalpy ◽  
Heating Rates ◽  
Scanning Calorimetry ◽  
Dsc Measurements ◽  
Kinetics Of

Differential scanning calorimetry (DSC) was used to evaluate the curing kinetics of two commercial urea-formaldehyde (UF) adhesives having different formaldehyde to urea (F/U) ratio of 1.112 (UF1) and 1.086 (UF2). DSC measurements were done in dynamic scanning regime with heating rates of 5, 10, 15 and 20?C?min-1 in order to determine the activation energy for each adhesive. Obtained data were analyzed using isoconversional methods with application of Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose kinetic models. In addition, different catalyst levels were tested at the heating rate of 10?C/min. Results showed that the adhesive with higher F/U ratio achieved higher activation energy, while having lower peak temperature of curing reaction. It was also noticed that the increase of catalyst level influenced the increase of reaction enthalpy of the adhesive with lower F/U ratio.

Comparing fast inductive tempering and conventional tempering: Effects on microstructure and mechanical properties

2018 ◽  
Vol 115 (4) ◽  
pp. 407 ◽  
Author(s):  
Annika Eggbauer Vieweg ◽  
Gerald Ressel ◽  
Peter Raninger ◽  
Petri Prevedel ◽  
Stefan Marsoner ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Impact Energy ◽  
Charpy Impact ◽  
Heat Treating ◽  
Processing Route ◽  
High Heating Rate ◽  
Heating Rates ◽  
High Heating ◽  
Tempering Treatment ◽  
Carbide Distribution

Induction heating processes are of rising interest within the heat treating industry. Using inductive tempering, a lot of production time can be saved compared to a conventional tempering treatment. However, it is not completely understood how fast inductive processes influence the quenched and tempered microstructure and the corresponding mechanical properties. The aim of this work is to highlight differences between inductive and conventional tempering processes and to suggest a possible processing route which results in optimized microstructures, as well as desirable mechanical properties. Therefore, the present work evaluates the influencing factors of high heating rates to tempering temperatures on the microstructure as well as hardness and Charpy impact energy. To this end, after quenching a 50CrMo4 steel three different induction tempering processes are carried out and the resulting properties are subsequently compared to a conventional tempering process. The results indicate that notch impact energy raises with increasing heating rates to tempering when realizing the same hardness of the samples. The positive effect of high heating rate on toughness is traced back to smaller carbide sizes, as well as smaller carbide spacing and more uniform carbide distribution over the sample.

scholarly journals Remote or Removed: Predicting Successful Engagement with Online Learning during COVID-19

2021 ◽  
Vol 7 ◽  
pp. 237802312098820
Author(s):  
Thurston Domina ◽  
Linda Renzulli ◽  
Brittany Murray ◽  
Alma Nidia Garza ◽  
Lysandra Perez
Keyword(s):  
Elementary School ◽  
Student Engagement ◽  
High Speed ◽  
Initial Period ◽  
Learning Opportunities ◽  
Academic Learning ◽  
Socioeconomic Resources ◽  
Using Data ◽  
School Programming ◽  
Remote Learning

Using data from a spring 2020 survey of nearly 10,000 parents of elementary school parents in one large southeastern public school district, the authors investigate predictors of elementary school student engagement during the initial period of pandemic remote learning. The authors hypothesize that household material and technological resources, school programming and instructional strategies, and family social capital contribute to student engagement in remote learning. The analyses indicate that even after controlling for rich measures of family socioeconomic resources, students with access to high-speed Internet and Internet-enabled devices have higher levels of engagement. Exposure to more diverse socioemotional and academic learning opportunities further predicts higher levels of engagement. In addition, students whose families remained socially connected to other students’ families were more likely to engage online.

scholarly journals Energetic-Materials-Driven Synthesis of Graphene-Encapsulated Tin Oxide Nanoparticles for Sodium-Ion Batteries

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2550
Author(s):  
Yingchun Wang ◽  
Jinxu Liu ◽  
Min Yang ◽  
Lijuan Hou ◽  
Tingting Xu ◽  
...  
Keyword(s):  
Tin Oxide ◽  
Energetic Materials ◽  
High Speed ◽  
Coulombic Efficiency ◽  
Sno2 Nanoparticles ◽  
Direct Synthesis ◽  
Exothermic Reaction ◽  
Rate Capability ◽  
Rapid Expansion ◽  
Core Shell

By evenly mixing polytetrafluoroethylene-silicon energetic materials (PTFE-Si EMs) with tin oxide (SnO2) particles, we demonstrate a direct synthesis of graphene-encapsulated SnO2 (Gr-SnO2) nanoparticles through the self-propagated exothermic reaction of the EMs. The highly exothermic reaction of the PTFE-Si EMs released a huge amount of heat that induced an instantaneous temperature rise at the reaction zone, and the rapid expansion of the gaseous SiF4 product provided a high-speed gas flow for dispersing the molten particles into finer nanoscale particles. Furthermore, the reaction of the PTFE-NPs with Si resulted in a simultaneous synthesis of graphene that encapsulated the SnO2 nanoparticles in order to form the core-shell nanostructure. As sodium storage material, the graphene-encapsulated SnO2 nanoparticles exhibit a good cycling performance, superior rate capability, and a high initial Coulombic efficiency of 85.3%. This proves the effectiveness of our approach for the scalable synthesis of core-shell-structured graphene-encapsulated nanomaterials.

scholarly journals Mechanism of the improvement of the energy of host–guest explosives by incorporation of small guest molecules: HNO3 and H2O2 promoted C–N bond cleavage of the ring of ICM-102

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yiwen Xiao ◽  
Lang Chen ◽  
Kun Yang ◽  
Deshen Geng ◽  
Jianying Lu ◽  
...  
Keyword(s):  
Bond Cleavage ◽  
Exothermic Reaction ◽  
High Energy ◽  
Ring Structure ◽  
High Energy Density ◽  
Initial Reaction ◽  
Heating Rates ◽  
Thermal Stabilities ◽  
Guest Molecules ◽  
Molecule Reaction

AbstractHost–guest materials exhibit great potential applications as an insensitive high-energy–density explosive and low characteristic signal solid propellant. To investigate the mechanism of the improvement of the energy of host–guest explosives by guest molecules, ReaxFF-lg reactive molecular dynamics simulations were performed to calculate the thermal decomposition reactions of the host–guest explosives systems ICM-102/HNO3, ICM-102/H2O2, and pure ICM-102 under different constant high temperatures and different heating rates. Incorporation of guest molecules significantly increased the energy level of the host–guest system. However, the initial reaction path of the ICM-102 molecule was not changed by the guest molecules. The guest molecules did not initially participate in the host molecule reaction. After a period of time, the H2O2 and HNO3 guest molecules promoted cleavage of the C–N bond of the ICM-102 ring. Stronger oxidation and higher oxygen content resulted in the guest molecules more obviously accelerating destruction of the ICM-102 ring structure. The guest molecules accelerated the initial endothermic reaction of ICM-102, but they played a more important role in the intermediate exothermic reaction stage: incorporation of guest molecules (HNO3 and H2O2) greatly improved the heat release and exothermic reaction rate. Although the energies of the host–guest systems were clearly improved by incorporation of guest molecules, the guest molecules had little effect on the thermal stabilities of the systems.

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