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2 pages, 169 KiB

Open AccessEditorial

Special Issue: Thermal Analysis of Materials

by Sergey V. Ushakov and Shmuel Hayun

Materials 2021, 14(17), 4923; https://doi.org/10.3390/ma14174923 - 30 Aug 2021

Viewed by 1866

Abstract

The measurement of any physical property as a function of temperature brings the method used into the realm of thermal analysis [...] Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

Research

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13 pages, 1597 KiB

Open AccessArticle

Measurements of Density of Liquid Oxides with an Aero-Acoustic Levitator

by Sergey V. Ushakov, Jonas Niessen, Dante G. Quirinale, Robert Prieler, Alexandra Navrotsky and Rainer Telle

Materials 2021, 14(4), 822; https://doi.org/10.3390/ma14040822 - 9 Feb 2021

Cited by 12 | Viewed by 3516

Abstract

Densities of liquid oxide melts with melting temperatures above 2000 °C are required to establish mixing models in the liquid state for thermodynamic modeling and advanced additive manufacturing and laser welding of ceramics. Accurate measurements of molten rare earth oxide density were recently [...] Read more.

Densities of liquid oxide melts with melting temperatures above 2000 °C are required to establish mixing models in the liquid state for thermodynamic modeling and advanced additive manufacturing and laser welding of ceramics. Accurate measurements of molten rare earth oxide density were recently reported from experiments with an electrostatic levitator on board the International Space Station. In this work, we present an approach to terrestrial measurements of density and thermal expansion of liquid oxides from high-speed videography using an aero-acoustic levitator with laser heating and machine vision algorithms. The following density values for liquid oxides at melting temperature were obtained: Y₂O₃ 4.6 ± 0.15; Yb₂O₃ 8.4 ± 0.2; Zr_0.9Y_0.1O_1.95 4.7 ± 0.2; Zr_0.95Y_0.05O_1.975 4.9 ± 0.2; HfO₂ 8.2 ± 0.3 g/cm³. The accuracy of density and thermal expansion measurements can be improved by employing backlight illumination, spectropyrometry and a multi-emitter acoustic levitator. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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19 pages, 8825 KiB

Open AccessArticle

Comparison of the Properties of Natural Sorbents for the Calcium Looping Process

by Krzysztof Labus

Materials 2021, 14(3), 548; https://doi.org/10.3390/ma14030548 - 24 Jan 2021

Cited by 7 | Viewed by 2489

Abstract

Capturing CO₂ from industrial processes may be one of the main ways to control global temperature increases. One of the proposed methods is the calcium looping technology (CaL). The aim of this research was to assess the sequestration capacity of selected carbonate [...] Read more.

Capturing CO₂ from industrial processes may be one of the main ways to control global temperature increases. One of the proposed methods is the calcium looping technology (CaL). The aim of this research was to assess the sequestration capacity of selected carbonate rocks, serpentinite, and basalt using a TGA-DSC analysis, thus simulating the CaL process. The highest degrees of conversion were obtained for limestones, lower degrees were obtained for magnesite and serpentinite, and the lowest were obtained for basalt. The decrease in the conversion rate, along with the subsequent CaL cycles, was most intense for the sorbents with the highest values. Thermally pretreated limestone samples demonstrated different degrees of conversion, which were the highest for the calcium-carbonate-rich limestones. The cumulative carbonation of the pretreated samples was more than twice as low as that of the raw ones. The thermal pretreatment was effective for the examined rocks. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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10 pages, 2739 KiB

Open AccessArticle

Investigation and Possibilities of Reuse of Carbon Dioxide Absorbent Used in Anesthesiology

by Bartłomiej Rogalewicz, Agnieszka Czylkowska, Piotr Anielak and Paweł Samulkiewicz

Materials 2020, 13(21), 5052; https://doi.org/10.3390/ma13215052 - 9 Nov 2020

Cited by 4 | Viewed by 2940

Abstract

Absorbents used in closed and semi-closed circuit environments play a key role in preventing carbon dioxide poisoning. Here we present an analysis of one of the most common carbon dioxide absorbents—soda lime. In the first step, we analyzed the composition of fresh and [...] Read more.

Absorbents used in closed and semi-closed circuit environments play a key role in preventing carbon dioxide poisoning. Here we present an analysis of one of the most common carbon dioxide absorbents—soda lime. In the first step, we analyzed the composition of fresh and used samples. For this purpose, volumetric and photometric analyses were introduced. Thermal properties and decomposition patterns were also studied using thermogravimetric and X-ray powder diffraction (PXRD) analyses. We also investigated the kinetics of carbon dioxide absorption under conditions imitating a closed-circuit environment. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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16 pages, 4528 KiB

Open AccessArticle

Study of Industrial Grade Thermal Insulation at Elevated Temperatures

by Amalie Gunnarshaug, Maria Monika Metallinou and Torgrim Log

Materials 2020, 13(20), 4613; https://doi.org/10.3390/ma13204613 - 16 Oct 2020

Cited by 8 | Viewed by 3432

Abstract

Thermal insulation is used for preventing heat losses or heat gains in various applications. In industries that process combustible products, inorganic-materials-based thermal insulation may, if proven sufficiently heat resistant, also provide heat protection in fire incidents. The present study investigated the performance and [...] Read more.

Thermal insulation is used for preventing heat losses or heat gains in various applications. In industries that process combustible products, inorganic-materials-based thermal insulation may, if proven sufficiently heat resistant, also provide heat protection in fire incidents. The present study investigated the performance and breakdown temperature of industrial thermal insulation exposed to temperatures up to 1200 °C, i.e., temperatures associated with severe hydrocarbon fires. The thermal insulation properties were investigated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and by heating 50 mm cubes in a muffle furnace to temperatures in the range of 600 to 1200 °C with a 30 min holding time. The room temperature thermal conductivity was also recorded after each heat treatment. Upon heating, the mineral-based oil dust binder was released at temperatures in the range of 300 to 500 °C, while the Bakelite binder was released at temperatures in the range of 850 to 960 °C. The 50 mm test cubes experienced increasing levels of sintering in the temperature range of 700 to 1100 °C. At temperatures above 1100 °C, the thermal insulation started degrading significantly. Due to being heat-treated to 1200 °C, the test specimen morphology was similar to a slightly porous rock and the original density of 140 kg/m³ increased to 1700 kg/m³. Similarly, the room temperature thermal conductivity increased from 0.041 to 0.22 W/m∙K. The DSC analysis confirmed an endothermic peak at about 1200 °C, indicating melting, which explained the increase in density and thermal conductivity. Recently, 350 kW/m² has been set as a test target heat flux, i.e., corresponding to an adiabatic temperature of 1200 °C. If a thin layer of thermally robust insulation is placed at the heat-exposed side, the studied thermal insulation may provide significant passive fire protection, even when exposed to heat fluxes up to 350 kW/m². It is suggested that this is further analysed in future studies. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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19 pages, 5798 KiB

Open AccessArticle

High-Temperature Structural and Electrical Properties of BaLnCo₂O₆ Positrodes

by Iga Szpunar, Ragnar Strandbakke, Magnus Helgerud Sørby, Sebastian Lech Wachowski, Maria Balaguer, Mateusz Tarach, José M. Serra, Agnieszka Witkowska, Ewa Dzik, Truls Norby, Maria Gazda and Aleksandra Mielewczyk-Gryń

Materials 2020, 13(18), 4044; https://doi.org/10.3390/ma13184044 - 11 Sep 2020

Cited by 20 | Viewed by 3961

Abstract

The application of double perovskite cobaltites BaLnCo₂O_6−δ (Ln = lanthanide element) in electrochemical devices for energy conversion requires control of their properties at operating conditions. This work presents a study of a series of BaLnCo [...] Read more.

The application of double perovskite cobaltites BaLnCo₂O_6−δ (Ln = lanthanide element) in electrochemical devices for energy conversion requires control of their properties at operating conditions. This work presents a study of a series of BaLnCo₂O_6−δ (Ln = La, Pr, Nd) with a focus on the evolution of structural and electrical properties with temperature. Symmetry, oxygen non-stoichiometry, and cobalt valence state have been examined by means of Synchrotron Radiation Powder X-ray Diffraction (SR-PXD), thermogravimetry (TG), and X-ray Absorption Spectroscopy (XAS). The results indicate that all three compositions maintain mainly orthorhombic structure from RT to 1000 °C. Chemical expansion from Co reduction and formation of oxygen vacancies is observed and characterized above 350 °C. Following XAS experiments, the high spin of Co was ascertained in the whole range of temperatures for BLC, BPC, and BNC. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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14 pages, 3827 KiB

Open AccessArticle

Effect of Structure and Composition of Non-Stoichiometry Magnesium Aluminate Spinel on Water Adsorption

by Yuval Mordekovitz, Yael Shoval, Natali Froumin and Shmuel Hayun

Materials 2020, 13(14), 3195; https://doi.org/10.3390/ma13143195 - 17 Jul 2020

Cited by 26 | Viewed by 3274

Abstract

MgAl₂O₄ is used in humidity sensing and measurement, and as a catalyst or catalyst support in a wide variety of applications. For such applications, a detailed understanding of the surface properties and defect structure of the spinel, and, in particular, [...] Read more.

MgAl₂O₄ is used in humidity sensing and measurement, and as a catalyst or catalyst support in a wide variety of applications. For such applications, a detailed understanding of the surface properties and defect structure of the spinel, and, in particular, of the gas interactions at the spinel surface is essential. However, to the best of our knowledge, very limited experimental data regarding this subject is currently available. In this work, four spinel samples with an Al₂O₃ to MgO ratio (n) between 0.95 and 2.45 were synthesized and analyzed using X-ray photoelectron spectroscopy and water adsorption micro-calorimetry. The results showed that the spinel composition and its consequent defect structure do indeed have a distinct effect on the spinel-water vapor surface interactions. The adsorption behavior at the spinel-water interface showed changes that resulted from alterations in types and energetic diversity of adsorption sites, affecting both H₂O uptake and overall energetics. Furthermore, changes in composition following appropriate thermal treatment were shown to have a major effect on the reducibility of the spinel which enabled increased water uptake at the surface. In addition to non-stoichiometry, the impact of intrinsic anti-site defects on the water-surface interaction was investigated. These defects were also shown to promote water uptake. Our results show that by composition modification and subsequent thermal treatments, the defect structure can be modified and controlled, allowing for the possibility of specifically designed spinels for water interactions. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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19 pages, 2002 KiB

Open AccessArticle

Thermal Analysis of High Entropy Rare Earth Oxides

by Sergey V. Ushakov, Shmuel Hayun, Weiping Gong and Alexandra Navrotsky

Materials 2020, 13(14), 3141; https://doi.org/10.3390/ma13143141 - 14 Jul 2020

Cited by 31 | Viewed by 5631

Abstract

Phase transformations in multicomponent rare earth sesquioxides were studied by splat quenching from the melt, high temperature differential thermal analysis and synchrotron X-ray diffraction on laser-heated samples. Three compositions were prepared by the solution combustion method: (La,Sm,Dy,Er,RE)₂O₃, where all [...] Read more.

Phase transformations in multicomponent rare earth sesquioxides were studied by splat quenching from the melt, high temperature differential thermal analysis and synchrotron X-ray diffraction on laser-heated samples. Three compositions were prepared by the solution combustion method: (La,Sm,Dy,Er,RE)₂O₃, where all oxides are in equimolar ratios and RE is Nd or Gd or Y. After annealing at 800 °C, all powders contained mainly a phase of C-type bixbyite structure. After laser melting, all samples were quenched in a single-phase monoclinic B-type structure. Thermal analysis indicated three reversible phase transitions in the range 1900–2400 °C, assigned as transformations into A, H, and X rare earth sesquioxides structure types. Unit cell volumes and volume changes on C-B, B-A, and H-X transformations were measured by X-ray diffraction and consistent with the trend in pure rare earth sesquioxides. The formation of single-phase solid solutions was predicted by Calphad calculations. The melting point was determined for the (La,Sm,Dy,Er,Nd)₂O₃ sample as 2456 ± 12 °C, which is higher than for any of constituent oxides. An increase in melting temperature is probably related to nonideal mixing in the solid and/or the melt and prompts future investigation of the liquidus surface in Sm₂O₃-Dy₂O₃, Sm₂O₃-Er₂O₃, and Dy₂O₃-Er₂O₃ systems. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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11 pages, 2866 KiB

Open AccessArticle

Spark Plasma Sintering Apparatus Used for High-temperature Compressive Creep Tests

by Barak Ratzker, Sergey Kalabukhov and Nachum Frage

Materials 2020, 13(2), 396; https://doi.org/10.3390/ma13020396 - 15 Jan 2020

Cited by 8 | Viewed by 3022

Abstract

Creep is a time dependent, temperature-sensitive mechanical response of a material in the form of continuous deformation under constant load or stress. To study the creep properties of a given material, the load/stress and temperature must be controlled while measuring strain over time. [...] Read more.

Creep is a time dependent, temperature-sensitive mechanical response of a material in the form of continuous deformation under constant load or stress. To study the creep properties of a given material, the load/stress and temperature must be controlled while measuring strain over time. The present study describes how a spark plasma sintering (SPS) apparatus can be used as a precise tool for measuring compressive creep of materials. Several examples for using the SPS apparatus for high-temperature compressive creep studies of metals and ceramics under a constant load are discussed. Experimental results are in a good agreement with data reported in literature, which verifies that the SPS apparatus can serve as a tool for measuring compressive creep strain of materials. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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13 pages, 11582 KiB

Open AccessArticle

Robust Interferometry for Testing Thermal Expansion of Dual-Material Lattices

by Weipeng Luo, Shuai Xue, Cun Zhao, Meng Zhang and Guoxi Li

Materials 2020, 13(2), 313; https://doi.org/10.3390/ma13020313 - 9 Jan 2020

Cited by 2 | Viewed by 2728

Abstract

Dual-material lattices with tailorable coefficients of thermal expansion have been applied to a wide range of modern engineering systems. As supporting techniques for fabricating dual-material lattices with given coefficients of thermal expansion, the current existing methods for measuring the coefficient of thermal expansion [...] Read more.

Dual-material lattices with tailorable coefficients of thermal expansion have been applied to a wide range of modern engineering systems. As supporting techniques for fabricating dual-material lattices with given coefficients of thermal expansion, the current existing methods for measuring the coefficient of thermal expansion have limited anti-interference ability. They ignore the measuring error caused by micro-displacement between the measurement sensor and the test sample. In this paper, we report a robust interferometric test method which can eliminate the measurement error caused by micro-displacement between the measurement sensor and the test sample. In the presented method, two parallel plane lenses are utilized to avoid the measurement error caused by translation, and the right lens is utilized as an angle detector to eliminate the measurement error caused by rotation. A robust interferometric testing setup was established using a distance measuring set and two plane lenses. The experiment results indicated that the method can avoid the measurement error induced by translation and has the potential to eliminate the measurement error induced by rotation using the rotational angle. This method can improve the anti-interference ability and accuracy by eliminating the measurement error. It is especially useful for high-precision thermal expansion measurement of dual-material lattices. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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19 pages, 14109 KiB

Open AccessArticle

Thermophysical Measurements in Liquid Alloys and Phase Diagram Studies

by Yuri Kirshon, Shir Ben Shalom, Moran Emuna, Yaron Greenberg, Joonho Lee, Guy Makov and Eyal Yahel

Materials 2019, 12(23), 3999; https://doi.org/10.3390/ma12233999 - 2 Dec 2019

Cited by 6 | Viewed by 3454

Abstract

Towards the construction of pressure-dependent phase diagrams of binary alloy systems, both thermophysical measurements and thermodynamic modeling are employed. High-accuracy measurements of sound velocity, density, and electrical resistivity were performed for selected metallic elements from columns III to V and their alloys in [...] Read more.

Towards the construction of pressure-dependent phase diagrams of binary alloy systems, both thermophysical measurements and thermodynamic modeling are employed. High-accuracy measurements of sound velocity, density, and electrical resistivity were performed for selected metallic elements from columns III to V and their alloys in the liquid phase. Sound velocity measurements were made using ultrasonic techniques, density measurements using the gamma radiation attenuation method, and electrical resistivity measurements were performed using the four probe method. Sound velocity and density data, measured at ambient pressure, were incorporated into a thermodynamic model to calculate the pressure dependence of binary phase diagrams. Electrical resistivity measurements were performed on binary systems to study phase separation and identify phase transitions in the liquid state. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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15 pages, 3456 KiB

Open AccessArticle

A Different Approach to Estimate Temperature-Dependent Thermal Properties of Metallic Materials

by Luís Felipe dos Santos Carollo, Ana Lúcia Fernandes de Lima e Silva and Sandro Metrevelle Marcondes de Lima e Silva

Materials 2019, 12(16), 2579; https://doi.org/10.3390/ma12162579 - 13 Aug 2019

Cited by 9 | Viewed by 2956

Abstract

Thermal conductivity, λ, and volumetric heat capacity, ρc_p, variables that depend on temperature were simultaneously estimated in a diverse technique applied to AISI 1045 and AISI 304 samples. Two distinctive intensities of heat flux were imposed to provide a more [...] Read more.

Thermal conductivity, λ, and volumetric heat capacity, ρc_p, variables that depend on temperature were simultaneously estimated in a diverse technique applied to AISI 1045 and AISI 304 samples. Two distinctive intensities of heat flux were imposed to provide a more accurate simultaneous estimation in the same experiment. A constant heat flux was imposed on the upper surface of the sample while the temperature was measured on the opposite insulated surface. The sensitivity coefficients were analyzed to provide the thermal property estimation. The Broydon-Fletcher-Goldfarb-Shanno (BFGS) optimization technique was applied to minimize an objective function. The squared difference objective function of the numerical and experimental temperatures was defined considering the error generated by the contact resistance. The temperature was numerically calculated by using the finite difference method. In addition, the reliability of the results was assured by an uncertainty analysis. Results showing a difference lower than 7% were obtained for λ and ρc_p, and the uncertainty values were above 5%. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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13 pages, 5218 KiB

Open AccessArticle

Effect of Intermetallic Compounds on the Thermal and Mechanical Properties of Al–Cu Composite Materials Fabricated by Spark Plasma Sintering

by Kyungju Kim, Dasom Kim, Kwangjae Park, Myunghoon Cho, Seungchan Cho and Hansang Kwon

Materials 2019, 12(9), 1546; https://doi.org/10.3390/ma12091546 - 10 May 2019

Cited by 39 | Viewed by 4170

Abstract

Aluminium–copper composite materials were successfully fabricated using spark plasma sintering with Al and Cu powders as the raw materials. Al–Cu composite powders were fabricated through a ball milling process, and the effect of the Cu content was investigated. Composite materials composed of Al–20Cu, [...] Read more.

Aluminium–copper composite materials were successfully fabricated using spark plasma sintering with Al and Cu powders as the raw materials. Al–Cu composite powders were fabricated through a ball milling process, and the effect of the Cu content was investigated. Composite materials composed of Al–20Cu, Al–50Cu, and Al–80Cu (vol.%) were sintered by a spark plasma sintering process, which was carried out at 520 °C and 50 MPa for 5 min. The phase analysis of the composite materials by X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) indicated that intermetallic compounds (IC) such as CuAl₂ and Cu₉Al₄ were formed through reactions between Cu and Al during the spark plasma sintering process. The mechanical properties of the composites were analysed using a Vickers hardness tester. The Al–50Cu composite had a hardness of approximately 151 HV, which is higher than that of the other composites. The thermal conductivity of the composite materials was measured by laser flash analysis, and the highest value was obtained for the Al–80Cu composite material. This suggests that the Cu content affects physical properties of the Al–Cu composite material as well as the amount of intermetallic compounds formed in the composite material. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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21 pages, 6118 KiB

Open AccessArticle

Scanning Rate Extension of Conventional DSCs through Indirect Measurements

by Hannes Fröck, Michael Reich, Benjamin Milkereit and Olaf Kessler

Materials 2019, 12(7), 1085; https://doi.org/10.3390/ma12071085 - 2 Apr 2019

Cited by 10 | Viewed by 3136

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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15 pages, 5024 KiB

Open AccessArticle

Hydration Kinetics of Composite Cementitious Materials Containing Copper Tailing Powder and Graphene Oxide

by Shuhua Liu, Qiaoling Li and Xinyi Zhao

Materials 2018, 11(12), 2499; https://doi.org/10.3390/ma11122499 - 8 Dec 2018

Cited by 12 | Viewed by 3069

Abstract

The hydration heat evolution curves of composite cementitious materials containing copper tailing powder (CT) and graphene oxide (GO) with different contents are measured and analyzed in this paper. The hydration rate and total hydration heat of the composite cementitious materials decrease with the [...] Read more.

The hydration heat evolution curves of composite cementitious materials containing copper tailing powder (CT) and graphene oxide (GO) with different contents are measured and analyzed in this paper. The hydration rate and total hydration heat of the composite cementitious materials decrease with the increase of CT dosage, but improve with the increase of CT fineness and GO dosage. The hydration process of the cementitious systems undergoes three periods, namely nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D), which can be simulated well using the Krstulovic–Dabic model. The hydration rates of the three controlling processes of the composite cementitious system decrease with the increase of CT content, but improve slightly with the increase of CT fineness. GO enhances the controlling effect of the NG process of the cementitious systems with or without CT, thus promotes the early hydration as a whole. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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11 pages, 4337 KiB

Open AccessArticle

Accelerating Cementite Precipitation during the Non-Isothermal Process by Applying Tensile Stress in GCr15 Bearing Steel

by Feng Wang, Dong-Sheng Qian, Peng Xiao and Song Deng

Materials 2018, 11(12), 2403; https://doi.org/10.3390/ma11122403 - 28 Nov 2018

Cited by 13 | Viewed by 3285

Abstract

In this work, the non-isothermal process of GCr15 bearing steel after quenching and tempering (QT) under different tensile stress (0, 20, 40 MPa) was investigated by kinetic analysis and microstructural observation. The Kissinger method and differential isoconversional method were employed to assess the [...] Read more.

In this work, the non-isothermal process of GCr15 bearing steel after quenching and tempering (QT) under different tensile stress (0, 20, 40 MPa) was investigated by kinetic analysis and microstructural observation. The Kissinger method and differential isoconversional method were employed to assess the kinetic parameters of the microstructural evolution during the non-isothermal process with and without applied stress. It is found that the activation energy of retained austenite decomposition slightly increases from 109.4 kJ/mol to 121.5 kJ/mol with the increase of tensile stress. However, the activation energy of cementite precipitation decreases from 179.4 kJ/mol to 94.7 kJ/mol, proving that tensile stress could reduce the energy barrier of cementite precipitation. In addition, the microstructural observation based on scanning and transmission electron microscopy (SEM and TEM) shows that more cementite has formed for the specimens with the applied tensile stress, whereas there is still a large number of ε carbides existing in the specimens without stress. The results of X-ray diffraction (XRD) also verify that carbon in martensite diffuses more and participates in the formation of cementite under the applied tensile stress, which thus are in good agreement with the kinetic analysis. The mechanisms for the differences in cementite precipitation behaviors may lie in the acceleration of carbon atoms migration and the reduction of the nucleation barrier by applying tensile stress. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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15 pages, 2250 KiB

Open AccessArticle

Pyrolysis and Combustion of Polyvinyl Chloride (PVC) Sheath for New and Aged Cables via Thermogravimetric Analysis-Fourier Transform Infrared (TG-FTIR) and Calorimeter

by Zhi Wang, Ruichao Wei, Xuehui Wang, Junjiang He and Jian Wang

Materials 2018, 11(10), 1997; https://doi.org/10.3390/ma11101997 - 16 Oct 2018

Cited by 44 | Viewed by 6131

Abstract

To fill the shortages in the knowledge of the pyrolysis and combustion properties of new and aged polyvinyl chloride (PVC) sheaths, several experiments were performed by thermogravimetric analysis (TG), Fourier transform infrared (FTIR), microscale combustion calorimetry (MCC), and cone calorimetry. The results show [...] Read more.

To fill the shortages in the knowledge of the pyrolysis and combustion properties of new and aged polyvinyl chloride (PVC) sheaths, several experiments were performed by thermogravimetric analysis (TG), Fourier transform infrared (FTIR), microscale combustion calorimetry (MCC), and cone calorimetry. The results show that the onset temperature of pyrolysis for an aged sheath shifts to higher temperatures. The value of the main derivative thermogravimetric analysis (DTG) peak of an aged sheath is greater than that of a new one. The mass of the final remaining residue for an aged sheath is also greater than that of a new one. The gas that is released by an aged sheath is later but faster than that of a new one. The results also show that, when compared with a new sheath, the heat release rate (HRR) is lower for an aged one. The total heat release (THR) of aged sheath is reduced by 16.9–18.5% compared to a new one. In addition, the cone calorimetry experiments illustrate that the ignition occurrence of an aged sheath is later than that of a new one under different incident heat fluxes. This work indicates that an aged sheath generally pyrolyzes and it combusts more weakly and incompletely. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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25 pages, 1994 KiB

Open AccessReview

Lifetime Prediction Methods for Degradable Polymeric Materials—A Short Review

by Angelika Plota and Anna Masek

Materials 2020, 13(20), 4507; https://doi.org/10.3390/ma13204507 - 12 Oct 2020

Cited by 103 | Viewed by 10316

Abstract

The determination of the secure working life of polymeric materials is essential for their successful application in the packaging, medicine, engineering and consumer goods industries. An understanding of the chemical and physical changes in the structure of different polymers when exposed to long-term [...] Read more.

The determination of the secure working life of polymeric materials is essential for their successful application in the packaging, medicine, engineering and consumer goods industries. An understanding of the chemical and physical changes in the structure of different polymers when exposed to long-term external factors (e.g., heat, ozone, oxygen, UV radiation, light radiation, chemical substances, water vapour) has provided a model for examining their ultimate lifetime by not only stabilization of the polymer, but also accelerating the degradation reactions. This paper presents an overview of the latest accounts on the impact of the most common environmental factors on the degradation processes of polymeric materials, and some examples of shelf life of rubber products are given. Additionally, the methods of lifetime prediction of degradable polymers using accelerated ageing tests and methods for extrapolation of data from induced thermal degradation are described: the Arrhenius model, time–temperature superposition (TTSP), the Williams–Landel–Ferry (WLF) model and 5 isoconversional approaches: Friedman’s, Ozawa–Flynn–Wall (OFW), the OFW method corrected by N. Sbirrazzuoli et al., the Kissinger–Akahira–Sunose (KAS) algorithm, and the advanced isoconversional method by S. Vyazovkin. Examples of applications in recent years are given. Full article

(This article belongs to the Special Issue Thermal Analysis of Materials)

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