Long-term Thermal Stability Research Articles

FTIR assessment and investigation of synthetic antioxidant on the fuel stability of Calophyllum inophyllum biodiesel

‘Fuel Stability’ is one of the most significant properties of biodiesel, which insists the biodiesel stability during prolonged storage period. Poor resistance to oxidation process is the main hurdle for biodiesel commercialization in the global fuel market. Biodiesel degradation by the products yielded from oxidation process may deprive the fuel properties and obviously engine performance. Dosage of synthetic antioxidants is an appropriate method for improving the fuel stability of biodiesel. The present research work investigates the effects of tert-butyl hydroquinone (TBHQ) antioxidant additive concentrations on the oxidation stability, long-term storage stability and thermal stability of Calophyllum inophyllum biodiesel. Fourier Transform Infra-red (FTIR) spectroscopy was used to characterize the oxidation variability of biodiesel, following the FTIR spectrum regions of CH and OH bonds for various concentrations of TBHQ. Dosage of TBHQ at 1000ppm concentration (B100A3) with pure biodiesel enhances the oxidation stability by 94.658%, storage stability by 14.466% and thermal stability by 37.269%; meanwhile further dosage of antioxidant deteriorates the formation of hydrophobic and hydrophilic clusters between antioxidant and biodiesel compounds, which is characterized through FTIR spectrum. It is concluded that by dosing 1000ppm of TBHQ antioxidant with Calophyllum inophyllum biodiesel could enhance the storage period.

A novel La-containing additive for the long-term thermal stabilization of poly(vinyl chloride)

A new thermal stabilizer, La-Gly (Gly = n-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]-glycin), was synthesized. Through discoloration and dehydrochlorination tests at 180 °C, La-Gly is found to possess high stabilizing efficiency for poly(vinyl chloride) (PVC): as the mass ratio of La-Gly to PVC resin is increased from 0.3/50.0 to 2.0/50.0, the time to degradation of PVC samples increases from 90 min to 190 min. Studies on combinations of La-Gly and ZnSt2, and of La-Gly and dibenzoyl methane (DBM) show that the initial color of PVC is improved, as the ratio of ZnSt2 to La-Gly or DBM to La-Gly is increased from 0.3/1.2 to 1.2/0.3. One sample (50.0 g PVC, 0.6 g ZnSt2, 0.9 g La-Gly, 3.4 g tributyl citrate) shows the best balance between initial color and long-term thermal stability (140 min). Studies on dynamic thermal stability of the samples (50.0 g PVC, x g La-Gly, 3.4 g tributyl citrate, x = 0.3, 0.6, 0.9, 1.2, 1.5, 2.0) show that when x equals 1.2, the thermal dynamic stability time is 24.5 min, much longer than 6.4 min and 4.8 min, respectively, for two controls (50.0 g PVC, 1.5 g LaSt3, 3.4 g tributyl citrate; 50.0 g PVC, 0.6 g CaSt2, 0.9 g ZnSt2, 3.4 g tributyl citrate).

Comprehensive Insights into the Thermal Stability, Biodegradability, and Combustion Chemistry of Pyrrolidinium-Based Ionic Liquids.

The use of ionic liquids (ILs) as advanced electrolyte components in electrochemical energy-storage devices is one of the most appealing and emerging options. However, although ILs are hailed as safer and eco-friendly electrolytes, to overcome the limitations imposed by the highly volatile/combustible carbonate-based electrolytes, full-scale and precise appraisal of their overall safety levels under abuse conditions still needs to be fully addressed. With the aim of providing this level of information on the thermal and chemical stabilities, as well as actual fire hazards, herein, a detailed investigation of the short- and long-term thermal stabilities, biodegradability, and combustion behavior of various pyrrolidinium-based ILs, with different alkyl chain lengths, counteranions, and cations, as well as the effect of doping with lithium salts, is described.

Degraded thermal stability of p-type Bi2Te3-based polycrystalline bulks for thermoelectric power generation at service temperature of 473 K

The Bi2Te3-based bulks are promising thermoelectric materials in the low temperature waste heat recovery area. However, their thermal stability needs to be addressed before they are applied in practical thermoelectric devices. In this work, the long-term thermal stabilities of the microstructure, thermoelectric properties and mechanical properties for the p-type Bi0.44Sb1.56Te3 polycrystalline bulks have been investigated at 423 and 473 K. The results indicated that the samples could keep the satisfying thermal stability when the service temperature was fixed at 423 K, and the grain size, the volume, the density and the thermoelectric properties of the samples remained almost unchanged during long term service, and the electrical transport properties were even improved with prolonging the servicing time to 168 h. However, when the service temperature was fixed at 473 K, the volume expansion was obvious with prolonging service time, and great quantity of voids were appeared in the bulks due to Te volatilization, which resulted in the obvious increase of the electrical resistivity and the deterioration of the electrical transport properties, and the unsatisfactory decrease of the power factor and the figure of merit. These results suggest that the long-term service temperature of p-type Bi2Te3-based polycrystalline bulks is only 423 K for the low-temperature thermoelectric power generation.

Improved Long-Term Stability of Transparent Conducting Electrodes Based on Double-Laminated Electrosprayed Antimony Tin Oxides and Ag Nanowires

AbstractWe fabricated double-laminated antimony tin oxide/Ag nanowire electrodes by spin-coating and electrospraying. Compared to pure Ag nanowire electrodes and single-laminated antimony tin oxide/Ag nanowire electrodes, the double-laminated antimony tin oxide/Ag nanowire electrodes had superior transparent conducting electrode performances with sheet resistance ~19.8 Ω/□ and optical transmittance ~81.9%; this was due to uniform distribution of the connected Ag nanowires because of double lamination of the metallic Ag nanowires without Ag aggregation despite subsequent microwave heating at 250°C. They also exhibited excellent and superior long-term chemical and thermal stabilities and adhesion to substrate because double-laminated antimony tin oxide thin films act as the protective layers between Ag nanowires, blocking Ag atoms penetration.

Strong Improvement of Long-Term Chemical and Thermal Stability of Plasmonic Silver Nanoantennas and Films.

Silver (Ag) nanostructures and thin films are advantageous plasmonic materials as they have significantly lower losses than gold (Au). Unfortunately, Ag nanostructures suffer from poor chemical and thermal stability, which limit their applications. Here, the mechanisms leading to the deterioration of Ag nanostructures are clarified. It is first shown that oxygen alone cannot oxidize Ag nanostructures. Then, experiments using X-ray photoelectron spectroscopy reveal that the amount of sulfur in ambient air is too low for efficient tarnishing of the Ag surface. Finally, water is found to be the most critical factor for the degradation of Ag nanostructures and thin films. At high relative humidity, adsorbed water forms a thin film enabling the migration of Ag ions at the Ag/air interface, which deteriorates the Ag nanostructures. A dehydration treatment is developed which alters the morphology of the deposited silver, leading to an improved chemical and thermal stability of the Ag nanostructures and films, which then remain stable for more than 14 weeks under ambient laboratory conditions. In addition, dehydration also improves significantly the root-mean-square roughness for Ag thin films deposited on a glass substrate.

Thermal characteristics and declining permafrost table beneath three cooling embankments in warm permafrost regions

This article analyses the long-term thermal stability of the newly constructed Gonghe-Yushu Expressway (GYE) embankments with special structures in the warm permafrost regions of the south-eastern Tibetan plateau to ensure driving comfort and safety. Using field monitoring and numerical calculation methods, the ground temperature distribution characteristics, changes in the artificial permafrost table (APT), and the heat budget around the permafrost tables of three types of embankments (insulated board embankment [IBE], crushed rock embankment [CRE] and ventilated embankment [VE]) are studied. The results indicate the following: 1) each embankment plays a positive role in cooling the underlying permafrost in cold seasons but melts the underlying permafrost during warm seasons, 2) the ground temperature effect is increased in the shallow and deep layers on the shoulders of each embankment, 3) the heat budget around the permafrost table of each embankment is characterized by the absorption of heat, and the IBE has the greatest heat absorption capacity; and 4) calculations have determined that the APT of each embankment declines linearly over time, and a model is developed to calculate permafrost table change established for each embankment. The model may provide reference for predicting the service year and declining extent of APT of expressway embankments in warm permafrost regions.

Demonstrating the Instability of SiC Ohmic Contacts and Drain Terminal Metallization Schemes Aged at 300 °C

The long-term thermal stability of the drain contacts of three different commercially available SiC MOSFET devices has been determined at a storage temperature of 300 °C. Existing literature suggests that, at this temperature, the nickel silicides associated with ohmic contact creation should be stable, but this was found not to be the case. Our TEM and EDX work revealed silicide phase transformations, further silicide growth and severe thermally-driven degradation of the drain contact metallization stack on top of the silicide layers. We attribute this instability and growth of the silicides to the high storage temperature and large supply of nickel atoms available from the metal stack. The nickel atoms diffuse and decompose the original silicides to enable the formation of a new low temperature Ni32Si12 phase, and slowly decompose the SiC substrate to form additional nickel silicide.

Development and Optimization of Tailored Composite TBC Design Architectures for Improved Erosion Durability

Rare-earth pyrochlores, RE2Zr2O7, have been identified as potential thermal barrier coating (TBC) materials due to their attractive thermal properties and CMAS resistance. However, they possess a low fracture toughness which results in poor erosion durability/foreign object damage resistance. This research focuses on the development of tailored composite air plasma spray (APS) TBC design architectures utilizing a t′ Low-k secondary toughening phase (ZrO2-2Y2O3-1Gd2O3-1Yb2O3; mol.%) to enhance the erosion durability of a hyper-stoichiometric pyrochlore, NZO (ZrO2-25Nd2O3-5Y2O3-5Yb2O3; mol.%). In this study, composite coatings have been deposited with 30, 50, and 70% (wt.%) t′ Low-k toughening phase in a horizontally aligned lamellar morphology which enhances the toughening response of the coating. The coatings were characterized via SEM and XRD and were tested for erosion durability before and after isothermal heat treatment at 1100 °C. Analysis with mixing laws indicated improved erosion performance; however, a lack of long-term thermal stability was shown via isothermal heat treatments at 1316 °C. An impact stress analysis was performed using finite element analysis of a coating cross section, representing the first microstructurally realistic study of mechanical properties of TBCs with the results correlating well with observed behavior.

Thermal Stability of the Eutectic Composition in NaCl-CaCl2-MgCl2 Ternary System Used for Thermal Energy Storage Applications

The ternary eutectic chloride salt (NaCl-CaCl2-MgCl2) was designed and prepared for thermal energy storage over 550°C in a concentration solar power system. The melting temperature and fusion enthalpy of the eutectic salt were measured experimentally using the Differential Scanning Calorimeter (DSC) technique which were determined to be 420.83°C and 201.50 J/g, respectively. The thermal stability including the short-term and the long-term thermal stability of the ternary system was investigated by the Thermo-gravimetric Analyzer (TGA) technique and the DSC technique. The thermal properties of the eutectic mixture kept stable during the short-term thermal cycling test. The weight loss of the eutectic salt was less than 5%, and the melting temperature and fusion enthalpy changed slightly as the temperature increased below 650°C in the long-term isothermal stability study. The thermal stability test revealed that the ternary eutectic system demonstrated excellent thermal stability below 650°C which was taken as the upper limit temperature of the ternary system. The eutectic composition was characterized by the X-Ray Diffraction (XRD) technique before and after thermal treatment to provide preliminary analysis on the mechanism of thermal instability. The results suggested that the ternary eutectic chloride salt was a potential candidate for applying in high-temperature thermal energy storage.

A study about the influence of single-scale and dual-scale structures on surface wettability

Surface morphology is known as the key factor to obtain lyophobic surface. This paper illustrates two superhydrophobic surfaces with different surface morphologies including single-scale nanorod structure and dual-scale flower-like structure. We compared contact angles of many liquids and dynamic behavior of water droplet impinging on the nanorod structured surface to those of on the flower-like structured surface. It was found that both the single-scale nanorod structure and the dual-scale flower-like structure can achieve superhydrophobicity. However, the dual-scale flower-like structure is superior to the single-scale nanorod structure in terms of repelling the droplet with low surface tension. In addition, we investigated stability and corrosion resistance of these two superhydrophobic surfaces, showing that both the single-scale nanorod and the dual-scale flower-like structured superhydrophobic surfaces had excellent long-term stability and thermal stability. Nevertheless, the dual-scale flower-like structured superhydrophobic surface was more stable under outside vibration and had better corrosion resistance than the single-scale nanorod structured superhydrophobic surface.

Thermal properties and thermal stability of the ternary eutectic salt NaCl-CaCl2-MgCl2 used in high-temperature thermal energy storage process

The ternary eutectic chloride salt (NaCl-CaCl2-MgCl2) was designed and prepared for thermal energy storage over 500°C in a concentrated solar power system. The thermal properties of the eutectic salt were measured experimentally using the Differential Scanning Calorimeter (DSC) technique, and the thermal stability including the long-term and short-term thermal stability of the ternary system was investigated by the Thermo-gravimetric Analyzer (TGA) technique and the DSC technique. The results indicated that the melting temperature and fusion enthalpy were 420.83°C and 201.50J/g, respectively, and the specific heat capacity was 1.49J/(g·°C). In the long-term isothermal stability study, the total weight loss of the eutectic salt was less than 5% below 650°C, and the melting temperature and fusion enthalpy changed slightly as the temperature increased. The ternary eutectic system demonstrated excellent thermal stability below 650°C, which was defined as the upper temperature limit of the ternary system. During the short-term thermal cycling test, the stability and recyclability of the ternary salt were verified in future during the working temperature, generally 50°C lower than the upper temperature limit. The eutectic composition before and after thermal treatment was characterized by the X-ray Diffraction (XRD) technique to analyze the mechanism of thermal instability. The mechanism of thermal instability turned out to be the thermal decomposition of the generated magnesium chloride hexahydrate at high temperature. It was proved that the ternary eutectic chloride salt was a potential candidate for high-temperature thermal energy storage applications up to 650°C.

Long-term thermal stability of addition-type polyimide resins derived from pyromellitic dianhydride, 2-phenyl-4,4′-diaminodiphenyl ether, and 4-phenylethynylphtalic anhydride

The previously developed TriA-X polyimide resin, consisting of pyromellitic dianhydride/2-phenyl-4,4′-diaminodiphenyl ether; 9,9-bis(4-aminophenyl)fluorene/4-phenylethynylphthalic anhydride (PEPA), was exposed for 3000 h to air at 180, 240, and 270°C or a vacuum environment at 270°C, in order to study its long-term thermal stability. The weight loss and dimensional changes were measured. Elemental analysis was also conducted in order to estimate the TriA-X degradation process. The TriA-X exhibited excellent thermal stability at 180°C and a very small degree of degradation at 240°C, with the degradation becoming significant at 270°C. The latter was primarily dominated by the oxidation of a chain-extension moiety formed by the cure reaction of the end-cap PEPA.

Thermal cycling testing of Zn–Mg–Al eutectic metal alloys as potential high-temperature phase change materials for latent heat storage

This article presents the thermal stability testing results of five high-temperature phase change materials for their potential use in latent thermal energy storage systems. The tested materials are eutectic metal alloys [Zn84Al8.7Mg7.3, Zn88.7Al11.3, Zn92.2Mg7.8, Zn72Mg28 and Mg70Zn24.9Al5.1 (at.%)] with phase change temperatures in the range of 340–380 °C. The five candidates have been selected not only for their adequate melting temperature and high fusion enthalpy, but also for the availability and appropriate costs [2–3 $/kg (Rodriguez-Aseguinolaza in J Therm Anal Calorim 117:93–99, 2014)] of Zn, Al, and Mg primary metals. As it is well known and demonstrated in previous works, the use of metal alloys presents noticeable benefits on the TES solutions based on their implementation. The particular advantages introduced by the Zn–Mg–Al system in terms of maximization of the storage capacity and appropriate operation temperature justify a deeper analysis of these alloys, previously studied, for a complete thermal performance. In this work, with the aim of reproducing a realistic thermal cycling behaviour in real heat storage applications, the selected candidates have been subjected to short- and long-term thermal cycling tests by 100 and 500 melting/solidification cycles, respectively. These experiments permitted to detect any potential evolution of the thermodynamic and structural properties of the investigated materials that could be sign of an undesirable chemical decomposition or phase segregation. As a conclusion, the Zn84Al8.7Mg7.3, Zn88.7Al11.3, Mg72Zn28 and Mg70Zn24.9Al5.1 alloys have been identified as very promising latent heat storage materials due to their long-term thermal stability.

Mechanically robust re-crosslinkable polymeric hydrogels for water management of void space conduits containing reservoirs

A unique preformed particle gel with re-crosslinkable ability to re-form bulk gel for chemical enhanced oil recovery of void space conduits containing reservoir is described herein. The formation of the bulk gel was achieved by reversible ionic crosslinks of the preformed particle gels as induced by brine under reservoir conditions. The re-crosslinked hydrogel with ionic features showed rubber-like mechanical behaviors, a critical parameter of the particle gels to increase plugging efficiency. The re-crosslinking ability of the preformed particle gels under different salinity could be controlled by tuning the ionic interactions within the hydrogel. In addition, the long-term thermal stability of the re-crosslinked bulk gel has been demonstrated. Furthermore, the re-crosslinked bulk gels could significantly reduce permeability of large fractures as demonstrated by core flooding experiments compared with traditional preformed particle gels. The re-crosslinkable bulk gel with robust mechanical properties could offer the candidate to block void space conduits containing reservoirs for enhanced oil recovery.

Polyethylene/Layered Aluminosilicate Nanocomposites: Investigation of Thermal Stability under Static and Dynamic Conditions

Based on linear low-density polyethylene and maleated polyethylene a polymer nanocomposites containing modified montmorillonite have been obtained, structure is investigated by XRD analysis. In turn, by the methods of thermal analysis in static and dynamic modes, the resistance of polymer nanocomposites to oxidative destruction it was investigated. In parallel with this, a comparative analysis of the thermal stability of polymer nanocomposites and polymer compositions containing commercially available organic antioxidants for stabilization of materials based on polyolefins. By results of the analysis carried out in a dynamic mode, for a series of polymer composites the activation energy of thermooxidative destruction was calculated. It is shown that the nanocomposites based on polyethylene, containing the modified montmorillonite not only not concede to polymer compositions with antioxidants in to thermal stability, but also exceed their. Accelerated tests, carried out at relatively high temperatures allowed evaluate the durability of polymer nanocomposites to thermooxidative destruction. Received results allow approve about a long-term thermal stability of these materials in the processing, and in the exploitation conditions.

Novel low melting point binary nitrates for thermal energy storage applications

19 kinds of different ratio of binary mixed molten salt have been formulated, and the formulation of a low melting point binary molten salt has been exploited and its primary thermophysical properties were presented here. The eutectic temperature of the selected binary salt mixture was determined to be 116.9℃. Further the decomposition point, specific heat, density, viscosity, thermal conductivity and corrosion were determined respectively. Sensible thermal storage cost of the novel eutectic mixture was found to be lower than that of conventional solar salt and HITEC salt. The performance of the binary salt mixture taken at different stages during the test of 1200-h exposure to constant high temperature was discussed based on the results obtained from long-term thermal stability studies. The results show that thermodynamic properties of the molten salt show perfect repeatability before and after the experiments, and most variations rate of the thermal physical properties is within±10%, which can be considered as an implication that the candidate has good thermal stability. Therefore, this new kind of binary molten salt thermal storage materials is more competitive and promising to be used in solar power generation systems while providing a comprehensive data for its engineering application and theoretical research.

Interfacial properties of Cu/Ni/Mg2Si joints prepared in one step by the spark plasma sintering method

Abstract Cu/Ni/Mg2Si thermoelectric bonded joints were prepared in one step by the spark plasma sintering (SPS) method using Mg and Si powders to form Mg2Si. The microstructure and elemental distribution across the interfaces were determined, and the formation of new phases at the interface was investigated and related to joint properties, including shear strength and contact resistance. Joint formation was accompanied by the formation of two ternary Mg-Si-Ni layers, an η-layer with Ni2Si as a precipitate next to Ni, and an ω-layer next to Mg2Si. The formation and characteristics of these layers played a major role in determining the shear strength and contact resistance. It was determined that a reactive sintering temperatures in the range 1023–1053 K with a 15–20 min hold time provided the best properties. The maximum shear strength of the joints obtained is 26 MPa for samples sintered at 1023 K. For these samples the contact resistance was 1.44 mΩ cm2; the minimum value of 1.28 mΩ cm2 was measured for samples sintered at 1073 K. Long-term thermal stability of joints was also investigated.

Gelation Performance and Feasibility Study of an Environmental Friendly Improved Inorganic Aluminum Gel for Conformance Control Under Harsh Reservoir Conditions

Despite its successful application in controlling excessive water production in many mature oilfields, polymer gel is facing some application limitations under harsh reservoir conditions. To settle these problems, an environmental friendly improved inorganic aluminum gel that composed of polyaluminum chloride (PAC) as main agent, urea as activator, and sodium sulfate as syneresis inhibitor was developed. The effects of mass ratios of PAC and urea, component concentrations and temperature on gelation performance were studied. The gel compatibility with various formation brines, long-term thermal stability, and permeability reduction ability were evaluated to account for the feasibility of gel application. Results showed that as the mass ratio of PAC and urea increased, the gelation time increased and the degree of syneresis decreased. The gelation time and the degree of syneresis decreased with the increase of sodium sulfate concentration, which indicated that sodium sulfate could play a role in accelerating gelation and inhibiting gel syneresis. The gelation time decreased with increasing temperature. The gel could tolerate sodium chloride concentration up to 150 g·L−1 and calcium chloride concentration up to 25 g·L−1. After aging for 120 days at 130 °C, no syneresis was observed in gel samples, which indicated that the gel had good, long-term thermal stability. The gel had good permeability reduction ability and was effective in plugging high permeability zone. Thus, these results indicated that the improved inorganic gel could be a potential candidate for conformance control under harsh reservoir conditions.

Excellent stability of thicker shell CdSe@ZnS/ZnS quantum dots

Evolution of the long-term (400 h) thermal stability of green CdSe@ZnS alloyed core/shell QDs (A-QDs) and CdSe@ZnS/ZnS (alloyed core/shell)/thick shell QDs (AS-QDs) under 85 °C, 85% relative humidity conditions in air.