Long-term Thermal Stability Research Articles

Phase transitions in higher-melting imidazolium-based ionic liquids: Experiments and advanced data analysis

As thermal energy storage becomes an increasingly important topic, good knowledge of properties of phase-change materials (PCM) is essential. Among other properties, a good PCM should show a large enthalpy of melting, reproducible melting/solidification cycles, and long-term thermal stability. Temperatures and enthalpies of fusion should be determined at a possibly large range of conditions to allow for a critical evaluation of the experimental data and assessment of the material application potential.In this work, imidazolium-based ionic liquids (ILs) with long alkyl chain substituents 1-hexadecyl-3-methylimidazolium chloride and 1-hexadecyl-3-methyl-imidazolium saccharinate were studied in view of their possible use as phase-change materials. Differential scanning calorimetry (DSC) and the heat-leak modulus (HLM) methods were used to determine the temperatures and the enthalpies of phase transitions in the studied ILs, enabling us to study the influence of the heating and cooling rates on the measured properties. Enthalpies of fusion near to or larger than 100 J·g−1 were found in the studied ionic liquids, making them promising candidates for thermal energy storage. Peaks corresponding to possible liquid crystalline phases in the DSC traces of 1-hexadecyl-3-methylimidazolium saccharinate were observed, pointing to more complex phase behaviour of the studied ionic liquids.Finally, to critically evaluate the experimental data measured in this work, methods based on mathematical gnostics were used. Repeatability of measurements and the degree of mutual agreement between the methods used in this work could thus be determined.

Synergism of polyvinyl alcohol fiber to hydrogel for profile modification

Water production is getting worse along with the continuous water injection in the reservoir with fracture, but common hydrogels cannot be successfully applied for water shutoff due to its poor resident ability in fracture. In this work, an interpenetrating network hydrogel has been developed innovatively by polyvinyl alcohol (PVA) fiber and common polyacrylamide (PAM) hydrogel. Plugging ability, long-term thermal stability and the interaction between PVA fiber and hydrogel were detailedly studied. Results show that PVA fiber is beneficial to the stability of the PAM hydrogel, and the syneresis rate can be decreased from 30% to 3% on the 120th day. PVA fiber accelerates the hydrogel gelation, and the high concentration of fiber leads to good hydrogel strength. PVA fiber increases the amount of the bound water in hydrogel, leading the hydrophilcity increase of hydrogel. An interpenetrating network is formed on the micrometer level, resulting from the three-group crosslinking among polymer, cross-linker and fiber. Compared with common PAM hydrogel, the interpenetrating network hydrogel has better water shutoff effect and EOR performance. Core flow experiment and micromodel test show that the interpenetrating network hydrogel forms an effective bridge in fracture, and it is hard to be moved due to the water washing. The introduction of fiber to hydrogel is an innovative research, which not only improves the water shutoff effect of hydrogel in fracture, but also provides reference to increase the performance of drilling fluid, fracturing solution and EOR polymer utilized in petroleum engineering.

A “one stop” thermal stabilizer, zinc arginine complex, with excellent comprehensive thermal stability effect on poly(vinyl chloride)

A “one stop” thermal stabilizer, zinc arginine complex (Zn(Arg)2), with excellent excellent initial whiteness, whiteness retention and long-term thermal stability time for PVC, was conveniently synthesized in water solution. The successful synthesis of Zn(Arg)2 was confirmed by FTIR, TGA and element analysis. Besides the longer Congo red and static thermal stability time than nitrogen-containing thermal stabilizer reported, Zn(Arg)2 also had better initial whiteness, whiteness retention and dynamic thermal stability time showed by Congo red test, discoloration test and torque rheology test. Especially, the static thermal stability time was more than 150 min, and the dynamic thermal stability time reached 78 min. The excellent thermal stability effect of Zn(Arg)2 on PVC was ascribed to the simultaneous possession of three mechanisms: absorbing HCl, replacing labile chlorine atoms and complexing ZnCl2. Moreover, PVC with Zn(Arg)2 also showed excellent transmittance tested by vis-uv-near infrared spectrophotometer. Therefore, Zn(Arg)2 is a “one stop” thermal stabilizer with good application prospects in transparent PVC.

Comparative Study on Enhancing Oil Recovery under High Temperature and High Salinity: Polysaccharides Versus Synthetic Polymer.

The synthetic water-soluble polymer, partially hydrolyzed polyacrylamide (HPAM), has been most widely used for enhanced oil recovery (EOR); however, its poor thermal stability and weak salt tolerance impede further application in high-temperature and high-salinity oil reservoirs. To address such deficiencies, three polysaccharides, xanthan gum, diutan gum, and scleroglucan, were examined in comparison with HPAM on rheological behaviors, shearing resistance, long-term thermal stability, and core flooding test. It was found that all of these three polysaccharides were less sensitive to salinity and shearing time, while HPAM showed a monotonous decrease in viscosity with increasing monovalent cations and shearing history. After 90 days of aging at 85 °C and 10.1 × 104 mg·L–1 of total dissolved solids with 1.0 × 103 mg·L–1 of Ca2+, the viscosity of diutan gum and scleroglucan solutions nearly remained unchanged; on the contrary, the viscosity of xanthan gum and HPAM solutions drops massively. Core flooding tests at 85 °C with the same initial viscosity demonstrated that all polymers showed good transportation in porous media, and 16, 13, and 11% of oil recovery were obtained by diutan gum, scleroglucan, and xanthan gum, respectively, while only 10% was obtained from HPAM. These comparative results may underpin the potential of diutan gum and scleroglucan to be used in the EOR process in HTHS oil reservoirs.

Design and Synthesis of a New Mannitol Stearate Ester-Based Aluminum Alkoxide as a Novel Tri-Functional Additive for Poly(Vinyl Chloride) and Its Synergistic Effect with Zinc Stearate.

Thermal stabilizers, lubricant, and plasticizers are three crucial additives for processing poly(vinyl chloride) (PVC). In this study, a new mannitol stearate ester-based aluminum alkoxide (MSE-Al) was designed and synthesized as a novel additive for PVC. The thermal stability and processing performance of PVC stabilized by MSE-Al were evaluated by the Congo red test, conductivity measurement, thermal aging test, ultravioletevisible (UV–Vis) spectroscopy test, and torque rheometer test. Results showed that the addition of MSE-Al could not only markedly improve the long-term thermal stability of PVC, but also greatly accelerate the plasticizing and decrease the balance torque, which demonstrated that MSE-Al possessed a lubricating property. Thus, MSE-Al was demonstrated to be able to provide tri-functional additive roles, e.g., thermal stabilizer, plasticizer, and lubricant. The test results for the thermal stability of PVC indicated that the initial whiteness of PVC stabilized by MSE-Al was not good enough, thus the synergistic effect of MSE-Al with zinc stearates (ZnSt2) on the thermal stability of PVC was also investigated. The results showed that there is an appreciable synergistic effect between MSE-Al and ZnSt2. The thermal stabilization mechanism and synergism effect of MSE-Al with ZnSt2 are then discussed.

Titanium nitride nanoparticles for the efficient photocatalysis of bicarbonate into formate

Metallic nanoparticles can act as efficient photocatalysts thanks to the surface plasmons that they support, which are capable of harvesting light and generating hot carriers. Recently, titanium nitride (TiN) nanostructures have emerged as promising candidates for this application due to their much lower cost, and therefore greater sustainability, than structures made of noble metals, as well as their expected long-term thermal stability. In this work, we demonstrate that, under solar illumination, TiN nanoparticles, in combination with titanium dioxide (TiO2) nanostructures, can significantly increase the photocatalytic production of formate through the simultaneous photoreduction of bicarbonate and oxidation of glycerol. Importantly, we also show that TiN nanoparticles alone can provide an enhancement of the photocatalytic efficiently when compared to TiO2 nanocatalysts. Furthermore, by characterizing the morphology and material properties of the TiN nanoparticles after the reaction, we confirm that they remain stable under reaction conditions for extended periods of solar light exposure (8 hours). The results of this work advance our understanding of TiN nanoparticles as efficient photocatalysts and their use for the production of valuable chemicals.

Thermal stability analysis of a lightweight Al-Zn-Mg-Cu alloy by TEM and tensile tests

Long-term thermal stability plays an important role in practical applications of Al-Zn-Mg-Cu alloys. In the present work, thermal stability of the T7452-treated 7085 Al alloy was assessed at temperatures of 100, 125, 150 and 175 °C for 100, 500 and 1000 h, through hardness, electrical conductivity and tensile tests after thermal exposure. The nanoscale precipitates under different thermal exposure conditions were also qualitatively studied by transmission electron microscopy (TEM). The results show that thermal stability of the alloy is more sensitive to thermal exposure temperature than to exposure time. The hardness increases first and then decreases with the increase of exposure temperature while it decreases gradually as exposure time prolongs. However, the variation of electrical conductivity is opposite. The tensile strength, yield strength and hardness after 100 °C/100 h thermal exposure increased by 2.4%, 6.7% and 9.2% than those of the alloy without thermal exposure, respectively. The precipitate sequence during thermal exposure is coincident with that of aging. In addition, as thermal exposure deepens, the average radius of precipitates increases while the volume fraction decreases. Meanwhile, the grain boundary precipitates coarsen and transform from continuous to discrete. The influence of precipitates on properties of the alloy is discussed quantitatively.

Recent development of Supercapacitor Electrode Based on Carbon Materials

AbstractSupercapacitor has gained significant attention due to its fast charging/discharging speed, high power density and long-term cycling stability in contrast to traditional batteries. In this review, state-of-the-art achievements on supercapacitor electrode based on carbon materials is summarized. In all-carbon composite materials part, various carbon materials including graphene, carbon nanotube, carbon foam and carbon cloth are composited to fabricate larger specific surface area and higher electrical conductivity electrodes. However, obstacles of low power density as well as low cycling life still remain to be addressed. In metal-oxide composites part, carbon nanotube, graphene, carbon fiber fabric and hollow carbon nanofibers combine with MnO2respectively, which significantly address drawbacks of all-carbon material electrodes. Additionally, TiO2is incorporated into graphene electrode to overcome the low mechanical flexibility of graphene. In organic active compounds part, conducting polymers are employed to combinate with carbon materials to fabricate high specific capacitance, long-term thermal stability and outstanding electroconductivity flexible textile supercapacitors. In each part, innovation, fabrication process and performance of the resulting composites are demonstrated. Finally, future directions that could enhance the performance of supercapacitors are discussed.

Long-term stability of precipitated phases in CLAM steel during thermal aging

China Low Activation Martensitic (CLAM) steel as one of 9%Cr ferritic-martensitic steels was designed as the structural materials for fusion reactors and lead-based Reactor in China. The long-term thermal stability of precipitated phases in CLAM steel at 550 °C was systematically studied in this paper, including coarsening kinetics, number density and shape stability. Based on large data statistics, the coarsening kinetics of M23C6 carbide, MX carbonitride and Laves phase were analyzed to develop a coarsening model of each precipitated phase, respectively. The results showed that the coarsening rate of Laves phase was about 100 times than that of M23C6 carbide after aging for 20,000 h at 550 °C. The number density of precipitated phases increased firstly and then decreased with increasing of aging time due to a dynamic equilibrium process of the precipitation and dissolution of precipitated phase. The results will help to deep understand degradation mechanisms after thermal aging.

Thermal Cycling of Calcium Chloride Hexahydrate With Strontium Chloride as a Phase Change Material for Latent Heat Thermal Energy Storage Applications in a Nondifferential Scanning Calorimeter Set-Up

Calcium chloride hexahydrate (CaCl2·6H2O) is an attractive candidate as a phase change material for supplemental cooling in air-cooled thermal power-plant since it has a low-phase transition temperature of 29.3 °C and a relatively large volumetric energy storage density of 289 MJ/m3. The volumetric energy storage density is approximately double the energy densities of comparable paraffins with similar melting points. However, calcium chloride hexahydrate often requires high degree of supercooling to initiate solidification and long-term thermal stability has impeded the adoption of calcium chloride hexahydrate in the latent heat thermal energy storage system. There are only a few literatures which report on long-term stability of pure calcium chloride hexahydrate accurately. In this paper, the effects of sodium chloride and strontium chloride in mitigating supercooling in calcium chloride hexahydrate over 1000 melt–freeze cycles and thermal stability at elevated temperatures were studied in large sample size. Since there is not much data available on calcium chloride hexahydrate with nucleating additives, the current data available do not provide an insight into the effects of thermal cycling on supercooling. Therefore, this study also aims to measure the reliability of calcium chloride hexahydrate and report it, in terms of variations in melting temperature, supercooling, energy storage density, and change in mass over 1000 melt–freeze cycles. The results have shown that strontium chloride as heterogenous nucleators reduces supercooling by 2.5 °C and survived up to 1000 melt–freeze cycles (i.e., 2.7 years).

Development and Investigation of Lanthanum Sulfadiazine with Calcium Stearate and Epoxidised Soyabean Oil as Complex Thermal Stabilizers for Stabilizing Poly(vinyl chloride).

Lanthanum sulfadiazine (LaSD) was synthesized from sulfadiazine and lanthanum nitrate using water as solvent under alkaline conditions, and was used as a novel rare earth thermal stabilizer to stabilize poly(vinyl chloride) (PVC). The structure of LaSD was characterized by elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR) and thermo- gravimetric analysis (TGA). The influence of lanthanum sulfadiazine with calcium stearate (CaSt2) and epoxidized soybean oil (ESBO) on stabilizing PVC was studied by using the Congo red test, oven discoloration test, UV-vis spectroscopy and thermal decomposition kinetics. The results showed that the addition of LaSD as a thermal stabilizer can significantly improve the initial whiteness and long-term stability of PVC. In addition, the synergies between LaSD, ESBO, and CaSt2 can provide outstanding improvement in the long-term thermal stability of PVC. When the ratio of LaSD/ESBO/CaSt2 is 1.8/0.6/0.6, its thermal stability time is 2193 s which is the best state for stabilizing PVC. Furthermore, comparing the reaction energy (Ea) and the variations in the conjugate double bond concentration in PVC samples, the order of thermal stability of PVC was PVC/LaSD/ESBO/CaSt2 > PVC/LaSD/ESBO > PVC/LaSD. The thermal stability mechanism of LaSD on PVC was studied by the AgCl precipitation method and FTIR spectrum. The results showed that the action of LaSD on PVC was achieved through replacing unstable chlorine atoms and absorbing hydrogen chloride.

Using thermal analysis technology to assess the thermal stability of 1,3-dimethylimidazolium nitrate

1,3-Dimethylimidazolium nitrate ([Mmim]NO3), an ionic liquid, is a versatile and novel solvent for the petrochemical industry. Nevertheless, under high temperature conditions or thermal upset scenarios, [Mmim]NO3 can be decomposed in a manner that produces an explosion or other serious safety problems. The aim of this research was to investigate the thermal stability of [Mmim]NO3 by simultaneous thermogravimetric analyzer and high pressure differential scanning calorimetry. Isothermal experiments indicated that [Mmim]NO3 would be decomposed at a temperature substantially lower than the onset temperature. A pseudo-zero-order rate expression was applied to characterize the thermal decomposition kinetics of [Mmim]NO3, and related thermokinetic parameters were further obtained. Moreover, the temperature at which the thermal decomposition of ILs reached 10.0% for a given time of 10.0 h (T0.1/10h) was defined to assess the long-term thermal stability, which can be used as the maximum operating temperature of [Mmim]NO3. The results of this study may provide relevant processes for safer control based on the thermal hazard assessment of [Mmim]NO3.

Thermal energy storage and thermodynamic properties of (E)-3-m-tolylbut-2-enoic acid as a medium temperature phase change material

ABSTRACTPhase change materials (PCMs) that can store and release heat energy over the temperature range from 363 to 393 K are crucial for solar absorption cooling, and it is worthy to seek new solid-liquid PCMs candidates that melt and crystallize in this temperature range. In this paper, (E)-3-m-tolylbut-2-enoic acid (mTBEA) was applied as a PCM candidate. Its thermal energy storage properties and thermal stability were systematically investigated. The results showed that mTBEA melted at 382.9 ± 0.5 K and crystallized at about 364 K, with a melting enthalpy (ΔfusH) of 138.4 ± 6.9 J g−1 and showed good long-term cyclic stability and thermal stability. The supercooling of mTBEA was stabilized at about 20 K, indicating that the conservation condition of melted mTBEA could be simple. In addition, the melted mTBEA could release all the absorbed thermal energy upon crystallizing. Besides, mTBEA exhibited good thermal stability for it to be applied as PCM. Hence, mTBEA is a promising PCM candidate for solar absorption cooling. Furthermore, the heat capacity of mTBEA was measured by modulated temperature differential scanning calorimetry (MTDSC) over the temperature range from 198.15 to 431.15 K, and the molar thermodynamic functions, [HT-H298.15]m and [ST-S298.15]m, were calculated based on the fitted molar heat capacity data.

Improving salt tolerance and thermal stability of cellulose nanofibrils by grafting modification

Poor colloid stability of cellulose nanofibril (CNF) hydrogels at high temperature and high salinity can severely limit their industrial applications. This paper aims to prepare cellulose nanofibril hydrogels with improved salt tolerance and thermal stability. This was attained by simultaneous grafting of N,N-Dimethylacrylamide (DMA) and Butyl Acrylate (BA) onto the CNF surface based on the ceric ammonium nitrate-induced radical polymerization. The modified and original CNF samples were characterized by FT-IR, FBRM and rheological measurements. The FBRM results showed that the maximum salinity (NaCl) the CNF hydrogels can withstand increased from 1 wt% to 8 wt% after the simultaneous grafting of DMA (2 g/L) and BA (3 g/L). Moreover, rheological analysis results showed that the modified CNF hydrogels exhibited a much improved long-term thermal stability and a “salt-thickening” effect. As nano-cellulose based materials, the modified CNF hydrogels may have great potential as a promising petrochemical alternative for enhanced oil recovery applications.

Synthesis and Study of Zinc Orotate and Its Synergistic Effect with Commercial Stabilizers for Stabilizing Poly(Vinyl Chloride).

Zinc orotate (ZnOr2), which is a new kind of poly(vinyl chloride) (PVC) stabilizer, is prepared in this work through the precipitation method, and its impact on the thermal stability of PVC is measured by thermogravimetric analysis (TG), Congo red test, and discoloration test. The results exhibit that the thermal stability of PVC is positively enhanced after the addition of ZnOr2. In contrast with a commercial thermal stabilizer, zinc stearate (ZnSt2), a noteworthy improvement was observed that ZnOr2 could postpone the “zinc burning” of PVC. This is principally ascribed to the Or anion in the structure of ZnOr2 being able to absorb the HCl released by PVC, and to supersede unstable chlorine atoms in the structure of PVC. In addition, blending ZnOr2 with calcium stearate (CaSt2) in diverse mass ratios can significantly accelerate the thermal stability of PVC. Optimum performance was achieved with a CaSt2:ZnOr2 ratio of 1.8:1.2. Moreover, an outstanding synergistic effect can be observed when CaSt2/ZnOr2 is coupled with other commercial auxiliary stabilizers. The initial color and long-term stability of PVC including CaSt2/ZnOr2 is significantly increased when pentaerythritol (PER) is added, while dibenzoylmethane (DBM) can only improve its long-term thermal stability.

Low-Temperature Plasma-Enhanced Atomic Layer Deposition of Tin(IV) Oxide from a Functionalized Alkyl Precursor: Fabrication and Evaluation of SnO2-Based Thin-Film Transistor Devices.

A bottom-up process from precursor development for tin to plasma-enhanced atomic layer deposition (PEALD) for tin(IV) oxide and its successful implementation in a working thin-film transistor device is reported. PEALD of tin(IV) oxide thin films at low temperatures down to 60 °C employing tetrakis-(dimethylamino)propyl tin(IV) [Sn(DMP)4] and oxygen plasma is demonstrated. The liquid precursor has been synthesized and thoroughly characterized with thermogravimetric analyses, revealing sufficient volatility and long-term thermal stability. [Sn(DMP)4] demonstrates typical saturation behavior and constant growth rates of 0.27 or 0.42 Å cycle-1 at 150 and 60 °C, respectively, in PEALD experiments. Within the ALD regime, the films are smooth, uniform, and of high purity. On the basis of these promising features, the PEALD process was optimized wherein a 6 nm thick tin oxide channel material layer deposited at 60 °C was applied in bottom-contact bottom-gate thin-film transistors, showing a remarkable on/off ratio of 107 and field-effect mobility of μFE ≈ 12 cm2 V-1 s-1 for the as-deposited thin films deposited at such low temperatures.

High-efficiency perovskite solar cells based on self-assembly n-doped fullerene derivative with excellent thermal stability

Perovskite solar cells are promising photovoltaic devices with high efficiency beyond 23%, but thermal instability is one of the key obstacles for the commercialization. To prolong thermal stability, (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl) phenyl)dimethylamine is doped into a state-of-the-art fullerene derivative with a hydrophilic triethylene glycol type side chain as electron transport layer in planar perovskite cells with low-temperature process (<100 °C). The addition of dopant in electron transport layer results in stable layered structure. We observe that the increase of electron transport layer conductivity and optimized reduction of work function facilitate charge extraction and improve the energy level alignment. As a result, CH3NH3PbI3-based n-i-p perovskite cells with doped electron transport layer exhibit a hysteresis-free power conversion efficiency of 18.5%, outperforming the ones based on pristine electron transport layer (16.2%) or the other fullerene derivatives. Strikingly, the corresponding unsealed devices in air show long-term thermal stability. Devices sustain 85% of their initial efficiency after 1000 h storage under 60 °C. Our work bodes well for the dawn of commercialization of perovskite devices, providing the chance for the exploration of such high-efficiency devices with long-term thermal stability on flexible substrates.

Facile one-pot synthesis of long-term thermally stable CDs@AlOOH toward white-light illumination

The CDs doped boehmite composite (CDs@AlOOH) is directly achieved through a facile, low-cost and green one-step decomposition route with tunable fluorescence emission and long-term thermal stability.

Magnetron sputtering methods for surface modification of shape memory alloys for applications in orthodontics and endodontics

Various magnetron-sputtering methods for surface modification of shape memory alloys (SMA) are described in this paper. These methods belong to the most effective methods, which enable mechanical reinforcing of the SMA, showing numerous advantages over conventional methods of electro-polishing. In addition, surface modified SMA, particularly with equiatomic TiNi coatings, is crucial for further development of various endodontic instruments; wires and brackets used for orthodontic teeth movements. Active coatings with bactericide properties and coatings that can be used as barrier for release of toxic Ni ions from the bulk body of SMA obtained by various magnetron-sputtering methods can be successfully combined. Therefore, the review of these methods is given in this paper, with their main characteristics and drawbacks. Magnetron sputtering deposition involves surface modification of SMA in a single-layer, multilayer, graded layers, and nanocomposite thin coatings for obtaining systems with superior functional characteristics. These are hardness, scratch, abrasion, and erosion resistance, improved adhesion to various technologically important substrate materials such as polymers, hydrophobicity or hydrophilicity, long-term chemical, thermal, and environmental stability, gas and vapor impermeability, and others. This paper is critical review of the advances in the development of magnetron sputtering modified SMA products in dentistry, with in advance predictable physicochemical, structural and antimicrobial properties.

Removal of Dibenzyl Disulfide (DBDS) by Polyethylene Glycol Sodium and Its Effects on Mineral Insulating Oil

Dibenzyl disulfide (DBDS) is the major corrosive sulfur compound in mineral insulating oils, which will corrode the copper wires of windings in the oil-immersed power transformers and reactors and eventually cause operation failures. This paper studies the method to eliminate DBDS in insulation oils using the Polyethylene Glycol Sodium (Na-PEG) reagent. The preparation method of the Na-PEG reagent from NaOH and polyethylene glycol 400 is studied in the laboratory. The effect of the Na-PEG reagent dosage and reaction temperature on eliminating DBDS in insulating oils is studied, and a treatment process is recommended. An automatic processing device to remove DBDS from the transformer oil is developed, and the short-term electrical properties and long-term thermal stability of the insulating oil after the Na-PEG reagent treatment are tested. The results show that the Na-PEG reagent can efficiently eliminate DBDS in the insulating oil (the DBDS concentration decreases from 448 mg/kg to less than 5 mg/kg (undetectable) within 1 hour) and will not significantly negatively affect the oil properties such as the breakdown strength at the power frequency, dissipation factor or acidity. A preliminary exploration of the reaction mechanism is explored.