Wide Range Of Thermal Stability Research Articles

Alkylation of low eutectic energy-containing carrier molecules: Design and synthesis

A novel low eutectic energy-carrying carrier molecule has been developed that satisfies three criteria: intrinsic energy, effective lowering of the melting point of other carriers, and a wide range of thermal stability. In this study, two new compounds, APAD1 and APAD2, were synthesized by alkylation of molecular side groups and their structures were confirmed by FT-IR, NMR, and XRD. The melting points of APAD1 and APAD2 were 117 °C and 97 °C, respectively, and the decomposition temperatures were 266 °C and 242 °C, respectively, which were significantly lower compared to DATNEB. This method extends the synthesis of low eutectic carrier molecules for composite casting.

New hydrogen-bonded liquid crystal supramolecular systems: role of (+ I)-alkoxy substituents in promoting molecular ordering

Novel H-bonded liquid crystals (HBLCs) are synthesized and examined for their mesomorphic behavior. The HBLCs are prepared with Schiff base proton acceptors containing 8 and 18 carbons in the alkyl chain and the proton donor with 4-substituted benzoic acids. All the compounds exhibit smectic A mesophases, with one of the compounds exhibiting LC properties below 298 K. It is interesting to note that the ethoxy-substituted HBLCs exhibit a wide range of thermal stability. Density functional theory calculations revealed the formation of two hydrogen bonds between the substituted acids and the pyridine ring based on the orientation of the donor and the acceptor moieties. There are no significant changes observed in the hydrogen bond length with the increase in the chain length of the proton acceptor moiety, indicating the dilution of the cores by the longer alkyl chain lengths is compensated with the (+ I) effect of alkoxy substituents. Quantum chemical modeling studies on these molecules revealed the reduction in the HOMO–LUMO energy gap by approximately 0.3 eV for oxy-containing compounds, making them more chemically reactive by donating electrons (+ I) into the aromatic cores. These materials provide a significant breakthrough in designing innovative LC materials. This work is in support of the SDG-9 of the United Nations.Graphical abstract

Evaluation of glass-transition temperature and influence of low-temperature condition on the moduli of acrylonitrile-butadiene rubber

Medium acrylonitrile-butadiene rubbers (ABR) (30–45% acrylonitrile (ACN)) are commonly used in several sealing components for the aerospace industry due to their wide range of thermal stability (−40 °C to +108 °C), good abrasion, lightweight viscoelastic and tear resistance properties. Since sealings manufactured using a popular method, viz., moulding followed by milling, has several cons, like difficulty in transferring the used moulds to other supplementary working units, increased manufacturing cost due to increased processing steps and time, etc. There is a need for advanced and green manufacturing methods, like abrasive water jet machining, to produce intricate shapes/sizes in single or batch-size elastomeric components during failure or damage. Several researchers have suggested machining ABR at low-temperature (cryogenic) conditions instead of room temperature, which helps to get good quality machined surface due to the increased modulus of ABR. Hence, the low-temperature study of ABR is imperative due to the prominent market for cryogenic machining of ABR. In this direction, it is necessary to explore the effect of low temperature on ABR’s thermal and dynamic mechanical properties, which is essential for successfully developing the components required for several aerospace applications. The primary focus of the work is to explore the effect of low temperatures (–50 °C to 100 °C) on ABR’s storage and loss modulus. The low-temperature properties of ABR are enhanced by adding a sulfur accelerator followed by Zinc oxide activators to achieve optimum vulcanisation. The glass-transition temperature (Tg) range was measured using profound characterisation techniques such as Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analyser (DMA). The result shows that the transition phase occurred from –36.59 °C to –12.65 °C, which resulted in a phase change of ABR34 from rubbery to glassy (tough) due to a noticeable increase in the observed modulus values.

Extraction and characterization of pectin from fruit peels of Irvingia gabonensis and pulp of Cola milleni and Theobroma cacao as precursor for industrial applications

Pectin is a complex polysaccharide that makes up about one third of the cell wall of higher plants. It was extracted from fruit peels of Irvingia gabonensis and pulp of Cola milleni and Theobroma cacao using acid extraction and alcohol precipitation methods. The effects of temperature and time on the yield and physicochemical properties of the extracted pectin were evaluated. Optimum yields of pectin from C. milleni, I. gabonensis, and T. Cacao were 10.73%, 19.83%, and 11.73% respectively at extracting period of 150 min and temperature of 100 °C. Although there was significant difference in moisture content, degree of esterification, equivalent weight, and methoxyl content of the extracted pectins, there was no significant difference in yield, protein, and ash content at 95% confidence interval. The monosaccharide composition of the three pectins shows that the extracted pectin composed of galacturonic acid and minor neutral sugars. Major functional groups in the extracted pectin show peaks in the region between 1000 and 2000 cm−1. The bands observed between 1627–1651 cm−1 and 1739–1793 cm−1 indicated the presence of the carbonyl group stretching. The surface morphologies of the extracted pectins show irregular shapes, non-smooth surfaces, and unequal sizes which also reveals more silica nodes in cocoa pulp pectin than in other pectins. Thermogravimetric analysis of the pectin samples shows multi-step stages of thermal decomposition, indicating wide range of thermal stability. The overall results specified that the pectins extracted from these plants are suitable for industrial applications.

A novel amperometric H2O2 biosensor constructed by cress peroxidase entrapped on BiFeO3 nanoparticles

Herein, we synthesized ferromagnetic BiFeO3 nanoparticles with sizes of 20–60 nm and rhombohedral distorted perovskite structure without any co-formed impurity phases by sol-gel method. Structural, morphological, magnetic, electronic and textural properties of BiFeO3 nanoparticles were characterized by using XRD, SEM-EDX, TEM, FTIR, XPS, VSM, UV-DRS, PL and BET techniques. The peroxidase was isolated from the Cress (Lepidium sativum) and purified by using precipitation of ammonium sulfate and chromatographic techniques; gel filtration and ion exchange chromatography which is showed wide range of thermal stability, maximum activity in the acidic environment and close to the body temperature. Afterwards, a novel amperometric biosensor based on Cress peroxidase entrapped on BiFeO3 nanoparticles modified carbon paste electrode was prepared for the first time to sensitive detection of H2O2. The prepared H2O2 biosensor was operated with the aid of choro-amperometry technique by applying −0.8 V vs Ag/AgCl electrode. The developed biosensor exhibited a linear response towards to H2O2 in the concentration range of 2.0 10−7 to 1.0 10−5 M under the optimal conditions and limit of detection and quantification were estimated as 7.0 10−8 M (2.7 μg L−1) and 2.0 10−7 M (8.7 μg L−1), respectively. The repeatability of the electrode was calculated as 19.2 for 2.0 10−7 M (N = 7) and the accuracy was 81.2% for this concentration. In addition, the H2O2 biosensor exhibited excellent stability up to ten days. Finally, the sensor developed was used for the analysis of H2O2 in milk samples and satisfactory recoveries were obtained under the operating conditions.

Thermoluminescence of feldspar as a multi-thermochronometer to constrain the temporal variation of rock exhumation in the recent past

Natural thermoluminescence (TL) in rocks reflects a dynamic equilibrium between radiation-induced TL growth and decay via thermal and athermal pathways. When rocks exhume through Earth's crust and cool from high to low temperature, this equilibrium level increases as the temperature dependent thermal decay decreases. This phenomenon can be exploited to extract thermal histories of rocks. The main advantage of TL is that a single TL glow curve has a wide range of thermal stabilities (lifetime <ka to Ba), and hence can provide multiple constraints on thermal histories. Here we constrain the distribution of kinetic parameters of TL in feldspar using a glow curve deconvolution method and fitting infinitesimal sub-peaks using a general order kinetic model. Each peak corresponds to a different but closely located energy level E. Forward modeling is applied for different time-temperature histories to estimate the sensitivity and limitation of each signal for different cooling rates. The results show that it is possible to constrain thermal histories between ∼30 °C and ∼80 °C. The results also illustrate that shallower traps, i.e. with lower activation energies, can be exploited to constrain lower cooling histories >100 °C/Ma, whereas deeper traps, i.e. with higher activation energies, provide constraints on thermal histories for higher cooling rates (>300 °C/Ma). Finally, we show how the path of rock exhumation (i.e., depth vs. time) can be constrained using an inverse approach. The newly developed methodology is applied to rapidly cooled samples from the Namche Barwa massif, eastern Himalaya to suggest a trend in exhumation rate with time that follows an inverse correlation with global temperature and glaciers equilibrium altitude line (ELA).

ALUMINA PHASE TRANSFORMATION FROM THERMAL DECOMPOSITION OF AMMONIUM ALUM SYNTHESIZED FROM KANKARA KAOLIN

Thermal stability of transitional alumina phases produced from ammonium alum using Kankara kaolin as starting material was studied. Wet beneficiation method was employed to purify the starting material, after which it was calcined and dealuminated with sulphuric acid. The elemental composition, mineralogical, and physiological analyses were carried out using X-ray fluorescence (XRF), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) techniques respectively. The ammonium alum was thermally treated by varying the calcination temperature from 700 to 1200°C and varying the time of calcination from 1 to 4 h. The formation of gamma alumina began at calcination temperature of 825°C for calcination time of 3 h, which was found to be lower than reported works of 900°C. It was found to be stable at higher temperature of 1125°C, above which phase transformation to alpha alumina was observed. The observed wide range of thermal stability of the gamma alumina phase gives it good advantage to be used for high temperature applications, such as support for catalyst promoters. Alpha alumina phase formation began at 1150°C and was fully formed at 1200°C. BET specific surface area of 166 m 2 /g was obtained for the gamma alumina phase which was high enough for it application as support for catalyst, catalyst and adsorbent. http://dx.doi.org/10.4314/njt.v36i3.23

ALUMINA PHASE TRANSFORMATION FROM THERMAL DECOMPOSITION OF AMMONIUM ALUM SYNTHESIZED FROM KANKARA KAOLIN

Thermal stability of transitional alumina phases produced from ammonium alum using Kankara kaolin as starting material was studied. Wet beneficiation method was employed to purify the starting material, after which it was calcined and dealuminated with sulphuric acid. The elemental composition, mineralogical, and physiological analyses were carried out using X-ray fluorescence (XRF), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) techniques respectively. The ammonium alum was thermally treated by varying the calcination temperature from 700 to 1200°C and varying the time of calcination from 1 to 4 h. The formation of gamma alumina began at calcination temperature of 825°C for calcination time of 3 h, which was found to be lower than reported works of 900°C. It was found to be stable at higher temperature of 1125°C, above which phase transformation to alpha alumina was observed. The observed wide range of thermal stability of the gamma alumina phase gives it good advantage to be used for high temperature applications, such as support for catalyst promoters. Alpha alumina phase formation began at 1150°C and was fully formed at 1200°C. BET specific surface area of 166 m2/g was obtained for the gamma alumina phase which was high enough for it application as support for catalyst, catalyst and adsorbent. http://dx.doi.org/10.4314/njt.v36i3.23

Electrochemical Cycling Behavior of Pyrrolidinium Ionic Liquid Tethered TiO2 Nanoparticle-Hybrid Electrolytes: Influence of Grafting Density

Exploring new electrolyte materials is important to comprehend high performance secondary charge storage devices for effective utilization of renewable energy. Ionic liquids with broad electrochemical voltage window and wide range of thermal stability are prospective materials for the same. As an improved version of this class of materials, we report herein, on the synthesis of novel pyrrolidinium based ionic liquid tethered nanoparticle hybrid electrolytes and compared their conductivity and electrochemical cycling behaviors. Hybrid electrolytes are prepared by covalently grafting N-Methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide to the surfaces of pre-synthesized TiO2 nanoparticles at three different core volume fractions, ranging from 0.11 to 0.46. Uniform dispersion of the core nanoparticle within the matrix of the electrolytes improves their mechanical properties. With increasing core volume fractions, the electrical conductivity slightly decreases due to increasing viscosity. Nevertheless, nanoparticle grafting significantly improves the electrochemical performance of the electrolytes. The electrolytes show very good capacitance retentivity (>90%) and long-term cycling stability above room temperature even at the lowest grafting density within symmetric stainless steel electrodes. Impressive room temperature electrochemical performance of these materials within symmetric supercapacitor cell containing CMS graphite as electrodes further demonstrates the applicability of these hybrid materials as promising electrolytes for secondary charge storage devices.

A Step toward the Development of High-Temperature Stable Ionic Liquid-in-Oil Microemulsions Containing Double-Chain Anionic Surface Active Ionic Liquid

Owing to their fascinating properties and wide range of potential applications, interest in nonaqueous microemulsions has escalated in the past decade. In the recent past, nonaqueous microemulsions containing ionic liquids (ILs) have been utilized in performing chemical reactions, preparation of nanomaterials, synthesis of nanostructured polymers, and drug delivery systems. The most promising fact about IL-in-oil microemulsions is their high thermal stability compared to that of aqueous microemulsions. Recently, surfactant-like properties of surface active ionic liquids (SAILs) have been used for preparation of microemulsions with high-temperature stability and temperature insensitivity. However, previously described methods present a limited possibility of developing IL-in-oil microemulsions with a wide range of thermal stability. With our previous work, we introduced a novel method of creating a huge number of IL-in-oil microemulsions (Rao, V. G.; Ghosh, S.; Ghatak, C.; Mandal, S.; Brahmachari, U.; Sarkar, N. J. Phys. Chem. B2012, 116, 2850-2855), composed of a SAIL as a surfactant, room-temperature ionic liquids as a polar phase, and benzene as a nonpolar phase. The use of benzene as a nonpolar solvent limits the application of the microemulsions to temperatures below 353 K. To overcome this limitation, we have synthesized N,N-dimethylethanolammonium 1,4-bis(2-ethylhexyl) sulfosuccinate (DAAOT), which was used as a surfactant. DAAOT in combination with isopropyl myristate (IPM, as an oil phase) and ILs (as a polar phase) produces a huge number of high-temperature stable IL-in-oil microemulsions. By far, this is the first report of a huge number of high-temperature stable IL-in-oil microemulsions. In particular, we demonstrate the wide range of thermal stability of [C6mim][TF2N]/DAAOT/IPM microemulsions by performing a phase behavior study, dynamic light scattering measurements, and (1)H NMR measurements and by using coumarin-480 (C-480) as a fluorescent probe molecule.

Cold-active hydrolases producing bacteria from two different sub-glacial Himalayan lakes

Microorganisms, native to the cold environments have successfully acclimatized their physiological, metabolic, and biological features, exhibiting uniqueness in their enzymes, proteins, and membrane structures. These cold-active enzymes have immense biotechnological potential. The diversity of culturable bacteria in two different water lakes (the sub-glacial freshwater and the brackish) of Himalayas was analyzed using SYBR green staining and cultural methods. A total of 140 bacteria were isolated and were grouped as psychrophiles, psychrotrophs, and psychrotolerant organisms, based on their optimal temperature for growth. The amplified ribosomal DNA restriction analysis using three restriction enzymes facilitated the grouping of these isolates into 96 genotypes at ≥85% polymorphism. Phylogenetic analysis using 16S rRNA gene sequences revealed that the bacterial strains from both lakes belonged to Firmicutes, Proteobacteria (α, β, and γ) or Actinobacteria. Screening of the germplasm for the activity of different cold-active hydrolases such as protease, amylase, xylanase, and cellulase, revealed that about 16 isolates were positive, and exhibiting a wide range of stability at various temperature and pH. Our results suggest that the distinctly different ecosystems of sub-glacial freshwater and brackish water lakes have diverse groups of bacteria, which can be an excellent source of extracellular hydrolases with a wide range of thermal stability.

Side-chain electro-optic polymer modulator with wide thermal stability ranging from −46°Cto95°C for fiber-optic gyroscope applications

Electro-optic (EO) polymer modulators with a wide range of thermal stability from −46°Cto95°C for fiber-optic gyroscope applications are reported. The synthesized EO side-chain polymer used has a glass transient temperature (Tg) of 200°C and a large EO coefficient of 25.2pm∕V in a real device measurement. Mach–Zehnder (MZ) intensity and optical phase modulators are implemented based on this high-Tg side-chain EO polymer, exhibiting ∼3.75V half-wave voltage with 1.5cm interaction length and 2.3cm total length at 1.55μm wavelength. The optical fiber-to-lens insertion loss is ∼7.5dB in the MZ interferometers and ∼6dB in the straight waveguides. We examine the long-term thermal stability of these devices and demonstrate their ability to meet the strict requirements of various EO device applications, particularly fiber-optic gyroscopes.

Ionic liquids by proton transfer: vapor pressure, conductivity, and the relevance of DeltapKa from aqueous solutions.

We describe the behavior of the conductivity, viscosity, and vapor pressure of various binary liquid systems in which proton transfer occurs between neat Brönsted acids and bases to form salts with melting points below ambient. Such liquids form an important subgroup of the ionic liquid (IL) class of reaction media and electrolytes on which so much attention is currently being focused. Such "protic ionic liquids" exhibit a wide range of thermal stabilities. We find a simple relation between the limit set by boiling, when the total vapor pressure reaches one atm, and the difference in pK(a) value for the acid and base determined in dilute aqueous solutions. For DeltapK(a) values above 10, the boiling point elevation becomes so high (>300 degrees C) that preemptive decomposition prevents its measurement. The completeness of proton transfer in such cases is suggested by the molten salt-like values of the Walden product, which is used to distinguish good from poor ionic liquids. For the good ionic liquids, the hydrogen bonding of acid molecules to the proton-transfer anion is strong enough that boiling points, but not melting points, may maximize at the hydrogen-bonded dianion composition. High boiling liquids of this type constitute an interesting class of high-temperature protonic acid that may have high-temperature fuel cell applications.

Contributions to the radiation chemistry of octasilsesquioxanes:: unique traps for atomic hydrogen and free radicals at ambient temperature

Evidence was given for trapping of H-atoms in fluid solutions of octasilsesquioxanes. Use was made of the positive effect of scavengers on the yield of trapped H-atoms. Carbon and silicon-centered radicals formed simultaneously through radiation chemical processes were detected. Most of the radical species were identified by the simulation of the corresponding ESR spectra. A wide range of thermal stability is covered by the radicals depending on the chemical nature of the substitutents of the cages and the precursors.

Spin-stand characterization of thermal stability in high density disk media

An experimental technique has been developed to characterize the thermal stability of recording media. We measured the remanent magnetization decay in a significant range under various reverse fields in a short time scale. By directly fitting the experimental data with an Arrhenius-Neel type model, the effective energy barrier distribution has been estimated. Unlike other previously reported techniques, this new technique enables more accurate analysis of energy barrier distribution and reliable evaluation of long-term stability for media with a wide range of thermal stability.

Evaluation of different chemical methods for cros-linking collagen gel, films and sponges

Collagen-based films and sponges are widely used as biomaterials. The rate of their biodegradation can be reduced by treating them with different cross-linking agents. The efficiency of different reticulation procedures on thermal stability (measured by differential scanning calorimetry) and susceptibility to bacterial collagenase digestion of the final material (films or sponges) is compared. The chemical agents used on collagen gels or directly on collagen sponges and films were glutaraldehyde (GTA), hexamethylene diisocyanate (HMDC), cyanamide, 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) and the two acyl azide methods (with hydrazine or diphenylphosphorylazide (DPPA)) developed in the authors' laboratory. Under these experimental conditions, collagen stabilization by the different agents increased in the following order: cyanamide <EDC<HMDC<hydrazine<DPPA<GTA. Sponges with the highest thermal stability were obtained by treating collagen gel with 0.5% GTA for 1 h at pH 5.5 (initial T d=75.8°C; after 3 months, T d=75.6°C). Direct treatment of collagen films with DPPA gave similar thermal stability (T d=72.6°C) and collagenase resistance when compared with treatment with 0.6% GTA for 96 h (T d=74.6°C). It is demonstrated that collagen sponges and films can be prepared with a wide range of thermal stability (49–75.8°C) and collagenase digestion resistance (10–100%). Recent biocompatibility studies show, however, that DPPA and EDC are the best choices for preparing cross-linked collagen sponges and films.

THE THERMOLYSIS OF PENTA-COORDINATE PHOSPHORUS HETEROCYCLES

Abstract Small-ring heterocycles are an important class of penta-coordinate phosphorus compounds, whose properties—including thermolysis—have been extensively studied.1,2 It is noteworthy that these compounds display a wide range of thermal stability—certain examples decompose completely below -40°C, while others are stable indefinitely at > 300°C—yet any thermolysis reaction almost invariably takes place at the phosphorus centre. Diverse conditions have been employed: reactions have been carried out in the melt, in solution and in the gas phase, and ionic, radical and concerted mechanisms have been advanced to explain the results. In this article, we hope to rationalise this behaviour and to give a representative survey of the field. Unfortunately, a truly comprehensive review is literally not possible at this time, since in the older literature, P(v) intermediates are often written without evidence of their existence, or, betaine structures are assigned to species which are in fact phosphoranes. Two cla...

Temperature classes for dry-type transformers

INSULATING MATERIALS currently are classified into classes O, A, B, C, and H (AIEE Standard Number 1). Although this classification may be adequate as a rough indication of the nature of a material, it does not appear to be adequate for establishing standard operating temperature limits either for materials, or, particularly, for a complete apparatus. The inherent difficulties in establishing these limits are 1. The organic resins, which are used as a bonding agent in composite insulation, have a wide range of thermal stability. 2. The nature of the inorganic component (whether split mica or glass fiber) in composite insulation largely determines the aging properties of insulation, used as a dielectric barrier. 3. The function of the composite organic-inorganic material in the complete apparatus influences its life, whether a dielectric barrier, or just a spacer. 4. The mechanical arrangement of insulation influences its life, confined and supported, self-supporting, or acting as a mechanical support.