Isothermal Gravimetric Analysis Research Articles

Synthesis and Properties of Fully Biobased Crosslinked Starch Oleate Films.

Starch oleate (degree of substitution = 2.2) films were cast and crosslinked in the presence of air using UV curing (UVC) or heat curing (HC). A commercial photoinitiator (CPI, Irgacure 184) and a natural photoinitiator (NPI, a mixture of biobased 3-hydroxyflavone and n-phenylglycine) were used for UVC. No initiator was used during HC. Isothermal gravimetric analyses, Fourier Transform Infrared (FTIR) measurements, and gel content measurements revealed that all three methods were effective in crosslinking, with HC being the most efficient. All methods increased the maximum strengths of film, with HC causing the largest increase (from 4.14 to 7.37 MPa). This is consistent with a higher degree of crosslinking occurring with HC. DSC analyses showed that the Tg signal flattened as film crosslink densities increased, even disappearing in the case of HC and UVC with CPI. Thermal gravimetric analyses (TGA) indicated that films cured with NPI were least affected by degradation during curing. These results suggest that cured starch oleate films could be suitable for replacing the fossil-fuel-derived plastics currently used in mulch films or packaging applications.

Influence of the Co/Ni Ratio and Dendritic Segregations on the High-Temperature Oxidation Resistance of Multinary Co-Rich Superalloys at 850\xa0\xb0C and 1050\xa0\xb0C

Excellent inherent oxidation resistance is a prerequisite for the use of superalloys in many high-temperature applications. To achieve this goal, typically continuous alumina and chromia scale growths are assured through sufficient Cr and Al additions. Since the intended γ/γ′-microstructure of superalloys is only stable within a certain compositional window, the maximum concentrations of these protective scale forming elements are, however, dependent on the overall alloy composition. The latter is a severe drawback, especially for Co-rich superalloys, as for these the maximum content often is insufficient for reaching the desired continuous scale growth. In recent years, the addition of significant Ni levels was identified to improve the high-temperature oxidation properties in the case of simple model alloy systems. In this study, we compare the high-temperature oxidation behavior of two complex Co-rich multinary single-crystalline γ/γ′-strengthened superalloys that only differ regarding their Co/Ni ratios to the commercial Ni-base superalloy CMSX-4. Therefore, time-resolved isothermal gravimetric analysis (TGA) in synthetic air at 850 °C and 1050 °C for 100 hours, scanning electron microscopy analysis (SEM), and electron probe microanalysis (EPMA) were conducted. The results point out that a high Co-content beneficially affects the oxidation resistance at 850 °C, meaning that the Ni-base CMSX-4 is slightly outmatched by the Co-rich competitors. In contrast, at 1050 °C, the commercial (most Ni-rich) alloy performed best and, clearly, an increasing Co-content was identified to deteriorate the oxidation resistance. This temperature-dependent influence of the nominal Co/Ni ratio on oxidation resistance is shown to be especially pronounced for dendritic regions. Consequently, the latter could be identified to especially determine the overall oxidation kinetics.

Protective Alumina Scale Growth at 900\xa0\xb0C for a Ni- and Cr-Free Co-Base Model Alloy with \u03b3/\u03b3\u2019-Microstructure: Synergistic Effects by Combining Shot-Peening and Halogenation

The oxidation resistance of novel γ/γ’-strengthened Co-base superalloys is clearly outmatched by their Ni-base counterparts within the high-temperature regime. Therefore, surface modification strategies to foster protective alumina growth seem auspicious. This study elucidates the impact of fluorination and shot-peening on protective alumina formation at 900 °C for a quaternary Co-base model alloy (Co-Al-W-Ta system) which is well known for an exceptionally low inherent oxidation resistance. Time-resolved isothermal gravimetric analysis (TGA) in synthetic air, detailed electron microscopic analysis, and X-ray diffraction (XRD) were used. For polished samples, no pronounced enhancement of oxidation resistance could be obtained by halogenation. However, in case of shot-peened samples (halogen-free), an increased tendency for alumina formation is found compared to polished surfaces. The very early stages of oxidation were identified to be especially crucial with respect to sustainable protective scale growth. Most noteworthy is the observation of a strong synergistic effect derived by a combination of halogenation and shot-peening, leading to significantly increased oxidation resistance.

Influence of the microstructural homogeneity on the high-temperature oxidation behavior of a single crystalline Ni-base superalloy

Additive manufacturing by means of selective electron beam melting (SEBM) was recently demonstrated as an intriguing technique for the generation of single crystalline (SX) CMSX-4, a commercial Ni-base superalloy. The objective of this study is to compare the high-temperature oxidation resistance of SX SEBM-samples to their conventional counterparts which are derived by Bridgman investment casting. Therefore, time-resolved isothermal gravimetric analysis (TGA) was conducted at 850 and 1050 °C in synthetic air for 100 h. Due to solution annealing prior to oxidation, solidification induced elemental segregations could be homogenized completely in case of the SEBM-material, whereas they remained apparent for the conventional Bridgman samples. With residual elemental segregations inhomogeneous oxide scales emerged during exposure, exhibiting above-average scale thicknesses upon dendritic regions. Consequently, TGA revealed a higher mass gain in case of present segregations. In conclusion, a better high temperature oxidation resistance is observed for the homogeneous SEBM material.

Gasification and physical-chemical characteristics of carbonaceous materials in relation to HIsarna ironmaking process

HIsarna ironmaking process is one of the emerging technologies being developed to mitigate the increasing carbon footprint from the steel making industry. This innovative process offers flexibility with the type of reductants used in the smelting reduction vessel for the conversion of iron ore to liquid hot metal. Natural gas is well known for being a relatively clean fossil fuel producing carbon black and hydrogen when it undergoes thermal decomposition. The gasification reactivity of carbon black compared to the carbonaceous materials used in HIsarna process is investigated in this work using isothermal gravimetric analysis (TGA) method at 1250 °C, 1350˚C and 1450 °C under atmospheric pressure. Furthermore, physical-chemical characteristics of the individual carbonaceous materials, which may influence the reactivity, are evaluated systematically. The experimental results show that carbon black is the least reactive followed by thermal coal and charcoal. It was found that the effect of the morphology of the carbonaceous materials on the reactivity is dominant compared to the surface area of the materials. In addition, the reactivity increases with the alkali index (AI) and the level of the amorphousness of the material’s structure. Three well-known kinetic models, i.e. the volumetric model (VM), the grain model (GM) and the random pore model (RPM) were applied to predict the gasification behaviour of the three carbonaceous materials. The random pore model best describes the gasification reaction of the selected samples due to the influence of the pore diffusion on the reaction. It is observed that the activation energy of the samples are not following the order of reactivity, this can be explained by the kinetic compensation effect.

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with \u03b3/\u03b3\u2032-Microstructure - Influence of \u03b3\u2032-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

The improvement of the high-temperature oxidation resistance remains an ambitious goal for the design of new γ/γ′-strengthened Co-base superalloys, since their oxidation resistance beyond 800 °C still ranks behind their Ni-base counterparts. To better understand the origin of the poor oxidation resistance at higher temperatures, this study focuses on early stages of oxidation of four quaternary (Co-Al-W-Ta system) Co-base model alloys with a two-phase γ/γ′-microstructure and varying γ′-volume fraction at 800 °C, 850 °C and 900 °C. Based on time-resolved isothermal gravimetric analysis (TGA) in synthetic air and detailed electron microscopic analysis, the role of the γ-channel width (or γ′-volume fraction), the surface preparation prior to exposure (polishing versus shot-peening), and the heating conditions (synthetic air versus argon) on protective alumina growth is elucidated. Firstly, for alloys of increased γ′-volume fractions slower oxidation kinetics prevailed. Secondly, the two-phase microstructure was found to decisively affect the propagation of the internal oxidation front at the early stages of oxidation. Thirdly, shot-peening prior to exposure together with a lack of oxygen availability during heating was identified to foster protective alumina growth, accompanied by TCP-phase formation in the substrate. The critical role of a high Al availability in the alloy for a rapid growth of protective alumina and the relating challenges in alloy development regarding, for example, phase stability in this relatively novel Co-base alloy class are discussed in detail.

Tuning Porosity of Reduced Graphene Oxide Membrane Materials by Alkali Activation.

The alkali-activation method allows for obtaining highly porous carbon materials. In this study, we explored the effect of activation temperature and potassium hydroxide concentration on the pore structure of reduced graphene oxide (rGO), as potential membrane material. Above 700 °C, potassium species react with the carbon plane of rGO to form nanopores. This activation process is deeply studied through DSC measurements and isothermal gravimetric analysis. The porosity of the formed materials consists of both micro- and mesopores, with most of the pores having a size smaller than 10 nm. The specific surface area and pore volume increase with increasing the potassium hydroxide/graphene oxide weight ratio (KOH/GO) up to 7 (897 m2∙g−1 and 0.97 cm3∙g−1, respectively). However, for a synthesis mixture with KOH/GO of 10, the specific surface area of the produced material drops to 255 m2∙g−1. The film-forming ability of the porous reduced graphene oxide (PRGO) was tested by drop-casting on porous silicon carbide substrates. In this case, continuous PRGO films were obtained only from dispersions with 5 g∙L−1 GO loading and KOH/GO ≤3. Such films can still have high specific surface area and pore volume (up to 528 m2∙g−1 and 0.53 cm3∙g−1) and main pore volume <10 nm. Hence, they can potentially be applied as membrane devices, but their scalability and their adhesion on the substrate under realistic filtration conditions still remain challenges.

Oxygen chemisorption and low-temperature oxidation behaviors of sub-bituminous coal

The effective utilization of sub-bituminous coals should be extended as an energy source for power generation because of their low cost and long minable years. However, sub-bituminous coal may undergo spontaneous combustion owing to high reactivity with oxygen in low-temperature air compared with bituminous coal. Therefore, the objective of this study is to elucidate the low-temperature oxidation behaviors of sub-bituminous coal. In particular, transition from oxygen chemisorption to low-temperature oxidation of sub-bituminous coal has been experimentally examined in detail. Isothermal gravimetric analyses are conducted for several bituminous and sub-bituminous coal samples at temperatures varying between 356 K and 476 K in oxygen-enriched air. The chemical compositions of emission gas are continuously monitored under low-temperature oxidation conditions. The changes in the chemical structure of the coals are analyzed using Fourier transform infrared (FTIR) spectrometry. The experimental results show that the mass of all tested coals, including those of bituminous and sub-bituminous coals, increases at temperatures below 426 K as a result of oxygen chemisorption. At 476 K, the mass of sub-bituminous coal increases slightly with low H2 and CO2 emissions at the beginning and subsequently decreases with high CO and CO2 emissions. This mass change indicates that the transition from oxygen chemisorption to low-temperature oxidation occurs during this period. In addition, the FTIR spectra of sub-bituminous coals show the existence of carbonyl groups even in raw coal samples. These carbonyl groups are considered to contribute to the formation of CO2 and H2 from the beginning of reactions, triggering the transition from oxygen chemisorption to low-temperature oxidation.

Molecular Composite Coatings on Nafion Using Layer-by-Layer Self-Assembly.

Controlled growth of nanometer-scale multilayered coatings of negatively charged sulfonated poly(benzobisimidazole) (SPBI), complexed with positively charged poly(2-vinylpyridine) (P2VP) on quartz, and Nafion membrane as substrates has been explored. Both polymers, SPBI and P2VP, possess a net charge in methanol as a result of the dissolution of SPBI by complexation with triethylamine (TEA) and the protonation of P2VP with HCl, respectively, and thereby can form a multilayered molecular composite of alternating anionic SPBI and cationic P2VP via an electrostatic layer-by-layer (LbL) self-assembly. UV-vis absorption spectrophotometry was used to monitor the buildup and growth rate of such SPBI/P2VP multilayer films. Atomic force microscopy (AFM) was used to determine the roughness and thickness of the resulting SPBI/P2VP multilayers. As a result, it was found that a steady-state linear growth regime for the LbL self-assembled SPBI/P2VP multilayer films and coatings onto quartz and Nafion membranes was observed after completion of the first few deposition cycles, indicating the successful formation of the SPBI/P2VP multilayered assembly in methanol solutions. In addition, the SPBI/P2VP multilayer films in the perpendicular direction (flat view) demonstrated isotropic orientation distribution on the Nafion membrane, while the SPBI/P2VP multilayer films examined by X-ray scattering in the parallel direction (edge view) revealed anisotropic orientation, the combined observations indicating confinement of SPBI rods to the plane of the coating. We further found that the SPBI/P2VP multilayer coated Nafion possesses good thermal stability, as indicated by isothermal gravimetric analysis at 310 °C, and it was further observed that SPBI/P2VP multilayer coatings using the LbL self-assembly technique on Nafion membrane significantly increased the membrane stiffness, despite the small coating thickness employed.

Kinetic studies on the loss of water from α- d-glucose monohydrate

Although the dehydration of α- d-glucose monohydrate is an important aspect of several industrial processes, there is uncertainty with regard to the applicable rate law and other factors that affect dehydration. Therefore, the dehydration of three glucose monohydrate samples has been studied using isothermal gravimetric analysis. Dehydration follows a one-dimensional contraction (R1) rate law for the majority of kinetic runs, and an activation energy of 65.0 ± 3.9 kJ mol −1 results when the rate constants are fitted to the Arrhenius equation. Fitting the rate constants to the Eyring equation results in values of 62.1 ± 3.7 kJ mol −1 and −77.8 ± 4.7 J mol −1 K −1 for Δ H ‡ and Δ S ‡, respectively. The impedance effect on the loss of water vapor has also been investigated to determine the values for activation energy, enthalpy, and entropy for diffusion of water. The results obtained for the activation parameters are interpreted in terms of the absolute entropies of anhydrous glucose and the monohydrate.

Kinetics of Reduction Roasting of Hematite to Magnetite in Crude Niobium Concentrate under Microwave Irradiation

In this paper, the method of microwave reduction roasting was applied to investigate the heating and weight loss process from hematite to magnetite in crude niobium concentrate under the protection of argon. The kinetics of microwave reduction roasting of hematite in crude niobium concentrate were analyzed and calculated at the temperature range of 500°C ~850°C by way of non-isothermal thermogravimetry and isothermal gravimetric analysis. Results from this investigation demonstrated that the activation energy of microwave reduction roasting calculated by non-isothermal thermogravimetry was 26.5769kJ•mol-1, and the activation energy calculated by isothermal gravimetric analysis was 64.1203kJ•mol-1. Compared with the method of reduction roasting under resistance heating, the activation energy of microwave reduction roasting was small, and the reaction rate was fast.

New Semifluorinated Siloxane-Grafted Copolyimides: Synthesis and Comparison with Their Linear Analogs

A siloxane-grafted new diamino monomer DBPDMS has been prepared and used as a co-monomer in combination with the fluorinated diamine monomer TFBB to prepare siloxane-grafted polyimides. The polymers have been characterized by means of GPC, IR, and NMR. Their thermal, mechanical, and surface properties have been evaluated and compared with the homopolyimide and with polyimides where polysiloxane is incorporated in the main chain. DSC revealed melting of the grafted siloxane chain at sub-ambient temperature and a glass transition corresponding to the main polymer chain at high temperature. Isothermal gravimetric analysis at 350 °C indicated that grafted siloxane moiety can be removed thermally from the polymer chain without affecting the polymer backbone.

Carbon Dioxide Postcombustion Capture: A Novel Screening Study of the Carbon Dioxide Absorption Performance of 76 Amines

The significant and rapid reduction of greenhouse gas emissions is recognized as necessary to mitigate the potential climate effects from global warming. The postcombustion capture (PCC) and storage of carbon dioxide (CO2) produced from the use of fossil fuels for electricity generation is a key technology needed to achieve these reductions. The most mature technology for CO2 capture is reversible chemical absorption into an aqueous amine solution. In this study the results from measurements of the CO2 absorption capacity of aqueous amine solutions for 76 different amines are presented. Measurements were made using both a novel isothermal gravimetric analysis (IGA) method and a traditional absorption apparatus. Seven amines, consisting of one primary, three secondary, and three tertiary amines, were identified as exhibiting outstanding absorption capacities. Most have a number of structural features in common including steric hindrance and hydroxyl functionality 2 or 3 carbons from the nitrogen. Initial CO2 absorption rate data from the IGA measurements was also used to indicate relative absorption rates. Most of the outstanding performers in terms of capacity also showed initial absorption rates comparable to the industry standard monoethanolamine (MEA). This indicates, in terms of both absorption capacity and kinetics, that they are promising candidates for further investigation.

Estimation of intramolecular cyclization activation energies via isothermal gravimetric analysis: A technical note

Isothermal gravimetric analysis was used to monitor the weight loss of 4 exploratory compounds as an indicator of their solid-state thermal stability. Data obtained from TGA were further processed via a model-free isoconversional method to estimate the activation energy values. These values ranged from 140 to 218 kJ/mol and were inversely related to their corresponding surface areas. Based on their activation energy values, the relative stability of these 4 exploratory compounds can be ranked as C>D>B>A and their formulation development activities can be prioritized.

Thermogravimetric Analysis for the Determination of Water Release Rate from Microcrystalline Cellulose Dry Powder and Wet Bead Systems

The purpose of this work was to determine the total amount of water contained in dry powder and wet bead samples of microcrystalline cellulose, MCC, (Avicel® PH-101), taken from various stages of the extrusion/marumerization process used to make beads and to determine the kinetic rates of water release from each sample. These samples were allowed to equilibrate in controlled humidity chambers at 25°C. The total amount of water in each sample, after equilibration, was determined by thermogravimetric analysis (TGA) as a function of temperature. The rates of water release from these samples were determined by using isothermal gravimetric analysis (ITGA) as a function of time. Analysis of the results for these studies suggest that water was released from these systems by several different kinetic mechanisms. The water release mechanisms for these systems include: zero order, second order, and diffusion controlled kinetics. It is believed that all three kinetic mechanisms will occur at the same time, however; only one mechanism will be prominent. The prominent mechanism was based on the amount of water present in the sample.

Synthesis, characterization, and thermal properties of alternate copolymers containingN,N′-bis(diphenylsilyl)tetraphenylcyclodisilazane

Hexamethyldisilazane was used as the starting material to synthesize N,N′-bis(hydroxydiphenylsilanyl)tetraphenylcyclodisilazane (BHPTPC). By condensation polymerization of BHPTPC with α,ω-bis(dialkylamino)dimethylsiloxane, a series of alternate copolymers containing N,N′-bis(diphenylsilyl)tetraphenylcyclodisilazane was synthesized. GPC studies show that the highest molecular weight was obtained at a ratio of 1.005 : 1 (BHPTPC: α,ω-bis(dimethyl amino)dimethylsiloxane). Data of DSC indicate that the temperature of glass transition (Tg) and temperature of melting point (Tm) decreased with the increasing of dimethylsiloxane segments units. Three stages of degradation were found in the thermogravimetric analysis curves. The activation energy of the copolymer (with m = 2, 3, and 7) was calculated by using Flynn–Wall–Ozawa method. The activation energy of the copolymer with m = 2, 3, and 7 at second stage is 214, 211, and 184 kJ/mol, respectively. Isothermal gravimetric analysis shows that for the same temperature and the same time, the weight loss of the alternate copolymer was greatly less than that of common polydimethylsiloxane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 611–617, 2007

Synthesis and properties of polysiloxane containing N,N′‐bis(diphenylsilyl)tetraphenylcyclodisilazane

AbstractA new kind of polysiloxane containing N,N′‐bis(diphenylsilyl)tetraphenylcyclodisilazane was prepared by the anionic polymerization with a “seed solution” as initiator. The synthesis of monomers N,N′‐bis(hydroxydiphenylsilyl)tetraphenylcyclodisilazane (BHPTPC), N,N′‐bis(chlorodiphenylsilyl)tetraphenylcyclodisilazane (BCPTPC), and 1,3‐dichloro‐1,1,3,3‐tetraphenyldisilazane (DCTPS) are all reported in this study. The synthesized polysiloxane containing N,N′‐bis(diphenylsilyl)tetraphenylcyclodisilazane was characterized by 1H–NMR, 29Si–NMR, gel permeation chromatography (GPC), and intrinsic viscosity. The thermal stability of the polysiloxane was studied by isothermal gravimetric analysis (IGA). The results demonstrated that the synthesized polysiloxane containing N,N′‐bis(diphenylsilyl)tetraphenylcyclodisilazane had excellent thermal stability. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 82: 929–933, 2001

Synthesis and Characterization of Some Bismaleimides Containing Ether Groups in the Backbone

New bismaleimides containing ether groups in the backbone were synthsized and characterized. They were prepared by reacting maleic anhydride with various diamines (having ether groups). Monomers were characterized by infrared and poton nuclear resonance spectroscopy as well as by elemental analysis. The thermal properties of the bislmaleimides were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), differential thermogravimetry (DTG) and isothermal gravimetric analysis (IGA).

Synthesis and Characterization of New Highly Organosoluble Poly(ether imide)s Bearing a Noncoplanar 2,2‘-Dimethyl-4,4‘-biphenyl Unit and Kink Diphenylmethylene Linkage

Two new bis(ether anhydride)s, 2,2‘-dimethyl-4,4‘-bis[4-(3,4-dicarboxyphenoxy)]biphenyl dianhydride (4A) and bis[4-(3,4-dicarboxy phenoxy)phenyl]diphenylmethane dianhydride (4B), were prepared in three steps starting from nitrodisplacement of 4-nitrophthalonitrile with 2,2‘-dimethylbiphenyl-4,4‘-diol and bis(4-hydroxyphenyl)diphenylmethane, respectively, followed by alkaline hydrolysis of the intermediate bis(ether dinitrile)s and subsequent dehydration of the resulting bis(ether diacid)s. A series of new highly organosoluble poly(ether imide)s were prepared from the bis(ether anhydride)s and various diamines by conventional two-stage synthesis. The resulting poly(ether imide)s had inherent viscosities in the range of 0.55−0.81 dL·g-1. GPC measurement revealed that the polymers exhibited number-average molecular weight and weight-average molecular weight up to 45 000 and 82 000, respectively. All the polymers showed typical amorphous diffraction patterns. Almost all the poly(ether imide)s showed excellent solubility and readily dissolved in various solvents such as N-methyl-2-pyrrolidinone, N,N-dimethylacetamide (DMAc), N,N-dimethylformamide, pyridine, cyclohexanone, tetrahydrofuran, and chloroform. These polymers had glass transition temperatures in the range of 224−256 °C. Thermogravimetric analysis showed that all polymers were stable, with 10% weight loss recorded above 489 °C in nitrogen. The isothermal gravimetric analysis results demonstrated that these poly(ether imide)s showed weight losses of 7.0−10.5% after isothermal aging at 350 °C in static air for 20 h. These tough and flexible polymer films could be easily obtained by solution cast from the DMAc solution. These polymer films had tensile strength of 84−116 MPa and tensile modulus of 1.9−2.7 GPa.

Synthesis and Characterization of New Functional Bismaleimides

Functional bismaleimides containing γ-lactone, carboxyl, aldehyde, hydroxyl, azomethine or cinnamoyl groups were synthesized from maleimido benzoic acid via its acid chloride with phenolphtaleine, 5,5′-methylene-bissalicylic acid, 5,5′-methylene-bissalicylaldehyde, glycerol, tartaric acid and 3,4-bis(hydroxyethan-2-tioether)- p-maleimidobenzoic acid, by simple condensation or polymer analogous reactions on some of these reactive bisimides. The monomers were characterized by IR, 1H-NMR and elemental analysis. The DSC curves of all the samples showed an exotherm in the temperature range of 134–310 °C, which is attributable to curing reactions. Thermogravimetric analysis of the uncured resins indicated good thermal stability and a char yield of bismaleimide resins in accordance with the calculated C/H ratio. Their relative thermoxidative stability was evaluated by isothermal gravimetric analysis.