Acceleration of the cationic polymerization of an epoxy with hexanediol

Thin films of 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate were UV irradiated (1.1 J cm^-2) under isothermal conditions ranging from 0 to 50°C. Under these conditions the polymerization advanced quickly but only to a conversion level of less than 10% before the reaction rate slowed by more than an order of magnitude. This drop off in rate was not caused by the glass transition temperature, T _g, reaching or exceeding the reaction temperature, T _rxn, since the epoxide's T _g remained at least 40°C below T _rxn. Raising the sample temperature above 60°C caused a sharp increase in the conversion level. At 100°C conversion exceeds 80% and the ultimate T _g approaches 190°C. The addition of 10 mass% 1,6-hexanediol, HD, to the epoxy caused the conversion at room temperature to quintuple over the level obtained without the alcohol present. The heat liberated from this alcohol epoxy blend during cure on a UV conveyor belt system caused the sample's temperature to increase by about 100°C above ambient whereas the epoxy alone under these conditions only experienced a modest temperature rise of about 26°C. If the amount of HD in the blend is increased above 10% the heat of reaction at 23°C decreases due to HD being trapped in a nonreactive crystalline phase. Boosting reaction temperatures above 50°C melts the HD crystals and yields significantly improved conversion ratios. As the level of alcohol blended with the epoxy is raised its ultimate T _g is lowered and when the concentration of alcohol in the blend nears 30 mass%T _g drops below room temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effects of preparation temperature on microstructure and electrochemical performance of calcium carbide-derived carbon

Calcium carbide-derived carbons (CCDCs) produced by chlorination of CaC₂ at various temperatures (400–800 °C) possess highly controllable microstructure and porosity, allowing them to serve as excellent electrode materials for the application of supercapacitor. This paper focused on the effect of pore size and specific surface area (SSA) of CCDC on its electrochemical behavior. Microstructure and micropore characteristics of CCDC were characterized by N₂ adsorption/desorption isotherms, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that SSA and average pore size increased with the increase of synthesis temperature from 400 °C to 600 °C, and then decreased when temperature reached to 800 °C. Meanwhile, a correlation between specific capacitance and SSA of micropores (less than 2 nm in diameter) has been studied. It has been found that the supercapacitor using the CCDC prepared at 600 °C as electrode material in 6 M KOH showed the maximum specific capacitance and energy density (53.61 F g^?1 and 7.08 W h kg^?1), outstanding rate capability, lower IR drop and 96 % retention of initial capacity over 5,000 cycles.     

Co-solvent effects for preventing broadening or loss of early eluted peaks when using concurrent solvent evaporation in capillary GC. Part 2: n-Heptane in n-pentane as an example

Co-solvent effects are applied to allow use of concurrent solvent evaporation for applications requiring analysis of compounds eluted less than some 50° above the column temperature during sample introduction, i.e. at oven temperatures below some 100–120°C. Required conditions such as GC even temperature, concentration of the co-solvent and length of the uncoated pre-column (retention gap) are studied theoretically as well as experimentally for the case of n-heptane as co-solvent in n-pentane.     

Application of pyrolysis-capillary gas chromatography with NPD detection in thermal degradation of polyphosphazenes study

Polyphosphazenes represent a unique class of polymers with a backbone composed of alternating phosphorous and nitrogen atoms. The thermal behaviour and decomposition of a variety of polyphosphazenes depends on the type of side groups present. Especially those that bear aryloxy side groups, possess a high temperature stability as well as excellent flame resistance. Pyrolysis-capillary gas chromatography has been used in a study of three polyphosphazene samples for thermal stability characterisation. Degradation products were detected with three single detectors for flame ionisation (FID), nitrogen-phosphorous sensitivity (NPD) and mass spectrometry (MSD) at different pyrolysis temperatures ranging from 300°C up to 800°C. The NPD responses for phosphorous or nitrogen fragments of polyphosphazenes have been used for the construction of degradation product schemes and the examination of the thermal stability of the polyphosphazene’s backbone. Partial identification of the degradation products present in the gaseous phase was achieved by MSD. The polyphosphazenes thermal degradation conversion rates were at a maximum at 450–500°C. At various pyrolysis temperatures, the calculated N/P peak area ratio is a function of the degree of polyphosphazene-N=P-chain degradation, and reflective of the nitrogen — phosphorous detector sensitivity. NPD proved to be suitable tool for characterization of polyphospazene thermal stability.     

A new high temperature gas chromatograph incorporating a temperature programmable direct injector

A high temperature gas chromatograph has been developed which is capable of operating at column oven temperatures up to 500°C. In addition, the detector can operate at temperatures up to 500°C, and the injector up to 450°C. The injector on this instrument is a temperature programmable direct injector, designed specifically to introduce labile or high molecular weight samples into the GC without molecular weight discrimination. The design of this GC and injector will be described, and high temperature applications will be discussed.     

Thermogravimetric analysis of cellulose insulation and determination of activation energy of its thermo‐oxidation using non‐isothermal,model‐free methods

The aim of the work was to determine the effect of heating rate on initial decomposition temperature and phases of thermal decomposition of cellulose insulation. The activation energy of thermo‐oxidation of insulation was also determined. Individual samples were heated in the air flow in the thermal range of 100°C to 500°C at rates from 1.9°C min^?1 to 20.1°C min^?1. The initial temperatures of thermal decomposition ranged from 220°C to 320°C, depending on the heating rate. Three regions of thermal decomposition were observed. The maximum rates of mass loss were measured at the temperatures between 288°C and 362°C. The activation energies, which achieved average values between 75 and 80.7 kJ mol^?1, were calculated from the obtained results by non‐isothermal, model‐free methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of temperature and concentration on mechanism and kinetics of thermally induced deposition from coffee extracts

Production of soluble (instant) coffee powders typically involves extraction of roasted coffee by water followed by evaporation in order to concentrate extracts before spray or freeze drying to produce dry coffee powder. In the course of evaporation, deposition of dissolved material from coffee extracts is a major cause of fouling at the heat exchange surfaces of evaporators. Therefore, in order to improve the design and optimization of evaporation processes of coffee extracts, better understanding of the deposition mechanism and kinetics is needed. In this study, optical waveguide lightmode spectroscopy (OWLS) was used to monitor the initial formation of nanometer scale deposits on surfaces exposed to coffee extracts. OWLS measurements were complemented by light scattering from extract solutions, gravimetry of macroscopic deposits, and scanning electron microscopy imaging of deposited layers. Primary molecular-scale layers of about 1 mg m^?2 were rapidly formed in the first stage of deposition, even at ambient temperature, followed by the secondary deposition with kinetics strongly dependent on temperature. Secondary deposition rates were low and largely independent of the extract concentration at ambient temperature, but became strongly dependent on the extract concentration at elevated temperatures. In particular, activation energies for the deposition between 25°C and 70°C were much higher for the original extract (13.3 mass %, solids) than for diluted extracts (up to 1.3 mass %, solids). Furthermore, heating of the original extracts above 60°C resulted in rapid aggregation of suspended macromolecules into large clusters, while only gradual aggregation was observed in diluted extracts.     

Cesium release during high-temperature pre-treatment of fuel fragments with a burn-up of 61 GWd/tU

The electrolytic reduction process in pyroprocessing of used fuel requires that fuel fragments be pre-treated to remove cesium and iodine. The effect of high temperatures and fuel fragment size on release of cesium was investigated over 10 h at a temperature of 1300–1400 °C for fuel fragments with an O/U ratio of 2.2. Re-fragmentation of the original fragments was observed as changes in cesium release count rates as fuel was heated from 484 to 1329 °C. The release of cesium is highly dependent on the size of fuel fragments and most of the cesium is released as the temperature is held at the maximum target value.     

Capillary gas chromatography of tert-butyldimethlysilylamino acids with PTV injection

The programmable temperature vaporizing injector (PTV) has been used to study the effects of injection temperature and initial heating period on the FID response factors of TBDMS derivatives of 17 protein amino acids. The relative response factors were calculated for injection temperatures of 50°C, 90°C, 160°C, 220°C, and 260°C with different initial heating periods (1 s, 5 s, and 10 s) and the results compared with the values obtained for the calculated response factors obtained under classical split injection conditions (300°C, continuous). Except for expected peak broadening effects, the initial heating period does not seem to have significative effects on relative peak areas. The response to the derivatives of alanine, glycine, α-aminobutyric acid, valine, proline, methionine, cysteine, phenylalanine, asparagine, and arginine was only slightly affected by increasing the injection temperature whereas the response factors for the derivatives of serine, threonine, glutamic acid, lysine, histidine, tyrosine, and tryptophan were strongly dependent upon initial injection temperatures, decreasing rapidly at temperatures above 160°C. The cold split-splitless injection is clearly advantageous over the classical hot injection techniques for the analysis of this type of aminoacid derivative.     

Thermal decomposition temperatures of metal sulfates

The thermal decomposition of sixteen metal sulfates was studied by thermogravimetry at heating rates of 2 and 5°C min^?1 in flowing air and high-purity nitrogen. Their decomposition behaviors, especially the initial decomposition temperatures, were examined with relation to the thermodynamic functions for decomposition. Of the factors possibly influencing the decomposition temperature, the equilibrium SO₃ pressures over the sulfates were evaluated: the equilibrium pressures at the initial temperatures for sulfates of metals, of which the oxidation state was unchanged during decomposition, were nearly equal to 1×10^?4 atm at 2°C min^?1 in flowing nitrogen.     

Thermal history and melting behavior of poly(ethylene terephthalate)

Low molecular weight poly(ethylene terephthalate) samples were crystallized isothermally at 120–245°C from both the amorphous state and the melt. Isothermal annealing of these polymers at 215°C provided polymers which exhibited multiple melting peaks in thermal analysis, referred to as form I and form II, as assigned by Bell and Dumbleton. In these samples the peak temperature of the form II melting endotherm and the average crystallite size are dependent on the temperature of initial crystallization. This result requires a mechanism for retaining some structural feature during the conversion from morphological form I to form II. DSC thermograms obtained at varying heating rates on samples showing only form II endotherms support the assignment of superheating as the cause of the shift to higher peak temperatures with increasing heating rate.     

Influence of annealing temperature on the electrochemical and surface properties of the 5-V spinel cathode material LiCr0.2Ni0.4Mn1.4O4 synthesized by a sol–gel technique

LiCr_0.2Ni_0.4Mn_1.4O₄ was synthesized by a sol–gel technique in which tartaric acid was used as oxide precursor. The synthesized powder was annealed at five different temperatures from 600 to 1,000 °C and tested as a 5-V cathode material in Li-ion batteries. The study shows that annealing at higher temperatures resulted in improved electrochemical performance, increased particle size, and a differentiated surface composition. Spinel powders synthesized at 900 °C had initial discharge capacities close to 130 mAh g^?1 at C and C/2 discharge rates. Powders synthesized at 1,000 °C showed capacity retention values higher than 85 % at C/2, C, and 2C rates at 25 °C after 50 cycles. Annealing at 600–800 °C resulted in formation of spinel particles smaller than 200 nm, while almost micron-sized particles were obtained at 900–1,000 °C. Chromium deficiency was detected at the surface of the active materials annealed at low temperatures. The XPS results indicate presence of Cr⁶⁺ impurity when the annealing temperature was not high enough. The study revealed that increased annealing temperature is beneficial for both improved electrochemical performance of LiCr_0.2Ni_0.4Mn_1.4O₄ and for avoiding formation of Cr⁶⁺ impurity on its surface.     

Kinetics of polyesterification III: Solid-state polymerization of polyethylene terephthalate

Experimental studies on the solid-state polymerization (SSP) of polyethylene terephthalate (PET) for the particle sizes of 14–16 mesh at 170–200°C and for the particle sizes of 14–18 mesh at 210–240°C are carried out under a vacuum of about 60 mtorr. Analysis of the data of the concentrations of hydroxyl and carboxyl groups and the number average molecular weight during the SSP allows determinations of the rates of esterification and ester interchange separately. It is found that at the temperature 170–200°C and the particle size 80–100 mesh the SSP is end-group diffusion limiting, and that at the temperature 210–240°C and the particle size 14–16 mesh the ester interchange is ethylene glycol diffusion limiting and the esterification is predominantely end-group diffusion limiting due to higher diffusion rate of water. These phenomena are explored by an assistance of the proposed rate expressions for the end-group diffusion limited reactions and diffusion models for the by-products, water, and ethylene glycol.     

Fire resistance properties of heavyweight magnetite concrete in comparison with normal basalt- and quartz-based concrete

Nowadays application of radiation shielding structures grows over the world. Nuclear buildings represent one of the most complicated radiation shielding structures; that is why a particular type of concrete is required to withstand different conditions during their lifespan. Unique properties such as the behaviour under elevated temperatures, radiation shielding, and thermal stability properties are essential to guarantee the fire resistance safety of nuclear buildings. However, some gaps are still there, warranting further investigation, particularly the thermal stability and fire-resistance properties of the heavyweight concrete. The properties are mechanical, physical, and deformation properties of concrete after being subjected to elevated temperature. This paper investigated the fire resistance properties of three concrete mixes. There were magnetite-based concrete, basalt-based concrete, and quartz-based concrete. Compressive and flexural strength, spalling, mass loss, porosity, and scanning electron microscopy were measured for the three concrete types after being subjected to different temperature steps at 20, 150, 300, 500, and 800 °C. The three types of concrete showed different fire resistance properties. Magnetite-based concrete has better heat/fire resistance than basalt- and quartz-based concrete; there was no significant change up to 500 °C, and explosive spalling occurred at 800 °C. Correspondingly, the maximum change in porosity and reduction in the compressive and flexural strength occurred at 300 °C, which indicates the good thermal stability of magnetite-based concrete. Concerning basalt-based and quartz-based concretes, cracks were observed at 500 °C, and cracks with colour change and small spalling were initiated at 800 °C. Therefore, the maximum growth in the porosity and the high reduction in the compressive and flexural strength in basalt-based concrete occurred at 800 °C. Likewise, the extreme change in the porosity occurred at 500 °C, and the drastic reduction in the compressive and the flexural strength in the quartz-based concrete was relatively high at 500 °C and 800 °C. The SEM observations and analysis obtained the appearance of microcracks, voids and degradation of C-S-H in different concrete mixes at 500 and 800℃.

     

Dehydration investigations of a refractory concrete using DTA method

The base mix refractory concrete is corundum-based, containing corundum as refractory aggregate and CAC as hydraulic binder, with a spinel as an additive. The authors investigated the dehydration reactions which occur from the moment when water is added (at the beginning of components mixing), to the moment when installed refractory concrete lining is put into the service. Sintering process kinetic of low-cement content refractory concrete was investigated by means of differential thermal analysis at four different heating rates (5, 10, 20, and 30?°C/min). Thus, temperature was increased from 20 to 1100?°C. It was noticed that first dehydration step occurs at lower temperatures, indicating at a desorption of physically adsorbed and interlayer water molecules. Second dehydration step, at higher temperatures is due to dehydroxylation of the lattices and decomposition of the interlayer anions.     

Solid Phase Micro-extraction – Gas Chromatography–Mass Spectrometry to Characterize Pyrolysis Products from Textiles

Headspace solid phase micro-extraction gas chromatography–mass spectrometry (HS-SPME GC–MS) was used for identifying thermally labile volatile compounds from cotton, wool, polyester, olefin, silk, and acrylic. Volatile compounds were generated from the textiles using a pyrolysis apparatus prior to GC–MS. Pyrolysis temperatures ranged from 190 to 550°C. Each textile displayed a unique chromatogram containing compounds that were consistent with the chemical structure of the textile. Experimental parameters that were investigated included the temperature, sample size, and sampling time to determine their effect on the number and intensity of peaks in the chromatograms as well as to identify optimum conditions for analysis. Heating of each sample was achieved using a resistively heated Pt wire. Full pyrolysis at 550°C of the textiles appeared to give the best results in terms of peak height relative to background. A range of sample sizes (0.02–1.5?mg) were used and, generally, ≤0.02?mg was used for identifying the textiles. The reproducibility of retention times for selected compounds in the chromatograms was less than 1% relative standard deviation. The combination with mass spectrometry provided valuable structural information.     

On the synthesis and characterization of ZnO/MgO nanocomposite by thermal evaporation technique

ZnO/MgO nanocomposites have been synthesized by an easy and cost effective thermal evaporation technique. Various growth temperatures ranging from 800 to 900 °C were tried. It is observed that the process temperature plays a key role in the formation of ZnO/MgO nanocomposite and the proper formation of ZnO/MgO nanocomposite occurs at 875 °C temperature as confirmed by X-ray diffraction studies. Scanning electron microscopic images indicate that the ZnO/MgO nanocomposite is formed as agglomerated nanoparticles distributed over a large area. Energy dispersive X-ray analyses also reveal that the Mg composition in the synthesized nanocomposite strongly depends on the process temperature. Photoluminescence (PL) spectrum exhibits a blue shift for the ZnO/MgO nanocomposite synthesized at 875 °C indicating the incorporation of Mg into the ZnO crystal lattice. A higher PL intensity ratio of band-edge to deep band emission has been observed for this sample indicating the presence of low crystalline defects.     

Influence of water domain formed in hexadecane core inside cross-linked capsule particle on thermal properties for heat storage application

The influence of a water domain formed in n-hexadecane (HD) core in cross-linked polymer capsule particles on the thermal properties of encapsulated HD was studied from the view point of heat storage application. The capsule particles were prepared by micro-suspension polymerization of divinylbenzene at 70 °C utilizing the Self-assembling of Phase-Separated Polymer (SaPSeP) method that the authors proposed. The water domain was not observed for particles taken just after the polymerization and kept at 70 °C, but it was gradually formed with an increase of the size during cooling process from 70 °C to room temperature. In differential scanning calorimetric thermograms, pure HD had a single peak because of solidification (T _s) at 15 °C, and the encapsulated HD containing the water domain had two peaks of T _s1 and T _s2, at 6 and 1 °C, respectively. That is, the encapsulated HD containing the water domain required longer time and lower temperature to complete the solidification than the pure HD, which is negative for its application. However, the lower temperature-side peak at T _s2 gradually disappeared with an increase of capsule particle diameter, which seems to be based on the decrease of total interfacial area between the water domains and encapsulated HD in the capsule particles.     

Temperature effect on the recovery of SO2-Poisoned GC/Nano-Pt electrode towards oxygen reduction

The SO₂ poisoning of Pt nanoparticle (n-Pt) modified glassy carbon (GC/n-Pt) electrode and the recovery of its activity for the oxygen reduction reaction (ORR) were studied using cyclic voltammetry at ambient (25 °C) and elevated (70 °C) temperatures. Recovery of the GC/n-Pt electrode by cycling the potential within the ORR range (1.0 to 0.2 V (standard hydrogen electrode)) in 0.1 M H₂SO₄ was not effective at 25 °C, but at 70 °C the onset potential of the ORR was almost the same as that at the fresh GC/n-Pt electrode. For the two different temperatures used here, the recovery on cycling the potential between 0.4 and 1.7 V was efficient. However, the number of cycles and the amount of charge required for the recovery at 70 °C were the smallest, which is of great interest for the proton exchange membrane fuel cell performance. The recovery using such a wide potential range at 70 °C resulted in an enhancement of the electrocatalytic activity of the GC/n-Pt electrode over a non-poisoned (bare) GC/n-Pt electrode.     

Kinetic and equilibrium phenomena in the system: Acetone vapor and polycarbonate film

Amorphous films of Lexan polycarbonate have been exposed to acetone vapor at controlled temperatures and partial pressures in order to study sorption kinetics and thermodynamics and polymer crystallization behavior. Sorption isotherms show a discontinuity is slope at or near the depressed glass transition, which itself was identified by torsion pendulum measurements. Crystallization abruptly begins to occur at partial pressures equal to or slightly above that of the solubility transition and is manifested by delayed desorption and whitening phenomena. In this process 20% crystallinity is usually developed, as measured by calorimetry which, however, produces a 40% drop in acetone solubility. Although the depressed glass temperature is near 0°C. in saturated atmospheres—a drop of 145°C.—the melting point is only depressed 60 or 70°C. Such disparity probably accounts for the enhanced polycarbonate crystallization rate in acetone over that in the dry bulk polymer above the normal T_g.