Variable Heating Rate Research Articles

Comparative analysis of bark and woodchip biomass piles for enhancing predictability of self-heating

Along with the inherent woody biomass supply needs within the bioenergy industry, self-heating risks associated with stored biomass piles continue to threaten worker safety, have the potential to cause serious damages to plant infrastructure and can result in the complete loss of feedstock stores. Though bark and woodchips can both be utilized as a feedstock, their physical and chemical properties differ significantly. Self-heating risks and dynamic pathways leading up to such events were therefore expected to vary as well. A large-scale industrial storage trial was conducted in Point Tupper, Nova Scotia along with comparative physical tests to determine whether wood self-heating models could be used successfully for piles primarily consisting of softwood bark (from local sawmills). Modeling with established bark variables yielded accurate predictions of pile temperature when compared with actual temperature sensor data (R2 = 0.94). Following the start of the simulation (Day 1 = November 10, 2015), it was found that the average bark pile temperature peaked at 58.4 °C on Day 33 with varying heating rates between the pile layers. The woodchip pile simulation in comparison, was found to peak on Day 23 with an average temperature of 64.9 °C. A sensitivity analysis highlighted significant self-heating variables, revealing those associated with microbial activity as being some of the most influential on temperature profile during initial storage stages. Our overall results indicated that bark piles heat at a slower rate compared to woodchips while retaining more heat over time. Wood parameters are insufficient for modelling bark pile dynamics and the use of specific bark parameters is necessary.

Experimental investigation of effects of variation in heating rate, temperature and heat flux on fire properties of a non-charring polymer

During fire, charring and non-charring polymers undergo reactions in the solid phase (pyrolysis) and in the gas phase (combustion). These reactions can be modelled using computational fluid dynamics-based fire modelling for the prediction of fire growth and spread. Given that many fire properties vary with temperature including heating rate and radiation flux, improvements in fire simulations can be made by accounting for these variations. This study characterizes the fire properties of the non-charring synthetic polymer poly(methyl methacrylate) (PMMA) for coupled pyrolysis and combustion simulation. Under pyrolysis, the heat of reaction of PMMA varies with heating rate due the change in residence time facilitating volatilization at any given temperature, particularly at higher heating rates. As a result, the volatiles are formed when the sample has reached higher temperature and therefore more heat flow is needed to assist this process at higher heating rates. Similarly, combustion parameters are also found to vary with the incident radiation flux; however, the variation is relatively minimal. In this study, thermal conductivity and specific heat capacity did not vary with temperature for PMMA.

Synthesis, kinetics and thermal stability of napthalenic polyimide silica nanocomposites

In this work synthesis, structural morphology, degradation profile and kinetic parameters of napthalenic polyimide (NPI) silica based nanocomposites have been reported. The NPI matrix were reinforced with modified and unmodified silica particles for comparison. The structure of NPI, organically modified napthalenic polyimide nanocomposites (ONPNC) and napthalenic polyimide nanocomposites (NPNC) were confirmed by FTIR spectroscopy. Morphology of the fabricated NPI-SiO2 nanocomposites was examined by field emission scanning electron microscopy (FE-SEM). The degradation kinetics of the nanocomposites was established by thermogravimetric analyzer (TGA) with variable heating rates (β) of 5, 10 and 15 °C/min were used. The kinetic data were fitted to Flynn-Wall-Ozawa and Kissinger models for calculating the apparent activation energy (Ea). The results indicate that the modified silica has a significant impact upon the calculated kinetic parameters (Ea) values for thermal decomposition of ONPNC. Thermal stability and degradation kinetics suggest that these nanocomposite films could be used as polyelectrolyte membrane in fuel cell devices. The conclusion was drawn based on the results of FTIR, FE-SEM, TGA and degradation kinetics.

Cathodoluminescence and thermoluminescence of ZnB2O4:Eu3+ phosphors prepared via wet-chemical synthesis

In present work, a series of Eu doped zinc borate, ZnB2O4, phosphors prepared via wet chemical synthesis and their structural, surface morphology, cathodoluminescence (CL) and thermoluminescence (TL) properties have been studied. Phase purity and crystal structure of as-prepared samples are confirmed by X-ray diffraction measurements (XRD) and they were well consistent with PDF card No. 39-1126, indicating the formation of pure phase. The thermoluminescence (TL) behaviors of Eu activated ZnB2O4 host lattice are studied for various beta doses ranging from 0.1 to 10 Gy. The high-temperature peak of Eu activated sample located at 192 °C exhibited a linear dose response in the range of 0.1–10 Gy. Initial rise (IR) and peak shape (PS) methods were used to determine the activation energies of the trapping centres. The effects of the variable heating rate on TL behaviour of Eu activated ZnB2O4 were also studied. When excited using an electron beam induced light emission (i.e cathodoluminescence, CL) at room temperature (RT), the as-prepared phosphors generate reddish-orange color due to predominant emission peaks of Eu3+ ions located at 576–710 nm assigned to the 5D0→7FJ (J=1,2,3, and 4) transitions. The maximum CL intensity for Eu3+ ions at 614 nm with transition 5D0→7F2 was reached Eu3+ concentration of 5 mol%; quenching occurred at higher concentrations. Strong emission peak for Eu3+ ions at 614 nm with transition 5D0→7F2 is observed. The CL experimental data indicate that ZnB2O4:Eu3+ phosphor as an orange-red emitting phosphor may be promising luminescence materials for the optoelectronic applications.

Thermoluminescence and radioluminescence of alexandrite mineral

The thermoluminescence (TL) of natural alexandrite (BeAl2O4) was investigated using different methods, namely Tm-Tstop, Tm as a function of beta irradiation dose, glow curve best fitting, variable heating rate, and TL fading as a function of time after irradiation, in addition to radioluminescence (RL) measurements under X-ray excitation as a function of the temperature. The chemical composition and the concentration of secondary mineral phases were determined by scanning electron microscopy and Energy-dispersive X-ray spectroscopy. TL measurements with heating rate = 1 K/s revealed five individual TL peaks at about 355 (peak I), 405 (peak II), 435 (peak III), 530 (peak IV), and 580 K (peak V). The activation energy E and the frequency factor s associated with each of them were determined by different methods. Within irradiation doses from 1 to 10 Gy, analysis of the Tm position indicated that all glow peaks exhibited a first-order kinetics TL mechanism. TL fading at room temperature was 15% for peak IV and 5% for peak V within 2 days after irradiation. RL measurements revealed luminescence centers attributed to Cr3+, Mn4+ and Fe3+ impurities. Overall, the results suggest that natural alexandrite has a potential use in dosimetry.

Effects of different heating patterns on the decomposition behavior of white pine wood during slow pyrolysis

This study investigated the effect of different heating rates on the pyrolysis behavior of the white pine wood residues. The raw materials were tested via two heating patterns with variable heating rates and compared with three other heating patterns with constant heating rates. The yields and characteristics of products such as char, pyrolysis oil and non-condensable gases under different heating rates were also determined. The gas, liquid, and solid phase yields of the products via heating with decreasing heating rates were similar to the yields obtained from constant heating rate at 2.3°C/min. The pyrolysis process by decreasing heating rates resulted in 30.04 % char, 44.53% bio-oil, and 25.43% non-condensable gases, which displayed higher char yield and pyrolysis gas than the other heating patterns. The results of thermo-gravimetric analysis showed that variable heating rate significantly changed the weight loss profiles during pyrolysis. It was observed during gas chromatography test that CO and CO2 were released earlier than CH4 and H2. The analysis of the chemical components confirmed that the bio-oil produced by heating process with decreasing rates contains less macromolecular organic matter content than the other patterns. Keywords: pyrolysis, variable heating rates, constant heating rate, product yields DOI: 10.25165/j.ijabe.20181105.3156 Citation: Wang Y J, Kang K, Yao Z L, Sun G T, Qiu L, Zhao L X, et al. Effects of different heating patterns on the decomposition behavior of white pine wood during slow pyrolysis. Int J Agric & Biol Eng, 2018; 11(5): 218–223.

Non-isothermal oxidation kinetics of nano-laminated Cr2AlC MAX phase

A highly pure Cr2AlC MAX phase is prepared through the sintering method by varying the aluminum content. The non-isothermal oxidation kinetics of the Cr2AlC phase is examined through a TGA/DTA technique, at variable heating rates (10, 20, 30, 40 °C/min). The TGA/DTA results show that the oxidation of the Cr2AlC phase occurred in two stages. The multi-stage kinetic analysis is performed to establish the nature of the oxidation process. The activation energy is calculated by following the Kissinger-Akahira-Sunose (KAS) and the Friedman (FR) iso-conversional kinetic methods. The reaction mechanism involved during the oxidation process is proposed through the integral master-plots method.

Investigating the thermal stability of TT-OSL main source trap

Thermally-Transferred Optically Stimulated Luminescence (TT-OSL) from quartz is an extended-range luminescence dating technique, with an assumed potential to date sediments as old as early Pleistocene (0.8–2.6 Ma). However, one of the main drawbacks of the TT-OSL signal is its relatively low thermal stability. The few and scattered estimates in the literature of the relatively low thermal stability highlight the possibility that some reported TT-OSL ages are thermal artefacts (i.e. minimum ages only). In this study, we rigorously investigate the thermal stability of the main TT-OSL source trap, using a combination of laboratory and analytical techniques (varying heating rates, isothermal decay, alongside several models) on multiple aliquots of a modern sand sample from the eastern Mediterranean coastal plain. The varying heating rates method constrains the Arrhenius parameters of the TT-OSL main trap to E = 1.50 ± 0.06 eV and s = 1012.8±0.6 s−1; these values translate into a trap lifetime of 3.2−1.9+4.8 Ma at 10 °C. Isothermal decay data further exhibits significant departures from first-order kinetic behavior, which can be well captured by either the general order kinetics model, or a Gaussian distribution of first-order systems. However, extrapolations of these models to geological timescales are at odds with a large volume of observations, thus suggesting that the deviation from first-order kinetics may be a laboratory artefact. Overall, our study reinforces the concern, that thermal loss progressively affects the TT-OSL signal in the Ma-scale age range, and that some previously reported results may be “minimum ages” only.

The effect of Ag addition on the crystallization kinetics and glass forming ability of Zr-(CuAg)-Al bulk metallic glass

In this study, the effect of Ag addition on the crystallization kinetics and glass forming ability (GFA) of Zr-(CuAg)-Al based bulk metallic glasses were investigated. X-ray diffraction (XRD) has been used to identify the amorphous nature and crystalline phases of the as cast samples. The crystallization and glass transition kinetics of the as-cast samples have been examined under non-isothermal conditions using differential scanning calorimetry (DSC). The DSC experiments have been carried out at different heating rates for all the samples. The heating rate dependence of crystallization and glass transition temperatures has been used to evaluate activation energy associate to these processes. In addition to this Avrami exponent has been measured at all heating rate using Various Heating Rate (VHR) method. The GFA and thermal stability of the samples have been investigated using the Trg, γ and fragility parameters. These parameters were found to be composition dependent, which indicated that among the studied bulk metallic glass systems the sample having 9 at. % Ag possessed maximum thermal stability.

Cu nanoparticles encapsulated with hollow carbon spheres for methanol oxidative carbonylation: Tuning of the catalytic properties by particle size control

Cu nanoparticles (NPs) encapsulated within a hollow carbon spheres (Cu@HCS) is an effective catalyst with optimal structural design for the oxidative carbonylation of methanol to dimethyl carbonate (DMC). Control of the structural properties of both the shell and the core plays a vital role in determining the catalytic properties. In this study, mesoporous HCS with an average diameter of 190 nm and a shell thickness of 15 nm were obtained using silica micropheres as a hard template and by tuning the amount of resorcinol and formaldehyde. Cu@HCS catalysts were fabricated by hydrothermal impregnation followed by hydrogen reduction, and the size of Cu NPs was delicately controlled by varying heating rate of reduction process. The results show that a thin mesoporous carbon shell of Cu@HCS is beneficial to the diffusion of reactants and products, and that Cu NPs with very small size can provide a large active specific surface area. In comparison with the commercial CuCl catalyst, the Cu@HCS-5 catalyst displays superior catalytic activity; its turnover frequency and apparent activation energy reaches 23.1 h−1 and 20.5 kJ·mol−1, respectively. In addition, it exhibits higher stability than that of CuCl because the carbon shell prevents the aggregation and leaching of copper NPs during the reaction. With the advantages in catalytic activity, corrosion effect, and recovery performance, the Cu@HCS catalyst has a promising potential for realizing the cleaner production of DMC.

Temperature lag effect on TL glow peaks: Corrections on kinetic parameters

Analyses on TL glow curves recorded with various heating rates for some ternary and quaternary crystals were accomplished using peak maximum temperatures (Tmax) which are experimentally obtained and corrected according to temperature lag effect proposed by Kitis and Tuyn. Curve fitting, initial rise, peak shape and variable heating rate methods were applied to experimental and corrected TL peaks. In spite of the fact that heating rate does not affect activation energy of a TL peak, analyses performed on the experimentally obtained TL curves resulted in an increment of the activation energy with increasing heating rate. However, as the corrected TL data were used for the analyses, the activation energy values of each TL peak recorded with different heating rate were in good agreement with each other. The detailed analyses on studied samples were given in the present paper.

Thermal Properties of Multilayer Nanocomposites Based on Halloysite Nanotubes and Biopolymers

This paper reports a novel procedure to fabricate multilayer composite biofilms based on halloysite nanotubes (HNTs) and sustainable polymers. Among the biopolymers, the non-ionic (hydroxypropyl cellulose) and cationic (chitosan) molecules were selected. The nanocomposites were prepared by the sequential casting of ethanol solutions of hydroxypropyl cellulose and aqueous dispersions of chitosan/HNTs. The composition of the bio-nanocomposites was systematically changed in order to investigate the effect of the hydroxypropyl cellulose/HNTs ratio on the thermal properties of the films, which were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). DSC studies were conducted in the static air (oxidative atmosphere), while TG measurements were carried out under nitrogen flow (inert atmosphere). The analysis of DSC data provided the enthalpy and the temperature for the oxidative degradation of the bio-nanocomposites. These results were helpful to estimate the efficacy of the well-compacted middle layer of HNTs as a flame retardant. TG experiments were performed at a variable heating rate and the collected data were analyzed by the Friedman’s method (non-isothermal thermogravimetric approach) with the aim of studying the kinetics of the hydroxypropyl cellulose degradation in the multilayer nanocomposites. This work represents an advanced contribution for designing novel sustainable nanocomposites with excellent thermal behavior as a consequence of their peculiar multilayer structure.

Curing behavior of epoxy/Fe3O4 nanocomposites: A comparison between the effects of bare Fe3O4, Fe3O4/SiO2/chitosan and Fe3O4/SiO2/chitosan/imide/phenylalanine-modified nanofillers

In this study, Fe3O4 magnetic nanoparticles (MNPs) were synthesized (B-MNP) and then modified with SiO2 to form Fe3O4/SiO2 core/shell MNPs. The Fe3O4/SiO2 MNPs were chemically functionalized with chitosan so as to gain Fe3O4/SiO2/Chitosan (CH-MNP). The CH-MNP was functionalized with a macromolecule containing imide and phenylalanine precursors to gain Fe3O4/SiO2/Chitosan/imide/phenylalanine based MNPs (CH-IM-MNP). The differences in chemical structures of the synthesized MNPs were quantified by FTIR and TGA analyses, where grafting ratios of ca. 6 and 28% were calculated for CH-MNP and CH-IM-MNP nanoparticles, respectively. Nanocomposites were prepared by addition of very low (0.1 wt.% nanoparticle based on 100 parts by weight of epoxy) to epoxy/amine systems. Curing behavior of the blank and MNPs-incorporated nanocomposites were studied by nonisothermal DSC analyses varying heating rate, which allowed for giving useful insights into the effect of chemical surface functionalization of MNPs on the curing potential/behavior of epoxy/amine systems. Analysis of fracture surface of the blank and MNPs-incorporated systems using SEM micrographs revealed a very high potential of cure when CH-IM-MNP added to epoxy/amine formulation.

IGNITION AND COMBUSTION OF W–TEFLON–AL MIXTURES

Relationships between ignition and product structure formation in W–Teflon (Tf)–Al powder mixtures was explored by thermodynamic and structural analyses. The use of tungsten as one of mixture components was dictated by the need to obtain high-density condensation products. Aluminum was used as a heat-generating agent to reduce ignition temperature and increase mixture combustion temperature. Combustion experiments used compositions with a fixed tungsten-to-Teflon ratio, while aluminum content varied according to the formula: (1 – x)(0,8W + 0,2Tf) + xAl = const. After intermixing in the AGO-2 planetary mill in hexane environment, the powders were compressed into 0,01–0,02 g samples and then heated in a BN crucible in argon environment under atmospheric pressure at a variable crucible heating rate. The sample temperature increased sharply on the thermogram once the ignition temperature was reached. It is shown that as the heating rate increases, the ignition temperature of systems grows, and this may be due to transfer from thermal explosion mode to ignition mode. Low-aluminum mixtures yielded large amounts of gaseous products during ignition and combustion, and this results either in defragmentation of combustion product or in formation of porous cakes. The analysis of products obtained with high-aluminum systems indicated WAl4 as a main product. For higher aluminum content results of thermodynamic calculations strongly differed from experimental ones owing to the lack of thermodynamic data for tungsten aluminides in the Thermo software and to the strong mismatch between the actual reaction conditions and adiabatic equilibrium ones. Calculated and experimental results suggest that the formation of fused high-density products (ρW2C = = 17,2 g/cm3) is possible at an optimal aluminum content ≈10 wt.%. When this value is exceeded, the main product, WAl4, has a much lower density (ρWAl4 = 6,6 g/cm3), which is inadequate for practical implementation.

Determination of thermoluminescence kinetic parameters of white and blue chalcedony exposed to X-ray irradiation

The study reveals the thermoluminescence (TL) properties of white and blue chalcedony minerals which this mineral mined two different regions (Edirne and Eskişehir, respectively) of Turkey. With the help of various characterization techniques (such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR)), the gem-quality of the samples was tested. The TL glow curves of the samples irradiated with X-rays show intense main TL glow peak having the maximum temperatures at 100 °C and 121 °C with a heating rate of 2 °C/s, respectively. The TL kinetic parameters of the samples are reported here for the first time. Activation energy (E), frequency factor (s) and the order of kinetics (b) of these peaks have been determined in detail by using various heating rates (VHR) and peak shape (PS) methods and verified by Computerized Glow Curve Deconvolution (CGCD). The CGCD method was used to determine the number of peaks associated with the TL glow curves. The values of E calculated with these three methods are a good agreement.

Synthesis of Large Mesoporous-Macroporous and High Pore Volume, Mixed Crystallographic Phase Manganese Oxide, Mn2O3/Mn3O4 Sponge.

The controlled synthesis of mixed crystallographic phase Mn2O3/Mn3O4 sponge material by varying heating rates and isothermal segments provides valuable information about the morphological and physical properties of the obtained sample. The well-characterized Mn2O3/Mn3O4 sponge and applicability of difference in reactivity of H2 and CO2 desorbed during the synthesis provide new developments in the synthesis of metal oxide materials with unique morphological and surface properties. We report the preparation of a Mn2O3/Mn3O4 sponge using a metal nitrate salt, water, and Dextran, a biopolymer consisting of glucose monomers. The Mn2O3/Mn3O4 sponge prepared at 1 °C·min-1 heating rate to 500 °C and held isothermally for 1 h consisted of large mesopores-macropores (25.5 nm, pore diameter) and a pore volume of 0.413 mL/g. Furthermore, the prepared Mn2O3/Mn3O4 and 5 mol %-Fe-Mn2O3/Mn3O4 sponges provide potential avenues in the development of solid-state catalyst materials for alcohol and amine oxidation reactions.

Thermal degradation behaviors and reaction mechanism of carbon fibre-epoxy composite from hydrogen tank by TG-FTIR

Thermal degradation behaviors and reaction mechanism of Carbon fibre-epoxy composite, obtained from Chinese widely applied hydrogen storage tank, were studied by thermogravimetry combined with Fourier transform infrared spectrometry at varying heating rates. The pyrolysis of carbon fibre-epoxy composite mainly occurs at 550–750 K. The average value of final residue is 72.42%. The calculated activation energies increase exponentially from 206.27 KJ/mol to 412.98 KJ/mol with the average value of 276.6 KJ/mol. The fourth reaction order model is responsible for the pyrolysis of carbon fibre-epoxy composite. The absorption spectra of the evolved gases provided the information that the main evolved products are H2O, CO2, CO (acid anhydride, ketone or aldehyde), ε- caprolactam, alcohols and phenol. Moreover, CO group > alcohols > phenol > ε- caprolactam > CO2 > H2O. Epoxy is the main pyrolysis crude material in carbon fibre-epoxy composite.

Temperature Modulated Nanomechanical Thermal Analysis

The response of microcantilever deflection to complex heating profiles was used to study thermal events like glass transition and enthalpy relaxation on nanograms of the biopolymer Poly(lactic-co-glycolic acid) (PLGA). The use of two heating rates enables the separation of effects on the deflection response that depends on previous thermal history (non-reversing signal) and effects that depends only on the heating rate variation (reversing signal). As these effects may appear superposed in the total response, temperature modulation can increase the measurement sensitivity to some thermal events when signals are isolated. Initially, it was shown how the signal can be processed to extract reversing, total and non-reversing signals and how the temperature modulation affects the cantilever sensitivity to temperature. Then, this technique was used to study how the different aging times affects the non-reversing curve but has no effect on the reversing curve, enabling more precise extraction of glass transition (Tg) in aged samples. With non-reversing data at different aging times, we measured the aging rate by means of average relaxation time ( $\tau$ ) using the Cowie-Ferguson model, obtaining $\tau = 348$ minutes for PLGA aged at 20 °C and at 50% RH. Tg for PLGA at 50% RH was measured as 37.8 °C using the reversing signal with 0.32 °C of variation between aging times.

Influence of heating rate on reactivity and surface chemistry of chars derived from pyrolysis of two Chinese low rank coals

A series of char samples were derived from pyrolysis of two typical low-rank coals in China (Shengli lignite and Shenmu bituminous coal) at low, medium and fast heating rates, respectively, to the same pyrolysis temperature 750 °C. Then these chars were characterized by means of thermogravimetric analysis and Fourier transform infrared spectrometer with the aim to investigate the influence of heating rate in pyrolysis process on gasification reactivity and surface chemistry of them. Besides, a homogeneous model was used to quantitatively analyze the activation energy of gasification reaction. The results reveal that Shengli lignite and its derived chars behave higher gasification reactivity and have less content of oxygen functional groups than Shenmu coal and chars. Meanwhile, chars derived from Shengli lignite at 50 °C/min and Shenmu coal at 200 °C/min have the greatest gasification reactivity, respectively. The oxygen functional groups in Shengli lignite are easily thermo-decomposed, and they are less affected by the heating rate, while that in Shenmu coal have a significant change with the variation of heating rate. In addition, there is no good correlation between the change of oxygen functional groups and that of the gasification reactivity of the derived chars from pyrolysis at different heating rates.

Desorption characteristics and kinetic parameters determination of molecular sieve by thermogravimetric analysis/differential thermogravimetric analysis technique

The kinetics of the thermal desorption of CO2adsorbed on zeolite 13X were obtained using a differential thermogravimetric analyser under two different carrier gas conditions. The varying heating rates were set as 8, 12, 16, and 20 K min−1, respectively. The desorption activation energy of the physisorption sites for this experiment evaluated by an integral method without prediction of the reaction order ranged from 12.15 to 14.12 kJ mol−1(CO2as the carrier gas) and 43.32 to 50.42 kJ mol−1(Ar as the carrier gas), respectively. The desorption activation energy of the chemisorption sites ranged from 57.95 to 58.53 kJ mol−1(CO2as the carrier gas) and 74.02 to 79.92 kJ mol−1(Ar as the carrier gas), respectively.