Heating Rate Conditions Research Articles

Optimization of the oxidative fast pyrolysis process of sugarcane straw by TGA and DSC analyses

The objective of this work was to evaluate the influence of the oxygen percentage, heating rate, and total gas flow variables in the pyrolysis process of sugarcane straw through thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses. The experimental conditions of oxygen percentage, heating rate, and total gas flow were optimized using the design of experiments and canonical analysis. The investigated conditions show that to optimize the whole pyrolysis process, the best values for carrying out the process are oxygen concentrations and heating rates around the central level of 10%, and 298 K/min, respectively, where the total gas flow, within the studied constrains, was not statistically significant for the pyrolysis process, according to the regression equations. This condition resulted in approximate values of required heat and percent residual residue of 181.74 kJ/kg and 9.89%, respectively. In addition, the percentage of remaining residue decreases as the heating rate decreases and the percentage of oxygen in the gas mixture increases. The optimum oxygen percentage obtained was also validated by carrying out an autothermal fast pyrolysis in a pilot plant scale.

DMMP pyrolysis and oxidation studies at high temperature inside a shock tube using laser absorption measurements of CO

Dimethyl methyl phosphonate (DMMP) is an organo-phosphorous compound (OPC) used as a fire suppressant and a simulant for sarin, a chemical warfare agent. There exists a critical need to gather combustion data at high heating rate and high temperatures conditions, similar to what exists during destruction process of chemical weapons. In the present work, DMMP pyrolysis and oxidation were carried out behind reflected shock waves at temperatures of 1300–1700 K and pressures of 1.5–1.8 atm. Lean, stoichiometric, and rich DMMP mixtures (Φ = 0.23, 0.5, 1, 2) were investigated for oxidation experiments. Laser absorption spectroscopy utilizing a quantum cascade laser near 4.9 µm was used to measure intermediate CO concentration formed during the pyrolysis and oxidation processes. To the best of our knowledge, we present the first intermediate concentration data at the reported conditions for DMMP. A tentative kinetic model, based on the AramcoMech2.0 mechanism with Lawrence Livermore National Lab (LLNL)’s OPC incineration chemistry, was utilized in Chemkin-Pro to predict CO yield during the processes. The model provided fair prediction of CO yield during DMMP pyrolysis, however, overpredicted the CO yield for oxidation. Sensitivity and rate of production analyses were carried out to understand important reactions leading to CO formation.

Activation of homogeneous precursors for formation of uniform and refined α precipitates in a high-strength β-Ti alloy

The influence of heating rates and interrupted aging treatments on α precipitation in the β-quenched Ti-6Cr-5Mo-5V-4Al alloy has been investigated. Microstructure observations reveal that slow heating rates and low temperature pre-aging produce much refined and uniform distributions of intragranular α precipitates in comparison to aging using fast heating rates at a high temperature only. For interrupted aging treatments, the nucleation rate and refinement of α are gradually enhanced with increasing pre-aging time, but this is dependent on the final aging temperature: at high final aging temperatures, the distribution of α precipitates is similar to single aging at the same temperature. The kinetics of phase transformation was analyzed by thermal mechanical analysis (TMA) under the framework of the Johnson–Mehl–Avrami (JMA) theory. Coupled with microstructural observations, it is suggested that epitaxial growth of pre-existing α phase formed during heating to the aging temperature is the governing mechanism under slow heating rate conditions, while for interrupted aging treatments, the mechanism for intergranular α precipitation is consistent with that of fast heating rate single temperature aging treatments. For interrupted aging, the formation of uniform and refined α precipitates essentially relies on activation of homogeneous precursors associated with chemical partitioning and structural modulation which provide a strong driving force for nucleation of α.

Processing of CaLa2S4 infrared transparent ceramics: A comparative study of HP and FAST/SPS techniques

AbstractThe densification of CaLa2S4 (CLS) powders prepared by combustion method was investigated by the use of Field‐Assisted Sintering Technique (FAST) and Hot Pressing (HP). CLS powders were sintered using FAST at 1000°C at different pressures and heating rates and sintered by HP under 120 MPa from 800°C to 1100°C for 6 hours with a heating rate of 10°C/min. Comparison of both techniques was further realized by use of the same conditions of pressure, dwell time, and heating rate. Complementary techniques (XRD, SEM‐EDS, density measurements, FTIR spectroscopy) were employed to correlate the sintering processes/parameters to the microstructural/compositional developments and optical transmission of the ceramics. Both sintering techniques produce ceramics with submicrometer grain size and relative density of about 99%. Nevertheless, HP is more suitable to densify CLS ceramics without fragmentation and also reach higher transmission than FAST. Transmission of 40%–45% was measured out of a possible maximum of 69% based on the Fresnel losses in the 8‐14 μm window when HP is applied at 1000°C for 6 hours under 120 MPa. In both techniques, ceramics undergo reduction issues that originate from graphitic sintering atmosphere.

Biochar from pyrolysis of biological sludge from wastewater treatment

It was studied the production of biochar by pyrolysis of biological sludge from wastewater treatment in the pulp and paper industry. The pyrolysis process was conducted in bench-scale fixed-bed reactor using distinct operating conditions of heating rate (2, 10, 20 and 30 ºC/min) and peak temperature (300, 375, 450, 525, and 600 ºC). The biochar yield is in the range 0.40 to 0.73 kg/kg dry sludge, and decreases with increasing peak temperature and heating rate. The organic matter content of the biochar is in the range 55.9 to 75.3%wt. (dry basis). Both the temperature increase and the heating rate increase promote the decrease of biochar volatile matter content within values between 14.4 and 48.4%wt. (dry basis). The biochar ash content increases with peak temperature and heating rate, and it has values in the range 24.7 to 44.1%wt. (dry basis). The corresponding fixed carbon content is between 26.2 and 42.4%wt. (dry basis), and increases with an increase in the peak temperature. The carbon concentration in the biochar is in the range 42.8 to 47.0%wt. (dry basis). The biochar pH is in the range 6.9 to 11.2, and the electrical conductivity (EC) is in the range 2.2 to 5.0 mS/cm.

An experimental investigation on the ductility and post-form strength of a martensitic steel in a novel warm stamping process

In this study, a new lightweight forming technology, the fast-warm stamping technique, was proposed to form a martensitic steel (MS-W900Y1180 T) into a complex shaped component. The mechanical properties such as ductility and post-form strength (PFS) of the MS-W900Y1180 T (MS1180) steel were examined via uniaxial tensile tests at various temperatures (25–500 °C) and strain rates (0.01–5/s). Special attention has been paid to the effect of heating rate on thermo-mechanical properties and microstructure of the MS1180 steel with different heating rates. The results indicate that the ductility and post-form hardness of the MS1180 steel were improved by 25.7% and 5% respectively with increasing heating rate from 1 to 150 °C/s, which is attributed to the finer precipitated carbides and lower recovery at fast heating rate conditions. A U-shaped panel component was successfully formed using the proposed forming technology in a cycle time within 10 s. The fast-warm stamped components exhibited a post-form strength of 1140 MPa.

Synthesis of nitrogen-doped flower-like carbon microspheres from urea-formaldehyde resins for high-performance supercapacitor

Nitrogen-doped carbon microspheres are synthesized from urea-formaldehyde (UF) resins by a direct carbonization method without any surfactants. UF resins provide not only carbon source, but also nitrogen source. The flower-like urea-formaldehyde resins carbon (UFC) has been successfully obtained through adjusting preparation parameters, including mole ratio of urea to formaldehyde, stirring time, reaction time, pH value, curing condition of HCl and heating rate. Flower-like UFC microspheres consist of nanosheets with the thickness of 50 nm. UFCN2 (UF resins carbonized in N2 atmosphere) possesses a high N element percent of 11.73%, the large specific surface area of 611 m2 g−1 and a large specific capacitance of 276.79 F g−1 at the scan rate of 2 mV s−1. Even at 500 mV s−1, the specific capacitance still maintains 127.50 F g−1. More importantly, UFCN2 exhibits a high capacitance retention of 98.41% after 5000 charge/discharge cycles at 1 A g−1, indicating its good cycle stability.

The Effect of Rapid Heating and Fast Cooling on the Transformation Behavior and Mechanical Properties of an Advanced High Strength Steel (AHSS)

The major goal of this work was to study the effect of rapid heating and fast cooling on the transformation behavior of 22MnB5 steel. The effect of the initial microstructure (ferrite + pearlite or fully spheroidized) on the transformation behavior of austenite (during intercritical and supercritical annealing) in terms of heating rates (2.5, 30 & 200 °C/s) and fast cooling, i.e., 300 °C/s rate, were studied. As expected, the kinetics of austenite nucleation and growth were strongly related to the heating rates. Similarly, the carbon content of the austenite was higher at lower intercritical annealing temperatures, particularly when slower heating rates were used. The supercritical temperatures used in this study were similar to those used during commercial hot stamping operations, i.e., 845 and 895 °C, respectively, followed by a fast cooling rate. The prior austenite grain size (PAGS) was not strongly influenced by the nature of the initial microstructure, heating rate, reheating temperatures (845 or 895 °C), at 30 s holding time. The decomposition of austenite using fast cooling rates was examined. The results showed that 100% martensite was not obtained. The observed low temperature transformation products consisted of mixtures of martensite-bainite plus undissolved Fe3C carbides and small amounts of martensite-austenite (M-A). At higher supercritical temperatures, i.e., 1000 °C and 1050 °C, the final microstructure showed an increase in the volume fraction of martensite and a decrease in the volume fraction of bainite. The Fe3C and the M-A microconstituent were not observed. The best combination of tensile properties was obtained on samples reheated in the lower temperature range (845 to 895 °C). Interestingly, when the samples where reheated at the higher temperature range (1000 to 1050 °C) and fast cooled, the results of the mechanical properties did not exhibit significantly higher strength levels independent of heating rate or initial microstructural condition. This can be attributed to the change in the microstructural balance %martensite+%bainite as the reheating temperature increases. The results of this study are presented and discussed.

A redox reaction model for self-heating and aging prediction of Al/CuO multilayers

Sputter-deposited Al/CuO multilayers capable of highly energetic reactions have been the subject of intense studies for tunable initiation and actuation. Designing high performance Al/CuO-based initiator devices definitively requires reliable prediction of their ignition and reaction kinetics including self-heating or ageing as a function of heating rate and environmental conditions. The paper proposes a heterogeneous reaction model integrating an ensemble of basic mechanisms (oxygen diffusion, structural transformations, polymorphic phase changes) that have been collected from recent experimental investigations. The reaction model assumes that the rate of reaction is limited by the transport of oxygen across the growing layer of Al2O3 separating Al and CuO. Importantly, we show that the model predicts reasonably all exotherms through a wide range of temperature (ambient – 1000°C), all resulting from a pure diffusion process as experimentally observed for such Al/CuO multilayers. The model shows how the temperature ramp affects the structure of the multilayer and especially the growth of alumina-based interfacial regions. It highlights the importance of the interfacial chemistry evolution such as the native mixture of AlxCuyOz transformation into a thin amorphous alumina, and the polymorphic phase transformation of this latter. The first one occurring at ∼350°C results in a loss of continuity of the interface leading to the accelerated redox reaction whereas the second one occurring between 500 and 600°C produces a denser barrier to oxygen diffusion leading to the stop of redox reaction. We finally use the model to simulate thermal annealing as usually performed in accelerated ageing experiments. We theoretically observe and experimentally validate that a two weeks exposure of the multilayers at 200°C starts degrading the multilayers thermal properties whereas when the temperature remains below 200°C, the material keeps its entire integrity.

Comparison of single particle combustion behaviours of raw and torrefied biomass with Turkish lignites

This study investigated the combustion behaviour of single pulverized biomass and lignite coal particles under high temperature–high heating rate conditions. Selected fuels included three important agricultural residues in Turkey (olive residue, almond shell, and hazelnut shell), and two lignite coals from the regions of Tunçbilek and Soma in Turkey. Biomass fuels were either raw or torrefied at 275 °C for 30 min in nitrogen. The biomass fuels were sieved to a size cut of 212–300 µm, and the coals were sieved to 106–125 µm. An optically-accessible drop tube furnace, operated at a wall temperature of 1400 K, was used to burn single fuel particles in air. High-speed cinematography and three-colour pyrometry were used to characterise the combustion behaviour of the fuel particles. All biomass particles ignited homogeneously forming large and circular volatile matter envelope flames, followed by distinct char combustion phases. The Tunçbilek lignite also ignited homogeneously and burned in two combustion stages, first forming bright sooty and elongated flames with contrails, upon extinction of which char combustion ensued. The Soma lignite exhibited extensive fragmentation which resulted in surface ignition of the fragments and gas-phase ignition of the main non-fragmented particle. The cumulative burnout times of all raw and torrefied biomass particles of the selected size cut were shorter or equal to those of the Tunçbilek lignite but longer than those of the Soma lignite. This result signifies the appropriateness for co-firing such biomass fuel particles in furnaces designed for the former coal, rather than those designed for the latter.

Thermoluminescence glow curve for UV induced Sr3MgSi2O8 phosphor with its structural characterization

The present paper reports the synthesis and characterization of Sr3MgSi2O8 phosphor. The phosphor was prepared by solid state reaction method. Average crystal size for the phosphors yielded was in nanometre range, which was calculated by using X-ray diffraction analysis and confirmed by field emission gun scanning electron microscopy and transmission electron microscopy technique. Sample shows cubic structure and the particle size calculated by Scherer’s formula was around 48 nm. For recording TL glow curve every time 2 mg phosphor was irradiated by 254 nm UV source. Sample shows well resolved peak at 123 °C. Various parameters like heating rate and exposure time were optimized. The obtained glow curve for optimized condition of heating rate and UV exposure time was analysed by computerized glow curve deconvolution technique technique. Kinetic parameters were calculated by using Chen’s peak shape method for all the deconvoluted peaks.

Identifying unified kinetic model parameters for thermal decomposition of polymer matrix composites

Predicting thermal responses of composite materials requires accurate input parameters derived from reliable thermal property characterization and kinetic models. Composite material properties and decomposition kinetics vary with temperature and heating rate. Typically, conventional kinetic models derived from thermogravimetric analysis data result in multiple sets of kinetic model parameters, which are difficult to implement into numerical simulations under widely varying temperature and heating rate conditions. Here, a methodology was developed to reliably predict decomposition processes of composite materials with a single (i.e., unified) set of kinetic model parameters. The unified kinetic model parameters for each of four different composite materials were used to accurately predict decomposition kinetics observed over the entire range of experimental temperatures and heating rates. Furthermore, this broadly applicable methodology may predict decomposition from limited data sets, and is expected to extrapolate reliably measurable data to experimentally challenging heating rates and temperatures.

Influence of heating rate and aging temperature on omega and alpha phase precipitation in Ti[sbnd]35Nb alloy

Metastable β Ti alloys based on Nb exhibit features that make them suitable for load-bearing biomedical applications, so it is crucial to evaluate their phase transformation and properties. This paper discusses the effects of aging heat treatments on the microstructure, phase transformation and mechanical behavior of Ti35Nb alloy. Samples were solution heat treated in the β field, quenched and aged under different conditions of heating rates, isothermal aging temperature and isothermal aging time. To enhance the alloy's mechanical behavior, thermal analysis and high temperature X-ray diffraction experiments coupled with Vickers hardness tests were employed to determine the temperature range of isothermal ω phase precipitation, as well as α phase precipitation temperature, thereby providing information to optimize aging heat treatment conditions. Results indicate that Ti35Nb alloy subjected to a heating rate of 30 °C/min and an isothermal aging temperature of 500 °C applied for 4 h would ensure high mechanical strength and low elastic modulus. The application of these aging conditions led to a microstructure consisting of very refined α phase precipitates homogeneously dispersed in the β phase matrix, presenting an ultimate tensile strength of 972 MPa, elongation of 7.5% and elastic modulus of 78 GPa, making this aged alloy a promising candidate for biomedical applications. These results shed light on the correlations between phase transformations, microstructure and mechanical behavior in high solute content TiNb alloys for biomedical applications.

Thermal degradation of typical plastics under high heating rate conditions by TG-FTIR: Pyrolysis behaviors and kinetic analysis

Pyrolysis of plastics has gained more attention recently due to the advantages of environmental protection and energy conversion. In this study, low-density polyethylene (LDPE), polypropylene (PP) and polyvinyl chloride (PVC) were studied under high heating rate conditions to investigate pyrolysis behaviors and find the most suitable kinetic reaction mechanisms. The TG and DTG curves for LDPE were similar to those for PP, but different from those for PVC. It was found that high heating rate led to the shifting of initial, end and peak temperatures to higher values. The FTIR results showed the main products of LDPE and PP were alkanes and alkenes, and the major products of PVC were HCl, alkenes and a small number of aromatic compounds. A comparative study of model-free methods like Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS) and Friedman method were discussed to calculate activation energy. Kinetic reaction mechanisms were predicted by using model-fitting methods including Coats-Redfern and Criado method. The pyrolysis reaction mechanism of LDPE was summarized as contracting sphere model, PP was summarized as contracting cylinder model, whereas that of PVC was concluded that two-dimension nucleation for the first stage and three-dimension diffusion (Jander) for the second stage.

Thermal decomposition kinetics of basic carbonate cobalt nanosheets obtained from spent Li-ion batteries: Deconvolution of overlapping complex reactions

Abstract A new non-isothermal method of kinetic analysis was employed to investigate the thermal decomposition kinetic modeling of the basic carbonate cobalt nanosheets (n-BCoC) synthesized from spent lithium-ion batteries (LIBs). Fraser–Suzuki function was applied to deconvoluting overlapping complex processes from the overall differential thermal curves obtained under the linear heating rate conditions, followed by the kinetic analysis of the discrete processes using a new kinetic analysis method. Results showed that the decomposition of n-BCoC in air occurred through two consecutive reactions in the 136–270 °C temperature intervals. Decomposition started by hydroxide component (Co(OH)2) decomposition until to 65% and simultaneously carbonate phase decarbonation began. The process was continued by CO2 evolution and finally carbonate cobalt nanosheets have been produced. The reaction mechanism of the whole process can be kinetically characterized by two successive reactions: a phase boundary contracting reaction followed by an Avrami–Erofeev equation. Mechanistic information obtained by the kinetic study was in good agreement with FT-IR (Fourier transform infrared spectroscopy) and SEM (scanning electron microscopy) results.

On the determination of thermal degradation effects and detection techniques for thermoplastic composites obtained by automatic lamination

Automatic lay-up and in-situ consolidation with thermoplastic composite materials is a technology under research for its expected use in the profitable manufacturing of structural aeronautical parts. This study is devoted to analysing the possible effects of thermal degradation produced by this manufacturing technique.Rheological measurements showed that there is negligible degradation in PEEK for the temperatures reached during the process. Thermogravimetric analysis under linear heating and constant rate conditions show that thermal degradation is a complex process with a number of overlapping steps. A general kinetic equation that describes the degradation of the material with temperature has been proposed and validated. Attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed that there is no remarkable degradation. The use of a combination of in-situ and ex-situ experimental techniques, including kinetic modelling, not only provides reliable information about degradation but also allows setting optimal processing conditions.

Heating rate effect on liquid Zn-assisted embrittlement of high Mn austenitic steel

The effect of heating rate on liquid metal embrittlement (LME) of a galvanized twinning induced plasticity (TWIP) steel was investigated by hot tensile testing. The specimens were heated with different heating rates to 600, 700 and 800 °C, and elongated to 40%. During the hot tensile tests, various Fe-Zn intermetallic compounds were formed depending on the heating rate and the deformation temperature, and they were distinguished by X-ray diffraction and energy dispersive spectroscopy. δ and Γ were observed in the coating after 600 °C deformation regardless of heating rate. Since both phases did not liquefy at 600 °C, the steel was not embrittled. Heating to 700 °C sometimes produced δ which would be liquid at 700 °C. It was only produced at the highest heating rate and embrittled the steel. Γ was produced at 800 °C regardless of heating rate. Hence, the steel suffered from LME in all heating rate condition. Based on the results, the importance of selecting temperature and heating rate to study LME by hot deformation testing is discussed.

On the particle sizing of torrefied biomass for co-firing with pulverized coal

In biomass harvesting and fuel preparation processes, grinding causes a prominent energy consumption penalty, which results in an analogous cost impact. This is due to the fibrous and tenacious nature of biomass. Torrefaction of biomass makes it brittle, as it diminishes its fibrous nature and, hence, it enhances its grindability. Nevertheless, grinding costs are still important and increase with decreasing targeted particle size. Therefore, this study introduces a methodology for assessing the torrefied biomass grind size that is suitable for firing or co-firing with coal in existing pulverized fuel boilers. It examines combustion of biomass of different origins, herbaceous, woody, or crop-related. Biomass was torrefied for 30 min at 275 °C in nitrogen. It was subsequently ground and sieved to various size cuts, which reflect the mean widths rather than the lengths of these typically elongated particles. Subsequently, the particles were burned, one at a time, in a drop tube furnace (DTF) under high temperature and high heating rate conditions. Luminous burnout times were observed pyrometrically and cinematographically for a number of single particles from various size cuts. Such burnout times were then contrasted with those of individual coal particles in the size range of 75–90 µm, i.e., at the upper end of particle sizes burned in coal-fired boilers. Based on this comparison, the nominal sieve size of the examined torrefied biomass particles whose overall observed burnout times matched those of the 75–90 µm coal particles was determined to be 212–300 µm. Hence, to minimize the grinding cost of co-firing such torrefied biomass with coal in existing boilers, its finer pulverization may not be necessary.

Reactive Sintering Mechanism and Phase Formation in Ni-Ti-Al Powder Mixture During Heating.

This work aims to describe the formation of intermetallics in the Ni-Ti-Al system in dependence on the heating rate, which has been determined previously as the crucial factor of thermal explosion self-propagating synthesis (TE-SHS). The tested alloys contained 1–7 wt % aluminum. Thermal analysis has been realized by the optical pyrometer under the conditions of high heating rates up to 110 °C·min−1. TE-SHS process in Ni-Ti-Al system is initiated by exothermic reaction of nickel aluminides Ni2Al3 and NiAl3 at the temperature of 535–610 °C. The next reactions occur in dependence on the heating rate. Samples containing 1–3 wt % of aluminum exhibit the similar initiation temperature as Ni-Ti binary mixture. The samples containing 5 wt % and more of aluminum were fully reacted after sintering at 800 °C with the heating rate of 300 °C·min−1 and the initiation temperature of the TE-SHS was observed close to Al-Al3Ni eutectic temperature (between 630–640 °C).

Slow pyrolysis of walnut shells in nitrogen and carbon dioxide

Previous studies have shown that increased carbon dioxide concentration upon heat up affects the products of coal pyrolysis and in particular that chars prepared under carbon dioxide rich atmospheres are less reactive than chars prepared in nitrogen, and consistently tars are more aromatic. In the present work, this issue is investigated with reference to a biomass, namely walnut shells (WS), where the lignin component prevails over cellulose and hemicellulose.Preliminary experiments of thermal degradation have been carried out using a thermogravimetric (TG) apparatus, under constant heating rate conditions, in flows of either nitrogen or carbon dioxide. Derivative thermogravimetric (DTG) curves reveal the existence of multiple peaks, which are typically associated with the degradation of different ligno-cellulosic components. A multiple parallel reaction scheme has therefore been used to fit the experimental data and kinetic parameters have been obtained.Walnut shells were also pyrolyzed in a fixed bed reactor at 600 °C in either nitrogen or carbon dioxide so as to collect pyrolysis products in amounts sufficient for further analysis. Char and tar samples have been characterized using different techniques (e.g. GC–MS, elemental analysis, TGA, SEM) revealing limited differences. Combustion rates of the chars have been measured by means of non-isothermal thermogravimetric experiments in air and again small differences have been observed between the samples prepared under carbon dioxide and nitrogen.It has been concluded that under the low heating rate conditions typical of the thermogravimetric apparatus and fixed bed reactor used in the work, the effects of carbon dioxide on liquid and solid products of biomass pyrolysis exist but are less important than for coal.The work is complementary to another paper, which addresses the effect of carbon dioxide on biomass pyrolysis under high temperature and fast heating rate conditions in a drop tube reactor.