Effect Of Heating Rate Research Articles

Evaluation of oxygen concentration on low-temperature oxidation kinetics of long-flame coal

Oxygen concentration is the vital environmental factor affecting the evolution of coal spontaneous combustion. Long-flame coal was heated from 30 to 800 °C at different oxygen concentrations (3, 5, 9, 13, 17, and 21 mass%) and heating rates (2.0, 5.0, 10.0, and 15.0 °C/min). The thermal reaction process was explored and analyzed. The effects of oxygen concentration on characteristic temperature and related parameters were assessed. The effects of heating rate and oxygen concentration on characteristic temperature and related parameters were evaluated. Under the condition of oxygen deficiency, the oxidation rate of coal was low, it took more time to consume the active groups in a given quality coal, and the increase of oxygen concentration had a strong positive effect on early and late combustion. The apparent activation energy (Ea) increased and decreased the conversion degree of oxygen absorption (mass gain) and high-temperature combustion stage, respectively. With the decrease of oxygen concentration, Ea in each stage decreased. These results contribute to the understanding of the evolution of coal fires in oxygen-lean environments.

Effect of coal grade and heating rate on the thermal degradation behavior, kinetics, and thermodynamics of pyrolysis of low-rank coal

ABSTRACT The work investigates the thermal degradation characteristics, kinetics, and thermodynamics of low-rank coals of three different grades selected from coal mines of Odisha, India by thermogravimetric analysis in temperatures ranging from 30°C to 1000°C under a nitrogen atmosphere at five heating rates of 5, 10, 15, 20, and 25°C min−1. The kinetic parameters are computed using model-fitting methods assuming first-order kinetics in the 250–635°C temperature range of major weight loss. The average activation energy of the reaction at different heating rates is found to be in the range of 55–65 kJ/mol. The average entropy change is found to vary from −180.03 to −165.887 J/K/mol1, the average enthalpy change varies from 51.1758 to 57.574 kJ/mol and that of free energy change varies from 189.718 to 177.9 kJ/mol. In addition, the composition of the oil obtained by pyrolysis of the coal in a semi-batch reactor at different temperatures is analyzed by FTIR and GC-MS techniques. The composition of the oil is found to be affected by the pyrolysis temperature.

Effect of pre-oxidation temperature and heating rate on the microstructure of lignin carbon fibers

Lignin is a biopolymer with high carbon content, making lignin-based carbon fiber an important research direction. In the process of carbonization to prepare carbon fibers, lignin fibers are easily softened and fused, which destroys the microstructure of fibers, thereby reducing the quality of lignin-based carbon fibers. Therefore, it is non-negligible to pre-oxidize lignin fibers before carbonization to prevent fiber fusion and maintain fiber structure. Therefore, the effects of pre-oxidation temperature and heating rate on the structure of pre-oxidation lignin fibers with controllable diameter and thickness prepared by melt-blowing were studied in detail. During pre-oxidation, crosslinking and aromatization of lignin fibers occurred, and alkyl and benzene rings were mainly oxidized to form carbonyl groups. The aromatization degree of the pre-oxidized product was recorded at 280 °C and 0.25 °C/min, and the oxygen content reached 15 %–20 %, making it suitable for the preparation of bio-based carbon fibers. On this basis, carbon fibers with porous morphology can be prepared with a graphitization of 0.54 and a resistivity of 0.02 Ω cm−1. These materials are expected to be applicable in sensors, catalytic materials and other fields.

Vat photopolymerization of low-titanium lunar regolith simulant for optimal mechanical performance

Recently additive manufacturing of lunar regolith to utilize in-situ resources of the Moon for deep space exploration has attracted attention. However, most previous works have been limited by low precision, inferior mechanical properties, and complex processes, such as ball grinding. Furthermore, the regional distribution difference of the lunar regolith which shows compositional diversity, demands the exploration of manufacturing of low-titanium lunar soil, which has not been comprehensively studied before. Herein, the vat photopolymerization and heat treatment of raw low-titanium lunar regolith simulant were investigated to achieve high dimensional precision and high mechanical properties. The influence of solid content and photoinitiator concentration on printability is carefully examined based on the characterization of rheological behaviors and curing depth. Then the vat photopolymerization is used to build green bodies with good interlayer bonding strength and high dimensional precision. Besides this, the effect of the debinding heating rate and sintering temperature on samples were optimized in air and nitrogen to enhance the mechanical properties of printed samples. Finally, the optimal sintered parts with a flexural strength of 108.8 MPa and compressive strength of 222.8 MPa were obtained.

Effect of Hydrothermal Carbonization Parameters and Performance of Carbon Dioxide Adsorption on Pineapple Peel Waste Biochar

AbstractLow‐cost biochar adsorbents were prepared from pineapple peel waste (PPW) via hydrothermal carbonization (HTC) for CO2 capture. The effects of hydrothermal carbonization temperature, retention time, and heating rate were studied. The hydrochar samples were further carbonized to produce pineapple peel biochar adsorbents. The effects of CO2 concentration in the feed, adsorption temperature, and feed flow rate on adsorption capacity were investigated in a fixed‐bed column adsorption system. The experimental data were analyzed using pseudo‐first‐order and pseudo‐second‐order kinetics, and the Avrami equation. The CO2 adsorption capacity of this system was improved with increasing CO2 feed concentration and decreased with rising temperature and feed flow rate. The Avrami kinetics model was best fitted to the experimental data. The CO2 adsorption performance of PPW biochar (PPW‐BC) in a fixed‐bed column was successfully predicted by the Thomas and Yoon‐Nelson models. The prepared PPW‐BC adsorbents could be a viable option for CO2 capture because they were synthesized from a low‐cost biomass source and are environmentally benign.

RECENT DEVELOPMENTS IN COMPUTERISED ANALYSIS OF THERMOLUMINESCENCE GLOW CURVES: SOFTWARE CODES, MECHANISMS AND DOSIMETRIC APPLICATIONS

The computerised deconvolution of thermoluminescence glow curves into component glow peaks is discussed in detail with special emphasis on advances of the subject post 2013. A plethora of computer codes have been developed using models based on first-order kinetics, second-orders kinetics, interactive traps and continuous distributions of activation energies. The glow curves of several materials are displayed and discussed along with new and improved dosimetric applications:precision effects of heating rate, heavy charged particles, mixed field α/ϒ dosimetry, fading and dose-response linearity. Finally recommendations are made for future efforts.

Effects of heating rate on morphological evolution, microstructure, and mechanical properties of nanoporous gold

The effects of heating rate during the thermal coarsening of nanoporous gold (NPG) on its morphological evolution, microstructure, and mechanical properties are studied using molecular dynamics simulations. The simulation results show that lower heating rates promote the coarsening of NPG and decreasing porosity. The coarsening proceeds until the end of the heating process, followed by structural relaxation and recovery of the crystalline structure during the cooling process. NPG coarsened at lower heating rates has better mechanical strength. NPG under compression has a much higher dislocation density than that under tension, which results in a significant tension/compression asymmetry. During compression, NPG necking preferentially occurs at smaller ligament junctions and the orientation is [110].

Low-Vacuum Pyrolysis of YBCO Films by Using Fluorine-Free Metal Organic Chemical Deposition

The preparation of YBCO superconducting films by using metal organic chemical deposition (MOD) involves low-temperature pyrolysis and high-temperature treatment. The former process generally requires the introduction of water vapor and other gases. The study on pyrolysis in a low vacuum environment and non-carrier gas atmosphere has never been reported. In this work, we explored a low vacuum pyrolysis scheme with simple Argon gas decompression and a carrier-free atmosphere. The effects of heating rate on the microstructure of pyrolysis films were investigated, and the high-temperature treatment temperature (Th) was also optimized. Compared with conventional pyrolysis, the present low-vacuum pyrolysis does not employ the flowing dry or wet gases, facilitating the internal gas release during film decomposition. More importantly, the efficiency was greatly improved with reduced pyrolysis time. The obtained film surface is free of CuO particle, which leads to a lower roughness. We also investigated the effect of Th on the final YBCO film texture and superconductivity. As Th increased from 810 °C to 815 °C, the BaCuO2 phase decreased with enhanced c-axis orientation being evident by XRD and Raman spectra. As a result, the critical current density (Jc) increased from 0.38 MA/cm2 to 1.2 MA/cm2 (77 K, self-field).

Spark plasma sintering of UO2 nanopowders: Pressure, heating rate and current effects

We analysed with different methods the densification of UO2 nanopowders in SPS under constant heating rate (CHR) and isothermal sintering conditions. The apparent activation energy of densification in SPS (75 kJ/mol with CHR method) is significantly smaller than in conventional sintering. It is shown that this is likely not an effect of the applied current. We also observed a threshold stress at 64 MPa for the transition from pressure-insensitive sintering (stress exponent n≈0) to pressure-assisted sintering, suggesting that the contribution of the capillary stresses in such nanopowders is comparable with the typical stress applied in SPS.

Kinetic parameters and anomalies in heating rate effects of the thermoluminescence from rock salt from Tuzluca in Turkey

In this work, thermoluminescence (TL) characteristics and kinetic parameters of naturally occurring rock salts were presented. The samples were crushed and compressed into pellets before being irradiated with beta radiation doses ranging between 0.1 Gy and 15 Gy. TL responses exhibited four peaks at about 95 °C, 182 °C, 265 °C, and 360 °C in the glow curve. By increasing the heating rates, we observed an increase in the peak maximum temperature and the area of each peak as well as in the full width half maximum (FWHM), which shows an anomalous heating-rate effect. Taking a rock salt sample, the standard deviation was less than 1%, which was a good indication of repeatability. Using the initial rise (IR) and variable heating rate (VHR) approaches, the trapping parameters were calculated. The findings suggest that salt samples from the Tuzluca district in Turkey may be useful as radiation dosimeters.

Development of Ni-doped Fe/Ca catalyst to be used for hydrogen-rich syngas production during medicine residue pyrolysis

In this work, the catalytic pyrolysis of herbal residues (HR) by Ni–Fe/Ca catalysts and the effects of intrinsic ash and heating rate on the activity of Ni–Fe/Ca catalysts were investigated in a fixed-bed reactor. The results showed that the strong interaction of Fe and Ca formed Ca2Fe2O5, which inhibited the formation of CaCO3, shifted the weakly and moderately acidic sites to high temperatures, promoted the conversion of tar and char, and inhibited the formation of CO2. The H2 yield increased to 54.6 mL/g at 5% Fe/Ca catalyst. The addition of Ni to Fe/Ca improved the catalyst dispersion and promoted the adsorption of alkaline sites, while Ni formed a stable Fe3Ni2 alloy with Fe. The yields of H2 and CO increased from 54.6 mL/g and 63.4 mL/g (0.5% Fe/Ca) to 95.5 mL/g and 70.0 mL/g (0.5% Ni–Fe/Ca), respectively. The CO2 generation was suppressed at high temperatures and the calorific value of pyrolysis gas was significantly increased. Moreover, the acid wash pretreatment improved the tar yield, the alkaline sites in the Ni–Fe/Ca catalyst contributed to the conversion of aromatics and the reforming of CO2, and the presence of AAEMs promoted the redox reaction between gas and solid. The increase in the heating rate (100 °C/min) was beneficial to improve the activity of the Ni–Fe/Ca catalyst. The yields of H2 and CO reached 121.7 mL/g and 71.9 mL/g, respectively.

Effects of powder size and pre-sintering heating rate on dental recycled zirconia

Objective: To evaluate the effects of pre-sintering heating rate and powder size on dental recycled zirconia. Methods: Recycled zirconia powders were sieved to obtain the large (50 μm<particle diameter≤125 μm) and small (particle diameter≤50 μm) particles, these powders were then formed into green bodies. According to the pre-sintering heating rates, the recycled-zirconia green bodies were divided into 3 groups: group A, pre-sintering heating rate of 2 ℃/min; group B, pre-sintering heating rate of 5 ℃/min; group C, pre-sintering heating rate of 8 ℃/min. The relative density open porosity and machinability of the recycled zirconia pre-sintered bodies were evaluated and compared with the commercial zirconia pre-sintered bodies. Zirconia pre-sintered bodies were then fully sintered according to the manufacturer's instructions. The relative density, open porosity, linear shrinkage and flexural strength of fully sintered zirconia were further compared. The microstructure of fracture surfaces and the crystalline structure were analyzed by scanning electron microscope and X-ray diffractometer, respectively. Results: With the same particle size, the recycled zirconia pre-sintered at different heating rates showed no significant differences in the relative densities, and the open porosities (P>0.05). When the pre-sintering heating rates were 2 ℃/min, 5 ℃/min, and 8 ℃/min, the flexural strengths of the large-particle recycled zirconia were (421.2±54.7), (444.2±70.1) and (427.5±68.4) MPa, the flexural strengths of the small-particle recycled zirconia were (750.1±74.1), (777.2±95.5) and (746.7±73.0) MPa, respectively. The flexural strength of commercial zirconia was (988.4±129.8) MPa. The flexural strengths of the recycled zirconia were significantly lower than that of the commercial zirconia (P<0.05). At the same pre-sintering heating rate, the flexural strengths of the small-particle recycled zirconia were significantly higher than that of the large-particle recycled zirconia (P<0.05). Conclusions: Compared with the large particles, small-particle recycled zirconia powders can effectively improve the properties of recycled zirconia, while the pre-sintering heating rate has no effect on the properties of the recycled zirconia.

Production and Characterization of Maximum Liquid Oil Products through Individual and Copyrolysis of Pressed Neem Oil Cake and Waste Thermocol Mixture

In this study, individual and copyrolysis experiments were performed with pressed neem oil cake (NOC) and waste thermocol (WT) to produce high grade liquid oil. The effects of reactor temperature, heating rate, feed ratio, and reaction time on product yields were investigated to identify the optimum parameters for maximum oil yield. The maximum oil yield of 49.3 wt%, 73.4 wt% and 88.5 wt% was obtained from NOC pyrolysis, copyrolysis, and WT pyrolysis under optimized conditions. During copyrolysis, the maximum oil product was obtained under NOC/WT ratio of 1 : 2 and at the temperature of 550°C. The liquid oils obtained from thermal and copyrolysis were subjected to detailed physicochemical analysis. When compared to biomass pyrolysis, the copyrolysis of WT and NOC had a substantial improvement in oil properties. The copyrolysis oil shows higher heating value of 40.3 MJ/kg with reduced water content. In addition to that, the copyrolysis oil obtained under optimized conditions is analyzed with Fourier transform infrared spectroscopy (FT-IR) and Gas chromatography–mass spectrometry (GC-MS) analysis to determine the chemical characterization. The analysis showed the presence of aliphatic and aromatic hydrocarbons in the oil.

The effect of ultrafast heating rate on the elemental distribution between phases in a low carbon steel

This work focuses on the effect of heating rate, i.e. conventional heating (CH) and ultrafast heating (UFH) rates on the elemental distribution between phases in a low carbon steel. Microstructural characterization was carried out using an Electron Backscatter Diffraction (EBSD) and Atom Probe Tomography (APT) technique. Nanohardness of individual microconstituents was measured. It is shown that the applied heat treatments result in the formation of multiphase microstructures consisting of a ferritic matrix with embedded martensite and retained austenite. The ferritic matrix of the CH material was fully recrystallized, whereas both recrystallized (coarser) and non-recrystallized (finer) ferritic grains were present in the matrix of the UFH material. APT analysis indirectly confirmed that recrystallized grains after both heat treatments have a lower carbon content, when the non-recrystallized grains after UFH have a higher carbon content. It correlates with the nanohardness results, i.e. non-recrystallized grains show higher hardness, while recrystallized grains have a lower hardness. The segregations of C and Mn atoms at the martensite/ferrite interface were observed after both treatments. It is hypothesized that the segregations are formed under negligible partitioning local equilibrium condition during CH, whereas the solute drag effect results in the formation of interface segregation during UFH.

Effect of heating rate on asperities pattern formed in sol-gel derived nanocomposite hydrophobic coatings

Effect of heating rate on asperities pattern formed in sol-gel derived nanocomposite hydrophobic coatings

Pyrolysis characteristics and kinetic study of coal in a novel concentrating photothermal thermogravimetric analyzer: Effect of heating rate

Coal pyrolysis is the initial reaction of vast utilization technologies, and the quantitative description of pyrolysis characteristics and accurate kinetic parameters under the wide range of heating rates are of significant challenges. The effect of heating rate from 5 ℃/min to 1000 ℃/min on coal pyrolysis in a novel concentrating photothermal thermogravimetric analyzer was systematically investigated. A new temperature control scheme especially for the ultra-fast heating process was proposed, guaranteeing the absolute temperature control error was less than 4 ℃ throughout the whole heating process. As the heating rate increased from 5 ℃/min to 1000 ℃/min, the absolute value of maximum mass loss rate increased linearly from 4.18 wt%/min to 66.06 wt%/min, and the specific reaction rate for coal conversion at 20% and 50% also increased linearly by 15.4 times and 16.4 times, respectively. The mean activation energies exhibited the exponential decrease tendency from 235.41 kJ/mol to 28.37 kJ/mol. The transformation rates for functional groups of chars were accelerated with the heating rate, and the char with same conversion rate would be more condensed. The activation energy of coal during pyrolysis under heating rate of 1000 ℃/min was binomially correlated with the ratio of small aromatic rings to large ones in char.

Effect of debinding and sintering profile on the optical properties of DLP-3D printed YAG transparent ceramic

With no extra assistance of CIP or HIP, YAG transparent ceramics were successfully fabricated by digital light processing (DLP) stereolithography method followed by careful debinding and vacuum sintering. We systematically studied the effect of heating rate, atmosphere during debinding and the heating rate, holding time during sintering on the light transmittance of YAG ceramics. All results indicated that debinding in the 95N2/5H2 mixture is the key controlling factor for achieving better densification and optical properties, regardless of the sintering profile. However, a lower heating rate can indeed promote the densification process and balance some shortcomings linked with the debinding in air. At least, three different debinding processes and three different sintering profiles are combined, which leads to a high in-line transmittance of ∽77%.

The effect of heating rate on BaZrxTi1-xO3 thin film for x=0.4 and x=0.6 as capacitors

BaTiO3 (BT) was successfully produced on a Fluorine doped tin oxide (FTO) substrate using the sol-gel method by adding Zirconium (Zr) according to the stoichiometric equation BaZrxTi1-xO3 (BZT) at compositions x = 0.4 and x = 0.6. This research aims to increase the capacitance and dielectric constant of BZT as a capacitor. BZT thin films were annealed for 2 h at 800 °C with heating rates of 5 °C/min and 10 °C/min. Based on the results, variations in the heating rate affect the size of the sample, the capacitance, and the dielectric constant values. The films were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Impedance Spectroscopy. XRD results obtained the same plane peaks, but 2θ different angles indicate tetragonal plane structure. According to SEM characterization with 50,000 times magnification, the sample with composition x = 0.4 had an average grain size of 0.36 μm ± 0.11 and 0.32 μm ± 0.08 at a heating rate of 5 °C/min and 10 °C/min, respectively. Samples with composition x = 0.6 at a heating rate of 5 °C/min had an average grain size of 0.33 μm ± 0.09 and 0.18 μm ± 0.01 at a heating rate of 10 °C/min. Impedance spectroscopy characterization, the capacitance value for a frequency of 0.1 Hz, composition x = 0.4 with a heating rate of 5 °C/min and 10 °C/min has a value greater than composition x = 0.6 at the same heating rates. Furthermore, the dielectric constant value for a frequency of 0.1 Hz, composition x = 0.4 with a heating rate of 5 °C/min and 10 °C/min is more significant than composition x = 0.6.

Synthesis of Egyptian Blue and mechanisms

Egyptian Blue (EB, Cuprorivaite, CaCuSi4O10) is a novel candidate for nanomaterial-based sensors in water, as its infrared (IR, 910 nm) emission has high quantum yield in comparison with current commonly-used IR reporters. IR signals for bioimaging and environmental sensing penetrate biological matrices (i.e. tissues) deeper and with less scattering than visible light. This work reports the effects of heating rate on the solid state synthetic yield of EB and formation mechanism is discussed. EB synthesis was investigated with thermogravimetric analysis coupled with mass spectrometry and in-situ high temperature X-ray diffraction. A reproducible maximum in EB yield was observed at a heating rate of 7 °C/min with samples containing CaCO3 precursor. We report the optimized reaction conditions, yields, and the photoluminescent response of the synthesized EB layered materials. The precursor content (O2, CaCO3, CuO and SiO2) also had a subtle effect on EB yield.

Effects of heating rate on thermal degradation behavior and kinetics of representative thermoplastic wastes

Waste thermoplastics are the most common solid wastes, and thermal degradation has excellent advantages in the disposal of these wastes and obtaining valuable hydrocarbon fuels. As a significant factor, the heating rate is crucial to the thermal degradation process. Consequently, thermal degradation behavior and kinetics of representative thermoplastics under different heating rates were investigated by using thermogravimetric analysis and differential scanning calorimetry in the air. Kinetic parameters were estimated by using the Coats-Redfern method. Subsequently, the Shuffled Complex Evolution (SCE) method was used to optimize kinetic parameters, and the optimized results were compared with the calculated kinetics of distributed activation energy model (DAEM) method to find the effects of heating rate on kinetic parameters. The results showed that with the increase of heating rate, thermogravimetric curves moved to the right, which corresponded to a higher temperature range. The number of mass loss rate peaks and exothermic peaks decreased. Additionally, activation energy was the same at the determined minimum and maximum heating rates, and other heating rates had little effect on kinetic parameters. Moreover, the calculated activation energy of the DAEM method at the minimum heating rate of 5 K/min was closest to the optimized values of the SCE method, indicating that the lower the minimum heating rate was, the more accurate the activation energy was.