Influence Of Different Heating Rates Research Articles

Biopolymeric transitions under pyrolytic thermal degradation of Pigeon pea stalk

In this article, thermogravimetric analysis (TGA) is used to explore biopolymeric transitions in Pigeon pea stalks (PPS) at various heating rates (10, 20, 30 and 40 °C/min). The appeared transitions of TG-signals were analyzed in depth and discussed critically in terms of biopolymeric changes occurring within the major bioconstituents of PPS due to the influence of different heating rates. The intersection points of the deconvoluted conversion rate spectrum were taken as the stage transition points from one biopolymeric region to another. The stage transition points for hemicellulose to cellulose were at 328 °C and from cellulose to lignin at 356 °C, respectively, at a heating rate of 10 °C/min. This article is presenting the stage transition points first time and highlights the procedure of obtaining them using the conversion rate spectrum. The kinetics of individual bioconstituents of the PPS was also thoroughly investigated. The average activation energy was highest for hemicellulose 283–287 kJ/mol, followed by cellulose (134–137 kJ/mol) and lignin (30–41 kJ/mol). The pyrolysis of PPS followed the multistage reaction mechanism (F1 and A4) based on the Z-master plot technique.

Nanocrystal evolution during ultra-fast heating in an amorphous Fe85B15 alloy

During the crystallization of Fe-based metallic glasses the precipitation of the BCC-Fe nanocrystals smaller than the exchange length (30–40 nm) has been reported as an effective strategy for a reduced coercivity and an increased saturation magnetization. In binary Fe-B alloys it has been shown that nanocrystals well below the exchange length can be obtained by rapid heating above 100 K/s. In order to determine if the fast heating process can yield a further refinement in nanocrystal size, the influence of different heating rates (0.17–5000 K/s) on the crystallization behavior of an amorphous Fe85B15 alloy was investigated using Flash DSC and TEM. Above a critical heating rate (500 K/s), the number density and diameters of BCC-Fe nanocrystals become saturated due to diffusion-field impingement that enriches the amorphous matrix with B that leads to the precipitation of Fe3B nanocrystals that deteriorate the magnetic properties.

High Quality and Maximizing the Production of CNTs from the Pyrolysis of Waste Polypropylene

Thermal decomposition of plastics by pyrolysis into oil is a successful way of treating wastes. Nevertheless, the production of carbon nanotubes (CNTs) from wastes improves the feasibility of the waste management process. An experimental setup was developed to study the influence of different heating rates on the produced oil by pyrolysis of waste polypropylene (WPP), and the influence of using foamed nickel on the produced CNTs as a function of operating temperature and heating rate. Different heating rates of 5, 10, and 20 °C/min were examined, as well as the different carbon vapor deposition (CVD) temperatures of 600, 700, and 800 °C were studied. It has been found that increasing the heating rate from 5 to 20 °C/min increases the oil yield from 59.3 to 71%, but on the other hand it decreases the quality of the oil. It has been also found that increasing the heating rate decreases the quality of CNTs, i.e., uniform CNTs with small diameter and small wall thickness, and as well as the quantity. The physical properties of the produced CNTs have been improved by increasing the CVD temperature; however, the quantity of CNTs decreased. The highest yield of CNTs produced was 43.12% at the lowest CVD temperature and heating rate examined, i.e., 600 and 5 °C/min, respectively. The optimum heating rate and CVD temperature for the pyrolysis of waste polypropylene to achieve the highest quality of CNTs with moderate production of 39.34%, is the lowest heating rate examined, i.e., 5 °C/min, with a moderate CVD temperature of 700 °C.

Toughening of a dicyandiamide‐cured epoxy resin: Influence of cure conditions on different rubber modifications

AbstractCure kinetics of modified epoxy resins cured with dicyandiamide are studied. The influence of different heating rates in the curing process, such as curing behavior, morphology, and thermo‐mechanical properties, is studied. Additionally, three different post‐cure cycles at 180°C are employed. Two butadiene‐based toughening agents are used, a carboxyl‐terminated polybutadiene‐co‐acrylonitril (CTBN) prepolymer and a functionalized block copolymer of polytetrahydrofuran and hydroxyl‐terminated polybutadiene. The amphiphilic block copolymer enables investigations with a bimodal particle size morphology. All results are contrasted with those of the neat resin and butadiene‐free block polymer. Faster curing processes result in smaller average particle sizes and better fracture toughness of the modified epoxy resins. Further improvements are achieved with additional post‐cure cycles at 180°C. An increased interfacial adhesion between the particles and the epoxy matrix is considered to be the main mechanism. Optimized lengths of the post‐cure process can be determined with the butadiene‐based toughening agents indicating a competing thermal degradation. Longer post‐cures than 40 min lead to lower fracture toughness in the butadiene‐based modified materials. In general, similar influences of the curing and post‐curing process on the bimodal and unimodal distributed system can be observed differing in more intense dependencies of the bimodal system.

In Situ Measurement Method for Temperature Profile Optimization During Thermocompression Bonding Process

Thermocompression bonding (TCB) is an important process in electronic packaging and is widely seen as a promising technology for miniaturized electronic devices. However, this process usually yields a lower throughput compared to more conventional mass-reflow processes, mainly because the thermal distribution uniformity across the bonding plane, as required for reliable joints, is achieved with longer bonding dwell times. Higher throughputs could be achieved by reducing the dwell time and increasing the heating rates, but this comes at the cost of higher temperature variations between the center and edges of the bonded component, leading to defects such as nonwet or bridged. Reliable temperature distribution measurements are thus needed to eliminate these joint defects. We present a novel method of temperature measurements to quantify the thermal limits of the TCB process. A microfabricated sensor with high temporal and spatial resolution was designed and fabricated for in situ temperature profile measurements up to 250 °C. This work aims to evaluate the influence of different heating rates on the temperature distribution across the chip surface, as well as on the resulting bonding quality. The bonding quality was assessed by the evaluation of bonding pull strength and interfacial defect characterization. The results demonstrate that slow heating rates (50 °C/s) lead to bridge defects and high heating rates (>80 °C/s) induce nonwetting defects in the solder joints. The solder joint defects can be related to the temperature uniformity measurements performed with the RTD sensor, thus providing a mean to more efficiently optimize the TCB heating rate in industrial processes.

Structural and luminescence characterization of Ce3+ and Mn2+ co-activated zinc silicate nanocrystal obtained by gel combustion synthesis

The structural, morphological, and luminescence properties, including photoluminescence (PL) and thermoluminescence (TL), of newly produced Zn2SiO4 co-activated by Ce3+ and Mn2+ ions using the gel-combustion synthesis, are investigated in deep. To determine the co-dopant effect precisely, non-doped, Ce3+ doped, and Ce3+ and Mn2+ double doped Zn2SiO4 phosphors are evaluated. The fluorescence decay curves indicate that a shorter decay time at relatively high Mn concentrations takes place. The TL glow curve readouts observed by applying the dose range between 0.1 and 2000 Gy after 150 °C preheat are performed at a linear heating rate of 2 °C/s from room temperature (RT) to 500 °C. An anomalous heating rate behavior is observed when the influence of different heating rates on TL characteristics is reported. An excellent agreement is found between the TL kinetic parameters analyzed by the initial rise (IR) with TM–Tstop analysis and computerized glow curve deconvolution (CGCD) methods.

The influence of different heating rates on mortality of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Abstract In order to elucidate the ability of stored product insects to resist high temperature at varying temperature conditions, the influence of different heating rates on the mortality of all life stages of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) was investigated. After acclimation from 28 to 42, 44 and 46 °C at different heating rates (0, 1.25, 2.50, 5.00, and 10.00 °C/h), eggs, larvae, pupae, and adults of T. castaneum were exposed at 50 °C for 0 (as a control), 10, 15, 20, 25 and 30 min, respectively. The corrected mortality of T. castaneum was determined after 24 h. The results showed that different exposure times and heating rates had significant effects on the mortality of T. castaneum. The mortality of all life stages of T. castaneum with the same acclimation experience increased significantly with the increasing exposure time, and acclimation improved the heat tolerance of T. castaneum. The mortalities exposed at 50 °C for 30 min of T. castaneum eggs (acclimated to 46 °C at 5.00 °C/h), larvae (acclimated to 44 °C at 2.50 °C/h), pupae (acclimated to 46 °C at 5.00 °C/h), and adults (acclimated to 46 °C at 2.50 °C/h) were 62.50%, 54.44%, 58.89% and 53.33%, respectively, significantly lower than that of corresponding life stages of T. castaneum acclimated at 1.25 and 10.00 °C/h. The present results are in favor of developing an effective heat treatment protocol for pest control.

Thermal stability, degradation kinetic and structural characterization of novel aromatic amide compounds

In this study, six novel amide compounds with three different structures were synthesized. At the beginning of the study, two novel amide compounds were formed using 3,7-Dihydroxy-2-naphthoic acid, 2-Amino-5-methylphenol and 2-Amino-3-chloro-phenol as basic materials. Then, the polymerization of the synthesized amide compounds were conducted with oxidative polycondensation method in which NaOCl was used as oxidant. Finally, copper complexes were synthesized using polymers as ligand. All synthesized compounds have been characterized by IR, UV–vis and H NMR spectral studies, LC-MS and GPC chromatographic studies, and SEM analysis. Thermal stabilities of amide monomers, polymers and copper complexes were determined by TGA technique. Furthermore, thermodynamic parameters of the degradation process were determined for all synthesized compounds with the use of non-isothermal method: Flynn-Wall-Ozawa method. The variation of the heating rate at TGA technique has allowed us to investigate and discuss the influence of different heating rates on decomposition of the compounds.

EFFECT OF PYROLYSIS HEATING RATE ON THE CHEMICAL COMPOSITION OF WOOD VINEGAR FROM EUCALYPTUS UROGRANDIS AND MIMOSA TENUIFLORA

ABSTRACT Among the parameters used in the biomass carbonization process, the heating rate is one of the most important. The objective of the present work was to assess the influence of different heating rates on the chemical composition of wood vinegar (WV) from two wood species. Dried disks of Eucalyptus grandis and Mimosa tenuiflora wood were used as raw material. Carbonization runs were carried out in a laboratory muffle furnace at three heating rates (0.7, 1.0 and 1.4 °C/min), with 10 runs at each heating rate, reaching 450 °C. Yields of charcoal, pyrolysis liquids and gases were determined for all carbonization conditions. Crude pyrolysis liquid from each wood species and each heating rate was bi-distilled, yielding purified WV samples. These samples were extracted with ethyl acetate and the organic fraction was analyzed by gas chromatography-mass spectrometry to obtain qualitative and semi-quantitative data. Results showed that lower heating rates produce higher yields of charcoal, while higher heating rates lead to higher yields of pyrolysis liquids and gases. Totals of 57 and 42 chemical compounds were identified in the WV of Eucalyptus and Mimosa, respectively, divided into the following groups: alcohols, ketones, furans and pyrans, and phenolic compounds. In general, higher heating rates led to greater contents of furans and pyrans and lower concentrations of phenolic compounds.

Effect of heat treatment conditions on magnesium borate fibers prepared via electrospinning

The influence of different heating rates as well as different atmospheres on magnesium borate fibers produced by electrospinning was investigated in this work. The green fibers were prepared from sol–gel precursors, using polyvinyl-pyrrolidone (PVP) as processing aid. Crystalline fibers with the typical necklace structure and average diameter in the range 300–500 nm were produced when heating up to 900 °C in air. The main phase detected by XRD analysis was in this case Mg2B2O5. On the other hand, the fibers slowly heated in reducing atmosphere to 800 °C exhibited similar dimension but a different morphology. The crystalline grains were presumably smaller, hence the necklace effect was absent. This sample also revealed a much higher specific surface area in comparison to the samples calcined in air. Mg3B2O6 was here the main crystalline phase, while a part of boron was lost during the thermal treatment.

Effects of heating rates and SBE loading on sintered properties of spent bleach earth/recycled glass composite

The purpose of this study is to investigate the influence of different heating rates on the properties of glass ceramic composite (GCC) at different spent bleach earth (SBE) loadings. GCC was prepared using SBE and recycled soda lime silicate (SLS) glass. The particle size of SLS glass was approximately <45μm. The GCC was formed by uniaxial dry pressing at weight fractions of SBE loading of 40 wt. %, 45 wt. %, and 55 wt. %. The GCC was then sintered at different heating rates of 2 oC/min, 4 ˚C/min, 6 oC/min and 8 ˚C/min at 700 oC of sintering temperature. The GCC specimens were analysed in terms of their physical properties, while crystalline phase and microstructure were characterized using X-Ray diffraction and scanning electron microscope (SEM), respectively. The results from X-Ray diffraction pattern showed that quartz and wollastonite phases were formed with no major changes on the phases as the heating rate increased. The results indicate that the variation of heating with 2 oC/min interval does not give a remarkable result of physical properties on GCC. High loading of SBE sintered at 2 oC/min of heating rate produced low water absorption, density and porosity. SEM analysis showed that the physical properties and crystalline phases were correlated to the SBE loading and changes in the heating rate. The study concluded with the prospect of continuing the work of optimisation on schedule heat treatment at sintering temperature regimes.

Fundamental investigation of laser beam melting of polymers for additive manufacture

By selective laser sintering (SLS), polymer powders are molten layer by layer to build conventional prototypes or parts in small series with geometrical freedom that cannot be achieved by other manufacturing technologies. The SLS process is mainly defined by the beam–matter interaction between powder material, laser radiation and different material characteristics by itself. However the determination of these different material characteristics is problematic because powder material imposes certain requirements that cannot sufficiently be provided by conventional measurement methods. Hence new fundamental investigation methods to determine the optical and thermal material characteristics like the thermal diffusivity, thermal conductivity, or the influence of different heating rates on the melting behavior are presented in this paper. The different analysis methods altogether improve the process of understanding to allow recommendations for the future process controlling.

Low-temperature partial transient liquid phase diffusion bonding of Al/Mg 2Si metal matrix composite to AZ91D using Al-based interlayer

Partial transient liquid phase diffusion bonding of an aluminium metal matrix composite (Al/Mg 2Si) to magnesium alloy (AZ91D) was performed using two heating rates. The influence of different heating rates on the microstructure, microhardness and shear strength has been studied. With a decrease in heating rate from 20 to 2 °C/min, the Mg content in the bond line decreased and the microstructure was altered. The composition and microstructure of the joined areas were examined by X-ray diffraction (XRD) and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (EDS). It was found that a heating rate of 2 °C/min resulted in an increasing in the shear strength of the joints. The kinetics of the bonding process accelerated due to the increase of solute diffusivity through grain boundaries of the metal matrix composite. Results suggest that Mg and Si contained in the interlayer favours the partial disruption of oxide films, facilitating the bonding process.

Effect of Heating Rate on the Responses of LiF: Mg, Cu, Na, Si Thermoluminescent Phosphor

In the current work the glow curves for LiF:Mg,Cu,Na,Si thermoluminescent material were measured and analyzed by using a function approximating to the well-known Randall-Wilkins first-order expression. The influence of different heating rates on thermoluminescent glow-peak maximum temperature, peak height and integrated area of the glow peak was investigated for LiF:Mg,Cu,Na,Si phosphor. The results show that the glow-peak temperature, peak height and glow peak area increase with increasing heating rate, while the full width at half maximum of glow peak almost keeps constant in the range of heating rates studied.

Effect of heating rates on microstructure and superconducting properties of pure MgB 2

The influence of different heating rates, ranging from 5 to 30 K min −1, on the microstructure and superconducting of the MgB 2 bulk was investigated. No obvious variation in the grain size was found for the samples heated from 5 K min −1 to 20 K min −1 except for the changes in morphologies. Moreover, the grain refinement was obtained under the heating rate of 30 K min −1. The critical current density ( J c) suggested that the 5 K min −1 sample had the best performance in high field. Here, the differential thermal analysis (DTA) was employed to analyze the kinetics of MgB 2 phase formation with the different heating rates. The results showed that the large amount of MgB 2 formed at low temperature, which lead to compact structures under the slow heating rate. The fast heating rate would promote the evaporation of Mg at high temperature, which was considered to generate the vacancy and impurities in the sample.

Influence of heating rate on thermoluminescence of Mg2SiO4 : Tb dosimeter

In this paper the influence of different heating rates on thermoluminescence (TL) kinetics, glow-peak temperatures, heights and integrated TL intensities of the main glow peak of recently produced Mg2SiO4 : Tb dosimeters are reported. The TL properties of the phosphor were investigated after β-irradiation at room temperature. Glow curve shape, peak shape, repeated initial rise and variable heating rate methods were used to analyse the TL kinetics of the main glow peak at 473 K. Results show that the TL glow peak of Mg2SiO4 : Tb phosphor obeys second-order kinetics. Analysis of the main dosimetric peak by using the methods mentioned above revealed that activation energy (E) is about 1 eV and the pre-exponential factor (s) is in the range 1010–1011 s−1. In addition it is ascertained that the glow-peak temperature increases with heating rate. The glow-peak height showed two maxima in the heating rate range investigated. The behaviour of the integrated TL intensities and the maximum glow-peak temperatures related to the heating rate have been discussed in terms of thermal quenching and clustering formation.

Effect of Heating Rate on Phase and Microstructural Evolution During Pressureless Sintering of a Nanostructured Transition Alumina

Deagglomeration of a nanocrystalline transition alumina performed using different techniques was first demonstrated to be active in the achievement of a better powder compaction ability under uniaxial pressing and consequently in the development of a highly dense and homogeneous microstructure during pressureless sintering. A major effect, however, was associated to the heating rate chosen during the densification cycle. In fact, the influence of different heating rates (10°C/min or 1°C/min) on phase and microstructural evolution during sintering was investigated in depth on the above best green bodies. A low‐rate thermal cycle leads to a significant reduction of the α‐Al2O3 crystallization temperature and promotes a more effective particle rearrangement during phase transformation. As a consequence, in the low‐rate treated material, it was possible to avoid the development of a vermicular structure as usually expected during the densification of a transition alumina and to yield a more homogenously fired microstructure.

Thermal decomposition of pyrotechnic mixtures containing either aluminum or magnesium powder as fuel

Thermal behavior of energetic materials is critical to safe production, storage, handling or even demilitarization. In this work, the thermal behavior of Al, Mg, CuO, KMnO 4 and also three mixtures containing Al + CuO, Mg + CuO and Mg + KMnO 4 were studied experimentally using differential scanning calorimetry and thermogravimetry. These mixtures are sometimes used as pyrotechnic mixtures in military industries. Also, the influence of different heating rates (5, 10, 15 and 20 °C/min) on the DSC behavior of the mixtures was verified. The results showed that as the heating rate was increased, melting points and ignition temperatures of the mixtures were increased. On the other hand, TG–DSC analysis for Mg + KMnO 4 mixture indicates that this mixture melts at 283.0 °C and decomposed at 292.1 °C. By replacing KMnO 4 with CuO as the oxidizer of the magnesium, these temperatures enhanced to 368.7 °C and 408.3 °C, respectively. However, replacing Mg with Al in the Mg/CuO mixture decreases the melting and ignition temperatures of the mixture to 231.4 °C and 271.9 °C, respectively. The activation energy for each pyrotechnic mixture was computed. Also, the values of Δ S #, Δ H # and Δ G # of their reaction were calculated.

Influence of the Heating Rate on the Pasting Properties of Various Flours

AbstractViscoamylographic tests were carried out on six commercial flour samples, three wheat flours (WF), two semolinas (S) and one rice flour (RF), using the Brabender Micro Visco‐Amylo‐Graph (MVA). The slurries were subjected to a definite temperature profile (30°C‐95°C, 95°C×30 min, 95°C‐50°C, 50°C×30 min), stirring at 250 min−1 and using a 300 cm·gf cartridge and recording the viscosity (in Brabender Units, BU) as a function of temperature and time. The aim of this work was to evaluate the influence of different heating rates (1.5, 3.0, 5.0, 7.5, 10.0°C/min) on the pasting properties of the various flours. The peak viscosity of WFs and Ss increased when high heating rates were applied, while the RF showed similar pasting properties independently of the heating rate. These behaviours were mainly ascribed to the different molecular organisation of the starch granules, responsible of different swelling and gelatinising extents, and also to a different kinetic of alpha‐amylase inactivation according to the heating rate applied. The key role of the alpha‐amylase activity in controlling the pasting viscosity of the different samples was demonstrated by the viscoamylographic test performed in the presence of silver nitrate as enzyme inhibitor.

Heating rate effects on the thermoluminescence of fluorite

In this work, we investigated the influence of different heating rates on the thermoluminescence (TL) glow-peak temperature, height and “integrated TL intensities” (integrated TL intensity or sums of intensities above background across the peak) of the two high-temperature glow-peaks of a Nigeria fluorite sample. The results show that the glow-peak temperatures of the two peaks increase with heating rate. The glow-peak height showed two maxima at 10 and 20 ∘ C s - 1 for peak III and at 10 and 25 ∘ C s - 1 for peak IV in the range of heating rate investigated. The behaviour of the integrated TL intensities of the two peaks with heating rate has been explained in terms of clustering and thermal quenching. The results showed that thermal quenching may be larger for peak III than for peak IV.