Influence Of Heating Rate Research Articles

Effect of Heating Rate on Microstructural Developments in Cold Heading Quality Steel used for Automotive Applications

CHQ (Cold Heading Quality) steels are assumed to be non-heat treatable so strengthened by cold forming which is a quick and mass production makes it low cost manufacturing process. In this study, microstructure and phase transformation in steels is a fundamental aspect of governing the properties. A large number of studies are dedicated on the subject phase transformations owing to availability of several commercial steel grades. Due to several grades of steels commercially available shows differently behavior so it is hard to conclude that phase transformation is universally understood completely. In this study the influence of heating rate on the development of microstructure of CHQ steel has been studied thoroughly by using different heating techniques.For characterization, optical microscope connected with high resolution camera and SEM (Scanning Electron Microscope) was utilized to interpret the microstructural results. In addition, heat treatment methods have been utilized as to vary the microstructure in the steel under experimentation. It was found that heating rate could have major effect on phase transformation of CHQ steel (under study). Rate of heating enhances the austenite development kinetics with respect to dwell time and such austenite has been changed to martensite upon cooling. In addition, heating rate also promotes nucleation sites for the formation of austenite phase of CHQ steel.

Residual mechanical properties of high strength steels after exposure to fire

This paper presents an experimental investigation on residual mechanical properties of high strength steels (HSS) after exposure to fire. A test program was conducted to study the post-fire mechanical properties of cold-formed HSS. A total of 41 tensile coupon specimens was extracted from cold-formed tubular sections with nominal yield stresses of 700 and 900 MPa. The specimens were exposed to various elevated temperatures ranged from 200 to 1000 °C and then cooled down to ambient temperature before testing. Stress-strain curves were obtained and the mechanical properties of Young's modulus, yield stress (0.2% proof stress), ultimate strength, ultimate strain and fracture strain of the cold-formed high strength steel materials after exposure to elevated temperatures were derived. The post-fire retention factors that obtained from the tests were compared with existing predictive equations in the literature. The influence of heating rate on post-fire mechanical properties was also investigated. New predictive curves for the determination of residual mechanical properties of HSS after exposure to fire are proposed. It is demonstrated that the proposed predictive curves are suitable for both cold-formed and hot-rolled HSS with nominal yield stresses ranged from 690 to 960 MPa.

Geochemical behavior of hazardous volatile elements in coals with different geological origin during combustion

The geochemical behaviors of hazardous elements in the combustion process of Chinese coals with different geological origins at different temperatures were studied. The analyzed coal samples were placed in a fixed bed reactor with a quartz tube and heated to six desired temperature points, from 400 °C to 900 °C with 100 °C for each interval. The mineral morphology and composition of coal and coal ash were determined by X-ray fluorescence (XRF), scanning electron microscope-X-ray Energy Dispersive Spectrom (SEM-EDS) and X-ray powder diffraction techniques (XRD). Sequential chemical extraction procedure was used to describe the modes of occurrence of selected hazardous elements in coal. The content of arsenic (As) in coal and coal ash was analyzed by inductively coupled plasma mass spectrometry (ICP-MS), and the content of selenium (Se) and mercury (Hg) in coal ash was analyzed by atomic emission spectrometry (AES) and atomic fluorescence spectrometry (AFS). The volatile characteristics of As, Se and Hg in coal were studied by thermogravimetry (TG). The results show that: 1) the mineral phases of Liuzhuang (LZ) and Huajiahu (HJH) coal samples are mainly composed of clay minerals and silicate minerals and the contents of As, Se and Hg were closely related to the organic matter and inorganic mineral in coal; 2) As mainly exists in organic matter and Se, Hg mainly exists in silicate minerals. The organic As in coal is closely related to the low-rank, low ash content and low As content of coal. The modes of occurrence of Se and Hg may be related to the low element content, low sulfide content in coal and stable sedimentary environment; 3) the relationship between volatilization rate (Vr) of As, Se and Hg elements and combustion temperature is the closest. The differences of Vr of As, Se and Hg elements in coal of different geological origin are mainly related to elements concentration and coal quality; 4) at different heating rates, the Vr curves of As, Se and Hg elements have the characteristics of “S” type, logarithmic type and linear type, respectively; The Initial stable temperature of Vr is different under the influence of element geochemical characteristics. The volatility of As reaches the maximum at 800 °C, and Se and Hg reach the maximum at 700 °C and 600 °C, respectively; 5) The heating rate and the difference of coal quality under different geological origin are important factors affecting the Vr of As, Se and Hg. The maximum weight loss temperature (TP) can be used as an important index to reflect the influence of coal quality and heating rate on the Vr of hazardous elements (As, Se and Hg).

Numerical simulation of cook-off characteristics for AP/HTPB

Abstract The present study is devoted to researching the thermal security problems of large-scale solid rocket motor with Ammonium perchlorate/Hydroxyl-terminated polybutadiene (AP/HTPB). A two-dimensional axisymmetric model for the cook-off of solid rocket motor is established. The reaction kinetics for the cook-off process of AP/HTPB is described by the two-step global chemical mechanism. Numerical predictions of the cook-off behavior for the propellant are conducted at fast heating rate of 1.45–2.45 K/s, and slow heating rate of 0.001–0.003 K/s, respectively. The results show that in the fast cook-off condition, the initial ignition position of AP/HTPB occurs in the annular region of the outer wall of propellant without exception, and the center point in the region is (889.1, 149.5). For the region, the axial width is 1.8 mm and radial thickness is 0.8 mm. However, in the slow cook-off condition, the ignition center position is shifted along the axial direction toward the right end face of the propellant with the increase of heating rate. Therefore, the influence of heating rate on ignition temperature and ignition delay time is nonnegligible within a certain range.

Influence of heating rate and mechanical activation on the reaction between kaolin and aluminium powder

In this work, the effect of heating rate and mechanical activation on the reaction of kaolin and aluminium powder was investigated. A batch comprised of 89.5 wt% kaolin and 10.5 wt% aluminium powders was mixed and milled in a planetary ball-mill for 1, 5, 10, 20 and 40 h. The mixture powders were heat treated with a heating rate of 5, 10, 15, 20, 30 and 40 °C/min, respectively. After milling for 20 and 40 h, the results showed the formation of free silicon, quartz and nacrite (Al2Si2(OH)4) at room temperature. The kaolinite dehydroxylation, aluminium oxidation and the θ- to α-Al2O3 transformations are highly affected by heating rate and mechanical activation. As compared with the smallest heating rate, the mixtures heated with faster heating rate show the disappearance of the peak corresponding to the oxidation of aluminium and the appearance of a second peak corresponding to the formation of α-Al2O3. The intensity of the last peak increases with increasing of the heating rate and milled at lower milling time. The effects of heating rate in the reaction of kaolin and aluminium powder are attributed to the amorphization of kaolinite, the diffusion of Al3+ to form an amorphous alumina layer on the particle surface and the generation of microcracks at the particle surface of aluminium powder.

Experimental planning of the synthesis of strontium molybdate by EDTA-citrate and its structural influence, morphology and optical bandgap

It was initially used a 23 experimental design with central point in triplicate to synthesize strontium molybdate by EDTA-citrate combined complexation method, where the influence of pH (6, 7.5 e 9), calcining time (3, 4 e 5 h) and heating rate (5, 7 e 10 °C min−1) was investigated. Single-phase powders were obtained when calcined at 650 °C with tetragonal crystalline structure. The heating rate is the most influent independent variable on the intensities of the X-ray diffractions peaks. The synthesized powders are shown as agglomerates with irregular spherical and bipyramidal morphology. According to the experimental design, the conditions of calcining time of 3 h and heating rate of 10 °C min−1 show the lowest values of energy band gap (4.18 and 4.17 eV) for pH 6 and 9, respectively. The statistical models generated were able to describe the phenomena observed.

Influence of calcination time and heating rate on the phase-chemical structure of Pd-doped SiO2 organic-inorganic membrane materials in air

ABSTRACTPd-doped SiO2 organic-inorganic hybrid materials were synthesized using sol-gel technique. The Pd-doped SiO2 samples were calcined at the temperature 350°C for several different time in air atmosphere with two different heating rates. Influence of calcination time and heating rate on the phase-chemical structure of Pd-doped SiO2 membrane materials was discussed by XRD, XPS, FTIR and TG-DTG analysis. The results indicate that the two factors have great influence on the crystal structure of Pd element and minor influence on the chemical structure. A longer calcination time and a slower heating rate can facilitate the oxidation of Pd0 to PdO, and should be conducive to the decomposition of Si-CH3 groups and the dehydration condensation of Si-OH groups. In order to prevent metallic Pd0 in Pd-doped SiO2 organic-inorganic membrane materials from being oxidized in air, the calcination time and heating rate should be chosen carefully.

Study of thermal analysis and kinetic decomposition of polybutadiene acrylonitrile acrylic acid (PBAN)

This paper describes thermochemical properties and decomposition characteristics of polybutadiene acrylonitrile acrylic acid (PBAN). The thermal behavior of PBAN samples containing various amounts of nitrile groups was determined by simultaneous thermogravimetric analysis and differential scanning calorimetry (TG/DSC). The results indicate that nitrile content in PBAN affects thermal behavior markedly. The influence of heating rate on the DSC behavior of the PBAN was investigated, while thermal decomposition of these compounds followed the first-order law. The kinetic parameters such as activation energy and frequency factor for these compounds were obtained from the DSC data by non-isothermal methods. Also the impact of different ratio of nitrile content in PBAN on glass transition temperature (Tg) of this terpolymer was measured.

Rice Husk Gasification: from Industry to Laboratory

Rice husk gasification (RHG) has been increasingly paid attention in rice-producing countries. Nevertheless, information related to this technology remains small and fragmented. In this paper, the status of RHG has been summarized, highlighting domestic and industrial applications, as well as a scientific review. Moreover, an experimental parametric study was performed to measure: a) the influence of temperature and heating rate on RH pyrolysis, and b) the role of temperature, partial pressure, and heating rate on RHG, under H2O or CO2 atmosphere. Regarding pyrolysis, an increase in the final pyrolysis temperature lowers the RH char yield but does not have much effect on the char morphology. Regarding gasification, an increase in the reaction temperature from 900 to 1000°C accelerates about 4.8 and 7 times the char conversion rate, under 0.2 atm of CO2 or H2O, respectively. The conversion rate decreases about 1.8 times when CO2 partial pressure decreases from 1 to 0.2 atm, and about 1.6 times when H2O partial pressure decreases from 0.4 to 0.1 atm. At 900°C and 0.2 atm, steam gasification was about 3.5 times faster than Boudouard reaction.

Thermal inactivation of Aspergillus flavus in peanut kernels as influenced by temperature, water activity and heating rate

Infection of Aspergillus flavus, which can produce aflatoxin, is a major problem for peanut safe storage. Thermal inactivation kinetics of Aspergillus flavus is essential to design an effective heat treatment process. In this study, thermal inactivation kinetics of Aspergillus flavus in peanut kernel flour at four water activity (aw) levels (0.720, 0.783, 0.846, and 0.921) with three temperatures for each aw was studied using a thermal-death-time heating block system and fitted with first-order kinetic and Weibull models. The influence of heating rates on thermotolerance of Aspergillus flavus was also investigated. The results showed that the Weibull distribution model had better coefficient of determination from 0.954 to 0.996, as compared to that (from 0.866 to 0.980) of the first-order kinetic model. An upward concavity was found with the inactivation curve, indicating a tailing effect. Model parameters (D, δ, and p) were estimated with the modified Bigelow equations to predict survival curves of Aspergillus flavus at any temperature and aw. The reduced heat resistance of Aspergillus flavus at high heating rates above 1 °C/min suggests that developing fast thermal processes is preferred for pasteurizing peanuts in food industry. A case study was presented for applying the cumulated lethal time model to design the industrial heating process based on the thermal kinetics of Aspergillus flavus.

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.

Combined Effect of Heating Rate and Microalloying Elements on Recrystallization During Annealing of Dual-Phase Steels

Adjusting ferrite recrystallization kinetics during annealing is a way to control the final microstructure and thus the mechanical properties of advanced cold-rolled high-strength steels. Two strategies are commonly used for this purpose: adjusting heating rates and/or adding microalloying elements. The present work investigates the effect of heating rate and microalloying elements Ti, Nb, and Mo on recrystallization kinetics during annealing in various cold-rolled Dual-Phase steel grades. The use of combined experimental and modeling approaches allows a deeper understanding of the separate influence of heating rate and the addition of microalloying elements. The comparative effect of Ti, Nb, and Mo as solute elements and as precipitates on ferrite recrystallization is also clarified. It is shown that solute drag has the largest delaying effect on recrystallization in the present case and that the order of solute drag effectiveness of microalloying elements is Nb > Mo > Ti.

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.

Catalytic cracking of waste cooking oil for biofuel production using zirconium oxide catalyst

In the present work, catalytic cracking of waste cooking oil (WCO) for the production of liquid fuels has been studied in a semi batch reactor under N2 atmosphere. Catalytic cracking was performed at a temperature range of 400–500 °C using zirconium oxide (ZrO2) as a catalyst. The influence of temperature, heating rate, residence time and catalyst loading on the product yield has been studied. The physicochemical properties such as calorific value, density, flash point and kinematic viscosity of organic liquid product (OLP) was analysed for its suitability for fuel application. The chemical compositions and functional groups present in OLP were identified by gas chromatography-mass spectrometry (GC-MS) and Fourier transformed infrared spectroscopy (FTIR). From the overall study, the optimal ZrO2 load, reaction temperature, residence time and heating rate were found to be 4 wt%, 475 °C, 120 min and 10 °C/min, respectively at which 83 wt% of OLP was obtained. From the results of catalyst characterization, it was confirmed that the catalyst can be regenerated after use.

Kinetic Study and Thermal Decomposition Behavior of Magnesium-Sodium Nitrate Based on Hydroxyl-Terminated Polybutadiene

This paper has been utilizing the simultaneous ThermoGravimetric analysis and Differential Scanning Calorimetry (TG–DSC) to investigate the thermal decomposition of magnesium-sodium nitrate pyrotechnic composition based HTPB resin. The thermal behaviors of different samples with various fuel-oxidizer ratio contents were determined. Decomposition kinetic was investigated by evaluating the influence of DSC heating rate (4, 7, 10, 13 oC/min) on the behavior of the illumination flares. The results as expected showed that the decomposition temperature of the illumination flares decreases with the increase in the DSC heating rate, while thermal decomposition of the sample followed the first-order law. Furthermore, Magnesium-sodium nitrate illumination flares with HTPB resin have been studied for luminous efficiency by varying fuel/oxidizer ratio. The kinetic and thermodynamic parameters of the illumination flares decomposition under ambient pressure were obtained from the resulted DSC data via non-isothermal methods proposed by ASTM E698 and Flynn-Wall-Ozawa. Also, the critical temperature of ignition temperature was estimated at about 455 oC.

Study of Heating Rate Effect on Thermoluminescence Glow Curves of LiF: Mg, Cu, P

The samples of LiF: Mg,Cu,P powder (xeri: GR-200) were irradiated by the gamma radiation resource with varied exposed dose. The glow curves of thermoluminescence (TL) material were observed with the defferent heating rates. The influence of heating rate on the thermoluminescence property of LiF: Mg,Cu,P was analyzed. The results showed that as the heating rate increases, the peak intensity at the maximum decreases and shifts to higher temperature. The thermoluminesecnce sensitivity of the material also changes and has the optimal value at 6oC/s. This value is also adaptable for measurement of natural environmental and archaeologicaldose.

Influence of heating rates on the products of high-temperature pyrolysis of waste wood pellets and biomass model compounds

The effect of heating rates ranging from 5 °C min−1 to 350 °C min−1 on the yields of pyrolysis products of wood and its main pseudo-components (cellulose, hemicellulose and lignin) have been investigated at a temperature of 800 °C in a horizontal fixed bed reactor. Results showed a successive dramatic increase and decrease in gas and liquid yields, respectively, while the yields of solid products showed a gradual decrease as heating rates increased. Increased gas formation and an increasingly aromatic oil/tar support the theory of rapid devolatilization of degradation products with increasing heating rate, leading to extensive cracking of primary pyrolysis vapours. Solid products with coal-like calorific value and large surface areas were obtained. CO became the dominant gas both on a mass and volume basis, at the heating rate of 350 °C min−1 for all samples except xylan, which also produced a significant yield of CO2 (20.3 wt% and 25.4 vol%) compared to the other samples. Cellulose produced a gas product with highest calorific value of 35 MJ kg−1 at the highest heating rate. Results also indicate that the three main pseudo-components of biomass each exert a different influence on the products of high temperature pyrolysis of woody biomass.

Influence of heating rate on the physical and electrochemical properties of mixed metal oxides anodes synthesized by thermal decomposition method applying an ionic liquid

Electrochemical oxidation has been focus of recent study in order to supply the growing demand for environmentally friendly wastewater treatment systems. In that sense, the development of efficient and durable mixed metal oxides (MMO) is a growing research field. Herein we propose a novel thermal decomposition methodology applying ionic liquid (IL) for the synthesis of Ti/Sn50SbxCe50−x anodes (where x = 10, 20, 30 or 40). The different MMOs were synthesized through thermal decomposition applying various heating rates (3, 6 and 9 °C min−1) reaching a calcination temperature of 600 °C. Furthermore, X-ray diffraction, scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and electrolysis measurements were carried out. For the synthesized electrodes it was possible to notice a higher superficial area, porosity and electrochemical conductivity for the Sn50Sb40Ce10 electrode. Additionally, the redox couple Ce+4/Ce+3 was more intensely seen for this electrode which presented the best outcomes for Atrazine electrolysis, promoting a 58% concentration removal after 1 h electrolysis at current density as low as 1 mA cm−2.

Вплив швидкості нагріву і ступеня окиснення вугілля на температуру його займання

Вплив швидкості нагріву і ступеня окиснення вугілля на температуру його займання

The Effect of Si Substitution for SiC on SHS in the Ti–Si–C System

Investigated was the effect of Si substitution for SiC on SHS in the Ti–Si–C system. Starting powders were intermixed to obtain 3Ti–SiC–C and 3Ti–Si–2C green mixtures and then green compacts by uniaxial pressing. The influence of heating rate, reactor temperature, and replacement of SiC by Si was studied by XRD, SEM, and TEM. In combustion products obtained in optimized conditions, Ti3SiC2 was found to be predominant. In comparison with conventional methods, our products obtained in a one-step low-temperature process contained minimal amounts of undesired impurities and required no finishing processes such as chemical purification.