Min Heating Rate Research Articles

Control of the γ-alumina to α-alumina phase transformation for an optimized alumina densification

In this work, we studied the aptitude to sintering green bodies using γ-Al2O3 transition alumina as raw powder. We focused on the influence of the heating rate on densification and microstructural evolution. Phase transformations from transition alumina γ→δ→θ→α-Al2O3 were studied by in situ X-rays diffraction from the ambient to 1200°C. XRD patterns revealed coexistence of various phase transformations during the heating cycle. DTA and dilatometry results showed that low heating rate leads to a significant reduction of the temperature of the α-Al2O3 alumina formation. Around 1190, 1217 and 1240°C were found when using 5, 10 and 20°C/min of heating rate, respectively. The activation energy for θ-Al2O3→α-Al2O3 transformation calculated by Kissinger and JMA equations using dilatometry method were 464.29 and 488.79kJ/mol, respectively and by DTA method were 450.72 and 475.49kJ/mol, respectively. In addition, the sintering of the green bodies with low heating rate promotes the rearrangement of the grains during θ-Al2O3→α-Al2O3 transformation, enhancing the relative density to 95% and preventing the development of a vermicular structure.

Thermal and Catalytic Degradation Kinetics of High-Density Polyethylene Over NaX Nano-Zeolite

Thermal and catalytic pyrolysis of waste plastics in an inert atmosphere has been regarded as a creative method, since pyrolysis can convert plastics waste into hydrocarbons that can be used either as fuels or as a source of chemicals.
 Natural Iraqi kaolin clay was used to synthesis the NaX nano- zeolite by hydrothermal conditions with average particle size equal to 77.63nm.Thermal decomposition kinetics of high-density polyethylene (HDPE) in the absence and presence of catalysts nano NaX Zeolite was investigated. Thermal and catalytic degradation of HDPE was performed using a thermogravimetric analyzer in nitrogen atmosphere under non-isothermal conditions 4, 7 and 10 °C/min heating rates were employed in thermogravimetric analysis (TGA) experiments.
 First-order decomposition reaction was assumed, and for the kinetic analysis Coats and Redfern (CR) method was used. The apparent activation energy (Ea) was evaluated. Results showed that the NaX nano-zeolite decreases the activation energy (Ea) of HDPE pyrolysis further than the thermal pyrolysis.

Production and characterization of bio-oil from the pyrolysis of waste frying oil.

In this present work, the disposal of waste frying oil was explored. The experiment tests were performed under nitrogen (N2) atmosphere at 5°C/min heating rate from the ambient temperature to 500°C. In these operating conditions, the obtained pyrolitic liquid fraction was 76wt% formed by 63.87wt% of crude bio-oil and 12.13wt% of aqueous fraction. The chemical characterization using FTIR, GC, and GC/MS has revealed that the bio-oil is a complex chemical mixture of linear saturated, unsaturated, and cyclic hydrocarbons and oxygenated compounds such as carboxylic acids, ketones, aldehydes, and alcohols. Moreover, the produced bio-oil can be considered as promising fuel with high calorific value (∼39MJ/kg). However, the higher acidity (∼125mg KOH/g sample) and viscosity (9.53cSt at 40°C) limit currently its direct use in engines. Therefore, although several promising results, further investigations are requested to improve the bio-oil quality in order to find an environmentally friendly issue to waste frying oil.

Crystallization kinetics of glass–ceramics prepared from high-carbon ferrochromium slag

Glass-ceramics were successfully prepared from high-carbon ferrochromium slag (HCFS), and the optimum heat-treatment conditions were determined by analysis of the crystallization kinetics. The parent glass is first prepared in five different ratios of HCFS to waste glass (R(H/W)), then heat-treated separately at five heating rates (α) and monitored by DSC. As the value of R(H/W) increases from 0.60 to 1.67, the crystallization activation energy (Ec) decreases from 253.41 to 183.52kJ/mol. The nucleation and crystallization temperatures decrease from 641.7 to 612.2°C, and 822.8–814.7°C, respectively, and both are lower than that of ordinary metallurgy slag. These results indicate that using HCFS to produce glass-ceramics both facilitates its production and saves energy. The crystallization index (n) increases with increasing R(H/W), and when n exceeds 2.32, all of the parent glass samples with different R(H/W) crystallize as bulk crystallization. The crystallization index (n) increases as the heating rate α decreases from 25 to 5°C/min, with a maximum value of n (5.94) observed when α is 5°C/min. These conditions produce the largest aspect ratio and highest density of the crystal grain in the glass-ceramics. Our results show the optimal HCFS-based glass-ceramics were obtained with a R(H/W) of 1.29 and a 5°C/min heating rate; under those conditions, the parent glass nucleates and crystalizes at 627.1 and 820.9°C, respectively.

Non-isothermal pyrolysis of de-oiled microalgal biomass: Kinetics and evolved gas analysis

Non-isothermal (β=5, 10, 20, 35°C/min) pyrolysis of de-oiled microalgal biomass (DMB) of Chlorella variabilis was investigated by TGA-MS (30–900°C, Argon atmosphere) to understand thermal decomposition and evolved gas analysis (EGA). The results showed that three-stage thermal decomposition and three volatilization zone (100–400°C, 400–550°C and 600–750°C) of organic matters during pyrolysis. The highest rate of weight-loss is 8.91%/min at 302°C for 35°C/min heating-rate. Kinetics of pyrolysis were investigated by iso-conversional (KAS, FWO) and model-fitting (Coats-Redfern) method. For Zone-1and3, similar activation energy (Ea) is found in between KAS (α=0.4), FWO (α=0.4) and Avrami–Erofe’ev (n=4) model. Using the best-fitted kinetic model Avrami–Erofe’ev (n=4), Ea values (R2=>0.96) are 171.12 (Zone-1), 404.65 (Zone-2) and 691.42kJ/mol (Zone-3). EGA indicate the abundance of most gases observed consequently between 200–300°C and 400–500°C. The pyrolysis of DMB involved multi-step reaction mechanisms for solid-state reactions having different Ea values.

Valorization of Bambara groundnut shell via intermediate pyrolysis: Products distribution and characterization

This study provides first report on thermochemical conversion of residue from one of the underutilized crops, Bambara groundnut. Shells from two Bambara groundnut landraces KARO and EX-SOKOTO were used. Pyrolysis was conducted in a vertical fixed bed reactor at 500, 550, 600 and 650 °C; 50 °C/min heating rate and 5 L/min nitrogen flow rate. The report gives experimental results on characteristic of the feedstock, impact of temperature on the pyrolysis product distribution (bio-oil, bio-char and non-condensable gas). It evaluates the chemical and physicochemical properties of bio-oil, characteristics of bio-char and composition of the non-condensable gas using standard analytical techniques. KARO shell produced more bio-oil and was maximum at 600 °C (37.21 wt%) compared to EX-SOKOTO with the highest bio-oil yield of 32.79 wt% under the same condition. Two-phase bio-oil (organic and aqueous) was collected and analyzed. The organic phase from both feedstocks was made up of benzene derivatives which can be used as a precursor for quality biofuel production while the aqueous from KARO consisted sugars and other valuable chemicals compared to the aqueous phase from EX-SOKOTO which comprised of acids, ketones, aldehydes and phenols. Characteristics of bio-char and composition of the non-condensable were also determined. The results show that bio-char is rich in carbon and some minerals which can be utilized either as a solid fuel or source of bio-fertilizer. The non-condensable gas was made up of methane, hydrogen, carbon monoxide and carbon dioxide, which can be recycled to the reactor as a carrier gas. This study demonstrated recovery of high quality fuel precursor and other valuable materials from Bambara groundnut shell.

A study on pyrolysis of Canada thistle (Cirsium arvense) with titania based catalysts for bio-fuel production

The catalytic pyrolysis of Cirsium arvense was performed with titania supported catalysts under the operating conditions of 500°C, 40°C/min heating rate, 100mL/min N2 flow rate in a fixed bed reactor for biofuel production. The effect of catalysts on product yields was investigated. The amount of pyrolysis products (bio-char, bio-oil, gas) and the composition of the produced bio-oils were determined by proton nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FT-IR), gas chromatography/mass spectrometry (GC–MS) and elemental analysis (EA) techniques. Thistle bio-oils had lower O/C and H/C molar ratios compared to feedstock. The highest bio-char and bio-oil yields of 29.32wt% and 36.71wt% were obtained in the presence of Ce/TiO2 and Ni/TiO2 catalysts respectively. GC–MS identified 97 different compounds in the bio-oils obtained from thistle pyrolysis. 1H NMR analysis showed that the bio-oils contained ∼55–77% aliphatic and ∼6–19% aromatic structural units.

From woody biomass waste to biocoke: influence of the proportion of different tree components

This paper assesses the feasibility of producing a metallurgical quality charcoal (biocoke) through slow high temperature pyrolysis of woody biomass. The samples used for the experiments were different types of olive wood biomass from southern Spain as well as eucalyptus trunks from Uruguay. The experiments were conducted in a two-step process: a pyrolysis semi-batch reaction at 750 °C and 3 °C/min heating rate, followed by a second step of thermal treatment at 900 °C of the pyrolysis vapours. The type of raw material used plays an important role with respect to the amount and quality of the different pyrolysis products. With the operating conditions used, high solid (24–26 wt%) and gas yields (43–54 wt%) were obtained. The solids obtained (biocoke) fulfil the requirements of good metallurgical reducers. However, leaves and bark are detrimental to biocoke quality and should be avoided. Pyrolysis gases are rich in CO and hydrogen, whereas pyrolysis liquids are mainly composed of water.

Porcelain production by direct sintering

Most of the energy consumed during the processing of porcelains is accounted by the heating rate, dwell time and cooling rate employed. Efforts are made in this study to lower the total energy consumption, and thereby total emissions, by optimizing the porcelain processing parameters. Porcelain samples processed at 5, 15 and 30°C/min heating rates were compared with samples processed under direct sintering. X-ray diffraction and microstructural characterisation confirmed that the phase evolution, such as mullite formation in the porcelain, is heating rate independent while glass formation is heating rate dependent, and directly sintered porcelain had physical and mechanical properties comparable to conventionally heat-treated samples. Direct sintering reduced total processing time by ∼50% and also lowered the sintering temperature from 1200°C to 1175°C, suggesting that the direct sintering method provides benefits meaning it may in future replace conventional porcelain processing.

Influence of calcining temperature on the pozzolanic characteristics of elephant grass ash

The influence of calcining temperature on the pozzolanic properties of elephant grass ash (EGA) for application as a supplementary cementitious material is reported. Five different calcining temperatures were used (ranging from 500 to 900 °C for 3 h at 100 °C increments) after a first calcining step at 350 °C for 3 h, a 10 °C/min heating rate, and a 0.04 constant volumetric ratio between the sample and the internal furnace chamber. After calcining and high energy grinding, all ashes were characterized based on particle size distribution, oxide composition, loss on ignition, B.E.T. specific surface area, X-ray diffraction, and scanning electron microscopy. The pozzolanic behavior was investigated based on pozzolanic activity index test and compressive strength of concretes up to 180 days of curing. An expressive decrease in loss on ignition values and, consequently, increase in silica content of EGA produced at higher temperatures were observed. Overall, the results demonstrated that 600 °C was the most suitable temperature for producing EGA. Additionally, the replacement of 20% (in volume) of cement by 600 °C-calcining EGA did not change significantly the 28-day compressive strength of concrete, and increased the strength after 180 days of curing in relation to a reference concrete.

A TG–FTIR investigation to the co-pyrolysis of oil shale with coal

Thermal characteristics and gas compositions during co-pyrolysis of oil shale with two types of coal, bitumite and lignite, at various blend ratios were investigated using the TG–FTIR coupling technique. The samples were pyrolyzed within the temperature range of 100–950°C at 30°C/min heating rate. The thermal characteristics of oil shale was similar to that of bitumite at the devolatilization stage. The synergetic effect observed during the co-pyrolysis of oil shale with lignite could be attributed to lignite’s high-volatile feature. The optimum proportion of oil shale in the mixture was 50% which led to 1.4% increase in the gas/liquid yield and in the ratio of aromatic C-H/aliphatic C-H in the gaseous products identified by FTIR. Bitumite inhibited the pyrolysis process at the early stage of temperature range from 130°C to 400°C during the co-pyrolysis with lignite. This suppression of bitumite existed in the whole pyrolysis process in the co-pyrolysis with oil shale.

Synthesis and spark plasma sintering of the α-Si3N4 nanopowder

A two-step process (milling and then heat treatment) was used for the preparation of α-Si3N4 nanopowder. The influence of the milling time and heat treatment temperature as processing parameters were investigated on the formation of α-Si3N4. Silicon nitride ceramic was produced by spark plasma sintering at 1700°C for 15min, using MgSiN2 additive. The optimum sample was produced in a 30h milling time, heat treatment at 1300°C, and a 22°C/min heating rate conditions. X-ray fluorescence analysis showed that the purity of the final product is above 98%. Nanoindentation hardness and Young’s modulus of the SPS-ed sample were measured as 17±2.0GPa and 290±11.0GPa, respectively.

Response surface method for optimization of phenolic compounds production by lignin pyrolysis

Lignin pyrolysis has a significant opportunity of producing commodity phenolic chemicals from natural biomass resources or industrial byproducts. Bio-oil production of lignin pyrolysis in a fixed-bed system was systematically characterized by response surface methodology (RSM) to optimize operating variables such as temperature, heating rate, and loading mass. According to the mathematical model of RSM, the predicted maximum bio-oil yield of 30.1% and the actual bio-oil yield of 29.3% were obtained under the optimum condition: 669°C temperature, 15°C/min heating rate, and 6.97g loading mass. Temperature significantly influenced both the yield and the chemical composition of lignin bio-oils because pyrolytic decomposition of lignin consisted of temperature-dependent stepwise reactions. The bio-oil under the optimum condition produced not only the higher yield but also the higher content (43.2%) of the primary product (i.e., 2-methoxyphenol).

Chemical and Thermal Evaluation of Commercial and Medical Grade PEEK Sterilization by Ethylene Oxide

Many polymers have been used as biomaterials due to their physicochemical characteristics and structural versatility. However, usage on the human body requires sterilization in order to prevent microbial contamination and diminish the risk of rejection or inflammation. This study presents the use of thermogravimetric analysis (TGA) as an alternative to monitor the presence of residual ethylene oxide from polymers sterilization processes. This is a simple technique and does not require sample preparation stages which can imply in some ethylene oxide loss. Ethylene oxide has been used to sterilize polymeric biomaterials, but with restrictions in the amount used due to the difficulty in removing the toxic waste after the sterilization procedure. Samples of commercial (PEEKc) and medical (PEEKm) grade poly(ether ether ketone) (PEEK) were manufactured in the form of cylindrical tubes, hygienized and sterilized with ethylene oxide. PEEKs showed no chemical changes, but exhibited thermal changes by TGA, which evidenced weight loss between 100 and 500oC that was attributed to the removal of residual ethylene oxide, so this technique, at a 10oC‧min-1 heating rate, can be used to monitor the sterilization processes.

Optimization of process parameters for spark plasma sintering of nano-structured ferritic Fe-18Cr-2Si alloy

Spark plasma sintering (SPS) process parameters were optimized in terms of densification, microhardness and corrosion resistance to develop a nano-structured Fe-18Cr-2Si ferritic alloy. The powders were mechanically alloyed (MA) in a planetary ball mill and subsequently SPS was carried out under different processing conditions. Powders and sintered samples were characterized using X-Ray Diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD phase evolution studies on ball milled powders confirmed the formation of a crystallized alloy after 100h milling. XRD of sintered alloy confirmed the development of a nano-structured ferritic alloy with a crystallite size in the range of 20–40nm. Maximum densification of 96.0%, Vickers hardness of 710HV and pitting potential (Epit=−430mVSCE) was achieved at a sintering temperature of 1100°C, for 15min holding time, at 50°C/min of heating rate and at an applied pressure of 60MPa.

MBF 20으로 브레이징한 STS304 콤팩트 열교환기 접합부의 미세조직에 미치는 가열속도의 영향

Abstract Effect of heating rate on microstructure of brazed joints with STS 304 Printed Circuit Heat Exchanger (PCHE),which was manufactured as large-scale(1170(L) × 520(W) × 100(T), mm), have been studied to comparebonding phenomenon. The specimens using MBF 20 was bonded at 1080℃ for 1hr with 0.38℃/min and 20℃/min heating rate, respectively. In case of a heating rate of 20℃/min, overflow of filler metal was observedat the edge of a brazed joints showing the height of filler metal was decreased from 100㎛ to 68㎛. At the center of the joints, CrB and high Ni contents of γ-Ni was existed. For the joints brazed at a heating rate of 0.38℃/min, the height of filler was decreased from 100㎛ to 86㎛ showing the overflow of filler was not appeared. At the center of the joints, only γ-Ni was detected gradating the Ni contents from center. This phenomenon was driven from a diffusion amount of Boron in filler metal. With a fast heating rate 20℃/min, diffusion amount of B was so small that liquid state of filler metal and base metal were reacted. But, for a slow heating rate 0.38℃/min, solid state of filler metal due to low diffusion amount of B reacted with base metal as a solid diffusion bonding.Key Words : PCHE (Pring cicuit heat exchanger), Brazing, MBF 20, Boron diffusion, Microstructure.ISSN 2466-2232Online ISSN 2466-2100

Chemical evaluation and kinetics of Siberian, north regions of Russia and Republic of Tatarstan crude oils

ABSTRACTIn this research, thermal characteristics and model free kinetics of five different °American Petroleum Institute gravity crude oil samples from different locations were studied using combustion calorimetry and thermogravimetry (TGA) techniques. Higher heating values of crude oils were determined from the combustion calorimetry experiments. It was shown that these values increase with an increase in saturate fraction and °API gravity of studied samples and decrease with an increase in viscosity, aromatics fraction, and resin fraction of crude oils. In thermogravimetry, experiments were performed at 10, 20, and 30°C/min heating rates under an air atmosphere. Thermal characteristics of the samples such as reaction intervals and corresponding peak temperatures, mass loss, and residue of the crude oil samples were also determined. Two different model free kinetic methods, known as Ozawa–Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS), were used in order to determine the activation energy values of the crude oil samples studied.

Three alternative raw materials for improving the performances of Li4SiO4 pebbles

Currently, Li4SiO4 has been considered one of the best candidates for tritium breeders. In order to improve the crush load and the density of Li4SiO4 pebbles with reasonable pores and small grains for tritium breeding, three alternative raw materials were used for fabricating Li4SiO4 pebbles: the fabrication of Li4SiO4 pebbles from Li2CO3 and SiO2, the fabrication of Li4SiO4 pebbles from Li2CO3 and Li2SiO3 (for the first time), and the fabrication of Li4SiO4 pebbles from Li4SiO4. The Li4SiO4 pebbles were fabricated by a graphite bed process and sintered in Ar with a series of sintering techniques which based on the different reaction paths deduced from the TG-DTA and XRD results. And they were compared particularly with regard to their effects on the crush load and the density. The results show that the optimal crush load, density, and open porosity of the Li4SiO4 pebbles using Li2SiO3 and Li2CO3 as raw materials reached 64.7N, 90.3%, and 9.2%, respectively, at sintering technique i, i.e., two holding temperatures (650 and 750°C) with 5°C/min heating rate.

EFFECT OF DIAMETER AT BREAST HEIGHT OF LEUCAENA LEUCOCEPHALA ON BIO CHAR PRODUCTION IN TUBE FURNACE PYROLYSIS

Renewable energy produced from biomass is a green way to reduce the greenhouse effect. Fast-growing wood species, as the energy source, create independent and fast harvesting cycle for energy fuel stock. The aim of this study was to determine the effect of tree diameter at breast height (DBH) of a local wood species i.e. leucaena leucocephala, on char yield during pyrolysis. The calorific value (CV) of bio char was also determined in order to analyse the bio char product produced by pyrolysis process. The tree samples were classified into three DBH i.e. 4, 8 and 12 cm and only tree stem was selected for pelletization. The wood pellets were pyrolyzed at 300, 400, 500, 600 and 700 °C with 40 °C/min of heating rate and holding time of 30 min in inert condition. The largest difference percentage of bio char yield production is only 1 % while the largest difference of CV is 0.7 MJ/kg which happened at temperature 300 °C. In this study, it was found that any DBH does not give any significant effect to the production of bio char as well as its CV.

Catalytic pyrolysis of microalgae Tetraselmis suecica and characterization study using in situ Synchrotron-based Infrared Microscopy

In this study, the direct and catalytic pyrolysis of microalgae Tetraselmis suecica was conducted to determine the composition of bio-oil obtained. Thermogravimetric analysis showed that at high heating rate, the decomposition temperature and volatile matter evolution increased. Direct pyrolysis results identified the optimum temperature for bio-oil production to be 400°C. The bio-oil produced from catalytic pyrolysis showed a decrease in the oxygenated compounds which indicate that the addition of zeolite catalyst (Si/Al=30, 60) can improve the bio-oil composition. However, zeolite catalyst (Si/Al=30) showed a higher decrease in the oxygenated compounds compared to (Si/Al=60). Furthermore, this study found that some functional groups are still present in the char of T. suecica biomass at 550°C (5°C/min heating rate), while most already disappeared at 350°C (150°C/min heating rate) when using in situ Synchrotron-based Infrared Microscopy.