Effect Of Final Temperature Research Articles

Effect of final temperature and heating rate on the mechanical and optical properties of a zirconia veneering ceramic

PurposeTo evaluate the effect of firing temperature and heating rate on the volumetric shrinkage, translucency, flexural strength, hardness, and fracture toughness of a zirconia veneering ceramic. Material and methodsZirconia veneering ceramic specimens (N = 45) with varying final temperatures (730 °C, 750 °C, and 770 °C) and heating rates (70 °C/min, 55 °C/min, and 40 °C/min) were fabricated (n = 5). Each specimen's shrinkage, translucency, flexural strength, hardness, and fracture toughness were determined. Two-way analysis of variance, Scheffé test, and Pearson's correlation analysis were used to evaluate data (α = 0.05). ResultsThe shrinkage (44.9 ± 3.1–47.5 ± 1.6 vol%) and flexural strength (74.1 ± 17.4–107.0 ± 27.1 MPa) were not affected by tested parameters (P ≥ 0.288). The interaction between the main factors affected the translucency, hardness, and fracture toughness of the specimens (P ≤ 0.007). Specimens with 770 °C final temperature and 70 °C/min heating rate had the lowest (21.8 ± 3.2 %) translucency (P ≤ 0.039). The hardness ranged between 4.98 ± 0.51 GPa (730 °C; 70 °C/min) and 5.60 ± 0.37 GPa (770 °C; 70 °C/min). Fracture toughness ranged between 0.54 ± 0.04 MPa√m and 0.67 ± 0.08 MPa√m with the highest values for specimens fired at 730 °C with 70 °C/min (P ≤ 0.001). There was a positive correlation between translucency and hardness (r = 0.335, P = 0.012), and a negative correlation between fracture toughness and all parameters other than shrinkage (translucency: r = −0.693/P < 0.001, flexural strength: r = −0.258/P = 0.046, hardness: r = −0.457/P < 0.001). ConclusionsHeating rate and final temperature should be considered while fabricating veneered zirconia restorations with tested ceramic as they affected the translucency, hardness, and fracture toughness.

Experimental Investigation on the Pore Structure Evolution of Coal in Underground Coal Gasification Process

Underground coal gasification (UCG) has been shown to be a promising method for deep coal resources. A series of complicated chemical reactions can induce a considerable change in the pore structure of coal and thus promote the UCG process in turn. Currently, most studies on the effect of elevated temperature on the pore structure of coal were not involved in an air atmosphere, bringing a series of difficulties to understanding the pore structure evolution of gasified coal in the UCG process. The objective of this work was to investigate the pore structure evolution of coal heated in nitrogen and air atmospheres at elevated temperatures. Thermogravimetry tests were first conducted to gasify coal samples, and then, the method scanning electron microscopy was used to observe the microscopic morphology of the pore structure. Besides, the effect of final temperature, atmosphere, pressure, and residence time on the thermal dynamics of coal at elevated temperatures was comprehensively discussed. Results indicated that the temperature range of a heating process of coal can be classified into three stages, 25–320 °C, 320–750 °C, and 750–1000 °C. For the three temperature ranges, drying, primary pyrolysis, and secondary pyrolysis can dominate, respectively, under a nitrogen atmosphere, while the combustion and gasification process will prevail at a high temperature under an air atmosphere. Because of mass loss, the coal was becoming porous during the heating process. Compared with the intact structure of coal when the temperature is lower than 300 °C, the pore space can interconnect under moderate-temperature conditions (500 °C) like a honeycomb, and then, only an ash framework remained under a higher-temperature condition (700 °C) under an air atmosphere. In comparison, the coal heated in a nitrogen atmosphere can gradually turn into a porous char. This investigation can provide some new insights into the pore structure evolution of gasified coal and contribute to the mechanisms of a UCG process.

Improved mesophilic anaerobic digestion of swine wastewater by ammonia stripping with microwave irradiation

ABSTRACT Ammonia (NH3) stripping by microwave irradiation was used to increase the efficiency of anaerobic digestion. The effects of final temperature (FT) (80 ≤ FT ≤ 100°C) and microwave irradiation time (MIT) (2.5 ≤ MIT ≤ 5.5 min) of NH3 stripping, and hydraulic retention time (HRT) (7 ≤ HRT ≤ 20 d) in anaerobic digester were quantified. NH3 concentration decreased from 2794 to 140 mg/L within 5.5 min at FT = 100°C. The highest cumulative biogas production (>1800 mL/L) and efficiency of volatile solid removal (> 68%) were achieved at FT = 100°C and MIT = 5.5 min. The removal efficiency of volatile solid in digesters fed with untreated swine wastewater (control) and swine wastewater treated by NH3 stripping decreased as HRT decreased. The highest relative improvement of properties compared to the control occurred at 10 or 15 d HRT. Increases in biogas production compared to the control increased with the NH3 stripping as HRT was reduced to 10 d (243% higher at 10 d). The methane content of the produced biogas was 64–69% for control and 68–75% with NH3 stripping in the range of 10–20 d HRT. NH3 stripping using microwave irradiation is an effective pretreatment to improve the anaerobic digestion of swine wastewater.

Slow pyrolysis of coconut wood (Cocos nucifera L.) and bio-char compositions

Biomass in the form of coconut wood (Cocos nucifera L.) was pyrolysed in an externally heated batch reactor. In order to determine the lignin, cellulose and hemicellulose content was used a Van Soest method as reference method. The effects of final temperature and heating rate on the yields and compositions of the bio-char were investigated. Pyrolysis runs were performed using reactor temperatures were 375 °C, 475 °C and 575 °C with heating rates of 5 min−1, 10 min−1 and 20 min−1. The bio-char yields were significantly influenced by the process conditions. The result showed that the bio-char mass decreased with increasing the final temperature, but increased with the increase of heating rate. The activation energy increases with increasing final temperature and heating rate. While the highest activation energy was 38.89 kJ mol−1 and the obtained on bio-char product amounted to 6858.84 cal/g at the final temperature 575 °C and heating rate 5 min−1. It was characterized by Fourier transform infrared spectroscopy. This study showed that FTIR spectra have the potential to be an important source of information for a quick evaluation of the chemical composition of coconut wood (Cocos nucifera L.).

Hydrothermal Liquefaction of Rice Straw Using Methanol as Co-Solvent

Hydrothermal liquefaction (HTL) is a promising thermochemical process to treat wet feedstocks and convert them to chemicals and fuels. In this study, the effects of final temperature (300, 325, and 350 °C), reaction time (30 and 60 min), rice-straw-to-water ratio (1:1, 1:5, 1:10, and 1:15 (wt./wt.)), methanol-to-water ratio (0:100, 25:75, 50:50, and 75:25 (vol.%/vol.%)), and alkali catalysts (KOH, NaOH, and K2CO3) on product yields, composition of bio-crude, higher heating value (HHV) of bio-crude and bio-char, and energy recovery on HTL of rice straw are investigated. At the optimal processing condition corresponding to the final temperature of 300 °C, 60 min reaction time, and rice-straw-to-water ratio of 1:10 at a final pressure of 18 MPa, the bio-crude yield was 12.3 wt.% with low oxygen content (14.2 wt.%), high HHV (35.3 MJ/kg), and good energy recovery (36%). The addition of methanol as co-solvent to water at 50:50 vol.%/vol.% improved the yield of bio-crude up to 36.8 wt.%. The selectivity to phenolic compounds was high (49%–58%) when only water was used as the solvent, while the addition of methanol reduced the selectivity to phenolics (13%–22%), and improved the selectivity to methyl esters (51%–73%), possibly due to esterification reactions. The addition of KOH further improved the yield of bio-crude to 40 wt.% in an equal composition of methanol:water at the optimal condition. The energy-consumption ratio was less than unity for the methanol and catalyst system, suggesting that the process is energetically feasible in the presence of a co-solvent.

Effect of final temperature on charcoal stiffness and its correlation with wood density and hardness

Mechanical performance is important for charcoal used in blast furnaces as charcoal layers may support the load of iron ore within blast furnaces without breaking. Pyrolysis temperature influences charcoal quality and its chemical composition; however, the effect of temperature on physical-mechanical properties is still unknown. Thus, the aim of this study was to establish the effect of pyrolysis temperature on the density, stiffness and hardness of charcoal and the correlations among them. Four pyrolysis processes were performed at final temperatures of 300, 450, 600 and 750 °C using wood specimens from nine different tree species. Stiffness of wood and charcoal was determined by ultrasound and dynamic hardness by a portable hardness tester. In short, density, dynamic hardness and stiffness of charcoal tend to decrease with increasing temperature. Pyrolysis at 450 °C decreases charcoal stiffness by approximately 30%, while hardness is reduced from 29 MPa in wood specimens to approximately 3 MPa in charcoal pieces produced from the same specimens. Considering the wood, the highest values of stiffness were presented by the same materials which presented highest density, confirming high positive correlation between wood properties. The correlation between density and stiffness in charcoal is higher than in wood. However, correlation between density and dynamic hardness or stiffness and dynamic hardness is higher for wood than for charcoal. Ultrasound was able to determine differences in stiffness between the materials at different pyrolysis temperatures. These findings are useful to identify the best production temperature for industrial charcoal with adequate mechanical properties.

Effect of processing parameters on the grain refinement of vanadium nitrogen microalloyed steel

AbstractThe effect of processing parameters on the grain refinement of vanadium nitrogen microalloyed steel was investigated by performing hot deformation tests. The interaction between static recrystallization and precipitation was analyzed and the effect of final temperature, cooling rate and holding time on the microstructure of the tested steel is discussed. The results showed that smaller ferrite grains could be obtained with lower temperature or higher cooling rate. It was found that carbonitrides could precipitate at temperatures around 850 °C, which could retard recrystallization. The precipitated particles could inhibit grain growth and promote ferrite nucleation, which leads to ferrite grain refinement. Therefore, fine ferrite grains could be obtained by performing multi-pass compression testing at this specific finishing temperature followed by appropriate holding.

Temperature Effect of Hot Rolling Process on Microstructure, Strength and Fracture Toughness of X65 Pipeline Steel

The present work investigates the effect of final temperature of hot rolling process on strength and fracture toughness of API X65 pipeline steel. It has been shown that decreasing the finish rolling temperature from 900 to 800 °C in non-recrystallization region causes a decrease in ferrite grain size by about 16% and change the morphology of ferrite microstructure in non-recrystallization region from polygonal ferrite to quasi-polygonal ferrite. It has been found after measuring the fracture toughness parameter (JIC) for two samples hot rolled in non-recrystallization and dual-phase (α + γ) regions that fracture toughness value of 158 kJ/m2 is reduced by 25% to 118 kJ/m2 due to the probability of proeutectoid ferrite generation in microstructure during rolling in dual-phase region which reduces flexibility and facilitates the crack growth. The results of fatigue crack growth test and da/dN–Δk curve indicate that the fatigue crack growth rate in the dual-phase region of hot-rolled steel is higher than that in the non-recrystallization region due to the inhomogeneity of microstructure and lower fracture toughness.

Thermal Degradation and Microwave-Assisted Pyrolysis of Green Algae and Cyanobacteria Isolated from the Great Salt Plains

Seven algae strains isolated from the Great Salt Plains of Oklahoma (UTEX SP20, SP22, SP38, SP46, SP47, SP48, and SP50) were examined in this study. Biomass thermal degradation behavior of each strain was evaluated by thermogravimetric analysis. Kinetic parameters were determined using an iso-conversional approach. Algal biomass was used for bio-oil production via microwave-assisted pyrolysis, and the effects of final temperature on product yields and bio-oil composition were evaluated. Thermogravimetric analyses revealed that pyrolysis of algal biomass took place in three stages, with major weight loss occurring at the second stage from around 150°C to 400°C. Biomass of SP38 had the lowest average apparent activation energy (102.8 kJ mol-1), indicating that biomass of SP38 requires the least energy for pyrolysis among the seven strains. SP46 was selected out of the seven strains for microwave-assisted pyrolysis because of its high final biomass concentration and biomass productivity. As the final temperature increased from 450°C to 750°C, the bio-oil yield increased from 4.6% to 22.5% during microwave-assisted pyrolysis of biomass generated by SP46. The major compounds in the bio-oil were acids, aliphatic hydrocarbons, aromatic hydrocarbons, phenols, and organic nitrogen compounds. Microwave-assisted pyrolysis of algal biomass did not produce polycyclic aromatic hydrocarbons at temperatures higher than 450°C.

Conventional heating vs. microwave sludge pretreatment comparison under identical heating/cooling profiles for thermophilic advanced anaerobic digestion

This research evaluates whether there is any advantage of selecting one of the thermal methods of sludge pretreatment, conventional heating (CH) and microwave hydrolysis (MW), over another to enhance municipal sludge disintegration and performance of thermophilic anaerobic digestion (AD). For this purpose, a custom-built CH system simulating MW hydrolysis under identical heating and cooling profiles was used. The effects of three main pretreatment parameters including pretreatment method (CH and MW), heating ramp rate (3, 6 and 11°C/min) and final temperature (80, 120 and 160°C) on sludge solubilization and performance of thermophilic batch AD were evaluated. The effects of CH and MW hydrolysis were observed to be similar for sludge disintegration and digester performance (p-value>0.05), while the effects of final temperature and heating ramp rate were proven to be different (p-value<0.05). According to the results, it is essential to apply MW and CH pretreatments under identical experimental condition for an unbiased comparison which supports the findings of the author’s earlier study under mesophilic condition. Failing to address this issue explains the significant inconsistency observed among the findings of the previous CH vs. MW comparison studies that were unable to implement identical thermal profiles (between CH and MW) during sludge pretreatment. In comparison with mesophilic AD, thermophilic AD revealed lower biodegradation rate constant at the highest pretreatment temperature tested (160°C), suggesting its higher sensitivity to the inhibitory effects of thermal pretreatment at the elevated temperatures.

Mathematical modelling of slow pyrolysis of segregated solid wastes in a packed-bed pyrolyser

Waste segregation is being explored as one of the potential effective ways for waste management, where wastes are separated for either recycling or energy recovery. In this paper, three segregated wastes, contaminated waste wood, cardboard and waste textile are pyrolysed in a slow-heating packed-bed reactor for the purpose of solid, liquid and gas recovery. The effect of final temperature was investigated and product yields and compositions were measured. Mathematical modelling was employed to simulate the heat, mass transfer and kinetic processes inside the reactor. Both a parallel reaction model and a function group model were used to predict the product yields as well as their compositions. Char yield of 21–34%, tar 34–46% and gas 23–43% were obtained. It is found that packed-bed pyrolysis produces 30–100% more char compared to standard TGA tests and the local heating rate across the packed-bed reactor differs remarkably from the programmed wall-heating rate and varies greatly in both time and space. Mathematical modelling suggests that wood has higher tar cracking ability than cardboard and textile wastes during pyrolysis, and the effects of mineral contents in the fuel need to be explored. CO 2, CO, tar and water are the main released species during the major stage of the pyrolysis processes which occurs between 250 and 450 °C, whereas noticeable quantity of hydrogen and light hydrocarbons is observed only at higher temperature levels and at the final stage.

Pyrolysis of a Turkish lignite at high heating rates

The products of pyrolysis of Tunçbilek lignite at high heating rates were investigated using the Curie-point technique. The effects of final temperature and pressure are discussed.