Effect Of Heating Rate Research Articles

Effect of heating rate on crystallisation and properties of R2O–CaO–MgO–CuO–Al2O3–SiO2 glass-ceramics

R2O–CaO–MgO–CuO–Al2O3–SiO2 (RNa, K) glass-ceramics were fabricated using the melt-quenching method and the effect of heating rate on the microstructure and properties of the glass-ceramics was investigated. The results demonstrated that the main crystal phase of the samples was clinoenstatite, and the secondary crystal phases were forsterite and diopside. With an increase in heating rate, the diffraction peak intensity of clinoenstatite gradually increased, and the morphology of the particles changed from short columns to long needles. When the heating rate was 1 °C/min, the sample exhibited flexural strength and Vickers hardness of 7.38 GPa and 84.33 MPa, respectively. When the heating rate was 10 °C/min, the Cu+ content in the sample reached the maximum of 2.1 wt%, which is 1.4 times of Cu+ in the brown sample obtained by heat-treatment at 1 °C/min. The colour of the sample intensified as the heating rate was increased from 1 °C/min to 20 °C/min, and the sample heated at 10 °C/min was brownish-red. The heating rate has a significant effect on the colour of glass-ceramics with the same CuO content, providing a new approach for regulating the colour of glass-ceramics. Further, this study has significant prospects in enriching the colour of glass-ceramics for architectural decoration and reducing production costs.

Effects of Different Heating and Cooling Rates during Solution Treatment on Microstructure and Properties of AA7050 Alloy Wires.

In the present study, the effects of varying heating and cooling rates during the solution treatment process on the microstructure and properties of AA7050 alloy wires were investigated using tensile tests, metallographic microscopy, electron backscattered diffraction, and transmission electron microscopy. It was found that the recrystallized grain size of the alloy, subjected to method of rapid heating, exhibited a smaller and more uniform distribution in comparison to method of slow heating. The low density of η' strengthening phases after the artificial aging treatment was formed using air cooling method. Meanwhile, by using the water quenching method sufficient solute atoms and more nucleation sites were provided resulting in a large number of η' strengthening phases being formed. In addition, the alloy processed using the water quenching method displayed higher strength than that treated using the air cooling method for the T6 and T73 states. Furthermore, coarse precipitates formed and less clusters were observed in the matrix, while high density nanoscale clusters and no continuous precipitation are formed when using the water quenching method.

Physical and Mechanical Properties and Damage Mechanism of Sandstone at High Temperatures

The physical and mechanical properties of rocks change significantly after being subjected to high temperatures, which poses safety hazards to underground projects such as coal underground gasification. In order to investigate the effect of temperature on the macroscopic and microscopic properties of rocks, this paper has taken sandstone as the research object and conducted uniaxial compression tests on sandstone specimens at different temperatures (20–1000 °C) and different heating rates (5–30 °C/min). At the same time, the acoustic emission (AE) test system was used to observe the acoustic emission characteristics of the rock damage process, and the microstructural changes after high temperature were analyzed with the help of a scanning electron microscope (SEM). The test results show that the effect of temperature on sandstone is mainly divided into three stages: Stage I (20–500 °C) is the strengthening zone, the evaporation of water and the contraction of primary fissures, and sandstone densification is enhanced. In particular, the compressive strength and elastic modulus increase, the macroscopic damage mode is dominated by shear damage, and the fracture micromorphology is mainly brittle fracture. Stage II (500–600 °C) is the transition zone, 500 °C is the threshold temperature for the compressive strength and modulus of elasticity, and the damage mode changes from shear to cleavage damage, and the sandstone undergoes brittle–ductile transition in this temperature interval. Stage III is the physicochemical deterioration stage. The changes in the physical and chemical properties make the sandstone compressive strength and modulus of elasticity continue to decline, the macroscopic damage mode is mainly dominated by cleavage damage, and the fracture microscopic morphology is of a more toughness fracture. The effect of different heating rates on the mechanical properties of sandstone was further studied, and it was found that the mechanical properties of the rock further deteriorated under higher heating rates.

Coal gangue‐based ceramics foams by water spray granulation and post particle stacking method

AbstractFoamed ceramics were prepared by the water spray granulation and post particle stacking method using coal gangue as the main raw material. The effects of raw material weight ratio (i.e., raw material composition by varying the content of dolomite and talc), calcination temperature, time, and heating rate on the pore structure and properties of the samples were investigated and the foaming mechanism of foamed ceramics was revealed. The crystalline phase of foamed ceramics mainly consisted of quartz, anorthite, and enstatite. The decrease of dolomite content and the increase of talc content in the raw materials led to the initial decrease and then increase of the pore size dispersion coefficient, while the apparent porosity and water absorption of the samples gradually decreased, and the apparent density increased. The sample with a composition of gangue:waste glass:dolomite:albite:talc of 65:5:10:10:10 and calcined at 1200°C for 10 min with a heating rate of 1°C/min has the optimized uniform pore structure. This study provides a high value‐added utilization of coal gangue, and the experimental basis for the preparation of low‐cost foamed ceramics.

Modeling initiation and propagation of thermal runaway in pouch Li-ion battery cells: Effects of heating rate and state-of-charge

The implementation of lithium-ion batteries (LIB) in battery energy storage systems (BESS) for utility-scale renewable energy generation has led to increased fire and explosion hazards. These hazards are attributable to the heat and flammable gases released during LIB thermal runaway (TR). TR can be triggered within an individual LIB cell and cause intra-cell TR propagation (TRP), the energy release from which causes TR in adjacent cells, leading to inter-cell TRP. Safety assessments are critical to preventing such incidents, and numerical modeling is a key tool in developing such assessments. This work presents an inverse modeling approach utilizing measurements of cell-level experiments of large-format 63Ah pouch cells used in BESS. Such an approach is a practical alternative to existing approaches that rely on a detailed thermochemical characterization of LIB internal components which are seldom available when dealing with commercial batteries encountered in BESS. Owing to the critical role played by gas and solid venting for external flaming and inter-cell TRP, we develop an approach to capture these quantities in the model. Two key parameters affecting TRP are the state-of-charge (SOC) and heating rate. The former provides some control of the system hazard, the latter affects TR behavior of LIB cells subject to different levels of preheating often encountered in BESS fires. We develop the capability to capture the effects of these parameters in the model. To determine model parameters, we rely on existing single-cell experimental data at different heating rates, and augment this with new experiments for the same type of cells at different SOCs. The modeling results recover the experimental TR and intra-cell TRP behavior quantitatively. Analysis reveals that, at lower heating rates, the temperature is greater at the time of the onset of TR, but the location is farther away from the heated cell surface; its location and the greater internal temperature then facilitate faster intra-cell TRP. When SOC is lower, the reduced internal heat release delays the onset of TR, and we find that its location moves away from the heated surface and intra-cell TRP is slower. Our findings provide physical insights to TR initiation and intra-cell propagation in support of large-scale TRP model development.

Preparation and characterization of palladium nanoparticle-embedded carbon nanofiber membranes via electrospinning and carbonization strategy.

Carbon nanofiber membranes (CNMs) are expected to be used in many energy devices to improve the reaction rate. In this paper, CNMs embedded with palladium nanoparticles (Pd-CNMs) were prepared by electrospinning and carbonization using polyimide as the raw material. The effects of carbonization temperature, carbonization atmosphere, and heating rate on the physicochemical properties of the as-obtained Pd-CNMs were studied in detail. On this basis, the electrocatalytic performance of Pd-CNMs prepared under optimal conditions was characterized. The results showed that highly active zero-valent palladium nanoparticles with uniform particle size could be distributed on the surface of carbon nanofibers. Under vacuum conditions, at a carbonization temperature of 800 °C and a heating rate of 2 °C min-1, Pd-CNMs have lower H2O2 yield, lower Tafel slope (73.3 mV dec-1), higher electron transfer number (∼4), and superior durability, suggesting that Pd-CNMs exhibit excellent electrocatalytic activity for ORR in alkaline electrolyte. Therefore, polyimide-derived CNMs embedded with Pd nanoparticles are expected to become an excellent cathode catalyst layer for fuel cells.

Transformation study and characterization of Cu-BTC MOF-derived nanoporous copper oxide.

This study provides a systematic and comprehensive investigation of the transformation process of copper-based metal-organic frameworks (Cu-BTC MOFs) into nanoporous copper oxides (P-CuOx) through controlled calcination. While calcination is a well-established method for producing MOF-derived oxides, previous studies have primarily focused on their applications. Most of them often lack detailed exploration of the transformation process and decomposition mechanisms though it is crucial for achieving tunability in MOF-derived structures. Our study addresses this gap by offering valuable insights that can guide the production of various MOF-derived oxides with tunable structural and functional properties. In this report, we have meticulously analysed the combined effects of calcination parameters, including temperature (250-500 °C), heating rate (0.5-10 °C min-1), and duration (1 and 2 hours) on the phase transformation, morphological features, and optical properties of Cu-BTC during its transformation to P-CuOx. Results revealed that fine adjustments to these calcination parameters allow precise control over phase purity, surface area, and porosity, achieving a high surface area of 113 m2 g-1 for derived P-CuO. Furthermore, the P-CuOx materials exhibited strong visible-light absorption, highlighting their potential for solar energy harvesting applications. This approach opens opportunities for designing advanced materials with customized performance characteristics. The findings have broad applicability and enable the research community to fully exploit MOF-derived oxides for designing advanced materials with customized properties for diverse applications, including energy, sensing, and biomedical.

Synthesis of value-added aromatic chemicals from catalytic pyrolysis of waste wind turbine blades and their kinetic analysis using artificial neural network

This research aims to convert the resin fraction of waste wind turbine blades (WTB) into value-added aromatic chemicals using catalytic pyrolysis. The catalytic study on WTB made of glass fibre/unsaturated polyester resin (UPR) was performed on two different types of zeolite catalysts (ZSM-5 and Y-type) using a thermogravimetric (TG) analyser. The effect of catalyst and heating rate on the abundance and composition of the synthesised aromatic chemicals was observed using TG-FTIR and GC/MS. The kinetics and thermodynamic behaviour of catalytic pyrolysis of WTB was also studied using traditional modelling techniques (KAS, FWO, Friedman, Vyazovkin, and Cai) and an artificial neural network (ANN). TG-FTIR results showed that the gases released from the catalytic process were very rich in aromatic groups, while GC/MS analysis revealed that benzene, toluene, and ethylbenzene (BTE) were the main constituents of the synthesised aromatic chemicals with abundance estimated at 36% (ZSM-5 at 10°C/min) and 64% (Y-type at 15°C/min) accompanied by a significant reduction in styrene formation up to 16.2% (main toxic element in the UPR). Besides, it contributed to reduction of the activation energy of the reaction up to 126 KJ/mol (ZSM-5) and 100 KJ/mol (Y-type). The trained ANN model also showed high performance in predicting the thermal decomposition zones of WTB at unknown heating rates with R2 close to 1. Accordingly, the use of catalytic pyrolysis of WTB over a Y-type zeolite catalyst is highly recommended for decomposition of UPR to aromatic chemicals BTE and reduction of styrene in the produced fuel.

Micropollutants in biochar produced from sewage sludge: A systematic review on the impact of pyrolysis operating conditions

Biochar obtained from sewage sludge serves as a valuable soil amendment in agriculture, enhancing soil properties by increasing the nutrient content, cation exchange capacity, water retention, and oxygen transmission. However, its utilisation is hampered by the presence of micropollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOCs). Previous studies indicate that the type and amount of micropollutants can be significantly adjusted by selecting the right process parameters. This literature review provides an overview of how (1) pyrolysis temperature, (2) carrier gas flow and type, (3) heating rate, and (4) residence time affect the concentration of micropollutants in biochar produced from sewage sludge. The micropollutants targeted are those listed by the European Biochar Certificate (EBC) and by the International Biochar Institution (IBI), including PAHs, PCDD/Fs, PCBs and VOCs. In addition, per- and poly-fluoroalkyl substances (PFAS) are also considered due to their presence in sewage sludge.The findings suggest that higher pyrolysis temperatures reduce micropollutant levels. Moreover, the injection of a carrier gas (N2 or CO2) during the pyrolysis and cooling processes effectively lowers PAHs and PCDD/Fs, by reducing the contact of biochar with oxygen, which is crucial in mitigating micropollutants. Nevertheless, limited available data impedes an assessment of the impact of these parameters on PFAS in biochar. In addition, further research is essential to understand the effects of carrier gas type, heating rate, and residence time in order to determine the optimal pyrolysis process parameters for generating clean biochar.

Research on the Combustion Performance of Municipal Solid Waste in Different Sorting Scenarios: Thermokinetics Investigation via TG-DSC-FTIR-MS.

Waste sorting is regarded as one of the most important strategies for municipal solid waste (MSW) management. The changes in the combustion parameters after MSW sorting had a significant impact on the actual operation of the boiler. In the present study, the effects of heating rate on combustion characteristics and dynamics of MSW in different sorting scenarios were studied using the thermogravimetry (TG)-differential scanning calorimetry (DSC)-Fourier transform infrared (FTIR)-mass spectrometry (MS) technique. TG-DSC analysis showed that the heat released from MSW combustion at different heating rates ranged from 1394.1 to 4130.1 J/g. According to the TG-DTG curves, the combustibility of 30% sorted MSW was increased by 1.2 times compared to that of the unsorted scenario. In the 30% sorted scenario, the average activation energies were estimated to be 161.24 and 159.93 kJ/mol based on the Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods, respectively. Based on the Coats-Redfern (CR) method, the minimum activation energies for unsorted and 20% sorted scenarios were 148.74 and 135.53 kJ/mol at 523 to 606 K, respectively, while they were 29.42 and 33.22 kJ/mol at 606 to 780 K. XRF analysis showed that the alkali and alkaline earth metal oxides in the ash contributed to a high risk of slagging and scaling. This work can provide a scientific basis for the real situation of MSW incineration.

Crosslinking and pyrolysis of a methyl-silsesquioxane: Effect of heating rate on fabrication of polymer derived mullite ceramics using thermoplastic shaping

Poly-silsesquioxanes have been numerously used to produce SiO2 or SixOyCz ceramics through pyrolysis under different atmospheres. In this study, crosslinking and pyrolysis behavior of a commercial methyl-silsesquioxane, was examined using thermogravimetry analysis and a lower SiO2 yield was observed after pyrolysis at low heating rates of 0.3 and 0.6 K/min under air atmosphere, namely 69.1 and 75.0 wt%, respectively. Using ceramic thermoplastic shaping techniques, a low heating rate, below 2 K/min, is usually required to remove processing additive (e.g., binders) gradually and avoid failures like blisters, pores, and cracks. A mixture of SILRES® MK and γ-Al2O3 was prepared to produce a mullite ceramic with Al2O3/ SiO2 ratio of 60/40 wt%. As expected, the stoichiometric ratio of alumina to silica was altered using a heating rate of 0.6 K/min and mullite ceramic with 61.70/37.70 wt% of Al2O3/ SiO2 ratio was obtained. By mixing above the crosslinking temperature of SILRES® MK, a constant ratio of alumina to silica could be achieved successfully, even at low heating rates. In addition, microstructure indicated the growth of needle-like mullite crystals with some amount of SiO2-rich ternary amorphous phase (MgO–Al2O3–SiO2) between the needle grains. Elemental analysis revealed that MgO sintering additive was mainly in the amorphous SiO2-rich phase.

Biochar gasification: Insights from pyrolysis atmospheres and gasification heating rates

Gasification is a promising technology for the synthesis of syngas and hydrogen, with char reactivity being a pivotal factor in the design of industrial gasifiers. Despite extensive studies on the gasification characteristics of biochar, the influence of the pyrolysis atmospheres on the evolution of biochar pore structure and its reactivity in gasification remains poorly understood. This study aims to bridge this gap by comprehensively investigating the effects of char preparation atmospheres (i.e., CO2, H2O, and N2) on ensuring gasification reactivities at varied heating rates. Biochars were synthesized in a horizontal tube furnace at 700 °C with a low heating rate (10 °C min−1) under three different atmospheres: N2, CO2, and H2O. Subsequent gasification reactivities were investigated using i) a thermogravimetric analyzer (TGA) at a low heating rate (10 °C min−1) and ii) a wire mesh reactor (WMR) at a high heating rate (1000 °C s−1), both under CO2 atmosphere at 950 °C. The results showed that the presence of an active atmosphere (CO2 and H2O) during pyrolysis significantly impacts the biochar’s aromaticity, crystalline structure, and surface morphology. The functional group concentration and surface area trends indicated that CO2 and H2O atmospheres during pyrolysis enhance biochar reactivity compared to the N2 atmosphere, with the highest reactivity observed for biochars produced under H2O. Furthermore, biochar gasification reactivity was markedly higher using the WMR compared to TGA, underscoring the pronounced effects of heating rate on gasification behavior. The high heating rate in WMR preserved the biochar’s porous and amorphous structure, whereas the TGA gasification encountered diffusional limitations and thermal annealing effects. These insights underscore the need to consider pyrolysis atmosphere and heating rate in gasification studies, offering a more comprehensive understanding of biochar’s behavior under practical gasification conditions.

The Effect of Carbonisation Heating Rates on the Properties of N-Doped Teak Sawdust Waste Activated Carbon

Biomass can be utilised in place of non-renewable raw resources like coal and petroleum residue in the production of activated carbon. Each biomass, however, requires different manufacturing process parameters to obtain the desired activated carbon characteristics due to their different chemical compositions. This study aims to examine the effects of carbonisation heating rates (8°C/min, 10°C/min and 12°C/min) on the characteristics of teak sawdust-derived activated carbon. Furthermore, finding the proper carbonisation heating rate to provide the optimum characteristics is the originality of this study. Activation was carried out at a temperature of 600°C, and simultaneously, 200 mL/min of nitrogen was doped. Thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and adsorption isotherm tests were performed as part of the characterisation. The results revealed that activated carbon carbonised at a rate of 10°C/min produced the best properties. This activated carbon contained 10.8% moisture, 15.26% volatile, 1.73% ash and 72.43% fixed carbon. The majority of the structure is mesopore, with an average pore diameter of 2.43 nm, a pore volume of 0.369 cm3 /g and a specific surface area of 409.698 m2 /g. Its ability to adsorb nitrogen was 239.102 cm3 /g. The successful production of activated carbon from biomass waste derived from teak sawdust offers hope for untapped sawdust waste and has the potential to be used in a number of applications that need adsorption mechanisms.

Effect of Heating Rate on the Annealing Behavior of Aluminium Alloys

This contribution presents a study on the effect of heating rate maintained during annealing treatment on the final microstructure and mechanical properties of cold rolled Al1050 sheet. This study is focused on microstructure and texture evolution of Al1050 annealed at various heating rates, annealing temperatures, and holding times. It was observed that the longer exposure time for deformed microstructure affects the Vickers hardness values, grain size, and texture intensity. It seems that the crystallographic texture evolution is not affected by heating rate on quantitative level since the same set of orientations tended to evolve in all studied cases. The sample annealed at slow heating rate in a box-type furnace produced recrystallized microstructure with fine grain size, and comparatively lower texture intensity & hardness.

A numerical model to prevent the thermal degradation of CFRPs at extreme heating rates – The laser processing of CF/PEEK

This study proposes a coupled thermal-chemical numerical model for preventing the thermal degradation of carbon fibre (CF) reinforced polymers at extreme heating rates. Its applicability is demonstrated in a laser-heating case study of CF-reinforced poly-ether-ether-ketone (CF/PEEK). The kinetic parameters of the PEEK matrix, derived from thermogravimetric analysis at conventional heating rates, are introduced in the model and an extrapolation approach is applied to investigate the laser heating of CF/PEEK. The results show that the model captures the heating rate effect on the decomposition of the material, and is used to identify the processing conditions that can reach high temperatures without triggering the thermal degradation mechanisms of the PEEK matrix. Then, a multi-technique experimental investigation takes place to identify the processing conditions that first trigger the thermal degradation mechanisms of CF/PEEK in the examined laser-heating case study. Interestingly, a good agreement is found between the experimental and numerical investigations which validates the model and the applied extrapolation approach.

Study on induction healing properties of OGFC asphalt mixture with high elasticity and high viscosity modifier

Induction healing is a promising preventive maintenance method of asphalt pavement, but the healing properties of Open-Graded Friction Course (OGFC) asphalt mixture with high elasticity and high viscosity modifier (HEV) were not clear. OGFC asphalt mixture used for induction heating was prepared by adding steel wool fibers and HEV. The effects of HEV and steel wool on the properties of OGFC mixture were studied. The particle loss resistance, water stability, porosity, induction heating and self-healing properties of OGFC-13 asphalt mixture with different steel wool contents were measured. The results showed that HEV slightly improved the properties of resistance to particle loss, fracture strength and water stability of OGFC-13 asphalt mixture, had little effect on the induction heating rate and porosity, but reduced the healing rate by 10%. The addition of steel wool to OGFC-13 can enhance the particle loss resistance, heating rate and healing effect, and the optimal dosage is 8% of the volume fraction of bituminous binder. The healing rate rose steadily as the heating temperature increased. At the optimal healing temperature of 110 ℃, healing depth ratios of the mixtures without and with HEV were 56.3% and 43%, respectively, and the fracture energy healing rates were 72.4% and 63.1%, both at a high healing level. The incorporation of steel fibers and HEV reduced the porosity and water permeability of OGFC very slightly, and the porosity and water permeability of OGFC did not change significantly after induction heating. It is concluded that induction heating has a potential to heal the cracks within OGFC mixture with HEV to prevent surface raveling which is the primary damage of OGFC.

Thermochemical conversion of neem seed biomass to sustainable hydrogen and biofuels: Experimental and theoretical evaluation

This study aims to investigate the potential of neem seeds as a renewable energy source for producing bio-oil and syngas through both experimental and theoretical approaches. Neem seeds underwent thermal pyrolysis in a semi-batch reactor after undergoing acid wash pre-treatment. The effects of pyrolysis temperatures (350–550 °C) and heating rates (10–40 °C/min) on product yields were analyzed, and the highest achieved bio-oil yield was 60.2 % at 450 °C and a heating rate of 40 °C/min. In the theoretical section, the Aspen Plus software was employed to simulate the process of steam gasification of neem seeds to identify optimal operating conditions for maximizing hydrogen production and cold gas efficiency (CGE) while maintaining an ideal H2/CO ratio. By analyzing the impact of operating parameters such as steam-to-biomass (S/B) ratio and temperature on the composition of the syngas stream, H2/CO ratio, and CGE, the study determined that the optimal operating conditions are an S/B ratio of 0.9 and temperatures ranging from 650 to 750 °C. The findings of this study can shed light on the potential of neem seed as a non-edible biomass source for renewable energy production, which can help reduce greenhouse gas emissions and mitigate the negative impacts of traditional energy sources on the environment.

Kinetic analysis of slow pyrolysis of oily sludge at medium temperature (350 ℃–650 ℃) and the effects of heating rate on pyrolysis

ABSTRACT Pyrolysis is an effective way for the harmless treatment of oily sludge. The composition, physicochemical properties, and pyrolysis of oily sludge were experimentally studied in the present study. The Starink and Coats-Redfern methods were used to analyze the pyrolysis kinetics of oily sludge. Pyrolysis of oily sludge is divided into four stages: water evaporation stage, light component evaporation stage, heavy component pyrolysis stage, and final pyrolysis stage. The light component evaporation and heavy component pyrolysis stages are the main stages of medium-temperature pyrolysis. The pyrolysis characteristic parameters under heating rates of 10, 20, 30, and 40 K/min were obtained, and the effects of heating rates on the pyrolysis characteristics of oily sludge were discussed. The results show that with the increase in heating rate, the temperature range of each stage expands, and the temperature of the pyrolysis peaks also increases, with an average increase of 14.88%. The activation energies of the main pyrolysis stages obtained by the Starink method and Coats-Redfern method are consistent. In the light component evaporation stage, the activation energies obtained by the two methods are 61.93kJ/mol and 68.6kJ/mol, while the activation energies are 294.88kJ/mol and 367kJ/mol in the heavy component pyrolysis stage. The pyrolysis mechanism functions are obtained, and the pyrolysis kinetic equations under 10, 20, 30, and 40 K/min were constructed and validated by comparison with the results of the calculated properties and experimental measurement. This study can provide a better insight into the heat and mass transfer processes of oily sludge in pyrolysis reactors for further development and optimization.

Effects of thermal program on physicochemical properties and photocatalytic activity of g-C3N4 prepared by dicyandiamide pyrolysis

Graphitic carbon nitride (g-C3N4) can be prepared by the pyrolysis of dicyandiamide, and its properties and performance are greatly affected by the pyrolysis parameters. In this study, the effects of heating rate and pyrolysis time on the physicochemical properties and photocatalytic activity of the obtained g-C3N4 are systematically investigated, and the results are used to guide the controllable production of g-C3N4 in industry. The results show the heating rate has a significant impact on the pore structure, crystallinity, number of amino functional groups, and the stability of structure. The pyrolysis time mainly affects the texture and layer structure of g-C3N4 products. In addition, the polymerization pathways during the dicyandiamide pyrolysis are analyzed through in-situ TG-MS combined with XRD analysis, elucidating the process of dicyandiamide forming complete g-C3N4 products with high polymerization degree by polyaddition, polycondensation and rearrangement. This study provides useful reference strategies for the design of large-scale controllable industrial production of g-C3N4 through pyrolysis of dicyandiamide.

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.