Effects Of High-temperature Treatment Research Articles

HZSM-5 zeolites undergoing the high-temperature process for boosting the bimolecular reaction in n-heptane catalytic cracking

High-temperature treatment is key to the preparation of zeolite catalysts. Herein, the effects of high-temperature treatment on the property and performance of HZSM-5 zeolites were studied in this work. XRD, N2 physisorption, 27Al MAS NMR, and NH3-TPD results indicated that the high-temperature treatment at 650 °C hardly affected the inherent crystal and texture of HZSM-5 zeolites, but facilitated the conversion of framework Al to extra-framework Al, reducing the acid site and enhancing the acid strength. Moreover, the high-temperature treatment improved the performance of HZSM-5 zeolites in n-heptane catalytic cracking, promoting the conversion and light olefins yield while inhibiting coke formation. Based on the kinetic and mechanism analysis, the improvement of HZSM-5 performance caused by high-temperature treatment has been attributed to the formation of extra-framework Al, which enhanced the acid strength, facilitated the bimolecular reaction, and promoted the entropy change to overcome a higher energy barrier in n-heptane catalytic cracking.

Effects of High Temperature Treatments on Strength and Failure Behavior of Sandstone under Dynamic Impact Loads

With the increasing demand for resource consumption, the mining depths gradually increase, resulting in increases of temperature at tens or even hundreds of degrees. High temperature could damage to interior structures and alter the mechanical properties of rock mass. Therefore, studying the effects of temperature on dynamic mechanical properties and failure behaviors are of great significance for deep resources exploitation. In this study, to study the effects of high temperature treatment on the strength and failure behavior of typical sandstones, specimens were prepared and heated to different degrees. The longitudinal wave velocity, volume, and density of specimens before and after high-temperature treatment were examined. Then, the Thomas Hopkinson (SHPB) test was conducted on specimens with different air pressures and the dynamic stress-strain curve, peak stress, peak strain, and other dynamic characteristics were obtained. The variations regulations and failure behavior of sandstone under the effects of high-temperature treatments and different impact loads were analyzed and discussed from the aspects of stress-strain, peak strength, and peak strain. It was observed that with the increase of heating temperature, the average density, average wave velocity, peak strength, and average elastic modulus of the sandstone specimens all showed a decreasing trend and the highest decreasing rated occurred at the temperature between 600 °C and 800 °C. The obtained results provided a certain theoretical basis for deep mine exploitation, especially for mines with high temperature.

Delayed effect of thermal treatment on breaking physical seed dormancy: intrapopulation variation and implications for soil seed banks

Background Many studies have focused on the dormancy-breaking response to heat treatment of freshly matured seeds and immediately after thermal shock. Aims We evaluated whether the full effect of dry heat scarification in freshly matured seeds could be delayed over time and the possible influence of previous storage in the soil. Methods Adenocarpus argyrophyllus was the model species selected to explore our hypotheses by analysing the: (a) influence of scarification treatments; (b) seedling emergence during 5 years after dry heat scarification of freshly matured seeds, and evaluating intrapopulation variation; (c) seedling emergence after dry heat scarification of seeds rescued from soil; and (d) ability to form persistent soil seed banks. Key results Dry heat scarification of freshly matured seeds only resulted in 22.5% germination. However, exposure to pre-sowing thermal shock stimulated seedling emergence during the first few years post-planting, with high intrapopulation variation. In seeds recovered from soil, thermal shock before reseeding increased the seedling emergence rate. Conclusions and implications Our results show that, to avoid incomplete interpretation, studies of thermal treatment on the breaking of physical seed dormancy should allow the seeds sufficient time to exhibit the complete effects of high temperature treatment, thereby preventing underestimation.

Effects of high-temperature treatment and iron reduction index on tensile strength of basalt continuous fiber

Iron plays an important role in enhancing the tensile strength of basalt fibers (BFs); however, the origins of tensile-strength variation at high temperatures are not well understood. In this work, we prepared BFs with different iron reduction indices (IRI = Fe2+/Fetotal) and explored the effects of high temperature and IRI on tensile strength. The results show that BFs with higher IRIs retained better tensile strength after high-temperature treatment at 600°C for 1 h. The surface morphology was analyzed by scanning electron microscopy to observe the nanocrystalline layers on the surface of BFs with higher IRIs, and the main composition of the crystals was CaO. The formation of nanocrystalline layers increased the tensile strength of the BFs. Moreover, results from transmission 57Fe Mössbauer spectroscopy and Fourier transform infrared spectroscopy indicate that BFs with lower IRIs formed more ferric tetrahedral structures (Fe3+(tet)) after high-temperature treatment, which depolymerized Si(Al)-O-Si(Al) tetrahedral structures, resulting in lower tensile strength. A better understanding of the origin of microstructures in different iron coordination states and the tensile strength of BFs at high temperatures will assist in the development of advanced iron-bearing glass fiber products suitable for high-temperature environments.

Study on influencing factors of photocatalytic performance of CdS/TiO2 nanocomposite concrete

Abstract In this study, a high-energy ball mill was used to composite nano-TiO2 and CdS, and three kinds of nanocomposite photocatalysts TiO2, CdS/TiO2-R400, and CdS/TiO2-R600 were prepared, which can respond to visible light. The photocatalytic concrete test block was prepared by mixing the nanocomposite photocatalyst and other masses with cement by incorporation method. To study the effect of the photocatalyst content on the photocatalytic performance of nanoconcrete, a total of four catalyst contents (0, 2%, 5%, and 8%) were set. The effects of high-temperature treatment (400°C) and different light sources (ultraviolet and visible light) on photocatalytic efficiency were also considered. The results show that the catalytic efficiency of CdS/TiO2-R400 under two light sources is higher than that of the other two photocatalysts. Compared to ultraviolet light sources, the photocatalytic efficiency of CdS/TiO2 nanocomposite concrete under visible light is lower, and the efficiency is below 9%. The optimal amounts of CdS/TiO2 nanocomposite photocatalyst under ultraviolet and visible light are 2% and 5%, respectively. The high-temperature treatment can improve the photocatalytic performance of CdS/TiO2 nanocomposite photocatalyst by 2% to 3%.

Effects of high temperature treatment of carbon nanotube arrays on graphite: increased crystallinity, anchoring and inter-tube bonding

Thermal treatment of carbon nanotubes (CNTs) can significantly improve their mechanical, electrical and thermal properties due to reduced defects and increased crystallinity. In this work we investigate the effect of annealing at 3000 °C of vertically aligned CNT arrays synthesized by chemical vapor deposition (CVD) on graphite. Raman measurements show a drastically reduced amount of defects and, together with transmission electron microscope (TEM) diffraction measurements, an increased average crystallite size of around 50%, which corresponds to a 124% increase in Young’s modulus. We also find a tendency for CNTs to bond to each other with van der Waals (vdW) forces, which causes individual CNTs to closely align with each other. This bonding causes a densification effect on the entire CNT array, which appears at temperatures >1000 °C. The densification onset temperature corresponds to the thermal decomposition of oxygen containing functional groups, which otherwise prevents close enough contact for vdW bonding. Finally, the remaining CVD catalyst on the bottom of the CNT array is evaporated during annealing, enabling direct anchoring of the CNTs to the underlying graphite substrate.

고온 열처리가 폴리페닐렌 설파이드 필름의 미세구조에 미치는 영향

220℃에서 17일까지의 열처리가 선형성이 큰 순수 폴리페닐렌 설파이드(PPS) 수지를 용융압착하여 제조한 PPS 필름의 미세구조에 미치는 영향을 색차분석기, X-선 광전자 분광분석기(XPS), FTIR 분광분석기, 시차주사열량계, X-선 회절분석기를 사용하여 분석하였다. 열처리시간이 길어짐에 따라 PPS 필름은 점차 갈색으로 변하였으며 미열처리 시료와의 색차가 커졌다. XPS와 FTIR 분석 결과, 열처리에 의해 PPS 분자사슬 사이에 산화가교가 되었다가 이어서 벤젠링 가교가 형성되었다. 열처리에 의해 DSC 1차 승온 시의 첫 번째 용융온도는 높아졌지만 두 번째 용융온도는 거의 비슷하였으며, 용융 후 강온 시의 용융결정화 온도는 낮아졌다. 또한 열처리시간이 길어지면 승온 시의 용융열은 증가하고 강온 시의 용융 결정화열은 감소하는 경향을 나타내었지만, 열처리에 의해 PPS 결정구조가 변하지는 않았다.

Effect of high temperature treatment on the microstructure and elastoplastic properties of polyacrylonitrile-based carbon fibers

The effects of high temperature treatment (2000–2800 °C) on the microstructure evolution and elastoplastic properties of polyacrylonitrile-based carbon fibers were investigated. It is found that the uneven shrinkage of the carbon fiber surfaces leads to formation of bulges whose length-to-width ratios increase with increasing heat treatment temperature. Because of the shrinkage stress, a closely stacked and curved graphene layer can be found in the sub-surface region of the carbon fibers. In the longitudinal section, the continuity of the graphite-like ribbons in the sub-surface region is worse than that in the skin region and the cross-linking regions between the graphite-like ribbons still contain a lot of defects after heat treatments. As the indentation depth increases, the axial and transverse elastic modulus of the carbon fibers decrease, which are related to the needle-like pores and the ordered graphite-like crystallites. The improvement of the slip between the graphene layers and the breakage of the graphite-like crystallites and the cross-linking regions are responsible for the decrease in axial elastic modulus with increasing heat treatment temperature. By contrast, the transverse elastic modulus is low and the excellent elasticity in the transverse direction is due to the curved graphene layers and the needle-like pores.

Effects of Al2O3 coating induced structural and mechanical changes of C/C composites

Different C/C composites, identified as Cf/C, CAl2O3/C, C1600/C and C1600-Al2O3/C, were fabricated by condensation of different treated 3D needle-punched carbon fiber preforms through a thermal gradient chemical vapor infiltration (TG-CVI) method. Effects of high temperature treatment and Al2O3 coating of the carbon fiber preforms on matrix texture and mechanical properties of C/C composites were investigated. SL PyC is obtained for Cf/C and C1600/C, which preforms are without Al2O3 coating. Whereas the texture of carbon matrix for CAl2O3/C, and C1600-Al2O3/C changes to RL under the same deposition conditions, indicating that Al2O3 coating layer significantly affects the texture of carbon matrix. Heat treatment of the carbon fiber preforms at 1600 °C for 4 h obviously increase the toughness of the C/C composites. The fracture toughness increased by 226% from 0.938 MPa/m2 for Cf/C to 3.061 MPa/m2 for C1600-Al2O3/C. The significant toughness increasing is attributed to the unique fracture mode for C1600-Al2O3/C, where a hollow “cylindrical” PyC matrix is pulled out and a corresponding big hole is left with a central fiber in it. The flexural strength, however, is mainly affected by the final density of the C/C composites.

Pore structure regulation and carbon dioxide adsorption capacity improvement on porous BN fibers: Effects of high-temperature treatments in gaseous ambient

Recently, capture and storage of carbon dioxide (CO2) has been an effective strategy to address global warming caused by excess CO2. Porous boron nitride (BN) with tunable porosity, excellent chemical stability and thermal stability have been considered as promising materials for CO2 adsorption. Here, porous BN fibers with high specific surface area have been used as promising adsorbent for CO2 capture. The effects of high-temperature treatments in different gaseous ambient on the microstructure evolution and CO2 adsorption capacity of porous BN fibers are studied in detail. Interestingly, the porous BN fibers after high-temperature post-treatment in NH3 gas show enhanced CO2 adsorption capacity, as compared with pristine porous BN and nearly three times more than porous BN nanosheets reported before. The NH3-treatment can effectively restrain the damage of pore structure caused by high-temperature annealing, especially micropores. Moreover, in the NH3-treatment process, the impurities (B-O) of porous BN fibers can react with NH3 to form B-N-H, which is the root cause of the enhancement of CO2 adsorption capacity of porous BN fibers.

Effects of High Temperature Treatment on the Sprouting and Elongation Rate of Asparagus Spears

Effects of High Temperature Treatment on the Sprouting and Elongation Rate of Asparagus Spears

Effects of high temperature treatment on physical-thermal properties of clay

High temperature changes the internal microstructure of clay and consequently affects its physical and thermal properties. In this paper, the influence of firing temperature (up to 900 °C) on the thermo-physical properties of clay is analyzed through laboratory tests and the relationship between thermal conductivity and density is revealed. Furthermore, the variation of surface characteristics including clay color and cracking is reported. The results obtained indicate that the thermal conductivity and diffusivity as well as the bulk density of clay decrease rapidly as the temperature increases from room temperature to 200 °C, and then become approximately constant. From the Thermogravimetric Analysis (TG) and Differential Thermal Analysis (DTA) tests it is also shown that there are two significant stages for the clay exposed to high temperature: 25–200 °C and 400–700 °C. The evaporation of adhered water and bound water are proved to be the main reason for the first stage of clay mass loss at 25–200 °C, while the decomposition of minerals is considered as the second stage of mass loss in the temperature range of 400–700 °C. In addition, the combustion of organic matter in clay is the main reason for its darkening at 300–400 °C.

Effects of high-temperature heat treatment on the microstructure and mechanical performance of hybrid Cf-SiCf-(Al2O3p) reinforced geopolymer composites

Abstract Hybrid C f and SiC f reinforced geopolymer composites with Al 2 O 3 particles were successfully fabricated, and the effects of high-temperature treatment on the microstructure evolution and mechanical properties of C f -SiC f -(Al 2 O 3p )/KGP composites were investigated. Results showed that the amorphous matrix of C f -SiC f -(Al 2 O 3p )/KGP composites transformed into kalsilite and leucite phase after treated at 1000 and 1200 °C, respectively, due to the addition of fibers hindering crystallization of the geopolymer matrix. The addition of Al 2 O 3p was helpful to increase the thermal stability of composites after high-temperature treatment. Flexural strength and Young's modulus of the composites decreased after high temperature treatment and showed the maximum values at 1000 °C. All the composites showed a non-catastrophic fracture behavior after heat treated, which was attributed to fiber pulling-out and debonding.

In situ processing of MWCNTs/leucite composites through geopolymer precursor

A serial of multi-walled carbon nanotubes (MWCNTs) reinforced geopolymer composites were prepared, and then heated at elevated temperature to fabricate MWCNTs/leucite composites by in situ transformation. Effects of high-temperature treatment on the microstructure evolution and mechanical performance of the composites were investigated. The results indicated that the introduction of MWCNTs could improve the mechanical properties of geopolymer, and the optimum content was 3wt%. The mechanical performance declined instead with the further increase in MWCNTs content up to 5wt%, which could be attributed to the agglomeration of MWCNTs. Significant improvements in mechanical properties were achieved after the composites were treated in a temperature range from 950°C to 1200°C relative to their original state before heat treatment. The significant improvements could be described to the matrix densification, and leucite formation as well as the proper interface bonding state between carbon nanotube and leucite matrix.

Improving mechanical strength of Ti-Ni-Si joints for joining carbon/carbon composites by thermal cycling treatment

Ti-Ni-Si compound was used to join carbon/carbon (C/C) composites by hot-pressing sintering. Effects of high temperature treatment and thermal shock on the bonding strength of Ti-Ni-Si joints were investigated. After the joints were treated for 10h at 1000°C, the average shear strength was increased to 30.89±0.75MPa, which was 30.01% higher than the original ones, accompanied by homogeneous Ti-Ni-Si interlayer with few defects. Fracture toughness of the joints after thermal treated for 5h possessed significant improvement from 1.44±0.32 to 4.10±0.56MPam1/2 attributing to the decrease of free Si and the increase of ternary compound Ti4Si7Ni4 in the interlayer. After heat treatment at 1000°C for 5h and thermal shock between 1000°C and room temperature for 30 times, the average shear strength of those joints increased from 23.76±0.50 to more than 30MPa. The improvement of the mechanical strength of Ti-Ni-Si joints was attributed to the multi-component diffusion reactions to seal the defects in the Ti-Ni-Si joints during heat treatment and thermal cycling tests. This work could provide new insight to understand strengthening of the bonding between C/C composites instead of weakening after the joints experiencing thermal shock.

Identification of heat-responsive genes in carnation (Dianthus caryophyllus L.) by RNA-seq.

Carnation (Dianthus caryophyllus L.) is an important flower crop, having substantial commercial value as a cut-flower due to the long vase-life and wide array of flower colors and forms. Standard carnation varieties perform well under cool climates but are very susceptible to high temperatures which adversely affect the yield and the quality of the cut-flowers. Despite several studies of carnation contributing to the number of expressed sequence tags (ESTs), transcriptomic information of this species remains very limited, particularly regarding abiotic stress-related genes. Here, transcriptome analysis was performed to generate expression profiles of heat stress (HS)-responsive genes in carnation. We sequenced a cDNA library constructed with mixed RNA from carnation leaves subjected to 42°C HS (0, 0.5, 1, and 2 h) and 46°C HS (0.5, 1, and 2 h), and obtained 45,604,882 high quality paired-end reads. After de novo assembly and quantitative assessment 99,255 contigs were generated with an average length of 1053 bp. We then obtained functional annotations by aligning contigs with public protein databases including NR, SwissProt, KEGG, and COG. Using the above carnation transcriptome as the reference, we compared the effects of high temperature treatments (42°C: duration 0.5, 2, or 12 h) delivered to aseptic carnation seedlings, relative to untreated controls, using the FPKM metric. Overall, 11,471 genes were identified which showed a significant response to one or more of the three HS treatment times. In addition, based on GO and metabolic pathway enrichment analyses, a series of candidate genes involved in thermo-tolerance responses were selected and characterized. This study represents the first expression profiling analysis of D. caryophyllus under heat stress treatments. Numerous genes were found to be induced in response to HS, the study of which may advance our understanding of heat response of carnation.

Effects of High Temperature Treatment on the Mechanical Properties of Basalt Fiber Reinforced Aluminous Composites

Article presents the results of an experimental program aimed at investigating of the mechanical properties of composites based on aluminous cement with the addition of basalt fibres, which could be used in the manufacture of components resistant to high temperatures, including the retention of mechanical properties. Silica composites based on Portland cement and silica aggregates are not able to resist the effects of high temperatures [1], therefore a heat resistant mixtures in this experiment includes only components that are able to resist the effects of high temperatures.

Effects of high temperature treatment on microstructure and mechanical properties of laser-clad NiCrBSi/WC coatings on titanium alloy substrate

Laser-clad composite coatings on the Ti6Al4V substrate were heat-treated at 700, 800, and 900°C for 1h. The effects of post-heat treatment on the microstructure, microhardness, and fracture toughness of the coatings were investigated by scanning electron microscopy, X-ray diffractometry, energy dispersive spectroscopy, and optical microscopy. The wear resistance of the coatings was evaluated under dry reciprocating sliding friction at room temperature. The coatings mainly comprised some coarse gray blocky (W,Ti)C particles accompanied by the fine white WC particles, a large number of black TiC cellular/dendrites, and the matrix composed of NiTi and Ni3Ti; some unknown rich Ni- and Ti-rich particles with sizes ranging from 10nm to 50nm were precipitated and uniformly distributed in the Ni3Ti phase to form a thin granular layer after heat treatment at 700°C. The granular layer spread from the edge toward the center of the Ni3Ti phase with increasing temperature. A large number of fine equiaxed Cr23C6 particles with 0.2–0.5μm sizes were observed around the edges of the NiTi supersaturated solid solution when the temperature was further increased to 900°C. The microhardness and fracture toughness of the coatings were improved with increased temperature due to the dispersion-strengthening effect of the precipitates. Dominant wear mechanisms for all the coatings included abrasive and delamination wear. The post-heat treatment not only reduced wear volume and friction coefficient, but also decreased cracking susceptibility during sliding friction. Comparatively speaking, the heat-treated coating at 900°C presented the most excellent wear resistance.

Effects of High Temperature Treatments on PPB’s in a P/M Superalloy

FGH96 components of aircraft engines were produced by a processing route of hot isostatic pressing plus heat treatment (as-HIP). The prior particle boundaries (PPB’s) could be found in those articles in spite of the lower carbon content in the alloy. Attempts to eliminate or reduce PPB’s in as-HIP FGH96 alloy have been carried out by either increasing the HIP temperature from 1180oC to 1230oC or taking an appended annealing treatment at 1230oC. Based on experimental results, a thermodynamic analysis by using Jmat Pro has been conducted to understand the effects of high temperature treatments on PPB’s in FGH96 alloy. PPB’s found in as-HIP FGH96 alloy were mainly constituted by MC carbides enriched in Ti and Nb. The results of a thermodynamic analysis presented that carbides precipitated on TiN nucleus and grew up to form PPB’s. High temperature treatments, both increasing HIP temperature and taking a high temperature annealing treatment after HIP, could reduce the equilibrium amount of MC carbides and the surface segregation of Ti in powder particles, and turned the continuous precipitates into broken particles on PPB’s. Although the PPB’s could not be completely eliminated by high temperature treatments, an obvious improvement in rupture life of the material could be observed.

Effects of High Temperature Treatment on Thermal Cyclic Behavior of Thermal Barrier Coatings

Ni3Al based alloy IC10 has been developed for turbine blades and vanes of advanced aero-engines and other high temperature structural components. Conventional two-layered structure thermal barrier coatings (TBCs) were produced by EB-PVD onto Ni-based superalloy. The thickness of bond coat and top coat was approximately 60μm and 120μm, respectively. After thermal barrier coatings were produced, it was heated at 1523K for 2hs, 6hs, 14hs and 20hs under 1×10-2Pa, respectively. After heat treatment was done, the thermal cyclic test was carried out by exposure to air at 1373K for 0.5h, and then cooled to room temperature within 5 minutes by forced air cooling. Scanning electron microscopy (SEM) was employed to study the microstructure of the coatings. After thermal cycled in air at 1373K for TBCs without heat treatment at 1523K, its lifetime is about 810 hours. After 760hs thermal cycles, the spallation occurred on the TBCs that the heat treatment was treated at 1523K for 2hs. The lifetime of TBCs, which the heat treatment was treated at 1523K for 6hs, was 710hs. The lifetime of TBCs, which the heat treatment was treated at 1523K for 14hs and 20hs, was 600hs and 560hs, respectively. The results showed that, with the increasing of the time of heat treatment, the weight gain increased evidently during thermal cycled. The results showed that heat treatment at 1523K affect the lifetime of TBCs during thermal cyclic evidently.