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Sökning: WFRF:(Peizhong Feng)

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1.
  • Akhtar, Farid, et al. (författare)
  • TiB 2 and TiC stainless steel matrix composites
  • 2007
  • Ingår i: Materials letters (General ed.). - : Elsevier BV. - 0167-577X .- 1873-4979. ; 61:1, s. 189-191
  • Tidskriftsartikel (refereegranskat)abstract
    • Stainless steel matrix composites reinforced with TiB2 or TiC particulates have been in situ produced through the reactive sintering of Ti, C and FeB. X-ray diffraction analysis confirmed the completion of reaction. The TiB2, TiC and steel were detected by X-ray diffraction analysis. No other reaction product or boride was found, indicating the stability of TiB2 and TiC in steel matrix. The SEM micrographs revealed the morphology and distribution of in situ synthesized TiB2 and TiC reinforcements in steel matrix. During sintering the reinforcements TiB2 and TiC grew in different shapes. TiB2 grew in hexagonal prismatic and rectangular shape and TiC in spherical shape.
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2.
  • Binbin, Song, et al. (författare)
  • Oxidation properties of self-propagating high temperature synthesized niobium disilicide
  • 2014
  • Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 85, s. 311-317
  • Tidskriftsartikel (refereegranskat)abstract
    • NbSi2 monoliths were prepared by self-propagating high temperature synthesis (SHS) and hot pressing (HP) and their oxidation behavior was investigated at various temperatures (823-1123 K) in air. The combustion mode of SHS reaction was steady state combustion, and the combustion product was single-phase NbSi2. Oxidation studies show that the highest mass gain was 0.95675 kg m(-2) at 1023 K. In cyclic oxidation, the oxidation rate was reduced and the mass gain was only 0.15507 kg m(-2). A dense protective amorphous SiO2 scale formed at 823 K and 923 K whereas a porous multilayer SiO2 and alpha/beta-Nb2O5 oxide scales formed at and above 1023 K and spalled off. Pest oxidation of NbSi2 monoliths was not observed in hot pressed NbSi2 monoliths.
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3.
  • Akhtar, Farid, et al. (författare)
  • Enhanced sintering, microstructure evolution and mechanical properties of 316L stainless steel with MoSi(2) addition
  • 2011
  • Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 509:35, s. 8794-8797
  • Tidskriftsartikel (refereegranskat)abstract
    • Sintering 316L stainless steel to near full density with an appropriate sintering additive can ensure high mechanical properties and corrosion resistance. We present here a sintering approach which exploits the dissociation of ceramics in steels at high temperatures to activate sintering densification to achieve near full dense 316L stainless steel materials. MoSi(2) ceramic powder was used as a sintering additive for pre-alloyed 316L stainless steel powder. Sintering behavior and microstructure evolution were investigated at various sintering temperatures and content of MoSi(2) as sintering additive. The results showed that the sintering densification was enhanced with temperature and MoSi(2) content. The distribution of MoSi(2) was characterized by XMAPs. It was found that MoSi(2) dissociated during sintering and Mo and Si segregated at the grain boundaries. Excess Mo and Si were appeared as separate phases in the microstructure. Above 98% of theoretical density was achieved when the specimens were sintered at 1300 degrees C for 60 min with 5 wt.% MoSi(2) content. The stainless steel sintered with 5 wt.% MoSi(2) exhibited very attractive mechanical properties.
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4.
  • Akhtar, Farid, et al. (författare)
  • Microstructure and property evolution during the sintering of stainless steel alloy with Si 3 N 4
  • 2008
  • Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 472:1-2, s. 324-331
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper describes the sintering of a martensitic stainless steel alloy with addition of Si3N4. Sintering behavior was studied at different sintering temperatures ranging from 1250 to 1400 °C with different holding times (20–80 min) and with varying Si3N4. Results showed that the samples were densified rapidly via liquid phase sintering mechanism. Nearly full density was obtained at 1300 °C after 60 min of holding time with 5 wt% Si3N4. Temperature above 1350 °C and Si3N4 content 10 wt% caused slumping of the samples. Two weight percent Si3N4 was found chemically stable in steel alloy. Above 2 wt% Si3N4 dissolved in the steel matrix. The distribution of dissolved Si and N was characterized by XMAP. When N content reached much above its solubility limit in steel alloy it diffused out leaving pores in steel alloy with considerable decrease in the sintered density. The mechanical properties of the sintered product with varying Si3N4 were measured. A maximum ultimate tensile strength of 1011 MPa was achieved with 2 wt% Si3N4 sintered at 1300 °C after 60 min of holding time. Fracture morphologies of tensile samples are also reported.
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5.
  • Akhtar, Farid, et al. (författare)
  • TiC-maraging stainless steel composite: microstructure, mechanical and wear properties
  • 2006
  • Ingår i: Rare Metals. - 1001-0521 .- 1867-7185. ; 25:6, s. 630-635
  • Tidskriftsartikel (refereegranskat)abstract
    • Particulate TiC reinforced 17-4PH and 465 maraging stainless steel matrix composites were processed by conventional powder metallurgy (P/M). TiC-maraging stainless steel composites with theoretical density >97% were produced using conventional P/M. The microstructure, and mechanical and wear properties of the composites were evaluated. The microstructure of the composites consisted of (core-rim structure) spherical and semi-spherical TiC particles depending on the wettability of the matrix with TiC particles. In TiC-maraging stainless steel composites, 465 stainless steel binder phase showed good wettability with TiC particles. Some microcracks appeared in the composites, indicating the presence of tensile stresses in the composites produced during sintering. The typical properties, hardness, and bend strength were reported for the composites. After heat treatment and aging, an increase in hardness was observed. The increase in hardness was attributed to the aging reaction in maraging stainless steel. The specific wear behavior of the composites strongly depends on the content of TiC particles and their interparticle spacing, and on the heat treatment of the maraging stainless steel.
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6.
  • Cai, Xiaoping, et al. (författare)
  • Fabrication of Highly Porous CuAl Intermetallic by Thermal Explosion Using NaCl Space Holder
  • 2018
  • Ingår i: JOM. - : The Minerals, Metals, and Materials Society. - 1047-4838 .- 1543-1851. ; 70:10, s. 2173-2178
  • Tidskriftsartikel (refereegranskat)abstract
    • A high-porosity CuAl-based intermetallic compound with composition Cu-50 at.% Al has been successfully prepared by thermal explosion (TE) using NaCl as space holder. The results showed that the NaCl particles were completely removed from the green compact by water leaching. The temperature of the specimen during the TE and the evolution of the porous microstructure were investigated. The TE was ignited at 560°C, and the specimen temperature increased to 775°C in 3 s, resulting in formation of intermetallic CuAl and CuAl2 phases in the final product. A porous CuAl-based intermetallic compound with up to 62 vol.% open porosity was produced when adding 60 vol.% NaCl. The compound exhibited a bimodal pore size structure, including large pores (200 μm to 300 μm) that replicated the NaCl particles and small pores (5 μm to 10 μm) interspersed in the pore walls. Moreover, the large pores were interconnected by channels and formed an open CuAl-based intermetallic cellular structure, having great potential for use in heat exchange and filtration applications.
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7.
  • Cai, Xiaoping, et al. (författare)
  • Oxidation Resistance of Highly Porous Fe-Al Foams Prepared by Thermal Explosion
  • 2018
  • Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 49A:8, s. 3683-3691
  • Tidskriftsartikel (refereegranskat)abstract
    • Open-cell Fe-Al intermetallic foams were successfully prepared by a simple and energy-saving thermal explosion (TE) process. The effects of the Fe/Al molar ratio (Fe-(40–50) at. pct Al) and thermal treatment temperature on the TE temperature profile, phase composition, pore characteristics, and oxidation resistance of the prepared foams were investigated. The results showed that the Al content significantly influenced the ignition (Tig) and combustion (Tc) temperatures of the TE process; in particular, as the Al content decreased, Tig increased gradually from 623 °C to 636 °C and Tc decreased from 1059 °C to 981 °C. FeAl was identified as the dominant phase in the thermally treated foams. The Fe-Al intermetallic foams displayed an open porosity of 60 vol pct, with pores connected with each other to form an open pore structure. The formation of the pores was attributed to the expansion of interparticle pores in the pressed body during the TE reaction. X-ray photoelectron spectroscopy analysis of the Fe-50Al foam showed that the Al 2p and O 1s binding energies were 74.5 eV and at 531.4 eV, respectively. The formation of a surface alumina layer in the early stages of the oxidation process resulted in the parabolic oxidation rate law, and the Fe-50Al foams exhibited an excellent resistance to oxidation at 650 °C in air. These results suggest that the synthesized Fe-Al foams represent promising materials for applications involving an oxidizing environment and high temperatures.
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8.
  • Cao, Zhejian, 1991-, et al. (författare)
  • Calcium/strontium chloride impregnated zeolite A and X granules as optimized ammonia sorbents
  • 2022
  • Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 12:54, s. 35115-35122
  • Tidskriftsartikel (refereegranskat)abstract
    • Calcium chloride (CaCl2) impregnated zeolite A and strontium chloride (SrCl2) impregnated zeolite A and X composite granules were evaluated as ammonia sorbents for automotive selective catalytic reduction systems. The SrCl2-impregnated zeolite A granules showed a 14% increase in ammonia uptake capacity (8.39 mmol g(-1)) compared to zeolite A granules (7.38 mmol g(-1)). Furthermore, composite granules showed 243% faster kinetics of ammonia sorption (0.24 mmol g(-1) min(-1)) compared to SrCl2 (0.07 mmol g(-1) min(-1)) in the first 20 min. The composite CaCl2/SrCl2 impregnated zeolite A granules combined the advantages of the zeolites and CaCl2/SrCl2, where the rapid physisorption from zeolites can reduce the ammonia loading and release time, and chemisorption from the CaCl2/SrCl2 offers abundant ammonia capacity. Moreover, by optimizing the content of SrCl2 loading, the composite granules maintained the granular form with a crushing load of 17 N per granule after ammonia sorption-desorption cycles. Such structurally stable composite sorbents offer an opportunity for fast ammonia loading/release in automotive selective catalytic reduction systems.
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9.
  • Cao, Zhejian, et al. (författare)
  • Carbon-reinforced MgCl2 composites with high structural stability as robust ammonia carriers for selective catalytic reduction system
  • 2020
  • Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier. - 2213-3437. ; 8:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Novel carbon-MgCl2 composites were designed as robust ammonia carriers for selective catalytic reduction (SCR) system, with graphite (Gt) and graphene nanoplatelets aggregates (GNA) as additives to MgCl2. The cylindrically pelletized composites manifested high structural stability above the melting temperature of MgCl2 with 95 % mass retention, whereas the pure MgCl2 pellets completely lost their structural integrity. With the support of carbon additives, molten MgCl2 in the composites was isolated and retained the sample-to-holder angle of 90°, contrary to pure MgCl2 of 5.7° contact angle at 1073 K. Furthermore, the composites demonstrated rapid ammonia sorption and desorption kinetics, due to the enhanced surface area and creation of additional microporosity. Our results demonstrated that 20 wt.% GNA-80 wt.% MgCl2 (GNA20) composite presented 83 % faster kinetics in ammonia sorption and 73% faster in the first-2-minutes of desorption compared to the pure MgCl2. The enhancement of both structural stability and sorption kinetics makes the GNA20 composite a robust ammonia carrier.
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10.
  • Cao, Zhejian, 1991- (författare)
  • Structured Ammonia Carriers for Selective Catalytic Reduction
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Air quality has been one of the long-term focuses in society and has raised people’s concern regarding its amelioration in the post coronavirus disease 2019 (COVID-19) pandemic era. Nitrogen oxides (NOx), including NO and NO2, as one of the most harmful air pollutants, have been stringently monitored in most countries due to their devastating impact on the environment and human health. The transport sector, as the primary source of NOx, therefore, is regulated with ever-evolving NOx emission standards for vehicles. One typical approach to abate NOx from vehicle exhaust is using ammonia (NH3) to reduce NOx and produce environmentally friendly nitrogen (N2) and water (H2O) by selective catalytic reduction (SCR). Conventional urea-based SCR systems using urea as an indirect ammonia source have presented a series of problems, including low conversion efficiency with the lowering of exhaust temperature, freezing of urea solution in low-temperature regions, and emission of carbon dioxide (CO2) as a by-product.Solid SCR systems have emerged as a new direction for NOx reduction (DeNOx) in both industry and research, owing to their high NOx converting efficiency at low exhaust temperatures with direct ammonia dosing. In solid SCR systems, the ammonia storage and delivery unit is a critical part influencing DeNOx performance. The most popular ammonia carriers in solid SCR systems are alkaline earth metal halides (AEMHs), such as MgCl2, CaCl2, and SrCl2. AEMHs face two main challenges as ammonia carriers: (1) low kinetics of ammonia absorption and desorption for urban driving and engine idle scenarios; (2) poor structural stability in terms of thermal melting spread due to heat accumulation and dramatic volume expansion/shrinkage during ammonia absorption-desorption cycles.In this thesis, various physisorbents and chemisorbents, including metal-organic frameworks (MOFs), zeolites, and carbon-reinforced AEMHs, are designed, fabricated, and evaluated as optimized ammonia carriers for solid SCR systems.MOFs [M2(adc)2(dabco)] (M = Co, Ni, Cu, Zn) in this research have demonstrated physisorption of ammonia and superior kinetics of adsorption and desorption compared to MgCl2. Among the synthesized MOFs, Ni2(adc)2(dabco) possessed the highest ammonia uptake capacity, resulting from its high specific surface area. Ni2(adc)2(dabco) released 6 times the mole fraction of ammonia in the first 10 minutes compared to Mg(NH3)6Cl2, indicating that physisorbents can offer a solution to shorten the buffer time for ammonia dosing in SCR. To combine the physisorption of microporous materials with the chemisorption of AEMHs, SrCl2-impregnated zeolite granules as well as three-dimensional (3D) printed zeolite units to carry AEMHs were designed. By optimizing the parameters in the ion exchange and impregnation process, the fabricated SrCl2-impregnated zeolite granules showed two stages of ammonia sorption, including a rapid adsorption stage from the zeolites and an abundant absorption stage from SrCl2. The SrCl2-impregnated zeolite A granules retained 73% of the compressive strength of the pristine CaA granules after ammonia cycles, indicating excellent structural stability of the composite granules. The feasibility of applying 3D printing technology to co-structure AEMHs and zeolites was examined by designing zeolite NaX units to carry MgCl2. A 3D-printed NaX scaffold was successfully fabricated with an optimal formulation of zeolite NaX ink after rheological studies.Carbon materials were selected to form composites with AEMHs, including graphite (Gt), graphene nanoplatelets aggregates (GNA) as additives, and graphene networks as the scaffold. The pelletized carbon-MgCl2 composites containing 20 wt% Gt/GNA presented high structural integrity up to 800 °C above the melting point of MgCl2. Besides, the introduction of nanopores from GNA could promote ammonia diffusion in the MgCl2, resulting in enhanced kinetics of ammonia sorption and desorption. A porous SrCl2 structure scaffolded by graphene networks was fabricated by freeze-casting. The optimized porous SrCl2 with 80 wt% SrCl2 loading maintained its macro- and micro-structure, accommodating the volume swing after 20 ammonia sorption–desorption cycles without disintegration. Furthermore, the porous SrCl2 demonstrated superior kinetics of ammonia sorption and desorption by possessing more surface sites for ammonia adsorption and a shorter diffusion length in the SrCl2 particles. This structuring approach was verified with other AEMHs, including MgCl2 and CaCl2.The results from this thesis offer several solutions to structure AEMHs and their composites as ammonia carriers for SCR, with rapid kinetics and enhanced structural stability. Potential directions for optimizing the ammonia carriers are suggested, such as combining physisorbents (MOFs, zeolites, etc.) and chemisorbents (AEMHs) in flexible networks and optimizing the volumetric ammonia uptake capacity while maintaining the structural stability of the ammonia carriers.
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11.
  • Feng, Peizhong, et al. (författare)
  • Combustion synthesis of (Mo1-xCrx)Si-2 (x=0.00-0.30) alloys in SHS mode
  • 2012
  • Ingår i: Advanced Powder Technology. - : Elsevier BV. - 0921-8831 .- 1568-5527. ; 23:2, s. 133-138
  • Tidskriftsartikel (refereegranskat)abstract
    • Combustion synthesis was adopted to successfully synthesize molybdenum-silicon-chromium (Mo-Si-Cr) alloys by the mode of self-propagating high-temperature synthesis (SHS). The experimental study of combustion synthesis of Mo-Si-Cr alloys was conducted on elemental powder compacts. Powder compacts with nominal compositions including MoSi2, (Mo0.95Cr0.05)Si-2, (Mo0.90Cr0.10)Si-2, (Mo0.85Cr0.15)Si-2, (Mo0.80Cr0.20)Si-2, (Mo0.75Cr0.25)Si-2 and (Mo0.20Cr0.30)Si-2 were employed in combustion synthesis experiments. The combustion mode, combustion temperature, flame-front propagation velocity and product structure were investigated. The results showed that Mo-Si-Cr alloys were synthesized by an unsteady state combustion mode with a spiral-trajectory reaction front. The peak combustion temperature reduced with the addition of Cr to Mo-Si system. The flame-front propagation velocity decreased with an increase in Cr content of the powder compact. The X-ray diffraction (XRD) results showed that the crystal structure of the combustion product changed from CIIb-type structure (Mo0.90Cr0.10)Si-2 to C40-type structure (Mo0.80Cr0.15)Si-2 with increase in Cr content of Mo-Cr-Si alloys. The intensities of diffraction peaks of the C40-type phase gradually increased with increase in Cr content.
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12.
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13.
  • Feng, Peizhong, et al. (författare)
  • Effect of the composition of starting materials of Mo--Si on the mechanically induced self-propagating reaction
  • 2008
  • Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 456:1-2, s. 304-307
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of the raw materials composition of Mo–Si powders mixture on mechanical alloying has been investigated using a high-energy vibratory type ball-milling machine. The phase transformation of powders mixture is characterized by means of X-ray diffractometer. The results show that the molybdenum silicide is formed by the mechanically induced self-propagating reaction in relatively broad composition range from the molar ratio of Mo:1.5Si to Mo:2.5Si. As the content of silicon increases, the amount of critical stored energy for mechanically induced self-propagating reaction is increased, whereas the favorable Mo–Si reactive interface is decreased, and the difficulty of formation of Mo(Si) supersaturated solid solution is enhanced. These factors prolong the incubation period of mechanically induced self-propagating reaction from 60 to 130 min. Compared to stoichiometry of MoSi2, the excess amount of Mo acts as accelerant, and the redundant Si acts as diluting agent.
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14.
  • Feng, Peizhong, et al. (författare)
  • Mechanically activated reactive synthesis of refractory molybdenum and tungsten silicides
  • 2008
  • Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 26:3, s. 173-178
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, processing of elemental powders mixtures was carried out by mechanical alloying (MA) and heat treatment in vacuum at 700–1000 °C for 1 h. The phase transformation of the powders was investigated by X-ray diffractometer (XRD). The results showed that mechanical alloying promoted the formation of a solid solution of elemental powders. The energy stored in the powders was increased as a result of exterior energy and the barrier energy of the formation of the compound could be exceeded easily. Intermetallics of MoSi2, WSi2, Mo5Si3, Mo3Si and SiC/MoSi2 composite powders were synthesized by mechanically activated reactive synthesis (MARS). The mechanically induced self-sustaining reaction was observed in MoSi2 and MoSi2 + 10 wt%SiC stoichiometry system. It has concluded that mechanically activated reactive synthesis is an effective method for the preparation of high melting-point refractory compounds.
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15.
  • Feng, Peizhong, et al. (författare)
  • Self-propagating high temperature synthesis of MoSi 2 matrix composites
  • 2006
  • Ingår i: Rare Metals. - 1001-0521 .- 1867-7185. ; 25:3, s. 225-230
  • Tidskriftsartikel (refereegranskat)abstract
    • MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagating high temperature synthesis (SHS). Pure MoSi2 was obtained and a compound of MoSi2 and WSi2 was synthesized in the form of predominant solid solution (Mo, W)Si2. By adding aluminum of 5.5 at.% to Mo-Si, the crystal structure of MoSi2 changed into a mixture of tetragonal CIIb MoSi2 and hexagonal C40 Mo(Si, Al)2. The (Mo, W)Si2-Mo(Si, Al)2-W(Si, Al)2 composite materials were synthesized by adding aluminum of 5.5 at.% to Mo-W-Si. However, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. SHS is an effective technology for synthesis of MoSi2 and MoSi2 matrix composites.
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16.
  • Jiang, Zhiwu, et al. (författare)
  • Combustion synthesis and mechanical properties of MoSi2­-ZrB2­-SiC ceramics
  • 2018
  • Ingår i: Journal of the Ceramic Society of Japan. - : Ceramic Society of Japan. - 1882-0743 .- 1348-6535. ; 126:7, s. 504-509
  • Tidskriftsartikel (refereegranskat)abstract
    • MoSi2ZrB2SiC ceramics were synthesized using Mo, Zr, Si and B4C powders by self-propagating high-temperature synthesis and densifying by spark plasma sintering. The effects of MoSi2 content on the combustion synthesis process, microstructure, and mechanical properties of the ceramics were investigated. The results showed that combustion synthesis is an unstable mode, spiral combustion. The Gibbs calculations and combustion temperature curves indicate there are two reactions occurring at the same time. The volume fraction of the four different phases and their relative densities were also measured and calculated. Compared to pure MoSi2, the 1.0MoSi20.2ZrB20.1SiC (M10) ceramic exhibits excellent mechanical properties with its maximum Vickers hardness and fracture toughness being 14.0 GPa and of 5.5 MPa m1/2, respectively. The hardness is in agreement with the rule of mixture. The morphology of indentation cracks reveals that the fracture toughness improves as a result of toughening mechanisms such as crack bridge, crack deflection, and microcracks.
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17.
  • Jiang, Zhiwu, et al. (författare)
  • In Situ Fabrication and Properties of 0.4MoB-0.1SiC-xMoSi2 Composites by Self-propagating Synthesis and Hot-press sintering
  • 2018
  • Ingår i: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 44:1, s. 51-56
  • Tidskriftsartikel (refereegranskat)abstract
    • Mo, Si and B4C powders were used to fabricate 0.4MoB-0.1SiC-xMoSi2 composites by self-propagating high-temperature synthesis (SHS) and hot pressing (HP). The effects of MoSi2 content (x=1, 0.75, 0.5 and 0.25) on phase composition, microstructure and properties of the composites were investigated. The results showed that the 0.4MoB-0.1SiC-xMoSi2 composite exhibited Vickers hardness of 10.7–15.2 GPa, bending strength of 337–827 MPa and fracture toughness of 4.9–7.0 MPa∙m1/2. The fracture toughness increased with the increasing volume fraction of MoB and SiC particles which were promoted by the toughening mechanisms, such as crack bridging, cracks deflection and crack branching. Moreover, the electrical resistivity showed an increasing trend with decreasing volume fraction of MoSi2.
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18.
  • Jiao, Xinyang, et al. (författare)
  • Effect of heating rate on porous TiAl-based intermetallics synthesized by thermal explosion
  • 2017
  • Ingår i: Materials and Manufacturing Processes. - : Taylor & Francis. - 1042-6914 .- 1532-2475. ; 32:5, s. 489-494
  • Tidskriftsartikel (refereegranskat)abstract
    • TiAl-based porous materials were synthesized by a novel process of thermal explosion (TE) reaction. The effect of heating rate on expansion behavior of powder assemblies, phase compositions and pore structures were investigated. Results showed that the actual temperature of specimen increased rapidly from 655-661 °C (furnace temperature) to 1018–1136 °C (combustion temperature) in a short time interval of 25–55 s, indicating that an obvious TE reaction occurred at different heating rates (1, 2, 5 and 10°C · min−1). TE reaction in Ti/Al powder assemblies resulted in formation of open-celled TiAl-based intermetallics. When the heating rate was set at 5 °C · min−1, the maximum open porosity of 59% was obtained in Ti-Al bodies, which experienced the highest combustion temperature (1136°C) and underwent maximum volume expansion (48%). The pore size distribution was uniform and pores were interconnected in TE products.
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19.
  • Jiao, Xinyang, et al. (författare)
  • Exothermic behavior and thermodynamic analysis for the formation of porous TiAl3 intermetallics sintering with different heating rates
  • 2019
  • Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 811
  • Tidskriftsartikel (refereegranskat)abstract
    • Porous TiAl3 intermetallcis are of great interest due to its excellent properties and widely applied in filtering apparatus, separation material and catalyst carrier. In this study, interconnected pore-structures have been synthesized by diffusion or thermal explosion (TE) reaction sintering with different heating rates. The thermal characteristics such as temperature-time curves, exothermic change and visual images indicate that the sample experienced a significant TE reaction at higher heating rates. Results shown that the sample was ignited at 672 °C and then rapidly increased to combustion temperature of 1169, 1110 and 933 °C in tens of seconds with the heating rate of 15, 10 and 5 °C∙min−1 respectively. Meanwhile, TE represented the uniformity of volume combustion, instantaneous reaction and rapid cooling to furnace temperature, the amount of heat released during TE reaction dropped from 1303 to 963 J g−1. This indicates that the entire sintering process was controlled by TE and the pre-diffusion reaction before the melting temperature of Al atom, which would affect the subsequent combustion reaction. Thermodynamic data explained that the reaction mechanism is mainly step-controlled diffusion reaction at a low heating rate (1 °C∙min−1), while the energy gradually accumulated and thermal explosion (TE) reaction become obvious with the increasing of heating rate (from 2 to 15 °C∙min−1).
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20.
  • Jiao, Xinjang, et al. (författare)
  • Hierarchical porous TiAl3 intermetallics synthesized by thermal explosion with a leachable space-holder material
  • 2016
  • Ingår i: Materials letters (General ed.). - : Elsevier BV. - 0167-577X .- 1873-4979. ; 181, s. 261-264
  • Tidskriftsartikel (refereegranskat)abstract
    • Porous TiAl3 intermetallics were synthesized by thermal explosion (TE) reaction with NaCl as space holder material, from Ti-75Al at.% elemental powders. Results showed that the actual temperature of specimen climbed rapidly from 667 °C to 1106 °C. As a consequence, porous TiAl3 intermetallics with high open porosity (>80%) can be easily achieved when adding NaCl particles above 50 vol%. XRD patterns showed that only single-phase TiAl3 compound was synthesized via TE. Hierarchical porous TiAl3 materials displayed three pore structures, including large pores replicating from original NaCl particles, small pores among the skeletons, and tiny pores precipitated from particle skeletons. Moreover, porous TiAl3 intermetallics exhibited a uniform pore size distribution and formed an open-cellular structures allowing for the liquid-gas separation and filtration applications
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21.
  • Jiao, Xinyang, et al. (författare)
  • Microstructure Evolution and Pore Formation Mechanism of Porous TiAl3 Intermetallics via Reactive Sintering
  • 2018
  • Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer. - 1006-7191 .- 2194-1289. ; 31:4, s. 440-448
  • Tidskriftsartikel (refereegranskat)abstract
    • Porous TiAl3 intermetallics were fabricated through vacuum reactive sintering from Ti–75Al at.% elemental powder mixture. The phase compositions, expansion behaviors, pore characteristics and microstructure evolution of TiAl3 intermetallics were investigated, and the pore formation mechanism was also proposed. It was found that the actual temperature of compacts showed an acute climb from 668 to 1244 °C in 166s, while the furnace temperature maintained the linear growth of 5 °C/min, which indicated that an obvious thermal explosion (TE) reaction occurred during sintering, and only single-phase TiAl3 intermetallic was synthesized in TE products. The open porosity increased from 22.2 (green compact) to 32.8% after reactive diffusion sintering at 600 °C and rised to 58.7% after TE, then decreased to 51.2% after high-temperature homogenization at 1100 °C. Therefore, TE reaction is the dominated pore formation mechanism of porous TiAl3 intermetallics. The pore evolution in porous TiAl3 intermetallics occurred by the following mechanisms: certain intergranular pores remained among powder particles of green compact, then low-temperature sintering resulted in a further increase in porosity due to the Kirkendall effect. Moreover, TE reaction gave rise to a dramatic volume expansion because of the rapid increase in temperature, and high-temperature sintering caused densification and a slight shrinkage.
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22.
  • Kong, Ge, et al. (författare)
  • Recycling Molybdenum Oxides from Waste Molybdenum Disilicides: Oxidation Experimental Study and Photocatalytic Properties
  • 2019
  • Ingår i: Oxidation of Metals. - : Springer. - 0030-770X .- 1573-4889. ; 92:1-2, s. 1-12
  • Tidskriftsartikel (refereegranskat)abstract
    • To recycle elemental molybdenum from waste molybdenum disilicide (MoSi2) heating elements, the MoSi2 was first disintegrated to MoO3 and SiO2 powders in air at a pest oxidation temperature of 500 °C. X-ray diffraction (XRD) patterns confirmed the completion of the pest oxidation reaction. The mixture of MoO3 and SiO2 powders were heated to 950 °C in a tube furnace to evaporate MoO3, and the XRD patterns of the residue showed that only SiO2 was left in the crucible, confirming that the MoO3 was removed through thermal evaporation. The collected MoO3 crystals had a striped morphology. Photocatalytic performance of MoO3 showed superior activity in comparison with commercial MoO3 and P25 for the degradation of methylene blue under visible light irradiation. The photocatalytic degradation activity of MoO3 synthesized by thermal evaporation at 950 °C was 99.25% in 60 min.
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23.
  • Liu, Yanan, et al. (författare)
  • A novel fabrication strategy for highly porous FeAl/Al2O3 composite by thermal explosion in vacuum
  • 2018
  • Ingår i: Vacuum. - : Elsevier. - 0042-207X. ; 149, s. 225-230
  • Tidskriftsartikel (refereegranskat)abstract
    • The high porosity of FeAl/Al2O3 composites was successfully prepared via a low-energy consumption method of thermal explosion (TE) in vacuum from reactant mixtures of Fe, Al and Fe2O3. The temperature profiles, phase compositions, microstructure, porosity and pore size of the products were investigated. The TE reactions were ignited between 639 and 648 °C and maximum combustion temperatures reached to 1196–1867 °C. XRD patterns showed that FeAl, Fe2Al5 and Al2O3 were formed via TE reaction, and FeAl and Al2O3 were evolved as dominant phase after the final sintering at 1100 °C. The FeAl/Al2O3 composites exhibited an interconnected pore structure with porosities and pore size of 52–61% and 27–32 μm, respectively.
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24.
  • Liu, Yanan, et al. (författare)
  • Fabrication and Characterization of Highly Porous FeAl‐Based Intermetallics by Thermal Explosion Reaction
  • 2019
  • Ingår i: Advanced Engineering Materials. - : John Wiley & Sons. - 1438-1656 .- 1527-2648. ; 21:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Porous FeAl-based intermetallics with different nominal compositions ranging from Fe–40 at% Al to Fe–60 at% Al are prepared by a novel process of thermal explosion (TE) mode. The results show that the Al content significantly affects the combustion behavior of the specimens, the ignition temperature of the Fe–Al intermetallics varies from 641 to 633 °C and the combustion temperature from 978 to 1179 °C. The porous materials exhibit uniform pore structures with porosities and average pore sizes of 52–61% and 20–25 µm, respectively. The TE reaction is the dominant pore formation mechanism regardless of the alloy composition. However, differences in the porosity and average pore size are observed depending on the Al content. The compressive strength of porous Fe–Al intermetallics is in the range of 23–34 MPa, duly applied as filters. Additionally, a surface alumina layer is formed at the early stage and both of the oxidation process and the sulfidation process follows the familiar parabolic rate law in the given atmosphere, exhibiting excellent resistance to oxidation and sulfidation. These results suggest that the porous Fe–Al intermetallics are promising materials for applications in harsh environments with a high-temperature sulfide-bearing atmosphere, such as in the coal chemical industry.
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25.
  • Liu, Yang, et al. (författare)
  • Novel Fabrication and Enhanced Photocatalytic MB Degradation of Hierarchical Porous Monoliths of MoO3 Nanoplates
  • 2017
  • Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Porous monoliths of MoO3 nanoplates were synthesized from ammonium molybdate (AHM) by freeze-casting and subsequent thermal treatment from 300 to 600 °C. Pure orthorhombic MoO3 phase was obtained at thermal treatment temperature of 400 °C and above. MoO3 monoliths thermally treated at 400 °C displayed bimodal pore structure, including large pore channels replicating the ice crystals and small pores from MoO3 sheets stacking. Transmission electron microscopy (TEM) images revealed that the average thicknesses of MoO3 sheet were 50 and 300 nm in porous monoliths thermally treated at 400 °C. The photocatalytic performance of MoO3 was evaluated through degradation of methylene blue (MB) under visible light radiation and MoO3 synthesized at 400 °C exhibited strong adsorption performance and best photocatalytic activity for photodegradation of MB of 99.7% under visible illumination for 60 min. MoO3 photocatalyst displayed promising cyclic performance, and the decolorization efficiency of MB solution was 98.1% after four cycles
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