To study the modification mechanism of activated carbon (AC) by Fe and the low-temperature NH3-selective catalytic reduction (SCR) denitration mechanism of Fe/AC catalysts, Fe/AC catalysts were prepared using coconut shell AC activated by nitric acid as the support and iron oxide as the active component. The crystal structure, surface morphology, pore structure, functional groups and valence states of the active components of Fe/AC catalysts were characterised by X-ray diffraction, scanning electron microscopy, nitrogen adsorption and desorption, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively. The effect of Fe loading and calcination temperature on the low-temperature denitration of NH3-SCR over Fe/AC catalysts was studied using NH3 as the reducing gas at low temperature (150 °C). The results show that the iron oxide on the Fe/AC catalyst is spherical and uniformly dispersed on the surface of AC, thereby improving the crystallisation performance and increasing the number of active sites and specific surface area on AC in contact with the reaction gas. Hence, a rapid NH3-SCR reaction was realised. When the roasting temperature remains constant, the iron oxide crystals formed by increasing the amount of loading can enter the AC pore structure and accumulate to form more micropores. When the roasting temperature is raised from 400 to 500 °C, the iron oxide is mainly transformed from α-Fe2O3 to γ-Fe2O3, which improves the iron oxide dispersion and increases its denitration active site, allowing gas adsorption. When the Fe loading amount is 10%, and the roasting temperature is 500 °C, the NO removal rate of the Fe/AC catalyst can reach 95%. According to the study, the low-temperature NH3-SCR mechanism of Fe/AC catalyst is proposed, in which the redox reaction between Fe2+ and Fe3+ will facilitate the formation of reactive oxygen vacancies, which increases the amount of oxygen adsorption on the surface, especially the increase in surface acid sites, and promotes and adsorbs more reaction gases (NH3, O2, NO). The transformation from the standard SCR reaction to the fast SCR reaction is accelerated.
Cu doped Mg(OH)2 nanoparticles were synthesized with varying concentrations from 0 to 10% by a chemical synthesis technique of coprecipitation. X-rays diffraction (XRD) of the samples confirms that all the samples acquire the hexagonal crystal structure. XRD results indicated the solubility limit of dopant in the host material and the secondary phase of CuO was observed beyond 3% Cu doping in Mg(OH)2. The reduction in the size of nanoparticles was observed from 166 to 103 nm for Mg(OH)2 and 10% Cu doped Mg(OH)2 samples, respectively. The shift in absorption spectra exhibited the systematical enhancement in optical bandgap from 5.25 to 6.085 eV. A good correlation was observed between the bandgap energy and crystallite size of the nanocrystals which confirmed the size induced effect in the nanoparticles. The transformation in the sample morphology was observed from irregular spherical particles to sepals like shapes with increasing the Cu concentration in the host material. The energy dispersive X-Ray (EDX) analysis confirmed the purity of mass percentage composition of the elements present in the samples.
The carbon-coated ZnO nanospheres materials have been synthesized via a simple hydrothermal method. The effect of carbon content on the microstructure, morphology and electrochemical performance of the materials was investigated by XRD, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy and electrochemical techniques. Research results show that the spherical ZnO/C material with a carbon cladding content of 10% is very homogeneous and approximately 200 nm in size. The electrochemical performances of the ZnO/C nanospheres as an anode materials are examines. The ZnO/C exhibits better stability than pure ZnO, excellent lithium storage properties as well as improved circulation performance. The Coulomb efficiency of the ZnO/C with 10% carbon coated content reaches 98%. The improvement of electrochemical performance can be attributed to the carbon layer on the ZnO surface. The large volume change of ZnO during the charge-discharge process can be effectively relieved.
The crystal structures and electronic structures (including band gap, project density of states, partial charge density, effective mass and electron localization function) of the 2D lead iodide perovskites hybrids with different organic spacer cations of 4-fluorophenylethanaminium (4F-PEA+), ethanolamine (EA+), thienylethylamine (TEA+) were investigated using first-principles calculations. It was found the higher dipole moment, the stronger the hydrogen bonding between the organic amino and iodide in the inorganic layer, and the larger the [PbI6]4− octahedral distortions in these crystal structure. Further quantifying the degree of the distortions using OctaDist software showed that the distortion of adjacent [PbI6]4− octahedra had a decisive effect on the band gap. Specifically, the greater deviation of Pb-I-Pb bond angles from 180°, together with the larger distortion of multiple [PbI6]4− octahedron resulted in a wider band gap, which was verified by calculated band gap using different DFT methods. The results outlined the relationships of hydrogen bonding, ocathedra distortion and band structure in 2D perovskites, highlighting the importance of the cations on the structural tuning and optoelectronic properties.
We demonstrated a chemical process in the fabrication of a SERS fiber probe with an ultrahigh sensitivity. The synthesis was carried out by preparing Au@Ag core-shell nanorods (Au@Ag-NRs) self-assembled on polyelectrolyte (PE) multilayers, for which Au@Ag-NRs were controlled by adjusting the silver layer thickness. The effect of silver layer thickness of Au@Ag-NRs on the SERS performance of the fiber probe was investigated. The SERS fiber probe shows the best performance when the silver layer thickness is controlled at 8.57 nm. Under the condition of optimizing silver layer thickness, the fiber probe exhibits ultra-high sensitivity (i e, 10−10 M crystalline violet, CV), good reproducibility (i e, RSD of 3.5%) and stability. Besides, electromagnetic field distribution of the SERS fiber probe was also investigated. The strongest enhancement is found within the core of fiber, whereas a weakened electromagnetic field exists in the fiber cladding layer. The SERS fiber probe can be a good candidate in ultra-trace detection for biomedical and environmental areas.
The effects of particle size, gradation and solid loading of silicon nitride (Si3N4) on the rheological behavior and curing properties of ceramic slurry are studied by stereolithography (SLA). The results show that the particle size of Si3N4 powder has a significant influence on the rheological properties and stability of the slurry. When m D50 = 13 µm:m D50 = 23 µm = 3:7, the slurry viscosity is low and the sedimentation is slow. The most important thing is that with the increase of the solid loading of the slurry, the viscosity of the slurry increases, the stability becomes higher, and the curing thickness decreases. The curing thickness of Si3N4 ceramic slurry with solid loading of 50 vol% can reach nearly 50 µm. The above results finally show that the process optimizes the formulation of the slurry in rheological and curing properties.
Inorganic halide double perovskites A2B′B″X6 have gained significant interests for their diverse composition, stable physicochemical properties, and potential for photoelectric applications. The influences of trivalent and monovalent cations on the formation energy, decomposition energy, electronic structure and optical properties of cesium-based lead-free Cs2B′B″Br6 (B′ = Na+, In+ Cu+, or Ag+; B′= Bi3+, Sb3+, In3+) are systematically studied. In view of the analysis and results of the selected double perovskites, for the double perovskites with different B-site trivalent cation, the band gap increases in the order of Cs2AgInBr6, Cs2AgSbBr6 and Cs2AgBiBr6, with Cs2AgBiBr6 possessing the highest thermodynamic stability. Therefore, the Bi-based perovskites are further studied to elucidate the effect of monovalent cation on their stability and electronics. Results show that the thermodynamic stability rises in the sequence of Cs2NaBiBr6, Cs2InBiBr6, Cs2AgBiBr6 and Cs2CuBiBr6. Notably, Cs2CuBiBr6 exhibits a relatively narrow and appropriate band gap of 1.463 4 eV, together with the highest absorption coefficient than other compounds, suggesting that Cs2CuBiBr6 is a promising light absorbing material that can be further explored experimentally and be applied to optoelectronic devices. Our research offers theoretical backing for the potential optoelectronic application of cesium-based lead-free halide double perovskites in solar energy conversion.
Two carbonation approaches are considered for studying the effects on the hardening mechanisms of slurries made of 100 wt% electric arc furnace steel slag (EAF) slag or 80 wt% EAF slag incorporating 20 wt% of Portland cement, which are applied during the hot-stage pretreatment with simulated gas for raw steel slag or the accelerated carbonation curing of slurry. The mechanical strengths, carbonate products, microstructures and CO2 uptakes were quantitatively investigated. Results manifest that accelerated carbonation curing increases the compressive strengths of steel slag slurry, from 17.1 MPa (binder of 80 wt% EAF and 20 wt% cement under standard moisture curing) to 36.0 MPa (binder of 80 wt% EAF and 20 wt% cement under accelerated carbonation curing), with a CO2 uptake of 52%. In contrast, hot-stage carbonation applied during the pretreatment of steel slag increases the compressive strengths to 43.7 MPa (binder of 80 wt% carbonated EAF and 20 wt% cement under accelerated carbonation curing), with a CO2 uptake of 67%. Hotstage carbonation of steel slag is found for particle agglomeration, minerals remodeling and calcite formed, thus causing an activated steel slag with a dense structure and more active components. Accelerated carbonation curing of steel slag slurry paste results in the newly formed amorphous CaCO3, calcite crystalline and silica gels that covered the pores of the matrix, facilitating microstructure densification and strength improvement. Adopting the combinative methods of the hot-stage CO2 pretreatment and accelerated carbonation curing creates a promising high-volume steel slag-based binder with high strengths and CO2 storage.
The distribution characteristics of air voids in ultrathin asphalt friction course(UAFC) samples with different gradations and compaction methods were statistically analyzed using X-ray computed tomography (CT) and image analysis techniques. Based on the results, compared with the AC-5 sample, the OGFC-5 mixture has a higher air void ratio, a larger air void size and a greater number of air voids, with the distribution of internal air voids being more uniform and their shapes being more rounded. The two-parameter Weibull function was applied to fit the gradation of air voids. The fitting results is good, and the function parameters are sensitive to changes in both mineral gradation and compaction method. Moreover, two homogeneity indices were proposed to evaluate the compaction uniformity of UAFC samples. Compared with the Marshall method, the SGC method is more conducive to improve the compaction uniformity of UAFC samples. The compaction method significantly influences the air void distribution characteristics and compaction uniformity of AC-5 sample, but has a less significant impact on OGFC-5 sample. The experimental results in the study provides a solid foundation for further explorations on the internal structure and mixture design of UAFC.
We completed the uniaxial tensile test of mortar in the range of strain rate from 10−6 to 10−4 s−1 in the section containing softening, and carried out acoustic emission monitoring (AE) simultaneously. A series of AE parameters and spectrum analysis methods were used to identify the damage evolution process and cracking mechanism of mortar at different strain rates. The results show that, with the increase of strain rate, the peak stress and tensile elastic modulus of mortar increase obviously, and the stress level corresponding to the starting point of AE activity increases significantly as well, which indicates that the mechanical properties and AE characteristics of mortar have obvious strain rate effect. With the increase of strain rate, the cumulative AE hit decreases gradually, while the average AE hit rate increases significantly, indicating that the increase of strain rate reduces the damage degree of internal microstructure of the specimen, but the crack propagation speed increases. In the pre-peak stress stage, the average of AE ringing count and signal energy decreases with the increase of strain rate, while the average of duration increases; in the post-peak stress stage(f t − 30% f t), the average of the three AE parameters all increase with the increase of strain rate, indicating that the strain rate effect on the damage process of mortar is different before and after peak stress, and the damage mechanism represented by different parameters is also different. In the whole process of uniaxial tensile of mortar, with the increase of strain rate, the scatter distribution of AE frequency-amplitude becomes more discrete, and the b-value shows a decreasing trend. In addition, the average level of AE peak frequency decreases with the increase of strain rate, while that of ca8 band wavelet energy spectrum coefficient increases. It is indicated that the increase of strain rate enables the crack propagation state of mortar specimen to become unstable, and the width of macrocrack increases but the proportion decreases.
Compared with the control sample without limestone powder (LP), the mechanical properties of the sample with 30% LP can be significantly improved by using a small amount of water reducer to reduce the water-cement ratio, without significantly affecting the fluidity of the fresh mixture and increasing the economic cost. In addition, compared with the sole addition of limestone powder, dual addition of metakaolin and limestone powder can effectively improve the strengths. The reason of this phenomenon was investigated by means of XRD, TG-DTG, SEM, LF-NMR and isothermal calorimetry, etc. The reactive aluminum-rich phases in metakaolin react with limestone powder in the hydration process, and the formed calcium carboaluminate reduces the porosity and makes the hardened paste denser. The addition of ground granulated blast furnace slag can also improve the strength of the specimen added with limestone powder, whereas, the effect is inferior to that of metakaolin, for the ground granulated blast furnace slag contains less reactive aluminate phases, and accordingly, the amount of calcium carboaluminate generated is lower than that of metakaolin.
High-strength pervious concrete (HSPC) with porosity ranging from 0.08% to 2.011% was prepared. The mechanical properties and rainstorm waterlogging resistance of HSPC were evaluated, and a design method of HSPC pore characteristics (porosity and pore diameter) based on the mechanical properties and rainstorm waterlogging resistance was proposed. The results showed that the reduction of effective cross-sectional area caused by artificial channels was the main factor affecting flexural strength but had limited influence on compressive strength. Compared with the concrete matrix without artificial channels, the compressive strength of HSPC with porosity of 2.011% decreased by 7.4%, while the flexural strength decreased by 48.3%. The permeability coefficient of HSPC can reach 16.35 mm/s even at low porosity (2.011%). HSPC can meet the requirements of no rainstorm waterlogging, even if exposed to 100-year rainstorms. When the mechanical properties and rainstorm waterlogging resistance are compromised, the recommended porosity ranges from 1.1% to 3.5%, and the recommended pore diameter ranges from 0.8 to 2.7 mm.
This study investigates the influence of using ground palm oil fuel ash (G-POFA) from 10%–30% as cement replacement (by weight) on the cement mortar’s pH under various curing conditions. These findings were supplemented by thermal gravimetric analysis (TGA). Moreover, the resistance of G-POFA blended cement mortars to water absorption and sorptivity was determined. Further, the k-value test was carried out to explain the pozzolanic and filler behavior of G-POFA and to support the results obtained from TGA. It was found that there was no significant impact of several curing conditions on the pH of mortars. The mortar with 10% G-POFA in replacement of cement (G-POFA-10) exhibited the best resistance against water absorption and sorptivity.
To reveal the deterioration mechanism and service life of concrete durability in the western saline soil area, the indoor accelerated test of the concrete specimen was simulated in the coupled environment of salt erosion and dry-wet cycles in the west saline soil area of China. The deterioration mechanism of concrete durability was revealed through the relative dynamic elastic modulus, relative quality evaluation parameters, SEM, and XRD evaluation indexes. Random Wiener distribution function was used for modeling life prediction. The results show that the relative dynamic elastic modulus evaluation parameter as an evaluation index of concrete durability under various environmental coupling effects is more reliable than the relative quality, there were holes and cracks in the concrete, and needle-like and layered crystals grow from the internal cracks. The corrosion products include ettringite, gypsum and other expansive crystals and non-gelling Mg(OH)2; the expansion stress caused by physical, chemical reaction, and temperature change under the action of dry-wet cycle aggravates the formation and development of cracks. The random Wiener distribution function can describe the degradation process of concrete specimen durability, and the established concrete reliability function can intuitively reflect the service life of concrete specimens.
This study aims to clarify the effects of curing regimes and lightweight aggregate (LWA) on the morphology, width and mechanical properties of the interfacial transition zone (ITZ) of ultra-high performance concrete (UHPC), and provide reference for the selection of lightweight ultra-high performance concrete (L-UHPC) curing regimes and the pre-wetting degree LWA. The results show that, under the three curing regimes (standard curing, steam curing and autoclaved curing), LWA is tightly bound to the matrix without obvious boundaries. ITZ width increases with the water absorption of LWA and decreases with increasing curing temperature. The ITZ microhardness is the highest when water absorption is 3%, and the microhardness value is more stable with the distance from LWA. Steam and autoclaved curing increase ITZ microhardness compared to standard curing. As LWA pre-wetting and curing temperatures increase, the degree of hydration at the ITZ increases, generating high-density CSH (HD CSH) and ultra-high-density CSH (UHD CSH), and reducing unhydrated particles in ITZ. ITZ micro-mechanical properties are optimized due to hydration products being denser.
In order to expand the advantages of strong durability and high compressive strength of calcium silicate hydrates(C-S-H), at the same time to make up for the poor early mechanical strength of magnesium silicate hydrates (M-S-H), we present the features and advantages of C-S-H and M-S-H and a comprehensive review of the progress on CaO-MgO-SiO2-H2O. Moreover, we systematically describe natural calcium and magnesium silicate minerals and thermodynamic properties of CaO-MgO-SiO2-H2O. The effect of magnesium on C-S-H and calcium on M-S-H is summarized deeply; the formation and structural feature of CaO-MgO-SiO2-H2O is also explained in detail. Finally, the development of calcium and magnesium silicate hydrates in the future is pointed out, and the further research is discussed and estimated.
Soda residue-magnesium oxychloride cement is prepared with soda residue from ammonia soda process method, magnesium oxide and magnesium sulfate heptahydrate as main raw materials, and its consolidation mechanism of chloride ion is studied. The results show that the hydration products of soda residue-magnesium oxychloride cement are mainly 5-phase, gypsum and brucite, which exist in the matrix in needle rod shape, long plate shape and hexagonal plate shape, respectively. When the molar ratio of MgO/MgCl2 is 8:1, the concentration of MgSO4 is 29%, and the mass ratio of soda residue: magnesium oxide: magnesium sulfate heptahydrate is 45.8:36.4:17.8. The chloride ion consolidation effect of the sample is the best, and the chloride ion consolidation content of the 7 d sample is about 93%. The chloride ion consolidation content of the 28 d sample is about 96%.
Due to the presence of old mortar (OM) and interfacial transition zone (ITZ), recycled concrete aggregate (RCA) is inferior to natural aggregate (NA). The purpose of this paper was to study the effect of accelerated carbonation on the macro-properties and micro-properties of RCA under different pressure (0.05, 0.15, 0.30 MPa). The macro-property tests included colour change, apparent density, water absorption, and crushing value of RCA. The micro-property tests included scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), and Vickers micro-hardness (VMH). The results showed that the change trends of apparent density, water absorption, and crushing value of RCA displayed exponential relationships as pressure increasing, with the optimum pressure of 0.30 MPa. SEM images indicated that the calcite caused by the hydration products in RCA and the Ca(OH)2 derived from saturated lime water improved the properties of RCA; as the apparent density increased, the water absorption and crushing value decreased. The results of XRD and TG-DSC indicated that, as the pressure increased, the masses of Ca(OH)2 in carbonated RCA gradually decreased, while those of CaCO3 gradually increased, which demonstrated that the carbonation degree gradually increased. Besides, ITZ-2 was the weakest phase in RCA, but its improvement degree of VMH by accelerated carbonation was higher than that of OM. However, RCA was not completely carbonated, but only carbonated in a certain depth after 24 h accelerated carbonation.
In order to investigate the corrosion mechanism of recycled reinforced concrete (RRC) under harsh environments, four recycled coarse aggregate (RCA) contents were selected, and saline soil was used as an electrolyte to perform electrified accelerated corrosion experiments. The relative dynamic elastic modulus and relative corrosion current density were considered to describe the deterioration law of the RRC in saline soil. The results indicated that as the energization time increased, the corrosion current density, corrosion potential, and polarization resistance of the steel bar decreased gradually. Compared with ordinary reinforced concrete, when the RCA content was 30%, the ability of the RRC to resist corrosion was improved slightly; however, when the RCA content exceeded 30%, the corrosion resistance of the RRC deteriorated rapidly. Scanning electron microscopy revealed that for a dense RRC, less corrosion products were generated in the pores inside the concrete and on the surface of the steel bar. X-ray diffraction results indicated that SO4 2− can generate ettringite and other corrosion products, along with volume expansion. The main corrosion products generated on the surface of the steel bars included Fe2O3, Fe3O4 and FeO(OH), which were the corrosion products generated by steel bars under natural environments. Therefore, using saline soil as an electrolyte is more consistent with the actual service environments of RRC. Both the relative dynamic mode and relative corrosion current density of the degradation parameters conform to the Weibull distribution; furthermore, the relative dynamic mode is more sensitive and the corresponding reliability curve can better describe the degradation law of RRC under saline soil environments.
The effects of carbon distribution on the microstructure and thermal conductivity of ductile iron were investigated in the present study. The microstructure of as-cast and quenched ductile iron were characterized by OM and SEM. Results showed that the microstructure of as-cast ductile iron was composed of spheroidal graphite, ferrite with the volume of 80%, and a small amount of pearlite, and quenched ductile iron was composed of spheroidal graphite, coarse/fine acicular martensite (α M phase) and high-carbon retained austenite (γ phase). The volume fraction of retained austensite and its carbon content for direct quenched ductile iron and tepmered ductile iron were quantitatively analysed by XRD. Results revealed that carbon atoms diffused from α M phase to γ phase during tempering at low temperatures, which resulted in carbon content in retained γ phase increasing from 1.2 wt% for the direct quenched sample to about 1.9 wt% for the tempered samples. Consequently, the lattice distortion was significantly reduced and gave rise to an increase of thermal conductivity for ductile iron.
Based on the mass action concentration theory, a novel thermodynamic analysis for the raw material ratio in the procedure of preparing Ti−6Al−4V alloy by aluminothermic reduction process is proposed in this paper, which is originated from TiO2, Al particles, and V2O5 as feedstocks, and the relevant equilibrium thermodynamics was calculated through this new method. The results show that the range of aluminum addition coefficient in raw material to experiment should be controlled within 61.5%–100%, which can significantly reduce the number of experimental groups. This method is ready to regulate the matter of excessive aluminum content in reactants for materials preparation, especially for those reactions including elements that are effortless to combine with aluminum to form the corresponding intermetallics or alloys. In addition, it can also be used in general metallurgy or material preparation process to effectively predict the composition and proportion of equilibrium components under certain conditions.
The interface structure and electronic properties of Fe(110)/Al(110) are investigated by the first-principles plane-wave pseudopotential method. The interface segregation position of Si and Mg is determined, and the effect of Mg and Si on the interface binding of Fe(110)/Al(110) is analyzed by combining the work of separation and charge density. The results show that the Fe(110)/Al(110) interface energy of Fe-Hollow coordination is smaller and the interface structure is more stable. The Fe(110)/Al(110) interface separation surface in the form of Fe-Hollow coordination appears at the sub interface layer on the side of Al (110) near the interface. The interface structure of Mg and Si segregation is similar to that of undoped alloy elements. The calculations also suggest that Mg and Si segregate on the Al (110) side of the interface and occupy the Al lattice on the Al (110) side. The segregation of Mg and Si elements will reduce the interface binding, primarily because the Fe-Si bond and Fe-Mg bond are weaker than Fe-Al bond.
The relationship between the microstructure and the practical performance of two different copper-beryllium alloys including their lifetime has been investigated. Herein, two valves made of two different alloys with very similar compositions and the same heat treatment methods were investigated by various standard techniques including metallography, X-ray diffraction, chemical composition, microhardness, and thermal conductivity measurements. Although both alloys experienced the same heat-treatment processes, they revealed different thermal and mechanical properties due to the minor difference in their chemical composition. The alloy providing a longer lifetime (40% more) as the tip had a higher thermal conductivity of 280.3 W (m·K)−1 (about two times that of the other alloy). Regarding the metallography images and the measured thermal conductivity values of the alloys, the extended lifetime of the nozzle with the optimum performance is ascribed to its biphasic microstructure and the minor grain boundaries and interfacial thermal resistance. And important difference in the chemical composition was investigated in this study.
The microstructure and mechanical properties of the TB8 titanium alloy were controlled by a secondary processing technology of solution-equal channel angular pressing (ECAP)-aging treatment, which combined strong plastic deformation with heat treatment. The effects of ECAP and heat treatment on the microstructure and properties of the titanium alloy were systematically investigated by optical microscopy (OM), scanning electron microscopy (SEM), hardness tests, and tensile property analysis. The results indicate that the metallographic structure without ECAP treatment is mainly equiaxed β-phase, while that after ECAP treatment is equiaxed β-phase with grain fragmentation, slip bands, and new small grains. After 850 °C solution-ECAP-520 °C aging treatment, the titanium alloy has the smallest grain size, while the directionality of tissue growth along the ECAP direction is the most apparent. Under the same solution-aging conditions, the hardness of the titanium alloy increases from 431.5 to 531.2 HV compared to that without ECAP treatment, i e, increases by 23.11%, and the tensile strength increases from 1 045.30 to 1 176.25 MPa, i e, increases by 12.5%.
The influence of thermal-cold cycling treatment on mechanical properties and microstructure of 6061 aluminum alloy was investigated by means of tensile test, optical microscopy(OM), X-ray diffraction(XRD) and transmission electron microscopy(TEM). The cryogenic treatment mechanism of the alloys was discussed. The results show that thermal-cold cycling treatment is beneficial since it produces a large number of dislocations and accelerates the ageing process of the alloy and yields the finer dispersed β″ precipitates in the matrix. This variation of microstructural changes leads to more favorable mechanical properties than the other investigated states, while grain boundary precipitation is coarse and distributed discontinuously along grain boundaries, with a lower precipitation free zone (PEZ) on the both sides of precipitated phase. As a result, the tensile strength, elongation and conductivity of 6061 aluminum alloy after thermal-cold cycling treatment are 373.37 MPa, 17.2% and 28.2 MS/m, respectively. Compared with conventional T6 temper, the mechanical properties are improved significantly.
We performed thermal simulation experiments of double-pass deformation of hypereutectoid rails with different microalloying elements at a cooling rate of 1°C/s and deformation of 80% to explore the influence of rare-earth and microalloying elements on the structure of hypereutectoid rails and optimize the composition design of hypereutectoid rails. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and other characterization techniques were employed to quantitatively analyzed the effects of different microalloying elements, including rare-earth elements, on pearlite lamellar spacing, cementite characteristics, and dislocation density. It was found that the lamellar spacing was reduced by adding various microalloying elements. Cementite lamellar thickness decreased with the refinement of pearlite lamellar spacing while the cementite content per unit volume increased. Local cementite spheroidization, dispersed in the ferrite matrix in granular form and thus playing the role of dispersion strengthening, was observed upon adding cerium (Ce). The contributions of dislocation density to the alloy strength of four steel sheet samples with and without the addition of nickel, Ce, and Ce–copper (Cu) composite were 26, 27, 32, and 37 MPa, respectively, indicating that the Ce-Cu composite had the highest dislocation strengthening effect. The Ce−Cu composite has played a meaningful role in the cementite characteristics and dislocation strengthening, which provides a theoretical basis for optimizing the composition design of hypereutectoid rails in actual production conditions.
A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained after 4 passes of equal channel angular pressing (ECAP). Tension–compression asymmetry in yield and work hardening behavior of UFG CP Ti were investigated by uniaxial tension and compression tests. The experimental results reveal that UFG CP Ti exhibits a relatively obvious tensioncompression asymmetry in yielding and work hardening behavior. The basal and prismatic <a> slip are suppressed either for tension or compression, which is the easiest to activate. The tension twin system $\{10\bar{1}2\}<\bar{1}011>$ is easily activated in compression deformation due to the prismatic fiber texture based on the Schmidt factor, consequently resulting in a lower yield strength under compression than tension. ECAP can improve the tension-compression asymmetry of CP Ti due to grain refinement. The interaction among the dislocations, grain boundaries and deformation twins are the main work hardening mechanisms for compression deformation, while the interaction between the dislocations and grain boundaries for tension deformation. Deformation twins lead to the higher work hardening under compression than tension.
A simple and effective superhydrophobic mesh was designed and made to separate oil-water mixture. Alkali-activated fly ash reacted with 1-bromooctadecane to prepare superhydrophobic modified fly ash (MFA) with low surface energy through Williamson ether synthesis. The MFA powder was then coated uniformly on a stainless steel mesh (SSM) along with the epoxy resin E44 and curing agent T31 to give the superhydrophobic MFA-modified stainless steel mesh (MFA-SSM). The MFA-SSM has a high static water contact angle (CA) of 150.1° and can separate various oil or organic solvent from water with >95% separation efficiency. The oil-water separation efficiency remained high after 30 runs of petroleum ether/water separation. The developed superhydrophobic stainless steel mesh is expected to have wider use in oil-water separation.
Polyamide 6 (PA6) was employed as a charring agent of intumescent flame retardant (IFR) to improve the flame retardancy of ethylene-vinyl acetate copolymer (EVA). Different processing procedures were used to regulate the localization of IFR in the EVA matrix. Localizations in which IFR was dispersed in the PA6 phase or in the EVA phase were prepared. The effect of the localization of IFR on the flame retardancy of EVA was investigated. The limited oxygen index (LOI), vertical burning (UL 94) and cone calorimeter test (CCT) showed that the localization of IFR in the EVA matrix exhibited a remarkable influence on the flame retardancy. Compared with EVA/IFR, a weak improvement in the flame retardancy was observed in the EVA/PA6/IFR blend with the localization of IFR in the PA6 phase. When IFR was regulated from the PA6 phase to the EVA matrix, a remarkable increase in the flame retardancy was exhibited. The LOI was increased from 27.8% to 32.7%, and the UL 94 vertical rating was increased from V-2 to V-0. Moreover, an approximately 41.36% decrease in the peak heat release rate was exhibited. A continuous and compact intumescent charring layer that formed in the blends with the localization of IFR in the EVA matrix should be responsible for its excellent flame retardancy.
Porous polymer (pyrrolopyrrole) was successfully prepared via domino-ring-formation reaction. The chemical-physical properties of cyanided covalent triazine frameworks (CTF-CN) were characteriazed by fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), specific surface area analyzer (BET) and thermogravimetric analysis (TGA), respectively. The experimental results of adsorption of chloranil (TCBQ) in aqueous solution indicated that CTF-CN exhibited distinctive adsorption capacity toward TCBQ owing to its large specific surface area. Specifically, the adsorption equilibrium of as-prepared polymer was executed within 5 h and the calculated adsorption capacity was 499.76 mg/g. Furthermore, the adsorption kinetics could be well defined with the linear pseudo-second-order model, which implies that the chemical interaction are relative important in the course of TCBQ removal. Finally, the current studies verify that CTF-CN has unique rigid and nano-porous framework structure, which can be employed for the treatment of a series of harmful aromatic substances.
We improved the adhesion between silicon based insulating materials and epoxy resin composites by adding the adhesion promoter cycloborosiloxane (BSi, cyclo-1,3,3,5,7,7-hexaphenyl-1,5-diboro-3,7-disiloxane). The experimental results show that the addition of BSi in the silicone rubber (SR) system significantly increases the tensile shear strength between BSi and epoxy resin (EP), reaching 309% of the original value. On this basis, the mechanism of BSi to enhance the adhesion effect was discussed. The electron deficient B in BSi attracted the electron rich N and O in EP to enhance the chemical interaction, combined with the interfacial migration behavior in the curing process, to improve the adhesion strength. This study provides the design and synthesis ideas of adhesive aids, and a reference for further exploring the interface mechanism of epoxy resin matrix composites.