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A β-solidifying TiAl alloy with a refined microstructure and ultra-fine yttrium-rich precipitates that was consolidated by spark plasma sintering was investigated by scanning and transmission electron microscopies. Two categories of yttrium-rich precipitates, Y2O3 and YAl2, with sizes ranging from tens to hundreds of nanometers were found to be dispersed within the matrix uniformly. The crystallographic relationship between the two precipitates and the γ-TiAl matrix was determined by the selected area electron diffraction and high-resolution transmission electron microscopy. This spark plasma sintered TiAl alloy was characterized by a uniform duplex microstructure, and it exhibited excellent tensile properties at room temperature. Typically, specimen sintered at 1150°C has an ultimate tensile strength of 1113.1 MPa, yield strength of 881MPa, and a moderate plastic elongation of 1.41%.

Bifilm defects have been proposed to be critical for the generation of various metallurgical defects in castings and have been reported to exist in various composition-based alloys. However, the geometry structure of bifilm defects has not yet been well understood. This present work reconstructed the bifilm defects in a nickel-aluminium bronze alloy casting in three-dimensional (3D) space through the use of computer tomography technology. It was shown that the shape of the bifilm defects is very complex and different from a spherical defect in 3D space. The bifilm defects were experimentally extracted successfully by an electrolysis method and were imaged, which confirmed the folded double-layer structure of the bifilm defects. These results will shed new light on the understanding of bifilm defects and improve the defect control engineering of castings.

Most of the metallurgical defects in castings can be initiated by oxide bifilms reported in various alloys. However, investigations of bifilm defects in nickel-aluminium bronze castings and their fracture behaviors were absent to date, which was explored in the present work. The results showed that there are two types of defects, i.e. smooth oxide film separating from the alloy matrix (old bifilm) and crinkled oxide film tightly adhering to the matrix (young bifilm). Thermodynamics and energy spectrum analysis proved that the bifilm was Al2O3. The inferred bifilm thickening speed curve also suggests that they come from different stages of the casting process. A fracture model was proposed to understand the fracture behaviors associated with the Young's modulus of the two types of bifilm defects. These results will shed new light on the understanding of bifilm defects failure and improve the defect control of castings.

Fast prediction of adsorption isotherms is of great importance in the structural characterization and property prediction of zeolites prior to the synthesis of the target zeolite. Here, we employ f...

In this paper, we report the results obtained from the hot compression behaviour of co-spray-formed Al-Si/7075 bimetallic gradient alloys by investigating the five selected layers divided evenly from top to bottom. It was found that with a decrease in the strain rate and an increase in temperature, the hot compression flow stress of deposited alloys decreases gradually, as expected. The relationship between flow stress, temperature and strain rate follows the Arrhenius relationship. The deformation activation energy of the co-spray formed gradient alloy gradually increases from bottom to top in the height direction, which are 100.15, 167.35, 185.54, 208.78 and 220.83 KJ/mol, indicating that the degree of difficulty in the deformation of the alloy is affected by changes in the silicon content of the alloy. Finally, the flow stress constitutive equation is calculated for each layer of alloy material, which is instructive for the subsequent study of the densification process of co-spray-formed gradient alloys.

Bimetallic gradient alloys have attracted research attention recently due to their potential applications in the aerospace and automobile industries. In this study, Al-20Si/7075 bimetallic gradient alloys were successfully manufactured by co-spray forming and the roll process. We investigated the thermal expansion behavior of the gradient alloy. It was found that the coefficients of thermal expansion increased with silicon content and increased temperature, reaching the highest point at 573 K, after which they decreased on account of the relaxation of residual thermal stress and the silicon desolvation from the supersaturated aluminum phase. The measured thermal expansion coefficient can be roughly predicted through the traditional theoretical models. Our results revealed the thermal expansion behavior of Al-20Si/7075 bimetallic gradient alloys and would improve the development of new type aluminum–silicon alloy for electronic packaging.

The piezoelectric properties of poly(vinylidene fluoride) (PVDF) are determined by the prevalence and orientation of its polar β-crystal phase, which can be tuned by processing conditions, additives, mechanical stretching or post-treatment. Here, the effects of three types of processing conditions on the crystalline structure evolution of PVDF was investigated; electrospinning, solution-casting and melt-compression. An ionic liquid (1-allyl-3-methylimidazolium chloride (AMIM)) used as an additive in aiding the electrospinning process, also affected the crystalline structure of the electrospun PVDF nanofibers. The total crystallinity, crystalline phase content and dielectric properties of the PVDF samples prepared by the different conditions were evaluated. The FTIR and DSC analyses show that the melt-compressed PVDF contains a high proportion of the paraelectric α-phase with a low total crystallinity, whereas the solution-cast PVDF contains a high proportion of polar γ-phase and a higher total crystallinity. In the case of the electrospun PVDF nanofibres, the addition of AMIM improved the morphology, uniformity and promoted the formation of the polar β and γ crystalline phases. X-Ray scattering analysis refined the crystal phase contents derived from FTIR, and also determined the ordered lamellar macromorphology formed by the three processing techniques. Furthermore, AMIM enhanced the a.c. conductivity and relative permittivity of the electrospun PVDF nanofibres by an order of magnitude, showing the effectiveness of using the ionic liquid AMIM, to improve the morphology and properties of electrospun PVDF nanofibers.\ud \ud

Ternary transition metal chalcogenides provide a rich platform to search and study intriguing electronic properties. Using angle-resolved photoemission spectroscopy and ab initio calculation, we investigate the electronic structure of Cu2TlX 2 (X = Se, Te), ternary transition metal chalcogenides with quasi-two-dimensional crystal structure. The band dispersions near the Fermi level are mainly contributed by the Te/Se p orbitals. According to our ab-initio calculation, the electronic structure changes from a semiconductor with indirect band gap in Cu2TlSe2 to a semimetal in Cu2TlTe2, suggesting a band-gap tunability with the composition of Se and Te. By comparing ARPES experimental data with the calculated results, we identify strong modulation of the band structure by spin–orbit coupling in the compounds. Our results provide a ternary platform to study and engineer the electronic properties of transition metal chalcogenides related to large spin–orbit coupling.

Defects in MOFs can benefit light absorption and charge transfer for photocatalytic application, nevertheless, studies on interplay between structural defects and photocatalytic properties of MOFs are in infancy. Herein, a series of UiO-66-NH2 with different kinds of defects were created for regulating CO2 photocatalytic reduction. Theoretical calculations in combination with experimental data verified that the sample with ligand-vacant (UiO-66-NH2-LV) defect performed better than non-defect, missing-cluster and monocarboxylate compensated ones in the photocatalytic CO2 reduction reactions. UiO-66-NH2-LV shows superior photocatalytic activity with the highest CO yield of 30.5 μmol g−1h−1, which is 9.2 times higher than that of the sample with missing-cluster (UiO-66-NH2-MC), as well as the highest quantum yield (QY) of 0.90%. DFT calculations further demonstrate the correlation between discriminative photocatalytic activities in defect structures and tunable electronic properties characterized by absorption energy, Eabs, and charge transfer energy, ELMCT, in the photocatalytic process. The ligand-vacant defect with the lowest sum of Eabs and ELMCT will lower photocatalytic reaction energy barrier in the rate-limiting step among the elementary reaction step during CO2 photoreduction. The insights gained from this study will guide the MOFs defect-engineering for enhancing CO2 photocatalytic capacity.

ZSM-5/MCM-41 composite molecular sieve has been hydrothermally synthesized through a two-step crystallization process using palygorskite (PAL) as silicon and aluminum source. The products were characterized by various means and their catalytic properties for acetalization of cyclohexanone and esterification of acetic acid and n-butanol were also investigated. In the first step ZSM-5 zeolite could be formed from the acid-treated PAL after hydrothermal treatment using tetrapropylammonium bromide as template. XRD patterns, N2 adsorption and desorption data, and TEM images show that the composite obtained in the secondary step had a well-ordered mesoporous MCM-41 phase and a microporous ZSM-5 zeolite phase. Compared with ZSM-5, ZSM-5/MCM-41 composite possessed more total acid amount, weak acid sites and large pore structure due to the formation of MCM-41 and exhibited higher catalytic activity for the acetalization and esterification reaction.

Using 3,6,3′-biphenyltricarboxylic acid (H3L1) and N1,N4-di(pyridin-4-yl)terephthalamide (L), two coordination polymers (CPs) formulated as Co3L2(L1)2(H2O)8·3H2O (1) and ZnL0.5(HL1)(H2O)·2H2O (2) have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. CP 2 exhibits a uninodal 3-connected two-dimensional (2D) framework with {63}-hcb topology and DFT calculation reveals that it is a semiconductor. CP 2 shows photocurrent response under visible light illumination (650 nm > λ > 350 nm). Based on CP 2, a device based on FTO/TiO2/perovskite CH3NH3PbI3/CP 2 was constructed, which yielded a much larger photocurrent density than CP 2 in aqueous electrolyte solution under visible light illumination (650 nm > λ > 350 nm), and it is ascribed to the matched valence-band maximum (VBM) and conduction-band minimum (CBM) energy levels of CP 2 and CH3NH3PbI3. In the presence of methanol, the photocurrent response generated on the device can be remarkably improved, which is due to the photoinduced holes captured by methanol, leading to the more efficient separation of the photoinduced electrons and holes.

Bifilm defects are proposed to be critical among the metallurgical defects generated in castings. However, direct investigations of individual bifilm defects separated from the casting matrix were absent to date. In this study, separated bifilm defects in nickel-aluminium bronze were investigated systematically. The results showed that an electrolysis method can successfully separate the bifilms from the casting matrix. Al2O3 with an amorphous state, a γ-phase structure, and an α-phase structure were observed in the separated bifilms, respectively, violating the conventional prediction of only α-Al2O3 existing in the final casting. The thickness of the bifilm defects was not uniform and varied in a wide range from several nanometres to several hundred nanometres. Upon analysis, the thinner bifilm presented a much smaller Young’s modulus in comparison to the crystallised Al2O3. The thicker bifilm was intergrown with several single crystals and covered by smooth and faceted faces. These results suggest the complex bifilms form in cast nickel-aluminium bronze alloys and more investigations are therefore required in future.

The high oxidation of aluminum alloy would result in abundant oxidation defects. In recent years, bifilm has been increasingly recognized as a source of the metallurgical defects. The crack defects in aluminum alloy casting was investigated in the present work from the viewpoint of bifilm. Computed tomography has been used to image the defects in three dimensions which demonstrated the complexity of the bifilm defect. Detailed energy spectrum analysis showed that the bifilm has different compositions at different thickness. Simulations suggested that the defect is affected by flow field, thus could be eliminated by process optimization. These results would shed new lights on the understanding of the formation of bifilm defects and improve the defects control engineering of castings.

Pd–B amorphous alloy was successfully supported on the surface of natural nanoclay palygorskite (PAL) via a simple chemical reduction method. Compared with the conventional supported Pd catalyst, the Pd–B/PAL amorphous catalyst possessed the ultra-high selectivity (100%) to o-chloroaniline (o-CAN) in the hydrogenation of o-chloronitrobenzene (o-CNB) to o-CAN and avoided the dechlorination of o-CNB. XPS analysis results indicated that PAL support could reduce the electron density of Pd atoms and suppressed the hydrogenolysis of C–Cl bond. Meanwhile, the Pd–B/PAL amorphous catalyst exhibited a good stability and is a prospective catalyst for the selective hydrogenation of CNB to CAN.

This study deals with the densification of a pre-alloyed TiAl powder with excessive yttrium addition by spark plasma sintering (SPS) technique. The gas-atomized Ti–43Al–5Nb–2V–1Y (at. %) powders were sintered at various temperatures between 1100 and 1250 °C, applying a uniaxial pressure of 40 MPa. The microstructures of pre-alloyed powders and SPSed TiAl alloy samples were analyzed by scanning and transmission electron microscopies. In addition, the compression tests of SPSed alloys was carried out at room temperature (RT). Attention is focused on the existing form and distribution of excess yttrium in the initial powders and the SPSed samples. The initial powder exhibits a dendrite structure, and yttrium-rich phases (YAl2) are segregated along the interdendritic zone. After sintering, duplex, nearly lamellar (NL) and fully lamellar (FL) microstructures were obtained as a function of the sintering temperature. For duplex and NL microstructures, the YAl2 phases are fine granular precipitates in homogeneous dispersion state. Conversely, stripe-like YAl2 precipitates, which surround the α2/γ lamellar colonies, emerged in the FL microstructures. Excessive sintering temperature leads to grain growth and serious segregation of the YAl2 phases, and it deteriorates the mechanical properties of this alloy eventually.

This paper reviews domestic and foreign study result of the calculation method and variation of solid propellant and other viscoelastic material ratio of solid propellant, the viscoelastic material's Poisson's ratio as well as Poisson's ratio's influence on the structure performance of solid propellant.

This paper studies the damage process induced by dewetting microcracks in composite solid propellant. A nonlinear viscoelastic constitutive model for composite soild propellant is presented. The damage variable D is derived from the microcrack system and is function of microcrack size density. The damage evolution equation is determinded by the extending of microcrack. Form the proposed model of microrack evolution process, an explicit form of damage evolution equation which is a function of stress field is given. The cracking event N and the new crack surface area damage ΔA formed by microcrack extension are defined. Material constants are determinded by acoustic emission tests. The rationality of our model has been confirmed by tension tests.

Hollow ZSM-5 crystals were successfully synthesized through a simple one-step hydrothermal crystallization method in the presence of polyacrylamide (PAM) as template. The influences of crystallization temperature, PAM concentration, and the type of PAM on the morphology and pore structure of hollow ZSM-5 zeolite as well as the stability and formation mechanism of hollow structure were investigated. Hollow ZSM-5 crystals could be synthesized by adding three types of PAM with different surface groups. Crystallization temperature and PAM concentration played crucial roles in the formation of hollow ZSM-5 crystals. Low crystallization temperature or high PAM concentration was beneficial for the formation of hollow ZSM-5 crystals with embedded large voids in the framework structure. Egg-shell like hollow ZSM-5 crystals formed with less amount of PAM at high temperature due to the decomposition of the PAM network. Moreover, the surface walls of those hollow ZSM-5 crystals possessed microporous crystalline framework. Hollow ZSM-5 crystals exhibited good thermal and hydrothermal stability, and anti-pressure ability. ZSM-5 crystallization in the presence of PAM was in good agreement with the surface-to-core crystallization process. The fast growth of ZSM-5 nuclei on the surfaces of PAM hydrogel resulted in the formation of single crystals with hollow structure after they consumed the synthesis gel and ZSM-5 nuclei in the PAM hydrogel network.

Magnetic composite fibers with wollastonite (WO) core and Ni shell were prepared by electroless plating using natural mineral WO fibers as supporters. Zeolite P layers were then loaded on the surface of Ni/WO fibers by in situ hydrothermal method. The sample structure and properties were characterized via SEM, XRD, SQUID, EDX, and N 2 adsorption. The compact Ni–P coatings on the surface of WO fibers resulted in good magnetic properties of the Ni/WO fibers and zeolite P/Ni/WO fibers. After two crystallization cycles, a continuous zeolite P layer could be formed on the surface of Ni–P coating. The zeolite loading improved the stability of Ni–P coating in the acid solution, resulting in that the zeolite P/Ni/WO fibers can be used at a wide pH range of 3–7. Zeolite P/Ni/WO fiber exhibited a good sorption property for Cu 2+ in the aqueous solution (12.48 mg/g) and could be reused after regeneration, indicating that it could be an effective and reusable adsorbent for metal ions from a liquid system.

Sodalite submicron crystals and microspheres were successfully synthesized from natural palygorskite clay through a two-step approach by varying the synthetic parameters. The effects of initial NaOH concentration, SiO 2 /Al 2 O 3 molar ratio, and aluminium source on the morphology and particle size of synthetic sodalite were investigated, as well as the formation scheme of synthetic sodalite. Experimental results showed that the alkalinity of the synthesis gel controlled by initial NaOH concentration and SiO 2 /Al 2 O 3 molar ratio was a critical factor for the formation of sodalite crystals and microspheres. Sodalite crystals could be synthesized at high initial NaOH concentration and SiO 2 /Al 2 O 3 molar ratio, however, low initial NaOH concentration and SiO 2 /Al 2 O 3 molar ratio were beneficial for the formation of sodalite microspheres via submicron crystal aggregation.

The distribution model of temperature for the billets was established based on the porosity formation mechanism. By calculating the numerical relationship between the temperature of the deposition layer and the formation ability of the porosity, the distribution of porosity for spray formed 7075 aluminum billets was predicted and the influence of superheat on the formation probability of porosity was analyzed. The results show that a denser billet can be obtained with the average temperature of 813 K of the droplets and a liquid fraction of 50%. The porosity would increase whether the temperature further increased or decreased. Finally, the 7075 aluminum alloy was prepared by spray deposition technique with the optimum process parameters. It can be found that the distribution and types of the porosity were different at different locations. These results are in good agreement with the porosity distribution law.

A natural mineral, palygorskite clay, was used to synthesize pure zeolite X via a two-stage method. The synthetic parameters, such as calcination, crystallization time, and SiO2/Al2O3molar ratio, were investigated. The results indicated that calcination enhanced the extraction of silica from palygorskite clay and was beneficial for the formation of zeolite X. Micro-sized pure zeolite X with the particle size of 1-4 μm was obtained in the gel with the SiO2/Al2O3molar ratio range of 1.93 to 3 after hydrothermal treatment at 80 °C for 5 h. The synthetic zeolite X showed high specific surface area (487 m2/g) and low Si/Al ratio (1.17).

Attapulgite clay coated Ag/AgBr/TiO2 visible light photocatalyst was prepared by an impregnation-deposition-precipitation method. The catalyst was characterized via powder X-ray diffraction (XRD), TEM, UV-Vis spectroscopy, and EMAX, and their photocatalytic activity was examined by degradation of methylene blue in water under sunlight. The results showed that the catalyst exhibited high efficiency for the degradation of methylene blue and the catalyst activity maintained effectively after successive cyclic experiments under sunlight, attributed to adsorption of dye on attapulgite clay and high dispersion of AgBr and TiO2 nano-sized particles on the surface of attapulgite clay.

Attapulgite clay and Poly aluminum chloride (PAC) combination process was adopted for enhanced coagulation on micro-polluted raw water, TOC and NH3-N served as water quality indexes. Results showed that, when the dosage of PAC was 15 mg/L and the dosage of attapulgite clay after 350 °C heat modification was 200 mg/L, the removal rates of TOC and NH3-N reached 82.5% and 75.3% respectively under optimal cogulation conditions, which increased by 72.2% and 230.3% respectively compared with traditional PAC process, and spared 1/4 of PAC dosage. Attapulgite clay and PAC enhenced process reflected advantages of low cost, easy handling, high removal rate, accelerated settlement, sludge reduction, less residual aluminium, chemical and biological safety, and so on. Its application in water supply treatment field was in good prospect.

Broad beans were divided into six groups and implanted with N+ beam of 30 KeV, 8 × 1016/cm2 per time for various radiating times respectively. Besides the statistics of its vigor of germination, the M1 root-tip cells of these broad beans were systematically analyzed on their changes in mitotic percentage, morphology and behavior of chromosomes, along with the structure of cytoskeletons, including microtubule and intermediate filament. Based on all results of these studies, our opinions have been expressed in the report on the mechanism of low-energy N+ beams effecting on higher dicotyledons such as broad bean.