微波固相法合成纳米ZnO及其光催化性能研究

以ZnSO4.7H2O,H2C2O4.2H2O为原料,在微波条件下制得前驱体ZnC2O4.2H2O,经洗涤、干燥、焙烧得产品。采用XRD对产物的物相组成、粒度进行分析,结果表明:该产品为粒径15.5 nm的六方晶型的氧化锌。以该氧化锌为催化剂,对亚甲基蓝溶液进行光催化降解。结果发现,经500℃焙烧1.5 h所得的纳米氧化锌其用量为75 mg时,对50 mL质量浓度为5 mg/L的亚甲基蓝溶液的降解效果最好,在紫外灯下降解2 h,降解率可达98%。     

CO2 capture enhancement by forming tetra-n-butyl ammonium bromide semiclathrate in graphite nanofluids

In this work, CO₂ capture was experimentally investigated by forming tetra-n-butyl ammonium bromide (TBAB) semiclathrate in a new system of TBAB + graphite nanofluids. The experiments were carried out at 3.5 MPa and 277.15 K. Compared to the TBAB solution and the TBAB + sodium dodecyl sulphate (SDS) solution, it was found that the system of TBAB + graphite nanofluids was preferable for CO₂ capture, and 0.2 wt.% graphite nanoparticles (GNP) was an optimal concentration for the enhancement of hydrate growth in TBAB + graphite nanofluids. At this GNP concentration, CO₂ consumption gained at 0.29 mol% TBAB is greater than that acquired at 0.62 and 2.57 mol% TBAB. CO₂ consumption obtained in TBAB + graphite nanofluids is larger than other systems containing GNP. Moreover, the morphologies of TBAB + CO₂ semiclathrate formed in TBAB solution, TBAB + SDS solution, and TBAB + graphite nanofluids were presented, and the mechanism of CO₂ capture using TBAB semiclathrate formation in graphite nanofluids was presented. Therefore, it is an efficient way to capture CO₂ by forming TBAB semiclathrate in graphite nanofluids.     

Kinetic and property parameters of poly(ethylene naphthalate) synthesized by solid-state polycondensation

A low molecular weight prepolymer with reactive end groups was annealed at temperatures between 200 and 245°C to obtain kinetic parameters for solid-state polymerization of poly(ethylene naphthalate) (PEN). An equation was developed to describe the relationships among time, temperature, and final molecular weight for PEN. The intrinsic viscosity and melting point during polymerization were used to monitor the molecular weight and the thermal stability of the resulting resins. The effect of moisture concentration on solid-state polymerization was also investigated. Hydrolytic degradation caused initial reductions of the molecular weight if prepolymers were solid-stated without being dried. With increased exposure to solid-state conditions, however, the hydrolytically degraded resin dried and repolymerized at rates similar to those samples that had undergone hydrolysis. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2055–2061, 2001     

Characterization and property of magnetic ferrite ceramics with interesting multilayer structure prepared by solid-state reaction

Polyhedral MnFe₂O₄ with multilayer structure was successfully synthesized, and the possible originating mechanism of multilayer structure was firstly determined in current study. The phase formation, morphology evolution and interface reaction of the solid-state reaction of MnO₂ and Fe₂O₃ mixture under air and reduction atmospheres were comparatively investigated, and the microwave absorption property of polyhedral MnFe₂O₄ with multilayer structure were discussed via the XRD, SEM, XPS, TEM, AFM and vector network analyzer measurements. Experiment results showed that multilayer MnFe₂O₄ can be synthesized both in the air at 1200–1300 °C and in 4 vol%CO at 1000–1100 °C. The reduction atmosphere was favorable to the formation of multilayer structure of MnFe₂O₄ due to the occurrence of multilayer MnO as the intermedium. In addition, morphology evolution demonstrated that the particle size of MnO₂ after reduction was decreased remarkably which was also beneficial to the formation of MnFe₂O₄. However, air atmosphere is unfavorable to the generation of MnFe₂O₄ due to the recrystallization growth of Fe₂O₃ to lump impeding the element diffusion. Resultantly, the required temperature for the synthesis of MnFe₂O₄ in air was much higher than that in 4 vol% CO. One possible mechanism for the polyhedral MnFe₂O₄ with multilayer structure was based on the combination of the greater growth speed of (111) plane in the cubic MnFe₂O₄ crystal and terrace-ledge-kink (TLK) growth model. Moreover, multilayer MnFe₂O₄ prepared by the solid-state reaction presented good microwave absorbing property compared with that of the ferrites synthesized via the representative wet chemistry and combined methods.     

Enhanced photovoltaic property by forming p-i-n structures containing Si quantum dots/SiC multilayers

Si quantum dots (Si QDs)/SiC multilayers were fabricated by annealing hydrogenated amorphous Si/SiC multilayers prepared in a plasma-enhanced chemical vapor deposition system. The thickness of amorphous Si layer was designed to be 4 nm, and the thickness of amorphous SiC layer was kept at 2 nm. Transmission electron microscopy observation revealed the formation of Si QDs after 900°C annealing. The optical properties of the Si QDs/SiC multilayers were studied, and the optical band gap deduced from the optical absorption coefficient result is 1.48 eV. Moreover, the p-i-n structure with n-a-Si/i-(Si QDs/SiC multilayers)/p-Si was fabricated, and the carrier transportation mechanism was investigated. The p-i-n structure was used in a solar cell device. The cell had the open circuit voltage of 532 mV and the power conversion efficiency (PCE) of 6.28%.

PACS

81.07.Ta; 78.67.Pt; 88.40.jj     

Manipulation of upconversion property and enhancement of sensitivity by tailoring the local structure

Tailoring the local crystal environment around the activators is one of an important way to enhance the upconversion (UC) luminescence intensity. Herein, we substitute the Y³⁺ lattice with La³⁺ ion gradually in Y₂Ti₂O₇:Yb³⁺, Er³⁺ phosphor and investigate the effect of La³⁺ concentration on the UC luminescent properties as well as the temperature sensing behaviors. During the phase transformation process from cubic Y₂Ti₂O₇ to monoclinic La₂Ti₂O₇, the La³⁺ ions also play an important role on the adjustment of size and morphology of particles. Furthermore, the cooperation of La³⁺ ion is in favor of the crystal growth toward the easy growth directions. The UC luminescence intensities can be enhanced efficiently with the increasing of La³⁺ concentration. The sensitivity for temperature sensing can be improved by the increasing of La³⁺ concentration in the Y₂Ti₂O₇ and La₂Ti₂O₇ two-phase coexistence system and the maximum S_A is 45.3 × 10⁻⁴ K⁻¹ at 410K when the La³⁺ concentration is 80%. The maximum S_A and corresponding temperature can be adjusted by controlling the La³⁺ concentration, which means that (Y_0.94-xLa_x)₂Ti₂O₇: Er³⁺/Yb³⁺ phosphors may be applicable to different working environment.     

Multiple property enhancement in bismuth ferrite-based ferroelectrics by balancing nanodomain and relaxor state

Bismuth ferrite-barium titanate (BF-BT)-based ferroelectrics have received widespread attention due to its adjustable structure features and multifunctional characteristics. Property optimization (ferroelectricity, piezoelectricity, electrostrain, electrostriction) for different application scenarios can be realized by increasing BT content gradually, while it is still difficult to integrate multiple performance advantages in the same component. To solve the problem and achieve the simultaneous enhancement of property parameters, defect engineering was adopted in this work to balance domain configuration and relaxor state via selective oxides modification strategy. Compared with the nanodomain engineered relaxor ferroelectrics with improved electrostrain and degraded ferroelectricity, the defect-mediated ceramics doped with MnO₂ present both enhanced electrostrain and ferroelectricity. Multiscale structure analysis (crystal structure, defect structure, and domain structure) and property characterization (ferroelectricity, strain property, and leakage current density) suggested that the defect dipoles induced by Mn substitution can effectively refine domain size and maintain ferroelectric state at room temperature, and the easier domain switching caused by weak-correlated polar dipoles greatly improves both the strain and ferroelectricity. Especially, the defect dipoles-mediated nanodomain and property enhancement can be only observed in BFO-Mn ceramics, and infeasible for other oxides (e.g., CuO and CeO₂). We believe that this work can provide some guidance to modify electrical properties in BF-BT-based ferroelectrics.     

改进固相法合成LiNixCoyMn1-x-yO2正极材料及性能研究

采用同相法制备正极材料LiNi1/3Co1/3Mn1/3O2,用X射线衍射仪(XRD)、扫描电子显微镜(SEM)/透射电镜(TEM)分析材料的结构和形貌特征,用LAND电池测试系统测试材料的电化学性能(充放电容量和循环性能等).以LiOH·H2O,H2C2O4·2H2O,Ni(AC)2·4H2O,Co(AC)2·4H2O和Mn(AC)2·4H2O为原料,采用固相法在不同煅烧温度和煅烧时间下制备的层状正极材料LiNi1/3Co1/3Mn1/3O2具有典型的α-NaFeO2型层状结构特征,晶型结构完整.电化学性能测试结果表明,在850℃下保温15 h合成的正极材料电化学性能最优,在电流密度为120 mA/g、充放电电压在2.75～4.5 V时,经30次循环后放电比容量为163.5 mA·h/g,容量保持率为94%;50次循环后为157.2 mA·h/g,容量保持率为90.8%.     

Flexible vinyl resiliency property enhancement with hollow thermoplastic microspheres

This paper demonstrates an enhancement in resiliency and rebound properties of vinyl plastisol based materials incorporating hollow thermoplastic microspheres; and their characterization using Dynamic Mechanical Analysis involving the time‐temperature superposition technique. These materials have a wide range of applications, including automotive underbody coatings, gaskets, sealants, and recreational and athletic articles.     

Synchronous improvement of piezoelectric property and temperature stability in PSN-PMN-PT ceramics by forming composites with ZnO

Relaxor ferroelectric materials with high piezoelectric properties always suffer from low phase transition temperature, making them difficult to satisfy the demands for high-temperature environment applications. In this work, we proposed a composite approach to improve the piezoelectricity and temperature stability of PSN-PMN-PT ceramics at the same time. The ZnO nanoparticles as a second phase were introduced into the PSN-PMN-PT matrix to form composite ceramics. When the ZnO content reaches 5 mol%, the piezoelectric constant d₃₃ increases from 529 pC/N for pure PSN-PMN-PT ceramic to 590 pC/N. Meanwhile, the retained d₃₃ after annealing at 200 °C keeps 92% of the value before annealing, indicating the thermal depolarization behavior is suppressed by the composite method. The synchronous improvement of the d₃₃ and thermal depolarization behavior for PSN-PMN-PT/ZnO composite ceramics is related to the local electric field and stress field caused by the addition of ZnO particles. Our results pave a simple and effective way to develop next-generation PT-based relaxor ferroelectric ceramics.     

墙地砖压制成形用陶瓷粉料的工艺性能

分析了陶瓷墙地砖的压制成形过程及陶瓷粉料的组成,并详细地论述墙地砖压制成形用陶瓷粉料的工艺性能及成形后的坯体质量。     

Surface maleylation and naphthaloylation of chitin nanofibers for property enhancement

Surface N-maleylation and N-naphthaloylation of chitin nanofiber (NF) were achieved by reaction with maleic and naphthalic anhydrides in water, respectively. Maleyl and naphthaloyl groups were sufficiently introduced to an amino group on a surface-deacetylated chitin NF. The characteristic nanofiber morphology was maintained after maleylation and naphthaloylation. These NFs were homogeneously dispersed in several organic solvents. Especially, naphthaloyl chitin NF was dispersed even in aromatic solvents, owing to the high level of solvation interactions with the naphthaloyl group. The NF dispersions in those aromatic solvents exhibited a dispersive-to-precipitate transition response at approximately 29 °C. Moreover, the naphthaloyl chitin NF dispersion cut harmful ultraviolet light. The maleyl chitin NF formed a self-standing gel after cross-linking polymerization.     

Mechanical property enhancement of semicrystalline polymers—A review

Processing plastics below their melting points has been shown to be an effective way to significantly enhance the mechanical, chemical, and physical properties of semi-crystalline thermoplastics. A number of techniques have been developed that are capable of producing highly oriented fibers, films, and shapes. In general, these techniques can be classified as drawing, extrusion, arid rolling, with some very specific modifications having been made to each, that affects the performance of the process. Of particular interest is the rate of production, the range of thicknesses achievable, the uniformity of properties in the product, and the extent, if any, of biaxiality in the product. In recent years, the productivity of such forming processes has been increased by reducing the level of molecular entanglement among neighboring molecules. As an alternate to these orientation processes, techniques have been developed which rely on strain Induced crystallization to enhance the modulus of molded parts and extrudates from a melt. This paper constitutes a review of these techniques with emphasis on the process parameters, polymers investigated, and properties of the resulting materials.     

The mechanical property and phase structures of wheat proteins/polyvinyl alcohol blends studied by high-resolution solid-state NMR

The phase structures of thermally processed wheat proteins (WP) and polyvinyl alcohol (PVOH) blends were studied by solid-state high-resolution NMR spectroscopy. The intermolecular interactions among the multi-component systems and the behavior of each component in the blends on scales of nanometers were examined. The mechanical properties of the blends were also measured and related to the phase structure studies. The results indicated that the polymer chains of WP could be homogeneously mobilized when thermally processed with glycerol and water as plasticisers, but the glycerol predominately associated with WP rather than PVOH in the blends. The intermolecular hydrogen bonding interactions between WP and PVOH caused some extent of miscibility in the system on scales of nanometers especially when the PVOH content was low. The tensile strength and modulus of the blends were improved as compared to WP. However, the intermolecular interactions were relatively weak and could not be further enhanced by increasing PVOH component in the blends. The particle miscible WP/PVOH blends contained plasticised WP and PVOH phases in conjunction with the miscible WP/PVOH phase. Increasing the PVOH content in the blends did not result in an increase of the percentage of the miscible phase and the blends tented to be immiscible while the elongation of the blends was reduced when increasing the PVOH content in the blends.     

Morphological evolution and mechanical property enhancement of natural rubber/polypropylene blend through compatibilization by nanoclay

Nanocomposites of natural rubber (NR)/polypropylene (PP) (80/20 wt %) blends filled with 5 phr pristine clay were prepared by melt‐mixing process. Effects of clay incorporation technique via conventional melt‐mixing (CV) and masterbatch mixing (MB) methods on nanostructure and properties of the blend nanocomposites were investigated. The XRD, SAXS, WAXD, and TEM results showed that the clays in the NR/PP blend nanocomposites were presented in different states of dispersion and were locally existed at the interface between NR and PP as well as dispersed in the NR matrix. The presence of clay caused unique morphological evolution such as fine fibrillar PP domains. The tensile strength was improved over the unfilled NR/PP blends by 53% and 224%, and the storage modulus at 25 °C was increased by 78% and 120% for the NR/PP/clay nanocomposites prepared by CV and MB methods, respectively. Significant improvement in both properties was particularly obtained from the MB method due to finer dispersion fibrillar PP phase in the NR matrix and stronger interfacial adhesion between NR and PP fibers, as suggested from DMA. The oil resistance of blend nanocomposites was also improved over that of the unfilled NR/PP blend, and this property was further progressed by the masterbatch mixing method. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44574.     

A new soluble aramide with pendant phthalonitrile units and polymer property enhancement by nitrile cure reactions

A new soluble aramide with pendant phthalonitrile units was prepared, while its properties including solvent resistance and thermal properties can be enhanced by further thermal treatment around the glass transition temperatures of the polymers for an extended period of time. The cured polymers were characterized by thermogravimetric analysis, differential scanning calorimetry and FTIR techniques. Such improvement in polymer properties can be attributed to the nitrile cure reactions, indicated by the observation of the decrease in nitrile absorbance and the characteristic triazine band on the FTIR spectra.     

改进固相法合成LiNi_xCo_yMn_(1-x-y)O_2正极材料及性能研究

采用固相法制备正极材料LiNi1/3Co1/3Mn1/3O2,用X射线衍射仪(XRD)、扫描电子显微镜(SEM)/透射电镜(TEM)分析材料的结构和形貌特征,用LAND电池测试系统测试材料的电化学性能(充放电容量和循环性能等)。以LiOH.H2O,H2C2O4.2H2O,Ni(AC)2.4H2O,Co(AC)2.4H2O和Mn(AC)2.4H2O为原料,采用固相法在不同煅烧温度和煅烧时间下制备的层状正极材料LiNi1/3Co1/3Mn1/3O2具有典型的α-NaFeO2型层状结构特征,晶型结构完整。电化学性能测试结果表明,在850℃下保温15 h合成的正极材料电化学性能最优,在电流密度为120 mA/g、充放电电压在2.75~4.5 V时,经30次循环后放电比容量为163.5 mA.h/g,容量保持率为94%;50次循环后为157.2 mA.h/g,容量保持率为90.8%。     

高性能聚脲弹性体防水涂料的制备及成型工艺对力学性能的影响

通过分子结构设计,成功合成了高性能聚脲弹性体涂料,通过黏度-温度曲线选定了最佳的喷涂工艺参数。采用拉伸、红外光谱、凝胶含量和扫描电镜等表征手段,研究了成型工艺对材料力学性能的影响。结果表明,采用喷涂工艺成型制备聚脲样片的拉伸强度值为25MPa,而采用溶液涂膜法制备聚脲样片的拉伸强度为54.2MPa,综合分析后认为,二者拉伸强度的差异是由于喷涂及固化过程中在聚脲样片内部产生了大量气孔所致,并通过扫描电镜照片进行了验证。