α-Bi2O3/β-Ni(OH)2 composites: Effective solar light photocatalysts for organic pollutants degradation

α-Bi₂O₃/β-Ni(OH)₂ composites exhibited perfect photocatalytic properties for organic pollutants degradation under sunlight irradiation. Pure α-Bi₂O₃ and β-Ni(OH)₂ were prepared by coprecipitation method and then mechanically mixed in different proportions to form α-Bi₂O₃/β-Ni(OH)₂ composites. The XRD and FTIR analyses have well emphasized the formation of monoclinic α-Bi₂O₃ and hexagonal β-Ni(OH)₂ phases with high crystallinity. The SEM micrographs of α-Bi₂O₃ and β-Ni(OH)₂ powders displayed a rod and sheet shaped grains, respectively. The band gap of the pure α-Bi₂O₃ was estimated to be 2.87 eV. Pure β-Ni(OH)₂ revealed three absorption bands in the UV–visible light region. α-Bi₂O₃/β-Ni(OH)₂ composites have a more intense absorption in the visible light region compared to pure α-Bi₂O₃ sample. Modification of α-Bi₂O₃ by β-Ni(OH)₂ induced a superior photocatalytic activity especially at β-Ni(OH)₂ content of 12 wt% in α-Bi₂O₃ (BN-12 composite). This composite showed high efficiencies of 99%, 96%, 91% and 90% for methylene blue, Congo red, methyl orange and 4-niropheniol degradation in 80, 80, 180 and 300 min under sunlight irradiation, respectively. The remarkable photocatalytic activity of the α-Bi₂O₃/β-Ni(OH)₂ composite was attributed to the new states in charge separation, charge transportation and the intensive absorption of visible light. α-Bi₂O₃/β-Ni(OH)₂ composite (BN-12) has a great potential in removing of cationic and anionic dyes beside phenolic compounds from wastewater.     

Thermoelectric properties of non-stoichiometric CaMnO3-δ composites formed by redox-activated exsolution

A novel synthesis route for preparing well-defined composites based on CMO (CaMnO₃) has been established taking advantage of the unique phase relations in the system Ca-Mn-O at reducing- and oxidizing atmosphere, respectively. Samples corresponding to stoichiometric CMO and composites with 5 and 10 vol % of Ruddlesden-Popper (Ca₄Mn₃O₁₀)- and spinel (CaMn₂O₄)-phases, respectively, were prepared with final densities >91 %. The presence of secondary phases significantly enhanced the electrical conductivity compared to stoichiometric CMO. The highest electrical conductivity was observed for CMO with 10 vol % spinel varying between 55 and 75 S/cm at temperatures between 100 and 900 °C. This composition also exhibited the highest figure-of-merit (zT) in this study, reaching 0.083 at 800 °C.     

Bayesian model selection and parameter estimation for fatigue damage progression models in composites

A Bayesian approach is presented for selecting the most probable model class among a set of damage mechanics models for fatigue damage progression in composites. Candidate models, that are first parameterized through a Global Sensitivity Analysis, are ranked based on estimated probabilities that measure the extent of agreement of their predictions with observed data. A case study is presented using multi-scale fatigue damage data from a cross-ply carbon–epoxy laminate. The results show that, for this case, the most probable model class among the competing candidates is the one that involves the simplest damage mechanics. The principle of Ockham’s razor seems to hold true for the composite materials investigated here since the data-fit of more complex models is penalized, as they extract more information from the data.     

Fabrication and piezoelectric properties of BaTiO3/BaTiO3-Bi(Mg1/2Ti1/2)O3-BiFeO3 composites

We fabricated xBaTiO₃ (BT)/(1-x)[BaTiO₃-Bi(Mg_1/2Ti_1/2)O₃-BiFeO₃] (BT-BMT-BF)?+?0.1?wt%MnCO₃ composites by spark plasma sintering and investigated the effect of BT content x, BT powder size, and BT-BMT-BF composition on piezoelectric properties. For xBT/(1-x)(0.3BT-0.1BMT-0.6BF) +?0.1?wt%MnCO₃ (x?=?0–0.75) composites with a 0.5-µm BT powder, the dielectric constant was increased with x, and the relative density was decreased at x?=?0.67 and 0.75, creating optimum BT content of x?=?0.50 with a piezoelectric constant d₃₃ of 107?pC/N. When a larger 1.5-µm BT powder was utilized for the composite with x?=?0.50, the d₃₃ value increased to 150?pC/N due to the grain size effect of the BT grains. To compensate for a compositional change from the optimum 0.3BT-0.1BMT-0.6BF due to partial diffusion between the BT and 0.3BT-0.1BMT-0.6BF grains, a 0.5BT/0.5(0.275BT-0.1BMT-0.625BF)?+?0.1?wt%MnCO₃ composite with the 1.5-µm BT powder was fabricated. We obtained an increased d₃₃ value of 166?pC/N. These results provided a useful composite design to enhance the piezoelectric properties.     

A novel route for synthesis of alumina–chromium carbide composites from PTFE-activated Cr2O3/Al/C combustion

Fabrication of alumina-chromium carbide composites was investigated by PTFE-activated Cr₂O₃/Al/C combustion synthesis. PTFE was employed as not only a reaction promoter, but a carburizing agent. Three reaction systems were prepared with different contents of carbon for the synthesis of Cr₂₃C₆, Cr₇C₃, and Cr₃C₂. The amounts of PTFE were selected to ensure combustion synthesis in the SHS (self-propagating high-temperature synthesis) mode and to provide carbon in quantities of 15 and 25?mol% of the total carbon. Experimental results showed that the combustion wave velocity and temperature decreased with increasing carbon, but increased with PTFE. A correlation between combustion wave velocity and temperature contributed to determination of the activation energy E_a =?89.15?kJ/mol for the combustion reaction. The increase of PTFE also improved formation of chromium carbides. As a result, the Cr₂₃C₆– and Cr₇C₃–Al₂O₃ composites were produced with almost no impurities. Due to a loss of carbon in carbothermic reduction, the Cr₃C₂–Al₂O₃ composite was obtained with Cr₇C₃ as the secondary carbide. SEM micrographs and DES analyses indicated that spherical carbide grains with a size of 0.5–3.0 μm were synthesized.     

Synthesis and properties of YBa2Cu3O7-δ – Y2Ba4CuWO10.8 superconducting composites

YBa₂Cu₃O_7-δ (YBCO) is a well-known high-temperature superconductor. However, its critical current density and thus maximum trapped magnetic field can be improved significantly by introducing the secondary phases (artificial pinning centers). In this contribution, we successfully prepared YBCO single-grain bulks with Y₂Ba₄CuWO_10.8 phase serving as a source of pinning centers. This phase was prepared by solid-state reaction and further refined by milling. In the next step single-grain YBCO bulks with homogeneously distributed Y₂Ba₄CuWO_10.8 were prepared by top-seeded melt growth. Precursors as well as the final product were characterized by XRD, SEM and EDS. The phase composition of YBCO bulks containing Y₂Ba₄CuWO_10.8 was analyzed using Rietveld analysis. Thermal stability of YBCO bulk was studied by STA. Furthermore, PPMS was used to study electrical resistivity and critical current density. Bulk superconducting properties such as levitation force and trapped field ability were also measured.     

Tailored dielectric tunability of alkali niobate-based antiferroelectric/relaxor-ferroelectric composites

High dielectric tunability, low loss and an appropriate level of dielectric permittivity are basic requirements of ferroelectric materials for tunable microwave devices. In this study, 0.96NaNbO₃-0.04CaZrO₃/0.88(K_0.5Na_0.5)NbO₃-0.12SrZrO₃, antiferroelectric/relaxor-ferroelectric composites were designed to tailor dielectric tunability. By tailoring the microstructure of the composites, a high dielectric tunability of 51.78% with a low loss of 0.015 was achieved at the composition ratio of 15/85. The nonlinear behaviours of the composites were explored by Johnson model; with increasing antiferroelectric phase, the contribution of the polarization to the free energy was increased between the antiferroelectric and relaxor-ferroelectric. Furthermore, the high resistance layer at the grain boundary region greatly inhibited the long-term migration of electrons and defective ions (mainly oxygen vacancies) in the composites. Therefore, the dielectric loss was remarkably decreased, and the excellent tunability was still preserved in the composite ceramics.     

浸渗法制备ZTA陶瓷/铁基复合材料研究进展

浸渗法制备ZTA陶瓷颗粒增强铁基复合材料的研究取得了很大进展。针对陶瓷预制体制备,铁水对陶瓷预制体的浸渗,陶瓷与铁水的润湿性,复合材料界面结合,复合材料耐磨性等方面的研究进行了论述。解决铁水对预制体的润湿性是实现浸渗的先决条件,常用的方法有在陶瓷预制体中添加活性元素,通过化学镀、气相沉积以及包覆等方法对陶瓷表面进行改性等;在陶瓷与金属基体间形成过渡层可以改善结合界面的组织结构,促进陶瓷与金属基体形成冶金结合;铁水对陶瓷预制体的浸渗机理,以及ZTA陶瓷复合材料的耐磨机理尚需要深入研究。     

氮化铝基导热复合材料的制备及性能

以AlN角形粉和AlN球形粉为填料,以PDMS为有机基体,制备不同固含量的导热复合材料,研究了AlN形态、AlN填充分数及粉体表面改性等对导热复合材料粘度及热导率的影响。研究结果表明,与角形AlN粉体相比,球形AlN粉体可显著降低复合材料的粘度,因而有利于获得更高的填充分数和更大的复合热导率。利用KH570对AlN粉体进行表面改性,有利于降低界面热阻,提高复合热导率,改性浓度(质量分数)为2.0%时,复合材料热导率可提高22.5%。     

石墨烯/碱式硫酸镁晶须/PVC复合材料的制备及性能表征

以改进的Hummers法制备还原氧化石墨烯(RGO),以RGO和碱式硫酸镁晶须(MHSHw)为填料,采用机械球磨法制备RGO/MHSHw/PVC复合粉料,经平板硫化机热压成型得三相复合板材。考察了RGO和MHSHw对复合材料电阻率、阻燃性能及力学性能的影响。结果表明:RGO具有很好的片层结构和导电性;当MHSHw添加量为5%,RGO添加量为1%时,RGO/MHSHw/PVC复合板材的表面电阻率为4×106Ω/square,比纯PVC下降8个数量级,达到了商业抗静电效果,拉伸强度达到最大值17.61 MPa,比纯PVC提高了44.04%,复合板材氧指数>33%,具有阻燃性能,得到力学性能优良兼具有抗静电和阻燃性能的复合材料。