纳米晶NiCrC涂层长时加热的显微组织和硬度变化

目的 探讨纳米晶NiCrC涂层长时高温条件下的显微组织和硬度演变规律。方法 采用超音速火焰（HVAF）喷涂低温球磨纳米晶合金粉末（液氮介质）制备了纳米晶NiCrC涂层,在650 ℃空气环境中对涂层进行总时长200 h的等温热处理。采用扫描电子显微镜、X射线衍射仪、透射电子显微镜、维氏显微硬度计等方法,对涂层样品的显微组织、物相构成、晶粒尺寸和显微硬度进行了测试分析,同时对原料粉末也进行了相同条件下的对比分析。结果 NiCrC涂层显微组织的主要特征为：纳米晶金属相基体中弥散分布着细小的碳化物颗粒。在保温过程中,纳米晶涂层发生了再结晶和晶粒长大,并伴随有合金基体的脱溶及碳化物的析出、相变和后续生长等现象。该涂层显示出优良的高温热稳定性,在650 ℃保温50 h后,晶粒平均尺寸由初始态的41 nm增长至相对稳定值约100 nm。保温后涂层的硬度总体有所提升,由初始的697HV300（15 s）先升高至最大值801HV300（15 s）,而后降至相对稳定值729HV300（15 s）左右。纳米晶粉末的组织和硬度变化特点与涂层相似。结论 在650 ℃保温过程中,纳米晶NiCrC涂层中的合金相脱溶和晶粒长大导致涂层金属相基体的软化,但细小碳化物颗粒的析出强化以及由相变（Cr7C3→Cr23C6）引起的体积分数增加,不但补偿了基体的软化,而且使涂层的整体硬度有所提高。     

Thermal expansion behaviour of Sr- and Mg-doped LaGaO3 solid electrolyte

Thermal expansion coefficients (TECs) of Sr- and Mg-doped LaGaO₃ were measured continuously from room temperature up to 1000 °C. It was observed that TECs increased with the increase in dopant concentration. In the continuous TEC curve depression due to a structural change from orthorhombic to rhombohedral of the material was also observed. It was found that at a given Sr content varying the amount of Mg content led to an increase in the phase transformation temperature whereas the reverse was found to be true with the increase in Sr content. The thermal expansion was found to increase with increasing oxygen vacancies irrespectively of the type of the dopant responsible for causing the vacancy. This increase was attributed to the weakening of the binding energy as a result of the creation of additional oxygen vacancies.     

Electrochemical reduction of noble metal compounds in ethylene glycol

The effect of temperature on both the electrochemical oxidation of pure ethylene glycol and the reduction of AuCl₄⁻ in ethylene glycol at a rotating disk glassy carbon electrode has been investigated using linear sweep voltammetry. As the temperature is increased from 25°C up to 60°C, ethylene glycol begins to oxidize at lower potentials, whereas the reduction potential of AuCl₄⁻ is independent of temperature. Reduction current densities, however, increase as temperature increases. Room temperature reduction of several noble metal species in ethylene glycol was also investigated. Metal reduction potentials at both a platinum and a glassy carbon electrodes follow the sequence: AuC1₄⁻>Ag⁺>PtC1₆²⁻>Pd(NH₃)₄²⁺. The oxidation potential of ethylene glycol at both electrodes was found to be more positive than the reduction potential of the gold, silver, platinum and palladium precursors. These results predict that the spontaneous formation of noble metal particles by chemical reduction with ethylene glycol is thermodynamically unfavorable at 25°C. Gold and silver particles, however, are easily prepared at room temperature using the polyol process, which is a redox based process for the preparation of finely divided metals by chemical reduction of the corresponding metal precursors with ethylene glycol. Since measured potentials are the sum of a thermodynamic and a kinetic contribution (the overpotential), metal reduction in the polyol process seems to be aided by the overpotential. Therefore, measured potentials have been correlated to the chemical conditions at which noble metal particles are synthesized in the polyol process. It was found that as the potential difference between ethylene glycol oxidation and metal reduction increases, both the reaction temperature and time needed for metal synthesis increases. These electrochemical results may contribute to have a better understanding of the fundamentals of the polyol process, and for optimizing such reaction parameters as temperature, time and solution chemistry.     

Novel electrochemical sensing platform based on palygorskite nanorods/Super P Li carbon nanoparticles-graphitized carbon nanotubes nanocomposite for sensitive detection of niclosamide

We reported an one-pot ultrasonic-assisted method for the preparation of palygorskite nanorods/Super P Li carbon nanoparticles-graphitized carbon nanotubes (PNRs/SPCNPs-g-CNTs) nanocomposite, which was used to modify the glassy carbon electrode (GCE) for the fabrication of PNRs/SPCNPs-g-CNTs/GCE sensor. For the PNRs/SPCNPs-g-CNTs nanocomposite, PNRs with good stability presented large specific surface area and high adsorption, which promoted the enrichment of NA molecules on the electrode surface. SPCNPs with pearl chain-like nanostructure exhibited good electrical conductivity, and the combination of SPCNPs and g-CNTs with high graphitization degree formed an interconnected carbon conductive network with excellent electrical conductivity, which enhanced the charge transport efficiency. Moreover, the interconnected carbon conductive network of SPCNPs-g-CNTs not only promoted the dispersion degree of PNRs but also made up for the poor conductivity property of PNRs. When used for the detection of niclosamide (NA), an acceptable limit of detection (3.6 nM) was achieved at the PNRs/SPCNPs-g-CNTs/GCE sensor in linear NA concentration range of 0.01–10 μM. The PNRs/SPCNPs-g-CNTs/GCE sensor exhibited good reproducibility, repeatability, and anti-interference performance. For the practicability measurement, the fabricated sensor showed good practicability with satisfactory recoveries (97.0–102.7%) and low RSD values of 0.99–4.78% for the detection of NA in tap water and lake water samples.