Effect of annealing on microstructure and properties of Si_3N_4-AlN composite ceramics

Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN （30%, mass fraction） composite ceramics with La203 as sintering additive were prepared by hot-pressing at 1 800 ℃ and subsequently annealed at 1 450 ℃ and 1 850 ℃ for 2 h and 4 h, respectively. The materials were characterized by XRD and SEM. The effect of annealing process on the phase composition, sintering performance, microstructure, bending strength, dielectric loss and thermal conductivity of the materials was investigated. The results showed that both annealing at 1 850 ℃ and 1 450 ℃ promoted the phase transformation of α-Si3N4 to β-Si3N4. After annealing at 1 850 ℃, grain growth to a certain extent occurred in the materials. Especially, the elongated β-Si3N4 grains showed a slight increase in diameter from 0.2 μm to 0.6 μm approximately and a decrease in aspect ratio. As a result, as the annealing time increased to 4 h, the bending strength declined from 456 MPa to 390 MPa, whereas the dielectric loss decreased to 2.15× 10^-3 and the thermal conductivity increased to 16.3 W/（m.K） gradually. When annealed at 1 450 ℃, increasing the annealing time to 4 h significantly promoted the crystallization of glassy phase to La2Si6N803 phase in the materials, which led to the increase in bending strength to 619 MPa and thermal conductivity to 15.9 W/（m·K）, respectively, and simultaneously the decrease in dielectric loss to 1.53× 10^-3.

不同植物生长调节剂对猕猴桃单果重及营养成分的影响

以‘米良一号’猕猴桃为试材,用CPPU(12.50 mg/L)和6–BA、NAA、GA3(各设质量浓度50,100,200 mg/L)处理花后2周幼果,以清水处理为对照,检测成熟猕猴桃单果重、果形指数、蛋白质、可溶性固形物、可溶性糖和矿质元素等指标。结果表明:4种植物生长调节剂均可以促进果实的增大,除6–BA的增重效果不显著外,其他处理与对照的差异均达显著水平,但果实的水分含量并无显著增加;CPPU处理对果形指数没有影响,但能显著提高可溶性固形物和蛋白质含量,显著降低可滴定酸和V–C含量,显著增加Ca、P和Mg含量,显著减少B含量;施用6–BA能提高果形指数和可溶性糖含量,降低可滴定酸含量,蛋白质和V–C含量随着6–BA浓度的递增而提高,且显著高于对照,6–BA处理能显著增加Ca和Mg的含量,降低K含量;100、200 mg/L NAA处理可使果形指数明显增加,果实可溶性固形物和可溶性糖含量与NAA处理浓度呈正相关关系,且显著高于对照,而V–C含量与NAA浓度呈负相关关系,NAA处理可提高Ca、Mg含量,降低K含量。施用GA3可显著提高蛋白质、V–C、Ca和P的含量,促进Mg的积累,显著降低可滴定酸和K的含量,而对可溶性固形物和可溶性糖含量的影响不明显。

铝合金表面三嗪二硫醇和硅烷纳米复合薄膜的制备及表征

通过电化学方法,在铝合金表面制备6-N,N-二丁基胺-1,3,5-三嗪-2,4-二硫醇单盐(DBN)的纳米聚合薄膜(PDB),然后采用自组装技术对铝合金表面PDB膜进行十六烷基三甲氧基硅烷化处理,形成疏水性的高分子纳米复合薄膜(CPDB)。通过循环伏安法解释了DBN在铝合金表面的反应及PDB的生长过程,同时分析了CPDB膜的形成机理。借助傅里叶变换红外光谱仪(FT-IR)、X射线光电子能谱仪(XPS)、扫描电子显微镜(SEM)、接触角测量仪对铝合金表面薄膜的特性进行了表征。结果表明,PDB膜形成后铝合金表面的接触角从未镀膜的89.9°上升到124.3°,CPDB膜形成后接触角达135.8°;SEM和XPS测定表明该方法可以有效地在铝合金表面获得均匀致密的高分子纳米复合薄膜。