水耕条件下弱结构耕层土壤性状微层化现象的研究

由于土壤颗粒的选择性沉降,弱结构农田中水耕作用可导致耕层内上下之间物质组成的差别。为了解这种差异化是否会影响土壤性状的分异,本文选择代表性农田比较分析了水耕与旱耕条件下耕作层内上下部之间土壤性状的差异,并与结构发育良好的土壤进行了比较。结果表明:长期水耕的弱结构农田耕作层上下土壤之间颗粒组成、有机质、全氮含量、CEC、有效磷、速效钾、微生物生物量碳和Cu、Zn、Cd、Pb的含量均存在明显的分异,粗颗粒(砾石和砂粒)由上至下增加,而细颗粒(粘粒)从上至下减少。从0~2 cm土层至18~20 cm土层,土壤有机质、全氮、CEC分别下降达49.77%、48.77%和38.25%;土壤有效磷、速效钾和微生物生物量碳分别下降21.23%、13.54%和29.24%;从0~4 cm土层至16~20 cm土层,Cu、Zn、Cd和Pb的含量分别由27.43~28.33、65.45~71.43、0.13~0.15、24.73~27.65 mg/kg下降至23.74~24.32、53.66~54.54、0.053~0.067、18.78~19.54 mg/kg;但土壤pH的变化不明显。结构良好的农田长期水耕对以上性状的影响较小或没有影响。长期旱耕的耕作层中有机质、全氮、CEC、速效养分、微生物生物量碳和Zn、Pb含量也呈上高下低的趋势,但上下之间的差异较小,对耕作层中颗粒组成、pH、Cu和Cd的分布无明显影响。研究认为,长期水耕可导致弱结构耕作层土壤性状的非均质化,可能会影响作物对土壤养分的吸收,应重视对其结构的改良。

多壳层化中空微球两相陶瓷生物材料制备研究

利用硅灰石(CaSiO3)和β-磷酸三钙(β-TCP)在骨损伤环境中降解速率存在显著性差异的基本特性,以海藻多糖凝胶球为模板,运用层–层包裹方法构建CaSiO3、β-TCP交替包裹的多壳层化中空微球。首先,将海藻酸钠与硅酸钠的混合水溶胶逐滴加入到温和搅拌的硝酸钙水溶液中,形成由水合硅酸钙盐为壳层的海藻多糖基复合微球,然后将该复合微球依次浸入到含β-TCP的海藻酸钠溶液和含CaSiO3的海藻酸钠溶液中,温和搅拌后将微球悬浮液分离,再经真空冷冻干燥和850℃煅烧处理,从而获得以CaSiO3为最内壳层并具有双壳层或三壳层的中空微球。按类似步骤也可以制备以β-TCP为最内壳层的多壳层中空微球。运用SEM、EDX、XRD和FTIR对该类微球的微结构和组成进行了分析。运用弱酸性Tris缓冲液(pH=5.2)对双壳层中空微球的降解。实验证明,缓冲液中硅、磷浓度变化特征与其外壳层、内壳层化学组成(即β-TCP或CaSiO3)密切相关。本研究结果对构建降解速率阶段可调的复合陶瓷多孔生物材料以及研究原位骨再生效率与孔道网络演化规律之间关系等具有重要学术价值。

Experimental investigation of vibration pretreatment-microwave curing process for carbon fiber reinforced resin matrix composites

The vibration pretreatment-microwave curing process is an efficient,low energy consumption,and high-quality out-of-autoclave curing process for carbon fiber resin matrix composites.This study aims to investigate the impact of vibration pretreatment temperature on the fiber weight content,microscopic morphology and mechanical properties of the composite laminates by using optical digital microscopy,universal tensile testing machine and thermo-gravimetric analyzer.Additionally,the combined mode of Bragg fiber grating sensor and temperature measurement fiber was employed to explore the effect of vibration pretreatment on the strain process during microwave curing.The study results revealed that the change in vibration pretreatment temperature had a slight impact on the fiber weight content when the vibration acceleration remained constant.The metallographic and interlaminar strength of the specimen formed at a vibration pretreatment temperature of 80℃ demonstrated a porosity of 0.414% and a 10.69% decrease in interlaminar shear strength compared to autoclave curing.Moreover,the introduction of the vibration energy field during the microwave curing process led to a significant reduction in residual strain in both the 0°and 90°fiber directions,when the laminate was cooled to 60℃.

Effect of Mo and ZrO_(2)nanoparticles addition on interfacial properties and shear strength of Sn58Bi/Cu solder joint

The influence of Mo and ZrO_(2)nanoparticles addition on the interfacial properties and shear strength of Sn58Bi solder joint was investigated.The interfacial microstructures of Sn58Bi/Cu,Sn58Bi+Mo/Cu and Sn58Bi+ZrO_(2)/Cu solder joints were analysed using a scanning electron microscope(SEM)coupled with energy dispersive X-ray(EDX)and the X-ray diffraction(XRD).Intermetallic compounds(IMCs)of MoSn_(2)are detected in the Sn58Bi+Mo/Cu solder joint,while SnZr,Zr_(5)Sn_(3),ZrCu and ZrSn_(2)are detected in Sn58Bi+ZrO_(2)/Cu solder joint.IMC layers for both composite solders comprise of Cu_(6)Sn_(5) and Cu_(3)Sn.The SEM images of these layers were used to measure the IMC layer’s thickness.The average IMC layer’s thickness is 1.4431μm for Sn58Bi+Mo/Cu and 0.9112μm for Sn58Bi+ZrO_(2)/Cu solder joints.Shear strength of the solder joints was investigated via the single shear lap test method.The average maximum load and shear stress of the Sn58Bi+Mo/Cu and Sn58Bi+ZrO_(2)/Cu solder joints are increased by 33%and 69%,respectively,as compared to those of the Sn58Bi/Cu solder joint.By comparing both composite solder joints,the latter prevails better as adding smaller sized ZrO_(2)nanoparticles improves the interfacial properties granting a stronger solder joint.