Direct Observation of Internal Structure in Spray-Dried Alumina Granules

The internal structure of spray-dried alumina granules was characterized by optical microscopy by immersing them in a liquid having a refractive index close to that of alumina. This method provides a unique technique for the detailed analysis of the internal structure of spray-dried granules.     

Effect of cobalt oxide on surface structure of alumina supported molybdena catalysts studied by in situ Raman spectroscopy

A set of Co promoted 10% Mo/Al₂O₃ samples have been characterized by means of Raman spectroscopy under ambient as well as in situ dehydrated conditions. Under ambient conditions, the degree of the polymerization of surface molybdenum oxide species decreases with increasing Co loading. Under dehydrated conditions, the polymeric molybdenum oxide species is absent with the addition of only 0.2% Co. At low Co loadings (2%), before the formation of CoMoO₄ compound, the spectral features are very similar under ambient conditions. Dehydration causes the upward shift of the Mo=O symmetric stretching mode. A broad band around 920–930 cm^–1 was thus observed. This band has been suggested to be associated with the Co-Mo interaction species. In contrast to crystalline CoMoO₄, this species shows a reversibility on H₂ reduction-O₂ reoxidation treatments. From the results obtained, it is proposed that cobalt oxide interacts with the most polymerized molybdenum oxide species to form Co-Mo interaction species and/or crystalline CoMoO₄; therefore, the amount of the surface molybdenum oxide species decreases with a change in the molecular structure as a function of the Co concentration.     

Static and Cyclic Fatigue of Alumina at High Temperatures: II, Failure Analysis

Failure mechanisms of an alumina, tested at 1200°C under static and various cyclic loading conditions, were examined. Slow crack growth of a single crack is the dominant mechanism for the failure in specimens under cyclic loading with a short duration of maximum stress at all applied stress levels, as well as at high applied loads for static loading and cyclic loading with a longer hold time at maximum stress. At low stress levels, failure of static loading and cyclic loading with a longer hold time at maximum stress might occur by formation and/or growth of multiple macrocracks. More importantly, for all the given loading conditions. The viscous glassy phase behind the crack tip could have a bridging effect on the crack surfaces. A simplified model for calculating effective stress intensity factor at the crack tip under static and various cyclic loading demonstrated a trend consistent with the stress–life data.     

氧化铝/莫来石复合陶瓷断裂行为研究

用X射线衍射方法测定了氧化铝/莫来石复合陶瓷的残余应力,并通过计算加以验证。在莫来石含量比较小的情况下,氧化铝/莫来石复合陶瓷基体拉应力与莫来石体积含量成线性关系。通过模型分析了氧化铝基体和莫来石颗粒的应力状态及其对裂纹扩展的影响。由莫来石颗粒引入的基体拉应力使裂纹倾向于向晶内扩展。观察了氧化铝/莫来石复合陶瓷断裂方式的转变,计算了穿晶断裂比率与基体应力的关系,进而建立了莫来石含量、基体应力、穿晶断裂比率三者的对应关系。这为复合陶瓷材料的制备和性能分析提供了可靠基础。     

抗菌薄膜的最新研究进展

介绍了抗菌薄膜的抗菌机理。综述了抗菌薄膜的种类和最新研究进展。提出了抗菌薄膜研究的发展趋势,即无机抗菌薄膜以纳米复合型抗菌薄膜为主要的发展趋势;天然抗菌薄膜以壳聚糖抗菌薄膜为主要的发展方向;高分子抗菌薄膜以含吡啶基团的聚合物抗菌薄膜为拓展方向;光催化型无机抗菌薄膜以纳米TiO2复合抗菌薄膜为主要的拓展趋势。     

阳极氧化工艺对氧化铝纳米孔膜形成过程及结构的影响

采用高纯度的铝片为阳极，以铂网为阴极，在3％～5％草酸溶液中，电压在30～70V，温度控制在17～25℃范围内进行恒压阳极氧化制备氧化铝膜，并采用环境扫描电镜观察纳米孔形貌，金相显微镜测量氧化膜厚度。研究了电解电压、电解液浓度、温度等条件对氧化铝多孔膜结构的影响。结果表明：氧化膜形成速度、纳米孔孔径、胞径、孔壁厚度、氧化膜厚度受电解电压影响显著，随着电解液浓度和温度的增大，氧化膜生长速度加快，纳米孔孔径、孔壁厚度等都随之增大，在相同时间内生成的氧化膜厚度增大。     

Mechanical Properties of Alumina/Silicon Carbide Whisker Composites

The improvement of mechanical properties of Al₂O₃/SiC whisker composites has been studied with emphasis on the effects of the whisker content and of the hot-pressing temperature. Mechanical properties such as fracture toughness and fracture strength increased with increasing whisker content up to 40 wt%. In the case of the high SiC whisker content of 40 wt%, fracture toughness of the sample hot-pressed at 1900° decreased significantly, in spite of densification, compared with one hot-pressed at 1850°. Fracture toughness strongly depended on the microstructure, especially the distribution of SiC whiskers rather than the grain size of the Al₂O₃ matrix.     

高铝质强化日用瓷釉料

通过调整软质熔剂和硬质熔剂的种类和数量 ,研制出了适合刚玉质强化瓷的釉面硬度 7373MPa、白度 75 .9%、光泽度 89.3%且高热稳定性的透明釉料     

An NMR study of acid sites on chlorided alumina catalysts using trimethylphosphine as a probe

The MAS-NMR spectra of adsorbed trimethylphosphine (TMP) were used to determine the concentration of Brønsted and Lewis acid sites on pure and chlorinated-Al₂O₃ samples. Chlorination with CHCl₃,CCl₄ or AlCl₃ promoted the formation of Brønsted acid centers, which are characterized by the protonated adduct of TMP. This adduct has a³¹P chemical shift of ca. –3.8 ppm and a J_P–H scalar coupling of 517 Hz. Additional resonances in the –44 to –54 ppm range are attributed to Lewis acid-base pairs. In some cases a partially resolved J_P–Al coupling is observed, which confirms the assignment. Upon thermal treatment of a chlorinated sample at temperatures > 200°C, the concentration of Brønsted acid centers decreased; the concentration of one type of Lewis acid increased and another remained almost constant. In a parallel set of experiments the initial conversion ofn-hexane at 150°C and the yields of cracking and isomerization products were determined. Comparable functional relationships were observed between the loss of Brønsted acid sites and the decrease in yields of both cracking and isomerization products. These results suggest that Bransted acidity is responsible for the cracking and isomerization ofn-hexane over chlorided aluminas at 150°C.     

耐磨抗冲击氧化铝陶瓷异型件的研制

主要研究了高铝快速磨罐、弧形衬板、球磨机磨口、研钵等异型件的配方及注浆成型工艺。试验配制了高铝泥浆用复合稀释荆及复合添加剂，使制品的显微结构均匀，密度得到了显著提高。