A method of predicting the number of clusters using Rand's statistic

Distributional and asymptotic results on the moment of Rand's C_k statistic were derived by DuBien and Warde [1981. Some distributional results concerning a comparative statistic used in cluster analysis. ASA Proceedings of the Social Statistics Section, 309–313.]. Based on those results, a method to predict the number of clusters is suggested by applying various agglomerative clustering algorithms. In the procedure, the methods using different indexes are examined and compared based on the concept of agreement (or, disagreement) between clusterings generated by different clustering algorithms on the set of data. Our method having practical generality works better than the other methods and assigns statistical meaning to C_k values in determining the number of clusters from the comparison.     

Ion-cyclotron resonance study of elementary stages of the catalytic oxidation of CO by N2O in the presence of VIA-group metal ions

Gas phase reactions of Mo⁺ and W⁺ ions with the molecules of various oxidants (NO, O₂, N₂O, CH₂O, C₂H₄O) were studied using ion cyclotron resonance. In oxidation with N₂O the mono-, di- and trioxide metal cations are formed consecutively. The trioxide MO₃ ⁺ ions of both metals react with CO to form CO₂ and MO₂ ⁺ ions. In this way, catalytic reaction N₂O + CO N₂ + CO₂ occurs in the gas phase with MoO₃ ⁺ /MoO₂ ⁺ and WO₃ ⁺/WO₂ ⁺ couples as catalysts. The rate constants have been measured for both stages of the catalytic cycle as well as for the stages of the catalyst preparation. Metal-oxygen bond energies were estimated for MoO_x ⁺ and WO_x ⁺ species with various x. The mechanism of CO oxidation with MoO_x ⁺ and WO_x ⁺ cations as catalysts in the gas phase is discussed in comparison with that for the oxidation over classical solid oxide catalysts.     

Selective oxidation reactions over titanium and vanadium metallosilicate molecular sieves

Selective oxidation reactions like the oxyfunctionalization of alkanes, hydroxylation of aromatics and sulfoxidation of thioethers have been carried out with dilute hydrogen peroxide over titanium and vanadium metallosilicate molecular sieves with MEL topology, viz., TS-2 and VS-2. Though both the catalysts possess similar activities, substantial differences in the product distribution are observed. The oxyfunctionalization of the primary carbon atoms of the alkanes and the oxidation of the methyl substituents of the aromatic hydrocarbons distinguish VS-2 from TS-2. Both the catalysts are found to be equally active in the hydroxylation of phenol, though they possess different activities in different solvents. In general, the oxidations are deeper over VS-2 than on TS-2.     

Application of a counter-current gaseous diffusion model to the oxidation of hafnium carbide at 1200 to 1530°C

A counter-current gaseous diffusion model is presented to describe the oxidation of hafnium carbide between 1200 and 1530°C. The model separates the porous hafnia scale into two gas diffusion regions separated by a flame front, where O ₂ and CO react to form CO ₂.In the outer region, O ₂ and CO ₂ counter-diffuse; in the inner region, CO ₂ and CO counter-diffuse. The concentration gradients of each gaseous specie in the pores of the hafnia are determined and the rate of oxidation is calculated. A porosity of 2% and a pore radius of 0.01 m are representative of the values observed in hafnia during the early stages of HfC oxidation. These values lead to predictions of parabolic rate constants that are close to those measured by thermogravimetric analysis. In addition, the predicted and measured parabolic rate constants are shown to have the same dependence upon temperature and oxygen partial pressure.     

B4C-部分石墨化炭黑复合粉体的合成及其抗氧化性

分别以64.7%的硼粉 35.3%的炭黑或55%的硼粉 45%的炭黑为试样组成,分别在真空和非真空条件下,采用自蔓延燃烧法于1400℃保温10~20min进行了B4C-部分石墨化炭黑复合粉体的合成研究。采用XRD、SEM及电子探针等方法对合成粉体的物相及形貌进行了分析;以差热法(TG-DSC)研究了合成粉体的氧化特性。结果表明:炭黑和硼粉加入量(w)分别为45%和55%时,经自蔓延燃烧反应后可以得到粒度均匀的碳化硼(B4C)粉体,且碳黑已部分石墨化。与工业B4C相比,复合粉体中的B4C具有更好的保护碳不被氧化的特性。     

亚硫酸铵的氧化反应动力学研究

利用鼓泡反应装置,对亚硫酸铵氧化过程各影响因素进行了研究。通过改变pH、亚硫酸铵浓度、空气流量及温度,研究了亚硫酸铵的氧化反应动力学。实验结果表明,空气流量低于380 L/h时,反应速率随流量的增大而增加;pH为5.5左右时,氧化速度最快;高浓度(≥3 mol/L)的亚硫酸铵不能被迅速完全地直接氧化成硫酸铵。     

Co-M/Al2O3上环己烷的选择性氧化研究

采用溶胶-凝胶法制备了Co-M/Al₂O₃(M=Cu，Zn，Ni)催化剂。在没有任何有机溶剂或助剂的条件下，研究了以空气为氧化剂的环己烷选择性氧化。所制备四种催化剂的活性为Co-Ni/Al₂O₃ >Co/Al₂O₃ >Co-Zn/Al₂O₃ >Co-Cu/Al₂O₃。在Co-Ni/Al₂O₃中Co、Ni的质量分数分别为4.0%和3.0%时活性最好。以Co-Ni/Al₂O₃为催化剂，在4.5 MPa、443 K下反应120 min，环己烷转化率达9.9%，环己酮和环己醇的总选择性达94.6%，n(酮)∶n(醇)为2.8。Co-Ni/Al₂O₃催化剂连续使用五次后活性基本不变。     

反应结合SiC电热材料的高温氧化特征

研究了反应结合SiC电热材料在1100～1580℃空气介质中加热时的氧化特征。结果表明：加热温度高于1420℃后，材料基体中的残留Si熔化并流动到表面形成SiO2。氧化后形成的SiO2与表面氧化层融为一体，提高了表面氧化层的致密度，有利于材料的抗氧化性能。1500℃左右为材料的抗氧化性能转折温度。在1500℃以下氧化时，反应结合SiC的抗氧化行为与重结晶SiC接近；高于1500℃氧化时，材料表面发生破坏性氧化，引起电热材料的失效。1500℃氧化后的表面氧化层中同时存在低温石英、方石英和非晶态SiO2。     

炭黑填充导电丁腈橡胶研究

研究了用华光化工厂产导电炭黑填充丁腈橡胶的导电性规律。探讨了配方、加工工艺、混炼胶存放、胶料老化以及测试条件等诸多因素与导电性的关系。优选出了硬度７０左右的胶料，其体积电阻率为２．２２Ω·ｃｍ。