Influence of Heating Rate and Calcining Temperature on Properties of 95 Polycrystalline Alumina Fiber

The swung gel fibers were heated to 400 ℃ at 0.5, 1, 1.5, 2, 2.5, 3 and 4 ℃·min-1 of heating rate, respectively, and soaked for 1 h; then heated to 600 ℃ at 3 ℃·min-1 of heating rate and soaked for 1 h; at last calcined at 1 000, 1 100, 1 200, 1 300, and 1 400 ℃ for 1 h, respectively. The average single fiber tensile strengths of fibers after calcining at 600 ℃ or higher temperatures were determined and their surface morphology was observed. The results show that: (1) when the heating rate below 400 ℃ is 0.5-1 ℃·min-1, the average single fiber tensile strengths of 95 polycrystalline alumina fibers after calcining at 600 ℃ and 1 000-1 100 ℃ exceed 1 000 and 800 MPa, respectively, surface of the fibers after calcining at 1 000-1 100 ℃ is smooth, α-Al2O3 appears at 1 200 ℃, and a large amount of α-Al2O3 forms above 1 300 ℃; (2) when the heating rate exceeds 3 ℃·min-1, the fibers pulverize obviously.     

Fractal Dimension of Alumina Aggregates Grown in Two Dimensions

The concepts of fractal geometry are applied to the analysis of 0.4-μm alumina constrained to agglomerate in two dimensions. Particles were trapped at the bottom surface of a drop of a dilute suspension, and the agglomeration process was directly observed, using an inverted optical microscope. Photographs were digitized and analyzed, using three distinct approaches. The results indicate that the agglomerates are fractal, having a dimension of approximately 1.5, which agrees well with the predictions of the diffusion-limited cluster–cluster aggregation model.     

片状粉末表面特性的分形分析

根据片状粉末表面几何特征,提出了用分形方法对其进行描述. 将数码相机拍摄的不同片状粉末的显微照片输入计算机,采用计算分形盒子维的DBC算法对其灰度值进行编程计算,可获得颗粒表面的分形维数. 计算得到的分维数的数值在2~3之间,且粉体表面越不光滑,表现在灰度值的起伏越大,则分维数的数值也越大,与人们视觉上对粗糙表面的观察相吻合. 在一定程度上可有效地反映粉体表面的光滑性,从而为片状粉体表面特性的分析和研究提供了一个新思路.     

焙烧温度对银催化剂性能的影响研究

文章研究了焙烧温度对环氧乙烷银催化剂性能的影响。结果表明,在焙烧过程中,催化剂中的有机物在T+50℃(T为基本焙烧温度)以前基本挥发或氧化分解,α-Al2O3载体性质稳定。随焙烧温度的升高,银催化剂活性下降;焙烧温度以控制在T+150℃~T+200℃之间为宜。     

烧成制度对多孔氧化铝陶瓷膜支撑体性能的影响

研究了多孔氧化铝陶瓷膜支撑体烧成温度与孔隙率/容重的关系,利用热重-微商热重(TG-DTG)分析,制定了支撑体的烧成曲线.结果表明,经此烧成曲线,成功烧出了孔隙率在34％以上,孔径在2.23～6.75 μm之间,耐酸碱度在98％以上,机械强度高的支撑体.     

多孔Al2O3陶瓷底膜的表征方法

研究了Al2O3陶瓷底膜的表征方法。首先，根据毛细管作用原理、润湿现象及Laplace方程，采用异丙醇作为润湿剂，求出底膜的孔径、干膜流量和湿膜流量，用这些数据，导出孔径分布函数，并作出孔径分布函数与孔径关系图，其次，采用GB1966-80的方法，测定了Al2O3陶瓷底膜的孔隙率。     

氧化铝膜的制备

制备氧化铝膜的具体过程包括:预处理(清洗→退火→除去自然氧化铝膜→电化学抛光)、阳极氧化(稳流氧化→除膜→稳压氧化)和后续处理(稀磷酸扩孔)。通过扫描电子显微镜(SEM)、X射线能谱仪(EDS)、X射线电子衍射(XRD)、精密pH计和TT-230涡流测厚仪,对其进行了表征。研究了电解液浓度,氧化温度、电压、时间和扩孔时间对膜形成的影响。确定了新的氧化工艺,拓展了氧化温度的范围(15.0～40.0℃)。制备出了具有高度有序的氧化铝模板。     

Effect of Micmcracking on the Fracture Toughness and Fracture Surface Fractal Dimension of Lithia-Based Glass-Ceramics

The effect of thermally induced microcracks on the fracture toughness and fractal dimension of fully crystalline lithia disilicate glass-ceramics was studied. The fracture toughness, K _IC, for the nonmicrocracked lithia disilicate, 3.02 ± 0.12 MPa·m^1/2, was significantly greater than the value of 1.31 ± 0.05 MPa·m^1/2 for the microcracked specimens. The fractal dimensional increment, D *, was 0.24 ± 0.01 for nonmicrocracked lithia disilicate specimens compared with a value of 0.18 ± 0.01 for the microcracked specimens. The relationship between K _IC and D * implies that the two materials exhibit dissimilar fracture behavior because of microstructural differences. Estimates of the characteristic length involved in the fracture process, a ₀, indicate that the materials have an identical fracture process at the atomic level. This apparent contradiction may be explained by the scale on which the measurements were taken. It is suggested that fractal analysis at the atomic level would yield equivalent D * values for the two different microstructures.     

Efficient Preparation of Submicrometer α-Alumina Powders by Calcining Carbon-Covered Alumina

A simple method is described to prepare submicrometer α-alumina by burning carbon supported on the surface of γ-alumina in oxygen flow at a temperature of 800°C. The burning of carbon generates a large amount of heat and leads to a rapid increase in the local temperature inside the pores of alumina. When the temperature is high enough for the phase transformation, α-alumina is obtained in a very short time. It was found that, for carbon contents between 6 and 10 wt%, all the γ-alumina could transform into α-alumina after burning of carbon in oxygen for a short time, and the transformed particle sizes of α-alumina were mostly no more than 1 μm.     

分形维数测定方法对测量结果的影响分析

本文采用小岛法和盒计法测定了粉末PVC/NBR共混型热塑性弹性体拉伸断面形貌的分形维数,分析比较了盒计法和小岛法的差异。根据测算结果得出结论：虽然两者所得结果有所差异,但两者在揭示材料组织结构,评价、探索材料断裂演化规律方面,所得结果一致,并无差别。此外,首先需要根据研究对象的分布特点,选择恰当的、合适的测定方法计算出分形维数,才能更真实准确地揭示出研究对象的分形特性、材料组织结构与断裂演化规律、分形形成的动力学机制。     

Modulation of Transmission Spectra of Anodized Alumina Membrane Distributed Bragg Reflector by Controlling Anodization Temperature

We have successfully prepared anodized alumina membrane distributed Bragg reflector (DBR) using electrochemical anodization method. The transmission peak of this distributed Bragg reflector could be easily and effectively modulated to cover almost any wavelength range of the whole visible spectrum by adjusting anodization temperature.     

The Influence of the Fractal Dimension of Rough Surfaces on the Adhesion of Elastic Materials

Abstract

In this paper we analyse the adhesion between a rubber block and a rigid randomly rough profile. The focus of the investigation is on the influence of the work of adhesion and of the fractal dimension Df of the rough profile on the contact behaviour. In particular, we analyse how the contact area and the power spectral density of the deformed profile are affected by the two aforementioned quantities. We find that at sufficiently small loads the influence of Df is negligible. However, the scenario strongly changes at higher loads as Df strongly affects the number of contact spots. Calculations show that the contact area depends linearly on the work of adhesion, whereas only a negligible influence of the work of adhesion is found on the power spectral density (PSD) of the deformed profile.     

混凝土界面过渡区表面形貌的分形维数表征

为定量表征不同混凝土界面过渡区的微观形貌,引入表面分形维数参数,并用投影覆盖法实现其求算.研究结果表明,界面过渡区的表面形貌的表面分形维数介于2～3之间,且线性回归分析的相关系数均大于0.95,强的相关性表明所选用的界面过渡区的表面形貌具有明显的分形特征.     

Influence of Surface Residual Stress State on Crack Path Evolution in Polycrystalline Alumina

The residual stress distribution in polycrystalline alumina is estimated by an object-oriented finite element method. By combining the microstructural image, individual grain orientation, and the crystal elastic properties, the residual stress distribution under a plane stress assumption is obtained by an analysis cooling of the sample through 1000°C. Furthermore, the residual stresses associated with grain boundary areas are investigated and discussed in the context of the concomitant influence on the observed crack path.     

Laser Machining of Structural Alumina: Influence of Moving Laser Beam on the Evolution of Surface Topography

Laser machining technique has emerged as an innovative tool to effectively machine the structural ceramics, which previously was nearly impossible using various conventional machining techniques. However, obtaining a desired surface finish via laser machining is still a critical issue. As many physical phenomena act simultaneously during laser machining, it is very difficult to understand their influence in real time and predict the surface topography. To address this issue, a multiphysics‐based finite‐element modeling approach was implemented to understand the influence of moving laser beam (with lateral overlap) on the generation of corresponding surface topography/profile/roughness during laser machining of structural alumina. A computation model that coupled heat transfer and computational fluid dynamics was designed to understand the combined influence of Marangoni convection, recoil pressure, cooling rates, and surface tension on the evolving surface topography during laser machining of structural alumina under various machining conditions. Both computational and experimental results evidently showed the systematic increase in surface roughness parameters with the increase in lateral overlap (0, 17, 33, 50, 67, and 83%). The results of the computational model are also validated by experimental observations with reasonably close agreement (±3.5%).     

Influence of Temperature on Membrane Permeability during Pervaporative Aroma Recovery

Abstract

The influence of operating temperature on membrane permeability was studied and compared with the effect of temperature on the driving force for permeation. A hydrophobic polyoctylmethyl siloxane membrane was used. For the feed mixture, an aqueous solution of aroma compounds containing four alcohols, one aldehyde, and five esters, all of which are important contributors to apple juice flavor, was used. Temperature had a strong effect on mass transfer and selectivity, both of which increased with increasing temperature. However, the selectivity for a component with a high activation energy for permeation increased more with temperature than did a component with a low activation energy for permeation. This caused a variation in the aroma composition of the permeate. The study showed that it is possible to estimate the activation energy for permeation of aroma compounds, and thus the influence of temperature on the internal mass transfer, through their hydrophobicity, size, and a complementary comparison of the activation energies for permeation for some other permeants of the same chemical group.     

Influence of Light Calcining Hydration of Magnesite on MgO Sintering

Sintered magnesia clinker(also called sintered MgO) was prepared with Mg(OH)2(prepared by light calcining hydration of magnesite) and magnesite as starting materials,respectively,by the technical process:light calcining(850 ℃ 1 h) → grinding → molding → firing(1 600 ℃ 3 h).The morphology and structure of light calcined MgO powders prepared with magnesite or Mg(OH)2 were analyzed by XRD,SEM and FT-IR.The sinterability and microstructure of sintered magnesia prepared with magnesite or Mg(OH)2 were researched....     

非对称氧化铝陶瓷超滤膜的研制及性能测试

采用固体颗粒烧结法制作膜载体,溶胶-凝胶法制备α-Al2O3薄膜,制作了非对称氧化铝复合陶瓷超滤膜。密度为2.703g/cm3,孔隙率为23.51%。用铬黑T、甲基橙等作为探针分子,对制作的超滤膜孔径进行了测定,结果表明,本超滤膜截留相对分子质量在327～417,即膜孔径约为2nm。透水率为2000～3450mL/m2·h。     

多孔纳米氧化铝模板的制备研究

在草酸电解液中,通过电化学两步氧化法制备了纳米多孔氧化铝膜,应用高分辨扫描电镜观察了氧化铝膜的形貌,并且估算了平均孔径和孔密度.讨论了铝片厚度、第一步氧化时间和氧化电压对多孔氧化铝膜的影响.平均孔径随铝片厚度增加而减小,而随第一步氧化时间和氧化电压的增加而增加;孔密度则随铝片厚度增加而增加,随第一步氧化时间和氧化电压的增加而减小.     

氧化铝微滤膜的制备及表征

通过固相粒子烧结法分别制备了膜孔径为0.1,0.4,0.8,1,3μm的氧化铝微滤膜.氧化铝微滤膜膜厚与涂膜液中氧化铝的含量成正比.采用SEM,干湿膜法孔径测定仪及过滤等方法对膜进行了表征,过滤法作为测定氧化铝膜完整性的方法之一,对测定工业生产的氧化铝微滤膜的完整性具有现实意义.