煤的表面分形及其随压力的变化

煤是一种具有复杂结构的物质,可以用分形维数定量表征其微孔特征．用孔度法处理不同煤的吸附数据,发现分形维数能反映煤的表面结构遭受破坏的程度．在煤的变质系列中,中变质程度煤的分形维数最小．     

水射流解离煤的分形特征

利用高压水射流粉碎机与球磨机对煤进行超细解离,对解离后的煤颗粒进行了扫锚电镜分析,利用扫锚电镜图像。基于图像处理技术与分形理论,计算了粒度分布分形维数、边界形状分形维数与节理表面分形维数。利用上述3种分维数对解离后的煤颗粒的分形特征进行了研究。     

分形理论在ATO水浆分散形貌与导电性关系中的应用

ATO水浆是一种良好的无机导电浆料。运用分形理论对其分散形貌与导电性能之间的关系进行了初步研究,结果表明浆料形貌中的枝杈结构越明显,导电链路越多,分形维数越大,则浆料的导电性能越好。研究表明,浆料分形维数在1.82以上时,其表面电阻在107Ω数量级。     

煤粉分形维数对低阶煤配煤成浆性能的影响

分形理论能够较为准确地描述煤粉的特征,为研究煤粉分形维数与水煤浆成浆浓度的关系,选取东胜矿区低阶煤(民达、东川和纳林庙煤)及准格尔矿区的黑岱沟煤样,将东胜煤与黑岱沟煤进行配煤、配煤结合粒度制浆。利用激光粒度仪测定了配煤后煤浆的粒度分布曲线,并用分形理论分析了不同粒度煤粉的分形特征。     

CO2载体CaO循环煅烧/碳酸化反应的分形特征

捕捉煤燃烧释放出的CO₂时,作为CO₂载体的CaO微观结构特性对其循环碳酸化性能具有显著影响。采用分形维数作为表征CaO微观结构的特征参数,研究在循环煅烧/碳酸化反应过程中CaO的分形特征及其对CO₂捕捉性能的影响规律。结果表明,随着循环次数的增加CaO分形维数逐渐下降,CaO孔道也由粗糙和不规则变得越来越平滑和有规则性。煅烧温度升高则CaO分形维数下降。分形维数较大的CaO具有较高的碳酸化速率。在碳酸化过程的前10 min内CaO的分形维数迅速减小,此后随时间变化缓慢。在分形维数D≤2.61的实验范围内,CaO分形维数与其循环碳酸化转化率呈线性正相关;当D＞2.61时,可能存在临界分形维数D_cr,当D＞D_cr时随着分形维数的进一步增大CaO转化率反而减小。     

CO2载体CaO循环煅烧/碳酸化反应的分形特征

捕捉煤燃烧释放出的CO₂时,作为CO₂载体的CaO微观结构特性对其循环碳酸化性能具有显著影响。采用分形维数作为表征CaO微观结构的特征参数,研究在循环煅烧/碳酸化反应过程中CaO的分形特征及其对CO₂捕捉性能的影响规律。结果表明,随着循环次数的增加CaO分形维数逐渐下降,CaO孔道也由粗糙和不规则变得越来越平滑和有规则性。煅烧温度升高则CaO分形维数下降。分形维数较大的CaO具有较高的碳酸化速率。在碳酸化过程的前10 min内CaO的分形维数迅速减小,此后随时间变化缓慢。在分形维数D≤2.61的实验范围内,CaO分形维数与其循环碳酸化转化率呈线性正相关;当D＞2.61时,可能存在临界分形维数D_cr,当D＞D_cr时随着分形维数的进一步增大CaO转化率反而减小。     

热解温度与煤焦微结构及分形特征关系研究

采用扫描电子显微镜 ( SEM)研究了不同热解温度条件下煤焦的微观结构 .结果表明 ,煤焦结构与煤化程度和热解温度有密切的关系 ,烟煤煤焦的微观结构以孔隙为主 ,无烟煤煤焦以裂隙为主 ,且其微观结构具有良好的统计自相似性 ;并采用分形维数定量表征煤焦在不同温度下的孔隙和裂隙特征 ,研究了煤焦分形维数与热解温度、煤化程度的关系及内在机理 ,发现分形维数随煤化程度增加而减少 ,随热解温度提高而增大 .     

淮南煤焦颗粒内部孔隙结构在燃烧过程中的变化

用氮气等温吸附/脱附（77 K）方法测量了淮南低变质煤及其在850℃条件下燃烧得到半焦的内部孔隙结构.通过分析得到有关煤焦颗粒内部孔隙结构的参数及其与燃尽率之间的关系.由吸附/脱附曲线判断煤焦孔洞的形状呈多样性.结合吸附理论,认为分形BET和分形Freundlich方程回归得到的分形维数分别表征颗粒内部大中孔表面分形维数和微孔体积分形维数.发现在燃烧过程中煤焦的表面分形维数及体积分形维数具有不同的变化趋势.     

镁橄榄石隔热材料孔体积分形维数特征

采用压汞法研究在熔盐介质中制备的镁橄榄石多孔隔热材料中孔的分形结构,测定了多孔隔热材料中孔的分形维数,探讨了孔的分形维数与孔隙率、孔分布及材料强度之间的关系。结果表明:熔盐介质中制备的镁橄榄石多孔隔热材料的孔结构具有分形特征,孔径4.6μm的样品中孔的分形维数不具有准确性,孔径4.6μm的样品中孔的分形维数具有规律性。烧成温度不同的样品中孔径4.6μm的分形维数波动在2.563 0~2.766 1之间,且分形维数越大,显气孔率越小,耐压强度越小。不同熔盐含量样品孔径4.6μm的孔体积分形维数在2.534 1~2.972 2之间,且分形维数越小,显气孔率越大。当分形维数大于2.535 7时,分形维数越小,耐压强度越大。     

硫化物催化剂结构性质与合成甲醇反应性能的关联(Ⅱ)──表面形貌的分形几何特征

应用分形几何理论研究了硫化物催化剂的表面性质及其与合成甲醇反应性能的关系．由分形维数定量地表征了催化剂表面形貌的几何特征．提出了催化剂表面分形维数具有特定的分布,并用正态分布函数进行了拟合．考察了助催化剂和载体对催化剂表面分形维数的影响,由此探讨了分形维数与催化剂结构和反应性能的关系．对甲醇的时空收率和分形维数进行了关联．     

Fractal Characteristics of Fracture Surfaces

Quantitative fractography is often used to study material failure mechanisms. During calculation of surface or profile roughness parameters, the magnification used in obtaining fractographic data is found to influence the value of the parameters. Fractal geometry has been developed into a tool capable of defining surface and profile topography without sensitivity to magnification, and several studies have related fractal dimension ( D _F) to other physical or mechanical properties. In this study, we obtained the fractal dimension of profiled fracture surfaces of one glass and three proprietary dental porcelains. The fracture toughness ( K _1c) of these materials was also measured using the indentation-strength method. Results show the surfaces to be fractal. No quantitative relationship between fractal dimension and toughness was found. Differences in K _1c were demonstrated between some materials. It is postulated that the size range within which fractal dimension can be defined as constant is dependent on the toughening mechanism, and that the relationship between K _Ic and D _F cannot be identical for all materials.     

煤的分形表面结构

介绍了分形理论在煤表面结构研究中的应用。对煤分形表面结构的实验技术方法进行了较为详细的评述。对煤在处理过程中其表面分维的变化进行了简明的介绍。最后，简要地讨论了煤的分形表面结构的研究方向。     

The use of fractal analysis in the textural characterization of coals

The materials studied were four bituminous coals as well as the corresponding coal samples oxidized in air at 543 K for different periods of time. The method proposed by Friesen and Mikula, the procedure of Neimark and the methodology of Zhang and Li were successfully employed to analyze mercury porosimetry data from a fractal perspective. Fractal dimensions as well as fractal profiles are sensitive to oxidation treatment, being useful to follow the changes undergone by the coal samples. The evolution of the fractal dimension of coals with oxidation is determined by a balance between two main mechanisms of pore development: the oxidation of the pore surface itself that tends to lower the fractal dimension and the access of mercury to previously non-accessible regions that tends to increase this dimension.     

分形理论对煤粉粒度和孔隙的表征

介绍了分形理论的定义,说明自相似性和标度不变性是分形的2个重要特征。从粒度分形规律和煤粉研磨超细化分形2个方面对煤粉超细化分形进行了研究,说明煤粒研磨过程中,绝大部分能耗用在小颗粒的研磨上,颗粒表面分形维数越大,研磨能耗越高,颗粒形状越不规则,能耗越大。详细介绍了气体吸附法、压汞法和扫描电镜图像法3种测定煤粉孔隙分形维数的方法,阐述了煤粉粒度和孔隙的分形规律及国内外相关研究现状,着重说明了煤粉的研磨、高效燃烧、煤粒与孔隙发育程度的关系及煤粒孔隙的特点与瓦斯存在形式的关系。最后提出了煤粉粒度和孔隙的研究方向。     

Microstructure and fractal analysis of fat crystal networks

This paper reviews the study of the morphology and physical properties of fat crystal networks. Various microscopical and rheological methods can be used to quantify the microstructure of fats, with the ultimate aim of relating structure to mechanical response. Even though a variety of physical models have been proposed to explain the relationship between the mechanical properties of fats and their microstructure, the fractal scaling model most closely describes the experimentally observed behavior. Mass fractal dimensions determined by microscopy and rheology can be used successfully to quantify the microstructure of fats since fractal dimension values are sensitive to the combined effects of crystal size, morphology, and the spatial distribution of mass within the fat crystal network. Methods used to determine the fractal dimension of a fat crystal network such as box counting, particle counting. Fourier transform, light scattering and oil migration are explained in detail here. The relationship between fractal dimensions determined by microscopy and rheology are discussed in light of the fact that different measures of the fractal dimension describe different microstructural features in a fat crystal network.     

Fractal Analysis of Toughening Behavior in 3BaO.5SiO2Glass-Ceramics

The objective of this paper was to analyze the crystal aspect ratio (AR), the fracture toughness, and the fractal dimension of 3BaO^.5SiO₂ glass-ceramics and to relate the topography of fracture surfaces to fractal behavior. These analyses demonstrate that crystal morphology strongly affects the fracture path, the fracture toughness, and the fractal dimension. Fracture toughness increased from 0.7 ± 0.1 MPa^.m^1/2 for the glass to 2.2 ± 0.6 MPa^.m^1/2for the glass-ceramic with an AR of 8.1 while the fractal dimensional increment ( D *) for the glass and the glass-ceramic increased from 0.10 ± 0.01 to 0.25 ± 0.02, respectively. The materials with lower aspect ratios (AR = 1.4 and 3.6) exhibited the predicted relationship between toughness and D * while the glass-ceramic with an aspect ratio of 8.1 did not satisfy the expected relationship because of multiple toughening mechanisms.     

Direct image-based fractal characterization of micromorphology of calcium carbonate fouling crystals

Researches on macroscopic fouling behavior and micromorphology are usually conducted separately. In this paper, the relationship between the macroscopic fouling behavior and micromorphology on different materials is established. A direct fractal-characterization approach based on the micrographs of calcium carbonate fouling crystals is presented. The box-counting method is used to characterize the fouling crystals. For fractal measurements, t-distribution tests of linear regression hypothesis are performed at the significance level of 0.01. If all listed absolute t-statistics with the minimum of 164 are higher than the corresponding t value, the fouling crystals are determined as fractal, with a confidence level of 99%. The fractal dimensions obtained from the micrographs of different visual fields of a specimen are demonstrated to be almost identical, with maximum and minimum relative values of 4.42% and 0.75%, respectively, and standard deviations ranging from 0.0062 to 0.0266. The irregularity of the crystal morphology indicates larger fractal dimensions. Comparison and analysis of the relationship between macroscopic fouling behavior and micromorphology show that the larger fractal dimension of crystal morphology suggests a small amount of surface fouling. Thus, the reasons for the differences in the macroscopic fouling behaviors of different materials are revealed geometrically.