Microstructural elements, types

As the properties of materials are cJosely related to their structures, the realization of a material with certain properties can be achieved through stmcture control. The stmcture of ceramic materials, however, consists of many types of microstructural elements sucdi as particJes, grains, pores, defects, fibers, layers, and interfaces. These microstmctural elements can be classified by size into four scale levels (i) atomic-molecular scale (ii) nanoscale (iii) microscale, and (iv) macroscale, as shown in Figure 8.1. Besides their physical and chemical nature, other features of these elements including their morphology, configuration, distribution, and orientation are also important. It is obvious, therefore, that there are many factors which can control the structure of materials - not only the types of the elements, but also their features. 

These three passive systems are important in the technique of anodic protection (see Chapter 21). The kinetics of the cathodic partial reaction and therefore curves of type I, II or III depend on the material and the particular medium. Case III can be achieved by alloying additions of cathodically acting elements such as Pt, Pd, Ag, and Cu. In principle, this is a case of galvanic anodic protection by cathodic constituents of the microstructure [50]. 

Properties As we have observed, an essential element in chemical products are their properties, basically because they are sold and bought for what they do. Some of these properties belong to components that form the chemical product, and others belong to the chemical product as a whole. Usually, the latter properties are those that depend on the chemical product microstructure. Some properties do not depend on the environment with which they interact and some others do. Figure 1 shows the type of interactions that occur between the chemical product and the environment. 

The use of optical methods to study the dynamics and structure of complex polymeric and colloidal liquids subject to external fields has a long history. The choice of an optical technique is normally motivated by the microstructural information it provides, its sensitivity, and dynamic range. A successful application of an optical measurement, however, will depend on many factors. First, the type of interaction of light with matter must be correctly chosen so that the desired microstructural information of a sample can be extracted. Once selected, the arrangement of optical elements required to perform the required measurement must be designed. This involves not only the selection of the elements themselves, but also their alignment. Finally, a proper interpretation of the observables will depend on one s ability to connect the measurement to the sample s microstructure. 

The chemical microstructures of cis-polyisoprene (HR) vulcanised with sulfur and N-t-butyl-2-benzothiazole sulfenamide (TBBS) accelerator were studied as a function of extent of cure and accelerator to sulfur ratio in the formulations by solid-state 13C NMR spectroscopy at 75.5 MHz [29]. Conventional (TBBS/Sulfur=0.75/2.38), semi-efficient (SEV=1.50/1.50) and efficient (EV=3.00/1.08) vulcanisation formulations were prepared, which were cured to different cure states according to the magnitude of increase in rheometer torque. The order and types of the sulfurisation products formed are constant in all the formulation systems with different accelerator to sulfur ratios. However, the amount of sulfurisation has been found to vary directly with the concentration of elemental sulfur. 

Once the structure of a complex fluid has been simulated, computed, or derived by analytic theory, one would like to calculate the stress tensor a and compare it to experimental stress measurements. The appropriate expression for the stress tensor depends on the type of complex fluid. However, if the idealized microstructure is built out of many small, point-like elements located at positions x,, i = 1,2,..., N, and on each such point a nonhydrodynamic force F, is exerted by the rest of the microstructure, then a can be obtained from the general Kirkwood (1949) formula (Doi and Edwards 1986) ... 

The EDS type of X-ray spectrometer is commonly included as a part of SEMs and TEMs. The reason for using EDS rather than WDS is simply its compactness. With EDS in an electron microscope, we can obtain elemental analysis while examining the microstructure of materials. The main difference between EDS in an electron microscope and in a stand-alone XRF is the source to excite characteristic X-rays from a specimen. Instead of using the primary X-ray beam, a high energy electron beam (the same beam for image formation) is used by the X-ray spectrometer in the microscopes. EDS in an electron microscope is suitable for analyzing the chemical elements in microscopic volume in the specimen because the electron probe can be focused on a very small area. Thus, the technique is often referred to as microanalysis. 

The periodic unit cell results are directly comparable to the IMT predictions, because both approaches represent the same matrix/inclusion type microstructure. However, such comparisons have to be done carefully since some assumptions regarding the finite element calculations are not equivalent for the extended unit cell approaches and the present mean-field method. The plane stress analysis of the unit cell models does not take into account the constraints in the out-of-plane direction. In contrast, within the present IMT formulation the inclusions are enclosed three-dimensionally by the matrix material. In contrast to the plane stress unit cell models, the constraint in the out-of plane direction is accounted for. Accordingly, these predictions are denoted as full internal constraint. To overcome this internal constraint in order to simulate the plane stress model assump-... 

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