Microstructures/microstructured materials nature

The microstructure of hi ly porous paints/building materials/natural building stone necessitates... 

Genetic engineering and supramolecular self-assembly offer a wide scope for controlling fibre composition and microstructure. The number and variety of materials that could be engineered with these techniques is extremely large. Much effort will be required to comprehensively characterise and efficiently refine the load-bearing properties of the new fibres. It is therefore opportune to reflect on the factors that determine the characteristics of hierarchical microstructure in natural fibres, and the ability of such microstructures to resist fracture. 

The structure and properties of biofibers, mainly of cellulose, were described in this chapter. First, the hierarchy microstructure of natural plant fiber and then a variety of crystal modifications of cellulose were mentioned. The ultimate mechanical properties (modulus of 138 GPa and strength of 17.8 GPa) and thermal properties (thermal expansion coefficient of 10 order) were emphasized as quite excellent for cellulosic fiber, enough for use as reinforcement in the composites. With the manifestation of these intrinsic properties in macroscopic material, the oH-cellulose composite was shown to possess excellent mechanical properties, thermal resistance, and optical transparency, besides being composed of fully sustainable resources and hence, biodegradable. Nowadays, the interest in cellulosic nanocomposites has increased considerably [60, 61] and they are expected to be used in many fields such as electronic devices, vehicles, and windmills to replace glass and/or carbon fibers. 

The sequence just outlined provides a salutary lesson in the nature of explanation in materials science. At first the process was a pure mystery. Then the relationship to the shape of the solid-solubility curve was uncovered that was a partial explanation. Next it was found that the microstructural process that leads to age-hardening involves a succession of intermediate phases, none of them in equilibrium (a very common situation in materials science as we now know). An understanding of how these intermediate phases interact with dislocations was a further stage in explanation. Then came an nnderstanding of the shape of the GP zones (planar in some alloys, globniar in others). Next, the kinetics of the hardening needed to be... 

This chapter is entitled Precursors of Materials Science and the foregoing major Sections have focused on the atomic hypothesis, crystallography, phase equilibria and microstructure, which I have presented as the main supports that made possible the emergence of modern materials. science. In what follows, some other fields of study that made substantial contributions are more brielly discussed. It should be remembered that this is in no way a le.xihnok, my task is not to explain the detailed nature of various phenomena and entitities, but only to outline how they came to be invented or recognised and how they have contributed to the edifice of modern materials science. The reader may well think that I have paid too much attention, up to now, to metals that was inevitable, but I shall do my best to redress the balance in due course. 

As with chemical etches, developing optimum conversion coatings requires assessment of the microstructure of the steel. Correlations have been found between the microstructure of the substrate material and the nature of the phosphate films formed. Aloru et al. demonstrated that the type of phosphate crystal formed varies with the orientation of the underlying steel crystal lattice [154]. Fig. 32 illustrates the different phosphate crystal morphologies that formed on two heat-treated surfaces. The fine flake structure formed on the tempered martensite surface promotes adhesion more effectively than the knobby protrusions formed on the cold-rolled steel. 

One may now ask whether natural systems have the necessary structural evolution needed to incorporate high-performance properties. An attempt is made here to compare the structure of some of the advanced polymers with a few natural polymers. Figure 1 gives the cross-sectional microstructure of a liquid crystalline (LC) copolyester, an advanced polymer with high-performance applications [33]. A hierarchically ordered arrangement of fibrils can be seen. This is compared with the microstructure of a tendon [5] (Fig. 2). The complexity and higher order of molecular arrangement of natural materi-... 

Most materials, be they natural or synthetic, have limited utility. However, technical ingenuity has increased the utility of these materials beyond anyone s wildest imagination. The enormous range of steel that can be produced by adding carbon or other elements to give it the required balance of properties, such as strength and hardness, related to changes in their microstructure [1-3] is just one example. 

Owing to hydrogen embrittlement, the mechanical properties of metallic and nonmetal-lic materials of containment systems may degrade and fail resulting in leaks. Hydrogen embrittlement depends on many factors such as environmental temperature and pressure, purity of metal, concentration and exposure time to hydrogen, stress state, physical and mechanical properties, microstructure, surface conditions, and the nature of the crack front of material [23]. 

Bipolar plates in PEMFCs were conventionally made of graphite with excellent corrosion resistance, chemical stability, and high thermal conductivity. However, graphite has a high cost, poor mechanical properties, and very little formability due to its microstructural nature. This limits its further applications as plate material and forces a search for alternative solutions. Nevertheless, the performance, durabilify, and cosf of fhe graphite plate (e.g., POCO graphite and graphite plates) have been taken as benchmark references to compare with those of alternative materials. 

The separation efficiency (e.g. permselectivity and permeability) of inorganic membranes depends, to a large extent, on the microstructural features of the membrane/support composites such as pore size and its distribution, pore shape, porosity and tortuosity. The microstructures (as a result of the various preparation methods and the processing conditions discussed in Chapter 2) and the membrane/support geometry will be described in some detail, particularly for commercial inorganic membranes. Other material-related membrane properties will be taken into consideration for specific separation applications. For example, the issues of chemical resistance and surface interaction of the membrane material and the physical nature of the module packing materials in relation to the membranes will be addressed. 

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