Texture transformations

According to Bohn, the study of chemistry was fundamental to perfecting all the other arts and sciences. No one who wished to be successful in medicine could ignore chemistry, and the real professors of natural philosophy in our age, he noted, were men of the body who understood the texture, nature, and structure of the body s various parts. Most of all, however, the universality of chemistry consisted in the fact that it alone displayed the means by which mixed bodies were dissolved and their textures transformed. Chemistry could thus alter the innate properties of bodies and direct them into other things. It is incredible, says Bohn, how much power the chemist has. It was this noble and excellent part of philosophy that Bohn had loved. . . since boyhood. What he really loved, however, was the power to make things different than they were before, to force nature, as it were, into different shapes and structures, and from that to learn what was fundamental to her construction. In this, as we shall see, Bohn shared an important attitude toward the creation of knowledge that had recently been expressed in a more philosophical setting as the experimental method. 

Obao Exfoliating Shower Gel (France) L Oreal Microbeads, AHA Softens die roughness of skin and eliminates dead cells. New skin effect contains AHA to help die renewal of the cells. Exfoliated skin sees its texture transformed. A skin like new, soft, velvety, toned... 

Figure 12.34. Schematic illustration of a polymer-stabilized cholesteric texture (PSCT) in (a) the planar texture, (b) the focal conic texture, and (c) the homeotropic texture. Transforming the homeotropic ahgned state (c) back to the planar of focal conic state depends on the history of the voltage.

Many defects originate from a non-parallel coalescence of germs (Fig. 40). In addition, mechanical constraints generate edge and screw dislocations, or another pattern called elementary pinch (Fig. 41), which is also found in cholesterics and probably at the origin of focal domains in smectics. This pattern seems, therefore, to be essential in texture transformations. 

Schematic representation of shear-induced texture transformations.

Figure 2-11. Example of textural transformation observed under different electric fields on a lOpm film of a biphenyl based material...

Kumar K P, Keizer K and Burggraaf A J 1994 Stabiiization of the porous texture of nanostructured titania by avoiding a phase transformation J. Mater. Sc/. Lett. 59... 

The polyamides are soluble in high strength sulfuric acid or in mixtures of hexamethylphosphoramide, /V, /V- dim ethyl acetam i de and LiCl. In the latter, compHcated relationships exist between solvent composition and the temperature at which the Hquid crystal phase forms. The polyamide solutions show an abmpt decrease in viscosity which is characteristic of mesophase formation when a critical volume fraction of polymer ( ) is exceeded. The viscosity may decrease, however, in the Hquid crystal phase if the molecular ordering allows the rod-shaped entities to gHde past one another more easily despite the higher concentration. The Hquid crystal phase is optically anisotropic and the texture is nematic. The nematic texture can be transformed to a chiral nematic texture by adding chiral species as a dopant or incorporating a chiral unit in the main chain as a copolymer (30). 

Selenium is added up to 0.1% to silicon steels (2—4% Si) used in transformer cores to enhance the development of the secondary recrystallization texture which, in turn, improves the magnetic characteristics. Selenium alloying additions to the melt may be made as elemental Se, nickel—selenium, or ferroselenium. The recovery depends on the melting practice and method of addition. Normally, it is in the range of 66%, but may be as high as 90%. 

To date, there has been relatively little work reported on the mesophase pitch rheology which takes into account its liquid crystalline nature. However, several researchers have performed classical viscometric studies on pitch samples during and after their transformation to mesophase. While these results provide no information pertaining to the development of texture in mesophase pitch-based carbon fibers, this information is of empirical value in comparing pitches and predicting their spinnability, as well as predicting the approximate temperature at which an untested pitch may be melt-spun. 

Metallurgists originally, and now materials scientists (as well as solid-state chemists) have used erystallographic methods, certainly, for the determination of the structures of intermetallic compounds, but also for such subsidiary parepistemes as the study of the orientation relationships involved in phase transformations, and the study of preferred orientations, alias texture (statistically preferential alignment of the crystal axes of the individual grains in a polycrystalline assembly) however, those who pursue such concerns are not members of the aristocracy The study of texture both by X-ray diffraction and by computer simulation has become a huge sub-subsidiary field, very recently marked by the publication of a major book (Kocks el al. 1998). 

Transmission electron microscopes (TEM) with their variants (scanning transmission microscopes, analytical microscopes, high-resolution microscopes, high-voltage microscopes) are now crucial tools in the study of materials crystal defects of all kinds, radiation damage, ofif-stoichiometric compounds, features of atomic order, polyphase microstructures, stages in phase transformations, orientation relationships between phases, recrystallisation, local textures, compositions of phases... there is no end to the features that are today studied by TEM. Newbury and Williams (2000) have surveyed the place of the electron microscope as the materials characterisation tool of the millennium . 

Damage to epicuticular waxes Altered photosynthesis Increased water loss Accumulation of acidic anions Leaching of ions, sugars, etc. Mineral imbalances Altered metabolism Increased susceptibility to winter freezing injury Death of fine roots Destabilization of trees Reduced water/mineral uptake Reduced water uptake Cations leached below roots Accumulation of acidic anions Altered structure/texture Altered microflora Reduced litter decomposition Altered N transformations Solubilization of metal ions... 

Figure 2. Fonnation of ring and oblique texture patterns, a - several randomly rotated artificial crystallites and its Fourier transform (inset) b - reciprocal space with rings and zero tilt Ewald sphere c - 60° tilt of the Ewald sphere (reflection centers lie on the ellipse) d - the diffraction pattern as it is seen on the image plane.

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