Study Gradient Materials

Spatial variation of structure in a natural sample or in a technical part (e.g., gradient materials for hip-joints) can be studied by means of microfocus [44] beams (microbeams). The size of the probing X-ray beam limits the spatial resolution. 

Gradient Materials are studied at microfocus beamlines with a spatial resolution down to 1 jj.m. Current development of nanobeam optics will soon allow for spatial resolutions down to 50 nm. 

Miyamoto, Y, Nakanishi, H., Tanaka, I., Okamoto, T and Yamada, O., Processing study for the functionally gradient material TiC-Ni by the gas-pressure combustion sintering. Proceedings of the First US-Japanese Workshop on Combustion Synthesis, Tokyo, Japan, 173 (1990b). 

Williamson R.L., Rabin B.H. and Byerly G., "Residual Stresses in Joined Ceramic-Metal Structures FEM Studies on Interlayer and Creep Effects", in 3rd International Symposium on Structural and Functional Gradient Materials, ed. Ilschner, B. and Cherradi, N., PPUR, Lausanne, (1994), 215-221. 

In situ analysis of mineral content and crystallinity in bone. Bone, a functionally gradient material, is composed of protein and mineral components which give rise to spectral absorptions in the mid and far-infrared spectral range. Recently, Miller et al. (2001) have initiated an investigation of cross sections of human iliac crest bones, collecting the IR absorption spectra around a human osteon. The focus of this investigation was to measure the acid phosphate content and determine mineral crystallite perfection from the . spectra. The crystallite perfection was determined from a concurrent study of the correlation of IR absorption spectra with X-ray powder diffraction results from a series of synthetic hydroxyapatite crystals and natural bone powders of various species and ages. 

Model Study 1 Cell Migration on Bioactive Gradient Materials... 

Overview. Microbeam experiments are carried out if the structure iu a small volume element of the sample is to be studied. Compared to macrobeam applications, the advantage of this method is the possibility to study spatial variations of nanostructure. An example of a matching scientific question is the analysis of the core-shell structure of polymer fibers, or the study of nanostructure variations in nanostructured gradient materials which are developed for medical applications. All the corresponding experiments are carried out in a scanning microbeam setup . 

As regards clinical work, in vitro studies have proved to be very valuable for example, the study of materials and cements for dental work and hip-joint prostheses. One may predict that in vivo studies will emerge. Indeed, having the subject nearly outside the magnet has considerable advantages. For human patients, the question of the safety aspects of the large gradients will need to be addressed. 

An additional advantage to neutron reflectivity is that high-vacuum conditions are not required. Thus, while studies on solid films can easily be pursued by several techniques, studies involving solvents or other volatile fluids are amenable only to reflectivity techniques. Neutrons penetrate deeply into a medium without substantial losses due to absorption. For example, a hydrocarbon film with a density of Ig cm havii a thickness of 2 mm attenuates the neutron beam by only 50%. Consequently, films several pm in thickness can be studied by neutron reflecdvity. Thus, one has the ability to probe concentration gradients at interfaces that are buried deep within a specimen while maintaining the high spatial resolution. Materials like quartz, sapphire, or aluminum are transparent to neutrons. Thus, concentration profiles at solid interfaces can be studied with neutrons, which simply is not possible with other techniques. 

The Lewis acid Hg3( i-C6F4)3 also forms a pi-acid/pi-base interaction with TR(carb). In addition to the crystal structure demonstrating the ABBABB pattern observed in other stacked materials which retain the aurophilic Au-Au interactions between four of the six basic Au(I) atoms of the BB moieties, studies have shown that the oligomeric acid/base interection is retained in solution. Pulsed gradient diffusion NMR studies [70] suggesting the oligomeric sizes and coupling... 

The Knoop test is a microhardness test. In microhardness testing the indentation dimensions are comparable to microstructural ones. Thus, this testing method becomes useful for assessing the relative hardnesses of various phases or microconstituents in two phase or multiphase alloys. It can also be used to monitor hardness gradients that may exist in a solid, e.g., in a surface hardened part. The Knoop test employs a skewed diamond indentor shaped so that the long and short diagonals of the indentation are approximately in the ratio 7 1. The Knoop hardness number (KHN) is calculated as the force divided by the projected indentation area. The test uses low loads to provide small indentations required for microhardness studies. Since the indentations are very small their dimensions have to be measured under an optical microscope. This implies that the surface of the material is prepared approximately. For those reasons, microhardness assessments are not as often used industrially as are other hardness tests. However, the use of microhardness testing is undisputed in research and development situations. 

---