Gradient carbonate

Diffusion of Carbon. When carbon atoms are deposited on the surface of the austenite, these atoms locate in the interstices between the iron atoms. As a result of natural vibrations the carbon atoms rapidly move from one site to another, statistically moving away from the surface. Carbon atoms continue to be deposited on the surface, so that a carbon gradient builds up, as shown schematically in Figure 5. When the carbon content of the surface attains the equihbrium value, this value is maintained at the surface if the kinetics of the gas reactions are sufficient to produce carbon atoms at least as fast as the atoms diffuse away from the surface into the interior of the sample. 

An important advancement in carburizing has been the development of diffusion models to calculate the carbon gradient as a function of time as the gas composition and temperature change (13). Such models can be coupled with computer control of the gas composition and temperature to produce desired carbon profiles. 

When endosymbiosis is established in the inner cortical cells, it is thought that both intercellular hyphae and arbuscules are involved in carbohydrate transfer from plant to fungi and mineral nutrients go in the opposite direction (Smith and Read, 1997). The molecules that control arbuscule development, maintenance and senescence are unknown. However, because of the proximity with vascular tissue (the source of sugars for roots), it has been proposed that a carbon gradient may be involved as a signal (Blee and Anderson, 1998). 

Pig, g Carbon gradient profile of atmosphere, vacuum, and plasma carburiz-ing of AISI 8620 steel at 980 °C (1800 °F) saturation conditions for 30 min and foilowed by direct oil quenching. Source Ref 12... 

The neutron autoradiography technique, which was said to allow measuring boron concentrations 5 1 ppm in massive samples, was used to measure boron concentrations along the carbon gradient of a carburized B-Fe alloy [1978Cam], A new analytical method based on the spectral lines was used for accurate determination of B in B-C-Fe alloys [1975Tve],... 

Fig. 6. (a) The effect of sub2ero cooling on the hardness gradient in a carburized and quenched 3312 steel where (e) is oil quenched from 925 to 20°C and ( ) is cooled to -195°C. The initial quench to 20°C does not convert all of the austenite to martensite because the high carbon content in the surface region lowers the temperature below 20°C. Subsequent cooling to -195°C converts most of the retained austenite to martensite, raising the hardness, (b) The... 

By beginning with methane, the diamonds formed have only in them. These tiny diamonds may then be used as the carbon source to form large (5 mm) single crystals by growth from molten catalyst metal in a temperature gradient. The resulting nearly pure crystals have outstanding thermal conductivities suitable for special appHcations as windows and heat sinks (24). 

The continuous production of high purity methyl or ethyl carbonate from the alcohol and chloroformates has been patented (80). Chloroformate and alcohol are fed continuously into a Raschig ting-packed column in which a temperature gradient of 72—127°C is maintained between base and head of the column HCl is withdrawn at the head, and carbonate (99%) is withdrawn at the base. 

Majetich and coworkers have studied magnetic properties of carbon-coated Co[32], Gd2C3, and FIo2C3 nanocrystals[33] formed in the chamber soot. A brief account on the coated Co nanocrystals is given here. They extracted magnetic nanocrystals from the crude soot with a magnetic gradient field technique. 

Heavy isotopes endow the compounds in which they appear with slightly greater masses than their unlabeled counterparts. These compounds can be separated and quantitated by mass spectrometry (or density gradient centrifugation, if they are macromolecules). For example, O was used in separate experiments as a tracer of the fate of the oxygen atoms in water and carbon dioxide to determine whether the atmospheric oxygen produced in photosynthesis arose from HgO, COg, or both ... 

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