Compaction of carbonates

Arc-melting Well mixed (in some cases partially pre-reacted) compacts of carbon and the metal may be reacted by melting arc-melting may be especially suitable. An advantage of melting in comparison with solid-state reactions may be related to the fact that arc-melted pieces have a smooth surface less susceptible to contamination. This method was found especially effective for refining and for the preparation of solid solutions mainly of the 4th and 5th carbides groups. 

Ebhardt G. (1968) Experimental compaction of carbonate sediments. In Recent Developments in Carbonate Sedimentology of Central Europe (eds. G. Muller and G. Friedman), pp. 58-65. Springer-Verlag, Berlin. 

Fig 7. Compaction of carbonate and siliceous sand following the same procedure as in Chuhan et al. 2002. Microporous carbonate sand comprises carbonate fossil shells which initially compact readily. At stresses above 20 MPa, however, it is no more compressible than quartz sand. Recent carbonate ooids from Florida are less compressible than quartz at high stresses. 

The evidence obtained in compaction experiments is of particular interest in the present context. Figure 3.22 shows the results obtained by Avery and Ramsay for the isotherms of nitrogen on compacts of silica powder. The hysteresis loop moved progressively to the left as the compacting pressure increased, but the lower closure point did not fall below a relative pressure of 0-40. Similar results were obtained in the compaction of zirconia powder both by Avery and Ramsay (cf. Fig. 4.5), and by Gregg and Langford, where the lower closure point moved down to 0-42-0-45p° but not below. With a mesoporous magnesia (prepared by thermal decomposition of the hydrated carbonate) the position of the closure point... 

Fig. 4J2 Adsorption isotherms of carbon tetrachloride (at 298 K) on ammonium phosphotungstate compact, (1) before, (2) after preadsorption of n-nonane. (3) is the isotherm of nitrogen, after preadsorption, for reference. Open symbols, adsorption solid symbols,...

Carburization by Thermal Diffusion. Carburization of chemically processed metal or metal-compound powders is carried out through sohd-state, thermal diffusion processes, either in protective gas or vacuum. Carbide soHd solutions are prepared by the same methods. Most carbides are made by these processes, using loose or compacted mixtures of carbon and metal or metal-oxide powders. HaUdes of Group 5 (VB) metals recovered from ores by chlorination are similarly carburized. 

Carbon—graphite materials employed for mechanical appHcations are prepared by mixing selected sizes and types of carbon and graphite with biader materials such as pitches and resias. The mixtures are formed iato compacts and baked to temperatures of ca 1000—3000°C. Specific raw materials and processiag techniques are employed to obtain desired properties for the finished carbon—graphite materials (24). 

FIG. 20-78 Reaction in compacts of magnesium carbonate when pressed (P = 671 kg/cnr ). (a) Stress contour levels in kilograms per square centimeter, (h) Density contours in percent solids, (c) Reaction force developed at wedge responsible for stress and density patterns. [Tf ain, Trans. Inst. Cbem. Eng. (London), 35, 258 (1957).]... 

Diamond is a naturally occurring form of pure, crystalline carbon. Each carbon atom is surrounded by four others arranged tetrahe-drally. The result is a compact structural network bound by normal chemical bonds. This description offers a ready explanation for the extreme hardness and the great stability of carbon in this form. 

A carbon rod is used as a current collector for the positive electrode in dry cells. It is made by heating an extruded mixture of carbon (petroleum coke, graphite) and pitch which serves as a binder. A heat treatment at temperatures of about 1100 °C is used to carbonize the pitch and to produce a solid structure with low resistance. For example, Takahashi [23] reported that heat treatment reduced the specific resistance from 1 Q cm to 3.6xlO"1Qcm and the density increased from 1.7 to 2.02 gem- 1. Fischer and Wissler [24] derived an experimental relationship [Eq. (1)] between the electrical conductivity, compaction pressure, and properties of graphite powder ... 

Other treatments " have led to scales that are based on different principles, for example, the average of the ionization potential and the electron affinity, " the average one-electron energy of valence shell electrons in ground-state free atoms, or the compactness of an atom s electron cloud.In some of these treatments electronegativities can be calculated for different valence states, for different hybridizations (e.g., sp carbon atoms are more electronegative than sp, which are still more electronegative than and even differently for primary, secondary,... 

Chemical vapor deposition (CVD) of carbon from propane is the main reaction in the fabrication of the C/C composites [1,2] and the C-SiC functionally graded material [3,4,5]. The carbon deposition rate from propane is high compared with those from other aliphatic hydrocarbons [4]. Propane is rapidly decomposed in the gas phase and various hydrocarbons are formed independently of the film growth in the CVD reactor. The propane concentration distribution is determined by the gas-phase kinetics. The gas-phase reaction model, in addition to the film growth reaction model, is required for the numerical simulation of the CVD reactor for designing and controlling purposes. Therefore, a compact gas-phase reaction model is preferred. The authors proposed the procedure to reduce an elementary reaction model consisting of hundreds of reactions to a compact model objectively [6]. In this study, the procedure is applied to propane pyrolysis for carbon CVD and a compact gas-phase reaction model is built by the proposed procedure and the kinetic parameters are determined from the experimental results. 

The chemistry of living processes is complex, and many carbon-based molecules found in living organisms have extremely complicated stmctures. Because of this complexity, chemists have developed line structures, which are compact representations of the stmctural formulas of carbon compounds. Line structures are constructed according... 

Typical results of the dry pelletizing process when a charge of carbon black and its plus 52-mesh seeds is tumbled in a drum (12) are shown in Figs. 31 and 32. Initially, the seeds grow in size rapidly by snowballing. The dip in the bulk density of the seeds (Fig. 32) suggests that the deposited layers are quite porous in the beginning but get compacted in due course to... 

Powder metallurgical methods These include reaction of the elements and car-bothermal reduction methods. Fine powders of the metal (Hf, V, Nb, Mo, W, etc.) and carbon (graphite, lampblack) may be mixed, possibly in wet conditions with an organic solvent to be removed later, then pressed and compacted into pellets or bricks to be heated at high temperature (1800-2000°C). To perform the carbother-mal reduction, mixtures of carbon with an oxide (of Ti, V, Cr, etc.) are compacted and heated. An additional heat treatment in a high vacuum may be useful to remove O, N, etc. below a low level. 

Coal/coke conductivity as a function of carbonization and/or compaction... 

---