Traveling solvent method

The transformation of the epitaxial layer polytype to a structure different from 3C, 6H or 15R was first obtained with the use of liquid phase epitaxy by the travelling solvent method [63]. The authors employed scandium-based solutions and they observed the 4H-SiC layer growth on substrates of the 6H polytypes. Later, the detailed studies of Vodakov et al [64] showed that the 6H to 4H polytype transition occurs when the growth is performed onto the carbon face and only if the melt contains excess carbon. No polytype transformation occurred if the melts were free from excess carbon or contained excess silicon. In [63] no carbon was added to the solvent intentionally, so most probably it entered the melt via reaction with the graphite... 

The specific electrical resistivity of SiC single crystals depends on purity. Values at room temperature range from 2.1-0.4 Ohm-cm. Single crystals formed by the traveling solvent method have the higher purity needed for rectifier applications in... 

Kuroda, K, I.H. Choi, T. Egi, H. Unoki and N. Koshizuka, 1996, NdBa2Cu3 07 /, single crystals grown by the Travelling Solvent Floating Zone Method, in Proc. ISS 95, Hamamatsu, Japan, eds H. Hayakawa and Y. Enomoto, Vol. VIII of Advances in Superconductivity (Springer, Tokyo) pp. 329-332. 

The use of molten metal solvents in the traveling solvent technique is clearly possible. The general aspects of the technique are discussed by Wolff and Mlavsky (1974) and can easily adapt to the various fluxes discussed here. This method is especially important when large crystals are desired. 

Fig. 1.14 The quasibinary phase diagram SnSe-ZnSe and the setup for the traveling heater method (THM). ZnSe single crystal grown by THM and using SnSe as solvent (top...

Separations by column liquid chromatography (HPLC) and TIC occur by essentially the same physical processes. The two methods have often been considered as competitors when it would be more realistic to consider then as complementary, both having their own strengths and weaknesses. In HPLC each sample component must travel the complete length of the column and the total separation time is determined by the time required for the slowest moving component to reach the detector. While for TLC the total time for the separation is the time required for the solvent front to migrate a predetermined distance, and is independent of the migration distance of the sample components. Excessively retained components result in a considerable loss of time in HPLC while components accumulated at the head of the column are completely eluted, and if this is not possible, permanent alteration of the... 

The problems associated with the separation of phosphate esters are the tendency of the spots to diffuse difficulty of reproducing RF values variability of RF values with complexity of the mixture being resolved and distance of solvent travel proper purification and equilibration of the filter paper effect of inorganic ions in natural mixtures and the choice of suitable solvent mixtures for desired separations. The problem of detecting the separated spots is somewhat simpler. In addition to methods applicable to the detection of reducing sugars (e.g., use of aniline salts fructose esters are detected by naphthoresorcinol-acid), methods depending on phosphomolybdate formation are most commonly used. Hanes and Isher-... 

The stationary phase in SEC is a highly porous substrate whose pores are penetrated best by small solute molecules. Because larger solute molecules are unable to enter as deeply into the pores, they will travel further down the column in the same time. The largest molecules, which are totally excluded from the pores, are eluted first from the column. Because the solvent molecules are usually the smallest, they are normally the last to be eluted. The rest of the solute molecules are eluted between these two extremes, at a time dependent on their ability to penetrate into the pores. In SEC, therefore, unlike other chromatographic methods, the entire sample often is eluted before the solvent dead time peak, t0, as shown in Figure 2.13.53... 

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