Crucible method

The best compromise seems to be fast- rotation for the crystal and slow or no rotation for the crucible. Of all the possible methods of stirring the melt, the static-crucible method seems to be the best, and this is the method used by most crystal-growers. The next best method seems to be rotating the crucible at a slow rate, counter to the direction of the crystal rotation. It is clear that crystal- rotation needs to dominate the stirring pattern so that mixing of the melt continues while the crystal is growing. 

Ignition temperature was used with partial success (52, 57, 74, 135,189). Results depended critically on the method used—e.g., adiabatic compression, ignition limits in tubes, or crucible method. Jackson (70, 86, 87) determined ignition temperatures for a large number of hydrocarbons by the crucible method and developed correlations with structure. 

The standard crucible method used for coal may be unsuitable for coke because coke often requires a higher temperature for removal of the last remnants of the volatile matter. A thermogravimetric procedure in nitrogen at 1000°C (1830°F), or higher if necessary, for a specified period (30 minutes or more) may be desirable for coke. However, the precise conditions must be acknowledged formally when the yield of volatile matter is declared. 

Uehara 4 31 has suggested the crucible method to examine the combustibility of the oxidizer-sawdust mixtures but has noted that the results may be affected by humidity. Consequently, he has built the apparatus shown in Fig. 3.22 and has achieved good reproducibility in his data. The Fire Research Institute of the Ministry of Home Affairs and the Hazardous Material Laboratory of Japan Carlit Co., Ltd. use an apparatus similar to Uehara s. 

The best compromise seems to be fast- rotation for the crystal and slow or no rotation for the crucible. Of all the possible methods of stirring the melt, the static-crucible method seems to be the best, and this is the method used by most crystal-growers. 

The double crucible method and the rod-in-tube method are used primarily for higher-loss fibers made... 

An example of the crucible method is that due to Bridgman and Stockbarger (see Figure 7.20d). The melt is contained in a crucible with a conical bottom which is lowered slowly from a hot to a cold zone. The two sections of the furnace, which are kept at about 50 °C above and below the melting point of the substance, respectively, are isolated by a thermal shield. The bulk of the solidified material, apart from the tip of the cone where the nuclei gather, is a single crystal. This method has proved successful for many semiconductor materials and alkali halides. 

Process. Single filaments of clad fiber may be made by redraw of rod in tubing or, alternatively, by a double-crucible method, which is essentially a Vello-type delivery system, where a second glass, rather than air, is delivered through the center of the bell. A version of the latter method is illustrated in Fig. 6.43. 

DIN 51069-2-1972. Testing of ceramic materials comparing test of the resistance of refractory bricks to the attack of solid and liquid materials at high temperatme, crucible method (withdrawn). 

The double crucible method to draw optical fibres uses two crucibles positioned into each other. The inner crucible contains the glass material from which the core is drawn whereas the outer crucible holds the melt for the... 

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