Static crucible

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. 

In this case, we see that heat radiates from both the sides and the top of the melt even though the crucible is being heated by the eddy-currents from the RF-generator coupling. Note also that the crystal being pulled also radiates heat. However, this is for a static crucible. The circular currents set up in the melt are the results of the crystal being turned as it grows. The circular heat flow pattern causes the surface to radiate heat. 

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. 

Stirring Patterns Observed for a Static and Rotating Crucible... 

Figure 8.17 Weight-change versus time data showing that increased chromium concenttation in Ni-Cr-Al alloys ( , Ni-8 wt% Cr-6 wt% Al A, Ni-15 wt% Cr-6 wt% Al) extends the initiation stage for hot corrosion attack induced by immersion in a crucible with 1 g Na2S04 in static air isothermally at 1000 °C.

ISO 11907-2. 1995 [121] is a static method of lest used to determine the corrosivity of fire gases. The specimens (600 mg) in the form of granules or chips arc heated with an electric resistance wire (800 C) in a crucible. The effluent is contained within a closed cabinet of 20 liters volume maintained at 50 C and 65% rh. The corrosion detector consists of a resistance etched copper plated laminate, and the corrosivity is assessed as the variation in electrical resistance due to attack on the copper circuit. Two operating procedures are given, one for the condensing mode, in which the corrosion sensor is water cooled to 40 C. and one for the non-condensing mode, without water cooling to the sensor see Fig. 22. 

Data measured under the following conditions static air, CDR-I model DSC (Shanghai Balance Instrument Factory), 10°Cmin , sample mass ca. 1 mg, pressure-resistant sealed crucible made of soft stainless steel. 1. Melting peak 365 K (92 °C) decomposition peak Tp 711 K (438 °C). 2. Melting peak Tp 398 K (125 °C) decomposition peakTp685K(412°C)[5]. 

Figure 11.23 DTA curve of hexogen in static air. The inset is a partial DTA curve of RDX (industrial product) in static air. [60] The conditions of measurements were as follows sample mass, 16 mg (170 mg n-AKO, placed below the sample) reference material, a-Al20, (ca 190 mg) heating rate, 5 C min NiCr-NiSi thermocouples DTA sensitivity (total deflection), 250 gV paper speed, 120 mm h, pla-tinium crucible apparatus, simultaneous TG-DTA (Model 4.1, Beijing Optical Instrument Factory)...

Static capsules or pots of specieJ design are used to measure the solubility of solids in liquids. Eichelberger et al. [SO] used bimetallic capsules made by welding two crucibles. 

In the Crucible Test a well, drilled or moulded in a block of the refractory to be tested is filled with the selected slag and the block heated to the required temperature, for a specified time. The block is then removed, cooled, sectioned and the slag/refractory interface examined. The test is simple, but is static, and does not allow a temperature gradient to be studied. The reaction layer built up at the interface may produce erroneous results. The Pill Test is similar - a pellet of slag can be measured. In the Drip Test a stream of slag pellets falls on to a refractory block... 

Long and Norrish 103) measured the heat of combustion, using a static bomb calorimeter. The solid products of combustion consisted mainly of ZnO, admixed with ZnC03 and hydrated ZnO. Combustion was usually incomplete, and traces of soot remained in the crucible. Corrections were made for soot formation, and for formation of ZnC03 the corrected value, AH°= —482.8 + 2 kcal/mole, relates to the formation of ZnO (c, hexagonal), CO2, and H2O (liq) as sole products. Accepting AHf° (ZnO, c) = — 83.2 0.3 kcal/mole 143), the derived heat of formation is AHf° (Me2Zn, liq) = 6.5 + 2 kcal/mole. 

The heat of combustion of tetraethylgermanium using a static bomb calorimeter has been measured by Rabinovich et al. (136), and also by Pope and Skinner (130a). Rabinovich et al. reported AH°= —1515.6 1.5 kcal/mole, and stated that the solid product is Ge02 (c, tetragonal). No mention was made of incomplete combustion. Pope and Skinner, however, found that although combustion is almost complete, small amounts of unburned Ge (and/or GeO) remain in the crucible. After correction for this. Pope and Skinner obtained AH° = —1519.3 0.8 kcal/mole. The difference from Rabinovich s value is not fully accounted for by the correction made for incomplete combustion of the metal. 

The clinker-like product was melted at 2000°C, crushed, and remelted at the same temperature. The melting operations were performed in carbon crucibles in a static He atmosphere. The ingot obtained contained very small amounts of a second phase at the grain boundaries, Hampl [5]. In a similar way, black Gd2Se3 powders were prepared in an evacuated quartz bomb at 600°C and melted in Ta or Mo crucibles to dense, brittle, reddish gray ingots, Methfessel et al. [6]. 

The crucible was constructed in such a way that no mechanical force is acting on the inner crucible, because the weight of the upper crucible is supported by the outer crucible. This simulates a suspended stress-free biological shield in contrast to a wall which is loaded by its own weight or additional static forces. Consequently, the realized stress-free situation gives the optimum condition for stabilization of the crucible. Any other situation would lead to earlier failure of the cylinder. 

The flexural strength of the specimen before and after oxidation was tested with three-point bending of 3 by 4 by 36 mm bars, using a 30 mm span and a crosshead speed of 0.5 mm min. The specimen was supported on a graphite crucible, and the temperature of the specimen center was measured by a multi-wavelength pyrometer with measurement range of 1000-2500 °C. The isothermal oxidation of the specimens was carried out in static air at constant temperatures of 1000 15, 1200 15 and 1400 15 °C, each for several different times. Our investigation had confirmed that the predominant phases for the as-sintered ceramic were ZrB, SiC and a small quantity of ZrC. 

---