Melting monitoring

Vigorous stirring is necessary for a reasonable rate of reaction. The mixture remains heterogeneous both before and after the iron reagent melts. Monitoring of the reaction by GLPC (2-m 5% OV-1 or SE-30) is recommended to assure maximum conversion before the reaction is stopped. 

It is feasible to use a liber-optic-assisted visible spectrophotometer to measure the color of a stream of molten pigmented polymer in-line. In-line melt monitoring can distinguish within specification color from out of specification color. Also, it can be used to detect pigment degradation and to determine the upper temperature thresholds for pigmented polymer processing. However, because of the many factors that determine color perception, off-line and in-line results are not equivalent. 

The irradiation temperature of the surveillance specimens could be higher (up to 20 °C) than the RPV wall temperature. Supplementary measurement using melting monitors showed that specimen temperature is close to 300 °C, i.e. at least 12 °C higher than the RPV inner wall. Temperature monitoring by diamond powder is not adequate for determination of the irradiation temperature since the results show far too large a scatter. 

Optical properties also provide useful stmcture information about the fiber. The orientation of the molecular chains of a fiber can be estimated from differences in the refractive indexes measured with the optical microscope, using light polarized in the parallel and perpendicular directions relative to the fiber axis (46,47). The difference of the principal refractive indexes is called the birefringence, which is illustrated with typical fiber examples as foUows. Birefringence is used to monitor the orientation of nylon filament in melt spinning (48). 

As the polymer molecular weight increases, so does the melt viscosity, and the power to the stirrer drive is monitored so that an end point can be determined for each batch. When the desired melt viscosity is reached, the molten polymer is discharged through a bottom valve, often under positive pressure of the blanketing gas, and extmded as a ribbon or as thick strands which are water-quenched and chopped continuously by a set of mechanical knives. Large amounts of PET are also made by continuous polymerization processes. PBT is made both by batch and continuous polymerization processes (79—81). 

The ability of XPD and AED to measure the short-range order of materials on a very short time scale opens the door for surface order—disorder transition studies, such as the surface solid-to- liquid transition temperature, as has already been done for Pb and Ge. In the caseofbulkGe, a melting temperature of 1210 K was found. While monitoring core-level XPD photoelectron azimuthal scans as a function of increasing temperature, the surface was found to show an order—disorder temperature 160° below that of the bulk. 

The molecular weight of the polymer is a function of the extent of polymerization and could he monitored through the melt viscosity. The final polymer may he directly extruded or transformed to chips, which are stored. 

PCs all have one thing in common. They monitor the process variables, compare them to values known to be acceptable, and make appropriate corrections without operator intervention. The acceptable range of values can be determined by using melt flow analysis software and/or trial and error when the machine is first starting its production. Using the software approach, the acceptable process values are known before the mold or die is ever built. It should be noted that none of the PC solutions address the problem of the lack of skilled setup people. Most of the PC systems available today are rather complex and require skilled people to use them efficiently or at least start up the line. 

The reactants are loaded in a magnesia crucible and heated by a resistance furnace to 800°C (Figure 3). Once the CaCl2 is molten, a tantalum stirrer and a Ta-Ni thermocouple sheath are lowered into the melt. While stirring, the reaction is monitored with a thermocouple. Once the reaction is complete, the stirrer and thermocouple well are retracted and the melt is allowed to cool. Figure 4 shows a typical DOR product and salt/crucible residue. A typical product button weighs 600 g and the process yield is >99%. Essentially no purification takes place in the reduction step, meaning that the product button is no purer than the feed. 

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