Freezing cycles

Some compounds expand so much during the melting and freezing cycles... 

Starch acrylonitrile in 10% emulsion Freezing cycles, number Block copolymerization %... 

The higher crystalline fraction of the radiation cross-linked polyethylene even after a melt-freeze cycle has great technological merit for the heat-shrink packaging and electrical connector products. ... 

Environmental and accelerated ageing tests were performed on the indoor dye modules described in Sect. 7.6 in order to detect failure mechanisms. Contrary to expectations, many modules survived humidity/freeze cycling tests (10 cycles, 85%, 20 h at 55°C per cycle) without major degradation, demonstrating the capability of the sealing concept (see Fig. 7.8). This was also true for temperature cycling (between —5 and 55°C). However, it has... 

The scheduling of the annealing protocol, including the notion of cooling and freezing cycles, was as before. The previous ratio of Ii to l2 of 2 and the optimal values of g 0.98-0.99 were found to be adequate. The value of Tq was a little lower at 20j.. 

The physical instability of emulsions involves creaming, flocculation, coalescence, or breaking, whereas the chemical instability can be a result of hydrolysis of the stabilizing moieties. In order to assess the stability of the emulsion, heating and freezing cycles and centrifugation and steam sterilization can be employed. 

Values of Water Content (wtot), Enthalpy, T nseu peak and Unfrozen Water Content (UFW) from Ice Melting Curves, After Freeze Cycle on DSC, of Dough According to Formulation... 

Figure 33. The increase in weight percent solids as a function of freezing cycle for various MFT samples (D. Sego, unpublished data).

Preserved with EDTA (first choice) or heparin (second choice) short-term storage and transport at + 4°C, long-term storage at — 20°C. Avoid thawing and freezing cycles transport at —20°C thawing in a water bath at 37°C directly before DNA extraction. 

ISO 20340 salt-spray cycles ISO 20340 includes an optional freeze cycle... 

Corti et al. [101] studied the freezing of water and water-methanol mixtures in Nafion 117 and they found that the amount of freezable water, determined from the area of the ice fusion peak of the DSC scan, increased from 1 % to 23 % as the relative humidity increases from 84 % to 100 %. However, the presence of methanol in the membrane increased the amount of freezable water up to 61 % for methanol 25 v/lw% aqueous solutions, reaching an apparent limit of 65 % for more concentrated methanol solutions. This result would indicate that the degradation of the MEA in DMFC under freezing cycles could be worse than that observed for hydrogen feed PEM fuel cells. 

WUlcox et al. proposed a gelation scheme in support of the above hypothesis. When a PVA solution is subjected to a number of FTCs, during the first freezing cycle, ice crystallizations cause the remaining polymer solution to concentrate, bringing the molecular chains closer together. This promotes PVA crystallite... 

A fundamental paradigm of freeze-drying is to understand that, in almost every case, there is no direct correlation between the structure of a frozen product and its temperature since all structural features depend essentially on the thermal history of the material. In other words, the knowledge of the temperature of a frozen solution is not enough to allow the operator to know its structure since this latter depends, essentially, upon the way this temperature has been reached, i.e., upon the freezing cycle. 

Repeated thawing/freezing cycles should be avoided. 

After the sample is frozen, the entire apparatus is evacuated by opening the stopcock. When the evacuation is complete, the stopcock is closed, and the Dewar flask is removed. The sample is allowed to thaw, and then it is frozen again. This freeze-thaw-freeze cycle removes any air or gases fhat were trapped in the frozen sample. Next, the stopcock is opened to evacuate the system again. When the second evacuation is complete, the stopcock is closed, and the Dewar flask is moved to the other arm to cool the empty container. As the sample warms, it will vaporize, travel to the other side, and be frozen or liquefied by the cooling solution. This transfer of the liquid from one arm to the other may take quite a while, but no heating is required. 

Zone refining uses repeated melting and freezing cycles to purify materials through crystallization. 

---