Freeze drying freezing rate effects

Thijssen, H. A. C., Rulkens, W. H. Effect of freezing rate on rate of sublimation and flavour retention in freeze-drying, p. 99-114. International Institute of Refrigeration (Comm. X, Lausanne, 1969)... 

Kim AI, Knopp S, Akers MJ, Nail SL. The physical state of mannitol after freeze-drying effects of mannitol concentration, freezing rate, and a noncrystallizing cosolute. J Pharm Sci 1998 87 931-935. 

Freezing processes can be divided into two categories one type is so slow, so that they run under almost equilibrium conditions others are too fast to approach the equilibrium situation. Figures 1.14.1-1.14.3 show the effect of the freezing rate on the structure of the dried product. In Figure 1.14.1, milk has been frozen slowly (0.2-0.4 °C/min) in trays. In Figure 1.14.2, mannitol solution has been frozen in vials at a rate of-1 °C/min the arch at the bottom represents the vial bottom. In Figure... 

Van Winden, E.C.A. Zhang, W. Crommelin, D.J.A. Effect of freezing rate on the stability of liposomes during freeze-drying and rehydration. Pharm. Res. 1997, 14, 1151-1156. 

LeeM.K.,Kim,M.Y.,Kim,S.J.,andLee,LH.,Cryoprotectants for freeze drying of drug nano-suspensions Effect of freezing rate, J. Pham. Sci., 2009, 98, 4808 817. 

Schoug, S., Olsson, J., Carlfors, J., Schnurer, J., Hakansson, S. (2006). Freeze-drying of Lactobacillus coryniformis Si3-effects of sucrose concentration, cell density, and freezing rate on cell survival and thermophysical properties. Cryobiology, 53(1), 119-127. 

In addition to the effects of formulation factors on freeze-drying behavior, it is important for the pharmaceutical scientist to understand basic principles of heat and mass transfer in freeze-drying [29,30]. Because of the high heat input required for sublimation (670 cal/g), transfer of heat from the heated shelf to the sublimation front is often the rate-limiting step in the coupled heat... 

The primary characteristic necessary for a liner, cover, or cutoff wall is low permeability, which essentially enables them to slow down the seepage or diffusion of chemicals. Clay is therefore the main material used to construct these containment systems. The thickness and chemical compatibility of containment systems are of concern in assessing the performance of a system. For example, clay liners are constructed as a simple liner that is 2 to 5 ft thick. In composite and double liners, the compacted clay layers are usually between 2 and 5 ft thick, depending on the characteristics of the underlying geology and the type of liner to be installed. Regulations specify that the clay used can only allow water to penetrate at a rate of less than 1.2 in./yr. However, the effectiveness of clay liners can be reduced by fractures induced by freeze-thaw cycles, drying out, and the presence of some chemicals. 

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