Permeation oxygen

The permeation technique as discussed in the context of permeation membranes in Section 11.2, can also be used to determine diffusion coefficients and minority conductivities (in fact X (T ICg by evaluating the transients, 

As the oxygen partial pressure ratio, and hence, is known, the ambipolar conductivity is readily determined from the flux. This knowledge can be further used to calculate the partial conductivities, and by knowing Lf from the transient (i.e., by also evaluating the delay time ) to derive the thermodynamic factor (i.e., the chemical capacitance). 

As described in Section 11.2 variants of the permeation techniques use systems in which electronic and ionic pathways are locally separated, e.g., an ion conductor which is internally short-circuited by percolating metallic inclusions (or materials in which grain boundary and bulk possess different conductivity types (e.g., nano- Ce02)). In all these cases the permeation flux is determined by the lowest partial conductivity. 

A related method to separate electronic and ionic conductivities has been extensively discussed by Riess. As in the previous 

The stabilization of carbon fiber precursors is done in an air atmosphere, and oxygen is required all through the fiber, for the chemical reactions going on (cf. Sect. 3). 

Oxygen diffusion in PAN homopolymer is very poor, due to the high molecular order. Again copolymerization helps to relieve the situation. Fig. 2 shows — for the cases of AN/Sty and AN/Butadiene copolymers — how the Oj-permeation increases with increasing comonomer content (experimental data of Salame ). The figure also includes the Oj-permeation of a number of other homopolymers (as 100% comonomer ). Assuming a similar type of dependence of the -permeation on the amount of the respective monomers M in a copolymer AN/M, the Oj 

Theoretical attempts to correlate permeation with properties of the various monomers have not been entirely successful. However, molar volume and polarity appear to be important properties, the smaller and more polar comonomers giving rise to less Oj-permeation. No data are available for vinyl bromide however, on the grounds of molar volume and polarity, it may be assumed that O -permeation in VBr is similar to that in VCl. 

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The dimensions of permeabiUty become clear after rearranging equation 1 to solve for P. The permeabiUty must have dimensions of quantity of permeant (either mass or molar) times thickness ia the numerator with area times a time iaterval times pressure ia the denomiaator. Table 1 contains conversion factors for several common unit sets with the permeant quantity ia molar units. The unit nmol/(m-s-GPa) is used hereia for the permeabiUty of small molecules because this unit is SI, which is preferred ia current technical encyclopedias, and it is only a factor of 2, different from the commercial permeabihty unit, (cc(STP)-mil)/(100 in. datm). The molar character is useful for oxygen permeation, which could ultimately involve a chemical reaction, or carbon dioxide permeation, which is often related to the pressure in a beverage botde. 

Figure 9. A coated and uncoated 1-gallon, high density bottle under test for oxygen permeation inward. Copper and ammonia solution in the container are chemically influenced by entering oxygen, which provides a quantitative basis for the measurement.

Ammonia analysis for oxygen permeation through polyethylene,... 

R Shah, LL Augsburger. Oxygen permeation in banded and non-banded hard gelatin capsules (abstr). Pharm Res 6 S-55, 1989. 

Nylon barrier layers are used in packaging films and blow molded bottles. In these applications, their excellent resistance to oxygen permeation are valued when packaging greasy foods, such as potato crisps (chips), that rapidly turn stale when exposed to oxygen. 

Schematics of an oxygen membrane reactor for catalytic POx of methane. A blown up section on the left-hand side shows the details of the ceramic membrane wall explaining the mechanism of oxygen permeation across the membrane. /- is the chemical potential of oxygen and ai and

Ogumi, Z., Takehara, Z. and Yoshizawa, S. 1984. Gas permeation in SPE method. 1. Oxygen permeation through Nation and Neosepta. JoHrMflZ of the Electrochemical Society 131 769-773. 

Biichi, F. N., Wakizoe, M. and Srinivasan, S. 1996. Microelectrode investigation of oxygen permeation in perfluorinated proton exchange membranes with different equivalent weights. Journal of the Electrochemical Society 143 927-932. 

Zhang, L., Ma, C. and Mukerjee, S. 2003. Oxygen permeation studies on alternative proton exchange membranes designed for elevated temperature operation. Electrochimica Acta 48 1845-1859. 

Waterman et al. [103] determined the theoretical rate of oxygen permeation through a standard 30-cc bottle when stored in a well-sealed container. This equated to an uptake of 0.2 mMol of oxygen per year. In addition to permeation through the container walls, the key vulnerability in any container-closure system is the closure. With screw-topped closures leakage can be significant. Hence for... 

Li et al. [107] also reported the change in residual radical concentration vs oxygen permeation time for a homopolymerization of EGDMA. At 110°C, the radical concentration decreased by approximately 12.5% in 90 min. While at 180 °C, the radical concentration dropped nearly 62.5% over the same time period. While these reactions occurred over a relatively short time period, the temperatures were quite high and certainly one would expect significantly reduced rates at lower temperatures below the glass transition temperature of... 

Polyvinylidene chloride (PVDC), polyethylene (LDPE and HDPE), polypropylene (PP), PVC, and polystyrene all have excellent resistance to oxygen permeation. Polyethylene also has relatively good resistance to the permeation of water, which makes it an excellent choice for bread bags. 

Decreased Oxygen Permeation Through the Epoxy Coating.. .. 58... 

Gas permeation through Teflon AF thin films is extraordinarily high, with permeation rates increasing as PDD content increases. AF-2400 has an oxygen permeation rate of 99,000 cB (centi-Barrers) and a carbon dioxide permeation rate of 280,000 cB compared to 420 cB and 1200 cB for PTFE respectively. These unusually high permeation rates are thought to be the direct result of the microvoids present in the copolymer. 

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