Structure defects from fluorination

It is shown that electrolytic manganese dioxide, which has been obtained from fluorine-containing electrolytes differs from traditional types of Mn02 obtained by state-of-the-art synthesis methods. This material is characterized by the increased amount of structural defects. It is shown that crystalline structure with a large number of defects has a higher catalytic and electrochemical activity. 

The results indicate that both NH4,TMA-fl and NH.,K-L are de-aluminated upon fluorination. Strong supporting evidence comes from framework I. R. data where the shifts in band position to higher wave numbers are as much as 20 cm-1. However, there is no evidence of structure stabilization. Also McBain water adsorption data give no indication of surface hydrophobicity. Therefore, it is likely that structure defects are formed in these two zeolites as a result of dealumination and cause low thermal stability. 

That is why in the current chapter we will confine ourselves to the ionic transfer discussion of fluorine-conductive fluorites and tysonites from a slightly different standpoint we wiU try to observe an influence of various doping types on the structure features and the defect structure of nonstoichiometric fluorine-containing phases. 

Table IV shows the reactivity ratios rG and r, derived from the probabilities in Table III in accord with a first-order Markov model (2), where it is assumed that the more likely propagating terminal radical structure is 1 (—CHF-) and not 0 (—CH2). This assumption is consistent with gas phase reactions of VF with mono-, di-, and trifluoromethyl radicals, which add more frequently to the CH2 carbon than to the CHF carbon (20). The reactivity ratio product is unity if Bernoullian statistics apply, and we see this is not the case for either PVF sample, although the urea PVF is more nearly Bernoullian in its regiosequence distribution. Polymerization of VF in urea at low temperature also reduces the frequency of head-to-head and tail-to-tail addition, which can be derived from the reactivity ratios according to %defect — 100(1 + ro)/(2 + r0 + r,). Our analysis of the fluorine-19 NMR spectrum shows that commercial PVF has 10.7% of these defects, which compares very well with the value of 10.6% obtained from carbon-13 NMR (13). Therefore the values of 26 to 32% reported by Wilson and Santee (21) are in error.

At 188 MHz four additional defect resonances (1, 5, 6, and 7) appear in the F NMR spectrum of PVFj [sec (b) in Figure 2.13]. Ferguson and Brame [57] also observed these additional defect peaks and tentatively assigned them to defect structures drawn in Figure 2.13(b) based on a-, fi-, and y-substituent effects derived from the CFj resonances observed in various saturated, partially fluor-inated linear alkanes. In addition to dp p, and 5 F chemical shifts were also calculated for the ddect fluorines 1,5,6, and 7. F y-effects(yp,cHp Vf.cf ... 

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