Alkaline glasses

Adventitious losses of the reagent, due, e.g., to the chemical action of the alkaline glass vessels, slight absorption by the corks, etc., are almost identical for the actual and the control experiments and therefore do nor affect the difference in result between the two experiments. 

Ketene acetal is best stored in a bottle made of alkaline glass which is preferably new and dusted with sodium ter/.-but oxide (Note 7). The glass stopper should be very well greased. Even with these precautions a small amount of a voluminous precipitate of the white polymer will develop. 

Jagner [28] has also described a semi-automatic titration for high-precision determination of chlorine in seawater, where it has been used for the potentiometric determination of total halides (silver electrode) and alkalinity (glass electrode), and for the photometric titration of total alkaline-earth metals. Several titrations can be effected simultaneously. 

Hara, A. Takei, M. Takeuchi, F. Suga, K. Yoshino, K. Chida, M. Kakehi, T. Ebiko, Y. Sano, Y. Sasaki, N. 2004. High performance low temperature polycrystalline silicon thin film transistors on non-alkaline glass produced using diode pumped solid state continuous wave laser lateral crystallization. Jpn. J. Appl. Phys., Pt. 1 43 1269-1276. 

Fig. 2. Idealized structures of a trap for etr in water-alkaline glasses a trap for etr is made up of (a) six or (b) three molecules of H20. The data are from ref. 7.

Fig. 10. Model of the structure [36] of a trap for anion radicals O in water-alkaline glasses.

As for the samples which were not only stored but also irradiated at different temperatures (in particular, at 77 and 120 K), further, more detailed investigations [39] of the effect of temperature on the kinetics of reaction (4) atT > 77 K, as well as a comparison of these data with those on the reaction etr with other acceptors in water alkaline glasses [39,40], showed the non-activated electron tunneling to be the predominant channel of reaction (4) only at sufficiently low temperatures (T < 93 K). At 93 K and above, the dominant channel appears to be the activated tunnel transfer with the activation energy Ea = 3.1 0.4kcalmol (Chap. 5, Sect.2.3). 

In this connection there arises a natural question, whether there exists a similar correlation for the parameters ve, ae, and a characterizing the rate of tunneling reactions. The question is answered by Fig. 23(a) and (b) presenting the data of Table 2. As can be seen from the figures, for the reactions of etr in water-alkaline glasses the dependences between log i e, a,., and a in a number of the reactions studied have the form of a field of points, i.e. the compensation effect is missing. This fact, in particular, allows one to conclude that the differences observed in the values of the parameters ve, ae, and a for various reactions reflect the real situation rather than that they are the consequence of systematic errors in measurements or data treatments. 

A systematic study of the effect of temperature on the kinetics of et[. decay in reactions with CrO - and NO, in water-alkaline glasses (10M NaOH) in the time interval 10 6 to 10 3s and over a broad range of temperatures (80-202 K) was carried out in refs. 89 and 90. At low enough temperatures the etr decay curves obtained at different temperatures and presented in the coordinates n(t)/n(t0), log t/ta were shown to coincide. On reaching a certain critical temperature (T 150-170 K), however, the reaction rate increases. 

As noted earlier, the parameter V = V + a contains two terms, one of which characterizes the capture of stabilized electrons et, and the second, that of thermalized electrons et , by the acceptor. Since the value of V = (4/3)7tRt = (nal/6) n3vet grows monotonously with time, the relative contribution of these terms depends on the moment of measuring the radiation yield. From the values of the parameters ve, and a found from the analysis of kinetic curves for etr decay in the presence of different acceptors in the water alkaline matrices (see Table 2) one can draw certain conclusions about the relationship between V" and a. In Table 5 the values of a found for a number of reactions of etr in water-alkaline glasses are compared with those of V calculated for different times,t, from the relationship... 

Parameters a and V = (jra j/6)ln3 v t, calculated from the data of Table 2 for the reactions of etr with various acceptors in water-alkaline glasses... 

Fig. 28. Dependence of the diffusion coefficient, D, of e on temperature in a water alkaline glass (10 M NaOH) calculated from the data of refs. 40,89 and 90 using eqn. (27). The broken line is the thermogram of the same water-alkaline matrix.

Let us use the obtained values of the diffusion coefficients D in water-alkaline glasses to estimate the contribution of diffusion to the decay of etr by reaction with acceptors at low temperatures. Let us estimate, for example, the temperature at which, for a typical concentration of acceptor additive N = 10 2M and for a maximal time of observation t = 106s, the condition 4nRDDNt = 0.01 [or, which is the same thing, exp( —4nRDDNt) = 0.99] will be fulfilled, i.e. the decay of et by the diffusion channel will amount to 1%. Taking into account the abnormally high mobility of solvated electrons [114] it is reasonable to assume that the main contribution to D is made by the diffusion of elr rather than by that of the acceptor. In this case, all the values of D obtained above must be related to the same process, the diffusion of e. ... 

In the radiolysis of water-alkaline glasses containing nitrate ion, NO , the anion radical NO - is formed. This possesses strong electron-donor... 

Despite the dependence of the reaction rate on temperature, the tunneling mechanism of electron transfer from NO3- to CrO and Co(en)3 at 77 K appears to be the most probable one since, in water- alkaline glasses at 77 K, the diffusional motion, even for et which most likely possess a higher mobility than NOg, cannot provide the necessary reaction rate (see Chap. 6) ... 

As is known from the literature [59 a], illumination of frozen solutions containing trapped electrons in the e,7 absorption band results in a decrease in the concentration of e,7. It is also well known that, for water-alkaline glasses, with such illumination, a transition of an electron from a trap into the conduction... 

With the aid of electron tunneling it appears possible to regulate the selectivity of redox conversions. For practically important reactions this has not been realized so far, but that this approach may prove to be useful is demonstrated, e.g. by the data presented in Table 6. In this table, a comparison is made between the rate constants for reactions of three different acceptors with hydrated electrons in liquid water at 298 K and the characteristic times, t, for reactions of the same acceptors with trapped electrons in solid water-alkaline glasses at 77 K. The values of x have been calculated using the values of ve and ae from Ref. [21]. It can be seen in the liquid, when due to diffusion the reagents can approach to within short distances of each other (direct collisions), that the rate constants for all three... 

Ki. The pH of the solutions in the present study was determined by using a "high-alkalinity" glass electrode, taking due precautions to avoid carbonation of the solutions. 

Metastable sulfur allotropes are light-sensitive and should be protected from direct exposure to sun-light or other intense illumination. These materials are also very sensitive towards nucleophiles including alkaline glass smfaces. Therefore, pure and dry solvents should be used and the glassware should be treated with concentrated hydrochloric acid followed by rinsing with water and drying in an oven prior to use. 

Among the first investigations which showed electron stabilization in the polar glasses at low temperatures was the work of Ershov et al. (30). This work employed the EPR method to identify e tr in the alkaline aqueous solutions irradiated at 77 °K. Later on these conclusions were confirmed in a large number of publications (3, 5, 6, 8, 37, 42, 54, 55). (Earlier the optical absorption of e tr in the irradiated alkaline glass was detected in other works (see 41, 58). 

Most thorough measurements of the e tr yields have been taken by the EPR method in the alkaline glasses. In accordance with papers 18, 28, 30, 32, 37, 42, 54,and 55, G(e tr) for 10M glassy alkaline solution is equal to 1.5-3.0. Such scattering is caused by the errors inherent with the EPR method and by the fact that these yields have been determined at rather considerable absorbed doses when there is no linear relationship between... 

The yield of the thermalized electrons which are produced during the radiolysis of the alkaline glass has been determined by reference to their reactions with the N03 ions (22). The latter ions interact with the electrons to produce N032 ion-radicals each of which yields during defreezing 0.5 ion of N02 ... 

Hence, when the electrons are fully scavenged (which occurs when adding 0.1M of NOf3"), G(e therm) should equal 2G(N02"). It has been found that G(e"therm) comprises 3.0 ( 10%)—i.e., it equals G(e tr)-(The full scavenging of electrons was checked by the disappearance of e tr color. In these conditions G(N032 ) as measured by EPR method is equal to 3.0 ( 30% ).) Therefore, it may be concluded that in the alkaline glass all the electrons which avoided the decay in the spurs are captured by the traps after thermalization. 

In case of the frozen solutions of other electrolytes the yield of e tr are substantially less than in the alkaline glasses (see Table III). This is explained first of all by the differences in the behavior of the thermalized electrons. The alkali is inert relative to the electrons. In other glassy solutions the thermalized electrons partially participate in the reactions with the dissolved substances. Thus, in the case with 10M aqueous glass of NaC104 the electrons partially react with C104 in accordance with... 

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