The influence of low intensity microwave electromagnetic field on aqueous solutions.

Morariu, Gheorghe ; Miron, Mihai ; Alexandru, Marian 等

1. INTRODUCTION

The following systems: for fixed and mobile communication, the satellite and the terrestrial television systems, the wireless computer networks, the radio control systems, all of them use the microwave electromagnetic field as an information carrier.

The substances found in the radiant zones are exposed to the the phenomenon of radiation with the microwave. The most characteristic effects of this radiation are:

* The heating effect in volume (because of free ions).

* The effect of ionization-deionization under the influence of the radiant field.

These two effects can be demonstrated by modifying the pH of a particular solution. The experimental results are based on measurements for aqueous solutions with both types of pH: acid and alkaline, in a microwave radiant field that has the same intensity as the radiant field generated by a mobile phone.

2. FUNDAMENTAL CONCEPTS FOR PH

The "potential of hydrogene" or pH, is defined as the cologarithm of the activity of the dissolved hydrogen ions ([H.sup.+]).

pH = -[log.sub.10] [C.sub.H.sup.+] (1)

[C.sub.H.sup.+] represents the activity of the hydrogen ions, and is expressed as:

[C.sub.H.sup.+] = [H.sup.+] [f.sub.H] (2)

Where, [H.sup.+] is the concentration of the hydrogen ions [mol/liter] and [f.sub.H] is the activity coefficient of the hydrogen ions. The solutions that have pH values between 1 and 7 are said to be acidic and for values between 7 and 14 we have alkaline solutions.

The concentration of the hydrogene ions of an unknown pH solution is expressed ideally with the Nernst equation (International Organization for Standardization, 1992):

E = [E.sub.0] + [R x T/2.303 x F]ln(a) (3)

Where, E is the measured potential; [E.sub.0] is the standard electrode potential; R is the universal gas constant (8314 J/ (kmol.K)); T is the temperature [Kelvin]; F is the Faraday constant (96500[degrees]C/mol) and a is the concentration of the ions inside the solution.

The following equation is equivalent to (3) (IUPAC, 2001):

E = [E.sub.0] + [(60mV) x T/300]lg(a) (4)

3. ANALYSIS METHOD

Some observations can be made based on equation (4):

* The variation of E (the measured potential which determines the pH value) is linear dependent on the solution temperature T for a constant concentration of the hydrogen ions.

* The variation of E is linear dependent on the logarithm of the concentration of the hydrogen ions for a particular solution.

* The measured potential E depends on the product T lg(a).

Only for a constant concentration of the hydrogen ions, the pH unit varies solely with the temperature and the following equation can be used:

E([1.sub.pH] (T)) = 54.2/273 x T (5)

Where, [1.sub.pH] is the electric equivalent of the pH unit in mV and T is the temperature [Kelvin].

For pH = 7, the pH unit is invariant since its equivalent in mV is zero (null). Therefore, we can consider that pH = 6 is the first pH unit that has an electrical equivalent with negative polarity (acid), and pH = 8 is the first pH unit that has an electrical equivalent with positive polarity (alkaline).

The variation of temperature, from an initial value [T.sub.a] to a final value [T.sub.b], leads directly to a variation of the absolute value of the electric equivalent for the pH solution used, according to the equations (6), for acidic solutions) and (7), for alkaline solutions (University of Waterloo, CaCt):

E(7 - pH ([T.sub.a])) [right arrow] E(7 - pH ([T.sub.b])) = 7 - pH([T.sub.a])/273 x 54,2 x [T.sub.b] (6)

E(pH ([T.sub.a]) - 7) [right arrow] E (pH([T.sub.b]) - 7) = pH([T.sub.a]) - 7/273 x 54,2 x [T.sub.b] (7)

Where, pH([T.sub.a]) is the numerical indication for pH at temperature [T.sub.a]; pH([T.sub.b]) is the numerical indication for pH at temperature [T.sub.b] and E(pH([T.sub.x])) is the electrical potential for pH at a certain temperature. (Covington et al., 1985)

The ionization-deionization phenomenon in solutions with a known pH is emphasized by analyzing the deviations from linearity of the equations (6) and (7), depending on temperature.

4. MEASUREMENTS

The experimental results refer to measurements with aqueous solutions with different pH values. The distilled water has a pH value of 6.5. Different solutions containing ammonium (N[H.sub.4]) have a pH value of 10. The center frequency of the radiant field is 1900 MHz, with a frequency span of 200 MHz (from 1800 to 2000 MHz).

The samples used for measurements have pH values of 6.5 and 10. Ten measurements were performed for every time interval. Six time intervals were considered: 10 s, 20 s, 30 s, 40 s, 50 s and 60 s. Therefore, we have a total number of sixty measurements for both pH values. The results of the measurements are presented in Figures 1, 2, 3 and 4. This analysis is characteristic to the ionization-deionization phenomenon.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

The exposure of aqueous solutions to microwave radiation is simultaneously analyzed with the thermographic instrument in Figures 5 and 6. The pH values are 6.5 and 10 (Zemaitis et al., 1986).

5. CONCLUSION

According to the theory, the microwave electromagnetic field around the center frequency of 1900 MHz should affect the pH value of different aqueous solutions. The measurements have shown a certain influence on the ionization-deionization phenomenon. For pH=6.5, the tendency is towards pH 7 (null potential) while for pH=10, the tendency is towards pH 9. By using thermographic analysis, we have observed that the effects of the exposure to microwaves are manifested in a different way for the two solutions: acid and alkaline.

The pH modification is dependent on the time duration of microwave exposure and on the chemical compositions of the solution, for constant field intensity. The experimental results emphasize the complexity of the phenomenon.

6. REFERENCES

Covington, A. K.; Bates R. G. & Durst R. A.: Definitions of pH scales, standard reference values, measurement of pH, and related terminology, Pure Appl. Chem. 57, 1985, pp 531-542

International Organization for Standardization: Quantities and units--Part 8: physical chemistry and molecular physics, Annex C (normative): pH., 1992

IUPAC Provisional Recommandation: The Measurement of pH --Definition, Standards and Procedures--Report of the Working party on pH, 2001, http://www.iupac.org/reports/ provisional/abstract01/rondinini_prs.pdf, Accessed: 2008-09-16

University of Waterloo: The pH Scale. http://www. science.uwaterloo.ca/~cchieh/cact/c123/ph.html, Accessed: 2008-10-04

Zemaitis, J. F.; Clark, D. M.; Rafal, M. & Scrivner, N. C.: Handbook of Aqueous Electrolyte Thermodynamics: Theory & Application, Wiley, 1986, Ch.4., 0-8169-0350-6