Published in Soil Sci. Soc. Am. J. 68:1024 (2004).
© 2004 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
COMMENTS & LETTERS TO THE EDITOR
Response to "Comments on ‘Low Frequency Impedance Behavior of Montmorillonite Suspensions
Polarization Mechanisms in the Low Frequency Domain'"
Lynn M. Dudley*,a,
Stephen Bialkowski
,b and
Dani Or
,c
a Dep. of Plants, Soils, and Biometeorology Utah State Univ., Logan, UT 84322
b Dep. of Chemistry and Biochemistry Utah State Univ., Logan, UT 84322
c Civil and Environmental Engineering Univ. of Connecticut Storrs, CT 06269
In Dudley et al. (2003), spectral features at frequencies less than about 10 to 100 kHz were only discussed in general in relation to complex plane plots and not assigned a mechanism because electrode polarization was not separated from other relaxation phenomena. The complex plane plot of the impedance, Fig. 2a
in Dudley et al. (2003)(shown here), is similar to Fig. 3 of Klein (2004) where electrode polarization is the relaxation mechanism. As we stated, "A DDL [diffuse double layer] not only exists at the clay-water interface, but also at the electrode interface and motion of ions associated with either DDL could result in a Warburg impedance" (Dudley et al., 2003). Whether an impedance plane plot at frequencies < 2 kHz is a line (Dudley et al., 2003, Fig. 2a) or an arc (Klein, 2004, Fig. 3) does not change our statement.
View larger version (22K):
[in this window]
[in a new window]
|
Fig. 2. An impedance plane plot of the real (') and imaginary ('') components of the impedance, Z, and modulus, M ( –1), for the small particle-size separate of Ca-saturated clay (data collected at 55°C).
|
|
There is a significant difference between the complex plane plots of the modulus for clay suspensions (Dudley et al., 2003, Fig. 2b) and deionized water (Klein, 2004, Fig. 4). The modulus emphasizes high frequency relaxation phenomena and Fig. 2b (Dudley et al., 2003) indicates the presence of a relaxation not evident in Fig. 4 (Klein, 2004). An expectation-maximization algorithm revealed a relaxation process at a frequency of about 1 MHz for Ca-montmorillonite and 7 MHz for Na-montmorillonite. As noted by Klein (2004), Ishida et al. (2000) reported a relaxation at about 1 MHz in clay suspensions using TDR (time domain reflectometry). Given the difference between the modulus plots and the findings of Ishida et al. (2000), relaxation in the MHz range was most likely the result of a relaxation mechanism involving the clay–water interface, either Maxwell–Wagner or field-induced motion of ions in the DDL.
NOTES
* ldud{at}cc.usu.edu 
stephen.bialkowski{at}usu.edu
dani{at}engr.uconn.edu
REFERENCES
- Dudley, L.M., S. Bialkowski, D. Or, and C. Junkermeier. 2003. Low frequency impedance behavior of montmorillonite suspensions: Polarization mechanisms in the low frequency domain. Soil Sci. Soc. Am. J. 67:518–526.[Abstract/Free Full Text]
- Ishida, T., T. Makino, and C. Wang. 2000. Dielectric-relaxation spectroscopy of kaolinite, montmorillonite, allophane, and imogolite under moist conditions. Clays Clay Miner. 48:75–84.[Abstract/Free Full Text]
- Klein, K. 2004. Comments on "Low frequency impedance behavior of montmorillonite suspensions: Polarization mechanisms in the low frequency domain". Soil Sci. Soc. Am. J. 68:(this issue).
