Effect of Sodium Ions on the Dielectric Conductivity of Porous Silica in Humid Environments

1990 ◽  
Vol 195 ◽  
Author(s):  
Wanqing Cao ◽  
Rosario Gerhardt ◽  
John B. Wachtman
Keyword(s):  
Relative Humidity ◽  
Silica Surface ◽  
Porous Silica ◽  
Sodium Content ◽  
Silica Gels ◽  
Interfacial Region ◽  
Relaxation Processes ◽  
Sodium Ions ◽  
Frequency Range ◽  
Dielectric Conductivity

ABSTRACTPartially sintered silica gels were immersed in different NaCI solutions to deliberately introduce a small amount of sodium ions ranging from 387 to 9900 ppm. Dielectric measurements were carried out in the frequency range 12 to 107Hz under various relative humidity conditions. Two relaxation processes were observed in the impedance and modulus planes and were assigned to two separate regions in the hydrated silica surface. The top region is expected to be rich in hydrated sodium since its modulus relaxation time depends strongly on the relative humidity as well as the sodium content. The interfacial region is believed to be composed of structured water since its dielectric conductivity is affected mainly by the amount of water adsorbed on the pore surfaces.

scholarly journals HIGH DIELECTRIC CONSTANT COMPOSITE BASED ON CHLOROPHYLL A ENTRAPPED NANOPOROUS SILICA GEL

2012 ◽  
Vol 02 (03) ◽  
pp. 1250016 ◽  
Author(s):  
J. S. MANNA ◽  
M. K. MITRA ◽  
S. MUKHERJEE ◽  
G. C. DAS
Keyword(s):  
Dielectric Constant ◽  
Chlorophyll A ◽  
Silica Gel ◽  
Room Temperature ◽  
Chlorophyll Concentration ◽  
Porous Silica ◽  
Diameter Distribution ◽  
Interfacial Region ◽  
Relaxation Processes ◽  
Heterogeneous Distribution

Chlorophyll a (naturally occurring Mg porphyrene) has been entrapped in nano/porous silica gel using sol–gel method at room temperature, producing a stable composite. HRTEM observation reveals regular nanoscale [around 15–20 nm diameter] distribution of aggregated polycrystalline chlorophyll a within porous silica matrix. UV-vis study also corroborates the presence of various aggregated chlorophyll a species within the system. Low field measurement shows almost 400 times enhancement of dielectric constant (1700) with incorporation of only 0.125 mg/ml of chlorophyll and the loss is 0.5 at room temperature at 100 Hz. The dielectric constant of the composite reaches 2500 as chlorophyll concentration becomes 1 mg/ml. Observed strong space charge response to the external field and strong frequency dispersion of the dielectric properties of the composite can be attributed to the long-range electron delocalization [nomadic polarization] in chlorophyll a aggregates. The electric modulus (M*) formalism used in this study enabled us to distinguish and separate various relaxation processes. It is found that with increasing chlorophyll concentration D.C. relaxation time decreases exponentially at room temperature. It is shown that observed relaxations do not perfectly follow the Debye response in high frequency region due to heterogeneous distribution of chlorophyll aggregates. The low values of room temperature activation energy calculated from Arrhenius plot reveal that polaronic hopping phenomena is absent at grain-interfacial region due to low thermal energy.

Relaxation of excitations in porous silica gels

1988 ◽  
Vol 128 (1) ◽  
pp. 199-207 ◽  
Author(s):  
J.M. Drake ◽  
P. Levitz ◽  
S.K. Sinha ◽  
J. Klafter
Keyword(s):  
Porous Silica ◽  
Silica Gels

Sodium and lithium movements and axonal function in cockroach nerve cords

1975 ◽  
Vol 62 (1) ◽  
pp. 231-241
Author(s):  
RR Bennett ◽  
PB Buchan ◽  
JE Treherne
Keyword(s):  
Normal Saline ◽  
Action Potentials ◽  
Sodium Content ◽  
Significant Decline ◽  
Rapid Recovery ◽  
Sodium Ions ◽  
Bathing Medium ◽  
Sodium Regulation ◽  
Equivalent Reduction ◽  
Nerve Cords

Exposure to sodium-deficient (tris) saline caused an appreciable decline in the sodium content of intact connectives in the absence of equivalent reduction in the amplitude of the recorded action potentials. Return of sodium-depleted connectives to normal saline resulted in a rapid recovery of axonal function despite only a partial (less than 70%) recovery in sodium content. Replacement of sodium ions by those of lithium in the bathing medium resulted in a substantial accumulation of this cation. Lithium movements exhibited a marked asymetry, no significant decline in concentration being observed upon return to normal saline. These results are tentatively interpreted in terms of an exchangeable glial sodium fraction and are discussed in relation to extra-axonal sodium regulation.

scholarly journals Some Peculiarities of Silica Modification Under High Reagent Pressure. I. Methodological Aspects

1995 ◽  
Vol 12 (3) ◽  
pp. 231-238 ◽  
Author(s):  
V.V. Sidorchuk ◽  
V.A. Tertykh ◽  
R. Leboda ◽  
Z. Hubicki
Keyword(s):  
Thermal Analysis ◽  
Surface Reaction ◽  
Silica Surface ◽  
Porous Silica ◽  
Physicochemical Characteristics ◽  
Geometrical Parameters ◽  
Duration Of Treatment ◽  
Preparation Conditions ◽  
Modification Process ◽  
Methodological Aspects

The effect of the following factors on the chemical and geometrical modification of aerosilogel (prepared from aerosil) was studied: the physicochemical characteristics of the modifying reagent pressures, the preparation conditions for the silica surface, the reaction temperature, the reagent pressures, the duration of treatment and the method employed for the modification process. The course of the surface reaction was followed by IR spectroscopy, differential thermal analysis and adsorption. During high-pressure modification, the geometrical parameters of the porous silica structure may be changed.

Selective adsorption and stable solidification of radioactive cesium ions by porous silica gels loaded with insoluble ferrocyanides

2014 ◽  
Vol 57 (11) ◽  
pp. 1470-1476 ◽  
Author(s):  
XiangBiao Yin ◽  
Yan Wu ◽  
Hitoshi Mimura ◽  
Yuichi Niibori ◽  
YueZhou Wei
Keyword(s):  
Selective Adsorption ◽  
Porous Silica ◽  
Silica Gels ◽  
Radioactive Cesium ◽  
Cesium Ions

A NMR investigation of adsorption/desorption hysteresis in porous silica gels

1998 ◽  
Vol 16 (5-6) ◽  
pp. 679-682 ◽  
Author(s):  
P Porion ◽  
A.M Faugère ◽  
P Levitz ◽  
H Van Damme ◽  
A Raoof ◽  
...  
Keyword(s):  
Porous Silica ◽  
Silica Gels ◽  
Desorption Hysteresis ◽  
Adsorption Desorption

Preparation and in vitro evaluation of porous silica gels

Biomaterials ◽  
2002 ◽  
Vol 23 (21) ◽  
pp. 4277-4284 ◽  
Author(s):  
Janet Gallardo ◽  
Pablo G Galliano ◽  
J.M.Porto López
Keyword(s):  
Porous Silica ◽  
Silica Gels ◽  
In Vitro Evaluation

Sol-Gel Derived Porous Silica Gels Impregnated with Sulfuric Acid

2002 ◽  
Vol 149 (8) ◽  
pp. E292 ◽  
Author(s):  
Atsunori Matsuda ◽  
Takao Kanzaki ◽  
Kiyoharu Tadanaga ◽  
Toshiro Kogure ◽  
Masahiro Tatsumisago ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Sol Gel ◽  
Porous Silica ◽  
Silica Gels
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