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Gold colloid as applied to the H2S gas sensor
Materials Chemistry 6 (1981) 505 - 508
SHORT COMMUNICATION
GOLD COLLOID AS APPLIED TO THE H2S GAS SENSOR
Vapour of gold was deposited upon one side of both surfaces of a fluorocarbon polymer "teflon" sheet in vacuum. This teflon f'dm whose thickness was about 0.5 mm behaved like a semipermeable membrane, to wit, it was pervious to gas mol. ecules, but it was watertight. Two types of the gold deposit were prepared by controlling the degree of vacuum in the deposition operation, which gave the electron diffraction patterns as reproduced in Figures 1 and 2. From the half-width values
Fig. 1 - Electron diffraction pattern from the gilded surface o f teflon. Wavelength o f the electrons: 0.0332 ~ Distance between the object and the screen: 50 cra. Positive: direct print. Particle size of gold: about 500 A.
of the reflections, the mean particle size of gold in Fig. 1 and that in Fig. 2 were estimated to be about 500 A "and 50 A, respectively. These gilded surfaces of teflon sheet played the r61es of electrode in contact with a dilute H2SO 4 solution whose specific weight was 1.2 gm]cc. The disposition for the present experiment is illustrated in Fig. 3. o39o-e035/st/o~osos-ot$2.00/0 Copyrilht © 1981by CENFORS.R.L. All rilihts of reproductionin any form reserved
506
Fig. 2 - Wavelength o f the electrons: 0.0369 A. Particle size o f goid: about 50 A.
The Au particles wetted with the H2SO 4 solution were charged negative in a colloidal state, and so they were characterized by the zeta-potential responsible for cataphoresis 1. This potential is larger for the 50 A size particles o f gold in Fig. 2 than for the 500 A size ones in Fig. 1, since it is inversely proportional to R, R being the radius of an Au particle. It is here assumed that the particle sizes of Au as estimated oh Fig. 1 and 2 are approximately equal to R. Hence, it is plausible that the smaller colloid particles of Au charged negatively should attract acidic gas molecules like H2S, SOs, NOx, C12 eic. than the larger ones.
I
M ~ '
31ran
III ,
Fig. 3 - Disposition o f the parts in the intrument. I." input gas o f H2S. II: semi ~ permeable membrane o f teflon. III: A u colloid. IV: H2S04 solution. M: ammeter.
A sudden rise of electric current I took place in the circuit illustrated in Fig. 3, when the H2S gas that had been diffused through the teflon membrane reached the Au colloid particles. This is due to the fact that the charged particles of Au were discharged when contacted with the H~S molecules. The two typ#s o f gilded
507 electrode in question gave the observations shown in Fig. 4. The maximum I measured on ammeter M was 130/zA for the Au electrode of Fig. 2, whereas it remained only 10/~A for that of Fig. 1. The concentration of H2S'gas here used was 100
I00
|
60
|
120
sec
Fig. 4 - Electric currents measured on M in lapse o f time after H2S gas has been supplied to the sensor o f Fig. 3.
ppm in air. These observations were all carried out at room temperature (about 20°C). The data obtained with the H2S gas are summarized by the equation I x R = const. This constant (about 5 × 103/~A.A) varied with the sorts of input gas to be detected. The silver colloid had also the same sensor property similar to that of the gold one. However, the former was inferior to the latter, insofar as corrosion resistance to the sensor gases was concerned. S. Yamaguchi Y A M A G U C H I - L A B 2-72 Kotake-cho Nerima-ku - TOKYO, 176 -Japan.
Received 28 July 1981
508
REFERENCES
1.
R.A. ZSIGMONDY - KolloMchemie, Leipzig, p. 139, 1925; M.V. SMOLUCHOWSKI - Bull acad. Cracov~e, p. 182, 1903; Collected Papers I, p. 403, 1923; W.H. WESTPHAL -Physikalisches W6rterbuch, Springer, p. 327, 1952; HOLLEMAN-WIBERG - Lehrbuch der anorganischen Chemie, 71.-80, Auflase, Berlin, p. 509, 1971.
SHORT COMMUNICATION
GOLD COLLOID AS APPLIED TO THE H2S GAS SENSOR
Vapour of gold was deposited upon one side of both surfaces of a fluorocarbon polymer "teflon" sheet in vacuum. This teflon f'dm whose thickness was about 0.5 mm behaved like a semipermeable membrane, to wit, it was pervious to gas mol. ecules, but it was watertight. Two types of the gold deposit were prepared by controlling the degree of vacuum in the deposition operation, which gave the electron diffraction patterns as reproduced in Figures 1 and 2. From the half-width values
Fig. 1 - Electron diffraction pattern from the gilded surface o f teflon. Wavelength o f the electrons: 0.0332 ~ Distance between the object and the screen: 50 cra. Positive: direct print. Particle size of gold: about 500 A.
of the reflections, the mean particle size of gold in Fig. 1 and that in Fig. 2 were estimated to be about 500 A "and 50 A, respectively. These gilded surfaces of teflon sheet played the r61es of electrode in contact with a dilute H2SO 4 solution whose specific weight was 1.2 gm]cc. The disposition for the present experiment is illustrated in Fig. 3. o39o-e035/st/o~osos-ot$2.00/0 Copyrilht © 1981by CENFORS.R.L. All rilihts of reproductionin any form reserved
506
Fig. 2 - Wavelength o f the electrons: 0.0369 A. Particle size o f goid: about 50 A.
The Au particles wetted with the H2SO 4 solution were charged negative in a colloidal state, and so they were characterized by the zeta-potential responsible for cataphoresis 1. This potential is larger for the 50 A size particles o f gold in Fig. 2 than for the 500 A size ones in Fig. 1, since it is inversely proportional to R, R being the radius of an Au particle. It is here assumed that the particle sizes of Au as estimated oh Fig. 1 and 2 are approximately equal to R. Hence, it is plausible that the smaller colloid particles of Au charged negatively should attract acidic gas molecules like H2S, SOs, NOx, C12 eic. than the larger ones.
I
M ~ '
31ran
III ,
Fig. 3 - Disposition o f the parts in the intrument. I." input gas o f H2S. II: semi ~ permeable membrane o f teflon. III: A u colloid. IV: H2S04 solution. M: ammeter.
A sudden rise of electric current I took place in the circuit illustrated in Fig. 3, when the H2S gas that had been diffused through the teflon membrane reached the Au colloid particles. This is due to the fact that the charged particles of Au were discharged when contacted with the H~S molecules. The two typ#s o f gilded
507 electrode in question gave the observations shown in Fig. 4. The maximum I measured on ammeter M was 130/zA for the Au electrode of Fig. 2, whereas it remained only 10/~A for that of Fig. 1. The concentration of H2S'gas here used was 100
I00
|
60
|
120
sec
Fig. 4 - Electric currents measured on M in lapse o f time after H2S gas has been supplied to the sensor o f Fig. 3.
ppm in air. These observations were all carried out at room temperature (about 20°C). The data obtained with the H2S gas are summarized by the equation I x R = const. This constant (about 5 × 103/~A.A) varied with the sorts of input gas to be detected. The silver colloid had also the same sensor property similar to that of the gold one. However, the former was inferior to the latter, insofar as corrosion resistance to the sensor gases was concerned. S. Yamaguchi Y A M A G U C H I - L A B 2-72 Kotake-cho Nerima-ku - TOKYO, 176 -Japan.
Received 28 July 1981
508
REFERENCES
1.
R.A. ZSIGMONDY - KolloMchemie, Leipzig, p. 139, 1925; M.V. SMOLUCHOWSKI - Bull acad. Cracov~e, p. 182, 1903; Collected Papers I, p. 403, 1923; W.H. WESTPHAL -Physikalisches W6rterbuch, Springer, p. 327, 1952; HOLLEMAN-WIBERG - Lehrbuch der anorganischen Chemie, 71.-80, Auflase, Berlin, p. 509, 1971.