Hirata Minoru

Ida Mitsuo

Kawada Shuji

井田 光雄

河田 脩二

Kanazawa University Repository for Academic Resources

The Changes in Dieledric Properties of羽Taterduring Adsorption by Solids Mitsuo IDA.* Minoru HIRATA* and Shuji I(A W ADAネ(Recieved 18 June 1964) 1. Introduction Kurosaki et a1. (1) found that when glass c10th was巴xposedto water vapour， its tan o rapidly increased to a maximum and then gradually decreased to a constant value， and that the surf旦cedc concluctivity of glass and some other substances showed similar changes on exposure to water vapour. These investigators attributed the phenomena to phase changes of the ac1sorbecl water from the amorphous to the crys明talline state. Similar time effects with evaporatecl films were reported by Weaver(幻，who considerecl that the capacitance and tan o reachecl their peak values when aclsorp四tion was compI巴te，and that some gradual rearrangement of the adsorbed water molecules then took place which r巴ducedtheir effect on the overal1 dielectric proper幽ties. The present authors founcl that a time effect， somewhat different from those of Kurosaki et a1， and Weaver， was produced when moisture was transferred to a specimen placed in dry乱ir，instead of a vacuum as in the cases cited above. Outlined in the present artic1e are the comparison of theresu1ts obtainecl when a specimen is placed in a vacuum and dry air respectively， and some explanation of the changes occurring in diel巴ctricproperties of water during adsorption by solids. The measure-ments were made on soda lime glass， mica， porous calcined diatomaceous earth， and filter paper， but as the results are generally alike in a1 of them， those obtained with soda lime glass ar巴 describedin detail， and the others only briefly. 2. Experimental Procedure It was devised to make the chamber (A) containing the specimen as small as possible to eliminate useless space. By a leak cock system the chamber could be connectεd with: (B) a vacuum pump working at 1O-2mmHg， ( C ) a large chamber containing dry air over concentrated sulfuric acid， or (D) a large chamber containing air of specified humidity， or cut off from a1 of them. Before taking measurements， the chamber (A) was connected with (B) for an hour， or with (C) for 24 hours. We call these as case 1 and case 2 respectively in， the following. The capacitance measurements were carried out at frequencncies as low * De戸art抑 6抑tof Physics， Faculty of Science， Ka持azawaU niver sity ~ 9 ~， 10 M. IDA， M. HIRA T A and S. KA W ADA as 3 c/s by the叩par旦tusdescribed previously(3) (4)， because the time effect during adsorption of water was especially conspicuous at v巴ry10w frequεncies. The surface dc conductivity was measur巴dwith a μμammeter of the Toa Dempa Co. The electrodes for the dielectric measurements were set as follows. For glass or mica two aluminum foils seperated by a slit were attached on the surf司cewith water and driεd， for caIcined di旦tomaceousearth， a coating of silver paste was given to each surface of the plate and fired， and for filter paper， two patches of air-drying silver paste were paint己don one surface with a s1it between them. 3. Results and Discussion In the following the results are divided in two cases : (Case 1) Moisture is transferred to a specimen placed in a vacuum. (Case 2) 恥10isture1S transfer1'ed to a specimen placed in dry丘lr.Soda lime glass The sli t between the electrodes was O. 37mm wide and 80mm long. CGase 1) The curves (a)， (b) and (c) given in Fig. 1 show the changes of capacitance of the gl呂ssplate observed after admission of humid air.'三 Thecapacitance inc1'easεs rapidlyto a peak and then gradually d色creasesto a cert註invalue and begins to increase again very slowly. These results resemble the experimental resu1ts obtained by Weaver with thin evaporated films. When the leak cock was closed旦tthe time of peak， the capacitance was found to remain almost unch如 ged，but when the cock was opened ag丘inthe capacitance began to change as curve (d) in Fig. 1. Therefore the adsorption should not be reg呂rdedas complete司tthe tim巴 ofmaximum capacトtance， but to proceed stil further after that. When the leak cock was closed at any time while the capacitance w旦sascending to the peak 01' descending from i t the capaciねncestopped changing and remained as it was. When the glass plate with adsosbed water was dried very sIowly by connecting (A) and (C) through a pinhole of the leak cock， the capacitance changed as shown in Fig. 2. The peal王inthis case perhaps corresponds to the peak in the adsorption， and seems to be due to the same C旦use. Fig. 3 shows the time dependence of surface dc conductivity of a sample of glass. Curves (a) and (b) correspond respectively to the cases whe1'e the diameter of the pinhole of the leak cock is O.35mm and O.10mm. Such time effect in the surface dc conductivity has some resemblance to the resuIts obtained by Kurosaki et aL with glasses of different kinds. When the le旦kcoek was closed at any time before the conductivity reached the peak， it stopp巴dascending and rem旦inedalmost un " The results described hereafter w日reobtain邑dwith air of官35'iIrelative humidity except where indicated Qtherwise， Dielectric Properties of Water during Adsorption moi~turc flow cut off flo¥" rcsl1mcd J ω3前 4f¥、予aQ___ ~帽固か -_tl_- ""1l~__聞かーベq '" 3 c/s 、ι :ー。ー 時二φ -ー---1>-一司ト・ー 伺司令一一(1)) 25 e/s Eー】ー---一ー i(a) 1000 c/s 60 120 TJME(min) Fig. 1 Capacitance changes during moisture adsorption measured at the frequencies indicated. (soda lime glass) (pF) 10 60 120 TIME(min) Fig. 2 Capactance changes when a glass plate with adsorbed water W昌吉 slowlydried. (soda lime glass) 180 180 11 12 M. IDA， M. _ HIRAT A and S. KA WAj)A XlO-8A 1000 500 (bJ (O.!Om同00 120 TIME(min) 180 Fig. 3 Surface conductivity changes during moIsture adsorption. (soda lime glass) xJO"A 200 100 。moisturc flow cut off 30 .60 TIM!l(m抽}Fig. 4 Surface conductivity changes官henmoisture f10w was cut off before it r斜 chedthe peak. (soda Iime glass) 9日Dielectric Properties of Water durIngAdsorptlon 13 ?? ?X W-8A;' 30 δ制}vF) 200 aビ/，????100 ゐ1 h '" • 宅怠診 d0'1 留 v守「喝@一@一、ち，-鳥匂r一-----令-一-- 一喝。-白令一叩一匂-0-__ 。6() 120 180 TlME(mIn) Fig. 5 The result of a simultaneous measurement of the capacitance and 印日ductivity. (soda Iime glass) Solid CUfve : Capacitance， Broken curv邑 Conductivity。30 xlO-8A 300 ???????????????， ?200 1 -mo且sturcf10w ; cut off 10' 1 ? flow rcsumed 100 + flow rcsutned 什L0-0- --。一一←+一一。--oJ40-_ .0...-0_-0_ _____吻一一寸ー →ー一一一←一一。一一十『曲 口曲 2.10TIME(mio) Fig. 6 The result of a simultaneous measurement of the capacitance 昌ndconductivity wh晋nrnoisture f10w was cut off at th母 timeof peak of the conductivity. (soda lime glass) 14 Fig.7 20 Fig.8 50 40¥. (pF) 30 10 M. IDA， M. HIRA T A and S. KA W ADA (0) /イrcsumed }ダ.' 、。ー〆〈拾〉‘ 1000cl、30 60 TlME(rnin) d ρ ， 0， ノ。〆p' ノ」9u 120 Capacital1ce ch品目gesduring moisture adsorption m切呂uredat the fr問uencies 同icate品。 (sodaIime glass) 3 cfs 30 60 。TIME(min)Capacitance ch昌ng巴swhen a glass pl昌tewlth adsorbed water was slowly dried. (soda Iime glass) 00 1Jielectric Properti目。fWater cturing Aclsorption 15 「??????????2帥3同](JO 60 120 180 TIME(min) Fig. 9 Surface conductivity chang巴sduring moisture adsorption. (soda lime glass) 60 〕??〔60 120 180 TIME(min) Fig. 10 Capacit丑ncechanges during moisture adsorption measured at the frequencies indicat巴d.(mica) 16 (pF) M. tDA， M. HIRA T A and S. KA W ADA 60 40 drying started 20 。130、 120. TIME(min) Fig. 11 Capacitance changes wh邑na mica plate with adsorbed water was slowly dried. (mica) soc xJu.SA 6[10 400 200 <E-mOI当tureflow cut off 60 120 180 TIME(min) 180 Fig. 12 Surface conductvity chang邑swhen moistur邑 flowwas cut off at the tim邑 ofth巴 p日ak.(mica) Dielectric Propertles of Water dudng Adsorpt!on 17 changed as shown in Fig. 4， but when the cock was c10sed at the time of the peal王the conductivity decr巴asedabrupt1y as in the c旦seit was kept open. These results were thought to show that different mechanisms are involved in the changes of ca-pacitance and conductivity of the water during adsorption. This supposition was confirmed by carrying out simultaneous measurement of the capacitance and conduc-tivity. The result is shown in Fig. 5 ancl Fig. 6， from which we see that the conductivity reaches the peal王morequickly than the capacitance， ancl decreases even if the leak cock is c10sed at that time. (Case 2) The curves (a)， (b) and (c) given in Fig. 7 show the changes of capacitance at 93タbrelative humidity for a glass plate. The capacitances increase rapiclly to maximum peaks and then gradually clecrease to certain values and begin to increase more rapidly than in case 1. The curve (d) shows the change of capacitance observed when the leak cock was c10sed at the time of the peak ancl op叩 edagain after about one hour. When a glass plate with ample adsorbed water was clried very slowly， the capacitance changed as shown in Fig. 8. The peak in this case perhaps corresponds to the peak in the adsorption， and seems to be clue to the same cause. Fig.9 shows the time dep巴ndenceof surface dc conductivity at 93タ;relative humidity. In this case the conductivity increases 1i1onotonollsly with time， and the curve has no peak. Comparison of Case 1 and Case 2 The capacitance measured at 3 c/s in case 2 showed conspicuollS increase after the minimum. This increase must be due to electrode polarization， which is especially marked at low frequencies and increase with the amount of adsorbed water (的。 Incase 1 the adsorption seems nearly to stop after the minimum. It ll1ust be due to the better degassing of the glass plate than in case 2. According Trouton(6) as quoted by Kurosaki et al. perfectly dried glass aclsorbed water vapour with greater difficu1ty than Imperfectly dried glass， owIng to the lack of water nuclei or active sites 01 its surface. The peak of capacitance app巴arsat an early stage of adsorption in both cases. We presul11e it to be l11ainly due to the cooperative orientational polarization of water molecules， which 1S more notable in a thin layer of water rather thal1 in a thick amorphous layer. The initial peak of the conductivity in case 1 must be due to some mechanism of wat巴rfilm which is far thinner than that for which the peak of capacitance occurs. And the abs巴nceof an 1ni tial peak In the conductivity in c出 e2 may be due to the thickness of the water layer exceeding the critical thickness lil11iting the occurence of the peak at the starting l110l11ent of adsorption. 18 M. lDA， M. HIRA T A and S匂 KAWADATo explain the various phenomena mentioned above we assume the change of the structure of water film during adsorption as follows. In the Initial stage of adsorp司tion， mutual hydrogen bonding of adsorb色dmolecules is stil incomplete and there are many gaps in the chains of hydrogen bondings. This situation is favourable for surface dc conductivity by the proton transfer along the chains of hydrogen bondings. In the next stage the hydrogen bondings of water molecules司re 旦ccomplishedwhich is favourable for electrie polarization due to the cooperative displacements of protons， but not for electrie conductivity due to proton transfer. After that， as the water film incr巴asesin thiekness and changes to a nearly aJTlOrphous stat邑 theelectric polarization due to the cooperative displacement of protons tends rather to decrease. But the effect of electrode polarization increases with the thickness of the water film. Mica The slit between the electrodes was O.5mm wide and 80mm long. (C丘se1) The effect of moisture on I11Ica is shown in 10 whieh gives changes in capacitanc色 withtil11e elapsed after admission of moisture. The increase of capaci句tance after the time of minil11ul11 point is more rapid than with glass， showing the difficu1ty of drying mica completely. The capacit在日cechange which occurs when a mica plate wi th adsorbed w昌terwas dried very slowly is shown in Fig. 11. Closing of the cock at the time of the peak of dc condctivity 111乱deit decrease abrupt1y as shown in Fig. 12. (Case 2) The curves shown in Fig. 13 were ob同inedat relative humidity. When a mic司pl司tewith sufficent adsorbεd water was dried very slowly， the c呂P乱cit旦ncechanged as the curve in Fig. 14 showing a conspicuous peak。Calcined diatomaceous earth The specimen used for our measurements was a plate (1.5mm x 15mm x 8mm). 1n this四 sewater is adsorbed on the internal surfaces of the porous material. (Case 1) The curves in Fig. 15 give the change in cap旦citance as a function of time after adl11ission of moisture into the evacuated vessel containing the specimen. The result of a simultaneous measurement of the capacitance丘nddc coductivity Is shown in Fig. 16. The conductivity r色achesthe peak more quickly than the cap乱cIt証nceas in the case for glass. (Case 2) Fig. 17 and Fig. 18 show r・espectively the time dεpendencεof capacit呂ncewhen DieiectrIc I'ropertles of Water during Adsorpt1on 30 (pF) 10 ::5 C/s 10日oc/s 30 60 TlME(min) Fig. 13 Capacitance chang巴sdnring moisture (82:'6 relative humidity) adsorption at the fr向日E邸 iesindicated. (mica) 国‘。(pF) 301 10 60 1.?9 100 TIME(min) 90 Fig. 14 Capacitance changes when a mica plate with adsorbed water was邑lowlydried. (mica) 19 20 M. tDA， M. ltIRATA and S. I<AwDA '30 (pF) 25 c/s 1000 cjs D 60 120 180 TIME(min) Fig. 15 Capacitance changes during miosture adsorption at the frequencies indicated. (calcined diatoma蜘 usearth) 30 (pF) Ir :ノ/0 " A …，四Hit¥ ，il\~ p' 目、〆4 ト「勺.1 9 ， 0o 1Of， ~ . l' '0、ー，0'柵・ e曲， ， ， d ，J ， F ，， 120 ， ， p〆'd ~ TIME(min) 180 Fig. 16 The result of a simultaneous measurement of the capacitance and conductivity. (calcined diatomaceous earth) 2.0 400 xlO岨A300 200 100 2刈ODielectric Properties of Water during Adsorption 150 (pF) 100 25 cjs 1000 cjs 写@60 120 180 TIME(min) Fig. 17 Capa巴itancechanges during moisture adSofption at the frequencies indicated. (pinhole of the leak cock is 1ふnmin diameter). (cacind diatomaceous earth) 150 (pF) 100 50 00 3 c/s -25 c/s -1000 c/s 12{) TIME(岡山〉180 Fig. 18 Capacitance changes during moisture adsorption at the frequencies indicated (pinhole of the leak cock is O.3mm in diameter)・(calci日eddi司tQfi司C邑o1Jsearth) 21 240 240 22 M .IDA， M. HIRATA and S. KAWADA 1明。(pF) 100 (b) 10 10 100 1000 (<i， i Fig. 19 Fr巴quencydependεnC耳sof the capacitance。(calcined diatomaceous earth) 60 ????(pF) 。20 τIME(min) 40 60 Fig. 20 Changes of capacitance at several relative humidities. (calcined diatomac号ousearth) 150 (pF) 100 r心Diel巴ctricProperties of "YVater during Adsorption moistuf<' f¥ow cut off '、引)TiME(min) Fig. 21 Capacitance changes when moisture flow was cut off and set up again. (calcined diatomaceous earth) fiO 401 (pF) 20 ~2i，c/s JOOOc/， 00 120 l自由TIME(min) Fig. 22 Capacitance changes during moisture adsorption measured 自tthe frequencie日indicated.(filter paper) 23 24 M. IDA， M. HIRA TA and S. KA WDA the diameter of the leak cock ls 1.5mm and O. 3mm. These show that the specimen adsorbs water very slowly when its rat色 offlow was diminished， but the height of the peak is independent of the rate. That is， the peak 1S not caused by the rapid flowing of moisture. The frequency dependence of the capacitance at the time of peak and at a fixed time of ascending after the minimum is shown by curves (a) and (b) in Fig. 19. The curv巴 (b)in log-log plotting is nearly a straight line showing that the mechanism of the capacitance at that time must be due to the electrode polarization mentioned in the previous paper(5). The curves in Fig. 20 show the ch司ngesof capacit旦nceat different relative humidities. The time dependence of capacitance when the mOlsture flow was stop回ped at the time of peal王ofcapaci tance and r巴sumedafter about half an hour is shown in Fig. 21. Filter tater The sli t between th巴 electrodeson the filter paper was lmm wide and 22mm long. (Case 2) An example of the time depend印 C色 ofthe capacitance 1S shown in Fig. 22. 4. Condusio宜18( 1) The timεeffect on capaci tance during adsorption of water 1S somewh丘tdif国ferent according as the specimen 1S placed in a vacuum or dry air. ( 2) The adsorption of water should not be regarded to邑ndat the time of initial maximum capacitance but to proceed stil further after that句( 3) A peak of capaci tancεappears also when a specimen with adsorbed water is dried very slowly. ( 4) When a specimen placed in a vacuum adsorbs moisture， the surface dc conduc叫tivity reaches a peak more quickly than the capacitanc鳥 andthe mechanism of the capacitance of the water during adsorption seems to be different from that of the dc conductivity. ( 5) If a NMR experimet is conducted in parallel wi th the dielectric measur，巴ment，a more accurate conclusion may be obtained about the changes of structure of water during adsorption. References 1) S. Kurosaki， S.Saito and G.Sato : J.Cher目。 Phys.23 (1955) 1846. 2) C. Weaver: Advances in Physics: 1 (1962) 83. 3) M.lda， S.Kawada and T. Kesho: Sci. Rep. Kanazawa Univ 7 (1960)5. 4) M. Ida and S. Kawada: Sci. Rep. Kanazawa Univ. 7 (1960) 5. 5) M. Ida and S. Kawada: J. Phys. Soc. Japan 18 (1963) 457. Sd. R邑p.Kanazawa Univ. 8 (1963) 279. 6) F. T. Trouton: Proc. Roy. Soc. (London) A 19 (1907) 383. 

The Change in Dielectric Properties of Water During Adsorption by Solids

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The Change in Dielectric Properties of Water During Adsorption by Solids

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