coloration due to colloidal ag particles formed in float glass

Coloration due to colloidal Ag particles formed in ¯oat glass

Satoshi Takeda *, Kiyoshi Yamamoto, Kiyoshi Matsumoto

Research Center, Asahi Glass Co., Ltd., 1150 Hazawa-cho, Kanagawa-ku, Yokohama 221-8755, Japan

Received 15 June 1999; received in revised form 17 August 1999

Abstract

Colloidal silver (Ag) particles are formed in a ¯oat glass by the heat-treatment with sputtered Ag ®lm in air. This

study deals with the coloration of the bottom face of ¯oat glass. The presence of those colloids in the glass gives rise to

yellow coloration. Secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM) and optical

spectra measurements are applied to investigate the e�ects on coloration from the heat treatment temperature, surface

corrosion and chemical state of tin at the bottom face of the glass. It is found that the colloidal Ag particle size becomes

smaller with depth, and that the Ag colloids governing the coloration mainly exist within �0.5 lm region of the glass

surface. It is also found that the di�used Ag concentration is greater in the glass with corroded layer near surface than

without the corroded layer, resulting in deeper yellow coloration. This fact may result from the di�erence in the ion-

exchange rate between Ag�±H�and Ag�±Na�. The remarkable change is observed in the depth pro®le of Ag con-

centration. The depth of change is dependent on a hump position in tin pro®le of the ¯oat glass. This result is discussed

in correlation with the chemical state of tin. Ó 2000 Elsevier Science B.V. All rights reserved.

1. Introduction

It is well-known that the formation of colloidalmetallic particles such as silver (Ag), gold (Au) andcopper (Cu) in glass causes yellow or ruby color-ation [1,2]. Gold ruby glass, which Andreas Cas-sius invented in the mid-seventeenth century, hasbeen used for stained glass and painting of china.The coloring is due to a surface plasmon resonancein the metal particles, which leads to an absorptionband at 390±420 nm in the case of Ag colloids,near 530 nm for Au colloids and 570 nm for Cucolloids [1±3].

Recently, metallic nanoparticles embedded inglasses have attracted much interest as materialsfor optical functional devices such as switches,shutters or waveguides [4,5], because of their un-ique properties which could not be observed inbulk materials [6]. For example, the third-orderoptical non-linearity is strongly enhanced near thesurface plasmon resonance frequency for theglasses doped with metal particles [5,6]. In thatsense, the metallic nanoparticles in glass is noveland interesting subject for studying.

The metallic colloidal particles in ¯oat glass arealso important from an industrial point of view. Inaddition to excellent ¯atness and parallel in largearea, the high productivity makes the ¯oat glassthe most popular in industrial uses for architec-ture, automobiles and displays such as liquidcrystalline display (LCD) or plasma display panels(PDPs). In case of the glass used for automotive

Journal of Non-Crystalline Solids 265 (2000) 133±142

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* Corresponding author. Tel.: +81-45 374 8792; fax: +81-45

374 8892.

E-mail address: [email protected] (S. Takeda).

0022-3093/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved.

PII: S 0 0 2 2 - 3 0 9 3 ( 9 9 ) 0 0 7 1 1 - 5

rear windows, silver is printed on glass as elec-trodes of defogging heater. The silver-printed glassis normally tempered or bended by heat treatmentin order to add safety or ®t the glass for automobileshape, so that the silver is di�used into the glass asAg�. The di�used Ag� is converted to metallic Agparticles by reducing species in the glass, resultingin yellow coloration. The coloration must be uni-form and constant for the practical uses from adesign point of view; while it is sometimes unstablefor products. The unstableness is serious problemfor glass manufacturing industry.

It is known that the coloration depends on thesize, shape, number and their local distribution ofthe colloidal metallic particles. These things de-pend on their formation process, that is to say, thenucleation and growth process of the colloids.Therefore, it is important to know informationabout the factors a�ecting the nucleation andgrowth process for controlling the coloration.

In the present study, the colloidal Ag particlesare formed by heat-treating ¯oat glass with sput-tered Ag ®lm in air. The e�ects on the colorationare investigated for heat treatment temperature,surface corrosion and chemical state of tin in thebottom face of the ¯oat glass. The purpose of thisstudy is to obtain some indications on how tocontrol the coloration due to the colloidal Agparticles in the ¯oat glass. Therefore, we adoptcommercial glasses as samples in this paper. It isknown that tin is present at the bottom face of ¯oatglasses as a result of direct contact with the moltentin bath, and that the tin is not uniformly distrib-uted in the glass [7]. The formation of colloidal Agparticles may be in¯uenced by the Sn distribution,especially the Sn2� distribution, because the Sn2�

can work as a reducing species of Ag�. Therefore,it is important to obtain information about thedistribution of Ag� and Sn2� for controlling thecoloration. Here, secondary ion mass spectrometry(SIMS) is applied to investigate the distribution ofAg and Sn. The SIMS is widely used in many ®eldssuch as semiconductors to obtain the detailed in-formation for in-depth distribution of impurities ordopants in materials because of its excellent sensi-tivity and high depth resolution.

The formation of colloidal Ag particles may bein¯uenced by the glass network structure because

the Ag� di�usion is a�ected by the structure aswell as by the Sn2� distribution. In this paper, thee�ect of the glass network structure on the Ag�

di�usion is also investigated using Li and Rb-dif-fused glass samples. The Li� and Rb� ions are notreduced in the glass, so that their di�usion repre-sents the mobility in the glass network structure.The coloration is evaluated by the optical spectrameasurements. From the results obtained, someindications how to control the coloration due toAg colloids formed in ¯oat glass are discussed.

2. Experimental

2.1. Sample preparation

Commercial soda±lime ¯oat glasses were usedin this study. The main compositions, thicknessand glass transition temperature (Tg) of the glassesare listed in Table 1. In an analysis of surfacecorrosion e�ect on the coloration, a corroded layerwas formed on the glass surface by immersing theglass substrate into 3N±HCl solution at 90� 1°Cfor 8 h. After removing the sample from the so-lution, it was rinsed with distilled water. In ananalysis of tin chemical state e�ect, two types of¯oat glass (Sample-A and Sample-B) were em-ployed. Each glass sample was manufactured on adi�erent ¯oat line although the glass compositionswere same.

The Ag ®lm was coated onto the bottom face ofthe glass with a thickness of 100 nm at roomtemperature by dc magnetron sputtering. Prior tothe Ag ®lm deposition onto the glass, surfacecontaminants were removed by successive ultra-sonic cleaning in the water with a neutral deter-gent, ethanol and distilled water. The Ag-coatedglass was heat-treated in air for 15 min. During theheat-treatment, a part of metallic Ag is oxidized byoxygen in the atmosphere and di�used into theglass as Ag�. The heat treatment conditions of theAg-coated glass are listed in Table 1. The tem-perature pro®les of the heat-treatment are shownin Fig. 1. It was controlled within �2°C. After theheat treatment, the samples were immersed in 7N±HNO3 solution for 10 s to remove the excess Ag®lm on the glass surface. Thereafter, the samples,

134 S. Takeda et al. / Journal of Non-Crystalline Solids 265 (2000) 133±142

Ag-di�used glasses, were rinsed with distilledwater.

Rubidium (Rb)-di�used glass was prepared byheat-treating the glass on which Rb containing®lm was casted by dipping into 0.1 M-RbCl so-lution. The heat treatment condition was listed inTable 1. The temperature pro®le was same as thatof the Ag-di�used glass. After the heat treatment,the sample was rinsed with distilled water. Lithium(Li)-di�used glass was also prepared by the sameprocedure as the Rb-di�used glass. 0.1 M±LiClsolution was used for obtaining the Li-containing®lm on the glass.

5%HF + 5%HCl solution was used for glassetching. The etching rate was estimated frommechanical measurement of the level di�erence

between etched and non-etched parts. The accu-racy of the measurement was within �5 nm.

2.2. Analytical method

The transmission spectra were measured atroom temperature in air using a dual beam spec-trometer. The optical absorption spectra werecalculated as the absorbance unit of transmissionspectra. The depth pro®les for Ag, Sn, Rb and Liwere measured by SIMS. The O�2 primary ionbeam was operated at 8 keV, 100 nA and rasteredon the area of 100� 100 lm2. The angle of inci-dence was 60° to the normal of the sample surface.The charge neutralization was accomplished usingan electron ¯ood gun. The time to depth conver-sion was performed under the assumption that theetching rate was constant during the pro®le. Theetching rate was determined by mechanicallymeasuring the depth of the crater after SIMSmeasurements. Its accuracy was within �5 nm.

The corroded layer of the HCl treated glass wasevaluated by X-ray photoelectron spectroscopy(XPS). XPS measurements were carried out with amonochromatized AlKa source. The detectionangle of X-ray photoelectron was 75° to thesample surface. The colloidal Ag particles formedin the glass were observed by transmission elec-tron microscopy (TEM). TEM specimens wereFig. 1. Temperature pro®les of heat-treatment.

Table 1

The main compositions, thickness and glass transition temperature (Tg) of the glass and the heat treatment conditions for each ex-

periment

Experiment (E�ect) Thickness (mm) Main composition (wt%) Tg (°C) Heat treatment

temperature of

Ag-coated glass (°C)

Heat treatment

temperature

2 72-SiO2, 13-Na2O, 8-CaO, 4-MgO,

2-Al2O3

562 380, 480, 580, 630, 650

and 680

Surface corrosion 2 72-SiO2, 13-Na2O, 8-CaO, 4-MgO,

2-Al2O3

562 650

Chemical state of tin Sample-Aa; 3 72-SiO2, 13-Na2O, 8-CaO, 4-MgO,

2-Al2O3

562 710

Sample-Ba; 3 72-SiO2, 13-Na2O, 8-CaO, 4-MgO,

2-Al2O3

562 710

Li-di�used glass; 2 72-SiO2, 13-Na2O, 8-CaO, 4-MgO,

2-Al2O3

562 680

Rb-di�used glass; 2 72-SiO2, 13-Na2O, 8-CaO, 4-MgO,

2-Al2O3

562 680

a Samples A and B were manufactured on di�erent ¯oat lined.

S. Takeda et al. / Journal of Non-Crystalline Solids 265 (2000) 133±142 135

prepared by focused ion beam (FIB) milling. Thecarbon (C) and tungsten (W) ®lms were depositedonto the Ag-di�used glass to preserve the samplesurface from the ion beam damage during thefabrication of the specimen.

3. Results

3.1. Heat treatment temperature

Fig. 2 shows the absorption spectra of Ag-di�used glasses heat-treated at various tempera-

tures from 380°C to 680°C. The absorption bandsare clearly observed at 390±410 nm due to thesurface plasmon resonance in the colloidal Agparticles for the samples heat-treated above580°C. This band intensity sharply increases whilethe peak position does not change in the range630±680°C. The full width at half maximum(FWHM) of the absorption band is unchanged at38 nm in the range 580±680°C. These results in-dicate that the number of Ag colloids is increasedbut their size does not grow. Fig. 3 shows thecross-sectional TEM image for the Ag-di�usedglass heat-treated at 650°C. The spherical colloi-dal particles are formed with an average size 5 nmin the glass.

Fig. 4 shows the SIMS depth pro®les of the Ag-di�used glasses heat-treated at various tempera-tures. The Ag concentration di�used into the glassincreases with increasing temperatures. The dif-fused Ag concentration drastically change between380°C and 480°C; however, the absorption band isnot observed for both, as shown in Fig. 2. Theseresults indicate that the colloidal Ag particle size isnot enough large for coloring at this temperaturerange. The remarkable change in Ag concentrationdisplayed as (a) in Fig. 4 is observed above 580°C.The depth of this change is almost the same as thatof a hump in tin pro®le. The tin hump is com-monly observed in commercial ¯oat glasses. This

Fig. 2. Absorption spectra of the Ag-di�used ¯oat glass heat-

treated at various temperatures from 380°C to 680°C.

Fig. 3. Cross-sectional TEM micrograph showing colloidal Ag particles formed in the bottom face of the ¯oat glass at 650°C.


result will be discussed later in correlation with thetin chemical state.

Fig. 5 shows the absorption spectra of Ag-dif-fused glasses heat-treated at 650°C as a function ofthe etched thickness for which the surface of thesample was etched by 5%HF ) 5%HCl solution.From the rough estimation of absorption bandintensity, 75% of the colorant exists within 0.5 lm

depth from the glass surface. After 3.0 lm glassetching, the band almost disappeared. The depth isalmost the same as that of the hump in the tinpro®le. After etching to a depth of 4.5 lm, theband is completely disappeared. These results in-dicate that the Ag colloidal particles governing thecoloration mainly exist within 0.5 lm region of theglass surface, and that little colorant is presentbeyond the hump. In Table 2, the FWHM of theabsorpstion band for the Ag-di�used glass isshown. The FWHM of the glass after 0.5 lm glassetching is greater than that of the base glass whilethe peak position is unchanged. After the glassetching of more than 1.0 lm, the FWHM is notchanged.

3.2. Glass surface corrosion

Fig. 6 shows the XPS depth pro®les of the glasswith and without 3N±HCl treatment. The depletedlayer of sodium is observed with a thickness of�50 nm for the HCl treated glass. The any changes

Fig. 4. SIMS depth pro®les of the Ag-di�used ¯oat glass heat-

treated at various temperatures from 380°C to 680°C.

Fig. 5. Absorption spectra of the Ag-di�used ¯oat glass heat-

treated at 650°C as a function of etched thickness of the glass by

5%HF + 5%HCl solution.

Fig. 6. XPS depth pro®les of Na and Si of the glass: without

and with 3N±HCl treatment.

Table 2

The full width at half maximum (FWHM) of the absorption

band at 390±410 nm for the Ag-di�used glass heat-treated at

650°C

Experiment

(E�ect)

Sample Ag-di�used glass FWHM

(nm)

Heat treatment

temperature

Base glass 38

After 0.5 lm glass etching 68



After 3.0 lm glass etching ±

Surface

corrosion

Without any treatment 54

With 3N±HCl treatment 38


are not observed in pro®les of other elements, in-dicating that the sodium ion is selectively extractedfrom the glass by ion-exchange reaction with H�.Consequently, H� enriched layer was formedwithin �50 nm of the surface.

Fig. 7 shows the absorption spectra of Ag-dif-fused glasses with and without the HCl treatment.While the peak position is unchanged at 405 nmfor both glasses, the peak intensity is greater forAg-di�used glass with the HCl treatment thanwithout the HCl treatment, resulting in deeperyellow coloration. The FWHM of the absorptionband is greater for the glass with HCl treatment, asshown in Table 2.

Fig. 8 shows SIMS depth pro®les for Ag-dif-fused glasses with and without HCl treatment, forwhich there is no di�erence in the tin pro®le. It isfound that the di�used Ag concentration of theglass is greater with the HCl treatment than that ofthe glass without the treatment. The surface Agconcentration is also greater for the glass with theHCl treatment than that of the glass without thetreatment. The di�erence in Ag concentration maybe ascribed to the di�erence in ion-exchange ratebetween Ag�±Na� and Ag�±H�. The di�usioncoe�cient may be greater for Ag�±H� than Ag�±Na�. Furthermore, as was pointed out before, theremarkable change in di�used Ag concentration isalso observed at the hump in tin pro®le.

Fig. 9 shows the cross-sectional TEM image ofthe Ag-di�used glass with 3N±HCl treatment. Thespherical colloidal particles with an average size�3 nm are observed. It is found that the colloidal

Ag particles are smaller than that without HCltreatment as shown in Fig. 3, and that the numberof Ag colloid increase compared with that ofnormal glass.

3.3. Chemical state of tin

Fig. 10 shows the transmission spectra for twotypes of Ag-di�used glasses (Sample-A and Sam-ple-B) heat-treated at 710°C. The main composi-tions and the heat treatment conditions are samefor them; while these glasses were manufacturedon di�erent ¯oat lines. The absorption of Sample-A is stronger than Sample-B, resulting in deeperyellow coloration.

Fig. 11 shows the SIMS depth pro®les for bothglasses. The depth of remarkable change in Agconcentration of Sample-A is deeper than that ofSample-B. Aforementioned, the depth is almostthe same as that of the hump in tin pro®le of theglass. It is also found that the slope of the Agpro®le shallower than the hump is almost the sameas that of the tin pro®le.

Fig. 12 shows the SIMS depth pro®les for Li,Rb and Ag-di�used glasses heat-treated at 680°C.There is no characteristic change in Li pro®le. The

Fig. 7. Absorption spectra of the Ag-di�used ¯oat glasses heat-

treated at 650°C: with and without 3N±HCl treatment.

Fig. 8. SIMS depth pro®les for the Ag-di�used ¯oat glass heat-

treated at 650°C: with and without 3N±HCl treatment.


slope of Rb pro®le is slightly changed near thehump position in tin pro®le displayed as (b). Thedegree of the change is smaller than that ofAg-di�used glass.

4. Discussion

4.1. Chemical state of tin in depth

As mentioned before, it is known that tin ispresent at the bottom face of ¯oat glasses as a

result of direct contact with the molten tin bath,and that the tin is not uniformly distributed in theglass. The oxidation states are changed with depth,and the penetration pro®le exhibits an anomaloushump [7±10].

Fig. 9. Cross-sectional TEM micrograph showing colloidal Ag particles formed in bottom face of the ¯oat glass with 3N±HCl

treatment. The heat treatment temperature was 650°C.

Fig. 10. Transmission spectra of the Ag-di�used ¯oat glasses

heat-treated at 710°C. These glasses were manufactured on

di�erent ¯oat lines.

Fig. 11. SIMS depth pro®les for the Ag-di�used ¯oat glasses

heat-treated at 710°C. These glasses were manufactured on

di�erent ¯oat lines.


The formation of colloidal Ag particles in ¯oatglass is closely related to stannous tin (Sn2�) pen-etration pro®le because Sn2� can work as the re-ductant of Ag� ion. As shown in Figs. 4, 8 and 11,the depth of remarkable change in di�used Agconcentration is observed near a hump position inthe tin pro®le of the glass. Furthermore, the slopeof silver pro®le up to the hump is almost same asthat of tin pro®le as seen in Fig. 11. These factsindicate that the redox reaction occurs betweenAg� and Sn2� via the reaction

2Ag� � Sn2� � 2Ag0 � Sn4�:

They also indicate that the Ag� di�usion is sup-pressed at the hump in tin pro®le. It is consideredthat the di�usion rate of ions in glass may be in-¯uenced by the glass network structure as well asthe change in oxidation states as a result of theredox reaction with the reducing species.

In order to clarify the origin of the suppressionof Ag� di�usion, Li and Rb-di�used glasses areexamined. The Li� and Rb� ions are not reducedin the glass, so that their di�usion may be mainly

in¯uenced by the glass network structure. Theradii of Li�, Rb� and Ag� are 0.60, 1.48 and 1.26�A, respectively [11]. The e�ect of the glass networkstructure on their di�usion is considered to begreatest for Rb� unless the Ag� is not converted toAg0 because the radius of Rb� is the largest amongthem.

As shown in Fig. 12, there is no characteristicchange in Li pro®le, indicating that the di�usion ofLi� is not a�ected by the host glass structure be-cause its size is small. The slope of Rb pro®le isslightly changed near the hump position in tinpro®le displayed as (b), indicating that the di�u-sion rate of Rb� is changed around the hump. Thisfact suggests that the glass network structure isdi�erent before and after the hump. It is alsofound that the degree of change is smaller for Rb-di�used glass than that of Ag-di�used glass al-though the radius of Rb� is larger than that ofAg�. These results mean that the di�erence in glassnetwork structure before and after the hump is nota major factor causing the remarkable suppressionof Ag� di�usion near the hump.

These results suggest that the suppression maybe mainly ascribed to the change in oxidationstates of Ag�. From the rough estimation ofabsorption band intensity shown in Fig. 5, 75%of colorant exists within 0.5 um depth from theglass surface, and little colorant is present after3.0 lm glass etching because the band is almostdisappeared. The 3.0 lm depth from the surfaceis almost the same as that of the hump. Thisresult indicates that the majority of the di�usedAg� may be reduced to Ag0 up to the hump.Namely, the remarkable suppression may be dueto the reduction of Ag�. Here, it is consideredthat the reduction has two e�ects on the silverpro®le. One is a decrease in di�usion rate of sil-ver because the di�usion coe�cient of neutralAg0 is much smaller than that of Ag� [12]. Theother is a decrease in concentration of Ag� ionsavailable for di�usion because once nuclei formin the glass one has ÔsinksÕ which serve to removesilver ions from the di�usion stream. Unfortu-nately, the SIMS analysis does not discriminatebetween the precipitated atomic Ag and Ag�

ions. Namely, the e�ects of di�usion and pre-cipitation of silver are not distinguished com-

Fig. 12. SIMS depth pro®les for the Li, Rb and Ag-di�used

¯oat glasses heat-treated at 680°C.


pletely at this stage. These e�ects may be de-convoluted by a study of varying the time as wellas the temperature of their heat treatment, and itwill be a future subject.

However, it is almost certain that the drivingforce of the remarkable suppression is due to thereduction of Ag� by Sn2�. Therefore, the sup-pression result from the fact that the Sn2� con-centration is greater in the region shallower thanthe hump because the Sn2� can work as reducingspecies of Ag�. According to the research of Wil-liams et al. [8] using M�ossbauer spectroscopy, theSn2�/Sn4� ratio was much higher in super®ciallayers than deeper. Nomura also investigated theSn2�/Sn4� ratio with depth, and reported that al-most all the species were Sn4� at the deeper layersthan the hump [10].

Taking these things into consideration, thecoloration may depend on the Sn2� distributionbecause it in¯uences the nucleation and growth ofAg colloids. Namely, the coloration di�erence asseen in Fig. 10 is ascribed to the di�erence in theSn2� distribution as shown in Fig. 11. The Sn2�

penetration pro®le probably result from the com-plex multi-component di�usion and redox reactione�ects, involving not only the tin and oxygen fromthe bath, but also some components of the glasssuch as iron, sulfur and other components.Namely, the depth pro®le of Sn2� in the glass de-pends on the penetration process of tin frommolten tin bath. It is known that the penetrationpro®le is in¯uenced by the contact time, tempera-ture pro®le and impurities in the atmosphere of the¯oat chamber and in the molten tin bath [13].Therefore, it is important to control the produc-tion conditions for obtaining the uniform andconstant coloration.

4.2. Glass surface corrosion

As shown in Fig. 6, the coloration is also in-¯uenced by the surface state of the glass even if theSn2� distribution is same. The change in the col-oration may be ascribed to the di�erence in thedi�usion rate of Ag� because the di�usion rate ofAg� in¯uences the nucleation and growth rate ofthe Ag colloids. Namely, the di�usion rate of Ag�

in¯uences the redox reaction rate with Sn2� andthe rate of aggregation in the formation of Agcolloids, resulting in the di�erence in the size,number and local distribution of the Ag colloidalparticles, as shown in Fig. 9. Therefore, controllingthe surface state of the glass is also important tocontrol the coloration.

4.3. Heat treatment temperature

As shown in Fig. 2, the heat treatment tem-perature also a�ects coloration. This result indi-cates that the nucleation and growth rate of the Agcolloids depend on the temperature. In addition, itis found that the peak intensity at 410 nm drasti-cally increases at 580°C. This temperature is nearlyTg of the glass substrate. This result suggests thatthe nucleation and growth of the Ag colloids areclosely related with the rigidness of the glass net-work structure. Namely, the looser glass structureaccelerates the di�usion and aggregation of Ag.Therefore, controlling the heat treatment condi-tions accurately is essential to obtain uniform andconstant coloration.

4.4. Chemical state of tin in depth and colloidal Agparticle size

It is found that the FWHM of the absorptionband around 400 nm for the Ag-di�used glass in-creases after 0.5 lm glass etching compared withthe glass before the etching while the peak positionis unchanged, as shown in Table 2. Kreibig andFragstein showed the spectral peak positions andthe FWHM of the theoretical absorption curves ofAg-particle embedded glasses, taking into accountthe mean free path e�ect [14]. They indicated thatthe peak position was kept constant when particlediameters were between 4 and 15 nm, and theFWHM decreased with increasing particle diame-ter up to about 20 nm. Applying this model to ourcase, it is suggested that the particle size is greaterwithin 0.5 lm region of the surface than deeperregion. The size di�erence may also result from theSn2� distribution because the nucleation andgrowth rate of the colloids is a�ected by the Sn2�

distribution.


5. Conclusions

In this paper, we have investigated the e�ects ofheat treatment temperature, surface corrosion andchemical state of tin at the bottom face of the ¯oatglass on coloration due to colloidal Ag particles. Ithas been found that the colloidal Ag particle sizebecomes smaller with depth, and that the Ag col-loids governing the coloration mainly exist within0.5 lm region of the glass surface in this study.The di�used Ag concentration is greater for theglass with corroded layer near surface than ordi-nary glass without the corrosion, resulting indeeper yellow coloration. The depth of remarkablechange in di�used Ag concentration is dependenton a hump position in tin pro®le of the ¯oat glass.These results may serve indications how to controlthe coloration of metallic colloidal particles in¯oat glass.

Acknowledgements

The authors are grateful to Hitachi InstrumentsEngineering for cross-sectional TEM observation.Their thanks are also due to Mr N. Aomine of

Asahi Glass for the coating of sputtered silver ®lmonto the glass.

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coloration due to colloidal ag particles formed in float glass

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