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An improved apparatus for measuring the inhomogeneity of glasses
Journal of Non-Crystalline Solids 80 (1986) 693-697 North-Holland, Amsterdam
693
A N I M P R O V E D A P P A R A T U S FOR M E A S U R I N G T H E I N H O M O G E N E I T Y OF GLASSES Teruo SAKAINO Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-Ku, Tokyo, 160 Japan
Sang-Soo L E E , Masanori I W A M O T O , Haruhiko O G A T A and Yoshihiko Y A M A T O Toyo Glass Co., Ltd, 1-3-1 Uchisaiwai-Cho, Chiyoda-Ku, Tokyo, lO0 Japan
An improved apparatus capable of quantatively measuring the inhomogeneity of glasses within several minutes was developed as a prototype for practical use. Inhomogeneities were measured for several kinds of glass articles on the market, such as plate, bottle and optical glasses etc. and a "relative homogeneity" has been proposed for the purpose of deciding a ranking of glasses measured in comparison to the powdered single crystal of CaF2 as a standard material of uniformity.
1. Introduction This type of apparatus, which is able to quantitatively measure the inhomogeneity of glasses in a powdered state by means of continuous variation in the refractive index of an immersion liquid, was originally d e v e l o p e d by Shelyubskii [1]. But it was not of practical convenience, because of 1) taking a rather long time to adjust the refractive index of a liquid by t e m p e r a t u r e variation, and 2) inconvenience, in the case of using a liquid of a binary system, because of instability in the refractive index due to evaporation during the measurement. In order to r e m o v e the inconvenience stated above, an i m p r o v e d apparatus was initially developed by one of the present authors [2-5] by changing t e m p e r a t u r e into pressure as the means of varying the refractive index of the liquid. T h e new apparatus published in the present study is similar to the original type for some points: 1) applying a pressure through water to the specimen, which can be regarded as a Christiansen filter, consisting of a p o w d e r e d glass and an immersion liquid of a refractive index similar to that of the glass, and 2) avoiding the light c o m p o n e n t s scattering not parallel to the optical axis with a focusing lens placed between the pressure c h a m b e r and a light receiving photodiode. But it has been improved in the following 0022-3093/86/$03.50 (~ Elsevier Science Publishers B.V. (North-Holland Physics Division)
694
T. Sakaino et al. / Measuring inhomogeneity of glasses
points: 3) using a He-Ne laser with a beam expander as a light source, 4) reducing the volume of the pressure chamber to make the pressure pump smaller, 5) replacing the oilpump with a small waterpump, and 6) eliminating a spheric aberration by replacing the usual focusing lens with a hyperboloid lens (which has not been provided yet).
2. Experimental procedure and results As shown in fig. 1, the apparatus consists of a He-Ne laser (1) radiating a monochromatic light of wave length 632.8 nm, a beam expander (2), a half-mirror (3) to lead a half beam to a Si-photodiode (15) to check the intensity of the light source, a pressure chamber (4), which is proof against high pressure up to 1000 kg/cm 2, including a Christiansen filter (5) consisting of a glass powder and an immersion liquid, a pressure sensor (14) to measure the pressure, a lens of hyperboloid (6), a light receiving Siphotodiode (7), an X - Y recorder (8), an amplifier (9), an analog/digital converter (10), a computer (11), a printer (12) printing out data of pressure and refractive indices and a cathode ray tube (13) to show data for pressure and refractive indices of the immersion liquid momentarily. The pressure chamber is independently shown in fi~. 2. The glass article to be measured is first ground with a steel mortar (ASTMC225-73, reapproved 1978) into particles from which a powder with a mean value of about 140/~m in diameter is sifted. Being subjected to
1 2 3 4 5
He-Ne Laser B e a m Expander* Half-Mirror Pressure Chamber C h r i s t i a n s e n Filter (Glass Powder+Liquid) 6 H y p e r b o l o i d Lens* 7 Si-Photodiode 8 X-Y Recorder 9 Amplifyer 10 A / D C o n v e r t e r ii C o m p u t e r 12 P r i n t e r 13 C a t h o d e Ray Tube 14 P r e s s u r e S e n s o r 15 S i - P h o t o d i o d e
J
15
* for h i g h e r accuracy
Fig. h Block diagram for optical and control system.
[
II
695
T. Sakaino et al. / Measuring inhomogeneity o[ glasses Immersion Liquid 2 Christiansen Filter (Glass P o w d e r + L i q u i d ) 3 Glass Cell 4 Pressure Sensor 5 Water 6 Window Glass 7 to P u m p 8 Bubble-Skimmer 9 Laser Beam
i
___7_k
.
I, Fig. 2. Pressure chamber. successively washing with water, ethanol and a 6 N - H C l solution, etching with a 1% H F solution and again washing with ethanol, acetone and ethyl ether, the powder is used as a specimen. The powder must be slowly put into a glass cell filled with an immersion liquid of refractive index similar to that of the glass and be enough to leave a large margin for the path of the laser beam. The sizes of the glass cell used in the present study are 10× 10, 1 0 x 20, 1 0 x 30 and 1 0 x 5 0 m m 2 on the inside, respectively. Before the measurement, the pressure is raised through water by a handpump up to a pressure high enough to be equivalent to the high end in the refractive index distribution of the glass specimen; after reaching an equilibrium state, the pressure is reduced gradually by opening a leakage valve to measure the transmission as a function of pressure and also to find the maximum transmission. From the authors' experience, some error appeared easily in packing density when putting a powder into the cell and consequently caused frequently a deviation in the light transmission to some extent, say 1 to 2%. Other kinds of errors, for example, the surface condition of each particle, stains at the surface of window glasses set in the pressure chamber, and others also necessarily resulted in a scattering of the values of transmission. T h e authors, therefore, inevitably came to a conclusion that, at present, the best plan is to derive the standard deviation regarded as a degree of the inhomogeneity for each specimen, using a rather simple equation and also with a rather simple apparatus, from ihe maximum light transmission observed for each specimen. It is furthermore noticed that even in this way a slight difference in quality can be distinguished between two kinds of BK-7, 'high homogenized-' and 'normal-' bland optical glasses on the market. As a result, the data have been obtained in the present study using the apparatus with neither the beam expander nor the expensive hyperboloid lens.
696
T. Sakaino et al. / Measuring inhomogeneity of glasses
Table 1 Maximum transmission, Tin, and relative homogeneity, Hr Tm CaF2 BK 7 (HH) BK 7 (NM) Bottle (A1) Bottle (A2) Bottle (B) TV Panel Float (A) Float (B) Jar (A) Jar (B)
0.943 0.925 0.882 0.889 0.867 0.413 0.691 a 0.759 0.428 0.830a 0.306a
100.0 76.4 45.9 50.4 41.6 6.60 16.0a 21.4 6.97 53.5 ~ 5.00~
a No color connection. M e a s u r e m e n t s were m a d e for various kinds of glass articles obtained on the market, some of which are slightly colored such as float glasses and bottle glasses, and a single crystal of calcium fluoride as a standard material of uniformity. Results obtained are given in table 1.
3. Consideration T h e relation between the degree of inhomogeneity of a glass and the m a x i m u m light transmission o b s e r v e d for the Christiansen filter consisting of the glass powder and a liquid has been discussed by Shelyubskii [1] and others [6-8]. Shelyubskii derived a simple equation with an assumption that the distribution of refractive indices caused by inhomogeneity in usual glasses can be r e g a r d e d as a Gaussian type: S 2 = - (In Tm)/a,
(1)
where S is the standard deviation, Tm is the m a x i m u m transmission observed when the refractive index of the liquid varies continuously, and a is a p a r a m e t e r concerning paekingness of the glass powder and the net light path in the Christiansen filter, etc. In the case of measuring colored glasses, S can be obtained by the next equation: S2=-(In
T~-ln
Tc)/a,
(2)
where T " is an apparent m a x i m u m transmission obtained for a colored glass as the Christiansen filter, and Tc is the transmission measured for the same colored glass of a platelet with a thickness substantially the same as that of the Christiansen filter. Since the net optical path of the Christiansen filter could be r e g a r d e d as ' e a c h nominal length of glass cell × 0 . 5 ' with
T. Sakaino et al. / Measuring inhomogeneity o[ glasses
697
considerable accuracy, in the present study, 1 0 m m for the Christiansen filter and 5 mm for a solid specimen have been standardized. In addition, the loss of the incident light in Christiansen filters has also been confirmed to conform to Lambert's law. In the case of bottle glasses, float glasses and others which are slightly colored glasses, the maximum transmissions observed directly were corrected according to eq. (2) and Lambert's law. Data with the steric symbol are indicated not to be corrected because of lack of the specimens. The relative homogeneity denoted by Hr is a concept proposed by the present authors for convenience, which is similar to the reciprocal of the standard deviation S and is calculated by the equation: H r = In T m o / l n Tm,
(3)
where Tm is the observed value for each specimen and T m o is a standard value observed for the Christiansen filter prepared with a single crystal of CaF2. T h e CaF2 crystal is known to be isotropic and is considered to have no deviation in the refractive index.
4. Conclusion A prototype for practical use was developed for quantitative measurement of the inhomogeneity of glasses. Several kinds of glasses on the market were measured and their degree of inhomogeneity was decided, which is compared with CaF2 single crystal as a standard material of homogeneity. Special features of the apparatus are: 1) a short time of measurement; 2) simplicity of operation; 3) a considerable accuracy; and 4) low running cost.
References [1] V.I. Shelyubskii, Steklo i Keram. 8 (1960) 17. [2] T. Sakaino, M. Yamane, A. Makishima and S. Inoue, Rep. Asahi Glass Ind. Techn. Prom. Soc. 31 (1977) 119. [3] T. Sakaino, M. Yamane and S. Inoue, J. High Pressure 16 (1978) 169. [4] T. Sakaino, M. Yamane and S. Inoue, Proc. Xlth Intern. Congr. on Glass, Prague 1977 (III), p. 407. [5] T. Sakaino, M. Yamane, A. Makishima and S. Inoue, Glass Technol. 19 (1978) 69. [6] H. lmagawa, Glass Technol. 14 (1973) 85. [7] H. Imagawa, J. Ceram. Soc. Japan 88 (1980) 373. [8] S. lnoue, S. Omi and M. Yamane, J. Ceram. Soc. Japan 89 (1981) 260.
693
A N I M P R O V E D A P P A R A T U S FOR M E A S U R I N G T H E I N H O M O G E N E I T Y OF GLASSES Teruo SAKAINO Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-Ku, Tokyo, 160 Japan
Sang-Soo L E E , Masanori I W A M O T O , Haruhiko O G A T A and Yoshihiko Y A M A T O Toyo Glass Co., Ltd, 1-3-1 Uchisaiwai-Cho, Chiyoda-Ku, Tokyo, lO0 Japan
An improved apparatus capable of quantatively measuring the inhomogeneity of glasses within several minutes was developed as a prototype for practical use. Inhomogeneities were measured for several kinds of glass articles on the market, such as plate, bottle and optical glasses etc. and a "relative homogeneity" has been proposed for the purpose of deciding a ranking of glasses measured in comparison to the powdered single crystal of CaF2 as a standard material of uniformity.
1. Introduction This type of apparatus, which is able to quantitatively measure the inhomogeneity of glasses in a powdered state by means of continuous variation in the refractive index of an immersion liquid, was originally d e v e l o p e d by Shelyubskii [1]. But it was not of practical convenience, because of 1) taking a rather long time to adjust the refractive index of a liquid by t e m p e r a t u r e variation, and 2) inconvenience, in the case of using a liquid of a binary system, because of instability in the refractive index due to evaporation during the measurement. In order to r e m o v e the inconvenience stated above, an i m p r o v e d apparatus was initially developed by one of the present authors [2-5] by changing t e m p e r a t u r e into pressure as the means of varying the refractive index of the liquid. T h e new apparatus published in the present study is similar to the original type for some points: 1) applying a pressure through water to the specimen, which can be regarded as a Christiansen filter, consisting of a p o w d e r e d glass and an immersion liquid of a refractive index similar to that of the glass, and 2) avoiding the light c o m p o n e n t s scattering not parallel to the optical axis with a focusing lens placed between the pressure c h a m b e r and a light receiving photodiode. But it has been improved in the following 0022-3093/86/$03.50 (~ Elsevier Science Publishers B.V. (North-Holland Physics Division)
694
T. Sakaino et al. / Measuring inhomogeneity of glasses
points: 3) using a He-Ne laser with a beam expander as a light source, 4) reducing the volume of the pressure chamber to make the pressure pump smaller, 5) replacing the oilpump with a small waterpump, and 6) eliminating a spheric aberration by replacing the usual focusing lens with a hyperboloid lens (which has not been provided yet).
2. Experimental procedure and results As shown in fig. 1, the apparatus consists of a He-Ne laser (1) radiating a monochromatic light of wave length 632.8 nm, a beam expander (2), a half-mirror (3) to lead a half beam to a Si-photodiode (15) to check the intensity of the light source, a pressure chamber (4), which is proof against high pressure up to 1000 kg/cm 2, including a Christiansen filter (5) consisting of a glass powder and an immersion liquid, a pressure sensor (14) to measure the pressure, a lens of hyperboloid (6), a light receiving Siphotodiode (7), an X - Y recorder (8), an amplifier (9), an analog/digital converter (10), a computer (11), a printer (12) printing out data of pressure and refractive indices and a cathode ray tube (13) to show data for pressure and refractive indices of the immersion liquid momentarily. The pressure chamber is independently shown in fi~. 2. The glass article to be measured is first ground with a steel mortar (ASTMC225-73, reapproved 1978) into particles from which a powder with a mean value of about 140/~m in diameter is sifted. Being subjected to
1 2 3 4 5
He-Ne Laser B e a m Expander* Half-Mirror Pressure Chamber C h r i s t i a n s e n Filter (Glass Powder+Liquid) 6 H y p e r b o l o i d Lens* 7 Si-Photodiode 8 X-Y Recorder 9 Amplifyer 10 A / D C o n v e r t e r ii C o m p u t e r 12 P r i n t e r 13 C a t h o d e Ray Tube 14 P r e s s u r e S e n s o r 15 S i - P h o t o d i o d e
J
15
* for h i g h e r accuracy
Fig. h Block diagram for optical and control system.
[
II
695
T. Sakaino et al. / Measuring inhomogeneity o[ glasses Immersion Liquid 2 Christiansen Filter (Glass P o w d e r + L i q u i d ) 3 Glass Cell 4 Pressure Sensor 5 Water 6 Window Glass 7 to P u m p 8 Bubble-Skimmer 9 Laser Beam
i
___7_k
.
I, Fig. 2. Pressure chamber. successively washing with water, ethanol and a 6 N - H C l solution, etching with a 1% H F solution and again washing with ethanol, acetone and ethyl ether, the powder is used as a specimen. The powder must be slowly put into a glass cell filled with an immersion liquid of refractive index similar to that of the glass and be enough to leave a large margin for the path of the laser beam. The sizes of the glass cell used in the present study are 10× 10, 1 0 x 20, 1 0 x 30 and 1 0 x 5 0 m m 2 on the inside, respectively. Before the measurement, the pressure is raised through water by a handpump up to a pressure high enough to be equivalent to the high end in the refractive index distribution of the glass specimen; after reaching an equilibrium state, the pressure is reduced gradually by opening a leakage valve to measure the transmission as a function of pressure and also to find the maximum transmission. From the authors' experience, some error appeared easily in packing density when putting a powder into the cell and consequently caused frequently a deviation in the light transmission to some extent, say 1 to 2%. Other kinds of errors, for example, the surface condition of each particle, stains at the surface of window glasses set in the pressure chamber, and others also necessarily resulted in a scattering of the values of transmission. T h e authors, therefore, inevitably came to a conclusion that, at present, the best plan is to derive the standard deviation regarded as a degree of the inhomogeneity for each specimen, using a rather simple equation and also with a rather simple apparatus, from ihe maximum light transmission observed for each specimen. It is furthermore noticed that even in this way a slight difference in quality can be distinguished between two kinds of BK-7, 'high homogenized-' and 'normal-' bland optical glasses on the market. As a result, the data have been obtained in the present study using the apparatus with neither the beam expander nor the expensive hyperboloid lens.
696
T. Sakaino et al. / Measuring inhomogeneity of glasses
Table 1 Maximum transmission, Tin, and relative homogeneity, Hr Tm CaF2 BK 7 (HH) BK 7 (NM) Bottle (A1) Bottle (A2) Bottle (B) TV Panel Float (A) Float (B) Jar (A) Jar (B)
0.943 0.925 0.882 0.889 0.867 0.413 0.691 a 0.759 0.428 0.830a 0.306a
100.0 76.4 45.9 50.4 41.6 6.60 16.0a 21.4 6.97 53.5 ~ 5.00~
a No color connection. M e a s u r e m e n t s were m a d e for various kinds of glass articles obtained on the market, some of which are slightly colored such as float glasses and bottle glasses, and a single crystal of calcium fluoride as a standard material of uniformity. Results obtained are given in table 1.
3. Consideration T h e relation between the degree of inhomogeneity of a glass and the m a x i m u m light transmission o b s e r v e d for the Christiansen filter consisting of the glass powder and a liquid has been discussed by Shelyubskii [1] and others [6-8]. Shelyubskii derived a simple equation with an assumption that the distribution of refractive indices caused by inhomogeneity in usual glasses can be r e g a r d e d as a Gaussian type: S 2 = - (In Tm)/a,
(1)
where S is the standard deviation, Tm is the m a x i m u m transmission observed when the refractive index of the liquid varies continuously, and a is a p a r a m e t e r concerning paekingness of the glass powder and the net light path in the Christiansen filter, etc. In the case of measuring colored glasses, S can be obtained by the next equation: S2=-(In
T~-ln
Tc)/a,
(2)
where T " is an apparent m a x i m u m transmission obtained for a colored glass as the Christiansen filter, and Tc is the transmission measured for the same colored glass of a platelet with a thickness substantially the same as that of the Christiansen filter. Since the net optical path of the Christiansen filter could be r e g a r d e d as ' e a c h nominal length of glass cell × 0 . 5 ' with
T. Sakaino et al. / Measuring inhomogeneity o[ glasses
697
considerable accuracy, in the present study, 1 0 m m for the Christiansen filter and 5 mm for a solid specimen have been standardized. In addition, the loss of the incident light in Christiansen filters has also been confirmed to conform to Lambert's law. In the case of bottle glasses, float glasses and others which are slightly colored glasses, the maximum transmissions observed directly were corrected according to eq. (2) and Lambert's law. Data with the steric symbol are indicated not to be corrected because of lack of the specimens. The relative homogeneity denoted by Hr is a concept proposed by the present authors for convenience, which is similar to the reciprocal of the standard deviation S and is calculated by the equation: H r = In T m o / l n Tm,
(3)
where Tm is the observed value for each specimen and T m o is a standard value observed for the Christiansen filter prepared with a single crystal of CaF2. T h e CaF2 crystal is known to be isotropic and is considered to have no deviation in the refractive index.
4. Conclusion A prototype for practical use was developed for quantitative measurement of the inhomogeneity of glasses. Several kinds of glasses on the market were measured and their degree of inhomogeneity was decided, which is compared with CaF2 single crystal as a standard material of homogeneity. Special features of the apparatus are: 1) a short time of measurement; 2) simplicity of operation; 3) a considerable accuracy; and 4) low running cost.
References [1] V.I. Shelyubskii, Steklo i Keram. 8 (1960) 17. [2] T. Sakaino, M. Yamane, A. Makishima and S. Inoue, Rep. Asahi Glass Ind. Techn. Prom. Soc. 31 (1977) 119. [3] T. Sakaino, M. Yamane and S. Inoue, J. High Pressure 16 (1978) 169. [4] T. Sakaino, M. Yamane and S. Inoue, Proc. Xlth Intern. Congr. on Glass, Prague 1977 (III), p. 407. [5] T. Sakaino, M. Yamane, A. Makishima and S. Inoue, Glass Technol. 19 (1978) 69. [6] H. lmagawa, Glass Technol. 14 (1973) 85. [7] H. Imagawa, J. Ceram. Soc. Japan 88 (1980) 373. [8] S. lnoue, S. Omi and M. Yamane, J. Ceram. Soc. Japan 89 (1981) 260.