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Effect of potassium nitrate treatment on the adsorption properties of silica porous glasses
Journal of Non-Crystalline Solids 345&346 (2004) 260–264 www.elsevier.com/locate/jnoncrysol
Effect of potassium nitrate treatment on the adsorption properties of silica porous glasses E. Rysiakiewicz-Pasek a
a,*
, V.A. Vorobyova b, S.A. Gevelyuk b, I.K. Doycho b, V.T. Mak
b
Institute of Physics, Wroclaw University of Technology, W. Wyspianskiego 27, Wroclaw 50-370, Poland b Odessa I.I. Mechnikov National University, Dvoryanska 2, Odessa 65026, Ukraine Available online 6 October 2004
Abstract The effect of treatment in KNO3 solution on the properties of silica porous glasses is presented. An interferometric method was used in determining the influence of humidity on the change in linear sizes and bending deflection of porous glass specimens before and after treatment. The influence of KNO3 processing on effusion properties of porous glasses for use as the scleral part of an eye prosthesis was investigated. Obtained results confirm the influence of secondary silica gel present inside pores on the adsorption properties of porous glasses. 2004 Elsevier B.V. All rights reserved. PACS: 81.05Kf; 81.05Rm
1. Introduction Sodium borosilicate glasses after thermal treatment and subsequent sodium borate phase leaching exhibit pronounced adsorption properties [1,2]. The change of the linear sizes is observed as they are placed in a humid atmosphere [3]. Such behaviour of porous glasses is undesired from the point of view of specific applications, e.g. in the production of elements of eye ball prosthesis. Porous glass filled with antibiotic allows avoiding the inflammatory processes being probable after eye ball enucleation and when the prosthesis is applied. The antibiotic should ooze out gradually over a sufficiently long time from the glass into the lachrymal liquid that surrounds the eye ball [4]. Thus it is important to find a method of decreasing tensions appearing in the glass as a result of moisture adsorption. A number of workers point to the fact that KNO3 treatment results in an in-
crease of mechanical strength in solid glasses [5,6]. Our work presents the investigation of the effect of KNO3 treatment on the mechanical properties of porous glasses and the influence of such treatment on the properties of eye ball prosthesis element made of those glasses. The mechanical properties have been investigated by an interferometric technique. This is an original method which allows detection of changes in linear sizes of a porous glass sample in relation to the humidity of the surrounding atmosphere [7,8]. Our earlier investigations show the efficiency of this nondestructive technique in the studies of porous glasses that were subjected to different post-fabrication treatments [9]. It can also be used to measure the bending of two-layer structures caused by variations in humidity [7]. The two-layer structure (a porous layer on a solid glass substrate) is a basis for eye ball prosthesis element.
2. Experimental *
Corresponding author. Tel.: +48 71 3203614; fax: +48 71 3283696. E-mail address: [email protected] (E. Rysiakiewicz-Pasek). 0022-3093/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2004.08.093
Silica porous glasses of A- and C-type were obtained by chemical leaching of sodium borate phase from the
E. Rysiakiewicz-Pasek et al. / Journal of Non-Crystalline Solids 345&346 (2004) 260–264
same initial sodium borosilicate glass but with different thermal processing. A and C porous glasses have been submitted to phase separation at the temperature of 490 C (165 h) and 650 C (100 h), respectively. The porosity of initial A-glasses was 49.8%, and of initial C-glasses was 54.4%. Porous glass samples were immersed into 2N KNO3 solution for 46 h. Pore size distribution spectra were received by a capacitive method using results of water vapour adsorption–desorption [10,11]. The measurements of humidity dependence of the linear sizes of the porous samples and the bending deflection of the two-layer structure were performed using a setup that included the Michelson interferometer. The mirror in one of the shoulders was in touch with the sample placed in the isolated chamber with variable atmosphere humidity. The humidity in the chamber was set by changing the humid and dry nitrogen ratio. Temperature and humidity were permanently monitored in the process of measurement. The He–Ne laser with wavelength 632.8 nm allowed to maintain the accuracy of interferometric measurements at the level of 0.01% [8]. Effusion properties were studied by means of a photoluminescent method. The glass samples saturated with the antibiotic (gentamicini sulphate) were placed into a physiological solution and the antibiotic effused into it. Every day the sample was placed into a fresh physiological solution. The photoluminescence intensity of both porous glasses in solution and of the applied solution was recorded using the setup described previously [4]. Measurements were stopped when the amount of the antibiotic in the solution became less than minimally effective level (about 25% of the amount of the antibiotic which was effused from A-glass on the first day). Two kinds of samples were investigated. The samples with dimensions of 10 · 20 · 0.5 mm3 were used to measure the effect of humidity on the linear sizes and for poroscopy. Two-layer samples with dimensions of 10 · 20 · 1 mm3, which consist of a thin (about 260 lm) layer of porous glass on a substrate of the initial glass were used for the investigation of the effusion properties and the measurement of humidity dependence of the bending deflection. The measurements were carried out both before and after the treatment of specimens in KNO3.
261
Fig. 1. KNO3-treatment effect on the pore size distribution spectra for A-glasses: (1) initial glass (porosity 0.498); (2) after treatment (porosity 0.487).
tained, but there is a shift of their contribution towards smaller size pores. Contrary to A-samples, the processing of C-samples in KNO3 results in disappearance of some fractions of the pore-sizes with a similar increase
3. Results The analysis of the obtained pore size distribution spectra for A-sample (Fig. 1) shows that after KNO3 treatment the contribution of small radii pores increased. One principal feature characterizing A-glasses should be noted: All fractions of the pore-sizes are main-
Fig. 2. KNO3-treatment effect on the pore size distribution spectra for C-glasses: (1) initial glass (porosity 0.544); (2) after treatment (porosity 0.556).
E. Rysiakiewicz-Pasek et al. / Journal of Non-Crystalline Solids 345&346 (2004) 260–264
in the participation of small size pores (Fig. 2). Figs. 1 and 2 show the pore sizes distribution spectra for small pores that dominate in the processes investigated in this work. Figs. 3 and 4 show the relative changes of linear sizes in porous A- and C-glass in relation to humidity of the surrounding environment before and after KNO3 treatment. The data can be compared with the bending deflection (Fig. 5) in relation to humidity for the same
60 50 bending deflection, mkm
262
40 30
-1 -2
20
-3 -4
10 0 -10 -20 0
25
50
75
100
humidity, % Fig. 5. Humidity bending deflection dependence curves for various glasses: (1) initial A-glass; (2) A-glass after KNO3-treatment; (3) initial C-glass; (4) C-glass after KNO3-treatment.
4
Fig. 3. Humidity dependence of the relative change of linear sizes of A-glasses during adsorption (A) and desorption (D): (1) initial glass; (2) after KNO3-treatment.
PL intensity. rel.un.
- 1 3.5
- 2 - 3
3
- 4
2.5 2 1.5 1 0.5 0 0
1
2
3
4
5
6
7
8
time. days Fig. 6. Effusion ability of A-glasses, processed and non-processed in KNO3 (PL intensity of initial A-glass before antibiotic saturation was used as a unit): (1) initial A-glass; (2) level of antibiotic exuded out of initial A-glass into physiological solution; (3) A-glass after KNO3treatment; (4) level of antibiotic exuded into the physiological solution out of A-glass after KNO3-treatment.
type of glass. Fig. 6 illustrates changes in the effusion ability of A-glass following KNO3 treatment. 4. Discussion Fig. 4. Humidity dependence of the relative change of linear sizes of C-glasses during adsorption (A) and desorption (D): (1) initial glass; (2) after KNO3-treatment.
The curve of adsorption (desorption) obtained from interferometric measurements is a result of a competi-
E. Rysiakiewicz-Pasek et al. / Journal of Non-Crystalline Solids 345&346 (2004) 260–264
tion between capillary squeezing forces and swelling forces of secondary silica gel. The above dependence for A-glasses, which are rich in secondary silica gel, is presented in Fig. 3. The comparison of data presented in Figs. 3 and 1, which shows a large number of fine pores in A-glasses, can be explained by compensation of swelling forces of secondary silica gel by increasing capillary squeezing force. The changes in pores sizes distribution spectra and introduction of the potassium ions into the inner surface of the pores after KNO3 treatment [12] affect the shape of the adsorption (desorption) curve. This leads to the abnormal behaviour of the desorption curve (the desorption curve passes below the adsorption curve in the range from 100 up to 35% of humidity) and to the appearance of a maximum in the region of 20% of humidity. The decrease of the amplitude of linear sizes changes after processing in KNO3 indicates the increase of the capillary squeezing forces as a result of finer pores formation. This is totally consistent with the results shown in Fig. 1. Apart from this, simultaneous inappreciable decrease of the silica gel swelling forces contribution takes place what is due presence of the potassium ions on the surface of silica gel particles. C-glasses contain initially much less secondary silica gel responsible for swelling forces [8]. However the amplitude of linear sizes change versus humidity is 2.5-fold higher in them than in A-glasses. This fact can be explained by a small quantity of the small size pores which are responsible for the formation of capillary squeezing forces (Fig. 2). KNO3 processing of C-glasses leads to the decrease of hysteresis between the adsorption and desorption curves together with simultaneous 2.5-fold decrease of the amplitude of Dl/l changes (Fig. 4). This is associated with the increase in the amount of the small size pores part and, accordingly, with the increase of the capillary squeezing forces after KNO3 processing. The decrease in Dl/l amplitude can also be attributed to the increase in the mechanical strength of the samples treated with KNO3. In order to clarify the influence of KNO3 processing on A- and C-porous layers on a solid glass substrate, a comparison of humidity bending deflection dependence curves of the specified samples was carried out in the humidity range from 10% up to 100% (Fig. 5) and the results were shown in Figs. 3 and 4. As a result of KNO3 treatment, imbalance of competing forces takes place that, eventually, leads to triple increase of the bending deflection amplitude at maintained shape of the curve for A-specimens. It should be noted that the position of a sample at 100% humidity has been accepted as the zero reference point of the bending deflection. At this humidity the sample was completely saturated with water and, accordingly, the capillary
263
squeezing forces were missing due to the occurrence of menisci on the sample surface. The decrease of humidity in A-samples processed in KNO3 causes initially drying of the surface layer with the capillaries formation and appearance of the squeezing forces. Further humidity decrease to about 50% results in drying of the physically bound water in capillaries. This is associated with the greatest change in the bending deflection. At humidity decrease to 10%, drying of the silica gel takes place that is shown in inappreciable squeezing of a sample. The number of small size pores in initial A-glass is much lower, therefore the capillary squeezing forces and the gel swelling forces are more counterbalanced, and the bending deflection amplitude is much lower in the humidity range from 100% to 10%. KNO3 treatment results in the opposite changes in Cglasses. For an initial sample the bending deflection amplitude is three times higher than in the sample processed in KNO3. Due to a similar character of changes in the Dl/l relation before and after KNO3 processing (Fig. 4) it is possible to conclude that the small pores formation leads to the increase in the capillary squeezing forces which essentially counterpoise swelling forces in the secondary silica gel. Thus, it is possible to speak about improvement of the mechanical properties of C-glass after KNO3 processing. However, as is known, the major requirement for the applicability of a material in ophthalmologic prosthetics is its ability to retain the biologically active substance (antibiotic – gentamicini sulphate) for a long time and to provide its permanent effusion level into the lachrymal fluid. Results of our investigation [1] indicate that A-glasses satisfy this requirement in the best way. It is because this type of glass contains a maximum quantity of secondary silica gel inside the pores, which plays a decisive role in the adsorption properties of porous glass. Basing on this fact, we have carried out comparative studies of effusion capability of A-specimens on the glass substrate, subjected and not subjected to KNO3 processing (Fig. 6). Fig. 6 shows that the photoluminescent intensity oscillations, which are typical for A-glasses [4], remain after KNO3 processing. Photoluminescent intensities of antibiotic in a physiological solution are indicated in the same figure by thin lines. It is seen that the sample processed in KNO3 soaks more quantity of antibiotic initially, but also expels it faster. This results from the fact that the physiological solution surrounding an untreated sample luminesces better, what means that it contains more gentamicini sulphate. Thus, KNO3 processing worsens the adsorption properties of A-glass. This is most probably associated with the fact that potassium ions cover both the inner surface of the pores and the particles of the secondary
264
E. Rysiakiewicz-Pasek et al. / Journal of Non-Crystalline Solids 345&346 (2004) 260–264
silica gel, what worsens secondary silica gel ability to adsorb gentamicini sulphate. 5. Conclusions 1. Comparison of the pore size distribution spectra for A- and C-glasses, before and after KNO3 processing, shows a shift of the typical pore sizes maxima inside the smaller radii with a simultaneous increase of the small pores part. 2. Results of investigation of the dependence of changes in linear size and bending deflection on the humidity indicate that KNO3 treatment of porous glasses leads to the improvement of their mechanical properties. 3. Introduction of KNO3 into A-glasses results in the decrease of their effusion properties since the potassium ions cover both the inner surface of the pores and the particles of the secondary silica gel, what deteriorates the ability of the secondary silica gel to adsorb the antibiotic.
References [1] F. Janowski, W. Heyer, Porose Gla¨ser, VEB Deutscher Verlag fu¨r Grundstoffindustrie, Leipzig, 1981. [2] A.F. Novikov, I.K. Meshkovski, J. Optical Technol. 8 (1995) 37. [3] I.K. Meshkovski, Compositional Optical Materials, SPB, St. Petersburg, 1998. [4] E. Rysiakiewicz-Pasek, S.A. Gevelyuk, I.K. Doycho, L.P. Prokopovich, E.D. Safronsky, Optica Appl. XXXIII (2003) 33. [5] M. Petzold, P. Grau, Silikattech. 39 (1988) 277. [6] M. Suszynska, M. Szmida, P. Grau, Sci. Eng. 319 (2001) 702. [7] Ya.O. Roizin, S.A. Gevelyuk, L.P. Prokopovich, D.P. Sawin, E. Rysiakiewicz-Pasek, K. Marczuk, J. Porous Mater. 4 (1997) 151. [8] S.A. Gevelyuk, I.K. Doycho, E. Rysiakiewicz-Pasek, K. Marczuk, J. Porous Mater. 7 (2000) 465. [9] S.A. Gevelyuk, I.K. Doycho, D.E. Lishchuk, L.P. Prokopovich, E.D. Safronsky, E. Rysiakiewicz-Pasek, Y.O. Roizin, Optica Appl. XXX (2000) 605. [10] E.D. Safronski, Y.O. Roizin, E. Rysiakiewicz-Pasek, Optical Mater. 5 (1996) 217. [11] S.J. Greg, K.S. Sing, Adsorption, Surface Area and Porosity, Academic, London, 1982. [12] C.J. Simmons, J. Am. Ceram. Soc. 64 (1981) 200.
Effect of potassium nitrate treatment on the adsorption properties of silica porous glasses E. Rysiakiewicz-Pasek a
a,*
, V.A. Vorobyova b, S.A. Gevelyuk b, I.K. Doycho b, V.T. Mak
b
Institute of Physics, Wroclaw University of Technology, W. Wyspianskiego 27, Wroclaw 50-370, Poland b Odessa I.I. Mechnikov National University, Dvoryanska 2, Odessa 65026, Ukraine Available online 6 October 2004
Abstract The effect of treatment in KNO3 solution on the properties of silica porous glasses is presented. An interferometric method was used in determining the influence of humidity on the change in linear sizes and bending deflection of porous glass specimens before and after treatment. The influence of KNO3 processing on effusion properties of porous glasses for use as the scleral part of an eye prosthesis was investigated. Obtained results confirm the influence of secondary silica gel present inside pores on the adsorption properties of porous glasses. 2004 Elsevier B.V. All rights reserved. PACS: 81.05Kf; 81.05Rm
1. Introduction Sodium borosilicate glasses after thermal treatment and subsequent sodium borate phase leaching exhibit pronounced adsorption properties [1,2]. The change of the linear sizes is observed as they are placed in a humid atmosphere [3]. Such behaviour of porous glasses is undesired from the point of view of specific applications, e.g. in the production of elements of eye ball prosthesis. Porous glass filled with antibiotic allows avoiding the inflammatory processes being probable after eye ball enucleation and when the prosthesis is applied. The antibiotic should ooze out gradually over a sufficiently long time from the glass into the lachrymal liquid that surrounds the eye ball [4]. Thus it is important to find a method of decreasing tensions appearing in the glass as a result of moisture adsorption. A number of workers point to the fact that KNO3 treatment results in an in-
crease of mechanical strength in solid glasses [5,6]. Our work presents the investigation of the effect of KNO3 treatment on the mechanical properties of porous glasses and the influence of such treatment on the properties of eye ball prosthesis element made of those glasses. The mechanical properties have been investigated by an interferometric technique. This is an original method which allows detection of changes in linear sizes of a porous glass sample in relation to the humidity of the surrounding atmosphere [7,8]. Our earlier investigations show the efficiency of this nondestructive technique in the studies of porous glasses that were subjected to different post-fabrication treatments [9]. It can also be used to measure the bending of two-layer structures caused by variations in humidity [7]. The two-layer structure (a porous layer on a solid glass substrate) is a basis for eye ball prosthesis element.
2. Experimental *
Corresponding author. Tel.: +48 71 3203614; fax: +48 71 3283696. E-mail address: [email protected] (E. Rysiakiewicz-Pasek). 0022-3093/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2004.08.093
Silica porous glasses of A- and C-type were obtained by chemical leaching of sodium borate phase from the
E. Rysiakiewicz-Pasek et al. / Journal of Non-Crystalline Solids 345&346 (2004) 260–264
same initial sodium borosilicate glass but with different thermal processing. A and C porous glasses have been submitted to phase separation at the temperature of 490 C (165 h) and 650 C (100 h), respectively. The porosity of initial A-glasses was 49.8%, and of initial C-glasses was 54.4%. Porous glass samples were immersed into 2N KNO3 solution for 46 h. Pore size distribution spectra were received by a capacitive method using results of water vapour adsorption–desorption [10,11]. The measurements of humidity dependence of the linear sizes of the porous samples and the bending deflection of the two-layer structure were performed using a setup that included the Michelson interferometer. The mirror in one of the shoulders was in touch with the sample placed in the isolated chamber with variable atmosphere humidity. The humidity in the chamber was set by changing the humid and dry nitrogen ratio. Temperature and humidity were permanently monitored in the process of measurement. The He–Ne laser with wavelength 632.8 nm allowed to maintain the accuracy of interferometric measurements at the level of 0.01% [8]. Effusion properties were studied by means of a photoluminescent method. The glass samples saturated with the antibiotic (gentamicini sulphate) were placed into a physiological solution and the antibiotic effused into it. Every day the sample was placed into a fresh physiological solution. The photoluminescence intensity of both porous glasses in solution and of the applied solution was recorded using the setup described previously [4]. Measurements were stopped when the amount of the antibiotic in the solution became less than minimally effective level (about 25% of the amount of the antibiotic which was effused from A-glass on the first day). Two kinds of samples were investigated. The samples with dimensions of 10 · 20 · 0.5 mm3 were used to measure the effect of humidity on the linear sizes and for poroscopy. Two-layer samples with dimensions of 10 · 20 · 1 mm3, which consist of a thin (about 260 lm) layer of porous glass on a substrate of the initial glass were used for the investigation of the effusion properties and the measurement of humidity dependence of the bending deflection. The measurements were carried out both before and after the treatment of specimens in KNO3.
261
Fig. 1. KNO3-treatment effect on the pore size distribution spectra for A-glasses: (1) initial glass (porosity 0.498); (2) after treatment (porosity 0.487).
tained, but there is a shift of their contribution towards smaller size pores. Contrary to A-samples, the processing of C-samples in KNO3 results in disappearance of some fractions of the pore-sizes with a similar increase
3. Results The analysis of the obtained pore size distribution spectra for A-sample (Fig. 1) shows that after KNO3 treatment the contribution of small radii pores increased. One principal feature characterizing A-glasses should be noted: All fractions of the pore-sizes are main-
Fig. 2. KNO3-treatment effect on the pore size distribution spectra for C-glasses: (1) initial glass (porosity 0.544); (2) after treatment (porosity 0.556).
E. Rysiakiewicz-Pasek et al. / Journal of Non-Crystalline Solids 345&346 (2004) 260–264
in the participation of small size pores (Fig. 2). Figs. 1 and 2 show the pore sizes distribution spectra for small pores that dominate in the processes investigated in this work. Figs. 3 and 4 show the relative changes of linear sizes in porous A- and C-glass in relation to humidity of the surrounding environment before and after KNO3 treatment. The data can be compared with the bending deflection (Fig. 5) in relation to humidity for the same
60 50 bending deflection, mkm
262
40 30
-1 -2
20
-3 -4
10 0 -10 -20 0
25
50
75
100
humidity, % Fig. 5. Humidity bending deflection dependence curves for various glasses: (1) initial A-glass; (2) A-glass after KNO3-treatment; (3) initial C-glass; (4) C-glass after KNO3-treatment.
4
Fig. 3. Humidity dependence of the relative change of linear sizes of A-glasses during adsorption (A) and desorption (D): (1) initial glass; (2) after KNO3-treatment.
PL intensity. rel.un.
- 1 3.5
- 2 - 3
3
- 4
2.5 2 1.5 1 0.5 0 0
1
2
3
4
5
6
7
8
time. days Fig. 6. Effusion ability of A-glasses, processed and non-processed in KNO3 (PL intensity of initial A-glass before antibiotic saturation was used as a unit): (1) initial A-glass; (2) level of antibiotic exuded out of initial A-glass into physiological solution; (3) A-glass after KNO3treatment; (4) level of antibiotic exuded into the physiological solution out of A-glass after KNO3-treatment.
type of glass. Fig. 6 illustrates changes in the effusion ability of A-glass following KNO3 treatment. 4. Discussion Fig. 4. Humidity dependence of the relative change of linear sizes of C-glasses during adsorption (A) and desorption (D): (1) initial glass; (2) after KNO3-treatment.
The curve of adsorption (desorption) obtained from interferometric measurements is a result of a competi-
E. Rysiakiewicz-Pasek et al. / Journal of Non-Crystalline Solids 345&346 (2004) 260–264
tion between capillary squeezing forces and swelling forces of secondary silica gel. The above dependence for A-glasses, which are rich in secondary silica gel, is presented in Fig. 3. The comparison of data presented in Figs. 3 and 1, which shows a large number of fine pores in A-glasses, can be explained by compensation of swelling forces of secondary silica gel by increasing capillary squeezing force. The changes in pores sizes distribution spectra and introduction of the potassium ions into the inner surface of the pores after KNO3 treatment [12] affect the shape of the adsorption (desorption) curve. This leads to the abnormal behaviour of the desorption curve (the desorption curve passes below the adsorption curve in the range from 100 up to 35% of humidity) and to the appearance of a maximum in the region of 20% of humidity. The decrease of the amplitude of linear sizes changes after processing in KNO3 indicates the increase of the capillary squeezing forces as a result of finer pores formation. This is totally consistent with the results shown in Fig. 1. Apart from this, simultaneous inappreciable decrease of the silica gel swelling forces contribution takes place what is due presence of the potassium ions on the surface of silica gel particles. C-glasses contain initially much less secondary silica gel responsible for swelling forces [8]. However the amplitude of linear sizes change versus humidity is 2.5-fold higher in them than in A-glasses. This fact can be explained by a small quantity of the small size pores which are responsible for the formation of capillary squeezing forces (Fig. 2). KNO3 processing of C-glasses leads to the decrease of hysteresis between the adsorption and desorption curves together with simultaneous 2.5-fold decrease of the amplitude of Dl/l changes (Fig. 4). This is associated with the increase in the amount of the small size pores part and, accordingly, with the increase of the capillary squeezing forces after KNO3 processing. The decrease in Dl/l amplitude can also be attributed to the increase in the mechanical strength of the samples treated with KNO3. In order to clarify the influence of KNO3 processing on A- and C-porous layers on a solid glass substrate, a comparison of humidity bending deflection dependence curves of the specified samples was carried out in the humidity range from 10% up to 100% (Fig. 5) and the results were shown in Figs. 3 and 4. As a result of KNO3 treatment, imbalance of competing forces takes place that, eventually, leads to triple increase of the bending deflection amplitude at maintained shape of the curve for A-specimens. It should be noted that the position of a sample at 100% humidity has been accepted as the zero reference point of the bending deflection. At this humidity the sample was completely saturated with water and, accordingly, the capillary
263
squeezing forces were missing due to the occurrence of menisci on the sample surface. The decrease of humidity in A-samples processed in KNO3 causes initially drying of the surface layer with the capillaries formation and appearance of the squeezing forces. Further humidity decrease to about 50% results in drying of the physically bound water in capillaries. This is associated with the greatest change in the bending deflection. At humidity decrease to 10%, drying of the silica gel takes place that is shown in inappreciable squeezing of a sample. The number of small size pores in initial A-glass is much lower, therefore the capillary squeezing forces and the gel swelling forces are more counterbalanced, and the bending deflection amplitude is much lower in the humidity range from 100% to 10%. KNO3 treatment results in the opposite changes in Cglasses. For an initial sample the bending deflection amplitude is three times higher than in the sample processed in KNO3. Due to a similar character of changes in the Dl/l relation before and after KNO3 processing (Fig. 4) it is possible to conclude that the small pores formation leads to the increase in the capillary squeezing forces which essentially counterpoise swelling forces in the secondary silica gel. Thus, it is possible to speak about improvement of the mechanical properties of C-glass after KNO3 processing. However, as is known, the major requirement for the applicability of a material in ophthalmologic prosthetics is its ability to retain the biologically active substance (antibiotic – gentamicini sulphate) for a long time and to provide its permanent effusion level into the lachrymal fluid. Results of our investigation [1] indicate that A-glasses satisfy this requirement in the best way. It is because this type of glass contains a maximum quantity of secondary silica gel inside the pores, which plays a decisive role in the adsorption properties of porous glass. Basing on this fact, we have carried out comparative studies of effusion capability of A-specimens on the glass substrate, subjected and not subjected to KNO3 processing (Fig. 6). Fig. 6 shows that the photoluminescent intensity oscillations, which are typical for A-glasses [4], remain after KNO3 processing. Photoluminescent intensities of antibiotic in a physiological solution are indicated in the same figure by thin lines. It is seen that the sample processed in KNO3 soaks more quantity of antibiotic initially, but also expels it faster. This results from the fact that the physiological solution surrounding an untreated sample luminesces better, what means that it contains more gentamicini sulphate. Thus, KNO3 processing worsens the adsorption properties of A-glass. This is most probably associated with the fact that potassium ions cover both the inner surface of the pores and the particles of the secondary
264
E. Rysiakiewicz-Pasek et al. / Journal of Non-Crystalline Solids 345&346 (2004) 260–264
silica gel, what worsens secondary silica gel ability to adsorb gentamicini sulphate. 5. Conclusions 1. Comparison of the pore size distribution spectra for A- and C-glasses, before and after KNO3 processing, shows a shift of the typical pore sizes maxima inside the smaller radii with a simultaneous increase of the small pores part. 2. Results of investigation of the dependence of changes in linear size and bending deflection on the humidity indicate that KNO3 treatment of porous glasses leads to the improvement of their mechanical properties. 3. Introduction of KNO3 into A-glasses results in the decrease of their effusion properties since the potassium ions cover both the inner surface of the pores and the particles of the secondary silica gel, what deteriorates the ability of the secondary silica gel to adsorb the antibiotic.
References [1] F. Janowski, W. Heyer, Porose Gla¨ser, VEB Deutscher Verlag fu¨r Grundstoffindustrie, Leipzig, 1981. [2] A.F. Novikov, I.K. Meshkovski, J. Optical Technol. 8 (1995) 37. [3] I.K. Meshkovski, Compositional Optical Materials, SPB, St. Petersburg, 1998. [4] E. Rysiakiewicz-Pasek, S.A. Gevelyuk, I.K. Doycho, L.P. Prokopovich, E.D. Safronsky, Optica Appl. XXXIII (2003) 33. [5] M. Petzold, P. Grau, Silikattech. 39 (1988) 277. [6] M. Suszynska, M. Szmida, P. Grau, Sci. Eng. 319 (2001) 702. [7] Ya.O. Roizin, S.A. Gevelyuk, L.P. Prokopovich, D.P. Sawin, E. Rysiakiewicz-Pasek, K. Marczuk, J. Porous Mater. 4 (1997) 151. [8] S.A. Gevelyuk, I.K. Doycho, E. Rysiakiewicz-Pasek, K. Marczuk, J. Porous Mater. 7 (2000) 465. [9] S.A. Gevelyuk, I.K. Doycho, D.E. Lishchuk, L.P. Prokopovich, E.D. Safronsky, E. Rysiakiewicz-Pasek, Y.O. Roizin, Optica Appl. XXX (2000) 605. [10] E.D. Safronski, Y.O. Roizin, E. Rysiakiewicz-Pasek, Optical Mater. 5 (1996) 217. [11] S.J. Greg, K.S. Sing, Adsorption, Surface Area and Porosity, Academic, London, 1982. [12] C.J. Simmons, J. Am. Ceram. Soc. 64 (1981) 200.