US3723144A - Borosilicate opal glasses - Google Patents

Abstract

THIS INVENTION RELATES TO THE PRODUCTION OF BOROSILICATE OPAL GLASSES WHEREIN THE OPAL PHASE IS READILY ATTACHED BY WATER AND DETERGENTS. IN THE GLASSES OF THE PRESENT INVENTION, THE OPAL PHASE IS MADE DISCONTINUOUS, I.E., THE PARTICLES THEREOF COMMONLY EXHIBIT A SPHERICAL CONFIGURATION, SUCH THAT DEEP LEACHING IS EXHIBITED. THE GLASSES CONSISTS ESSENTIALLY, IN WEIGHT PERCENT ON THE OXIDE BASIS, OF 0.5-2.5% LI2O, 7-10% ZNO, 11-14% B2O3, AND 71-76% SIO2.

Description

March 27, 1973 PLANNER)! ETAL 3,723,144

BOROSILICATE OPAL GLA SSES Filed May 10, 1971 v e Sheets-Sheet 1.

a rf IN [/5 N TORS.

James E. F lannry Jacques 6. Lemoine AT TORNEY' March 1973 E, FLANNERY ETAL 3,723,144

BOROSILICATE OPAL GLASSES 6 Sheets- INVENTORSL: James E. F Ianhery Jacques .G. Lemoine BY AT ORNE March 27, 1973 E, FLANNERY ET AL BOROSILICATE OPAL 'GLASSES 6 Sheets-Sheet 3' Filed May 10, 1971 INVENTU'RSI. James E F lannery Jacques 6. Lemaine 1 7d! 27. 1973 J, E. FLANNERY ETAL $723,144

. BOROSILICATE OPAL GLASSES I Filed lay 10, 1971 6 Sheets-Sheet 4 INVENTORS. James E. F Iannery Jacques G. Lemaine BY A ORNEY March- 27, 1973 J. E. FLANNERY ET AL BOROSILICATE OPAL GLAS SES 6 Sheets-Sheet 5 Filed May 10, 1971 ine ORNEY March 27, 1973 J- E. FLANNERY 3,723,144

BOROSILICATE OPAL GLAS SE5 6 Sheets-Sheet 6 Filed May 10, 1971 m sm R!- W F N. WE w James Jacques AT ORNEY United States Patent 3,723,144 BOROSILICATE OPAL GLASSES James E. Flannery, Corning, N.Y., and Jacques G. Lemoine, Fontainebleau, France, assignors to Corning Glass Works, Corning, NY.

Filed May 10, 1971, Ser. No. 141,765 Int. Cl. C03c 3/08 U.S. Cl. 106-54 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the production of borosilicate opal glasses wherein the opal phase is readily attacked by water and detergents. In the glasses of the present invention, the opal phase is made discontinuous, i.e., the particles thereof commonly exhibit a spherical configuration, such that deep leaching is inhibited. The glasses consist essentially, in weight percent on the oxide basis, of 0.5-2.5% Li O, 710% ZnO, 11-14% B 0 and 71-76% SiO CROSS REFERENCE TO RELATED APPLICATION U.S. application Ser. No. 94,834, filed Dec. 3, 1970 in the names of Gerald B. Carrier and James E. Flannery.

A translucent or almost opaque white glass can be produced through the inclusion therein of colorless, nonmetallic crystalline or amorphous particles. These particles, having a dilferent index of refraction from that of the base glass, scatter the light within the body of the glass and diffuse the transmitted light. Such glasses have been referred to as opals and have seen such diversitied applications as tableware, culinary ware, lamp globes, and wall paneling.

Most frequently, the opacity exhibited by opal glasses is dependent upon a phase separation occurring within the body of the glass wherein a light-diffusing phase is uniformly precipitated throughout a transparent glassy matrix. The light diffusing effect results from the fact that the separated phase, whether it be amorphous, crystalline, or only voids, has an index of refraction different from that of the matrix glass such that light scattering with consequent loss of transparency occurs.

The opacifying phase may be relatively continuous through all or a portion of the glass body. Conversely, it can be particulate or otherwise relatively discontinuous. Where the separated phase is continuous within itself, deep leaching can occur. However, if the precipitated phase can be made discontinuous, then paths for leaching will not be available and only those portions of the soluble phase which are exposed at the surface of the glass will be dissolved. This, of course, presupposes that the baseglass is relatively inert to the attacking medium.

In the manufacture of opal glasses, an opalizing agent is included in the glass batch which will form a compound that is soluble in the 'glass melt but which will precipitate therefrom during the cooling of the melt to an amorphous body or upon a subsequent heat treatment thereof. Opal glasses produced from conventional soda lime glass composition were Well known to the art and commonly utilized metal halide, sulfate, or phosphate salts as opalizers. Nevertheless, the high coefficients of thermal expansion exhibited by these glasses, viz., up to 90X C. over the range 25 -300 C., foreclosed their use where reasonable resistance to thermal shock was required, as, for example, in ovenware. In view of this deficiency, opal glasses having a borosilicate base composition were developed. These glasses demonstrate coefficients of thermal expansion over the range 25 300 C. between about ZS-SOX 10 C. and, therefore, exhibit sufficient thermal shock resistance for use in glassware applications involving high temperature gradients resulting from zone heating or thermal cycling.

U.S. Pat. No. 3,275,492 describes one group of such borosilicate-type glasses having good resistance to thermal shock within a broad range of opal densities. Opalizing agents for borosilicate-type glasses include ZnO, MgO, CaO, BaO, NiO, CoO, MnO, and C with, optionally, such secondary opalizers as the halides, phosphates, or sulfates. These glasses exhibit good melting and forming properties but, unfortunately, are subject to chemical attack from certain commonplace solutions. For example, tableware and culinary ware made therefrom manifest surface attack after being in contact with hot detergent solutions such as are experienced in dishwashers. This chemical attack all too soon leads to surface roughness which, in itself, is aesthetically unpleasing and further entrains staining from food coming into contact therewith.

A study of this lack of chemical durability has pointed out two principal causes therefor: First, and most impor tant, the opal phase is soft and highly susceptible to chemical attack; and, Second, the opal phase is relatively continuous in the glassy matrix. Thus, the opal phase s much less resistant to chemical attack than the surrounding matrix glass. Therefore, inasmuch as this separated phase is highly soluble in the contacting detergent solution, continuity of this phase within the glass body provides leaching paths which permit the attacking solution to migrate deep into the body. Such deep penetration and solution can obviously be a serious problem in such applications as ovenware where food entering the resultant voids may cause discoloration or staining. Where, however, the precipitated soluble phase is developed in the form of individual droplets with few or no interconnections, an attacking medium can leach only those droplets near the surface of the body and deep penetration resulting from chemical attack can be obviated.

In U.S. application Ser. No. 94,834, filed Dec. 3, 1970 in the names of Gerald B. Carrier and James E. Flannery, one method for securing discontinuity in the separated phase is disclosed. That application describes the addition of minor amounts of M00 and/or W0 and/ or As O to the base glass batch consisting of 70-80% SiO and 53-15% B 0 with optional additions of alkali metal and bivalent metal oxides. The preferred opal glasses contain 1-6% of alkali metal oxides, 3-4% total of the bivalent metal oxides ZnO, CaO, and MgO, and 0.2-3% total of M00 W0 and As O Electron micrograph comparisons of the internal structures of conventional borosilicate opal glasses and the opal glasses of that invention showed a significant difference in the microstructure of the precipitated phase. In the conventional opal glass, the opacifying phase appeared as a series of interconnecting, irregularly-shaped droplets scattered throughout the cross section. In contrast, the separated phase in the new glasses appeared as individual, disconnected droplets.

The mechanism through which the M00 W0 and/ or As O operate to achieve the highly discontinuous opal phase could not be explained, it being theorized that those metal oxides had some effect upon the surface tensions of the matrix glass and/or the opacifying phase which promoted the development of that phase in the form of small discontinuous droplets. Although the resulting improvement in chemical durability imparted to the opal glasses through the additions of M00 W0 and/or AS203 thereto was very real, such additions add materialy to the cost thereof and, particularly with respect to AS203, comprise a toxic hazard in the mixing and melting of the batch ingredients. Therefore, means were sought to accomplish the same function but without the use of these metal oxides.

Further, the opal products of that invention exhibited a soft white appearance whereas, for such applications as dinnerware and culinary ware, a bright white body is seemingly highly desirable to the user.

Therefore, the principal object of the instant invention is to produce an opal borosilicate glass exhibiting a very bright white appearance with improved chemical durability, the improved chemical durability being due to the opacifying phase being present in the form of very small, discontinuous, spherically-shaped droplets, wherein the glass batch consists essentially only of Li O, B ZnO, and SiO Other objects will become apparent from the following description and the appended electron micrographs wherein:

FIG. 1 is a replica electron micrograph illustrating the cross-sectional microstructure of a conventional opal borosilicate glass;

FIG. 2 is a replica electron micrograph depicting the cross-sectional microstructure of an opal borosilicate glass containing M00 made in accordance with the process described in application Ser. No. 94,834;

FIGS. 3-6 are replica electron micrographs demonstrating the cross-sectional microstructure of opal borosilicate glasses having compositions within the parameters of the instant invention; and

FIGS. 7-11 are replica electron micrographs illustrattogether, will be converted to the desired oxide in the proper proportions. The batch ingredients in Table I were melted in closed platinum crucibles at about l450- 1600 C. for about 16 hours. The melt was poured onto a steel plate to form a patty about in diameter and in thickness. No fining agent was employed but, where desired, conventional fining agents can be utilized. The patty was immediately transferred to an annealer operating at about 650 C. Although the opal phase will generally strike in spontaneously as the melt is cooled to an amorphous solid, a denser opacity can be secured by heat treating the glass body at about 700-800 C. for about 5 minutes to one hour. Inasmuch as this opacifying process is both time and temperature dependent, longer exposure times will be required at lower temperatures than at higher temperatures to achieve the same degree of opacity. In any event, nevertheless, the same microstructure of phase separation is observed in the secondarily heat treated articles as is present in the spontaneously opacified articles.

Table I also includes measurements of various physical properties (Softening Point, Annealing Point, Strain Point, Expansion, and Density) secured on the opalized bodies; these determinations being understaken according to conventional procedures. The coefllcients of thermal expansion lO C.) were measured over the range 0- 300" C.

TABLE I S102, percent 74. 83 73. 34 75. 48 74. 9 73. 95 74. 74. 65 75. 60 73. 60 78. 60 77. 60 B203, percent 12.60 12.36 12.88 12. 7 12. 60 12.65 11.00 12.00 14.00 9. 00 9. 00 N820, percent 3.05 3.0 ZnO, percent 8. 63 8. 46 8.82 8.7 8. 60 8. 0 8. 50 8. 50 8. 50 8. 50 T102, percent- 0. 76 0. 75 0. 78 0.80 0. 0 0.80 0. 80 0.80 0.80 A1203, percent 0.05 0. 05 0.05 0.05 0. 0. 05 0.05 0.05 0.05 Zl02, percent O. 08 2. 10 0. 05 0. 05 0. 05 0. 05 M003, percent 1. 96 L120, percent 1.99 1. 2 1.90 3.00 3.00 3.00 4. 00 K20, percent 2. 3 Softening point, C 894 980 901 +970 978 974 Annealing point, C 622 659 625 636 703 678 709 Strain point, C 592 586 562 588 658 617 662 Expansion 28. 1 29. 2 28.0 26.0 36. 8 31.5 32. 4 31. 8 36. 9 Density 2. 83 2. 311 2.331 2. 337 2. 331 2. 370 2.331 2. 324 2. 343 2. 358

ing the cross-sectional microstructure of opal borosilicate glasses having compositions approaching, but outside of, the parameters required in the present invention.

We have discovered that opal borosilicate glass articles exhibiting a very bright white appearance and greatly improved chemical durability, particularly with respect to resistance to detergent attack, can be secured through the spontaneous opalization and/or the subsequent heat treatment of glass bodies consisting essentially, by weight on the oxide basis, of 0.5-2.5% L120, 7l0% ZnO, 11-14% B 0 and 71-76% SiO Electron microscopy studies of the interior of these articles have shown the opacifying phase to be present as separate droplets, essentially spherical in shape, with little or no interconnection. That these ranges of components are critical to the operability of the invention is visually confirmed in a comparison of FIGS. 3-6 With FIGS. 7-11 as well as in the results of the detergent solubility test tabulated hereinafter. It is apparently possible to produce durable borosilicate phase-separated opal glasses, wherein the opacifying material is present as a discontinuous phase, in compositions falling within the above-defined, straitly limited ranges without the addition of M00 W0 and AS203 to affect the interfacial tension between the glassy matrix and the opacifying phase. These glasses are suitable for many applications, e.g., tableware and ovenware, because they combine good chemical durability with good thermal shock resistance and uniform opacity.

Table I records several examples of glasses falling within and without the compositional parameters of the instant invention in weight percent on the oxide basis. The batch ingredients may comprise any materials, either the oxides or other compounds which, on being melted To determine the effect of composition changes upon the microstructure of the opalized bodies, replica electron micrographs were made of the cross section of each example. Hence, FIGS. 1-11 are electron micrographs of Examples 1-11, respectively. (The white bar at the base of each photograph represents one micron.) A study of these photographs clearly illustrates the substantial efiect which minor compositional changes have upon the configuration of the separated opal phase. Thus, the opal phase in FIG. 1, a conventional borosilicate opal glass of commerce, assumes a continuous type of structure, i.e., the droplets are interconnected. In contrast to that configuration, the articles shown in FIGS. 2-6 contain the precipitated phase as very small, spherically-shaped droplets. Example 2 includes the surface tension agent M00 required in the above-discussed patent application, whereas Examples 3-6 fall within the compositional limitations of the instant invention. Thus, Examples 3-6 clearly indicate that the presence of such surface tension agents is not required to achieve the development of the opal phase in discontinuous droplets (less than 0.5 micron in diameter) where the composition of the glass is included within the narrow parameters of the present invention. FIGS. 7-11 dramatically demonstrate the extreme criticality of the outlined compositional variables of the instant invention. Hence, even very minor excursions outside of the reported U 0 and B 0 ranges produce the opal phase as interconnected rather than discontinuous droplets.

The chemical durability of each example recited in Table I with regard to its resistance to detergent attack was measured by subjecting the glasses to strong detergent solutions at elevated temperatures in accordance with well-known procedures. The specific test employed in volved preparing a water solution containing 0.3% by weight of Super Soilax Brand detergent and immersing the glass samples to be tested therein while the solution is maintained at 95 C. At two hour intervals, glass samples are removed from the solution, coated with DY- CHEK dye, a penetrating organic liquid, and permitted to stand for five minutes to allow the dye to migrate into the body. Thereafter, the dye is removed, the stain resistance of the glass being graded in accordance with the difliculty of this removal. Hence, if after standing the dye can be removed completely with a dry cloth, the glass is categorized AA. If removable with a water soaked cloth, the glass is classed A. Where a cloth soaked in detergent solution will remove the stain, the glass is graded B. If the stain can only be removed by rubbing with a cleansing powder, the glass is given a C rating and, where unremovable, the glass is classed F.

Table 11 illustrates the correlation between chemical durability and the presence of the separated phase as very small, discontinuous droplets. Thus, Examples 2-6 exhibit at least a class A stain after 16 hours of immersion in the detergent solution whereas Examples 1 and 7-11 fail after 2-8 hours. Here, again, is confirmation of the compositional requirement set out to assure the operability of the instant invention. Furthermore, Examples 3-6 demonstrate chemical durability paralleling that exhibited by Example 2 containing M This factor unequivocally shows that within the stringent compositional limitations imposed here, a product can be manufactured having detergent durability essentially on a par with the products of the above-described application containing M00 W0 and AS203.

TABLE II 16 hours 24hours Example 4h0urs Shours compositions to aid melting and forming, to improve chemical durability, to inhibit unwanted devitrification, or to modify some other physical property but the total of all such inclusions must not exceed about 5% by weight, since a fine balance is drawn between the various components to insure the development of a discontinuous opal phase in very small spherically-shaped droplets.

Furthermore, the presence of Na O in the glass has been found to be particularly detrimental to the durability thereof. Therefore, Na O is preferably absent from the composition although up to about 0.5% by weight can be tolerated. K 0 appears to aid durability but its inclusion in amounts greater than about 3% by weight tends to inhibit opalization, requiring extended secondary heat treatment of the glass to secure a dense opacity. The presence of A1 0 improves durability but quantities in excess of about 1.5% appear to have an adverse effect upon opalization.

Examples 4 and 5, exhibiting the best resistance to detergent, reflect the preferred composition ranges of the invention, viz, 1-2% Li O, 89% ZnO, 12-13% B 0 and 73.5-% SiO We claim:

1. A borosilicate opal glass exhibiting a very bright white appearance with excellent resistance to detergents wherein the opal phase is present as discontinuous, spherically-shaped droplets, said glass consisting essentially by weight on the oxide basis, of about 0.5-2.5 Li O, 7-10% ZnO, 11-14% B 0 and 71-76% SiO the total of Li O, ZnO, B 0 and SiO constituting at least by weight of the composition, and 0-0.5 Na O, 03% K 0, and 01.5% A1 0 2. A borosilicate opal glass according to claim 1 wherein said glass consists essentially, by weight on the oxide basis, of about 1-2% Li O, 8-9% ZnO, 12-13% B 0 and 73.5-75% SiO References Cited UNITED STATES PATENTS 1,652,259 112/ 1927 Taylor 106---54 3,275,492 9/1966 Herbert 106-54 3,413,133 11/1968 Stalego 106-54 1,192,474 1916 Taylor 106-54 OTHER REFERENCES Volf, M. 13., Technical Glasses; London, 1961, pp. 28-30.

Ingerson, E., et al.; The Systems K O-ZnO-SiO ZnO-B O SiO and Zn SiO Zn GeO in Amer. .lourn. Sci., 246, 1948, pp. 31-40.

HELEN M. MCCARTHY, Primary Examiner

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