I
times faster than that of the adjacent unexposed glass. Pieces can be produced by this process which are so intricate that their manufacture by mechanical means would be impossible. Kew glasses are being developed that will transmit or retard radiations of specific frequencies. Glasses of improved faculties for the absorption of infrared and ultraviolet rays have been produced as well as glasses capable of absorbing slow neutrons. Glass is in use for automobile windshields covered with a transparent electric current-conducting film that will generate enough heat to deice itself. A glass that shuts out intense heat has been developed by permanently bonding a thin transparent film to the outer side of glass panels. The glasses used are the borosilicate type in which the coatings are similar to those used for electrical conductivity.
With the coated slide toward the source of heat, 60% of the infrared rays are reflected. Glass is being fabricated in fibers 2 or 3 microns in diameter and in 1600-pound windows for supersonic wind tunnels. There is apparently no limit to the horizons for the uses of glass. The industry is in strong capable hands and expansion will undoubtedly continue. LITERATURE CITED
(1) Simpson, H. E., J . Can. Cerum. SOC., 21, 52-7 (1953). RECEIVED for review March 11, 1953.
ACCEPTED
July 7, 1963
Recent Developments in Radiation-Sensitive Glasses S. D. STOOKEY Corning Glass Works, Corning, N. Y .
Photography in glass is growing in new applications, photosensitive compositions, and processes. Brief descriptions are given of the nature and present applications of photosensitive metal-colored and opal glasses, a glass for photoengraving and chemical machining, and a gamma-ray dosimeter glass. A new process, described here for the first time, converts a photosensitive glass to a high-strength crystalline material. Another new process reproduces photographic images in ordinary window glass, providing permanence and dimensional stability.
HE announcement of the first practical photosensitive glass
Tis,in 1947 has been followed by development of other types
of photosensitive glass, new related products, and applications. Some of these have been logical developments from the same research, and others, such as gamma-ray dosimeters developed by Schulman, Weyl et al. ( 1 , 5 ) , have resulted in answer to the requirements of work with atomic energy. This paper reviews the present status of the previously reported glasses and describes new developments.
tion is nucleated by submicroscopic silver particles formed photographically within the glass. Commercial uses of photosensitive opal are based on its ability to control and diffuse light, the beauty and versatility of the three-dimensional photographic design, and durability of the material. It has been used in architecture (decorative lightdiffusing windows in the United Nations Assembly Building; interior and exterior wall facings), in lighting, and in appliances of various kinds in the form of nonglare lighting units, name plates, and clock dials.
PHOTOSENSITIVE METAL-COLORED CLEAR GLASS
Two glasses of this type (Corning Code 8600) are in commercial production as polished plate. One, in which the photographic image may be colored blue, purple, or ruby-red, contains gold as the photosensitive coloring agent. This glass is designated photosensitive “red-blue.” The other, designated as “sepia,” develops a red-brown image consisting of gold and palladium. The photograph is transparent, three-dimensional, and as permanent as the glass itself. The chief commercial use is in reproduction of portrait and scenic photographs, but these glasses are also being employed in decorative and commemorative windows and illuminated photomurals. PHOTOSENSITIVE OPAL
Photosensitive opal glass (Corning Code 8601) develops a threedimensional white translucent image, in an otherwise clear matrix. It is manufactured as flat rolled or as polished plate. The image consists of microscopic light-diffusing crystale whose precipita-
174
CHEMICALLY MACHINABLE PHOTOSENSITIVE GLASS
A photosensitive opal glass (Corning Code 8603) in which the three-dimensional image is highly soluble in dilute hydrofluoric acid was first described a t the XIIth International Congress of Pure and Applied Chemistry (3). This glass can be cut, drilled, photoengraved, or sculptured by forming the photographic image and immersing the glass in dilute hydrofluoric acid. This new glass appears to h a d an important future in the photoengraving field, and even to broaden the scope of photoengraving, because-in contrast to the homogeneous metals now employed-the image can be etched up to 50 times faster than the unexposed glass. This makes possible, by a relatively simple process adapted to mass production, more accurate reproduction and deeper cuts than can be obtained with metals. It now appears that this process may have broad applications in the printing industry, as halftone plates, engraving dies, and master plates for electrotypes, rubber printing, and newspaper printing.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 46, No. 1
-Ceramics
and Glass-
flexural strength, toughness. hardness, thermal shock endurance, temperature of deformation, and electrical resistivity. The conversion process can be applied either to the glass formed by conventional methods, or to an article which has been “chemically machined.” The crystalline product is essentially lithium silicate, probably bonded with c i few per cent of potassium oxide-alumina-silica glass. The microstructure consists mostly of lathlike crystals in random orientation. CONVERSION PROCEDCRE.Exposure to ultraviolet light in the 300- to 350-mp band ( 2 ) . Development by heat treatment (3). Continuation of heat treatment a t higher temperature until crystallization process is completed. One of the important factors making the process possible is the fact that the 600” development forms a crystalline skeleton which is sufficiently rigid to permit heating to h i g h e r t e m p e r a t u r e s without deformation, Kormally, the glass n-ould soften a t 637” C. Its high strength and toughness compared to ceramic m a t e r i a l s formed by conventional methods are believed to be due partly to its Perforated Glass in Honeycomb Structure, Made by Chemical freedom from internal flaws and voids, partly Machining to the fine-grained interlaced lathlike crystalline structure, and partly to the inherent Some experimental uses of this glass have been given ( 3 ) . strength of the lithium dicate crystals. Its conversion into a high-strength crystalline material is described below. REPRODUCING PHOTOGR4PHS IN PLATE OR WINDOW GLASS GAMMA-RAY DOSIVETER GLASS
Dosimeters, capable of measuring total gamma-ray dosage from very low levels up through the lethal range, are now in volume production for the armed forces. These are made from a potassium, aluminum, phosphorus, silver, barium oxide glass
A process has been developed by which a photographic image is produced within the surface of a glass article, by transfer of silver from a photographic emulsion. The image may be black and opaque, or transparent bron-n or j*ellow.
(1,6).
Exposure to gamma-rays converts this glass to a phosphor.
If, after such irradiation, the glass is exposed to ultraviolet light, it emits visible light whose intensity is proportional to the gammaray dosage. The fluorescence is evidently due to neutral silver atoms formed b y reduction of silver ions during gamma-ray exposure. CONVERSIONOF GLASS TO HIGH-STRESGTHCRYSTALLIYE STRUCTURE.The photosensitive glass has other valuable and unusual properties in addition to its preferential solubility. It has now been found that an article of this glass can be transformed, without distortion (except for a 3% volume shrinkage), into an almost completely crystalline material which is nonporous, very fine-grained, and superior to the original glass in
TABLEI. COMPARATIVE
OF
PROPERTIES
GLASS 8603
ASD
CRYSTALLIXE PRODUCT
Property
Flexural strength, Ib./sq. inch Abraded Polished Mob hardness Softening point, C. Linear expansion coefficient (0-30O0) Pe: 0 c. Density Electrical reeistivity (log&! , 243 C . ) Electrical power factor, % 60 cycles 1 megacycle Dielectric constant 60 cycles 1 megacycle Porosity
January 1954
Fotoform Glass 4000-6000
...
5.5 637
83.7 X IO-; 2,3352
...
23 1.5
Crystallized Form 20,000 36,000 7.5 1000 (sharp melting point) 100
x
10-7
2.8927 16.5
0.63
0.27
9.75
5.5
None
None
6.9
5.2
Gamma-Ray Dosimeter This process, called “photo-staining.” can be applied to nearly all glasses (except those which discolor when heated in reduced atmospheres) containing alkali metal ions. I t involves oxidation of the silver in the emulsion image a t elevated temperature, migration of silver ions into the glass surface in exchange for alkali metal ions, and reduction of the silver ions to metal within the glass.
INDUSTRIAL AND ENGINEERING CHEMISTRY
175
30 minutes. At this stage a "latent image" of colorless silver ions is present in the glass surface. 3. Heat the iece in reducing atmosphere-for example, a flowing stream or20 to 50% hydrogen in nitrogen-for 15 to 60 minutes a t 450' to 500' C., to reduce the silver ions to metallic silver. Clean the surface by washing.
Name Plates and Dials in Photosensitive Opal Glass
APPLICATIONS FOR PHOTO-STAIN.The photo-stain process is believed to be a practical method for photographic reproduction of two-dimensional images which are permanent, dimensionally stable, scratch-resistant, and impervious to chemical attack and heat. It is a relatively inexpensive method and when the manufacturing techniques are sufficiently perfected it is expected to be suitable for manufacture of accurate scales, engineering drawings, calibrated instrument faces, dials, reticles, and cross-hairs in transparent glass. It may be employed in making reproductions of halftone or continuous tone prints, as well as line drawings.
Designs are i n three dimensions, white translucent patterns i n clear glass. May be used with or without colored glazes
CONCLUSION
PROCEDURE. 1. Produce the photographic image in a silver halide emulsion by conventional methods. Fix and wash thoroughly. The emulsion may be applied to the glass either beforehand or after the image is developed, as stripping film is now employed in the printing industry. The emulsion must contain enough silver to prevent the image from being carried away from the glass during the heat treatment in step 2. Some emulsions which have been used successfully are Kodak 33, Kodak L-1 spectrographic emulsion, Kodalith (Eastman), and Reprolith (Ansco) stripping films. 2. Apply a thin coat of paste (24 weight % ferric sulfate plus 75 weight % yellow ochre, dispersed in an oil or a water vehicle) over the photographic emulsion and allow it to dry. (The ferric sulfate aids in oxidizing the silver during heat treatment, and the ochre aids ion exchange and prevents distortion of the silver image as the emulsion decomposes.) Heat the piece rapidly (within 10 minutes-slow heating carbonizes the gelatin and makes it difficult to fire out) to about 450" C. and hold it for
A number of new products and processes have resulted from the discovery that actinic radiation can cause photochemical reactions in glass. It seems saje to predict a useful and expanding future for photosensitive glasses and related products. Sun and Kreidl ( 4 ) have discussed coloration of glass by radiation, and provided an exhaustive bibliography. LITERATURE CITED
(1) Schulman, Ginther, and Evans,
U.S. Patent
2,524,839
(Oct. 10,
1950).
(2) Stookey, S.D., IND.ENG.CHEM., 41, 856 (1949). (3) Ibid., 45, 115 (1953). (4) Sun, K. H., and Kreidl, N. J., Glass. Ind., 33, 511 (October 1952).
(5) Weyl, Schulman, Ginther, and Evans, J. EZectrochem. Soc., 95, 70 (1949). RECEIVED for review March 23, 1953.
ACCEPTEDOctober 10, 1953.
Application of Glass Fibers in Filtration Processes CLAYTON A. SMUCKER AND WAYLAND C. MARLOW, JR. Owens-Corning Fiberglas Corp., Newark, Ohio
Glass fibers have properties that are significant in filtration applications. Great versatility of products is obtained through combination of various fiber sizes, structures, and bonding materials. Further investigation of glass fiber products is needed for the solution of specific filtration problems.
T
HE ancient art of glass making was known to the Egyptians and has been practiced as a craft or an industry for almost 5000 years. The fact that glass can be made in fiber form has also been known for a long time, but such fibers were first produced and sold on a broad commercial scale less than 20 years ago. In the few years since its appearance on the commercial market, glass fiber has been produced in a variety of forms for many unrelated applications, and its production now assumes the status of a major business. The fundamental properties of glass fiber led t o the firet commercial application in the field of filtration, but the present rate of consumption for this use represents only a small portion of its ultimate potential. 176
BASIC PROPERTIES OF GLASS FIBERS
Glass fibers possess a combination of unique properties which distinguish them from both natural and synthetic organic materials. Glass will not burn. Glass is heat-resistant. The degree of heat resistance is a function of composition and ranges from 1000' to 1800' F. The physical properties of glass are not adversely affected by extremely low temperatures. Glass is resistant to attack by chemical agents. Although tremendously large surfaces are exposed when glass is produced in fibers of small diameter, it is nevertheless very resistant to most
INDUSTRIAL AND ENGINEERING CHEMISTRY
VoI. 46, No. 1
