[1]United States Patent Office 3@460@967 P a t e n t e d A u g . 1 2 , 1 9 6 9 2 lized layer of glass containing an in situ-formed phosphor, 3,460,967 can be materially increased by contacting the said glass SUP,FACE TREATMENT OF GLASSES wit h an alkaline solution at a temperature and for a petiod Richard W. Pettierew, Perrysburg, Ohio, assignor to of time sufficient to increase its brightness, specifically Owens-IlUnois, Inc., a corporation of Ohio cat hodolumineseent brightness, after the excess alkaline No Drawing. Filed Oct. 23, 1965, Ser. No. 504,201 5 Int. Cl. C03c 17120; C09k 1136 sol ution has been removed therefrom; and removing the U.S. Cl. 117-62 9 Claims excess alkaline solution form the treated glass, e.g., by wash ing. The fluorescent screens conventionally employed in ABSTRACT OF THE DISCLOSURE io electron-discharge tubes such as cathode-ray tubes and the like utilize solid state-sintered phosphors. The probProcess for increasing the cathodc>lumineseent brightness of a - lass screen having a surface crystallized layer of -lass containing an in situformed phosphor, includincontacting the glass with an alkaline solution such as al- 15 kali metal hydroxide at a temperature and for a peliod of time sufficient to increase the cathodolumineseent brightness after the excess alkaline solution has been removed; and then removin.- excess alkaline solution. 20 This invention relates broadly to the surface treatment of -lasses and, more particularly, to a method of increasin@ the cathodoluminescent bri.-htness, under electron bombardment, of a glass screen having a phosphor in its 25 surface. Still more particularly the invention is concerned with a method of treating, for the above-stated purpose, a glass screen having or containing a surfacecrystallized layer of glass holding an in situ-formed phosphor material. 3 0 It was su-gested prior to the present invention (see Jones U.S. Patent 2,523,026) that the maintenance of fluorescent lamps containing an alumina-based phosphor as a coating on the surface of the lamp be improved by treating the phosphor with water or with hydrochloric 3 5 or benzoic acids in order to remove most of the lithia impurity in the phosphor. The patentee states that "the fluorescent brightness is not visibly reduced" by the treatment. There is no disclosure of usin.- alkaline solutions for the intended purpose. 4 0 In U.S. Patent 3,060,129 Hockstra et al. disclosed that the light output of luminescent alkaline-earth halophosphates activated with trival@-nt antimony or with trivalent antimony and bivalent manganese can be increased by washing the phosphor with an aqueous solution of an in- 45 organic reducing acid havin.a a pH of 0.9-2.0, e.g., phosphorous or sulfurous acid, removin.- particles having a grain size smaller than approximately two microns, and then either (a) rinsin@ with water to remove the reducinacid or (b) rinsing with hydrochloric acid to remove 5 0 any calcium sulfite formed during washing with the reducing acid and fnally with water to remove the hydrochloric acid. Colborne in U.S. Patent 2,325,110 and Froelich et al. in U.S. Patent 2,575,755 disclose various techniques for 55 increasing the luminosity and stability of phosphors. Thus, Colborne suggests that the operation of a cathode-ray tube having a luminescent screen be improved by incorporating in the screen mixture or by applying to the screen compound of an alkali reducible to an oxide thereof, 60 hydroxide, halide, nitrate or organic salt of an alkali, and baking the tube to deposit a layer of an oxide of the alkali from the said compoudd upon the luminescent screen. Froelich et al. incorporate with the phosphorformin.- ingredients, prior to firing, a hydroxide of an 65 alkali metal or a salt thereof such as the phosphate, sulfate, nitrate, carbonate, borate and chloride. The present invention is based on my discovery that the bri.-htness of a fluorescent screen in an electrondischar.ae device such as a cathode-ray tube, more particu- 70 larly the cathodoluminescent brightness, under electron bombardment, of a glass screen having a stirfacecrystallems involved in securing optimum brightness and stability from such screens are exemplified in the aforemenmentioned prior-art patents. However, in the case of fluorescent screens of the kind involved in this invention, i.e., glass screens having a surfacecrystallized layer of glass containin.- an in situ-formed phosphor, e.g., a zinc silicate or zinc silicate- type phosphor, or such a silicate activated with bivalent manganese, tetravalent titanium or tetravalent uranium, the problems are entirely different. This is especially true from the standpoint of securing optimum cathodoluminescent brightness from the initial fluorescent screen. One reason for the difference in the problems encountered in the manufacture of the prior-art fluorescent screens and the present screens is becatise the glass holds the in situ-formed crystalline phosphor in a glassy matrix, thereby impartin.- physical strength and mechanical ruggedness to the layer of phosphor material contained therein. However, this -,Iassy matrix and/or a thin layer of glass formed immediately below the phospbor and over the top of the underlyin.- crystals may be responsible for the fact that often one does not obtain a fluorescent screen having as high an initial brightness as may be desired for certain commercial applications. One method of increasing this initial brightness is to apply a phosphorforming film, followed by heat treatment, over the surface-crystallized glass containing the in situ-formed phosphor. However, in many cases the resulting improved brightness is still inadequate for many applications. The present invention is one solution to the problem of achieving a further improvement in brightness from both uncoated (i.e., uncoated with an applied phosphor film) fluorescent glass screens of the kind with wliich this invention is concerned and such screens that have been coated with a phosphor film as briefly described in the preceding paragraph and more fully hereafier. 'nis problem was not encountered by those prior-art investigators who were concerned with fluorescent screens comprised of solid state-sintered phosphors, and a teachiiig with regard to the one is in no sense of the word a teachin.- with respect to the other, especially since the phosphors are in an entirely different environment. I am unable to explain with certainty why the treatment of a glass article, such as a screen or faceplate, of the kind with which this invention is concemed with an alkaline solution results in an increase in its cathodoluminescent brightness, especially in view of the fact that art acid-etchin- treatment was found to result in adimiiiution of catbodoluminescent brightness. However, the following comments and observations may be helpful to those skilled in the art in advancing a theoretical explanation. In connection with the inventigations leading to the present invention and the inventions disclosed and claimed in the copending applications mentioned later herein, an extensive study was made of the zinc silicate glass system. During the course of this study it was surprisingly found that when glasses in this system, e.g., potassiumzinc silicate and calci um-aluminum-zinc silicate each containing about 0.5 percent MnO,, were either lightly abraded or etched with an acid prior to a brightness
[2]3 measurement, then thei abraded or the etched areas showed a cathodoluminescent brightness only about onefifth that of the surrounding undistrubed areas, sometimes with an accompanying change of color. This suggested that (a) a thin-film phosphor was present on the surface and was removed by abrading or by acid-etchin.the glass surface and/or (b) the crystal phosphor in the glass was poisoned by impuriiies that were introduced by the abrading or acid-etching treatments. Specimens of a calcium-aluminum-zine silicate surfa ce-crystallizable glass were spraycoated with a solution of zinc acetate in methanol and then subjected to a cont-rolled heat treatment to produce a surface-crystallized glass. The specimens, prepared to exactly the right shape and size for an electron-diffraction sample holder, were then subjected to electron-diffraction analysis. Very clear ring patterns were produced from what appeared to be a uniform polycrystalline layer on the surface. An analysis of these data produced an exact niatch with the a spacings and intensities of a manganese oxide (Mn3O4) spinel. This cubic spinel pattern was @eneral with all specimens examined, except for a few areas that showed some linescorresponding to ZnO in addition to the spinel. No similarity was found between these patterns and the published patterns of any zinc silicate. Since the presence of zinc silicate was positively identified by X-ray diffraction analysis and the luminescent properties of the specimens of calcium-aluminum-zine silicate glasses containing 0.5 MnO seemed to be the same as man.-anese-activated zinc silicate, the weight of the evidence supported the conclusion that there must be a thin layer of some contamination on the surface of the specimens, possibly excess manganese oxide and zinc oxide. The subsequent discovery that soaking the samples in 3-normal NAOH, followed by washing, greatly improved the cathodoluminescent bri.- htness further supported this conclusion. However, acid-etching or abrading the samples after they bad been immersed in the sodium hydroxide solution still completely destroyed the cathodoluminescence of the samples, thus raising considerable doubt about the role of the aforementioned thin layer. It was also found that, after treatin,@ with an alkaline solution (specifically an aqiueous solution of sodium hydroxide), the calcium-aluminum-zinc silicate glass containing MnO gave a much sharper cubic spinel electrondiffraction pattern than before leacbing. However, samples of the same glass composition containing no MnO, which had been sprayed with a niethanol solution of zinc acetate and then subjected to a controlled heattreatment to effect surface-crystallization, also gave a sharp spinel diffraction pattern. Since there was no manganese in the glass composition and apparently no manganese was added during the spr4ying proce;ss, this meant that the spinel phase that formed on the surface either was not a manganese compound or that considerable manganese was picked up during the heat treatment. Subsequent tests in cleanatmosphere furnaces also developed the spinel phase in the apparent absence of manganese. Hence it was concluded that the crystal phase formed on the surface either was not a manganese compound or that an appreciable amount of manganese was picked up by the surface by some obscure means not understood. Surface-crystallized glass specimens that were acidetched or abraded prior to electron-diferaction analysis showed no crystallinity, but instead a diffuse amorphous scattering. Further abrading, so that the crystals grown in the glass were exposed, gave (i.e., with the zinc silicate studied) a slight diffraction pattern of zinc silicate in addition to the diffuse background scattering. A distinct zinc silicate diffraction pattern could be obtained only when sufficient inaterial had been ground away so that the subcrystals became exposed. Hence it was concluded that the cathodoluminescent phosphor not only was con3,460,967 4 centrated in a thin film on the surface but also that a thin layer of glass was formed irnmediately below the phosphor and over the top of the underlying crystals. Perhaps, then, the alkaline solution that is applied to the surface-crystallized glass in practicing this invention coacts, in a manner which is not understood, with both the -Iassy matrix and the phosphor material. Whatever the theoretical explanation may be, the fact rer@iains that in practicing the present invention a -lass 10 body havin.- a surface-crystallized layer of glass containifig or holding an in situfornied phosphor is treated with an alkaline solution whereby the said layer is modified in such a way that increased cathodoluminescent brightness results after the excess alkaline solution has been removed. 15 Particularly us-.ful as the alkaline-treating agents are the hydroxides of the alkqli metals (sodium, potassium, lithium, cesium and rubidiu@m), and ammonium hydroxide. Other examples of strong bases that may be used are solvent solutions of the alkali-metal alkoxides, aryls and 2o amides, e.g., sodium and potassium methoxides, ethoxides, n-p'ropoxides, isopropoxides and tert.-butoxides, sodium and potassium amides, phenyllithium, indenyllithium, lithium ethylphenylamide, lithium diphenylamide; and the salts, with alkali-forming metals (Group I-A and II-A 25 metals) of alkanes, aralkanes, nitriles, amines, etc., dianiline calcium, ethyl sodium, etc. Such strong bases have been described as being salts, with an alkali-forming metal, of an acid having a pKa of from 15 to 75. Other strong bases that may be employed include solvent solutions of 30 the strongly basic quaternary ammonium hydroxides, e.g., tetr,@methyl ammonium hydroxide, tetraethanol ammonium hydroxide, benzyl trimethyl ammonium hydroxide and others well known to those skilled in the art, and especially tho@e quaternary ammonium hydroxides that are commer35 cially available. One may employ water solutions of the forbgoing strong bases that are at least partly soluble in wgier and decompose only slightly (if at all) in water. Solutions in an or,@anic solvent, e.g., a lower alkanol such as methanol, ethanol, etc., may be used, as desired or as 40 m@iy be required. Preferably the alkaline solution employed is one havin.- a basicity at least the equivalent of that of a 1-normal aqueous solution of sodium hydroxide. Among the preferred alkaline treating solutions tised iii practicing this invention may be mentioned solutions, 45 especially aqueous solutions, of the alkali-metal hydroxid&@ and of ammonium hydroxide. Thus one may use aqueous solutions of sodium hydroxide having a normality b6tween 3 and 9, more partictilarly between about 4 and I about 8, and specifically about 6. 50 Any suitable ineans may be employed in contacting the glass to be treated with the alkaline-treating soltuion. Contacting can be effected by immersing the glass in the bath of the treating solution, which normally is preferred; or by spraying, brushing, padding or any of the other known 55 m4bans for applying liquids to a substrate. This step may b@ carried out continuously, semi-continuously or by batch operations. The application temperature, that is, the temperature of the treatin,@ solution at the time the glass is contacted 60 therewith (as by immcrsion, for example) is generally within th-. range of from about 1 IO' F. up to the boiling point of the treating solution at atmospheric pressure. For instance, the temperature of the solution while the -lass is immersed therein or otherwise contacted with the solu65 tion may be within the range of frorn about 120' F. to about 200' F., still more particularly from about 150' F. to about 17G' F., and specifically about 160' F. The time of the treatment may range from I second or less to one 70 hour or more, more particularly from 10 to 15 seconds to 10 to 15 minutes, the shorter periods of time being used at the higher temperatures. In other words, the duration of the treatment varies, in most cases, inversely with the application temperature of the treating SOILItion. If de75 sired, the glass to be treated may be preheated, e.g., up to
[3]3,460,967 5 6 the temperature of the treatin@@ solution, before the solun escent brightness of the flnal product, comprises those tion is applied thereto. c onsisting essentially of the following constituents calGood results have been obtained with particular glasses c ulated in weight percent on the oxide basis: by immersing the glass to be treated in an aqueous solution Si O2 ------------------------------------- 45-60 of sodium hydroxide having a norn-lality of about 6, the Z nO ------------------------------------- 15-45 temperattire of the said solution bein.- about 160' F. while 5 K 20 -------------------------------------- 0-25 the glass was immersed therein, and the time of the treatN a2O ------------------------------------- 0-25 ment rangin- from about 3 minutes to about 6 minutes. Thereafter t@he excess sodium hydroxide was removed w herein the total K20+Na2O is at least 10 weight perfrom the treated glass by water-washing, specifically with c ent but less than 25 wei,-ht percent. pure (i.e., distilled) water. Deionized water can be used 10 Within the scope of the above broad class of glasses set instead of distilled water, if desired. fo rth in the precedina paragraph, and which may be more To the best of my knowledge and belief, any ass b roadly described as bein@ zinc silicate glasses, are those article or body adapted for use as a fluorescent screen and - lasses consisting essentially of the following constituents having a surface-crystallized layer of glass holding (for 15 c alculated in weight percent on the oxide basis: instance, in a -Iassy matrix) and insitu-formed phospbor si o9 ------------------------------------- 46-51 material can have its cathodoluminescent bri.-htness inZ nO ------------------------------------- 28-37 creased by treatin,- the -lass with an alkaline solution n N a2O ------------------------------------ 2- 12 accordance with the present invention. Illustrative exK 20 ------------------------------------- 5- 12 amples of such glasses are those produced by the con20 C aO ------------------------------------- 0- 3 trolled heat treatment of a surface-crystallizable (includA 1203 ------------------------------------ 0- 4 ing potentially surface-crystallizable) glass consistina. esB aO ------------------------------------- 0- 2 sentially potentially surface-crystallizable) -lass consisting S b2O3 ------------------------------------ 0- 0.2 essentially of the followin- constituents calculated in MnO ------------------------------------- 0- 0.5 weight percent on the oxide basis: 25 w herei-i the total K20+Na2O is at least 10 weight perSiO2 ------------------------------------- 40- 60 cent but not more than 17 weight percent. A1203 ------------------------------------ 5- 15 More specific examples of zinc silicate glass composiZnO ------------------------------------- 15- 35 tion.s that can be surface-crystallized (especially after having been surface-roughened) by subjecting the glass CaO ------------------------------------- 0- 24 30 to a controlled heat treatment, and the surface-crystalBaO ------------------------------------- 0- 20 lized -lass containing in situ-formed phosphor material in SrO -------------------------------------- 0- 10 its surface layer then treated in accordance with this inM@ @o ---------------------- --------------- 0- 10 vention to increase its cathodoluminescent brightness, are Na2O ---------------------- -------------- 0-8 those containin.- or consisting essentially of the following K20 ---------------------- --------------- 0-8 35 oxides in wei@ht percent (i.e., constituents calculated in Li,O ---------------------- --------------- 0- 2 weight percent on the oxide basis): Glass Sio2 ZnO Na2O K20 MnO A1203 cao mgo BaO Sb2O3 * --------- 48.0 35. 0 12.0 5.0 0.5 -------------------------------------------------- * --------- 50.5 28. 8 2. 0 8.0 0.5 4. 0 2.75 1.2 2. 75 ---------- * --------- 46. 0 37.0 7. 5 7. 5 0.5 --------------------------------------- 2. 0 * --------- 50.0 35.0 3. 0 12.0 0.5 -------------------------------------------------- wherein the total Na2O+K20+Li2O is no more than 8 45 Other examples of zinc silicate .-lasses which, in their weight percent, the total CaO+BaO+SrO+MgO is s urface-crystallized state, can be treated in accordance within the ran.@e of from 6 to 36 weight percent and, w ith this invention to improve their cathodoluminescent when the total Na2O+K20+Li2O is zero, then the total b rightness are given in my copendin.- application Ser. No. CaO+BaO+SrO is at least 6 wei.-ht percent. 4 86,197, filed Sept. 9, 1965, assi.-ned to the same assignee A more specific example of a glass within the fore.-o50 a s the present invention, and which by this cross-referin.- ran,-es of approximate proportions is as follows: e nce is made a part of the disclosure of the instant apGlass composition A: pl ication. sio - ------------------- ---------------- 50.8 A nother group of in situ surfa ce-crystallizable and A1203 ------------------ ---------------- 8.2 catho dolumin-,s,-ent, in situ surface-crystallized (surface ZnO ------------------ ------------------ 22.0 55 semic rystallized) glass compositions or bodies which can CaO ---- -- 18.0 be iised as hereinbefore described in carrying the present SrO ------------------------------------ 0.5 invention into effect cornprises those consistin,@ essentialLi2O ----------------------------------- 0.5 ly of the followin.@ oxides in weight percent: MnO ----------------------------------- 0.5 Tn the above composition the MnO activator is 0.5% by 60 SiO 2 ------------ -------------------------- 45-65 weight of the total of the other components of the glass. mgo ------------ ------------------------- 10-20 Numero us examples of other surfacecrystallizable Zn O ------------ -------------------------- 0-30 glasses, the constituents of which are within the broad Na2 O ------------ ------------------------- 0-17 ran-es set forth in the second paragraph - immediately preK20 ------------ -------------------------- 0-20 0-3 cedin,, are given in Table I and elsewhere in my copend6,5 Li2 O ------------ -------------------------- ing application Ser. No. 311,639, filed Sept. 26, 1963, now Ca O ------------ -------------------------- 0-10 abdndon ed and assigned to the same assignee as the presTiO 2 ------------ ------------------------- O@5 ent invention. Such glasses may be termed zincaluminum ZrO 2 ------------ ------------------------- 0-5 silicate glasses. Mn O ------------ ------------------------- 0-2 Another class of surface-crystallizable (including po70 CU 20 ------------ ------------------------- 0-2 tentially surface-crystallizable) glass compositions that Cu O ------------ -------------------------- 0-2 can be surface-crystallized (especially after having been Sb2 O3 ------------ ------------------------- 0-2 surfaceroughened) by means of a controlled beat treatment, and then treated with an alkaline solution in ac- and wberein the amount of Na2O+K20+Li2O is at least cordance with this irivention to increase the cathodolumi- 75 10 wei.-ht peicent.
[4]3,460,967 7 The surface-crystallizable glasses broadly described in the preceding paragraph yield cathodoluminescent (including potentially cathodoluminescent) glass bodies or articles having a crystalline-containin,-, more particularly a magnesium silicate-type, crystalline-containing, surface 5 layer formed in situ. This surface-crystallized.,@lass havin.- -an in situ-formed phosphor material held in a alassy matrix in its surface layer can be treated with an alkalinetreating agent in accordance with this invention to increase its cathodolumineseent brightness. Within this broad group of glass compositions are at least two sub-.-roups A and 10 B which, based on their cathodoluminescent and other charatceristics, are not the full equivalent of each other. SUB-GROUP A 1,5 The glass compositions in this sub--roup consist essentially of the following oxides in wei.-ht percent: SiO2 -------------------------------------- 45-50 mgo ------ ------------------------------- 10- 15 Ca O -------------------------------------- 15- 35 ZnO ------ -------------------------------- 25- 30 20 B,o.. ............................................. 65-85 Na2O ------ ------------------------------- 12- 17 SiO 2 -------------------------------------- 0-10 TiO - ------------------------------------- 0- 5 A]2 03 ------------------------------------- (-10 ZrO2 ------ ------------------------------- 0- 5 Na2 O ------------------------------------- 0-10 MnO ------ ------------------------------- 0- 2 Mn O ------------------------------------- 0-2 CU20 ------ ------------------------------- 0- 2 25 SM 103 ------------------------------------........ 0-2 CuO ------ -------------------------------- 0- 2 Gd2 O3 ------------------------------------ 0-2 Sb2O3 ------ ------------------------------- 0- 2 Y20 3 ------------------------------------- 0-2 SU B-GROUP B Dy2O3 ------------------------------------ 0-2 The glass compositions in this sub-group consist essen30 and wherein the total'amount of tially of the following oxides in wei.-ht percent: Na2O+K20+SiO2+A]203 sio2 -------------------------------------- 60-65 (i.e., when any or all are present) is not more than 10 MgO ------------------------------------- 10- 20 weight percent. Na2O ------------------------------------- 0-12 35 More specific examples of glass compositions within the K20 -------------------------------------- 0-20 group described in the preceding paragrapb are those Li2O -------------------------------------- 0- 3 consistin.- essentially of the following oxides in approxiCaO -------------------------------------- 0- 10 mately the specified w,-ight percentages: TiO2 ------------------------------------- 0-5 Glass composition H: ZrO2 ------ ------------------------------- 0- 5 40 Ca O 8 MnO ------ ------------------------------- 0- 2 B20 3 ------------------------------ 67 CI]20 ------ ------------------------------- 0- 2 SiO 2 ---------------------------- 5 CuO ------ -------------------------------- 0- 2 Mn O, SM203, Gd2Ol, Y203 or DY203 a 0.05-1.5 Sb2O3 ------ ------------------------------- 0-2 and wherein the amount of Na2O+K20+Li2O is at least 45 Glass composition 1: 10 Nveight percent. CaO --------------------------------- --- 15 A specific example of a surface-crystallizable glass comB203 -------------------------------- I -- so Na2O --------------------------------- position within the sc<)pe of sub-group A is a composition ---- 5 consisting essentially of the following oxides in the folMnO, SM203, Gd2O3, Y20, or Dy2O, 0.05-1.5 lowing approximate weight percentages: 50 Glass Composition J: Glass composition F: CaO --------------------------------- --- 15 SiO2 ------------------------------- 45.0 B203 ----------------- ------------------- 75 mgo ------------------------------- 15.0 sio - ------------ ------------------------ 5 ZnO ------------------------------- 25.0 55 Na2O ----------------------------------- 5 Na2O ------------------------------ 15.0 Mno, SM203, Gd2O3, Y203 or Dy2O3 --- a 0.05-1.5 Mno ------------------------------- a 0.2-1.0 Glass composition K: Preferablv ibout 0.5. CaO ------------------------- ----------- 15 When this surface-crystallizable -jass composition is subB203 ------------------------------------- 79 jected to controlled heat-treatment, there is obtained a 60 A1203 ----------------------------------- 1 cathodoluminescent, in situ surface-crystallized, - lass Na2O ----------------------------------- 5 composition which luminesces red when subjected to lowMnO, Sln2O3, Gd2O3, Y203 or Dy2O3 --- a 0.05-1.5 ivoltage electron bombardment. Preferably 0.1-1.0. A specific example of a surface-crystallizable glass composition within the scope of sub-group B is a cofnposition 65 By controlled heat treatment of the surfacecrystallizconsisting essentially of the followin.- oxides in the speciable glasses described in the two preceding paragraphs, fied approximate wei.-ht percentages: there are obtained luminescent, especially cathodolumiGlass composition G: nescent, glass bodies or structures having a crystallineSiO2 ----------------------------------- 60.0 , containing, more particularly a calcium boratetype mgo ---------------------------------- 10.0 i 0 crystalline-containing, surface layer formed in sitli; that is, a surface-crystallized layer of glass holdirig an in situK20 ----------------------------------- 20.0 formed phosphor material. CaO ----------------------------------- 10.0 Other examples of calcium borate-typp glasses which, TiO2 ---------------------------------- a 1- 3 in their surface-crystallized state, can be treated with an Preferably tbout 2.0. 75 alkaline solution in accordance with the instant invention 8 When this surface-crystallizable glass composition is subjected to controlled heattreatment, there is obtained a cathodoluminescent, in situ surface-crystallized, glass composition which luminesces blue when subjected to Iowvoltage electron bombardment. Other examples of ma,-nesium silicate or magnesiumsilicate type glasses which, in their surface-crystallized state, can be treated in accordance with the present invention to improve their cathodolumineseent brightness are -given in my copendin.- application Ser. No. 486,215, filed Sept. 9, 1965, assigned to the same assignee as the present invention, and which by this cross-reference is made a part of the disclosure of the instant application. Still another group of in situ surface-crystallizable and cathodoluminescent (includin.a potentially cathodoluminescent) surface-crystallizedglass compositions or bodies comprises those consisting essentially of the following oxides in weight percent:
[5]3,460,967 9 to increase their cathodoluminescent bri.-htness are given in my copending application Ser. No. 504,068, filed Oct. 23, 1965 concurrently herewith and assi,-ned to the same assianee as the present invention, and which by this cross-reference is made a part of the disclosure of the instant application. From the fore-.oing description of the various groups, sub-,-roups and species of surface-crystallizable @lasses that can be surface-crystallized and then treated with an alkaline solution to increase their cathodoluminescent 1 0 bri,-htness, numerous other examples of compositions of -lass articles, such as cathodoluminescent screens, containin.- or having a surf ace-crystallized layer of glass holdin@ an in situ-formed phosphor material wiR be apparent to those skilled in the art. 15 The cathodolumineseent surface-crystallized glasses that are treated in accordance with this invention include those obtained by a controlled heat treatment of a surfacecrystallizable (includin- potentially surfac e-crystallizable) glass that may have been rou.-hened on at least some of 20 the exposed surfaces thereof thereby to introduce nucleating centers that will initiate the @rowth of crystals in said exposed surfaces ivhich normally can be crystallized in situ only when a sufficient amount of added nucleating agent is present. Roughenin.a may be effected by -rindin,-, sand25 blastin@ shotblastin@ etchin-, "vapor" honin.@, or by any other S'U'Itable means' "Vapor"' honin@ is effected by spraying a slurry of finely divided abrasive particles such as silica, alumina, silicon carbide, etc., suspended or dispersed in a liouid carrier, e.@, water, upon the glass sur30 face to be rou,@hened. The aforementioned rouahenina treatment is such as will provide a frosted (including frosted-like) surface upon clear, uncolored glass that has been subjected to this treatment. VVhen such a surface is obtained li.-ht scatter35 L-i@- is effected, and the "valleys" and "rid.-es" that are produced have sharp or relatively sharp angles rather than rounded ed.-es or rounded projections and depressions. Eqi-iivalent roughening treatments may be applieci to translucent or opaque glasses. The rou.-hen;ng treat40 ment may be applied to the unannealed @lass if it is sufficiently strona to withstand handlin.- and roughening; or to the annealed glass. The glass with its roughened exposed surfaces is then subjected to a controlled heat treatment that extends 45 through its annealing temperature or ran,-e to a higher temperature approachin.- but not substantially above its Littleton softening point, e.g., temperatures rangin.@ from 1000'-1200' F. at initial heatin-, upward to a maximum of about 1900'-2000' F. or hi,-her, and heattrea'L'lng 5 0 times ran,@ina from a few seconds to 24 hours or more. Additional and more detailed information on glasses that may be subjected to the aforesaid rou,-hening treatment, the roti,-henina techniques employed, the heattreating conditions in-effecting surface-crystallization of 55 the roughened glasses, etc., are -iven in my copending application Ser. No. 486,191 filed Sept. 9, 1965, assi,-ned to the same assi,-nee as the present invention, and which by this cross-reference is made a part of the disclosure of the instant application. In this copending application 6 0 there is disclosed and claimed the method Nvhich includes the step of roughenin.a at least some of the exposed surfaces of a potentially surface-crystallizable -lass in order to introduce nucleating centers that initiate the -rowth of 65 crystals in exposed surfaces of the said glass. Reference is also made to my aforementioned copendin- application Ser. No. 486,215; 486,197 and 504,068 for, detailed information on the controlled heat treatment to which the surface-crystallizable @lasses disclosed in the 7 0 respective applications are subjected in order to effect surface-crystallization thereof and thereby obtain a cathodluminescent surface-crystallized glass that can be treated in accordance with the present invention in order to im10 The copendin- applications identified in the precedinpara-raph also give detailed information for coating the surface-crystallizable or the surface-crystallized glass with solutions of a metallic salt, e.g., zinc acetate, with or without an activator, e.g., manganous acetate, fohowed by controlled heat treatment to obtdin the desired cathodoluminescent glass. A single or a plurality of different phosphor films or layers may be applied in this way, followed by controlled heat treatment after the application of each coating. A treatment with an alkaline solution in accordance with this invention may be applied, as desired or as may be required, after each or after two or more of the aforesaid coatings have been deposited by sprayin.- or otherwise upon the glass, followed by the aforementioned heat treatment. In order that those skilled in the art may better understand how the persent invention can be carried into effect, the following examples are -iven by way of illustration and not by way of limitation. AR parts and percenta.-es are by wei.-ht unless otherwise stated. Example I A cast sample of glass composition A, about 2 inches wide and 9 inches long, is annealed by heatin- to a temperature of about 1225' F., held at that temperature for about 15 minutes, and then allowed to cool slovily to ambient temperature (about 20'-30' C.). The annealed specimen is roughened on one surface by holdholding it a.-ainst a revolvin.- cast-iron wheel over which 240-mesh grit, specifically silicon carbide, suspended in water is flowing. In roughening the exposed surface of the specimen maximum effort is made to obtain a continuous rou,-hened surface, and to secure the frosted-like appearance hereinbefore described. The extent of roughenin- is sufficient to remove all of the "as cast" surface of the glass. The thickness of the roughened glass is about 0.2 inch. A spray-coating composition is prepared by dissolving 1 gram of zinc acetate, Zn(C2H302)2-2H20, in 99 grams of methanol. The rou.-hened glass specimen is heated to abotit 300' F., and then spray-coated with the zinc acetate solution making 12 passes with a De Vilbiss spray gun (Series 502). This results in the formation of a very thin coatin@ of zinc acetate on the surface of the glass. The coated glass specimen is then heated to 1650' F., and held at that temperature for 2 hours, after which it is allowed to cool to room temperature. The heat treatment effects surface-crystallization of the -lass. X-ray examination shows the presence of crystalline, manganeseactivated zinc orthosilicate in the glass surface. The glass sample luminesces green under 2 to 5 kv. electron bombardment. The surface-crystallized sample is cut into parts, and the backside of each part is ground and polished. One part is used as a control specimen. Another part of the surface-cr37stallized sa@mple is immersed in 6-normal aqueous NAOH at 160' F. for 3 minutes, while a third part is immersed in the same solution for 6 minutes. T'he treated samples are washed with distilled water to remove the alkaline-treatin- sglution, and then dried. The results of cathodolumine'scent brightness tests in footlamberts are as follows: 2 kv. 200 ua./in.2 Control, ft.-L -------------------------------- 96 After 3 minutes in NAOH solution, ft.-L --------- 132 After 6 minutes in NAOH solution, ft.-L --------- 137 From the foregoing it is seen that nearly a 43% increase in cathodolumineseent brightness is obtained after 6 minutes' immersion in the 6-normal aqueous NAOH solution. Example 2 Part of Example I (immersion time of 6 minutes) is prove the cathodoluminescent brightness thereof. 75 repeated with the exception that the application of a
[6]3,460,967 11 coating of 1% zinc acetate in methanol is omitted. The results of cathodoluminescent brightness tests in footlamberts are as follolvs: 2 kv. 200,ua./in.2 Control, ft.-L -------------------------------- 2.7 5 After 6 minutes in NAOH solution, ft.-L ------ ---- 4.9 The NaOH-treated sample showed an increase in cathodoluminescent brightness of 81.5% over that of the control specimen. Instead of usin- 6 N NAOH as in Examples 1 and 2 10 similar results are obtained by using 3 N NAOH and a longer immersion time, e.g., from 10 to 20 minutes. Example 3 A sample of -lass composition A, which has been 15 heat-treated as described in Exa@mple I to produce a green luminescin.- crystallized surface skin, is immersed for 3 minutes in 6 N aqueous KOH solution at about 160' F., rinsed with distilled water and dried. The results of cathodoluminescent bri.-htness tests on two control 20 samples and on the treated sample are as follows: 2 kv. 100 ua./in.2 Control A, ft.-L ------------------------------- 20 Control B, ft.-L ------------------------------- 21 25 KOH-treated sample, ft.-L ---------------------- 37 Tle KOH-treated sample showed an increase in cathodoluminescetit brightness approximately 80% more than that of the average brightness value for the '@wo control specimens. 30 Similar results are obtained when ammonium hydroxide (commercial -rade) is substituted for potassium hydroxide in treatir@g the glass. Lower temperatures and Ion,-er immersion periods may be used in such cases, e.-., 120'-130' F., to decrease the amount of ammonia 35 evolved during the treating period. The most persistent and reproducible thin-film phosphor is a cubic spinel phase formed on s urface-crystallizable -,lasses sprayed with metallic salt, specifically metallic 40 acetate, solutions and heat-tr,-ated above 1500' F. The diffraction patterns from these thin films closely match the reported pattern for the Mn3O4 spinel, even in the apparent absence of manganese. Since the thickness of these films is less than one micron, it is impossible to identify the chemical composition by presently available 45 techniques. By changin- the chemical spray solution or the heat-treatment time and temperatures, it is possible to produce many different luminescent phosphors with the same spinel surface structure. Thus, glass A, for in tance, can be used as a substrate to produce most of 50 the colors throu,-h the spectrum. This is illustrated by the followin.- example. Example 4 Except as noted hereafter the same glass composition 55 and the same procedure are employed as in Example 1. When a 1% methanol solution of barium acetate is substituted for a similar solution of calcium acetate and the heat treatment is at 1650' F., a surface-crystallized glass having an in situ-formed phosphor that lun-iinesces red 60 under low-voltage electron bombardment is obtained. Using the same zinc acetate solution as in Example I and heat-treating at 1500' F. yields an in situ-formed phosphor that produces a yellow lumineseer,.ce under low-voltage electron bombardment. The same samples 65 @when heat-treated at 1650' F. cathodoluminesce bright green. A glass composition that is the same as that of glass A except that it contains no manganese, when sprayed with a 1% methanol solution of zinc acetate and heat-treated at 1650' F. as in Example 1, luminesces blue 70 under electron bombardment. Controls of each of the aforementioned glasses and correspondin- specimens treated by immersion for 3 minutes and 6 minutes in 6-normal aqueous NAOH at 160' F., followed by washing in distilled water and drying, are 75 12 tested for their cathodoluminescent brightness. All of the treated samples show increased brightness values as compared with the controls when tested as described under Example 1. Illustrative examples of other glasses that may be substituted in the foregoina examples for the particular -@lass employed in the individual example are glasses B, C, D or E; glass F containing 0.5% MnO; glass G containing 2.0% TiO2; or glasses H, I, J or K. The compositions of all of these @-lasses have been given in the portion of this specification prior to the examples. I
