United States Patent (19) 11 Patent Number: 4,464,475 Beall Et Al
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United States Patent (19) 11 Patent Number: 4,464,475 Beall et al. 45) Date of Patent: Aug. 7, 1984 54) GLASSCERAMICARTICLES CONTAINING Primary Examiner-Mark Bell OSUMLTE Attorney, Agent, or Firm-C. S. Janes, Jr. (75) Inventors: George H. Beall, Big Flats; Agustin M. Chirino, Elmira; Kenneth Chyung, (57) ABSTRACT Painted Post; Francis W. Martin; This invention is directed to the production of glass Mark P. Taylor, both of Painted ceramic bodies exhibiting high strength and capable of Post, all of N.Y. being used at temperatures of 1300 C. and higher. Bar 73 Assignee: Corning Glass Works, Corning, N.Y. ium osumilite constitutes the predominant crystal phase and the inventive bodies have overall compositions (21) Appl. No.: 457,652 consisting essentially, in weight percent, of: 22 Filed: Jan. 13, 1983 (51) Int. Cl. ................................................ CO3C 3/22 SiO2 51-68 52) U.S. C. ............................................ 501/9; 501/8 Al2O3 17.5-30 58) Field of Search ........................................ 501/8, 9 MgO 5-12 BaO 3.5-15 (56) Si 0-1 References Cited Nb2O5 0-20 U.S. PATENT DOCUMENTS Ta2O5 0-0 TiO2 0-12 2,920,971 1/1960 Stookey .................................. 501/8 ZrO2 0-6 3,480,452 11/1969 Fleischner et al. ... 501/9 3,573,939 4/1971 Beall................. ... 501/5 3,713,854 1/1973 Beall..... ... 501/9 The bodies can be utilized in monolith form and are 3,839,053 10/1974 Rittler ..................................... 501/8 very useful as matrices for fiber reinforced structures FOREIGN PATENT DOCUMENTS suitable for high temperature applications. 1459178 12/1976 United Kingdom .................... 501/9 1535202 12/1978 United Kingdom.................... 501/8 5 Claims, No Drawings 4,464,475 1. 2 fibers with the concomitant generation of gaseous spe GLASS-CERAMIC ARTICLES CONTAINING cies resulting in fiber strength degradation. The matrix OSUMILTE viscosity at a desired use temperature should be at least on the order of 1013 poises (the annealing point); other BACKGROUND OF THE INVENTION 5 wise, the load transfer through the shear strength of the The production of glass-ceramic articles had its gene matrix is too low to maintain efficient reinforcement. sis in U.S. Pat. No. 2,920,971. As is explained in that As was noted above, Ser. No. 380,464 discloses glass patent, a glass-ceramic article is prepared through the ceramic compositions suitable for extended use at tem controlled crystallization in situ of a precursor glass peratures up to 1100° C. and brief exposures to tempera body. That preparation involves three basic steps: first, O tures up to 1200° C. For certain applications, e.g., jet a glass-forming batch commonly containing a nucleat engine components, glass-ceramics sufficiently refrac ing or crystallization-promoting agent is melted; sec tory to withstand long term exposures to temperatures ond, the melt is simultaneously cooled to a temperature up to 1300° C. would be highly desirable. Also, the below the transformation range thereof and a glass capability of acting as a matrix for SiC fibers, i.e., there body of a desired geometry shaped therefrom; and, 15 being essentially no reaction between the matrix and the third, the glass body is exposed to temperatures above SiC fibers, would be an added plus. However, to satisfy the annealing point and often above the softening point that high temperature requirement, the glass-ceramic of the glass to generate crystals in situ. To achieve matrix must demonstrate such refractoriness subsequent greater uniformity in crystal size, the parent glass may to the crystallization in situ process that the viscosity of frequently be initially exposed to a temperature some 20 the body is at least 1013 poises at 1300 C. what above the transformation range to develop a myr In addition, where SiC fiber-containing composites iad of nuclei in the glass, following which the tempera are envisioned, it is much to be preferred that the glass ture is raised to cause the growth of crystals on those ceramic exhibit a relatively low coefficient of thermal nuclei. expansion and good sinterability so that the composite Glass-ceramic products have also been prepared by 25 articles can be fabricated at relatively low temperatures firing glass frits, i.e., glasses in the form Öf finely and pressures (~ 1000 C. and ~ 1000 psi). Not only is divided powders, which frequently will not include a good sinterability at relatively low temperatures desir nucleating agent in their compositions. That is, surface able from the practical points of view of ease and cost of crystallization resulting from the high surface area pres producing composites, but also higher temperatures ented by the very finely-divided glass powders is relied 30 hazard reactions taking place between the matrix and upon to promote uniformly fine-grained crystallization. the SiC fibers, In general, glass-ceramic articles are desirably highly The glass-ceramics of Ser. No. 380,464 consist essen crystalline; U.S. Pat. No. 2,920,971 specifies at least tially, expressed in terms of weight percent on the oxide 50% crystalline. Because of this high crystallinity, basis, of: glass-ceramic articles take on physical properties more 35 closely akin to those of the crystal phase than those of the parent glass. Moreover, the composition of any Li2O 1.5-5 Al2O3 15-25 residual glassy matrix will be quite dissimilar from that SiO2 60-75 of the precursor glass inasmuch as the components of ZrO2 1-5 the crystal phase will have been removed therefrom. 40 Nb2O5 0-10 Because of the wide variety of physical properties Ta2O5 0-0 that can be enjoyed in glass-ceramic products through Nb2O5 -- Ta2O5 1-10 the many different types of crystal phases which can be MgO 0-0 developed therein, glass-ceramics have found utility in such diverse applications as radomes, dental constructs, 45 Where those compositions are to be used to fabricate culinary ware, printed circuit boards, dinnerware, and composite articles with SiC fibers, TiO2 will be essen matrices for storage of radioactive materials. tially absent therefrom and 0.5-3% As2O3 will be incor A combination of thermal stability, thermal shock porated into the composition. TiO2 behaves as a flux resistance, and mechanical strength is vital when a ma and, hence, adversely affects the refractoriness of the terial is to be subjected to severe thermo-mechanical 50 product. Furthermore, TiO2 appears to form titanium environments. Dielectric requirements may also dictate silicide intermetallic compounds at the interface of the that the material be essentially free from alkali metals, SiC fiber-matrix interface during formation of the com especially sodium. posite body, thereby leading to reduced fracture tough Serial No. 380,464, filed May 20, 1982 in the names of ness in the composite. , J. J. Brennan, C. K. Chyung, and M. P. Taylor under 55 Arsenic, added as As2O5 to the parent glass batch, the title GLASS-CERAMIC COMPOSITIONS OF substantially improves the resistance of the glass-ceram HIGH REFRACTORINESS, describes glass-ceramic ics to oxidation. It was hypothesized that, since arsenic compositions in the Li2O-MgO-Al2O3-SiO2 system can'exist in two oxidation states, viz., Astand As, it which are capable of long term use at temperatures up acts as an oxygen buffer to trap oxygen as it migrates to 1100 C., and short term exposure to 1200° C. Those inwardly from the surface of the composite. glass-ceramics contained beta-spodumene and/or beta Nb2O5 and Ta2O5 enhance the refractory character of quartz solid solution as the predominant crystal phase the glass-ceramics and were theorized to perhaps per and had, as their principal application, service as matri form as secondary nucleants (ZrO2 being the primary ces for SiC fiber reinforced composite bodies. It was nucleant). More importantly, however, Nb2Os and observed in that disclosure that, in an oxidizing atmo 65 Ta2O5 were discovered to provide in situ protection sphere, SiC fibers react with the matrix to deleteriously from SiC-glass interaction through the formation of affect the strength and fracture toughness of the com NbC and/or TaC at the SiC-glass interface and/or the posite articles, primarily due to the oxidation of the SiC development of a very thin protective layer around the 4,464,475 3 4 SiC fiber. Whatever mechanism is involved, the NbC osumilite glasses do not demonstrate a large volume and/or TaC reaction product acts to restrict active increase when crystallized in situ; on the contrary, a oxidation of the SiC fibers at elevated temperatures and slight shrinkage occurs. to inhibit SiC-glass interfacial reactivity. As a result, the Highly crystalline, Ba-osumilite articles can be pre Nb2O5 and/or Ta2O5 content in the glass-ceramic ma pared by two general procedures: (1) utilizing a devitri trix will be reduced to the extent of the carbide layer. fying frit; and (2) utilizing an internal nucleating agent. To secure highly crystalline bodies wherein the crys In the first practice, a finely-divided glass powder (frit) tals are quite uniformly fine-grained, the compositions is formed, the frit shaped into a desired configuration, will contain 2-3.5% Li2O, 1.5-6% MgO, and 1-3% and then fired to essentially simultaneously sinter the ZrO2. 10 powder to a solid body and develop crystallization. The OBJECTIVES OF THE INVENTION large surface area presented by the fine particles pro notes nucleation of the crystals. In the second proce The primary objective of the instant invention is to dure, a nucleating agent selected from the group of provide glass-ceramic products capable of extended use silicon metal, TiO2 and Nb2O5 is dissolved in the glass. attemperatures up to 1300 C., exhibiting relatively low 15 coefficients of thermal expansion (<30x10-7/°C.), Silicon metal is the most efficient nucleant in promoting high mechanical strength and fracture toughness, and osumilite crystallization.