GB1218093A - Process for modifying glass and other bodies - Google Patents

Abstract

1,218,093. Chemical-tempering of vitreous materials. GLAVERBEL. 8 Feb., 1968 [25 April, 1967; 30 Aug., 1967], No. 6388/68. Heading C1M. A process for modifying a physical and/or chemical property of a body of glass, vitrocrystalline or ceramic material, comprises an ion-exchange between the body and a contacting medium which is itself in contact with a regenerator material present as a separate phase and composed so that ions entering the medium from the article are taken up by the regenerator material in exchange for further amounts of ions which diffuse into the body. The medium may be gaseous in contact with a solid regenerator or it may be in a liquid state, e.g. a bath of molten salts with the regenerator material present as a disperse phase in the medium. The regenerator is advantageously significantly heavier or lighter in density than the medium and is maintained in dispersed condition by agitation of the medium. The regenerator preferably captures and releases ions more readily than the material of the body. The regenerator may be a natural mineral or glass, or ion-exchange material charged or enriched with ions which are to diffuse into the body, particularly clays, silicates, borates, vitreous and non-vitreous aluminosilicates and solid gels capable of fixing protons or alkali metal ions. At least one substance called an adjuvant which weakens the diffusion barrier at the interface between the body and medium is preferably present in the medium. The adjuvant, or part thereof, can be incorporated in the regenerator material. Different degrees of modification can be achieved wherein portions of the medium in contact with different zones of the body are separated and an adjuvant is present in one or more but not all of the portions and/or is present in different concentrations in the different portions. The adjuvant may be a halogen, an alkaline earth metal or salt containing an anion which is not present in the material undergoing treatment, a substance which functions as an acceptor of oxygen ions, e.g. CO 2 , NO 2 <SP>+</SP>, S 2 O 7 <SP>2-</SP>, Cr 2 O 7 <SP>2</SP>-, PO 3 -, a substance having an acid function, e.g. SO 4 <SP>2-</SP>, PO 4 <SP>2-</SP>, aromatic organic compounds such as polyphenylene oxides and polysulphones, a substance which gives rise to the formation of complexes, e.g. [FeM(CN) 5 ]Li, where M is a substituted monovalent ion migrating from the article, e.g. K +or Na<SP>+</SP>. The diffusion barrier can also be reduced by incorporating in the medium a substance which modifies the valency state of ions of the or at least one element which migrates from article, e.g. oxides, cyanides and chromates; this can be assisted by generating an electric field. Specific examples of treatments and temperatures are given. In the examples sheets of soda-lime glass, and a glass comprising in per cent by weight SiO 2 : 70, Na 2 O: 14, CaO: 13, Al 2 O 3 : 3, and bottles of soda-lime borosilicate glass are treated. A vitro-crystalline sheet comprising SiO 2 : 42À3, Al 2 O 3 : 31À2, Na 2 O: 10À4, K 2 O: 6À2, CaO: 1À8, TiO 2 : 7À4, As 2 O 3 : 0À7% by weight is also treated.