Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
501 70, C03C 0085, C03C 0087
The present invention relates to glass, of which the abrasion resistance is very high.
Glass is essentially a brittle material. Particularly, its strength decreases by fine surface defects which form during its use, and if a force is exerted to such defects, cracks will spread from these fine defects, leading to breakage.
Therefore, in order to increase the durability of glass, attempts have been made for a long time to improve abrasion resistance of the surface by incorporating a hard coating on the surface, for example. However, such a technique is not an attempt to essentially overcome the brittleness of glass itself. Accordingly, there is a problem that once the surface coating is removed by abrasion or deterioration, for example, its effects will no longer be obtained.
On the other hand, sodalime silica glass which is presently most widely employed, usually has the following composition, although there has been some change historically:
______________________________________ SiO.sub.2 66 to 75 wt %, MgO 0 to 5 wt %, CaO 7 to 12 wt %, Na.sub.2 O 12 to 20 wt %, K.sub.2 O 0 to 3 wt %, Al.sub.2 O.sub.3 0 to 4 wt %. ______________________________________
Not so much research has been done on the relationship between the composition and the hardness with respect to sodalime silica glass. According to general common knowledge, if the silica content is increased, the hardness will increase; if CaO is substituted for Na.sub.2 O, the network bonding will increase to improve the strength; an addition of Al.sub.2 O.sub.3 serves to increase the strength and the hardness as well.
Further, abrasion hardness corresponding to scratchability of the surface, is important for determining the practical strength of glass, but it does not necessarily have a good correlation with the Vickers hardness. This is believed to be attributable to the fact that the abrasion resistance is not only a factor relating to the hardness, but also susceptible to an influence of the frictional heat or falling off of glass fragments from a test piece due to formation and spreading of fine cracks.
In glass of sodalime silicate type, if the component ratio of silica is increased simply to increase the hardness in accordance with the conventional knowledge, it tends to be hardly meltable, whereby its production by a melting method with good productivity, will be impossible.
Glass having a relatively high silica component ratio, is disclosed in the specification of U.S. Pat. No. 3,811,853. However, such glass is limited to an application for decomposable containers, and it does not have adequate water resistance to be used as glass of general use.
An object of the present invention is to overcome the brittleness of glass itself thereby to prevent formation of abrasion marks by an external force during its practical use and to provide glass which is hardly breakable and which is relatively easily meltable in spite of high abrasion resistance. Another object is to provide glass which has, in addition to the above properties, durability (particularly water resistance) comparable to conventional sodalime silicate glass.
DISCLOSURE OF THE INVENTION
The present invention provides abrasion resistant glass, which consists essentially of the following components:
______________________________________ SiO.sub.2 75.5 to 85.5 (wt %), RO 1 to 8 (wt %), R'.sub.2 O 10 to 23.5 (wt %), RO + R'.sub.2 O 11 to 24.5 (wt %), Al.sub.2 O.sub.3 0 to 5 (wt %), ______________________________________ RO/R'.sub.2 O (weight ratio) at most 0.5, at least one member selected from Li, Na and K, and of which the density measured at room temperature is at most 2.41 g/cc.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view for explaining the definition of the brittleness in the present invention.
FIG. 2 is a graph showing the relation between the brittleness index value B and the abrasion wear by sand blasting.
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have studied
patent: 3811853 (1974-05-01), Bartholomew et al.
patent: 4177319 (1979-12-01), Jahn
patent: 4672152 (1987-06-01), Shinohara et al.
patent: 5264400 (1993-11-01), Nakaguchi et al.
patent: 5318931 (1994-06-01), Nakaguchi et al.
Asahi Glass Company Ltd.
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