Improved cement for electrical lamps
Publication Date: 2005-Nov-22
The IP.com Prior Art Database
Improved lamp cement for UHP lamps.
A Lithium Silicate-based cement (e.g. Glassbond, UK) is used for assembly of the components in UHP lamp production. Short curing times are used for reasons of productivity. The strength of the cement after this curing profile is often too low, causing loose burners and/or centre contacts.
An important factor in the strength properties of the cement is the Silica to Lithium Oxide ratio of the binder. Series of cements with gradually changing ratio were prepared and tested for their properties in UHP assembly.
The binder of the cement is a solution of Lithium Silicate in water at high pH (>10). Such soluble Silicate solutions usually are not stoichiometric but have excess Silica, which is present as very small (few nanometers) particles1. The other species present are probably Li+, Si(OH)4, HSiO3-, and OH-.
The composition is often reported as the oxide contents, SiO2 and Li2O, and the total amount of solids present. The ratio of SiO2 / Li2O is given in terms of weight ratios (WR), or molar ratios (MR). As the molecular weights of SiO2 and Li2O are 60 and 30, respectively, WR=2*MR.
Curing of cements based on soluble silicates involves the evaporation of water and condensation of silanol groups.
The WR value can be adjusted, for example, by adding LiOH or SiO 2 to the Lithium Silicate solution.
Cements made with liquids of WR 7.8 to 5.5 had a LL of about 1-1.4 % below the current standard level for L40...