Surface Glasses

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Surface Glasses

Surface preparation

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The preparation of the glass surfaces is intended primarily to improve the wetting properties and adhesion of the glass surface.

Glass is a transparent material, hard, tough and fragile because of its characteristics, it is used in a large number of products we use daily such as glasses, bottles, windows, lens etc. ..

Silicon oxide is the main chemical compound of glass, approximately 72% of ordinary glasses are made of silicon oxide (SiO2). During the manufacture of glass, compounds and additives added as carbonates, sulfates and nitrates of sodium and potassium, which improve the liquefaction of the glass.

The water presented in the environment as moisture reacts slowly with nitrates, carbonates and sulfates of sodium and potassium and produce form sodium and potassium hydroxide, also the moisture it reacts with silicon oxide the breaking inside structures of glass, it can produce a cracking of the material on the surface.

The set of hydroxides of sodium, potassium and silicon formed in the outer layer of glass is called gel layer, which has a low surface energy and high instability, resulting in a poor wetting and dismal adherence to any adhesive.

glass structure

A proper and accurate surface preparation of the glass allows us to eliminate the gel layer that is formed naturally on the surfaces of the glass.

Generally is not recommended the use of mechanical or chemical techniques such as blasting, sanding or etching in the glass as surface preparation, due they may cause microcracks on the surface and may reach the breaking of the glass.

Usually a good cleaning with organic solvents for a short time and with the help of adhesion promoters, primers and / or activators are enough to generate a fresh active surface of the glasses.

Polyurethane adhesives, silicones and silanes modified / hybrid polymer adhesives are generally used for adhesive bonding with glass, owing to their elongation. You can find glass adhesive joints with acrylate adhesives, these adhesives are reformulated especially for the use of glass, providing more elongation and removing certain compounds that can cause the yellowing of the glass.

In case that the adhesive joint is exposed to the outside, the transparency of glass allows UV light to pass through, so it is necessary to protect the adhesive, such as using black primer in order to prevent aging of the adhesive union and adhesive itself, that effect occur in polyurethanes adhesives, silanes modified adhesives are very resistant to U.V. compare with polyurethanes.

Last Updated on Saturday, 21 December 2013 19:45
 

Insulated Glass Surfaces

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The Insulated Glass unit consists of four surfaces. Surface 1 is that side of the glass lite that faces the exterior of the building. Surface 2 is other side of the Surface 1. Surface 4 is the side of the glass lite that faces the interior of the building. And the Surface 3 is the other side of surface 4.

IGU: The Process
Insulating glass is a glazed unit composed of two or more glass panes separated by spacers filled with dehydrated air or gas. The various machines used in the process of making insulated glass are washing unit, drying unit, spacer conveyor, butyl extruder, and pressing unit, which is vertical. The insulated glass is constructed in the following ways.

A hollow aluminium spacer bar is bent into the desired shape.
Holes are drilled in the spacer bar, which is filled with a desiccant such as silica gel or zeolite that helps in absorbing water vapour.
The drilled holes are sealed with a primary sealant such as butyl. Primary sealant is also applied to the sides of the spacer bar.
Two glass panes are placed along the side of the spacer bar and pressed with an automatic presser.
A secondary sealant such as polysulphide or silicon is applied along the sides of the whole unit. The insulating glass unit is ready.
 

On the surface of glasses

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Dynamics near the surface of glasses is generally much faster than in the bulk. Neglecting static perturbations of structure at the surface, we use random first order transition (RFOT) theory to show the free energy barrier for activated motion near a free surface should be half that of the bulk at the same temperature. The increased mobility allows the surface layers to descend much further on the energy landscape than the bulk ordinarily does. The simplified RFOT calculation, however, predicts a limiting value for the configurational entropy a vapor deposited glass may reach as a function of deposition rate. We sketch how mode coupling effects extend the excess free surface mobility into the bulk so that the glass transition temperature is measurably perturbed at depths greater than the naive length scale of dynamic cooperativity.

© 2008 American Institute of Physics

Last Updated on Tuesday, 25 December 2012 19:36
 

Surface of Glasses

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Dynamics near the surface of glasses is generally much faster than in the bulk. Neglecting static perturbations of structure at the surface, we use random first order transition (RFOT) theory to show the free energy barrier for activated motion near a free surface should be half that of the bulk at the same temperature. The increased mobility allows the surface layers to descend much further on the energy landscape than the bulk ordinarily does. The simplified RFOT calculation, however, predicts a limiting value for the configurational entropy a vapor deposited glass may reach as a function of deposition rate. We sketch how mode coupling effects extend the excess free surface mobility into the bulk so that the glass transition temperature is measurably perturbed at depths greater than the naive length scale of dynamic cooperativity.