Glass Defect : Glass Knot -- inhomegeneous glass

Hi to all glass people...

This is my 1st time in the forum... and hopefully got feedback from
people around the glass technology field.

As the topic of glass Knot:
1. What is glass knot?
2. Histories and experienced on this glass defects...

As I understand, Glass knot can be happened from reaction of
glass to refractories -- where the solution sac of the inhomogeneous
glass being crystalized and appeared in the products...

Wish can got people feedback on their knowledge on this..


Jean Louis HEITZ
Wed, 29/01/2003 - 14:47

Reply to [B]billyeoh[/B]:

A glassy knot results from the dissolution of a material whose composition differs from the pristine glass (---> solution sac), for example :
- refractory material corroded by glass
---> Al, (Zr) enriched glass
- contaminant in the raw materials (porcelain, vitroceramic in the cullets, heavy minerals in sand)

A glassy knot is usually prolonged by a cord.
Some residue of "digested" primary material can be present within te knot.
Some secondary (devitrification) crystals may be present within the knot.

The SEM/EDX (WDX) analysis helps to trace back to the origin oh the knot.

feel free to contect me for further information,

Jean Louis HEITZ

Guest User
Mon, 17/11/2003 - 10:58

Glass Knots

The reaction between the refractories and the glass is myth. AZS drip can occur from a poor firing setup and is usually caused by flame impingment on the refractories causing a drip to run into the melt.
Your best place to look is in the cullet you are using.It can become contaminated with low melting point ceramics or other glasses .
Best thing to do is to isolate a knot and grind it up to a fine powder and chemically analyze it. you don't have to know how much of each element is in it only what is thee. Pay particular attention to any metals . I would be looking for zinc which is a good indication of high MP ceramics in the cullet.


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