In porcelain industry, to achieve antibacterial properties, ZnO nanoparticles were added in the glaze in the blender. Then the final glaze covered the dishes and were dried in the furnace. While drying at about 800-900 centigrade degrees, a small amount of powder and glaze was swollen and separated from the surface. The swollen powders were floating in the furnace, subsequently sucked by the fan. This caused some problems for the fan and stopped it from working.
Do you have any ideas why this has happened and how we can solve it?
the XRD and XRF analysis of the lifted powder was done and the results show that it mostly contains Zn particles. You can find the results in the attachment.
According to the attached XRF analysis, the glazing frit contains bismuth and arsenic trivalent oxides (Bi2O3; As2O3). Upon heating in oxidizing atmosphere (air), these trivalent oxide components may possibly become partially oxidised to their pentavalent state, and/or disproportionate to both their elemental and pentavalent states. Such redox reactions may possibly lead to an increase of oxygen activity in the melted frit. That could perhaps contribute to the occurrence of oxygen-rich bubbles in oxygen-supersaturated fused frit, which, to some extent, can be resorbed upon cooling. The added ZnO particles seemingly favoured the nucleation of such bubbles. The frit glazing also contains a significant content of PbO which may partially oxidize to Pb3O4, and combined with As2O3, can be expected to contribute as opacifier for the glaze.
Some attention should also be paid to any other possible degassing effect; such as contributed by moisture, calcination of carbonates, volatility of oxides, or by organics burn-off.
Dear Carlos Araújo Queiroz,
I deeply appreciate your help and great tips. I have to mention a few points regarding your comment.
First of all, the glaze that is used is not frit, but it is composed of all raw materials which are blended in water. The glaze formulation is attached. This solution is used to cover the products, and then it is cooked in the furnace. The heating steps consist of pre -heating, oxidation, reduction and fast cooling. I reckon our problem starts in the pre -heating step.
Secondly, based on the reports the amount of Pb in the glaze is less than 1%, and also the purity of the used nanopowder is more than 99.8%. We are wondering where this amount of Pb in XRF analysis has come from.
Do you have any ideas how we can solve this problem??
Anyway, thank you very much for your consideration.
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