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Chapter 6
Figure 6.6
o
The backscattered and secondary EDX mapping at 10kV of the surface of the 200 o C sample after exposure to 85 C/85% RH.
White spots were also reported in reference [3], who looked at the damp heat
degradation of ZnO:Al/Ag/ZnO:Al low emissivity (low-e) coating. They observed
that the size was mainly influenced by the aluminium content in the film, but the
individual spots were not chemically analyzed. Very high aluminium concentrations
(10%) in ZnO:Al lead to hazy samples, while the largest spots were obtained for
samples without any aluminium. In this case, the quantity or size of these spots is not
o
significantly different for the RT and 200 C samples.
In backscattered SEM, it was observed that these spots contain lighter elements than
ZnO:Al (Figure 6.5b). The nature of these spots was studied by EDX mapping at 10 kV
(Figure 6.6). Naturally, the elements zinc, oxygen and aluminium were encountered, but
the presence of carbon, silicon and calcium was less expected, but also observed. The
spots and stains seem to consist of mostly calcium and carbon, but oxygen, silicon and
aluminium were certainly also present, while the zinc has disappeared from these spots.
The origin of the unexpected elements was studied. One possible source was the
destilled water in the climate chamber. This water was therefore checked by ICP-
MS on residual cations and 0.55 mg/l Na and 0.35 mg/l Si were found. However, no
aluminium and calcium were detected. It is known that aluminium, silicon and calcium
are present in the glass, so it is likely that the calcium has migrated from the glass,
which might also be possible for the aluminium and silicon. It can be expected that
these migrating cations will react with H O, CO or O from the air to form carbonates
2
2
2
or hydrates. It is proposed that the spots and stains occur when the samples are
removed from the climate chamber. The thin water film on the surface can then dry-
out and form little dots or coffee stains and leave salts behind.
It should be noted that the zinc oxide film is in these experiments in direct contact
186
Figure 6.6
o
The backscattered and secondary EDX mapping at 10kV of the surface of the 200 o C sample after exposure to 85 C/85% RH.
White spots were also reported in reference [3], who looked at the damp heat
degradation of ZnO:Al/Ag/ZnO:Al low emissivity (low-e) coating. They observed
that the size was mainly influenced by the aluminium content in the film, but the
individual spots were not chemically analyzed. Very high aluminium concentrations
(10%) in ZnO:Al lead to hazy samples, while the largest spots were obtained for
samples without any aluminium. In this case, the quantity or size of these spots is not
o
significantly different for the RT and 200 C samples.
In backscattered SEM, it was observed that these spots contain lighter elements than
ZnO:Al (Figure 6.5b). The nature of these spots was studied by EDX mapping at 10 kV
(Figure 6.6). Naturally, the elements zinc, oxygen and aluminium were encountered, but
the presence of carbon, silicon and calcium was less expected, but also observed. The
spots and stains seem to consist of mostly calcium and carbon, but oxygen, silicon and
aluminium were certainly also present, while the zinc has disappeared from these spots.
The origin of the unexpected elements was studied. One possible source was the
destilled water in the climate chamber. This water was therefore checked by ICP-
MS on residual cations and 0.55 mg/l Na and 0.35 mg/l Si were found. However, no
aluminium and calcium were detected. It is known that aluminium, silicon and calcium
are present in the glass, so it is likely that the calcium has migrated from the glass,
which might also be possible for the aluminium and silicon. It can be expected that
these migrating cations will react with H O, CO or O from the air to form carbonates
2
2
2
or hydrates. It is proposed that the spots and stains occur when the samples are
removed from the climate chamber. The thin water film on the surface can then dry-
out and form little dots or coffee stains and leave salts behind.
It should be noted that the zinc oxide film is in these experiments in direct contact
186
