Aluminum properties
Carefully crafted with pure 0.9999% aluminum, the SPI Aluminum Weighing
Dishes are offered in three different sizes and two edge finishes, crimped and smooth,
to match every technical size requirement. The weighing
dishes are generally used as a disposable item and their reuse is certainly not recommended.
The most often asked for size (given below in terms of diameter in mm) is "Medium",
or SPI# 01257-MB. For the EM laboratory, the most frequent use is during
"pre-embedding" procedures. For the plasma ashing of organics, these small
aluminum weighing dishes are excellent substrates. They can also be easily
cut out into small pieces with a scissors or razor blade, mounted onto an
SEM mount, with the ashed residues examined in the SEM, in situ.
Other applications:
The main applications for these dishes are for routine weighing and moisture testing.
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Upper temperature limits of use:
Although the melting point of aluminum is cited at 660.32°C (1220.58°F), it
is not recommended that the aluminum weighing dishes above the range of
482°C to 649°C (900°F to 1200°F) depending on whether in vacuum or air.
The "secret" about aluminum weighing dishes:
There is a "food grade" release material present on the aluminum weighing dishes.
It is a miniscule amount but it is, nevertheless, there. We are told that the benefits
of having the release material present far outweigh any draw backs and from what we
have seen, this seems to be the case for most users. We want to stress that the
presence of this release layer is not a unique feature of the SPI aluminum weighing
dishes; it is prevalent throughout the industry of firms making these aluminum dishes.
So what if you absolutely do not want this layer present and you want to remove it?
In small quantities, the release material is easily removed by wiping with
toluene or xylene. In larger quantities, it may be possible to remove it by
oxidation in a muffle furnace. Perhaps the best way, however, is a low
temperature oxygen plasma treatment in the
SPI PlasmaPrep™ II low temperature plasma etcher/asher.
So will I notice a difference in powder behavior when weighing once the layer
if removed? Perhaps. Without the layer there can be a tendency for a
powder to stick (e.g. not release) from the aluminum surface, mainly due to
charges on the powder. The best way to deal with this problem then is to employ the
Zerostat® AntiStatic Gun which will discharge the powder.
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