How important is the condition of windows?
Since your Mastersizer is an optical instrument, reliable and repeatable wet and dry measurements depend on the cleanliness and good condition of cell windows.
Windows should be inspected regularly and any smears or dirt should be removed. If the windows show any sign of scratches or damage, they should be replaced.
How do I know when windows need to be replaced?
If cleaning the windows (see below) fails to give a good clean background, it may be time to replace them. Holding a window and viewing the reflection of a fluorescent light on its surface as the window is angled back and forth is a useful way of seeing scratches and defects that may be causing the problem. If any scratches are observed, the window should be replaced immediately.
Buy replacement windows online:
Mastersizer cell windows and seals (PMW4015) The cell windows are critical components of the Mastersizer and need to be kept clean and scratch free. Part PMW4015 provides a replacement pair of cell windows and Viton Seals that can be used on all Mastersizer Wet Dispersion Cells (excluding the Hydro 2000µP).
Cell Windows (MVC4002) Pair of windows for the Hydro 2000P.
Scirocco 2000 Windows and window rings (PMD4015) Pair of Cell Windows bonded into retaining rings. For use on Scirocco 2000.
How do I know when they need to be cleaned?
Window cleanliness is best gauged by the ability to obtain good background measurements as illustrated below:
A good clean background on a wet system should look very similar to this...
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Look for:
- No more than 100 units of scattering recorded by the first detector
- Limited fluctuations over time
The flow of air through a dry cell will cause a slightly higher degree of fluctuation over time than seen in a wet system
- The same decrease in the signal is observed across the detector range.
- The same maximum acceptable value of 100 applies.
Poor background - material stuck to the windows
A 'hump' in the data is often an indication of material stuck to the cell windows
Poor background - contaminated dispersant
- Particulate contamination causes fluctuations in the background over time.
- Bubbles in the dispersant can also result in a similar background.
- One cause of bubbles is air leaks caused by aging tubing losing its flexibility and failing to seal at the joins between the cell or the sample dispersion unit.
If you suddenly find that more rinses than usual are required to obtain a good background, on your wet sample dispersion unit, check the cleanliness of the cell windows.
