Testing Water and Acid Corrosion Resistance of DuraBeryllium Coated X-Ray Windows

Moxtek’s most robust coated beryllium x-ray windows are DuraBeryllium Plus windows. This already robust Duraberylium window has an additional thin coating of polymer “Plus” applied. The Plus layer is highly resistant to chemicals and water.

DuraBeryllium Plus windows successfully withstand constant exposure to heated water as well as to other chemicals. A number of tests were done on DuraBeryllium windows as seen in the test summary below. Part 1 of this application note details exposure of DuraBeryllium Plus to water, KOH, and HCl. Part 2 will be released later in 2012 and will include details of exposure of this window to other harsh chemicals.

X-ray Transmission

DuraBeryllium protective layers provide corrosive shielding as well as a hermetic barrier to the beryllium foil. These are highly thin protective layers and the resulting x-ray attenuation is equivalent to about 1µm of beryllium, having little impact on x-ray transmission.

In order to demonstrate strength of the DuraBeryllium window, Moxtek pressure and thermal cycled 30 mounted windows. All the 30 mounted windows were exposed to 10,000 cycles (15psi to atmosphere). Ten of these endcaps went through an additional 10,000 cycles. It was observed that all these windows withstood the pressure and thermal cycling without failure. The flowchart below details the testing procedure used.

Pressure and Thermal Cycling Testing Flow Chart

Figure 1. Pressure and Thermal Cycling Testing Flow Chart

Corrosion Resistance

8µm DuraBeryllium windows are highly robust when continuously exposed to water at both room temperature and at 65ºC. However, uncoated 8µm beryllium windows will corrode when exposed to water within days. The flowchart below details the testing procedure used.

Corrosion resistance testing flow chart

Figure 2. Corrosion resistance testing flow chart

Visual Observation

The images in Figure 3 were taken four months after exposure to H2O at room temperature. As seen in the images, there was some discoloration on the window coating but all windows were leak tight.

Visual observation of corrosion.Note: Corrosion observed on only 2 of the 7 DuraCoat® Plus endcaps

Figure 3. Visual observation of corrosion.Note: Corrosion observed on only 2 of the 7 DuraCoat® Plus endcaps

KOH Exposure Test (Exposure = 1 week)

Under extreme KOH exposure for one week, DuraBeryllium Plus did not develop any leaks. A small amount of visual polymer delamination was observed after 6 days. Prolonged exposure to KOH will eventually dissolve the polymer “Plus” layer.

10% KOH Exposure at room temperature

Figure 4. 10% KOH Exposure at room temperature

HCl Exposure Test

HCl reacts quickly with bare beryllium and corrodes 8µm Be windows within minutes. Both DuraBeryllium Plus and DuraBeryllium add some resistance to this harsh chemical but only for a few hours.

Conclusion

It is observed that DuraBeryllium Plus windows demonstrate remarkable resistance to corrosion after prolonged exposure to heated water. Corrosion on DuraBeryllium Plus windows is minimal and delimitation is non-existent after continuous exposure times of over 6 months without any windows developing a leak. DuraBeryllium Plus windows are affected by exposure of HCl. This chemical will slowly dissolve the outer polymer layer but the beryllium window will still be protected by the inner DuraCoat layer. More testing will be completed at Moxtek to determine resistivity of the DuraCoat to this chemical and will be reported in a later application note. HCl reacts quickly with bare beryllium and corrodes through a 8µm Be foil within minutes. Both DuraBeryllium Plus and DuraBeryllium add some resistance to this harsh chemical but only for a few hours.

DuraCoat Plus layers are applied to all Moxtek 8µm thick DuraBeryllium Plus window. The DuraCoat Plus layers consist of very thin layers of DuraCoat and polymer. These protective layers are very thin, and have little impact on x-ray transmission.

This information has been sourced, reviewed and adapted from materials provided by Moxtek, Inc.

For more information on this source, please visit Moxtek, Inc.

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