Nikita Bernier wrote:

Nikita Bernier wrote: Nikita Bernier wrote:  Friday, August 10, 2012, 19:54   Target boat with TaC coating, inside covered with a 0.002 inches thick Ta foil, wrapped with a 0.002 inches thick Ta foil, contains a Ta foil with TaO coating. See John's Ipad for their recipes. Evaporator #2 is now auto-ramping overnight at 0.2 A/min, up to 830 A, with the maximum voltage limited at 14 V, between 2.00e-05 (Good vacuum) and 3.00e-05 Torr (Bad vacuum).    Saturday, August 11, 2012, 19:15 Heating process was going smoothly up to 400 A. See Attachment 1. Around 420 A, vacuum went up again and the voltage increased more quickly. It seems like resistance is building up. After reaching 530 A, the current was tapped down to 420 A in an effort to save the Ta boat. See Attachment 2. The current will stay at 420 A for the weekend until John takes a look at this.    Monday, August 13, 2012, 13:46  TGHT was ramped down at 2 A/min and then tapped down to 0A. See Attachment 1.  The target boat will be cooled down for about an hour before turning off the chiller.

 Tuesday, August 14, 2012, 16:56

Summary:

The purpose of this experiment is to test the chemical and high temperature (1600C) resistance of a Ta foil (0.001" thick) coated with Ta2O5, so it can be used as the under-layer for the BeO sintering process.

The Ta2O5 (white powder, -325 mesh) was prepared in a non-aqueous solution and was sprayed on a piece of Ta foil. 

The coated foil was rolled up and inserted in a Ta-coated (previously sintered) target boat for heating.

The foil was heated up to 520A (~1200C) and evidently,Ta2O5 started to react with Ta foil, and the foil became brittle and cracked (see attachment#1).

In conclusion, Ta2O5 is not a good protection layer for Ta material - at least for our applications.