Laura Lambert wrote:

John Wong wrote: The purpose of this experiment is to determined the limiting operating temperature for Beta-SiC.  To do so, samples will be heated in sequence to observe any volatile Si coated on the window.  The coating is observed above 1400C for the conventional SiC (mixuture of alpha and beta) and this coating leads to HV shorting problem.  Thursday, May 19, 2016, 14:26 Beta-SiC (size ~1um) slurry was prepared and casted on a graphite foil.  Discs are cut into D-shape Average thickness (including graphite foil) = 0.349mm Graphite foil = 0.13mm Actual SiC thickness = 0.219mm (close to normal SiC thickness) Samples are loaded into a target boat. Total discs = 120 Total mass = 14.3507g Thursday, May 19, 2016, 14:32 Omega slope set to = 1.04 Heat-treatment #1: 1400C  Thursday, May 19, 2016, 17:04 TGHT ramping up to 250A at 0.5A/min    Friday, May 20, 2016, 08:53 IGP1 = 9.2e-6 Torr. Increasing ramping rate to 1.0A/min up to 250A  Friday, May 20, 2016, 09:17 IGP1 = 2.1e-5 Torr TGHT = 215A, 3.1V OMEGA = 1035C Stopping auto-ramp and tapping up manually...  Friday, May 20, 2016, 12:26 OMEGA slope changed to 1.04 OMEGA reached ~1430C and kept there for ~1hr. no change. no coating on window observed tapped up manually to OMEGA =1500C TGHT = 350A, 5.8V  Friday, May 20, 2016, 14:17 Not much change to window. Might be beginning of light dusting, hard to tell. Will be better observed after longer period of time at 1500C Will remain at 1500C over weekend.

 Tuesday, May 24, 2016, 11:15

Sample has been heated over the long weekend.  Temp dropped to 1400C.  TGHT at 350A/5.78V.  Vac at 1.5e-7 Torr.

It is hard to tell if there is any coating on the window.  Will increase temperature to 1800C

 Tuesday, May 24, 2016, 11:43

Temp at 1620C. TGHT at 440A/7.7V. 

At this temperature, the coating would have been seen for the conventional SiC target material.  But, no much of change on the window since the TGHT was tapped up from 1400C.

Continue to increase TGHT to reach 1800C

 Tuesday, May 24, 2016, 11:58

Temp at 1680C/TGHT 470A/8.4C - a very light film on the window was observed.  Not sure if this film was left from previous processes; it is just that the target container is getting very bright and hard to see.

 Tuesday, May 24, 2016, 12:15

TGHT at 510A/9.16V - Observed coating on window.  Omega got interfered, therefore temp is unknown.  But it was read at ~1720C before the window was getting coated and temp started to dropped.

Will leave at this stage for now...

 Tuesday, May 24, 2016, 16:57

Window is fully coated.  Based on the heating curve, at 500A, the temp should be at ~1900C (wrapped with a layer of heat shield).  Temperature reader dropped to1340C due to the coating interference. 

Cooling down TGHT at 2A/min. And will exam the materials tomorrow...