I am very new to the vacuum-furnace world and work for a company that sinters stainless mesh in a single-chamber vacuum furnace. In our process, we will generally run several jobs in a load (all stainless). My questions relate to the method we use to separate the mesh. We use a ceramic paper, which becomes “dirty” after repeated use. In fact, when I change my diffusion pump oil it is caked with the fibers from this material. I have also seen some instances where it seems the paper itself becomes bonded to the mesh and becomes very difficult to remove. I was wondering if you might be able to recommend a different way or product to help eliminate or reduce these issues.    

Ceramic paper is used by a number of companies in the industry in their vacuum furnaces to prevent parts from sticking together. It is relatively inexpensive, easy to use and is (in general) effective for its intended purpose. However, it has quite a number of detrimental features: it affects (lengthens) pump-down times since it is hydroscopic (i.e. absorbs moisture as it sits around outside the furnace and subsequently releases that moisture during initial pump-down and heat-up); it is easily mechanically damaged; it becomes more and more brittle after first and subsequent uses, allowing fibers to be released (as you have found); and it absorbs all sorts of contaminants (carbon-bearing and other) such as oils, dirt, etc. This explains why, in your case, the paper becomes bonded to the stainless steel. In your application, I would recommend that the paper be discarded either after each use or after just a few uses (before it becomes dark).  

There are a number of substitute materials and methods that you may find better in your application but, once again, each has pros and cons. As far as ceramic-fiber materials go, you might wish to check out a product from Thermal Ceramics called K-Shield BF paper. This is used by a number of commercial heat treaters. It has an organic-free binder, which is a plus (many data sheets like the one you sent do not list the binder type). Commercial heat treaters I’ve talked with recommend a 1/32-inch (0.8 mm) paper and only a one-time usage before you throw it away. If bought in bulk, it must be stored in such a way as to prevent moisture pickup. There are also a number of spray powders on the market, the two most popular being boron nitride and aluminum-oxide powders. You might also consider using a vacuum brazing stop-off compound painted on the surface of a separator screen (it must be thoroughly dry). Be aware that many of these products go on one color and turn another color after use, which might affect the brightness/color of the stainless. Wall Colmonoy makes a green (as I recall) brazing stop-off that comes out black after use, and the boron-nitride spray goes on white and comes out a grayish white.