| Author | Message | ||
     Howard Mark (hlmark) Senior Member Username: hlmark Post Number: 532 Registered: 9-2001 |
Joelle - I think that whatever you use, Fluorlon or ceramic (especially if thinner than you might otherwise want), you would do well to put a piece of reflective metal behind it, even a piece of aluminum foil. \o/ /_\ | ||
| Joelle Rahm� (rahm�) Junior Member Username: rahm� Post Number: 7 Registered: 10-2011 |
Thanks Art! Especially for that last piece of advice. I don't have a lot of time for this test and custom made (if they accept) will probably take a long time. Joelle | ||
| Art Springsteen (artspring) Senior Member Username: artspring Post Number: 50 Registered: 2-2003 |
Joelle, I'm sure the 3-4 mm thick alumina ceramic would work, as would the Fluorilon FW99, especially if you backed the Fluorilon with something reflective (even aluminum foil). The problem you will have is getting Coors to make you what you need. This will be a custom part and if our experience is any indicator, they really don't like doing custom parts. | ||
| Joelle Rahm� (rahm�) Junior Member Username: rahm� Post Number: 6 Registered: 10-2011 |
Hi, Thank you Art and Howard for your answers! Having used a ceramic tile in the past (3mm thick cheap electrical isolant) for testing purposes, I found it indeed quite reflective, even at this low thickness. So I'm wondering if a high purity Alumina tile from Coors, at a similar thickness of 3-4 mm would be a reliable reference in my system. This tile would be applied against the same background used to measure my samples (i.e. small agricultural pellets). This request for a thin reference is mainly due to the reduced space I have in my NIR configuration. What do you think? Thanks, Joelle | ||
| Howard Mark (hlmark) Senior Member Username: hlmark Post Number: 531 Registered: 9-2001 |
Art - the comment about getting equivalent reflectance with 3 mm Fluorilon + SS backing as 8.25 mm Fluorilon is interesting, but is it really equivalent? Meaning: have you ever had the opportunity to check whether the diffusivity of the thinner layer + [mirror] is as good as the thicker layer? I agree that the ceramic is not as diffusive as Fluorilon (or various other forms of what amount to powdered Teflon). On the other hand, having used ceramic pieces as reference reflectors for many years before Fluorilon became available I have to disagree with the statement that once they get dirty "it's all over"! Ceramic is physically much more robust than any of the Tefon variants, and often can be cleaned, and will stand up to the cleaning process better. The most common contaminant, in any case, is moisture which will become adsorbed on any porous material, so the Fluorilon is no protection against that. This is said not to denigrate Fluorilon, but simply to recognize that each material has its own advantages. \o/ /_\ | ||
| Art Springsteen (artspring) Senior Member Username: artspring Post Number: 49 Registered: 2-2003 |
I guess I should comment on this, as I'm the progenitor of the thickness specifications for Fluorilon� and Spectralon�. Yes, 7 mm is what is specified for low density sintered PTFE. We ship our standards at 8.25 mm thickness.* The reason is that's what fits our sample cups and gives the highest reflectance. Another way of boosting the reflectance if you are under that thickness is to back the material with a thin piece of (semi) polished stainless steel. Using this technique, we've had customers tell us they can get appx. the same reflectance as an 8.25 mm thick pieces with a 3mm thick piece of Fluorilon. As for the Coors Ceramic- we were supplying this to an NIR manufacturer for a while. It was quite thick (12 mm), but we use the same stuff for a color reference at 8 mm thick. I just don't like the surface finish, plus once it's contaminated, that's the end of the game. It's also VERY expensive compared to Fluorilon. *in theory, that is the 'opaque thickness' above which you get no increase in reflectance. That's not totally true (the stainless steel backing does give you minimally more reflectance) but it's a good first approximation. | ||
| Joelle Rahm� (rahm�) New member Username: rahm� Post Number: 5 Registered: 10-2011 |
Hi all, I have read through all the topics relative to the use of a ceramic tile as a reflectance standard. I couldn't find anything about the required thickness of such tiles. As I understand, Foss 6500/5000 used to have one in their devices (replaced now by Fluorilon?) and one can order it from Coors. I wonder if there is a minimal thickness required when using a high purity Alumina reference tile like it is the case for Spectralon (I had read somewhere that a reference made of Spectralon needs to be at least 7mm thick). Can anyone help me on that? Or if anyone has a device that uses a ceramic tile as reference, could you check what is its thickness? And what about the fluorilon reference: how thick it is/should be? Thank you! Joelle |