EMI/RF - Page 1
Forum section: electronics / repair

author: GEuser
author_rank: Frequent Contributor
timestamp: August 11, 2016, 04:29:00 am
content: Q

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 11, 2016, 11:00:33 am
content: Good to know.I've seen a "stainless steel loaded" product that, practically speaking, didn't seem to be much more than heavy gray paint. Didn't do anything for RFI.Conversely, I've used boxes lined with the stuff (real, usefully conductive paint, that is; usually a silver to golden color), which did a fine job. It's pretty awesome seeing ~kV ESD pulses simply wash over and around a plastic box, with >40dB isolation on the inside.They're even available with IP67 or similar ratings, which surprised me. The gasket looked like a white o-ring that someone dropped in a little dust, but it's actually quite conductive, and keeps water out!Tim

author: Ian.M
author_rank: Super Contributor
timestamp: August 11, 2016, 11:16:36 am
content: For 'cold galvanising' to be effective against corrosion, the zinc particles must make electrical contact with each other and the substrate, so there is an incentive for the paint manufacturer to come up with a conductive formula even though that's not its intended use. However it will oxidise more readily than a Nickel based screening spray, loosing conductivity with time, so you may need to over-coat it with lacquer to protect it.

author: Cerebus
author_rank: Super Contributor
timestamp: August 14, 2016, 09:15:03 pm
content: Quote from: GEuser on August 12, 2016, 12:33:54 amI think you're misunderstanding Ian.M. He's saying that for this paint to do its job as an anti-corrosive galvanizing spray it is required perforce to be conductive and that's a useful side effect from our point of view so it makes good shielding.The mechanism for it protecting your gates is that the zinc preferentially oxidises instead of the steel. Zinc isn't a particularly noble metal, it corrodes quite easily. Zinc granules, that you'll find in any chemistry laboratory, always have a fine coating of white zinc oxide. In galvanization it protects by corroding away over time as it donates electrons to the iron which requires a galvanic path between zinc and iron.Ian.M's concern is that, in the shielding use, natural surface oxidisation of the tin particles may, over time, lower their conductivity. I don't find this unrealistic, but equally I don't know if the effect would be enough to be of concern.

author: Ian.M
author_rank: Super Contributor
timestamp: August 15, 2016, 01:23:43 am
content: I merely pointed out that the conductivity of cold 'galvanising' paint is likely to deteriorate quicker than nickel loaded screening paint. Anybody who doesn't think zinc oxidises in air is delusional. Without doing a full quantitative chemical analysis and comparing with a reference sample that has been stored under inert gas, you cant tell how badly oxidised the zinc particles actually are, and unless you work for a paint research lab, you are unlikely to have the facilities (or need) for such an analysis.The test probes are another matter - if your probes are made of brass that is so soft you have to resharpen them after only fifty measurements, you are *NEVER* going to see enough oxide buildup to cause problems. However I dont resharpen my probes daily and have had probes that did not make reliable contact probe to probe even after cleaning with IPA soin my experienceoxide buildup can be a real problem.I didn't contradict or dismiss your experimental findings, so have no idea why you are exhibiting such a severe case of butt-hurt!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 15, 2016, 06:32:52 am
content: Quote from: GEuser on August 15, 2016, 04:25:27 amWell, zinc corrosion is primarily environment driven...I suppose the overall conductivity would depend on sneak paths through layers of flat platelets. Conductivity (and galvanizing effectiveness) will depend most critically upon how those paths oxidize. If the binder (paint base) provides an effective oxidation barrier, then the surface will oxidize first, and the paint will last the longest.Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 15, 2016, 07:52:41 am
content: That one looks like it might be evaporated (in vacuum), or plated (electroless, in solution), which is also a common method.Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 15, 2016, 03:11:06 pm
content: Electroless can be had from Caswell Plating, probably among others. IIRC, it's not terribly cheap, and is hazardous waste (don't pour it down the drain!). Results may vary; plating is extremely critical of surface prep.Vacuum would be a fair sight harder to obtain from a bottle,but some amateurs have taken it on, e.g. for telescope aluminizing. Cool projects, but a lot of work!Tim

author: Cerebus
author_rank: Super Contributor
timestamp: August 15, 2016, 04:39:09 pm
content: Quote from: GEuser on August 15, 2016, 12:42:58 amI don't see why you're getting in such a tizzy dear. I was just trying to add a little clarification. Y'know, trying to be be helpful. If you want to deny electrochemistry, feel free.

author: Cerebus
author_rank: Super Contributor
timestamp: August 16, 2016, 01:25:36 pm
content: Quote from: GEuser on August 16, 2016, 03:04:26 amMeh, whatever. You're clearly a lost cause...