Information for Removal of Residual Boron Nitride

Boron Nitride coatings that are water-based or solvent-based can be removed by simple
wiping with a wet-cloth [wetted with water or solvent … depending on which type of coating]
if they have been applied and only dried and/or have “seen” very little heat. Also, soaking in
water (for water-based) or solvent (ethanol or acetone or a “mix” of them) will allow
coating removal. If either water- or solvent-based coatings “see” heat over a few hundred
degrees Centigrade, the coatings are baked on such that the removal of residual Boron
Nitride requires mechanical means of removal such as:

  • Scrubbing with a scrub-pad or light abrasive-pad such as plastic ones used to scrub dishes.
  • Light sandpapering [since BN is so soft, it does not require much effort to abrade it off of a surface]
  • Light wirebrushing
  • Light grit-blasting or light shot-blasting
  •  CO2 [dry ice] blasting
  • Water-jet powerwashing [similar to the WaterPik used for teeth cleaning but, of course, with much stronger water stream; also similar to the power-washers used for cleaning driveways]
  • Ultrasonic-cleaning baths/tanks have been shown to aid the removal of residual BN from surfaces.

Chemical removal of BN is quite difficult/tedious … but is described here for reference [Note: we do not have specifics on this technique, although it has been reported to work on aluminum substrates.]:
Boron nitride is not easily removed and cannot be dissolved off due to its chemical inertness/stability. To remove boron nitride paint from a material such as a metal or ceramic, a harsh/aggressive acid wash is thus normally used. Typically, the acid wash contains water and a mixture of acids such as sulfuric and hydrofluorosilicic [HFC] acids. Other acids which may be included in acid washes including mineral acids such as nitric, hydrochloric, hydrofluoric, and phosphoric as well as organic acids such as acetic and formic acids. The acid, or acid components, in the acid wash can facilitate the complete removal of boron nitride from the material by affecting the residual suspension agent/binder phases or by slightly dissolving the substrate enough to get the boron nitride layer to release. The acid wash preferably should be aqueous containing enough acid to adequately remove the boron nitride paint. In some cases, the pH can be in the range of less than 1, such as 0.25 up to 5. Often, a pH at or below 2 may be used. An example of an acid wash is an aqueous solution comprising a mixture of sulfuric acid along with hydrofluorosilicic acid (also referred to in the art as fluosilicic acid and fluorosilicic acid) — i.e., 3.5% of sulfuric acid (approx. 35 cc “concentrated” acid to 1000 cc water … with approx. 3 cc of 23% solution of HFC) at 40 C or about 100 F].

A mixture of hydrochloric acid along with fluosilicic acid has been shown to be effective in leaching aluminum ores to remove the aluminum oxide in U.S. Pat. No. 3,816,605 granted on Jun. 11, 1974 to Belsky; thus, this mixture can also be considered for leaching boron nitride paint that contains aluminum oxide resulting from a suspension agent/binder phase, such as used in BN-Lubricoat.

Information for Removal of Residual Yttrium Oxide

Yttrium Oxide coatings which can be used in all environments (inert, vacuum, nitrogent and even including air/oxygen atmospheres) include:

The “Y” [Yttrium Oxide] coatings are very thermodynamically stable and have the interesting advantage that Yttrium Oxide can be easily “leached” off. The Yttrium Oxide is readily dissolved [i.e., like an Alka-Seltzer in water] when contacted with a dilute nitric acid solution [i.e., 1:1 to 3:1 water:conc.nitric]. Thus, any residual Yttrium Oxide is easily removed by the ‘leach’.

By using Yttrium Oxide as a “primer” coating with other hard-to-remove coatings (such as Boron Nitride ones) as the “topcoating”, it is possible to easily dissolve off the underlying Yttrium Oxide coating and thus remove all the residual coating/paint material.