Zinc Tetroxy Chromate. A Rust-Inhibitive Primer Pigment

Abstract

The excellent rust-inhibitive properties of chromates are generally recognized; zinc yellow, perhaps most important of the chromate pigments, is finding extensive use in metal primers for the protection of ferrous and nonferrous metals and alloys. Efforts to overcome the effect of a relatively high content of water-soluble sulfate as well as a tendency to blister under exposure to high humidity or water have resulted in the development of a new zinc chromate pigment, ZnCr04.4Zn(OH),.This zinc tetroxy chromate is much less soluble in water than is ordinary zinc yellow and hence yields more water-resistant H E outstanding corrosion-inhibitive properties of the chromate ion are well recognized by scientists and tech-T nologists charged with the production, design, and maintenance of metals and metal structures (1, 9, 10,11,16,16) although the exact nature of the protective film produced by chromates is still a point of controversy (3). The development of the stainless steels, with their relatively high content of chromium, and the increasing use of chromates in the pretreatment of metal articles (2, 8) to enhance their resistance to corrosion are but two of the many applications of the unique properties of this element and its compounds to the problem of conserving metals. Atmospheric Exposure Tests on Chromate PigmentsPaint technologists have not neglected the chromate pigments ( I ) , and their value in priming paints for metal protective service is more widely recognized today than ever before. Our own interest in the chromate pigments was stimulated by the excellent results frequently obtained during investigations of various metal-protective primers. Typical results for a representative series of such paints after 5.5-year exposure a t an angle of 45" facing south in a semiindustrial atmosphere are shown in Figures 1 and 2.The 5 X 10 inch (12.7 X 25.4 om.) panels shown in Figure 1 were cut from exposed, larger, copper-bearing black iron panels which had been finished with one coat (right half) and two coats (left half) of raw linseed oil primers containing the pigments indicated. To permit a better portrayal of the results of these tests, these sections were cut as shown in Figure 1. The small sections (1 X 2 inches, or 2.5 X 5.1 cm.) marked B were washed with soap and water to remove the dirt and grime which had accumulated during the exposure and show the condition of the paint films (Figure 2). I n order to determine to what extent the paints had protected the metal, paint films. Since it is essentially free from corrosion-inciting ions such as sulfate, none of its water-soluble chromate is needed to counteract the effect of eelfcontained harmful ions, and all is available for combating external corrosive agents. Laboratory fresh and salt water immersion tests, tide-water-level exposures, and electrode potential measurements have demonstrated the water resistance and corrosion-inhibitive properties of priming paints containing zinc tetroxy chromate. Exterior exposures indicate excellent durability and weath...

Historical primers and paints used for aeronautical protection and colouring during WWII: A multi-techniques approach on archaeological parts

“…Couples with a  13 C value greater than 100 ppm deal with a polymerized phthalate present in the composition of nitrocellulose paint through phthalate plasticizers or alkyd resin ( 13 C = 167ppm). Nitrocellulose can also be found in the HSQC spectrum (in negative by the pairs  13 C-1 H (ppm)): 68-3.65; 68-4.2; 66-3.5 and 65-4.35 [26] and also detected in the 13 C spectrum (Figure B.2).Those results are also in good agreement to previous results published by Mejia-Gonzalez on plasticized nitrocellulose [26]. Finer information and better signal detection could be obtained using larger magnetic field, helping with the gain of signal/noise ratio and allowing to show certain missing correlations on the 2D coupling spectra.…”

“…An NMR analysis was performed only on the beige paint of the sample MS733. NMR spectrum was acquired on BRUKER spectrometer operating with Advance NEO console at 300 MHz for all spectra at 298 K. 1D-NMR and 2D-NMR experiments were: 1 H, 13 C, heteronuclear single quantum correlation spectroscopy (HSQC) and heteronuclear multiple-bond correlation spectroscopy (HMBC) from 1 H- 13 C. The chemical shifts (d) have been reported in ppm calibrated with the solvent resonance as the internal standard CDCl3 and DMSO-d6. The solutions were filtered on Célite® to remove eventual aluminium residue that can intercept binder signals.…”

“…In the particular case of corrosion inhibitor pigments [11], chromate-based compounds were used. They included zinc chromate [12], zinc-potassium tetroxychromate [13], potassium chromate K2Cr2O7, barium chromate, strontium chromate, lead chromate [14] and others… After decades of usage, abandonment and/or repainting campaigns by volunteers' associations in the case of collection aircraft, the original protection deposited on the alloys is frequently lost and at best, difficult to identify. Although little of the original surface of the aircraft wrecks remains due to their long stay on the ground or in the sea, these remains are a rare and highly valuable cultural testimony of the technological solutions used by manufacturers.…”

Analysis of Chromate-based Primers for Protection of Aluminium Alloys on Historical Aircraft

“…Zinc tetroxychromate (4ZnCrO4•K2O•3H2O) is a well-known pigment that was developed in the 19 th century [16]. This compound was tested as a corrosion inhibitive pigment in the early 1940s [2] and proved to be an excellent inhibitor as well as being resistant to humidity. Hence, it has been widely used in aeronautics industry as corrosion inhibitor for aluminium alloys, particularly in France [5,17].…”

“…However, very early in the history of the alloy, the low corrosion resistance of Duralumin was a major concern and developing solutions for its protection was a priority for engineers and scientists. The corrosion inhibitive properties of chromates were well-known in the area of metal protection [2] and consequently, one of the first solutions to protect Duralumin from corrosion was the addition of chromate pigments to a paint primer. Chromates could be associated with various cations, namely, zinc, potassium, potassium-zinc, barium, strontium, lead, etc.…”