Green chromating

Chromate conversion coatings are thin, noncrystalline, adherent surface layers of low solubiHty phosphoms and/or chromium compounds produced by the reaction of suitable reagents with the metal surface (2,3). The two classes of chromate coatings are chromium phosphates (green chromates) and chromium chromates (gold chromates). 

Nagle MG, Osorio D. 1993. The tuning of human photopigments may minimize red-green chromatic signals in natural conditions. Proc Biol Sci 252 209-213. 

The red chromaticity coordinate is given by x, and the green chromaticity coordinate is given by y. The tristimulus values are linear in /(A) and thus the absolute intensity information has been lost in the calculation of the chromaticity coordinates x, y). AU color distributions, /(A), that appear to an observer as having the same color will have the same chromaticity coordinates. 

Fluorescent complex formed Yellow-green Chromate, periodate, peroxodisulfate, and hexacyanoferrate(l 11) must be reduced 0.04... 

Chromates(V), (CrO ) ". Dark green species which hydrolyse and disproportionate to Cr III) and Cr(VI) (K2Cr04 plus KOH in melt). 

A reducing agent (for exampie sulphur dioxide) reduces the yellow chromate or orange dichromate to the green chromium(III) state. 

Wood Preservation. The use of chromium compounds ia wood preservation is largely because of the excellent results achieved by chromated copper arsenate (CCA), available ia three modifications under a variety of trade names. The treated wood (qv) is free from bleeding, has an attractive ohve-green color, and is paintable. CCA is widely used, especially ia treating utility poles, bull ding lumber, and wood foundations. About 62% of all the chromic acid produced ia the United States is consumed by the wood preservation industry (77,167) (see Building materials, survey). 

Other Color Order Systems. The Natural Color System (24), abbreviated NCS, developed ia Sweden is an outgrowth of the Hesselgren Color Adas, and uses the opponent color approach. Here colors are described on the basis of their resemblances to the basic color pairs red-green and blue-yeUow, and the amounts of black and white present, all evaluated as percentages. Consider a color that has 10% whiteness, 50% blackness, 20% yellowness, and 20% redness note that the sum is 100%. The overall NCS designation of this color is 50, 40, Y50R iadicating ia sequence the blackness, the chromaticness (20 + 20), and the hue (50% on the way from yellow to red the sequence used is Y, R, G, B, Y). 

Chromating Chromating is considered in Section IS.3. The chromate film on zinc is adherent and can be drab, yellow-green or colourless in appearance the colour varies considerably with the method of application. It retards white rust , the white deposit which sometimes forms on fresh zinc surfaces which are kept under humid conditions (see Section 4.7). A chromate film is damaged by heat and if used as a basis for paint adhesion, should preferably not be heated above 10°C, nor for longer than 1 h. 

Procedure. Prepare a 0.25 per cent solution of diphenylcarbazide in 50 per cent acetone as required. The test solution may contain from 0.2 to 0.5 part per million of chromate. To about 15 mL of this solution add sufficient 3M sulphuric acid to make the concentration about 0.1M when subsequently diluted to 25 mL, add 1 mL of the diphenylcarbazide reagent and make up to 25 mL with water. Match the colour produced against standards prepared from 0.0002M potassium dichromate solution. A green filter having the transmission maximum at about 540 nm may be used. 

Apochromat Microscope objective that has better color correction than the much more common achromat objectives corrected chromatically for two wavelengths of light (red and blue). Apochromatic objectives are corrected chromatically for three colors (red, green and blue) and spherically for two colors, which practically eliminates chromatic aberration. 

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