Seeking Dow 19 Mag Treatment Chemistry

A. Dow 19 is 1 oz. Chromic Acid, 1 oz. Calcium sulphate (plaster of Paris), and water to make one gallon.

A. I have also searched for DOW 19 to pre treat Magnesium control surfaces as required by Allied Signal and Raytheon. I have located the ingredients to make it, and their instructions. They are as follows.

Mix 1.3 ounces of chromic acid (flake) and 1 ounce of calcium sulphate with enough water to make 1 gallon of solution.
Stir vigorously for at least 15 minutes to ensure saturation of the solution with calcium sulphate.
Maintain solution at 21 °C to 32 °C (70-70 °F).

The ingredients can be found locally almost anywhere.

A. Hi, Chris. That would be by weight. Although cooks might measure solids by volume for kitchen convenience, in the laboratory solids like chromic acid flake are invariably measured by weight rather than volume. Good luck.

Regards,

A. You could try an old Lycoming piston engine mix I have used for years:
Magnesium Treatment
Selenious acid, hydrated selenium dioxide
Molecular formula: H2SeO3
10% W/V Selenious Acid 100 ml
10% W/V Chromic Acid +(0.1v/v H25.4) 100ml
----------
Make touch-up solution in the following manner:
Prepare a solution of sodium di-chromate by mixing 3/4 lb. sodium dichromate with 1/2 gallon water;
Prepare a nitric acid solution by combining 3/4 lb. nitric acid (sp. g. 1. 42) with 1/2 gallon water
Combine the sodium dichromate solution and the nitric acid solution.

Coat the newly machined or cleaned surfaces with dichromate touch-up solution.
Apply the solution with a brush or Q-tip [affil links] and allow to stand for one minute
Wash solution off with water or wipe off with a damp cloth.
Be careful not to allow dichromate solution to come in contact with eyes or skin

A. I believe you are looking for MIL-M-3171 type IV (Brush-On)

DOW 7 is TYPE III
DOW 19 is TYPE VI

A. Unfortunately, I cannot answer all of your questions. The first one regarding the chance of success is extremely difficult to answer without knowing all of the product requirements. What I can tell you is the weld repair of castings is regularly performed, and some distortion may occur as a result. You should have the Dow 19 coating removed prior to welding. Discuss this with your coating vendor.

Based on the photo that you provided, I doubt that you will be able to seal all of the porosity, unless you apply weld metal over a large portion of the boss, which will likely result in distortion. If the cost to scrap the casting is significant, then you probably should attempt the repair, and be prepared to grind the weld back to the desired shape. Small porosity can be sealed by a suitable resin, such as one of the products from Loctite.

Good luck,

A. Vacuum impregnation will seal microporosity in the casting. The large holes, as Toby pointed out, can be "macro-sealed" using a 2-part air curing epoxy such as a Loctite material or other impregnant (there are a number of manufacturers). Weld repair of porosity is not entirely possible since there is always gas produced that must escape, thus creates a leak path around the weld. Vacuum impregnation (ref. MIL-STD-276, Method B) can repair swiss cheese castings and hold up under pressure or vacuum.

A. "AIVODIZING" is probably "anodizing" and "ROMIC ACID" is probably another container of chromic acid.

If these are waste products rather than new unopened containers, the person or entity who occupied the building before you is probably liable for proper disposal despite anything that may have been said in the sale papers about "including all contents". I am not a lawyer, but I understand that there is a principal that contract terms are automatically void which are "contrary to public policy" -- and in the USA today the generator of hazardous wastes is responsible for hazardous wastes from "cradle to grave".

If I were you, I'd talk to my attorney about the possibility of enforcing that policy rather than thinking you can use these chemicals, because you probably can't. Good luck.

A. Dow 19 is also available from Beechcraft. It is used on their magnesium control surfaces. I have made it in the past from the chromic acid and calcium sulphate recipe but I have found it easier to procure from Beechcraft than purchasing chromic acid from a chemical supplier.