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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Preventing radiator corrosion using sodium phosphate, analyzing its effects on various water types and engine materials.

Identifier  ExFiles\Box 27a\3\  Scan087
Date  27th November 1929
  
To. Hs.{Lord Ernest Hives - Chair}
x4516.
C-to Sq. Bv.

H13/EA27.11.29.
Laboratory.

Re Blocking of Radiators - Your Ref.
R1/M22.11.29. - Further to my notes
H11/EJW.26.10.29. and H11/EJW./2.11.29.

Sodium phosphate as a dry powder is being made locally (in Derby) into tablets containing about half an ounce each. A 40/50 radiator would need 3 such tablets. Three more tablets would be added to the same water (including any more water added to make up evaporation losses) after 3 months or so, or if the radiator was filled with fresh water.

The addition of sodium phosphate is beneficial with any type of water, including the peaty variety.

There is no marked difference between the amount of corrosion with neutral waters, such as soft water, condensed steam water or distilled water, since oxygen, the principle corrosion agent, from the indrawn air, dissolves in all of them to about the same extent. If the bulk of this oxygen could be prevented from entering the radiator and dissolving in the water, there would be a great reduction in the amount of corrosion sludge produced, other things being equal. This method corrosion reduction would in itself be very beneficial and sodium phosphate would then be unnecessary. On the other hand the sodium phosphate treatment should be adequate by itself.

An analysis of the corrosion products or sludge, when RR50L alloy is connected to cast iron and radiator tubes (tinned) shows that the amount of aluminium corrosion is negligible (even in the absence of sodium phosphate). The amount of corrosion sludge is roughly proportional to the area of cast iron surface exposed to the water (if unprotected by an oxydising or sealing heat-treatment, which is now being tried on production). This suggests that the effect of the aluminium head may be less important from the corrosion point of view than anticipated, in any case any slight disadvantage that could be proved would be easily outweighed by its advantages, including the tremendously greater heat conductivity of the aluminium head, i.e. four times as great as cast iron.

The electrolytic effect does not appear to be great under normal radiator conditions owing to the water being a poor conductor. Action is also reduced by oxide films which hinder action other than the highly localised electrolytic type, i.e. between adjacent constituents of the cast iron for example.

The graphite does slow down corrosion in time, but this might be too late to avoid choking up closely spaced radiator tubes. This choking appears to be accelerated if the products of corrosion become caked by semi-drying or sedimentation. Such conditions may arise if a radiator is emptied or left standing when it contains a considerable quantity of corrosion products. (this should not be possible when using sodium phosphate and oxydised cast iron).

The Water in a radiator should be changed as little as possible by owners, especially if treated with sodium phosphate,
  
  


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