Zinc Dithiophosphates 61
formulations. This has generally been limited to the European market, having been pioneered in
Germany.
ZDDPs, in combination with sulfurized olefi ns, are also used to replace chlorinated paraffi ns
in medium- to heavy-duty metalworking fl uids. This is due to the possible carcinogenicity of the
low-molecular-weight analogs of chlorinated paraffi n. European formulators, and to a certain extent
Japanese formulators, use ZDDPs in this way. The use of ZDDPs in metalworking fl uids in the
United States is limited due to environmental concerns. The U.S. Environmental Protection Agency
classifi es them as marine pollutants.
In conclusion, after 50 years, ZDDPs still enjoy a wide variety of uses in the lubrication indus-
try, with production volumes remaining at high levels. The majority of ZDDP production is used
in automobile engine oil. The impact of the GF-2 and GF-3 phosphorus-level specifi cation of 0.1%,
however, was reduction of ZDDP production in the past 10 years. The Ford Motor Company is
currently evaluating engine oils with 0–0.6% phosphorus levels in fl eet tests in preparation for the
looming GF-4 standard in 2004, which will require engine oils to have minimal impact on emis-
sion system deterioration. This could further negatively impact ZDDP production. The need to
understand clearly how ZDDPs function in terms of wear and oxidation protection is reinforced by
the need to develop satisfactory phosphorus-free alternatives to ZDDP. The development of such
chemistries, within the economic and functional limits that ZDDPs impose, will be a daunting task
for future researchers. Until that time, the elimination of ZDDPs from various industrial lubricants
will mandate either higher costs or less performance.
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