Lubricant additives are one or several compounds added to the lubricant to impart certain new characteristics to the lubricant or to enhance some of the existing characteristics within the lubricant. This is the most classic concept. We can understand that: Additives are chemical substances with the following characteristics: ① They can endow the base oil with properties or performances that it does not inherently possess; ② They can improve the original properties or performances of the base oil; ③ The dosage of additives generally ranges from a few percent to a few millionths.
Let’s categorize the additives roughly, and we can see:
Cleaners, dispersants, anti-wear agents, extreme pressure agents, friction modifiers, preservatives, and rust inhibitors – these are all for protecting the lubrication surface.
② Viscosity index improvers and pour point depressants, these are used to enhance the physical properties of lubricants;
③ Antioxidants, metal passivators, and anti-foaming agents – these are for protecting the lubricant itself.
So, I often say that for any type of lubricant, regardless of its specific variety, in the development of its formula (refer to my article on my understanding of the concept of “formula”), if the three main points can be grasped, namely the antioxidant property, lubricity, and rheological property of the oil, then a good lubricant product can basically be produced.
The most common types of additives are as follows, and this can be found in most textbooks. What I want to emphasize here is that the development of science and technology is advancing rapidly, and new functional materials and concepts are emerging constantly. It is believed that in the field of materials, China has a large number of papers published in domestic and foreign journals, ranking among the top in the world and can be called a “paper power” country! However, this is of no use. The manufacturing level of new materials in China is not satisfactory. Many high-tech fields are constrained by basic materials. The same is true for lubricant additives. Before a “revolutionary” breakthrough becomes a reality, it is advisable to use some new concepts cautiously and thoroughly develop hundreds of known additive varieties and their derivatives to the fullest extent. This is the only way to produce high-quality lubricant products.
Thus, we should have a precise understanding of the commonly used additives in our daily lives. Accurate use of these additives is a practical way to improve the quality of our products, it is also an attitude of showing respect for science, and at the same time, it can steadily enhance the overall level of our lubricant industry.
Cleaner: Various sulfonates, phenates, salicylates. It adheres to the substrate of the sediment through chemical reactions or physical adsorption, neutralizes the substances, and keeps them in a dissolved state in the oil.
Surfactant: Various diisobutyramides, dibutyric esters, and Mannich bases. Through the adsorption of polar groups, they combine with oil sludge and soot (tarry matter) to prevent their aggregation and maintain dispersion in the oil.
Antioxidant: ZDDP (di-alkyl disulfide phosphoric acid zinc), shielding phenol, aromatic amine, sulfide alkyl phenol, organic acid copper salt. It interrupts the chain reaction of free radicals at the initial stage of oxidation or decomposes peroxides, terminates the free radical reaction, thereby delaying the oxidation of the lubricating oil.
Metal passivator: Organic amines containing nitrogen and sulfur, sulfides, phosphonates and other chelating agents. These substances form a passivation film on the metal surface by complexing with metal ions, thereby reducing the catalytic effect of the metal on oxidation.
Anticorrosive and anti-rust agents: ZDDP, basic metal sulfonates, fatty acids, fatty amines. The polar groups preferentially adsorb onto the metal surface, forming a protective film that prevents corrosion of non-ferrous metal surfaces and rusting of ferrous metal surfaces.
Friction improver: Organic fatty acids, fatty amines, molybdenum sulfophosphate, sulfurized olefins from animal and plant oils, phosphonate esters. They preferentially adsorb onto the metal surface, forming a stable adsorption film, which reduces friction under conditions close to the boundary lubrication.
Extreme pressure anti-wear agent: ZDDP, phosphoric ester, sulfide olefin, sulfide fatty acid, borate (ester), compounds containing S, P, and N, which form a solid film with low shear strength on the metal surface through chemical reactions, preventing contact between metals.
(To be continued)
Author: Li Yunpeng, Institute of Petrochemical Sciences, Professor, Senior Engineer, and Postgraduate Supervisor. After graduating as a postgraduate from Nankai University in 1987, he joined the Institute of Petrochemical Sciences and has been engaged in the research and development of lubricating oils and additives for nearly 30 years. He has published over 70 papers in domestic and international academic journals, holds 15 invention patents, and the products he led in developing have won the first prize of national science and technology once, along with several other awards.
