Kinetics, isotherms and enthalpy of adsorption of zinc di-n-alkyl(di-n-alkylphenyl, di-n-dialkylphenyl)dithiophosphates (ZDTPs) lubricating oil additives on zirconia partially stabilized by yttria (PSZ) powder from hydrocarbon solution at temperatures 25°C and 35°C were done. The adsorption enthalpy has been determined using a Montcal calorimeter. ZDTP adsorption isotherms are Langmuir-like. The adsorption quantities and differential molar enthalpies DH a d À Á of ZDTPs adsorption on PSZ are low for n-alkyl derivatives, the adsorption decreases with the increasing length of the hydrocarbon chain of the additive ZDTP, the unexpectedly for di-n-propyl ZDTP the differential molar enthalpies of adsorption at 25°C are very low, near zero and for di-n-dialkylphenyl ZDTP only at lower coverage ratios are endothermic, at higher surface coverage for this and remaining additives are exothermic. At 35°C all n-alkyl ZDTPs adsorb on PSZ endothermically endothermic, while both aryl ZDTPs exhibit exothermic effects. All ZDTPs are reversibly physisorbed at 25°C and at 35°C except for both mono-and dialkylphenyl ZDTPs, which are weakly chemisorbed.
Wear investigations concerning the different structures and metal atoms of metal dialkyldithiophosphates (MeDTPs) were conducted using a ball‐on‐disc apparatus. Steel ball bearings (3.175 mm in diameter) and counterface discs, made of hot pressed ZrO2 partially stabilised by Y2O3, were used. The synthesised MeDTPs were made up of primary linear aliphatic alcohols with hydrocarbon lengths varying from 8 to 16 carbon atoms, and contained the following metals: zinc(II), iron(III), gallium(III), antimony(III), and copper(II). Tests were performed at room temperature. The sliding speed was set to a constant 0.03 m/s, and a constant 30 N load was used. The additives investigated were used as solutions in n‐hexadecane.
The study also focused on the influence of additive concentration on wear. It was found that the effectiveness in reducing wear depends both on the metal atom and on the length of the hydrocarbon chain in the additive's molecules. The lowest wear volumes were observed for additives with n‐octyl and n‐tetradecyl hydrocarbon chains. The worst antiwear performance was observed for n‐dodecyl derivatives. For almost all additives, more concentrated solutions resulted in less wear. Some friction coefficient results are also presented.
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