G. Cholakov, N. Georgiev, Chr. Ivanova, K. Stanulov 299 Journal of the University of Chemical Technology and Metallurgy, 40, 4, 2005, 299-306 INTRODUCTION Ultradisperse diamond powder (UDDPs) with di- mensions in the nanoscale are produced by detonation of carbon-containing explosives under conditions of negative oxygen balance [1]. Because of their particle size, which is smaller by three orders of magnitude than the size of dynamically synthesized diamond, and spe- cific conditions of formation, UDDPs exhibit some unique properties and especially a high and peculiarly manifested chemical activity. The latter allows for sur- face modifications and outlines a wide range of poten- tial applications [2, 3]. Different UDDPs on the market range from pure diamond powders to products containing also soot in different proportions, depending on the depth of removal of the soot originally present after the detonation synthesis [3]. In lubricants, which are of particular interest in this work, UDDPs are predomi- nantly used in the form of suspensions [4]. The high surface activity leads to the aggregation of UDDP particles and to a varying stability of the suspensions, STABILITY OF ULTRADISPERSE DIAMOND POWDERS IN OIL SUSPENSIONS G. Cholakov, N. Georgiev, Chr. Ivanova, K. Stanulov University of Chemical Technology and Metallurgy 8 Kl. Ohridski, 1756 Sofia, Bulgaria E-mail: cholakov@uctm.edu ABSTRACT Nanosized ultradisperse diamond powders (UDDPs) have shown potential for application in different industrial products. In lubricating oils they are introduced in the f orm of suspensions in organic liquids. Previously we have proposed an express method for determination of the concentration of powders in oil suspensions. The aim of this work is to present our results on the application of the UV-VIS method for determination of the stability of UDDPs in oil and to compare the effect of different stabilizers used as lubricant additives and the influence of ultrasonic treatment on UDDP stability in oil. The stability of UDDP suspensions has been followed for up to 75 days in storage. The obtained results show that powders containing soot are more easily stabilized than those with pure diamond. Ultrasonic treatment has an ambivalent effect and it is very important to determine correctly the time which would produce the required stability. Certain additives widely used in lubricants can ensure stability higher than that of a commercial product used for comparison. However, when preparing a concentrate for particular formulated oil the eventual effect of the additive package already present on the stability of UDDP in the doped oil should be considered. Keywords: ultra disperse diamond powders, lubricants, UV-VIS spectrometry, oil suspensions, solid lubricants. Received 10 November 2005 Accepted 30 November 2005