In the paper, ultrafine diamonds and specified class of related nanomaterials are investigated. We consider basic physical and chemical parameters of the nanodiamond: specific surface area, pore volume, particle size. Also, processes of nanodiamonds heating and loading are studied. We present an approximate composition of a nanodiamond with impurities and various elements contained in ultrafine nanodiamonds. A method of nanodiamond cleaning that allows to get rid of a significant number of impurities is proposed. The data of thermal and mass spectrometric analysis after nanodiamond purification are presented. A technique for obtaining a suspension based on detonation nanodiamond for steel surface modification is developed, and the equipment for such technique is described. Also, carbon distribution in the surface layer of a steel sample is analyzed along with a microhardness at different surface locations of the steel sample. Additionally, a panoramic picture of the steel sample with a 100 times magnification is provided. The analysis of the relationship between structure of steel surface with embedded nanodiamond particles and microhardness distribution reveals the explicit dependence of the microhardness on the percentage of carbon at the same depth.