Study On The Preparation Of Co-Al Hydrotalcite-like Compounds And Tribological Properties

Co-Al hydrotalcites （Co-Al-LDHs） had been prepared in different ways. The crystal structure and outward appearance, IR property and thermal stability of the hydrotalcites had been studied by XRD, TEM, FT-IR and TG-DTA. The tribological properties was evaluated by four-ball friction test, gear friction test and so on. The principal results of this paper are as follows.Co-Al-CO₃ hydrotalcite was prepared by co-precipitation method. The optimized process parameters are: concentration of salt solution 1mol/L,reacting at 70℃and crystallizing at 80℃for 12h. Sample obtained under this condition was well crystallized. It had a morphology of hexagonal sheet with diameter of about 100 nm, thickness of about 15nm. The order of the conditions’influence on average particle size is: crystallization time, concentration of salt solution, crystallization temperature and reaction temperature. The order of the conditions’influence on particle size distribution is: crystallization time, reaction temperature, crystallization temperature and concentration of salt solution.Co-Al-CO₃ hydrotalcite was also prepared by hydrothermal method.The optimized process parameters are: molar ratio of Co/Al 3:1,using mixed solvent of water-ethyl hydrate and crystallizing at 120℃for 5h.Sample obtained under this condition was well crystallized. It had a morphology of homogeneous and regular hexagonal sheet with diameter of about 150²00 nm, thickness of about 20 nm. The results also show that by controlling the reaction conditions,a series of Co-Al-CO₃ hydrotalcites can be successfully obtained.Compared to co-precipitation method,preparation by hydrothermal method is more convenient for manipulating and designing,and needs shorter crystallization time.The synthesis of the dodecylsulfate and borate pillared hydrotalcite had been carried out by anion exchange method and hydrothermal method respectively. Compared to that obtained by the anion exchange method, the sample obtained by hydrothermal method had a higher crystallinity. Pillared hydrotalcites had an improved amorphous character than Co-Al-CO₃ hydrotalcites, but they still maintained layered structure. Basal spacing increased because of the intercalation, resulting in its bigger inner specific surface area than Co-Al-CO₃-LDHs.The tribological properties of Co-Al-CO₃ hydrotalcites,dodecylsulfate and borate pillared hydrotalcites had been evaluated by four-ball friction test,gear friction test and air compressor test.Experimental results show that all samples have excellent friction-reducing property.Co-Al-CO₃ hydrotalcites has the most excellent friction-reducing property, of which friction coefficient reduces by 49.1% than basic oil’s.Moreover,the oil temperature and power dissipation is lower and more stable than that of basic oil. Through analysis, hydrotalcites’s good friction-reducing property is concerned with its layered structure.