Chloride Anion Exchange Of MgAl Layered Double Hydroxide And Their Tribological Properties Investigation

The development of modern engineering technology makes layered solid lubricant materials on friction, wear and lubrication issues have received increasing attention, and which is urgently required to adapt to the development of a solid lubricant material. Hydrotalcite compound (LDHs) is a class of anionic layered structure which is adjustable material, those materials have been used in many areas, such as catalysis, adsorption, functional additives and optical electromagnetic materials etc. To expend the application of those materials, this paper will be based on the synthesis and anion exchange of Mg/Al (2:1)-LDHs and Mg/Al (4:1)-LDHs, focuses on investigating the tribological properties of these materials as lubricant additives in polyethylene glycol200.Synthesis of the feeding molar ratio were Mg/Al=2and Mg/Al=4carbonate type hydrotalcite-like compound by using the method of urea. The experimental results show, the optimum synthesis conditions for Mg/Al (2:1)-CO3-LDHs:the molar ratio of NO3and urea is2, the reaction temperature is100℃, the reaction time is24h; And the optimum synthesis conditions for Mg/ Al (4:1)-CO3-LDHs:the molar ratio of NO3-and urea is2, the reaction temperature is100℃, the reaction time is12h;Under the protection of N2, the experiments which are using ion exchange "acid salt method" by adjusting the concentration of NaCl solution, pH and temperature of reaction solution to make the carbonate-type of Mg/Al (2:1) LDHs and Mg/Al (4:1)-LDHs exchange into chloridion-type. The optimum conditions for the exchange is:concentrated sodium chloride solution is3.0mol/L, the reaction solution is pH=6.0, the reaction temperature is100℃and the reaction time is4h.The tribological properties of carbonate and chloride ionic type of Mg/Al-LDHs sample as solid lubricant added to the base oil polyethylene glycol200were evaluated by four-ball tester, respectively. The experimental results show, in the aspect of bearing capacity, when0.25wt.%Mg/Al(2:1)-CO3-LDHs was added to PEG200, maximum nonseizure load (PB) value is549N, higher than that of base oil for39N; when0.25wt.%Mg/Al (2:1)-Cl-LDHs is added to PEG200, PB value is598N, higher than that of base oil for88N; And when0.5wt.%Mg/Al (4:1)-CO3-LDHs is added to PEG200, PB value is549N, higher than that of base oil for39N; when0.5wt.%Mg/Al (4:1)-Cl-LDHs is added to PEG200, PB value is598N, higher than that of base oil for88N; The bearing capacity of Mg/Al-Cl-LDHs is improved obviously, and Mg/Al (2:1)-LDHs added amount is less than Mg/Al (4:1)-LDHs added. In terms of anti-wear performance, when0.25wt.%Mg/Al (2:1)-CO3-LDHs or Mg/ Al (2:1)-Cl-LDHs is added to PEG200, its wear scar diameters (WSD) is0.388mm and0.324mm, respectively, that is decreased by25.4%and37.7%, respectively; when0.25wt.%Mg/Al (4:1)-C03-LDHs or Mg/Al (4:1)-Cl-LDHs is added to PEG200, its WSD is0.388mm and0.343mm, respectively, that is decreased by25.4%and36.0%, respectively. The experiment results show that the anti-wear ability of Mg/Al-Cl-LDHs is better than that Mg/Al-CO3-LDHs. In the aspect of anti-friction, friction coefficient of base oil PEG200almost the same as that added Mg/Al-LDHs. The results show that Mg/Al-LDHs materials have no advantage in friction propertiesSEM show that the worn surfaces of the steel ball lubricated with PEG200have a larger wear scar diameters, surface roughness and scf-atches deeper. After Mg/Al-LDHs materials are added to PEG200, the worn surfaces of the steel ball have a smaller ball wear scar diameter and relatively smooth surface. Further illustrate the Mg/Al-LDHs materials show good anti-wear properties. The EDS spectra show that no chemical elements other than steel components were detected on the wear surface after the antiwear test. No complicated tribochemical reactions between the additive and steel ball. The powder XRD and SEM patterns show that the crystal structure of the sample does not change, and its LDHs characteristic peaks are present, indicating that the sample maintaine the original crystal structure before and after the lubricating test.