Tribological Property Of Calcium Borate Additives In High Alkaline Lubricant

Using oleic acid and cetyltrimethylammonium bromide(CTAB)as modifiers respectively,surface modified calcium borate additives were prepared by plasma-assisted ball-milling.The morphology and structure of calcium borate additives were characterized by scanning electron microscopy,X-ray diffraction,fourier infrared spectrometer and synchronous thermal analysis.The dispersibility and tribological properties of calcium borate additives in high alkaline lubricants were tested.After the prepared calcium borate additive is observed with SEM,it is found that the particle size of calcium borate modified with oleic acid is between 50 nm and 300 nm,while that of primary particle of calcium borate modified with CTAB is only 50 nm,and the ball-milled powers gather into aggregate with the size of about 500 nm.The XRD analysis shows that plasma assisted ball milling refines quickly the grain size of calcium borate,but doesn't change the crystal structure of it.As for the FTIR and STA analysis,it is shown that plasma assisted ball milling leads to bond breaking of oleic acid and CTAB,thus generating methylene-CH2 active group which aggregates with the surface of original calcium borate powder.As is shown from the test of gravitational sedimentation,obvious precipitation and separation are present 3 days after the original calcium borate is added to high alkaline lubricant,while no obvious separation are observed 100 days after the calcium borate modified with oleic oil and CTAB are added to high alkaline lubricant,which is a basically steady state.It shows that oleic oil and CTAB are good surface modifiers for calcium borate,making the powder surface oleophilic.The result of test of physical and chemistry property shows that,with the essentially constant viscosity,flash point and pour point of high alkaline lubricant,TBN of compound oil for calcium borate modified with oleic oil and CTAB increase 31.16% and 33.43% respectively,which is of significance for the reduction of metal detergent and ash.A test of tribological property is conducted on high alkaline lubricant compounded with two surface modified calcium borate additives,the result of which shows that with the increasing of load,both the friction coefficient and friction volume of compound oil for calcium borate nanoparticle gradually decreases,and the friction coefficient is stable during the test.The test of electron spectroscopy conducted on the surface of friction pair shows that such elements as B,Ca and O are present in the surface,which illustrates that additive of calcium borate nanoparticle spreads out and forms a film under the shearing of friction and covers the surface of friction pair,thus reducing friction of and repairing the surface.Compared with calcium borate modified with oleic oil,calcium borate modified with CTAB can achieve better effect of antifriction and anti-wear.As the load increases,calcium borate modified with CTAB,whose particle size is smaller,can disperse and extend easily under the shearing of friction,achieving easier spreading out and film formation of calcium borate modified with CTAB on the surface of friction pair.Acidizing treatment is conducted on the formulated compound oil with sulfuric acid and acid working condition of marine diesel engine is simulated to test the property of antifriction and anti-wear of calcium borate additive.The result of the above test shows that additive of calcium borate nanoparticle can demonstrate good ability of antifriction and anti-wear.However,sulfuric acid can react chemically with calcium carbonate in the micelle of detergent and additive of calcium borate nanoparticle and generate calcium sulfate,which mingles on the surface of deposited film of calcium borate and affects the strength of film covered on the surface of friction pair,leading to easy cracking and peeling of protective film of calcium borate.