Study On The Synthesis Of Nano-MgO And The Preparation And Properties Of MgO/LDPE Composites

In recent years, with the rapid development of EHVDC transmission in domestic, the requirement of power system to EHVDC transmission cable has become increasingly high. The space charge which easily formed in the DC electric field can make the distribution of the electric field distort, make the polymer aging and even cause insulation breakdown. So, if the polymer insulation power cables shall meet the requirement of EHVDC transmission, it must restrain the concentration effect of space charge in dc field. According to reports, a small amount of nano-MgO added in PE can effectively reduce the effects of space charge and can satisfy the requirement of EHVDC transmission. But there is very few domestic study in this respect. In this paper, the synthesis technology and calcination technology of magnesium hydroxide were studied. Meanwhile, the surface treatment of nano-MgO by coupling agent and the preparation technology of MgO/PE composites were studied, and the test and analysis of mechanical properties and space charge distribution of MgO/PE composites is carried out.First, the Mg(OH)₂ was synthesized using the homogeneous precipitation method with the Mg(NO₃)₂ as raw material and the CO(NH₂)₂ as precipitating agent. The optimum condition of synthesis of Mg(OH)₂ was determined.The partical diameter and aggregation state of the nano-MgO were measured using the XRD and SEM. The effects of the calcining technology and the dosage of the dispersant PEG on the partical diameter and aggregation state of the nano-MgO were discussed. The optimal calcining technology of Mg(OH)₂ and the dosage of the PEG were determined. The average size 50 nm and well dispersed nano-MgO was prepared under the optimal calcining technology and the dosage of the PEG.Secondly, the surface of nano-MgO was teated using the titanate coupling agent KH-105. The effects of the coupling agent dosage, treatment temperature and treatment time on the activation index of nano-MgO were discussed. This paper also tried to determine the optimal coupling agent dosage, treatment temperature and treatment time of the nano-MgO surface treatment. The results showed that the aggregation state was significantly improved after the treatment using the KH-105.Lastly, The MgO/LDPE composites were prepared using the direct method and masterbatch method. The mechanical properties and space charge distribution of MgO/LDPE composites were analyzed by the tensile test and PEA. The effect of the nano-MgO content on the mechanical properties and space charge distribution of MgO/LDPE composites were discussed. The results showed that the mechanical property of the MgO/PE composite was the best when the adding amount of the nano-MgO is 1wt%. It could reduce the space charge concentration of the MgO/PE composites effectively when the adding amount of nano-MgO was 0.5wt%²wt%. When the adding amount of nano-MgO was 2wt% it could achieve the best effect.