Abstract: A series of quasi ternary phase diagrams of alkyl phenol polyoxyethylene ether(OP-10)+n-octanol+n-hexane+water(brine) system has been drawn based on experiments.We investigated the influence of cosurfactant n-octanol and CaCl₂ solution on the microemulsion region respectively.The results show that the relative area of microemulsion region in the ternary system gradually increases with the mass ratio of n-octanol to OP-10 increasing.When the mass ratio of n-octanol to OP-10 is 1:2.5,the microemulsion region has the largest relative area,and then the relative area of microemulsion region decreases as the proportion of n-octanol is increased.An appropriate amount of cosurfactant n-octanol promotes the formation of microemulsion phase,whereas excessive n-octanol is unfavorable to the formation of microemulsion phase.By fixing the mass ratio of n-octanol to OP-10 at 1:2.5 and changing the molar concentration of CaCl₂,the microemulsion region exhibits the largest relative area in quasi ternary phase diagram of OP-10+octanol+cyclohexane+CaCl₂ aqueous solution system when CaCl₂ concentration is 0.1 mol/L.Therefore,microemulsions have been prepared with five different molar ratios of barium ions to calcium ions,and a calcium carbonate and barium carbonate coprecipitation product are obtained by the reaction with an equi molar amount of sodium carbonate.The coprecipitation product were characterized by scanning electron microscopy(SEM).The precipitation mainly tends to form large cubic structure when the composition of microemulsion is calcium salt.However,when the molar ratios of Ca²⁺ and Ba²⁺ are 3:1,1:1,or 1:3,mainly rectangular pyramid,spherical,and corn cob shape precipitation particles are formed,respectively,and the barium salt fully converts into irregular polyhedron shape as well.