Construction Of Cementitious Composites With Piezoelectric Properties Based On Titanium Bearing Blast Furnace Slag

With the increasing consumption of disposable resources,energy and environmental problems become more and more severely,the concept of green and sustainable development is increasingly popular.Taking Panzhihua Iron and steel company as an example,a large amount of titanium bearing blast furnace slag(Ti-slag)is produced in the smelting process of vanadium titanium magnetite.Although a lot of manpower and material resources in the comprehensive utilization of Ti-slag have been devoted in our country,and has produced rich basic research results.However,due to various factors such as complex process,high cost and serious secondary pollution,mature industrialization has not been realized.The composition of titanium bearing blast furnace slag is essentially similar to Portland cement,but the free Ti O₂ in titanium slag will lead to cement volume expansion and other problems.Based on the theory of mineral phase reconstruction of Ti-slag system and the coordinated regulation of valuable components,a new resource utilization approach for preparing piezoelectric cementitious materials based on titanium slag was proposed,which provided theoretical and technical basis for the implementation of related research process routes.The main research contents are as follows:(1)Thermodynamic calculation shows that the decomposition of Ca Ti O₃ phase in Ti-slag is the key step to obtain the target phase.Combined with experiments and first principles calculation,it is found that the formation mechanism of piezoelectric phase Pb Zr_xTi_1-xO₃(PZT)binary solid solution can be divided into two parts:firstly,Ti O₂ is displaced from pyroxene phase by Zr O₂,then further reacted to Pb Zr O₃ in the addition of Pb O and further form PZT phase with Pb Ti O₃,Pb Zr O₃ is the reaction product of Pb O and Zr O₂;Secondly,when the temperature is higher than 815.6?,Ca Ti O₃ reacts with Pb Zr O₃ to form Pb Ti O₃,and then reacts with Pb Zr O₃ to form PZT phase.In this system,feldspar phase is the source of cementitious activity,and the formation of this phase needs reaction temperature higher than 831.5?.According to the above reaction characteristics,the modification and reconstruction process can be divided into three stages:firstly,Pb Zr O₃ and cubic PZT phases are formed by calcination at 700?for1h;secondly,Ca Ti O₃ is decomposed into tetragonal PZT phase and feldspar phase by calcination at 800-910?for 2h;finally,PZT phase is homogenized at 750?for 1h;(2)Through the modification and reconstruction of Ti-slag,the second stage of the thermal system was kept at 870?for 2h to obtain a cementitious material containing a higher crystallinity Pb Zr_xTi_1-xO₃(PZT)solid solution,with a piezoelectric constant d₃₃ value of 6.0 p C/N,the silicate phase is transformed from the pyroxene phase to the feldspar phase,the gelling activity is greatly improved compared with the original Ti-slag,and the silicate phase dissolution rate is 11.5%.The results of heavy metal leaching experiments show that the leaching concentration of Pb in the material is 0.26 mg/L,which meets the national environmental protection requirements;(3)The feasibility of preparing piezoelectric ceramics was explored.The sample was calcined at 1200-1300?.It was found that the calcined sample with smooth surface and high density had piezoelectric constant of 2.8 p C/N.When the temperature is higher than 1200?,on the one hand,the binding energy of Ca and Ti-O octahedron increases accompaning with part of PZT phase changing into Ca Ti O₃ and Pb Zr O₃;on the other hand,the decomposition of Pb Zr O₃ at high temperature makes the ceramics porous and the density decreases,and the combined effect of the two results in the significant decrease of piezoelectric properties;Ti-slag and combining free Ti O₂ into PZT phase,the transformation of Ti from pervoskite and diopside to piezoelectric functional phase was realized by the mineral phase reconstruction,and the formation of cementitious active component was promoted.This thesis provides a theoretical basis for solving the incompatibility of pure PZT material used in cement concrete on a large scale,creats new inspiration for the development of piezoelectric concrete for intelligent road,rail roadbed and structural health monitoring.Furthermore,our research provides a new idea for the green short process with high value-added value utilization for refractory Ti-slag in China.