Preparation technology optimization of diatomite porous ceramic irrigation emitter

Abstract: Sub-surface irrigation is an efficient traditional irrigation method, which gains extensive interests in arid regions due to its efficient utilization of water, low manufacturing cost and free of clogging of emitters. Sub-surface irrigation has been realized by using ceramic emitters, such as pitchers, pots and ceramic pipes. The existing preparation process of porous ceramic emitter is expensive and complex. In this study, a new preparation process of diatomite porous ceramics irrigation emitter with good performance and low cost was proposed. The porous ceramic was prepared by a sintering technology using clay, diatomite, calcium sulfate and silica sol as raw materials. The clay, diatomite and calcium sulfate were mixed evenly, and then a suitable amount of silica sol was sprayed into the powder blend. Ceramic green bodies were produced by filling the powder blend in a die mold and cold pressing with a pressure of 12 MPa. The green bodies were sintered at 1 060 -1 090?C in air atmosphere for 2.5 hours; the porous ceramic irrigation emitters had been prepared completely. The effects of the sintering temperature and the content of diatomite in green body on the phase composition, microstructure, linear shrinkage, open porosity and Vickers hardness of porous ceramic were analyzed. The hydraulic conductivity of porous ceramic was calculated according to the relationship between the pressure and flow rate of irrigation emitters. Taking into consideration linear shrinkage, open porosity, Vickers hardness and hydraulic conductivity, the optimal preparation process of porous ceramic irrigation emitter with low linear shrinkage, appropriate open porosity and high Vickers hardness was selected. The results showed that with the increase of diatomite content, the porous ceramics decreased in Vickers hardness and linear shrinkage and increased in open porosity and hydraulic conductivity. The sintering temperature had a great effect on the performance of porous ceramics. As the sintering temperature increased, the porous ceramics decreased in Vickers hardness and linear shrinkage and increased in open porosity and hydraulic conductivity. The porous ceramics were consisted of quartz (?-SiO2), cristobalite (SiO2), anorthite (CaAl2Si2O8), wollastonite (CaSiO3) and anhydrite (CaSO4). There were lots of well-connected open pores among the particles in the porous ceramics. The porosity increased as the content of diatomite increased. The adjustment of preparation technology had much influence on hydraulic conductivity of porous ceramics. The porous ceramics increased in hydraulic conductivity with the increase of diatomite content and the decrease of the sintering temperature. As to the porous ceramics, the hydraulic conductivity was a power function relationship with open porosity. The porous ceramic irrigation emitter showed the best performance when the sintering temperature was 1 075?C and the content of diatomite was 15%. Under such conditions, the porous ceramics had the Vickers hardness of 448 MPa, the open porosity of 26.3%, but its linear shrinkage only 4.9%. When the pressure was 10 kPa, the flow rate of porous ceramic irrigation emitter was 1.64 L/h. This kind of porous ceramic irrigation emitter has both good capacity of outflow and excellent material performance, which is the optimal technique to prepare porous ceramic irrigation emitter. The study provides valuable information for preparation and performance optimization of diatomite porous ceramic irrigation emitter.