| Subsurface drip irrigation technology has been widely used in developed countries for its excellent effect of water saving and production increasing,but its further development has been restricted by the high energy consumption and the environmental problems caused by the heavy use of plastics.To solve the problems above,inspired by clay pot irrigation,a research team from the northwest agriculture and forestry university introducted the microporous ceramic material into the research and development of emitters,and used the micropores connected by ceramics to replace the complex labyrinth channels in traditional emitters for seepage irrigation.The microporous ceramic root irrigation technology was developed with characteristics of micro pressure,small flow and adaptive irrigation,which has good water saving effect to increase production.However,due to unclear quantitative relationship between the raw material formulation,preparation process and the properties of ceramic materials,there are still many problems such as lack of standardized preparation methods,inaccurate flow control and large manufacturing deviation,which seriously affect the application effect.Therefore,based on the materials science,and combined with theory,data analysis,laboratory test and numerical simulation,this paper analyzed the influence of raw material formula and preparation process on the performance of microporous ceramic materials and the hydraulic performance of emitters,revealed the response relationship between the hydraulic performance and key parameters of ceramic materials(porosity),built the outflow model for micro porous ceramic,selected the optimum raw material formula and preparation process,and put forwarded a set of micro porous ceramic standardized preparation methods,preliminary to the following conclusion:(1)Based on the material science theory and Meta-analysis,the formulation and preparation process of micro porous ceramic materials that can be used to prepare the emitter were preliminarily selected.In the preparation of the main raw materials of the micro porous ceramic emitter,it was determined that the sintered clay or quartz sand with stable properties was used as the skeleton material,and the sodium feldspar and silica sol were used as the property improvers.The pore-making agent should be organic pore-making agent,and with content less than 50%.According to the different substrate microporous ceramics,the corresponding sintering temperature control range was put forward.1000℃ is the boundary of sintering temperature between clay-based(less than 1000℃)and sand-based(more than 1000℃)micro porous ceramics.(2)The influence law of the raw material formulation and preparation process on the properties of micro porous ceramic materials was proved,and the suitable raw material formulation and process for the preparation of micro porous ceramic emitters were optimized.For clay-based micro porous ceramics,the main factor affecting the porosity is the content of pore-making agent.When the content of pore-making agent(wheat straw)increases from 10% to 25%,the open porosity increases by 7.4%.Using two-step sintering method,the strength of micro porous ceramics can be increased by more than 2 times,and the pore size range and pore uniformity can be effectively controlled.For sand-based micro porous ceramics,increasing the content of pore-making agent and decreasing the content of adhesive,molding pressure and sintering temperature can improve the porosity,but the density and flexural strength decrease accordingly.The morphology of different matrix particles also has a certain influence on the material properties.After sintering,the spherical quartz sand can significantly improve the flexural strength and pore uniformity of micro porous ceramics due to the large average contact area between particles,it is too expensive.Ball grinding of ordinary irregular quartz sand particles can greatly reduce the cost by passivation its edges and corners to increase the sphericity,and can ensure that its material properties meet the requirements of preparing emitters.Based on data analysis,theoretical derivation and experimental verification,aiming at the research and development of emitters with high porosity,high strength,low cost,it is proposed: clay used as skeleton material,wheat straw with content(10%,15%)chosen as the pore-forming agent,silica sol selected as a performance modifier,with moulding pressure of 12 MPa,using two step sintering process(first heats up to 950℃,rapid temperature to 900℃,insulation 2h)to prepare clay porous ceramic material;Sand-based micro porous ceramic materials were prepared with ball-ground quartz sand(particle size 50 m,content 45%)as the skeleton material,dextrin(content 10%)as the pore-making agent,silica sol as the property improver,sodium feldspar and alumina(2:1:2)as the binder,with molding pressure of 14 MPa and sintering temperature of 1200℃.(3)The reaction mechanism of the hydraulic performance for the micro-porous ceramic emitter with raw material formulation and preparation process were revealed,and the theoretical and empirical outflow model of the micro porous ceramic emitter was constructed.According to the test data and the analysis of variance,the influence order of the raw material formula and preparation process on the hydraulic performance of the micro porous ceramic emitter is as follows: the content of the pore-making agent is first,followed by the molding pressure and the content of the binder,the last is sintering temperature.Based on the statistical analysis,the mathematical relationship between the discharge of micro porous ceramic emitter and the content of pore-making agent,adhesive,mould pressure,sintering temperature and structural parameters was established.Based on the Carman-Kozeny theory and Hagen-Poisseuille law,a theoretical model for the discharge of ceramic micro porous emitters is constructed,which provides a scientific basis for the accurate control of the discharge of ceramic micro porous emitters.(4)The drying and stirring parameters in the preparation process of micro porous ceramic emitter were defined,and the standardized preparation method of micro porous ceramic emitter was proposed.Analyses the mixing process(feeding sequence,mixing time and stirring speed and drying process,drying temperature and time)on performance of microporous ceramic irrigation equipment,(porosity and bending strength)and the influence of hydraulic performance,flow rate and flow deviation),the results showed that the mixing process,the first dry mix,add silicon sol and the secondary feeding way can avoid similar raw materials together,increase the porosity distribution uniformity;The mixing time was 15 minutes,and the pore uniformity and flexural strength were optimized.In the drying process,as the drying time increases,the deviation of the strength and flow rate of the billet first increases and then decreases.When the drying temperature is between 80℃ and 90℃,the destruction of microstructure of the billet by rapid evaporation of water can be avoided.Considering the requirements of the cost,flow and strength of the emitter,a set of standardized preparation process of the micro-porous ceramic emitter was established:A.Raw materials: should be prepared according to the situation,including screening(325 mesh),impurity removal,pre-burning,etc.;B.Mixing: weighing and mixing according to the raw material formula,firstly mixing the dry materials,and then adding silica sol in the second feeding sequence,stirring at low speed for 15 min before taking out;C.Moulding: the moulded pressure is suitable to use 12~14MPa;D.Drying: the billet is dried in the box drying box,the drying time is 9 hours,and the drying temperature is 80℃-90℃;E.Green body sintering: after complete cooling after drying,put into the tunnel furnace or box furnace at the set temperature(clay-based 950℃,sand-based 1200℃)sintered into a micro-porous ceramic emitter. |
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