Preparation And Properties Of Porous Iron Tailing Ceramic/Paraffin Composite Phase Change Materials For Thermal Energy Storage

Iron tailings are an industrial waste from the ironmaking process.Among which the fine-particle iron tailings are the part that could be hardly used at present,and are only stocked by tailing dams,usually causing economic,environmental and health-related problems.The porous ceramics were prepared in this thesis by fine-particle iron tailings which collected from Beijing Miyun district.Then,the porous tailing ceramics were used as the carriers to successfully fabricate the porous iron tailings ceramics/paraffin composite phase change materials and the enhanced phase change materials by adding some graphene.The preparation technology,mechanical properties,thermal physical properties and heat transfer process of the phase change energy storage materials were deeply studied.This dissertation is composed of seven chapters:introduction of the recycling of iron ore tailings and the application of phase change energy storage materials,experimental materials and procedure,the phase transformation and mechanism of iron tailings in high temperature,the preparation and characterization of porous ceramics,the preparation and physic/thermal performance of CPCMs,the physic/thermal properties of NCPCMs.The production of the high-performance CPCMs made from iron tailings is meaningful for environmental protection and reduction of industrial pollution.The chemical composition,phase composition,grain size and phase change in high temperature of fine-particle tailings,which collected from Miyun district in Beijing,were investigated by using a variety of analysis methods including XRD and SEM.The results show that the iron tailings are consist of SiO2 and clay minerals like montmorillonite,clinochlore,illite,calcite.When the temperature is below 963?,a-quartz transforms into ?-quartz,and clay minerals including clinochlorite,illite transforms into the glass phase,montmorillonite is resolved.Then,Orthoclase,microcline and hematite are generated at about 900?.The orthoclase and microcline form a eutectic material with quartz,aluminosilicate above 963?,which led to the densification of porous ceramics.Augite,diopside and anorthite are generated in the range of 1000? to 1120? with a decrease of the quartz phase.The suitable range of sintering temperature of the iron tailings is from 1070? to 1120?.High-porosity and high-strength porous ceramics were fabricated by foam-gelcasting technology with the fine-grain iron tailings as raw materials.The effects of preparation parameters on the phase composition,microstructure and mechanical strength of porous ceramics were investigated.The results show that the sintering temperature,ball-milling time and soaking time have significant effects on the porosity,compressive strength and microstructure of the porous iron tailings ceramics.Longer soaking time with lower sintering temperature could improve the compress strength of sample with similar porosity.The universal model deduced in this paper makes a good description of the relationship between porosity and thermal conductivity.The new composite phase change materials were developed for thermal energy storage with the porous ceramics as the carriers.The phase composition,microstructure and chemical stability of the CPCMs were characterised by XRD,SEM and DSC.The results demonstrate that the porous ceramics have excellent chemical compatibility and wettability with the paraffin,and the porous ceramics can efficiently prevent the liquid paraffin from leaking.The CPCMs achieved the thermal conductivity of 0.30?0.45 W/(m·K)which is higher than the base paraffin wax,and the measured thermal conductivity was in good agreement with results predicted from the universal model.The thermal energy storage density of CPCMs can be adjusted in the range of 71?123 kJ/kg.The latent heat of CPCMs only decreased by 4%after 100 melting/solidification cycles.The novel composite phase change materials have broad application prospects.The NCPCMs were fabricated by spontaneous melt infiltration of paraffin wax which added highly conductive nano-graphene.By adjusting the fabrication parameters,optimal NCPCMs had the thermal conductivity of 0.40?0.60 W/(m·K)and the latent heat of 69.5?121.3 kJ/kg.After 25 melting/solidification cycles,the graphene remained well dispersion in the NCPCMs,while the weight loss of NCPCMs was less than 2%if the porosity of porous ceramics was smaller than 85%.The new composite materials show the excellent thermal physical properties,chemical stability and demonstrated fast charging/discharging in thermal energy storage systems.The adjustable-porosity porous ceramics with high mechanical properties were fabricated by using the barely useless fine-grain iron ore tailings.This material could be applied to the indoor hot water healed floor heating system.This technique develops a new direction of iron tailings resource utilization,and the new products will be wildly applied in energy conservation of architecture and civil engineering.