Investigation On The Structure And Properties Of Zn/Mg/Al-layered Double Hydroxides/Shenfu Coal Composites

Focus on the preparation and application of the prevention materials for the coalspontaneous combustion and the novel halogen-free flame retardant materials, the preparation,structure and properties of Zn/Mg/Al-LDHs/Shenfu coal composites (CLCs) were explored,according to the micro-nano pore structure and functional group characteristic of Shenfu coal(SFC) as well as the studies on the preparation and properties of Zn/Mg/Al layered doublehydroxides (Zn/Mg/Al-LDHs). The results are with significant theoretical meaning to thepreparation and application of the novel mineral functional nano-composites.Effect of low temperature oxidation of SFC on its humic acid (HA) yield and thedistribution of its different HA fractions (black humic acid (HAIII), brown humic acid (HAII)and fulvic acid (HAI)), and effect of pretreatments (low temperature oxidation, de-ashing aswell as removing HA) on the pore distribution of SFC were investigated by FTIR, XRD,GC-MS and the low temperature nitrogen gas adsorption methods. The results show that thetotal HA yields in the oxidized SFC increase with the oxidation temperature and the oxidationtime. The yields of different HA fractions for the pretreated SFC are in the increasing order ofHAI, HAII, HAIII. The mesopore system of pretreated SFC increases, while the specific surfacearea decreases.Zn/Mg/Al layered double hydroxides (Zn/Mg/Al-LDHs) were prepared by using theco-precipitation method, and effects of metal ion ratio, anion species, microwave andultrasound irritation, pH and the crystallization time on the composition, structure and thermalproperties of Zn/Mg/Al-LDHs were also investigated by using XRD, FTIR, SEM andTG-DSC analysis. The results indicate that the complexation and adsorption interactionbetween HAs and metal ions on the surface of LDH layers induce a bending growth ofZn/Mg/Al-CO3-LDH layers along the curved HA surface, which leading to theZn/Mg/Al-HAs-LDHs clusters with spherical shape. The uniformity of Zn/Mg/Al-LDHsparticles can be improved, and the particle size and the agglomeration degree can be decreased by microwave and ultrasound assisted co-precipitation method. The thermal stabilities ofZn/Mg/Al-LDHs are related to the metal ratio. When increasing Mg2+ion ratio, the thermalstabilities of Zn/Mg/Al-LDHs decrease, and their temperature range of endothermicdecomposition become broad.CLCs were prepared by using the in-situ co-precipitation method. The results show thatthe crystalline degree of CLCs decreases with increasing the mass fraction of SFC. Themorphology of Zn/Mg/Al-LDHs on the surface of CLCs can be controlled through changingthe oxidation temperature of SFC and the crystallization time. The controlling mechanism isthe coupling interaction of the complexation and adsorption between metal ions with thesurface functional group and the pore of SFC.The thermal properties of LDHs-SFC mixture and CLCs were studied by using theTG-DSC analysis method, and the prevention property of the coal spontaneous combustionwas also investigated. The results show that when Zn2Al1-CO3-LDHs, Mg2Al1-CO3-LDHs,Zn1Mg1Al1-CO3-LDHs are mechanically added in SFC, the critical temperature of SFCspontaneous combustion is higher when the loading amount is3%,5%and15%, respectively.The fire prevention efficiency is the highest when nano-fiberous Zn1Mg2Al1-CO3-LDHscomponents are dispersed in SFC in the CLCs composting form, because of the formation ofmetal oxides-carbon (LDOs-C) barrier from CLCs in coal spontaneous combustion process.The prevention mechanism of the coal spontaneous combustion process is the processes ofcoupling interaction between the exothermic oxidation process of SFC and the endothermicdecomposition process of Zn/Mg/Al-LDHs and CLCs. CLCs behave a special self-healingproperty.CLCs/EVA composites were prepared by using the blending method. The fire retardantproperties of CLCs/EVA composites were also evaluated by using the indexes such as the heatrelease rate, the limiting oxygen index and the UL94fire retardant level. The results show thatCLCs have higher fire retardants efficiency and smoke suppressing properties. The fireretardant level increases with increasing the filling amount of CLCs, so that, the synergy fireretardant effect lies in Zn/Mg/Al-LDHs with SFC. CLCs have significant strengthening andtoughening effect in CLCs/EVA composites.