Sintering Behavior And Properties Of Porous Alumina Ceramics For Water Treatment

Porous alumina,as an important ceramic membrane support material,has become a research hotspot in the field of ceramic membranes due to its advantages of stable chemical properties and good mechanical properties.At present,some shortcomings,such as high cost,easy to form biological pollution,poor corrosion resistance,limit their wide applications in the field of water treatments.In view of the above problems,Alumina powder was used as the matrix,Fe,Cu or medium-entropy alloy（MEA）as the sintering aids to prepare porous alumina ceramics by powder metallurgy method.The effects of sintering temperature,holding time,metal content and other factors on sintering behavior,microstructure,mechanical properties,antibacterial action,and corrosion resistance of alumina porous ceramic materials were investigated.The main conclusions are as follows:（1）After the addition of Fe powder into Al₂O₃ ceramic,the microstructure of iron-containing porous alumina ceramics is mostly composed ofα-Al₂O₃,Na Al Si O₄ and Al₃Fe₅O₁₂ inter-particle phases.During the sintering process,the Fe element undergoes Fe→Fe₂O₃→Al₃Fe₅O₁₂ phase transformation.During this process,the oxidation of Fe to Fe₂O₃ causes significant volume expansion,leading to a decrease in the sintering shrinkage of porous ceramics and an increase in the pore size,throat diameter,and porosity.Compared to sintering parameters such as sintering temperature and holding time,iron content has a more significant impact on sintering shrinkage,porosity,and bending strength of Fe-Al₂O₃porous ceramics.Compared to Fe-free aluminum ceramics with Al₂O₃particles connected by acid-intolerable Na Al Si O₄ phase,Fe-Al₂O₃ has higher acid corrosion resistance due to the presence of Al₃Fe₅O₁₂phase with excellent chemical stability between Al₂O₃ particles.（2）The microstructure of copper-containing Al₂O₃ porous ceramics is composed ofα-Al₂O₃ particles and the bonding phases between particles（Na Al Si O₄,Cu Al₂O₄,and Cu O）.Cu element can promote sintering by forming eutectic liquid phase with Al₂O₃ and reducing the sintering activation energy of the system.As the sintering temperature exceeds the melting point（1446°C）of Cu O,the content of band-like Cu O phase in the system gradually increases,while the content of granular Cu Al₂O₄ phase gradually decreases.The addition of Cu significantly reduces the number of pores and throats in the porous structure,leading to a decrease in the porosity of porous ceramics.Compared to extending the holding time,increasing the sintering temperature and Cu content can improve the mechanical properties of Cu-Al₂O₃ porous ceramics more effectively.The increase in Cu content increases the Cu²⁺release rate and bactericidal activity of copper-containing Al₂O₃ ceramics.Among them,the bactericidal rates of 8Cu-1500 porous alumina ceramics against Staphylococcus aureus and Escherichia coli reached 96.1 and 97.3%,respectively.However,excessive addition of Cu elements can lead to an increase in the Cu O content at the particle connection,resulting in a decrease in the acid corrosion resistance of ceramics.（3）Considering the antibacterial function of Cu element and the enhancing effect of Fe element on the acid corrosion resistance of ceramics,Fe and Cu powder（with a total content of 10 wt.%）were added to Al₂O₃powder simultaneously.As the ratio of Cu/Fe gradually increased,the sintering shrinkage and bending strength of the porous alumina ceramics gradually increase,while the porosity gradually decreases.The reason is that the sintering of iron-containing Al₂O₃ porous ceramics is dominated by solid-phase sintering,while the addition of Cu can promote liquid-phase sintering.The Cu O liquid phase has good wettability relative to Al₂O₃,which can further tighten Al₂O₃ particles,improve sintering density and particle-bonding strength.According to first principles calculations,Cu（Al/Fe）O₄ exhibits higher thermodynamic stability than Cu Al₂O₄ spinel structure.As the content of iron powder increases,the ratio of weakly acid resistant Cu O to highly stable Cu M₂O₄（M=Al/Fe）spinel phase around alumina particles decreases,resulting in improved acid resistance and reduced Cu²⁺release rate of the system.Therefore,changing the Fe/Cu ratio can adjust the acid resistance and antibacterial ability of alumina ceramics.The results also indicated that minimizing the introduction of sodium elements can avoid the generation of Na Al Si O₄.The newly formed Al₂Si O₅ has high corrosion resistance,which is beneficial for improving the acid resistance of the alumina ceramic system.（4）Adding Fe Cr Ni entropy alloy powder to copper containing alumina resulted in the formation of AB₂O₄（A=Cu/Ni,B=Al/Fe/Cr）spinel phase with complex composition.The A position in the spinel structure is mostly occupied by Cu and Ni,while the B position is mainly occupied by Fe and Al.Compared to the spinel phase,Cr element prefers to diffuse into the Al₂O₃ matrix.The addition of medium entropy alloy elements promotes the formation of spinel phase,which increases the number of pores and throats in porous alumina,thereby increasing the porosity.However,the bending strength of porous alumina containing medium entropy alloy elements did not significantly decrease,due to an increase in the content of generated spinel phase,which is conducive to the improvement of particle interface strength.Compared to single Fe element addition,medium entropy alloy elements can promote the formation and stability of spinel phase,exhibiting a stronger stabilizing effect on copper in alumina ceramics,thus resulting in less copper ion release and higher acid corrosion resistance.Therefore,balancing the ratio of incorporated Cu to MEA can achieve good bactericidal effects as well as acid and alkali corrosion resistance in Al₂O₃ porous ceramics.This paper contains 101 figures,9 table and 329 references.