Densification-of-fly-ash-under-alkaline-hydrothermal-hot-pressing-conditions

14thInternationalConferenceonthePropertiesofWaterandSteaminKyoto360DensificationofflyashunderalkalinehydrothermalhotpressingconditionsZ.Matamoros-Veloza1,*,J.C.Rendón-Angeles2,K.Yanagisawa3andM.M.Cisneros-Guerrero11DepartmentofMetal-Mechanical,TechnologicalInstituteofSaltillo,Coahuila25280,México*E-mail:zullyma@fenix.its.mx2ResearchCenterforAdvancedStudiesoftheNPI,CampusSaltillo,Saltillo,Coahuila25900,México3ResearchLaboratoryofHydrothermalChemistry,KochiUniversity,Kochi780-8520,JapanLargevolumesofflyashareannuallyproducedatpowerplantCo.oftheFederalElectricityCouncil(Coahuila,MEXICO),andthissolidwastehasbecomeanenvironmentalproblembecauseofshortageofstoragerestrictionsandenvironmentalpollution.Theflyashconsistsofsphericalparticles(particlesizeof20�m)andcontainsanamorphoussilicatephaseandtwocrystallinephases(MulliteandQuartz)asmajorconstituents.Flyashcompactswerepreparedwiththeadditionof15wt%ofanalkalinesolvent(NaOHsolution5and10M)byhydrothermalhotpressingattemperaturesintherangeof150-250ºC,fordifferentreactionintervals(30-120min)withaloadingpressureof17MPa.TensilestrengthofthecompactswasmeasuredbytheBraziliantest.ThestructuralchangesofthecrystallinephasesduringthetreatmentweredeterminedbyX-raydiffractionanalyses,andmicrostructuralaspectsofthespecimenswereobservedbyscanningelectronmicroscopy.AlthoughX-raydiffractionresultsshowedthatthecrystallineMulliteandQuartzphasesdidnotreacteveninconcentratedNaOHsolutionsathightemperature,thedensificationwasachievedbythedissolutionoftheamorphousphase.Alowstrength(3MPa)wasobtainedonthecompactpreparedwith5MNaOHsolutionat250°C.Incontrast,thestrengthoftheflyashcompactswasfurtherincreasedupto30MPabyincreasingtheNaOHconcentrationto10M.1.IntroductionNowadays,theannualproductionofflyashishigheachyear.Anamountbetween10-20wt%offlyashiscommonlyproducedbythecombustionofbituminouscoalinpowerplants.Thecombustionofbituminouscoalinpowerplantscommonlyproducesflyash,10-20wt%fromthecoal.Theflyashwastesolidiscollectedbycyclones,electricprecipitators