文档名：叶绿泥石水化机理及膨胀特性的分子动力学
摘要：高铁路基膨胀灾害工程实例发现,部分膨胀是由叶绿泥石水化膨胀引起的,但目前国内外学者对叶绿泥石膨胀特性研究较少,相关机理尚未明确.采用多尺度表征的方法研究了宏观和纳观尺度下叶绿泥石的膨胀特性,运用分子动力学模拟方法研究了叶绿泥石水化机理及动力学响应下的键能变化.结果表明:叶绿泥石具有一定的膨胀潜力.通过不同数量水分子的吸附试验,得到层间域极限数量为32个,吸附位置为硅氧骨干形成的六方空穴,且仅能形成1层饱和水分子层.随着水分子增多,膨胀加剧,直至达到极限,极限状态的晶格常数为a=21.52?,b=18.61?,c=14.54?.水化模型经室温恒压的动力学模拟,发现模拟过程中静电作用能贡献最多,vanderWaals作用能次之,键伸缩能最少.随着水化的加剧,水分子之间的相互作用变弱,径向分布函数峰值右移,层间水分子扩散性增强,且表现出靠近滑石层的倾向,水氧与滑石层氢原子形成的氢键键长1.8?,层间水与黏土矿物的径向分布函数峰值右移,同时氢键中的氢原子与受体原子之间的距离增加,氢氧配位数增加,这导致氢键键长增加,键角减小,黏土层开始产生膨胀.
Abstract：IntroductionClaymineralcrystalsaremostlyformedbystackinglayersofsilicon-oxygentetrahedralsheetsandaluminum-oxygenoctahedralsheets.Theybasicallyhavewaterabsorptionandexpansionbecauseoftheiruniquelayeredcrystalstructure.Claymineralsafterhydrationandexpansionusuallycauseseriousengineeringproblems,whichhaveanegativeimpactonengineeringconstruction.Theyhavereceivedextensiveresearchattention.Itisgenerallybelievedthatthehydrationexpansionofclaymineralsismainlydividedintotwostages,i.e.,crystalexpansionandosmoticexpansion.Crystalexpansioniscausedbytheexpansionofwatermoleculesintotheinterlayerofclayminerals.Permeationexpansionisduetothelatticesubstitutionofclayminerals,whichleadstotheimbalanceofvalenceandelectricityofthecrystal.Massiveexchangeableionsaregatheredonthesurfaceofthecrystal.Aftertheseionsaredissociatedinwater,theywillrepeleachotherwithnegativechargeundertheactionofthediffusiondoublelayer,resultinginexpansion.Comparedwithosmoticexpansion,thedegreeofcrystalexpansionissmall,kaolinite,illite,pennineandotherinterlayercation-freeclaymineralsdonothaveanexpansibility.However,theproblemofexpansiondisasteroccursundertheworkingconditionrichinpennine,indicatingtheresearchvalueofpenninehydrationexpansion.However,thewaterabsorptioncharacteristics,expansioncharacteristicsandhydrationmechanismofpennineinnano-scalearenotyetclear,andrelatedresearchneedstobecarriedout.Inthispaper,amoleculardynamicsstudyonwaterabsorptionofmesophyllpenninewascarriedouttoexplainthehydrationcharacteristicsofmesophyllpenninenanocrystalstructure.Thechangesofenergy,structureandchemicalbondofmesophyllpennineintheprocessofhydrationexpansionwerediscussed.MaterialsandmethodTheringcuttersampleswithdifferentpenninecontents(i.e.,0%,20%and100%)werepreparedwithpenninemixedwithquartz.Theno-loadexpansionratewasmeasured.Theparticlesizeofthesoilsamplewascontrolledtobe200mesh(0.075μm),thedensityofthesoilsamplewas1.8g/cm3,andtheinitialwatercontentwas10%.Thehydrationdegreeofpenninewithdifferentwatercontentswasanalyzedbythermogravimetricanalyzer,andthewatercontentcontrolledwas0%,5%and10%.ThemicrostructureandcrystalparametersofpenninesampleswereanalyzedbyX-raydiffractometerandscanningelectronmicroscope.Thecrystalmodelwasestablishedbasedontheresultsofthemicroscopictest.Thesorptionmodulewasusedtocarryouttheadsorptiontest.Ahydrationmodelcontainingdifferentamountsofwatermoleculeswasestablishedthroughtheadsorptiontest.ThegeometryoptimizationtaskundertheForcitemodulewasusedtooptimizethestructureofthemodel.ThemoleculardynamicssimulationofthemodelwascarriedoutusingtheDynamicstaskundertheForcitemodule,andtheexpansiondeformationofpenninewassimulatedviadynamiccalculationundertheNPTensemble.TheClayffforcefieldsuitableforclaymineralswasusedinthesimulationprocess.Thesimulatedtemperatureis298Kandthesimulatedpressureis0.001GPa.Thetimestepis1fs,thenumberofiterationstepsis100000,andthetruncationradiusis12.5?.ThechargecalculationmethodistheForcefieldAssigned.Thenon-bondenergyCoulombinteractionwascalculatedbytheEwaldsummethod.ThevanderWaalsinteractionenergywascalculatedbyanatom-basedmethod.ResultsanddiscussionTheexperimentalresultsoftheno-loadexpansionrateshowthattheno-loadexpansionrateoftheringknifesampleincreaseswiththeincreaseofthecontentofpennine,indicatingthatthepenninehasanexpansibility.Thethermogravimetricanalysisshowsthatthehighertheinitialwatercontentis,thehigherthedegreeofhydrationofthepenninewillbe.Inadditiontothefreewateradsorbedbetweentheparticles,somewatermoleculesarebondedbetweenthecrystallayersviahydrogenbonding.Theresultsofmoleculardynamicssimulationshowthatpennineiselectricallyneutralduetothesimultaneoussubstitutionofhigh-valencecationsandlow-valencecations,sothecrystalexpansionoccurs.Afterthewatermoleculesentertheinterlayer,theyareembeddedinthehexagonalholesofthesilicon-oxygenbackbonelayer.Theoxygenatomsinthewatermoleculesformahydrogenbondconnectionwiththehydroxideionsinthetalclayer,whichcontrolsthehydrationlimitofthepenninecrystal.Intheprocessofhydrationandexpansionofpennine,itisdominatedbyelectrostaticinteractionenergy,andfollowedbyvanderWaalsforce,andthebondstretchingenergyisthesmallest.Comparedwithmontmorillonite,penninehydrationismoredifficult.Thepeakoftheradialdistributionfunctionofwatermoleculesshiftstotherightasthedegreeofhydrationincreases,indicatingthatthespacingofwatermoleculesandthediffusivityofwatermoleculesincrease.Aftermassivewatermoleculesenterthecrystal,thetotalnumberofhydrogenbondsincreases,theaveragecoordinationnumberofoxygenatomsandhydrogenatomsincreases.However,thehydrogenbondlengthincreases,thebondangledecreases,andthecrystalexpands.ConclusionsTheexperimentalandsimulationresultsshowedthatwhenwatermoleculesenteredtheinterlayerofthecrystal,pennineexpandedslightly,whichwasconsistentwithkaoliniteandillitewithoutcationsintheinterlayer.Thehydrationexpansionofpennineconformedtothelineargrowthlawasawhole.Penninecrystalscontinuedtoexpanduntilthelimitasthehydrationdegreeincreased.Thelatticeconstantsinthelimitstatewereaof21.52?,bof18.61?,andcof14.54?.Thelimitadsorptionamountofthecrystalwascontrolledbythecrystalstructure.Afterwatermoleculesenteredtheinterlayerofthecrystal,theadsorptionsitewasinthehexagonalholesofthesilicabackbonelayer,andeachhexagonalholecouldonlyadsorbonewatermolecule.Whenthewater-absorbedpennineexpandedunderdynamicconditions,theelectrostaticinteractionenergywasthelargest,thevanderWaalsforcewasthesecond,andthebondstretchingenergywasthesmallest.Whenwatermoleculesenteredtheinterlayerofpennine,hydrogenbondscouldbeformedorstrengthened.Thecoordinationnumberofhydrogenandoxygenandthelengthofhydrogenbondformedincreased,butthebondangledecreasedwiththeincreaseofthenumberofwatermolecules.
作者：张瑞 余飞 佟凯文 黄康 张伟 戴张俊 陈善雄 Author：ZHANGRui YUFei TONGKaiwen HUANGKang ZAHNGWei DAIZhangjun CHENShanxiong
作者单位：中国科学院武汉岩土力学研究所岩土力学与工程国家重点实验室,武汉430071;中国科学院大学,北京100049中国科学院武汉岩土力学研究所岩土力学与工程国家重点实验室,武汉430071
刊名：硅酸盐学报 ISTICEIPKU
Journal：JournaloftheChineseCeramicSociety
年，卷(期)：2024, 52(7)
分类号：TU443
关键词：叶绿泥石 水化膨胀 分子模拟 径向分布函数
Keywords：pennine hydrationexpansion molecularsimulation radialdistributionfunction
机标分类号：O641TK126O4
在线出版日期：2024年7月24日
基金项目：国家自然科学基金，中国科学院青年创新促进会项目叶绿泥石水化机理及膨胀特性的分子动力学[
期刊论文] 硅酸盐学报--2024, 52(7)张瑞 余飞 佟凯文 黄康 张伟 戴张俊 陈善雄高铁路基膨胀灾害工程实例发现,部分膨胀是由叶绿泥石水化膨胀引起的,但目前国内外学者对叶绿泥石膨胀特性研究较少,相关机理尚未明确.采用多尺度表征的方法研究了宏观和纳观尺度下叶绿泥石的膨胀特性,运用分子动力学模...参考文献和引证文献
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