简介:在不添加任何分散剂和改变pH值的情况下,通过两步法将比表面积为150m^2/g的气相SiO2纳米颗粒制备成均匀稳定、透明度高、分散性能好的纳米流体。并对该功能性纳米流体进行了导热系数、黏度、表面张力和壁面接触角的测量。低体积分数下,功能性纳米流体较基液的导热系数几乎没有变化,但黏度却有较大改变。传统固液两相混合物黏度模型不再适用功能性纳米流体的计算,其主要原因是传统公式低估了分子间作用力对纳米流体黏度的影响。因此,建立了功能性纳米流体的黏度经验公式。由于纳米颗粒的存在提高了沸腾表面的粗糙度,从而使纳米流体的壁面湿润性能大大提高。实验结果表明,纳米流体的黏性和壁面接触角是沸腾换热发生骤变的关键。
简介:InordertoimprovethemechanicalpropertiesofSiO2aerogel-glassfibercomposites,effectsofdifferentsolvents(cyclohexane,n-hexane,ethanol,acetone)anddifferentdispersingmodes(planetaryballmilling,ultrasonicdispersionandmechanicalstirring)anddispersingduration(10-40min)onthedispersionofchoppedalkali-freeglassfiberbundleswerestudiedtodeterminethebestdispersionprocess.Onthisbasis,thematerialswerebatchedaccordingtothemassfractionofSiO2aerogelpowdertochoppedalkalifreeglassfiberbundlesof90:10,andacertainamountofzincoxidelight-screeningagentandphenolicresinbinderwereadded.SiO2aerogelglassfibercompositespecimenswerepreparedbydirectaddingchoppedalkalifreeglassfiberbundlesandpre-dispersedchoppedalkalifreeglassfiberbundles,respectively.Thecoldcrushingstrengthandthethermalconductivityatdifferentsurfacetemperatures(300,400,500and600℃,respectively)ofthespecimensweremeasured.Theresultsshowthat:(1)theoptimumdispersionprocessofchoppedalkali-freeglassfiberbundlesisusingethanolassolventandmechanicalstirringfor30min;(2)pre-dispersionofchoppedalkali-freeglassfiberbundleshaslittleeffectonthethermalconductivityofSiO2aerogel-glassfibercompositesbutcanimprovethecoldcrushingstrength.
简介:Ni/SiO2andbimetallicNixGa/SiO2catalystswithdifferentNi/Gaatomicratios(x=10~2)wereinvestigatedfortheselectivehydrogenationofacetylene.ItwasfoundthatNixGa/SiO2showedhigherselectivitytoethylenethanNi/SiO2.ThisisattributedtotheformationNi-GaalloyandNi3Gaintermetalliccompound(IMC)wheretherewasachargetransferfromGatoNi,whichisfavorableforreducingtheadsorptionstrengthandamountofethyleneonNiatoms.Asaresult,theover-hydrogenation,theC–Cbondhydrogenolysisandthepolymerizationweresuppressed,andsubsequentlytheselectivitytoethylenewasenhanced.WiththedecreaseofNi/Gaatomicratio,theactivityandstabilityoftheNixGa/SiO2catalystsincreasedfirstandthendecreased,whiletheethyleneselectivitytendedtoincrease.Ni5Ga/SiO2exhibitedthebestperformance.Undertheconditionsof180°C,0.1MPa,andareactant(1.0vol%acetylene,5.0vol%H2and94vol%N2)withthespacevelocityof36,000mLh-1g-1,theacetyleneconversionmaintainedat100%onNi5Ga/SiO2during120htimeonstreamandtheselectivitytoethylenewas75%~81%afterreactionfor68h.ItwasalsofoundthattheformationofNi-GaalloyandNi3GaIMCsuppressedtheincorporationofcarbontoformNiCx,subsequentlyenhancingthecatalyststability.Additionally,withincreasingtheGacontent,thecatalystacidamountandstrengthtendedtoincrease,whichpromotedthepolymerizationandcarbondepositionandsothecatalystdeactivation.
简介:背景:传统静电纺丝纳米纤维制造过程相对复杂,制造条件要求高,无法适应创伤、烧/烫伤等组织缺损的应急事件中快速组织修复的需求。目的:观察手持式静电纺丝聚乳酸/明胶可降解纳米纤维膜对小鼠皮肤缺损原位修复的效果。方法:①采用自制3D打印的手持式静电纺丝设备制备聚乳酸/明胶可降解纳米纤维膜,检测其接触角、水蒸气透过率;②以浓度100%,50%,20%的聚乳酸/明胶可降解纳米纤维膜浸提液培养胎鼠成纤维细胞,采用CCK-8细胞毒实验评估材料残留溶剂毒性;将胎鼠成纤维细胞与聚乳酸/明胶可降解纳米纤维膜共培养(实验组),设置单独细胞培养为对照,Alamarblue法检测细胞增殖,活/死染色观察细胞存活率,扫描电镜观察细胞形态;③在18只Balb/c小鼠背部制作直径2cm皮肤全层缺损,实验组进行手持静电纺丝原位聚乳酸/明胶可降解纳米纤维膜修复后纱布包扎,对照组进行纱布包扎,术后8周进行缺损部位苏木精-伊红和Masson染色,观察缺损皮肤修复效果。结果与结论:①聚乳酸/明胶可降解纳米纤维膜的接触角为(32.68±5.68)°,属亲水材料,适宜细胞黏附;24h水蒸气透过率为(4.21±0.11)×103g/m2,可满足皮肤外敷料的要求;不同浓度的聚乳酸/明胶可降解纳米纤维膜浸提液无明显的细胞毒性;②实验组胎鼠成纤维细胞具有与对照组细胞等同的细胞活性,但具有更快的增殖速度与更长的增殖时间;③苏木精-伊红和Masson染色显示,实验组小鼠皮肤伤口全层愈合,材料降解完全,毛囊再生;对照组小鼠皮肤未全层愈合;④结果表明,手持式静电纺丝聚乳酸/明胶可降解纳米纤维实现小鼠皮肤全层缺损的原位修复。
简介:摘要:采用不同掺量的纳米碳纤维制备了纳米碳纤维改性混凝土材料,测试了其抗压强度、劈拉强度等基础力学性能指标,并从微观层次探究了纳米碳纤维对混凝土的改性作用。结果表明:适量的掺入纳米碳纤维能提高混凝土的力学性能,当掺量为 0.3%时,材料的基本力学强度指标改善效果最好,抗压强度和劈拉强度相较于素混凝土分别提高了 9.2%、 13.2%和 17.5%;纳米碳纤维在混凝土内部能够形成立体网状结构,因此可以较好地改善混凝土的微观形貌特征,增强混凝土的韧性和整体性,并能在混凝土破坏时消耗掉部分断裂破坏能。研究成果为高耐久性防护材料的研究和应用奠定了基础。
简介:TheSiO2nanoparticleswerecoatedonthesurfaceofgrapheneoxide(GO)bysol-gelmethodtogettheSiO2-Gcompound.TheSiO2-GwasrestoredandoleophylicallymodifiedtopreparehydrophobicmodifiedSiO2-G(HM-SiO2-G)whichwassubsequentlyaddedtosiliconerubbermatrixtopreparetwo-componentroomtemperaturevulcanized(RTV-2)thermalconductivesiliconerubber.Themorphology,chemicalstructureanddispersityofthemodifiedgraphenewerecharacterizedwithSEM,FTIR,Raman,andXPSmethods.Inaddition,theheat-resistancebehavior,mechanicalproperties,thermalconductivity,andelectricalconductivityoftheRTV-2siliconerubberwerealsostudiedsystematically.TheresultsshowedthattheSiO2nanoparticleswerecoatedongrapheneoxidesuccessfully,andHM-SiO2-GwasuniformlydispersedinRTV-2siliconerubber.TheadditionofHM-SiO2-Gcouldeffectivelyimprovethethermalstability,mechanicalpropertiesandthermalconductivityofRTV-2siliconerubberandhadnogreatinfluenceontheelectricalinsulationperformance.
简介:摘要纳米技术在许多方面运用都能较好的解决问题,运用也十分广泛。本文对与纳米技术进行了一定的介绍并简单介绍了纳米技术的具体合成以及纳米技术的三个发展阶段,并且对其发展前途以及国家对他的重视程度进行了预测。和其在陶瓷领域中,微电子学上和生物工程上、在医学上等的应用,并在这些领域所获得的巨大贡献。