Seite - 135 - in Advanced Chemical Kinetics

Δμo¼ ΖþΖ�e 2 4πεoε rþþr�ð Þ (2) whereεo represents thepermittivity invacuumandε isdielectric constantofagivensolution. r+ and r�present the radii of ions charged. Based on Eqs. (1) and (2), Chen andChang [12] proposed thebelowequation: 2γ rkTρ ¼ lnCþ ΖþΖ�e 2 4πεoεKT rþþr�ð Þ (3) wherem is the weight of the solute molecule; γ is the interfacial energy in J/m2, the term interfacial energy canalsobewritten asnm�1; r is theparticle size of a spherical particle and C is the solute concentration. The author linearized Eq. (3) in terms of particle size r(Y) and dielectric constant ε(X). It was assumed that only dielectric constant is significant and other properties are insignificant.However, according to Israelachvili [11],Coulombic interaction is muchweakened inwater. So, it canbepostulated that, for homologousmixtureofwater and alcohol, theCoulombic interactionwill beveryweak.Hence, it canalsobehypothesised that thesurface tensionof solventwilldirectlyaffect thenucleationandgrowthofparticles. 2.Experimental 2.1.Materialsandmethod Analytical-gradeFeCl3�6H2OandNH4OH(B&MScientific,CapeTown,R.S.A)wereusedas theyarewithoutanyfurtherpurification.Deionisedwaterandalcohol (methanol, ethanoland propanol) weremixed together with different ratios to vary the surface tension of solvent. Ammoniumhydroxide,NH4OH,wasaddeddropwiseuntil themixturepHreachedavalue of 10.Acertain amountofFeCl3�6H2Owasadded to the solution tomakeup0.05Msolution (unlessstatedotherwise),andthesolutionwasstirreduntil the ironsaltwasdissolved.ThepH of the final solution (prior toheating)wasrecorded.ThepHwasalwayskeptconstantat~2 to isolate the effect of pH on the particle growth in each case. The solutionwas replaced in a teflon-linedpressureautoclave.Thetemperaturewas100�C.Areactiontimeof2hwasusedto synthesise theparticles. 3.Resultsanddiscussion 3.1.Correlationbetweenparticle sizeandalcohol surface tension Three different alcohols (methanol, ethanol and propanol) were used to tune the surface tension of the solvent. If the hypothesis conceived earlier is true, then therewill be a qualita- tive relationship between particle size,De, and surface tension of solvent, γ. The particles synthesised in this studywere rod-shapedparticles. The length anddiameter of theparticles were measured from TEM images. A minimum number of 250 particles was counted for Hydrothermal Precipitation of β-FeOOH Nanoparticles in Mixed Water/Alcohol Solvent http://dx.doi.org/10.5772/intechopen.70503 135