Preparation And Stability Of Titanium Dioxide Dispersion

Titanium dioxide（TiO₂）is widely used in many fields such as paints,coatings,paper making,and cosmetics.The stability of its dispersions has an important impact on its application performance.In this work,commercially available TiO₂（CA-TiO₂）was chosen to study its dispersion stability in water and organic solvents,and the effects of various factors on its dispersion stability were investigated.In addition,small-size TiO₂ samples were synthesized by liquid-phase precipitation and microemulsion methods,and their dispersion stability in water was investigated and compared with CA-TiO₂.It is expected to deepen the understanding of the dispersion stability of TiO₂ and to provide useful information for the development and application of related products.The main research contents and conclusions of this thesis:（1）Preparation and characterization of TiO₂ nanoparticlesUsing Ti（SO₄）₂ as the titanium source and ammonia water as the alkali source,two TiO₂ samples（LP-TiO₂）were prepared by the liquid-phase precipitation method under different conditions,denoted as LP-TiO₂-1 and LP-TiO₂-2.LP-TiO₂-1 is of the rutile-type structure,showing needle-shaped aggregates with～80 nm in size,and its isoelectric point（IEP）is-6.4.LP-TiO₂-2 is of the anatase-type structure,showing sphere-like particles with-25 nm in size and IEP～6.0.Using tetrabutyl titanate as a titanium source and the W/O-type SFMEs formed by nbutanol,ethanol and water as the reaction medium,four TiO₂ samples（ME-TiO₂）were prepared under different conditions,denoted as ME-TiO₂-1,ME-TiO₂-2,ME-TiO₂-3,and ME-TiO₂-4.All the ME-TiO₂ samples are mainly of the anatase-type structure,showing sphere-like particles with～5-10 nm in size and IEP～4.0.The CA-TiO₂ sample is of the rutile-type structure,showing irregular blocky particles with～120 nm in size and IEP-7.0.（2）Stability of TiO₂ aqueous dispersionThe dispersion stabilities of CA-TiO₂,LP-TiO₂,and ME-TiO₂ in aqueous phase were investigated.The effects of pH,phosphate dispersants,solvent,and silica sol on the dispersion stability were determined.The Zeta potentials and average hydraulic diameters（d_h）of the dispersions under different conditions were measured to explore the relevant mechanisms.The results show that,with an increase in pH（1-12）,the dispersion stability of TiO₂ samples decreases first and then increases,with the most unstable near their IEPs.The dispersants phosphates can reduce their IEPs,improve their dispersion stability,and broaden the pH range in which the dispersions remain stable;their order to enhance stability is:Na₄P₂O₇>NasP₃O₁₀≈Na₆P₆O₁₈>Na₂HPO₄>NaH₂PO₄.The appropriate dosage of phosphate（Na₄P₂O₇）is 100-500 mg/L,and the excessive dosage may reduce the dispersion stability.Adding PEG-200 to CA-TiO₂ aqueous dispersion can significantly improve its dispersion stability.Mixing CA-TiO₂ with silica sol（SiO₂）can improve its dispersion stability and broaden its stable pH range.Phosphates can improve the stability of CA-TiO₂/SiO₂ dispersions,and Na₄P₂O₇ shows the best effect.The stability results of TiO₂ and TiO₂/SiO₂ dispersions are consistent with the results of Zeta potentials and d_h measurements.The higher the Zeta potentials,the smaller the d_h values,and the higher the stability of the dispersions.In addition,the dispersion stability of CA-TiO₂ is observed to be similar to those of LP-TiO₂-1 and ME-TiO₂-1（or no significant effect of particle size on dispersion stability is observed）,and the dispersion stability of the rutile-type TiO₂ tends to be higher than that of the anatase-type TiO₂.（3）Stability of TiO₂ organic dispersionThe surface free energy（γ）of commercially available TiO₂（CA-TiO₂）was measured using the contact angle method,including the total surface free energy(γ_t,s)and its dispersion component(γ_d,s)and polarity component(γ_p,s).Based on the correlations between y and solubility（δ）parameters,the Hildebrand solubility parameter(δ_t,s)as well as the Hansen dispersion component polarity component(δ_p,s),and hydrogen bond component(δ_h,s)were obtained.A total of 70 organic solvents and mixed solvents were chosen,and the dispersion stability of CA-TiO₂ in the solvents was determined.The applicability of the"characteristic parameter matching principle"（CPM principle）was examined for TiO₂ organic dispersions,and suitable solvents for dispersing TiO₂ were selected.The results show that the γt,s,γd,s,and γp,s of CA-TiO₂ are about 44.5,33.6,and 1 0.9 mJ/m²,and its δ_t,s,δ_d,s,δ_p,s,and δ_h,s are about 27.5,17.5,13.7,and 9.8 MPa^1/2.When the characteristic parameters of solvents are closer to those of TiO₂（or the characteristic parameter distance is smaller）,the stability of TiO₂ dispersions in the solvents is higher,indicating that the CPM principle is applicable to TiO₂ dispersions.In addition,the viscosity of solvents is also an important factor affecting the dispersion stability of TiO₂.The mixed solvent strategy can be used to obtain effective solvents,significantly improving the dispersion stability of TiO₂.