Influence of calcination temperature on microstructure and surface charge of membrane top layers composed of zirconia nanoparticles

The purpose of the research is to investigate the changes in microstructure and physicochemical characteristics, mainly surface charge (i.e. zeta potential) of zirconia membrane top layer during calcination. Zirconia is one of the most commonly preferred materials for ceramic membrane top layers due to its superior durability. The physicochemical properties of the top layer composed of submicron / nano particles is necessary not only for Donnan exclusion but also for dynamics of membrane fouling. In the present research the possibility of preparation of zirconia top layers with varying surface charge with changing calcination temperature was shown and a correlation between phase transformation and surface charge was determined

Preparation and characterization of nanocrystalline titania powders by sonochemical synthesis

Nanocrystalline mesoporous titania powders were synthesized by hydrolyzing titanium isopropoxide in ethanol-water mixtures which were ultrasonically treated without using any templates or chemicals. Titanium isopropoxide-ethanol mixture was added dropwise to a water-ethanol mixture placed in an ultrasonic bath. The properties of the sonochemically synthesized powder were compared with those of the powders prepared without ultrasonic treatment along with Degussa P-25 titania powder. The phase structure, crystallite size, surface area, particle size, powder density were determined and sintering behavior was analyzed in this work. The nanotitania powder prepared during ultrasonic induced hydrolysis (TiO 2-U) was determined to be formed from a mixture of anatase and brookite phases at 25°C. The brookite phase in nanotitania powder prepared without ultrasonic treatment (TiO 2-NoU) was detected at 70°C. The anatase-rutile phase transformation was completed in the 500-700°C range for both powders. The average crystallite sizes of the powders at 25°C were determined as 10 and 5nm for TiO 2-NoU and TiO 2-U, respectively. The surface area decreased from 238 to106m 2/g for TiO 2-NoU and from 287 to 82m 2/g for TiO 2-U when the calcination temperature was increased from 200 to 500°C. The evolution of the N 2 adsorption-desorption behavior with calcination temperature and the corresponding pore size distributions/volumes was attributed to the formation of closely packed submicron aggregates during powder synthesis and calcination. The sintering behavior was concluded to be controlled by 7-10nm crystallites and the submicron aggregates. The determination of the densification behavior of titania powders prepared by different methods with various levels of dopants may prove to be very useful for a better understanding of the phase/pore structure evolution which is crucial for a significant number of applications

Preparation and characterization of nanocrystalline titania

Nanokristal seramikler, ileri seramiklerin gelecekteki uygulamalannda önemli etkileri olabilecek özgün kimyasal, fiziksel ve mekanik özelliklere sahiptir. Bu çalışmada, tItanyum; izopropoksit'ten titan seramikleri hazırlanması ve karakterizasyonu incelendi. Şekillendirilmiş yapılar 650-850 C aralığında hava ortamında sinterlendi. Sol-jel prosesi ve jellerin kontrollü kurutulması ile elde edilen seramiklerin yoğunluklan teorik yoğrunluğun %79-99' u olarak bulundu. Sollar, jeller ve çökertme yöntemleriyle hazırlanan tozlardan preslenen peletlerin sinterlerne işlemi öncesi ve sonrası yoğunlukları sırasıyla teorik yoğunluğun %40-52 ve %55-83' ü olarak bulundu.Nanocrystalline ceramics possess unique chemical, physical and meehanical properties which may have a significant impact on the future applications of advanced cemmies. The preparatiion and characterization of titania ceramics from titanium isopropoxide precursor was investigated in this work. Green bodies were air gintered in the 650-850°C range for the determination of the sintering behaviour. The sintered densities of the cerainics prepared by sol-gel processing and controlled drying of the gels were in the 79-99% of theoretical density. The green and sintered densities of the pellets prepared by uniaxial pressing of powders derived from sols, gels and precipitation were in the 40-52% and 55-83% respectively

Effects of processing on the properties and permeability of pure gases through sol-gel silica membranes

N2, O2 and CO2 pure gas permeation through sol-gel derived silica membranes were determined and the effects of processing parameters on the microstructure of the membrane was investigated. Silica sols were prepared in an alcoholic solution by hydrolysis and condensation of TEOS as a function of acid content. The thickness of the silica membranes was determined to be about 2μm and significant infiltration into the support was observed from the SEM pictures. The supported membranes were heat treated in the 50-400°C. The N2 permeabilities of silica membranes varied in the 2.2*10-10-2.7*10-8 mol/m2.s.Pa range for single layer membranes dipped for 10s. in the sol. The CO2 permeability of these membranes varied in the 1.2*10-9-6.95 *10-8 mol/m2.s.Pa range. The sols became viscous and gelled at 50°C in 16 hours. The O2 permeability increased with aging time. The optimum dipping time during processing was determined to be 10 seconds. The increase in the acid content of the sols were observed to increase permeabilities of the membranes significantly

Preparation and characterization of polyLactide-hydroxyapatite biocomposites

In the present study, the preparation and characterization of polylactide-Hydroxyapatite(HA) composite films for biomedical applications have been studied. The effects of number of parameters such as polymer type, HA loading, surface modification and its concentration on the mechanical and microstructural properties of the composites were investigated. Poly-L-Lactide and 96/4 Poly(L-Lactide co D-Lactide) copolymer-HA composites containing 10-40 wt% HA particles have been prepared by solvent casting technique. The HA powder was synthesized by precipitation technique. Interfacial interactions between HA and polylactide polymer were modified to improve filler compatibility and mechanical properties of the composites by surface treatment of the HA with two different silane coupling agents; 3-aminopropyltriemoxysilane (AMPTES) and 3-mercaptopropyltrimethoxysilane (MPTMS) at three different concentrations(0.5-2 wt%). Silane treatment indicated improvements in the mechanical properties of the composites compared to the untreated HA loaded polylactide composites. Tensile test results showed that the maximum improvement in the mechanical properties of the composites was obtained for PLA composites containing 1 wt% aminofunctional silane treated HA and 0.5-wt% mercaptopropyltrimethoxy silane treated HA for PDLA composites. Scanning electron microscopy studies also revealed better dispersion of silane treated HA particles in the polymer matrix

Alumina/water suspensions in the presence of PEO-PPO-PEO triblock copolymers

The aim of this study was to investigate the stability and dispersion behaviour of aqueous alumina suspensions in the presence of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) type triblock copolymers. For this purpose alumina suspensions at various solids loadings were prepared using four different methods. These are: Method I: powder and water were stirred only; Method II: powder and water were stirred and ultrasonic treatment was applied; Method III: powder and water were stirred in the presence of block copolymers; Method IV: powder and water were stirred and ultrasonic treatment was applied in the presence of block copolymers. These suspensions were characterized by means of rheological measurements. Sedimentation and turbidity measurements were also conducted to support these results and to investigate the stability of these systems for longer times. Surface tension measurements were performed to investigate the adsorption behaviour of block copolymers onto alumina surface. It was found that the use of PEO-PPO-PEO type triblock copolymers improved the dispersion behaviour of aqueous alumina suspensions in the presence of ultrasonic treatment at low solids loadings. However their effect was not significant at high solids loadings and without ultrasonic treatment

Impact of titania phase structure and surface reactivity on the photocatalytic degradation of various dyes and textile wastewater

Titania (TiO2) powders have been prepared by precipitation method in different precipitation media which contain sulfate, nitrate or organic species. Photocatalytic degradation of different dyes and a real textile wastewater have been conducted with these powders along with commercial powder Degussa P25 for comparison. Ethyl alcohol (organic medium), sulfuric acid (sulfate medium) and nitric acid (nitrate medium) have been used to dissolve titanium precursor for the precipitation of TiO2 in ammonia solution. UV-Vis DRS and XPS results indicate that S doping in sulfate medium precipitated powder and N doping in nitrate medium precipitated powder has been occurred and the presence of S or N containing impurities on the grain boundaries have been improved light absorption of TiO2 significantly. However, these powders have exhibited low surface reactivities. The highest surface reactivity has been obtained with the powder precipitated in organic medium which also has the highest crystallite sizes (76 nm rutile and 34 nm anatase crystallites) with relatively low rutile weight percentage (10.0%). The surface-normalized rate constants of this powder are 0.02038 min-1.m-2 in real textile wastewater degradation and 0.0161 min-1.m-2 in methyl orange degradation, which are 0.01563 and 0.0091 min-1.m-2, respectively, for Degussa P25. Results have shown that this powder show 30-70% higher surface reactivities compared to Degussa P25. The main structural difference of organic medium precipitated powder and Degussa P25 has been found to be the anatase-rutile weight ratio and crystallite size of rutile phase whereas band gap energy of Degussa P25 is lower and other properties are not significantly different

Preparation of particulate/polymeric sol-gel derived microporous silica membranes and determination of their gas permeation properties

Monodisperse silica sols with well-defined spherical particles ranging in size from 5 to 310 nm were prepared through Stober process. Both particulate and polymeric sol-gel routes were employed for the preparation of stable silica sols. The use of polymeric species in combination with particulate silica spheres may allow the design of predefined membrane pore structures with high thermal stability by cubic/random/close packing of monodisperse spherical particles incorporated into the polymeric network. The size and volume content of spheres were varied in order to modify the consolidation behaviour of 2-structural silica membranes which would enhance the thermal stability. The low shrinkage level for sphere loaded 2-structural systems compared to the pure polymeric counterparts might be explained by the decrease in the structural free energy of the polymeric/particulate 2-structural system. The thermal stability of the microporous membranes may thus be improved by incorporating particulates into the polymeric network through the formation of a lower extent of thermally induced microcrack formation. The N2 permeation through 90 nm silica sphere added silica membranes remained constant when they were heat treated in the 250-400 °C range indicating the stability of the pore network. © 2009 Elsevier B.V. All rights reserved

The surface charge of unsupported nano-structured titania ceramic membrane top layers with varying calcination temperatures

Titania is one of the most preferable ceramic membrane materials of superior durability (as zirconia) when compared to that of other ceramics, e.g. alumina or silica. The surface charge of the membrane top layer is an important parameter of the separation performance of the multilayer ceramic membrane due to the Donnan exclusion mechanisms. In this study, the change of the surface charge of unsupported nano-structured titania top layer is investigated with calcination temperature variation. The effect observed indicates the possibility of preparation of tailor-made top layers for multilayer ceramic membranes. © 2019, University of Chemical Technology and Metallurgy