Colloidal Silica Suspensions Research Articles

Rheological Behavior of an Aqueous Suspension of Oxidized Carbon Nanohorn (CNHox).

Oxidized carbon nanohorn (CNHox) a carbon nanomaterial that has attracted attention due to its unique material properties. It is expected to be applied in various areas like cancer treatment, gene-expression technology, fluids with high thermal conductivity, lubricants, and so on. While the rheological measurements of suspensions provide information on the effective size and interactions of suspended particles, the rheological behaviors of aqueous suspensions of CNHox have never been systematically investigated. To clarify the rheological behaviors of aqueous suspensions of CNHox, their viscosity and dynamic viscoelasticity were measured with changing particle concentration and salt concentration. The viscosity of a CNHox suspension showed yield stress at low shear rates and showed shear-thinning behavior with increasing shear rates. The viscosity of 5 weight % CNHox suspensions was comparable to that of 60 weight % silica suspensions. This high viscosity at a low CNHox concentration is probably due to the porous structure and large effective volume of the CNHox particle. The estimated effective volume of CNHox calculated by the Krieger-Dougherty equation was 18.9 times larger than the actual volume calculated by the mass concentration and density. The dependence of rheological behavior of the CNHox suspension on salt concentration was weak compared to that of the colloidal silica suspension. This weak dependence on salt concentration may be due to the roughness of the particle surface, which would weaken the effect of electric double-layer interactions and/or van der Waals interactions between particles. These rheological behaviors of the aqueous suspension of CNHox shown in this research will be useful in efforts to improve the efficiency of its utilization for the various applications.

Applying colloidal silica suspensions injection and sequential gelation to block vertical water flow in well annulus: laboratory testing on rheology, gelation, and injection

We evaluated the application of silica suspension injection and sequential gelation to block vertical water flow in the annuli of long-screened wells. First, we studied the viscosity, rheological behavior, and gelation performance of colloidal silica suspensions in batch tests. Then, we tested the injection of silica suspensions and the water flow blocking efficiency of the later formed silica gel in column and bench-scale sandbox experiments. Micron-sized fumed powder silica suspensions and nanosized silica suspensions recovered from geothermal fluids were tested in this work. Fumed silica suspensions showed shear thinning, while nanosized silica suspensions exhibited Newtonian flow behavior. During the gelation process, the nanosized silica suspension changed from a Newtonian fluid to a shear thinning fluid while increasing its overall viscosity. At comparable concentrations, the nanosized silica suspensions have much lower viscosity than that of the fumed silica suspensions. Increases in the Na+ concentration and silica particle concentration in these suspensions shortened the gelation time. Silica suspension gelation in sand columns completely blocked the water flow and sustained the injection pressure up to 50 psig (344.7 kPa). A silica suspension was successfully injected into the target zone in the annulus of a bench-scale sandbox mimicking long-screened wells in the field. The silica gel formed in the annulus effectively blocked chemical transport through the gelled zone. Our research reveals that a process using silica suspension injection and sequential gelation technology is promising for blocking the vertical water flow and chemical transport through the filter pack in targeted zones within the annulus of long-screened well systems.

Two-point microrheology and diffusing wave spectroscopy

The dynamics of charged and hard-sphere silica colloidal suspensions are measured using diffusing wave spectroscopy and are interpreted by the Generalized Stokes–Einstein Relation (GSER). At high concentration, the resulting moduli are in good qualitative agreement with bulk rheology, including the frequency response, but are higher by a quantitative factor. We show that the “two-point” GSER, which derives from the correlated motion of the colloidal particles, provides a better quantitative agreement between bulk and microrheology. The two-point GSER applies generally when the average scattering vector sampled by the multiple scattering events corresponds to a length scale greater than the scatterer diameter. We discuss applications for characterizing colloid interactions by measuring the high-frequency moduli of suspensions and extend the two-point analysis to tracer particle microrheology measurements of a semiflexible biopolymer network.

Biomediated control of colloidal silica grouting using microbial fermentation

Colloidal silica grouting is a ground improvement technique capable of stabilizing weak problematic soils and achieving large reductions in soil hydraulic conductivities for applications including earthquake-induced liquefaction mitigation and groundwater flow control. In the conventional approach, chemical accelerants are added to colloidal silica suspensions that are introduced into soils targeted for improvement and the formation of a semi-solid silica gel occurs over time at a rate controlled by suspension chemistry and in situ geochemical conditions. Although the process has been extensively investigated, controlling the rate of gel formation in the presence of varying subsurface conditions and the limited ability of conventional methods to effectively monitor the gel formation process has posed practical challenges. In this study, a biomediated soil improvement process is proposed which utilizes enriched fermentative microorganisms to control the gelation of colloidal silica grouts through solution pH reductions and ionic strength increases. Four series of batch experiments were performed to investigate the ability of glucose fermenting microorganisms to be enriched in natural sands to induce geochemical changes capable of mediating silica gel formation and assess the effect of treatment solution composition on pH reduction behaviors. Complementary batch and soil column experiments were subsequently performed to upscale the process and explore the effectiveness of chemical, hydraulic, and geophysical methods to monitor microbial activity, gel formation, and engineering improvements. Results demonstrate that fermentative microorganisms can be successfully enriched and mediate gel formation in suspensions that would otherwise remain highly stable, thereby forgoing the need for chemical accelerants, increasing the reliability and control of colloidal silica grouting, enabling new monitoring approaches, and affording engineering enhancements comparable to conventional colloidal silica grouts.

Physico-mechanical properties of metakaolin and diatomite-based geopolymers

Geopolymers (inorganic polymers) are sustainable materials obtained from the dissolution of an aluminosilicate precursor by a high-alkaline liquid medium. Many studies point out that the properties of such materials depend on essential parameters, such as precursor, activating solution, SiO2 source, curing temperature, and others. This work evaluated the combination of two aluminosilicates (metakaolin and calcined diatomite) with Na-based alkaline liquid reagents (containing sodium silicate or colloidal silica) and how they affected the physico-mechanical properties of the prepared geopolymers after curing at 40 °C for 24 h. The following tests were carried out to characterize the compositions: in situ Young’s modulus evolution as a function of time; cold crushing strength; apparent porosity; and structural analyses via XRD and FTIR measurements. The synthesized geopolymers showed amorphous inorganic structure containing residual crystalline phases (quartz and illite), which are in tune with the Si-O-Si and Si-O-Al bonds identified in the ATR-FTIR spectra. The samples presented cold crushing strength and Young’s modulus up to 39.4 MPa and 13.4 GPa, respectively. The geopolymerization reactions were favored when using colloidal silica suspension, which led to the development of silicate-free geopolymers with enhanced performance at low temperature.

Aggregation kinetics of a concentrated colloidal suspension under oscillatory flow.

The aggregation behavior of an attractive colloidal silica suspension under oscillatory flow is studied using rheological measurement. We show that the competition between the aggregation of the particles and the aggregate breakup under external stress leads to a non-monotonous evolution of the elastic modulus with time. Remarkably, under certain conditions, the elasticity is not an increasing function of time but exhibits a maximum. The value of the maximum of the elastic modulus depends on the applied shear amplitude and the ionic strength of the suspension. Scaling laws that describes the evolutions of the elastic modulus as a function of the salinity and of the deformation amplitude are proposed and discussed.

Silica-based consolidants: Enhancement of chemical-physical properties of Vicenza stone in heritage buildings

Natural stones interact with the environment and undergo several chemical and physical weathering processes that cause the progressive loss of cohesion and degradation/disintegration of the material in the longer term. So, in order to retain the integrity of the historical patrimony and its undeniable impact on society, innovative materials and methodologies have been used in stone conservation field in recent years, also using a more environmentally-friendly approach. In this study, the interaction of three inorganic silica-based consolidant compounds with a valuable artistic calcareous rock, Vicenza stone, is discussed. This specific lithotype results to be still scarcely investigated, despite its high historical relevance and intrinsic features, especially porosity, which make it extensively susceptible to degradation. In particular, a colloidal suspension of silica made by particles with an average diameter of 10–20 nm, and two alkaline silicate solutions (lithium silicate and sodium silicate) are evaluated. An extensive characterization of both treated and untreated Vicenza stone samples was achieved by means of chemical–physical and morphological investigations (water absorption, open porosity, capillary absorption, ultrasonic pulse velocity and static contact angle measurements, Hg intrusion porosimetry, color evaluation, FTIR spectroscopy and SEM analyses). FTIR analyses revealed that all the consolidants exhibited a moderate penetration within the substrate, anyway a significant surface interaction with the stone, especially in the case of alkaline silicates, is proved by the results of SEM analyses, capillary absorption, static contact angle and color change. The improvement of the surface properties after treatments represents an essential and preliminary assumption to enhance the durability performance of Vicenza stone.

Characterising the sedimentation of bidisperse colloidal silica using analytical centrifugation

This study investigates the settling behaviour of bidisperse colloidal silica suspensions in two different size ratios (100:500 nm and 500:800 nm) with various mixture ratios and volume fractions, using an analytical photocentrifuge. For dilute systems, translation of settling rate profiles to size distributions resulted in more accurate measurements for both monodisperse and bidisperse systems than using dynamic light scattering, in comparison to SEM. However, a critical limitation was also observed, as distinction between upper (smaller particle) and lower (larger particle) interfaces could only be measured for total volume fractions <∼0.02. For 500:800 mixtures, results were compared with Richardson-Zaki and modified Batchelor model predictions. The Batchelor model proved more accurate at predicting the lower interface rate, while both models over predicted the upper interface, likely due to increased drag that was most evident with higher fractions of smaller particles. For 100:500 cases, higher centrifugal rotation speeds were required to settle the 100 nm particles, and the influence of Brownian motion was evident. It was also found that the smaller particles obtained a lower initial settling rate than its terminal velocity, due to induced anisotropic effects or backflow from the 500 nm fraction, which was again more evident with a greater proportion of smaller particles.

Climbing Colloidal Suspension

Mixtures of powder and liquid are ubiquitous in nature as well as industries and exhibit complex flowing and deforming behaviors, including sol to gel transition under shear stress. In order to better understand the characteristic features of this type of mixture, we observed the behavior of a mixture of colloidal silica particles and water as a model system under vibration. The mixture showed different states, from powder-like to viscous fluid-like, with increasing content of water. At certain concentrations of silica particles (around 70 wt. %) and under relatively faster vibration (over 17 Hz), we observed that the colloidal suspension of silica particles and water climbed up the wall of a container against gravity. The main purpose of this paper is to report how we can observe the climbing suspension of colloidal silica. The rheological measurements of the climbing suspension demonstrated that the climbing suspension showed shear-thickening behavior, where force chain networks and normal stress differences are considered to develop. Therefore, we speculate that the transient formation and breaking of force networks and normal stress differences under vibration contribute to the occurrence of the climbing suspension. The tunable nature of colloidal suspensions may help to elucidate the climbing mechanism in the future.

Effect of reactive silica sources on the properties of Na-metakaolin-based geopolymer binder

Geopolymer has been pointed out as a potential sustainable material for applications with distinct complexities. Regarding the synthesis and processing of such materials, there are still some technical challenges associated with the particularities of the selected raw materials. This work investigated the role of reactive silica sources on the setting time, physical and mechanical properties of Na-metakaolin-based geopolymer binder. In this sense, different activating solutions (AS) were analyzed containing plain NaOH or NaOH combined with sodium silicate, or silica fume, or colloidal silica. The setting behavior, cold crushing strength and elastic modulus evolution as a function of time (up to 16 days) of the designed formulations were measured after curing the prepared samples at 40 °C for 24 h. The most promising compositions were then fully characterized and had their properties evaluated after thermal treatments in the 200 to 1000 °C temperature range. The results indicated that the best performance was obtained for the geopolymer containing colloidal silica (GP-CS) in its activating solution. Such binder also exhibited fast setting, good thermal stability, suitable cold crushing strength (7.1 MPa) and low porosity (2.3%) after firing the samples at 1000 °C. FTIR and DRX profiles of GP-CS highlighted the generation of a high number of Si-O-Al bonds, which induced the crystallization of mullite phase at 1000 °C and enhanced the mechanical strength of this geopolymer. Thus, the use of colloidal silica suspension to design novel activating solutions is an interesting route to prepare geopolymers with improved performance and thermal stability.

Conditions for Shake-Gel Formation: The Relationship between the Size of Poly(Ethylene Oxide) and the Distance between Silica Particles.

Colloidal silica suspensions are widely used in many fields, including environmental restoration, oil drilling, and food and medical industries. To control the rheological property of suspensions, poly(ethylene oxide) (PEO) polymers are often used. Under specific conditions, the silica-PEO suspension can create a phenomenon called a shake-gel. Previous works discussed the conditions necessary to form a shake-gel and suggested that the bridging effect of the polymer is one of the important mechanisms for shake-gel formation. However, we noted that the influence of PEO size compared to the separation distance between silica particles regarding shake-gel formation has not been systematically investigated, while the PEO size should be larger than the particle-particle separation distance for polymer bridging in order to form gels. Thus, we conducted a series of experiments to examine the effects of the radius of gyration of the PEO and the distance between the silica particles by controlling the PEO molecular weight and the silica concentration. Our results elucidated that the radius of gyration of the PEO should be 2.5 times larger than the distance between the silica surfaces in order to promote the formation of a shake-gel. This result supports the hypothesis that the bridging effect is the main cause of shake-gel formation, which can help us to understand the conditions necessary for shake-gel preparation.

Colloidal photonic crystals formation studied by real-time light diffraction

Abstract Colloidal suspensions crystallize by a natural sedimentation process under certain conditions, the initial volume fraction being one of the parameters that govern this process. Here, we have developed a simple in-situ, real-time, optical characterization technique to study silica colloidal suspensions during natural sedimentation in order to shed new light on this crystallization process. This technique monitors small variations in the wavelength of the reflectance features, allowing the analysis of the formation of the first layers of the crystal with sub-nanometer precision, and their dynamics, which is crucial to ensure a high quality in the final sample. The experimental results indicate that, in certain range of volume fraction, spontaneous crystallization of a colloidal fluid occurs at the bottom of the suspension, as a phase change, then through evaporation of the water it compacts to near close-packed and, eventually, dries. Understanding self-assembly at these scales is paramount in materials science and our results will contribute to improve and characterize the quality and crystallinity of the materials used in this process.

Fissure Grouting Mechanism Accounting for the Time-Dependent Viscosity of Silica Sol.

Subject to the complex hydrogeological environment where underground engineering is located, the grouting prevention and control of microfissure water ingress are increasingly strict. Silica sol grout has been increasingly used in field tests because of its fine particles and good injectability. Therefore, it is necessary to examine the time-dependent viscosity of silica sol grout and clarify its diffusion law in a rock fissure. In this study, the time dependence of the viscosity of silica sol grout was studied, and then the grout viscosity was subdivided into a slow growth period, accelerated growth period, and rapid curing period according to the growth rate. The effects of the concentration of colloidal silica suspension, the concentration of accelerant, and the mixing volume ratio of the two on the growth of the slurry viscosity were studied. A parameter λ was introduced to comprehensively characterize the influence of the three factors on the rheological properties of the slurry. The relationship between the gel induction time and λ and the accelerating growth stage of the slurry gel was obtained by data fitting. The time-dependent equation of the silica sol solution was established. The difference in the grouting diffusion law between silica sol grout and cement–sodium silicate grout (C-S grout) is compared and analyzed by a stepwise calculation method under two grouting modes (constant-pressure grouting and constant-rate grouting). The results show that under the condition of constant-pressure grouting, the silica sol grout migrates and diffuses continuously for a long time, while the C-S grout is close to the final diffusion form at 15–20 s, and the maximum diffusion distance is much smaller than that of silica sol grout. Under the condition of constant-rate grouting, the grouting pressure driving C-S grout increases sharply with time. Compared with C-S grout, silica sol grout has the obvious advantages of a longer effective diffusion time and lower energy consumption. The research results have certain theoretical significance and reference value for the engineering design of silica sol grouting.

Hetero-network hydrogels crosslinked with silica nanoparticles for strategic control of thermal responsive property.

Two thermoresponsive copolymers with different lower critical solution temperatures (LCSTs) were crosslinked using silica nanoparticles to afford hybrid hydrogels exhibiting two distinct thermo-responsivities. The thermo-responsive copolymers were synthesised by free radical polymerisation from a monomer with a reactive side chain (3-methacryloxypropyl trimethoxysilane (S)) and water-soluble monomers with different thermo-responsivities (N-isopropyl acrylamide (N) or N-(3-methoxy propyl)acrylamide (M)). The obtained reactive copolymers, poly(N-isopropyl acrylamide-co-3-methacryloxypropyl trimethoxysilane) (pNS) and poly(N-(3-methoxy propyl acrylamide-co-3-methacryloxypropyl trimethoxysilane)) (pMS), were characterized by multiple techniques including 1H NMR and FTIR spectroscopy. The hetero-network hybrid hydrogels were easily prepared by mixing aqueous solutions of the copolymer with an aqueous colloidal silica suspension; their gelation properties could be tuned by varying the amounts of pNS, pMS, and Si. Differential scanning calorimetric analysis showed that the hetero-network hydrogel exhibited a critical two-step phase transition at temperatures around the LCST of each copolymer (33 °C for pNS, 73 °C for pMS), indicating that each polymer does not disturb the phase transitions of the other. The deswelling of the hetero-network hydrogel could be controlled with respect to temperature and time.

Size measurement of silica nanoparticles by Asymmetric Flow Field-Flow Fractionation coupled to Multi-Angle Light Scattering: A comparison exercise between two metrological institutes

In this work we present a comparison exercise between two metrological institutes for size measurement of silica nanoparticles by Asymmetrical Flow Field-Flow Fractionation (AF4) coupled to static light scattering. The work has been performed in the frame of a French inter-laboratory comparison (ILC) exercise organized by the nanoMetrology Club (CnM). The general aim of this multi-technique comparison was to improve the measurement process for each technique, after establishing a well-defined measurement procedure. The results obtained by two national metrological institutes (NMIs), the LNE (France) and the SMD (Belgium) by AF4-UV-DRI-MALS will be presented and discussed. Three different samples were characterized: the reference material ERM®-FD304, which is a suspension of colloidal silica in aqueous solution and two silica bimodal samples consisting of two populations of SiO2 nanoparticles of unknown size in aqueous solution, with different populations’ ratios. The procedure for the preparation of the sample before the analysis, and main separation parameters have been previously defined between the two institutes and will be described. The principals measured parameters were the weight-average (dge_w), number-average (dge_n) and z-average (dge_z) geometric diameter; the average hydrodynamic diameter (dh); and the diameter obtained by external calibration using polystyrene latex standards (dcal). Results between the two NMIs were comparable and coherent with the expected size values of those obtained by other techniques like Scanning Mobility Particle Sizer (SMPS) and Scanning Electron Microscopy (SEM) also involved in this ILC exercise. Where discrepancies are observed, they leave the results compatible within their uncertainties and underpin the challenges in analysing data and reporting results, making AF4 a powerful tool to compare to other measurement techniques.

Structured NiFe catalysts derived from in-situ grown layered double hydroxides on ceramic monolith for CO2 methanation

Monolithic catalysts for CO2 methanation have become an active research area for the industrial development of Power-to-Gas technology. In this study, we developed a facile and reproducible synthesis strategy for the preparation of structured NiFe catalysts on washcoated cordierite monoliths for CO2 methanation. The NiFe catalysts were derived from in-situ grown layered double hydroxides (LDHs) via urea hydrolysis. The influence of different washcoat materials, i.e., alumina and silica colloidal suspensions on the formation of LDHs layer was investigated, together with the impact of total metal concentration. NiFe LDHs were precipitated on the exterior surface of cordierite washcoated with alumina, while it was found to deposit further inside the channel wall of monolith washcoated with silica due to different intrinsic properties of the colloidal solutions. On the other hand, the thickness of in-situ grown LDHs layers and the catalyst loading could be increased by high metal concentration. The best monolithic catalyst (COR-AluCC-0.5M) was robust, having a thin and well-adhered catalytic layer on the cordierite substrate. As a result, high methane yield was obtained from CO2 methanation at high flow rate on this structured NiFe catalysts. The monolithic catalysts appeared as promising structured catalysts for the development of industrial methanation reactor.

Comparison of different silica sources in the development of plasma sprayed 45S5 bioactive glass coatings

45S5 bioactive glass coatings were deposited by plasma spraying from liquid feedstocks. In these feedstocks, the SiO2 needed to achieve the 45S5 bioactive glass composition has been provided either as tetraethyl orthosilicate (typical precursor of glasses by sol–gel), or as colloidal silica suspension or mixtures of both sources. The synthesised materials were analysed in terms of rheology and sedimentation tests, and subsequently deposited onto metallic substrates under two different spraying distances. The resulting coatings were characterised on the basis of microstructure and phase nature.All feedstocks developed preserved the composition of the 45S5 bioactive glass and showed adequate viscosity and stability to be transported and injected into the plasma plume. However, different coating microstructures were achieved when using tetraethyl orthosilicate or colloidal silica suspensions. Besides, regardless the source of silica an improvement of the coatings microstructure and phase nature have also been observed when the spraying distance was significantly reduced.

Hybrid Sol-Gel Silica Coatings Containing Graphene Nanosheets for Improving the Corrosion Protection of AA2024-T3.

In the present work, nanostructured graphene nanosheets were added to hybrid silica sols and deposited on aluminium alloy A2024-T3 to study the effect on the corrosion behaviour. Sols were prepared using tetraethyl-orthosilicate (TEOS), 3-glycidoxypropyl-trimethoxysilane (GPTMS) and a colloidal silica suspension (LUDOX) as silica precursors with adding chemically modified graphene nanosheets (GN-chem). The graphene nanosheets were modified through a straightforward and simple hydrothermal approach and then, dispersed into a silica sol (SiO2/GN-chem). ATR-FTIR was used to optimize the silica sol–gel synthesis and to confirm the cross-linking of the silica network. The corrosion behaviour of the SiO2/GN-chem coatings was also analysed by electrochemical measurement (potentiodynamic polarization) in 0.05 M NaCl solution. The results showed that the incorporation of modified graphene nanosheets into hybrid silica sol–gel coatings affected the corrosion properties of the substrates. An improvement in the corrosion resistance was observed likely due to the enhanced barrier property and hydrophobic behaviour obtained by incorporation of GN-chem and colloidal silica nanoparticles.

Experimental analysis of the impact protection properties for Kevlar® fabrics under different orientation layers and non-Newtonian fluid compositions

Use of colloidal silica suspensions impregnated in Kevlar® fabrics is new avant-garde of protection equipment for stab wounds and piercing objects. Kevlar® fabrics impregnated with non-Newtonian fluids have been used for protection against sharp blows, mainly due to their lightweight, good flexibility, and superior resistance properties. The aims of this investigation are to demonstrate that Kevlar® fabric impregnated with shear thickening fluids could be improved its performance through the use Aminopropyltrimethoxysilane, as well as by increasing the concentration of silica nanoparticles in its composition. Friction tests on yarns showed that Kevlar® yarns with shear thickening fluids (sample C3—25% Silica and 75%polyethylene glycol with 38% aminopropyltrimethoxysilane), presented higher strength values (10.5 N) when compared with other samples. Impact resistance tests showed that Kevlar® samples with highest concentration shear thickening fluids nanoparticles and oriented fabric layers (C3 OR) presented better performance regarding to penetration depth of stabs P1 (17 mm), S1 (18 mm) and as well as residual energy dissipation, when compared with the standard and other samples. Addition of shear thickening fluids cause reduction in the flexibility of the Kevlar® fabrics, producing sample with 42.74% less flexibility than the standard sample (C3). Adhesion tests for C3 samples exhibited more stable wettability and spreading rate, i.e., a greater adhesion of shear thickening fluids in Kevlar® fabrics than other samples due to its composition (higher concentration of nanoparticles and superior amount of silane agent). Finally, results showed that the shear thickening fluids composition as well as Kevlar® layers orientation should be used to improve the performance of Kevlar® fabrics under impact tests.

Anodic Oxide Growth on Heat-Treated Titanium

It has been reported that self-organized nanotubular oxide layers are formed on various metals and alloys by anodization in fluoride containing electrolytes. In particular, the nanotubular structure of TiO2 has been extensively studied due to a wide range of application of TiO2. To tune the properties of the layers, the optimization of anodization condition has been carried out. However, in such trials, the chemical aspects of anodization condition have been mainly focused, that is, only few works has reported the metallurgical aspects of the condition. In the present work, we examined the effects of heat-treatment on anodization behavior and resulting morphology of the TiO2 architecture. Specimens were cut from pure titanium sheets (purity; 99.5 %). The specimens were encapsulated into a silica quartz tube where the vacuum level was controlled less than approximately 2x10-5 torr. The specimens in the silica tube were heat-treated under several conditions. After the heat-treatments, the surface of the specimens was ground with SiC abrasive papers and then mirror-finished with diamond pates and colloidal silica suspension. The specimens were anodized at 50 V in a mixture of ethylene glycol, water and ammonium fluoride. After the anodization, the surface and cross-sectional morphology of resulting oxide layers was observed. Under an optimized heat-treatment condition examined, the specimen consisting of large grains in millimeter range was obtained. The anodization of the specimen revealed that its current behavior was similar to that obtained on as-received specimen. In addition, the obtained structure of anodic oxide layer on the heat-treated specimen was also similar to that on as-received specimen, that is, nanotubular structure was obtained. However, the thickness of the nanotubular oxide layer and the ordering of nanotubes were clearly different. Higher thickness of nanotubular oxide layer was obtained and improved ordering of nanotubes was found on the heat-treated specimen. These results indicate that the substrate property could affect not only the growth but also arrangement of nanotubes.