Papers by Author: Charles C. Sorrell

Abstract: TiO₂ films of varying mineralogical and microstructural characteristics were fabricated on sand-blasted Ti6Al4V plates by anodisation in 2 M sulphuric acid (H₂SO₄) and 2 M phosphoric acid (H₃PO₄) at 120 V and 300 mA/cm² for 10 min and 15 min, respectively. The film formed by anodisation in H₂SO₄ consisted of both anatase and rutile while the film formed by anodisation in H₃PO₄ consisted only of rutile. This inconsistency is attributed to the presence of anatase below the level of detection in the sample anodised in the H₃PO₄, which consisted of a thinner TiO₂ anodised film. SEM images demonstrated that H₂SO₄ resulted in arcing and resultant porosity while H₃PO₄ did not. Profilometry revealed that the former was rougher than the latter and that the latter was nearly the same roughness as the sand-blasted plate. These observations are consistent with the conclusion that H₃PO₄ formed a thinner anodised film and that the greater thickness from H₂SO₄ resulted in asperity formation, which enhanced arcing and densification. Although the anatase-rutile mixture and the greater roughness of the sample anodised in H₂SO₄ could be expected to have yielded superior performance, the fact that it did not is attributed to the greater bulk density and associated lower surface area of the TiO₂ matrix. Preliminary cell culture tests showed that human osteoblast-like cells (MG63) were attached effectively on smooth anodised films (on polished plates) after 4 h of incubation while cell proliferation was confluent after 2 days. The major finding of the present work is that X-radiation in clinical doses (<200 cGy) is sufficient to cause degradation of organic species via photocatalysis.

Abstract: The present work reviews current practices in quantitative XRD analysis of anhydrous and hydrated Portland cement. While Part 1 of this two-part work reviews the conventional internal standard method and the reference intensity ratio (RIR) method, Part 2 reviews the more commonly used computer-based methods, which include the Rietveld method (with or without internal standard) and the G-factor method (with external standard). Further, some critical general aspects of the experimental procedures that affect the accuracy of the analysis are discussed.

Abstract: Portland cement is one of most important construction and building materials and its properties depend strongly on the mineralogical composition. Consequently, accurate analysis of the mineralogical composition of anhydrous Portland cement is crucial for both product quality control and optimisation of performance following initial hydration. In the latter sense, analysis of the mineralogical composition of hydrated Portland cement paste is critical to understand (1) the mechanism and kinetics of hydration of unmodified pastes and those modified with additives and (2) the resultant properties of cement pastes, mortars, and concretes. Such analyses typically are undertaken by quantitative X-ray diffraction (XRD).The present work reviews current practices in quantitative XRD analysis of anhydrous and hydrated Portland cement. To this end, Part 1 of this two-part work briefly mentions the point-counting method and the Bogue calculation method. The more commonly applied internal standard method and reference intensity ratio (RIR) method are discussed in more detail.

Abstract: Anodic oxidation is an electrochemical method for the production of ceramic films on a metallic substrate. It had been widely used to deposit the ceramic coatings on the metals surface. In this study, the surface morphology and crystallinity of titanium foil was modified by anodising in mixture of β-glycerophosphate disodium salt pentahydrate (β-GP) and calcium acetate monohydrate (CA). The experiments were carried out at high voltage (350 V), different anodising time (1, 3, 5 and 10 min) and current density (10 and 20 mA.cm^-2) at room temperature. Anodised titanium was characterised by using glancing angle X-ray diffraction (GAXRD), field emission scanning electron microscope (FESEM) and focused ion beam (FIB) milling. The result of the experiment show that colour, porosity, crystallinity and thickness of the titanium films depended strongly on the current density. More porous surface and large amount of anatase was produced at higher current density. FIB results indicated that the thickness of oxide layer increased as increasing of current density.

Abstract: Gel oxidation is an effective thermochemical method for the preparation of bioactive titanium surfaces. This study aims to investigate the effect of low concentration of NaOH on gel oxidation of titanium when subjected to various temperatures. Titanium foils were soaked in NaOH aqueous solutions with the concentration of 0.5 M or 1.0 M, followed by oxidation in the range of 400°C to 800°C. The crystallinity of the film was determined using glancing angle X-ray diffraction (GAXRD). The microstructures were examined using field emission scanning electron microscope (FESEM). Focused ion beam milling (FIB) was used for cross-sectional imaging. At low NaOH concentration, the amount of sodium titanate hydrogel, if present, was too low to detect after gelation. Subsequent oxidation at 400°C was insufficient to form sufficient anatase and/or rutile to be detectable by GAXRD. Oxidation at 600°C and 800°C resulted in the detection of rutile. The concentration of the NaOH solution was important that it affected the dissolution or retention of the anatase passive oxidation layer whereby low concentrations of the NaOH solution (0.5 M and 1.0 M) resulted in a low degree of dissolution.

Abstract: Anodic oxidation is used to evaluate the effects of pure titanium in a sulphuric acid electrolyte in order to evaluate the relationship between the TiO₂ anatase crystalline phase formation and anodisation parameters. Multiple characterisation techniques were used and found that the thickness showed significant increase in TiO₂ at 70V, FESEM observed significant porosity at the arcing voltage commencement (100V). XRD analysis observed anatase peak threshold at 70V, However Raman Microscopy showed anatase significance formation between 20V-30V. We conclude that anatase presents at low voltage 20-30V while rutile peaks increase initially (100V and 150V) and the amount and /or crystallinity of anatase are/is influenced by the applied voltage.

Abstract: Anodic oxidation is a surface modification method which combines electric field driven metal and oxygen ion diffusion for formation of oxide layer on the anode surface. Anodised titanium has been widely use in biomedical applications especially in dental implant. This study aimed to investigate the effect of electrolyte concentration on titanium. Specifically, the titanium foil was anodised in mixture of β-glycerophosphate disodium salt pentahydrate (β-GP) and calcium acetate monohydrate (CA) with different concentration (0.02 M + 0.2 M and 0.04 M + 0.4 M), anodising time (10 min), applied voltage (150, 200, 250, 300 and 350 V) and current density (10 mA.cm^-2) at room temperature. Surface oxide properties of anodised titanium were characterised by using glancing angle X-ray diffraction (GAXRD), field emission scanning electron microscope (FESEM), focused ion beam (FIB) milling and digital camera. With increasing electrolyte concentration, the oxide layer became more porous. The GAXRD results also showed that rutile formed at high applied voltage (≥300 V) when the higher concentration of electrolyte was used.

Abstract: Anodic oxidation is an electrochemical method for the production of a ceramic film on a metallic substrate. It involves the use of an electrical bias at relatively low currents while the substrate is immersed in a weak organic acid bath. The films produced are usually dense and stable, with variable microstructural features. In the present work, ceramic films of the anatase and rutile polymorphs of TiO₂ were formed on high-purity Ti foil (50 μm) using mixtures of β-glycerophosphate disodium salt pentahydrate (β-GP) and calcium acetate monohydrate (CA) solutions. The experiments were carried out at varying voltages (150-350 V), times (1-10 min), and current density (10 mA.cm^-2) at room temperature. The ceramic films were characterised using digital photography, glancing angle X-ray diffraction (GAXRD), and field emission scanning electron microscopy (FESEM). The thicknesses of the films on Ti were measured using focused ion beam (FIB) milling. The colour, microstructures, and thicknesses of the films were seen to be strongly dependent on the applied voltage. At bias <200 V, single-phase anatase was observed to form on Ti, while at higher bias (250 V), rutile formed due to the arcing process.

Abstract: Sodium titanate gels have been formed on the surface of titanium metal using sodium hydroxide solution and then oxidised at 400° - 800°C. The reaction sequence for these processes with increasing temperature is Ti sodium titanate gel crystalline sodium titanate gel porous (top) and dense (bottom) anatase porous (top) and dense (bottom) rutile. These samples were subsequently soaked in simulated body fluid in order to study the precipitation of hydroxyapatite.

Abstract: Anodic oxidation is an electrochemical method for the production of an oxide film on a metallic substrate. It involves the application of an electrical bias at relatively low currents while the substrate is immersed in an acid bath. The films can be very dense and stable, with a variety of microstructural characteristics. In the present work, films of the anatase polymorph of TiO₂ were formed on high-purity Ti foil (50 μm thickness) using phosphoric acid (0.3 M H₃PO₄). The conditions of oxidation involved the application of potentials (5 to 350 V) and current densities (5 to 60 mA.cm^-2) for 10 min at room temperature. The films were characterised using a digital photography, laser Raman microspectroscopy, and field emission scanning electron microscopy. The thicknesses of the oxide films on Ti were measured using a thin film analyser based on optical spectroscopy principles. The colours, thicknesses, and microstructures of the films depended strongly on the applied voltage and current density. At bias more than 15 V, single-phase anatase was observed to form on Ti at low (5 mA.cm^-2) and higher (up to 60 mA.cm^-2) current density.