Håkan Mattsson

Surface spectroscopic characterization of titanium implant materials

Abstract Titanium is one of the most commonly used biomaterials for dental and orthopedic applications. Its excellent tissue compatibility is mainly due to the properties of the stable oxide layer which is present on the surface. This paper reports a detailed spectroscopic characterization of the surface composition of non-alloyed Ti implant materials, prepared according to procedures commonly used in clinical practice (machining, ultrasonic cleaning and sterilization). The main methods of characterization are XPS and AES, and complementary information is obtained by SIMS, EDX and NMA (nuclear microanalysis). The surface of the implants is found to consist of a thin surface oxide which is covered by a carbon-dominated contamination layer. By comparison with reference spectra from single crystal TiO2 (rutile) the composition of the surface oxide is shown to be mainly TiO2, with minor amounts of suboxides and TiNx. The thickness of the surface oxides is 2–6 nm, depending on the method of sterilization. The surface contamination layer is found to vary considerably from sample to sample and consists of mainly hydrocarbons with trace amounts of Ca, N, S, P, Cl. Some differences in surface composition between directly prepared surfaces, and some possible contamination sources, are identified and discussed shortly.

Multi-technique surface charaterization of oxide films on electropolished and anodically oxidized titanium

The widespread use of pure Ti in biomedical applications and in basic biomaterials research has led to an increasing interest in the properties of its surface oxides, and how they can be modified. In this work, which was part of a broad surface characterization of oxide films on pure Ti and Ti-6A1-4V, the chemical composition of anodic oxide films formed on pure Ti during electropolishing and anodic oxidation was investigated using multi-technique surface analysis (XPS, AES/SAM, SIMS, RBS and NRA). XPS and AES Ti line shapes show that the oxide formed is mainly TiO2, but the chemical composition can be modified by anion adsorption and/or incorporation when H2SO4 or H3PO4 electrolytes are used. Modification of the anodic oxide film composition also occurs during sterilization; increased Ca and H levels are observed by SIMS and NRA after autoclaving. AES and XPS depth profiles, together with RBS measurements, show that the oxide thickness depends linearly on the anodizing potential in the range 5–80 V, with a growth constant αm≈ 1.1 × 1016 oxygen atoms/V⋯ cm2. The present results are compared with parallel studies of the composition and microstructure of thermal and anodic oxides on pure Ti and Ti-6A1-4V. The demonstrated systematic variation of oxide properties opens up the possibility to study the influence of specific surface properties on the biological response to Ti materials.

Characterization of Combustion Chamber Deposits from a Gasoline Direct Injection SI Engine

Combustion chamber deposits (CCDs) from a gasoline direct injection stratified charge SI engine were analysed. The engine was run with two fuels: a typical European base fuel, containing 9.8% MTBE, and a low volatility worst case fuel. The worst case fuel is a standardized European fuel, CEC RF 86-A-96, prone to form deposits. It contains high amounts of aromatics and olefins but no MTBE. The deposits were analyzed in several ways; thermal desorption followed by gravimetric analysis, fast neutron activation analysis and solid-state 1 3 C nuclear magnetic resonance spectroscopy. Up to 50% of the deposits, formed inside the GDI engine, consist of volatiles. The composition of the deposits is strongly related to the composition of the engine oil. The fraction of volatiles in the deposits decreased in the order: cylinder head, piston squish surface and piston bowl. The deposits from the piston squish surface contained the highest fraction of oxygen, about 30 %. The non-volatile part of the deposits was highly oxidized. The organic oxygen in the non-volatile part was found in different types of carbon compounds: oxygenated aliphatics, carboxyls and carbonyls. The fuels used in this study apparently did not significantly affect the content of oxygen and the volatile organic found in the deposits.

A method for in-situ quantification of oxygen in oil using fast neutron activation analysis

Abstract The feasibility of an experimental methodology for in-situ quantification of oxygen in bulk oil using fast neutron activation analysis (FNAA) has been studied. The method was applied for determination of oxygen in 100 ml (∼ 90 g) rapeseed oil. The amount of oxygen in the rapeseed oil using the in-situ FNAA was estimated to 10.6 ± 2.6 weight %. Using cyclic fast neutron activation analysis (cFNAA), the amount of oxygen in the oil was determined in average 9.9 ± 0.4 weight %. Based on Monte Carlo calculations on water, the optimal radius and height of a cylindrical container where the activity is distributed through stirring of the water would be about 10 cm and 44 cm, respectively. These dimensions give a volume of about 14 liters, which is suitable for any type of oil. The accuracy in the in-situ FNAA can be increased by a more precise determination of oxygen in rapeseed oil in the beginning of a dynamic process using cFNAA or alternatively by a better background subtraction.

Collimation and background in the pulsed neutron activation method for determination of water flow in pipes

In a Pulsed Neutron Activation (PNA) flowmeter, the water in a pipe is bombarded with neutron pulses, which introduce activity into the pipe. The activity is mixed with the flow, and gamma radiation emitted from the activity is measured with a detector downstream. The average velocity of the water is then calculated using the time-resolved detector signal. In this paper, the effect of collimation of the neutron radiation has been investigated. Such a collimation would increase the accuracy of the measurement, but the use of a collimator requires the distance between the pipe and the neutron source to be increased, with a corresponding loss in count rate. The results show that this loss makes neutron collimators in PNA of little use. In addition, a method to identify and subtract the background originating from stationary sources in a PNA measurement was developed.

Remarks on pulsed neutron activation

In the article “Simulation of Pulsed Neutron Activation for Determination of Water Flow in Pipes” [1] an experimental study of PNA (Pulsed Neutron Activation) was presented. In the work reported in the article, colour was injected into a pipe to obtain an estimate of the radial transport of the induced activity in PNA experiments. The purpose of the article was to qualitatively determine the effect of the inhomogeneous initial activity distribution in PNA techniques. The result showed that the effect of inhomogeneous initial activity distributions could in some cases be expected to influence the PNA measurement with a few percent. Thus, this effect has to be taken into account for purposes of PNA measurements with high accuracy. In a Letter to the Editor [2] the article has been criticized and an alternative model for interpreting the data is presented. The criticism is mainly focused on the accuracy of the method used. However, we fail to see the justification on many points of the criticism as well as the validity of the alternative model.