Teresa Dorado

Sol–gel coatings for protection and bioactivation of metals used in orthopaedic devices

The aim of this work is the production and characterisation of sol–gel coatings for protection and bioactivation of metals used as standard surgical implant materials, such as stainless steel 316 L (ASTM F138), Co based alloys (ASTM F75) and titanium alloy Ti-6Al-4V (ASTM F67). These films should both prevent degradation of the substrates by wear or corrosion, and bioactivate the material for inducing the formation of a hydroxyapatite (HA) rich layer onto the material surface, thereby permitting a natural bonding to living tissues. Formation of HA layers can be observed on performing in vitro tests by soaking the material in simulated body solutions. The work describes the development of coatings containing bioactive glass and glass-ceramic particles in hybrid methyl-triethoxysilane (MTES) and tetraethylorthosilicate (TEOS) acidic sol, applied by dip-coating to surgical alloys, AISI 316 L, ASTM F75 and ASTM 67, with the aim of accomplishing both high corrosion resistance of the metal in the body environment and adhesion of the implant to the surrounding tissue. The performance of the coated metal was evaluated in vitro by electrochemical techniques including potentiodynamic polarisation curves and electrochemical impedance spectroscopy, to follow the formation of hydroxyapatite on the surface, as well as the in vitro release of ions by plasma atomic emission spectroscopy (ICP-MS) after up to one year of immersion. In vivo behaviour was evaluated by subcutaneous tests and endomedullar implantation in Hokaido rats to study possible rejection reactions and natural bonding to living tissue.

Study of heterogeneities in steels and determination of soluble and total aluminium and titanium concentration by laser ablation inductively coupled plasma mass spectrometry

A methodology for bulk analysis of Al and Ti and for determination of soluble and total Al and Ti concentration in steel samples by laser ablation inductively coupled plasma mass spectrometry was developed. The spatial distribution (both at surface and within the sample) of the insoluble fraction of Al and Ti was also qualitatively estimated. Certified reference materials (CRMs) SS-451 to 460 (carbon steel) and 064-1 (Nb/Ti interstitial free steel), from BAS, and JK 2D (carbon steel) and JK 37 (highly alloyed steel), from SIMR, were studied. It was demonstrated that the insoluble fraction of Al and Ti is heterogeneously distributed. A series of nine glass samples (fused beads) with fixed Fe content and different Al and Ti contents was prepared by melting appropriate amounts of Fe(2)O(3), Al(2)O(3) and TiO(2) with a lithium tetraborate-sodium carbonate mixture. Quantitative determinations were performed by using calibration graphs obtained from the synthetic fused beads, with (57)Fe as internal standard; line scan laser sampling mode was used, focusing the laser beam at the sample surface. The optimized laser operating parameters were: laser pulse energy of 1.5mJ, pulse repetition rate of 5Hz, scanning speed of 5microm s(-1) and preablation time of 20s. The concentrations obtained for bulk analysis of CRM samples corresponded with the certified values within the experimental uncertainty. An acceptable concordance between certified and found values was attained for the determination of soluble and total Al and Ti in CRM 064-1 sample.

Spark ablation inductively coupled plasma mass spectrometry analysis of minor and trace elements in low and high alloy steels using single calibration curves

A unidirectional high current pulse spark with a very fast rise-time, ensuring a rapid and complete transfer of energy to the sample, was used as the sampling system for the analysis of carbon steels and highly alloyed steels with the same operating conditions. The sparking operating conditions were optimised and a restrictive path was designed to decrease the quantity of eroded material reaching the plasma, in order to prevent deposition of material in the torch injector, and to minimise sampling cone blockage and drift effects. Spark ablation sampling efficiency and effectiveness of the restrictive path were evaluated. To compensate for differences in the amount of material ablated or for a variation in drift, 57 Fe and 55 Mn were used as internal standards. The calibration procedure was applied to the analysis of the elements Al, B, Co, Cu, Mn, Nb, P, Si, and V, present in the following certified reference materials: BCS (Bureau of Analysed Samples) SS-456 to SS-460 (residual series); CRMs (European Committee for Iron and Steel Standardisation) No 285-2 (Maraging steel), No 292-1 (niobium stabilised steel), No 295-1 (highly alloyed steel), and No 296-1 (jethete steel). When plotting intensity ratios (I X /I IS ) versus concentration ratios (C X /C IS ) linear calibration curves over the entire range of tested concentrations, with correlation coefficients better than 0.999, were obtained. Determination limits below 1 µg g –1 were found and the precision was better than 2.8%. It has also been shown to determine carbon contents at concentration levels greater than 0.03% with RSD values below 3%. For the elements As, Sn, Ti, W and Zr, only present in one or two of the Standard Materials, the sensitivity was also evaluated. Furthermore, the possibility of obtaining reproducible transient signals from sparking periods of only a few seconds was demonstrated.

Depth profile analysis of copper coating on steel using laser ablation inductively coupled plasma mass spectrometry

A commercial highly focused (Gaussian) nanosecond UV (266 nm) Nd:YAG laser ablation system coupled to an inductively coupled plasma quadrupole mass spectrometer was examined as a tool for depth profile analysis of copper coating on steel. The studied samples were Standard Reference Materials 1361b and 1362b from NIST, which consist of a set of eight coupons of an AISI 1010 cold rolled sheet steel substrate with a uniform coating of copper (certified copper coating thickness: 5.9, 12.3, 25.3, 40.6, 52.0, 77, 130, and 199 μm). Depth resolution was determined from the normalized depth profiles as a function of irradiance, which was varied by changing the laser pulse energy and the focusing conditions, as well as coating thickness. At lower irradiances, depth resolution values were higher for irradiances obtained by changing the laser pulse energy, whereas at higher irradiances this parameter was higher for irradiances obtained by changing the focusing conditions. At moderate irradiance levels, the results obtained were quite similar, and, in addition, the best depth resolution was attained in this irradiance range, which was obtained by using a moderate laser energy (about 2 mJ per pulse) and by focusing the laser beam below the sample surface (approximately 2000 μm). Depth resolution increased linearly with coating thickness. For the eight studied samples the ablation rate was approximately 1 μm per pulse and the depth resolution values were between 0.8 μm for the thinnest coating and 26 μm for the thickest one.

Boron determination in steels by inductively coupled plasma atomic emission spectrometry. Comparative study of spark ablation and pneumatic nebulization sampling systems

An experimental study for the determination of boron in steels by inductively coupled plasma atomic emission spectrometry is presented. A comparison is made of spark ablation and pneumatic nebulization (after microwave digestion) sampling systems. A one-step microwave digestion procedure for total boron content using diluted aqua regia(HCl + HNO3, 3 + 1) and high pressure vessels was developed. The influence of microwave power and time on the dissolution of boron compounds is discussed. The strongest available conditions (0 Ω, 600 V, 600 Hz) were required for spark ablation sampling. The stability of spark sampling during the spark ablation-ICP process was tested by plotting iron and boron emission versus sparking time. The iron content of collected and dissolved spark-produced particles was analysed and showed that the amounts of aerosol from different boron steels samples during 90 s sparking processes were fairly similar. The analytical performance of both systems was evaluated. Using pneumatic nebulization, after microwave digestion of the sample, a detection limit for boron of 2.6 µg g–1 and overall relative standard deviation (RSD) values of 1–3.5% were found. For spark ablation the detection limit for boron was 0.65 µg g–1, the overall RSD ranging from 0.5 to 1.5%. A comparison of the data for British Chemical Standards (BCS) Certified Reference Materials (CRMs) Carbon Steel Residual Series (Group B) and Spectroscopic Standard (SS) 456/1 to 460/1, indicated that the accuracy of both methods was satisfactory.

Evaluation of a Desolvating Microconcentric Nebulizer in Inductively Coupled Plasma Mass Spectrometry to Improve the Determination of Arsenic in Steels

A desolvating microconcentric nebulizer (D-MCN) was used in inductively coupled plasma mass spectrometry (ICP-MS) in order to improve the determination of As in steels. To dissolve the samples, we applied a hydrochloric-nitric-hydrofluoric acid decomposition procedure. The isobaric interference of 40Ar35Cl+ due to the presence of Cl from the hydrochloric acid was minimized by using the desolvating device. Compared to results achieved with cross-flow nebulization, the As sensitivity was found to be 2.4 times higher, while the depression matrix effect caused by 0.1% m/v of Fe in the As signal was 3 times lower. The limit of quantification (LOQ) calculated as the concentration corresponding to 10 times the standard deviation of a procedural blank solution (0.1% m/v pure iron solution) was 0.12 μg g−1 (10 times better than that for the cross-flow nebulizer), and the background equivalent concentration (BEC) was about 25 times lower due to the absence of the most significant polyatomic interferences. The relative standard deviation calculated from six replicates at a concentration level of 10 times the detection limit was 0.8%. Three certified reference materials from the National Institute of Standard and Technology—NIST 365, 2165, and 2167—were analyzed; and recovery tests were performed on pure iron solutions spiked with different As contents. The close agreement of the values demonstrates the accuracy of the method.

Spark Ablation Inductively Coupled Plasma Mass Spectrometry Applied to the Semi-Quantitative Panoramic Analysis of Ferroalloys

The coupling of inductively coupled plasma mass spectrometry (ICP-MS) with spark ablation (SA) was applied for the semi-quantitative determination of impurities in different types of ferroalloys. The sparking operating conditions were optimized, and a restrictive path including a cyclone and a spray chamber was used to decrease the quantity of sparked material reaching the plasma, to prevent torch injector and sampling cone blockage. Samples were mixed in a 1:2 sample-to-graphite ratio and pressed into pellets for direct solid sampling by the spark. The advantage of the technique includes the benefit of easily determining some refractory elements that are very difficult to dissolve. The method was tested on three different types of ferroalloys: Fe-Ti, Fe-Nb, and Fe-V. A single standard ferroalloy sample was used as an external calibration sample to create a complete response curve for each type of ferroalloy base. Industrial ferroalloys, chemically characterized by using different analytical methods, were applied as calibration samples. The use of a calibration sample closely matching the ferroalloy material to be analyzed was found to be essential if accurate analyses were to be obtained. Certified Reference Materials of the three ferroalloys types tested—BAS (Bureau of Analyzed Samples) 579-1 (Fe-Nb alloy); BAM (Bundesanstalt für Materialprüfung) 589-1 (Fe-Ti alloy); and BAS 577-1 (Fe-V alloy)—were analyzed to evaluate the accuracy attainable in this panoramic mode. Most of the results, ranging from 0.05% to 5% m/m, were observed to be accurate to within 6–18.6% of the certified value, and the precision was better than 17.8% relative standard deviation. Determination limits based on 10 times the standard deviation of six replicates of a blank graphite pellet were on the μg g−1 level.

Study of X-ray fluorescence spectrometry and spark ablation inductively coupled plasma atomic emission spectrometry for chromium determination in ferrochromium from bulk metal samples

A study of chromium determination in ferrochromium by X-ray fluorescence and spark ablation inductively coupled plasma atomic emission spectrometry was made. Bulk test samples were prepared by re-melting the ferroalloy diluted with iron in an induction furnace. Calibration samples were obtained from an industrial ferroalloy, using different FeCr+Fe dilution ratios, in order to cover the chromium concentration range that is probably present in these materials. A study is presented of the influence of the carbon contents on Cr Kα line intensities and on the amount of spark aerosol produced, as well methods of compensating for the effect. The total variance and the average instrumental variation were calculated from the values obtained for samples with the same chromium concentration and variable carbon contents. The criterion applied to test the agreement of the two methods showed that the difference between the results provided by both techniques can be explained by random errors. Accuracies were tested by analysing a series of ferrochromium reference materials.

Determination of trace elements in unalloyed steels by flow injection inductively coupled plasma mass spectrometry

A direct multi-element flow injection inductively coupled plasma mass spectrometry (FI-ICP-MS) method is described for the determination of trace elements in unalloyed steels. The applicability of FI-ICP-MS combined with microwave sample digestion for simultaneous analysis of trace amounts of Al, Ti, V, Cr, Co, Ni, Cu, As, Zr, Nb, Mo, Ta, W, Pb and Bi in unalloyed steels samples has been investigated. The advantage offered by FI-ICP-MS in comparison with conventional solution nebulization results in detection limits in the nanogram of analyte per gram of Fe range, because of the small dilution factor. Severe depression matrix effects caused by the Fe were encountered when the signal was compared with that from HNO3 solutions. The FI and ICP operating parameters were optimized and suitable internal standards were added to correct for these matrix effects and for ion signal instability. Samples were analysed using a delivery rate of 2.8 ml min–1, a nebulizer flow rate of 1.100 ml min–1, a forward power of 1.5 kW and Be, Tl and Rh as internal standards, along with HNO3 multielement standard calibration solutions (without Fe matrix matching). Results are given for two pure Fe reference materials (CRM 097 and NIST 365). The relative standard deviation for all analytes was <3% for concentrations above 1 µg g–1.

Study of the parameters in microwave dissolution methods using a magnetic stirring device in the microwave unit. Application to dissolution of high-carbon ferrochromium

Microwave sample preparation methods have come a long way since the earliest experiments with domestic microwave ovens. This study concerned the decomposition of ferrochromium samples containing a high proportion of insoluble carbides by means of a focused microwave digestion system. The experimental results showed that samples were completely decomposed in HNO3–HF mixed acids. Optimization of the microwave dissolution programmes involved the study of acid mixture volume, the control of pressure and temperature inside a reference vessel, power control and the influence of magnetic stirring during the dissolution processes. Chromium was determined potentiometrically in each of the intermediate digests obtained during optimization of the procedure, for demonstration of the successive recoveries of this element. The selected dissolution procedure provided a recovery of 99–100% Cr under the following conditions: 5 min at 250 W/30 min at 400 W/15 min at 500 W (without stirring) and 5 min at 250 W/15 min at 400 W/5 min at 500 W (with stirring) and showed excellent reproducibility with a slightly improved RSD when magnetic stirring was used. The accuracy was determined using three high-carbon ferrochromium reference materials: ECRM 585-1 from the Bureau of Analysed Samples, BAM 530-1 from the Bundesanstalt fur Materialprufung and BCS 204-4 from British Chemical Standards. The results were compared with those obtained using a classical dissolution procedure. The microwave solutions could also be used for the simultaneous determination of major and minor elements in FeCr samples by spectroscopic techniques.