Juan C. Fariñas

Microwave-assisted Acid Dissolution of Sintered Advanced Ceramics for Inductively Coupled Plasma Atomic Emission Spectrometry

The microwave-assisted acid dissolution of sintered bodies of 28 structural and electronic advanced ceramic materials was systematically evaluated. These materials included zirconia-based ceramics, such as m-ZrO2 (a non-stabilized monoclinic zirconia), Ca-PSZ and Mg-PSZ (two partially stabilized zirconias), Y-FSZ (a fully stabilized zirconia) and Ce-TZP, Yb-TZP and Y-TZP/Ce (three tetragonal polycrystalline zirconias); alumina-based ceramics, such as Al2O3, mullite and spinel; ceria-based ceramics, such as CeO2–Gd2O3 (cubic ceria gadolinia); titania-based ceramics, such as TiO2; titanate-based ceramics, such as Al2TiO5, BaTiO3 and BIT (bismuth titanate); lead titanate-based ceramics, such as Ca-PT, La-PT, Nd-PT, Sm-PT and Gd-PT; lead zirconate titanate-based ceramics, such as PZT and PLZT; niobate-based ceramics, such as PMN (lead magnesium niobate); non-oxide-based ceramics, such as AlN, BN, Si3N4 and SiC; and oxide and non-oxide-based ceramics, such as β′-sialon (silicon aluminium oxynitride). Fifteen acids or mixtures of acids were tried, including HCl, HNO3, H2SO4, aqua regia, H2SO4–(NH4)2SO4 and mixtures of these acids with HF and with H2O2. A commercially available laboratory medium pressure microwave oven was used. Eleven optimized microwave methods were developed. These methods are simple (three stages maximum), fast (15–35 min digestion time) and mild (20–60% of the microwave oven power). By applying these microwave methods, it was possible to dissolve completely all the sintered advanced ceramics, except SiC and β′-sialon. These two non-oxide ceramics were the only samples that could not be dissolved by any of the acids or mixtures of acids tested. The microwave-assisted acid dissolution was compared for ICP-AES with conventional dissolution procedures, i.e., alkali fusion in a platinum crucible and in a graphite crucible and acid decomposition by conductive heating at elevated pressure (in a PTFE bomb). It was demonstrated that microwave-assisted dissolution presents many advantages over the other procedures. When compared with acid decomposition by conductive heating in a PTFE bomb, one of the most important advantages is the drastic shortening of the digestion time from hours to minutes. When compared with alkali fusions, one of the most important advantages is the use of smaller amounts of high-purity acids, which contain less impurities than the fluxes; because of this, matrix effects and contamination from the attack reagents are lower, and consequently there is an improvement in the analytical figures of merit of ICP-AES.

Effect of colloidal stability of ceramic suspensions on nebulization of slurries for inductively coupled plasma atomic emission spectrometry

The direct solid analysis of ceramic powders can be carried out by inductively coupled plasma atomic emission spectrometry (ICP-AES) using slurry sample introduction. However, a highly stable suspension is needed in order to obtain a representative aerosol for introduction into the ICP. In this work, the importance of the effect of the rheology and the stability of the ceramic suspensions on the analytical results provided by slurry nebulization ICP-AES is demonstrated. The basic concepts involved in the stabilization and homogenization of ceramic slurries are discussed. A general overview of the stabilizing mechanisms (electrostatic, steric and electrosteric) and the role of the different stabilizing additives, and the most adequate use of them, is described. Alumina (Al2O3) slurries, as a case study, are discussed. The rheological parameters, such as zeta potential, viscosity and sedimentation have been studied by changing the pH of the slurry and by introducing different dispersing additives (Dolapix PC-33, Darvan-7, Darvan-C, sodium hexametaphosphate, glycerol plus Kodak photoflow, Triton X-100 and Produkt PKV-5088). Their effect on stability is discussed, as well as the relationship between the stability of the slurry and the intensity and precision of the measurements provided by ICP-AES. It is clearly demonstrated that higher intensities and lower relative standard deviation values are obtained for a well-dispersed, stable slurry.

Chemical analysis by inductively coupled plasma atomic emission spectrometry of semiconducting ceramics of barium titanate doped with various metal oxides

The Ba and Ti macroconstituents as well as the impurities and dopants content (Al, Ca, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Nb, Ni, P, Pb, Si, Sr, W, Zn and Zr) in a dense (> 98% theoretical) barium titanate sample have been determined by inductively coupled plasma-atomic emission spectrometry after one of these decomposition routes: (a) decomposition with HCl in a PTFE-lined pressure vessel, (b) fusion with Na2CO3 in a platinum crucible, and (c) fusion with Li2B4O7 in a graphite crucible. Matrix effects were taken into account. Detection limits for minors and trace elements were determined. High sensitivity and good precision were attained.

Matrix effect of aluminium, calcium and magnesium in axially viewing inductively coupled plasma atomic emission spectrometry

The matrix effect due to Al, Ca and Mg in axial view mode ICP-AES was investigated over analyte lines with total excitation energy from 1.62 to 16.51 eV. A global qualitative explanation of the action of the matrix is proposed. The energy is directly transferred between matrix and analyte specimens (atoms or ions) during inelastic collisions, which are particularly relevant in the 1.62–8 eV excitation energy range, where the direct action with argon specimens is less probable to occur. Concrete applications of this global qualitative explanation are given, taking into account the resonance energy effect and the spin conservation rule. The characteristic matrix effect of Al and Ca for lines excited by charge transference mechanism was observed. In the presence of Mg, other possible matrix–analyte interactions may reduce the efficiency of this mechanism. The particular behavior of the matrix effect for lines in the 10.5–11.5 eV energy range can be considered as experimental evidence of the Penning ionization–excitation mechanism, which probably actuates along other matrix–analyte interactions.

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.

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.

Determination of macro-constituents in advanced ceramic materials by inductively coupled plasma atomic emission spectrometry

An analytical method was developed for the determination of macro-constituents by inductively coupled plasma atomic emission spectrometry in the following six advanced ceramic materials: calcia partially stabilized zirconia (Ca-PSZ), yttria–ceria–tetragonal zirconia polycrystalline (Y-TZP/Ce), barium titanate (BaTiO3), gadolinium-modified lead titanate (Gd-PT), lead zirconate–titanate (PZT) and lanthanum-modified lead zirconate–titanate (PLZT). The dissolution of the samples was achieved by using the following methods: decomposition with HCl in a poly(tetrafluoroethylene)(PTFE)-lined pressure vessel at 160 °C for 16 h; decomposition with HF + H2SO4 in a PTFE-lined pressure vessel at 170 °C for 16 h; decomposition with (NH4)2SO4+ H2SO4 in a glass beaker; decomposition with (NH4)2SO4+ H2SO4 in a platinum dish; fusion with Na2CO3+ Na2B4O7 in a platinum crucible; and fusion with Li2B4O7 in a graphite crucible. The precision of the determination of the macro-constituents with regard to the wavelength, integration time, dilution of the sample solution and use of an internal standard was studied. In general, the highest precision was obtained by employing the most sensible analytical line of each element, by working with elevated integration times (700–1000 ms), by diluting the sample solution 1 + 9 or 1 + 19 and by using V or Y as an internal standard. The analytical results obtained following three different methods of dissolution for each advanced ceramic material were in excellent agreement. Good precision and accuracy were attained; the relative standard deviations for the results obtained for each element for each dissolution method are <1%.

Improvement in the ion exchange chromatographic separation of rare earth elements in geological materials for their determination by inductively coupled plasma atomic emission spectrometry

Ion exchange chromatographic separation of the rare earth elements (REEs) in geological materials for their determination by inductively coupled plasma atomic emission spectrometry has been improved. The time taken for the procedure, the consumption of reagents and the external contamination of the samples have been reduced. The emission of corrosive vapours has been totally eliminated. The efficiency of the chromatographic separation by elution with two concentrations of hydrochloric acid has been confirmed at higher flow rates in a high pressure chromatographic column. A prototype has been designed to combine the use of a pressure operated chromatographic column with the simultaneous evaporation of the eluates and the recovery of the acid. The column was charged with the solution resulting from the decomposition of the sample and the matrix elements were eluted with 2 mol l–1 HCl and the REEs with 6 mol l–1 HCl. The REE fraction from the column was concentrated by distillation. The whole process (separation and concentration) was performed in 1 h 15 min. The saving in time reached a factor of 30. The recoveries of the REEs during the ion exchange procedure ranged from 96 to 105%. The accuracy and precision have been evaluated by analysing seven geological reference materials: NIM-G (Granite), NIM-L (Lujavrite), NIM-N (Norite), SY-2 (Syenite), SY-3 (Syenite), MRG-1 (Gabbro), and JB-1a (Basalt). Differences between obtained and certified values were not statistically significant for α= 0.05 (t-test). The precision varied from 1.8 to 18.2%.

Determination of impurities in lead zirconate–titanate electroceramics by inductively coupled plasma atomic emission spectrometry

An analytical method was developed for the determination of Al, Ba, Ca, Hf, Mg, Si and Sr impurities and Co, Cr, Cu, Fe, Mn, Nb, Ni, P, W and Zn dopants in lead zirconate–titanate (PZT) electroceramics by inductively coupled plasma atomic emission spectrometry. A niobium-doped dense PZT ceramic sample was used. Sample dissolution was achieved by using: decomposition with HF + H2SO4 in a poly(tetrafluoroethylene)-lined pressure vessel at 170 °C for 16 h followed by evaporation to dryness and dissolution of the residue with HCl; decomposition with (NH4)2SO4+H2SO4 in a glass beaker followed by evaporation to dryness and dissolution of the residue with HCl; and fusion with Li2B4O7 in a graphite crucible and dissolution of the melt with 1+24 v/v HNO3. For each element, an analytical line free from spectral interference was selected. The decomposition reagents present in the final solutions of the sample (HCl and Li2B4O7–HNO3), and the Ti and Zr macro-constituents, decrease the emission signals substantially. Nevertheless, the inter-element effect of Pb is negligible. The correction of these matrix effects was carried out by preparing standard solutions, for obtaining detection limits, and calibration by matrix matching. The 3σ detection limits of the impurities were determined using the three decomposition methods and correction of the matrix effects. The lowest values of the detection limits were obtained using acid decompositions, and were between ≈0.1 µg g–1 for CaO, MgO and SrO, and 461 µg g–1 for P2O5. The analytical results obtained for 17 minor and trace elements using the three decomposition methods were in excellent agreement. Good precision and accuracy were attained; the relative standard deviations for the results obtained for each element for each dissolution method ranged in general from 3 to 7%.

Determination of rare earth and concomitant elements in magnesium alloys by inductively coupled plasma optical emission spectrometry

An Inductively Coupled Plasma Optical Emission Spectrometry method for simultaneous determination of Al, Ca, Cu, Fe, In, Mn, Ni, Si, Sr, Y, Zn, Zr and rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) in magnesium alloys, including the new rare earth elements-alloyed magnesium, has been developed. Robust conditions have been established as nebulizer argon flow rate of 0.5mLmin(-1) and RF incident power of 1500W, in which matrix effects were significantly reduced around 10%. Three acid digestion procedures were performed at 110°C in closed PFA vessels heated in an oven, in closed TFM vessels heated in a microwave furnace, and in open polypropylene tubes with reflux caps heated in a graphite block. The three digestion procedures are suitable to put into solution the magnesium alloys samples. From the most sensitive lines, one analytical line with lack or low spectral interferences has been selected for each element. Mg, Rh and Sc have been studied as internal standards. Among them, Rh was selected as the best one by using Rh I 343.488nm and Rh II 249.078nm lines as a function of the analytical lines. The trueness and precision have been established by using the Certified Reference Material BCS 316, as well as by means of recovery studies. Quantification limits were between 0.1 and 9mgkg(-1) for Lu and Pr, respectively, in a 2gL(-1) magnesium matrix solution. The method developed has been applied to the commercial alloys AM60, AZ80, ZK30, AJ62, WE54 and AE44.