María F. Barba

Statistical analysis of the fracture behaviour of porous ceramic Raschig rings

Microstructural control during processing is necessary to assure uniform performance of random packed columns filled with ceramic Raschig rings. In this work, the statistical analysis of the fracture strength of three series of Raschig rings fabricated using three different green processes, uniaxial pressing, extrusion and slip casting, is proposed as a method of comparing the reliability of the three processes. The rings were prepared from industrial and urban wastes and contained hydroxyapatite as agent for the ionic exchange that leads to the immobilisation of heavy metals. Strength values were determined by the diametric compression of ring test and results were analysed using Weibull statistics. Results were correlated with scanning microscope observations of fracture surfaces. Simple monomodal two parameter Weibull statistics have been demonstrated to be suitable to analyse the fracture behaviour of the rings. From the stand point of strength reliability, extrusion is proposed as the most adequate green forming method.

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.

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%.

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%.

Characterization of two frit ceramic materials in low cost fertilizers

Two frit ceramic materials were prepared from minerals (phosphate and feldspar) and other low-cost materials (bones and glass cullet). These powders can be used in agriculture as fertilizers since they are able to release the nutrient elements at a low rate. The above materials were characterized by X-ray Diffraction, Photoluminescence Spectroscopy, Scanning Electron Microscopy and Inductively Coupled Plasma Atomic Emission Spectrometry. The dissolution kinetic of macro and micro nutrients, components from frit materials, was also studied.

Surface dissolution of calcium phosphate glass ceramics in dilute acid conditions

Abstract Calcium phosphate glass–ceramic materials in the P2O5–CaO–SiO2–K2O system were prepared from mineral and industrial waste raw materials. They were characterized by chemical analysis, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Tricalcium phosphate (α and β-Ca3(PO4)2), tetracalcium phosphate (Ca4P2O9) and glassy phases were identified in various proportions. The materials were treated in water, ammonium citrate, ammonium acetate and citric acid solutions. The mechanism of attack of the different phosphate phases in dilute acid conditions was established mainly following the P, Si, Ca, K concentrations versus time by inductively coupled plasma optical emission spectroscopy (ICP–OES). The results show that these glass–ceramic materials can be used as controlled released fertilisers.

Near-infrared photoluminescence in phosphate minerals and related glass-ceramics

Fertilizing glass–ceramics were prepared and characterized by photoluminescence (PL) spectroscopy. These materials, and some of the related phosphorites, unexpectedly exhibited intense PL emission in the near-infrared region. In the 1100–1250 nm range a very intense doublet at 1161 and 1149 nm and a less intense band at 1214 nm were assigned to emission from the uncommon ionic species MnV. Therefore, one of the d2 ions such as CrIV and MnV which are of growing interest in the field of solid-state lasers, was found in minerals for the first time. In order to obtain further information about these materials, structural and spectroscopic properties of the raw materials were recorded separately. As far as the coordination of MnV is concerned, the hypothesis of partial substitution of PV by MnV in the phosphate lattice appears to be quite reliable. Typical PL emission of neodymium was also observed both in glass–ceramics and in raw materials.