P. Callejas

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.

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.

Microstructure Characterization of Basalt Glass-Ceramics

Glasses and basalt glass-ceramics from the Spanish basalt rocks of the Canary Islands were obtained. Temperature-time-transformation (TTT) curves of the original glasses were taken, and scanning electron microscopy with energy-dispersive x-ray microanalysis was performed in order to characterize the microstructure. Potential applications of these basalt glass-ceramics are as wear-resistant materials and as a candidate matrix for nuclear-waste immobilization.

Microanalysis of the surface in glass-ceramics obtained from muscovite−amblygonite

A new family of glass-ceramics obtained from muscovite-amblygonite mixtures showing a schiller effect or reflecting surface has been obtained. This effect has not been observed in the bulk material. The raw materials contain about 1% iron as Fe21. In order to elucidate the correlation between surface structure and/or composition and the schiller surface effect, several surface analysis methods, (ESCA, RBS, EPR and reflection Mössbauer spectroscopy) have been used. It seems that a solid solution of Fe31 in the spodumene crystal lattice precipitated from the surface is related to the reflecting effect, which can be controlled by solution of iron oxides in theβ-spodumene solid solution.

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.

Microstructure and Microanalysis of Bioglasses and Glass-Ceramics from the MgO-CaO-P2O5-SiO2 System with ZrO2

Glasses and glass-ceramics formulated from the MgO-CaO-P2O5-SiO2 system depicting high crystallization trend of wollasto-nite and apatite phases have been obtained. In some cases CaF2 and Zr O2 has been added in order to nucleate the fluorapatite crystalline phase and to improve the mechanical properties. The microstructure of original glasses and glass-ceramics resul ting from controlled thermal treatments has been observed by — TEM and SEM. Likewise, EDX microanalysis have been carried out. The Vickers microhardness and the stress intensity factor (Kic) have been determined.

Influence of the Processing Route on Reliability of Raschig Rings for Wastewater Treatments

Ceramic Raschig rings are used as fillers in the columns for wastewater treatment to immobilise heavy metals in polluted waters. Their effectiveness is determined by properties such as porosity and specific surface area. Therefore, microstructural control during processing is necessary to assure uniform performance of random packed columns filled with Raschig rings. In this work, Weibull statistics of the stress to fracture of rings placed under diametrical compression loading is proposed as a method to compare reliability of the rings. Three green processing methods, uniaxial pressing, extrusion and slip casting, have been used to obtain rings using industrial and urban wastes as raw materials (diatoms from beer industry, sludges from paper industry and animal bones). Significant differences between the Weibull parameters for the three series of the same material were found indicating that the most reliable processing route was extrusion. The same analysis was done for uniaxially pressed rings containing hydroxyapatite as single-phase. In spite of differences between the actual strength values, Weibull parameters were coincident for both uniaxially pressed series.

New black glasses in the CdO-Al2O3-SiO2 system useful for optical devices

Abstract A new family of black glasses with CdOAl 2 O 3 SiO 2 glassy matrices and Cu, CuMn, and CuSe additions have been The spectral transmittance was related to the microstructure observed by TEM and SEM electron microscopies. These microstructural observations and XRD analyses showed that these black glasses contained precipitated CuO and cadmium silicate crystals in a phase-separated glassy matrix. These new black glasses could be useful for various optical devices.