Determination of the photocatalytic function of coatings on ceramic substrates

Photocatalysis is a process in which the impingement of UV radiation on a semiconductor causes the organic matter in contact with the semiconductor to degrade. The process is found in various applications that require the use of the photocatalyst (semiconductor) in suspension or supported on a substrate.
The application of photocatalytic coatings onto ceramic substrates yields multifunctional surfaces with self-cleaning properties related to their capacity to degrade, and even mineralise, organic compounds present in water or air.
The photocatalytic coatings supported on ceramic substrates are obtained by applying suspensions of nanometre-sized particles (10-9 m) onto the substrate. Owing to the small particle size, this type of material has different properties from those of macroscopic materials.
The recent appearance of photocatalytically active materials requires having a method for determining and quantifying photocatalytic activity. No standard is currently available for determining the photocatalytic function of materials. The present study was undertaken, therefore, to fine-tune a test method that would allow determination of the photocatalytic function in materials supported on a ceramic substrate

In situ X-ray difraction study of hidration of CaAl2O4 - amorphous silica mixtures

The influence of the amorphous silica on the mechanism of hydration of the calcium monoaluminate (CaAl2O4) has been studied at ambient temperature with a water/solids ratio of 0.5. The evolution of the hydrated phases, formed in the first instants of the reaction, has been studied by laboratory X ray diffraction with a time resolution of 36 min. The integration of selected diffraction peaks of the phases: Ca2Al2O5·8H2O (Ca2Al2(OH)10·3H2O), CaAl2O4 and Ca4Al2(OH)12(CO3)·5H2O, has allowed to establish the kinetics of the reaction. This way, it has been shown that the amorphous silica causes a drastic decrease in the period of induction of the hydration and accelerates the formation of the metastable crystalline hydrates Ca2Al2(OH)10·3H2O and Ca4Al2(OH)12(CO3)·5H2O. These results have been confirmed by Thermogravimetry, Differential Thermal Analysis and Scanning Electric Microscopy. The hydration mechanism proposed confirms previous data of Nuclear Magnetic Resonance of Solids (RMN) of 29Si of the authors of this paper.

Experimental and thermodynamic analysis of the Al/C ratio on the microchemistry and microstructure of MgO-C-Al materials.

The microchemistry and microstructure of MgO-C-Al materials with high magnesia content and different Al/C ratio have been established between 1100º and 1800ºC, under strong reducing condition. The experimental results have been discussed as a function of thermodynamic stability of different phases of the MgO-C-Al system, theoretically determined at different temperatures and partial pressures of Mg(g), Al(g) and CO(g).
Both studies have allowed established a complete description of the reaction process in all compositions studied.

Influence of synthesis parameters on the hydroxyapatite production by combustion method.

In this work the synthesis of hydroxyapatite by combustion method has been studied. The influence of temperature, time of reaction, Ca/P molar ration and pH parameters have been considered in order to obtain hydroxyapatite powder with nanometric size through a rapid and simple method like the combustion synthesis.
Calcium nitrate and ammonium phosphate have been used as raw materials and urea has been added as fuel. The reaction has been carried out in an oven. Powder characterization was performed by XRD, DTA-TG, FTIR, FESEM and N2 adsorption.

Performance of cubic-(La,Sr)TiO3+δ as SOFC anodes.

The performance and potential application of the cubic members of the La4Srn-4TinO3n+2 series of compounds, i.e. n≥12, prepared by solid state reaction are discussed. Although these phases can be indexed as cubic perovskites by X-ray diffraction (XRD), there exists some oxygen beyond the ABO3 stoichiometry accommodated in linear defects reminiscent to the oxygen rich layers in La2Ti2O7. In the present work, we report preliminary fuel cell tests of the n=12,14 and 16 of the La4Srn-4TinO3n+2 series, which reveal moderate responses under hydrogen, but also some promising results implying activation favouring methane oxidation.

Phase stability study in SrZrO3 vs sintering temperature

Abstract. Recent studies of the phase transitions in SrZrO3 using X-ray and Neutron Diffraction, together with Perturbed Angular Correlation spectroscopies reveal that the phase diagram of this compound is not simple. The temperatures of the transitions appear to be highly dependent of the thermal history. In this work we present for the first time a study of the phase stability as a function of the annealing using the Impedance Spectroscopy technique. This work will focus on the Pnma ® Imma (second order) and the Imma ® I4/mcm (first order) phase transitions, previously reported at 750º C and 840º C respectively.

Electrical answer of the SnO2-TiO2 thick films shaping with ceramics powders obtained by Pechini method.

Tin oxide is the compound more used in the gas sensor production, mainly to reduce gases like CO and H2. Their electrical properties are strongly dependent of its surface. For this is of great importance to synthesize nanoscale tin oxide particles to use they later in the films conformation. The synthesis of SnO2-TiO2 nanoparticles by polymeric precursor method is reported in this work. The particles were characterized by DTA/TG, FT-IR, XRD and SEM. Also, the electrical response of thick films measured under oxygen and carbon monoxide atmospheres is was analyzed.

Chemical synthesis of bone-like carbonate hydroxyapatite from hen eggshells and its characterization

Carbonate hydroxyapatite (CHAp) was synthesized from domestic hen eggshells by using three alternative wet chemical methods at room temperature. In the first method, the powdered eggshells were reacted directly with H3PO4. In the other two methods, calcium acetate was obtained in a first step by dissolving the eggshells in acetic acid. Then, calcium acetate was reacted with Na3PO4·12H2O and (NH4)2HPO4 in the second and third methods, respectively. The synthesized CHAp was characterized by X-Ray Diffraction (XRD), Fourier Transformed Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Fine and poorly crystallized CHAp was obtained under all experimental conditions employed. Among all synthesized materials, the one produced by the first method showed the closest resemblance to bovine bone, which was related to similar carbonate contents in both materials. In general, acicular CHAp crystals with a size ranging from 10 to 100 nm were obtained, which had an aspect ratio of ∼1/4. The morphology of the synthesized CHAp crystals was consistent with their estimated carbonate content.

Electrochemical impedance spectroscopy analysis of thermal barrier coatings after isothermal oxidation

This investigation correlates the microstructure of a thermal barrier coating, analysed through scanning electron microscopy and X-ray microanalysis, with the electrochemical impedance spectroscopy data which show the variation in electrical properties after isothermal oxidation. A thermal barrier coating comprising a ceramic top layer, ZrO2 8Y2O3 (weight %), and an overlay coating, Ni 22Cr 10Al 1Y (weight %), air plasma sprayed over a nickel base alloy In 600 substrate was studied. These materials were heat treated in air at 1050 ºC for 72, 144 y 336 h. A thermally grown oxide layer, mainly comprising Cr y Al oxides, was formed between the ceramic and the overlay coating. This layer modified the electrical response of the thermal barrier coating in the electrochemical impedance spectroscopy tests.

Analysis of the molten zone in the growth of the Al2O3-ZrO2(Y2O3) eutectic by the laser floating zone technique.

In this work a study of the floating zone during the growth of bars of Al2O3-ZrO2(Y2O3) by the laser floating zone technique is presented. The axial thermal gradient in the solidification interface has been calculated and compared with the experimental one of 6.5*105 K/m. For this calculation the coefficients of heat transference during the solidification process have been determined. The floating zone profile has been also studied and the maximum stable length for the zone determined, verifying the stability criterion established by some authors. The study is completed with an estimation of the laser power necessary to carry out the growth. This value is compared with the measured one during the growth of 2 mm diameter bars.

Ir spectroscopic study of the hydrolysis reaction of TEB: evaluation of borosilicate gels

Triethylborate (TEB) is a boron alkoxide largely used in the synthesis of sol-gel prepared materials. This method requires the hydrolysis and condensation of the synthesis reagents, usually alkoxides, for obtaining a gel which can be transformed into different materials, such as glasses or ceramics, as a function of the thermal treatment applied. Infrared spectroscopy is one of the routine techniques used in the study of the sol-gel reaction due to the easy handling of the sample and the fast speed of the analysis.
In this work, the study of the hydrolysis and condensation reactions of TEB is carried out by studying their vibrational bands located at 893 cm-1, which shows a continuous decrease as the hydrolysis is performed, and 1194 cm-1, which increases with the proceed of the condensation. A proposed calibration line for the quantitative analysis of the hydrolysis extension of TEB in several TEOS-TEB gels evidence that between 20 and 33% of the TEB molecules have not been hydrolysed during the sol-gel reaction for forming such gels.

Ceramic materials nanoindentation: load and indenter geometry effects.

A lot of research has been published about the determination of mechanical properties like hardness and elastic modulus using depth sensing indentation techniques. The Oliver and Pharr method allows calculating these properties through the experimental force-displacement curve. However, several phenomena could affect the analysis of experimental data. Discrepancies from the nominal results could be induced by size effect and indenter geometry. In this work, indentation size and indenter geometry effects on hardness and elastic modulus have been studied using several maximum loads and two different indenter geometries: Berkovich and spherical. Mechanical properties changes have been observed with indentation load in both geometries. These tendencies depend on the indenter geometry.

Use of coupled TG-DSC-QMS-FTIR thermal analysis techniques in characterizating clays and ceramic compositions used in ceramic tile manufacture. Quantification of carbon compounds

In this study, a work methodology has been developed for t evolved gas analysis (EGA) in clay raw materials and ceramic compositions used in ceramic tile manufacture using coupled thermal analysis techniques (TG-DSC-QMS-FTIR). The different types of gases (CO2, CO, NOx, F, SOx) evolving from these raw materials during a thermal cycle up to a peak temperature of 1200ºC were characterised. The possibility of using this calorimeter for the quantification of the CO2 gases evolving from the organic and inorganic carbon (carbonates) present in the studied clay materials was also evaluated. The measurements were validated with different reference materials, and the results were compared with those obtained with other analysis techniques, such as thermogravimetry (TG), calcimetry, and coulometry.
The thermal analysis technique (TG-DSC-QMS-FTIR) is a suitable technique for analysing evolved gases with low uncertainties for carbon compounds quantification. Furthermore, the methodology allows the mineralogical origin identification of the elements present in the evolved gases.

Hybrid styrene-methacrylate-silica sol-gel membranes combining sulfonation and tungstophosphoric acid doping for PEMFC

Contrary to internal combustion engines, proton-exchange membrane fuel cells (PEMFC) used in transportation operate with zero emissions of environmental pollutants. The increase of the operation temperature in PEMFC above 100°C is a great concern for the application of this type of cells in electric vehicles. Hybrid organic-inorganic membranes with nano-sized interfaces can combine the main properties of their components to meet this objective. Styrene-methacrylate-silica membranes doped with phosphotungstic acid (PWA) were prepared through acid catalyzed sol-gel process and free-radical copolymerization. Additionally, sulfonation processes of aromatic rings to produce attached SO3H groups were applied to increase the proton conductivity. The effect of sulfonation degree and PWA doping on the membrane properties such as chemical and thermal stability, water uptake, ion exchange capacity, and proton conductivity were investigated. The measurement of conductivity shows a general increase with rising temperatures and with the increasing of SO3H groups density, reaching a maximum value of 3.2 10-3 S/cm at 130ºC and 100%HR.

Influence of post-fire cooling on porcelain tile mechanical properties

This study was undertaken to determine the influence of post-fire cooling on generation of residual stress and mechanical properties in porcelain tile. The test pieces were prepared and subjected to different types of cooling. Macroscopic stresses were determined by the strain relaxation method with incremental cutting. Microscopic stresses on the quartz particles were analysed by X-ray diffraction (XRD). During fast cooling, a macroscopic residual stress profile, characteristic of tempering processes in glasses, was observed to develop with the ensuing increase in mechanical strength. XRD analysis showed that the quartz particles were subjected to tension, additionally strengthening the material. However, the quartz also gave rise to microstructural deterioration owing to crack generation and growth. Such microstructural deterioration limits the increase in mechanical strength, in particular for the high cooling rates used after the allotropic transformation of quartz.

Materials and vapour-phase techniques for the synthesis of ceramic coatings

A survey on recent advances in the synthesis of hard ceramic coatings is given, including materials processes and techniques.  Emphasis is made on the parameters which control the coating properties (crystalline structure, morphology, etc), namely arrival energy of the atoms to the growing surface and substrate temperature. Some relevant coating materials are discussed in relation to their applications either as hard protective coatings or with decorative purposes, namely: the family of metal nitrides, carbides, and oxides, in different layer structures (monolithic, multilayers and nanocomposites) and ternary compounds of the BCN system.  

Effect of washed with etilendiamine about the properties of the tin oxide nanoparticles

Tin oxide, is a compound used in many technological applications among them as gas sensor and in the production of varistors, electronic devices, electrocatalitic electrodes and fotovoltaic cells, among others. In this work the controlled precipitation method was used to synthesize tin oxide of nanometric size using tin sulfate precursor. The control of different stages of the synthesis process was carried out through the variation of the system pH registrations, potentiometric titration,; This curve contain information on the different processes that take place in the system and it can be used to guarantee the process reproducibility. Additionally we propose a mechanism to explain the nucleation of solid phase in the solution. The hydrolysis and policondensation reactions are very important for this mechanism. Precipitate washing with an ethylendiamine solution permitted eliminated of SO42- and it permitted to obtain the tin oxide as the principal crystalline phase at room temperature. The characteristics of the obtained ceramic powder were determined using infrared espectroscopy (FTIR), X-ray diffraction (XRD), and transmission electron microscopy (TEM).

Surface Modification by High Power Diode Laser (HPDL) of CaZrO3 Thermal Sprayed Barrier Coatings

The aim of this investigation is to modify the surface of thermal sprayed CaZrO3 coatings to reduce their porosity and improve their properties. A high power diode laser was used to produce the melting of the superficial ceramic coating. Different parameters have been evaluated in the process, in particular laser beam power/energy and the laser scanning speed. Microstructural changes induced by the laser treatment were evaluated by light microscopy and environmental scanning electron microscopy. The coatings were also characterized by X ray diffraction in order to detect the possible phase transformations.

Femtosecond laser micromachining of LTCC ceramics. Fabrication of microhotplates for a carbon monoxide sensor

In present work, the processability of LTCC (Low Temperature Co-fired Ceramics) by means of femtosecond laser ablation is shown. This kind of material, with a clear technological interest in the development of microsensors, possesses a high mechanical fragility in the sintered state and, consequently, contact methods for micromaching (micromilling, microgrinding, etc.) lead to fracture or the appearance of microcracks. The paper has been structured in two different parts. Firstly, a detailed study of the process has been performed, obtaining the fundamental parameters, as ablation threshold and incubation factor and a parametrization of width and height of microchannels as a function of fluence and feedrate. Afterwards, these results have allowed the fabrication of simple structures as boxes, passing-through holes and 21/2D structures. Finally, the technological interest of the material and the process is shown. This way, microheaters in LTCC have been fabricated as initial stage of a carbon monoxide chemoresistive sensor. The system allows the heating of a 1mm x 1mm area up to 490ºC with almost no heat dissipation to the surrounding area.

Airborne Sound Insulation of Glazing Systems.

In this paper, the Ookura & Saito model is applied to determine the Airborne Sound Insulation of glazing systems. In particular, the calculations that appear are for monolithic glasses of different thicknesses and laminated glasses from different types. There are different prediction models of the airborne acoustic behaviour of multilayer panels (and the laminated glasses can be considered like such). In all of them, the input data are the elastic constants and the loss factor. The monolithic glasses and the intermediate layer have been characterized according to different Standards. The results are compared with experimental measurements and data of the study of Marsh (1), obtaining a range of acceptable adjustment. 

Infiltration of reinforcement materials in the oxidation behaviour and the mechanical properties to carbon fiber reinforced carbon matrix (C/C) composites

In the present study, attention was focused on the adaptation of different methods in order to incorporate reinforcement materials just like SiC and B4C to carbon fiber reinforced carbon matrix (C/C) composites. Hot petroleum pitch impregnation and also at room temperature, and toluene were used as drivers to incorporate reinforcement materials and oxidation inhibitors, just like B2O3, H3BO3 and B4C to (C/C) matrix. Hermetic crucibles and graphite have been used in order to obtained carbonization process. Oxidizing atmospheres were used in order to improve the oxidation matrix after the carbonization process. Different methods of infiltration have been evaluated in order to test which of these produce bigger increment on mechanical properties and oxidation protection of the final materials. The different tested materials were studied by means of techniques like scanning electron microscopy (SEM) and micro-analysis by energy dispersive spectroscopy (EDS). Results of flexural test were finally compared.

Mejora de sensores vítreos sol-gel para la conservación preventiva de materiales históricos frente a la acidez.

Sensors based on sol-gel glassy coatings doped with 2[4-(dimethyl-amino) phenylazo] benzoic acid are able to change their optical absorption when they are submitted to different concentration of H3O+ and OH-. The sensors behaviour in field tests was studied in Cracow (Poland), varying the normal procedure of operation to improve their response. Both the sensors optical parameters and the environmental conditions (temperature, humidity, pressure, SO2 and NOx concentrations) were measured. The sensors response was analysed in terms of their visible absorbance changes, which are due to local neutralisation reactions in the sensors surface by the join effect of acid pollutants and humidity. Correlations between the main acid pollutant (SO2) concentration and the sensors response are established to provide a relation between the optical absorption and the environmental pH. The sensors are able to detect and monitorise environmental acidity, as well as to alert on the pollutant concentration that may damage most of the historical materials

Lanthanum chromite materials as potential symmetrical electrodes for Solid Oxide Fuel Cells

A commonly used interconnector material has been tested as electrode for a new concept of Solid Oxide Fuel Cell, where the same material could be used, simultaneously, as interconnector, anode and cathode. We have found that a typical substituted chromite, such as La0.7Ca0.3CrO3-δ (LCC) can be considered a good candidate for such configuration, due to its high electronic conductivity in both reducing and oxidising conditions, and moderate catalytic properties for oxygen reduction and hydrogen oxidation. The symmetrical design renders performances of 100 mWcm-2 at 950ºC, using O2 and H2 as oxidant and fuel respectively. Performances exceeding 300 mWcm-2 can be predicted for a 100µm-thick YSZ electrolyte.

Mechanical behaviour of structural ceramics

The use of ceramic materials in structural applications is limited by the lack of reliability associated with brittle fracture behaviour. In order to extend the structural use of ceramics, the design of microstructures which exhibit flaw tolerance due to toughening mechanisms which produce an increase in crack growth resistance during crack propagation has been proposed.
This work is a review of the mechanical behaviour of structural ceramic materials and its characterisation. Firstly, the basic brittle fracture parameters and the statistical criteria to determi   ne the probability of exceeding the safety factors demanded for a particular application are analysed. Then, the toughening mechanisms which can be developed in the materials through microstructural design as well as the mechanical characterisation of toughened ceramics are discussed. The experimental values of linear elastic fracture toughness parameters (critical stress intensity factor, KIC, and critical energy release rate, GIC) are not intrinsic properties for toughened materials and depend on crack length and the loading system. In this work, the different mechanical parameters proposed to characterise such materials are reviewed. The following fracture parameters are analysed: work of fracture (γWOF), critical J-integral value (JIC) and R-curve. For the determination, stable fracture tests are proposed in order to ensure that the energy provided during the test is no more than the necessary one for crack propagation.

Study of directionally solidified eutectic Al2O3-ZrO2(3%Y2O3) doped with TiO2

An study of directionally grown samples of the eutectic composition in the Al2O3-ZrO2 (3 mol% Y2O3) system, with small TiO2 additions (1 wt%), is presented. The microstructural changes induced by this addition are analysed using SEM (EDX) techniques. The mechanical changes, when TiO2 is added, are studied by measuring the flexural strength by three point bending. Also, the toughness is determined by Vickers indentation method. When slow growth rates (10 mm/h) are used, interpenetratred and homogeneous microstructure is obtained, independently of the TiO2 doping. When growth rates are higher (300 and 1000 mm/h) the structure changes and the phases are organized in form of colonies or cells, which have smaller size when TiO2 is present. This size reduction is accompanied with an increase of the toughness.

Structural metastability through thermal spray.

Recent research in the field of nanostructured ceramic materials has underscored the importance of using feedstock powders with metastable phases. During material consolidation the metastable structure evolves into a dual structure where the grain growth stops when the crystallites reach their respective equilibrium grain size. The mutual suppression of the grain growth is a direct consequence of the immiscibility of the two phases in the solid state. Due to their small grain size and uniform structure, these nanocomposites exhibit very interesting properties such as higher hardness and toughness.
Metastable structures can be produced using Atmospheric Plasma Spray (APS) technique from commercially available micron-sized feedstock powders. The starting immiscible phases become molten  and are homogenized during their short residence in the hot zone of the plasma jet. Afterwards, the molten droplets accelerated by the plasma jet are quenched in a liquid medium, such as water, or onto a nitrogen chilled substrate forming metastable phases.
The main target of this work has been the synthesis of metastable ceramic powders through atmospheric plasma spraying  (APS) and quenching route. The viability for producing these metastable phases and the structural characterization have been carried out. 

Effect of the deposition temperature in the structural and optical characterics of boron nitride thin films obtained by CVD

Boron nitride (BN) thin films were deposited on silicon substrates by thermal CVD using mixtures of ammoniac and diborane. The effect of the deposition temperature (T) on the structural and optical characteristics of the BN samples was studied in the temperature range of 500 – 1000 ^oC. The deposition rate reached its maximum (1600 Å/min) at T = 900 ^oC. The activation energy (Ea) of the reaction NH₃ + B₂H₆, determined from the Arrhenius plot, is of 13.6 kcal/mol in the 500 – 900 ^oC range. The Infrared spectroscopy revealed the existence of different bands corresponding to B-H, N-H and B-N bonds. The concentration of B-H and N-H species is below the detection limit of IR spectroscopy in the BN films deposited at T ≥ 800 ^oC. The chemical analysis by XPS spectroscopy showed the presence of B-B and B-N bonds. An increase of the deposition temperature lead to a decrease of B-B bonds, which favors the formation of quasi-stoichiometric BN at T = 1000 ^oC. At this temperature, the resulting BN films are highly transparent with a refractive index of 1.7. The BN films deposited at T ≤ 900 ^oC are amorphous, nevertheless at T = 1000 ^oC they are partially crystallized with a turbostratic structure.

Environmental degradation of the mechanical properties of single-crystal erbia-doped zircona fibers

The flexure strength of tetragonal ZrO₂(Er₂O₃) single-crystal monofilaments manufactured by the laser-heated floating zone method was measured as a function of the environment (air vs. water) and temperature (from 25 to 800ºC) at loading rates spanning three orders of magnitude to ascertain their susceptibility to the environmental conditions. These mechanical tests were completed with parallel tests on fully-annealed monofilaments (to relieve the thermal residual stresses induced during growth) and by detailed analysis of the fracture surfaces using scanning electron microscopy and micro-Raman spectroscopy. While environmental susceptibility of ZrO₂(Y^₂O^₃) in previous investigations was always associated with the destabilization of the tetragonal phase, monoclinic phase was not detected on the fracture surfaces of the ZrO2(Er2O³) monofilaments and it was concluded that slow crack growth in this material at high temperature or immersed in water was due to stress-corrosion cracking.

Aerogels with applications in biomedicine and environment

It is possible to synthesise inorganic-organic hybrid materials incorporating the organic phase to a sol prepared from a metal organic under high power ultrasounds.  When both phases are chemically bonded a sono-ormosil (from ORganic MOdified SILicate) results, also known as hard ormosil.  One of the applications of these materials concerns the biotechnologies since they become bioactive when are doped with Ca, fulfilling this way the preliminary condition to be considered for bone implants.  The addition of silicate particles allows modifying the pore volume and radius. We have used these gels with particles, as precursor of the bioactive component, in order to act on the porosity for controlling the density and adequate the mechanical strength to that of the human cancellous bone.  In like manner, the pores becomes chemically active and be used as structural support for noxious atmospheric gas sequestration.

Bricks of the walled complex of Talamanca de Jarama, Madrid: Criteria for their differentiation

The walled complex of Talamanca de Jarama has a long history of wars that have destroyed it several times. Due to this fact, the Wall has gone through many reconstruction and enlargement processes (9th, 13th, 14th and 17th century), to which the restorations performed during the last century (20th) must be added. The main building materials are bricks together with rammed-earth and stones.
The bricks studied under Polarizing Microscopy (OM), X-ray powder diffraction (XRD), spectrocolourimetry, ultrasounds and mercury intrusion porosimetry (MIP), allowed us to distinguish five types, each of them belongs to different manufacturing periods. The oldest bricks (type I) and the most recent ones (type V), are those that differentiate the most. The five types of bricks show heterogeneities due to a deficient manufacture, which is responsible for their decay process, despite the fact that these bricks have been placed recently, during the last intervention.

Study of a Mixed Alkaline–Earth Effect on Some Properties of Glasses of the CaO-MgO-Al2O3-SiO2 System

In the present work, we studied a “Mixed Alkaline–Earth Effect”, i.e. the non-linear behaviour showed by the glass transition temperature as well as by the compressive strength of glasses of the CaO-MgO-Al2O3-SiO2 system, when a part of the CaO contained in them was substituted by a BaO/SrO mixture, in variable molar proportions. An important factor for the occurrence of this phenomenon was the difference in atomic weight, ionic radii and field strength of the Ba2+ and Sr2+ ions in comparison with those corresponding to the Ca2+ ion. Another factor considered was the likely occurrence of a microphase separation caused by the addition of BaO and/or SrO, together with the presence of F- and Mg2+ in the glasses. Other glass properties studied as a function of the CaO substitution level were density, glass molar volume, oxygen molar volume, packing fraction, and chemical resistance in neutral, basic and acidic aqueous media. In general, the structural reinforcement of the glass network caused by the partial substitution of CaO by a BaO/SrO mixture was accompanied by an improvement in the alkaline resistance of the materials, which were found to be suitable for applications in corrosive environments, especially in basic media.

Bioactive glasses and glass-ceramics

Since the late 1960´s, a great interest in the use of bioceramic materials for biomedical applications has been developed.
In a previous paper, the authors reviewed crystalline bioceramic materials “sensus stricto”, it is to say, those ceramic materials, constituted for non-metallic inorganic compounds, crystallines and consolidates by thermal treatment of powders at high temperature. In the present review, the authors deal with those called bioactive glasses and glass-ceramics. Although all of them are also obtained by thermal treatment at high temperature, the first are amorphous and the second are obtained by devitrification of a glass, although the vitreous phase normally prevails on the crystalline phases.
After an introduction to the concept of bioactive materials, a short historical review of the bioactive glasses development is made. Its preparation, reactivity in physiological media, mechanism of bonding to living tissues and mechanical strength of the bone-implant interface is also reported. Next, the concept of glass-ceramic and the way of its preparation are exposed. The composition, physicochemical properties and biological behaviour of the principal types of bioactive glasses and glass-ceramic materials: Bioglass®, Ceravital®, Cerabone®, Ilmaplant® and Bioverit® are also reviewed. Finally, a short review on the bioactive-glass coatings and bioactive-composites and most common uses of bioactive-glasses and glass-ceramics are carried out too.

Obtaining of β- Ca3(PO4)2 polycrystalline fibers for its employment as a filler in bone replacement material.

β-TCP is a calcium phosphate ceramic widely employed by orthopaedic restorative surgery as a filler material in bone healing processes, due to its great osteoconductive capacity and great resorption rates. This material is available in several forms such as powders, dense and porous blocks, etc, depending on the pathology and the osseous defect to be treated.
As an alternative to the β-TCP forms already available in the market, this work describes how to produce polycrystalline fibres by extruding plastic mixtures prepared with β-TCP powders, methyl cellulose (MC) and water. The rheology of the mixtures was studied versus time and frequency. The obtained fibres have different sizes and characteristics upon to the composition and rheology of the mixtures. The obtained diameters are between 150 µm and 350 µm.
Finally, it has been prepared biphasic composites β-TCP/Hidroxylapatite (HA) with controlled microstructure, by employing the obtained fibres.

Sintering of glasses in the system RO-BaO-SiO2 (R= Mg, Zn) for sealing SOFC

Glasses of composition 50SiO2•30BaO•20ZnO, mol% (Zn1.5-50), 55SiO2•27BaO•18ZnO, mol% (Zn1.5-55), and 55SiO2•27BaO•18MgO, mol% (Mg1.5-55) present good properties for application in sealing planar solid oxide fuel cells with an intermediate temperature of operation (850ºC) (IT-SOFC). The sealing must take place on sintering the glass powder during the start-up of the cell between 700 and 850ºC. Further treatment at the operation temperature provokes the crystallisation of barium silicates with the subsequent increase of viscosity and seal rigidity.
This work is a study of the sintering behaviour of these glasses using different heating rates and particle-size distributions of the glass powder in order to obtain dense and homogeneous seals. The glasses Zn1.5-55 and Mg1.5-55 with a particle size <63 µm heated at 2ºC/min reach final densities higher than 95%. A good agreement has been demonstrated between the measured sintering kinetics and those predicted with the sintering model of Clusters formation in the absence of concurrent crystallisation.

Design of glass elements in building: A proposal for the Spanish code.

This paper reports on a probabilistic model for design of glass plates and the procedure to determine the allowable load of specified types of glass, as a proposal for a new Spanish code for structural glass. After the experimental material characterization, the design model, implemented in the Windesign software, allows the user to calculate either the probability of failure of a monolithic glass plate for a given dimensions and specific loading, or to determine the plate thickness needed to withstand a known loading for a given probability of failure. Moreover, a comparative analysis among the results obtained by the model proposed here and the current foreign glass design standards, such as the American ASTM E 1300-02, the Italian UNI 7143-72, the French NFP 78-201-1 and the New Zealander NZS 4223 is presented.

Archaeometric characterization of pigments and mortars from Gothic wall paintings (13-15th Centuries)

A novel investigation on samples of gothic wall paintings (13-15th Centuries) has been carried out. They were found in some Churchs of Slovenia, being not yet studied using technics of materials analysis. One of them is selected: the Church of “Anunciación de María”, city of Crngrob, Slovenia. The scientific investigation of the Gothic wall painting samples was mainly based in the preparation of the so-called stratigraphic sections (cross-sections) from the original small samples. This procedure allows to study the different layers of mortar as support and the painting itself. Next, these preparations were examined using several instrumental techniques commonly applied in materials characterization at the ICMSE, for instance, digital photography, optical and electronic microscopies, IR spectroscopy and EDX for chemical analysis. Aditional information concerning pigments and mortars was obtained by IR transmision spectroscopy using KBr pellets, as well as using XRD.
Samples studied at the ICMSE can be classified in two groups, which allows to appreciate two procedures or techniques of wall paintings performed at the Church of Crngrob. The first is typical of Gothic Italian paintings: technic of so-called fresco buono over several layers of mortars, using marble powder to get a white and smooth surface.
The results of the present study have also allowed to characterize and identify the inorganic pigments and mortars used in these wall paintings. They were found to be the appropiate for this kind of technical work. For instance, they have been applied iron oxides to get the yellow, orange and even green colours, but surprisingly it has not been found neither malachite (copper pigment of green colour) nor copper compounds to get a green colour. In older layers of wall paintings, the pigment cinnabar was used to get the red colour. It is a mineral used typically in Italy. As revealed in this research, no aglutinant except the lime coming from the mortar as support were used in these Gothic wall paintings. Moreover, this feature, besides of cinnabar application, allows to establish the 1400-1410 wall paintings in the artistic Italian current named Trecento. The second procedure to paint is a typical of North Europe: one or two layer of mortar with a fine layer of lime. This is used to improve the strenght of lime as an aglutinant in the mortar.
With this study, it is concluded that the Italian and North-European artistic currents met in Slovenian territory, which is appraisable as much stilistic (Art History) as scientific (Chemical and Physical analysis) point of views. This kind of investigation allows to know better the Central European Art and the Slovenian Art in the Adriatic zone, as well as the general map of European Art in the Middle Age.

Characterization of slate foams with portland clinker additions

The decomposition of constituents of slates under non-oxidizing atmosphere leads to the manufacturing of foams. Thus die pressing at 80MPa of slates powders (particle size <80 microns)  mixed with a solid agglomerate, allows a green density close to 1,8 g/cm3 . The heating of compacts  under  N2-5%H2 atmosphere allows to reach a final density of 2,2 g/cm3 at 1050ºC, meanwhile at 1150ºC the compact foaming leads to densities lower than 0,4 g/cm3. Clínquer addition (5% and 10%) modifies the foam density and pore size at 1150ºC. It is necessary to increase the sintering temperature up to 1175ºC to achieve densities close to 0,4 g/cm3 when a 10% of Clínquer is added. The foams with Clínquer shows a high pore size and a compression strength within the range of glass foams: 0.4-1.5MPa.

Setting behaviour of waste-based cements estimated by impedance spectroscopy and temperature measurements

This work describes the study of phase development during the setting of various clinker formulations prepared with industrial wastes or by-products, namely sludges (generated in the Al-anodising and surface coating industrial processes, in potable water filtration/cleaning operations and in the cutting process of natural marble) and foundry sand. For comparison, similar formulations were also prepared with commercial high purity grade raw materials and processed in identical conditions. To circumvent the experimental restrictions imposed by the use of Vicat’s needle (i.e. large amount of material), electrical resistivity measurements were conducted by alternate current (a.c.) impedance spectroscopy to follow the hydration process and setting behaviour. During setting, the temperature evolution of the water/cement pastes was also recorded. Impedande spectroscopy (IS) studies were found to be a reliable method and, in some systems, can be a more sensitive technique to detect on-going hydration reactions.

Synthesis and characterization of CdS NP’S by microwaves

This paper present the results of the synthesis and characterization of semiconductor nanoparticles of CdS by microwaves. Thioacetamide (TAA) and CdCl2 were the initial materials. The synthesis was carried out under controlled potency of 1000W, with 60 seconds on or off, as well as the pH was regulated to different values: 8, 9 and 10. The nanocompounds were analyzed by UV-Vis spectroscopy, Textural Analysis from adsorption isoterms with N2 by BET method, Atomic Force Microscopy and X-Ray Diffraction. Textural analysis shows the size of pore distribution narrow, as well as superficial area of 106.4 m2/g. AFM micrographies shown particle nanometrics, the results of X-Ray Difraction analysis probing the same. Spectras of UV-Vis shown that nanoparticle is less according the pH used in the synthesis, affecting the band gap energy.

A kinetic study on the development of porosity in porcelain stoneware tile sintering

The aim of this work is to develop a mathematical model to study the mechanism of elimination of total porosity as a function of soaking time using the Navier-Stokes. Then, parameters of the model such as kinetic constants and apparent activation energy are calculated on the basis of experimental data for a standard porcelain stoneware tile composition. The theoretical data calculated from the model are in good agreement with the experimental data. Using the model developed, it is possible to estimate the best soaking time to obtain minimum total porosity at a given firing temperature . The effects of nepheline on sintering process of porcelain stoneware tile is investigated. It was found that when the nepheline syenite content of the starting mix was increased to 10%, the constant kp of the kinetic equation also increased. The results showed that addition of nepheline to composition of porcelain stoneware bodies was influenced remarkably suitable soaking time to obtain the minimum total porosity and increased shrinkage and bulk density while total and closed porosity fall down.

Development of waste-based ceramic pigments

We report the preparation of ceramic pigments using industrial wastes as primary sources. In this context, the use of Al-rich sludge generated in the wastewater treatment unit of an anodising or surface coating industrial plant, and a galvanizing sludge from the Cr/Ni plating process, will be detailed. The ceramic pigments reported here were prepared using typical solid state reactions involving the metal rich sludge. The main focus will be on the synthesis of chrome-tin orchid cassiterite (Sn,Cr)O2, chrome-tin red malayaite Ca(Cr,Sn)SiO5, victoria green garnet Ca3Cr2Si3O12, and chrome alumina pink/green corundum (Cr,Al)2O3 pigments. The pigments were fully characterised and then were tested in a standard ceramic glaze after. Typical working conditions and colour development will be reported.

Synthesis of ceramic pigments employing microwave radiation

Effect of microwave radiation on the development of ceramic pigments for tiles has been studied. Four compositions corresponding to different ceramic pigments (chrome-tin pink, cobalt-ferrite black, pink coral of iron in zircon and pink of chromium-tin sphene) have been prepared. Compositions using several synthesis methods (ceramic route and non-conventional methods) have been prepared and fired by microwave irradiation in a multimode, 1250 W power and 2450 MHz frequency, microwave equipment, and by conventional electric kiln. Results show that the efficiency of microwave firing show a great dependence on the mixing degree of precursors attained on the synthesis methods carried out, on microstructural parameters of powders and on the considered pigmenting system.

Order Promising Process, Product Pack, Tile Sector, Complementary Products.

The improvement of the customer service level is a key aspect in the competitive positioning of the ceramic sector companies. Within this context of improving the customer service level, the concept of “Product Pack” (P-P) arises as a mean to achieve product differentiation based on integral design and customer orientation. A P-P can be defined as a group of products that are complementary in its function and can be commercialised jointly. In order to increase the value perceived by the customer, it is necessary as well to give a rapid and reliable response to his/her order proposals. This article presents the problem description of the order promising process of a P-P in an Extended Collaborative Selling Chain (ECOSELL) domain, and develops a comparison with the traditional order promising process. Due to the absence of research about this topic, it is the objective of this article to define the starting point for future research by the characterization of all the possible scenarios that may appear in this context. On the basis of the aforementioned definition it is possible to design as well a generic methodology able to solve all the possible cases, to be exposed in a further work.

The order promising process of a product pack composed by products belonging to the tile sector and complementary products: Part II A solution methodology description

The globalisation, the increasing pressure of far East tile ceramic industries and the changes in the preferences of the customers, have converted the customer satisfaction in a key aspect for the European tile sector. In order to increase the customer satisfaction it is necessary to improve drastically the delivery and commercialisation functions. Within this context, the concept of “Product Pack” (P-P) arises as a mean to achieve product differentiation based on integral design and customer orientation. A P-P can be defined as a group of products that are complementary in its function and can be commercialised jointly. A methodology is proposed for a three levels structured solution in order to face any scenario in a reliable  and efficient way within the P-P order compromising process in an Extended Collaborative Selling Chain (ECOSELL) domain, to achieve the following objectives: 1) to solve any scenario with different kind of dependence on due date and delivery place of the P-P components, 2) to take in consideration any either customer or  network preference (satisfaction function) regarding due date and delivery place for the P-P, 3) to reduce the complexity of the global problem by splitting it in various sub-problems, 4) to coordinate the different supply chains involved in a P-P delivery, and 5) to combine the calculation of different availability levels in the extended collaborative supply chain (Available-To-Promise (ATP), and/or Capable To Promise (CTP), and Deliver To Promise (DTP)).

Reflections on the future of the European Ceramics Industry

The European Union thorough the European Ceramic Industries association, CERAME-UNIE, elaborate since 2004 a sectorial diagnostic and the published draft (9-09-2006) was transcribed in the Boletin Sociedad Española Ceramica y Vidrio issue 1 of 2007. This draft is a preliminary document that consisted in an instrument to initiate the mandatory debate in order to confront the sector expectation in the conference of the Parliament an the European Union that will be held in 2008. On behalf of the importance of the Spain Ceramic industry with a turnover of 6.000 M€ in the context of 27.000 M€ of the total of the European Ceramic industries, and due to the relevance of such spanish turnover on the Gross Domestic Product, it must necessary to analyze their own future strategy.

Electrochemical impedance spectroscopy analysis of thermal barrier coatings after isothermal oxidation

This investigation correlates the microstructure of a thermal barrier coating, analysed through scanning electron microscopy and X-ray microanalysis, with the electrochemical impedance spectroscopy data which show the variation in electrical properties after isothermal oxidation. A thermal barrier coating comprising a ceramic top layer, ZrO2 8Y2O3 (weight %), and an overlay coating, Ni 22Cr 10Al 1Y (weight %), air plasma sprayed over a nickel base alloy In 600 substrate was studied. These materials were heat treated in air at 1050 ºC for 72, 144 y 336 h. A thermally grown oxide layer, mainly comprising Cr y Al oxides, was formed between the ceramic and the overlay coating. This layer modified the electrical response of the thermal barrier coating in the electrochemical impedance spectroscopy tests.

Electrical answer of the SnO2-TiO2 thick films shaping with ceramics powders obtained by Pechini method.

Tin oxide is the compound more used in the gas sensor production, mainly to reduce gases like CO and H2. Their electrical properties are strongly dependent of its surface. For this is of great importance to synthesize nanoscale tin oxide particles to use they later in the films conformation. The synthesis of SnO2-TiO2 nanoparticles by polymeric precursor method is reported in this work. The particles were characterized by DTA/TG, FT-IR, XRD and SEM. Also, the electrical response of thick films measured under oxygen and carbon monoxide atmospheres is was analyzed.