Use of nanofiltration membrane technology for ceramic industry wastewater treatment

A study has been undertaken of an advanced wastewater treatment approach using polymer nanofiltration membranes, in an attempt to obtain water of sufficient quality to allow it to be reused in the same production process or, alternatively, to be discharged without any problems. The study has initially focused on the removal of organic matter (reduction of COD) and the most representative ions present in the wastewater, such as Na+ , Mg2+, Cl- , and SO4 2- . In a first part of the study, with a view to optimising the experimental phase, a simulation has been performed of the nanofiltration process using the NanoFlux software. Among other things, the simulation allows the most suitable membranes to be selected as a function of the permeate flow rate and desired level of retention in the substances to be removed. The subsequent experimentation was carried out in a laboratory tangential filtration system that works with flat membranes. It was found that retention values of about 90% were obtained for the studied substances, with a good permeate flow rate, using low operating pressures. These results demonstrate the feasibility of the studied technology and its potential as a treatment for improving ceramic industry wastewater qualit

Study of colloidal behaviour and rheology of Al2O3-TiO2 nanosuspensions to obtain free-flowing spray-dried granules for atmospheric plasma spraying

This work deals with the dispersion and stabilisation of nanosized Al2O3 and TiO2 particles in aqueous medium. The dispersing conditions were studied as a function of pH, dispersant content, solid loading and ageing. Well-dispersed nanosuspensions of Al2O3 with solids contents up to 15 vol.% and TiO2 with solids contents up to 30 vol.% were obtained by dispersing each type of nanoparticles with 4 wt% of polyacrylic acid-based polyelectrolyte. In order to obtain a concentrated 87 wt% Al2O3–13 wt% TiO2 suspension, a 15 vol.% homogeneous nanosuspension, composed by alumina and titania nanopowders, was prepared and then reconstituted by spray-drying into free-flowing powders. This spray-dried powder showed an adequate granule size distribution, a very high flowability and a reasonable density for diverse purposes, such as to be used in atmospheric plasma spraying as a feedstock to obtain nanostructured coatings

Influence of solids concentration on the microstructure of suspension plasma sprayed Y-TZP/Al2O3/SiC composite coatings

The present research focuses on the effect of feedstock suspension solid concentration on the microstructure of suspension plasma sprayed Y-TZP/Al2O3/SiC composite coatings. For this purpose, concentrated aqueous suspensions were prepared at 10, 20 and 30 vol.% of particles. Suspensions were characterised in terms of colloidal stability, rheological behaviour and sedimentation trend. The optimised suspensions were plasma sprayed, and the thickness, porosity, amount of resolidified particles and SiC content in the coatings were evaluated by optical microscopy, scanning electron microscopy and X-ray diffraction. The results revealed that stand-off distance and suspension solid content have a strong and similar influence on the coating microstructure due to the great impact that these two parameters exerts on the energy that particles and substrate receive during plasma operation. Thus, cauliflower-like microstructure is well-developed in most of the coatings, particularly for longer distances and lower solid contents. Porosity and amount of resolidified particles in the coatings are favoured by increasing the stand-off distance and decreasing the solids content, while thickness is strongly affected by solids content variation. On the other hand, Rietveld method from X-ray diffraction showed that large amount of the initial SiC was preserved in the final coatings whereas this amount remains almost constant for the three suspension feedstock tested

Alumina-zirconia coatings obtained by suspension plasma spraying from highly concentrated aqueous suspensions

Suspension plasma spraying (SPS) deposition represents an innovative technique to produce coatings that exhibit improved properties. However, the key to obtain coatings with superior functional properties relies on the investigation of the suspensions as starting materials. For this reason, the present work deals with the suspension preparation for SPS process and its influence on the resulting coatings. Laboratory-prepared 60/40 wt% alumina-zirconia suspensions were concentrated to avoid energy loss and were then successfully deposited by SPS technique. The liquid used was water instead of ethanol due to economical, environmental and safety reasons. The preparation of the suspension plays an important role in SPS process since stable and well-dispersed water suspensions are difficult to obtain. For this reason, colloidal behaviour characterisation of the starting particles as well as rheological optimisation of the feedstock suspensions were addressed in this research. Suspensions with different solid loadings (up to 30 vol.% or 72 wt%) were deposited using several spraying distances. All coatings displayed a bimodal microstructure consisting in partially melted zones surrounded by a fully melted matrix. α-Al2O3 and t’-ZrO2 constituted the main crystalline phases, but differences in the microstructure and properties of the coatings were observed. From these results, some relations between starting suspension and spraying parameters with coating characteristics were found. Thus the optimal spraying distance becomes shorter when the suspension solid loading increases.This work has been supported by the Spanish Ministry of Economy and Competitiveness, MINECO, (project MAT2015-67586-C3-R). M.D. Salvador thanks to CAPES – Programa Ciências sem Fronteiras (Brazil) for the concession of a PVE project Nº A086/2013. A. Borrell acknowledges the MINECO for her Juan de la Cierva-Incorporación contract (IJCI-2014-19839) and the Program to Support Research and Development (PAID-00-15) of the Universitat Politècnica de València

Comportamiento de tejas de diferente color (rojo y paja) frente al biodeterioro

La colonización biológica es un fenómeno que afecta de forma negativa a la durabilidad de los materiales de construcción. A nivel industrial se ha observado que las tejas de color paja muestran mayor tendencia a la colonización biológica que las tejas de coloración rojiza, incluso cuando ambas presentan características similares. El objetivo de este trabajo es determinar la causa de las diferencias de biocolonización entre tejas de diferente color. Para ello, se ha determinado la composición química de la superficie de tejas de color paja y de color rojo mediante WD-FRX, la composición mineralógica por DRX, la microestructura de la superficie mediante MEB-EDX, la distribución del tamaño de poros mediante porosimetría de mercurio, y la solubilidad (Ca, Mg, Na, K, Cl and SO 2- por ICP-OES y cromatografía iónica). Se ha evaluado la biorreceptividad midiendo la intensidad de fluorescencia con un fluorómetro, utilizando la cianobacteria Oscillatoria sp. Los resultados muestran una mayor concentración de calcio y azufre, y una mayor solubilidad de éstos, en la superficie de las tejas paja, y éstas presentan una mayor tendencia a la colonización. Por lo tanto, el hecho de que presenten sales solubles en superficie favorece la biocolonización, y con ello, el deterioro estético y funcional del tejado.Biocolonization of building materials is a critical problem for the durability of constructions. Industrial experience shows that straw coloured roofing tiles are more prone to colonization than red roofing tiles, even having similar characteristics. The aim of this work is to explain the difference of biocolonization between different colour roofing tiles. The chemical composition of the surface of straw coloured and red roofing tiles, the phase composition and the microstructure of the roofing tiles were determined by WD-XRF, XRD and SEM-EDX, respectively. The pore size distribution was carried out by Hg porosimetry. The solubility was studied by determining the soluble salts (Ca, Mg, Na, K, Cl and SO 2-) by ICP-OES and ionic chromatography. Roofing tile bioreceptivity was evaluated by determining fluorescence intensity using a pulse-amplitude-modulated (PAM) fluorometer, and cyanobacteria Oscillatoria sp. The results obtained show higher concentration of calcium and sulphur in straw coloured roofing tiles surface, and higher solubility than red roofing tiles. Moreover, according to the results obtained in bioreceptivity assays, straw coloured roofing tiles are more prone to colonization than red roofing tiles, so, there is a relationship between surface properties of roofing tiles and biocolonization, as it is observed in industrial products

Polishing of Porcelain Tiles in Industrial- and Laboratory-scale

This work reports the design and use of a laboratory-scale tribometer and a new developed tool-holder to reproduce the industrial polishing process for ceramic tiles in laboratory-scale. The mechanical conditions in a typical industrial polishing process were used to execute the tests in industrial-scale on a single polishing head test- rig. The results of spatial glossiness and roughness distribution from the industrial-scale test were taken as reference. After adaption of parameters the tests were repeated on a tribometer in laboratory-scale. The custom-made CNC- tribometer allows all parameters and kinematics used in the industry to be controlled and provides additionally a very high position accuracy of the tool. The new developed tool-holder provides similar contact conditions as known from the industrial process. The results of the evolution of glossiness and roughness from laboratory-scale test are compared with the data obtained from the test in industrial-scale and show that the tribometer and the new tool- holder accurately reproduce the polishing process from industrial-scale in laboratory

Microstructure assessment of suspension plasma spraying coatings from multicomponent submicronic Y-TZP/Al2O3/SiC particles

In this research, Suspension Plasma Spraying (SPS) technique was used for the thermal deposition of a multicomponent mixture made up of an Y-TZP/Al2O3 matrix with SiC particles. Two suspensions of Y-TZP and Al2O3 with different SiC particles content (6 wt% and 12 wt%) were tested as feedstocks in the SPS process. Three stand-off distances were varied in order to assess coating microstructure and evaluate the presence of SiC in the final coatings. Coatings were characterised in terms of porosity, microstructure and phase distribution. The estimate of the amount of SiC in the coating was carried out by XRD technique. Findings showed typical cauliflower-like SPS microstructure which intensifies with stand-off distance. Coatings porosity varied significantly between 8% and 25% whereas minimum porosity was found for the intermedium stand-off distance of 40 mm. Microstructure analysis also revealed the presence of SiC particles in the coatings which was confirmed by EDX analysis, overall XRD tests as well as TG analysis. Finally, evaluation of SiC content in the final coatings by means of XRD analysis showed that most of SiC particles (c.a 80%) of the feedstocks were preserved in the final coatings

Bioactive glass coatings by suspension plasma spraying from glycoletherbased solvent feedstock

Bioactive glasses are emerging as a substitute of hydroxyapatite in the development of bioactive coatings for biomedical applications. The deposition of these coatings is carried out by a wide range of methods, being atmospheric plasma spraying the most employed technique. However, the research on the deposition of these coatings from suspension feedstocks by thermal spraying is still incipient, therefore more research about this topic is needed. Thus, a bioactive glass suspension, composed of fine glass particles, was prepared and stabilised through rheological and sedimentation tests to be used as a feedstock in plasma spraying. The solvent used in the suspension preparation was dipropylene glycol methyl ether in order to develop a new type of bioactive suspension. Consequently, as a new type of solvent was used, its effect on the plasma torch properties was determined. On other hand, the rheological behaviour of the suspension feedstock was assessed by means of a simple viscosity model. This suspension was deposited onto metallic substrates by plasma spraying, employing several spraying distances. All coatings displayed a suitable adherence and similar thickness. However, the microstructure of the obtained coatings is highly affected by the spraying distance as it can be seen in coatings surface and cross-section field emission gun environmental scanning electron microscopy examination. Thus, a relation between the spraying distance and coatings microstructure was found. On the other hand, X-ray diffraction confirmed the amorphous nature of the obtained coatings

On the underestimated effect of the starch ash on the characteristics of low cost ceramic membranes

Starches are commonly used as a pore generator in the fabrication of low-cost ceramic membranes, since they are cheap, innocuous, environmentally friendly and easy to burn. Nevertheless, the influence of starches residues (ashes) generated during its burning off is dismissed. The present study analyses the influence of the starch ashes, generated by six different starches of similar particle size, on the characteristics of low-cost ceramic supports. The results indicated that starches gave rise to different amounts of ashes ranging from 0.17 to 0.71 wt%. In addition, these ashes contained some chemical elements in their composition, such as sodium, potassium or calcium, which can act as fluxes in the ceramic composition, modifying the characteristics of the obtained supports (mainly open porosity, water permeability and pore size distribution). It has also been observed that when the ash content grows the effect of the fluxing elements on the evolution of the microstructural features of the ceramic membrane (porosity, pore size or permeability) becomes more significant. Finally, tortuosity was calculated with a simple model derived from the Hagen–Poiseuille equation; the obtained data showed that tortuosity factor and its evolution with dwelling time were also affected by the starch ashes.This material is based upon work supported by the Spanish Ministry of Science and Innovation through the National Plan for Scientific Research, Development and Technology Innovation 2008–2011 (INNPACTO programme, project IPT-2011–1069-310000)

Solution precursor plasma spraying (SPPS): a novel and simple process to obtain bioactive glass coatings

This research addresses the use of an emerging plasma spray technique known as SPPS (Solution Precursor Plasma Spraying) to obtain bioactive glass coatings. In SPPS, the feedstock is a sol precursor of the bioactive glass instead of glass particles. Precursor feedstock composition (presence or not of acid catalyst), plasma torch enthalpy and stand-off distance of the spraying process have been varied to produce bioactive glass coatings of nominally 45S5 composition. A good quality coating was obtained when catalyst (0.2 M acid nitric) was used in the precursor and the plasma spraying took place with shorter stand-off distance and higher plasma enthalpy. Bioactivity in Simulated Body Fluid test was confirmed and an effect of the coating interconnected porosity to enhance bioactivity was observed