Pablo Galliano - Academia.edu (original) (raw)

Papers by Pablo Galliano

Metallurgical and Materials Transactions B, 2021

Slag waste from the steelmaking industry is generated in high amounts, so its reuse and recycling... more Slag waste from the steelmaking industry is generated in high amounts, so its reuse and recycling technologies are matters of industrial and academic interest. To get information for seeking new alternatives for reuse and/or recycling, white steelmaking slag obtained at the end of a ladle campaign was subjected to environmental conditions with different humidity (wet, normal and dry), with the aim of evaluating how the weathering process was modified. Slag degradation was monitored under these conditions for 49 days (7 weeks) via the evaluation of granulometric and mineralogical changes. Moreover, thermal treatments at 150°C and 650°C were performed on degraded samples to obtain additional information of the weathering process. The results showed that modifying the humidity by the used procedures can be an effective way to control the slag degradation. However, the weathering mechanism was not altered in the different environments, since the hydration of CaO and calcium aluminates was mainly responsible for the degradation just during the first 24 hours, even in a dry environment. Under wet conditions, a significant acceleration in weathering caused higher slag pulverization and the complete hydration of the lime; non-reacted MgO and calcium aluminates still remained at the end of the evaluation.

Ceramics International, 2021

Abstract This work complements an initial study regarding the mechanical behavior of MgO–C bricks... more Abstract This work complements an initial study regarding the mechanical behavior of MgO–C bricks at 1000 °C. In this case, two bricks bonded with phenolic resin, one of them containing aluminum, were treated at 600 °C and mechanically tested at RT and 600 °C. The thermal treatments attempt to simulate the in-service steelmaking ladle preheating process. At low temperatures, the binder pyrolysis is one of the main transformations and the Al melting neither its chemical reactions occur on a large scale yet. To evaluate the effects as the pyrolysis progresses, the soaking time at 600 °C was varied from 1 to 3 h. Although without significant chemical activity, the presence of Al affected the mechanical behavior of the tested bricks. The consolidation of the C–C network coming from the binder pyrolysis was identified as the main factor responsible for counterbalancing the material's degradation by microcracking. The heating combined with the low compressive pre-load applied on the tested specimens appears to close the microcracks and pores.

Journal of the European Ceramic Society, 2021

Abstract This work analyses the mechanical behavior of MgO-C refractories at an intermediate temp... more Abstract This work analyses the mechanical behavior of MgO-C refractories at an intermediate temperature of 1000 °C. Conditions similar to those occurring during the in-service pre-heating of steelmaking ladles are simulated by thermal treatment before the mechanical testing. Stress-strain curves were determined under compressive loading at RT and 1000 °C. The impact of the thermally activated physicochemical transformations on the mechanical response of the materials was evaluated in terms of parameters such as strength, fracture deformation, secant modulus and yield strength. The presence of Al seems to be deleterious when longer soaking times at 1000 °C were applied, which was attributed to the progressive damage related to in situ phase formation. On the other hand, when heating these types of refractories simultaneously with the application of a low compressive load, the closure of previously formed microcracks (self-healing) was considered to be mainly responsible for their mechanical behavior.

Ceramics International, 2018

During cooling and permanence outside, the solidified slag involved in the refinement process tak... more During cooling and permanence outside, the solidified slag involved in the refinement process taking place in the steelmaking ladles suffers attack by environmental components such as water vapor and gaseous CO 2 (weathering). The reactions involved are hydration and carbonation, and as a consequence, the pulverization of the slag occurs. In the present paper, the results of a study of the degradation of a typical steelmaking ladle slag over a period of eighteen weeks (126 days) are reported. To monitor the slag evolution, several experimental techniques were used, some of them rarely employed in this context, after dividing the initial slag batch in four granulometric fractions between > 7.2 mm and < 1.4 mm: granulometry by sieving, X-ray fluorescence (XRF), X-ray diffraction (XRD), and thermogravimetric (TGA) and thermal differential (DTA) analyses. As was already known, the main elements responsible for the slag degradation are free lime, followed by calcium aluminates and magnesia. It was also found that anhydrous and hydrated calcium aluminates are concentrated in the finest granulometric fractions and contribute to the generation of fines mainly during the final stage of hydration. The high percentage of particles smaller than 1.4 mm, with cementitious properties provided mainly by the presence of anhydrous calcium aluminates, are promising characteristics for alternative reusing of the studied ladle slag. Furthermore, slag weathering mechanisms are critical for understanding other steelmaking processes in which the slag is deeply involved, such as the protective role of the remaining thin slag layer against decarburation of ladle or converter working lining refractory bricks.

Boletín de la Sociedad Española de Cerámica y Vidrio, 2001

Procedia Materials Science, 2015

The MgO-C bricks are extensively used as lining work on different steel containers. Due to the hi... more The MgO-C bricks are extensively used as lining work on different steel containers. Due to the high temperatures of the process, these refractories are subjected to severe wear and corrosion processes, principally in the area of contact with the slag. These slags have variable contents of CaO, SiO 2 , Al 2 O 3 , MgO and FeO, varying in composition according to the process stage. In this paper, cup tests were performed at 1650 °C during 2 hours in air, using three kinds of commercial MgO-C bricks. They were put in contact with a high basicity slag. The corrosion degree and decarburization level sufferered by the refractories were analyzed and compared. Microstructural observations were performed in order to postulate the probable corrosion mechanisms acting on each material.

The crosslinking of blends of a silsesquioxane (SSO) derived from (3-methacryloxypropyl) trimetho... more The crosslinking of blends of a silsesquioxane (SSO) derived from (3-methacryloxypropyl) trimethoxysilane, variable amounts of a vinylester resin (VE, dimethacrylate of bisphenol A), and benzoyl peroxide (BPO) or dicumyl peroxide (DCP) as initiators, was followed by differential scanning calorimetry (DSC). For the neat SSO a thermally-initiated polymerization was observed in the 150-250 • C range, leading to a conversion close to 22% of the initial C C groups. The final conversion could be increased to a maximum value close to 83%, by adding an initiator and using a thermal cycle attaining temperatures in the range of 200 • C. The use of variable amounts of VE as a co-monomer produced a slight increase of the final conversion in SSO/VE/BPO blends. Neither the conversion of double-bonds nor the addition of the VE had any effect on the onset temperature of thermal degradation, which was associated to the presence of the methacryloxypropyl groups supplied by the SSO and the VE resin. However, a distinct two-step degradation process was observed in the presence of VE. Coatings based on SSO/VE/BPO blends exhibited more uniform thicknesses and lower values of the microhardness than those devoid of VE. However, the conversion of C C groups did not show any significant effect on the values of microhardness.

Ceramics International, 2014

A set of commercial tundish working lining materials was evaluated through a series of lab tests ... more A set of commercial tundish working lining materials was evaluated through a series of lab tests in order to determine the thermal evolution of both microstructure and mechanical properties, and their relationship with service conditions. Samples of each material were first cast with different water contents, then dried and fired at high temperatures. Microstructural characterization of these samples included density, porosity, pore size distribution determination and SEM observation. Particle size distribution, mineralogical (XRD) and chemical composition were also obtained. Thermogravimetric analysis was performed. Mechanical compressive strength for both green and fired (1600ºC) samples was also determined, as well as HMOR and dynamic elastic modulus of fired samples. Thermal shock resistance was evaluated by means of the mechanical characterization of sintered samples quenched in water. One of the failure mechanisms, rapid drying, was also studied. The impact of drying speed was evaluated by studying changes in the final compression resistance of sintered materials (1600ºC) obtained from materials previously submitted to different drying cycles with a gradual increase in the severity. Results showed good correlations between final properties, textural and microstructural features and materials processing conditions. Among them, water content was found to be a critical parameter that affects not only green samples porosity and mechanical strength, but also determines final mechanical properties after firing and sintering.

Advances in Science and Technology, 2014

A thermo-mechanical finite element model was developed by using FEA commercial software, in order... more A thermo-mechanical finite element model was developed by using FEA commercial software, in order to estimate thermal stress levels in a refractory lined steelmaking ladle shell during its first preheating stage. The model considers two refractory linings: an inner working lining and a permanent one besides the external ladle shell. In this way, stresses on both refractory lining and metallic shell due to restricted lining thermal expansion were simulated. Stress-strain curves of refractory lining materials at different temperatures were obtained through lab tests and then used for model optimization. Additionally, creep behavior in the steel shell under different tensile stresses and temperatures was also estimated taking into account previously obtained results from laboratory tests. In plant strain and temperature measurements were done by instrumenting the lower part of the ladle sidewall shell with high temperature strain gauges and thermocouples. Predicted stress evolution sho...

Journal of Sol-gel Science and Technology, 2003

Hybrids sols from tetraetoxysilane (TEOS) and 3-(methacryloxypropyl) trimethoxysilane (γ-MPS) wer... more Hybrids sols from tetraetoxysilane (TEOS) and 3-(methacryloxypropyl) trimethoxysilane (γ-MPS) were prepared in acid medium for different TEOS/γ-MPS ratios and were modified by the addition of a colloidal silica suspension. The stability of the different sols was evaluated by viscosity measurements; the sols showed a Newtonian behaviour and the ageing effect was negligible even after two months from their preparation. Coatings

Advances in Science and Technology, 2014

The MgO-C bricks are extensively used as lining work on different steel containers. Due to the hi... more The MgO-C bricks are extensively used as lining work on different steel containers. Due to the high temperatures of the process, these refractories are subjected to severe wear and corrosion processes, principally in the area of contact with the slag. These slags have variable contents of CaO, SiO2, Al2O3, MgO and FeO, varying in composition according to the process stage. In this paper, cup tests were performed at 1650 °C during 2 hours in air, using two commercial MgO-C bricks. They were put in contact with two different grades of slags, one with high basicity (HB) and the other rich in FeO (RF). The corrosion degree suffered by the refractory materials were analyzed and compared. Microstructural observations were performed in order to postulate the probable corrosion mechanisms acting on each material. The results establish that, in the case of HB slag, the attack is carried mainly through the filler region (matrix). In the case of RF slag attack, it is observed that Fe is the ma...

Journal of the European Ceramic Society, 2015

Abstract Al2O3–MgO–C (AMC) refractories are used in steelmaking vessels such as ladles, where the... more Abstract Al2O3–MgO–C (AMC) refractories are used in steelmaking vessels such as ladles, where they are part of the working lining's bottom and walls. Taking into account the conditions during the ladle operation, AMC refractories with high-melt corrosion resistance are required to provide good service performance. Moreover, due to the presence of graphite, AMC bricks should have low susceptibility to attack by oxidant gases. In this paper, the oxidation of commercial AMC refractories by air between 700 and 1400 °C and their corrosion by ladle basic slag at 1450 °C are examined. The experimental conditions for the chemical evaluation are similar to those to which AMC linings are exposed in some steps of the ladle operation. Differences in the chemical wear caused by both of the reagents among the studied bricks are associated to their differences in composition and microstructural and textural characteristics. In addition, the thermal evolution of each AMC refractory is considered.

Journal of Sol-gel Science and Technology, 1998

SiO2 and SiO2-CaO-P2O5 coatings have been prepared by dipping electropolished stainless steel 316... more SiO2 and SiO2-CaO-P2O5 coatings have been prepared by dipping electropolished stainless steel 316L samples and microscope glass slides in three different sol-gel solutions. Multilayered dense SiO2 coatings, and thick silica films obtained from equimolar contents of TEOS and MTES were used. The latter were able to strongly reduce both the corrosion attack on the steel and the iron diffusion to

Journal of Sol-gel Science and Technology, 2001

The aim of this work has been the preparation and evaluation of sol-gel coatings for clinical app... more The aim of this work has been the preparation and evaluation of sol-gel coatings for clinical applications. Research was focussed in the development of highly corrosion resistant and/or bioactive sol-gel coatings onto AISI 316L stainless steel. Hybrid SiO2 sol-gel coatings inhibited corrosion and Fe diffusion, although no signal of bioactivity was detected. The inclusion of Ca- and P-alcoxides in the

Journal of Sol-gel Science and Technology, 2000

The sol-gel method has been increasingly used to prepare organic-inorganic hybrid coatings with b... more The sol-gel method has been increasingly used to prepare organic-inorganic hybrid coatings with both glass and polymeric properties by including alkylalkoxides with one or more non-hydrolizable groups in the precursor alkoxide solution. When using MTES and TEOS precursors, it was found that the increase in Si–CH3 bond concentration in the coating augments the critical thickness, and strongly affects other properties.

Journal of Sol-gel Science and Technology - J SOL-GEL SCI TECHNOL, 2000

Sol-gel materials have been proposed in last years for clinical applications. In this work, bioac... more Sol-gel materials have been proposed in last years for clinical applications. In this work, bioactive sol-gel coatings were prepared from suspensions of up to 25% wt. of bioactive glass (CaO·SiO2·P2O5) particles in a hybrid sol obtained from TEOS and MTES. Thick dip-coatings showed in vitro bioactivity after a few days, but glass-particles dissolution promotes a slight reduction in the corrosion resistance. In order to overpass this problem, a two-stage sol-gel coating system that includes a first SiO2 hybrid film, acting as barrier against corrosion, and an external bioactive layer from glass particle suspension is proposed. The obtained samples revealed significant improvement in their electrochemical behaviour, and showed in vitro bioactivity.

Surface and Coatings Technology, 2006

Degradation of carbon steel has always been a concern. The use of coatings is especially recommen... more Degradation of carbon steel has always been a concern. The use of coatings is especially recommended in aggressive atmospheres at moderate temperatures. Ceramic films can be used to improve the resistance against high temperature oxidation and corrosion of metals. Amid the different options, a sol-gel process provides a low cost, simple and non-hazardous method for processing ceramic coating with controllable composition and microstructure. This work evaluates the electrochemical behaviour of carbon steel coated by sol-gel method. Hybrid organic-inorganic silica sol-gel coatings were obtained by dip coating of planar samples in an organically modified silica sol made from hydrolysis and polycondensation of tetra-orthosilicate (TEOS) and methyltriethoxisilane (MTES) by acidic catalysis. Coatings free of defects were obtained at a sintering temperature of 400-C. The coated samples were inspected by optical and electron microscopy and coating thickness was measured by using a Talystep surface roughness tester. Electrochemical evaluation was made by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. A comparison of the corrosion resistance of the coated metal with the uncoated one is presented. The measurements show the improvement of the corrosion resistance of the coated carbon steel.

Materials Research Bulletin, 1994

Materials Letters, 2005

Cobalt-based alloys are widely used for the fabrication of several devices that are surgically im... more Cobalt-based alloys are widely used for the fabrication of several devices that are surgically implanted in the body due to their good corrosion and wear resistance as well as their good biocompatibility. However, the carcinogenic potential of metal elements used in total hip arthoplasty components is a concern. This work describes the development of hybrid coatings containing methyltriethoxysilane (MTES) and

Materials Letters, 2003

CrCoMo alloys are generally known to be highly resistant to corrosion-induced failures and to spo... more CrCoMo alloys are generally known to be highly resistant to corrosion-induced failures and to spontaneously form passive oxide films when immersed in physiological environments. The stresses resulting from the use of the prosthesis can cause fracture and abrasion of the oxide film that covers the surface. This can result in crevice corrosion, with the corresponding decrease in pH leading to severe attack. Protective coatings deposited onto the metals would minimise the release of metallic ions from the substrate and the incorporation of bioactive particles would enable the adhesion to the bone tissue. This work describes the electrochemical behavior of CrCoMo alloys (F75) as cast, covered by a hybrid silica coating obtained by sol-gel. The silica sol-gel coating contains bioactive glass ceramic and vitreous particles of the system CaO-SiO 2-P 2 O 5 previously obtained by fusion, crystallization and milling. The performance of the alloy with and without coating is evaluated in simulated body fluid (SBF) pH 7.31 at 37 jC. As cobalt base alloys are susceptible to crevice attack, coated pieces are also tested in SBF acid solution (pH 0.7) in order to simulate the acidic media and the high chloride concentrations that develop when a crevice is formed. The electrochemical behavior has been evaluated by potenciodynamic polarization and electrochemical impedance spectroscopy. It was found that for both pH conditions the samples coated with double layer of glass ceramic particles showed lower passive current densities than those with monolayers. The coating improves the protection potential of the base material in the neutral solution. Besides, in the acidic solution, all the samples remain passive but the protection potential shifts to potentials more active than those measured in the neutral SBF.

Metallurgical and Materials Transactions B, 2021

Slag waste from the steelmaking industry is generated in high amounts, so its reuse and recycling... more Slag waste from the steelmaking industry is generated in high amounts, so its reuse and recycling technologies are matters of industrial and academic interest. To get information for seeking new alternatives for reuse and/or recycling, white steelmaking slag obtained at the end of a ladle campaign was subjected to environmental conditions with different humidity (wet, normal and dry), with the aim of evaluating how the weathering process was modified. Slag degradation was monitored under these conditions for 49 days (7 weeks) via the evaluation of granulometric and mineralogical changes. Moreover, thermal treatments at 150°C and 650°C were performed on degraded samples to obtain additional information of the weathering process. The results showed that modifying the humidity by the used procedures can be an effective way to control the slag degradation. However, the weathering mechanism was not altered in the different environments, since the hydration of CaO and calcium aluminates was mainly responsible for the degradation just during the first 24 hours, even in a dry environment. Under wet conditions, a significant acceleration in weathering caused higher slag pulverization and the complete hydration of the lime; non-reacted MgO and calcium aluminates still remained at the end of the evaluation.

Ceramics International, 2021

Abstract This work complements an initial study regarding the mechanical behavior of MgO–C bricks... more Abstract This work complements an initial study regarding the mechanical behavior of MgO–C bricks at 1000 °C. In this case, two bricks bonded with phenolic resin, one of them containing aluminum, were treated at 600 °C and mechanically tested at RT and 600 °C. The thermal treatments attempt to simulate the in-service steelmaking ladle preheating process. At low temperatures, the binder pyrolysis is one of the main transformations and the Al melting neither its chemical reactions occur on a large scale yet. To evaluate the effects as the pyrolysis progresses, the soaking time at 600 °C was varied from 1 to 3 h. Although without significant chemical activity, the presence of Al affected the mechanical behavior of the tested bricks. The consolidation of the C–C network coming from the binder pyrolysis was identified as the main factor responsible for counterbalancing the material's degradation by microcracking. The heating combined with the low compressive pre-load applied on the tested specimens appears to close the microcracks and pores.

Journal of the European Ceramic Society, 2021

Abstract This work analyses the mechanical behavior of MgO-C refractories at an intermediate temp... more Abstract This work analyses the mechanical behavior of MgO-C refractories at an intermediate temperature of 1000 °C. Conditions similar to those occurring during the in-service pre-heating of steelmaking ladles are simulated by thermal treatment before the mechanical testing. Stress-strain curves were determined under compressive loading at RT and 1000 °C. The impact of the thermally activated physicochemical transformations on the mechanical response of the materials was evaluated in terms of parameters such as strength, fracture deformation, secant modulus and yield strength. The presence of Al seems to be deleterious when longer soaking times at 1000 °C were applied, which was attributed to the progressive damage related to in situ phase formation. On the other hand, when heating these types of refractories simultaneously with the application of a low compressive load, the closure of previously formed microcracks (self-healing) was considered to be mainly responsible for their mechanical behavior.

Ceramics International, 2018

During cooling and permanence outside, the solidified slag involved in the refinement process tak... more During cooling and permanence outside, the solidified slag involved in the refinement process taking place in the steelmaking ladles suffers attack by environmental components such as water vapor and gaseous CO 2 (weathering). The reactions involved are hydration and carbonation, and as a consequence, the pulverization of the slag occurs. In the present paper, the results of a study of the degradation of a typical steelmaking ladle slag over a period of eighteen weeks (126 days) are reported. To monitor the slag evolution, several experimental techniques were used, some of them rarely employed in this context, after dividing the initial slag batch in four granulometric fractions between > 7.2 mm and < 1.4 mm: granulometry by sieving, X-ray fluorescence (XRF), X-ray diffraction (XRD), and thermogravimetric (TGA) and thermal differential (DTA) analyses. As was already known, the main elements responsible for the slag degradation are free lime, followed by calcium aluminates and magnesia. It was also found that anhydrous and hydrated calcium aluminates are concentrated in the finest granulometric fractions and contribute to the generation of fines mainly during the final stage of hydration. The high percentage of particles smaller than 1.4 mm, with cementitious properties provided mainly by the presence of anhydrous calcium aluminates, are promising characteristics for alternative reusing of the studied ladle slag. Furthermore, slag weathering mechanisms are critical for understanding other steelmaking processes in which the slag is deeply involved, such as the protective role of the remaining thin slag layer against decarburation of ladle or converter working lining refractory bricks.

Boletín de la Sociedad Española de Cerámica y Vidrio, 2001

Procedia Materials Science, 2015

The MgO-C bricks are extensively used as lining work on different steel containers. Due to the hi... more The MgO-C bricks are extensively used as lining work on different steel containers. Due to the high temperatures of the process, these refractories are subjected to severe wear and corrosion processes, principally in the area of contact with the slag. These slags have variable contents of CaO, SiO 2 , Al 2 O 3 , MgO and FeO, varying in composition according to the process stage. In this paper, cup tests were performed at 1650 °C during 2 hours in air, using three kinds of commercial MgO-C bricks. They were put in contact with a high basicity slag. The corrosion degree and decarburization level sufferered by the refractories were analyzed and compared. Microstructural observations were performed in order to postulate the probable corrosion mechanisms acting on each material.

The crosslinking of blends of a silsesquioxane (SSO) derived from (3-methacryloxypropyl) trimetho... more The crosslinking of blends of a silsesquioxane (SSO) derived from (3-methacryloxypropyl) trimethoxysilane, variable amounts of a vinylester resin (VE, dimethacrylate of bisphenol A), and benzoyl peroxide (BPO) or dicumyl peroxide (DCP) as initiators, was followed by differential scanning calorimetry (DSC). For the neat SSO a thermally-initiated polymerization was observed in the 150-250 • C range, leading to a conversion close to 22% of the initial C C groups. The final conversion could be increased to a maximum value close to 83%, by adding an initiator and using a thermal cycle attaining temperatures in the range of 200 • C. The use of variable amounts of VE as a co-monomer produced a slight increase of the final conversion in SSO/VE/BPO blends. Neither the conversion of double-bonds nor the addition of the VE had any effect on the onset temperature of thermal degradation, which was associated to the presence of the methacryloxypropyl groups supplied by the SSO and the VE resin. However, a distinct two-step degradation process was observed in the presence of VE. Coatings based on SSO/VE/BPO blends exhibited more uniform thicknesses and lower values of the microhardness than those devoid of VE. However, the conversion of C C groups did not show any significant effect on the values of microhardness.

Ceramics International, 2014

A set of commercial tundish working lining materials was evaluated through a series of lab tests ... more A set of commercial tundish working lining materials was evaluated through a series of lab tests in order to determine the thermal evolution of both microstructure and mechanical properties, and their relationship with service conditions. Samples of each material were first cast with different water contents, then dried and fired at high temperatures. Microstructural characterization of these samples included density, porosity, pore size distribution determination and SEM observation. Particle size distribution, mineralogical (XRD) and chemical composition were also obtained. Thermogravimetric analysis was performed. Mechanical compressive strength for both green and fired (1600ºC) samples was also determined, as well as HMOR and dynamic elastic modulus of fired samples. Thermal shock resistance was evaluated by means of the mechanical characterization of sintered samples quenched in water. One of the failure mechanisms, rapid drying, was also studied. The impact of drying speed was evaluated by studying changes in the final compression resistance of sintered materials (1600ºC) obtained from materials previously submitted to different drying cycles with a gradual increase in the severity. Results showed good correlations between final properties, textural and microstructural features and materials processing conditions. Among them, water content was found to be a critical parameter that affects not only green samples porosity and mechanical strength, but also determines final mechanical properties after firing and sintering.

Advances in Science and Technology, 2014

A thermo-mechanical finite element model was developed by using FEA commercial software, in order... more A thermo-mechanical finite element model was developed by using FEA commercial software, in order to estimate thermal stress levels in a refractory lined steelmaking ladle shell during its first preheating stage. The model considers two refractory linings: an inner working lining and a permanent one besides the external ladle shell. In this way, stresses on both refractory lining and metallic shell due to restricted lining thermal expansion were simulated. Stress-strain curves of refractory lining materials at different temperatures were obtained through lab tests and then used for model optimization. Additionally, creep behavior in the steel shell under different tensile stresses and temperatures was also estimated taking into account previously obtained results from laboratory tests. In plant strain and temperature measurements were done by instrumenting the lower part of the ladle sidewall shell with high temperature strain gauges and thermocouples. Predicted stress evolution sho...

Journal of Sol-gel Science and Technology, 2003

Hybrids sols from tetraetoxysilane (TEOS) and 3-(methacryloxypropyl) trimethoxysilane (γ-MPS) wer... more Hybrids sols from tetraetoxysilane (TEOS) and 3-(methacryloxypropyl) trimethoxysilane (γ-MPS) were prepared in acid medium for different TEOS/γ-MPS ratios and were modified by the addition of a colloidal silica suspension. The stability of the different sols was evaluated by viscosity measurements; the sols showed a Newtonian behaviour and the ageing effect was negligible even after two months from their preparation. Coatings

Advances in Science and Technology, 2014

The MgO-C bricks are extensively used as lining work on different steel containers. Due to the hi... more The MgO-C bricks are extensively used as lining work on different steel containers. Due to the high temperatures of the process, these refractories are subjected to severe wear and corrosion processes, principally in the area of contact with the slag. These slags have variable contents of CaO, SiO2, Al2O3, MgO and FeO, varying in composition according to the process stage. In this paper, cup tests were performed at 1650 °C during 2 hours in air, using two commercial MgO-C bricks. They were put in contact with two different grades of slags, one with high basicity (HB) and the other rich in FeO (RF). The corrosion degree suffered by the refractory materials were analyzed and compared. Microstructural observations were performed in order to postulate the probable corrosion mechanisms acting on each material. The results establish that, in the case of HB slag, the attack is carried mainly through the filler region (matrix). In the case of RF slag attack, it is observed that Fe is the ma...

Journal of the European Ceramic Society, 2015

Abstract Al2O3–MgO–C (AMC) refractories are used in steelmaking vessels such as ladles, where the... more Abstract Al2O3–MgO–C (AMC) refractories are used in steelmaking vessels such as ladles, where they are part of the working lining's bottom and walls. Taking into account the conditions during the ladle operation, AMC refractories with high-melt corrosion resistance are required to provide good service performance. Moreover, due to the presence of graphite, AMC bricks should have low susceptibility to attack by oxidant gases. In this paper, the oxidation of commercial AMC refractories by air between 700 and 1400 °C and their corrosion by ladle basic slag at 1450 °C are examined. The experimental conditions for the chemical evaluation are similar to those to which AMC linings are exposed in some steps of the ladle operation. Differences in the chemical wear caused by both of the reagents among the studied bricks are associated to their differences in composition and microstructural and textural characteristics. In addition, the thermal evolution of each AMC refractory is considered.

Journal of Sol-gel Science and Technology, 1998

SiO2 and SiO2-CaO-P2O5 coatings have been prepared by dipping electropolished stainless steel 316... more SiO2 and SiO2-CaO-P2O5 coatings have been prepared by dipping electropolished stainless steel 316L samples and microscope glass slides in three different sol-gel solutions. Multilayered dense SiO2 coatings, and thick silica films obtained from equimolar contents of TEOS and MTES were used. The latter were able to strongly reduce both the corrosion attack on the steel and the iron diffusion to

Journal of Sol-gel Science and Technology, 2001

The aim of this work has been the preparation and evaluation of sol-gel coatings for clinical app... more The aim of this work has been the preparation and evaluation of sol-gel coatings for clinical applications. Research was focussed in the development of highly corrosion resistant and/or bioactive sol-gel coatings onto AISI 316L stainless steel. Hybrid SiO2 sol-gel coatings inhibited corrosion and Fe diffusion, although no signal of bioactivity was detected. The inclusion of Ca- and P-alcoxides in the

Journal of Sol-gel Science and Technology, 2000

The sol-gel method has been increasingly used to prepare organic-inorganic hybrid coatings with b... more The sol-gel method has been increasingly used to prepare organic-inorganic hybrid coatings with both glass and polymeric properties by including alkylalkoxides with one or more non-hydrolizable groups in the precursor alkoxide solution. When using MTES and TEOS precursors, it was found that the increase in Si–CH3 bond concentration in the coating augments the critical thickness, and strongly affects other properties.

Journal of Sol-gel Science and Technology - J SOL-GEL SCI TECHNOL, 2000

Sol-gel materials have been proposed in last years for clinical applications. In this work, bioac... more Sol-gel materials have been proposed in last years for clinical applications. In this work, bioactive sol-gel coatings were prepared from suspensions of up to 25% wt. of bioactive glass (CaO·SiO2·P2O5) particles in a hybrid sol obtained from TEOS and MTES. Thick dip-coatings showed in vitro bioactivity after a few days, but glass-particles dissolution promotes a slight reduction in the corrosion resistance. In order to overpass this problem, a two-stage sol-gel coating system that includes a first SiO2 hybrid film, acting as barrier against corrosion, and an external bioactive layer from glass particle suspension is proposed. The obtained samples revealed significant improvement in their electrochemical behaviour, and showed in vitro bioactivity.

Surface and Coatings Technology, 2006

Degradation of carbon steel has always been a concern. The use of coatings is especially recommen... more Degradation of carbon steel has always been a concern. The use of coatings is especially recommended in aggressive atmospheres at moderate temperatures. Ceramic films can be used to improve the resistance against high temperature oxidation and corrosion of metals. Amid the different options, a sol-gel process provides a low cost, simple and non-hazardous method for processing ceramic coating with controllable composition and microstructure. This work evaluates the electrochemical behaviour of carbon steel coated by sol-gel method. Hybrid organic-inorganic silica sol-gel coatings were obtained by dip coating of planar samples in an organically modified silica sol made from hydrolysis and polycondensation of tetra-orthosilicate (TEOS) and methyltriethoxisilane (MTES) by acidic catalysis. Coatings free of defects were obtained at a sintering temperature of 400-C. The coated samples were inspected by optical and electron microscopy and coating thickness was measured by using a Talystep surface roughness tester. Electrochemical evaluation was made by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. A comparison of the corrosion resistance of the coated metal with the uncoated one is presented. The measurements show the improvement of the corrosion resistance of the coated carbon steel.

Materials Research Bulletin, 1994

Materials Letters, 2005

Cobalt-based alloys are widely used for the fabrication of several devices that are surgically im... more Cobalt-based alloys are widely used for the fabrication of several devices that are surgically implanted in the body due to their good corrosion and wear resistance as well as their good biocompatibility. However, the carcinogenic potential of metal elements used in total hip arthoplasty components is a concern. This work describes the development of hybrid coatings containing methyltriethoxysilane (MTES) and

Materials Letters, 2003

CrCoMo alloys are generally known to be highly resistant to corrosion-induced failures and to spo... more CrCoMo alloys are generally known to be highly resistant to corrosion-induced failures and to spontaneously form passive oxide films when immersed in physiological environments. The stresses resulting from the use of the prosthesis can cause fracture and abrasion of the oxide film that covers the surface. This can result in crevice corrosion, with the corresponding decrease in pH leading to severe attack. Protective coatings deposited onto the metals would minimise the release of metallic ions from the substrate and the incorporation of bioactive particles would enable the adhesion to the bone tissue. This work describes the electrochemical behavior of CrCoMo alloys (F75) as cast, covered by a hybrid silica coating obtained by sol-gel. The silica sol-gel coating contains bioactive glass ceramic and vitreous particles of the system CaO-SiO 2-P 2 O 5 previously obtained by fusion, crystallization and milling. The performance of the alloy with and without coating is evaluated in simulated body fluid (SBF) pH 7.31 at 37 jC. As cobalt base alloys are susceptible to crevice attack, coated pieces are also tested in SBF acid solution (pH 0.7) in order to simulate the acidic media and the high chloride concentrations that develop when a crevice is formed. The electrochemical behavior has been evaluated by potenciodynamic polarization and electrochemical impedance spectroscopy. It was found that for both pH conditions the samples coated with double layer of glass ceramic particles showed lower passive current densities than those with monolayers. The coating improves the protection potential of the base material in the neutral solution. Besides, in the acidic solution, all the samples remain passive but the protection potential shifts to potentials more active than those measured in the neutral SBF.