Low-temperature densification of Mg-doped hydroxyapatite fine powders under hydrothermal hot processing conditions

Densification of calcium hydroxyapatite fine powders doped with different concentrations of Mg (2, 4 and 6 mol % Mg, MgHA) was successfully achieved for the first time in a nearly fully dense state using the hydrothermal hot pressing (HHP) technique at low temperatures. Consolidation of MgHA powders was studied under different temperatures (150–240 °C), reaction times (1–6 h), and powder particle size (20 nm–1.5 μm). X-Ray diffraction analyses indicated that the particle densification under HHP conditions proceeded without any variation in the crystalline structure and regardless of the Mg content. The results from this work showed that an increase in temperature accelerates the reaction between MgHA particles and water (solvent) mixed during the hydrothermal treatment. Particle packing associated with bulk densification was achieved through a massive dissolution-recrystallisation mechanism, which induced the formation of small particles that rapidly crystallised on the surface of the partially dissolved original MgHA particles. The optimum conditions to obtain pellets with a high apparent density of 3.0758 ± 0.001 g/cm3 and tensile strength value of 12.6 ± 0.6 MPa were 10 wt% of water at a temperature of 240 °C with a 6 h reaction time and 6 mol % of Mg (MgHA3). The use of the HHP technique coupled with the fine particle size and reactivity of the MgHA precursor powders with water allowed us to produce disks that were compacted to a nearly full dense state with a low content of open porosity of 2.0%

Low-temperature densification of Mg-doped hydroxyapatite fine powders under hydrothermal hot processing conditions

Densification of calcium hydroxyapatite fine powders doped with different concentrations of Mg (2, 4 and 6 mol % Mg, MgHA) was successfully achieved for the first time in a nearly fully dense state using the hydrothermal hot pressing (HHP) technique at low temperatures. Consolidation of MgHA powders was studied under different temperatures (150–240 °C), reaction times (1–6 h), and powder particle size (20 nm–1.5 μm). X-Ray diffraction analyses indicated that the particle densification under HHP conditions proceeded without any variation in the crystalline structure and regardless of the Mg content. The results from this work showed that an increase in temperature accelerates the reaction between MgHA particles and water (solvent) mixed during the hydrothermal treatment. Particle packing associated with bulk densification was achieved through a massive dissolution-recrystallisation mechanism, which induced the formation of small particles that rapidly crystallised on the surface of the partially dissolved original MgHA particles. The optimum conditions to obtain pellets with a high apparent density of 3.0758 ± 0.001 g/cm3 and tensile strength value of 12.6 ± 0.6 MPa were 10 wt% of water at a temperature of 240 °C with a 6 h reaction time and 6 mol % of Mg (MgHA3). The use of the HHP technique coupled with the fine particle size and reactivity of the MgHA precursor powders with water allowed us to produce disks that were compacted to a nearly full dense state with a low content of open porosity of 2.0%

An Effective Surrogate Tracer Technique for S. aureus Bioaerosols in a Mechanically Ventilated Hospital Room Replica Using Dilute Aqueous Lithium Chloride

Finding a non-pathogenic surrogate aerosol that represents the deposition of typical bioaerosols in healthcare settings is beneficial from the perspective of hospital facility testing, general infection control and outbreak analysis. This study considers aerosolization of dilute aqueous lithium chloride (LiCl) and sodium chloride (NaCl) solutions as surrogate tracers capable of representing Staphylococcus aureus bioaerosol deposition on surfaces in mechanically ventilated rooms. Tests were conducted in a biological test chamber set up as a replica hospital single patient room. Petri dishes on surfaces were used to collect the Li, Na and S. aureus aerosols separately after release. Biological samples were analyzed using cultivation techniques on solid media, and flame atomic absorption spectroscopy was used to measure Li and Na atom concentrations. Spatial deposition distribution of Li tracer correlated well with S. aureus aerosols (96% of pairs within a 95% confidence interval). In the patient hospital room replica, results show that the most contaminated areas were on surfaces 2 m away from the source. This indicates that the room’s airflow patterns play a significant role in bioaerosol transport. NaCl proved not to be sensitive to spatial deposition patterns. LiCl as a surrogate tracer for bioaerosol deposition was most reliable as it was robust to outliers, sensitive to spatial heterogeneity and found to require less replicates than the S. aureus counterpart to be in good spatial agreement with biological results

Iron Calcium Carbonate Instability: Structural Modification of Siderite Corrosion Films

Corrosion research related to CO2-containing environments has focused over the past few decades on siderite formation (FeCO3) as a main corrosion product on carbon steel, yet the influence of Ca and other ions on its chemical and structural characteristics is not fully understood. Metal-localized corrosion is the biggest industrial challenge because of the unknown and unpredictable character of this phenomenon that frequently leads to failure. We report here the role of Ca and formation of iron-calcium carbonate (FexCayCO3) through a spiral growth model as in the calcite system and quantify the replacement of Fe2+ by Ca2+ ions in the structure of FeCO3 to form FexCayCO3. The incorporation of Ca2+ inhibits the completion of spiral segments on the growth of the rhombohedral crystals of FeCO3, promoting an enlargement of its structure along the c-axis. This leads to distortions in the chemical structure and morphology affecting the chemical and mechanical properties. Under flow conditions over time in an undersaturated environment, Ca is leached out from the expanded structure of FexCayCO3 increasing the solubility of the crystals, weakening the mechanical properties of the resulting corrosion films and stimulating localized corrosion

Study of a Local Structure at the Interface between Corrosion Films and Carbon Steel Surface in Undersaturated CO₂ Environments

Industries transporting CO2 gas-saturated fluids have infrastructures made of carbon steel. This is a good material with great mechanical properties but prone to corrosion and potential failure. Corrosion in sweet environments involves the formation of FeCO3 as a corrosion film, which is recognized to play a protective role under certain conditions. This work on the dissolution of corrosion films in sweet environments, under acidic and undersaturated conditions, demonstrates that the effects on the integrity of steel are far more significant than the damage observed on the surface of the corrosion film. Our results prove that dissolution of FeCO3 involved the presence of an amorphous phase, the intermediate formation of FeCl2 or FeCl+, and the presence of a phase with short distance atom–atom correlations. The amorphous phase was identified as a mixture of retained γ-Fe and Fe3C. Partially broken α-Fe and Fe3C structures were identified to prove the damage on the material, confirming the interface zone without evident damage on the corrosion film. Dissolution affected both the α-Fe and FeCO3, with the lattice [102̅] from the FeCO3 crystalline structure being the fastest to dissolve. The damage of steel at the molecular scale was evident at the macroscale with pit depths of up to 250 μm. The impact on the integrity of steel can be, therefore, more drastic than frequently reported in industrial operations of CO2 transport industries that use cleaning procedures (e.g., acid treatment, pigging) as part of their operational activities

Construcción del índice de términos de intercambio para Colombia

El documento compara tres índices alternativos para la medición de los Términos de Intercambio (TI) en Colombia: el ITI-PIB, que se construye con los deflactores implícitos del PIB; el ITI-CE, que utiliza el índice de valor unitario con información de comercio exterior y el ITI-IPP, basado en los precios de los bienes del Índice de Precios del Productor. Los índices propuestos son de tipo encadenado. Esta metodología tiene una ventaja sobre los índices tradicionales porque involucra los cambios en la estructura económica a través del tiempo. Los resultados sugieren que el comportamiento de los indicadores es similar, aunque pueden presentarse divergencias temporales. Estas se explicarían por las diferencias en las metodologías y las fuentes de información utilizadas para cada índice.Términos de Intercambio, Índices de Precios, Índices Encadenados. Classification JEL: C43, F10.

Actividad ictiotóxica de miconia coronata (bonpl.) d.c. (melastomataceae)

Miconia coronata (Bonpl.) DC., se homogenizó en n-hexano, diclorometano y acetona (70%). El homogenizado n-hexano se repartió entre n-hexano y MeOH. El homogenizado acetónico se fraccionó secuencialmente en EtOAc, n-BuOH y agua. Se desarrolló un ensayo semi-cuantitativo para la evaluación de ictiotoxicidad contra Poecillia reticulata. El rendimiento máximo (8.4%) y potente actividad ictiotóxica (50%) de la fracción EtOAc guió el fraccionamiento en DIAION HP-20. Los porcentajes de actividad ictiotóxica (%I.A) de las fracciones fueron 1 (5%), 4 (20%), 5 (60%), 6 (100%) y 9 (100%). La fracción metanólica del extracto n-hexano produjo β-Sitosterol por cromatografía en columna sobre SiGel

DISLOCACIÓN DE FACIES EN EL TOPE DE LA SECUENCIA CRETÁCICA DE LA SUBCUENCA DE NEIVA, VALLE SUPERIOR DEL MAGDALENA Y SUS IMPLICACIONES EN EL MODELO ESTRATIGRÁFICO SECUENCIAL COLOMBIANO

La identificación de un abrupto cambio de facies y ambientes de depósito entre los sedimentos de la llamada Formación Monserrate y la Formación San Francisco del Grupo Guaduala, permite reconocer una Dislocación de Facies en el tope de la secuencia marina del Cretácico colombiano en el Valle Superior del Magdalena, atribuida al levantamiento de la Cordillera Central y a la acreción de bloques tectónicos al Oeste del Sistema de Fallas de Romeral. Utilizando la integración de análisis detallados de sedimentología y estratigrafía en secciones de superficie y registros de pozos, se identificó la existencia de ambientes de depósito variantes entre el frente de costa medio y costa afuera proximal, que dominan la Formación Monserrate, mientras ambientes proximales, principalmente de lagos, pantanos y llanuras de inundación han sido interpretados para la Formación San Francisco. La ausencia de registro estratigráfico de la regresión de facies, desde ambientes marinos distales hasta ambientes continentales evidencia la discordancia o relación paraconforme de éstas unidades, donde los sedimentos de ambientes proximales fueron erodados o "bypassed". Esta superfcie y sus superfcies correlativas deben ser interpretadas como el límite de la secuencia marina del Cretácico colombiano y estarían evidenciando además, la primera fase del levantamiento pre-Andino. Palabras clave: Formaciones Monserrate y San Francisco, Cretácico Superior, dislocación de facies.    The identification of an abrupt facies change between the Monserrate and San Francisco formations allows us to identify a Facies Dislocation on top of the Cretaceous marine sequence of the Neiva sub-basin, due to the uplift of the Central Cordillera and the accretion of tectonic blocks, west of the Romeral Fault Zone. With an integrated detailed stratigraphic analysis in surface sections and wells, marine environments were identified for the Monserrate Formations, ranging from near offshore to middle shoreface. For the San Francisco Formation, continental environments were identified, ranging from coastal to fluvial plain, swamps and paleosoils. The lack of all the regression of facies, from deep marine environments to the continental realm is the principal evidence of the paraconformity between those units, implying that sediments from proximal environments were eroded or bypassed. This surface and their correlative surfaces have to be interpreted as the boundary of the marine sequence of the Cretaceous of Colombia in this area, and gives an evidence of the first pre-Andean uplift. Keywords: Monserrate and San Francisco Fms., facies dislocation, Upper Cretaceous. &nbsp

DISLOCACIÓN DE FACIES EN EL TOPE DE LA SECUENCIA CRETÁCICA DE LA SUBCUENCA DE NEIVA, VALLE SUPERIOR DEL MAGDALENA Y SUS IMPLICACIONES EN EL MODELO ESTRATIGRÁFICO SECUENCIAL COLOMBIANO

La identificación de un abrupto cambio de facies y ambientes de depósito entre los sedimentos de la llamada Formación Monserrate y la Formación San Francisco del Grupo Guaduala, permite reconocer una Dislocación de Facies en el tope de la secuencia marina del Cretácico colombiano en el Valle Superior del Magdalena, atribuida al levantamiento de la Cordillera Central y a la acreción de bloques tectónicos al Oeste del Sistema de Fallas de Romeral. Utilizando la integración de análisis detallados de sedimentología y estratigrafía en secciones de superficie y registros de pozos, se identificó la existencia de ambientes de depósito variantes entre el frente de costa medio y costa afuera proximal, que dominan la Formación Monserrate, mientras ambientes proximales, principalmente de lagos, pantanos y llanuras de inundación han sido interpretados para la Formación San Francisco. La ausencia de registro estratigráfico de la regresión de facies, desde ambientes marinos distales hasta ambientes continentales evidencia la discordancia o relación paraconforme de éstas unidades, donde los sedimentos de ambientes proximales fueron erodados o "bypassed". Esta superfcie y sus superfcies correlativas deben ser interpretadas como el límite de la secuencia marina del Cretácico colombiano y estarían evidenciando además, la primera fase del levantamiento pre-Andino. Palabras clave: Formaciones Monserrate y San Francisco, Cretácico Superior, dislocación de facies.    The identification of an abrupt facies change between the Monserrate and San Francisco formations allows us to identify a Facies Dislocation on top of the Cretaceous marine sequence of the Neiva sub-basin, due to the uplift of the Central Cordillera and the accretion of tectonic blocks, west of the Romeral Fault Zone. With an integrated detailed stratigraphic analysis in surface sections and wells, marine environments were identified for the Monserrate Formations, ranging from near offshore to middle shoreface. For the San Francisco Formation, continental environments were identified, ranging from coastal to fluvial plain, swamps and paleosoils. The lack of all the regression of facies, from deep marine environments to the continental realm is the principal evidence of the paraconformity between those units, implying that sediments from proximal environments were eroded or bypassed. This surface and their correlative surfaces have to be interpreted as the boundary of the marine sequence of the Cretaceous of Colombia in this area, and gives an evidence of the first pre-Andean uplift. Keywords: Monserrate and San Francisco Fms., facies dislocation, Upper Cretaceous. &nbsp