Sinterização de porcelanatos com fluxo viscoso: Uma revisão

n/

The REShiP Project: Renewable Energy for Ship Propulsion

In recent years the acknowledgement of the relations between the emissions of exhaust gas, in particular CO2, and their effects on climate and environment has grown to a wide level. Many countries and international organizations have begun to work to mitigate the problem and drive the society towards more sustainable sources of energy. Shipping is no exception and in 2018 the IMO – International Maritime Organization set the ambitious goal of reducing the CO2 emissions of the shipping industries of at least 50% within 2050, compared to the levels of 2008. This has introduced the need to research and develop new, sustainable energy sources and power systems for ships. The REShiP projects is aimed to identify a type of ship which would be suitable for an early adoption of a carbon free or carbon neutral fuel and a matching power generation system, tailored on specific routes. A small ferry powered by a hybrid combination of liquid hydrogen-fuelled fuel cells and Lithium-ion batteries has thus been identified. A mathematical model was developed to optimize the usage of fuel cell and batteries based on the ship operative profile. A multi objective optimization was implemented to minimize system performance degradation. To support the mathematical model a 7 kW PEMFC power generating unit was assembled and relevant data have been analysed. Following a regulatory framework research and in lack of comprehensive prescriptive rules, the design of the ferry and the prototype was done in accordance with the alternative design approach based on the risk assessment methodology, reaching a level of confidence appropriate to award an approval in principle

The polymorphism L412F in TLR3 inhibits autophagy and is a marker of severe COVID-19 in males

The polymorphism L412F in TLR3 has been associated with several infectious diseases. However, the mechanism underlying this association is still unexplored. Here, we show that the L412F polymorphism in TLR3 is a marker of severity in COVID-19. This association increases in the sub-cohort of males. Impaired macroautophagy/autophagy and reduced TNF/TNFα production was demonstrated in HEK293 cells transfected with TLR3L412F-encoding plasmid and stimulated with specific agonist poly(I:C). A statistically significant reduced survival at 28 days was shown in L412F COVID-19 patients treated with the autophagy-inhibitor hydroxychloroquine (p = 0.038). An increased frequency of autoimmune disorders such as co-morbidity was found in L412F COVID-19 males with specific class II HLA haplotypes prone to autoantigen presentation. Our analyses indicate that L412F polymorphism makes males at risk of severe COVID-19 and provides a rationale for reinterpreting clinical trials considering autophagy pathways. Abbreviations: AP: autophagosome; AUC: area under the curve; BafA1: bafilomycin A1; COVID-19: coronavirus disease-2019; HCQ: hydroxychloroquine; RAP: rapamycin; ROC: receiver operating characteristic; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; TLR: toll like receptor; TNF/TNF-α: tumor necrosis factor

Genetic mechanisms of critical illness in COVID-19.

Host-mediated lung inflammation is present1, and drives mortality2, in the critical illness caused by coronavirus disease 2019 (COVID-19). Host genetic variants associated with critical illness may identify mechanistic targets for therapeutic development3. Here we report the results of the GenOMICC (Genetics Of Mortality In Critical Care) genome-wide association study in 2,244 critically ill patients with COVID-19 from 208 UK intensive care units. We have identified and replicated the following new genome-wide significant associations: on chromosome 12q24.13 (rs10735079, P = 1.65 × 10-8) in a gene cluster that encodes antiviral restriction enzyme activators (OAS1, OAS2 and OAS3); on chromosome 19p13.2 (rs74956615, P = 2.3 × 10-8) near the gene that encodes tyrosine kinase 2 (TYK2); on chromosome 19p13.3 (rs2109069, P = 3.98 ×  10-12) within the gene that encodes dipeptidyl peptidase 9 (DPP9); and on chromosome 21q22.1 (rs2236757, P = 4.99 × 10-8) in the interferon receptor gene IFNAR2. We identified potential targets for repurposing of licensed medications: using Mendelian randomization, we found evidence that low expression of IFNAR2, or high expression of TYK2, are associated with life-threatening disease; and transcriptome-wide association in lung tissue revealed that high expression of the monocyte-macrophage chemotactic receptor CCR2 is associated with severe COVID-19. Our results identify robust genetic signals relating to key host antiviral defence mechanisms and mediators of inflammatory organ damage in COVID-19. Both mechanisms may be amenable to targeted treatment with existing drugs. However, large-scale randomized clinical trials will be essential before any change to clinical practice

Predicting viscosity and surface tension at high temperature of porcelain stoneware bodies: A methodological approach

The shear viscosity and the glass-vapor surface tension at high temperature are crucial to understand the viscous flow sintering kinetics of porcelain stoneware. Moreover, the pyroplastic deformation depends on the viscosity of the whole body, which is made up of a suspension of crystals dispersed in the melt. The existing fundamental theoretical background, along with semi-empirical constitutive laws for viscous flow sintering and glass densification, can be exploited through different approaches to estimate the physical properties at high temperatures starting from amount and chemical composition of the melt. In this work, a comprehensive attempt to predict the properties of the liquid phase is proposed by means of a detailed overview of existing models for viscosity and surface tension of glasses and melts at high temperature. The chemical composition of the vitreous phase and its physical properties at high temperature are estimated through an experimental approach based on the qualitative and quantitative chemical and phase analyses (by Rietveld refinement of X-ray powder diffraction patterns) of different porcelain-like materials. Repercussions on the firing behavior of ceramic bodies, are discussed. Comparative examples are provided for porcelain stoneware tiles, vitreous china and porcelain bodies, disclosing differences in composition and properties but a common sintering mechanism

High temperature viscosity of porcelain stoneware bodies

The viscosity of porcelain stoneware at high temperatures is crucial to understanding the vitrification path, the viscous flow sintering kinetics, and the pyroplastic deformation of this material. The final viscosity of porcelain stoneware has to be determined considering both the viscosity of the liquid phase formed by the melting of feldspars – and other minerals – and the viscosity of the body made up of a suspension of crystals dispersed in the melt. A fundamental theoretical background along with semi-empirical constitutive laws on viscous flow sintering, glass densification, as well as on the high viscosity of liquids and melts already exists. Different approaches are needed to measure/estimate the two viscosities and the parameterization depends on both the chemical composition of the liquid phase and persistence of crystal phases in the melt. In this work, a first attempt to predict the viscosity of a porcelain stoneware liquid phase is proposed by means of a detailed overview of preexisting models for high temperature viscosities of glasses and melts. Although models developed for glasses take into account a large number of oxides and they can be applied to melts characterized by a wide compositional range, the maximum concentration of alumina expected by these models is too low compared with that of the systems investigated here. On the other hand, the models proposed for granitic melts, although based on a lower number of oxides, take into account alumina levels closer to those of the systems of interest. In this contribution it is demonstrated that the latter models can be used to predict the viscosity at high temperature of porcelain-like bodies. Comparative examples are provided for porcelain stoneware tiles, vitreous china, and porcelain bodies

Phase evolution during reactive sintering by viscous flow: Disclosing the inner workings in porcelain stoneware firing

Porcelain stoneware is sintered by partial vitrification through viscous flow of a liquid phase formed at high temperature. This sintering process involves a complex evolution of both phase composition and chemistry of the liquid phase, according to the dynamic equilibrium established with the residual minerals and the new crystalline phases formed during firing. The present contribution overviews the evolution of phase composition and microstructure of seven body formulations during firing at different temperatures and dwell times. Each mixture was characterized from the chemical point of view and, once fired, by XRPD (quantitative phase composition), SEM and optical microscopy (microstructure). Moreover, the sintering behavior of the batches was investigated in isothermal conditions by optical thermo-dilatometric analysis. The results indicate that the continuous variation of the phase composition during the heating treatment affects the chemical composition of the liquid phase reflected on the densification kinetics and pyroplastic deformation of tiles

Viscous flow sintering of porcelain stoneware revisited

Porcelain stoneware tiles, as porcelain items, are sintered by vitrification through viscous flow of an abundant liquid phase formed at high temperatures. Such a process must be kept under strict control to achieve the desired properties of final products and prevent defects induced by pyroplasticity. This is particularly true for large tiles, where production emphasizes on requirements of uniform densification and minimal deformations at high temperatures. This contribution will critically overview the state-of-the-art of porcelain stoneware sintering and the challenges for the development of large slabs. The level of acquaintance with different phenomena involved in viscous flow sintering will be discussed, discerning what is already known, what is recognised, but still needs to be fully understood, and what could arise from in-depth comprehension. The KNOWNS: the evolution of microstructure and phase composition during firing is well known and phenomenological models have been developed for viscous flow densification of porcelain stoneware. Combined effects on pyroplasticity by liquid phase viscosity and solid load have been disclosed. The way by which Na/K ratio and other chemical keys of porcelain stoneware composition affect sintering kinetics is known. The role of mullite crystallisation/dissolution and beta-alpha quartz transition on technological properties has been recognised. The KNOWN UNKNOWNS: dynamic changes in composition and physical properties of the liquid phase during firing are envisaged, but vitrification and reactive sintering have not been modelled yet. In particular, there are uncertainties regarding the actual effect on sintering kinetics and pyroplasticity due to crystals suspended in the melt according to their variable shape and size distribution. The effect of starting porosity on densification degree and kinetics; the homogeneity and miscibility of liquid phases; gas solubility in the liquid phase at the highest firing temperatures (and its role on closed porosity and bloating); the Fe2+/Fe3+ ratio dependence on temperature and its consequence on the melt viscosity remain unclear. The UNKNOWN UNKNOWNS: modelling of densification curves and prediction of physical properties of porcelain stoneware tiles, through computational calculations, may prefigure the role of further variables not considered yet. The extension of such modelling efforts from laboratory to industrial scale may disclose the occurrence of scale effects, particularly in the case of large slabs and different shaping techniques. A better comprehension of kinetic aspects, resulting by the convolution of various factors, may unveil unexpected results, such as memory effects from raw materials or microstructural features