Degradação de tubos de aços ASTM A 249 TP-316L e AISI-316L instalados em reatores para polimerização de PVC/ Degradation of steel tubes ASTM A 249 TP-316L and AISI-316L installed in reactors for PVC polymerization

No processo de produção de resinas de Policloreto de Vinila (PVC) é comum a utilização de equipamentos fabricados em aços inoxidáveis devido à boa resistência à corrosão e excelentes propriedades mecânicas. Trocadores de calor utilizados em reatores para polimerização, sofrem uma exposição contínua a cloretos e ácido clorídrico, neste sentido, nas paredes internas dos tubos do trocador de calor ocorre aderência de produtos de corrosão provenientes da reação de polimerização, produzindo regiões mais susceptíveis à corrosão localizada. O presente trabalho teve como objetivo analisar o desempenho de tubos fabricados em aço inoxidável austenítico ASTM A 249 TP-316L e AISI-316L, empregados em trocadores de calor (TC) e tubos de purga (TP), respectivamente, que operam em meio a cloreto de vinila (VC) contido na reação para a polimerização de PVC.[1] A.R. Tacidelli. Aumento da produtividade em reatores de polimerização um estudo de caso. (Dissertação de Mestrado). Paraíba:  Universidade Federal de Campina Grande (2007).[2] F.P. Incropera, et al. Fundamentos de transferência de calor e de massa. 6. ed. Rio de Janeiro: LTC ( 2008).[3] R.E. Sonntag, C. Borgnakke, G.J. Van Wylen. Fundamentos da termodinâmica. 6. ed. São Paulo: Edgard Blücher (2003).[4] T. Bellezze, G. Giuliani, G. Roventi. Study of stainless steels corrosion in a strong acid mixture. Part 1: cyclic potentiodynamic polarization curves examined by means of an analytical method. Corrosion Science, 130, pp. 113-125 (2018).[5] Manual Villares Metals[6] TM Service Laboratório Metalúrgico (2017)[7] M. A. Rao, R. S.Babu, M.V. P. Kumar. Stress corrosion cracking failure of a SS 316 L high pressure heater tube. Engineering Failure Analysis, 90, pp. 14-22 (2018).[8] C.A.S Giraldo. Resistência à corrosão intergranular do aço inoxidável ferrítico UNS S43000: avaliação por método de reativação eletroquímica, efeito de tratamento isotérmico e mecanismo de sensitização. (Tese de Doutorado). São Paulo: Universidade de São Paulo (USP), p.85 (2006).[9] A.J. Sedriks. Corrosion of stainless steels. 2.ed.  New York: John Wiley & Sons (1996).[10] S.C. Dexter. Forms of Corrosion – Localized Corrosion. In: ASM Metals Handbook, Metals Park, ASM International, 13, pp. 226-262 (1987). [12] A. Pardo, et al. Pitting corrosion behaviour of austenitic stainless steels – combining effects of Mn and Mo additions. Corrosion Science, 50, pp. 1796-1806 (2008).[13] C. Boissy, C. Alemany, B.Normand. EIS evaluation of steady-state characteristic of stainless steel passive film grown in acidic solution. Electrochemistry Communications, 26, pp. 10-12 (2013).[14] K.M. Deen, M.A. Virk, C.I. Haque, et.al. Failure investigation of heat exchanger plates due to pitting corrosion. Engineering Failure Analysis, 17, pp. 886-893 (2010).[15] S. Al Saadi, Youngsun Yi, Pyungyeon Cho, et.al.  Passivity breakdown of 316L stainless steel during potentiodynamic polarization in NaCl solution. Corrosion Science, 111, pp. 720-727 (2016). <w:LsdException Locked="false" Priority="61" Name="Light List

Sn-0.5Cu(-x)Al solder alloys: microstructure-related aspects and tensile properties responses

In this study, experiments were conducted to analyze the effect of 0.05 and 0.1 wt.% Al additions during the unsteady-state growth of the Sn-0.5wt.%Cu solder alloy. Various as-solidified specimens of each alloy were selected so that tensile tests could also be performed. Microstructural aspects such as the dimensions of primary, lambda(1), and secondary, lambda(2), dendritic arrays, and intermetallic compounds (IMCs) morphologies were comparatively assessed for the three tested compositions, that is, Sn-0.5wt.%Cu, Sn-0.5wt.%Cu-0.05wt.%Al, and Sn-0.5wt.%Cu-0.1wt.%Al alloys. Al addition affected neither the primary dendritic spacing nor the types of morphologies identified for the Cu6Sn5 IMC, which was found to be either globular or fibrous regardless of the alloy considered. Secondary dendrite arm spacing was found to be enlarged and the eutectic fraction was reduced with an increase in the Al-content. Tensile properties remained unaffected with the addition of Al, except for the improvement in ductility of up to 40% when compared to the Sn-0.5wt.%Cu alloy without Al trace. A smaller lambda(2) in size was demonstrated to be the prime microstructure parameter associated with the beneficial effect on the strength of the Sn-0.5wt.%Cu(-x)Al alloys92CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO AMAZONAS - FAPEAM407978/2018-6; 307830/2017-92015/11863-5; 2016/18186-1; 2017/12741-6sem informaçã

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio

Pooled analysis of WHO Surgical Safety Checklist use and mortality after emergency laparotomy

Background The World Health Organization (WHO) Surgical Safety Checklist has fostered safe practice for 10 years, yet its place in emergency surgery has not been assessed on a global scale. The aim of this study was to evaluate reported checklist use in emergency settings and examine the relationship with perioperative mortality in patients who had emergency laparotomy. Methods In two multinational cohort studies, adults undergoing emergency laparotomy were compared with those having elective gastrointestinal surgery. Relationships between reported checklist use and mortality were determined using multivariable logistic regression and bootstrapped simulation. Results Of 12 296 patients included from 76 countries, 4843 underwent emergency laparotomy. After adjusting for patient and disease factors, checklist use before emergency laparotomy was more common in countries with a high Human Development Index (HDI) (2455 of 2741, 89.6 per cent) compared with that in countries with a middle (753 of 1242, 60.6 per cent; odds ratio (OR) 0.17, 95 per cent c.i. 0.14 to 0.21, P <0001) or low (363 of 860, 422 per cent; OR 008, 007 to 010, P <0.001) HDI. Checklist use was less common in elective surgery than for emergency laparotomy in high-HDI countries (risk difference -94 (95 per cent c.i. -11.9 to -6.9) per cent; P <0001), but the relationship was reversed in low-HDI countries (+121 (+7.0 to +173) per cent; P <0001). In multivariable models, checklist use was associated with a lower 30-day perioperative mortality (OR 0.60, 0.50 to 073; P <0.001). The greatest absolute benefit was seen for emergency surgery in low- and middle-HDI countries. Conclusion Checklist use in emergency laparotomy was associated with a significantly lower perioperative mortality rate. Checklist use in low-HDI countries was half that in high-HDI countries.Peer reviewe

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Characterization of solidification microstructures of the Sn-Mg eutectic welding alloy and correlation with mechanical properties

Orientador: Noé CheungDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: A busca por soluções viáveis para a substituição das clássicas ligas Sn-Pb utilizadas em procedimentos de soldagem conduziu ao estudo da solidificação da liga eutética do sistema Sn-Mg, uma vez que esta enquadra-se, a priori, como uma possível candidata à aplicação industrial. A liga foi submetida à solidificação unidirecional, na direção vertical e sentido ascendente, sob condições transitórias de fluxo de calor utilizando-se três tipos de substratos refrigerados à água, sendo dois deles comumente aplicados na indústria eletrônica: Cu, Ni e adicionalmente um em aço AISI 1020. O desenvolvimento de uma abordagem teórico-experimental determinou quantitativamente as variáveis térmicas, tais como velocidade de deslocamento da frente de solidificação (VE) e taxas de resfriamento (T'). Para a obtenção dos perfis térmicos teóricos aplicou-se um modelo numérico de transferência de calor unidirecional já desenvolvido previamente no Grupo de Pesquisas em Solidificação - GPS. Um mecanismo de busca automática por meio do confronto entre os perfis térmicos experimentais e teóricos foi utilizado para a determinação dos perfis de coeficiente de transferência de calor na interface metal/molde para cada um dos diferentes substratos utilizados neste trabalho, com o intuito de verificar a tendência de molhabilidade da liga sobre cada tipo de substrato. As microestruturas de solidificação foram caracterizadas por meio de técnicas metalográficas, apresentando a morfologia de um eutético fibroso. Os espaçamentos interfásicos (?G) foram medidos ao longo dos lingotes e correlacionados com as variáveis térmicas, microdureza e propriedades mecânicas obtidas por ensaios de tração. Leis experimentais na forma de potência com expoentes -0,55 e -1,1 relacionando ?G como função da taxa de resfriamento e velocidade de deslocamento da isoterma eutética, respectivamente, foram propostas para representar o crescimento eutético em condições transitórias de fluxo de calor. Equações tipo Hall-Petch foram propostas relacionando Microdureza, Limite de Resistência à Tração e Tensão de Escoamento com ?G. Adicionalmente, analisou-se a interação metalúrgica entre a liga com três substratos por meio das técnicas de caracterização: Microscopia Eletrônica de Varredura, Difração de Raios X e Espectroscopia por Energia Dispersiva de RaiosAbstract: The pursuit for feasible solutions replacing the traditional Sn-Pb alloys used in soldering procedures has led to the study of the Sn-Mg eutectic alloy solidification, as a possible candidate to industrial application. The alloy was submitted to vertical, upward and unidirectional solidification under transient heat flow regime. Three kinds of water-cooled substrates have been used to solidify the alloy, being two of them commonly applied in the electronic industry: Cu, Ni and additionally, AISI 1020 steel. The development of a theoretical-experimental approach determined the thermal variables, such as growth velocity (VE) and cooling rate (T ?). The theoretical thermal profiles were obtained through simulations of a heat transfer numerical model previously developed in the Solidification Research Group (GPS). An automatic search mechanism based on the comparison between experimental and theoretical thermal profiles was used to determine the metal/mold interface heat transfer profile, which indicates the tendency of alloy wettability in each type of substrate. The solidification microstructure presenting lamellae eutectic morphology was observed through metallographic techniques. The interphase spacings (?G) were measured along the ingots and correlated with thermal variables, micro-hardness and mechanical properties which were obtained by tensile tests. Power laws with 0.55 and -1.1 exponents expressing ?G as a function of (T ?) and VE, respectively, were found to better represent the eutectic growth under transient heat flow conditions. Hall¿Petch equations are proposed relating micro hardness, Ultimate Tensile Strength, and Yield Tensile Strength to ?G. In addition, the metallurgical interaction between the alloy and the three kinds of substrate was analyzed by characterization techniques: Scanning Eletron Microscope, X-Ray Diffraction and Energy-Dispersive X-Ray SpectroscopyMestradoMateriais e Processos de FabricaçãoMestra em Engenharia Mecânica351/14FuncampFAEPE

Transient unidirectional solidification, microstructure and intermetallics in sn-ni alloys

The present research work examines the microstructural arrangements formed during the transient solidification of eutectic Sn-0.2wt.%Ni and hypereutectic Sn-0.5wt.%Ni alloys. Also, it examines their respective correlations with solidification thermal parameters: eutectic growth rate (VE) and eutectic cooling rate (ṪE); length scales of matrix and eutectic phases: microstructural spacings and the corresponding tensile properties: ductility and strength. Both alloys were directionally solidified upwards under unsteady-state regime, and characterized by optical and scanning electron microscopy. Concerning the hypereutectic Sn-0.5wt.%Ni, the increase in Ni content is shown to influence both thermal behavior and cellular spacing (λC). The NiSn4 intermetallics is present in the eutectic mixture of both alloys, whilst in the Sn-0.5wt.%Ni alloy the primary phase has been identified by SEM-EDS as the Ni3Sn4 intermetallics. A β-Sn morphological cellular/dendritic transition occurs in the 0.2wt.%Ni eutectic alloy for ṪE> 1.2K/s. Despite that, regular cells in the hypereutectic alloy (0.5wt.%Ni) turns into plate-like cells for ṪE> 1.4K/s. If considered a reference cellular spacing about 20μm (i.e.,λ(c-1/2=0.22), the samples associated with the Sn-0.5wt.%Ni alloy are shown to be associated with higher tensile strengths, but much lower ductility as compared with the corresponding results of the eutectic alloy211CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão tem2015/11863-5; 2016/18186-1; 2017/12741-6; 2017/15158-0The authors are grateful for the financial support provided by FAPESP (São Paulo Research Foundation, Brazil: grants 2015/11863-5; 2016/18186-1; 2017/12741-6; 2017/15158-0), CNPq and the Postgraduate Program in Materials Science and Engineering (PPGCEM-UFRN

Transient Unidirectional Solidification, Microstructure and Intermetallics in Sn-Ni Alloys

<div><p>The present research work examines the microstructural arrangements formed during the transient solidification of eutectic Sn-0.2wt.%Ni and hypereutectic Sn-0.5wt.%Ni alloys. Also, it examines their respective correlations with solidification thermal parameters: eutectic growth rate (VE) and eutectic cooling rate (ṪE); length scales of matrix and eutectic phases: microstructural spacings and the corresponding tensile properties: ductility and strength. Both alloys were directionally solidified upwards under unsteady-state regime, and characterized by optical and scanning electron microscopy. Concerning the hypereutectic Sn-0.5wt.%Ni, the increase in Ni content is shown to influence both thermal behavior and cellular spacing (λC). The NiSn4 intermetallics is present in the eutectic mixture of both alloys, whilst in the Sn-0.5wt.%Ni alloy the primary phase has been identified by SEM-EDS as the Ni3Sn4 intermetallics. A β-Sn morphological cellular/dendritic transition occurs in the 0.2wt.%Ni eutectic alloy for ṪE> 1.2K/s. Despite that, regular cells in the hypereutectic alloy (0.5wt.%Ni) turns into plate-like cells for ṪE> 1.4K/s. If considered a reference cellular spacing about 20μm (i.e.,λ(c-1/2=0.22), the samples associated with the Sn-0.5wt.%Ni alloy are shown to be associated with higher tensile strengths, but much lower ductility as compared with the corresponding results of the eutectic alloy.</p></div

Transient Unidirectional Solidification, Microstructure and Intermetallics in Sn-Ni Alloys

<div><p>The present research work examines the microstructural arrangements formed during the transient solidification of eutectic Sn-0.2wt.%Ni and hypereutectic Sn-0.5wt.%Ni alloys. Also, it examines their respective correlations with solidification thermal parameters: eutectic growth rate (VE) and eutectic cooling rate (ṪE); length scales of matrix and eutectic phases: microstructural spacings and the corresponding tensile properties: ductility and strength. Both alloys were directionally solidified upwards under unsteady-state regime, and characterized by optical and scanning electron microscopy. Concerning the hypereutectic Sn-0.5wt.%Ni, the increase in Ni content is shown to influence both thermal behavior and cellular spacing (λC). The NiSn4 intermetallics is present in the eutectic mixture of both alloys, whilst in the Sn-0.5wt.%Ni alloy the primary phase has been identified by SEM-EDS as the Ni3Sn4 intermetallics. A β-Sn morphological cellular/dendritic transition occurs in the 0.2wt.%Ni eutectic alloy for ṪE> 1.2K/s. Despite that, regular cells in the hypereutectic alloy (0.5wt.%Ni) turns into plate-like cells for ṪE> 1.4K/s. If considered a reference cellular spacing about 20μm (i.e.,λ(c-1/2=0.22), the samples associated with the Sn-0.5wt.%Ni alloy are shown to be associated with higher tensile strengths, but much lower ductility as compared with the corresponding results of the eutectic alloy.</p></div