Materia-rio De Janeiro最新文献

{"title":"Evaluation of the behavior of mortars produced with fibers from the straw of carnauba: effects of the content of addition and length used","authors":"Antunes França Eduardo, Marcilene Vieira de Nóbrega, R. L. Ferreira","doi":"10.1590/S1517-707620210002.1279","DOIUrl":"https://doi.org/10.1590/S1517-707620210002.1279","url":null,"abstract":"The rendering mortars must be able to absorb small deformations, in order to guarantee the stability of the masonry (performance and durability). When this premise is not met, there is a greater propensity for the appearance of cracks, one of the main and worrying pathological manifestations in mortar coverings. One of the alternatives to combat this pathological manifestation is the addition of natural/artificial fibers in order to improve the mechanical properties (mainly the traction strength) and, consequently, the deformation capacity of the mortar. In this perspective, this work analyzed the behavior in the fresh and hardened state of mortars with the addition of fibers obtained from the straw of the carnauba (Copernicia prunifera), an abundant tree in the region of the Acu valley/RN (Brazil). For this purpose, mortars were produced in a 1:3 mass ratio (binder:aggregate) with the addition of 3% and 5% fiber from the carnauba straw (CSF) in relation to the cement mass and with the water/cement ratio (w/c) fixed at 0.72 for all mixtures. The effects of using fibers with different lengths (20, 40 and 60 mm) were also investigated. The properties of mortars were evaluated in a fresh (consistency) and hardened (compression and flexural strengths) state. The results indicated that the addition of CSF results in mortar with less consistency and mechanical strength. However, in general, the best performance was obtained for additions of up to 3% and for longer fiber lengths (20 mm). Keywords: Vegetable fibers. Carnauba. Mortar with fibers.","PeriodicalId":18260,"journal":{"name":"Materia-rio De Janeiro","volume":"1 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89606209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Workability maintenance of water-reducing admixtures in high-performance pastes produced with different types of Portland cement","authors":"P. D. Matos, R. Sakata, Maiara Foiato, W. L. Repette, P. Gleize","doi":"10.1590/S1517-707620210001.1225","DOIUrl":"https://doi.org/10.1590/S1517-707620210001.1225","url":null,"abstract":"This work evaluated the efficiency and workability manteinance of a polyfunctional (lignosulfonate-based) and a superplasticizer (polycarboxylate-based) admixture in high-performance pastes (water/cement ratios of 0.30, 0.33 and 0.36) produced with two types of Portland cement (one pozzolanic and one high early strength). The workability of the pastes was evaluated by the mini slump test immediately after mixing, and after 20 and 40 minutes. Furthermore, the mechanical strength of pastes with fixed w/c ratio (0.36) and mini slump (130 mm), produced with the different combinations of cements and admixtures, was evaluated. The results showed that the CP IV+lignosulfonate and CP V-ARI+polycarboxylate mixes presented the best workability maintenance over time. The pastes produced with CP V-ARI presented 28-day strengths about 22% higher than those produced with CP IV, for both admixtures. In turn, the lignosulfonate-containing pastes showed strengths about 10% higher than those produced with the polycarboxylate-based admixture. Overall, it was possible to obtain the same workability for high-performance Portland cement pastes produced with both admixtures and cements; however, the workability mantainance and mechanical strength highly depends on the combination of cement and admixture used.  Keywords: Cement paste; Workability maintenance; Polyfunctional; Superplasticizers; Mini slump.","PeriodicalId":18260,"journal":{"name":"Materia-rio De Janeiro","volume":"71 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90338321","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A nanofibrous membrane fluorescent sensor for fluoride ions prepared by electrospinning and host-guest interaction","authors":"Huan Zhang, Chen Zhou, Jing Sun, Xiao Li, Juan Tang","doi":"10.1590/S1517-707620210002.1258","DOIUrl":"https://doi.org/10.1590/S1517-707620210002.1258","url":null,"abstract":"A novel inclusion complexes nanofibrous membrane fluorescent sensor was prepared for recognizing F- via electrospinning and host–guest interaction. The host α-cyclodextrin on the surface of the electrospun nanofiber membrane is assembled into the guest azobenzene molecule which modified with F- fluorescent probe，and the formation of the inclusion complex is fixed on the surface of the nanofibrous membrane without external force，to prepare a novel surface controllable composite nanofiber membrane for F- detection. The inclusion complexes nanofibrous membrane exhibited favourable sensitivity and selectivity for F-. The introduction of F- would result in notable fluorescent decreasing of the membrane, but the other most common anions would not disturb the detection of F-. Moreover, this nanofibrous membrane was not only a fluorescent sensor for detecting F-, but also a good adsorbent for F- in solution. Keywords: Host–guest interaction，Nanofibrous membrane，Fluorescent sensor，Fluoride ions， Adsorbent","PeriodicalId":18260,"journal":{"name":"Materia-rio De Janeiro","volume":"73 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86159563","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Aplicación de drenaje electroosmótico a pasivos ambientales mineros","authors":"J. Valenzuela, M. Cánovas, P. González, C. Cuevas","doi":"10.1590/S1517-707620210001.1242","DOIUrl":"https://doi.org/10.1590/S1517-707620210001.1242","url":null,"abstract":"Chile es el mayor exportador de cobre del mundo. Sin embargo, este liderazgo tiene importantes costos medioambientales como la generacion de enormes cantidades de residuos solidos procedentes del tratamiento de las menas de cobre. Con objeto de abordar esta problematica, se propone la aplicacion de la tecnica de drenaje electroosmotico a ripios y relaves. La parte experimental del trabajo consiste en un diseno experimental con matrices solidas sinteticas. El porcentaje de finos y la humedad inicial se definen como factores de tres niveles. El volumen de liquido drenado se define como la variable respuesta. Los resultados muestran que el drenaje electroosmotico es mas eficiente que el drenaje gravitacional cuando el contenido de humedad y el porcentaje de finos se encuentran en su nivel mas alto. Mediante un analisis de varianza del diseno experimental, se corrobora el efecto de los factores y su interaccion en la variable de respuesta. Finalmente, se genera una ecuacion que describe la relacion entre las variables de respuesta y los factores del modelo.   Palabras claves: pasivos medioambientales mineros, drenaje electroosmotico, ANOVA, porcentaje de finos y reduccion de humedad.","PeriodicalId":18260,"journal":{"name":"Materia-rio De Janeiro","volume":"21 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86063749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A chemical patterning approach of dense and porous titanium surfaces by using a combination of concentrated acid and oxidant","authors":"A. Ribeiro, R. C. D. Silva, D. Way, Lais de Souza Alves, E. B. Silveira, F. Mendes, M. V. Oliveira","doi":"10.1590/S1517-707620210002.1284","DOIUrl":"https://doi.org/10.1590/S1517-707620210002.1284","url":null,"abstract":"Commercially dense pure titanium sheets and porous titanium samples processed by powder metallurgy were treated with a mixture consisting of equal volumes of H2SO4 and H2O2 for 2 or 4 hours. Characterization was performed by scanning electron microscopy, energy dispersive X-ray spectroscopy, confocal scanning optical microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The analyses showed that the chemical patterning approach using a combination of concentrated acid and oxidant was able to generate a nanotexture on dense and porous titanium surfaces. In addition, the treated samples presented an oxide layer consisting predominantly of titanium dioxide with negative charge conferred by the presence of hydroxyl groups, which is an important factor that favors apatite nucleation and protein adsorption. It was also observed that oxide formation was more effective on porous samples than on dense samples, which can be explained by the higher surface area intrinsic to porous media. Finally, the findings indicated that both treatment times promoted similar modifications in surface properties, such as nanotexture and chemical composition, suggesting that the time of 2 hours were enough to induce the surface alterations at the nanoscale. Keywords: titanium; surface modification; chemical oxidation, powder metallurgy.","PeriodicalId":18260,"journal":{"name":"Materia-rio De Janeiro","volume":"1 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75693838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Análise microestrutural de ligas semissólidas da série 7XXX submetidas a ensaios de compressão a quente entre placas paralelas","authors":"Luis Vanderlei Torres, E. Zoqui","doi":"10.1590/S1517-707620210001.1234","DOIUrl":"https://doi.org/10.1590/S1517-707620210001.1234","url":null,"abstract":"O presente trabalho visa a analise microestrutural de ligas de aluminio da serie 7XXX, a saber: AA7004 e AA7075, em vista de sua aplicacao nos processos de tixoconformacao. As ligas foram reaquecidas as temperaturas semissolidas, ou seja, as temperaturas correspondentes as fracoes solidas de 60% e 45% e mantidas nos tempos de tratamento termico de reaquecimento de 0, 30, 90 e 210 s e na sequencia submetidas a ensaios de compressao a quente entre placas paralelas. Como resultado, a condicao de 60% de fracao solida de ambas as ligas apresentaram diferencas significativas na aparencia das amostras tixoconformadas, com bordas mal preenchidas e quebradicas, quando comparadas com a condicao de 45% de fracao solida, isto devido as ligacoes existentes na microestrutura que possivelmente ainda estavam fortemente ligadas entre si, exigindo maior tensao para sua deformacao; a fracao solida de 45% adotada durante os ensaios foi satisfatoria, pois as bordas das amostras nao apresentaram trincas e/ou quebras intensas como tambem apresentou um bom acabamento superficial. Quanto ao seu comportamento microestrutural, as ligas semissolidas AA7004 e AA7075, apresentaram morfologia globular na regiao da borda das amostras com graos/globulos primarios bastante esferoidizados, devido aos fenomenos de ostwald ripening e coalescencia e na regiao central das amostras graos/globulos primarios totalmente deformados, com pouca presenca de liquido e grande presenca de fase solida, devido a deformacao imposta. Palavras-chave: Tixoconformacao, comportamento microestrutural, AA7004, AA7075.","PeriodicalId":18260,"journal":{"name":"Materia-rio De Janeiro","volume":"45 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84630728","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study of the interaction of the bioactive compound saponin from Glycyrrhiza glabra with a carbon nanotube matrix","authors":"C. Santos, Nélida Simona Marín Huachaca, A. D. S. Santos, Rodrigo Sá de Jesus, É. Almeida, L. C. Salay","doi":"10.1590/S1517-707620210001.1246","DOIUrl":"https://doi.org/10.1590/S1517-707620210001.1246","url":null,"abstract":"Saponins are bioactive compounds belonging to the secondary metabolism of plants widely used for their beneficial actions to human health. In this work the association of the saponin from Glycyrrhiza glabra with a matrix of multi-walled carbon nanotubes was promoted to obtain a composite material with improved functional characteristics. For this investigation, chemically modified electrodes (CME) based on carbon paste were developed. Firstly, a carbon paste electrode (CPE) modified with the addition of saponin (SAP) was developed. For the electrochemical optimization of this system, CPE/SAP, studies were carried out using cyclic voltammetry. The determination of parameters such as formal potential (Eo) and potential separation (ΔE) indicated that the saponin used as a carbon paste modifying agent generated a matrix that favors the transfer of electrons even at low applied potentials. The second step was performed by preparing the modified carbon paste electrode with the carbon nanotube matrix (CPE/CNT). This material, surprisingly, showed a redox pair probably due to the presence of iron atoms from the preparation method, something very beneficial for the purposes of this work. Next the saponin was associated to the carbon nanotube matrix in order to investigate the behavior of the hybrid material formed (CPE/SAP-CNT), which evidenced a significant improvement in the electron transfer process when the saponin interacts with the carbon nanotube matrix, increasing the anodic peak current by more than 3.6 times in relation to the CPE/SAP and 2.1 times when compared to the CPE/CNT. Another important issue concerns the stability of the systems, with the saponin associated with the carbon nanotube matrix presenting significantly improved stability, being able to be used for more than 8 hours or 200 voltammetric cycles with loss of signal of the order of only 2%, while the CPE/SAP showed a 60% loss of signal under the same conditions of use. Keywords: Saponin, muti-walled carbon nanotubes, modified electrodes, carbon paste.","PeriodicalId":18260,"journal":{"name":"Materia-rio De Janeiro","volume":"53 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83815314","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Torcímetro digital para teste de torção em materiais e avaliação dos parâmetros elasto-plásticos de cisalhamento","authors":"Maurício Ireno Betemps, R. Barbieri, G. Verran","doi":"10.1590/S1517-707620210001.1216","DOIUrl":"https://doi.org/10.1590/S1517-707620210001.1216","url":null,"abstract":"Neste trabalho estao mostrados o projeto, os principais componentes e os resultados obtidos com o prototipo de um torcimetro digital que foi construido para medir a variacao do ângulo de torcao em ensaios mecânicos de materiais. Este dispositivo foi construido utilizando um encoder magnetico, modelo AS5048A, com 14 bits de resolucao e para o processamento dos dados foi utilizada uma placa microcontroladora Arduino Mega 2560. Alem do baixo custo dos componentes eletronicos e mecânicos, outra vantagem do sistema de medicao desenvolvido e a grande quantidade de aplicativos gratuitos disponiveis para o processamento e aquisicao dos dados com a placa microcontroladora utilizada. Foram realizados testes para verificar a exatidao nas leituras da variacao angular e ensaios de torcao com corpos de prova tubulares de aluminio (liga AA6351T6) para avaliar o desempenho do sistema de medicao em ensaios monotonicos. A relacao de Ramberg-Osgood foi utilizada para descrever o comportamento do material e as tensoes de cisalhamento foram avaliadas empregando relacoes nao lineares propostas por diferentes autores. Os dados obtidos indicam que o torcimetro digital apresentou resultados satisfatorios para a obtencao do ângulo de torcao e as principais vantagens deste dispositivo incluem a medicao do ângulo de torcao sem contato, linearidade, boa acuracia, faixa de medicao ilimitada, tamanho reduzido e baixo custo para confeccao.  Palavras-chave: torcimetro, ensaio de torcao, ângulo de torcao.","PeriodicalId":18260,"journal":{"name":"Materia-rio De Janeiro","volume":"30 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79647905","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Análise comparativa da resistência à fadiga por fretting entre os cabos condutores feitos de liga de alumínio 900 MCM e 823 MCM","authors":"Erick Rocha Vieira, J. Ferreira, José Alexander Araújo, Remy Badibanga Kalombo, Cosme Roberto Moreira da Silva","doi":"10.1590/S1517-707620210001.1243","DOIUrl":"https://doi.org/10.1590/S1517-707620210001.1243","url":null,"abstract":"Com a necessidade de aperfeicoamento do processo de transmissao e distribuicao de energia eletrica, as industrias e concessionarias desse setor estao em busca de componentes mais otimizados para suas linhas de transmissao. Em consequencia, ha a necessidade de aprimorar a formacao do cabo condutor, que e o elemento mais oneroso das linhas eletricas. Nestas circunstâncias, condutores formados apenas por fios de aluminio aparentam ser mais vantajosos em relacao aos cabos com alma de aco, obtendo melhores indices de ampacidade/peso, diminuindo assim, o custo de transmissao. Neste cenario, o objetivo deste artigo, foi verificar a influencia do fenomeno de fadiga por fretting sob condicoes controladas, nos fios de liga de aluminio AA 6201 T81 e AA 1120 H19, que formam os condutores CAL 900 MCM e CAL 823 MCM, respectivamente. Para alcancar tal fim, criou-se um programa experimental capaz de adquirir os dados sobre a resistencia a fadiga dos cabos condutores e dos fios de forma separada, a fim de analisar a influencia do fretting sob o parâmetro de carga normal de contato de 750 N. Ao examinar os resultados, o condutor CAL 900 MCM obteve a menor resistencia a fadiga, apesar de ser constituido por uma liga com melhores propriedades mecânicas. O mesmo resultado foi obtido nos ensaios de fadiga por fretting nos fios, deste modo, pode-se inferir que a liga AA 6201 T81, embora possua melhor resistencia a fadiga, ela e mais suscetivel a falha na presenca de fretting quando comparada a liga AA 1120 H19. Palavras chaves: fadiga por fretting em fios, contato entre fios de aluminio liga AA 1120 H19, liga AA 6201 T81.","PeriodicalId":18260,"journal":{"name":"Materia-rio De Janeiro","volume":"112 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80171303","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Obtenção e caracterização de tecido multicamadas tridirecional de fibra de aramida visando aplicação em blindagem balística","authors":"Carlos Alberto Fernandes Marlet, M. C. Rezende","doi":"10.1590/S1517-707620210001.1247","DOIUrl":"https://doi.org/10.1590/S1517-707620210001.1247","url":null,"abstract":"O uso de tecidos no processamento de materiais compositos ja e uma realidade, em funcao das atraentes propriedades mecânicas que esse tipo de reforco confere aos compositos laminados e a maior facilidade de processamento. No entanto, os compositos laminados sao suscetiveis a falhas por delaminacao entre as camadas. Nesse sentido, a utilizacao de reforcos baseados em tecidos multicamadas tridirecionais (tecidos 3D), com filamentos em direcoes ortogonais, pode contribuir para um melhor desempenho do composito, com a reducao deste tipo de falha. Porem, o acesso a reforcos 3D ainda e muito restrito ao nivel mundial, devido a complexidade tecnologica envolvida no seu processamento. Nesse escopo, o presente trabalho visa contribuir com a area de processamento de compositos com a obtencao de um tecido 3D de fibras de aramida, obtido por meio da producao e combinacao de 6 camadas de tecido bidirecional, simultaneamente a amarracao das referidas camadas por filamentos do urdume, processo esse realizado em uma unica etapa. Para isto, um tear convencional foi adaptado e o tecido 3D produzido foi caracterizado por meio de ensaios tipicos da area textil, como gramatura, densidade linear e espessura, analises por estereoscopia e resistencias a tracao e ao impacto por queda de dardo. Analises por estereoscopia revelaram detalhes das direcoes transversal e ortogonal do tecido, que juntamente com os ensaios da area textil comprovaram o sucesso da obtencao do tecido 3D, com caracteristicas fisicas condizentes com o arranjo pretendido. Comparativamente, os resultados de resistencia a tracao mostraram que o tecido 3D possui maior elongacao que o tecido 2D comercial e os ensaios de impacto com 40 J mostraram que o tecido 3D resistiu sem perfurar e sem a delaminacao das camadas, como vantagens em relacao ao tecido 2D. Palavras-chave: Reforco tridirecional. Tecido 3D.  Fibras de aramida. Tecido multicamadas tridirecional.","PeriodicalId":18260,"journal":{"name":"Materia-rio De Janeiro","volume":"76 1","pages":""},"PeriodicalIF":0.4,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90005411","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}