Síntese e estudo das propriedades térmicas de materiais magnetocalóricos tricríticos

This work presents a novel and elaborate framework to evaluate promising materials for magnetocaloric application. In the first step, the molecular meanfield theory (Bean-Rodbell model) is applied to simulate various magnetic systems covering the first and second order transition. The magnetic systems of second order transition are analyzed to find the appropriate composition for a magnetic field change comparable to practical values (up to 2 Tesla). Moreover, the intrinsic hysteresis occurring in first order materials is estimated, under certain magnetic field change, and its impact on the materials’ cooling capacity is calculated. The most efficient candidate in terms of cooling capacity is detected via the comparison between materials of various transition behavior. A set of samples of La2/3(Ca1-xSrx)1/3MnO3 magnetocaloric family with transitions ranging from second to first order is produced and the data is fitted with the simulation tool to parameters such as spin value and the magnetovolume coupling parameter. Magnetic systems similar to experimental samples are simulated and the cooling capacity of the simulated system and experimental samples are compared to verify the theoretical model. The temperature dependence of the thermal conductivity of the La-Ca-Sr-Mn-O and Mn-Fe-P-Si systems are measured and show up to 50% change within the operating temperature ranges along with fully contrasting behaviour for the two families of magnetocaloric materials. It is also shown that the temperature dependence of thermal conductivity is coordinated with the order of the magnetic transition. By synthesizing La1-x(Ce, Pr, Nd)xFe11.6Si1.4 samples via a combination of induction melting and suction casting techniques, the substitution range is expanded up to x=0.4. The impact of La substitution on the magnetocaloric characteristics including magnetic entropy change, adiabatic temperature change, Tc and hysteresis is investigated. Finally, the phase transition order is studied using methods based on field dependence of magnetocaloric effect (including the Bean-Rodbell model).Este trabalho apresenta uma abordagem inovadora para a avaliação de materiais promissores para aplicações magnetocalóricas. Inicialmente, a teoria do campo médio molecular (modelo Bean-Rodbell) é aplicada para simular vários sistemas magnéticos que descrevem transições de primeira e de segunda ordem. Os sistemas magnéticos de transição de segunda ordem são analisados para encontrar a composição com performance otimizada para uma mudança de campo magnético comparável aos valores práticos (até 2 Tesla). Além disso, a histerese intrínseca que ocorre em materiais de primeira ordem é estimada, sob certas alterações de campo magnético, e o seu impacto na capacidade de arrefecimento dos materiais é calculado. O candidato mais eficiente em termos de capacidade de refrigeração é detectado através da comparação entre materiais com vários comportamentos diferentes na transição. Um conjunto de amostras da família magnetocalórica La2/3(Ca1-xSrx)1/3MnO3 com transições variando de segunda e primeira ordem foi produzido e os dados foram ajustados com a ferramenta de simulação e parâmetros como valor de spin e o parâmetro de acoplamento magneto-volume. Sistemas magnéticos semelhantes às amostras experimentais foram simulados e a capacidade de arrefecimento do sistema simulado e amostras experimentais foram comparadas para verificar o modelo teórico. A dependência da temperatura da condutividade térmica dos sistemas La-Ca-Sr-Mn-O e Mn-Fe- P-Si foi medida e mostra alterações de até 50% dentro das faixas de temperatura de operação, além de um comportamento totalmente contrastante para as duas famílias de materiais magnetocalóricos. Também é mostrado que a dependência na temperatura da condutividade térmica é coordenada com a ordem da transição magnética. Sintetizando a família de amostras de La1-x(Ce, Pr, Nd)xFe11.6Si1.4 por meio de uma combinação de técnicas de fusão por indução e fundição por sucção, a faixa de substituição é expandida até x = 0.4. O impacto da substituição de La nas características magnetocalóricas, incluindo alteração da entropia magnética, mudança de temperatura adiabática, Tc e histerese, é investigada. Finalmente, a ordem de transição de fase é estudada usando métodos baseados na dependência de campo do efeito magnetocalórico (incluindo o modelo Bean-Rodbell).Programa Doutoral em Ciência e Engenharia de Materiai

The influence of cobalt on the microstructure and adherence characteristics of enamel on steel sheet

In this study, the influence of cobalt (Co) on the microstructure and adhesion between enamel and steel substrate has been investigated. The result of press test indicated that the adhesion strength was greatly improved by Co inclusion. Scanning electronic microscope (SEM)revealed that the amount of dendrite increases in the interface while its average size decreases. The wavelength dispersive X-ray analysis (WDS) identified the existence of Co in the dendrite, which confirms that the Co was closely related to the change of interface morphology and the improvement of adhesion strength. Finally, the reasons for adhesion improvement were discussed

Enhancement of physical and reaction to fire properties of crude glycerol polyurethane foams filled with expanded graphite

The reation to fire of polyurethane foams (PUFs) has been a subject of increasing relevance, so in this study the reaction to fire performance of PUFs derived from crude glycerol (CG) has been improved using expanded graphite (EG). The influence of different loadings of EG on the physical–mechanical properties of composite foams has been assessed and the results obtained show that it has significant positive impact. Moreover, the reaction to fire of the PUF and EG/PUF composites has been investigated and the results obtained showed that the fire behavior of composite foams containing as little as 5 wt% of EG are significantly improved. Indeed a dramatic reduction of the rate of heat release, mass loss rate, effective heat of combustion and specific extinction area, has been observed even for a relative low amount of EG. Likewise, the use of Infrared Thermography as a function of time has proven that, when EG is used, the combustion stops suddenly and the temperature drops sharply compared with the behavior of the unfilled PUF sample, which suggests that EG acts like a flame extinguisher. The results obtained have proven the suitability of CG for the production of PUFs and that the addition of EG considerably improves the reaction to fire of composite foams.publishe

Tailoring Negative Thermal Expansion via Tunable Induced Strain in La–Fe–Si-Based Multifunctional Material

Zero thermal expansion (ZTE) composites are typically designed by combining positive thermal expansion (PTE) with negative thermal expansion (NTE) materials acting as compensators and have many diverse applications, including in high-precision instrumentation and biomedical devices. La(Fe1–x,Six)13-based compounds display several remarkable properties, such as giant magnetocaloric effect and very large NTE at room temperature. Both are linked via strong magnetovolume coupling, which leads to sharp magnetic and volume changes occurring simultaneously across first-order phase transitions; the abrupt nature of these changes makes them unsuitable as thermal expansion compensators. To make these materials more useful practically, the mechanisms controlling the temperature over which this transition occurs and the magnitude of contraction need to be controlled. In this work, ball-milling was used to decrease particles and crystallite sizes and increase the strain in LaFe11.9Mn0.27Si1.29Hx alloys. Such size and strain tuning effectively broadened the temperature over which this transition occurs. The material’s NTE operational temperature window was expanded, and its peak was suppressed by up to 85%. This work demonstrates that induced strain is the key mechanism controlling these materials’ phase transitions. This allows the optimization of their thermal expansion toward room-temperature ZTE applications

Evaluation and Classification Risks of Implementing Blockchain in the Drug Supply Chain with a New Hybrid Sorting Method

In blockchain technology, all registered information, from the place of production of the product to its point of sale, is recorded as permanent and unchangeable, and no intermediary has the ability to change the data of other members and even the data registered by them without public consensus. In this way, users can trust the accuracy of the data. Blockchain systems have a wide range of applications in the medical and health sectors, from creating an integrated system for recording and tracking patients’ medical records to creating transparency in the drug supply chain and medical supplies. However, implementing blockchain technology in the supply chain has limitations and sometimes has risks. In this study, BWM methods and VIKORSort have been used to classify the risks of implementing blockchain in the drug supply chain. The results show that cyberattacks, double spending, and immutability are very dangerous risks for implementation of blockchain technology in the drug supply chain. Therefore, the risks of blockchain technology implementation in the drug supply chain have been classified based on a literature review and opinions of the experts. The risks of blockchain technology implementation in the supply chain were determined from the literature review

A Technical Analysis Investigating Energy Sustainability Utilizing Reliable Renewable Energy Sources to Reduce CO2 Emissions in a High Potential Area

©2020 Elsevier Ltd. All rights reserved. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1016/j.renene.2020.09.042Reduction of carbon dioxide (CO 2) emissions will have a positive impact on the environment by preventing adverse effects of global warming. To achieve an eco-environment, the primary source of energy needs to shift from fossil fuels to clean renewable energy. Thus, increased utilization of renewable energy overtime reduces air pollution and contributes to securing sustainable energy supply to satisfy future energy needs. The main purpose of this study is to investigate several sustainable hybrid renewable systems for electricity production in Iran. In this regard, critical indicators that have the strongest impact on the environment and energy sustainability are presented in this study. After a comprehensive review of environmental issues, data was collected from the meteorological organization and a techno-economic assessment was performed using HOMER software. It was concluded that the hybrid configuration composed of photovoltaic (PV), wind turbine, diesel generator and battery produced the best outcome with an energy cost of 0.151$/kWh and 15.6% return on investment. In addition, the results showed that with a higher renewable fraction exceeding 72%, this hybrid system can reduce more than 2000 Kg of CO 2 emission per household annually. Although excess electricity generation is a challenge in stand-alone systems, by using the fuel cell, an electrolyzer, and a hydrogen tank unit, the amount of energy loss was reduced to less than one-sixth. These results show that selecting useful indicators such as appropriate implementation of policies of new enabling technologies and investments on renewable energy resources, has three potential benefits namely: CO 2 reduction, greater sustainable electricity generation and provides an economic justication for stakeholders to invest in the renewable energy sector.Peer reviewe

Effect of processing conditions on the properties of recycled cathode ray tube glass foams

Cathode ray tube glass waste was used to produce glass foams by a powder sintering route. The glass waste powder was mixed with small amounts (5 and 8 wt%) of coal fly ash, which acted as foaming agent, and the compacts of the mixed powders were heated at different sintering temperatures in the range 600-800 A degrees C for various dwell times (30-120 min). The effect of the different processing conditions on the microstructural characteristics (porosity, pore size and pore size distribution), mechanical resistance and thermal conductivity of the produced foams was investigated. The volume of pores tended to increase with sintering temperature and time, and glass foams (with a porosity higher than 50 %) were only achieved after sintering at 750 A degrees C. The average pore size increased with sintering temperature and dwell time, and pore growth was particularly accentuated at 800 A degrees C, where coalescence of the pores occurred, with a consequent decrease in compressive strength. Selected combinations of the sintering temperature, dwell time and foaming agent led to glass foams with a satisfactory microstructural homogeneity, which exhibited mechanical strength and thermal conductivity values similar to commercial foams used as thermal insulating materials