Reinforced concrete beam (RCB) elements show low mechanical performance when interfacial bonding strength (IBS) is not well controlled. New tailorable material-structure arrangements - Metamaterials - offer solutions to the IBS problem. This paper analyzes the mechanical characteristics of IBS on RCBs for reinforced cement mortar containing Metamaterial bars (MMB) that were machined from SAE 1020 Carbon steel. Each MMB has a stepped geometrical shape, with a cylindrical bar divided into equal-length segments, along with a ’rise height’ (p) change. Four geometries were defined, i.e., R0− Smooth bar, R1− p = 0.1mm, R2− p =0.3mm and R3− p=0.5mm. Three-point flexural strength tests were performed on the RCBs to determine the maximum bond strength (ML) between the MMB and cement mortar. Images of interfacial regions were obtained using SEM and 3D Roughness Reconstruction software to calculate the average roughness (Ra) and the roughness height (Rz). The reinforcement MMB geometry had a significant impact on the ML results, particularly on the first crack strength and the failure mode. The R3 geometry ML values were higher than the other tested geometries (44.5%). The results of the scale models are encouraging and offer a novel and prospective direction for further experimental and even numerical Metamaterial research to improve interfacial bond strength.

Abstract Calcium cobaltite (CCO) thermoelectric ceramics in Ca3Co4O9 and Ca2.95Ba0.05Co4O9 compositions were produced by a simplified chemical route developed in this study. Undoped ceramics sintered at 1193 K for 12 h presented a bulk density equivalent to 77% of the theoretical density, one of the highest values ever found for conventionally sintered undoped calcium cobaltite. The presence of barium improved densification, reaching 80% of the theoretical density. Thermoelectric properties were discussed based on X-ray diffraction patterns, scanning electron micrographs, Seebeck coefficient, electrical and thermal conductivity. Electrical characterizations presented values of about 6200 and 7000 S/m at 873 K for undoped and doped ceramics, respectively. However, all ceramics presented almost the same range of activation energy values, indicating the possibility of non-effective substitution through this methodology. The maximum global PF (power factor) was 0.10 mW.m-1.K-2 for the densest undoped sample and an overall ZT (dimensionless figure of merit) of 0.07 for the undoped ceramic at 873 K.

É conhecido que os mecanismos de aquecimento e os pós precursores definem as características microestruturais das cerâmicas. Especialmente, o crescimento anormal de cerâmicas de alumina pura desenvolvidos durante o método de sinterização convencional sugere que esse material é um candidato potencial para ser tratado no processo de sinterização em microondas. Cerâmicas de alumina produzidas com pós comercial (A1K) e quimicamente sintetizado foram sinterizados em fornos convencional e por microondas. Dois métodos foram empregados para preparar quimicamente os pós nanométricos: método de Pechini e por emulsificação em ácido oleico. As cerâmicas sinterizadas em microondas foram caracterizadas por densidade aparente e por microscopia eletrônica de varredura, e comparados com as amostras sinterizadas em forno convencional. Aluminas sinterizadas em microondas apresentaram uma granulometria fina, não relacionada com os pós precursores. Essa característica foi obtida para um tempo de queima menor do que o obtido em fornos resistivos. Contudo, uma alta densificação foi observada apenas em cerâmicas A1K (3,95 g/cm³) sinterizadas durante uma hora em microondas.

It is well known that the heating mechanism and powder precursor define the microstructural characteristics of ceramics. Especially abnormal grain growth of pure alumina ceramics developed during conventional sintering method suggests that this material is a potential candidate to be treated in microwave sintering process. Alumina ceramics produced with commercial (A1K) and chemically synthesized powders were sintered in conventional and microwave furnaces. Two methods were employed to prepare the chemically synthesized nanosized powders: Pechini method and emulsification with oleic acid. The microwave sintered samples were characterized by apparent density and scanning electron microscopy and compared with the samples sintered in a conventional furnace. Alumina ceramics sintered in the microwave furnace had fine grained microstructure, not related with the starting powders. This characteristic was achieved in a sintering time shorter than those produced in the conventional furnace. However, satisfactory densification was observed only to A1K ceramics (3.95 g/cm³) sintered during one hour in microwave furnace.

Cerâmicas de titanato e zirconato de chumbo dopadas com neodímio foram sinterizadas em um forno de microondas de uso doméstico modificado. Neste tipo de aquecimento, a energia eletromagnética é transferida diretamente para o material, sendo convertida em calor pelo material cerâmico, reduzindo o tempo e energia durante o processamento. Desta forma, foram produzidos corpos cerâmicos com tempo de sinterização que variou até 30 min, a 1100 e 1200 ºC. As fases foram investigadas por meio de difratometria de raios X. Corpos cerâmicos com densidade de 95% da teórica foram obtidos com tempo de sinterização de 10 min em 1100 ºC, com uma taxa de aquecimento de 400 ºC/min. Para as cerâmicas com densidade superior a 90% da teórica foram medidos os valores de constante dielétrica e fator de perda.

Ferroelectric ceramics based on lead zirconate titanate doped with neodymium were sintered using a modified microwave oven. In this process the energy is transferred directly to the material through the interaction between molecules of the material with the electromagnetic field. The microwave sintering process has an advantage to reduce the time and save energy. This type of process involves energy conversion, opposing to heat transfer. Ceramic parts were produced by thermal treatments at 1100 ºC and 1200 ºC up to 30 min. The formed crystalline phases were investigated by X-ray diffraction. Ceramic parts with densities above 95% of the theoretical density were produced in 10 min by heating at 1100 ºC, with heating rate of 400 ºC/min. Values of dielectric constant and loss factor of ceramics with density above 90%T.D. were determined.

A conformação de materiais cerâmicos por eletroforese é conhecida por ser de baixo custo e necessitar de pouca infra-estrutura para fabricação de recobrimentos e laminados cerâmicos. O método é simples, mas o principal problema é a toxicidade associada aos solventes orgânicos usualmente utilizados como meio de dispersão. Este trabalho visa obter corpos cerâmicos de alumina através do processo de eletroforese, utilizando barbotinas aquosas. Para determinar a estabilidade das barbotinas, contendo diferentes tipos de defloculantes, medidas qualitativas de viscosidade através do método de Pitot e pH foram realizadas. Estes parâmetros foram acompanhados em suspensões contendo entre 0,5 e 4,0% em massa de defloculantes como poli-acrilato de amônio (DREW), ácido para-amino benzóico (PABA) e quitosana. O maior valor de densidade a verde (37,5% da teórica) e taxa de deposição (33,2 mg/min) foi obtido para corpos cerâmicos depositados a 6,0 V/mm dispersados com DREW.

Electrophoresis forming is an economical and reliable method for the fabrication of coatings and laminate ceramics. The process is simple, but a major problem is the toxicity and environmental problem associated with the organic solvents usually employed as vehicle media. This work aims to obtain bodies of Al2O3 by electrophoretic deposition using aqueous slips. The stability of the slips was studied, as a function of the different dispersants, by qualitative measures of viscosity by the Pitot and pH method. These processing parameters were accomplished in suspensions containing between 0.5 to 4.0wt.% of dispersants as the poli(ammonium acrylate) (DREW), para-aminobenzoic acid (PABA) and quitosan. The largest value of green density, 37.5% of the theoretical density and deposition rate, 33.2 mg/min, was obtained for bodies deposited in 6.0 V/cm with DREW.