National Nuclear Energy Commission

About: National Nuclear Energy Commission is a government organization based out in Rio de Janeiro, Brazil. It is known for research contribution in the topics: Dosimetry & Laser. The organization has 3816 authors who have published 4694 publications receiving 59951 citations.

Carbonation-Related Microstructural Changesin Long-Term Durability Concrete

Abstract: This paper discusses the effects of carbonation on the microstructure of Portland cement concrete for long-term durability applications. A class C40 concrete (characteristic compression strength between 40 MPa and 44 MPa on the 28th day, according to Brazilian standard NBR 8953) was chosen for the experimental study of the carbonation effects, from which test samples were molded for accelerated test under a 100%-CO2 atmosphere after physical and mechanical characterization. It was observed that carbonation provoked a reduction of 5% to 12% of the concrete open porosity accessible to water. Flexural strength values obtained after the carbonation tests revealed a decrease of 12% and 25% in relation to the values obtained before tests on the 28th and 91st days, respectively.

Evaluation of porosity and discontinuities in zinc phosphate coating by means of voltametric anodic dissolution (VAD)

Abstract: In this study, the porosity and the presence of discontinuities, such as cracks, in zinc phosphate coatings were evaluated by the voltametric anodic dissolution (VAD) method. Zinc phosphate (PZn), zinc phosphate with niobium (PZn + Nb), and zinc phosphate with ammonium niobium oxalate (Ox) and benzotriazole (PZn + Ox + BTAH) coatings deposited on SAE 1010 carbon steel were investigated. Coating porosity was evaluated by estimating the charge densities associated with the substrate passivation process for samples with a phosphate layer and comparing the results to the charge densities for passivation of the same substrate without a coating phosphate layer. Weight loss measurements, induced coupled plasma optical emission spectroscopy (ICP-OES), and scanning electron microscopy (SEM) were also used to investigate the solubility of the phosphate layers tested. The electrolytes used were four buffer solutions with pHs of 7.0, 8.0, 10, and 12. Scanning rates of 30, 50, 100, and 150 mV s− 1 were used in the VAD tests. The porosities of the PZn, PZn + Nb, and PZn + Ox + BTAH layers were estimated by VAD to be 4.35, 1.96, and 1.37%, respectively. The lower porosities of the PZn + Nb and PZn + Ox + BTAH layers are related to their morphologies, which promote better surface coverage compared to the PZn layer.