Carlos Alberto Caldas de Souza

Effect of thermal aging conditions on the corrosion properties and hardness of a duplex stainless steel

The corrosion properties of a 22.5 wt. (%) Cr duplex stainless steel were investigated after long-term aging of 3000, 5000 and 7000 hours at 300 and 400 oC. The corrosion resistance was measured based on mass loss in a FeCl3 10 wt. (%) solution and electrochemical measurements in a 0.1 M H2SO4 solution. The results indicate that the corrosion resistance decreased steadily up to 5000 hours of aging. However, the samples subjected to 7000 hours of aging showed better corrosion resistance than those aged for 3000 and 5000 hours. This effect is attributed to the phase transformation that occurs during aging, a finding which was confirmed by hardness, transmission electron microscopy and X-ray photoelectron spectroscopy measurements.

Stabilization of electric-arc furnace dust in concrete

Electric-arc furnace dust (EAFD) is a by-product of steel production and recycling. This fine-grained material contains high amounts of zinc and iron as well as significant amounts of potentially toxic elements such as lead, cadmium and chromium. Therefore, the treatment and stabilization of this industrial residue is necessary. Concrete is a well-known suitable environment for stabilization/solidification of materials which have leachable elements in need of fixation. The effect of the EAFD content on the mechanical and chemical performance of Portland cement concrete is investigated in this paper. The effect of the EAFD content on the setting time of cement slurry was also analyzed. The axial compressive strength of the concrete samples increases with the EAFD addition in the range of 10 to 20 wt. (%) EAFD; also the tensile strength increases with the EAFD addition. An increase in EAFD content significantly increases the setting time of the concrete. The acetic acid leaching and water solubilization tests indicate low mobility of the potentially toxic elements from the EAFD concrete composite. The results of the immersion tests show that the addition of EAFD to the concrete seems to reduce chloride penetration, which may help prevent pitting corrosion in reinforced concrete.

Corrosion resistance and glass forming ability of Fe47Co7Cr15M9Si5B15Y2 (M=Mo, Nb) amorphous alloys

In the present work the effect of substituting Mo with Nb on the glass forming ability and corrosion resistance of Fe-Co-Cr-M-Si-B-Y (M=Mo, Nb) ribbons with high corrosion resistance is investigated. The X-ray powder diffraction pattern indicates that the alloy containing both Nb and Mo presented greater glass forming ability than the alloy containing either of these elements separately. The results obtained indicate that Mo is more effective in enhancing corrosion resistance than the Nb in 4.0 M HCl solution. The alloy containing both Nb and Mo presented greater overall corrosion resistance than the alloy containing only one of these elements.

Efeito da eletrodeposição de Zinco e da liga Zinco-Níquel na corrosibilidade das armaduras de concreto armado

O presente trabalho avaliou os parâmetros de corrosao das barras de aco revestidas com Zinco (Zn) e com a liga Zinco-Niquel (Zn-Ni), por eletrodeposicao, comparando-as com as tradicionalmente utilizadas, sem revestimento. Para isso, utilizaram-se amostras de concreto armado que foram submetidas a ensaios acelerados de corrosao por acao de cloretos (câmara de nevoa salina – “salt spray” e ciclos de imersao e secagem). O potencial de corrosao das armaduras foi medido para monitoramento qualitativo do processo e, apos o fim dos ensaios, estimaram-se as taxas de corrosao das barras, atraves da perda de massa, para analise quantitativa. As barras revestidas com Zn e Zn-Ni se mostraram mais resistentes a corrosao, quando comparadas com as barras convencionais, em ambientes com forte acao de cloretos e o envelhecimento por ciclos se mostrou muito mais eficiente na aceleracao do processo de corrosao.

Evaluation of the Incorporation of Waste Generated from Titanium Dioxide Manufacturing in Red Ceramics

Rotary-vacuum-filter mud (RVFM) is waste generated during the manufacturing process of titanium dioxide. In this work, RVFM and ceramic bricks containing different ratios of this waste are investigated. The mud samples were characterized using thermal analysis (TG/DTG). The aim of the present work was to determine the effect of adding RVFM on the ceramic properties of clay, such as apparent porosity, water absorption, linear shrinkage and flexural strength, used to produce red ceramics (bricks and roofing tiles). Samples were dried out at 110°C and fired at 800°C, 950°C and 1100°C. The addition of RVFM tends to increase the apparent porosity and water absorption and to decrease the flexural strength of the ceramic specimens. Based on the results, ceramic specimens with 20% RVFM content that are burned at 800oC can not be used as bricks, and ceramic specimens with 20% RVFM content that are fired at 800oC and 950°C can not used as roofing tiles, according to Brazilian standards.

Human Factors and Helicopter Accidents: An Analysis Using the Human Factors Analysis and Classification System (HFACS)

Due to their maneuverability and operational flexibility, helicopters have become an important alternative means of transport in great metropolitan areas in Brazil in the last decade. Nonetheless, the number of helicopter accidents has increased in parallel. From 2006 to 2015, 211 accidents occurred and 1030 people died. The main aim of this article is to examine the causal factors that lead to the human error in the helicopter accidents which occurred in Brazil between 2006 and 2015 using HFACS. The most frequent HFACS categories were: decision error (68%), skill-based errors (59%), violations (33%), physical environment (15%), issues with inadequate supervision (46%), and organizational processes (15%). By identifying the higher level human errors leading to helicopter accidents, HFACS is useful a tool for accident investigations and accident prevention strategies. The current study provides practical suggestions for top managers for a better helicopter operational safety environment.

Influence of Potassium Sodium Tartrate on the Corrosion Resistance of Electroplated Amorphous Fe-Cr-P Based Alloys

The effect produced by adding Cr and potassium sodium tartrate to the plating bath on the characteristics and corrosion resistance of electrodeposits of amorphous Fe-Cr-P based alloys was investigated. The presence of Cr in the Fe-Cr-P-Ni amorphous electrodeposits increases their corrosion resistance due to the formation of a passive film. The addition of tartrate to the plating bath of Fe-Cr-P-Ni amorphous alloy does not affect the formation of the amorphous structure and increases the Cr content of the deposits at 150 C/cm and 500mA/cm. However, the presence of tartrate promotes microcracking and decreases the corrosion resistance of the deposit.

Study of Corrosion Resistance of FeNbCuSiB Alloys with Mo Addition

Nanocrystalline FeCuNbSiB alloys obtained from partial crystallization of amorphous alloys have attracted technological attention due to their excellent magnetic properties. The effect of Nb addition on FeCuSiB based alloys structure is known. The effect of Nb and/or Mo addition on the structure and corrosion resistance of FeCuSiB based alloys were investigated. The addition of Mo and/or Nb decrease the crystalline grain size, increase the crystalline fraction and the corrosion resistance of FeCuSiB alloy. These effects are more effective in Nb presence than in Mo presence. However the crystalline fraction and corrosion resistance of Fe73,5Cu1Nb1,5Mo1,5Si13,5B9 nanocrystalline alloy is almost the same when compared with the Fe73,5Cu1Nb3Si13,5B9 nanocrystalline alloy.