Papers by Author: Antonio Eduardo Martinelli

Abstract: The effect of a microwave-assisted hydrothermal (MWH) treatment on the structural, thermal, and electrical properties of NiO/ZrO₂:8 mol%Y₂O₃(YSZ)/CeO₂ (60/20/20 wt.%) composite was investigated. Powders were synthesized by a hydroxide coprecipitation-impregnation technique, in which Ni and Ce oxides were coprecipitaed in a suspension containing YSZ. Simultaneous thermogravimetry and differential thermal analysis revealed that MWH treatment promotes the crystallization of coprecipitated phases. X-ray diffraction analysis was used for phase identification and the calculated lattice parameters indicated the formation of YSZ:CeO₂ solid solution during sintering. Impedance spectroscopy measurements showed that the electrical properties of the composite samples were not significantly affected by the MHW.

Abstract: External corrosion is one of the most common causes of oilwell casing failure. Hostile environments can be due to acidizing treatments. Although it is common to add corrosion inhibitors and oxygen scavengers in acidic solutions to control external casing corrosion, their real efficiency is unknown yet. Therefore, it is important to establish how aggressive to steel are the different hostile environments to help decide which acidic systems can be used. A comparative evaluation of the corrosion of steel immersed in hardened cement slurries submitted to commonly acidizing agents is suggested. The performance of Special Class Portland Cement Slurries reinforced with polished SAE 1045 steel was evaluated by electrochemical measurements as a function of time. Open circuit potential, polarization curves and electrochemical impedance spectroscopy were studied. 15.0 wt% HCl, 12.0 wt% HCl + 3.0 wt% HF (regular mud acid), 10.0 wt% HAc + 1.5 wt% HF and a simulated hardened cement slurry pore solution were used as electrolytes. The most aggressive acid solution to plain Portland hardened cement slurries was the regular mud acid. 10.0 wt% HAc + 1.5 wt% HF electrolytes were the least aggressive ones, showing open circuit potentials around +250 mV compared to -130 mV of the simulated hardened cement slurry pore solution after the first 24 hours of immersion. This behavior was observed during two months at least. Similar corrosion rates were shown between both electrolytes, around 0.01 μA.cm^-2. Total impedance values, insipient arcs and large polarization resistance capacitive arcs on the Nyquist plots, indicating passivity process, confirmed the behaviour of the system in the 10.0 wt% HAc + 1.5 wt% HF electrolyte.

Abstract: Mud acid attack of 14 lbm/gal Portland cement composites with 15 % of nonionic aqueous polyurethane was investigated. Plain Portland hardened cement slurries showed the loss of weight around 23 %. The addition of aqueous polyurethane resulted in longer durability, with reduction around 87 % on the loss of weight without influence on the compressive strength or fratographic. The mechanism is related with the decreased porosity and permeability due to the polymeric net formation on the bulk and minor quantities of Ca⁺², preferentially leached to the acidic solution. In this way, Portland-aqueous polyurethane composites are possible solutions to oil well cementing submitted to steam injection and mud acid acidizing operations.

Abstract: Tricone drill bits with hard ceramic inserts are often used in oil well drilling operations. However, the cutting action and breakdown of the rock formation produces failures on the tricone bits, which mainly are related to wear, partial or total rupture of the drill bit body or ceramic inserts, thermal shock, and corrosion. Brazing is a well established technique to joint metal-metal, ceramic-ceramic and ceramic-metal materials. Wetting phenomena plays an essential role in the production of metal/ceramic interfaces if a liquid phase is present. Stabilized zirconia with yttria and magnesia can be an interesting material for hard ceramic inserts application on drill bits when oil well or the drilling fluid has acid characteristics. In this work, silver based brazing alloys were melted onto zirconia substrates under high vacuum. The effect of oxide stabilizers and the metallized surface on the wetting behaviour were studied. Better results were found for the yttria stabilized zirconia system using AgCu with 3% Ti as filler alloy.

Abstract: One of the major current environmental concerns is the excessive or inefficient consumption of non-renewable natural resources. The construction industry is one of the largest consumers of natural raw materials, playing an important role in the degradation of the environment. Recycling and reusing are concepts that can be effectively applied in the formulation of construction materials, especially mortars. In particular, calcareous quarry can replace, at least to some extent, the cement used in the composition of bricklaying mortars. The objective of this study was to prepare and characterize mortars containing calcareous quarry. The mortars were prepared using Portland CP II F – 32 cement, CH I hydrated lime, river sand and tap water. Different concentrations of residues, ranging from 5 to 30% were used to replace the cement. Mortars with volume ratio of 1:0.5:4.5, commonly used in bricklaying structural masonry, were evaluated. The water to cement ration was set to 1.45. The residue used was fully characterized to determine their specific mass, unitary mass, particle size distribution and morphology, and composition. The mortars were characterized both in their fresh and the results compared to those obtained from a residue-free composition. The results showed that the use of calcareous quarry partially replacing the cement did not significantly affect the performance of the mortars. Compositions containing up to 30% of calcareous quarry can be classified according to NBR 13281 (ABNT, 2005) as bricklaying mortars, and can be used by the construction industry.

Abstract: The presence of fissures in the cement material of an oil well due to thermo-mechanic conditions caused by steam injection and acidizing operations, tends to commit the mechanical integrity of the annular space, resulting in the environmental contamination of the phreatic sheets and oil producing zones. However, the development of new materials for oil wells cementing has lead to several researches to achieve the optimization of this process. This work proposes the formulation of portland/polyurethane nonionic composites as a new material for oil wells cementing. The results prove the ability of the formulated composite to improve the mechanical properties when compared with portland/water cement slurry. Also, were obtained significant improvements in mass losses when acids were present.

Abstract: High-energy milling has been used for production of nano-structured WC-Co powders. During the High-Energy Milling, the powders suffer severe high-energy impacts in the process of ball-to-ball and ball-to-vial wall collisions of the grinding media. Hard metal produced from nanostructured powders have better mechanical properties after appropriate sintering process. During the milling the particles size of WC and Co can be reduced and plastic deformed. In the present work, a mixture of WC-10%Co was produced by high energy milling. The starting powders of the WC (0.87 μm - Wolfran Bergau) and Co (0.93 μm - H.C.Starck) were used to produce the hard metal. The influence of the milling time on the particle size distributions and in the lattice strain was investigated. Milling time of the 2, 10, 20, 50, 70, 100 and 150 hours were used. The powders after milling were characterized by X-ray diffraction (XRD) and Scanning Electronic Microscopy (SEM). The results show that 10 h milling were enough to reduce the crystallite size of WC and the increase of the milling time reduces the crystallite size.

Abstract: Sewage sludge consists of a solid mixture of biological and mineral origin. It is the main byproduct of Effluent Treatment Stations. Its final draining has been a relevant environmental problem in several countries. In Brazil, due to the growth of the urban population and the requirements of environmental agencies, efficient ways for sludge disposal or effluent treatment have been investigated. Possible discarding solutions include incineration, pelletization, energy production and addition to fertilizers. This work focuses on the use of sludge in the ceramic industry for the production of light ceramic blocks, since this residue is basically composed of organic substances which volatilize during high temperature sintering. Mixtures containing different contents residue and clayed materials were prepared. For each mixture, after processing, the physical and mechanical properties of the burned pieces were measured, with emphasis on water absorption and linear shrinkage tests carried out as a function of the sintering temperature. Gresification diagrams were plotted for the temperature range of 850 °C to 1150 °C. The addition of the residue provided an increase in the porosity of the material. Light blocks were sintered and presented adequate mechanical resistance for application as building material.

Abstract: Transition-metal spinels are efficient catalysts in a number of heterogeneous processes, such as CO oxidation, catalytic combustion of hydrocarbons and oxychlorination of methane. The properties of catalytic materials are highly dependent on the synthesis route. Spinels are often produced at high temperatures by the calcination of precursors such as powder mixtures, slurries or resins. Combustion synthesis is a cost-efficient method used to produce homogeneous and fine particles with high reproducibility. Cu0.8Ni0.2Cr2O4 spinel was obtained by the combustion of metallic nitrates using urea as fuel. The resulting powders were calcinated at different temperatures and characterized by thermogravimetric and particle size analyses, X ray diffraction, and scanning electron microscopy. The effect of urea on the control of the process and particle morphology was investigated. The results revealed the formation of porous powders with increasing crystallinity as the calcination temperature increased. Crystallization of spinel started at 700 oC.

Abstract: Geopolymers are inorganic materials with ceramic characteristics that can be synthesized at room temperature from the setting of slurries. Their structure consists of aluminosilicate units that polymerize in alkaline environment. The setting rate and mechanical behavior of geopolymers strongly depends on the SiO2:Al2O3 molar ratio, polymeric precursor and polymerization cation. The present work reports the synthesis and characterization of 3.5:1 (SiO2:Al2O3) structural geopolymers prepared using either metakaolin (GPMK) or kaolin (GPK) as geopolymeric precursor in potassium hydroxide solution. GPMK depicted quick setting whereas GPK set only after 4 hours. The rheological characterization of the slurries revealed that plastic viscosity and yield point of GPK were 0.40 Pa.s and 14.2 Pa, respectively, whereas GPMK set instantly. The compressive strength of both geopolymers were measured after 24 hours and resulted in similar results, i.e., 4.6 MPa for GPMK and 4.4 MPa for GPK. The strength of both geopolymers was compatible to values typical of structural materials.