Materials Science Forum Vols. 591-593

Abstract: It well known that the operational conditions of rotary kilns affect strongly the quality of quicklime produced. This work presents a study about parametric optimization of rotary kilns for quicklime production (CaO) from thermal decomposition of calcite limestone (CaCO3). The approach used is based on the technique of design of experiments (DOE) to identify the most significant variables which affect the quality of oxide and, in addition, to determine better conditions of production. An experimental setup in laboratory scale was build in order to carry out the experiments. Calcination temperature, calcination time, rotation speed, particle mean diameter, heat flow and air flow rate were evaluate using a fractional factorial design. The parametric optimization shows that the raise of time and temperature of calcinations produces an increase of free CaO terms. However this operation is not useful due to sintering process observed in the BET surface area results. A correlation between quicklime reactivity and specific surface area could be established, in way that reactive quicklimes presented bigger areas. Finally, it was possible to determine the best conditions of quicklime production and to estimate a quadratic model by using a central composite design and a like surface response model. It was found that the best region of operation is about 900oC and 45 minutes of calcination time.

Abstract: Slaked lime is a suspension of hydrated lime in water that can contain up to 40% of solids in suspension. The quality of the suspensions of slaked lime depends on the quality of lime used and on a careful choice of the conditions during the hydration process. A high quality slaked lime is a product with a small quantity of insoluble residues, high specific surface area, high alkaline content and small particle size. Therefore, the objective of this work was to study the best conditions of temperature and concentration to produce a superior slaked lime. A statistic analysis was performed using the experimental results in order to optimize the operational conditions of the hydration process. The use of hydration water around 74 °C, of small particles of CaO (0.144 mm) and of a CaO/H2O ratio around 220 g/L contributed to the production a slaked lime suspension of fine quality.

Abstract: Experimental results describing the pressure drop and collection efficiency of a quartz micro-fiber filter are presented in this study. The filter utilized had a porosity of 0.698 and mean fiber diameter of 1.1!m. For the tests performed, the filter was a disk with an effective diameter of 3 cm. The permeability tests of the filters were measured by varying the superficial gas velocity from 0.013 to 1.49m/s and the temperature from 26.5 to 666oC. The collection efficiency tests were accomplished for temperatures ranging from ambient to 700oC at a filtration velocity of 0.05 m/s. The test powder utilized was a phosphate rock concentrate with a density 2973 kg/m3 and average diameter of 4.6!m. The permeability test results showed that, for the same gas velocity, the pressure drop increased with the gas temperature. This dependence was reflected in the measured values of the permeability constant, k1, which increased with temperature. The experimental points were well fitted by a linear correlation. The filtration tests also showed a clear dependence between filter efficiency and test temperature: smaller filter efficiencies were obtained as the gas temperature was increased.

Abstract: The pozzolanic reactivity of a commercial metakaolin (MK) manufactured in Brazil, was evaluated in pastes prepared with a type II Portland cement, when used in cement substitution degrees from 10 to 40 mass % by thermal analysis techniques. The reactivity during the early stages of hydration was studied in real time from Non-Conventional Differential Thermal Analysis curves, normalized by the effect of the specific heats of the raw materials. The total pozzolanic reactivity after 28 days of hydration was evaluated by the calcium hydroxide consumption, calculated from thermogravimetric and derivative thermogravimetric curves of the pastes, obtained on cement oxide calcined basis. This also allows one to a more accurate determination of the uncombined and total combined water in the pastes than usual procedures. The MK pozzolanic reactivity during the early stages and after a month is proportional to the cement substitution degree in the pastes.

Abstract: The setting reaction of magnesium phosphate cements starts with water addition to a mixture of ammonium phosphate and magnesium oxide, is very fast and takes place at room temperature (cold setting). Literature shows that controversy is still going on about the reaction mechanism, hence, about the effect on the setting time of factors such as the water/cement ratio or the magnesia specific surface area. This work is focused on the magnesia powder characteristics, which were varied by calcining MgO at temperatures ranging from 900 to 1050°C, for periods of 30 to 60 min. Cement pastes were obtained by mixing MgO and diammonium phosphate with water and setting aids. The pastes were left to set in air and were characterized in terms of mineralogical composition (XRD) and microstructure (SEM). The results obtained show how the combined effect of the magnesia characteristics can be used to control the workability and adjust the setting time.

Abstract: The titanium affinity by oxygen is one of main factors that limit the application of their alloys as structural materials at high temperatures. The objective of this work was evaluating the microstructure of the of the zirconia plasma sprayed coating Ti-6Al-4V alloy in creep test. Yttria (8 wt.%) stabilized zirconia (YSZ) (Metco 204B-NS) with a CoNiCrAlY bond coat (AMDRY 995C) was atmospherically plasma sprayed on Ti-6Al-4V substrates by Sulzer Metco. Constant load creep tests were conducted with Ti-6Al-4V alloy in air and in nitrogen atmospheres in uncoated samples and in air in coated samples at stress level of 56 MPa at 700°C. The microstructural analyze show that the predominant mechanism in the test conditions was characterized by formation and coalescence of micro cavities with shape and size varieties. The cavities are corrugated in discontinue regions, like inclusions and points involving dislocation. The size and shape of dimples are governed by number and distribution of nucleated micro cavities and by stress internal level present in the material.

Abstract: In this work is done a study on the sintered microstructure of ceramic tile paste incorporated with petroleum waste. The raw materials used were kaolin, sodic feldspar, quartz and petroleum waste. The ceramic tiles containing up to 5 wt% petroleum waste were prepared by uniaxial pressing and sintered at 1200°C. The microstructural evolution was examined by SEM. In addition, water absorption, linear shrinkage, and sintered density were determined. The results showed that the microstructure of the ceramic tiles is influenced by the added petroleum waste.

Abstract: This work presents preliminary results of powder glasses with bactericide effect obtained by ionic exchange between sodium ions, present in glass composition, and silver ions, present in the ionic exchange medium. The powder glass was submitted to ionic exchange in ionic medium containing different concentration of silver species. The results showed a bactericide effect dependence on AgNO3 concentration in the ionic medium. Agar Diffusion Test on Escherichia coli bacteria, EDS analyses was applied to the samples; the results showed there is a critical concentration of silver ions incorporated in the powder glass and a limit to bactericide effect. The tests and analyses reveled that 6 wt% of AgNO3 in ionic medium was the critical concentration.

Abstract: This paper presents some of the results of an investigation on the possible applications of use of waste concrete aggregates from mixer trucks concrete productions (WCA) in concrete. The investigation has been carried out using factorial design for experimental design. For the study, the physical and mechanical properties along their durability of concrete produced with WCA were investigated and the results presented. Concrete mixtures were prepared using WCA as the replacement of natural fine aggregate at the level 10%, 20% and 30 wt.% with water/cement ratios of 0.40, 0.50 and 0.60. Properties of fresh and hardened concrete were evaluated: fresh unit weight, consistency, 7-day and 28-day compressive strength were carried out in specimens. The necessary data for establishing a mix proportion design and a quality control method are obtained using a full factorial design 32. The influence of level of WCA on the mineralogical composition has been established, and its suitability for use in a concrete application has been assessed. Empirical contour plots for the physical-mechanical properties of fresh and hardened concrete with WCA were obtained via regression analysis, which predict that as the amount of waste increases, has no or little effect on the compressive strength of concrete mixes. The results form confirmation experiments justify the prediction from the statistical approach.

Abstract: The properties of thin hard coatings and consequently their functionality are influenced by microstructural characteristics such as mechanical properties. A variety of interlayers has been used in hybrid coatings for various purposes. The paper presents investigation results of the structure, erosion and corrosion resistance, and mechanical properties of the galvanic Ni/Cr, hybrid Ni/Cr + Zr/ZrN (galvanic + PVD) and monolithic nitride coatings deposited by PVD technique (dc magnetron sputtering) onto brass (CuZn40Pb2) substrates. The ceramic PVD coatings or layers are the Cr-, Ti-, TiAl-, Zr-nitrides. The investigation covered the metallographic analysis on the scanning electron microscope, mechanical properties and erosion test. The corrosion tests were made in a 1 M NaOH solution. It was found out that PVD coatings display high corrosion resistance.