Juliane Vicenzi

Recycling of iron foundry sand and glass waste as raw material for production of whiteware

The purpose of this study was to evaluate the production feasibility of triaxial whiteware using sand from cast iron moulds as a raw material instead of silica, and recycled glass in place of feldspar. Formulations were prepared using sand, glass waste, and white-firing clay such that only 50% of the composition was virgin material (clay). The ceramic bodies were formed by pressing and fired at different temperatures (between 1100 and 1300°C). Specimens were characterized in terms of green density prior to firing; and their flexural strength, linear shrinkage, and water absorption were measured after firing. The microstructure was determined by scanning electron microscopy. Possible environmental impacts of this recycling process were also evaluated, through solubility and leaching tests, according to Brazilian standards. Gaseous emissions during the firing process were also analysed. The results showed that it is possible to produce triaxial ceramics by using such alternative raw materials.

Protection against Erosive Wear Using Thermal Sprayed Cermet: A Review

Erosive wear is characterized by successive loss of material from the surface due to the continuous impact of solid particles. This type of wear affects numerous industries, such as power generation, mining, and the pneumatic transportation of solids. The worst case scenario normally occurs where there is a combination of both erosion and oxidation, especially at high temperatures. In order to minimize damage caused by erosive wear, many authors propose the use of better bulk materials or surface coatings, and generally cermets (ceramic carbides in metal matrices) are suggested. Various researchers have conducted experiments to study the wear mechanisms occurring in this kind of materials, but most of these experiments do not lead to similar results; in fact, there is no accordance among the authors, and moreover, some wear variables are ignored. In this book, studies undertaken in this field by several investigators have been discussed extensively. At the end of this book, table reviews are suggested to summarize the most important mechanisms of the erosive wear in bulk and coating cermets.

Influence of heating rate on the microstructure of glass foams

In the present study, glass foams made of ground soda-lime glass obtained from transparent glass bottles and dolomite were investigated. The objective of this paper was to evaluate the influence of the heating rate on the microstructure of the obtained material and on its properties. The technological characterization of the ceramic bodies involved the determination of the volumetric expansion and average diameter of the pore. The microstructure was investigated by optical microscopy and scanning electron microscopy. Experimental results showed that the heating rate influenced both the volumetric expansion and the average diameter of the pore. Lower heating rates resulted in lower volumetric expansions since more CO2 escaped from within the ceramic body.

Shear bond strength of metallic and ceramic brackets using color change adhesives

OBJECTIVE To determine the shear bond strength of orthodontic brackets using color change adhesives that are supposed to aid in removing excess of bonding material and compare them to a traditional adhesive. METHODS Ninety metallic and ninety ceramic brackets were bonded to bovine incisors using two color change adhesives and a regular one. A tensile stress was applied by a universal testing machine. The teeth were observed in a microscope after debonding in order to determine the Adhesive Remnant Index (ARI). RESULTS The statistical analysis (ANOVA, Tukey, and Kruskall-Wallis tests) demonstrated that the mean bond strength presented no difference when metallic and ceramic brackets were compared, but the bond resistance values were significantly different for the three adhesives used. The most common ARI outcome was the entire adhesive remaining on the enamel. CONCLUSIONS The bond strength was similar for metallic and ceramic brackets when the same adhesive system was used. ARI scores demonstrated that bonding with these adhesives is safe even when ceramic brackets were used. On the other hand, bond strength was too low for orthodontic purposes when Ortho Lite Cure was used.

Influência da adição de alumina na microestrutura da espuma vítrea (Effects of the alumina addition in the microstructure of foam glass)

In this work, the influence of the alumina addition on the properties of foam glass was studied. Alumina was introduced to the mixture in order to increase the refractoriness of the final product. Ceramic bodies were composed by ground soda-lime glass from transparent glass bottles, dolomitic lime and alumina. The ceramic bodies were formulated with 3 and 5 wt.% of dolomite lime, both without alumina and with 4 wt.% of this material, uniaxially pressed, and fired in the temperature range from 600 oC to 1000 oC at a heating rate of 150 K/h. The technological characterization of the ceramic bodies involved the determination of the volume expansion. The microstructure was investigated by optical microscopy and scanning electron microscopy. The experimental results show that the addition of alumina influenced the volume expansion of the ceramic bodies, decreasing the foaming.

SYNTHESIS OF WC-12wt%Co NANOCOMPOSITES BY HIGH ENERGY BALL MILLING AND THEIR MORPHOLOGICAL CHARACTERIZATION

In this work micrometric particles of WC and Co were processed by high energy ball milling in a planetary ball mill. We evaluated the phase formation and changes in microstructure of WC-12wt%Co as a result of the following milling parameters: ball-to-powder weight ratio, milling time and speed. The material was characterized by X-ray diffraction (crystalline phases and crystallite size), particle size analysis (average grain diameter), the BET method (surface area), and scanning electron microscopy (powder morphology). The average particle size (D50) and crystallite size were respectively 1.63μm and 13.8nm, for a surface area of 4.709 m2/g, using a ball-to-powder weight ratio of 1:20, a milling time of 5h and a milling speed of 500 rpm.

Influence of Inorganic Sealant in Hot and Cold Erosive Wear in Plasma Sprayed Alumina Coating

Plasma sprayed alumina coating is applied in many industrial applications in order to promote wear and corrosion resistance. Nonetheless, high porosity remained after deposition is a critical factor because it decreases the wear resistance. Some inorganic sealants can be used to reduce the open pores and superficial micro-cracks effect, improving the wear and corrosion resistance of alumina coatings. In this work, plasma sprayed alumina coating samples were divided into two groups: i) impregnated with inorganic sealant (AlPO4) and heat treated; ii) as deposited. Erosive wear tests were carried out in an erosion rig according to ASTM G76. The samples were subjected to an erodent flux, with impact angles of 30º up to 90º, at a velocity of 50m/s and temperatures of 25°C up to 400°C. The samples were characterized by SEM, Vickers microhardness, potentiodynamic anodic polarization and erosive wear rate. Results showed that erosive wear rate of alumina impregnated coating is lower than without the sealant. The sealed alumina coating presented higher mechanical properties; improved microstructural characteristics and the sealant promoted better lamellae contact, as can be observed by less sharpness in pits formation of microstructure.

Avaliação de materiais e revestimentos para o controle de incrustações do mexilhão dourado Limnoperna fortunei (Dunker, 1857)

Foram realizados experimentos objetivando selecionar materiais e revestimentos com propriedades antiincrustantes para o controle do bivalve Limnoperna fortunei no sul do Brasil, em duas localidades: no canal principal do rio Jacui, Porto Alegre, RS, e no reservatorio da UHE Ibitinga, medio rio Tiete, SP. Os materiais testados foram: aco galvanizado, aco carbono, aco cobreado e cerâmica. Os revestimentos utilizados foram tintas: basica sem oxidos; basica com oxidos em concentracao de 5% como: ZnO nanometrico, particulas de ZnO convencional, Cu2O nanometrico, particulas de Cu2O convencional; e as tintas comerciais R e antibacterias. Corpos de prova com e sem revestimento (seis replicas de cada), foram submersos na coluna d’agua dos dois locais selecionados para os experimentos, entre outubro de 2006 e fevereiro de 2007. Quanto aos materiais metalicos, o cobre metalico, o aco galvanizado e aco carbono revestido com tinta comercial R e tinta antibacterias se demonstraram promissores no controle de incrustacoes do mexilhao dourado. Quanto ao material cerâmico, o revestimento de tinta base com ZnO comercial apresentou os melhores resultados. Nos materiais com e sem revestimentos, com elevadas densidades do bivalve, foi verificado que existe uma relacao com a alta incidencia de biofilmes, corrosao do material metalico e deterioracao do revestimento.

Avaliação de revestimentos para proteção contra a descarbonetação de tijolos refratários MgO-C durante o aquecimento de panelas de aciaria

This work aims to evaluate the utilization of different coatings to prevent the decarburization of refractory bricks MgO-C used in ladles. This oxidation causes the loss of thickness of the bricks and the reduction of its useful live. The three types of coatings A, B e C were prepared in laboratory and then were applied on MgO-C bricks. The samples were tested at temperatures of 850oC, 950oC and 1050oC. It was verified that the three tested coatings only minimize the decarburization, since they vitrify and become effective at temperatures higher to the beginning of the oxidation temperature. Moreover, it was noticed that the thickness of the decarburized layer is directly proportional to the firing temperature. The coating that presented better results was C, which showed better characteristics of flowing and viscosity. Besides that, it vitrified at lower temperature comparing to coatings A and the B.

Identificação e avaliação dos mecanismos de ataque da escória SiO2-CaO-Al2O3-MgO em tijolos refratários de MgO-C

The present work has as objective to identify and to characterize the responsible mechanisms for the degradation of magnesia-carbon refractory bricks of a metallurgical ladle, due to the attack of the SiO2-CaO-Al2O3-MgO slag. For that, MgO-C refractory bricks used in the slag line were compared with bricks after the use (post mortem). The microstructure of the interfacial region refractory brick/slag was evaluated by mineralogical analyzes (X-rays diffraction), scanning electronic microscopy (SEM) and thin sections for petrography analyses (optic microscopy). It was possible to evidence that the brick post mortem presents, beyond the existing phases already in natura, new phases such as alumina, calcium silicate and gelenite, due to its reaction with the slag. The results suggest that the main way of degradation of the brick was the infiltration of the slag in the matrix and grains boundaries of the refractory brick. This causes to the pulling out of grains, compromising the original microstructure of the refractory material, diminishing its time of useful life.