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Search Results: 1 - 10 of 327507 matches for " Pandolfelli V. C. "
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Bauxitas refratárias: composi??o química, fases e propriedades - parte II
Pascoal, C.;Pandolfelli, V. C.;
Ceramica , 2000, DOI: 10.1590/S0366-69132000000300003
Abstract: bauxite shows a wide range of applications, according to its chemical and mineralogical composition. in the refractory industry, this raw material has partially or totally substituted fused alumina in bricks and castables, due to its high refractoriness and low cost. the major producers of refractory grade bauxite are, in this order, china, guyana and brazil. although brazil is one of the major suppliers of this raw material, very few studies have been carried out to understand its chemical, mineralogical and high-temperature properties. these papers present a review regarding the applications of south american and chinese refractory grade bauxites, including the microchemistry of their crystalline phases and their hot properties. this second part will focus mechanical properties at high temperatures, and a common problem in refractory bauxites, the secondary thermal expansion.
Bauxitas refratárias: composi??o química, fases e propriedades - Parte I
Pascoal, C.;Pandolfelli, V. C.;
Ceramica , 2000, DOI: 10.1590/S0366-69132000000200005
Abstract: bauxite shows a wide range of applications, according to its chemical and mineralogical composition. in the refractory industry, this raw material has partially or totally substituted fused alumina in bricks and castables, due to its high refractoriness and low cost. the major producers of refractory grade bauxite are, in this order, china, guyana and brazil. although brazil is one of the major suppliers of this raw material, very few studies have been carried out to understand its chemical, mineralogical and high-temperature properties. these papers present a review regarding the applications of south american and chinese refractory grade bauxites, including the microchemistry of their crystalline phases and their hot properties. this first part will focus the applications of this raw material, the changes that occur during calcination of the crude mineral, and the formation of the crystalline phases.
Bauxitas refratárias: composi o química, fases e propriedades - Parte I
Pascoal C.,Pandolfelli V. C.
Ceramica , 2000,
Abstract: A bauxita apresenta uma ampla faixa de aplica es industriais, de acordo com sua composi o química e mineralógica. No setor de refratários, esta matéria-prima tem adquirido grande importancia, uma vez que pode substituir parcial ou totalmente agregados de alumina eletrofundida em formados e monolíticos, devido a sua alta refratariedade e custo inferior. Entre os maiores produtores mundiais encontram-se a China, a Guiana e o Brasil. Embora seja um dos maiores produtores mundiais de bauxita refratária, no Brasil pouco se conhece de suas características químicas e mineralógicas, bem como suas propriedades em servi o a altas temperaturas. Esta seqüência de artigos apresenta uma revis o sobre as aplica es, fases cristalinas, características e propriedades a alta temperatura de bauxitas refratárias chinesas e sul-americanas. Nesta primeira parte ser o consideradas as aplica es da matéria-prima, as transforma es que ocorrem durante a calcina o das bauxitas e a forma o de fases cristalinas.
Bauxitas refratárias: composi o química, fases e propriedades - parte II
Pascoal C.,Pandolfelli V. C.
Ceramica , 2000,
Abstract: A bauxita apresenta uma ampla faixa de aplica es industriais, de acordo com sua composi o química e mineralógica. No setor de refratários, esta matéria-prima tem adquirido grande importancia, uma vez que pode substituir parcial ou totalmente agregados de alumina eletrofundida em formados e monolíticos, devido a sua alta refratariedade e custo inferior. Entre os maiores produtores mundiais encontram-se a China, a Guiana e o Brasil. Embora seja um dos maiores produtores mundiais de bauxita refratária, no Brasil pouco se conhece de suas características químicas e mineralógicas, bem como suas propriedades em servi o a altas temperaturas. Esta seqüência de artigos apresenta uma revis o sobre as aplica es, fases cristalinas, características e propriedades a alta temperatura de bauxitas refratárias chinesas e sul-americanas. Nesta segunda parte ser o consideradas suas propriedades mecanicas a alta temperatura e um problema freqüente na utiliza o de bauxitas refratárias, a expans o térmica secundária.
Características da sílica coloidal e seus efeitos em concretos refratários
Magliano, M. V. M;Pandolfelli, V. C;
Ceramica , 2010, DOI: 10.1590/S0366-69132010000200008
Abstract: the colloidal silica has been shown as a promising substitute for the aluminate cement as a binder for refractory castables. it can promote suitable mechanical strength for green bodies, reduce the explosion risk and does not develop phases with low melting point in the alumina systems. in addition, they can induce the in-situ mullite formation. nevertheless, the final properties of the castable can also depend on the colloidal suspension characteristics such as, solid concentration, surface area and stabilizing agents. this paper aims to compare the green and high temperature properties of castables using different types of colloidal silicas. the results showed that colloidal silica containing a high surface area builds up internal tensions and cracks during the drying process, which deteriorate the hot mechanical properties of the castables. besides that, they also reduce the workability and the free flow of the system. the results presented were also compared with the refractoriness of others binding systems such as aluminate cement and reactive alumina on colloidal silica containing castables.
Mulitiza??o em refratários utilizando diferentes fontes precursoras: revis?o
Magliano, M. V. M.;Pandolfelli, V. C.;
Ceramica , 2010, DOI: 10.1590/S0366-69132010000400009
Abstract: mullite is a ceramic phase currently applied in the refractory industries due to its excellent properties, high refractoriness and it is formed by the reaction of silica and alumina at elevated temperatures. in the literature, many works analyze its synthesis and reactions, as well as the in-situ formation or addition as pre-reacted powder. this review gathers the main works involving mullite synthesis, focusing on the mullitization kinetics, such as the formation of a metastable liquid phase. it also brings about a general view of the many different sources of silica and alumina, analyzing their characteristics and the properties of the resulting mullite. the study suggests that the use of high reactive alumina and silica favors the mullitization by reducing its formation temperature and the amount of residual liquid phase on the final product.
Sistemas ligantes para concretos refratários mulitizáveis
Magliano, M. V. M;Pandolfelli, V. C;
Ceramica , 2010, DOI: 10.1590/S0366-69132010000200003
Abstract: mullite based castables are usually applied for lining steel industries processing ladles due to their superior working performance. however, the presence of aluminate cement and sio2 can deteriorate their hot properties by the formation of eutectics and low melting point phases, which motivates the search for alternatives biding systems. in this paper, the three main binders for refractory castables (aluminate cement, hydratable alumina and colloidal silica) were added to different compositions and their green and hot properties were compared, aiming to define which one presents better performance. the results indicated the colloidal silica as a promising substitute to the aluminate cement as it favors the drying process, provides excellent hot properties, higher refractoriness and generates low residual liquid phase after sintering, when compared to a high alumina composition.
Obten??o e propriedades de ceramicas porosas pela técnica de incorpora??o de espuma
Romano, R. C. O.;Pandolfelli, V. C.;
Ceramica , 2006, DOI: 10.1590/S0366-69132006000200015
Abstract: porous ceramics materials, usually, associate low thermal conductivity, high superficial area, high permeability and high resistance to chemical corrosion. these are interesting features for refractory applications such as filters for high temperatures or thermal insulating purposes. several techniques have been reported to obtain porous ceramics: organic particle burn-out, replica technique and gelcasting of ceramic foams. however, these processing routes generally result heterogeneous materials with a broad of pore size distribution. therefore, in this work a novel technique is used in order to produce porous ceramics, where a stable foam, prepared independently, is mixed to a al2o3 suspension, producing materials with high porosity and homogeneous microstructure (narrow pores distribuition). besides that, their mechanical strength and weibull's modulus are presented and the results showed promissing perspectives for this developed technique.
Determina??o de fase vítrea em bauxitas refratárias
Pascoal, C.;Machado, R.;Pandolfelli, V. C.;
Ceramica , 2002, DOI: 10.1590/S0366-69132002000200004
Abstract: the refractoriness and thermal shock resistance of any material is deeply related to the crystalline and amorphous phases present. in 1969, h. m. rietveld developed a software that provides the complete characterization of single or multiphase materials. for nearly thirty years, since it was developed, the rietveld method has not been extensively used in quantitative analysis of natural raw material. this study has the objective to use this methodology along with other ones, in order to quantify the amorphous phase in refractory bauxites, considering its facilities and drawbacks. four techniques were chosen to determine the vitreous phase in refractories raw materials, using the rietveld method as theoretical basis. the fifth technique, named chemical dissolution in fluorydric acid, was used as a comparison method. the results illustrated that, despite the efforts, none of the techniques studied can be applied as a fast and reliable method to determine the amorphous content in refractories.
Fibras metálicas e sua influência no comportamento mecanico de concretos refratários durante a secagem
Peret, C. M.;Pandolfelli, V. C.;
Ceramica , 2005, DOI: 10.1590/S0366-69132005000100002
Abstract: the addition of fibers to refractory castables can improve their dry-out behavior by two main mechanisms: permeability increase or mechanical reinforcement. steel fibers present a great potential as reinforcement, because their tensile strength and modulus of elasticity are maintained even at high temperatures. in this work, the mechanical behavior and the resistance to spalling on the drying of a refractory castable containing short and long steel fibers (from 2 to 25 mm long) were evaluated, and compared to the behavior of the same castable with polyaramid (par) fibers. the steel fibers improved the work-of-fracture but were not efficient in avoiding damage upon drying. their volume, about one thousand times that of the polymeric fibers, results in a lower number of fibers per unit volume of the castable. therefore, localized stress fields in the matrix cannot have full benefit from the reinforcement provided by these fibers. the results attested the need of taking into account the magnitude of the expected stress fields in order to define the size and shape of the reinforcement particles that will lead to an optimum performance.
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