Antonio Carlos Vieira Coelho | Universidade de São Paulo (original) (raw)
Papers by Antonio Carlos Vieira Coelho
LWT - Food Science and Technology, 2013
Antimicrobial activity of cinnamon and clove essential oils is widely known; however their applic... more Antimicrobial activity of cinnamon and clove essential oils is widely known; however their application to polymeric materials is already limited. Based on results of their minimum inhibitory concentration against Penicillium commune and Eurotium amstelodami, cinnamon was chosen to be incorporated into cassava starch films in order to develop an active packaging. The effect of cinnamon essential oil were evaluated on antimicrobial activity, mechanical and barrier properties of films and the results were compared with those of control films (without antimicrobial agent). ANOVA (P < 0.05) showed that the essential oil content influenced significantly the properties of the films. The release of antimicrobial agent and the microstructure of cassava films incorporated with cinnamon essential oil were also studied. Furthermore, all films, containing different amounts of essential oil, showed effective antimicrobial activity against P. commune and E. amstelodami, fungi commonly found in bread products.
Revista IBRACON de Estruturas e Materiais, 2015
In this work, comments are made about indirect methods and direct Chapelle's method applied t... more In this work, comments are made about indirect methods and direct Chapelle's method applied to the determination of the reactivity of pozzolanic materials. The Chapelle's method is based on the lime-pozzolan reaction and quantifies the pozzolanic reactivity of any material intended to be applied by the cement industry. This lime consumption determination by the pozzolan through this reaction can be made with mass proportions - lime:pozzolan 1:1, as originally proposed by Chapelle or 2:1, as specified in Brazilian and French Standards. Comparative results with both proportions are presented for sugar cane bagasse ash, rice rusk ash, silica fume, fly ash, and metakaolin, commonly studied in our country. Statistical calculations showed that for some materials of similar characteristics to the researched RHA, FA e MK at issue, essays carried out with only 1g of CaO may be underestimating the amounts of CaO consumed per gram of pozzolanic material that can be obtained. Comments w...
Cerâmica, 2009
O mineral boemita, de composição (AlO)OH, na forma sintética pode ter estruturas cristalinas deno... more O mineral boemita, de composição (AlO)OH, na forma sintética pode ter estruturas cristalinas denominadas "boemita bem-cristalizada", "pseudoboemita" e "pseudoboemita fibrilar", caracterizáveis por difração de raios X e por microscopia eletrônica de transmissão. É feita uma revisão das propriedades e das aplicações desses tipos de boemita em cerâmica, catalisadores e ab/adsorventes, enfatizando a especificidade do tipo nas diversas aplicações. É descrito um método de preparação de sóis e géis aquosos de pseudoboemita fibrilar, muito pura, usando matérias-primas nacionais: alumínio em pó e ácido acético, não precisando usar Hg2+ como "ativador" da reação. Controlando o tempo de envelhecimento térmico dos produtos da reação, obtêm-se fibrilas de comprimento médio desde 53 nm até 720 nm. O método permite também preparar sóis aquosos monofásicos e bifásicos, bem como cristais coloidais de pseudoboemita fibrilar. As fibrilas de pseudoboemita com até...
Cerâmica, 2019
Resumo No processo de beneficiamento da vermiculita é gerado um resíduo fino para o qual atualmen... more Resumo No processo de beneficiamento da vermiculita é gerado um resíduo fino para o qual atualmente ainda não foi desenvolvida uma aplicação que possibilite a utilização em larga escala. Uma alternativa que vem sendo estudada é a associação com cimento Portland em composições de argamassas e concretos, em função da composição química do resíduo: elevada quantidade de alumínio, silício e magnésio, que podem apresentar interações com o ligante. Como o objetivo deste trabalho foi avaliar unicamente o impacto do uso do resíduo nas propriedades no estado endurecido das argamassas cimentícias, as composições foram misturadas utilizando-se a mesma relação água/sólidos, independente das alterações na consistência. Os teores de substituição foram variados de 5 a 20% e as propriedades no estado endurecido foram avaliadas a partir de ensaios de Arquimedes, resistência à tração na compressão diametral, módulo de elasticidade dinâmico e permeabilidade ao ar. Os resultados indicaram que até o teo...
Anais da Academia Brasileira de Ciências, 2000
Crystalline aluminium hydroxiacetate was prepared by reaction between aluminium powder (AL-COA 12... more Crystalline aluminium hydroxiacetate was prepared by reaction between aluminium powder (AL-COA 123) and aqueous solution of acetic acid at 96 • C±1 • C. The white powder of Al(OH)(CH 3 COO) 2 is constituted by agglomerates of crystalline plates, having size about 10µm. The crystals were fired from 200 • C to 1550 • C, in oxidizing atmosphere and the products characterized by X-ray diffraction, scanning electron microscopy and surface area measurements by BET-nitrogen method. Transition aluminas are formed from heating at the following temperatures: gamma (300 • C); delta (750 • C); alpha (1050 • C). The aluminas maintain the original morphology of the Al(OH)Ac 2 crystal agglomerates, up to 1050 • C, when sintering and coalescence of the alpha-alumina crystals start and proceed up to 1550 • C. High surface area aluminas are formed in the temperature range of 700 • C to 1100 • C; the maximum value of 198m 2 /g is obtained at 900 • C, with delta-alumina structure. The formation sequence of transition aluminas is similar to the sequence from well ordered boehmite, but with differences in the transition temperatures and in the development of high surface areas. It is suggested that the causes for these diversities between the two sequences from Al(OH) Ac 2 and boehmite are due to the different particle sizes, shapes and textures of the gamma-Al 2 O 3 which acts as precursor for the sequence gamma-to alpha-Al 2 O 3 .
RILEM Technical Letters
Calcium aluminate layered double hydroxides (Ca-Al LDHs) constitute a considerable part of cement... more Calcium aluminate layered double hydroxides (Ca-Al LDHs) constitute a considerable part of cementitious waste fines. Although cementitious waste fines have proven to be recyclable by thermal treatment at moderate temperatures (400–700 °C), understanding how each phase rehydrates and contributes to the binding properties of rehydrated cementitious materials is still necessary. In this study, the de(re)hydration of katoite is investigated through in situ techniques, and its applicability as an alternative cement or supplementary cementitious material (SCM) is discussed. The research employed X-ray diffraction, isothermal calorimetry, in situ wide-angle X-ray scattering (WAXS), and rotational/oscillatory rheometry. Katoite synthesized by a mechanochemical process was dehydrated at 400 °C, producing mainly mayenite. During rehydration, calorimetry presents high heat production in the first minutes. WAXS shows prompt recovery of katoite and increasing formation of monocarboaluminate (Ca-...
Calcium aluminate layered double hydroxides (Ca-Al LDHs) constitute a considerable part of cement... more Calcium aluminate layered double hydroxides (Ca-Al LDHs) constitute a considerable part of cementitious waste fines. Although cementitious waste fines have proven to be recyclable by thermal treatment at moderate temperatures (400–700 °C), understanding how each phase rehydrates and contributes to the binding properties of rehydrated cementitious materials is still necessary. In this study, the de(re)hydration of katoite is investigated through in situ techniques, and its applicability as an alternative cement or supplementary cementitious material (SCM) is discussed. The research employed X-ray diffraction, isothermal calorimetry, in situ wide-angle X-ray scattering (WAXS), and rotational/oscillatory rheometry. Katoite synthesized by a mechanochemical process was dehydrated at 400 °C, producing mainly mayenite. During rehydration, calorimetry presents high heat production in the first minutes. WAXS shows prompt recovery of katoite and increasing formation of monocarboaluminate (Ca-...
Materials Research, 2016
In this study, results related to boehmite synthesis by hydrothermal processes starting from a Ba... more In this study, results related to boehmite synthesis by hydrothermal processes starting from a Bayer commercial gibbsite are reported. The processes have been conducted from aqueous suspensions with initial acidic or alkaline pH, without or with acetate ion, at 160 o C for 72h to 168h. The final materials were characterized by X-ray diffraction (XRD), thermal methods (DTA and TGA) and scanning electron microscopy (SEM). The influence of the synthesis conditions on the morphology of the boehmite crystals obtained from the gibbsite at different hydrothermal processes are discussed.
LWT - Food Science and Technology, 2012
In this study, glycerol content and its incorporation method on tensile and barrier properties of... more In this study, glycerol content and its incorporation method on tensile and barrier properties of biodegradable films (BF) based on cassava starch were analyzed. ANOVA showed that the glycerol incorporation method did not influence the results (P > 0.05), however the glycerol content influenced significantly the tensile and barrier properties of the films (P < 0.05). Films prepared with lower glycerol content presented better tensile and barrier properties than films with higher content. Films were then prepared with addition of clay nanoparticles and their tensile and barrier properties and glass transition temperature were measured. ANOVA indicated that both glycerol and clay nanoparticles influenced significantly the tensile and barrier properties (P < 0.05), diminishing film permeability when clay nanoparticles were present, while the glass transition temperature was not influenced (P > 0.05).
Thermochimica Acta, 2000
The hydration of a commercial Portland cement blended with calcium carbonate was studied by therm... more The hydration of a commercial Portland cement blended with calcium carbonate was studied by thermal analysis. TG, DTA and DTG analyses were performed on pastes prepared with a water to cement weight ratio of 0.5, after different setting times during the ®rst 28 days of hydration. The analyses were run from 288C to 10008C with a 108C/min heating rate and 100 ml/ min of air as the purge gas. All the analyses were performed after a drying step at 288C in the equipment itself, using the purge gas as the drying agent, resulting in a more effective and less time-consuming method than other conventional drying procedures. The original cement contains a partially decomposed dihydrated calcium sulfate, which is regenerated after 1 h of hydration and is consumed in about 16 h of setting. The results indicate that TG and DTG curves are faster and more precise tools than DTA curves to identify and to quantify all the main hydrated and carbonated phases which are present in the pastes, especially in the case of this cement blended with calcium carbonate, the total content of which cannot be estimated correctly by DTA as hydration proceeds.
Clays and Clay Minerals, 2002
... Célia R. Montes 1 , Adolpho J. Melfi 1 , Adilson Carvalho 2 ,* , Antonio C. Vieira-Coelho 3 a... more ... Célia R. Montes 1 , Adolpho J. Melfi 1 , Adilson Carvalho 2 ,* , Antonio C. Vieira-Coelho 3 and Milton LL Formoso 4 ... the number of studies already carried out (Klammer, 1971; Suszcynski, 1975; Murray and Partridge, 1982; Silva and Duarte, 1983; Coura et al., 1986; Lucas et al ...
In this study, glycerol content and its incorporation method on tensile and barrier properties of... more In this study, glycerol content and its incorporation method on tensile and barrier properties of biodegradable films (BF) based on cassava starch were analyzed. ANOVA showed that the glycerol incorporation method did not influence the results (P > 0.05), however the glycerol content influenced significantly the tensile and barrier properties of the films (P < 0.05). Films prepared with lower glycerol content presented better tensile and barrier properties than films with higher content. Films were then prepared with addition of clay nanoparticles and their tensile and barrier properties and glass transition temperature were measured. ANOVA indicated that both glycerol and clay nanoparticles influenced significantly the tensile and barrier properties (P < 0.05), diminishing film permeability when clay nanoparticles were present, while the glass transition temperature was not influenced (P > 0.05).
Química Nova, 2007
Special clays are a group of clays different from the large volume of clay mineral products named... more Special clays are a group of clays different from the large volume of clay mineral products named "Industrial Clays": kaolins, ball clays, refractory clays, bentonites, fuller's earths, common clays. Two groups of special clays exist: rare, as in the case of hectorite and sepiolite and restricted areas, as in the case of white bentonite, halloysite and palygorskite (attapulgite). A review is given of the most important producers of the special clays and their properties in the Western World, as well as a discussion of the occurrence of these types of clays in Brazil.
ABM Proceedings
Resumo Durante estudos de síntese hidrotérmica (realizada em presença de ácido acético e em autoc... more Resumo Durante estudos de síntese hidrotérmica (realizada em presença de ácido acético e em autoclave à temperatura de 160 o C) com o propósito de obter-se boemita a partir de uma gibsita comercial, observou-se uma morfologia diferenciada nos cristais de boemita obtidos: os mesmos apresentaram-se na forma de placas finas de perfil pseudohexagonal. No entanto, quando a síntese é conduzida nas mesmas condições de temperatura somente em água destilada, a morfologia da boemita formada é a de cristais cúbicos. No intuito de tentar entender o mecanismo do crescimento dos cristais de boemita na presença de íons acetato, foram realizadas novas sínteses, envolvendo o mesmo procedimento de preparação, porém variando os meios nos quais a reação ocorre. A partir de novas sínteses realizadas com acetato de potássio em meio aquoso neutro (pH=7) ou ácido (pH=2), foi observado que a presença do íon acetato no meio reacional é determinante para a obtenção da morfologia lamelar. A estrutura cristalina dos cristais obtidos foi caracterizada por DRX e a sua morfologia foi examinada por MEV. Palavras-chave:Boemita; Síntese hidrotérmica; Difração de raios-X; Microscopia eletrônica de varredura.
ABM Proceedings
Resumo A boemita é importante na preparação de catalisadores, adsorventes, revestimentos, alumina... more Resumo A boemita é importante na preparação de catalisadores, adsorventes, revestimentos, alumina e materiais derivados de alumina quando porosidade e resistência mecânica são desejadas. Sob condições hidrotérmicas foram preparadas boemitas a partir de 3 precursores diferentes: de uma gibsita comercial, e de pseudoboemita fibrilar e de monohidróxido diacetato de alumínio, ambos sintetizados em laboratório. A síntese foi realizada em autoclave mantida à temperatura de 160 o C, em diferentes tempos de envelhecimento térmico. Ao final do tempo de síntese, as dispersões foram secas ao ar, à temperatura ambiente. A diferença nos materiais sólidos de partida pode ter alguns efeitos na morfologia final do cristal de boemita, sendo esse o objetivo desse trabalho. A estrutura cristalina dos cristais obtidos foi caracterizada por DRX e a morfologia foi examinada por MEV. Palavras-chave:Boemita; Síntese hidrotérmica; Difração de raios-X; Microscopia eletrônica de varredura.
LWT - Food Science and Technology, 2013
Antimicrobial activity of cinnamon and clove essential oils is widely known; however their applic... more Antimicrobial activity of cinnamon and clove essential oils is widely known; however their application to polymeric materials is already limited. Based on results of their minimum inhibitory concentration against Penicillium commune and Eurotium amstelodami, cinnamon was chosen to be incorporated into cassava starch films in order to develop an active packaging. The effect of cinnamon essential oil were evaluated on antimicrobial activity, mechanical and barrier properties of films and the results were compared with those of control films (without antimicrobial agent). ANOVA (P < 0.05) showed that the essential oil content influenced significantly the properties of the films. The release of antimicrobial agent and the microstructure of cassava films incorporated with cinnamon essential oil were also studied. Furthermore, all films, containing different amounts of essential oil, showed effective antimicrobial activity against P. commune and E. amstelodami, fungi commonly found in bread products.
Revista IBRACON de Estruturas e Materiais, 2015
In this work, comments are made about indirect methods and direct Chapelle's method applied t... more In this work, comments are made about indirect methods and direct Chapelle's method applied to the determination of the reactivity of pozzolanic materials. The Chapelle's method is based on the lime-pozzolan reaction and quantifies the pozzolanic reactivity of any material intended to be applied by the cement industry. This lime consumption determination by the pozzolan through this reaction can be made with mass proportions - lime:pozzolan 1:1, as originally proposed by Chapelle or 2:1, as specified in Brazilian and French Standards. Comparative results with both proportions are presented for sugar cane bagasse ash, rice rusk ash, silica fume, fly ash, and metakaolin, commonly studied in our country. Statistical calculations showed that for some materials of similar characteristics to the researched RHA, FA e MK at issue, essays carried out with only 1g of CaO may be underestimating the amounts of CaO consumed per gram of pozzolanic material that can be obtained. Comments w...
Cerâmica, 2009
O mineral boemita, de composição (AlO)OH, na forma sintética pode ter estruturas cristalinas deno... more O mineral boemita, de composição (AlO)OH, na forma sintética pode ter estruturas cristalinas denominadas "boemita bem-cristalizada", "pseudoboemita" e "pseudoboemita fibrilar", caracterizáveis por difração de raios X e por microscopia eletrônica de transmissão. É feita uma revisão das propriedades e das aplicações desses tipos de boemita em cerâmica, catalisadores e ab/adsorventes, enfatizando a especificidade do tipo nas diversas aplicações. É descrito um método de preparação de sóis e géis aquosos de pseudoboemita fibrilar, muito pura, usando matérias-primas nacionais: alumínio em pó e ácido acético, não precisando usar Hg2+ como "ativador" da reação. Controlando o tempo de envelhecimento térmico dos produtos da reação, obtêm-se fibrilas de comprimento médio desde 53 nm até 720 nm. O método permite também preparar sóis aquosos monofásicos e bifásicos, bem como cristais coloidais de pseudoboemita fibrilar. As fibrilas de pseudoboemita com até...
Cerâmica, 2019
Resumo No processo de beneficiamento da vermiculita é gerado um resíduo fino para o qual atualmen... more Resumo No processo de beneficiamento da vermiculita é gerado um resíduo fino para o qual atualmente ainda não foi desenvolvida uma aplicação que possibilite a utilização em larga escala. Uma alternativa que vem sendo estudada é a associação com cimento Portland em composições de argamassas e concretos, em função da composição química do resíduo: elevada quantidade de alumínio, silício e magnésio, que podem apresentar interações com o ligante. Como o objetivo deste trabalho foi avaliar unicamente o impacto do uso do resíduo nas propriedades no estado endurecido das argamassas cimentícias, as composições foram misturadas utilizando-se a mesma relação água/sólidos, independente das alterações na consistência. Os teores de substituição foram variados de 5 a 20% e as propriedades no estado endurecido foram avaliadas a partir de ensaios de Arquimedes, resistência à tração na compressão diametral, módulo de elasticidade dinâmico e permeabilidade ao ar. Os resultados indicaram que até o teo...
Anais da Academia Brasileira de Ciências, 2000
Crystalline aluminium hydroxiacetate was prepared by reaction between aluminium powder (AL-COA 12... more Crystalline aluminium hydroxiacetate was prepared by reaction between aluminium powder (AL-COA 123) and aqueous solution of acetic acid at 96 • C±1 • C. The white powder of Al(OH)(CH 3 COO) 2 is constituted by agglomerates of crystalline plates, having size about 10µm. The crystals were fired from 200 • C to 1550 • C, in oxidizing atmosphere and the products characterized by X-ray diffraction, scanning electron microscopy and surface area measurements by BET-nitrogen method. Transition aluminas are formed from heating at the following temperatures: gamma (300 • C); delta (750 • C); alpha (1050 • C). The aluminas maintain the original morphology of the Al(OH)Ac 2 crystal agglomerates, up to 1050 • C, when sintering and coalescence of the alpha-alumina crystals start and proceed up to 1550 • C. High surface area aluminas are formed in the temperature range of 700 • C to 1100 • C; the maximum value of 198m 2 /g is obtained at 900 • C, with delta-alumina structure. The formation sequence of transition aluminas is similar to the sequence from well ordered boehmite, but with differences in the transition temperatures and in the development of high surface areas. It is suggested that the causes for these diversities between the two sequences from Al(OH) Ac 2 and boehmite are due to the different particle sizes, shapes and textures of the gamma-Al 2 O 3 which acts as precursor for the sequence gamma-to alpha-Al 2 O 3 .
RILEM Technical Letters
Calcium aluminate layered double hydroxides (Ca-Al LDHs) constitute a considerable part of cement... more Calcium aluminate layered double hydroxides (Ca-Al LDHs) constitute a considerable part of cementitious waste fines. Although cementitious waste fines have proven to be recyclable by thermal treatment at moderate temperatures (400–700 °C), understanding how each phase rehydrates and contributes to the binding properties of rehydrated cementitious materials is still necessary. In this study, the de(re)hydration of katoite is investigated through in situ techniques, and its applicability as an alternative cement or supplementary cementitious material (SCM) is discussed. The research employed X-ray diffraction, isothermal calorimetry, in situ wide-angle X-ray scattering (WAXS), and rotational/oscillatory rheometry. Katoite synthesized by a mechanochemical process was dehydrated at 400 °C, producing mainly mayenite. During rehydration, calorimetry presents high heat production in the first minutes. WAXS shows prompt recovery of katoite and increasing formation of monocarboaluminate (Ca-...
Calcium aluminate layered double hydroxides (Ca-Al LDHs) constitute a considerable part of cement... more Calcium aluminate layered double hydroxides (Ca-Al LDHs) constitute a considerable part of cementitious waste fines. Although cementitious waste fines have proven to be recyclable by thermal treatment at moderate temperatures (400–700 °C), understanding how each phase rehydrates and contributes to the binding properties of rehydrated cementitious materials is still necessary. In this study, the de(re)hydration of katoite is investigated through in situ techniques, and its applicability as an alternative cement or supplementary cementitious material (SCM) is discussed. The research employed X-ray diffraction, isothermal calorimetry, in situ wide-angle X-ray scattering (WAXS), and rotational/oscillatory rheometry. Katoite synthesized by a mechanochemical process was dehydrated at 400 °C, producing mainly mayenite. During rehydration, calorimetry presents high heat production in the first minutes. WAXS shows prompt recovery of katoite and increasing formation of monocarboaluminate (Ca-...
Materials Research, 2016
In this study, results related to boehmite synthesis by hydrothermal processes starting from a Ba... more In this study, results related to boehmite synthesis by hydrothermal processes starting from a Bayer commercial gibbsite are reported. The processes have been conducted from aqueous suspensions with initial acidic or alkaline pH, without or with acetate ion, at 160 o C for 72h to 168h. The final materials were characterized by X-ray diffraction (XRD), thermal methods (DTA and TGA) and scanning electron microscopy (SEM). The influence of the synthesis conditions on the morphology of the boehmite crystals obtained from the gibbsite at different hydrothermal processes are discussed.
LWT - Food Science and Technology, 2012
In this study, glycerol content and its incorporation method on tensile and barrier properties of... more In this study, glycerol content and its incorporation method on tensile and barrier properties of biodegradable films (BF) based on cassava starch were analyzed. ANOVA showed that the glycerol incorporation method did not influence the results (P > 0.05), however the glycerol content influenced significantly the tensile and barrier properties of the films (P < 0.05). Films prepared with lower glycerol content presented better tensile and barrier properties than films with higher content. Films were then prepared with addition of clay nanoparticles and their tensile and barrier properties and glass transition temperature were measured. ANOVA indicated that both glycerol and clay nanoparticles influenced significantly the tensile and barrier properties (P < 0.05), diminishing film permeability when clay nanoparticles were present, while the glass transition temperature was not influenced (P > 0.05).
Thermochimica Acta, 2000
The hydration of a commercial Portland cement blended with calcium carbonate was studied by therm... more The hydration of a commercial Portland cement blended with calcium carbonate was studied by thermal analysis. TG, DTA and DTG analyses were performed on pastes prepared with a water to cement weight ratio of 0.5, after different setting times during the ®rst 28 days of hydration. The analyses were run from 288C to 10008C with a 108C/min heating rate and 100 ml/ min of air as the purge gas. All the analyses were performed after a drying step at 288C in the equipment itself, using the purge gas as the drying agent, resulting in a more effective and less time-consuming method than other conventional drying procedures. The original cement contains a partially decomposed dihydrated calcium sulfate, which is regenerated after 1 h of hydration and is consumed in about 16 h of setting. The results indicate that TG and DTG curves are faster and more precise tools than DTA curves to identify and to quantify all the main hydrated and carbonated phases which are present in the pastes, especially in the case of this cement blended with calcium carbonate, the total content of which cannot be estimated correctly by DTA as hydration proceeds.
Clays and Clay Minerals, 2002
... Célia R. Montes 1 , Adolpho J. Melfi 1 , Adilson Carvalho 2 ,* , Antonio C. Vieira-Coelho 3 a... more ... Célia R. Montes 1 , Adolpho J. Melfi 1 , Adilson Carvalho 2 ,* , Antonio C. Vieira-Coelho 3 and Milton LL Formoso 4 ... the number of studies already carried out (Klammer, 1971; Suszcynski, 1975; Murray and Partridge, 1982; Silva and Duarte, 1983; Coura et al., 1986; Lucas et al ...
In this study, glycerol content and its incorporation method on tensile and barrier properties of... more In this study, glycerol content and its incorporation method on tensile and barrier properties of biodegradable films (BF) based on cassava starch were analyzed. ANOVA showed that the glycerol incorporation method did not influence the results (P > 0.05), however the glycerol content influenced significantly the tensile and barrier properties of the films (P < 0.05). Films prepared with lower glycerol content presented better tensile and barrier properties than films with higher content. Films were then prepared with addition of clay nanoparticles and their tensile and barrier properties and glass transition temperature were measured. ANOVA indicated that both glycerol and clay nanoparticles influenced significantly the tensile and barrier properties (P < 0.05), diminishing film permeability when clay nanoparticles were present, while the glass transition temperature was not influenced (P > 0.05).
Química Nova, 2007
Special clays are a group of clays different from the large volume of clay mineral products named... more Special clays are a group of clays different from the large volume of clay mineral products named "Industrial Clays": kaolins, ball clays, refractory clays, bentonites, fuller's earths, common clays. Two groups of special clays exist: rare, as in the case of hectorite and sepiolite and restricted areas, as in the case of white bentonite, halloysite and palygorskite (attapulgite). A review is given of the most important producers of the special clays and their properties in the Western World, as well as a discussion of the occurrence of these types of clays in Brazil.
ABM Proceedings
Resumo Durante estudos de síntese hidrotérmica (realizada em presença de ácido acético e em autoc... more Resumo Durante estudos de síntese hidrotérmica (realizada em presença de ácido acético e em autoclave à temperatura de 160 o C) com o propósito de obter-se boemita a partir de uma gibsita comercial, observou-se uma morfologia diferenciada nos cristais de boemita obtidos: os mesmos apresentaram-se na forma de placas finas de perfil pseudohexagonal. No entanto, quando a síntese é conduzida nas mesmas condições de temperatura somente em água destilada, a morfologia da boemita formada é a de cristais cúbicos. No intuito de tentar entender o mecanismo do crescimento dos cristais de boemita na presença de íons acetato, foram realizadas novas sínteses, envolvendo o mesmo procedimento de preparação, porém variando os meios nos quais a reação ocorre. A partir de novas sínteses realizadas com acetato de potássio em meio aquoso neutro (pH=7) ou ácido (pH=2), foi observado que a presença do íon acetato no meio reacional é determinante para a obtenção da morfologia lamelar. A estrutura cristalina dos cristais obtidos foi caracterizada por DRX e a sua morfologia foi examinada por MEV. Palavras-chave:Boemita; Síntese hidrotérmica; Difração de raios-X; Microscopia eletrônica de varredura.
ABM Proceedings
Resumo A boemita é importante na preparação de catalisadores, adsorventes, revestimentos, alumina... more Resumo A boemita é importante na preparação de catalisadores, adsorventes, revestimentos, alumina e materiais derivados de alumina quando porosidade e resistência mecânica são desejadas. Sob condições hidrotérmicas foram preparadas boemitas a partir de 3 precursores diferentes: de uma gibsita comercial, e de pseudoboemita fibrilar e de monohidróxido diacetato de alumínio, ambos sintetizados em laboratório. A síntese foi realizada em autoclave mantida à temperatura de 160 o C, em diferentes tempos de envelhecimento térmico. Ao final do tempo de síntese, as dispersões foram secas ao ar, à temperatura ambiente. A diferença nos materiais sólidos de partida pode ter alguns efeitos na morfologia final do cristal de boemita, sendo esse o objetivo desse trabalho. A estrutura cristalina dos cristais obtidos foi caracterizada por DRX e a morfologia foi examinada por MEV. Palavras-chave:Boemita; Síntese hidrotérmica; Difração de raios-X; Microscopia eletrônica de varredura.