There has been progress in the surface modification of low carbon steel in order to enhance its surface hardness. This study contributes to this by investigating the introduction of carbon nanotubes and amorphous carbon in the carburization of mild steel. In order to achieve the goal, carbon nanotubes were synthesized in a horizontal tubular reactor placed in a furnace also called the chemical vapor deposition process at a temperature of 700oC. Catalyst was produced from Iron nitrate Fe(NO3)3.9H2O and Cobalt nitrate Co(NO3)2.6H2O on CaCO3 support while acetylene C2H2 was used as the carbon source and nitrogen N2 was used as contaminant remover. The as-synthesized carbon nanotubes were purified using nitric acid HNO3 and characterized using scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA) and fourier transform infrared spectroscopy (FTIR). It was found that as-synthesized carbon nanotubes had varying lengths with diameters between 42-52 nm from the SEM and the TGA showed the as-synthesized CNTs with a mass loss of 78% while purified CNTs had 85% with no damage done to the structures after using the one step acid treatment. The as-synthesized and purified carbon nanotubes were used in carburizing low carbon steel (AISI 1018) at two austenitic temperatures of 750oC and 800oC and varying periods of 10-50 minutes while amorphous carbon obtained by pulverizing coal was also used as comparison. The mild steel samples were carburized with carbon nanotubes and amorphous carbon in a laboratory muffle furnace with a defined number of boost and diffusion steps. The carburizing atmosphere consisted of heating up to the varying temperatures at a speed of 10oC/minute, heating under this condition at varying periods, performing a defined number of boost and diffusion processes at the varying temperatures and cooling to room temperatures under the same condition. The carburized surfaces were observed with the Olympus SC50 optical microscope and the hardness distribution of the carburized layer was inspected with a Vickers FM 700 micro-hardness tester. The as-synthesized and purified CNT samples showed higher hardness on the surface of the mild steel than the amorphous carbon. In the same vein, the change in the microstructures of vi the steel samples indicated that good and improved surface hardness was obtained in this work with the reinforcements but with purified CNT having the highest peak surface hardness value of 191.64 ± 4.16 GPa at 800oC, as-synthesized CNT with 177.88 ± 2.35 GPa and amorphous carbon with 160.702 ± 5.79 GPa which are higher compared to the values obtained at 750oC and that of the original substrate which had a surface hardness of 145.188 ± 2.66 GPa. The percentage hardness obtained for the reinforcement with the amorphous carbon, the CNT and the pCNT showed an increase of 5.47%, 10.04% and 15.77% respectively at 750oC when compared to that of the normal substrate carburized without reinforcements. Furthermore, at 800oC, the reinforcement with the amorphous carbon, the CNT and the pCNT show a percentage hardness increase of 7.04%, 14.68% and 22.05% when compared to that of the normal substrate carburized without reinforcements. Comparing the reinforcement potential of the amorphous carbon, the CNT and the pCNT at 750oC, the percentage hardness reveal that using pCNT displayed an increase of 10.89% over that of amorphous carbon and of 6.37% over that of CNT. In addition, the use of CNT as reinforcement at 750oC displayed a percentage hardness increase of 4.83% over that of the amorphous carbon carburized at the same temperature / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)

Materiais odontológicos inovadores que apresentem propriedades antimicrobianas são altamente desejáveis na cavidade oral. O objetivo deste estudo foi avaliar a atividade antimicrobiana do vanadato de prata nanoestruturado (&beta;-AgVO3) incorporado em duas resinas acrílicas frente a Candida albicans, Streptococcus mutans, Staphylococcus aureus e Pseudomonas aeruginosa, além de examinar as propriedades mecânicas e o padrão de incorporação do nanomaterial nas resinas. O nanomaterial foi caracterizado por difração de raios X (DRX), espectroscopia no infravermelho por transformada de Fourier (FTIV), análise elementar por energia dispersiva (EDS) e microscopia eletrônica de varredura (MEV). As propriedades antimicrobianas das resinas acrílicas incorporadas com diferentes porcentagens de &beta;-AgVO3 foram investigadas pelo método de redução do XTT, unidades formadoras de colônias (UFC) e microscopia confocal à laser e o comportamento mecânico por meio de ensaios de dureza e rugosidade superficial, resistência à flexão, à compressão e ao impacto. O padrão de incorporação do &beta;-AgVO3 nas resinas foi analisado por microscopia eletrônica de varredura (MEV) e análise elementar por energia dispersiva (EDS). Os dados foram analisados por ANOVA, Tukey e pelo teste Generalized Linear Models (&alpha;=0,05). Para ambas as resinas, em relação ao grupo controle, a incorporação de 5% e 10% de &beta;-AgVO3 reduziram significantemente a atividade metabólica de C. albicans e P. aeruginosa (p<0,05), enquanto que para S. mutans houve redução significante apenas com a incorporação de 10% (p<0,05). Não houve diferença na atividade metabólica pelo método do XTT frente a S. aureus (p> 0,05). Para ambas as resinas, observou-se uma redução significativa no número de UFC/mL de C. albicans para o grupo incorporado com 10% de &beta;-AgVO3 e de S. mutans para os grupos com 2,5%, 5% e 10% do nanomaterial (p<0,05). Para S. aureus e P. aeruginosa, houve redução significante com a incorporação de 5% e 10% (p<0,05). A dureza superficial da resina termopolimerizável permaneceu inalterada pela incorporação do nanomaterial (p>0,05) e da autopolimerizável aumentou com 0,5% (p<0,05). Concentrações maiores que 1% promoveram redução na resistência flexural das resinas (p<0,05) enquanto que a rugosidade superficial permaneceu inalterada (p>0,05). A resistência à compressão da resina autopolimerizável permaneceu inalterada (p>0,05) e da termopolimerizável reduziu com a incorporação de 0,5% e 10% (p<0,05). As concentrações de 5% e 10% promoveram redução significante na resistência ao impacto das resinas, em relação ao controle (p<0,05). A caracterização das resinas quanto a dispersão da carga utilizada mostrou a presença de domínios de &beta;-AgVO3 ao longo da matriz polimérica seguindo um padrão circular. Conclui-se que o método proposto foi capaz de promover atividade antimicrobiana às resinas acrílicas frente aos micro-organismos avaliados, sendo a mesma dependente da concentração do nanomaterial. Porém, alterações na dispersão do &beta;-AgVO3 na matriz dos polímeros são necessárias para não sacrificar as propriedades mecânicas e para potencializar o efeito antimicrobiano / Innovative dental materials that have antimicrobial properties are highly desirable in the oral cavity. The aim of this study was to evaluate the antimicrobial activity of nanostructured silver vanadate (&beta;-AgVO3) incorporated into two acrylic resins against Candida albicans, Streptococcus mutans, Staphylococcus aureus and Pseudomonas aeruginosa, while examining the mechanical properties and the pattern of nanomaterial incorporation into resins. The nanomaterial was characterized by X-ray diffraction (XRD), infrared spectroscopy Fourier transform (FTIR), elemental analysis by energy dispersive (EDS) and scanning electron microscopy (SEM). The antimicrobial properties of acrylic resins incorporated with different percentages of &beta;-AgVO3 were investigated by the reduction of XTT method, colony forming units (CFU) and confocal laser microscopy and the mechanical behavior through hardness, surface roughness, flexural, compression and impact tests. The pattern of incorporation of &beta;-AgVO3 resins was analyzed by scanning electron microscopy (SEM) and elemental analysis by energy dispersive (EDS). Data were analyzed by ANOVA, Tukey test and the Generalized Linear Models (&alpha; = 0.05). For both resins, compared to the control group, the incorporation of 5% and 10% &beta;-AgVO3 caused a significantly reduced in the metabolic activity of C. albicans and P. aeruginosa (p <0.05), while for S. mutans significant reduction was observed only with the incorporation of 10% (p <0.05). There was no difference in metabolic activity by XTT method against S. aureus (p> 0.05). For both resins, there was a significant reduction in the number of CFU / mL for C. albicans incorporated group with 10% &beta;-AgVO3 and S. mutans in groups with 2.5%, 5% and 10% of nanomaterial (p <0.05). For P. aeruginosa and S. aureus, there was a significant decrease with the incorporation of 5% to 10% (p <0.05). The surface hardness of the heat-cured resin was unchanged by the incorporation of the nanomaterial (p <0.05) and increased self-cured with 0.5% (p <0.05). Concentrations above 1% promote the reduction in flexural strength of the resins (p <0.05) while the surface roughness remained unchanged (P> 0.05). The compressive strength of the self-cured resin remained unchanged (P> 0.05) and heat-cured reduced with the incorporation of 0.5% and 10% (p <0.05). Concentrations of 5% and 10% caused a significant reduction in impact strength of resins, compared to control (p <0.05). The characterization of the resins as the dispersion of the filler used showed the presence of &beta;-AgVO3 domains along the polymer matrix following a circular pattern. It was concluded that the proposed method was able to promote antimicrobial activity to acrylic resins against microorganisms evaluated, with the same concentration dependent of the nanomaterial. However, changes in the &beta;-AgVO3 dispersion in the polymer matrix are necessary to do not sacrifice the mechanical properties and to enhance the antimicrobial effect

There has been progress in the surface modification of low carbon steel in order to enhance its surface hardness. This study contributes to this by investigating the introduction of carbon nanotubes and amorphous carbon in the carburization of mild steel. In order to achieve the goal, carbon nanotubes were synthesized in a horizontal tubular reactor placed in a furnace also called the chemical vapor deposition process at a temperature of 700oC. Catalyst was produced from Iron nitrate Fe(NO3)3.9H2O and Cobalt nitrate Co(NO3)2.6H2O on CaCO3 support while acetylene C2H2 was used as the carbon source and nitrogen N2 was used as contaminant remover. The as-synthesized carbon nanotubes were purified using nitric acid HNO3 and characterized using scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA) and fourier transform infrared spectroscopy (FTIR). It was found that as-synthesized carbon nanotubes had varying lengths with diameters between 42-52 nm from the SEM and the TGA showed the as-synthesized CNTs with a mass loss of 78% while purified CNTs had 85% with no damage done to the structures after using the one step acid treatment. The as-synthesized and purified carbon nanotubes were used in carburizing low carbon steel (AISI 1018) at two austenitic temperatures of 750oC and 800oC and varying periods of 10-50 minutes while amorphous carbon obtained by pulverizing coal was also used as comparison. The mild steel samples were carburized with carbon nanotubes and amorphous carbon in a laboratory muffle furnace with a defined number of boost and diffusion steps. The carburizing atmosphere consisted of heating up to the varying temperatures at a speed of 10oC/minute, heating under this condition at varying periods, performing a defined number of boost and diffusion processes at the varying temperatures and cooling to room temperatures under the same condition. The carburized surfaces were observed with the Olympus SC50 optical microscope and the hardness distribution of the carburized layer was inspected with a Vickers FM 700 micro-hardness tester. The as-synthesized and purified CNT samples showed higher hardness on the surface of the mild steel than the amorphous carbon. In the same vein, the change in the microstructures of vi the steel samples indicated that good and improved surface hardness was obtained in this work with the reinforcements but with purified CNT having the highest peak surface hardness value of 191.64 ± 4.16 GPa at 800oC, as-synthesized CNT with 177.88 ± 2.35 GPa and amorphous carbon with 160.702 ± 5.79 GPa which are higher compared to the values obtained at 750oC and that of the original substrate which had a surface hardness of 145.188 ± 2.66 GPa. The percentage hardness obtained for the reinforcement with the amorphous carbon, the CNT and the pCNT showed an increase of 5.47%, 10.04% and 15.77% respectively at 750oC when compared to that of the normal substrate carburized without reinforcements. Furthermore, at 800oC, the reinforcement with the amorphous carbon, the CNT and the pCNT show a percentage hardness increase of 7.04%, 14.68% and 22.05% when compared to that of the normal substrate carburized without reinforcements. Comparing the reinforcement potential of the amorphous carbon, the CNT and the pCNT at 750oC, the percentage hardness reveal that using pCNT displayed an increase of 10.89% over that of amorphous carbon and of 6.37% over that of CNT. In addition, the use of CNT as reinforcement at 750oC displayed a percentage hardness increase of 4.83% over that of the amorphous carbon carburized at the same temperature / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)

Materiais odontológicos inovadores que apresentem propriedades antimicrobianas são altamente desejáveis na cavidade oral. O objetivo deste estudo foi avaliar a atividade antimicrobiana do vanadato de prata nanoestruturado (&beta;-AgVO3) incorporado em duas resinas acrílicas frente a Candida albicans, Streptococcus mutans, Staphylococcus aureus e Pseudomonas aeruginosa, além de examinar as propriedades mecânicas e o padrão de incorporação do nanomaterial nas resinas. O nanomaterial foi caracterizado por difração de raios X (DRX), espectroscopia no infravermelho por transformada de Fourier (FTIV), análise elementar por energia dispersiva (EDS) e microscopia eletrônica de varredura (MEV). As propriedades antimicrobianas das resinas acrílicas incorporadas com diferentes porcentagens de &beta;-AgVO3 foram investigadas pelo método de redução do XTT, unidades formadoras de colônias (UFC) e microscopia confocal à laser e o comportamento mecânico por meio de ensaios de dureza e rugosidade superficial, resistência à flexão, à compressão e ao impacto. O padrão de incorporação do &beta;-AgVO3 nas resinas foi analisado por microscopia eletrônica de varredura (MEV) e análise elementar por energia dispersiva (EDS). Os dados foram analisados por ANOVA, Tukey e pelo teste Generalized Linear Models (&alpha;=0,05). Para ambas as resinas, em relação ao grupo controle, a incorporação de 5% e 10% de &beta;-AgVO3 reduziram significantemente a atividade metabólica de C. albicans e P. aeruginosa (p<0,05), enquanto que para S. mutans houve redução significante apenas com a incorporação de 10% (p<0,05). Não houve diferença na atividade metabólica pelo método do XTT frente a S. aureus (p> 0,05). Para ambas as resinas, observou-se uma redução significativa no número de UFC/mL de C. albicans para o grupo incorporado com 10% de &beta;-AgVO3 e de S. mutans para os grupos com 2,5%, 5% e 10% do nanomaterial (p<0,05). Para S. aureus e P. aeruginosa, houve redução significante com a incorporação de 5% e 10% (p<0,05). A dureza superficial da resina termopolimerizável permaneceu inalterada pela incorporação do nanomaterial (p>0,05) e da autopolimerizável aumentou com 0,5% (p<0,05). Concentrações maiores que 1% promoveram redução na resistência flexural das resinas (p<0,05) enquanto que a rugosidade superficial permaneceu inalterada (p>0,05). A resistência à compressão da resina autopolimerizável permaneceu inalterada (p>0,05) e da termopolimerizável reduziu com a incorporação de 0,5% e 10% (p<0,05). As concentrações de 5% e 10% promoveram redução significante na resistência ao impacto das resinas, em relação ao controle (p<0,05). A caracterização das resinas quanto a dispersão da carga utilizada mostrou a presença de domínios de &beta;-AgVO3 ao longo da matriz polimérica seguindo um padrão circular. Conclui-se que o método proposto foi capaz de promover atividade antimicrobiana às resinas acrílicas frente aos micro-organismos avaliados, sendo a mesma dependente da concentração do nanomaterial. Porém, alterações na dispersão do &beta;-AgVO3 na matriz dos polímeros são necessárias para não sacrificar as propriedades mecânicas e para potencializar o efeito antimicrobiano / Innovative dental materials that have antimicrobial properties are highly desirable in the oral cavity. The aim of this study was to evaluate the antimicrobial activity of nanostructured silver vanadate (&beta;-AgVO3) incorporated into two acrylic resins against Candida albicans, Streptococcus mutans, Staphylococcus aureus and Pseudomonas aeruginosa, while examining the mechanical properties and the pattern of nanomaterial incorporation into resins. The nanomaterial was characterized by X-ray diffraction (XRD), infrared spectroscopy Fourier transform (FTIR), elemental analysis by energy dispersive (EDS) and scanning electron microscopy (SEM). The antimicrobial properties of acrylic resins incorporated with different percentages of &beta;-AgVO3 were investigated by the reduction of XTT method, colony forming units (CFU) and confocal laser microscopy and the mechanical behavior through hardness, surface roughness, flexural, compression and impact tests. The pattern of incorporation of &beta;-AgVO3 resins was analyzed by scanning electron microscopy (SEM) and elemental analysis by energy dispersive (EDS). Data were analyzed by ANOVA, Tukey test and the Generalized Linear Models (&alpha; = 0.05). For both resins, compared to the control group, the incorporation of 5% and 10% &beta;-AgVO3 caused a significantly reduced in the metabolic activity of C. albicans and P. aeruginosa (p <0.05), while for S. mutans significant reduction was observed only with the incorporation of 10% (p <0.05). There was no difference in metabolic activity by XTT method against S. aureus (p> 0.05). For both resins, there was a significant reduction in the number of CFU / mL for C. albicans incorporated group with 10% &beta;-AgVO3 and S. mutans in groups with 2.5%, 5% and 10% of nanomaterial (p <0.05). For P. aeruginosa and S. aureus, there was a significant decrease with the incorporation of 5% to 10% (p <0.05). The surface hardness of the heat-cured resin was unchanged by the incorporation of the nanomaterial (p <0.05) and increased self-cured with 0.5% (p <0.05). Concentrations above 1% promote the reduction in flexural strength of the resins (p <0.05) while the surface roughness remained unchanged (P> 0.05). The compressive strength of the self-cured resin remained unchanged (P> 0.05) and heat-cured reduced with the incorporation of 0.5% and 10% (p <0.05). Concentrations of 5% and 10% caused a significant reduction in impact strength of resins, compared to control (p <0.05). The characterization of the resins as the dispersion of the filler used showed the presence of &beta;-AgVO3 domains along the polymer matrix following a circular pattern. It was concluded that the proposed method was able to promote antimicrobial activity to acrylic resins against microorganisms evaluated, with the same concentration dependent of the nanomaterial. However, changes in the &beta;-AgVO3 dispersion in the polymer matrix are necessary to do not sacrifice the mechanical properties and to enhance the antimicrobial effect