Friction stir processing (FSP) has recently become an effective microstructural modifications technique. Reported results showed that for different alloys, FSP produces very fine equiaxed and homogeneous grain structure. FSP is considered to be a new processing technique and more experimental and analytical investigations are needed to advance the industrial utilization of FSP. Most of the work that has been done in the friction stir processing field is experimental and limited modeling activities have been conducted. Attempts to develop a predictive model to correlate the resulting microstructure with process parameters are scarce. In this work, commercial 5052 Aluminum alloy sheets are friction stir processed at different rotational and translational speeds. The effects of process parameters on the resulting microstructure and mechanical properties are investigated. The results show that FSP produces very fine and homogenous grain structure, and it is observed that smaller grain size structure is obtained at lower rotational speeds. It is also observed that the hardness of the processed sheet depends strongly on the rotational and translational speeds and varies widely within the processed region. The results suggest that the temperature achieved during processing plays an important role in determining the microstructure and properties of the processed sheet. In addition, a new modeling approach based on experiments and theory is proposed to predict the grain size of the friction stir processed material as a function of process parameters. The proposed approach involves determination of the strain rate distribution in the processed (deformation) zone based on the velocity fields of the material and correlating the strain rate distribution with the average grain size of the resulting microstructure using Zener-Holloman parameter.

Thesis (M.A.)--Southern California College, 1993. / Includes bibliographical references (leaves 181-203).

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1946. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed June 14, 2010) Includes bibliographical references (p. 40) and index (p. 41).

Made available in DSpace on 2014-06-11T19:31:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-08-30Bitstream added on 2014-06-13T20:01:55Z : No. of bitstreams: 1 takeuchi_cyg_dr_arafo.pdf: 407509 bytes, checksum: 0260cea2f38a40a26f92bd996782c292 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo do presente estudo foi avaliar in vitro a microdureza, mudança de cor e presença de substâncias tóxicas após exposição à fumaça de cigarro na resina composta, dentina e esmalte dental e avaliar in situ a microdureza, rugosidade superficial e alteração de cor (?E) e luminosidade (?L) de resinas compostas frente à exposição à fumaça do cigarro associado à escovação. Para a fase in vitro foram confeccionados corpos-de-prova de resina composta (RC), esmalte (E) e dentina radicular bovina (DR) que foram planificados, polidos e expostos a fumaça de 10 cigarros/dia por 8 dias. Avaliou-se a microdureza Knoop e a alteração da cor (CIELAB) antes e depois do ato de fumar. Em seguida, as amostras foram preparadas para análise em microscopia eletrônica de varredura (MEV) e microanálise (EDS). Os dados da microdureza e da alteração de cor foram submetidos à ANOVA e Tukey (5%). A microdureza do E aumentou e da DR e RC diminuíram. Na alteração de cor a RC e o E apresentaram menor escurecimento do que a DR. Na fase in situ foram confeccionados corpos-de-prova com três tipos de resinas compostas que foram fixados em aparelho intrabucal palatino. Foram selecionados 22 voluntários, sendo 11 fumantes e 11 não-fumantes, que utilizaram o aparelho por 28 dias. A escovação dos espécimes foi realizada fora da boca, três vezes por dia somente na metade do dispositivo. Para os fumantes foi estipulado o consumo de 10 cigarros/dia. A mensuração da cor (CIELAB), da microdureza (KHN) e da rugosidade foram realizadas antes e após os 28 dias de exposição in situ. Os dados KHN foram analisados pela ANOVA e teste de Fisher's LSD. Os dados da rugosidade, ?E e o ?L foram analisados pelo método estatístico não-paramétrico Kruskal-Wallis, Wilcoxon e Friedman (p<0.05) que observaram que a fumaça de cigarro aumentou os valores... / The aim of this study was to assess in vitro the microhardness, color change and the presence of toxicant elements deriving from cigarette smoke in the composite resin, dentine and dental enamel and to evaluate in situ the microhardness, surface roughness and color change (?E) and lightness (?L) of composite resins upon cigarette smoke exposure associated with brushing. For the in vitro phase were fabricated specimens from composite resin (CR), enamel (E) and root dentin (RD) fragments that were wet ground and polished and exposed to the smoke of 10 cigarettes/day during 8 days. Knoop microhardness number (KHN) and the color was measured before and after exposure. After the samples were prepared for analysis with Scanning Electron Microscopy (SEM) and microanalysis (EDS). Data were submitted to ANOVA and Tukey's test (p<0.05). The microhardness of the E increased and the RD and CR decreased. The CR and E presented statistically significant less darkening and color change than RD. For the in situ phase were fabricated specimens three different composite resins that were attached to removable palatal appliance. Twenty-two volunteers took part in this study (11 smokers e 11 non-smokers) and received instructions to wear the appliances continuously by 28 days. For brushing of the specimens, the appliance was taken out the mouth and three times a daily was brushed. For the smokers, it was standardized consume of 10 cigarettes for day. The color changes (?E), microhardness (KHN) and surface roughness were measure before and after 28 days the exposure in situ. The microhardness data were analyzed by ANOVA and Fisher's LSD test. The roughness data, ?E and the ?L were analyzed by Kruskal-Wallis, Wilcoxon and Friedman (p<0.05). The cigarette smoke increased the microhardness and roughness values for smokers with brushing. Concluding that laboratory phase the cigarette smoke affected the... (Complete abstract click electronic access below)

Made available in DSpace on 2014-06-11T19:24:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-02-18Bitstream added on 2014-06-13T20:31:08Z : No. of bitstreams: 1 rastelli_ans_me_arafo.pdf: 843933 bytes, checksum: 3b62898b2965cd923e0392e3b0cc6a96 (MD5) / O objetivo desse trabalho foi avaliar a capacidade de polimerização, através da estrutura dental, de três diferentes fontes de luz (Halógena, Laser de Argônio e LEDs), por meio do teste de microdureza. Para isto, foram confeccionados corpos-de-prova em uma matriz metálica circular contendo um orifício na porção central com 4 mm de diâmetro e 2 mm de profundidade. Utilizou-se a resina composta microhibrida Charisma (Heraeus-Kulzer), na cor A2, para a confecção dos corpos-de-prova. Cinco corpos-de-prova foram confeccionados para cada situação diferente, perfazendo um total de 140 corpos-de-prova, distribuídos em 3 grupos da seguinte maneira: GRUPO I - fonte de luz halógena utilizada pelos tempos de exposição de 20 e 40 segundos, para as espessuras de 0 (grupo controle); 1,2 mm; 1,5 mm e 2,0 mm de faceta de estrutura dental; GRUPO II - fonte de luz de laser de argônio utilizada pelos tempos de exposição de 20 e 40 segundos, para as espessuras de 0 (grupo controle); 1,2 mm; 1,5 mm e 2,0 mm de faceta de estrutura dental e GRUPO III - fonte de luz à base de LEDs utilizada pelos tempos de 20, 40 e 60 segundos, para as espessuras de 0 (grupo controle); 1,2 mm; 1,5 mm e 2,0 mm de faceta de estrutura dental. Após a confecção dos corpos-de-prova, estes foram armazenados em estufa a 37ºC durante 24 horas. Após o período de armazenamento, procedeu-se o teste de microdureza Vickers, realizando-se 12 impressões para a superfície de topo (voltada à fonte de luz) e 12 para a superfície de base (oposta à fonte de luz). Os dados foram submetidos à Análise Estatística de Variância (P<0,05). Os valores dos desvios padrão das medidas de microdureza foram menores do que 1% da média, indicando diferença estatisticamente significante entre quase todos os grupos. Baseados nos resultados encontrados, pudemos concluir que... . / The objective of this study was evaluate the light-curing capacity, throught dental structure, of three differents light-curing device (Halogen, Argon Laser and LEDs), by microhardness testing. The specimes were made in a circular metallic mold with a of orifice in the cental portion measuring 4 mm in diameter and 2 mm in thickness. The composite resin was used the Charisma (Heraeus-Kulzer) at collor A2. Five samples was made by situation analyzed, adding up one hundred and forty samples: GROUP I - halogen light-curing device by exposure times of 20 and 40 seconds for the thickness 0 (control group); 1,2 mm; 1,5 mm and 2,0 mm of the structure dental facet; GROUP II - argon laser light-curing device by exposure times of 20 and 40 seconds for the thickness 0 (control group); 1,2 mm; 1,5 mm and 2,0 mm of the structure dental facet and GROUP III - LEDs light-curing device by exposure times of 20, 40 and 60 seconds for the thickness 0 (control group); 1,2 mm; 1,5 mm and 2,0 mm of the dental structure facet. After the polymerization procedures the specimes were stored at room temperature of 37ºC for 24 hours. After the storing, the microhardness testing was made, take effecting 12 impressions for the top surface and 12 for the botton surface. The hardness values means obtained were calculed and the statistically analised using Anova (P<0,05). According to the results, it was conclude that: 1) highest the thickness of the dental estructure face, have been a decreasing of the means values of microhardness, independent of the light-cured device utilized; 2) highest exposure times provided higher values means of the microhardness, independent of the light-cured device utilized; 3) the top surface showed the highest means values of hardness, independent of the light-cured device utilized; 4) the halogen light-cured device raised suitable... (Complete abstract, click electronic address below).

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / The aim of this study was to evaluate the effectiveness of three mechanical methods for removal of demineralized dentin. A total of thirty sound human third molars indicated for extraction. After extraction, the teeth were cleaned and stored properly. The occlusal enamel was removed with a diamond wheel to expose a flat dentin surface, and each tooth was sectioned longitudinally in the buccal-lingual direction. One half of each tooth was entirely covered with an acid-resistant varnish, except for an occlusal area of 16 mm2, and was submitted to pH-cycling model to produce demineralized dentin. The other half of each tooth was maintained with mineralized dentin. The pH-cycling procedure was taken in 8 days. Halves of teeth were reassembled with cyanoacrylate adhesive. Samples were randomly allocated into three groups according to the method of removal of demineralized dentin: G1 â steel bur, G2 â polymer bur; G3 â hand excavation. The procedure of demineralized dentin removal was performed by a single operator. Digital images were obtained and cavities depths were measured (Âm) using MacBiophotonics ImageJ software. Knoop microhardness measurements (kgf/mm2) were performed in all samples at 10 to 200 Âm depth from the bottom of cavities. Data for cavity depth and microhardness were analyzed using One-Way ANOVA and the post hoc tests (p<0.05). The steel bur provided a larger wear, resulting in a deeper depth after the removal of the demineralized dentin, followed by the hand excavator and the polymer bur had a lower depth. The hardness values obtained with the steel bur were higher, indicating that there was a higher standard of demineralized dentin removal, followed by the hand excavator. The use of polymer bur left dentin with low values of hardness, indicating that demineralized tissue still remained. The polymer bur looks to be more selective in the removal of the demineralized dentin when compared with the steel bur and the hand excavator. / O objetivo do estudo foi avaliar a efetividade de trÃs mÃtodos mecÃnicos na remoÃÃo de dentina desmineralizada. Utilizaram-se 30 terceiros molares humanos hÃgidos, indicados para extraÃÃo. ApÃs a extraÃÃo, os dentes foram devidamente limpos e armazenados. Removeu-se o esmalte oclusal com um disco de diamante para expor uma superfÃcie plana de dentina e seccionou-se cada dente longitudinalmente, no sentido vestÃbulo-lingual. Uma metade de cada dente foi totalmente coberta com um verniz Ãcido resistente, com exceÃÃo de uma Ãrea oclusal de 16 mm2, e submetida à ciclagem de pH para produzir dentina desmineralizada. A outra metade de cada dente foi mantida com a dentina mineralizada. A dentina desmineralizada foi criada por meio de procedimento de ciclagem de pH durante 8 dias. As metades dos dentes foram unidas novamente com adesivo de cianoacrilato. Alocaram-se aleatoriamente as amostras em trÃs grupos, segundo o mÃtodo de remoÃÃo da dentina desmineralizada: G1 â broca de aÃo esfÃrica; G2 â broca de polÃmero; G3 â cureta de dentina. Um Ãnico operador realizou o procedimento de remoÃÃo de dentina desmineralizada. ApÃs a remoÃÃo da dentina, as metades dos dentes foram separadas, incluÃdos em resina acrÃlica e polidas. As imagens digitais foram obtidas e as profundidades das cavidades foram medidas (Âm) com o uso do programa MacBiophotonics ImageJ. Realizaram-se medidas de dureza Knoop (kgf/mm2) em todas as amostras de 10 a 200 microns a partir do fundo das cavidades. Os dados de profundidade da cavidade e microdureza foram analisados utilizando One-Way ANOVA e os testes post hoc (p<0,05). A broca de aÃo proporcionou um maior desgaste, resultando em uma maior profundidade apÃs a remoÃÃo da dentina desmineralizada, seguida da cureta de dentina, e a broca de polÃmero teve uma menor profundidade. Os valores de dureza obtidos com o emprego da broca de aÃo foram maiores, o que indica que houve um padrÃo maior de remoÃÃo de dentina desmineralizada, seguidos dos valores da cureta de dentina, enquanto a broca de polÃmero apresentou nÃmeros menores de dureza, apontando ainda a presenÃa de tecido desmineralizado. A broca de polÃmero parece ser mais seletiva na remoÃÃo da dentina desmineralizada, quando comparada com a broca de aÃo e a cureta de dentina.

Orientador: Simonides Consani / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-13T02:07:33Z (GMT). No. of bitstreams: 1 Guiraldo_RicardoDanil_D.pdf: 566212 bytes, checksum: fb0b1aef64c61609d93e862d3667585d (MD5) Previous issue date: 2009 / Resumo: Para muitos tipos e tonalidades de resina composta, o grau de polimerização satisfatório não é alcançado através da espessura de 2 mm. A fim de tornar os objetivos do efeito da luz mais evidente, o estudo foi dividido em dois capítulos. Capítulo 1: O objetivo foi investigar a influência de diferentes cores de resinas compostas na transmissão de luz através do compósito e a diferença percentual de diminuição da dureza Knoop entre a base e o topo (PDD). Resinas compostas restauradoras (Filtek Z350 e Esthet X) foram utilizadas nas cores A1 e A3,5. A irradiância da unidade fotoativadora (LCU) foi mensurada com medidor de potência Ophir Optrônicos (780 mW/cm2). Vinte espécimes foram feitos para cada cor. Ensaios de transmissão da luz: A irradiância da luz que passou através dos compósitos foi mensurada (n=10). Ensaio de Dureza Knoop: A PDD do mesmo espécime foi calculado (n=10). Irradiância de luz que passou através do compósito cor A1 foi estatisticamente superior ao da cor A3,5 para ambos os compósitos (p=0,00001). Para Esthet X, a PDD da cor A3,5 foi estatisticamente maior do que a cor A1. Entretanto, para o Filtek Z350 não houve diferença significativa (p=0,03035). Diferentes resinas compostas influenciaram a transmissão da luz e a PDD. Cores escuras influenciaram a transmissão de luz, mas não estão necessariamente correlacionadas com a PDD. Capítulo 2: O objetivo foi investigar a influência de diferentes cores de resina composta na transmissão de luz através dos compósitos, dureza e densidade de ligação cruzada (DLC). O compósito Filtek Z250 foi utilizado nas cores A1, A3 e A3,5. A irradiância da unidade fotoativadora (LCU) foi mensurada com medidor de potência Ophir Optrônicos (900 mW/cm2). Trinta espécimes foram confeccionados para cada cor. Ensaios de transmissão da luz: a irradiância da luz que passou através dos compósitos foi mensurada (n = 10). A diferença na porcentagem de diminuição da dureza Knoop entre a base e o topo (PD) da mesma amostra foi calculada (n=10). A densidade de ligação cruzada foi calculada pelo amolecimento produzido pelo etanol, pelo decréscimo na dureza (n=10). A irradiância da luz que passou através do compósito na cor A1 foi estatisticamente superior que da cor A3, a qual também foi maior que da cor A3,5. A PDD da cor A3,5 foi estatisticamente maior que da cor A3, que também foi maior que a cor A1. Não houve diferença estatisticamente significativa na DLC. Cores escuras têm influência significativa na transmissão da luz através da resina composta e na dureza. Entretanto, a densidade de ligação cruzada não foi influenciada pelas cores mais escuras do compósito dental / Abstract: For many types and shades of resin, a high degree of cure is not achieved through a 2 mm thickness photo-activated resin composite. The study was divided into two Chapters in order to make the objectives clearer. Chapter 1: The aim was to investigate the influence of different composite resin shades on light transmission through the composite and the difference in percentage of decrease of Knoop hardness between bottom and top (PHD). Two restorative resin composites of shades A1 and A3.5 were used (Esthet X and Filtek Z350). Light curing unit (LCU) irradiance was measured with a power meter Ophir Optrônicos (780 mw/cm2). Twenty specimens were made for each color. Light transmission test: The irradiance of light that passed through the composite was measured. Knoop Hardness test: the PHD of the same specimen was calculated (n=10). Irradiance of light that passed through composite shade A1 was statistically higher than though shade A3.5 for both composite (p=0.00001). For Esthet X the PHD of shade A3.5 was statistically higher than that of shade A1 but for Filtek Z350 there was no difference (p=0.03035). Different composite resins influenced the light transmission and the PHD. Darker shades influenced the light transmission, but they are not necessarily correlated with the PHD. Chapter 2: The aim was to investigate the influence of different composite resin shades on light transmission through the composite, hardness and cross-link density (CLD). The composite Filtek Z250 was used in shades A1, A3 and A3.5. Light curing unit irradiance was measured with a power meter Ophir Optronics (900 mw/cm2). Thirty specimens were made for each shade. Light transmission test: Irradiance of light that passed through the composite was calculated (n=10). The difference in percentage of decrease of Knoop hardness between bottom and top (PHD) of the same specimen was calculated (n=10). The cross-link density was calculated by the softening effect produced by ethanol, by the decrease in hardness (n=10). Irradiance of light that passes through the composite shade A1 was statistically greater than though shade A3 that was also greater than though the shade A3.5. The PHD of shade A3.5 was statistically higher than that of shade A3, which that was also greater than that of shade A1. There was no statistically significant difference in CLD. Darker shades have a significant influence on light transmission through the dental resin composite and its hardness. However, the cross-link density was not affected by darker dental composite shades / Doutorado / Doutor em Materiais Dentários

Orientadores: Lourenço Correr Sobrinho, Carlos Jose Soares / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-19T04:51:56Z (GMT). No. of bitstreams: 1 Naves_LucasZago_D.pdf: 3401396 bytes, checksum: 30dc89e0c7e18900c68d45a72ce79505 (MD5) Previous issue date: 2011 / Resumo: O objetivo neste estudo foi avaliar as propriedades mecânicas, ópticas e de superfície da cerâmica termo-prensada IPS Empress Esthetic (Ivoclar Vivadent, Schan, Liechestein). Discos cerâmicos (12 mm x 0,9 mm) foram termo-prensados em forno específico do sistema (EP 500, Ivoclar Vivadent) e serviram como controle (TP1). Remanescentes (sprues e botões cerâmicos) do grupo controle foram reaproveitados e utilizados para a confecção de espécimes dos grupos de re-prensados (processados 2 vezes -TP2 e processados 3 vezes - TP3). Todos os processos de termo-prensagem foram realizados de acordo com as instruções dos fabricantes. A dureza Vickers (VHN) foi mensurada em durômetro HMV 2 (Shimadzu), com carga de 0,5 kgf aplicada por 10 segundos. Cinco medidas foram feitas para cada amostra (n = 5). A resistência à flexão biaxial (BFS) (ISO 6872) foi realizada para determinar a resistência dos discos prensados e re-prensados (n = 10), com velocidade de aplicação de carga de 0,5 mm/min., em máquina de ensaios mecânicos (4411; Instron Inc., Canton, MA, USA). Irradiância e características do espectro luminoso transmitido através da cerâmica (em três espessuras para cada termo-prensagem: 0,7; 1,4 e 2 mm) foram mensurados por meio de potenciômetro e espectrômetro digitais. Características de superfície foram avaliadas em microscopia eletrônica de varredura (MEV), em modo elétron secundário (SEI). Análise das micrografias foram realizadas no programa de pós-processamento de imagens ImageJ (NIH, Londres, Reino Unido), objetivando verificar a concentração cristalina da leucita e características de superfície em imagens 3D (plotagem de superfície). Os dados foram analisados estatisticamente (ANOVA + Tukey post hoc HSD, P <0,05). Os valores obtidos de dureza foram (em VHN) TP1: 589,1 ± 18,1; TP2: 551,8 ± 13,9; TP3: 552 ± 22,2 . Os grupos re-prensados (TP2, TP3) apresentaram média de dureza estatisticamente menor que o grupo controle (TP1). Os dados obtidos da resistência a flexão biaxial foram (em MPa) TP1: 219,70 ± 17,92; TP2: 180,66 ± 38,73; TP3: 171,85 ± 32,56. O grupo controle (TP1) apresentou média estatisticamente superior aos grupos re-prensados (TP2 e TP3). As micrografias mostraram aumento no tamanho e concentração de cristais de leucita, para os grupos experimentais. A análise das imagens mostrou diminuição da homogeneidade na distribuição dos cristais de leucita na fase vítrea e aumento na densidade cristalina após repetidas termo-prensagens. Redução da irradiância através dos corpos-de-prova foi detectada com o aumento da espessura da cerâmica, e alteração do perfil de emissão foi observada após repetidas termo-prensagens. O reaproveitamento do material cerâmico IPS Empress Esthetic alterou propriedades mecânicas e propriedades ópticas interferindo na passagem de luz através do corpo cerâmico. Sucessivas termo-prensagens alteraram também a microestrutura da cerâmica vítrea reforçada por leucita IPS Empress Esthetic / Abstract: The aim of this study was to evaluate the mechanical, optical and surface properties of one heat-pressed glass-ceramic material after repeated heat-pressing. One commercially available heat-pressed glass-ceramic system IPS Empress Esthetic was selected. Disc samples (12 mm x 0.9 mm) of each tested material were heat-pressed and used as control (TP1). Sprue and button parts of the pressed groups were retrieved and used for repeated heat-pressing to construct specimens of re-pressed groups (TP2 and TP3). All the heat-pressed casting procedures were performed according to the manufacturers' instructions. The Vickers hardness number (VHN) was measured with HMV 2 microhardness tester (Shimadzu), with a load of 0.5 Kgf applied for 10 seconds. Five measurements were made for each specimen (n=5). A biaxial flexural strength (BFS) test (ISO 6872) was performed to determine the strength of pressed and re-pressed glass-ceramic disc specimens (n = 10) at a crosshead speed of 0.5 mm/min. Light irradiance and spectrum characteristics transmitted through ceramic were measured using a power meter and a light spectrometer. Surface characteristics were examined with secondary electron imaging (SEI) in SEM. Post-processing image analysis were made in ImageJ (NIH, London, UK) software to access leucite crystalline density and plot surface characteristics in 3D images. The data were analysed statistically (ANOVA + Tukey's HSD post hoc test, P < 0.05). The VHN values obtained was TP1: 589.1 ± 18.1; TP2: 551.8 ± 13.9; TP3: 552 ± 22.2. The re-pressed groups (TP2, TP3) had a statistically significant lower VHN mean than the pressed control group (TP1). The BFS (MPa) values obtained was TP1:219.70 ± 17.92; TP2:180.66 ± 38.73; TP3: 171.85 ± 32.56. The pressed group (TP1) group had a statistically significant higher BFS mean than the re-pressed groups (TP2 and TP3). The SEM micrographs of the leucite-reinforced glass-ceramic material showed an increase in size and concentration of leucite crystals after repeated heat-pressing, post-processing imaging analysis showed inhomogeneity of leucite crystals distribution and increase in crystal density after repeated heat-pressing. A decrease in irradiance was detected with increasing ceramic thickness, and alteration in the emission profile was observed after repeated heat-pressing. Repeated heat-pressing treatment produced a statistically significant decresase in the mechanical properties and suggests alterations in optical properties in the evaluated IPS Empress Esthetic glass-ceramic material. Microstructural alterations was also detected / Doutorado / Materiais Dentarios / Doutor em Materiais Dentários

Sorghum and maize grain hardness is a very important criterion as grain hardness affects milling yield and product quality. There are several techniques that are used to determine grain hardness but the relationship between these techniques for distinguishing hardness in commercial sorghum and maize cultivars is not known. Moreover, the role of sorghum grain hardness with respect to malting performance is not understood, as is the role of phenolics in sorghum and maize hardness. Therefore this study investigated the relationships between sorghum and maize hardness techniques, and the influence of sorghum grain modification during malting and sorghum and maize phenolics on the hardness of these cereals. A study to determine the relationships between techniques used to measure hardness in commercial sorghum and maize cultivars was done in terms of decortication using the Tangential Abrasive Dehulling Device (TADD) (percentage kernel removed), Near Infrared Transmittance (NIT) Milling Index (MI), test weight (TW), thousand kernel weight (TKW), kernel size (KS), stress cracking (SC) and susceptibility to breakage (SB). It was found that not all grain quality techniques were related to each other. In non-tannin sorghum, TADD hardness, TW, TKW and kernel size > 3.35 mm were correlated and can be used to select for hardness. In maize, TADD hardness, NIT Milling Index and TW would be suitable for hardness evaluation. The influence of malting on sorghum hardness was monitored for a period of five days following steeping. The results showed that hardness parameters including pycnometer density, floaters, TADD hardness, TKW, Single Kernel Characterisation System-Hardness Index (SKCS-HI) reduced drastically by Day 2 of malting. TADD hardness was not correlated with Diastatic Power (DP), which could be attributed to inefficient decortication due to the softening of the grain outer layers, reduced dry matter (malting loss), loss of kernel orientation and endosperm collapse during endosperm modification. However, sorghum with high DP corresponded with low values of the measured hardness parameters. Thus, in sorghum with high DP amylases accessed the starchy endosperm faster, hence the decrease in hardness. Scanning electron microscopy (SEM) confirmed that modification was influenced by amylase activity and cultivars with low amylase modified slower than those with high amylase. Hence, amylase activity was more influential in malt hardness than original grain hardness. The phenolic acids in sorghum and maize bran and flour fractions were determined using HPLC-MS/MS. The phenolic acid content of the grain fractions was correlated with the grain hardness values. Maize bran ferulic acid content was more strongly correlated with TADD hardness but with sorghum, the relationship was weaker. Using HPLC-MS/MS, four diferulic acids were identified in sorghum and maize bran namely 8-5', 5-5', 8-O-4' and 8-5'- benzofuran form in quantities at least seven times less than ferulic acid. However, there was no correlation found between diferulic acids and hardness properties of both cereals. This study shows that TADD hardness and TW are an excellent way of estimating both sorghum and maize hardness that can be applied for cultivar evaluation. The study indicates that two days of malting would be sufficient to obtain malt suitable for milling. Ferulic acid of maize and sorghum bran seems to influence grain hardness of these cereals probably through cross-linking to arabinoxylan chains in the pericarp, hence reinforcing cell wall strength. / Thesis (PhD)--University of Pretoria, 2012. / Food Science / unrestricted

Orientador: Lourenço Correr Sobrinho / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-27T03:20:00Z (GMT). No. of bitstreams: 1 Guarda_GuilhermeBottene_D.pdf: 4899722 bytes, checksum: 60f4ee7ca07e4f49067ebdc1fbe3d374 (MD5) Previous issue date: 2015 / Resumo: O objetivo neste estudo foi avaliar a dureza Vickers, resistência à flexão biaxial, análise microestrutural e transmissão da luz da cerâmica vítrea prensada por calor após repetidas re-prensagem. Discos de cerâmica de IPS e.max Press (12,0 mm de diâmetro x 0,9 mm de espessura) foram prensadas e usadas como grupo controle (TP1). Sprues e botões cerâmicos restantes da primeira prensagem foram reaproveitados e utilizados para confecionar os grupos testes de re-prensagem (TP2 e TP3). Todos os procedimentos das termoprensagens foram feitas de acordo com as recomendações do fabricante. O teste de resistência à flexão biaxial (BFS) foi realizado para determinar a resistência dos discos cerâmica vítrea prensada (TP1) e re-prensada (TP2). Doze amostras por grupo (n=12) foram testadas, com velocidade de aplicação de carga de 0,5 mm/min., na máquina de ensaio universal (Instron). Para o teste de dureza Vickers foi realizado em um mucrodurômetro HMV 2 (Shimadzu) com carga de 500 gf por 15 segundos. Dez discos de cerâmica vítrea foram foram confeccionadas para primeira prensagem (TP1) e dez para cada reprensagem (TP2 e TP3), realizando 5 endentações por amostras. As características de superfície foram analisadas em MEV. Características de irradiancia e de espectro de luz transmitida através da cerâmica foram medidos utilizando-se um medidor de energia e um espectrômetro de luz. Os dados foram submetidos à analise de variância e teste de Tukey post-hoc (p <0,05). Os valores BFS em MPa (média e desvio-padrão) foram para TP1 (279,7 ±12,5), para TP2 (230,3 ±7,1) e para TP3 (220,8± 8,6). Os valores de TP1 foram significativamente maiores que os grupos TP2 e TP3. Os valores de dureza Vickers foram para TP1 (638,1 ±11,5), para TP2 (592,6± 6,6) e para TP3 (590,4 ±7,6). A dureza de TP1 foi significativamente maior que os grupos TP2 e TP3. As micrografias do material cerâmico em MEV mostrou aumento no tamanho e concentração dos cristais de disilicato de lítio (LeDiSi) após re-prensagem. A análise das imagens, re-prensagem mostrou homogeneidade na distribuição dos cristais de disilicato de lítio e aumento na densidade dos cristais. Redução na transmissão da luz foi detectada com aumento da espessura da cerâmica, alterações na emissão foi observada após repetidas prensagens. Conclui-se que a reutilização de material em repetidas re-prensagens diminuiu significativamente as propriedades de resistência à flexão biaxial e a dureza da cerâmica reforçada por di-silicato de lítio IPS e.max Press, alterou a microestrutura e influenciou na transmissão da luz através da cerâmica / Abstract: The aim of this study was to evaluate the Vickers hardness, biaxial flexural strength, microstructural analysis and light transmission of heat-pressed glass-ceramic material after repeated pressing. Ceramic discs of IPS e.max Press (12.0 mm in diameter x 0.9 mm thickness) were heat-pressed and used as control (HP1). Sprue and button parts of the heat-pressed material were retrieved and used for repeated heat-pressing to construct discs of two and three re-pressed groups (HP2 and HP3). All the heat-pressed casting procedures were performed according to the manufacturers' instructions. A biaxial flexural strength (BFS) test was performed to determine the strength of pressed (HP1) and re-pressed (HP2 and HP3) glass-ceramic disc specimens (n = 12) at a crosshead speed of 0.5 mm/min., in the universal testing machine (Instron). Vickers hardness test was conducted in a microhardness tester HMV-2 (Shimadzu) with a load of 500 g applied for 15 s. Ten glass-ceramic discs were made for pressed (HP1) and ten for re-pressed (HP2 and HP3) and five indentations were made for each disc. Surface characteristics were examined with SEM. Light irradiance and spectrum characteristics transmitted through ceramic were measured using a power meter and a light spectrometer. Data were submitted to ANOVA and Tukey¿s post-hoc test (p<0.05). The BFS values in MPa (mean ± standard deviation) were HP1 (279.7±12.5); HP2 (230.3±7.1) and HP3 (220.8±8.6). HP1 was significantly higher than HP2 and HP3. The VH values were HP1 (638.1±11.5); HP2 (592.6±6.6) and HP3 (590.4±7.6). HP1 was significantly higher than HP2 and HP3. In conclusion, repeated heat-pressing treatment produce a statistically significant decreased in the biaxial flexural strength and Vickers hardness of the IPS e.max Press glass-ceramic, microstructural alterations and alterations in light transmission throughout ceramic discs / Doutorado / Materiais Dentarios / Doutor em Materiais Dentários