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The cost of an aluminium extrusion die accounts for 35-50% of the total extrusion cost, hence it is important to understand the kinetics of extrusion die heat treatment. The main objective of die heat treatment is to increase the surface hardness so the surface wear property can be enhanced, which extends the die service life. Before the die material is case hardened by processes such as nitriding, the material is first heat treated to certain hardness. Thus the aim of this investigation is to understand the kinetics of carbon diffusion during steel austenitzation because it is significant to steel hardness property.H13 hot work tool steel, a well known material used as a die material for its superior mechanical and hardening properties, was used for the analysis of carbon diffusion during austenization. Samples made of H13 steel were subjected to four different atmospheric conditions: heat treatment without atmospheric control, heat treatment with stainless steel foil wrapping, pack carburization heat treatment and vacuum heat treatment. Three treatment time ranges were also applied for the carbon diffusion modelling. Some samples were further treated by gas nitriding to establish the effect of carbon content on the gas nitriding performance.It was found that decarburization occurred when atmospheric control did not take place during the heat treatment process. Through the carbon diffusion analysis, at austenitizing temperature of 1020ºC, the equilibrium surface carbon content at 1020ºC was 0.157wt%, with activation energy of carbon in H13 steel of 20,200cal/mol, and carbon diffusivity at 1020ºC was 1.97x10-8cm2/s.This study also proved that proper stainless steel foil wrapping on the heat treating material could restrict decarburization process, resulting in a constant hardness profile as vacuum heat treatment does. However the tempering characteristic between this two heat treatment methods are different to each other.For the pack carburization heat treatment, it was noted that the samples suffered from decarburization at early stage of heat treatment as carbon monoxide level was not adequate for carburization process.Results from the gas nitrided samples showed that the thickness and the hardness of the nitrided layer was independent to the carbon content in H13 steel. After 2 rounds of gas nitriding process, further nitriding seemed to have no significant effect on the hardness and thickness of the nitrided layer. Furthermore, the white layer was not observed in the nitrided samples which were heat treated without atmospheric control.

The cost of an aluminium extrusion die accounts for 35-50% of the total extrusion cost, hence it is important to understand the kinetics of extrusion die heat treatment. The main objective of die heat treatment is to increase the surface hardness so the surface wear property can be enhanced, which extends the die service life. Before the die material is case hardened by processes such as nitriding, the material is first heat treated to certain hardness. Thus the aim of this investigation is to understand the kinetics of carbon diffusion during steel austenitzation because it is significant to steel hardness property.H13 hot work tool steel, a well known material used as a die material for its superior mechanical and hardening properties, was used for the analysis of carbon diffusion during austenization. Samples made of H13 steel were subjected to four different atmospheric conditions: heat treatment without atmospheric control, heat treatment with stainless steel foil wrapping, pack carburization heat treatment and vacuum heat treatment. Three treatment time ranges were also applied for the carbon diffusion modelling. Some samples were further treated by gas nitriding to establish the effect of carbon content on the gas nitriding performance.It was found that decarburization occurred when atmospheric control did not take place during the heat treatment process. Through the carbon diffusion analysis, at austenitizing temperature of 1020ºC, the equilibrium surface carbon content at 1020ºC was 0.157wt%, with activation energy of carbon in H13 steel of 20,200cal/mol, and carbon diffusivity at 1020ºC was 1.97x10-8cm2/s.This study also proved that proper stainless steel foil wrapping on the heat treating material could restrict decarburization process, resulting in a constant hardness profile as vacuum heat treatment does. However the tempering characteristic between this two heat treatment methods are different to each other.For the pack carburization heat treatment, it was noted that the samples suffered from decarburization at early stage of heat treatment as carbon monoxide level was not adequate for carburization process.Results from the gas nitrided samples showed that the thickness and the hardness of the nitrided layer was independent to the carbon content in H13 steel. After 2 rounds of gas nitriding process, further nitriding seemed to have no significant effect on the hardness and thickness of the nitrided layer. Furthermore, the white layer was not observed in the nitrided samples which were heat treated without atmospheric control.

En este estudio se midió la microdureza Vickers del esmalte dental después de la exposición a tres bebidas industrializadas más consumidas en la ciudad de Lima y una bebida control, para evaluar el efecto erosivo de esta bebidas ácidas y su relación con la acidez titulable, el nivel de pH y el efecto buffer de las mismas. Se elaboraron 60 bloques de esmalte superficial de 2mm de espesor por 2-4mm de longitud; se colocaron en acrílico de curado rápido en moldes circunferenciales de 10mm de diámetro y 5mm de altura en diferentes colores (azul para la bebida carbonatada, anaranjado para la bebida refrescante, verde para la bebida isotónica y blanco para la bebida control; para poder diferenciarlos) los cuales se les dieron el paralelismo ente la superficie libre y la base del molde; luego se les dio un pulido tipo espejo para después ser llevados al microdurómetro Buehler donde se les midió la microdureza. Los datos obtenidos fueron analizados a través de la prueba estadística de TSTUDENT, ANALISIS DE VARIANZA ANOVA, TUKEY HSD, KRUSKAL WALLIS Y U DE MANN WHITNEY. Se concluyó que la microdureza superficial del esmalte disminuye significativamente luego de ser sometido a la acción de las bebidas ácidas estudiadas y que el efecto erosivo es inmediato y se incrementa con cada exposición. Se obtuvo como resultado que la bebida isotónica es más erosiva que las otras bebidas; y se concluyó que no hay una relación entre el efecto erosivo y los valores de pH, acidez titulable y efecto buffer las bebidas. / In this study we measured the Vickers microhardness of enamel after exposure to three industrialized beverages more consumed in the city of Lima, and a control beverage; we want to evaluate the erosive effect of the acidic beverages and their relation with the titratable acidity, the level of pH and buffer effect of this beverages. 60 blocks of surface enamel were made of 2mm thickness, and 2-4mm in length, were placed in fast curing acrylic circumferential mold of 10mm in diameter and 5mm in height, in different colors (blue for the carbonated drink, orange for the drink refreshing, green for the drink isotonic and white for the control beverage; to be differentiated); we gave them that the free surface being parallel with the base of the mold, then they were given a mirrorpolished for microhardness after that, they were being taken to Buehler where microhardness was measured. The data were analyzed by the statistical test T-STUDENT, ANALYSIS OF VARIANCE ANOVA, HSD TUKEY, YU WALLIS KRUSKAL WHITNEY MANN. It was concluded that the enamel surface microhardness decreases significantly after being subjected to the action of acidic drinks and the erosive effect is immediate and increases with each exposure. The result was that the isotonic beverage is more erosive than other drinks, and it was concluded that there is not a relationship between the erosive effect of pH values, titratable acidity and buffer effect of the beverages.

Este estudo in vitro teve como objetivo avaliar comparativamente a microdureza superficial e o desgaste de uma resina composta, FiltekTM Z-250 (3M/ESPE), sob influência de diferentes fontes de luz (LED Ultrablue IS - DMC, LED Ultralume 5 - Ultradent e halógena VIP - BISCO), com variação das densidades de potência (300, 600 e acima de 800mW/cm2) e energia (6, >8, 12, >16, 24, >32 J/cm2). Espécimes retangulares (15 x 5 x 4 mm) foram polimerizados, conforme os fatores de variação, totalizando 15 grupos (n=6). Em seguida receberam acabamento e polimento com lixas de abrasividade decrescente (300, 600, 1200 e 2000), sendo armazenados em água deionizada a 37º C por sete dias. As mensurações da microdureza Knoop foram realizadas com auxílio do Microdurômetro Shimadzu HMV-2, com carga estática de 100g por 5s nas superfícies de topo e lateral (50µm da superfície). Posteriormente os espécimes foram levados à máquina de ensaios para simulação de desgaste por escovação, utilizando-se escovas dentais macias (Oral B 30 Indicator) e creme dental (Colgate) diluído em água deionizada na proporção de 1:2 em peso. Ao final de 100.000 ciclos, a dureza da superfície lateral foi novamente mensurada e o desgaste da área escovada foi determinado por meio de perfilometria (Hommel Tester T 1000 basic - Hommelwerke). Os dados de microdureza e desgaste superficial obtidos foram submetidos à análise de variância (ANOVA) e teste de Tukey (p<0,05). Os resultados evidenciaram que a microdureza superficial da resina composta avaliada foi significantemente menor quando da fotoativação com VIP-300 mW/cm2, sendo que os maiores valores foram observados com o aparelho Ultralume 5. O desgaste superficial foi significativamente influenciado quando da utilização de baixa densidade de potência (300 mW/cm2) e energia de 6 J/cm2, tanto com o VIP como Ultrablue IS, que demonstraram maior efetividade quando da utilização de densidade de energia acima de 12J/cm2. De forma geral, observou-se correlação negativa quando da interação dos testes de dureza e desgaste superficial, ou seja, quando os valores de dureza aumentaram os de desgaste diminuíram inferindo, entretanto, que isoladamente o valor de dureza não constitui em parâmetro para qualificar o desempenho da resina composta quanto à resistência ao desgaste. / This in vitro study evaluated comparatively, the superficial microhardness and wear of a resin composite, FiltekTM Z-250 (3M/ESPE) under the influence of different light sources (LED Ultrablue IS/DMC, LED Ultralume 5/Ultradent and halogen VIP/BISCO); with power (300, 600 and above 800mW/cm2) and energy density (6, >8, 12, >16, 24, >32J/cm2) variations. Rectangular specimens (15 x 5 x 4 mm) were polymerized, as the variation factors, totalizing 15 groups (n=6). After, they were ground flat with water-cooled carborundum discs in decreasing abrasive order (300, 600, 1200 and 2000) and stored for seven days, before the tests, in deionized water at 37º C. The Knoop microhardness measurements were carried out using a microhardness tester (Shimadzu HMV-2), with a 100g static load applied for 5s on specimens\' top and lateral surfaces (50µm under surface). In sequence the specimens were taken to a machine for brushing simulation, using soft nylon bristles (Oral B 30 Indicator) and dental paste (Colgate) diluted in deionized water in the ratio of 1:2 in weight. After 100,000 cycles, the hardness of the lateral surface was again measured and the wear profile of the brushed area was determined by a profilometer (Hommel Tester T 100 basic/Hommelwerke). The microhardness and superficial wear data were submitted to the analysis of variance (ANOVA) and Tukey test (p<0.05). The results showed that the superficial microhardness of the evaluated resin composite was significantly lower when photoactivated with VIP-300 mW/cm2, being the biggest values observed for the Ultralume 5 device. The superficial wear was significantly influenced by the low power density (300 mWcm2) and energy density of 6 J/cm2. This was for both, VIP and Ultrablue IS, which demonstrated greater effectiveness when a density of energy above 12J/cm2 was used. In general, a negative correlation was observed between the two tests (wear and microhardness). In other words, there was an increase of hardness with the decrease in wear values, which demonstrates that only microhardness values do not constitute a parameter to qualify resin composite wear resistance behavior.

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xiii, 105 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 97-98).

Este estudo in vitro teve como objetivo avaliar comparativamente a microdureza superficial e o desgaste de uma resina composta, FiltekTM Z-250 (3M/ESPE), sob influência de diferentes fontes de luz (LED Ultrablue IS - DMC, LED Ultralume 5 - Ultradent e halógena VIP - BISCO), com variação das densidades de potência (300, 600 e acima de 800mW/cm2) e energia (6, >8, 12, >16, 24, >32 J/cm2). Espécimes retangulares (15 x 5 x 4 mm) foram polimerizados, conforme os fatores de variação, totalizando 15 grupos (n=6). Em seguida receberam acabamento e polimento com lixas de abrasividade decrescente (300, 600, 1200 e 2000), sendo armazenados em água deionizada a 37º C por sete dias. As mensurações da microdureza Knoop foram realizadas com auxílio do Microdurômetro Shimadzu HMV-2, com carga estática de 100g por 5s nas superfícies de topo e lateral (50µm da superfície). Posteriormente os espécimes foram levados à máquina de ensaios para simulação de desgaste por escovação, utilizando-se escovas dentais macias (Oral B 30 Indicator) e creme dental (Colgate) diluído em água deionizada na proporção de 1:2 em peso. Ao final de 100.000 ciclos, a dureza da superfície lateral foi novamente mensurada e o desgaste da área escovada foi determinado por meio de perfilometria (Hommel Tester T 1000 basic - Hommelwerke). Os dados de microdureza e desgaste superficial obtidos foram submetidos à análise de variância (ANOVA) e teste de Tukey (p<0,05). Os resultados evidenciaram que a microdureza superficial da resina composta avaliada foi significantemente menor quando da fotoativação com VIP-300 mW/cm2, sendo que os maiores valores foram observados com o aparelho Ultralume 5. O desgaste superficial foi significativamente influenciado quando da utilização de baixa densidade de potência (300 mW/cm2) e energia de 6 J/cm2, tanto com o VIP como Ultrablue IS, que demonstraram maior efetividade quando da utilização de densidade de energia acima de 12J/cm2. De forma geral, observou-se correlação negativa quando da interação dos testes de dureza e desgaste superficial, ou seja, quando os valores de dureza aumentaram os de desgaste diminuíram inferindo, entretanto, que isoladamente o valor de dureza não constitui em parâmetro para qualificar o desempenho da resina composta quanto à resistência ao desgaste. / This in vitro study evaluated comparatively, the superficial microhardness and wear of a resin composite, FiltekTM Z-250 (3M/ESPE) under the influence of different light sources (LED Ultrablue IS/DMC, LED Ultralume 5/Ultradent and halogen VIP/BISCO); with power (300, 600 and above 800mW/cm2) and energy density (6, >8, 12, >16, 24, >32J/cm2) variations. Rectangular specimens (15 x 5 x 4 mm) were polymerized, as the variation factors, totalizing 15 groups (n=6). After, they were ground flat with water-cooled carborundum discs in decreasing abrasive order (300, 600, 1200 and 2000) and stored for seven days, before the tests, in deionized water at 37º C. The Knoop microhardness measurements were carried out using a microhardness tester (Shimadzu HMV-2), with a 100g static load applied for 5s on specimens\' top and lateral surfaces (50µm under surface). In sequence the specimens were taken to a machine for brushing simulation, using soft nylon bristles (Oral B 30 Indicator) and dental paste (Colgate) diluted in deionized water in the ratio of 1:2 in weight. After 100,000 cycles, the hardness of the lateral surface was again measured and the wear profile of the brushed area was determined by a profilometer (Hommel Tester T 100 basic/Hommelwerke). The microhardness and superficial wear data were submitted to the analysis of variance (ANOVA) and Tukey test (p<0.05). The results showed that the superficial microhardness of the evaluated resin composite was significantly lower when photoactivated with VIP-300 mW/cm2, being the biggest values observed for the Ultralume 5 device. The superficial wear was significantly influenced by the low power density (300 mWcm2) and energy density of 6 J/cm2. This was for both, VIP and Ultrablue IS, which demonstrated greater effectiveness when a density of energy above 12J/cm2 was used. In general, a negative correlation was observed between the two tests (wear and microhardness). In other words, there was an increase of hardness with the decrease in wear values, which demonstrates that only microhardness values do not constitute a parameter to qualify resin composite wear resistance behavior.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: The importance of fluoride in the prevention of dental caries has been well documented in the literature, as it inhibits demineralization of the tooth structure and enhances remineralization. One of the major public health policies to prevent caries is to provide the population with an adequate amount of fluoride through community water fluoridation. Nowadays many people drink bottled water instead of tap water due to its easy access, convenience, and low cost. Besides fluoride, other minerals present in tap and bottled water, such as calcium and magnesium, are also important in decreasing dental caries prevalence. However, our knowledge of the role of bottled water in caries prevention and especially when combined with fluoride toothpaste usage is still poor. Objectives: The aim of this in-vitro study was to evaluate the effects of some bottled waters on fluoride toothpaste efficacy in enhancing caries lesion remineralization. Methodology: Early caries lesions were created in bovine enamel specimens and stratified into treatment groups based on Vickers surface microhardness (VHN). The present study followed a two (fluoride and fluoride-free toothpaste) by five (four bottled waters and tap water) factorial design. The treatment groups were bottled water with the following attributes: a) 309.9 ppm Ca/1.20 ppm F; b) 118.4 ppm Ca/0.16 ppm F; c) 1.00 ppm Ca/1.01 ppm F; d) 0.1 ppm Ca/0.04 ppm F, and tap water (48.7 ppm Ca/0.7 ppm F). The five water groups were paired either with 1100 ppm fluoride or fluoride-free toothpaste, yielding 10 groups. Specimens were pH-cycled for 10 days with the daily regimen comprised of twice daily toothpaste slurry, with four exposures to water in between. VHN was measured, again, and the difference calculated (ΔVHN). Data were analyzed using two-way ANOVA at a 5-percent significance level. Results: The two-way interaction between water and toothpaste was significant (p < 0.001). All groups except fluoride-free toothpaste/bottled water with 0.1 ppm Ca/0.04 ppm F (p = 0.411) had significant increases in VHN after pH cycling (p ≤ 0.023). Fluoridated toothpaste resulted in a higher rate of remineralization compared to fluoridefree toothpaste (all p < 0.001). Bottled water with 1.20 ppm F/309.9 ppm Ca exhibited the greatest extent of remineralization within fluoride toothpaste groups (p < 0.001) and higher remineralization than lower fluoride water in fluoride-free toothpaste groups (p ≤ 0.006). Within the fluoridated toothpaste group, tap water exhibited significantly less remineralization compared to all bottled waters (all p < 0.001). Conclusion: Within the limitation of this study, bottled water with higher fluoride and calcium concentrations might improve fluoridated toothpaste efficacy by enhancing remineralization of early enamel caries-like lesions.

Made available in DSpace on 2014-12-17T14:57:45Z (GMT). No. of bitstreams: 1 JoaoMVBSS.pdf: 1279159 bytes, checksum: ef7f747bef3ce7a51ca2e06bd484a1a5 (MD5) Previous issue date: 2006-05-31 / The hardness test is thoroughly used in research and evaluation of materials for quality control. However, this test results are subject to uncertainties caused by the process operator in the moment of the mensuration impression diagonals make by the indenter in the sample. With this mind, an automated equipment of hardness mensuration was developed. The hardness value was obtained starting from the mensuration of plastic deformation suffered by the material to a well-known load. The material deformation was calculated through the mensuration of the difference between the progress and retreat of a diamond indenter on the used sample. It was not necessary, therefore, the manual mensuration of the diagonals, decreasing the mistake source caused by the operator. Tension graphs of versus deformation could be analyzed from data obtained by the accomplished analysis, as well as you became possible a complete observation of the whole process. Following, the hardness results calculated by the experimental apparatus were compared with the results calculated by a commercial microhardness machine with the intention of testing its efficiency. All things considered, it became possible the materials hardness mensuration through an automated method, which minimized the mistakes caused by the operator and increased the analysis reliability / O ensaio de dureza ? amplamente empregado em pesquisa e avalia??o de materiais para controle de qualidade. Entretanto, os resultados desse ensaio est?o sujeitos a erros causados pelo operador do processo no momento da medi??o das diagonais da impress?o deixada pelo penetrador na amostra ensaiada. Desse modo, fora desenvolvido um equipamento de medi??o de dureza automatizado. O valor de dureza foi obtido a partir da medi??o da deforma??o pl?stica sofrida pelo material a uma carga conhecida. A deforma??o do material foi calculada atrav?s da medi??o da diferen?a entre o avan?o e o recuo de um penetrador de diamante sobre a amostra utilizada. N?o foi necess?rio, portanto, a medi??o manual das diagonais, excluindo-se a fonte de erro causada pelo operador. Gr?ficos de tens?o versus deforma??o puderam ser analisados a partir de dados obtidos dos ensaios realizados, assim como tomou-se poss?vel um completo monitoramento de todo o processo. Em seguida, as durezas calculadas pelo aparato experimental foram comparadas com as durezas calculadas em um microdur?metro comercial com o intuito de testar sua efici?ncia. Desse forma, tornou-se poss?vel a medi??o de dureza de materiais atrav?s de um m?todo automatizado, que excluiu os erros causados pelo operador e aumentou a confiabilidade dos ensaios