Study of thermal behaviors in CO2 laser irradiated glass

To understand mechanisms underlying laser-induced damage of BK7 and fused silica, we calculate the temperature field of the substrates with CO2 laser irradiating at a given laser power and beam radius. We find that the two glasses show different thermal behaviors. A model is developed for estimating the time t to heat the surface of the substrates up to a particular temperature T with cw CO2 laser irradiation. We calculate theoretically the duration t that the samples are irradiated, from the beginning to visual catastrophic damage, with the assumption of damage threshold determined by the critical temperature. The duration t that the samples are irradiated, from the beginning to visual catastrophic damage, is investigated experimentally as well. Here we take the melting point or softening point as the critical temperature, given the thermomechanical coupling properties, which is enough to cause damage for BK7. Damage features are characterized by the sound of visual cracks. Finally, we calculate stresses induced by laser heating. The analysis of stress indicates that the damage of BK7 is due to the stresses induced by laser heating. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Influence of Cr interlayer on the structure and optical properties of Ag films on glass substrate by magnetron sputtering

Optical properties and microstructure of Ag film on glass substrate with Cr intermediate layer were studied by using spectrophotometer and XRD. The spectra results showed that introducing Cr intermediate layer reduced the surface roughness and promoted the reflectivity of Ag film. The XRD analysis showed that the crystalline grains increased and the stress decreased. The adhesion was also improved by using the tape test method. (c) 2006 Published by Elsevier B.V.

Measurements of light scattering from glass substrates by total integrated scattering

A total integrated scattering (TIS) measurement was performed to investigate the surface and volume scattering of K9 glass substrates with low reflectance. Ag layers with thicknesses of 60 nm were deposited on the front and back surfaces of the K9 glass substrates by the magnetron sputtering technique. Surface scattering of the K9 glass substrate was obtained by the TIS measurement of the Ag layers on the assumption that the Ag layers and the K9 substrate had the same surface profile. Volume scattering of the substrates was deduced by subtracting the front and back surface scattering from the total scattering of the substrates. (c) 2005 Optical Society of America.

Nonpolarizing beam splitter designed by frustrated total internal reflection inside a glass cube

A method for the design of an all-dielectric nonpolarizing prism beam splitter utilizing the principle of frustrated total internal reflection is reported. The nonpolarizing condition for a prism beam splitter is discussed, and some single layer design examples are elaborated. The concept can be applied to a wide range of wavelengths and arbitrary transmittance values, and with the help of a computer design program examples of 400-700 nm, T-p = T-p = 0.5 +/- 0.01, with incident angles of 45 degrees and 62 degrees are given. In addition, the sensitivity and application of the design are also discussed. (c) 2006 Optical Society of America.

Effect of alumina and chromium interlayers on microstructures and optical properties of thin Ag films on glass substrates

Effects of alumina and chromium interlayers on the microstructure and optical properties of thin Ag films are investigated by using spectrophotometry, x-ray diffraction and AFM. The characteristics of Ag films in Ag/glass, Ag/Al2O3/glass and Ag/Cr/glass stacks are analysed. The results indicate that the insertion of an Al2O3 or Cr layer decreases the grains and influences the reflectance of Ag films. The reflectance of the Ag film can be increased by controlling the thickness of alumina interlayer. The stability of Ag films is improved and the adhesion of Ag films on glass substrates is enhanced by alumina as an interlayer.

Two Glass Transitions Associated to Different Dynamic Disorders in the Nematic Glassy State of a Non-Symmetric Liquid Crystal Dimer Dopped with gamma-Alumina Nanoparticles

In the present work, the nematic glassy state of the non-symmetric LC dimer -(4-cyanobiphenyl-4-yloxy)--(1-pyrenimine-benzylidene-4-oxy) undecane is studied by means of calorimetric and dielectric measurements. The most striking result of the work is the presence of two different glass transition temperatures: one due to the freezing of the flip-flop motions of the bulkier unit of the dimer and the other, at a lower temperature, related to the freezing of the flip-flop and precessional motions of the cyanobiphenyl unit. This result shows the fact that glass transition is the consequence of the freezing of one or more coupled dynamic disorders and not of the disordered phase itself. In order to avoid crystallization when the bulk sample is cooled down, the LC dimer has been confined via the dispersion of -alumina nanoparticles, in several concentrations.

Magnetoelectric metallic glass/polymer laminated composites: from fabrication to applications

131 p.

Comportamento mecânico de cerâmica produzida a partir de reciclagem de para-brisa de automóvel

É crescente o interesse nos materiais cerâmicos, devido as suas características como baixa massa específica e maior resistência a ambientes agressivos do que a maioria das ligas metálicas. Este trabalho tem o objetivo de produzir a partir de material descartado, cerâmicas em diferentes temperaturas de sinterização e avaliar a sua tensão de ruptura em ensaio de flexão de três pontos e a confiança desta medida. Devido ao custo de produzir pó de vidro, tanto pelo alto gasto de energia para fundir a matéria-prima como pelo consumo de minerais industriais, foi proposto utilizar vidro de para-brisa obsoleto reduzindo despesas operacionais e definindo um destino econômico e ambiental viável para estes rejeitos. A metodologia consistiu-se na obtenção do pó de vidro com características adequadas para ser conformado e sinterizado. Foram usadas duas composições e quatro tratamentos térmicos para obter oito materiais. Uma composição com apenas o pó oriundo da moagem de para-brisa e outra com este pó mais 4% de óxido de nióbio. A resistência à flexão dos produtos obtidos foi avaliada. Utilizou-se a estatística de Weibull para caracterizar estes resultados. Os resultados obtidos indicam que o material de composição pó de vidro e temperatura final de sinterização de 650C obteve a maior resistência mecânica entre os materiais sintetizados. A adição do óxido de nióbio provoca um decréscimo na resistência mecânica se comparada com o material sem a adição deste óxido. Entretanto, comparando as duas composições na mesma temperatura final de sinterização, a adição de óxido de nióbio provocou um aumento no módulo de Weibull, excetuando-se dois de oito materiais obtidos. As diferentes composições e temperaturas de sinterização afetaram as propriedades mecânicas dos materiais obtidos.

Characterisation of impact response of metallic foam/ceramic laminates

The impact response of laminated composites consisting of alternate layers of AI ahoy foam and Al2O3 was studied experimentally in low and intermediate velocity regimes. Low velocity impacts (1.2-2.8 m s(-1)) were conducted using an instrumented falling weight apparatus and were compared with static indentation tests (0.2 x 10(-4) m s(-1)). Intermediate velocity impacts were carried out by means of both Hopkinson bar (60 m s(-1)) and gas gun (200 m s(-1)) tests, Post-impact damage was assessed using X-ray radiography and microscopy, It was found that there is good correlation between low velocity impact and quasi-static responses. In both cases, penetration of the layered targets resulted in the formation of a distinctive plug. Increasing impact velocity (intermediate velocity range) snitched the penetration mode from plugging to fragmentation, giving rise to an increase in the absorbed energy. In this range, impacts led to localisation of damage in the region under the projectile, Furthermore, a comparison has been made between the penetration response of foam laminates and dense metal laminates of equivalent areal density. Preliminary results suggest that the dense metal laminates are superseded by the foam laminates on an energy absorption basis.