Hydrogen effusion from tritiated amorphous silicon

Results for the effusion and outgassing of tritium from tritiated hydrogenated amorphous silicon (a-Si:H:T) films are presented. The samples were grown by dc-saddle field glow discharge at various substrate temperatures between 150 and 300 °C. The tracer property of radioactive tritium is used to detect tritium release. Tritium effusion measurements are performed in a nonvacuum ion chamber and are found to yield similar results as reported for standard high vacuum technique. The results suggest for decreasing substrate temperature the growth of material with an increasing concentration of voids. These data are corroborated by analysis of infrared absorption data in terms of microstructure parameters. For material of low substrate temperature (and high void concentration) tritium outgassing in air at room temperature was studied, and it was found that after 600 h about 0.2% of the total hydrogen (hydrogen+tritium) content is released. Two rate limiting processes are identified. The first process, fast tritium outgassing with a time constant of 15 h, seems to be related to surface desorption of tritiated water (HTO) with a free energy of desorption of 1.04 eV. The second process, slow tritium outgassing with a time constant of 200-300 h, appears to be limited by oxygen diffusivity in a growing oxide layer. This material of lowest H stability would lose half of the hydrogen after 60 years. © 2008 American Institute of Physics

Tritiation of amorphous and crystalline silicon using T <inf>2</inf> gas

Incorporation of tritium in hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si) at 250 °C using tritium (T 2) gas at pressures of up to 120 atm is reported. The tritium is stored in a surface layer which is approximately 150 and 10 nm for a-Si:H and c-Si, respectively. The concentration of tritium occluded in planar and textured c-Si is linearly dependent on the total surface area. The tritium is stable and the dominant tritium evolution occurs at temperatures above 300 °C. The concentration of tritium locked in a-Si:H and c-Si was 20 and 4 at. %, respectively. Self-catalysis appears to be important in the tritiation process. © 2006 American Institute of Physics

Long-Range Correlations and Natural Time Series Analyses from Acoustic Emission Signals

This work focuses on analyzing acoustic emission (AE) signals as a means to predict failure in structures. There are two main approaches that are considered: (i) long-range correlation analysis using both the Hurst (H) and the detrended fluctuation analysis (DFA) exponents, and (ii) natural time domain (NT) analysis. These methodologies are applied to the data that were collected from two application examples: a glass fiber-reinforced polymeric plate and a spaghetti bridge model, where both structures were subjected to increasing loads until collapse. A traditional (AE) signal analysis was also performed to reference the study of the other methods. The results indicate that the proposed methods yield reliable indication of failure in the studied structures

Resistance and elastic stiffness of RHS "T" joints: part I - axial brace loading

This paper presents a study on the behaviour of welded “T” joints between RHS sections under brace axial loading. A finite element model was developed to investigate the influence of some geometrical variables on the joint’s response. The brace load (always in tension) was incremented up to joint failure, while the chord was kept unloaded. In the companion paper (part II) a complementary study including chord axial loading is presented. The force-displacement curves corresponding to the different geometries are analyzed and compared, focusing on the failure loads and elastic stiffness. Different failure criteria are discussed and applied to the present curves and a comparison of the numerical results with the Eurocode 3 provisions is presented and discussed

High-pressure and high-temperature tritium apparatus for the tritiation of materials

A tritium exposure apparatus has been designed and built for the purposes of generating a high-pressure tritium atmosphere at 523 K. The loading system consists of a uranium tritide storage bed, an intermediate tritium transfer chamber filled with 5A molecular sieve, and the sample exposure chamber. The loading system resides in a sealed glovebox with a nitrogen atmosphere that is continually purged through a Glovebox Clean-up System. The tritium used in each loading experiment is approximately 6000 Ci (22 TBq). The process entails transferring the tritium inventory from the uranium storage bed to the cryogenically cooled (77 K) molecular sieve chamber. The molecular sieve at liquid nitrogen temperature is capable of adsorbing tritium to densities of 290 Ci/gram at one atmosphere. At 523 K a maximum tritium pressure of 21 MPa is achieved. The loading apparatus is used to develop high-density radioactive isotope fuel for self-powered microelectronic and micromechanical devices. This paper presents the design specifics of the tritium exposure apparatus, the steps taken in generating the high-temperature, high-pressure tritium atmosphere and the performance characteristics of the apparatus. Additionally, the handling practices and equipment utilized to conduct the tests safely are presented

Evaluation of CHS tubular KK joints

The widespread use of tubular sections in regions like Western Europe and North America in addition structural and aesthetical reasons can be attributed to the high degree of development of their production technology. Despite this fact their use in Brazil in the past was limited to a few spatial roofs. Currently, the situation in the Brazilian market begins to change caused by the significant increase in the availability of structural hollow sections. This work presents an analysis of “KK” joints with circular hollow sections. A comparison between the analytical design formulations proposed by the Eurocode 3 Part 1.8, the 2nd edition of the CIDECT tubular joint design guide was performed. A finite element model was developed in the ANSYS program for each analysed joint typology. The modelling of a spatial truss made of circular hollow section elements was also performed to enable a comparison between a single joint and the response of the joint as a part of a full scale truss structure