Corrosion reactions in molten sulphates

The redox potential in sulphate melts is controlled by the partial pressures of oxygen and SO₃ in equilibrium with the melt. The rate for the reduction of oxygen is limited by the solubility. Higher rates are observed for the reduction of SO₃ which is identified as the principal oxidizing species. Equilibrium potentials for reversible metal-metal ion couples for the principal components of superalloys are negative relative to the redox potential for the melt. The anodic oxidation of the metal therefore proceeds irreversibly in conjunction with the cathodic reduction of SO₃ An oxide layer is formed on the surface of the metal when the metal ion concentration at the surface, combined with the oxide ion concentration in the melt, which is related to the partial pressure of SO₃, exceeds the solubility limit for the oxide. The corrosion behaviour will depend on the mass transport processes through this oxide layer. Temperature gradients through the molten sulphate, and oxide ion concentration gradients established as a consequence of the corrosion reaction, may influence the morphology of the corrosion product. The gradient between the oxygen chemical potential at the outer surface of the molten sulphate, defined by the oxygen partial pressure in the gas and the oxygen chemical potential at the metal/metal oxide interface, defined by the dissociation equilibrium for the metal oxide, combined with the transport of SO₃ through the molten sulphate, increases the sulphur chemical potential at the metal surface and leads to the formation of the metal sulphide. Stress in the protective oxide layer caused by the growth of the sulphide phase at the interface between the metal and the oxide will eventually fracture the oxide and cause accelerated corrosion.     

High‐Quality Electrochromic Polythiophenes via BF3·Et2O Electropolymerization

Electrochemical polymerization in the strong Lewis acid, boron trifluoride ethylether (BFEE), has been used to prepare electrochromic polythiophene (PTh) and its derivatives: poly(3‐methylthiophene) (PMeTh), poly(3‐bromothiophene) (PBrTh), and poly(3,4‐dibromothiophene) (PDBrTh). The polymerization processes and properties of the resultant films are compared, where possible, to those carried out in traditional organic electrochemical solvents. The polymerization of these high oxidation potential thiophene monomers in BFEE yielded good‐quality, homogenous, and smooth electroactive and electrochromic films that could be repeatedly switched in common electrochemical solvents up to 240, 1380, 560, and 420 cycles for PTh, PMeTh, PBrTh, and PDBrTh, respectively, for 50 % retention of electroactivity. A colorimetric study of these films showed distinctive color changes between red and blue as they were switched between reduced and oxidized states. These findings allow the use of commercially available high oxidation potential thiophene monomers to provide electrochromic polymers, avoiding the use of other custom‐synthesized monomers.     

Optimal design of large software-systems using N-versionprogramming

Fault tolerant software uses redundancy to improve reliability; but such redundancy requires additional resources and tends to be costly, therefore the redundancy level needs to be optimized. Our optimization models determine the optimal level of redundancy within a software system under the assumption that functionally equivalent software components fail independently. A framework illustrates the tradeoff between the cost of using N-version programming and the improved reliability for a software system. The 2 models deal with: a single task, and multitask software. These software systems consist of several modules where each module performs a subtask and, by sequential execution of modules, a major task is performed. Major assumptions are: 1) several versions of each module, each with an estimated cost and reliability, are available, 2) these module versions fail independently. Optimization models are used to select the optimal set of versions for each module such that the system reliability is maximized and total cost remains within budget     

用小型散热器对DirectFET封装功率MOSFET进行双面散热

本文探讨了可以用于生产厂封装的器件的各种热管理方案,并且引用了国际整流器公司的测试数据,来评估使用小型散热器改善这些器件散热性能的优点,并研究了在进行通电循环的情况下,在器件上直接安装散热器对器件可靠性的影响。     

Accelerating Scientific Discovery Through Computation and Visualization II

This is the second in a series of articles describing a wide variety of projects at NIST that synergistically combine physical science and information science. It describes, through examples, how the Scientific Applications and Visualization Group (SAVG) at NIST has utilized high performance parallel computing, visualization, and machine learning to accelerate research. The examples include scientific collaborations in the following areas: (1) High Precision Energies for few electron atomic systems, (2) Flows of suspensions, (3) X-ray absorption, (4) Molecular dynamics of fluids, (5) Nanostructures, (6) Dendritic growth in alloys, (7) Screen saver science, (8) genetic programming.     

Geothermal energy and the dissemination of information: the role of the International Geothermal Association

The International Geothermal Association (IGA), founded on 6 July 1988, is an international, worldwide, non-profit and non-governmental association whose objective and mission is to promote the research and utilization of geothermal resources, through the compilation, publication, and dissemination of scientific and technical data and information. The Information Committee (IC) of the IGA is responsible for advising the IGA Board on policies concerned with the collection, compilation, publication, exchange and dissemination of geothermal information, including information on utilization, development, technical findings, scientific research, meetings, publications and Association activities. The Committee is also responsible for the implementation of information policies determined by the Board.     

Surface activity of high-temperature perfluoropolyalkylether oil additives

Three additive materials for perfluoropolyalkylether-based high-temperature engine oils were studied, a bis-substituted dibenzothiazole, a diphenyl ether and a triphenyl phosphine. The focus of this work was to understand how the additives interacted with various surfaces to provide either anticorrosion or antiwear activity. In the case of the bis-substituted dibenzothiazole, the additive was found to form a thick, protective anticorrosion layer on the surface. The diphenyl ether served as another equally effective anticorrosion additive but failed to demonstrate surface activity. The third additive compound, triphenyl phosphine, was found to break down at the surface and form an inorganic polyphosphate which provided a level of both anticorrosion and antiwear function. This revised version was published online in August 2006 with corrections to the Cover Date.     

Stability of finite difference deconvolution II: simulation studies

Theoretical analysis of the stability of finite difference deconvolution (FDD) indicates that if the cumulative amount function is used to characterize the drug input the method is stable for any sampling schedule for an intravenous unit impulse response function. The analysis also indicates that the method is stable for an oral unit impulse response only for well designed sampling schedules. This article confirms these results through numerical simulation experiments. It is shown that the assumption that the unit impulse response is error-free has an influence on the performance of FDD which is generally of no practical significance, except possibly for the first few points estimated. It is also shown that there is no significant interaction between the statistical error due to data noise and the deterministic algorithm error. The major source of error in practice is likely to be the data noise in the input response function. The simulations confirm that, with the estimated cumulative amount function as the quantity estimated and, with a well designed sampling schedule for the case of an oral unit impulse response, FDD is in practice an accurate and stable method with acceptable precision under a typical error disturbance.