Vaporization of Protective Oxide Films into Different Gas Atmospheres

Oxidation of Metals - Vaporization often accompanies high-temperature oxidation and corrosion. In this review, vaporization under a vacuum as well as static gas and flowing gas conditions is...     

Thermodynamics of high-temperature aluminum,zirconium, and yttrium hydroxide and oxyhydroxide vapor species

Thermodynamic parameters are reported for gaseous hydroxides and oxyhydroxides of Al, Zr, and Y. The structures and vibrational frequencies are calculated using density functional theory with the B3LYP functional. This yields entropies at 298.15 K and heat capacities. The enthalpies are calculated from appropriate reactions and the CCSD(T) (Coupled Cluster, Singles, Doubles, and perturbative Triples) approach. The hydroxide groups are treated as hindered rotors for all species. The results are compared to the limited experimental and theoretical calculations for these species. Finally, the data are put into a database for a free-energy minimizer and the vapor pressures for each species are compared.     

Mechanisms of Transfer of Aluminium to PVD-Coated Forming Tools

Cold forging is a group of methods effectively used in a number of industrial applications to form aluminium. Tool life and complexity of the possible shapes are mainly restricted by galling; the uneven tool surfaces caused by lumps of transferred material lead to surface damage on successive parts formed and/or problems in successive forming operations, and high stresses occurring when forming complex shapes. Earlier investigations have shown that improved surface roughness of an uncoated steel tool decreases the amount of adhered aluminium on the tool, but does not decrease the friction in the long run. Testing has also shown that when using conventional forming tools it is very important to have sufficient lubrication to avoid galling. Addition of an optimized low-friction PVD-coating decreases the galling tendency and increases the tolerance to insufficient lubrication and lubricant film breakthrough, as long as the coating surface is smooth, whilst other similar coatings have little or no effect. The present article further investigates the mechanism behind the transfer of aluminium to the coatings. All coatings were found to be intact after testing, and so the differences were concluded to lie in the chemical properties of the coating and, if these are favourable, then in surface roughness on the micro scale.     

Investigation of the Equivalence of National Dew-Point Temperature Realizations in the ?50?°C to +?20?°C Range

In the field of humidity quantities, the first CIPM key comparison, CCT-K6 is at its end. The corresponding European regional key comparison, EUROMET.T-K6, was completed in early 2008, about 4?years after the starting initial measurements in the project. In total, 24 NMIs from different countries took part in the comparison. This number includes 22 EURAMET countries, and Russia and South Africa. The comparison covered the dew-point temperature range from ?50?°C to +20?°C. It was carried out in three parallel loops, each with two chilled mirror hygrometers as transfer standards in each loop. The comparison scheme was designed to ensure high quality results with evenly spread workload for the participants. It is shown that the standard uncertainty due to the long-term instability was smaller than 0.008?°C in all loops. The standard uncertainties due to links between the loops were found to be smaller than 0.025?°C at ?50?°C and 0.010?°C elsewhere. Conclusions on the equivalence of the dew-point temperature standards are drawn on the basis of calculated bilateral degrees of equivalence and deviations from the EURAMET comparison reference values (ERV). Taking into account 16 different primary dew-point realizations and 8 secondary realizations, the results demonstrate the equivalence of a large number of laboratories at an uncertainty level that is better than achieved in other multilateral comparisons so far in the humidity field.     

Semat—Three Year Vision

The purpose of writing this Three Year Vision paper is threefold. Firstly, it briefly recaps the progress Semat has made thus far; secondly, it lays out the future directions for people working actively within the Semat community; thirdly, it provides the background for seeking funding support from agencies, such as the European Community and the like. Funding support is necessary to sustain the ongoing activities of Semat and its growth into a broader community effort, as most people working within Semat are volunteers. As such, the paper may be both too much and too little for the wider supporter base. However, we intend to make our work fully transparent, hence, we publish it widely. We seek feedback and comments from supporters and signatories in order to improve the vision. In this context, other companion papers are being written to better address the specific needs for the practitioners, the industry and the academia.     

How and why network governance evolves: evidence from a public safety network

Public sector organizations increasingly form interorganizational networks that rely on technology to achieve what they cannot achieve independently. The governance of these public sector networks is complex due to the nature of interorganizational relationships and technology. This paper aims to increase our understanding of network governance by exploring the evolution of governance over the 40+ year lifespan of a public sector network. The historical case study is based on the technology affordance and organizational actualization concepts applied to three critical incidents in the history of a public safety network. The incidents provide evidence that technology and governance do interact, that timing matters and that future research is needed to understand more fully how and why network governance evolves and the implications of governance evolution on network performance.     

Schlüsselverteilung für Mobilgeräte

Digitale Zertifikate werden bereits in großem Umfang zur Verschlüsselung mit Desktop Clients wie Outlook eingesetzt. Damit ein Benutzer auch an all seinen Mobilgeräten verschlüsselte E-Mails lesen und an beliebige Empfänger verschlüsseln kann, müssen sein privater Schlüssel sowie die Zertifikate der Partner dort verfügbar sein.     

Tomography imaging of South African archaeological and heritage stone and pottery objects

We demonstrate the use of both neutron- and X-ray imaging in two projects. The first project, using both the methods to view the temper in a ceramic sherd in order to model the effect the chemical composition of the temper has on the bulk chemical composition of the sherd showed that X-ray imaging is superior to neutron imaging for a ceramic. The second project, to establish whether apparent incised lines on stone slabs (dated to greater than 180,000 years ago) are natural or artificial, i.e., whether they were deliberately incised or natural, random striations showed conclusively that the incisions are in fact surface manifestations of natural internal fractures in the rock.     

Active Oxidation of SiC

Silicon carbide (SiC) forms a protective condensed-phase oxide (SiO₂) in passive oxidation and a volatile sub-oxide (SiO(g)) in active oxidation. The transition between these two modes of oxidation and the rates of active oxidation are critical issues. A literature review indicates that impurity effects, the difference between active-to-passive and passive-to-active transitions, and the effect of total pressure on these transitions remain unexplored for SiC. Measurements were made in a thermogravimetric apparatus (TGA) by changing oxygen potentials either by blending O₂/Ar mixtures or changing total pressures in a pure oxygen gas stream to the point where a transition occurs. Specimens were examined with standard optical and electron-optical techniques. Active-to-passive and passive-to-active transitions were measured and found to be similar for SiC, which is in contrast to pure Si. The similarity in SiC is attributed to SiC/SiO₂ interfacial reactions producing the necessary conditions for passive scale formation (active-to-passive) or passive scale breakdown (passive-to-active). Comparable results were obtained in both the O₂/Ar and reduced total O₂ pressure cases for SiC.