eriks

By accident I stombled across a post inside a forum about the upcoming Google Net, which will create enormous possibilities for Google to develop new services and gain control over their costs. The discussion may be old, but open my eyes to this new problem.

The development of new services by Google has been discussed several times, and especially the customization of them. In order for Google to customize the services you have to control and supervise the traffic between the client and server. This is nothing unique for Google, but they have a world leading position in this techonlogy. Especially Gmail have been discussed in terms of privacy, as Google scan both incoming and outgoing emails to be able to present the user with the right ads at the right time.

The problem is really not the scanning itself but that it can be misused. Hacking of the service is very unlike as the syetem by Google is very much robust, but the implications of a customized site for the user can/and to some extent will be filtered/censored. The users will loose their own possibility to have control of what they read and when. A fundamental right in a democratic society is thereby lost.

However, the user will benefit from the filtering as the content will be structured, filtered and explained in the "right" language, as all possible sources are used to create your story. The benefits are therefore enormous and thus the road to pick is to not obvious.

The Poynter Institute and Robin Sloan och Matt Thompson have created a Flash movie covering the problem described with filtered and user customized media content. Matt Thompson describes the background to the film.

Two versions of the film exist and are found uinder the links below:
EPIC
EPIC (second version)

See it! It changed my view of new technology!

the clock has started to tick… there is now only two and a half week left until I will get on the airplane taking me to San Fransisco. The time there will be awesome… I will soon present the project at which I will work on in detail here, but until then you can browse the links rdvp and campware in the menu to the left to get an idea of what it is all about.

Industry is continuously looking for reduced costs and in some cases also reduced weights of their components at the same time as quality must be maintained or increased. One way of achieving this is to manufacture the components via powder metallurgy (P/M) and such components play an increasing role in various mechanical constructions. Two important properties of P/M components are contact fatigue strength and wear resistance, which mainly depend on the physical and chemical properties in the surface region of the component. The production process of such components involves both a form compression of the metal grains and a sintering step at high temperatures. Even if the sintering is performed in an almost inert atmosphere oxides are easily formed on the grain surface and due to the large surface to volume ratio this may severely affect the material properties. Thus a reduction step must be included during production. Although of basic importance for the product quality this chemical reduction step is by no means understood in all details and the present study is an atteempt to improve our understanding especially with respect to the kinetics of the process and the surface oxides of importance.

The dominating P/M-based process is uniaxial pressing and sintering of low-alloy ferrous powders. The sintering takes place in the temperature interval 1120-1350°C in specially designed furnaces under gas protection. It is of major importance to protect the metal powder from oxidation, and at the same time avoid that the surface is depleted in carbon. In many cases carbon is introduced into the surface region via a carburization step in the temperature region 800-1000°C in order to improve the mechanical strength and introduce compressive stresses.

The oxidation behavior is strongly dependent on the concentration level of oxygen-containing gases such as oxygen gas or water vapor, and on the composition of the alloy. In order to keep the cost of alloying elements down, there is a wish to move to the more oxidation-prone alloying elements chromium and manganese. This increases the importance of understanding the kinetics of the oxidation and reduction reactions during the various processing steps.

It has also been observed that nitrogen may enter the solid during sintering, and this may have an influence on the mechanical properties. The mechanism of nitrogen uptake is similar to carburization.

There are many parameters that influence carburization/decarburization, oxidation/reduction and nitrogen uptake, e.g. gas composition, temperature, time and prehistory, total porosity and pore geometry, alloy composition and microstructure.

Sintering is a fundamental step in P/M technology, which in principle is the unification of small, separate solid grains to large, three-dimensional microporous structures. Evidently, the strength of the final material will depend on the resulting bond area and bond strength between the grains, the grain properties, and the microporosity of the particles. An essential prerequisite to obtain good material properties is therefore to be able to control the surface properties of the grains during sintering. The small grains are very reactive and oxides form easily on the surface.

Since a typical P/M (sintering) process is performed at elevated temperatures in a streaming gas, a model must take into account both the composition and flow of the gas and the chemical (reduction) reactions at the gas/solid interface. Even if the primary processes occur in the immediate vicinity of the surface also some transport within the solid itself must be considered – especially so since the temperature is high and the grain size is small. Furthermore, the small grain size makes the total surface to volume ratio very high, and thus the influence of surface reactions is large.

Several studies of the reduction of surface oxides during sintering have been published and some will be presented and discussed later on. At this point, however, two important earlier studies will be mentioned focusing on the gas production during sintering of metal components – Danninger et al and Grabke. The study by Danninger has mainly influenced the experimental part of this work, whilst the study by Grabke has been of central importance for the modelling work.

Danninger used a combination of mass spectrometry and thermogravimetry, and the latter makes it possible to link the mass losses to a certain gas production peak. Danninger studied the granulate specimens after reduction of varioous powder compositions. The measured gas production of Astaloy CrM did show three gas peaks, which could be correlated to a certain reduction path. The peaks indicated the relative amounts of the different oxides reduced at certain temperatures. Water was produced at around 300°C, but as the mass loss was negligible, the amount of ferrous oxides had also to be negligble. The production of carbonoxides was located in two temperature regions around 1100 and 1250°C, respectively.

The works of Grabke focused on the problem of defining an appropriate kinetic model of the surface reactions for different types of gas atmospheres. Grabke has studied the effect of several gas atmospheres, and also processes other than carburization using electrical conductivity measurements on thin foils..

The sintering is performed in a temperature range up to 1250°C and in an atmosphere composed of a nitrogen-hydrogen mixture. Based on these facts – also taking into account some featues of the technical process – a simulation model is developed that describes the reaction kinetics of the reduction of surface oxides, and of the gas transport via diffusion and convection in the porous structure.