Effect of dopants on the sintering behaviour and stability of tetragonal zirconia ceramics

The microstrueture development during non-isothermal and isothermal sintering has been studied for tetragonal zireonia ceramics (TZP) containing carious amounts of Y, Ce and Ti. Smaller grain sizes were obtained when Ce-TZP was doped with yttrium. This could he attributed to segregation of yttrium to the grain boundaries, thus causing an impurity drag. With increasing temperature the grain growth in the Ce-TZP samples became faster, which could be attributed to the absence of a dragging force. The slow grain growth at low temperature in the Ce-TZP samples could he attributed to the slow diffusion kinetics of the diffusing species (trivalent and tetravalent cerium). The critical grain size for retainment of the tetragonal phase at room temperature is larger in the ECe-TZP systems compared to the Y-TZP amt Ce-TZP systems. The chemical stability increased by doping Y-TZP with cerium or titanium

Powder preparation and compaction behaviour of fine-grained Y-TZP

Two wet chemical preparation methods are described for yttria-doped tetragonal zirconia powders. Both methods yield powders with an extremely small crystallite size (8 nm) and a narrow size distribution. The agglomerate and aggregate structure of these powders have been investigated by several techniques. Gel precipitation from an alkoxide solution in water (ldquoalkoxiderdquo synthesis) results in a ceramic powder with irregular-shaped weak and porous agglomerates, which are built up from dense aggregates with a size of 18 nm. Gel precipitates formed from a metal-chloride solution in ammonia (ldquochloriderdquo synthesis) do not contain aggregates. Both types of agglomerate are fractured during isostatic compaction. Hydrolysis and washing under (strong) basic conditions probably decrease the degree of aggregation. The aggregate morphology and structure are key parameters in the microstructure development during sintering of a ceramic. Several characteristics of these powders are compared with those of a commerical one (Toyo Soda TZ3Y)

Political Transparency in the Media: The Old Media’s Influence on Politicians’ Twitter Behaviour

“Later today with my son to a football match: Heerenveen – Excelsior. It has been a long time since I was on a football stand. # Looking forward!” (Rouvoet, 02-04-2011, Twitter) This is a Tweet posted by André Rouvoet at the time that he was a politician. Significantly, he was a political figure who made his private activities transparent through a public medium. In this way, his Tweet denotes an important change in political communication, which has taken place over the past few decades. Ever since the fifties, the old media has been blurring the border between the private and public sphere, and has increased the transparency of politicians. (Pels, 2003, p. 42) Also the new media have the potential to continue this trend, as is demonstrated by Rouvoet’s Tweet. The distinction between old and new media will be maintained in the rest of this paper. The old media are defined as non-interactive print- and electronic media, such as newspapers and TV-programs. (Chun & Keenan, 2006, p. 284) To be more precise, this paper especially focuses on the popular and commercial part of the old media. The new media will be defined as online and interactive forms of mass communication, such as weblogs, Twitter and Facebook. (Ibid, p. 3) The fact that Rouvoet’s Tweet follows the trend that is visible in various older media, makes it interesting to investigate the extent to which other politicians copy these trends as well. This can reveal how influential this trend actually is, since politics is one of the parts of society in which the distinctions between the public and private sphere is most prominent. Therefore, this paper will be centred on the research question: To what extent does the way in which Dutch politicians use Twitter, reflect the dominant trend in the majority of the old media