Browsing by Author "Martinek, Klaus-Peter"

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    Local clouding of glass after machine dishwashing
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Martinek, Klaus-Peter; Wang, Chun; Krausch, Georg; Rädlein, Edda
    The local clouding of glasses after dishwashing near the mouth rims on a coffee pot made from borosilicate glass, on a wine cup made from lead crystal glass and near the stem base on a wine cup made from barium Silicate glass has been found to be due to damage during manufacture. The examined clouding is different from the two well known types of filming and etching cloudiness related to the reactions of glass with water and detergent in the dishwasher. The intensive study on the wine cup of lead crystal glass shows that a phase Separation was induced during the flame treatment on the sharp rim and base. The aggregates of Pb-rich spheres scaled off when the thin covering of SiO2 rich skin was eroded away and consequently holes were formed on the glass surface on the micrometre scale, which resulted in light scattering and the clouding of the glassware. Evaporation species from warmer regions onto the colder areas of the glass surface could be observed, but they are not the reason for the local clouding in this study. Dendritic thin corrosion products caused by air exposure could be detected on the undisturbed glass surface as well.
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    Study of surface changes on industrial glasses with AFM, FE-SEM, EDX, SNMS and LM : Part 1. Glass skin and corrosion
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Wang, Chun; Häfner, Wolfgang; Krausch, Georg; Rädlein, Edda; Tratzky, Stephan; Schramm, Manfred; Martinek, Klaus-Peter
    By combining different analytieal techniques, including modern high resolution imaging tools such as field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM), new phenomena in the surface, near surface and bulk structure of various industrial glasses (without any cleaning process) have been diseovered. Investigations of soda-lime-silica container glass and lead silicate glass tubings exposed to atmospheric and to dried air are presented. The results of the first part of this paper can be explained with an SiO2 rich skin on the glass, which can protect the glass against the attack of external media. If the skin was mechanically injured, inhomogeneous corrosion products on pm scale grew around the injured site after exposure to humid air for times between days up to one year. Microchannels were formed through the injured site due to restricted ion exchange, followed by a local increase of the pH value and consequently the dissolution of the glass network. Finally some stress in the glass, yielded during manufacture, can be partially released and the cutting behaviour is improved. Faster cooling results in a thinner skin and the ions in the glass are able to migrate to the surface more easily when surrounded by some reactive media. Slower cooling results in thicker skin and wax-like droplets instead of erystallites are formed on the surface at a later stage in humid air. The wax-like droplets can etch the glass skin locally, followed by the growth of inhomogeneous corrosion products similar to the injury induced corrosion. If the fresh glass surface was hot-end treated, the quality of the adjacent coating layer depended strongly on the thickness of the skin.
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    Three different reasons for surface damages of glasses after machine dishwashing
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Wang, Chun; Krausch, Georg; Decker, Markus; Martinek, Klaus-Peter
    A variety of glass eups has been investigated after treatment in a machine dishwasher. Three types of surface damages were found. The first type consists of clouding on the inner and outer surfaces appearing after about 1000 washing cycles. It can be related to the long range granular structure of glass, which is believed to be formed by thermal density fluctuation. During washing both water and detergents act as weak etchants, first eroding the smooth glass skin, then revealing the granular structure. As soon as the linkages between the granules are entirely broken by the etching, holes will manifest themselves at these sites. When the size of the holes (the hole width) reaches the half of the light wavelength, light scattering occurs and the glass seems cloudy. The second type is the sheet clouding on the outer surface appearing after about 100 washing cycles. It can be related to holes on the surface, which are formed by the loss of the sphere domain phase from the SiO2-rich matrix during washing. These domains result from phase separation induced by round-meldng of the sharp cutting edge, which is responsible for local clouding of glass. The third type is a golden film on the inner surface. These films are probably formed by complex formation between the glass surface and the organic compounds in the drinks. All of the damages studied here are irreversible.