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Eingeladener Vortrag
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The viscosity of silica glasses with different water contents was measured by penetration of sapphire microspheres in the range from 1012-1014·7 Pas at ambient pressure. Commercial silica glasses were used together with hydrous silica glasses, which were prepared by melting glass powder plus water in an internally heated pressure vessel at 2-3 kbar and 1350-1450°C. The temperature dependence of the viscosity of silica glasses with total water contents Cw of 5·4×10-4, 7·0×10-4, 1·00×10-2, and 1·55×10-2(Cw in mass fractions) can be described by Arrhenius equations. From the results, the linear dependence of the T12 isokom (K) with the logarithm of the water content was determined as T12=192-409 logCw. The analysis of the compositional dependence of the T12 isokom in the H2O-Na2O-SiO2 system reveals a temperature depression of up to 200 K for mixed water- and sodium-bearing glasses compared to H2O-SiO2 and Na2O-SiO2 glasses with same molar silica content. From these findings we conclude that protons may contribute significantly to the mixed alkali effect in glasses.
Use of Corrosion Resistant High-Alloyed Metallic Materials for Transport Tanks of Dangerous Goods
(2005)
In Germany the BAM-List Requirements for Tanks for the Transport of Dangerous
Goods is the basis for substance-related prototype approvals for tank containers designed for
the carriage of dangerous goods. Such approval is undertaken by the Federal Institute for
Materials Research and Testing (BAM). Compatibility evaluations of selected metallic
material groups as well as of polymeric gasket and lining materials under the influence of
dangerous goods and water-polluting substances are published in section 5 of the BAM-List.
According to the relevant regulations for rail, road and sea transportation a compulsory
internal inspection after certain intervals is required. The required corrosion resistance
depends on the length of the inspection interval.
There is a large number of dangerous goods with a high corrosivity to metals, where the standard
steels are not corrosion resistant. Chemical companies, transportation providers and tank
producers need tanks made of corrosion-resistant materials in order to protect the tank shell
and prevent contamination of high-value cargo as well as the environment. One solution is to
line the tank with a polymeric material, an alternative solution to corrosion problems is the
application of high-alloyed materials.
Only a narrow limited number of corrosion test results of these high-alloyed materials under
the influence of corrosive dangerous goods are available. In order to change this situation and
include the superaustenitic steels X1NiCrMoCuN25-20-7 (Alloy 926), X1NiCrMoCu32-28-7
(Alloy 31) and the nickel-based alloy NiCr23Mo16Al (Alloy 59) in the BAM-List, BAM,
IKS Dresden and ThyssenKrupp VDM started an comprehensive test program with welded
specimens made. The program comprises corrosion resistance evaluations of the high-alloyed
materials in substances representing 12 major groups of corrosive dangerous goods (e.g.
inorganic halogenides, organic acidic halogenides, halogenic carbonic acids, chlorosilanes,
chlorates, perchlorates, chlorites, hypochlorites and hydrogen sulphates).
The test results, presented in this paper, will be included in the upcoming 8th edition of the
BAM-List and therefore available for the costumer.
Crack growth velocity in alkali silicate glasses was measured in vacuum across 10 orders of magnitude with double cantilever beam technique. Measured and literature crack growth data were compared with calculated intrinsic fracture toughness data obtained from Young´s moduli and the theoretical fracture surface energy estimated from chemical bond energies. Data analysis reveals significant deviations from this intrinsic brittle fracture behavior. These deviations do not follow simple compositional trends. Two opposing processes may explain this finding: a decrease in the apparent fracture surface energy due to stress-induced chemical changes at the crack tip and its increase due to energy dissipation during fracture.
Stable crack growth was measured for nominal dry and water-bearing (6 wt%) soda-lime silicate glasses in double cantilever beam geometry and combined with DMA studies on the effects of dissolved water on internal friction and glass transition, respectively. In vacuum, a decreased slope of logarithmic crack growth velocity versus stress intensity factor is evident for the hydrous glass in line with an increase of b-relaxation intensity indicating more energy Dissipation during fracture. Further, inert crack growth in hydrous glass is found to be divided into sections of different slope, which indicates different water related crack propagation mechanism. In ambient air, a largely extended region II is observed for the hydrous glass, which indicates that crack growth is more sensitive to ambient water.