Analytische Chemie
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Pre-Inca civilizations like the coastal cultures Moche and Nazca (Early Intermediate) and the inland culture Wari (Middle Horizon) were agrarian societies which supported indigenous elites of impressive wealth, power, and organization. With the expansion of the Wari Empire, the polychrome style and technique of Nazca propagated to the other cultures. High status burials, most of the Late Moche Fine Line ceramics and a large corpus of ceramics with Wari-derived decoration have been recovered in San José de Moro since 1991. The degree of transfer of procedures in this highly interactive scenario is of special interest: is there a limitation to decoration or is it adopted by the local potters also regarding the formulation of the ceramic bodies? In this context the relative amount, size and type of incorporated non-plastic inclusions as temper are important.
Dielectric strength is a critical property for materials used as electrical insulators. The measurement of dielectric strength is well established and straightforward, but the values determined in a measurement are strongly dependent on the measurement setup and the specimen characteristics. For example, the size of the electrodes has a significant influence on the results. ASTM D149 covers a range of electrode sizes and does not unambiguously prescribe the quality of the electrodes. Thus, different test setups and procedures are used in the field. Consequently, a comparison of dielectric strength values of different origins, for example material supplier and customer, is often not meaningful.
To quantify the influence of the test procedure on the dielectric strength values, a batch of industrial thick-film substrates has been tested with different electrode configurations under AC conditions. Opposing cylinders with diameters of 6.4 mm and 25 mm, and a thick-film metallization with a diameter of 25 mm were used in the study. At least 20 specimens were tested with each type of electrodes. The results range from 21.7 ± 0.7 kV/mm measured with printed electrodes to 26.7 ±1.2 kV/mm measured with reused 6.4 mm cylinders. This means a difference of 23 %. Measurements performed with 6.4 mm cylinder electrodes produce significantly lower values (ANOVA, α = 0.01) if a new set of electrodes is used for each measurement instead of reusing the same pair of electrodes for the entire batch. The dielectric strength measured with new 25 mm cylinders is 11.2 % lower than the values determined with new 6.4 mm cylinders. No significant difference (ANOVA, α = 0.01) was found for measurements with printed electrodes and opposing 25 mm cylinders. Weibull evaluation of the data showed that all tested electrode configurations result in a similar reliability of the specimen (Weibull modulus) but in a significantly different characteristic dielectric strength (scale factor, Bonferroni, α = 0.05).
This study emphasizes the importance of a thorough and comprehensive documentation and communication of the test procedure for dielectric strength measurements. It further helps to evaluate the significance of differences in dielectric strength data provided by different sources.
The accurate EDS microanalysis of light elements such as boron and carbon by spectrum imaging will be demonstrated using a sintered hard ceramic material composed of the three major phases titanium boride (TiB2), titanium carbide (TiC), silicon carbide (SiC) and minor phases, sub-μm in size.
The combination of these three materials leads to improved mechanical and tribological properties. Silicon carbide is a material used for mechanical seals. It has the disadvantage of reduced failsafe running functions, causing increased wear when running dry. The added titanium components (TiC and TiB2) improve the failsafe running functions. This technology has already been transferred to industrial applications.