The paper describes the influence of graphite shape, size and amount to electrical properties of different cast irons. Experiments of electrical resistivity measurements were conducted during solidification of four different melts in different time intervals from melt treatment by inoculation and nodularization. Metallographic analyses were made in order to determine the shape, size, distribution and amount of graphite and correlate results with electrical resistivity measurements. It was found out that nodular graphite is giving the lowest electrical resistivity and is decreased during solidification. Electrical resistivity of lamellar cast iron is increased during solidification since lamellas interrupt metal matrix severely There is no significant difference in resistivity of vermicular cast iron from nodular cast iron. Smaller size of graphite and lower amount of graphite and higher amount of metal matrix also decrease resistivity.
In this paper an attempt to determine the relationship between the electrical resistivity and the tensile strength and hardness of cast iron of carbon equivalent in the range from 3.93% to 4.48%. Tests were performed on the gray cast iron for 12 different melts with different chemical composition. From one melt poured 6 samples. Based on the study of mechanical and electro-resistive determined variation characteristics of tensile strength, hardness and resistivity as a function of the carbon equivalent. Then, regression equations were developed as power functions describing the relationship between the resistivity of castings and their tensile strength and hardness. It was found a high level of regression equations to measuring points, particularly with regard to the relationship Rm=f(ρ). The obtained preliminary results indicate the possibility of application of the method of the resistance to rapid diagnostic casts on the production line, when we are dealing with repeatable production, in this case non variable geometry of the product for which it has been determinated before a regression equation.
The main objective of this study was to assess the environmental impact of the subsurface geological structure in Nam Son landfill by hydrogeophysical method. The Electrical Resistivity Tomography (ERT), Self- -Potential (SP) and Very Low Frequency (VLF) method was used for geological structure investigation. Three profiles (total 900 m long) of two-dimensional ERT, VLF density sections and 180 SP data points scattered within the study area near the disposal site were implemented. Surface water and groundwater samples were collected from 10 sites in the area for hydrochemical analysis. Interpretations of geophysical data show a low resistivity zone (<15 Ω m), which appears to be a fully saturated zone with leachate from an open dumpsite. There is a good correlation between the geophysical investigations and the results of hydrochemical analysis.
The main scientific goal of this work is the presentation of the role of selected geophysical methods (Ground-Penetrating Radar GPR and Electrical Resistivity Tomography ERT) to identify water escape zones from retention reservoirs. The paper proposes a methodology of geophysical investigations for the identification of water escape zones from a retention fresh water lake (low mineralised water). The study was performed in a lake reservoir in Upper Silesia. Since a number of years the administrators of the lake have observed a decreasing water level, a phenomenon that is not related to the exploitation of the object. The analysed retention lake has a maximal depth between 6 and 10 m, depending on the season. It is located on Triassic carbonate rocks of the Muschelkalk facies. Geophysical surveys included measurements on the water surface using ground penetration radar (GPR) and electrical resistivity tomography (ERT) methods. The measurements were performed from watercrafts made of non-metal materials. The prospection reached a depth of about 1 to 5 m below the reservoir bottom. Due to large difficulties of conducting investigations in the lake, a fragment with an area of about 5,300 m 2, where service activities and sealing works were already commenced, was selected for the geophysical survey. The scope of this work was: (1) field geophysical research (Ground-Penetrating Radar GPR and Electrical Resistivity Tomography ERT with geodesic service), (2) processing of the obtained geophysical research results, (3) modelling of GPR and ERT anomalies on a fractured water reservoir bottom, and (4) interpretation of the obtained results based on the modelled geophysical anomalies. The geophysical surveys allowed for distinguishing a zone with anomalous physical parameters in the area of the analysed part of the retention lake. ERT surveys have shown that the water escape zone from the reservoir was characterised by significantly decreased electrical resistivities. Diffraction hyperboles and a zone of wave attenuation were observed on the GPR images in the lake bottom within the water escape zone indicating cracks in the bottom of the water reservoir. The proposed methodology of geophysical surveys seems effective in solving untypical issues such as measurements on the water surface.
Wider application of silicon carbide (SiC) is anticipated for increasing the durability of various structural facilities. For this study, SiC was fabricated with decreased electrical resistivity for precision electrical discharge machining. Two-step reaction sintering by infiltration of molten Fe-Si alloy was applied for SiC fabrication. The procedure included first sintering at 973 K in Ar gas atmosphere and second sintering by spontaneous infiltration of molten Fe-75%Si alloy at 1693 K in vacuum. The sintered structure porosity became very low, forming 3C-type SiC. Results confirmed that molten Fe-75%Si alloy infiltration occurred because of reaction sintering. The electrical resistivity of the sintered SiC infiltrated by molten Fe-75%Si alloy can be improved to be two orders of magnitude lower than that by molten Si, consequently maintaining the high performance of SiC.