Electrostatic Charges of Abrasive Powders: A Role of Particle Size and Humidity

Electrostatically coated abrasives have drawn vast attention in many industrial applications. Therefore, influence of humidity on the electrical properties of α-SiC and α-Al2O3 abrasive powders with three μm-range particle sizes are here investigated using electrostatic charge and DC resistivity analysis. From the three particle size ranges used, 15–16 μm, 60–63 μm and 153–156 μm, the intermediate one (60–63 μm) is found to be associated with the highest charge values, measured using a double Faraday cup method, as well as the highest resistivity for both materials. However, comparing SiC and Al2O3 powders, the latter ones present about twice larger charges in dry and normal humidity states accompanied by several orders of magnitude larger resistivity. Under humid conditions all the powders reveal diminishing charge and resistivity values.

Synthesis and Characterisation of Zinc-doped Antimony Selenide

Antimony selenide substituted with Sb0.4Se0.6 and doped with zinc at three doping ratios (x=0, 0.01 and 0.03) was prepared via the solid state reaction method. The three prepared compositions were reacted thermally at 400 °C for 3 h. The structure of specimens was characterised via X-ray powder diffractometer to obtain the type of crystalline structure and lattice parameters of the prepared specimens, which showed a polycrystalline, orthorhombic structure. Optical characterisation was then achieved via UV-visible spectroscopy to exhibit the transmittance and reflectance spectra and estimate the band gap values of the prepared compositions. The samples showed high absorption spectra at low wavelengths (from 60% to 90%) and low reflectance values (from nearly zero to 17%). The band gap measurement showed an indirect transition, with values ranging from 1.2 eV to 1.23 eV. The electrical characteristics were represented by DC resistivity measurement at low temperature and AC conductivity measurement against frequency. The compositions showed a semiconducting behaviour in DC resistivity and compatible results in AC conductivity.

Development and Validation of a Low-cost DC Resistivity Meter for Humanitarian Geophysics Applications

Insufficient access to safe drinking water is one of the most challenging global humanitarian issues. The development of low-cost microcontrollers and the widespread availability of cheap electronics components raise the possibility of developing and using low-cost geophysical instrumentation with open-source designs and software solutions to circumvent geophysical instrumentation capital cost issues. To these ends, we alter an existing low-cost DC resistivity meter design and develop an optional modular Raspberry Pi data-logging system to improve the unit's functionality, usability and to ensure data integrity. Numerical modeling and physical testing demonstrates that the system is more robust than previously published low-cost designs and works in a more diverse range of geological scenarios - especially conductive environments. Our instrument was tested in a Geoscientists Without Borders (GWB) project jointly run between researchers from Colorado School of Mines (CSM) and Universit矤'Abomey-Calavi (UAC), Cotonou, Benin. A key project component involved CSM and UAC students constructing and validating two low-cost DC resistivity meters and then using these instruments for fieldwork aimed at better characterizing and monitoring the health of a local aquifer used as a groundwater source for communities in the Cotonou region. The low-cost instruments were successfully used alongside a commercial resistivity meter to acquire data for 2D inversion of aquifer hydrostratigraphy , indicating the presence of a clay-sand contact. The cost of the redesigned instrument and data logger respectively are $177 and $108 (in 2021 USD) with future cost reductions possible, which are fractions of the price of commercial resistivity meters.

Synthesis And Characterization of Cobalt-Zinc Spinel Ferrites For High Frequency Applications

Spinel ferrites are attractive for high frequency applications due to their larger direct current (dc) resistivity and low dielectric loss. In the present work, Co0.6Zn0.4HoxFe2-xO4 (x = 0.00 and 0.1) spinel ferrites were prepared by sol-gel method. The X-ray diffraction pattern showed that both samples had cubic spinel structure, while in sample (x = 0.1), the secondary phase (HoFeO3) was also observed. The dc resistivity was increased with the addition of holmium ions. As the temperature increased, the dc resistivity was decreased by proving their semiconducting nature. The dielectric properties were also measured as a function of temperature and frequency. The sample which was composed by the substitution of holmium ions contained low value of dielectric loss. The magnetic properties were also experimentally measured by applying the field up to 2000 oersted. The small area covered by hysteresis loop proved that both samples possessed soft nature of magnetic materials.

An Integrative Approach for Environmental Assessment and Water Resources Management Using Direct Current Resistivity (DC), Geographic Information System (GIS), Remote Sensing, and Gain and Loss Method

Sustainable water resource management is a crucial national and global issue (Currell et al., 2012). In arid areas, groundwater is often the major source of water or at least a crucial supplement to other freshwater resources for agriculture, industry and domestic consumption (Vrba and Renaud, 2016). The complexity associated with groundwater-surface water interactions creates uncertainty about water resource sustainability in semi-arid environments, especially with urbanization and population growth. Flood irrigation in the early 1900s increased the shallow groundwater table in the Treasure Valley (TV), but with increasing irrigation efficiencies, they have been declining since the 1960s with a mean decline rate of about 2.9-3.9x10^-9 (m/s) (Contor et al., 2011). Quantifying how much surface water is being exchanged with the shallow groundwater table through canals in the TV is necessary for gaining a better understanding of groundwater-surface water interactions in this heavily managed system. This knowledge would help evaluate alternative management options for achieving sustainable management of existing water resources. The key objectives of this project are to determine the seepage rate through some canal reaches in the TV, evaluate the integration of the gain and loss method, remote sensing, GIS, hydrogeophysical simulation, and direct current (DC) resistivity geophysical methods for water resource management. We hypothesize that the underlying lithology and size of canals affect the magnitude of the seepage rate. Flow measurements were collected weekly between July and August 2020 in canal reaches representing different sizes and lithological units to determine the seepage rate using the reach gain/loss method. Canal variability and measurement uncertainty were included in seepage estimation for the entire TV using 3 alternative scaling approaches. DC resistivity was used as a complementary method to monitor the seepage effect on the shallow GW aquifer over 2 months. This research evaluates to what extent canal size and its underlying lithology affects the seepage rate, and how the integration of methods may provide additional insight into groundwater exchange-surface water.