SOUTHERN JOURNAL OF SCIENCES

Cast iron alloys combine many elements such as carbon, iron, silicon, magnesium and can be usually classified according to their microstructure in ductile, gray, compacted, white, and malleable. Each one has particularities in terms of properties and applications. Hence, this study aims to evaluate the degree of nodularity (%) in a ductile cast iron alloy GGG 40. In this context, a methodology to investigate the degree of nodularity wasproposed. The ultrasonic method was used to determine the amount of ductile graphite as well as for parts release and thus facilitated the industrial operational execution. The effect of ultrasonic sound was investigated in sixtyseven ductile cast irons, and these analyses were further compared to the level of nodularity observed by metallography. Finally, based on the findings, the cast iron quality was guaranteed, leading to time savings, avoiding the microstructural examination, and thus promoting cost reductions.

Background: A client requested that the study group help determine suitable locations for a drilling regime on his lot, located on an upslope rocky knoll in Lawu Estate, Minna, Nigeria. There is no luxury of conducting an unimpeded wide-area survey for this housing Estate, as it is built up almost entirely. Therefore, the constrained area to be surveyed necessitated the adoption of the "electrical drilling," or vertical electrical sounding, mode of the geoelectrical method to satisfy the client's inquiry. Aim: To carry out a purpose-specific survey to pinpoint the best location in a built-up property at the upmarket Lawu Estate that would be suitable for a drilling regime targeted for household consumption. The specific objectives are to determine the subsurface layer structure, to identify fracture zones with potential for water accumulation, and to estimate the depths of potential aquifers. Methods: The survey crew reconnoitered the study area to georeference locations for the VES survey within the 30 m x 20 m lot. Owing to the extensive build-up at this lot, only a four-point traverse along the 30-metric dimension of the building's frontage was demarcated in the northeasterly direction, thereby limiting the survey crew's desire to define an appropriate survey grid. The VES data acquisition followed the "traditional" sequence of Schlumberger array layout measurements, in which the current and potential probes are maintained at the same relative spacing and the whole spread is progressively expanded about a fixed central point. Results: Log-log and pseudosection plots were generated from the acquired data, from which the conventional three-layer structure is deciphered, with a desired 193 Ωm for VES Station 4 at the third layer. Discussion: The acquired and processed data for this study were subjected to a suite of empirical rules-of-thumb procedures for interpreting VES data in the Nigerian Basement Complex geological province, with VES Station 4 showing the most encouraging 100% result. Conclusion: Drilling to a depth of 100 m at Station 4 is recommended based on the identified fractured basement at this depth.

Background: MQ-series gas sensors belong to the metal oxide semiconductor (MOS) family of sensors that can sense the presence of many gases. These sensors find their application in gas alarm systems as key components. While necessary sensor circuit output voltage value for alarm point in a stand-alone gas alarm system is desirable, but what exact combination of the sensor circuit parameters is required? Hitherto, the determination of these circuit parameters has not been given much attention in the research community. Aim: the purpose of this work is to explore a structured graphical approach of determination of MQ series gas sensor circuit parameters for a stand-alone gas alarm system that yields desired sensor circuit output voltage value for the alarm point; the main objective of the study was to develop mathematical model equations that relate the: (i) sensor resistance (RS) with the gas concentration (x) and the sensor resistance at standard calibration concentration of the sensor base gas in the clean air (Ro) and (ii) sensor circuit output voltage (VRL), load resistance (RL) and sensor resistance (RS). It is expected from the model equations developed that graphical correlations of the sensor circuits parameters will be generated. Using these graphs for a particular case of an MQ-4 gas sensor under the influence of LPG, the parameters that yield desired sensor circuit output voltage of 2V for 1000 ppm of LPG alarm point will be determined. Methods: Model equations were developed for the sensor dynamics, and based on these model equations, graphs for the determination of required sensor parameters were plotted for a case of MQ-4 gas sensor response to LPG. Results and Discussion: The results yielded optimal values for R_O,R_S and R_L of 20 kΩ, 30 kΩ and 20 kΩ respectively, for alarm settings of 1000 ppm and a desired sensor circuit output voltage of 2 V. Based on determined parameters, the calibration equation for determination of best concentration value for a given value of emulated LPG concentration was developed. Using the method proposed in this study makes the process of determining the MQ-series gas sensor circuit parameters less cumbersome as their value can easily be obtained from the resulting graphs. Conclusions: a structured graphical approach for determination of MQ-series gas sensor circuit parameters for alarm points in a stand-alone gas alarm system showed that using MQ-4 gas sensor and LPG as the target gas, and for a sensor circuit output voltage of 2 V for alarm point at 1000 ppm of LPG, the corresponding value of R_O, R_S and R_L obtained were 20 kΩ, 30 kΩ, and 20 kΩ respectively. Hence, a structured graphical approach is suitable for determining MQ series gas sensor circuit parameters for a stand-alone gas alarm system under the influence of its associated gases.