Tigernut starch is starch extracted from the tubers of Cyperus esculentus L. a perennial herb commonly known as tigernut. The effect of pH on the foaming, gelatinization, solubility, swelling, paste clarity, viscosity, freeze–thaw stability, and binder efficiency of the starch in buffer solutions of pHs 4, 7, and 9.2, representative of acid, neutral, and alkaline pHs were evaluated. Marked pH responsiveness was observed in all these parameters to varying degrees. The foaming capacity, paste clarity, freeze–thaw stability, swelling, and viscosity increased while only the gelatinization temperature decreased with increasing pH. The pastes obtained at pHs 4 and 7 showed marked instability by forming a mass of hard coarse gel with the first freeze–thaw cycle while the paste of pH 9.2 maintained its normal viscoelastic‐gel texture even after the fourth freeze–thaw cycle. The properties of the ascorbic acid granules and tablets produced by wet granulation, using the pastes as binder showed pH‐responsiveness, with the granule formed with the paste of pH 9.2 showing higher mechanical strength and lower disintegration time. This study thus shows the diversity in the physicochemical and binder properties of tigernut starch with changes in pH.

This paper presents the results of an experimental study of the effects of surface texture on the optical and light trapping properties of silicon wafers. Surface texture is controlled by anisotropic etching with potassium hydroxide (KOH) and isopropyl alcohol (IPA) solutions. The anisotropic etching of (001) crystalline silicon wafers is shown to result in the formation of {111} pyramidal facets on the surfaces of the wafers. A combination of profilometry, optical microscopy, scanning electron microscopy, and atomic force microscopy is used to study the effects of KOH/IPA etching on the morphology and roughness of the textured surfaces. The results show that IPA concentration has the strongest effect on the surface roughness of (001)-single crystal crystals at temperatures up to 80 °C. Above this value, evidence of temperature-induced cracking was revealed on the silicon substrate. The best volume concentration ratio of KOH:IPA is also found to be 2:4. The implications of the study are discussed for the design of light trapping in silicon solar cells.

This study presents the application of ternary phase diagrams to tropical almond biodiesel components separation and purification at two temperatures. The seed oil was extracted mechanically and alkaline transesterified to produce biodiesel. The oil and biodiesel were characterized using standard methods. Tie lines and binodal solubility curve data were determined using modified cloud point titration procedures. Gas chromatographic method was employed in the analysis of the phase compositions. The mixture of biodiesel, methanol and glycerol were investigated at 20 °C, 30 °C and withdrawal times of 2 to 32 minutes at 2 minutes intervals. Distribution coefficient, K and solvent selectivity, S analysis were performed. Results obtained showed that S > 1 indicating the ability of methanol to promote phase separation and purification. K < 1 implying that there was lower quantities of methanol solubilized in the biodiesel phase. The ternary phase diagrams provided the means of predicting the components distribution. Keywords: Production, Characterization, Tropical Almond Biodiesel, Purification, Ternary Phase Diagram

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Sawdust and rice husk are available in abundance and indigenous in Nigeria but have not been exploited because they cannot be used directly in combustion processes due to their loose form unless by pelleting or briquetting. This experimental study assesses the potential of pellets from sawdust (SD) and rice husk (RH). Pallet samples collected from mills were thereafter optimized in ratios (i.e. 90%RH:10%SD, 80%RH:20%SD, 70RH:30SD, 60%RH:40%SD, 50%RH:50%SD, 100%RH and 100%SD) using mixing ratio optimization model. Seven samples were produced using a manual screw press machine and were subsequently categorized in terms of calorific value (CV), proximate and ultimate analyses using the ASTM standards. Results showed that the 100%RH pellets have higher CV of 31,026.3kJ/kg and the 100%SD a value of 26,088.3kJ/kg while the optimized pellets range from 25,867.39kJ/kg to 27,063.60kJ/kg. The CV decreases with increasing ash content of the pellets. It was also observed from the proximate analysis that the 100%RH has low percentages of moisture content, volatile matter and ash content compared to others. The optimized pellets showed that SD has the tendency to reduce the sulfur content in RH; hence, a promising alternative source of energy to the conventional fossil fuel.

We investigate the effect of surface texturing on the light trapping properties of Silicon wafers as a function of reflection reduction and surface morphology. This was achieved by structuring a random square-based pyramids pattern on the surface of Silicon substrate using anisotropy etching. The light trapping effect was optimized for silicon solar cells by investigating the dependence of the silicon surface texturing on the process parameters such as etchant concentration, etching time and temperature. We study the surface morphology by analyzing the surface behaviour of the textured substrate using the atomic force microscope and scanning electron microscope. The results of roughness and optical reflection were obtained using the surface profiler and the UV/VIS the spectrometer respectively. In addition, an analytical modelling method was developed to determine the angles of incidence of light rays with each of the facets of the pyramids and the coordinate of the reflected light rays. The method used here is based on 3-D vector geometry of the pyramidal facets. The optimum parameters are found to be 40min, a temperature of 80oC and with KOH/IPA/DI in the ratio [2:4:46] by volume, yielding a surface roughness over 600 nm and a relative optical reflectance in the visible spectrum less than 10%, using polished Si as reference. The results and analysis of both the modelled and measured reflectance, suggest that the performance of the light trapping technique has a big potential in silicon solar cells application.

In this paper, the surface morphology of textured silicon substrates is explored. Prior to the surface morphology analysis, textured silicon substrates were obtained by KOH anisotropic texturing of polished silicon wafers. This was achieved by investigating of the dependence surface texturing on the process parameters; etchant concentration, etching time and temperature. The surface morphology of the textured silicon samples was obtained using atomic force microscopy that was operated in the tapping mode. The resulting atomic force microscopy (AFM) images were analyzed using the Nanoscope and Gwyddion software packages. The AFM analysis revealed more surface details such as the depth, roughness, section, and step height analysis. The analysis was limited to a length scale of a few micrometers, which carefully reveals the number of individualities of the initial stages of pyramid growth. The average roughness was found to be 593nm for an optimally textured silicon wafer. The implications of the study are then discussed for potential light trapping application in silicon solar cells.