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Mn 1- x Zn x Fe 2 O 4 ferrofluids were produced from natural sand for magnetic sensors and radar absorbing materials. The X-ray diffraction data showed that the Zn partially substituted the Mn and Fe ions to construct a spinel structure. The increasing Zn composition decreased the lattice parameters of the structure. The transmission electron microscopy images showed that the filler Mn 1- x Zn x Fe 2 O 4 nanoparticles tended to agglomerate in three dimensions. Lognormal and mass fractal models were used to fit the small-angle X-ray scattering data of the ferrofluids demonstrated that the ferrofluids formed chain-like structures with a fractal dimension of 1.12–1.67 that was constructed from primary particles with sizes of 3.6–4.1 nm. The filler, surfactant, and carrier liquid of the ferrofluids were confirmed by the functional groups of the metal oxides, tetramethylammonium hydroxide, and H 2 O, respectively. The secondary particles contributed to the saturation magnetization of the Mn 1- x Zn x Fe 2 O 4 ferrofluids. The Mn 1- x Zn x Fe 2 O 4 ferrofluids demonstrated excellent performance as magnetic sensors with high stability, especially compared with MnFe 2 O 4 ferrofluids. Furthermore, the ferrofluids exhibited excellent radar absorbing materials. The Mn 1- x Zn x Fe 2 O 4 ferrofluids prepared in this work may serve as a future platform for advancing magnetic sensors and radar absorbing materials.

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Most of the coal is used as fuel in power plants,cement industry and metal processing industry. Use of coal as fuelwill depend on the quality of the coal used. The main parameters thatdetermining the quality of coal is the calorific value. Meanwhile, the calorific value of a coalwill depend on several parameters, namely total moisture, total sulfur andash content. This study aims to determine the effect of the relationship betweenthe content of some of these parameters on the calorific value of a coal. Analysisperformed using the American Society for Testing and Materials (ASTM).The stages of this analysis include sample preparation, air dry loss testing, residualmoisture, total sulfur, ash content and gross calorific value. The results of the analysis showthat the higher the total moisture content, total sulfur and ash content, the higher thecauses the lower the calorific value of a coal.

Study of nickel leaching using sulfuric acid and phosphoric acid on the selectivity of low-grade laterite nickel ore under atmospheric conditions has been successfully carried out. In this study, the laterite nickel leaching process was carried out by varying the solution concentration and operating time. The concentrations of sulfuric acid and phosphoric acid solutions were varied at 5 M and 6 M concentrations, while the operating time was varied at 4 hours and 6 hours. For other operating conditions, it is kept constant with an operating temperature of 90 ℃, pulp density 15% w / v, particle size ≤ 200 mesh. After that, the analysis stage was carried out using an atomic absorption spectroscopy (AAS) tool to determine the nickel content in the sample. The results showed that the highest nickel recovery was obtained at the concentration of 5 M sulfuric acid solution of 2.60% and 5 M phosphoric acid of 2.59% with the optimum operating time at 4 hours of operating time.