Ignition study of facile spray drying prepared microspheres of nickel coated boron nanoparticles using a shock tube

Abstract

Boron is being widely explored as a potential additive for high energy fuels because of its extraordinary gravimetric and volumetric energy content. However, its application is obstructed by the surface oxide layer which forms on the core boron particles, degrading its combustion and ignition performance. This oxide layer has a high vaporization temperature. To improve the combustion and ignition performance of boron, nickel nanoparticles were coated on the boron particle surface using a simple and unique spray drying technique. Numerous samples were prepared while varying the boron and nickel particles weight percent ratios. Surface morphological analyses showed that the nickel coated boron particles formed microspheres. These microspheres had a size distribution in the range of 2–15 µm and a mean diameter of 4.64 µm. The coating density of the crystalline nickel nanoparticles on the boron surface increased as the nickel percent used for the sample preparation was increased. X-ray diffraction (XRD) identifies the coating of nickel particles over the boron surface without any phase formation. Field emission scanning electron microscopy (FE-SEM), line scanning, elemental mapping and energy dispersive spectroscopy (EDS) studies provided an elemental analysis of the nickel coated boron particles that confirmed the surfaces of the boron particles were coated with nickel particles, and formed intimate contact between them. The oxidation performance of nickel, boron, and boron coated with nickel particles was studied by thermogravimetric analysis (TGA). The beginning of oxidation and the exothermic peaks of pure boron appeared earlier after the coating with nickel. Also, a decrease in weight gain was observed at 1000 °C in the boron coated with nickel. A shock tube experiment showed the nickel coated boron has a lower ignition delay time than the pure boron. The ignition delay times of the nickel coated boron samples, such as B:Ni= 40:1 and B:Ni= 10:1 samples decreased by 12% and 16%, respectively, compared to pure boron. Thus, spray drying prepared nickel coated boron particles demonstrated a substantial improvement in ignition performance versus uncoated boron.