A novel red pigment displaying consistent properties up to a heating temperature of 1000 °C was synthesized, which indicates that the multilayer silica coating actually minimizes the agglomeration of the nanoparticles.

Extraordinary properties of traditional hyperbolic metamaterials, not found in nature, arise from their man-made subwavelength structures causing unique light−matter interactions. However, their preparation requiring nanofabrication processes is highly challenging and merely provides nanoscale two-dimensional structures. Stabilizing their bulk forms via scalable procedures has been a sought-goal for broad applications of this technology. Herein, we report a new strategy of designing and realizing bulk metamaterials with finely tunable hyperbolic responses. We develop a facile two-step process: (1) self-assembly to obtain heterostructured nanohybrids of building blocks and (2) consolidation to convert nanohybrid powders to dense bulk pellets. Our samples have centimeter-scale dimensions typically, readily further scalable. Importantly, the thickness of building blocks and their relative concentration in bulk materials serve as a delicate means of controlling hyperbolic responses. The resulting new bulk heterostructured material system consists of the alternating h-BN and graphite/graphene nanolayers and exhibits significant modulation in both type-I and type-II hyperbolic resonance modes. It is the first example of real bulk hyperbolic metamaterials, consequently displaying the capability of tuning their responses along both in-plane and out-of-plane directions of the materials for the first time. It also distinctly interacts with unpolarized and polarized transverse magnetic and electronic beams to give unique hyperbolic responses. Our achievement can be a new platform to create various bulk metamaterials without complicated nanofabrication techniques. Our facile synthesis method using common laboratory techniques can open doors to broad-range researchers for active interdisciplinary studies for this otherwise hardly accessible technology.

This manuscript reports characterization of the colorations and thermal behaviors of the silica-coated alpha-Fe2O3 and beta-FeOOH nanocapsules. Prepared beta-FeOOH and alpha-Fe2O3 nanoparticles were coated with silica using tetraethylorthosilicate (TEOS) and cetyltrimethyl-ammonium bromide (CTAB) as a surface modifier for the comparison of physical properties of both samples. XRD patterns of the silica-coated beta-FeOOH and alpha-Fe2O3 nanoparticles were heated to 1000 degrees C, show a hematite (alpha-Fe2O3) structure. The silica-coated beta-FeOOH nanoparticles became almost entirely hollow at 1000 degrees C due to their volume reduction. In addition, the coloration values of the transformation nano capsule alpha-Fe2O3 are lower than those of the silica-coated alpha-Fe2O3 nanostructures. On the other hand, the silica-coated alpha-Fe2O3 nanoparticles retained their colorations and shapes after being heated to 1000 degrees C. The morphologies, crystal structures and colorations of the as prepared samples were analyzed by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction and CIE colorimeter.

In this work, airborne brake wear particulate matter (PM) emissions from a brake system were investigated by time-resolved and temperature-dependent measurement using a dynamometer. The measurement was performed for representative friction materials, 3 low-steel (LS) and 4 non-steel (NS), which are currently in worldwide use. The PM emission factor was found to be varied as large as by one order of magnitude depending on the composition of friction materials(pads). The airborne particle mass emissions from the LS materials ranged from 1.88 to 3.14 mg/km/vehicle, while the emissions from the NS ranged from 0.3 to 2.34 mg/km/vehicle, which is, in general, smaller than the LS. The time-resolved data imply that particle emissions in the extra-high-speed region of the WLTC cycle, where friction occurs at high temperature (T disk > 150 °C), is much higher than in the low-speed region, and determines the total PM mass emission factor. It was found that the friction materials containing metals such as Cu and Sn (LS-2/-3 and NS-4/-5) exhibited a lower PM emission factor. This result suggests that copper and tin, which forms an effective lubricating tribolayer in the interface between the pad and disk at high temperature, remarkably reduces PM emissions. It has been also found that the surface roughness of worn brake pads is positively proportional to PM emissions according to surface topography analysis, which is consistent with composition effect. These findings suggest that tribological engineering to provide sliding frictional behavior at elevated temperature is crucial to reducing PM emissions.

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