Topological signatures and stability of hexagonal close packing and Barlow stackings

3D rendering of the experimental packing obtained via X-ray CT. A cut-out section shows the bulk crystallisation and partially crystallised regions.

Study That Led to the Discovery of Rhombohedral Close Packing and Hexagonal Close Packing as Two New and Independent Lattices

An ab-initio calculation of angles has been made between various directions on close packed basal plane with the tilted axis obtained by placing identical atoms on voids. Results obtained from simple calculations provide a lot of important information related to Rhombohedral Close Packed and Hexagonal Close Packed structures, effectively leading to their discovery as independent and genuine space lattices from close packed category of materials. En-route, we also propose a separate equation to calculate the angles between two given directions in the above mentioned close packed crystal systems. Modes of polytype formation in close packing of identical atoms is also briefly discussed.

Theoretical research of spinning triangle division on spun yarn torque

Purpose The purpose of this paper is to theoretically study the effects of ring spinning triangle division on spun yarn torques. Design/methodology/approach The case that the spinning triangle is divided into two parts, primary triangles and final triangle, is investigated. Theoretical model of yarn torque was given by linking the fiber tension in the spinning triangle to yarn torque under the assumption that the arrangement of fibers (substrands) in the substrands (yarn) is hexagonal close packing. Then, as an application of the proposed method, 14.6tex cotton yarns were taken as an example for the numerical simulations. Findings The fiber tensions in the divided spinning triangles and corresponding yarn torques were simulated numerically by using MATLAB software. The effects of division proportions and number of primary triangles on spun yarn torques are analyzed theoretically. Originality/value It is shown that suitable spinning triangle division is benefit for reducing yarn torque.

Epoxy-Glass Microballoon Syntactic Foams: Rheological Optimization of the Processing Window

In this paper, we discuss the chemorheology of epoxy based syntactic foams containing glass microballoons of varying density, with an aim of establishing the effect of microballoon loading on its processability. The primary objective is to determine the maximum microballoon loading that disperses uniformly in the resin without the aid of any diluent. The viscosity and dynamic mechanical properties of epoxy formulations containing varying amounts of glass microballoons were established by parallel plate rheometry. Our studies reveal that solventless processing of formulations with microballoon loading > 60% poses practical difficulties due to prohibitively high viscosities, although a packing efficiency of 74% is theoretically allowed in the case of hexagonal close packing. The presence of microballoons does not alter the curing mechanism. The mechanical properties of syntactic foams were inversely proportional to the loading and type of glass microballoons.

The Effects of Mo and Nb on the Microstructures and Properties of CrFeCoNi(Nb,Mo) Alloys

The effects of niobium and molybdenum additions on the microstructures, hardness and corrosion behaviors of CrFeCoNi(Nb,Mo) alloys were investigated. All of the CrFeCoNi(Nb,Mo) alloys displayed dendritic microstructures. The dendrites of CrFeCoNiNb and CrFeCoNiNb0.5Mo0.5 alloys were a hexagonal close packing (HCP) phase and the interdendrites were a eutectic structure of HCP and face-centered cubic (FCC) phases. Additionally, the dendrites of CrFeCoNiMo alloys were a simple cubic (SC) phase and the interdendrites were a eutectic structure of SC and FCC phases. The volume fraction of dendrites and interdendrites in these alloys were calculated. The influences of the volume fraction of dendrite in the alloys on the overall hardness were also discussed. The CrFeCoNiNb alloy had the larger volume fraction of dendrite and thus had the highest hardness among these alloys. The CrFeCoNi(Nb,Mo) alloys also showed better corrosion resistances in 1 M H2SO4 and 1 M NaCl solutions by comparing with commercial 304 stainless steel. The CrFeCoNiNb0.5Mo0.5 alloy possessed the best corrosion resistances in these solutions among the CrFeCoNi(Nb,Mo) alloys.

A closer look into close packing: pentacoordinated silicon in a high-pressure polymorph of danburite

Due to their high technological and geological relevance, silicates are one of the most studied classes of inorganic compounds. Under ambient conditions, the silicon in silicates is almost exclusively coordinated by four oxygen atoms, while high-pressure treatment normally results in an increase in the coordination from four- to sixfold. Reported here is a high-pressure single-crystal X-ray diffraction study of danburite, CaB2Si2O8, the first compound showing a step-wise transition of Si coordination from tetrahedral to octahedral through a trigonal bipyramid. Along the compression, the Si2O7groups of danburite first transform into chains of vertice-sharing SiO5trigonal bipyramids (danburite-II) and later into chains of edge-sharing SiO6octahedra (danburite-III). It is suggested that the unusual formation of an SiO5configuration is a consequence of filling up the pentacoordinated voids in the distorted hexagonal close packing of danburite-II.

Quantum confinement of molecular deuterium clusters in carbon nanotubes: ab initio evidence for hexagonal close packing

This study shows ab initio evidence for hexagonal close packing of D2 molecules in carbon nanotubes, with a = 3.6 Å and .