Simultaneous Growth Processes Research Articles

One-step growth of the interconnected carbon nanotubes/graphene hybrids from cuttlebone-derived bi-functional catalyst for lithium-ion batteries

Carbon nanotubes/graphene hybrid materials with excellent physicochemical properties can be widely applied in the fields of energy storage, electrocatalysis, sensing, etc. Reducing the self-stacking and achieving covalent interaction between carbon nanotubes and graphene are important to ensure a stable hierarchical architecture and effective mass transfer. Herein, we propose a one-step strategy to synthesize 3D interconnected carbon nanotubes/graphene hybrids on the easy-to-remove biomass-derived substrate. The calcined natural cuttlebone as bi-functional catalyst precursor can simultaneously grow carbon nanotubes and graphene by one-step chemical vapor deposition without the addition of extra metal catalysts, while the interconnected structure can act as the porous template for graphene growth. The simultaneous growth process can obtain covalent bonding between carbon nanotubes and graphene, while the crystalline quality and interlayer space can be adjusted by different carbon sources and growth parameters (e.g., temperature). The one-step grown carbon nanotubes/graphene hybrids with seamless interfaces and hierarchical interconnected 3D structure can effectively enhance the electron transfer as well as the electrolyte infiltration efficiency. When utilized as lithium-ion batteries (LIBs) anode, a high specific capacity (544 mAh g–1 at 0.1 A g–1), good rate capability (200 mAh g–1 at 6.4 A g–1 with an ultrashort charge time of 113 s), and excellent cyclic stability can be achieved. This simple and one-step carbon nanotubes/graphene hybrids fabrication strategy can be easily scale-up and applied in various fields.

Nitridation kinetics of Sm2Fe17 probed using Mössbauer spectroscopy

In this study, the Sm2Fe17 powder was subjected to nitridation at 743 K under N2 pressures of 0.05 and 0.1 MPa to investigate the growth kinetics of Sm–Fe–N. Two-phase growth of the fully nitride (FN) Sm2Fe17N3 phase and the nitrogen-poor (NP) Sm2Fe17Nx phase (0 < x < 3; x denotes the nitrogen content) was observed using 57Fe Mössbauer spectroscopy. Although the x value was greater at 0.05 MPa than at 0.1 MPa in the early stage of nitridation, the opposite trend was observed in the later stage. At a nitrogenation time of 24 h, nitridation was nearly complete at 0.1 MPa, while x tended to saturate and did not reach 3 at 0.05 MPa. The nitridation process was discussed based on two simultaneous growth processes: (i) the diffusion of the nitrogen atom in the NP phase and (ii) the nucleation and growth of the FN phase. A process combining N2 pressure and nitrogenation, which facilitated nitrogenation under low N2 pressure and high N2 pressure at the beginning and end of the nitridation process, respectively, achieved faster nitridation than process with a single N2 pressure.

Contrasting In Vitro Apatite Growth from Bioactive Glass Surfaces with that of Spontaneous Precipitation.

Body-fluid-exposed bioactive glasses (BGs) integrate with living tissues due to the formation of a biomimetic surface layer of calcium hydroxy-carbonate apatite (HCA) with a close composition to bone mineral. Vast efforts have been spent to understand the mechanisms underlying in vitro apatite mineralization, as either formed by direct precipitation from supersaturated solutions, or from BG substrates in a simulated body fluid (SBF). Formally, these two scenarios are distinct and have hitherto been discussed as such. Herein, we contrast them and identify several shared features. We monitored the formation of amorphous calcium phosphate (ACP) and its crystallization into HCA from a NaO–CaO–SiO–PO glass exposed to SBF for variable periods out to 28 days. The HCA growth was assessed semi-quantitatively by Fourier transform infrared spectroscopy and powder X-ray diffraction, with the evolution of the relative apatite content for increasing SBF-exposure periods evaluated against trends in Ca and P concentrations in the accompanying solutions. This revealed a sigmoidal apatite growth behavior, well-known to apply to spontaneously precipitated apatite. The results are discussed in relation to the prevailing mechanism proposed for in vitro HCA formation from silicate-based BGs, where we highlight largely simultaneous growth processes of ACP and HCA.

Longitudinal analysis of intervention effects on temptations and stages of change for dietary fat using parallel process latent growth modeling.

The Dietary Guidelines for Americans recommend a 20-35 percent daily intake of fat. Resisting the temptation to eat high-fat foods, in conjunction with stage of readiness to avoid these foods, has been shown to influence healthy behavior change. Data ( N = 6516) from three randomized controlled trials were pooled to examine the relationships among direct intervention effects on temptations and stage of change for limiting high-fat foods. Findings demonstrate separate simultaneous growth processes in which baseline level of temptations, but not the rate of change in temptations, was significantly related to the change in readiness to avoid high-fat foods.

Simultaneous Interfacial and Precipitated Supracrystals of Au Nanocrystals: Experiments and Simulations

Under solvent saturation, a precipitation of full-grown supracrystals on the one hand and the formation of well-defined supracrystalline films at the air-liquid interface on the other hand were previously observed for the first time (J. Am. Chem. Soc.2012, 134, 3714-3719). Here, these two simultaneous growth processes are studied by additional experiments and by Brownian dynamics simulations. The thickness of the supracrystalline films and the concentration of free nanocrystals within the solution are measured as a function of the nanocrystal size. The simulations show that the first process of supracrystal growth is due to a homogeneous nucleation favored by solvent-mediated ligand interactions, while the second one is explained in terms of a diffusion process caused by a decrease in the surface energy when the particles penetrate the air-liquid interface. It is also verified that the presence of thiol molecules at the air-solution interface does not hinder the formation of supracrystalline films.

The growth and morphology of core/shell heterostructured conical carbon fibers

Core/shell heterostructured conical carbon fibers with silicon-based cores and graphitic carbon sheaths have been grown on silicon carbide (SiC) surfaces exposed to the combustion of methane. The conical carbon fibers (CCFs), which taper from a circular base to a point, appear to form by two simultaneous growth processes, axial tip-growth and radial fiber thickening. Radial fiber thickening results from pyrolytic carbon deposition from gas-phase hydrocarbons. Oxidation of SiC surfaces is proposed to produce gas-phase silicon oxides, which feed axial tip-growth and install the silicon-based core. The unusual morphology of the CCFs, including bending, branching, curving and tapering, is proposed to result from the action and interplay of these two simultaneous processes.

Effects of zinc additive on the HPHT synthesis of diamond in Fe–Ni–C and Fe–C systems

In the series of experiments at 5.0–7.0 GPa and 1300–1800 °C with the duration from 15 min to 2 h, the diamond crystals were synthesized in the Fe–Ni–C and Fe–C systems with zinc additive and the capability of zinc for converting graphite to diamond were also investigated in this work. Compared with the diamond synthesis using conventional catalysts, much higher temperatures are required for the nucleation and growth of diamond in Fe–Ni–Zn–C and Fe–Zn–C systems. The morphology of synthesized diamond crystals changes regularly from cub-octahedron to octahedron in the Fe–Ni–C system with increasing zinc additive, while only octahedral diamonds form in the Fe–Zn–C system. The diamond growth is accelerated by appropriate addition of zinc in conventional catalysts while the excessive zinc additive may have a suppressive effect on the diamond nucleation. We also estabish the essential dependence of diamond nucleation and morphology on the composition of crystallization medium in the Fe–Ni–Zn–C and Fe–Zn–C systems. Based on our analysis of the diamond surface configuration, we suggest that the formation of the different defects on the {100} and {111} faces is most likely due to the two simultaneous growth process on the {111} faces.

The Longitudinal Study of Personality Disorders: History, Design Considerations, and Initial Findings

The Longitudinal Study of Personality Disorders (LSPD) began in 1990 and it is the first NIMH-funded prospective multiwave longitudinal study of all DSM-defined personality disorders (PDs). The LSPD, now in its 16th year, has focused on several major issues including: (a) the epidemiology of the PDs; (b) the stability of individual differences and mean levels of PD features over time; (c); patterns of individual growth in PD features over time; (d) the development of a neurobehavioral model that links personality and personality disorder; (e) specification of those neurobehavioral systems predicting change in borderline personality disorder; and (f) illumination of simultaneous growth processes in neurobehavioral systems and PD. The LSPD possesses a number of methodological enhancements designed to increase the validity of the longitudinal findings such as a prospective multiwave design, use of a validated structured interview and well-known self-report instrument for Axis II assessments, double measurement of all major constructs under study, use of blinded interviewers for all interview Axis II assessments, and use of a community sample. The history and context in which the LSPD was developed is reviewed, methodological issues related to the study of PDs are discussed, primary LSPD findings to date are summarized, and future directions of the LSPD are introduced.