The quality of X‐ray powder diffraction data and the number and type of refinable parameters have been examined with respect to their effect on quantitative phase analysis (QPA) by the Rietveld ...method using data collected from two samples from the QPA round robin Madsen, Scarlett, Cranswick & Lwin (2001). J. Appl. Cryst.34, 409–426. From the analyses of these best‐case‐scenario specimens, a series of recommendations for minimum standards of data collection and analysis are proposed. It is hoped that these will aid new QPA‐by‐Rietveld users in their analyses.
The step size, angular range and intensity of X‐ray powder diffraction data and the number and type of refinable parameters have been examined with respect to their effect on quantitative phase analysis by the Rietveld method.
Graphene fragments spanning a wide range of size and shape were studied computationally using the Debye scattering equation. The calculated diffraction patterns were analysed using the Scherrer ...equation to infer the fragment size, La. Comparison with the known fragment sizes reveals a strong affine relationship between La and the Scherrer quantity λ/(Bcosθ). To preserve this relationship, we propose modifying the Scherrer equation to include an empirical additive constant. Our approach solves the well-known problem of size-dependence in the shape factor and yields a universal expression by defining La as the square-root of the fragment area. The relationship between observed diffraction peak positions and unit cell parameters is also discussed.
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A description is given of the program pdCIFplotter. This program is used for visualizing powder diffraction data and models published in powder CIF format (pdCIF). In particular, support for the ...visualization of multi‐pattern data sets, such as in situ diffraction experiments, is provided by means of stack and surface plots. pdCIFplotter is written in Python 3 and can run wherever a compatible runtime is available. TOPAS macros for the production of pdCIF files are also presented.
A program is described for visualizing powder diffraction data and models published in powder CIF format.
A simple modification to an existing powder diffraction specimen holder is given to allow for the presentation of filter papers for analysis. A mild steel annulus holds the filter paper in place ...using magnets added to the rear of the specimen holder.
A simple way to modify powder diffraction specimen holders to allow for the presentation of filter papers is given.
Single‐atom catalysts (SACs) are the smallest entities for catalytic reactions with projected high atomic efficiency, superior activity, and selectivity; however, practical applications of SACs ...suffer from a very low metal loading of 1–2 wt%. Here, a class of SACs based on atomically dispersed transition metals on nitrogen‐doped carbon nanotubes (MSA‐N‐CNTs, where M = Ni, Co, NiCo, CoFe, and NiPt) is synthesized with an extraordinarily high metal loading, e.g., 20 wt% in the case of NiSA‐N‐CNTs, using a new multistep pyrolysis process. Among these materials, NiSA‐N‐CNTs show an excellent selectivity and activity for the electrochemical reduction of CO2 to CO, achieving a turnover frequency (TOF) of 11.7 s−1 at −0.55 V (vs reversible hydrogen electrode (RHE)), two orders of magnitude higher than Ni nanoparticles supported on CNTs.
A novel atomically dispersed transition‐metal single‐atom catalyst supported on carbon nanotubes is synthesized with atomic loading as high as 20 wt%, excellent selectivity, and activity for the electrochemical reduction of carbon dioxide.
ABSTRACT
Purpose
This study aims to investigate the influence of different storage humidity conditions on crystallization and aerosol performance of inhalable spray dried amorphous powder ...formulations (Ciprofloxacin hydrochloride as the model drug).
Methods
The spray dried samples were stored at 20%, 55% and 75% relative humidity (RH). Crystallinity was monitored by Powder X-ray diffraction (PXRD), and particle morphology was measured by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Aerosol performance was evaluated using a multi-stage liquid impinger (MSLI).
Results
PXRD diffractograms showed the spray dried Ciprofloxacin stored at 20% RH for three weeks were amorphous; whereas those stored at 55% RH and 75% RH started crystallizing after one hour. Fine particle fraction (FPF) of the particles was improved from 28% to 42% after storage at 55% RH for three days. Such improvement was attributed to the crystallization of amorphous powders, which led to increased particle roughness and reduced particulate contact area, as visualized by SEM and quantified by AFM. A linear relationship was observed between degree of crystallinity/crystallite size and FPF (R
2
= 0.94 and R
2
= 0.96, respectively). However, deterioration in aerosol performance was observed after storage at 75% RH due to formation of inter-particulate liquid/solid bridges, as confirmed by SEM.
Conclusions
This study provides a fundamental understanding in moisture-induced physical and aerosol instability of the spray dried powder formulations.
The construction of peak intensity, profile and displacement aberration functions based on the geometry of a powder diffraction measurement allows for physically realistic corrections to be applied ...in Rietveld modelling through a fundamental parameters approach. Parallel‐beam corrections for asymmetric reflection and Debye–Scherrer geometry are summarized, and corrections for thin‐plate transmission are derived and validated. Geometrically correct implementations of preferred orientation models are also summarized.
A variety of physically meaningful geometrical and preferred orientation corrections are derived and summarized. The application of these corrections allows for realistic modelling based on the fundamental parameters approach to be undertaken.
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The amino acid l-leucine has been demonstrated to act as a lubricant and improve the dispersibility of otherwise cohesive fine particles. It was hypothesized that optimum surface ...l-leucine concentration is necessary to achieve optimal surface and bulk powder properties. Polyvinylpyrrolidone was spray dried with different concentration of l-leucine and the change in surface composition of the formulations was determined using X-ray photoelectron spectroscopy (XPS) and time of flight-secondary ion mass spectrometry (ToF-SIMS). The formulations were also subjected to powder X-ray diffraction analysis in order to understand the relationship between surface concentration and solid-state properties of l-leucine. In addition, the morphology, surface energy and bulk cohesion of spray dried formulations were also assessed to understand the relation between surface l-leucine concentration and surface and bulk properties. The surface concentration of l-leucine increased with higher feed concentrations and plateaued at about 10% l-leucine. Higher surface l-leucine concentration also resulted in the formation of larger l-leucine crystals and not much change in crystal size was noted above 10% l-leucine. A change in surface morphology of particles from spherical to increasingly corrugated was also observed with increasing surface l-leucine concentration. Specific collapsed/folded over particles were only seen in formulations with 10% or higher l-leucine feed concentration suggesting a change in particle surface formation process. In addition, bulk cohesion also reduced and approached a minimum with 10% l-leucine concentration. Thus, the surface concentration of l-leucine governs particle formation and optimum surface l-leucine concentration results in optimum surface and bulk powder properties.
•Amorphous based mix design framework had been developed for blended geopolymers.•The varying composition of slag and fly ash in blended geopolymer is investigated.•The optimal amorphous Si/Al ratio ...of blended geopolymer is 2.3.•New amorphous ratio, (Na + 2Ca)/Al, is proposed with optimal ratio 3.2.
A new amorphous phase mix design framework had been successfully developed in consideration of calcium content through the combination of ground-granular blast-furnace slag (GGBFS) in fly ash (FA) blended geopolymers. The new framework has been developed considering the amorphous silicon, aluminium, sodium and calcium containing phases of the aluminosilicate sources to increase geopolymerisation reactivity and compressive strength. By utilising this new framework, this study found that the optimal amorphous Si/Al ratio of FA- and GGBFS-blended geopolymers are between 2.3 and 3.1. At 40–50% of FA replacement with GGBFS, it had been observed that blended geopolymers are able to achieve the majority of its 28 days compressive strength at 7 days. To account for the effect of calcium content, a new amorphous ratio, (Na + 2Ca)/Al, is proposed, with an optimal ratio of between 3.2 and 3.4.
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