The Role of Acid Concentration on Band Gap Shrinkage in Cellulose Nanocrystals Fabricated from Water Hyacinth

In this study, the fingerprint of the acid concentration during the hydrolysis process on the optical band gap of cellulose nanocrystals (CNCs) has been systematically studied. The CNCs have been prepared using hydrochloric acid at a hydrolysis temperature of 50°C and at a constant hydrolysis time of 4 hours but with varying hydrochloric cid concentrations of 5%, 10% and 15%. The crystalline structure and phase identification of the CNCs have been studied using XRD technique. UV-Vis Spectroscopy has been done and the optical band gap energy calculated by performing the Tauc’s plot. From the study, the grain size has been found to decrease with acid concentration while the band gap energy has been found to increase with increasing acid concentration. Further, the optical band gaps of the CNCs have been found to decrease with the increase in crystallite size. This shrinkage of the band gap has been attributed to the increased impurity concentration leading to the narrowing of the band gap due to the emerging of the impurity band formed by the overlapped impurity states

Clustering Application for Condition-Based Maintenance in Time-Varying Processes: A Review Using Latent Dirichlet Allocation

In the field of industrial process monitoring, scholars and practitioners are increasing interest in time-varying processes , where different phases are implemented within an unknown time frame. The measurement of process parameters could inform about the health state of the production assets, or products, but only if the measured parameters are coupled with the specific phase identification. A combination of values could be common for one phase and uncommon for another phase; thus, the same combination of values shows a high or low probability depending on the specific phase. The automatic identification of the production phase usually relies on clustering techniques. This is largely due to the difficulty of finding training fault data for supervised models. With these two considerations in mind, this contribution proposes the Latent Dirichlet Allocation as a natural language-processing technique for reviewing the topic of clustering applied in time-varying contexts, in the maintenance field. Thus, the paper presents this innovative methodology to analyze this specific research fields, presenting the step-by-step application and its results, with an overview of the theme.

Depressed 660-km discontinuity caused by akimotoite–bridgmanite transition

The 660-kilometre seismic discontinuity is the boundary between the Earth’s lower mantle and transition zone and is commonly interpreted as being due to the dissociation of ringwoodite to bridgmanite plus ferropericlase (post-spinel transition)1–3. A distinct feature of the 660-kilometre discontinuity is its depression to 750 kilometres beneath subduction zones4–10. However, in situ X-ray diffraction studies using multi-anvil techniques have demonstrated negative but gentle Clapeyron slopes (that is, the ratio between pressure and temperature changes) of the post-spinel transition that do not allow a significant depression11–13. On the other hand, conventional high-pressure experiments face difficulties in accurate phase identification due to inevitable pressure changes during heating and the persistent presence of metastable phases1,3. Here we determine the post-spinel and akimotoite–bridgmanite transition boundaries by multi-anvil experiments using in situ X-ray diffraction, with the boundaries strictly based on the definition of phase equilibrium. The post-spinel boundary has almost no temperature dependence, whereas the akimotoite–bridgmanite transition has a very steep negative boundary slope at temperatures lower than ambient mantle geotherms. The large depressions of the 660-kilometre discontinuity in cold subduction zones are thus interpreted as the akimotoite–bridgmanite transition. The steep negative boundary of the akimotoite–bridgmanite transition will cause slab stagnation (a stalling of the slab’s descent) due to significant upward buoyancy14,15.

Ultra-low temperature co-fired ceramics with adjustable microwave dielectric properties in Na2O-Bi2O3-MoO3 ternary system: A comprehensive study

Herein, a series of microwave dielectric materials in the Na2O-Bi2O3-MoO3 ternary system were studied via phase identification, microstructure characterization, spectral analysis and microwave dielectric properties test, such as Na2MoO4, Na6Mo10O33,...

ADVANTAGES AND DISADVANTAGES OF DIFFERENT METHODS FOR STUDYING THE PHASE-STRUCTURAL STATES OF MATERIALS (A REVIEW)

The paper provides a brief overview of the standard capabilities of X-ray techniques for studying materials with examples of modern performance of elemental and structural studies. X-ray research methods make it possible to reveal the elemental and phase-structural state. Thanks to modern software and electronic databases, the use of previously complex techniques is becoming simpler and more accessible. To illustrate the solution of specific problems, several examples of obtaining and decoding diffraction patterns and identifying the phase composition of the coating and ceramic material are given. An example of work in modern specialized software for acceleration and automation of phase identification is shown. For clarity, an example of identifying phases using electronic database cards is presented, which is still used today for manual decoding. The practice of interaction between researchers shows that even specialists in the field of X-ray structural analysis are not always aware of modern methods of processing and decoding the obtained data. The possibilities and algorithm of action in research can be interesting for students, engineers, researchers of materials science and mechanical engineering profile. Keywords: microscopy, X-raystructural analysis, X-rayfluorescence analysis

X-Ray Diffraction Techniques for Mineral Characterization: A Review for Engineers of the Fundamentals, Applications, and Research Directions

For many decades, X-ray diffraction (XRD) has been used for material characterization. With the recent development in material science understanding and technology, various new materials are being developed, which requires upgrading the existing analytical techniques such that intricate problems can be solved. Although, XRD is a well-established non-destructive technique, it still requires further improvements in its characterization capabilities, especially when dealing with complex mineral structures. The present review conducts comprehensive discussions on atomic crystal structure, XRD principle, its applications, uncertainty during XRD analysis, and required safety precautions, all in one place. It further discusses the future research directions, especially the use of artificial intelligence and machine learning tools for improving the effectiveness and accuracy of XRD technique for mineral characterization. It has been focused that how XRD patterns can be utilized for a thorough understanding of the crystalline structure, size, and orientation, dislocation density, phase identification, quantification, and transformation, information about lattice parameters, residual stress, and strain, and thermal expansion coefficient of materials. All these important discussions on XRD for mineral characterization are compiled in this short yet comprehensive review that would benefit specialists and engineers in the chemical, mining, iron, metallurgy, and steel industries.

Nb/Sn Liquid-Solid Reactive Diffusion Couples and Their Application to Determination of Phase Equilibria and Interdiffusion Coefficients of Nb-Sn Binary System

Nb3Sn plays an irreplaceable role in superconducting parts due to its stable performance under high field conditions. Accurate phase equilibria and interdiffusion coefficients are of great significance for designing novel Nb3Sn superconductors. However, the related experimental information is still in a state of scarcity because of the difficulty in fabrication of Nb-Sn alloys caused by the large difference in melting points of Nb and Sn. In this paper, a simple but pragmatic approach was first proposed to prepare the Nb/Sn liquid-solid reactive diffusion couples (LSDCs) at 1100 °C and 1200 °C, of which the phase identification of the formed layer and the measurement of composition-distance profiles were conducted. The formed layer in Nb/Sn LSDCs was confirmed to be Nb3Sn compound. While the measured composition profiles were employed to determine the phase equilibria according to the local equilibrium hypothesis and the interdiffusion coefficients with an aid of the latest version of HitDIC software. The determined phase equilibria of Nb3Sn, (Nb) and liquid show good agreement with the assessed phase diagram. While the calculated interdiffusion coefficients and activation energy for diffusion in Nb3Sn are consistent with both experimental and theoretical data in the literature. Moreover, the growth of the formed Nb3Sn layer in Nb/Sn LSDCs was also found to be diffusion controlled. All the obtained phase equilibria and interdiffusion coefficients are of great value for further thermodynamic and kinetic modeling of the Nb-Sn system. Furthermore, it is anticipated that the presently proposed approach of fabricating liquid-solid reactive diffusion couple should serve as a general one for various alloy systems with large differences in melting points.