Phosphorus Substitution Preference in Ye’elimite: Experiments and Density Functional Theory Simulations

Density functional theory (DFT) simulation has been recently introduced to understand the doping behavior of impurities in clinker phases. P-doped ye’elimite, a typical doping clinker phase, tends to form when phosphogypsum is used to manufacture calcium sulfoaluminate cement (CSA) clinkers. However, the substitution mechanism of P has not been uncovered yet. In this study, the influence of different doping amounts of P on the crystalline and electronic structure of ye’elimite was investigated using backscattered scanning electron microscopy–energy X-ray dispersive spectroscopy, X-ray diffraction tests, Rietveld quantitative phase analysis, and DFT simulations. Furthermore, the substitution preference of P in ye’elimite was revealed. Our results showed that increasing the doping amount of P increased the impurity contents in CSA clinkers, transforming the ye’elimite crystal system from the orthorhombic to the cubic system and decreasing the interplanar spacing of ye’elimite. Based on the calculation results of the defect formation energies, additional energies were required for P atoms to substitute Ca/Al atoms compared with those required for P atoms to substitute S atoms in both orthorhombic and cubic systems of ye’elimite. Combined calculation results of the bond length–bond order and partial density of states showed that the doped P atoms preferably substituted S atoms; the second possible substituted atoms were Al atoms, while there was only a slight possibility for substitution of Ca atoms. The substitution of P atoms for S atoms can be verified based on the elemental distribution in P-doped ye’elimite and the increasing residual CaSO4 contents. The transition of the crystal system and a decrease in the interplanar spacing for ye’elimite can also prove that the substitution of P atoms for Al atoms occurred substantially.

Shot peening increases resistance to cyclic fatigue fracture of endodontic files

The objective of this study was to assess the resistance to fatigue fracture of conventional nickel–titanium files after undergoing shot peening. Forty NITIFLEX endodontic files, number 30, were divided into two groups; one was submitted to shot peening treatment and the other was not. All instruments were tested for fatigue fracture in simulated canals with a TRI-AUTO ZX endodontic motor. One file of each group was subjected to a residual stress analysis by XRD. Finally, the fractured surface was observed and elemental analysis performed by means of SEM and EDX. Roughness analysis was made by focal variation microscope. The shot peening group showed greater resistance to fatigue fracture; there was no difference in the length of the fractured fragments. XRD results showed the presence of residual compression stresses in the file submitted to shot peening, a decrease in the interplanar spacing, and an increase in the full-width-at-half-maximum and the microstrains. SEM and EDX showed a ductile fracture with zones of fatigue and an equiatomic ratio between the nickel and titanium. Surface roughness increased after the file was subjected to the shot peening procedure. In conclusion, shot peening increases the resistance to fatigue fracture due to the presence of residual compression stresses in files manufactured from a conventional nickel–titanium alloy.

The Influence of Directly Plating Time on the Structure of Electroless Nickel on AZ91

In this paper, the influence of deposition time on the surface morphology, composition, structure, grain size and hardness of electroless nickel plated directly in neutral pH bath on AZ91 magnesium alloy are discussed by using SEM, EDS, XRD and microhardness test machine measurements. The results show that with the increasement of the plating time, the surface tends to be smooth, dense, and complete. The coating is composed of Ni and P and the content of P increases with the increasing the plating time. Furthermore, the XRD peaks for the coatings shift to the right and broaden gradually with prolonged plating time, which indicates that the interplanar spacing of the crystal and the grain size are simultaneously decreased. At the same time, the microhardness of the samples is also increased with increasing plating time.

Using biochar from spent coffee grounds to treat pollution in livestock wastewater

Four types of biochar material synthesized from spent coffee grounds by slow pyrolysis process CF1 (500(C/0.5h); CF2 (500(C/1.5h); CF3 (500(C/3h); CF4 (500(C/6h) is studied to treat two pollution parameters (COD and TSS) in livestock wastewater. Material characteristics were determined by SEM, EDX and BET methods. The results showed that the 4 samples of biochar materials were structured fiber clearly, the interplanar spacing which corresponds to the lattice plane. The C content in the biochar sample is higher than the initial raw material sample; the highest value recorded reaches 90.61% C (CF2). 100 mL of the original livestock waster water is filtered through columns with 4g of biochar CF1-CF4 during reaction times varied from 0h, 1h, 4h and 8h, the COD treatment efficiency and adsorption content of CF4 sample is highest of 96.41% and 188 mg/g after 8h, and the lowest value is 76.67% and 149.5 mg/g after 1h recorded in CF3 sample, however the COD value after treatment is still higher from 1.2 to 1.46 times than Vietnamese standard 62: 2016/MONRE - national technical regulation on the effluent of livestock. The CF3 material samples have the highest TSS treatment efficiency and adsorption content of 95.19% and 6.425 mg/g after 8h and the lowest of 66.78% and 4.575 mg/g recorded in CF1 samples after 1h, response the requirements of QCVN 62: 2016/MONRE. The results showed that biochar is a potential sorbent to removed pollutants from waste water.

Strong sequentially bridged MXene sheets

Titanium carbide (Ti3C2Tx) MXene has great potential for use in aerospace and flexible electronics due to its excellent electrical conductivity and mechanical properties. However, the assembly of MXene nanosheets into macroscopic high-performance nanocomposites is challenging, limiting MXene’s practical applications. Here we describe our work fabricating strong and highly conductive MXene sheets through sequential bridging of hydrogen and ionic bonding. The ionic bonding agent decreases interplanar spacing and increases MXene nanosheet alignment, while the hydrogen bonding agent increases interplanar spacing and decreases MXene nanosheet alignment. Successive application of hydrogen and ionic bonding agents optimizes toughness, tensile strength, oxidation resistance in a humid environment, and resistance to sonication disintegration and mechanical abuse. The tensile strength of these MXene sheets reaches up to 436 MPa. The electrical conductivity and weight-normalized shielding efficiency are also as high as 2,988 S/cm and 58,929 dB∙cm2/g, respectively. The toughening and strengthening mechanisms are revealed by molecular-dynamics simulations. Our sequential bridging strategy opens an avenue for the assembly of other high-performance MXene nanocomposites.

Study on the Crystal Structure of Coal Kaolinite and Non-Coal Kaolinite: Insights from Experiments and DFT Simulations

Coal is often coated by kaolinite in flotation, leading to a decrease in the quality of clean coal. The structure of the mineral determines its properties and flotation behavior. Therefore, to remove the kaolinite from coal efficiently, the difference in mineralogical characteristics between non-coal and coal kaolinite were analyzed using advanced instruments. The experiment results showed that, due to the substitution of the C atom for Si atom, the interplanar spacing of the kaolinite (001) surface became small with C-O-C, Al-O-C, and C-O-Si covalent bonds formed instead of Al-O-Si and Si-O-Si bond. Based on this, the models of monolayer and bilayer coal kaolinite (001) surfaces were built and the structure difference was compared through DFT calculation. The calculation results showed that the silicon atom of the kaolinite Si-O-(001) surface was easier to be doped by carbon atoms with external energy as the interplanar spacing of the kaolinite (001) surface decreased with the increase in doped carbon atoms (7.15440 Å→7.11859 Å→7.10902 Å→7.10105 Å). The structural difference between non-coal kaolinite and coal kaolinite were compared from the view of the experiment and quantum chemistry, which provides an important theory for subsequent research on the properties of coal kaolinite and its further processing and utilization.