Structural, Thermal and Magnetic Analysis of Fe75Co10Nb6B9 and Fe65Co20Nb6B9 Nanostructured Alloys

Two nanocrystalline ferromagnetic alloys of the Fe-Co-Nb-B system have been produced by mechanical alloying (MA). Their microstructure, thermal behavior and magnetic response were checked by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and vibrating sample magnetometry (VSM). After 80 h of MA, the alloys were nanostructured (bcc-Fe(Co)-rich phase). As the Co content increases, the density of the dislocations decreases. Besides, a higher concentration of Co causes an increase in the activation energy of the crystallization process. The calculated energies, 267 and 332 kJ/mol, are associated to the crystalline growth of the bcc-Fe-rich phase. The Co content of the samples has no effect on the value of the saturation magnetization, whereas the coercivity is lower in the alloy containing less Co. Samples were compacted and heat-treated. Optimal annealing reduces the coercivity by a factor of two. Results were compared with the data of Fe-Nb-B and Fe-Ni-Nb-B alloys.

AB-stacked nanosheet-based hexagonal boron nitride

Hexagonal boron nitride (h-BN) has been generally interpreted as having an AA stacking sequence. Evidence is presented in this article indicating that typical commercial h-BN platelets (∼10–500 nm in thickness) exhibit stacks of parallel nanosheets (∼10 nm in thickness) predominantly in the AB sequence. The AB-stacked nanosheet occurs as a metastable phase of h-BN resulting from the preferred texture and lateral growth of armchair (110) planes. It appears as an independent nanosheet or unit for h-BN platelets. The analysis is supported by simulation of thin AB films (2–20 layers), which explains the unique X-ray diffraction pattern of h-BN. With this analysis and the role of pressure in commercial high-pressure high-temperature sintering (driving nucleation and parallelizing the in-plane crystalline growth of the nuclei), a growth mechanism is proposed for 2D h-BN (on a substrate) as `substrate-induced 2D growth', where the substrate plays the role of pressure.

NON-AUTOCLAVE SILICATE COMPOSITES USING NON-TRADITIONAL RAW MATERIALS AND CRYSTAL FILLER

In the construction of buildings and structures, many wall materials are used, including silicate products of various functional purposes. In traditional production technology of such materials, the hardening process occurs due to the formation of a crystal structure in the CaO-SiO2-H2O system. There are various ways to modify the crystalline growth of the cementing substance, one of which is the use of various kinds of crystal seedings, in particular the use of natural and synthetic calcium hydrosilicates. The purpose of the experiments is to study the possibility of improving the performance properties of non-autoclave silicate composites by modifying the structure formation in the "lime-non-traditional aluminosilicate raw materials" system, which consists in the crystal-chemical regulation of the structure formation processes with a synthetic crystal filler CaO-SiO2-H2O (C-S-H). The use of synthetic crystalline filler C-S-H synthesized by hydrothermal synthesis in an autoclave at a pressure of 1 MPa and a temperature of 175 °C from a mixture of Ca(OH)2 and crystalline silica in a ratio different C/S=1 in the technology of non-autoclave silicate materials on the basis of alternative aluminium raw material allows to increase the operational indicators resulting products to 18 % or more. The optimal content of CaO and crystal filler C-S-H at which the maximum strength characteristics are provided is 8 % and 2.5 %, respectively, which allows to develop optimal compositions of raw materials for the technology of producing high-density non-autoclave silicate materials based on non-traditional aluminosilicate raw materials with a compressive strength of at least 20 MPa and more, with an average product density of no more than 2000 kg /m3.

Effect of pH in Morphological Properties of Brushite Microstructures Synthesized by Precipitation Method

Brushite microstructures with different morphologies were synthesized by precipitation method using a mixture of calcium lactate, potassium phosphate and potassium hydroxide as precursors. Potassium hydroxide was variation factor in synthesis process. This factor has an influence on morphology of nanostructures, changing from microplates to microfibers. On the other hand, bioceramic composites were obtained with brushite microstructures, using a mixture of brushite powders and gelatin. The amount of gelatin was added in different proportions. Brushite microplates and microfibers, with lengths in the order of micrometers, were obtained; the surface of microstructures is smooth and with well-defined edges. According to studies by XRD and FTIR, microstructures show a preferential crystalline growth. For bioceramic composites an effect of brushite microstructures was observed in compression test. Compounds with a greater amount of organic phase and microfibers show a greater resistance as compared to those formed by microplates. This value is in the range of human trabecular bone. This work presents a new route of synthesis to control morphology of brushite microstructures, as well as an improvement in mechanical properties of based brushite composites.

Prudent electrochemical pretreatment to promote the OER by catalytically inert “Iron incorporated metallic Ni nanowires” synthesized via the “non-classical” growth mechanism

This study provides new insight towards the non-classical “amorphous to crystalline” growth mechanism for metal nanowire synthesis and reports an electrochemical strategy to activate inactive materials into efficient electrocatalysts for the OER.

Механизмдействияингибиторовприобразованииосадкакарбонатакальциявобратноосмотическихаппаратах

Знание механизма образования осадков малорастворимых солей на обратноосмотических мембранах чрезвычайно важно при выборе мероприятий по их предотвращению и сокращению расхода концентрата. Проведенные исследования позволили сформулировать новый взгляд на механизм образования кристаллических отложений и роль ингибиторов в предотвращении этого процесса. В основе разработки экспериментальной методики лежит представление о том, что первая фаза кристаллизации зародышеобразование является гомогенной, т. е. происходит в застойных зонах в объеме концентрата при высоких значениях пересыщения по карбонату кальция. После образования кристаллы выносятся из застойных зон и осаждаются на поверхности мембраны, как и другие взвешенные частицы, содержащиеся в обрабатываемой воде. Представлены результаты изучения процесса адсорбции молекул полимерных ингибиторов на поверхности кристаллов при зародышеобразовании и кристаллическом росте на мембране. Приведены экспериментально полученные зависимости скорости адсорбции ингибиторов от их дозы, скорости образования карбоната кальция, скорости зародышеобразования от общей поверхности зародышевых кристаллов. Изучение микрофотографий показало зависимость размера и количества кристаллов от значения пересыщения в застойной зоне при зародышеобразовании, а также от эффективности ингибитора. Представлена методика, позволяющая определить концентрации растворенных солей в застойных зонах мембранного аппарата и значения пересыщения, соответствующие началу процесса кристаллизации, без добавления различных ингибиторов и с их использованием.Knowledge of the mechanism of precipitation of slightlysoluble salts on reverse osmosis membranes is extremely important while choosing measures to prevent it and reduce the consumption of concentrate. The conducted studies provided for enunciating a fresh approach to the mechanism of crystalline deposit formation and the role of inhibitors in preventing this process. The development of the experimental technique is based on the idea that the first crystallization phase crystal nucleation is homogeneous, that is, occurs in stagnant zones in the concentrate volume at high oversaturation with calcium carbonate. Upon the formation the crystals are removed from the stagnant zones and settled on the membrane surface like other suspended particles present in the treated water. The results of studying the adsorption of polymer inhibitor molecules on the crystal surface during nucleation and crystalline growth on the membrane are presented. The experimentally obtained dependences of the rate of adsorption of inhibitors on the dose of inhibitors, the rate of formation of calcium carbonate, the rate of nucleation, and on the total surface of the germinal crystals are given. The study of micrographs of crystals showed the dependence of the size and number of crystals on the oversaturation value in the stagnant zone during nucleation as well as on the effectiveness of the inhibitor. A method is presented that allows determining the concentration of dissolved salts in the stagnant zones of the membrane apparatus and the oversaturation values corresponding to the onset of the crystallization process eliminating the addition and use of various inhibitors.