Mechanochemical assisted synthesis of B4C nanoparticles

The present work reports on the preparation of boron carbide nanoparticles by the reduction of boron oxide with magnesium in the presence of carbon using the mechanochemical processing. The phase transformation and microstructure of powders during ball milling were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that during ball milling the B₂O₃–Mg–C reacted with a self-propagating combustion mode producing MgO and B₄C compounds. To separate B₄C from the milled powder mixture, an appropriate leaching process was used. After leaching, the purified powder mixture was characterized using XRD and transmission electron microscope (TEM). XRD studies indicated that the prepared particles were single phase crystalline B₄C. Moreover, TEM studies showed the size of B₄C particles were ranging from 10 to 80 nm.     

Novel low-temperature synthesis of tin(0) nanoparticles

In this paper, we report a novel low-temperature solution phase reduction of SnCl₂ with t-BuONa-activated NaH which affords colloidal Sn(0) nanoparticles with an average diameter of ca. 40 nm. The t-BuONa stabilized Sn(0) nanoparticles were characterized using X-ray powder diffraction, transmission electron microscopy, XPS, and EDS analyses. The influence of purification conditions on the aggregation state of Sn(0) particles is described.     

Mechanochemical synthesis of nanoparticles

The results of recent investigation of the mechanochemical synthesis of inorganic nanoparticles are reviewed. It was demonstrated that, by selecting suitable chemical reaction paths, stoichiometry of starting materials and milling conditions, mechanochemical processing can be used to synthesise a wide range of nanocrystalline particles dispersed within a soluble salt matrix. Selective removal of the matrix phase by washing the resulting powder with appropriate solvents can yield nanoparticles of the desired phase. This technique has been shown to have advantages over other methods of producing nanoparticles in terms of low cost, small particle sizes, low agglomeration, narrow size distributions and uniformity of crystal structure and morphology.     

Mechanochemical synthesis and sintering of (ZrO2)0.97(Y2O3)0.03

The (ZrO₂)_0.97(Y₂O₃)_0.03 tetragonal solid solution was prepared by solid-state reaction from mechanically activated powder mixtures. The effects of the activation medium and particle size on the sintering behavior of the material was examined.     

Mechanochemical synthesis of Co-C materials

Using mechanochemical processing, we prepared nonequilibrium Co-C solid solutions supersaturated with carbon to above 7 at %. X-ray diffraction characterization showed that the formation of fcc Co_{1 ? x} C _x solid solutions was accompanied by an increase in the probability of deformation stacking faults. In Co + C mixtures containing more than 10 at % carbon, the fcc solid solution converted to the metastable cobalt carbide Co₃C with an orthorhombic structure. We assessed the thermal stability of the nonequilibrium Co_{1 ? x} C _x solid solutions and the heat effect of the decomposition of the cobalt carbide Co₃C: ?ΔH = 23 kJ/mol.     

Mechanochemical synthesis of chromium-based alloys

This paper presents a detailed study of the formation of chromium-based alloys, Cr–Ta–W + plasticizing additives (Nb and Zr) and Cr–Ta–Si, during milling of powder mixtures in a Fritsch (P-7) planetary mill under an Ar atmosphere. It is shown that, after milling for 18 h, all the components of the starting mixtures convert into a Cr-based BCC solid solution. The powders of chromium alloys obtained in this study are readily compacted by hot isostatic pressing (HIP) under conditions typical of the processing of powders of high-temperature nickel alloys. Heating of the powders and compacts leads to the decomposition of the supersaturated solid solution and the formation of two forms of the Cr₂M Laves phase with cubic crystal lattices. The formation of a mixed-phase fine microstructure in the chromium alloys after HIP suggests that the materials studied here are potentially attractive as a base of next-generation chromium-based high-temperature alloys.     

Mechanochemical synthesis and shock wave consolidation of TiN(Al) nanostructure solid solution

This paper aims to report the study of the synthesis of a titanium nitride nanostructure solid solution through the reduction of aluminum nitride with titanium based on the stoichiometric reaction of 2Ti + AlN by mechanical alloying (MA) process at a ball-to-powder weight ratio of 15:1. A nanostructure solid solution of in-situ titanium nitride was formed through exchange reaction between Ti and AlN at the initial time of MA. XRD, SEM, EPMA, TEM, and particle size analysis (PSA) were used to characterize the products. It was found that the amount of Al resulting from decomposition of aluminum nitride dissolved in the TiN lattice increased in accordance with milling time, leading to the formation of TiN(Al) solid solution and a reduction of the TiN lattice interplanar distance. The milled powder displayed equiaxed morphology and a narrow size distribution of about 1 μm at the end of the milling process. In-situ TiN(Al) crystallites were of an average size of 6 ± 2 nm. Subsequent to MA, an underwater shock compaction method was applied to the prolonged milled powders to obtain bulk sample. The effect of this shock compaction on the selected sample resulted in the preservation of its nanostructure characteristics with no additional phase transformation which are considered advantageous in the use of high dynamic compaction method for ceramic materials.     

Mechanochemical modification and synthesis of drugs

Various aspects of the application of mechanochemistry and mechanical activation in the study of pharmaceutical materials are presented including the use of mechanical activation for modification of the physical and chemical properties of drugs and solid state synthesis of the drugs by mechanochemical methods. It is necessary to take the mechanochemical factors into account during grinding and tabletting the drugs.     

Mechanochemical synthesis of nanocrystalline titanium monoxide

Nanocrystalline cubic titanium monoxide, TiO_x (0.92 < x < 1.19), with mean crystallite size of ≈ 6 nm, was synthesized by mechanochemical treatment of Ti and TiO₂ (rutile) powder mixtures with molar ratios of 1:1, 1.10:1 and 1.25:1. The mechanochemical solid state reaction in a high-energy planetary ball mill was completed for 2 h in either air or argon atmosphere. During heating in vacuum at 900 and 1000 °C for 24 h, nanocrystalline TiO_x transforms to a well-crystallized, cubic or monoclinic TiO_x. The materials prepared were characterized by XRPD, TGA/DSC and SEM/EDS analysis.     

Mechanochemical synthesis of cobalt oxide nanoparticles

Cobalt oxide (Co₃O₄) nanoparticle was synthesized by thermal treatment of the precursor obtained via mechanochemical reaction of Co(NO₃)₂·6H₂O with NH₄HCO₃. Calcination of the precursor at 300 °C resulted in the formation of Co₃O₄ nanoparticles of 13 nm in crystal size. The precursor was examined by simultaneous differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The Co₃O₄ nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Effect of calcination temperature on Co₃O₄ crystal size was discussed. The activation energy (E) of Co₃O₄ nanoparticle formation during thermal treatment was calculated to be 15.9 kJ/mol.     

Mechanochemical synthesis of eco-friendly fertilizer from eggshell (calcite) and KH2PO4

The present article, based on reverse logistic, provides an environmentally beneficial and cost-effective method of producing calcium phosphate bioceramics (potassium calcium phosphates) aimed for soil conditioning, by a free-solvent mechanochemical process between eggshell waste and KH₂PO₄. The K₃CaH(PO₄)₂ and possibly CaKPO₄ phases formed provide a better nutrient management of P, K and Ca, when applied in soil system the material first release K and form hydroxyapatite and important P and Ca bioavailable source at pH ∼ 5, which comprises a large part of many countries soils.     

Mechanochemical synthesis, phase composition, and properties of Pb(Zn1/3Nb2/3)O3-based ferroelectric ceramics

Pb-containing relaxor ferroelectric ceramics are prepared by mechanochemical ceramic processing. Mechanochemical reactions in binary and ternary mixtures of the PbO-ZnO-Nb₂O₅ system are studied by x-ray diffraction. Disordered compounds with the columbite, changbaiite, and pyrochlore structures are prepared. The perovskite and pyrochlore phases in 0.9Pb(Zn_1/3Nb_2/3)O₃ + 0.1ABO₃ morphotropic phase boundary materials are shown to be in mechanochemical equilibrium. Among the ABO₃ additives studied, BaMnO₃ is the most effective for stabilizing the perovskite structure. The mechanochemical synthesis path has a strong effect on the phase composition of the resulting material. Conventional synthesis through a columbite phase leads to the predominant formation of a pyrochlore phase. Firing conditions also have a profound effect on the phase composition of the ceramics, but the disordered perovskite phase retains cubic symmetry.     

Mechanochemical synthesis of ultrafine ZrO2 powder

The synthesis of ultrafine zirconia powders by mechanochemical reaction of ZrCl₄ with CaO has been investigated using x-ray diffraction, TEM and DSC measurements. Mechanical milling resulted in a nanoscale mixture of CaO and amorphous ZrCl₄. with no evidence of any reaction having occurred. Subsequent heat treatment at temperatures above 300 °C resulted in the formation of separated particles of cubic ZrO₂,5–10 nm in diameter, within an CaCl₂ matrix. Measurements of the effect of particle size on the crystal structure of ZrO₂ are also reported.     

Mechanochemical synthesis of crystalline compounds in the Bi-V-O system

The phase composition of crystalline mechanochemical synthesis products in the Bi₂O₃-V₂O₅ system is determined by x-ray diffraction. The phases identified are sillenite, clinobisvanite, a fluorite phase, the high-temperature form of the Aurivillius phase -Bi₂VO_5.5-x , and new, metastable tetragonal fluorite-like solid solutions. The same compounds are obtained at other Bi : V ratios using Bi₂O₄ and VO₂ as starting reagents. Structural analysis of the synthesized compounds reveals high vacancy concentrations and substitutional disordering. The room-temperature ESR spectra of the samples show V⁴⁺ signals at g 2 and 4. The phase transitions characteristic of clinobisvanite and -Bi₂VO_{5.5 -x} are not detected by thermal analysis, in line with the structural data. Mechanical activation of high-purity -Bi₂O₃ converts it into the form; in the presence of impurities, the resulting phases have fluorite or slightly distorted fluorite-like structure.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 201–209.Original Russian Text Copyright © 2005 by Zyryanov.     

Mechanochemical modification of the phase diagrams of hexagonal oxide ferrimagnets

Mechanical activation and fine comminution of hexagonal oxide ferrimagnets by milling to a nanocrystalline state (ultradisperse powder), followed by sintering, leads to significant changes in the phase diagram, the temperature of synthesis, and the magnetic properties as compared to those of the materials obtained by traditional ceramic technology. The final material structure is formed through “chemical assembly”—sequential consolidation of nanodimensional particles (structure-forming blocks)—rather than through the formation of low-temperature phases and their decomposition with increasing temperature.     

Non-catalytic facile synthesis of superhard phase of boron carbide (B13C2) nanoflakes and nanoparticles

Boron Carbide is one the hardest and lightest material that is also relatively easier to synthesis as compared to other superhard ceramics like cubic boron nitride and diamond. However, the brittle nature of monolithic advanced ceramics material hinders its use in various engineering applications. Thus, strategies that can toughen the material are of fundamental and technological importance. One approach is to use nanostructure materials as building blocks, and organize them into a complex hierarchical structure, which could potentially enhance its mechanical properties to exceed that of the monolithic form. In this paper, we demonstrated a simple approach to synthesize one- and two-dimension nanostructure boron carbide by simply changing the mixing ratio of the initial compound to influence the saturation condition of the process at a relatively low temperature of 1500 degrees C with no catalyst involved in the growing process. Characterization of the resulting nano-structures shows B13C2, which is a superhard phase of boron carbide as its hardness is almost twice as hard as the commonly known B4C. Using ab-initio density functional theory study on the elastic properties of both B12C3 and B13C2, the high hardness of B13C2 is consistent to our calculation results, where bulk modulus of B13C2 is higher than that of B4C. High resolution transmission electron microscopy of the nanoflakes also reveals high density of twinning defects which could potentially inhibit the crack propagation, leading to toughening of the materials.     

Mechanochemical synthesis of sodium tungsten bronze nanocrystalline powders

Nanocrystalline powders of sodium tungsten bronze Na_xWO₃ (x∼0.88) have been prepared by mechanochemical process using starting materials of Na pieces and WO₃ powders in a planetary ball mill. The synthesis reactions proceed with increasing milling time and are almost completed after 44 h. Phase-pure nanoparticles of Na_xWO₃ with average size of 17 nm were directly obtained after a simple washing process to remove the by-product of Na₂WO₄. The resistivity was measured in the temperature range from 77 to 300 K. The sample displays semiconducting behavior and can be characterized by three-dimensional variable-range hopping. The mechanochemical process seems to be an attractive route to fabricate tungsten bronzes because of several advantages such as easy preparation, less cost, operating at low temperature and suitability for a large-scale production.     

Mechanochemical synthesis of granulated LTA zeolite from metakaolin

LTA zeolite can be prepared from dry mixes in a vibratory mill with an impact-shear loading conditions. For the synthesis of LTA zeolite, it is necessary to use the anhydrous ingredients (Al₂Si₂O₇–metakaolin, γ-Al₂O₃). The process of synthesis is controlled by X-ray diffraction, IR-spectroscopy, and atomic-force microscopy. The presence of structural water in the initial ingredients (Al₂Si₂(OH)₄–kaolin or Al(OH)₃) leads to the formation of feldshpatoids (nepheline, sodalite). It was established that the process of mechanical activation requires the synthesis of sodium aluminate of cubic and/or tetragonal crystal systems with a lattice parameters close to those for LTA zeolite. These sodium aluminate acts as a steric template for an “assembly” of the zeolite. The presence of sodium aluminate with some other crystal structure results in the formation of sodalite. There is an optimal time of mechanochemical activation, which is determined by the synthesis of sodium aluminate with cubic or tetragonal crystal structure. A model of the mechanochemical synthesis of LTA zeolite was proposed.