Papers by Keyword: Mechanochemical Activation

Abstract: In Ukraine, up to 75% of all electricity is supplied by thermal power plants, the main type of fuel for which is coal, which leads to the release of ash and slag waste at power plants in huge quantities. Every 10 years (according to statistical data) the amount of ash and slag produced at thermal power plants doubles. The use and creation of new modified consumers of coal-water fuel (CWF) and coal-water suspensions (CWS) occurs periodically. The ease of handling suspensions is captivating: in the energy sector, they can serve as the basis for the effective disposal of numerous accumulated wastes from coal preparation and oil refining, a significant reduction in the consumption of minerals for generating heat and electric energy, and minimizing the effect of heat power engineering on public health and the state of nature.

Abstract: Interaction of molybdenyl(VI) bis(acetylacetonate) with polyphenylsiloxane in xylene and under mechanochemical activation conditions has been investigated. The interaction of the above reagents under mechanical activation conditions proceeds with formation of soluble polymers similar to those obtained in a solution with the silicon/molybdenum ratio equal to 2.6. The crystal chemistry parameters of the fraction obtained in solution with the ratio Si/Mo = 1:2 have been calculated on the basis of the X-ray diffraction analysis data using the Debye–Shearer equation. It has been demonstrated that the chain cross-section found using the Miller–Boyer method coincides with that calculated geometrically on the basis of literature data on bond lengths and angles.

Abstract: As the demand for sustainable environment friendly materials increases, the biocomposites such as wood-polymer composite (WPC) have gained more attention in past years. Wood wastes and by-products like sawdust, chips, bark and wood residues as well as recycled polymers can serve as raw materials for production of WPC. However, there are still many issues obtaining WPCs, mainly a poor compatibility between a hydrophobic polymer matrix and a hydrophilic wood filler. In the present study, mechanical and mechanochemical activation of aspen wood waste were performed to increase their compatibility with recycled polypropylene matrix in the WPC, and the impact of both methods on the biocomposite properties were studied. It was found, that mechanochemical activation (MCA) of aspen wood particles leads to increased hydrophobicity of the obtained WPC compared to the WPC with mechanically activated (MA) particles. Work of adhesion with water was remarkably lower for the WPC modified by MCA which also correlates with moisture sorption results. Surface free energy of the WPC modified by MCA was lower compared to the WPC modified by MA, mostly due to decreased the polar component of surface free energy. The modulus of elasticity (MOE) were competitive for both the WPC formulations, however, MCA led to increased flexural strength of WPC compared to MA.

Abstract: This paper presents an experimental investigation of the mechanochemical activation the low-clinker binder production systems on the basis of CaO and Ca(OH)₂. It is shown that the effects of the mechanochemical interactions of the investigated components of low-clinked binders with the superplasticizer C-3 do not show a significant effect on the binders’- properties. The main influence is observed in the interaction of Portland cement and superplasticizer C-3. This study aimed to optimize the technological parameters of low-clinker binders’ production using different by-products. The expected economic effects of low - clinked binders is associated with the reduced amount of the clinker as one of the expensive components. Taking into account the cost of using the superplasticizer C-3 and various technological wastes the economic impact is expected to be 20-25% decrease of the total cost in the concrete production.

Abstract: This paper introduces the X-ray photoelectron spectroscopy (XPS) technique, well applicable for the analysis of the interfacial layer between polyvinyl alcohol and monocalcium aluminate in macro defect-free (MDF) cement. The experimental results explain the chemical reaction mechanism during the mechanochemical process, which is crucial for the formation of those non-traditional polymercement composite materials.

Abstract: The activation effect of ball-to-powder ratio and activation time on phosphorite ore that takes place in mechanochemical activation has been investigated in present paper, which is carried out in a planetary mill AGO-II. The results show that, particle sizes decreased after activation; the leaching rate of water-soluble P₂O₅ increased 4.6 percentage as ball-to-powder ratio rose from 8:1 to 40:1; the activated particle of samples has been highly dispersed, while the leaching rate of water-soluble P₂O₅ reached 10.1% after milling 15 minutes during activation, which was 4 times as high as the un-activated samples. The results show a potential utilization of low-medium grade phosphorite ore with mechanochemical activation directly.

Abstract: Mechanochemical activation (MCA) of electrode lignin was performed and the activated lignin was studied by IR-spectroscopy for different activation times. The activated lignin was tested for the ability of binding Cr₂O₇^2-, Cu²⁺, Ni²⁺ ions. It was established that structure deformation, which does not distort the stronger hydrogen bond lattice, but leads to the formation of highly developed surface with active functional groups, occurs in the course of MCA. Weaker inter-layer bonds are broken in the activation process and quickly recovered after the load release. The comparison of the sorption capacity of Cr₂O₇^2-, Cu²⁺, Ni²⁺ ions by the MCA treated vs. inactivated lignin for different activation times was performed.

Abstract: The main issue of the study is aluminum A356 alloy modification by TiC nanoparticles process. Nanoparticles of TiC were especially mechanochemically activated to remove the oxide layer on the particle surface in order to prevent its floating on the molten metal surface. Experimental results indicate that after T6 heat treatment the tensile strength of the modified alloy increased by 6.5%, yield strength increased by 9% and the elongation increased by 22%. A high resolution electron microscopy study shows that dislocation of the modified alloy concentrates near the grain boundary during the crystallization process, and these grain boundaries act as obstacles to dislocation motion. Based on these results, it was found that grain-size aluminum strengthening mechanism occurs in the nanoparticle carbide reinforcement process.

Abstract: Solid phase high energy mechanochemical interaction of α-Fe2O3(hematite) and Fe in powder mixture have been studied. The formation of amorphous iron-based magnetic phase in this process was detected by means of Mossbauer spectroscopy and magnetic measurements. The amount of this phase increases with Fe addition in reduced mixture. Its thermal stability have been studied by magnetic and DCS measurements at constant α-Fe2O3 and gradually increased Fe concentrations.

Abstract: An important aspect of previous sialon research in NZ has been the development of new synthesis methods, including refinements in carbothermal reduction and nitridation (CRN) methods and the use of mechanochemical activation of sialon precursors (either Al and Si nitrides and oxides or CRN mixtures). Mechanochemical activation of CRN mixtures of clay and carbon heated in N2 formed β-sialon (z = 2) at 1300oC (100oC lower than in unground mixtures) but 21R polytypoid and corundum were also formed. More recently, our attention has focussed on the technique of silicothermal reduction and nitridation (SRN) to synthesise other sialons, including the AlN polytypoids and Na and Li α-sialons. The interest in the polytypoids springs from their expected physical properties (thermal conductivity and good electrical insulation similar to AlN), their covalent bonding and relatively light weight arising from their high Al and N contents and their elongated crystal morphology which may improve the crack resistance of polytypoid composites with α-sialon. This paper describes the development of SRN single-step synthesis of high-purity dense 15R sialon from clay, Si and AlN, and the effect of additives on the synthesis and sintering of the product. A method is also described for SRN synthesis of Na and Li α-sialons from clay, Si and AlN using fluoride additives. Fluorides have the advantage of small size, high electronegativity, leading to their known facilitation of AlN synthesis. Furthermore, they do not readily enter the sialon structure but may toughen it by formation of glassy phases. Fluorides allow use of clay in this SRN synthesis by introducing M+ without additional oxygen, but have the disadvantage of generating SiF4 as a byproduct. The reaction using LiF proceeds readily at the very low temperature of 1200oC via an O-sialon intermediate by a mechanism which probably involves Si migration assisted by the formation of SiF4.The effect of mechanochemical activation (high energy grinding) on the SRN formation and sintering of Na and Li α-sialons, O and β-sialon has also been studied.Grinding the SRN O-sialon precursor promotes O-sialon formation in powders but not in pellets due to pre-reaction sintering, which is facilitated by the smaller particle size. Grinding Na and Li α-sialon SRN precursors forms a mixture of sialons rather than the target monophase product, while sintering of all the sialons is assisted by grinding their SRN precursors.