Papers by Keyword: Phase Boundary

Abstract: The research findings of colloid and chemical properties of poly-functional modifiers (PFM) with various chemical compositions and qualitative and quantitative proportions of polar organic substances with various molecular weights have been presented. The possibility of regulating the properties of PFM and concrete mixes, modified by them by means of not only changing the chemical composition of modifiers, but combining the types and quantity of active admixtures of polar organic substances with various molecular weights has been shown. It has been demonstrated that the modifiers under study possess the surface activity at solid-solution phase boundary, reducing the surface tension σ_solid-liquid (σ_s-l) At the same time the surface tension at the solution-air phase boundary can remain the same or reduce to a certain extent depending on the modifier’s chemical composition. PFM and superplasticizer (SP) SB-3, which have, unlike SP S-3, the certain surface activity at solid-solution boundary, increase the air entrainment into concrete mix by 0.5÷1.5%, additionally increasing the freeze-thaw resistance of concretes of both fluid and equal-workable compositions without affecting their strength. The adsorption of modifiers on the disperse phase of suspension is conditioned by dispersion forces and, independently of its kind, is of monomolecular nature. For the localization of PFM molecules on the surface of a particle, its molecule should have a system of bonded aromatic rings or conjugated double bonds. The adsorbed modifier’s molecules should make the disperse phase surface hydrophilic and for this purpose they should contain hydrophilic groups along the full length. All this predetermines the role of adsorption-solvation factor in modifiers’ mechanism of action.

Abstract: To prolong the lifetime and to improve the quality of pavements made of bituminous concretes it is necessary to apply innovative solutions during design of such building materials. The common way to increase the values of operational properties is to admix various modifying additives during production. Nanoscale additives currently constitute the big group of advanced modifiers. The known difficulty limiting the widespread practical use of nanotechnology is the necessity to ensure uniform distribution of nanoscale objects in the volume of material. Thus, to realize nanotechnology in construction it is necessary to use the various carriers for nanoscale modifiers. Several mineral materials (dolomite- and silica-based) were examined and results are presented in this paper. The optimal grain size is determined and optimal modes of grinding were identified to provide conformity of structural parameters for carriers. It is shown that total surface area of diatomite obtained by means of nitrogen absorption method is quite high due to structure of its pore space. It is stated that for structure with numerous contacts between grains, rheological properties of mixture are mostly determined by the thickness and properties of solvation shells on the grains. High surface activity of diatomite is confirmed by the rheology data. It is shown that there is the formation of adsorption layer during interaction between bitumen and surface of diatomite, and thickness of this layer is relatively high for the wide range of temperatures. It is found by means of IR spectroscopy that there is only physical sorption of bitumen on the diatomite and no new chemical compounds are forming.

Abstract: Phase stresses that arise from volume mismatch between austenite and martensite crystal lattices were studied at different stages of direct and reverse martensitic transformations in NiTi alloy for medical application. The absolute stress values of tensile and compressive stresses that operated in austenite and martensite respectively were shown to be Gaussian functions of phase composition: they increased from zero in the initial single-phase state, achieved maximum at the equilibrium between the initial and new phases and decreased to zero in the ultimate phase. Phase stress distribution on the surface of simulated two-phase sample and related distinctions in osteoblast-like cells’ behavior were analyzed. Negative effect of compressive stress on cell viability and probable mechanism of cell apoptosis are discussed. Recommendations concerning the choice of permissible size discrepancy between organ and implant as well as NiTi alloy composition to avoid/minimize negative consequences of two-phase state after implant installation are suggested.

Abstract: The (Na_0.52K_0.44)(Nb_0.9Sb_0.06)O₃-0.04LiTaO₃ (NKNS-LT) ceramics doped with various Cu₂O contents were prepared by the conventional solid state reaction method. The Cu₂O content was varied in the range of 0.1~0.4 wt%. The effects of Cu on microstructure, crystallographic phase transition, and piezoelectric properties were investigated. The material with perovskite structure had a tetragonal phase (T1) when Cu₂O concentration was less than 0.3 wt% and it was transformed to another tetragonal phase (T2) when the Cu₂O amount was greater than 0.3 wt%. The phase boundary between T1 and T2 phases was appeared at around 0.3 wt% of Cu₂O concentration. The piezoelectric properties were shown the maximum values at the composition of the phase boundary. The electro-mechanical coupling factor (k_p) was 0.42 and the piezoelectric charge constant (d₃₃) was 245 pC/N at the 0.3 wt% of Cu₂O concentration.

Abstract: Phase boundary is an important kind of interfaces for the dual-phase metals. Orientation relationship (OR) is a crucial factor affecting the performance of the phase boundaries and the dual-phase metals. Molecular dynamics simulation is performed to examine the structures of the bcc/fcc iron phase boundaries in Nishiyama–Wassermann (N–W) and Kurdjumov–Sachs (K–S) orientation relationships, and the performances of the dual-phase model with these ORs. The structural relaxation shows that the phase boundary with N-W relation has the lower energy than that in K-S relation. Stress-strain curves show that dual-phase model in N-W relation has the higher stiffness and strength than that in K-S relation. Simulation results show that phase boundary in N-W relation has a more exellent performance, and is preferred to be processed in heat treatment.