Formation Of Two-phase Structure Research Articles

Study on the Effect of PVAc and Styrene on the Properties and Microstructure of MMA-Based Repair Material for Concrete.

Methyl methacrylate (MMA) material is considered to be a suitable material for repairing concrete crack, provided that its large volume shrinkage during polymerization is resolved. This study was dedicated to investigating the effect of low shrinkage additives polyvinyl acetate and styrene (PVAc + styrene) on properties of the repair material and further proposes the shrinkage reduction mechanism based on the data of FTIR spectra, DSC testing and SEM micrographs. The results showed that PVAc + styrene delayed the gel point during the polymerization, and the formation of two-phase structure and micropores compensated for the volume shrinkage of the material. When the proportion of PVAc + styrene was 12%, the volume shrinkage could be as low as 4.78%, and the shrinkage stress was reduced by 87.4%. PVAc + styrene improved the bending strength and fracture toughness of most ratios investigated in this study. When 12% PVAc + styrene was added, the 28 d flexural strength and fracture toughness of MMA-based repair material were 28.04 MPa and 92.18%, respectively. After long-term curing, the repair material added with 12% PVAc + styrene showed a good adhesion to the substrate, with a bonding strength greater than 4.1 MPa and the fracture surface appearing at the substrate after the bonding experiment. This work contributes to the obtaining of a MMA-based repair material with low shrinkage, while its viscosity and other properties also can meet the requirements for repairing microcracks.

Intermetallic formation in a Ti–Cu dissimilar joint brazed using a Zr-based amorphous alloy filler

Microstructural evolution of the Ti–Cu dissimilar joints brazed by a Zr 41.2Ti 13.8Cu 12.5Ni 10.0Be 22.5 (at.%) amorphous alloy filler was investigated at a temperature of 820 °C for 1–20 min. As the brazing time increased, the overall composition of the joint sensitively changed from Ti-rich to Cu-rich owing to the different reactivity of the Zr in the filler with the Ti and Cu in the base metals. Based on such time-dependent compositional change, the formation of the intermetallic phases in the joint was basically divided into three stages; Stage (1): formation of interfacial Ti 2Cu, Stage (2): formation of two-phase structure with Ti 2Cu/TuCu and Cu 2TiZr, and Stage (3): transformation to Cu-rich phases. At Stage (2), the joint was fully produced isothermally by directional phase transformations with fine dendritic and columnar two-phase structures, revealing the highest bonding strength due to its controlled intermetallic morphology.

Fan-shaped growth of two-phase colonies of lamellar grains in metal systems

The specifics of two-stage longitudinal transverse (fan-shaped) growth of two-phase colonies of lamellar grains are considered in the theoretical aspect. Examples of formation of two-phase structures of the sectoral morphology in alloys are given.

Phase transitions and structural parameters of HIQ-40 liquid crystalline co-polyester

Abstract We describe the impact of thermal treatment on the structure and phase transitions of the liquid crystalline aromatic co-polyester, HIQ-40, comprising 40 mol% p-hydroxybenzoic acid (H), 30 mol% isophthalic acid (I), and 30 mol% p-hydroquinone (Q). Simultaneous, real-time wide and small angle X-ray scattering (WAXS, SAXS), differential scanning calorimetry, and optical ellipsometry were used to study initially isotropic, amorphous films of HIQ-40. Films were annealed above the glass transition temperature, Tg, at temperatures, Ta, from 130 to 290 °C. Depending upon Ta, thermal treatment results in formation of regions of nematic order and/or crystalline order in a disordered matrix. As Ta increases, molecular mobility in the amorphous phase increases resulting in a reduction in Tg. Two or three endothermic events are seen in all samples by thermal analysis. The lowest temperature endotherm is associated with melting of crystals formed either at Ta or during the thermal scan. The two higher temperature endotherm features result from transformation of crystal melt-to-nematic, and formation of more mobile nematic domains from constrained liquid, respectively, and are relatively insensitive to Ta. A strong Bragg scattering peak is seen for T a ° C corresponding to formation of two-phase structure comprising crystals and disordered phase. At higher temperatures, very strong scattered intensity in the SAXS pattern re-emerges, even after all WAXS crystal reflections have disappeared. Results suggest that a two-phase structure, of ordered nematic domains co-existing with less ordered regions, may be forming continuously above the crystal melting point.

Phase transformations in nanocrystalline mechanically alloyed Ni-Mo powders

The mechanical alloying process of Ni-20 at.% Mo powder mixture led to the formation of fcc Ni(Mo) solid solution, characterized by lattice parameter of 0.3612 nm, crystallite size 30 nm and lattice strain 0.8% The synthesis in argon of Ni-43 at.% Mo alloy, both under high and low energy conditions, resulted in the formation of two-phase structure: amorphous + nanocrystalline Mo. The presence of oxygen during milling in air and with addition of ethanol, reduced the structure refinement and formation of Ni(Mo) solid solution. Moreover, the amorphous structure was not observed in this case.

Phase Transition in Magnetic Bubble Lattices

A study is made of the temperature-induced phase transition in the magnetic bubble lattice (MBL) at which the MBL is decomposed into two coexistent phases, namely, blocks of a new lattice and stripe-domain areas. A thermodynnmic analysis of the process of formation of the stripe-domain nucleation centres is performed and the critical size of the nucleation centre is found. It is shown that if the film material characteristic length decreases with increasing tempernture the critical size of nucleation centre decreases and that at a certain temperature the MBL becomes unstable against the formation of two-phase structure. The dependence of the MBL thermal stability range on the bias field strength is obtained and the relative number of bubbles decomposed into stripes is found. A comparison with the experimcnt is made. [Russian Text Ignored].