Phase Formation Process Research Articles

The preparation, formation mechanism and magnetic properties of a Fe-Cr-Mn-N amorphous alloy

In this paper, the amorphous phase formation process, formation mechanism and magnetic properties, during the mechanical alloying (MA), have been investigated in Fe60Cr15Mn10N15 alloy, respectively. The results obviously indicate that amorphous Fe60Cr15Mn10N15 with a wide supercooled liquid region (SCLR, 82 K) can be obtained via 40 h MA process. With the milling time increasing gradually, the microstructures evolve from the initial crystalline powder, to completely amorphous phase, and eventually to amorphous phase with embedded Cr2N. By calculation, the mixing chemical enthalpy ΔHchem and amorphous formation enthalpy ΔHform have been obtained as −0.24 kJ/mol and −6.610 kJ/mol, respectively, implying the existence of thermodynamic advantage for the amorphous phase formation. In addition, the effect of 7 at% B and 7 at% Mo addition on the amorphous phase formation have also been studied, however, the diffraction peaks corresponding to Mo (Cr2N) still appear after 120 h milling. Meanwhile, isothermal annealing experiments were conducted at different temperatures, obtaining the microstructure evolution as: amorphous → amorphous alloy + Cr2N → α-Fe + Cr2N → α-Fe + CrN + Cr2N. And the hysteresis loops in amorphous Fe60Cr15Mn10N15 undergoing both the MA process and isothermal annealing procedure provide us with the evidence that this alloy system can exhibit excellent soft magnetic properties.

Formation of intermetallic compounds in the solid-liquid composites of the Ga-Ni system

The processes of formation of intermetallic compounds in the composite system of liquid gallium-nickel powder by the methods of x-ray diffraction, scanning electron microscopy and differential thermal analysis have been studied. A change in the phase composition was discovered and the influence of thermal treatment of the composites under investigation on the phase formation processes was analyzed. The mechanism of gallium enriched intermetallic compounds formation is proposed, taking into account the content of the composite, the temperature and the duration of chemical interaction of components in the melt-solid system.

Discharge and corrosion behaviors of the α-Mg and β-Li based Mg alloys for Mg-air batteries at different current densities

The discharge and corrosion behaviors of the wrought α-Mg and β-Li based Mg alloys at large current densities were investigated in this work. The β-Li phase strongly promotes the power density of Mg based anodes up to 58.9 mW/cm2 at 80 mA/cm2, due to the dissolvable discharge product. The α-Mg based alloy suffers significant hydrogen gas evolution. The β-Li phase memorably weakens the hydrogen evolution, due to prior dissolution of β-Li phase. The discharged surface becomes fine and dense after the fast and uniform consumption of the anodes at large current density. The corroded phase transform into particle-like clusters. Furthermore, the fine and dense precipitates play important roles in the spalling behavior of β-Li phase and surface film formation process. The corrosion behaviors connecting discharge properties are also discussed in detail.

Study of the microstructure modulation and phase formation of Ti[sbnd]Al3Ti laminated composites

It is extremely difficult to eliminate the voids and prepare densely TiAl3Ti laminated composites by using existing techniques. In this work, the endothermic semi-solid reaction and the self-propagating synthesis are employed to fabricate TiAl3Ti laminated composites. The SEM, EDS and XRD techniques are used to investigate the microstructure and phase formation process of TiAl3Ti laminated composites in detail. Results show that the endothermic semi-solid reaction technique can well eliminate the Kirkendall voids, while numerous voids are distributed in composites obtained by the self-propagating synthesis. It demonstrates that the interface phase evolution is Al3Ti, AlTi, AlTi3 and Al2Ti in sequence. The microhardness of both Ti and Al3Ti layers in the composite is tested and presents distinct behaviors with respect to sintering time. This work would suggest an effective way to fabricate densely TiAl3Ti laminated composites.

Effect of Microwave Energy on Phase Transformations of Aluminosilicates and Properties of Related Materials

This paper presents results of microwave processing of materials consisting of montmorillonite–hydromica clays and diatomite with combined additions based on an aluminum oxide modifier. We have determined the phase composition of fired materials prepared from mixtures before and after microwave processing. After microwave processing, an exothermic phase formation process has been identified in the temperature range 900–980°C. The samples based on bentonite clay and diatomite with a combined aluminum sodium chloride modifier have been found to contain particles less than 10 nm in size between aluminosilicate grains. After firing, the samples activated by microwave processing contain nanoscale inclusions and have enhanced strength.

Phase evolution and densification behavior of MIM418 superalloy utilizing master alloy approach

MIM418 superalloy was prepared by metal injection molding of master alloy powder and carbonyl Ni powder. Phase formation process and its evolution during heating process was followed by high temperature x-ray diffraction, and the relationship between phase transition, diffusion process and the densification behavior was discussed in detail. Microstructural characteristics of the samples during sintering process and the densification mechanism were investigated. Asynchronous diffusion of dissolvent elements, γʹ phase and carbides were observed. Severe outward diffusion of γʹ forming elements (Al) from the master alloy to the nickel powder leads to the precipitation of a large population of γʹ phase in the temperature range of 700–900 °C. The mass transfer of γ-partitioning elements (Cr, Mo) almost accomplished at 1100 °C. The phase transformation of carbides evolves from non-equilibrium MCʹ carbides in the master alloy powder to M23C6 carbides at 900–1100 °C, and finally to thermodynamically stable MC carbides in the homogenized sample. Accelerated diffusion and densification process were observed during transient liquid phase sintering process. The relatively density achieves 98.4% and ultimate strength (1047 MPa) is comparable with that of the prealloyed sample.

Phase Formation in Ti–Ni Binary System during Solid-State Synthesis

Much effort has been made to synthesize porous NiTi alloys using powder metallurgy techniques. However, the sintered products from elemental Ti and Ni powders often contain Ti2Ni and Ni3Ti in addition to the desired NiTi phase, and the thermal and mechanical properties of the sintered products are inferior comparing to cast or wrought NiTi alloys. This study investigated the solid-state diffusion reactions between elemental Ti and Ni powders during sintering to delineate the origin of the formation of these undesired intermetallic phases and proposed a physical model to explain the phase formation processes. The intermediate diffusion reaction products include Ti(Ni) and Ni(Ti) solid solutions, Ti2Ni, Ni3Ti and NiTi. The Ti2Ni and Ni3Ti intermetallic phases are the primary reaction products between Ti and Ni, and NiTi phase is formed only as a secondary reaction product from Ti2Ni and Ni3Ti. In addition, two NiTi phases of different Ni contents are formed from either Ti2Ni or Ni3Ti. These findings clarify some uncertainties and common misunderstanding on NiTi formation through elemental powder sintering and provide a guide for the design of powder metallurgy of Ti and Ni.

A Study of Processes of Phase Formation and Hardening in Molybdenum Alloys After Internal Nitriding

The laws of formation of phases and of hardening of binary and complexly alloyed molybdenum alloys with Nb, Zr and Ti under internal nitriding are studied. The structure of thin foils is determined, and the particles of the hardening phases are identified. The distribution of the nitride phases over cross section of 1-mm-thick specimens is studied. The visible length (diameter) and thickness of the particles are measured. The number of particles per unit volume is determined The effective diameters of the nitride particles and the interparticle distance are calculated for the case of their approximation by spheres. The conditions (laws) of high-temperature hardening of molybdenum alloys after internal nitriding are determined.

Modified Ion-Conducting Ceramics Based on Lanthanum Gallate: Synthesis, Structure, and Properties

A review is presented of the synthesis and complex investigation of modified ion-conducting ceramics based on heterosubstituted lanthanum gallate as a promising electrolyte material for solid oxide fuel cells. The effect the composition of multicomponent complex oxides has on the structure, microstructure, and electrophysical properties of ceramics is examined. Samples of ceramics with new compositions are produced via solid-state synthesis and modified with lithium fluoride. A drop is observed in the sintering temperature of the ceramics, caused by the liquid phase mechanism of sintering as a result of the low-melting superstoichiometric quantities of the additive. The effect lithium fluoride has on the process of phase formation, microstructure, and conductivity of the ceramics is investigated. It is found that samples modified with lithium fluoride display high density, dense grain packing, and high values of electrical conductivity at high temperatures.

Photoluminescent properties of AlN: Mn2+ phosphors

White light-emitting diodes (WLEDs), which have high luminous brightness, longevity, low energy consumption and friendliness of environment, could be employed in diverse fields. Nevertheless, commercial phosphors are short of red light component. New phosphors which can emit red light are required. Mn2+ doped aluminum nitride (marked as AlN) red phosphors were prepared by a simple solid-state reaction. X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS), as well as photoluminescence (PL) spectra are utilized to characterize the prepared samples. The preparing process of AlN phosphors, phase formation and crystal structure, morphology, and photoluminescence are detailedly investigated. For Mn2+ doped AlN phosphor(marked as AlN:Mn2+), it exhibits an intense red emission caused by the 4T1(4G)-6A1(6S) transition of Mn2+. The unusual red emission of Mn2+ is ascribed to the strong nephelauxetic and crystal field between Mn2+ and the tetrahedrally coordinated N3−. The oxygen-related defects in AlN have a great influence on the photoluminescence properties of the Mn2+ doped AlN. The AlN:Mn2+ phosphors exhibits a high brightness, high color purity, and lower saturation, which make it a great candidate of red phosphors for white light-emitting diodes (WLEDs).

Secondary phases formation in lanthanum-doped titanium-zirconium-molybdenum alloy

Lanthanum-doped titanium-zirconium-molybdenum (La-TZM) alloys have good mechanical properties, including high strength and toughness due to complex secondary phases. Herein, the formation process of the secondary phases in the La-TZM alloy was revealed by thermodynamics calculations. The ΔG values of possible reactions during sintering were obtained. Results show that the formation process of the secondary phases was controlled by different reactions at different stages. At the first stage (0–500 °C), the main reactions are listed as follows: TiH2+O2(g)→TiO2+H2↑(g), ZrH2+O2(g)→ZrO2+H2↑(g), C6H12O6→[C]+ H2O↑, [C]+ O2(g)→CO2(g)↑, [C]+Mo→MoC, La(NO3)3·6H2O→ La2O3+NO2↑+ NO↑+O2↑+H2O; [C]+TiH2→TiC + H2(g)↑, [C]+ZrH2→ZrC + H2(g)↑. At the secondary stage (680–960 °C), the dominant reactions include: TiH2→Ti + H2(g)↑, ZrH2→Zr + H2(g)↑. At the last stage (≥1200 °C), the primary reaction is Ti + Zr+[O]→ZrTiO4. The secondary phases in the La-TZM alloy include TiO2, ZrO2, ZrC, TiC, MoC, ZrTiO4, La2O3 and the solid Ti and Zr phases. These results can guide the design of new ingredients for Mo alloys.

Calcium phosphate composite cements based on simple mixture of brushite and apatite phases

The composite cements based on simple mixtures brishite and apatite with ratio 70/30, 50/50, 30/70 were developed. The processes of phase formation, microstructure and mechanical properties were studied. The kinetics of degradation in simulated body fluid depending on the microstructure and the materials phase composition was carried out. The biological test in vitro were performed using the MTT-test on the human fibroblast immortalized (hFB) cell line and the human osteosarcoma cell line MG-63. The materials didn’t have acute cytoxicity and possessed surface matrix properties. It was determined that the both line of cells actively proliferated, with viable cells values higher 20-60 % then control at all observation periods.

Formation of Compounds in the Ag2O–Sb2O3–MoO3 System on Heating

This paper presents a detailed study of phase formation processes in the AgNO3–Sb2O3–MoO3 system during heating in air. The compositions of the solid-state reaction products have been determined using thermogravimetry and qualitative X-ray diffraction. The results demonstrate that, at a final heat treatment temperature of 1023 K, synthesis yields a range of Ag2–xSb2–xMo x O6 compounds with the pyrochlore structure and 0.0 ≤ x ≤ 2.0. The structural parameters of the synthesized phases have been refined by the Rietveld method in space group Fd3m and their electrical conductivity has been measured.

Experimental study of structural, surface morphology, optical and luminescence properties of MAl2O4/Al2O3 (M = Co, Ni) composites

The novel alumina-based luminescence material of MAl2O4/Al2O3 (M = Co, Ni) were prepared by a polyacrylamide gel route. Influence of Co/Ni metal salt on the sample morphology, band-gap and luminescence properties were investigated by transmission electron microscopy (TEM), UV–vis spectrophotometer and fluorescence spectrophotometer. The results indicated that the Co/Ni metal salt added to the precursor solution could significantly effects the phase formation process, powder morphology, optical and luminescence properties of the prepared MAl2O4/Al2O3 (M = Co, Ni) composites. The Co metal salt or Ni metal salt introduced to Al2O3 precursor solution reduces the band-gap values and enhances the luminescence properties of MAl2O4/Al2O3 (M = Co, Ni) powders. It is confirmed that the interaction between the intra-band gap defects of CoAl2O4/NiAl2O4 and the oxygen vacancies on the surface of the C/amorphous alumina composite play a specific role for the determination of photoluminescence emission. Compared with the CoAl2O4/Al2O3 composites, the NiAl2O4/Al2O3 composites have a stronger the fluorescence intensity because of the wide band-gap value of NiAl2O4. A new luminescence mechanisms of MAl2O4/Al2O3 (M = Co, Ni) composites have been proposed on the basis of the experimental and computational results.

Synthesis of Zirconium Diboride Films and ZrB2/BC x N y Heterostructures

Using mechanochemical synthesis, we have prepared zirconium borohydride, Zr(BH4)4, as a precursor for ZrB2 film growth by chemical vapor deposition. We have carried out the thermodynamic modeling of phase formation processes in the Zr–B–(N)–H and Zr–B–(N)–H–O systems in a wide temperature range, from 100 to 2500°C, at various p(H2)/p(Zr(BH4)4) and p(NH3)/p(Zr(BH4)4) partial pressure ratios in the starting gas mixtures. A process has been proposed for the growth of zirconium diboride films by Zr(BH4)4 decomposition using two techniques: chemical vapor deposition and plasma-enhanced chemical vapor deposition. We also developed a process for the growth of multilayer ZrB2-and BC x N y -based structures.

The phase formation process of Bi0.5(Na0.8K0.2)0.5TiO3 thin films prepared using the sol-gel method

Lead-free Bi0.5(Na0.8K0.2)0.5TiO3 (abbreviated as BNKT) thin films were grown on Pt(111)/Ti/SiO2/Si substrates using a sol-gel/spin coating technique and were then annealed at different temperatures (350°C, 550°C, 750°C and 850°C). Analysis of the XRD patterns and FT-IR spectra were used to determine the main reactions and the phase formation process of BNKT thin films during the sol-gel process. The results show that the dielectric constant of the thin films attains a maximum at a set temperature and then decreases at higher annealing temperatures, which can be attributed to phase formation and transformation. Moreover, the morphologies of the BNKT thin films improve with the increase in grain size and the formation of distinct grain boundaries. Furthermore, through increasing the pH of the precursor solutions, the size of the sol-gel colloidal particles increases slightly and the grains formed from the corresponding solutions tend to be small and uniform.

ОБРАЗОВАНИЕ СОЕДИНЕНИЙ НА ОСНОВЕ ФЕРРИТА ВИСМУТА ПРИ ЧАСТИЧНОМ ЗАМЕЩЕНИИ ИОНОВ ВИСМУТА ИОНАМИ ЛАНТАНА И ПРАЗЕОДИМА

Using the solid-phase reaction method we obtained bismuth ferrite based compounds generated by partial substitution of bismuth ions with rare earth metal ions (lanthanum and praseodymium). We used thermogravimetric analysis and X-ray analysis at the temperature range from 297 to 1123 K to study the peculiarities of the processes of phase formation of reaction-products synthesis in the systems which contain oxides of iron, bismuth, lanthanum, and praseodymium; their compositions were also determined. For the final synthesis temperature of 1123 K we determined a homogeneous concentration area, where bismuth ferrite solid solutions with the structure of distorted perovskite exist. We studied the influence of lanthanum and praseodymium oxides on phase composition of bismuth ferrite compounds in the process of isovalent alloying of a part of bismuth ions by lanthanum and praseodymium ions. In the frequency range of 20 Hz – 1 MHz we determined the key parameters, which characterize electrical and magnetic properties of perovskite-like phases. We found that for the considered samples the frequency dependencies of complex magnetic permeability and electrical parameters (real and alleged part of permittivity) are of almost the same type. We showed that for the given frequency range both electrical (complex permittivity) and magnetic (complex magnetic permeability) parameters decrease with the frequency increase

Exploring the Peculiarities of LiFePO4 Hydrothermal Synthesis Using In Situ Calvet Calorimetry

Peculiarities of the hydrothermal synthesis of the lithium iron phosphate cathode material are studied using in situ Calvet calorimetry. Staging and temperature intervals of the phase formation process are determined as a function of the concentration of the initial reagents. Obtained results revealed a clear correlation between observed heat absorption behavior and lattice parameters, morphology, and electrochemical performance of the obtained LiFePO4 materials. Lowering temperature of the precursor dehydration leads to better Li/Fe ordering, smaller particle size of LiFePO4 samples, and the highest charge–discharge capacity measured in the Li-ion cell.

X-ray diffraction study of self-propagating high-temperature synthesis in the Zr–Al–C system

The phase formation process in the Zr–Al–C system during self-propagating high-temperature synthesis (SHS) has been studied by time resolved X-ray diffraction (TRXRD). The “nonuniqueness” of SHS routes in ternary solid-phase systems depending on synthesis initiation conditions has been established. No formation of ternary compounds belonging to the class of MAX phases has been observed in the considered system. It has been shown that the reaction responsible for the propagation of the combustion wave is the synthesis of ZrC, if SHS is initiated by a high-temperature pulse, and the end product also incorporates intermetallide zirconium phases. At the same time, the sequential formation of the Zr[Al] solid solution, the ZrAlC х phase, and the intermetallide ZrAl3, ZrAl2, and Zr2Al3 phases occurs in the bulk ignition of the 2Zr–Al–C mixture under the conditions of great heat withdrawal during the reaction between an Al melt and Zr particles. No initiation of the Zr–C reaction takes place due to a low enthalpy of the reactions between aluminum and zirconium.

Thermal analysis of reaction producing KXTiO2

Fabrication of bio-functional nanoparticles, used to modify the optical properties of cartilage, is performed in several stages. Self-propagating high-temperature synthesis (SHS) is one of the stages of production of oxide bronzes. Stage SHS determines the properties of the bio-functional particles. Only under certain thermophysical parameters of SHS, it is possible to obtain nanoparticles which have abnormally high photothermal effect. The paper presents the results of thermal analysis of phase formation processes of reaction KXTiO2. To control the thermal and structural parameters of synthesis, we used optoelectronic measuring system based on a high-speed video camera. Video analysis was performed in the program ImageJ. Particular attention is paid to optical micro-pyrometry combustion wave and the kinetics of the reaction producing potassium titanium oxide bronzes. Thermal analysis method has allowed to establish the possibility of two reaction flow scenarios. Slow reaction rate of the reaction medium is 0.5 sm2 s−1; the temperature gradient reaches 1000 degree s−1. The temperature gradient during emission of the substance is 1,000,000 degree s−1. And at the low-temperature reaction, the maximum reaction rate reaches 6 sm2 s−1; the temperature gradient is 4000 degree s−1. A short-lived transparent, with respect to optical radiation, phase of oxide bronze was detected. Solidified drops consist of reduced copper. Inside there is needle inclusions of potassium titanium oxide bronze.