Formation Of New Phase Research Articles

Influence of annealing temperature on the structure and properties of the nanograined NiAl intermetallic coatings produced by using mechanical alloying

Nanostructured NiAl intermetallic coatings were produced on carbon steel by using mechanical alloying in ambient temperature and pressure. Ni and Al powders were mixed with the composition of Ni–50at.% Al. Coatings were examined using X-ray diffraction and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) was also used to observe coating particles. Samples prepared after 480min ball milling were subjected to annealing treatment at temperatures range of 400°C to 600°C. Continued ball milling reduced the coarse grains of the coating to the nanoscale. The size of nanocrystalline grains in the Ni–Al coating ranged between 17nm and 96nm. The nanocrystalline grains had a tendency to grow with increasing annealing temperature. After annealing at 400°C, a solid state reaction between Al and Ni leads to the formation of new phases. With increasing annealing temperature to 600°C only NiAl peaks were observed on XRD pattern. After annealing the hardness of the coating initially decreased and then increased. Annealing treatment also improved wear resistance of the coating.

Observations on the Electrical Properties of Al-Sic Composite

The influence of SiC particulates addition on the electrical behaviors of Al / SiC matrix composites was studied. The composited samples were prepared from Al-SiC powdered mixtures having different SiC content in the range of 40-70 wt% SiC particulates with particle sizes lower than 45- μm. The resultant powders were then uniaxially pressed in cylindrical steel die to obtain a compact disc-shaped of 1.5 cm in diameter. The compacts were sintered in the temperature range of 800 ˚C and 1100 ˚C. Electrical and dielectric properties (a.c. Conductivity, dielectric constant, dielectric loss, and dielectric loss factor) were measured for these sintered samples in the frequency range 200 Hz – 6GHz. From the results obtained it was concluded that the formation of new phases (as proved by XRD) plays a major role in the properties of these composites. Also a jump-like behavior in the measured electrical conductivity and the abrupt changes in the dielectric constant behaviors suggest frequency- dependent two- mechanisms for conduction at different SiC content.

The Synthesis of Nanocomposites with Use of Cellulose

This work studied the synthesis of nanocomposites with cellulose use as crystallizing polymer on the basis of its ability to form crystalline particles with various parameters of an elementary cell – nanoparticles of a metal or oxide origin. The authors obtained high dispersed systems by dispersion of volume phases from solutions using condensation method. At using of this method, depending on the conditions of the formation process of the new phase can be obtained as systems with a size of several nanometers as well as more coarsely dispersed systems. The dispersiveness of a system, arising during formation of new phases, is determined by ratio speed of formation and nucleus growth of new phase a phase transition. The condensation process involves the formation of new phase according the heterogeneous or homogeneous mechanisms. The kinetics formation of new phase is determined by two stages: the formation of condensation centers (nucleus) and nucleus growth. In formation process of nanocomposite materials the natural polymer with known molecular structure<br />is used as matrix, in which we can put desired nanoparticles in the form of filler. In this work the authors used cellulose which has developed capillary-porous structure, including in-fibrillar porous with the size of 1.5-10 nm, and which is able to form crystallites with different parameters of lattice cell.

Thermal Stability of the MoS2 Phase in Injection Moulded 17-4 PH Stainless Steel

In the present paper, an analysis of the stability of the MoS2 compound in 17-4 PH stainless steel matrix during the sintering of powder injection moulded samples is presented. A feedstock containing 10% vol. of the solid lubricant phase MoS 2 , mixed with 17-4 PH stainless steel powder was prepared and injected. The sintering was carried out at various temperatures ranging from 650°C to 1,300oC. The progress of the dissociation process of MoS 2 as a function of sintering temperature and the formation of new phases were analyzed via X-ray diffraction. The microstructure of the resulting material was analyzed by SEM/EDS. As expected, for temperatures above 650oC, the results confi rm the decomposition of MoS 2 and formation of others sulphides during the sintering cycle. In addition, there occurs dissolution of molybdenum resulting from MoS2 decomposition.

Atomic Force Microscopy and X-ray Photoelectron Spectroscopy Study of NO2 Reactions on CaCO3 (101̅4) Surfaces in Humid Environments

In this study, alternating current (AC) mode atomic force microscopy (AFM) combined with phase imaging and X-ray photoelectron spectroscopy (XPS) were used to investigate the effect of nitrogen dioxide (NO2) adsorption on calcium carbonate (CaCO3) (101̅4) surfaces at 296 K in the presence of relative humidity (RH). At 70% RH, CaCO3 (101̅4) surfaces undergo rapid formation of a metastable amorphous calcium carbonate layer, which in turn serves as a substrate for recrystallization of a nonhydrated calcite phase, presumably vaterite. The adsorption of nitrogen dioxide changes the surface properties of CaCO3 (101̅4) and the mechanism for formation of new phases. In particular, the first calcite nucleation layer serves as a source of material for further island growth; when it is depleted, there is no change in total volume of nitrocalcite, Ca(NO3)2, particles formed whereas the total number of particles decreases. This indicates that these particles are mobile and coalesce. Phase imaging combined with force curve measurements reveals areas of inhomogeneous energy dissipation during the process of water adsorption in relative humidity experiments, as well as during nitrocalcite particle formation. Potential origins of the different energy dissipation modes within the sample are discussed. Finally, XPS analysis confirms that NO2 adsorbs on CaCO3 (101̅4) in the form of nitrate (NO3(-)) regardless of environmental conditions or the pretreatment of the calcite surface at different relative humidity.

Nanoparticles Consolidation Mechanism at High Pressure and High Temperature in Diamond-B-Si-Cu System

The synthesis of advanced materials with superior performance and properties is of growing scientific and technological interest. In particular, significant achievements have been attained in the synthesis of nanocomposites associated with superhard materials. This work investigates nanostructured composites obtained by high pressure and high temperature sintering of synthetic diamond combined with boron, silicon and copper. Diamond powder was mixed with B, Si and Cu, also in the form of powder. The mixture was then submitted to high energy wet milling until a nanopowder was formed. Sintering of this resulting nanopowder was carried out at 5.6 GPa of pressure and 1300°C. X-ray diffraction and scanning electron microscopy analysis revealed the formation of new phases in a well consolidated nanostructure with relatively high density.

Crack tip plasticity in single crystal UO2: Atomistic simulations

The fracture behavior of single crystal uranium dioxide under mode-I loading is studied using molecular dynamics simulations at room temperature. The initial cracks are introduced as elliptical notches on either {111} or {110} planes. Two crack tip shielding mechanisms, dislocation emission and metastable phase transformation are identified. Crack extension is observed for cracks residing on {111} plane only. The dislocations have a Burgers vector of 〈110〉/2 and glide on {100} planes. Two metastable phases, Rutile and Scrutinyite, are identified during the phase transformation, and their relative stability is confirmed by separate density-functional-theory calculations. Examination of stress field near the crack tips reveals that dislocation emission is not as an effective shielding mechanism as the phase transformation. The formation of new phases may effectively shield the crack if all phase interfaces formed near the crack tips are coherent, as in the case of cracks residing on {110} planes.

Capillary pressure of van der Waals liquid nanodrops

The dependence of the surface tension on nanodrop radius is important for the new-phase formation process. It is demonstrated that the famous Tolman formula is not unique and the size-dependence of the surface tension can distinct for different systems. The analysis is based on a relationship between the surface tension and disjoining pressure in nanodrops. It is shown that the van der Waals interactions do not affect the new-phase formation thermodynamics since the effects of the disjoining pressure and size-dependent component of the surface tension cancel each other.

Surface properties evolution of attapulgite by IGC analysis as a function of thermal treatment

At low temperatures, thermal treatment of attapulgite clay causes a loss of mass due to the elimination of linked, zeolitic and crystallized water molecules. At high temperatures, there is a junction of particles until total melting of the attapulgite fibers. This transformation reduces significantly the volume of the porous network resulting in the drop in the value of specific surface area and causing important changes in the textural, structural and surface properties of the raw attapulgite. The inverse gas chromatography shows sensitivity of the attapulgite sample to the effect of temperature through the decrease of the dispersive component of the surface energy γsd. The evolution of the nanomorphological index, a measurement of the surface nanorugosity, follows the appearance of surface roughness on carbonates with the increase of the temperature. The surface heterogeneity, determined by calculating the distribution functions of adsorption energies also underlines the morphology changes and the formation of new phases under the effect of temperature.

Thermal decomposition of different types of asbestos

Given the known carcinogenic effects, asbestos minerals are considered as general health hazard. Therefore, the elimination of asbestos materials from the environment is necessary. Asbestos minerals should be entirely transformed to a non-hazardous material. One of these methods is destructing the fibers structure of asbestos minerals by thermal treatment. Asbestos minerals are naturally occurring hydrous silicates, so that they decompose to release water by heating at high temperatures which may lead to changes in crystal structure and the formation of new phases without the dangerous properties. In this article, thermal behavior of asbestos minerals is investigated to observe the disappearance of this hazardous structure and to characterize products obtained by this way. Ten samples of asbestos minerals (six chrysotile samples from different locations, two samples of crocidolite, one amosite, and one tremolite) from different locations were tested. Mineralogical and morphological data (X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy) were obtained before and after differential thermal analysis.

In-Situ Formation of Titanium Boride and Titanium Carbide by Selective Laser Melting

Abstract In the present study the Selective Laser Melting of a high-energy ball milled Ti - B 4 C powder blend was performed. The mixing ratio of the powder blend was settled to fulfill the reaction 3 Ti + B 4 C→ TiC + 2 TiB 2. The in-situ synthesis of intermediate phases was performed by single line welding experiments on a pure titanium substrate. Phase identification by X-ray diffraction gave no indication for the formation of new phases due to the mixing of the powder in the ball mill. However, within the weld seam the XRD analysis proved the existence of Ti 2 C and TiB.

Improving the wear resistance of NiTi shape memory alloy thin films by nitrogen and carbon ion implantation

Annealed NiTi thin films (∼51.2 at.%Ni) were implanted with carbon and nitrogen ions with 80 keV energy and 3×1017 cm−2 ion dose. X-ray photoelectron spectroscopy confirmed the existence of implanted ions in the surface structure of the films. Atomic force microscopy showed an increase of roughness and decrease of grain size after ion implantation. Grazing incidence X-ray diffraction showed the formation of new phases in the films such as TiN, Ti2N, TiC and different kinds of oxides. Nanoindentation and nanoscratching tests revealed the improvement of wear behaviour of NiTi thin films after ion implantation via increasing nanohardness (3.1–6.2 and 7.3 GPa after carbon and nitrogen ion implantation, respectively) and decreasing of scratch coefficient (0.22–0.18 and 0.17 after carbon and nitrogen ion implantation) and wear depth.

High Temperature Structural Modifications of Intercalated Montmorillonite Clay Mineral with OH-Al Polymers

Two montmorillonitic clays were put into contact with a solution containing inorganic OH-Al polymers and subsequently washed and dried. The obtained solid (i.e.the clays with the OH -Al species in the montmorillonite interlayer) which was called the precursor, was subjected to a thermal treatment up to 1000 ¡ C using DTA-TG for analysis at low temperature. Additionally, the structural changes of the precursor by heating at 1030, 1100 and 1200 ¡ C for 2hours and that of the natural clays were examined. The crystallinity and formation of new phases was followed by x-ray diffraction analysis. Mullite and cordierite were originated depending on the different contents of aluminium and magnesium in the structure of natural montmorillonite, respectively, accompanied with other phases. The intercalated OH-Al species in both clays favored the increase in the mullite content in the final products. However, the transformation to this phase was directly related to the octahedral aluminium of the natural clay and thus mullite was found to be the dominant phase from montmorillomite containing higher octahedral Al.

Wear study of Ni–WC composite coating modified with CeO2

In the present investigation, Ni–WC composite powder was modified with the addition of CeO2 in order to form a new composition of Ni–WC–CeO2. The Ni–WC and Ni–WC–CeO2 compositions were used for coating deposition by high-velocity oxy-fuel (HVOF) spraying process so as to study the effect of CeO2 addition on microstructure, distribution of various elements, hardness, formation of new phases, and abrasive wear behavior. Further, the effect of load, abrasive size, sliding distance, and temperature on abrasive wear behavior of these HVOF-sprayed coatings was investigated by response surface methodology. To investigate the abrasive wear behavior of HVOF-sprayed coatings four factors such as load, abrasive size (size in micrometers), sliding distance (meters), and temperature (°C) with three levels of each factor were investigated. Analysis of variance was carried out to determine the significant factors and interactions. Investigation showed that the load, abrasive size, and sliding distance were the main significant factors while load and abrasive size, load and sliding distance, abrasive size and sliding distance were the main significant interactions. Thus an abrasive wear model was developed in terms of main factors and their significant interactions. The validity of the model was evaluated by conducting experiments under different wear conditions. A comparison of modeled and experimental results showed 4–9% error. The abrasive wear resistance of coatings increases with the addition of CeO2. This is due to increase in hardness with the addition of CeO2 in Ni–WC coatings.

Special features of the formation of new phases on heating barium titanate powders with zirconium dioxide micro- or nanopowders

powders, heating, concentration, phase composition, lattice parameters, modification, barium titanate, zirconium dioxide, grain. To modify barium titanate to displace the phase transition from 125°С toward lower temperatures, various elements replacing barium or titanium cations, in particular, zirconium atoms are used [1, 2]. The present work is aimed at investigation of the influence of the modification temperature of barium titanate powders with zirconium dioxide micro- or nanopowder in the interval 800–1200°С on the phase composition and diffusion reflection spectra of the compounds obtained. The BaTiO

Stability of Sc 2O 3 and CeO 2 co-doped ZrO 2 electrolyte during the operation of solid oxide fuel cells: Part II the influences of Mn, Al and Si

Mechanisms for decomposition of 10 mol% Sc 2O 3 and 1 mol% CeO 2 co-doped ZrO 2 (10Sc1CeSZ) electrolytes of a cathode-supported tubular-type SOFC during the long term operation for ≥ 100 h have been investigated by analyzing SEM, Raman spectroscopy and XPS of decomposed samples and also by additional examination for the effects of impurities (MnO 2, Al 2O 3 and Si) on the decomposition of electrolyte. The valence of manganese at the decomposed parts in the fuel side was found to become higher after the long term operation. This leads to the driving force for the decomposition of 10Sc1CeSZ into two phases by the large oxygen potential gradient developed on the surface in the fuel side. The kinetic factors for formation of new phases are considered to be as follows; the Si component in the fuel can be a trigger to form MnSiO 3 which worked at the nucleation points, and the valence changes of manganese in the electrolyte proceed the decomposition cycles consisting of two phase separation in the zirconia, pulverization of manganese-rich phase and detachment of zirconia-based oxides.

Enhanced hydrogen uptake/release in 2LiH–MgB2 composite with titanium additives

The influence of different titanium additives on hydrogen sorption in LiH–MgB2 system has been investigated. For all the composites LiH–MgB2–X (X = TiF4, TiO2, TiN, and TiC), prepared by ball-milling in molar ratios 2:1:0.1, five hydrogen uptake/release cycles were performed. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and attenuated total reflection infrared spectroscopy (ATR-IR) have been used to characterize crystal phases developed during the hydrogen absorption–desorption cycles.All the composites with the titanium additives displayed an improvement of reaction kinetics, especially during hydrogen desorption. The LiH–MgB2–TiO2 system reached a storage of about 7.6 wt % H2 in ∼1.8 h for absorption and ∼2.7 h for desorption. Using in-situ SR-PXD measurements, magnesium was detected as an intermediate phase during hydrogen desorption for all composites. In the composite with TiF4 addition the formation of new phases (TiB2 and LiF) were observed. Characteristic diffraction peaks of TiO2, TiN and TiC additives were always present during hydrogen absorption–desorption. For all as-milled composites, ATR-IR spectra did not show any signals for borohydrides, while for all hydrogenated composites B–H stretching (2450–2150 cm−1) and B–H bending (1350–1000 cm−1) bands were exactly the same as for commercial LiBH4.

Study and model development of erosive wear by RSM

In this study, composite powder (MEC1031C) was modified with the addition of 0.4 wt.% La2O3. The effects of La2O3 addition on microstructure, formation of new phases, and microhardness were studied. The La2O3 addition refines the microstructure, forms new phases, and increases microhardness of high-velocity oxy-fuel (HVOF) coatings. The erosive wear behaviours of HVOF-sprayed coatings were investigated by response surface methodology. To investigate and develop the erosive wear model of unmodified (without La2O3) and modified (La2O3 addition) HVOF-sprayed coatings, four factors, velocity ( V), impact angle ( A), temperature ( T), and feed rate (F), with each factor at three levels, were used. Analysis of variance was carried out to determine the significant factors and interactions. Investigation showed that the velocity, temperature, and feed rate were the main significant factors, while velocity–feed rate was the main significant interaction. Thus, an erosive wear model was developed in terms of main factors and their significant interactions. The validity of the model was evaluated by conducting experiments under different wear conditions. A comparison of modelled and experimental results showed 5–11 per cent error. The modified (La2O3 addition) HVOF-sprayed coating showed high erosive wear resistance compared to unmodified coating. This is due to the increase in hardness of the modified coating.

The comparison of mechanical behavior of MgO–MgAl 2O 4 with MgO–ZrO 2 and MgO–MgAl 2O 4–ZrSiO 4 composite refractories

Mechanical properties of different compositions obtained from the additions of 5, 10, 20 and 30 wt.% zircon (ZrSiO 4) into the MgO–spinel composite refractories and ZrO 2 into MgO have been examined, the variations that occurred have been determined, and the parameters affecting those factors have been investigated with the reasons. The density, strength, Young's modulus, fracture toughness, fracture surface energy and work of fracture were measured and evaluated. Microstructural variations and fracture surfaces have been examined and the formation of new phases has been identified depending on the additive type and quantity. The relationships between mechanical properties and structural variations for different compositions have been examined. In MgO–spinel materials, strength, Young's modulus and fracture toughness values decrease up to 20% spinel addition and stay almost constant for further loads. ZrO 2 addition displays same trend but not as effective as spinel. Besides, since ZrO 2 is stable in cubic form, it does not show any toughening mechanism. Forsterite formation is the most important factor for 2-fold improvement in the mechanical properties of MgO–spinel–zircon refractories. The more the zircon addition, the more the mechanical properties improve. The generation of natural bonding between matrix particles with forsterite formation, on the other hand, causes the fracture path to turn to transgranular fracture with an increase in fracture surface energy and a decrease in work of fracture, among which the latter is considered as an indicator of thermal shock resistance of the materials being high.

Microstructure and properties of plasma-sprayed bio-coatings on a low-modulus titanium alloy from milled HA/Ti powders

New composite hydroxyapatite/titanium (HA/Ti) coatings were fabricated by plasma spraying on Ti–24Nb–4Zr–7.9Sn alloy from milled precursor powders. The microstructures, mechanical properties and apatite-induction abilities of the coatings were investigated, and the influences of the initial HA/Ti ratios on microstructure and properties were highlighted. XRD, SEM and TEM were used to analyze the microstructures of the coatings. The micro-hardness and elastic modulus were determined by indentation tests and the bond strength was determined by tensile tests. The apatite-induction ability of the coatings was evaluated in simulated body fluid (SBF) with ion concentrations similar to those of human blood plasma. The results showed that the microstructure, mechanical properties and apatite-induction ability were dependent on the HA/Ti ratios of the original powders. The mechanical properties increased, and the apatite-induction ability decreased with increasing Ti content. Various chemical reactions occurred during the preparation of the coatings, including the decomposition of HA, the reaction between HA and Ti and the oxidization of Ti, which resulted in the formation of new phases, such as CaTiO3, Ca3(PO4)2, TiPx and titanium oxides in the different coatings. These new phases play an important role for the mechanical properties and the apatite-induction ability of the coatings.