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Niobium carbide has received widespread attention due to its high melting point, high strength, high chemical stability and high wear resistance, but the current preparation of niobium carbide coatings using plasma spraying technology suffers from low deposition efficiency, poor fusibility of the composite powders, high porosity, and high defects in the coating microstructure. Therefore, the microstructure and properties of NbC-Al 2 O 3 composite coatings prepared by plasma spraying NbC-Al 2 O 3 -SiC composite powder and reactive plasma spraying Nb 2 O 5 -SiC-Al composite powder were comparatively investigated in this paper. The reaction mechanism of Nb 2 O 5 -SiC-Al composite powder during plasma spraying as well as the mechanism of the formation of coatings were analyzed in detail. The results showed that compared with the ex-situ NbC-Al 2 O 3 -SiC coating fabricated by plasma spraying, the in-situ Nb 2 O 5 -SiC-Al composite coating prepared by reactive plasma spraying had an obvious layer structure, low porosity (5.8 %), high hardness (1141 HV 0.1), high toughness (22.94 J/m2), and good scratch resistance properties. [ABSTRACT FROM AUTHOR]

The coating based on the MoSi2–MoB–HfB2 system on the substrate of the C/C–SiC composite is prepared by the in situ reaction synthesis using the slurry-roasting deposition of the powder composition at 1620°C under an argon expansion pressure of ~1 Pa. The reaction mechanisms in the Mo–HfSi2–SiB4–C system predetermining the synthesis of secondary phases MoSi2, MoB, HfB2, and HfC are proposed. Thermodynamic calculations of possible chemical reactions are performed. Probable causes for a high porosity of the prepared coating are analyzed. [ABSTRACT FROM AUTHOR]

Quasi core–shell ZnO/rGO composites were prepared from Zn2(OH)2CO3 and graphite oxide (GO) as raw materials by solid-phase reaction. The effects of GO content and heating rate on the photocatalytic performance of the products were studied. XRD results showed ZnO/rGO composites were obtained at 300 °C for 2 h, and transmission electron microscopy results showed graphene was coated with ZnO nanoparticles with a particle size of about 20–50 nm and formed a quasi core–shell structure. The photocatalytic experiment results indicated the ZnO/rGO composites exhibited good photocatalytic performance. Under simulated sunlight irradiation, ZnO/30% rGO composite materials demonstrated the best photocatalytic activity for methylene blue, with a degradation rate of 99.6% after 60 min of illumination. Finally, a photocatalysis mechanism of quasi core–shell ZnO/RGO composites was proposed. [ABSTRACT FROM AUTHOR]

ZnO/reduced graphite oxide (rGO) composites were simultaneously prepared by the thermal reduction of graphite oxide (GO) and the decomposition of Zn(OH)2. The samples were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence, and DRS. Results indicate that Zn(OH)2 was heated and decomposed into ZnO at a low temperature (200 ℃), while GO was reduced to graphene. The synthesized ZnO particles were small and loaded on graphene layers. The ZnO/rGO photocatalysts exhibited excellent photocatalytic activity against methylene blue (MB) under simulated sunlight irradiation. The ZnO/50% rGO photocatalyst showed the best MB photodegradation rate of up to 99.7% within 3 min. Synchronous reaction provided an efficient, simple, and fast preparation method for ZnO/rGO composites, with an excellent solar photocatalytic degradation ability. [ABSTRACT FROM AUTHOR]

Porous TiAl3 intermetallic compounds were fabricated through thermal explosion(TE) by adding 60% volume of NaCl space holder. The mechanism of pore channel formation and microstructure in TiAl3 sintered disks was investigated. The research on pore channels was from micro to macro, and the formation process of pore channels was systematically described. It was found that the pore structure of TiAl3 was composed of three parts, macropores left by the space holder, thermal explosion micropores, and intergranular micropores. The raw material particle size controlled the morphology of micropores. Three kinds of channels were formed, crack microchannels, thermal explosion microchannels, and macroporous channels. The formation and propagation of crack microchannels were due to the excessive expansion of large Ti particles. The pore window structure between the in-situ pores of large Al particles was the main reason for the thermal explosion microchannel. Crack microchannels and thermal explosion microchannels were the media of macroporous channels. Different channel structures had different effects on the mechanical properties of TiAl3 products. Rich and connected pore channels enhanced direct contact between fluid and pore wall and improved filtration of porous TiAl3 intermetallic compounds. [ABSTRACT FROM AUTHOR]

MoSi2-based coatings on a CSC substrate are formed by reaction synthesis using slurry painting of powder compositions at 1500°C and a pressure of 8–9 mPa. Mechanisms are proposed for the reaction interaction in the Mo–Si–C and Mo–Si–C–HfB2 systems, which determine the synthesis of the secondary phases MoSi2, Mo4.8Si3С0.6, MoB, and HfC. Possible chemical reactions are thermodynamically calculated. Possible causes of the high porosity of the synthesized coatings are analyzed. [ABSTRACT FROM AUTHOR]

A method was tested to perform the solid-phase synthesis of ceramic wollastonite under hybrid microwave heating using such natural renewable raw materials as sea shells as a source of CaCO3 with the addition of commercial SiO2 powder. The XRD, SEM, TGA, and EDS methods were used to explore the effect of the mechanical homogenization time and the conditions for the chemical interaction of raw materials, provided that the required phase composition is reached. It was studied how temperature (800–1150°C) and time (15–60 min) of sintering affect the composition and structure of the ceramic wollastonite samples, including those in the presence of the strengthening additive sodium tetraborate. The formation of an apatite (Ca10(PO4)6(OH)2) layer on the surface of the obtained samples under conditions of their contact with artificial human blood plasma was assessed to confirm the biocompatible properties of these materials. The proposed method of synthesis is promising for obtaining a chemically pure valuable biomaterial in the form of synthetic wollastonite with the possibility of rational use of biogenic raw materials. [ABSTRACT FROM AUTHOR]

In this work, aluminum 6061-based powder blend feedstocks with reactive Ti-B/C additions were employed in two different additive manufacturing processes, laser powder bed fusion (L-PBF) and electron beam freeform fabrication (EBF3), to create micro- and nanoscale ceramic and intermetallic inoculants in situ and to examine the effect of feedstock inoculant content on microstructure and mechanical properties. Products of the reaction synthesis process were identified with X-ray diffraction and energy-dispersive spectroscopy to include Al3Ti, TiC, and TiB2. Electron back-scatter diffraction revealed significant grain refinement up to 74 × , mitigation of solidification cracking, and formation of an equiaxed grain structure with the addition of just 2 vol.% inoculant. Inoculants formed in situ were seen to induce approximately 5 × more grain refinement than pre-existing inoculants. The highest ultimate tensile strength and Young's modulus of 368 ± 2 MPa and 92.8 ± 1.6 GPa, respectively, were achieved at 10 vol.% inoculant in the L-PBF process. Strengthening mechanism calculations and the tensile data suggest a higher strengthening contribution via modulus mismatch and Orowan strengthening from the particles created by reaction synthesis than from Hall–Petch strengthening through grain refinement. [ABSTRACT FROM AUTHOR]

Porous Ni–Ti alloys were fabricated by reactive synthesis of Ni and Ti elemental powders. The corrosion behavior of porous Ni–Ti alloys was explored by electrochemical methods and weight change measurements at 298 K in seawater. The polarization curves and electrochemical impedance spectroscopy data show that porous Ni–Ti (6.5:3.5) alloys provide the best corrosion resistance. The values of corrosion current density and corrosion rate are 1.6944 × 10−4 mA/cm2 and 1.9929 mm/a, respectively. The corrosion behavior and corrosion mechanism of porous Ni–Ti alloys are also discussed. [ABSTRACT FROM AUTHOR]

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Αbstract: Nowadays, energy saving is one of the most important issues to be solved worldwide. This effort is supported by the synthesis and use of thermoelectric materials. A variety of techniques have been used to prepare silicides, such as ball milling, solid state reaction, sputtering and reactive deposition epitaxy. In this work, Mg2Si silicide powders were synthesized by Pack Cementation, a environmental friendly, low cost and simple technique. A series of experiments were carried out at various temperatures from 500 °C to 650 °C for different deposition time and various magnesium concentrations, in order to select the optimum synthesis conditions of Mg2Si. The particle size and the lattice strain of Mg2Si was evaluated by X-ray diffraction analysis using Williamson-Hall equation, X-ray photoelectron spectroscopy illustrated the surface contaminations from the environment and Scanning Electron Microscopy revealed the morphology of the as-synthesized thermoelectric compound. Thermogravimetry measurements of Mg2Si powder demonstrated a significant thermal stability up to 400ο C, as a thin magnesium oxide layer formed on the surface acts as a barrier-which is much higher than the temperature region of maximum thermoelectric efficiency.

Niobium carbide composite coatings were prepared on titanium alloy surface by plasma spraying NbC–Al 2 O 3 , Nb–SiC and Nb–SiC–Al composite powders, respectively. The phase composition, microstructure and formation mechanism of the three composite coatings were analyzed and their microhardness, toughness and scratch resistance were compared. The phases of the NbC–Al 2 O 3 system did not change during the plasma spraying process, and new phases (Nb 2 C, NbC and Nb 3 Si) were formed in the Nb–SiC and Nb–SiC–Al systems. TEM results of the Nb–SiC composite coating indicate that the new phases nanocrystalline Nb 2 C, submicron NbC and nanocrystalline Nb 3 Si were formed during the plasma spraying process. Compared with the NbC–Al 2 O 3 composite coating, the microstructure of the Nb–SiC and the Nb–SiC–Al composite coatings were uniform, and the porosity were relatively low, and the hardness was higher. The Nb–SiC–Al composite coating was denser than the Nb–SiC composite coating, the lamellar structure was obvious and the number of pores in the coating was the least, which is attributed to the better molten state of the composite powder by the addition of the Al to the Nb–SiC system. The Nb–SiC–Al composite coating had better toughness and scratch resistance. [ABSTRACT FROM AUTHOR]

Surface micro−structure for joining with thermoplastic parts was additively manufactured on an aluminum alloy (A5052) substrate by laser scanning on Al−Ti−C powder mixtures. The micro−structure consisted of particle−shaped protrusions with a few hundred micrometers. The effect of C content in Al−Ti−C powder mixtures on the micro−structure and constituent phases was investigated. The fraction of particle−shaped protrusion reached maximum when the C/Ti molar ratio was 0.8. Adhesiveness between the particle−shaped protrusions and A5052 substrate decreased drastically when the C/Ti molar ratio increased from 0.6 to 0.8. Changes in these structural factors were related to the formation of TiC and Al3Ti phases after the laser−irradiations. The A5052 substrate was joined with Polyamide−6 sheets via the micro−structure by hot−pressing. When the C/Ti molar ratio was 0.6, the joint strength reached maximum since both the fraction of particle−shaped protrusions and adhesiveness between particle−shaped protrusions and A5052 substrate were high. The constitute phases (TiC and Al3Ti phases) in the micro−structures were assessed by Scheil simulation for Al−Ti−C system to calculate the component partitioning and solidification path during solidification. These results were used to discuss the relation between the surface micro−structure and powder compositions.

Nano-crystalline Ti2SC powders were synthesized by a molten salt method with TiS2/3Ti/2C powders as raw materials and KCl–NaCl as the molten salt medium under argon protection. The effect of heat treatment temperature on the composition and morphology of Ti2SC powder was studied. Ti2SC powder can be synthesized at a relatively low temperature by the molten salt method. A high content of Ti2SC powder can be obtained at 1150 °C for 1.5 h. The particle size of the powder was 22.6 nm. Scanning electron microscopy and transmission electron microscopy showed that nano-sized Ti2SC had an average particle size of 20–30 nm. [ABSTRACT FROM AUTHOR]

In this paper, an Fe-Al based composite reinforced with ultra-fine Al2O3 oxides was obtained through sintering of aluminium, iron and mullite ceramic powders using self-propagated high temperature synthesis (SHS). The powder mixture with a 50%wt. content of the ceramic reinforcement was cold pressed and subsequently subjected to the sintering process in vacuum at 1200°C for 25 minutes under external loading of 25 kN. The complex microstructure of the Fe-Al matrix reinforced with ultra-fine Al2O3 oxides was found to be desired in high temperature applications since only 3% of the relative weight gain was observed after 100 hours of annealing at 900°C. [ABSTRACT FROM AUTHOR]

MoO 3 –Al composite powders were used for preparing in situ composite coatings. Effects of the composition of MoO 3 –Al composite powder on the microstructure and properties of the as-prepared coatings were investigated. The results show that the main phases of the as-prepared coatings were γ-Al 2 O 3 and Mo. An optimal composition (63 wt%) of MoO 3 in MoO 3 –Al composite powder was demonstrated. The porosity of the as-prepared composite coatings decreased first and then increased with the increase of MoO 3. This is attributed to the fact that the melting state of the powder during plasma spraying is closely involved in the content of MoO 3. The coating prepared by composite powder with 63 wt% MoO 3 had the most Al 2 O 3 and the highest microhardness. The wear resistance of 63 wt% MoO 3 composite coating was the best among four coatings with different content of MoO 3 , which is attributed to its high hardness and good toughness. [ABSTRACT FROM AUTHOR]

This paper reports a study into the formation of the phase composition, structure, and properties of arc welding coatings by the flux-cored electrode materials from the Fe-Mo-B-C system. The welding alloys were applied using the flux-cored arc welding (FCAW) electrodes, which consisted of a shell made from the low-carbon steel filled with a reaction powder mixture that contained boron carbide and molybdenum in a ratio of 1:1. The calculation of the phase composition of alloys that correspond to the surfaced layers by a CALPHAD method using the Thermo-Calc OpenCalphad software shows that under the equilibrium conditions the boride phases of molybdenum and ferrite cannot co-exist. The main phase of such alloys is a FeMo2B2 compound, which forms the eutectics with austenite. Given that the eutectic structures with borides are characterized by high brittleness, the introduction of components was conducted in the form of a reaction mixture in order to obtain the in situ formed boride phases in the form of separate structural components. Analysis of the results of studying the microstructure and phase composition of coatings reveals that they consist of three main structural components: the eutectic (FeMo2B2+ferrite) and the grains of molybdenum tetraboride MoB4. Thus, under the conditions of arc welding using the reaction mixture, an irregular structure is formed, which is favorable in terms of ensuring wear resistance due to the high microhardness of MoB427 GPa. The hardness of the coatings obtained is at the level of 63-65 HRC, and the wear resistance is higher compared to standard high-chromium alloys (grades T620 and T590) by 2-2.5 times. This makes it possible to recommend the coating of a given system for hardfacing the working surfaces of equipment in the coal, processing, woodworking industries, etc., where abrasive wear is the dominant type of surface wear [ABSTRACT FROM AUTHOR]

(VNbTaMoW)C high entropy carbide was fabricated by reaction synthesis using the constituent metal and graphite powders as raw materials. Phase formation and composition uniformity are analyzed using XRD, EDS and SEM. The phase composition for samples sintered at 1600℃ includes TaC, NbC, WC, MoC and VC according to XRD peak fitting and deconvolution. Samples sintered at 1850℃ form a single phase high entropy carbides, which exhibit high microhardness and relatively lower thermal conductivity of 9.2 W/m.K-1 at room temperature compared with binary carbides. Severe lattice distortion and high concentration of point defects are responsible for the low thermal conductivity of the high entropy (VNbTaMoW)C. [ABSTRACT FROM AUTHOR]

The physicochemical interactions between components in the Al/SiO2 aluminum matrix compositions under various temperature conditions of processing are studied. The synthesis of aluminum oxide ceramics in aluminum melts for the production of particulate reinforced Al-Si/Al2O3 alloys was performed. The addition of dispersed particles of silicon oxide ceramics was carried out by mixing into aluminum melt in a liquid-solid state. At the temperature-time processing of the Al/SiO2 compositions, alumina ceramic with a contact surface layer providing spontaneous wetting with liquid aluminum is realized.

The pore formation process has been studied for a high-temperature porous Mo–Si–B alloy produced by in situ reaction synthesis from elemental starting powders. The expansions, phase transformations, microstructure and pore parameters were investigated systematically as a function of the sintering temperature. For sintering temperatures of 1200°C and above, a multiphase mixture of the oxidation-resistant intermetallic compounds Mo3Si, Mo5Si3 and Mo5SiB2 was obtained. It was found that the porous alloys exhibit uniform skeletons with fine grains, high porosities and centred pore size distributions. Characterisation data obtained from samples sintered at temperatures from 1200 to 1600°C are used to deduce the processes which occur at each stage in the reaction synthesis. This helps to explain the formation mechanism for the pores and skeletons in this novel material. [ABSTRACT FROM AUTHOR]

Abstract The present study was attempted to highlight a novel direct reaction synthesis in which traditional casting plus rapid solidification techniques were implemented to produce Al-7079-TiC in situ composites with homogenous microstructure and improved dispersion strengthening by the reinforcing phases. Casted samples were effectively characterized by scanning electron microscopy followed by energy dispersive spectroscopy and X-ray diffraction. Ingot metallurgy showed a homogenous distribution of TiC particles inside the grain. This particle behavior acted as an excellent nucleation sites for the Al dendrites to grow unvaryingly. TiC reinforcements have semi coherent relationship with α-Al matrix. It was observed that eutectic boundary includes the second phases based on η (MgZn 2) and Mg(Zn, Cu, Al) 2. Almost 90% of the in situ reinforced TiC were homogenously distributed along the center of the grain. Thermal history conditions have shown an exothermic behavior during casting. Experimental results revealed the evolution of TiC particles in super-heated melt region, i.e. dissolution of titanium continued by reaction of titanium with diffused carbon in the Al matrix to form TiC particles. Further they acted as nucleation sites for the α-Al dendrites to grow homogenously. This study presents optimum process temperature for the Al-TiC in situ synthesis. [ABSTRACT FROM AUTHOR]

Abstract Porous Ni 3 Al intermetallic is successfully fabricated through elemental powder metallurgy of Ni-25 at% Al samples. The influences of sintering parameters, such as heating rate, isothermal treatment on the sintering behaviors of the samples are investigated. When the samples are heated continuously from room temperature to 1000 °C at a relatively high rate (>5 °C/min), the reaction between Ni and Al happens in an intense way. The heat suddenly released by the reaction produces liquid phase in the material, which facilitates the reaction significantly. Therefore, a sudden expansion (∼6%) occurs, resulting in severe deformation of the samples. The shape retention ability of the sample can be improved by isothermally treating the sample at a proper temperature (470–490 °C) for prolonged time or heating it up at a low heating rate. Under these sintering conditions, the reaction between Ni and Al happens in a much more controllable solid-state way. Therefore, the abrupt expansion can be decreased to ∼0.5%. During the solid-state reaction, imbalanced diffusion between Al and Ni results in more Al diffusing into Ni than the other way around, therefore creating pores on the Al side. As a result, homogeneous porous Ni 3 Al intermetallic samples can be fabricated and the regular shape of the sample can be well preserved. Highlights • The first systematic investigation of the kinetics of porous intermetallics fabricated by the Kirkendall effect. • Revealing the effects of heating rate and isothermal treatment on the sintering behavior of Ni-25 at% Al samples. • Revealing the relationship of shape retention ability of sintered Ni-25 at% Al samples and sintering parameters. [ABSTRACT FROM AUTHOR]

Abstract Data from the literature indicate a significant influence of powder refinement on the kinetics and the structure of an obtained material. Decreasing the size of aluminum particles has little or no effect, whereas decreasing the size of iron particles has a significant influence. In this work, detailed results from this research on the influence of removing large particles of iron on the structure and properties of Fe40Al sinters are presented. X-ray diffraction analysis has shown that the intensity of the iron peaks has dropped significantly. Similarly, in the hardness analysis, a twofold decrease in standard deviation was observed. This decrease in the standard deviation is related not only to a decrease in the fraction of areas rich in iron but also to a decrease in aluminum-rich phases (micro-hardness tests). Highlights • Six fractions of the following sizes were obtained <125 < 120 <112 < 106 <90 < 80 μm. • The increase in homogeneity is a result of reducing Fe areas and Al-rich phases. • During the FeAl reaction sintering, particles larger than 106 μm should be removed. [ABSTRACT FROM AUTHOR]

Titanium aluminide is synthesized in a chemical reaction of elemental powders. The synthesis is conducted at a high temperature in vacuum for two variants of pressure variation. To obtain a quality product at a minimum loss of the material to spillage, it is important to apply pressure at the right moment. The reaction synthesis is also accompanied by "swelling" of the billet. The temperature-pressure cycle is optimized. The results of the x-ray diffractometry show the presence of an aluminum-rich phase in the form of a shell surrounding the particles of pure titanium. [ABSTRACT FROM AUTHOR]

Since the last century, a variety of reactive synthesis methods has been extensively studied and developed to derive ceramic composite materials, which show superior mechanical and physical properties for numerous applications. Melt casting/infiltration is one of the preferred techniques to fabricate ceramic‐metal composites. In this article, different reactive processing routes and the properties of the synthesized ceramic‐metal composites are reviewed. The reaction forming techniques regarding raw material properties and processing parameters are discussed. [ABSTRACT FROM AUTHOR]

The Cu(Sn)-TiCx bonded diamond composites were prepared by in situ reaction sintering of Cu, Ti2SnC and diamond powders. Effect of Ti2SnC content on the phase composition, microstructure and grinding properties were studied. The result shows that Ti2SnC was decomposed to TiCx and Sn. And then, Sn atom dissolved into the crystal lattice of Cu and formed Cu(Sn) solution. The rich C formed at the interface between diamond and the matrix. Excess Ti2SnC inhibited the formation of Cu solid solution and reacted with Cu to form Cu3Sn. Additionally, its matrix was mainly composed of TiCx with better wear resistance, which may improve obviously the grinding performance of the composites. The grinding ratio value of copper-diamond composite was only 132. The grinding ratio value of the composite contained higher Ti2SnC content in the raw materials was 636. [ABSTRACT FROM AUTHOR]

High porosity of porous TiAl 3 intermetallics were prepared from Ti-75Al at.% elemental powders by NaCl as temporary space holder, combining with multilayer stacking technology and thermal explosion reaction. Results showed that space holder particles in green compact were completely removed before sintering and only single TiAl 3 phases were synthesized in sintered product. The porosity (>70%) can be easily obtained when adding 0, 30 or 50 vol.% NaCl in designed layers. SEM image indicated that the distribution of small pores (<80 μm) was uniform and embedded in pore walls of the skeleton without NaCl space holder. Large pores (300–500 μm) began to appear when added the NaCl particles and the number of large pores improved with the increase of space holder content. The sintered discs with three or five sintered layers exhibited a symmetrical graded pore size distribution: large pores replicating from space holder and small pores generated during the sintering process. The graded pore-structure can be designed by adjusting the compact structure in each layer, allowing for a widespread applications in specific filtration units and liquid-gas separation. [ABSTRACT FROM AUTHOR]

The TiAlN MAX-phase is synthesized by reaction sintering from Ti-AlN powder mixtures. The optimal synthesis mode of the compound containing less than 1% of the TiN impurity phase is established. It includes isothermal annealing at 1300°C for 2 h in argon at a pressure of 3 atm. The influence of the preliminary mechanical activation of the powder mixture and the reaction synthesis medium on the yield of the TiAlN phase are investigated. It is shown that the activation leads to an increase in the content of the secondary TiN phase. It is revealed that the vacuum synthesis also does not make it possible to form the singlephase TiAlN material. [ABSTRACT FROM AUTHOR]

Triphenylamine is a propeller-like structural chromophore with a nitrogen atom center. The compound has a large steric hindrance and hyper conjugation electronic effect, which can enhance the stability of the nitrogen atomic radical. Triphenylamine materials also have a high hole mobility due to their unique free radicals nature. In this review, we started with the methods of the synthesis including traditional Ullmann, Suzuki Coupling, Heck, Wittig, Stille, and Sonogashira Reaction synthesis, and also the basic experimental and theoretical methods for the characterization of triphenylamine materials. Then, we discussed the properties of triphenylamine, including the optoelectronics, electroluminescence, and electrochromism. Finally, we reviewed the recent progress in the main applications of triphenylamine materials in the field of organic optoelectronic solar cells, electroluminescence materials, and electrochromic materials. In conclusion, this review of triphenylamine materials is a valuable resource for both theorists and experimentalists who are focus on these exciting compound materials. [ABSTRACT FROM AUTHOR]

The influence of Ti powder purity on phase evolution during the reactive sintering of elemental Ni and Ti powders to form NiTi was studied using differential scanning calorimetry (DSC) and in-situ neutron diffraction. Reaction between the Ni and Ti is not significant until 600 °C. From 600 to 700 °C, Ti 2 Ni forms in mixtures made from high (HP) and low purity (LP) Ti powder. The Ni 3 Ti phase also grows in this temperature range in the LP mixture. The most significant phase evolution takes place between 700 and 920 °C. The α to β phase transformation in (Ti) begins at the eutectoid temperature (765 °C) and ends at 820 °C. The highest growth rates for all three intermetallic phases, including NiTi, and the decay rate of the elemental Ni occur in this temperature range. At approximately 1000 °C, all reactants are consumed and homogenization occurs, with NiTi continuing to grow at the expense of the other intermetallic phases. The Ti rich intermetallic phase persists above its melting point, due to the formation of a solid-solution with oxygen (i.e. Ti 2 Ni(O)). From 1100 to 1200 °C, the microstructure becomes a stable mixture of NiTi with a small fraction of Ti 2 Ni(O). The phase evolution is similar in the LP and HP mixtures. However, the rate of reaction is higher in the LP mixture due to the influence of impurities (O, Fe and Ni) on the diffusivities in the many phases involved. [ABSTRACT FROM AUTHOR]

Fabrication of the Mo 5 Si 3 –Al 2 O 3 composite with a broad composition range was studied by thermite-based combustion synthesis. The addition of two thermite mixtures composed of 0.6MoO 3 + 0.6SiO 2 + 2Al and MoO 3 + 2Al into the Mo–Si reaction system was thermally beneficial for the self-sustaining combustion process. The former thermite reagent is less exothermic than the latter. Moreover, experimental results showed that the combustion temperature and flame-front velocity decreased with increasing molar ratio of Mo 5 Si 3 to Al 2 O 3 formed in the composite. As a consequence, the MoO 3 /SiO 2 /Al-based reaction scheme was adopted to synthesize composites with Mo 5 Si 3 /Al 2 O 3 from 0.4 to 0.7, and MoO 3 /Al-based system was for the products with Mo 5 Si 3 /Al 2 O 3 from 0.8 to 1.6. The XRD pattern indicated Mo 5 Si 3 as the dominant silicide. Mo 3 Si was formed as the minor phase, because a small amount of Si dissolved in Al 2 O 3 . This was confirmed by the presence of both Al 2 O 3 and aluminum silicate, a solid solution of Al 2 O 3 and SiO 2 , in the final products. [ABSTRACT FROM AUTHOR]

• Developed an integrated process synthesis framework for process design. • The framework solves the process synthesis problem by integrating reaction synthesis and advanced separation techniques. • Three case studies are solved, including both new and retrofitting designs. • The framework can identify the most promising reaction pathway with its separation flowsheet for a given target product. • Process retrofitting with innovative separation techniques can highly improve process sustainability. With the increasing concern of the competitive market and carbon emissions, a sustainable, efficient process design becomes more and more important. The task of sustainable process design is to find efficient configurations and operating parameters to produce products or utilize materials. Currently, the scientific community's major focus is on separation synthesis, which aims to identify the best downstream separation configurations through different methods such as optimization, heuristic, and hybrid methods. Besides, innovative separation techniques with lower capital/operating costs and carbon emissions were proposed and identified to further improve the downstream process performance. However, most of the separations synthesis methods were based on conventional unit operations and usually applied for generating sustainable processes with a given reaction pathway without considering the possibilities of different raw materials. Generally, to produce a given target product, multiple reaction pathways are available, and each reaction pathway leads to different downstream processes. Also, applying intensification in the early stages of process design, e.g., separation synthesis, can generate sustainable process flowsheets with higher energy efficiency and lower environmental impact. This work aims to develop an integrated process synthesis framework, which includes reaction synthesis for the reaction pathways selection and separation synthesis involving intensified/hybrid units. So, for the new process design, given the product one needs to produce, this framework could identify the optimal reaction pathway with its best separation route. The developed framework was used to solve three case studies, including the new process design of dimethyl carbonate (DMC) production and retrofitting design of cumene and styrene production. For all the case studies, the framework was able to generate multiple innovative solutions that are sustainable and energy-efficient. [ABSTRACT FROM AUTHOR]

Despite the extensive use of Al-Cr mixtures to aluminize metal substrates, little is known on the reactivity between Al and Cr to control the aluminizing activity. In this work, Al and Cr reactivity was investigated by DSC from Al and Cr microparticles. The exothermic and endothermic reactions which occur upon heating mixtures of Al and Cr powders were identified. A highly exothermic reaction was observed for different Al-Cr compositions at a temperature of 637 ± 2 °C and was associated with the formation of Al x Cr y intermetallic compounds. The intensity of this reaction (heat flow) was found to be dependent on the initial Al-Cr ratio. Three Al-Cr compositions were selected from DSC tests and literature for slurry aluminizing. These compositions were deposited by slurry on pure Ni substrate to investigate the role of Cr on aluminizing by comparison with a conventional simple Al slurry coating. The addition of Cr was found to decrease the Al activity on the surface by forming Al x Cr y intermetallic compounds that limited the SHS reactions usually observed between Ni and Al during high-activity slurry processes. The synthesized Al x Cr y intermetallic phases then behaved as masteralloys, for a single step aluminizing process at high temperature to promote the outward diffusion of Ni. [ABSTRACT FROM AUTHOR]

The effect of Cd doping on the thermoelectric properties of synthetic tetrahedrites Cu 12−x Cd x Sb 4 S 13 (x = 0, 0.25, 0.5, 0.75, 1, 1.25 and 1.5) was studied. Powder X-Ray Diffraction and electron probe micro analysis confirm the presence of tetrahedrite as main phase with a trace of impurity phases. The influence of Cd substitution on Cu was confirmed by a systematic increase of electrical resistivity and Seebeck coefficient with doping content. Power factor decreased with doping content mainly affected by the significant increase in electrical resistivity. The total thermal conductivity was found to be reduced from 1.32 W/m-K for the sample with x = 0 to 0.71 W/m-K for the sample x = 0.75 at 623 K but showed an abrupt increment for x = 1 and decreased for the subsequent samples with x = 1.25 and x = 1.5. A combined result of power factor and thermal conductivity leads to thermoelectric figure of merit, zT = 0.9 at 623 K for Cu 11.25 Cd 0.75 Sb 4 S 13 . [ABSTRACT FROM AUTHOR]

A series of (SnPb)MnTe alloys with x = 0, 0.03, 0.06, 0.09, 0.12 and 0.15 were prepared by melting, quenching and spark plasma sintering (SPS) techniques to investigate their phases and thermoelectric properties. Mn was used as doped element in SnPbTe solid solution to reduce the carrier concentration, enhance the Seebeck coefficient and reduce the thermal conductivity of the material. Experimental results show that the SnTe-based solid solution single phase was formed in the alloys with x = 0 and 0.03. The minor irregular-shaped MnTe phase presents in the alloys with x ≥ 0.06, while the minor needle-like MnTe phase appears in the alloys with x ≥ 0.12, together with the SnTe-based solid solution matrix. The lattice parameter a of SnTe-based solid solution decreases nearly linearly as Mn content x increases up to 0.12, but keeps constant as x further increases. All the samples show p-type conduction. Mn doping in SnPbTe decreases its carrier concentration and thus increases its Seebeck coefficient. The solute Mn and Pb atoms in the SnTe-based solid solution, and the minor phases MnTe and MnTe, enhance the phonon scattering and thus reduce the thermal conductivity. As a result, the figure-of-merit ZT of the (SnPb)MnTe composites can be enhanced with proper Mn substitution. The maximum ZT of 0.65 was obtained in the sample (SnPb)MnTe at 723 K, which is higher than the 0.29 of its parent alloy SnPbTe. [ABSTRACT FROM AUTHOR]

Alumina dispersion strengthened copper (ADSC) composite was prepared by reaction synthesis (RS) process. Results show that nano-sized γ -Al 2 O 3 particles with about 10 nm in size are homogeneously distributed in copper matrix. A coherent interface relationship with (002) Cu // (133) γ -Al 2 O 3 , and [110] Cu //[011] γ -Al 2 O 3 characterizes along the explored interfaces of the composites. All of the interfaces are clear and closely combined with each other. The composites have high properties, the tensile strength can reach 570 MPa and the yield strength can reach 533 MPa at room temperature. Meanwhile, the softening temperature is higher than 1173 K. The electrical conductivity of the sample is 85% IACS and the Rockwell hardness can reach 86 HRB. [ABSTRACT FROM AUTHOR]

Reactive spark plasma sintering (RSPS) is an effective method for the consolidation of refractory compounds, including intermetallics. RSPS involves the SPS consolidation process and chemical reactions. SPS parameters such as the heating rate, maximum temperature, and dwell time influence the kinetics of the chemical reaction. To control the sintering process, it is critical to understand the relationship between the SPS parameters and different reaction modes. For a highly reactive Ni–Al system, we directly compare the consolidation kinetics under various SPS conditions. Comparing the RSPS and SPS schemes, we unequivocally conclude that the reactive mode permits an overall higher densification for the considered system. Two RSPS strategies are identified: i) RSPS under self-sustained reaction conditions occurring under a high heating rate and large volume-to-surface ratio, and ii) RSPS under relatively slow reaction rate conditions. The question of which strategy is best is addressed based on an analysis of the microstructures and mechanical properties of the fabricated materials. • Direct comparison of SPS, RSPS and RFSPS consolidate mode for intermetallic system. • Unequivocally showed that the reactive modes permit a higher densification. • The optimum consolidation strategies are suggested. • Material with exceptionally high mechanical properties fabricated in a minute. [ABSTRACT FROM AUTHOR]

Intermetallic compounds based on tantalum aluminides are of considerable interest in various industrial applications. In this work, the formation of tantalum aluminides has been studied in elemental powder mixtures containing 25, 50 and 66.7 at% Ta. A differential scanning calorimeter (DSC) was used to heat the samples up to 1500 K at 15 K min −1 . Phase evolution was studied by heating a few samples to temperatures below and above the observed DSC peaks. The heat treated samples were analyzed using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The results suggest an exothermic reaction between tantalum particles and molten aluminum, which leads to the formation of Al 3 Ta compound as the initial product. This reaction reached completion for the aluminum-rich samples and the corresponding DSC peak was very broad, containing two distinct steps which indicated the effect of a diffusion barrier during the reaction. In these samples, the Al 3 Ta product was stable upon further heating. A different behavior was observed for the equiatomic and tantalum-rich samples, an incomplete reaction with a considerable amount of unreacted tantalum. These samples were associated with a narrower reaction peak in the DSC plots, followed by a mildly exothermic peak at higher temperatures. The latter was found to correspond to the formation of Al 69 Ta 39 phase in the solid state, together with minor amounts of σ (Ta-rich) and φ (near equiatomic) phases. The Al 69 Ta 39 phase showed a tendency to disappear on prolonged heating. The σ and φ phases were observed to dominate as the major phases in tantalum-rich and equiatomic samples, respectively. Increasing the heating rate shifted the reaction peak for Al 3 Ta formation to higher temperatures and the apparent activation energies were estimated as 383 ± 13 kJ mol −1 and 439 ± 22 kJ mol −1 for the initial and final stages of this reaction. The heat of formation of Al 3 Ta was also estimated as −36 ± 7 kJ mol −1 in the interval 1050–1350 K. Studies on the effect of particle sizes of the reactants showed that, in most cases, the reaction peak shifted to lower temperatures on decreasing the tantalum particle size. A similar behavior was observed for aluminum in the tantalum-rich samples, while an inverse effect was seen in equiatomic and aluminum-rich samples. [ABSTRACT FROM AUTHOR]

High porosity TiAl-based intermetallics were prepared through thermal explosion (TE) from Ti–50Al at.% powders with NaCl as soluble template. The results showed that the space holder particles of NaCl were removed completely in green compacts, and porous Ti–Al materials were synthesized via a low-energy consumption method of TE at a temperature of 600 °C. TiAl was evolved as dominant phase in sintered materials at 1100 °C. With adding 80 vol.% NaCl to Ti–50Al at.% powders, the open porosity was significantly elevated up to 84%. Moreover, the porous materials exhibited a bimodal pore size distribution: large pores (200–500 μm) replicating NaCl particles and small pores (<50 μm) embedded in pore walls. The interconnected small and large pores make open cellular porous TiAl materials, which prescribe them promising for a wide range of applications in separation, heat insulation and catalysis. [ABSTRACT FROM AUTHOR]

Porous TiB 2 –TiC were prepared by SHS using Ti and B 4 C powder mixtures. The pores, phase constituents, microstructures and composition distribution of TiB 2 –TiC were analyzed. The influences of B 4 C particle size and pressure in green compacts on pore sizes and structures of final products were also discussed. Via combustion front quenching, the reaction process between Ti and B 4 C particles was achieved. The results showed that the pore size decreased and combination between TiB 2 and TiC became closer with the decrease of B 4 C particle size and increase of pressure. During the reaction, B 4 C particles decomposed layer by layer, and reacted with the melted Ti to form poor boron phases of TiB and Ti 3 B 4 with needle-like shapes, which existed in quenched samples. With further reacting, TiB and Ti 3 B 4 phases gradually changed to TiB 2 with rectangle and hexagonal-plate shapes. The regular TiB 2 particles were bound together by TiC, which constructed the skeleton of pores. [ABSTRACT FROM AUTHOR]

Metal-based reactive composites are high energy-density materials that have potential uses as multifunctional energetics. However, when composed of micron size particles they can be difficult to ignite and have slow reaction rates. Recent work has shown that mechanically activated (MA) materials can have increased ignition sensitivity and reaction rate, yet the role of microstructure refinement (i.e., mechanical activation duration) in controlling combustion behavior is not well understood. In this work, the combustion velocities and flame temperatures were measured for equiatomic MA Ni/Al reactive powders produced using different milling durations in a two-step dry/wet milling process. For MA Ni/Al pellets pressed to 70% of the theoretical maximum density, it was shown that the combustion velocities increase as the milling time increases from ∼9.4 cm/s at 25% of the critical reaction milling time (t cr ) to ∼20 cm/s at a milling time of 97% t cr . For the cases considered, the average maximum flame temperatures were measured to be ∼1873 ± 30 K for samples milled for 25% t cr to 1786 ± 30 K at 97% t cr . It was also found that hydrocarbon contaminants are milled into the MA Ni/Al composite particles during the wet milling step and result in expansion of the pellets during combustion. Differential scanning calorimetry coupled with Fourier transform infrared spectroscopy showed that the release of hydrocarbon contaminants occurs at a temperature of ∼630 K. It was also shown that the concentration of hydrocarbon contamination decreased as the dry milling times increased, which suggests particle structure and mechanical property evolution during initial dry milling also affects contamination during subsequent wet milling. [ABSTRACT FROM AUTHOR]

A compact process for fabricating micro-fine spherical TiAl–Nb alloy powders was developed with a combination of reaction synthesis and plasma spheroidization technique. Powders of TiH 2 , Al and Nb were firstly mixed and refined by high-energy ball milling, and the mixture was then heated at different temperatures ranging from 600 to 1200 °C for 2 h, allowing synthesis reaction to take place. Ultimately, the synthesized powders melt through radio frequency (RF) argon plasma and rapidly solidified into micro-fine spherical TiAl–Nb alloy powders. The fabrication process and powder characteristics were investigated. With the process described above, the alloy powders with high composition homogeneity and good sphericity can be fabricated. The obtained spherical powders perform a uniform equiaxed-grain microstructure dominated by a supersaturated α 2 -Ti 3 Al phase. The powders possess a micro-fine average particle size of 9.6 μm, with a distribution uniformity level of 0.622. [ABSTRACT FROM AUTHOR]

This paper presents the results of studies on the influence of oxygen partial pressure (vacuum level in the chamber) on the properties of FeAl intermetallics. One of the problems in the application of classical methods of prepared Fe-Al intermetallic is the occurrence of oxides. Applying a vacuum during sintering should reduce this effect. In order to analyze the effect of oxygen partial pressure on sample properties, five samples were processed (by a pressure-assisted induction sinteringPAIS method) under the following pressures: 3, 8, 30, 80, and 300 mbar (corresponding to oxygen partial pressures of 0.63, 1.68, 6.3, 16.8, and 63 mbar, respectively). The chemical and phase composition, hardness, density, and microstructure observations indicate that applying a vacuum significantly impacts intermetallic samples. The compact sintered at pressure 3 mbar is characterized by the most homogeneous microstructure, the highest density, high hardness, and nearly homogeneous chemical composition. [ABSTRACT FROM AUTHOR]

The crystal structure of a novel CePd 12 Ge 2 intermetallic was determined and refined from single-crystal X-ray diffraction data. The compound crystallizes in a tetragonal structure of a new type: space group I 4 1 md (No. 109), cell parameters a = b = 12.0819(9) Å, c = 6.4554(7) Å, V = 942.3(2) Å3, Z = 4. In a crystallographic unit cell, Ce atoms occupy one Wyckoff site (4 a). Two (16 c) sites and two (8 b) sites are filled with Pd atoms. One more position (8 b) is occupied by Ge atoms. An analysis of the features of the crystal structure revealed its relationship with the known binary type BaCd 11. Magnetic and transport properties of CePd 12 Ge 2 were studied. The results obtained show no signs of long-range magnetic ordering down to 1.7 K. However some hints on magnetic ordering below T ≈ 1.7 K may be proposed from magnetoresistance data. We also register low temperature logarithmic rise of resistivity indicating the main role of Kondo interactions in CePd 12 Ge 2. • New ternary germanide CePd12Ge2 found. • CePd 12 Ge 2 crystallizes in a tetragonal structure of a new type. • CePd 12 Ge 2 is a pronounced Kondo system. [ABSTRACT FROM AUTHOR]