Solid-state Displacement Reaction Research Articles

Multicomponent solid solution with pyrochlore structure

Multicomponent oxide with pyrochlore structure (A2B2O7), containing 7 different A-site cations and 3 B-site cations in equiatomic amounts, was synthesized. Powders with nominal composition (La1/7Sm1/7Nd1/7Pr1/7Y1/7Gd1/7Yb1/7)2(Sn1/3Hf1/3Zr1/3)2O7 were fabricated through a reaction of metal nitrates (A-site) and metal chlorides (B-site) with sodium hydroxide during the solid state displacement reaction. Room temperature synthesis initially resulted in the obtainment of amorphous powders, which crystallized after subsequent calcination to form single crystalline compounds. Crystalline high-entropy ceramic powders formation took place at temperatures as low as 750°C. During calcination, defective fluorite (F-A2B2O7) and crystal pyrochlore (Py-A2B2O7) structures coexist. A large number of cations induce the obtainment of stable high-entropy pyrochlores. Results showed that sintering at 1650°C lead to pure crystalline single-phase pyrochlore formation. High-density ceramic, free of additives, was obtained after powders were compacted and subjected to pressureless sintering at 1650°C. Multicomponent pyrochlore structure was investigated using the theoretical and experimental multi-methodological approach.

Heavily doped high-entropy A2B2O7 pyrochlore

A novel class of high-entropy pyrochlore compounds with multiple elements at the A and B site positions (A2B2O7) was successfully obtained. Powders with (La1/7Sm1/7Nd1/7Pr1/7Y1/7Gd1/7Yb1/7)2(Sn1/3Hf1/3Zr1/3)2O7 nominal composition were fabricated from pure metal oxides obtained through a reaction of metal nitrates (for site A) and metal chlorides (for site B) with sodium hydroxide during the solid-state displacement reaction (SSDR). The phase evolution was analyzed using XRD method. During the thermal treatment of ten individual metal oxides, the single pyrochlore phase was created. The present study showed that the highdensity (98%TD) ceramics with a hardness of 8.1GPa was successfully obtained after pressureless sintering at 1650 ?C for 4 h. Results of the Raman study and the Rietveld structural refinement showed that sintered highentropy ceramics is characterized by a single-phase pyrochlore structure, which was investigated in detail.

PH dependent catalytic redox properties of Mn3O4 nanoparticles

Manganese-based materials have unique redox properties, attractive to many applications in the energy, environment and biomedical sectors. In particular, Mn3O4 is known to act as both an oxidising and a reducing agent. However, pH-dependence of the redox properties of Mn3O4 nanoparticles is not yet well understood. In this study, Mn3O4 nanoparticles were mechanochemically synthesised and their redox catalytic activities were studied under different pH conditions. Mn3O4 nanoparticles with sizes between 10 and 90 nm were prepared via a mechanically-induced solid-state displacement reaction between MnCl2 and K2CO3 and subsequent heat treatment. The effect of pH on the oxidative decomposition of a model organic dye revealed that Mn3O4 nanoparticles showed oxidative catalytic activity only when pH was below 5. At a higher pH, Mn3O4 nanoparticles showed strong free-radical scavenging activities, suitable for reducing oxidative stress in many locations of the body and for creating new design of energy-storage materials.

Microstructure and properties of carbon nanotubes-reinforced magnesium matrix composites fabricated via novel in situ synthesis process

A novel carbon nanotubes (CNTs)-reinforced magnesium (Mg) matrix composite was successfully fabricated via an in situ synthesis of Mg on the surfaces of CNTs and a powder metallurgy (PM) process. The nanoscale Mg grains were first synthesized in situ on CNTs via the solid-state displacement reaction of lithium (Li) to Mg in anhydrous magnesium chloride (MgCl2) to obtain Mg-encapsulated CNTs (CNTs@Mg) composite powders. These were used to fabricate CNTs@Mg bulk composites via the PM method. In the CNTs@Mg in situ composite structure, the synthesized Mg grains were in contact with CNTs in a stacking manner, and nanoscale contact and diffusion bonding occurred at the CNTs–Mg interface, realizing not only strong interface bonding between CNTs and Mg but also the dispersion of CNTs in the Mg matrix. The CNTs@Mg composites exhibited improved mechanical properties. The microhardness, ultimate tensile strength (UTS), and breaking elongation of 4.0 wt% CNTs@Mg bulk composite were increased by approximately 43.5%, 33.4%, and 31.3% compared with pure Mg bulk, respectively. Furthermore, the mechanical properties of the CNTs@Mg bulk composites were superior to those of CNT/Mg composites fabricated via the traditional addition process. Therefore, the investigated CNTs@Mg composites are promising candidates for the field of lightweight structural materials.

Synthesis, characterization and sintering of Gd2Hf2O7 powders synthesized by solid state displacement reaction at low temperature

Pyrochlore compound (Gd2Hf2O7) powder was prepared by reacting gadolinium nitrate and hafnium chloride with NaOH during solid state displacement reaction at low temperature (SSDR). The SSDR process at room temperature initially yielded amorphous powders, which crystallized after subsequent calcination to form crystalline ceramics. The formation of crystalline Gd2Hf2O7 took place at temperature as low as 600 °C. The phase evolution with thermal treatment as well as powder properties such as crystallite size, lattice strain and lattice parameter were studied by X-ray powder diffraction (XRPD) at room temperature. High-density ceramic pellets free of any additives were obtained after compaction of the obtained powders and subsequent sintering at 1600 °C for 4 h in air. Rietveld analysis of X-ray diffraction (XRD) pattern of sintered sample showed that the unit cell parameter of the obtained Gd2Hf2O7 is 10.5501 (2) Å with x value = 0.345(2) in Wyckoff positions, indicating small distortion of octahedra. Hardness of the sintered samples was found to be 7.1 GPa. The thermal conductivity measurements performed in temperature range from room temperature to 1000 °C showed that thermal diffusivity of sintered samples was between 0.5 and 1 mm2/s whereas thermal conductivity was between 4 and 7 W/(m K).

Modeling thermal and irradiation-induced swelling effects on the integrity of Ti3SiC2/SiC joints

Previously, results for CVD-SiC joined by a solid state displacement reaction to form a dual-phase SiC/MAX phase joint subsequently irradiated at 800 °C to 5 dpa indicated some cracking in the joint. This paper elucidates the cracking origin by developing a model that accounts for differential thermal expansion and irradiation-induced swelling between the substrate and joint materials by using a continuum damage mechanics approach with support from micromechanical modeling. Damage accumulation in joined specimens irradiated at four temperatures (300 °C, 400 °C, 500 °C and 800 °C) is analyzed. We assume the experimental irradiation dose is sufficient to cause saturation swelling in SiC. The analyses indicate that the SiC/MAX joint survives irradiation-induced swelling at all the irradiation temperatures considered. The joint experiences only minor damage when heated to and irradiated at 800 °C as well as cooling to room temperature. The prediction agrees with the experimental findings available for this case. However, the joint heated to 300 °C suffers severe damage during irradiation-induced swelling at this temperature, and additional damage after cooling to room temperature. Irradiation at 400 °C and subsequent cooling to room temperature produced similar damage to the irradiation 300 °C case, but to a lesser extent. The joint heated to 500 °C and irradiated at this temperature suffered only very minor damage, but further moderate damage occurred after cooling to room temperature.

Synthesis of calcium chlorapatite nanoparticles and nanorods via a mechanically-induced solid-state displacement reaction and subsequent heat treatment

Abstract A mechanically activated solid-state displacement reaction has been investigated as a means of manufacturing apatite nanoparticles. Mechanical milling and subsequent heat treatment of a CaCl 2 , Na 3 PO 4 and NaCl reactant mixture resulted in the formation of chlorapatite nanoparticles embedded within a solid salt matrix. The size and morphology of the chlorapatite nanoparticles was found to depend on the temperature of the post-milling heat treatment. A low temperature of 400 °C yielded largely equiaxed nanoparticles with an average diameter less than 100 nm. In contrast, heat treatment at 775 °C resulted in the formation of chlorapatite nanorods with an average diameter below 200 nm and a [001] growth direction. In both cases, removal of the salt matrix by washing with water gave powders with low levels of agglomeration.

Synthesis and characterization of nanometric gadolinia powders by room temperature solid-state displacement reaction and low temperature calcination

Nanometric-sized gadolinia (Gd2O3) powders were obtained by applying solid-state displacement reaction at room temperature and low temperature calcination. The XRD analysis revealed that the room temperature product was gadolinium hydroxide, Gd(OH)3. In order to induce crystallization of Gd2O3, the subsequent calcination at 600∼1200°C of the room temperature reaction products was studied. Calculation of average crystallite size (D) as well as separation of the effect of crystallite size and strain of nanocrystals was performed on the basic of Williamson-Hall plots. The morphologies of powders calcined at different temperatures were followed by scanning electron microscopy. The pure cubic Gd2O3 phase was made at 600°C which converted to monoclinic Gd2O3 phase between 1400° and 1600°C. High-density (96% of theoretical density) ceramic pellet free of any additives was obtained after pressureless sintering at 1600°C for 4h in air, using calcined powder at 600°C.

Investigation of stearic acid additive effects on the mechanochemical synthesis of silver nanoparticles

The silver (Ag) powder was synthesized in a mechanochemical (MC) process by inducing a solid-state displacement reaction between silver chloride (AgCl) and copper (Cu). This process was carried out in argon atmosphere conditions using a planetary ball mill. The reaction caused the mixture of AgCl and Cu to change the composition of the mixture to Ag and copper chloride (CuCl). CuCl was separated from MC product by leaching with ammonium hydroxide. Thus, Ag powder was obtained as the final product. Stearic acid (C18H36O2) was used as the additive to improve dispersion of Ag powder during the MC process. The ground powders, formed in the presence and absence of additive, were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD determined that the reaction between AgCl and Cu was completed in 18 h milling. SEM and particle size analysis examinations revealed that the size of the particles in the synthesized metallic Ag powder was in the range of 30–300 nm.

Mechanochemical Synthesis of Silver Nanoparticles

The silver (Ag) powder was synthesised in a Mechanochemical (MC) process by inducing a solid-state displacement reaction between silver chloride (AgCl) and copper (Cu). This process was done in Argon atmosphere conditions using a planetary ball mill. The reaction caused the mixture of AgCl and Cu to change the composition of the mixture, of Ag and copper chloride (CuCl). CuCl was separated from MC product by leaching with ammonium hydroxide and Ag powder was obtained as the final product. Stearic acid (C18H36O2 ) was used as the additive to improve dispersion of Ag powder during MC process. The ground powders, formed in the presence and absence of additive, were characterised by X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD determined that the reaction between AgCl and Cu was completed in 18 h milling. SEM and particle size analysis (PSA) examinations revealed that the size of the particles in the synthesised metallic Ag powder was in the range of 30-300 nm.

Synthesis and sintering of nano-sized forsterite prepared by short mechanochemical activation process

The findings reported in this paper offer an affordable technique for the synthesis of nano-sized pure forsterite from magnesium chloride hexahydrate, sodium metasilicate nonahydrate and sodium hydroxide as precursors. The stoichiometric mixture of reagents was manually mixed and subjected to high-energy ball milling for a short time (∼10 min). The monitoring of as-milled powder by x-ray diffraction method confirmed that the solid-state displacement reactions occur during high-energy ball milling. After washing and drying, the resulting precursor was subjected to heat treatments in air at various temperatures ranging from 500 to 1100 °C for studying forsterite development. The heat-treated powders were characterized by XRD, STA, FTIR, BET, FE-SEM and TEM techniques. The results revealed that the hydrated compounds formed at room-temperature completely dissociate into periclase and forsterite from 600 °C. The more forsterite phase was generated by the increase of temperature from 600 to 800 °C by the consumption of periclase and amorphous silica present in precursor and finally single-phase forsterite was yielded at 900 °C/2 h. The TEM and FE-SEM results demonstrated that the as-prepared powder consists of separate particles with nearly spherical morphology, 20–60 nm mean particle size and 15.4 m2/g specific surface area. Sample sintered at 1500 °C/2 h had 89.5% theoretical density and homogeneous single-phase microstructure.

Mechanochemical Synthesis of Fe2O3 Nanoparticles

In this work, formation of iron oxide nanoparticles by mechanochemical reactions in different milling times was studied. During the mechanical milling, the solid-state displacement reaction of 3Na2CO3 + 2FeCl3.6H2O = 6NaCl + Fe2O3.6H2O + 3CO2 was induced to form iron oxide nanoparticles. A simple washing process was done to remove NaCl by-product and subsequently the particles dried at 105°C for 12h. Nanoparticles size and the mechanochemical effect were characterized by X-ray diffraction (XRD) and particle size analysis. Experimental results show that increasing the milling time can effectively reduce the nanoparticle size of Fe2O3. The average Fe2O3 nanoparticles size is about 14nm for 2h and 4nm for 5h milling process.

Thermodynamical Analysis of the Reaction between AlN and ZrO<sub>2</sub> and Experimental Substantiation

Two equations with discrepancies of solid-state displacement reactions between AlN and ZrO2 were analysed by thermodynamic calculation, and its results were substantiated by experiment. Results of thermodynamic calculation showed that the reaction equation of Bayer and Mocellin proposing could occured at 1411.26K, and it accord with TG-DTA and SEM analysis results, i.e. the reaction equation of Bayer and Mocellin proposing was true.

Low-activation joining of SiC/SiC composites for fusion applications

Research at PNNL has been directed at high-strength, low-activation joints using solid-state displacement reactions. This paper reports on further development and optimization of displacement reaction joints for the TITAN collaboration. The results reveal that fully dense and high-quality joints between SiC-composite bars are fabricated at 1623K–1723K using 30MPa pressure in purified argon atmospheres. Scanning electron micrographs reveal typical interpenetrating phase microstructures in the joints, which are about 10μm thick. Blocky SiC particles are observed to nucleate preferentially at the SiC-joint interface but are more plate-like within the joint. X-ray spectroscopy reveals a uniform distribution of constituent elements consistent with the interpenetrating phases.

Synthesis and characterizations of AgI nanoparticles via mechanochemical reaction

Silver iodide (AgI) nanoparticles were prepared by mechanochemical reaction technique (MCR) using silver nitrate (AgNO 3) and potassium iodide (KI) as reagents and distilled water as solvent. Mechanochemical reaction involves the mechanical activation of solid-state displacement reactions at low temperatures in a ball mill. AgI nanoparticles with well-defined morphology, size and phase compositions were obtained. TEM images show that the particle size of the AgI nanoparticles decreases as a function of milling time. The powder X-ray diffraction patterns show that they are mixture of γ- and β-phases. The superionic phase transition temperature (γ → α) was slightly decreased after milling. The ionic conductivity shows enhancement with temperature for all samples with the unmilled sample has the highest conductivity (4.12 × 10 −6 S cm −1) at room temperature. The growth kinetics for AgI nanoparticles were investigated. Two different values of activation energy were obtained indicated that there were two kind of mechanisms for the growth of AgI nanoparticles.

High Selectivity Slurries for STI CMP

Ceria particles were synthesized by two different methods, solid-state displacement reaction method and colloidal method and used for STI CMP. Calcined abrasives were used directly as well as after milling. The effect of calcination parameters on the crystal size was measured. The effect of synthesis method and conditions on the removal rates and the selectivities are presented. Colloidal ceria and calcined ceria showed enhanced selectivity in the presence of DL aspartic acid. There is a strong correlation between the polishing behavior and the calcination temperature and a weak correlation between the polishing behavior and the duration of calcination. Titania and zirconia based slurries were also employed and they exhibited higher selectivities in presence of the additive. Our results show that other multivalent abrasives, such as titania and zirconia, exhibit chemical tooth behavior and the interaction of the additive with the chemical tooth action may explain the enhanced selectivity.

Preparation of strontium hexaferrite magnets from celestite and iron ore fines by mechanochemical route

In the present investigation celestite and iron ore fines have been used for the preparation of strontium hexaferrite powder. The mechanical alloying process has been adopted to prepare strontium hexaferrite powder. The mixture of celestite after chemical upgradation and physically upgraded iron ore fines along with sodium carbonate was milled for different duration in a high energy planetary ball mill with tungsten carbide jar and ball to prepare strontium hexaferrite powder. A long duration of ball milling for different duration has led to solid-state displacement reaction. At the end of each experiment the product was washed thoroughly and dried. The X-ray diffraction study of milled powder after annealing shows the development of single phase strontium hexaferrite. The resultant powder was compacted under magnetic field and sintered to prepare the magnet after annealing the ferrite powder. The moderate value of coercivity, remanence and energy product were observed in this sintered magnet. The work illustrates the feasibility to prepare strontium hexaferrite magnetic powders directly from natural ores.

Preparation and firing of a TiC/Si powder mixture

This paper describes how the preparation and heat treatment of TiC/Si powders influences the phase reactions during firing. The powders are prepared by milling and some effects of powder preparation are discussed. A solid state displacement reaction according to: 3TiC + 2Si → Ti3SiC2 + SiC is a priori expected to take place during heat treatment. The firing procedure is investigated with respect to the effect of heat treatment time and temperature on the phases produced, especially Ti3SiC2. Samples were heat treated in a graphite lined furnace. Heat treated samples are analysed by x-ray diffraction, scanning electron microscope and energy dispersive spectroscopy. Ti3SiC2, TiC and SiC are dominant in the final products. The highest amount of Ti3SiC2 is achieved for short holding times (2–4 hours) at high temperatures (1350–1400°C). Ti3SiC2 appears to decompose at elevated temperatures or extended times, through a Ti3SiC2 → TiC + Si(g) type reaction. The activation energy of Ti3SiC2 phase formation is determined to be 289 kJ/mol, using the Mehl-Avrami-Johnson model.

(111) Faceted Ceria and Its Influence on STI CMP for Memory Devices Below 50 nm

We investigated the effects of (111) faceted ceria nanoparticles on the removal rate of oxide films in shallow trench isolation (STI) chemical mechanical planarization (CMP). The X-ray diffraction peak ratio of (111) to (200) for the (111) faceted ceria particles synthesized by a flash-creation method was 4.08, while the ratio for polyhedral ceria synthesized by a solid-state displacement reaction was 2.65. The highest surface density of atoms in the (111) plane led to an increase in removal rates. Faceted ceria slurry yielded a higher oxide removal rate and greater selectivity than the polyhedral ceria slurry in STI CMP evaluation. .

Nanoparticles of silver powder obtained by mechano-chemical process

The silver (Ag) powder was synthesised in a mechano-chemical (MC) process by inducing a solid-state displacement reaction between silver chloride (AgCl) and copper (Cu). The AgCl and Cu were ground in atmosphere conditions using a planetary ball mill. The reaction caused the mixture of AgCl and Cu to change the composition of the mixture, such as Ag and copper chloride (CuCl). CuCl was separated from MC product by leaching with ammonium hydroxide and we obtained Ag powder as the final product. Moreover, ascorbic acid (C6H8O6) was used as the additive to improve dispersion of Ag powder during MC process. The ground powders, formed in the presence of additive, were characterised by X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD determined that the reaction between AgCl and Cu was complete in almost all the experiments carried out. SEM examinations revealed that the size of the particles in the synthesised metallic Ag powder was in the range of 30–300 nm.