Solid-state Reactive Diffusion Research Articles

Mechanism of solid-state diffusion reaction in vacuum between metal (Fe, Ni, and Co) and 4H–SiC

Experiments were conducted to investigate the vacuum diffusion reactions between 4H–SiC and various metals (iron (Fe), nickel (Ni), and cobalt (Co)). The effects of temperature, time, and metallic materials on the diffusion reactions were systematically analyzed. Notably, a solid-state diffusion reaction between the metal and 4H–SiC was observed at low temperatures, and the mechanism governing the solid-state interface diffusion reaction between the single-crystal 4H–SiC and metals was elucidated. The results indicate that a chemical reaction occurs between the metal and 4H–SiC during solid-state diffusion, leading to the formation of metal silicides under vacuum conditions. The temperature threshold for the solid-state diffusion reaction between 4H–SiC and metals falls within the range of 550–650 °C. Interestingly, the diffusion reaction proceeds without soaking. Furthermore, the metal type significantly influenced the diffusion rate.

Fabrication and performance of Nb3Sn superconducting joints

Nb3Sn superconducting joints were developed, and the joint characteristics were investigated. The joints were prepared by powder metallurgy to sinter the precursor powders that were mechanically alloyed. The optimized parameters were confirmed through x-ray diffraction studies to confirm the stoichiometry of Nb, Sn, and Cu. First, the precursor powders after mechanical alloying were heat treated without the Nb3Sn wires. Electron backscatter diffraction was used to quantify the crystal morphology, phase distribution, grain boundaries, physical grain orientation, and so on. Small equiaxed Nb3Sn grains were formed after heat treatment. The high-angle grain boundaries in Nb3Sn indicated the complete solid-state diffusion reaction. After the Nb3Sn was successfully prepared, and the superconducting characteristics were measured, we introduce the Nb3Sn wires to prepare Nb3Sn joints and measure their electrical properties. To use the space as economically as possible, the joint was tested under different background fields to estimate the joint resistance under various locations in the magnet. The experimental method and the test results are reported in this work. The joint resistance was tested by using the current decay measure method. The electrical resistance of the Nb3Sn–Nb3Sn joints was on the 10−13 Ω level under the 5.5 T magnetic field.

Mg-Ag-Sb thin films produced by solid-state reactive diffusion

α-MgAgSb is a tellurium-free thermoelectric material that exhibits good thermoelectric properties near room temperature. Being made of relatively abundant elements compatible with the complementary metal oxide semiconductor (CMOS) technology, it is considered as a possible solution for the development of high-efficiency thermoelectric devices for heat waste harvesting in microelectronic setups. This study presents a first attempt to investigate the structural properties of MgAgSb thin films prepared by solid-state reactive diffusion. X-ray diffraction (XRD) was used to follow phase formation in thin films, first, in the case of the binary Ag3Sb and Mg3Sb2 compounds, and then, in the case of the ternary system Mg-Ag-Sb. For the later, in situ XRD was used to follow real-time phase formations during the reaction of the bilayerAg3Sb/Mg3Sb2. The results show that the phase α-MgAgSb can be produced by reactive diffusion at the interface of the bilayer. Furthermore, the three phases α, β, and γ are shown to coexist at 360 °C, which can be the result of the thin film geometry (surface and interface effects) or due to a different stoichiometry between these three phases contrasting with usual belief. At temperatures higher than 450 °C, γ-MgAgSb is the only phase stabilized in the film. This study serves as a benchmark for the production of pure α-MgAgSb thermoelectric thin films by reactive diffusion.

Silver enrichment and trace element deportment in hydrothermal replacement reactions: Perspective from the Nageng Ag-polymetallic deposit, East Kunlun Orogen, NW China

Mineral replacement reactions (dissolution-reprecipitation and solid-state diffusion) have been reported in various types of hydrothermal deposits. However, the metal transfer and partitioning between the parent and daughter minerals and the role of different replacement reactions in silver enrichment remains poorly understood. Here we present the petrographic textures, major and trace elements, and sulfur isotopes of different generations of pyrite and marcasite associated with replacement reactions from the Nageng epithermal Ag-polymetallic deposit, East Kunlun Orogen (EKO, NW China). The mineralization includes the pyrite-quartz (I), quartz-siderite-sulfides (II), quartz-fluorite-rhodochrosite-sulfides-sulfosalts (III), and quartz-calcite (IV) stage. This deposit is characterized by a metal zonation from deep-level Cu-Pb-Zn mineralization to shallow-level Ag-Pb-Zn mineralization, which correspond to main ore stages II and III, respectively. Stage II ores contain the colloform pyrite (Py1) and porous pyrite aggregate (Py2), both of which have higher Co, Ni, and W contents than stage III pyrite (Py3 and Py4) and marcasite (Mc1 and Mc2). In contrast, stage III pyrite/marcasite are enriched in Ag and other ore metals (e.g., Pb, Zn, Sb, Mn, and Sn). The sharp contact between Py3 and Py4/Mc1, together with the porosity in Py4/Mc1, suggests that Py3 and Py4/Mc1 represent the parent and daughter phase of dissolution and reprecipitation. The crystallographically-oriented and metallic inclusion-rich Mc1 has higher Ag concentrations (median 246 ppm) than Py3 (median 180 ppm), and commonly occurs in breccia-type ores related to hydraulic fracturing. This suggests that (i) the dissolution-reprecipitation reaction may have remobilized and concentrated silver and associated ore metals, and (ii) the fluid oxidation related to hydraulic fracturing may contribute to dissolution-reprecipitation reaction. However, the randomly-oriented Mc2 is porous and has homogeneous compositions. This, together with the prevailing occurrence with rhodochrosite in vein-type ores, indicates that Mc2 was transformed from Mc1 via Mn-rich fluid-driven solid-state diffusion under relatively mild physicochemical changes. Mc2 has the most homogeneous and highest Ag concentrations (avg. 1142 ppm) and other ore meals among all the studied Fe disulfides, suggesting that the marcasite has higher trace element compatibility than pyrite, and that the solid-state diffusion reactions promoted Ag enrichment more efficiently than dissolution-reprecipitation reactions. The mostly positive δ34S values (−1.09 to 8.50‰) of the Nageng pyrite and marcasite are consistent with a magmatic origin. The δ34S variations among different pyrite and marcasite generations are attributed to the fluctuations between episodic replenishment of magmatic fluids and subsequent oxidation in respond to hydraulic fracturing and mixing with meteoric water. Our findings reveal higher Ag compatibility of marcasite over pyrite, and that replacement reactions (especially solid-state diffusion) greatly promote ore metal enrichment.

Spatially selective, solid state etching of diamond using lithographically patterned FeCoB

Nanocrystalline layers of FeCoB (Fe:Co:B = 60:20:20 at atom ratio) enable spatially selective, microstructurally agnostic removal of diamond through a solid-state diffusion reaction. Lithographically fabricated 100-300 nm thick films of FeCoB are deposited on polycrystalline diamond substrates. Heat treatment at temperatures ranging from 700 °C–900 °C for 30 min–90 min are used to trigger the conversion of sp3 to sp2 carbon at the diamond-transition metal interface. The integrity of the solid-state etchant within the thermal processing window underpins the spatial selectivity with which the diamond is removed. Removal of the reaction products using solvothermal etching in an acid solution enables the recovery of the structured diamond surfaces. FeCoB offers material removal rates, which exceeds that possible with just Fe or Co – pointing to the key role of B. The interaction zone was excised using focused ion beam milling and characterized using electron microscopy. In addition, XRD and Raman spectroscopy were performed to study the phase composition of the interaction zone. The role of the transition metal-diamond interface is key to controlling the material removal; the stability of the interface determines the ability to faithfully replicate the ultrafine features that were lithographically patterned in the FeCoB.

Reaction Mechanism of ZrB2-ZrC Formation in Ni-Zr-B4C System Analyzed by Differential Scanning Calorimetry.

The reaction mechanism of ZrB2-ZrC formation in a 30% Ni-Zr-B4C system under argon was revealed by using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the reaction mechanism in the Ni-Zr-B4C system was complex. Initially, NixZry and NixBy intermetallics were formed via solid-state diffusion reactions between Ni, B4C and Zr. Then, the eutectic reaction between Ni2B and Ni4B3 lead to the formation of Ni-B liquid. The free C atoms dissolved into the Ni-B liquid to form a Ni-B-C ternary liquid, and then part of the Zr powder dissolved into the surrounding Ni-B-C ternary liquid to form Ni-Zr-B-C quaternary liquid. Finally, ZrB2 and ZrC formed and precipitated out of the saturated liquid. The eutectic liquid plays an important role during the formation of ZrB2-ZrC.

Tailoring atomic diffusion for in situ fabrication of different heterostructures

Atomic diffusion has been recognized as a particularly powerful tool in the synthesis of heterostructures. However, controlled atomic diffusion is very difficult to achieve in the fabrication of individual nanostructures. Here, an electrically driven in situ solid-solid diffusion reaction inside a TEM is reported for the controlled fabrication of two different hetero-nanostructures in the Ag-Te system. Remarkably, the morphology and structure of the as-formed heterostructures are strongly dependent on the path of atomic diffusion. Our experiments revealed that the surface diffusion of Te atoms to Ag nanowires leads to a core-shell structure, while the bulk diffusion of Ag atoms give rise to a Ag2Te-Te segmented heterostructure. Heat released by Joule heating caused the surface diffusion process to be replaced by bulk diffusion and thereby determined the structure of the final product. Our experimental results provide an insight into solid-state diffusion reactions under an electric field and also propose a new process for the fabrication of complex nanostructures.

Percolation theory applied in modelling of Fe2O3 reduction during chemical looping combustion

The study presents a new modelling approach applied to hematite to magnetite reduction, which is the dominant reaction in atmospheres with a high CO2/CO ratio, expected in chemical looping combustion. The structure of the Fe2O3 particle was simulated using the percolation theory, while the reduction was modelled using the stochastic approach to simulate nucleation, gaseous diffusion, solid-state diffusion, and chemical reaction. To account for differences between 3-D and 2-D pores, the model allowed for pore-hopping. The obtained results agreed with experimental results for Fe2O3 derived from natural ore (pyrite), and, to a lesser extent, with results for lab-synthesised Fe2O3 particles. The model provides useful insight into the complexity of the investigated process. For materials with undeveloped porosity, a simple shrinking-core approximation will be sufficient. In contrast, for materials with well-developed porosity, the models should incorporate information about the particle structure.

Lanthanum silicate-based layered electrolyte for intermediate-temperature fuel cell application

An oxide ion (O2−) conducting membrane cell, based on lanthanum silicate oxyapatite (La9.33+xSi6O26+1.5x, LSO), exhibiting low ohmic and polarization resistances in the intermediate-temperature region (~873 K) was developed. As a solid electrolyte, highly conductive Mg-doped LSO, La9·8(Si5·7Mg0.3)O26.4 (MDLS), modified with another kind of non-conductive lanthanum silicate, La2SiO5 was employed. Two kinds of silicate layers were successively spin-coated on a Ni-MDLS porous anode support, followed by thermal treatment aimed at improving ionic conductivity as well as densification of MDLS through solid state reactive diffusion. In addition, the Gd-doped CeO2, (Ce0.9Gd0.1)O1.95 (GDC) electrolyte layer, which plays an important role to prevent a reaction between the electrolyte and cathode materials, was spin-coated on the modified MDLS electrolyte. Finally, the cathode layer of porous (La,Sr)(Co,Fe)O3-δ was screen printed on the electrolyte layers. The resulting cell obtained from this study showed good fuel cell performance with a maximum power density of 94 mW cm−2 at 873 K, when operated with argon-diluted hydrogen and pure oxygen gasses.

Textured growth of polycrystalline MAX phase carbide coatings via thermal annealing of M/C/Al multilayers

Mn + 1AXn (MAX; n = 1–3) phases are ternary layered nitride and carbide compounds featuring a combination of metallic and ceramic properties. Highly basal-plane textured and polycrystalline Cr2AlC, Ti2AlC, and Ti3AlC2 single-phase coatings have been synthesized on both amorphous and polycrystalline substrates via controlled thermal annealing of magnetron-sputtered nanoscale multilayers built by individual transition metal, carbon, and aluminum layers. Formation of substitutional solid solution carbide phases was triggered via solid-state diffusion reactions during annealing. Lower ordered Ti2AlC initially crystallized at an intermediate temperature range and was recognized as an intermediate reactant in the case of synthesizing the Ti3AlC2 312 MAX phase via annealing corresponding stoichiometric multilayers. The crystallization onset temperatures identified via in-situ high-temperature x-ray diffraction measurements were approximately 480, 660, and 820 °C for Cr2AlC, Ti2AlC, and Ti3AlC2, respectively. Contrary to the usually observed columnar structure representative of magnetron-sputtered coatings, the coatings synthesized via the current approach are composed of plateletlike, elongated crystallites. The nanoscale multilayered design stimulates the textured growth of MAX structures during thermal annealing. More specifically, the preferred crystallographic orientation relationships among the as-deposited transition metal layers, the intermediate solid solution phases, and the end-product MAX phases facilitate the growth of textured MAX phase films.

Phase competition in solid-state reactive diffusion revisited-Stochastic kinetic mean-field approach.

Kinetic mean-field method for description of diffusion (introduced in 1990 by George Martin) is developed to 3D with the inclusion of the frequency noise. After this, it is applied to modeling of reactive diffusion-formation, competition, and growth of the ordered intermediate phases during interdiffusion. Results seem reasonable; hence, the method can be used for qualitative study of complicated cases of the competitive first-order transitions in closed and open systems with rigid lattices.

CrB2 Doping Effects on Critical Current Density and Flux Pinning of MgB2

A series of polycrystalline bulk samples of (MgB 2 ) 1-x (CrB 2 ) x with 0 ≤ x ≤ 10% were synthesized by a two-step solid-state diffusion reaction. Crystal structure, microstructure, superconductivity, and flux pinning behavior were investigated. The CrB 2 dopant was found to significantly depress superconductivity by substituting Mg with Cr. In addition, a portion of the unreacted CrB 2 appears as nanoparticle impurities inserted into the MgB 2 matrix, which enhances flux pinning. As a result, the critical current density of the (MgB 2 ) 1-x (CrB 2 ) x sample was significantly improved at low doping levels.

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

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

Role of Atomic Transport Kinetic on Nano-Film Solid State Growth

Nanostructures used to build current technology devices are generally based on the stack of several thin films (from few nanometer-thick to micrometer-thick layers) having different physical properties (conductors, semiconductors, dielectrics, etc.). In order to build such devices, thin film fabrication processes compatible with the entire device fabrication need to be developed (each subsequent process step should not deteriorate the previous construction). Solid-state reactive diffusion allows thin film exhibiting good interfacial properties (mechanical, electrical…) to be produced. In this case, the film of interest is grown from the reaction of an initial layer with the substrate on which it has been deposited, during controlled thermal annealing. In the case of the reaction of a nano-layer (thickness < 100 nm) with a semi-infinite substrate, nanoscale effects can be observed: i) the phases appear sequentially, ii) not all the thermodynamic stable phases appear in the sequence (some phases are missing), and iii) some phases are transient (they disappear as fast as they appear). The understanding of the driving forces controlling such nanoscale effects is highly desired in order to control the phase formation sequence, and to stabilize the phase of interest (for the targeted application) among all the phases appearing in the sequence.This chapter presents recent investigations concerning the influence of atomic transport on the nanoscale phenomena observed during nano-film reactive diffusion. The results suggest that nano-film solid-state reaction could be controlled by modifying atomic transport kinetics, allowing current processes based on thin-film reactive diffusion to be improved.

Improving electrochemical properties of LiNi1/3Co1/3Mn1/3O2 by enhancing thermal decomposition of carbonates to synthesize ultrafine powders

The ultrafine LiNi1/3Co1/3Mn1/3O2 powders with particle size in the range from 200 nm to 500 nm, good structural stability and higher structural integrity are directly synthesized by enhancing thermal decomposition of carbonates through a mechanochemical activation treatment to intensify the solid state diffusion reaction. These powders reveal a remarkable cycle stability from 143.8 mAh g−1 to 116.2 mAh g−1 in the range of 2.5–4.3 V and from 161.2 mAh g−1 to 134.2 mAh g−1 in the range of 2.5–4.5 V at 1 C after 200 cycles and an excellent rate capacity from 1 C to 6 C. Moreover, their superior performance can be maintained at high testing temperature (55 °C). Their discharge capacity releases 165.7 mAh g−1 at first cycle and decreases to 158.0 mAh g−1 at 1 C after 50 cycles in the range of 2.5–4.3 V, while it decreases from 191.5 mAh g−1 to 169.8 mAh g−1 with the cycle number from 1 to 50 in the range of 2.5–4.5 V.

Ti and nitride surface modification of copper by pack cementation

ABSTRACTCopper is widely applied however its disadvantages such as low hardness and poor oxidation resistance. TiN coatings are often used industrially for overriding such disadvantages of ferrous components. In this examination the deposition of TiN on Cu substrates is investigated for the first time by pack cementation process with which one or more elements can be deposited simultaneously by gas and solid-state diffusion reactions. This feature makes this process very attractive for industrial use as it is economic and time saving. Microstructural examination of the deposited samples revealed the formation of thick coatings corresponding to Ti–Cu phases. Focusing on the coating surface it was found that a TiN thin layer is formed. This was verified also from hardness measurements which showed that there was a significant increase of the surface hardness. Furthermore, the oxidation resistance of the coated samples has considerably increased as implied from the thermogravimetric measurements.

The Kirkendall void formation in Al/Ti interface during solid-state reactive diffusion between Al and Ti

In the current study, the formation of Kirkendall voids in Al/Ti interface during solid-state reactive diffusion between Al and Ti was investigated. In this regards, pure Al wire (grade 1100) was deposited on commercially pure Ti surface by means of GTAW processing and the prepared samples were annealed at 625 °C for different periods of time. The achieved results indicated that, during cladding process, a continuous layer of Al3Ti intermetallic compound with average thickness of about 2 µm, can be formed in Al/Ti interface. During annealing process, both Ti and Al diffused into each other and the growth of the Al3Ti layer occurred mainly towards the Ti side. At this condition, Kirkendall voids are formed and accumulated near to Al/Al3Ti interface. These voids started to connect to one another, coalesce into large gaps and resembling a line crack at the interface. The formed crack acts as a barrier in Al/Ti diffusing couple and inhibits the growth of Al3Ti phase.

Characterization on Solid Phase Diffusion Reaction Behavior and Diffusion Reaction Kinetic of Ti/Al

Abstract The solid phase diffusion reaction behavior between Ti and Al was characterized from 520 °C to 630 °C for different annealing time with titanium and aluminum being superfluous. When the samples are annealed up to 46 h, only intermetallic TiAl3 phase forms and grows at the Ti/Al interface. It can be found that the growth rate of TiAl3 towards TiAl3/Al interface is more rapid than that towards Ti/TiAl3 interface. Additionally, the solid-state diffusion reaction kinetic equation of TiAl3 was successfully established in the present work. The reaction activation energy of Ti/Al is calculated to be 170.1 kJ-mol−1 and dynamic index n is 0.5. Hence, the growth of TiAl3 is controlled by normal parabolic law with annealing time. Ti/Al powder compact was employed as experiment material to identify the proposed reaction kinetic equation for the growth of TiAl3. It is suggested that no extra aluminum is found in the specimen annealed at 590 °C/4.5 h, while the aluminum is still found at 590 °C/3.5 h, indicating that it is in a good agreement with the developed solid-phase diffusion reaction equation.

Synthesis and photoluminescence properties of Eu doped LiBaPO4 phosphors for solid state lighting

Phosphor LiBaPO4: Eu3+ was successfully synthesized by Pechini (citrate gel) method which is more efficient than conventional high temperature solid state diffusion reaction. X-ray diffraction analysis confirmed the single phase formation of LiBaPO4 with hexagonal crystal structure. Luminescence results showed that the phosphor could be efficiently excited by near UV with intense excitation peak at 393 nm and exhibited two bright red emission narrow bands. In the wavelength range 575–640 nm these bands are centered at 595 and 615 nm, corresponding to characteristics transitions 5D0→7F1 and 5D0→7F2 respectively of Eu3+, with maximum intensity peak at 615 nm. When Eu3+ in LiBaPO4:Eu3+ was reduced by the carbo-thermal reduction process to Eu2+ intense blue broad emission band centered at 472 nm was obtained for LiBaPO4:Eu2+ phosphor when monitored at 350 nm. Hence both of phosphors could be use in solid state lighting application for fabrication of white light emitting diodes.

Improving electrochemical properties of LiCoO2 by enhancing thermal decomposition of Cobalt and Lithium carbonates to synthesize ultrafine powders

Ultrafine LiCoO2 powders were directly synthesized by enhancing thermal decomposition of Cobalt and Lithium carbonates through a mechanochemical activation treatment to intensify the solid state diffusion reaction. Effects of activation treatment time on particle size and structure of the LiCoO2 compound were investigated. In the present study, the optimum mechano-chemical activation time was found to be 10h. In this study, the ultrafine LiCoO2 powders (particle size in the range from 200nm to 400nm) show good structural stability and higher structural integrity. X-ray photoelectron spectroscopy (XPS) results indicate that most of Co cations exist as Co3+, which contributes to the improvement of the electrochemical performance. Cyclic voltammetry (CV) curves of different cycles display almost a complete overlap, which can be regarded as another evidence of the excellent cycle performance. The LiCoO2 powders exhibit a high initial discharge specific capacity of 175.2mAh/g at 0.1C (274mA/g at 1C) and a remarkable cycle stability from 167.5mAh/g to 146.2mAh/g at 0.5C and from 147.5mAh/g to 115.2mAh/g at 3C after 100 cycles in the range of 3.3–4.3V. The apparent activation energy and the frequency factor of the decomposition of CoCO3 are 69.83kJ/mol and 1.369×106, respectively, indicating that the ultrafine in-process product of Co3O4 can be quickly prepared at a low temperature.