Liquid Phase Diffusion Research Articles

Superior performance of quaternary NC/GO/Al/KClO4 nanothermite for high speed impulse small-scale propulsion applications

Nanothermites are considered promising energetic materials and a key to develop new technologies in the field of energetics and propulsion. However, relatively low peak pressure, smaller thrust output, and incomplete combustion represent some of the potential problems associated with nanothermites. In this study to improve the combustion performance of nanothermites, varying quantities of nitrocellulose (NC) were introduced to produce the quaternary NC/GO/Al/KClO4 nanothermite using facile electrospinning. The morphology of nanothermites was characterized by SEM-EDX which confirmed that the nanoparticles were homogeneously dispersed without agglomeration. The combustion behavior of the composites was evaluated by igniting the samples at different packing densities (%TMD) in open acrylic tubes within a reaction chamber and using a 3.5 W continuous wave laser. High speed imaging captured the flame propagation and differential scanning calorimetry (DSC) was used to assess thermal behavior and energy output. Finally, for propulsion characterization, a small-scale test motor (STM) with a converging/diverging nozzle was used to evaluate the combustion performance of the prepared samples. In general, thrust output, specific and volumetric impulses (ISP and ISV), and total heat released exhibit remarkable enhancement with the addition of NC. Specifically, the total impulse (IFT) and ISP peaked at 5% NC/GO/Al/KClO4 at ~ 50% TMD, with IFT of 19.9 mN.s and ISP of 203.2 s. These are improvements of over 50% compared to the sample without NC (13.4 mN.s and 137.4 s). The ignition delay time and the power required to ignite the NC-enriched mixture is increased, but a sufficiently fast response is maintained for practical applications. Thermal analysis implies that addition of NC introduced another step to the GO/Al/KClO4 reaction: a gas− solid phase and liquid−liquid phase diffusion reaction, with the liquid−liquid phase reaction increasing with NC percentage. These results suggest that electrospinning is a simple technique for preparation of quaternary nanothermites that results in enhanced combustion performance and an improved suitability for small-scale propulsion applications.

Effect of mechanically alloyed sintering aid on sinterability of TiB2

High-melting-point borides are attractive for structural and functional materials used in extreme environments. However, their poor sinterability due to their high melting point and strong covalent bonding have prevented their further applications. In this study, a new sintering process, called transient liquid-phase diffusion sintering (TLPDS), has been developed for high-melting-point borides. TiB2 compacts were fabricated by spark plasma sintering at 50 MPa for 15 min at temperatures of 1300 and 1600 °C via TLPDS of TiB2 powder with a eutectic TiB–Ti powder as the sintering aid, prepared via mechanical alloying (MA). Differential scanning calorimetry results indicated that the melting temperature of the obtained sintering aid was lower than its equilibrium melting point. MA of the sintering aid suppressed the open pore fraction to one-third of that in the compact sintered with the aid prepared without MA when sintering at 1300 °C. We also propose a possible mechanism for TLPDS of TiB2.

Experimental and Numerical Study of Transient Liquid Phase Diffusion Bonded DZ40M Superalloys

Transient liquid phase (TLP) diffusion bonding of DZ40M cobalt-based superalloy was carried out using a self-made NiCrCoWB intermediate layer. The typical microstructure of the joint was investigated. The effect of holding time on the microstructural evolution and the tensile strength of the brazed joints was studied. The tensile strength of the joints TLP bonded at 1160 °C for 60 min reached the maximum value of 487 MPa, which was 88.6% of the base metal strength. The diffusion of boron and the evolution of the eutectic zone were numerically studied. The time needed for isothermal solidification completion was calculated and predicted, which was well in accordance with the experimental results.

Construction of the targeted and pH-sensitive paclitaxel drug delivery system RGD/PTX@ZIF-90 and anti-tumor activity research

Tumors area common cause of morbidity and mortality. High treatment efficiency and low drug toxicity are key for effective tumor treatment. Here, the pH-sensitive material ZIF-90 was synthesized by the liquid-phase diffusion method for loading paclitaxel (PTX), and the targeting peptide (RGD) was prepared by the solid-phase synthesis method to modify it (RGD/PTX@ZIF-90). The skeleton of RGD/PTX@ZIF-90 collapses in the acidic tumor microenvironment, thereby releasing PTX and mediating the controlled release of the drug. ZIF-90 below 300 nm was obtained by adjusting the ratio of metal ions and organic ligands in the characterization experiment. In addition, in vitro drug release experiments showed that the drug release rate was greater at pH = 5.5 than at pH = 7.4. The lethal rate of RGD/PTX@ZIF-90 to human breast cancer cells (MCF-7) was 44.5%, which was higher than the lethal rate of PTX alone (37.3%) in the cytotoxicity experiment and apoptosis experiment. Uptake experiments revealed that RGD/PTX@ZIF-90 mainly existed in the cytoplasm of MCF-7, which suggests that the drug had successfully entered the cell to achieve the therapeutic effect. The loading of the nano-medicine carrier ZIF-90 and the modification of the targeting peptide RGD significantly improve the therapeutic effect of PTX and indicate that this system could be used to treat breast cancer.

A Novel Rapid Manufacturing Process for Metal Lattice Structure.

A novel lattice structure manufacturing process is proposed in this article, which has the potential to overcome the manufacturing shortcomings of small-scale metal lattice structure. The proposed hierarchical process has four segments: Design, Bending, Dip, and Join (DBDJ). The proposed research use one-dimensional metallic wires/rods instead of powder, two-dimensional sheet, or liquid metal, which is highly transformative than the status quo. The topology-based design technique is focused to construct the lattice structure using a continuous thin rod. The layers are stacked in an additive manner to construct the three-dimensional lattice structure. The dip-coating meditate material transfer facilitates the node joining using transient liquid phase diffusion bonding, and hence, the manufacturing of the complex lattice structure is performed. The research framework provides a unique and holistic approach from design to manufacturing for realizing small-scale metallic lattice structure. A range of multiscale lattice structure is manufactured with the proposed DBDJ process. Very low relative density (∼3.8%) unit cell is achieved, and compressive tests demonstrate no failure at the joining node, which is reported in this article.

Ultra-fast growth (up to 100 nm s−1) of heavily doped EuBa2Cu3O7 film with highly aligned BaHfO3 nanocolumn structure

Ultra-fast growth (up to 100 nm s−1) of high temperature superconducting film was demonstrated by using an advanced pulsed laser deposition technique. Highly textured EuBa2Cu3O7−δ (EuBCO) film with 8 mol.% of BaHfO3 (BHO) was deposited on the IBAD-based Hastelloy substrates. Structure characterizations reveal formation of high density of BHO nanocolumns with diameter of ∼5 nm in the film, which is well beyond the expectation. Comparison study on different amount of BHO in EBCO film confirmed that nanocolumn formation strongly depends on the dopant level. The epitaxial growth process of BHO is dominated by ultra-fast self-assembly associated with enhanced diffusion of high flux element and liquid phase. Due to the correlated pinning landscape, a pronounced broad peak appears at B//c in the J c(θ) curves at 30 K 5 T, while a strong pinning force of about 900 GN m−3 at 4.2 K, 10 T (B//c) are achieved.

THE ROLE OF MASS-TRANSFER IN THE MATERIALS SURFACE LAYER STRUCTURING UNDER EXTREME HEATING

Possible causes of mass transfer acceleration of carbon atoms and alloying elements in the surface layers of steels and alloys under extreme heating, under pulsing laser irradiation in particular, are considered. The research shows that the anomaly accelerated mass transfer, including diffusion in particular, in steels and alloys under fast laser heating has a cooperative character and is a result of a simultaneous action of several processes of different physics. It is proved that the carbon atoms mass transfer parameters and alloying elements depend on the scale and the level of emerging tension, relaxation of which goes along with a local plastic deformation, and occurrence of increased number of linear defects in crystal structure. Experimental and theoretical studies have found that with the temperature of the laser heating lowered along the depth of the irradiated areas the mechanism of mass transfer will change as follows: atoms move in the fused spot area under the influence of Marangoni effect; a contact melting and liquid-phase diffusion occur at the boundaries with the solid matrix; Soret diffusion under the action of local plastic deformation also occur; atoms move along the irradiated zone in an atoms "drift" mechanism within the area of moving dislocations.

Maximum CO2 diffusion inside leaves is limited by the scaling of cell size and genome size.

Maintaining high rates of photosynthesis in leaves requires efficient movement of CO2 from the atmosphere to the mesophyll cells inside the leaf where CO2 is converted into sugar. CO2 diffusion inside the leaf depends directly on the structure of the mesophyll cells and their surrounding airspace, which have been difficult to characterize because of their inherently three-dimensional organization. Yet faster CO2 diffusion inside the leaf was probably critical in elevating rates of photosynthesis that occurred among angiosperm lineages. Here we characterize the three-dimensional surface area of the leaf mesophyll across vascular plants. We show that genome size determines the sizes and packing densities of cells in all leaf tissues and that smaller cells enable more mesophyll surface area to be packed into the leaf volume, facilitating higher CO2 diffusion. Measurements and modelling revealed that the spongy mesophyll layer better facilitates gaseous phase diffusion while the palisade mesophyll layer better facilitates liquid-phase diffusion. Our results demonstrate that genome downsizing among the angiosperms was critical to restructuring the entire pathway of CO2 diffusion into and through the leaf, maintaining high rates of CO2 supply to the leaf mesophyll despite declining atmospheric CO2 levels during the Cretaceous.

The microstructure and mechanical properties of YT5 cemented carbide/carbon-carbon composite joints prepared by transient liquid phase diffusion bonding using Ni/Cu/Ti multiple foils as joining materials

YT5 cemented carbides have been successfully joined to carbon-carbon (C–C) composites by transient liquid phase (TLP) diffusion bonding technique using Ni/Cu/Ti multiple foils as joining materials. The microstructure and mechanical properties of YT5/C–C composite joints are characterized and analyzed by electronic microscopy (SEM) with an energy disperse spectroscopy (EDS), X-ray diffraction (XRD) and general mechanical testing method. The results showed that multilayer gradient structure, i.e. YT5/Ti–C compounds/Ti–Ni + Ti–Cu compounds/C–Ti–W solid solution/C–C, was formed in the joints prepared by TLP diffusion bonding with the joining temperature changing from 960 to 1020 °C. There are various compounds including TiC, Ni2Ti, Cu4Ti3, Cu3Ti2 and Ti8C5 in the joints, and all interfaces were continuous and dense by element diffusion and chemical reactions during joining process. The average shear strength of joints prepared under 990 °C, 30 min achieves 21.4 MPa. Combined with shear morphology, load-displacement curves and phases on fracture surface, it can be inferred that fracture occurs in the interface region adjacent C/C composites side and presents a brittle fracture mode.

Visualization of Interactions between Depressurization-Induced Hydrate Decomposition and Heat/Mass Transfer

Abstract Visual evidences to understand the interactions between hydrate decomposition and heat/mass transfer are currently lacking. This study proceeds from the hydrate morphology to visualize the interactions between depressurization-induced hydrate decomposition and heat/mass transfer from different scales. Reactor-scale hydrate distribution evolution shows that the dominant influencing factor of hydrate decomposition transforms from heat transfer to mass transfer. More importantly, pore-scale visual evidences suggest that the mass transfer of gas shows significant effects on hydrate morphology evolution. Specifically, the limited gas diffusion in liquid phase could lead to the hydrate morphology evolution from patchy pore-filling to “grain-bridging” during hydrate decomposition. The combination of grain-bridging hydrate together with the water layer that wraps the hydrate is termed as “hydrate bridge” in this work. It is also worth noting that the grain-bridging hydrate could accelerate fluid flow in pores according to our seepage simulation results. These findings provide visual evidences for variations in physical properties of hydrate-bearing sediments during hydrate decomposition. Since physical properties of hydrate-bearing sediments play important roles in hydrate decomposition, the hydrate morphology evolution characteristics analyzed here are valuable for hydrate exploitation in field tests.

Mechanical Reliability of Al/Ni Reactive Bonding Element with Al Adhesion Layer

In recent years, as power modules have become more powerful and smaller, mechanically joints are required to have high mechanical strength and low thermal resistance. Nano-Ag sintering and Ni/Sn liquid phase diffusion bonding are known as examples of high heat resistant bonding technologies, but problems remain such as voids. One possible solution is using Al/Ni, a self-propagating exothermic multilayer film, as a heat source and using Al film as an adhesive layer for bonding. In this study, we focus on mechanical reliability of Al/Ni reactive bonding element with Al adhesion layer by four point bending test. The specimens were cut to 0.5 x 0.5 x 3.1 mm using a dicing saw after bonding, and the bond strength of each interface were measured using a four-point bending tester which was designed ourselves in our laboratory. Result of testing with different thicknesses of Al as the adhesive layer that the smallest variation and the highest bending strength were obtained when the thickness of Al was 10 μm. The average bending strength was 1.2 times higher than that of the conventional Sn-3.5Ag instantaneous joint, although the dispersion was larger than solder bonding.

Synthesis mechanism and properties of lightweight mullite-corundum refractories obtained through high temperature liquid-assisted micrometer-scale Kirkendall effect

At high temperature, the lightweight mullite-corundum refractory was prepared by the micrometer-scale Kirkendall effect using quartz, bauxite, and corundum as the main raw materials. In this paper, the preparation mechanism of the mentioned effect has been discussed. The results prove that the silicon-rich phase produced during high-temperature firing forms mullite by reacting with the corundum powder in the matrix. Due to the diffusion of the silicon-rich liquid phase to the matrix and the dissolution of the Al2O3 to the silicon-rich liquid phase, the cristobalite continuously dissolves into the silicon-rich liquid phase and leaves holes in the original position, thereby meeting the needs of the mullitization. The lightweight mullite-corundum refractory with high compressive strength (85.0 MPa), high refractoriness under load (1636 °C), and low thermal conductivity (1.55 W (m K)−1) were obtained by controlling the quartz particle size, addition of content, and firing temperature.

Estimation of Battery Separator Area, Cell Thickness and Diffusion Coefficient Based on Non-Ideal Liquid-Phase Diffusion Modeling

The aim of this work is to present a fast and in situ diffusion modeling technique to extract essential electrochemical parameters from liquid-phase diffusion which can be used to implement a realistic battery in a pseudo-2D finite element modeling environment. A generalized Warburg element was used within an extended Randles equivalent circuit to obtain an appropriate fit on non-ideal diffusion impedance. Based on the calculation method presented in this paper, the values of diffusion-related parameters such as the cross-sectional area of the separator Asep, cell thickness Lcell as well as liquid-phase and solid-phase diffusion coefficients Dl and Ds were derived, successfully. A characteristic cell which allowed the exchange current density i0 and reaction rate constant k0 to be calculated was also established. The experimental data was measured by electrochemical impedance spectroscopy (EIS), resistivity measurement and the galvanostatic intermittent titration technique (GITT). The results show that our hypothesis to extract essential electrochemical parameters from the tail part of diffusion impedance is correct. The applicability of our concept is confirmed by the prosperous validation results produced by computed tomography (CT) and battery dynamics simulation in finite-element environment. Due to the inherent limitations of the pseudo-2D Doyle-Fuller-Newman (DFN) model, our technique is accordingly valid within the current range of 0–1 C.

Mechanism of Ion-Diffusion Solid-Phase Reduction of Iron Oxides of Technogenic Origin in the Presence of the Liquid Phase and without it

The processes of iron oxides’ reduction have a complex physicochemical mechanism, with the participation of solid, liquid, and gaseous substances. The article discusses the existing models for the reduction of iron oxides and provides data on the thermodynamic possibility of carrying out the reactions of their reduction through the solid and gas phases. Experimental data on the reduction of iron from industrial scale, obtained by the DSC (differential scanning calorimetry) method, show the kinetic dependence of the rate and completeness of recovery on external factors: pressing pressure during sample preparation and the reagents’ composition. The pressing pressure, under conditions of iron ions’ solid-phase diffusion, has the significant effect by increasing the reagents’ contact area. Under conditions of iron ions’ comprehensive diffusion, the pressing pressure does not affect the reduction processes rate. The introduction of 10 mass.% flux into the raw mixture composition leads to a partially liquid-phase diffusion of iron ions and weakens the effect of the pressing pressure in this process. An ion diffusion-catalytic mechanism is proposed to describe the observed effects during the reduction of iron oxide of technogenic origin.

Wettability, Diffusion Behaviors, and Modeling of Ni Nanoparticles and Nanowires in Brazing Inconel 718

Ni nanoparticles (NPs) and nanowires (NWs) are compared as brazing filler metals for joining Inconel 718. NWs significantly enhance the strength of brazed joints compared to NP joints (270 MPa). Herein, joints formed with a pure NW pellet and a NW–NP mixed pellet yield average lap shear bonding strengths of 319.2 and 370 MPa, respectively. The experiment displays that the contact angle in brazing with NPs is higher than that with NWs. A modified Hart's equation is also proposed for predicting the effective interdiffusion coefficients of nanomaterials that account for surface diffusion in addition to lattice and grain boundary diffusion. The diffusion coefficients calculated by the modified Hart's equation are consistent with the values determined by Sauer–Friese analysis for NPs, but for NWs, the diffusion coefficients determined by Sauer–Friese are mainly controlled by grain boundary diffusion, significantly higher than those predicted by the modified Hart's equation due to size‐dependent transient liquid phase diffusion. This explains the enhanced brazing strength with NW fillers.

Features of Technogenic Iron Oxide Recovery

The overview of existing models for iron oxides reducing and an analysis of their applicability to technogenic formations is presented. The thermodynamic analysis data of iron oxides reducing reactions through solid and gas phases and experiment results presenting features of technogenic iron oxide reducing under conditions of solid-phase diffusion (limited diffusion) and partially liquid-phase diffusion (easier diffusion) of iron oxide ions. It is shown that under conditions of iron oxide ions solid-phase diffusion the reduction processes rate is significantly affected by the briquetting pressure, which increases the contact area of reacting substances. The briquetting pressure does not affect the reduction processes rate under conditions of partially liquid-phase diffusion of iron oxide ions. An ion-diffusion catalytic mechanism is proposed to describe the observed effects of technogenic iron oxide reducing.

Diffusion brazing of stainless steels influence of Ni-B filler alloy composition

Stainless austenitic (0.12C-18Cr-10Ni-Ti, wt-%) and ferritic-martensitic (0.16C-12Cr-Mo-Si-V-Nb-B, wt-%) steels were joined by transient liquid phase diffusion bonding (also called diffusion brazing) with the filler metals based on Ni-Cr-Si-(Fe)-B at 1160 °C for different bonding times from 15 to 40 min. It is shown that the braze joints have a heterogeneous diffusion zone with a boride network which is formed during isothermal solidification. The influence of the filler metals composition on the joint microstructure and tensile strength was studied. It is established that the initial concentration of boron and chromium in the filler metal plays an important role in the formation of the microstructure. It is shown that the use of the filler metal with the optimized composition of Ni-20Cr-7.5Si-4.5Fe-1.5B makes it possible to obtain the most homogeneous structure, leading to the best tensile strength of the joint of about 500 ± 40 MPa.

Grain growth kinetics and grain refinement mechanism in Al2O3/WC/TiC/graphene ceramic composite

The grain growth kinetics and grain refinement mechanism of Al2O3 grains and WC grains in Al2O3/WC/TiC/graphene ceramic composite were investigated in this work. The grain growth exponent of Al2O3 was determined as 2, which conformed to the growth mechanism of grain boundary diffusion. Meanwhile, the grain growth exponent of WC was determined as 3, which conformed to the grain growth mechanism of volume diffusion or liquid-phase diffusion. The different wettability of graphene to Al2O3 and WC was responsible for their different grain growth mechanisms. By analyzing grain growth activation energy, it can be concluded that the grain growth of Al2O3 and WC went through three stages: (1) softening stage, (2) rapid growth stage and (3) stable stage. The grain refinement mechanism of Al2O3 grains was graphene pinning effect and intragranular structure, and the grain refinement of WC grains could be attributed to the strong bonding interface between WC and graphene.

Analytical modeling of solution-phase diffusion in porous composite electrodes under time-dependent flux boundary conditions using Green’s function method

Mathematical modeling of species transport in a Li-ion cell is important for understanding and optimizing the performance of Li-ion cells in a wide variety of energy conversion and storage processes. Specifically, solid- and liquid-phase diffusion in the electrodes is an important process that governs cell performance. Most analytical and numerical models developed in the past have focused on a constant current boundary condition. However, time-dependent boundary conditions may be important in many applications, where the applied charging or discharging current changes with time. This paper presents an analytical solution for the solution-phase diffusion limitation problem for a composite electrode operating under time-dependent flux boundary condition and arbitrary initial conditions using the Green’s function approach. Results based on the analytical solution show good agreement with past work for constant current boundary conditions, as well as numerical simulation results. The results are used to predict the concentration distribution for linear, periodic, and step-function variations in current density as a function of time. Results from the step-function boundary condition address practical applications where sudden changes in the magnitude and direction of the imposed current may occur. Results derived for periodic functions are also of practical significance since other current profiles can be represented by series comprising periodic functions. This work expands the theoretical understanding of diffusion in Li-ion cells, and provides the basis for understanding and optimizing important charge/discharge processes in Li-ion cells.

Neural Network-Based Prediction of Liquid-Phase Diffusion Coefficient to Model Fuel-Oil Dilution on Engine Cylinder Walls

Neural Network-Based Prediction of Liquid-Phase Diffusion Coefficient to Model Fuel-Oil Dilution on Engine Cylinder Walls