Microcasting Process Research Articles

(Digital Presentation) Ultra-Thick Electrodes Utilizing Short Diffusion Path Via Novel Micro-Casting Process for Lithium-Ion Batteries

For achieving high energy density, one effective way is to increase the active materials which makes thick electrodes for Lithium-ion Batteries (LIBs). However, thickening electrode limits the charge transport and generates significant mechanical stress that results in poor performance and eventually failure. In this work, a novel micro-casting (µ-casting) process has been introduced to fabricate ultra-thick and 3D structured electrodes which can address the issues with low charge transport by establishing short diffusion path (SDP). SDP reduces the intercalation-induced stress, improves energy density and long-term stability. The µ-casting allows ultra-thick (~280 µm) cathode (NMC 811, LiNi0.8Mn0.1Co0.1O2) and anode (MCMB, MesoCarbon MicroBeads) to achieve 40% higher specific capacity and 30% higher areal capacity after 200 cycles, high C-rate performance and longer cycle life with a intensive high mass loading of 35.7 mg/cm2.

Enabling Ultrathick Electrodes via a Microcasting Process for High Energy and Power Density Lithium‐Ion Batteries

AbstractThickening electrodes is one effective approach to increase active material content for higher energy and low‐cost lithium‐ion batteries, but limits in charge transport and huge mechanical stress generation result in poor performance and eventual cell failure. This paper reports a new electrode fabrication process, referred to as µ‐casting, enabling ultrathick electrodes that address the trade‐off between specific capacity and areal/volumetric capacity. The proposed µ‐casting is based on a patterned blade, enabling facile fabrication of 3D electrode structures. The study reveals the governing properties of µ‐casted ultrathick electrodes and how this simultaneously improves battery energy/power performance. The process facilitates a short diffusion path structure that minimizes intercalation‐induced stress, improving energy density and cell stability. This work also investigates the issues with structural integrity, porosity, and paste rheology, and also analyzes mechanical properties due to external force. The µ‐casting enables an ultrathick electrode (≈280 µm) that more effectively utilizes NMC‐811 (LiNi0.8Mn0.1Co0.1O2) cathode and mesocarbon microbeads anode active materials compared to conventional thick electrodes, allowing high‐mass loading (35.7 mg cm−2), 40% higher specific capacity, and 30% higher areal capacity after 200 cycles, high C‐rate performance, and longer cycle life.

The thermally activated deformation behaviour of single-crystalline microcast aluminium wires

A microcasting process is used to produce high aspect ratio (>30) monocrystalline pure aluminium wires with a diameter between 14 and 115 µm. The role of thermal activation in the plastic deformation of these microwires is measured by means of (single) tensile stress relaxation tests. The microwires deform largely in an intermittent fashion, i.e., through repeated sudden displacement bursts, also during stress relaxation, implying that the bursts can be triggered through thermal activation. By separating the intermittent and the continuous parts of the stress relaxation load vs. time signal, we measure an activation area characteristic of the continuous relaxation mechanism. Haasen plots of the continuous relaxation data suggest the presence of a back-stress on the order of 2.5 MPa, which can be attributed to the thin layer of oxide covering the metal. Smaller (14–25 µm) diameter crystals oriented for single slip show highly scattered activation area values and a steeper rate of increase of data in the Haasen plot than all other samples, which conform, save for the back-stress, with what is observed in bulk aluminium. Present findings are consistent with data from commensurate aluminium crystals in replicated microcellular structures. Data of this work show that, in single slip within aluminium crystals, the coupling between the activation area and the flow stress is altered when crystals are below 30 µm in diameter. The absence of a systematic difference in data between samples produced of 4N or 5N aluminium suggests that this conclusion is characteristic of the pure metal.

Micromachined ceramic-based chipless LC resonator for high-temperature wireless sensing applications in harsh environments

The primary objective of this work was the fabrication and testing of a wireless LC resonator based on micro-patterned electroceramic materials for the monitoring of high-temperature systems. The two-dimensional planar LC resonator sensors were designed and simulated using ANSYS Maxwell software, and these sensors were then fabricated from electrically conductive La2NiO4/Al2O3 particulate inks. Initially, the phases of La2NiO4/Al2O3 composite were evaluated by XRD. The patterning and deposition of the ink were completed using a novel micro-casting process onto Al2O3 ceramic substrates, and the final pattern was bonded onto the substrate at 1200 °C for 2 h. The features and the reliability were analyzed by SEM microscopy. The frequency shift with respect to temperature was measured, which is directly related to changes in the sensor’s dielectric permittivity and pattern dimensions. The sensors were characterized at 500 °C–1000 °C in an ambient atmosphere with an RF signal ranging from 10–80 MHz at 175 kHz·s−1 sweep rate. The sensors showed a sensitivity of ∼350 kHz °C−1 from 500 °C–1000 °C. A new robust and adaptive signal processing approach was introduced to increase the degree of freedom for analyzing wireless sensors.

Architecture of high-strength aluminum\u2013matrix composites processed by a novel microcasting technique

As important lightweight structural materials, cast aluminum alloys have been largely used in the transportation and aerospace industries. In general, Al–Si-based alloys comprise more than 90% of all castings due to their excellent castability and corrosion resistance. However, even though various reinforcements have been introduced, the strength of these alloys is not that high, which severely limits their use for certain high-performance applications. Here, we report on a new strategy and technology to reinforce Al–Si alloys to increase their yield strength into the ~400–660 MPa range, a level that is 29–113% higher than that of all current cast Al–Si alloys, laboratory or commercial, and comparable to that of many high-strength steels but with ~40% lower density. By introducing continuous Ti–6Al–4V reinforcements into the Al–Si matrix through a novel microcasting process, the yield strength of the resulting alloy can be enhanced to between 4 and 6 times higher than that of the pure Al–Si alloy. The extraordinary reinforcing effect originates from the occurrence of multiscale strengthening mechanisms, including macroscale compound strengthening (the rule of mixtures amended by crack arrest mechanism), mesoscale strain-gradient strengthening, and microscale interface-affected-zone and nanoparticle strengthening. The core principle of our material design is to make all components of the composite fully participate in plastic (compatible) deformation, and thus, continuous reinforcements, instead of discrete reinforced structures (e.g., particles, whiskers, and short fibers), were introduced into the Al–Si alloy. Combined with 3-D printing technology, the present microcasting process can realize strengthening at the designed position by architecting specific reinforcements in the matrix.

Embedded Ceramic-Based Passive Wireless Sensors for Harsh-Environment Applications

Recent advancements in high temperature systems such as gasifiers, molten slag furnaces, super-heated steam turbines, and energy harvesting systems require in-situ temperature monitoring. Conventional temperature sensors such as thermocouples, thermistors, and resistance temperature devices (RTDs) are limited to such applications due to poor reliability. Additionally, these sensors require one end of the device to be maintained in a relatively cold junction which limits the integration with the sophisticated modern high temperature systems. To mitigate these issues, research has been focused on adapting wireless technology for measuring temperature in harsh environments where a conventional temperature sensor cannot be integrated with the system. Initially, research was focused heavily on fiber optics sensor systems, surface acoustic wave (SAW) sensors, laser interferometers, and infra-red sensors. However, these sensor systems have limited lifespan, poor reliability due to reactions taking place at the hot junction, and integration of the sensor with the high temperature system is challenging due to sophisticated design of the furnaces, gasifiers, or turbine blades. In order to mitigate these issues, research has been focused on adapting radio-frequency (RF) technology for high temperature systems. The objective of this work was to design and fabricate inductor-capacitor (LC) resonator based wireless sensors to monitor temperature systems above 500oC.The two-dimensional (planar) LC resonator sensors were designed using the ANSYS Maxwell simulation package. The inductor design was based upon a fifteen-turn coil. The coil geometry was based on a width of 0.15 mm and a spacing of 0.15 mm spacing between the turns. The outer diameter was ~20 mm and the inner diameter was near ~10 mm. The capacitor was based on an interdigitated capacitor (IDC) which could be easily printed onto a ceramic substrate, which would act as the dielectric. The common substrate used in this work was alumina (Al2O3) or yttrium-stabilized zirconia (YSZ). The LC circuit patterns were printed onto alumina or zirconia substrates using inks containing semi-conducting ceramic particles. A few different semi-conducting ceramic compositions were evaluated in this work. One example composition was the La2NiO4 (LN) composition, which displays relatively good high-temperature stability and high electrical conductivity in the range from >40 S/cm at temperatures above 450⁰C. The ceramic powder compositions were synthesized using a conventional solid-state reaction route by mixed the stoichiometric constituents by attrition-milling using zirconia media in ethanol. The resultant slurry was dried and calcined >1000°C for 4 h. X-ray diffraction (XRD) analysis was performed using Panalytical X-ray diffractometer to confirm single phase formation. The circuit patterns were fabricated by using a micro-casting process. Conventional photolithography was used to pattern the photoresist onto the ceramic substrates. The patterned photoresist acted as the molds to deposit the ceramic inks to form the desired LC patterns. The micro-casted patterns were dried and then fired in a muffle furnace to ~1200oC to densify the patterns and bond them to the ceramic substrates. During the firing process, the photoresist would be removed in situ through a basic pyrolysis mechanism. For initial testing in this work, platinum (Pt) interconnects connected to the contact pads were made using Pt ink and further connected to Pt wires to connect to the electrical analysis equipment. Figure 1 shows a magnified optical microscopy picture of a section of the inductor pattern, which shows the level of resolution of the ceramic pattern. The sensors were tested within a high temperature muffle furnace in air. Initial tests used matching sensors placed parallel to each other within the furnace. One sensor was attached using the Pt wires to a signal generator (HP E4433B, USA) to act as the interrogator. The second sensor was hard-wired to a signal analyzer (Tektronix RSA306B, USA). The sensors were characterized at 500 – 1000oC in an ambient atmosphere with an RF signal ranging from 10 – 80 MHz at 2 MHz/sec sweep rate. The sensors showed a sensitivity of 0.2 kHz/oC. Two signal processing methods were implemented in algorithm form (within MATLAB) to estimate the temperature given the frequency response of the sensor. The methods evaluated were the cross-correlation and minimization of absolute error methods. In addition to these two signal processing methods, a split window technique for analyzing the temperature/frequency correlation was used. The cross-correlation signal processing method showed the best fitting for the initial sensor testing. The first set of sensors based on the LN compositions demonstrated sensitivities ~0.2 kHz/oC up to 1000°C. The work will further discuss the results from all sensor compositions and geometries. In addition, the investigation of cyclic stability and repeatability analysis will also be discussed in the presentation. Figure 1

Desarrollo de un revestimiento de chamota/yeso para microfundición de joyería con esmeraldas preengastadas

Durante el proceso de microfundición de joyería con preengaste de gemas, el molde cerámico compuesto de sílice y yeso se estabiliza a temperaturas cercanas a 650 °C, mientras que la temperatura de vertido de la aleación preciosa ronda los 1000 °C. Por tal motivo, este método no es apropiado para gemas como la esmeralda, dada la gran susceptibilidad de esta al daño cuando se expone a temperaturas superiores a 350 °C. Teniendo en cuenta lo anterior, el objetivo del presente trabajo fue desarrollar un revestimiento cerámico de chamota-yeso que adquiera estabilidad dimensional a bajas temperaturas, con el fin de implementar el método de preengaste de esmeraldas para la obtención de piezas de joyería.La metodología experimental se dividió en tres etapas: i) caracterización química, mineralógica, granulométrica y térmica de las materias primas; ii) preparación y caracterización de las mezclas chamota-yeso-agua, incluyendo tiempos de vertido y fraguado de las pastas, junto a la permeabilidad y resistencia a la compresión y al choque térmico, y. además, análisis microestructural, y iii) evaluación del nuevo revestimiento en el proceso de microfundición con preengaste de esmeraldas. Se encontró que las condiciones más adecuadas para obtener el revestimiento chamota/yeso son: granulometría fina del refractario (100 % con pasante malla 200), relación chamota/yeso 75/25 y adición de 50 % de agua a la mezcla seca.Los resultados de la investigación permiten concluir que es posible someter las esmeraldas al proceso de microfundición de joyería, con gemas preengastadas, empleando el revestimiento chamota-yeso desarrollado aquí, cuyo tratamiento térmico no supera los 350 °C, así como una aleación de metal precioso de bajo punto de fusión (398 °C).

Influence of Wettability on Fluidity in Micro-Casting Process

Influence of Wettability on Fluidity in Micro-Casting Process

Fabrication and Testing of High-Temperature Nano-Derived Resistive-Type Microsensors for Hydrogen Sensing

Research has shown that chemical resistive-type sensors that utilize semiconducting nanoparticulates display relatively higher sensitivities and response rates over thin film sensors. Unfortunately, the ability to incorporate nanoparticulate semiconductors into a micro-platform, while maintaining the desired morphology, particle size, and composition, is challenging. In addition, there are few examples of microsensors utilizing nanomaterials for gas sensing at high-temperature (>500°C). In this work, two refractory nanomaterial compositions, 10 vol% SnO2/90 vol% Gd1.8Y0.2Zr2O7 and Gd1.6Sm0.4Zr1.9Sn0.1O7, were deposited by a microcasting process to a thickness of ∼100 μm over DC-sputtered (and patterned) Zr + Pt composite electrodes. The interdigitated electrodes (IDEs) were shown to be stable up to 1200°C for at least 15 h. The 10% SnO2/90% Gd1.8Y0.2Zr2O7 microsensor showed a 9.7% and 4.7% sensitivity at 600 and 1000°C, respectively, to 4000 ppm of H2 in N2 (with a 20% O2). A nano-SnO2 microsensor had sensitivities of 81.2% and 1.0% at 600 and 1000°C to 4000 ppm H2 in 20% O2/N2. The response time for the microsensor at 600°C showed a 63% greater sensitivity to 4000 ppm H2 in N2 compared to a traditional screenprinted sensor platform. The microsensor had 20 times the sensitivity compared to the screenprinted when tested in the same atmosphere.

Fabrication of x-ray absorption gratings via micro-casting for grating-based phase contrast imaging

Grating-based x-ray differential phase contrast (DPC) imaging has shown huge potential. For broad applications, it is essential that the key components are low-cost, especially the absorption gratings. We therefore proposed and developed a micro-casting process for fabricating x-ray absorption gratings with bismuth. This process is feasible for mass production at low cost, with a large format, and a high aspect ratio. To develop this kind of absorption grating, an array with deep trenches was fabricated by photo-assisted electrochemical etching in a silicon wafer. The trenches were then filled with bubble-free, molten bismuth via capillary action and surface tension. Bismuth was attractive as a filling material because of its great mass absorption coefficient, low cost and broad environmental compatibility. Furthermore, our micro-casting process provided bismuth absorption gratings with a clean surface and no need for post treatment. To test their performance in x-ray DPC imaging, two bismuth absorption gratings, one as a periodic source and another as the analyzer, were used with periods of 42 and 3 µm and depths of 110 and 150 µm, respectively. The acquired phase-contrast images demonstrated that the micro-casting process produces qualified gratings for x-ray DPC imaging.

A microcasted PDMS vacuum pad and its application for stacking thin ceramic layers

A PDMS vacuum pad for stacking very thin green sheets with a 3 µm thick dielectric layer is introduced and fabricated. Its applicability for producing multi-layer ceramic capacitors (MLCCs) is evaluated. Five micro-holes with a diameter and depth of 70 µm are formed on a single vacuum-line unit that is of 120 µm width, 100 µm depth and 2 mm length. Each vacuum-line unit with five micro-holes is deployed at 6 mm intervals on a PDMS vacuum pad of size 166 mm × 166 mm. To fabricate the PDMS vacuum pads, a mold with an obverse structure to that of the PDMS vacuum pad is needed. The metal mold has a two-stage nickel microstructure, the first stage for forming the vacuum lines and the second stage for forming the micro-holes. To fabricate the mold, micromachining processes, including photolithography, nickel/copper electroforming and chemical mechanical polishing, were conducted twice on a precision-machined SUS substrate with a size of 210 mm × 210 mm. The PDMS vacuum pads were fabricated through a microcasting process. Using the PDMS vacuum pad, 320 layers of green sheets, upon which nickel electrodes were patterned on 3 µm thick dielectric layers, were consecutively stacked. It has been observed that the stacked green sheets were very flat and uniform without any distortion or wrinkles. It is believed that the uniform stacking will greatly help to improve the production yield as well as enhance the reliability of MLCCs.

On the relationship between microcasting process, material states and mechanical properties in the gold alloy Stabilor ® G

The present study reports on the microstructural state and mechanical properties of cast micro-components made from the commercial Au-alloy; Stabilor ® G. Microscopy methods such as optical light-, scanning- and transmission-electron microscopy were used to obtain a variety of microstructural properties from the micro-specimens. The mechanical properties of the cast micro-specimens were determined by tensile testing on a universal micro-testing device. These properties obtained for Stabilor ® G micro-specimens were found to depend on the casting method and thermal condition applied during and after the production process. The microstructure and mechanical attributes of the specimens were used to develop a model which makes it possible to predict the yield stress of the cast specimens from only the structural properties namely grain size and precipitate particle size. The individual influences of the strengthening factors in the specimens, such as grain boundary and precipitates, were determined.

Fabrication of curved copper micromesh sheets using flexible PDMS molds

A unique fabrication method for a curved copper micromesh is proposed and demonstrated. A PDMS mold was fabricated using a microcasting process and then used as a flexible mold in copper electroplating. The fabricated copper micromesh was well formed and connected without any cracks within the entire mold area. The experimental results verified that the fabricated features of the copper micromesh accurately followed the shape of the microstructures and the curvature of the PDMS mold. This unique fabrication method provides an alternative means to produce curved or three-dimensional metal microstructures.

PDMS 유연 몰드를 이용한 구리 마이크로 메쉬 시트의 제작

A unique fabrication method for a copper micromesh is proposed and demonstrated. A PDMS mold was fabricated using a microcasting process and then used as a flexible mold in copper electroplating. The fabricated copper micromesh was well formed and connected without any cracks within the entire mold area. The experimental results verified that the fabricated features of the copper micromesh accurately followed the shape of the microstructures of the PDMS mold. This unique fabrication method provides an easy yet precise means of producing three-dimensional metal microstructures.

Replication techniques for a metal microcomponent having real 3D shape by microcasting process

In this paper, new replication techniques for a metal microcomponent having a real 3D shape were introduced. A helical gear was selected as one of a real 3D microcomponents for this study. The helical gear, which was made of photo-curable resin, was fabricated as a master pattern by microstereolithography (MSL) technology. Then, a silicone rubber mold was fabricated from the master pattern. Lastly, a final bismuth alloy pattern was transferred from the silicone rubber mold by the microcasting process. In this paper, the replication technique is described in detail from the master pattern to the final pattern with some investigation on factors related to the technique.

Fabrication of Ceramic Microstructures via Microcasting of Nanoparticulate Slurry

Fabrication of microstructures has been the subject of considerable attention in recent years. Techniques such as surface silicon micromachining and bulk silicon etch have emerged as practical methods for thin microstructures and processes such as LIGA (an acronym for the German words for lithography, electrodeposition, and molding) are being used to produce high aspect ratio structures from a limited set of electroformable metals and polymers. As microsystem technologies and application prospects continue to grow, it is of interest and much practical value to expand the material choices for LIGA‐scale microstructures to ceramics and a broader class of metals. To this end, this paper investigates a new technique for the fabrication of high aspect ratio ceramic or metal microparts. This technique is based on capillary‐driven microcasting and curing of an epoxy‐based metallic or ceramic nanoparticulate slurry into a sacrificial plastic mold produced by microinjection molding. The cured preform is subsequently heated to remove the organic phase and to sinter the particulate ceramic or metallic phase. The fabrication process is discussed in the paper along with illustration of example microparts produced using the process. A theoretical model of the fluid flow during the microcasting process is developed and validated with experimental data from the fabrication of rectangular rib sections.

Replication of LIGA structures using microcasting

Microcasting with a gold base alloy and an Al-bronze as a replication technique for LIGA structures is shown. A LIGA mold insert for injection molding is used to produce PMMA patterns as lost wax models in the microcasting process. Although there are several steps of replication the accuracy of the process is high and allows the fast manufacturing of middle size batches of microstructured parts. The mechanical properties can be varied within a wide range by choosing different casting alloys or cooling rates. Additionally the influence of the investment on the surface roughness is presented as well as results of flowlength tests showing maximal achievable aspect ratios with the gold base alloy and the Al-bronze.

Bi-Sn 합금을 이용한 3차원 미세 구조물의 제작기술 개발

In this paper, new replication techniques for a metal microcomponent having a real 3D shape were introduced. Helical gear was selected as one of a real 3D microcomponents for this study. The helical gear, which was made of photo-curable resin, was fabricated as a master pattern by microstereolithography technology. Then, a silicone rubber mold was fabricated from the master pattern. Lastly, a final bismuth alloy pattern was transferred from the silicone rubber mold by the microcasting process. In this paper, the replication technique is described in detail from the master pattern to the final pattern with some investigation on factors related to the technique.

Shape memory polymer nanocomposites

The paper describes the fabrication and characterization of composites with a shape memory polymer matrix and SiC nanoparticulate reinforcements. Composites based on a SMP matrix are active materials capable of recovering relatively large mechanical strains due to the application of heat. The composites were synthesized from a commercial shape memory polymer resin system and particulate SiC with an average diameter of 300 nm. Composites with weight fractions of 10%, 20%, 30%, and 40% nanoparticulate SiC were fabricated by casting samples with sizes ranging from a few hundred microns to several millimeters. The former size scale is consistent with a microcasting process for manufacturing microelectomechanical systems. The micro-hardness and elastic modulus of the nanocomposites increased by approximately a factor of 3 with the addition of 40 wt% SiC into the base resin. Unconstrained strain recoverability of the nanocomposites was found to depend on the fraction of SiC. For 180° bend tests, the recoverability of the nanocomposites was perfect for SiC weight fractions below 40%. For 40 wt% SiC, permanent bend strains were discovered. Constrained bending recovery force in the nanocomposites was shown to increase by 50% with the addition of 20 wt% SiC.

Shape Deposition Manufacturing With Microcasting: Processing, Thermal and Mechanical Issues

Shape deposition manufacturing (SDM) is a solid freeform fabrication (SFF) methodology for automatically building up material layers to form three-dimensional, complex-shaped, multi-material structures. Microcasting is a molten metal droplet deposition process which is able to create fully dense metal layers with controlled microstructures. SDM combines microcasting with other intermediate processing operations, such as CNC machining and shot peening, to create high quality metal parts. In this paper, a description is given of SDM and the microcasting process. An overview of thermal and mechanical issues associated with SDM and microcasting is presented, including the control of interlayer metallurgical bonding through substrate remelting, the control of cooling rates of both the substrate and the deposited material and the minimization of residual thermal stress effects. Thermal models are used to study the issue of localized remelting of previously deposited material by newly deposited molten droplets to achieve metallurgical bonding. Mechanical modeling provides insight into residual stress build-up during part manufacture and residual stress-driven debonding between deposited layers.