Ceramic–polymer composites are of interest for designing enhanced and unique properties. However, the processing temperature windows of sintering ceramics are much higher than that of compaction, extrusion, or sintering of polymers, and thus traditionally there has been an inability to cosinter ceramic–polymer composites in a single step with high amounts of ceramics. The cold sintering process is a low‐temperature sintering technology recently developed for ceramics and ceramic‐based composites. A wide variety of ceramic materials have now been demonstrated to be densified under the cold sintering process and therefore can be all cosintered with polymers from room temperature to 300 °C. Here, the status, understanding, and application of cold cosintering, with different examples of ceramics and polymers, are discussed. One has to note that these types of cold sintering processes are yet new, and a full understanding will only emerge after more ceramic–polymer examples emerge and different research groups build upon these early observations. The general processing, property designs, and an outlook on cold sintering composites are outlined. Ultimately, the cold sintering process could open up a new multimaterial design space and impact the field of ceramic–polymer composites.
- NSF-PAR ID:
- 10309416
- Date Published:
- Journal Name:
- Actuators
- Volume:
- 10
- Issue:
- 9
- ISSN:
- 2076-0825
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract -
Abstract Ceramics such as lead zirconate titanate (PZT) tend to dissolve incongruently, and thus pose a challenge in the cold sintering process. Moist lead nitrate has previously been shown to enable a cold sinter‐assisted densification of PZT by a viscous phase sintering mechanism. In this paper, lead acetate trihydrate is demonstrated to lower the required temperature of the cold sintering step to 200°C. This densification process was described as a two‐step process: cold sintering of PZT with lead acetate trihydrate and post‐annealing the as‐cold sintered PZT ceramics. Unlike in the case of lead nitrate, PZT densification with lead acetate trihydrate occurs by a liquid phase assisted sintering mechanism, leading to an as‐cold sintered relative density of 84% at 200°C. After performing a post‐anneal step at 900°C, >97% relative densities were achieved in samples that were cold sintered with lead acetate trihydrate. This step not only densified PZT but also refined the grain boundaries. In the post‐annealed samples, the room‐temperature relative permittivity at 100 Hz was ~1600, slightly higher than that reported in samples that used lead nitrate as a sintering aid; the loss tangent was about 3.8%. For measurements at 10 Hz, the remanent polarization in both cases was ~28 µC/cm2. Both Rayleigh analysis and aging studies showed that a higher irreversible contribution to the permittivity exists in samples that used lead nitrate as a cold sintering aid.
-
Robotic prostheses and powered exoskeletons are novel assistive robotic devices for modern medicine. Muscle activity sensing plays an important role in controlling assistive robotics devices. Most devices measure the surface electromyography (sEMG) signal for myoelectric control. However, sEMG is an integrated signal from muscle activities. It is difficult to sense muscle movements in specific small regions, particularly at different depths. Alternatively, traditional ultrasound imaging has recently been proposed to monitor muscle activity due to its ability to directly visualize superficial and at-depth muscles. Despite their advantages, traditional ultrasound probes lack wearability. In this paper, a wearable ultrasound (US) transducer, based on lead zirconate titanate (PZT) and a polyimide substrate, was developed for a muscle activity sensing demonstration. The fabricated PZT-5A elements were arranged into a 4 × 4 array and then packaged in polydimethylsiloxane (PDMS). In vitro porcine tissue experiments were carried out by generating the muscle activities artificially, and the muscle movements were detected by the proposed wearable US transducer via muscle movement imaging. Experimental results showed that all 16 elements had very similar acoustic behaviors: the averaged central frequency, −6 dB bandwidth, and electrical impedance in water were 10.59 MHz, 37.69%, and 78.41 Ω, respectively. The in vitro study successfully demonstrated the capability of monitoring local muscle activity using the prototyped wearable transducer. The findings indicate that ultrasonic sensing may be an alternative to standardize myoelectric control for assistive robotics applications.more » « less
-
The cold sintering process (CSP) is a low-temperature consolidation method used to fabricate materials and their composites by applying transient solvents and external pressure. In this mechano-chemical process, the local dissolution, solvent evaporation, and supersaturation of the solute lead to “solution-precipitation” for consolidating various materials to nearly full densification, mimicking the natural pressure solution creep. Because of the low processing temperature (<300°C), it can bridge the temperature gap between ceramics, metals, and polymers for co-sintering composites. Therefore, CSP provides a promising strategy of interface engineering to readily integrate high-processing temperature ceramic materials (e.g., active electrode materials, ceramic solid-state electrolytes) as “grains” and low-melting-point additives (e.g., polymer binders, lithium salts, or solid-state polymer electrolytes) as “grain boundaries.” In this minireview, the mechanisms of geomimetics CSP and energy dissipations are discussed and compared to other sintering technologies. Specifically, the sintering dynamics and various sintering aids/conditions methods are reviewed to assist the low energy consumption processes. We also discuss the CSP-enabled consolidation and interface engineering for composite electrodes, composite solid-state electrolytes, and multi-component laminated structure battery devices for high-performance solid-state batteries. We then conclude the present review with a perspective on future opportunities and challenges.more » « less
-
This paper reports a new 2D surface-micromachined optical ultrasound transducer (SMOUT) array consisting of 350 × 350 elements with highly uniform optical and acoustic performances. Each SMOUT element consists of a vacuum-sealed Fabry-Perot (F-P) interferometric cavity formed by two parallel partially reflective distributed Bragg reflectors (DBRs). Optical mapping in the 4 cm × 4 cm center region of the SMOUT array shows that the optical resonance wavelength (ORW) of > 94% of the elements falls within a narrow range of ≤ 10 nm. The center frequency, acoustic bandwidth and noise equivalent pressure (NEP) of the elements are determined to be 5 MHz, 5 MHz, and 20.7 Pa (with 16 times of signal averaging) or 172.5 Pa (without averaging) over a bandwidth of 10 MHz, respectively. The temperature and temporal stability of the SMOUT elements is also tested, which shows there is little variation in their ORW under large ambient temperature fluctuation and during continuous water immersion. To demonstrate its imaging capability, 2D and 3D PACT based on the SMOUT array is also conducted within a 3 cm × 3 cm field of view (FOV) at a depth of 3cm with no interrogation wavelength tuning. These results show that the SMOUT array could overcome some of the major limitations in existing ultrasound transducer arrays for PACT and provide a promising solution for achieving high-speed 3D imaging.