Ceramic-based humidity sensitive material with liquid polymeric delivery vehicle
Inventors
Rolin, Terry D. • Sherrard, Cameroun Grace • Small, Ian Kent
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-12110407-B1
Publication Date
2024-10-08
Expiration Date
2042-11-28
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Abstract
A humidity sensitive material includes a lanthanum-doped barium titanate (BaTiO3) co-doped with an alkali hydroxide. A polymeric liquid binder is used as a vehicle to deliver the humidity sensitive material to a substrate or electrode via a 3D-printing process. The humidity sensitive material is highly sensitive to changes in humidity and exhibits rapid and large changes in capacitance and impedance for just a relatively small change in humidity. The humidity sensitive material exhibits significantly large changes in impedance and capacitance over the entire 10-90% RH range. As a result of the high sensitivity of the humidity sensitive material, the log-linear response is significantly easier to calibrate in humidity sensing devices that use the humidity sensitive material.
Core Innovation
The invention describes a ceramic-based humidity sensitive material comprising lanthanum-doped barium titanate (BaTiO3) co-doped with an alkali hydroxide and delivered via a polymeric liquid binder that enables printing onto substrates or electrodes through a 3D-printing process. This material is characterized by high sensitivity to humidity changes, exhibiting rapid and large changes in capacitance and impedance over a relative humidity (RH) range of 10-90%. The log-linear response of the material facilitates easier calibration in humidity sensing devices incorporating this material.
The problem addressed by the invention is the complexity and cumbersome nature of conventional methods for forming ceramic-based dielectric humidity sensitive materials. Typically, these methods require multiple extensive steps including high-temperature sintering (1000-1300° C.), mixing with additional components to create printable mixtures, screen printing, and extensive multi-stage thermal processing to remove binders and solvents. These steps are time-consuming and inhibit mass production. The invention seeks to eliminate inconvenient firing stages and allow for simple curing at low or room temperatures, laser curing, ultraviolet (UV) curing, or combinations thereof, to enable simpler and more scalable manufacture of humidity sensing materials.
Claims Coverage
The patent includes four independent claims that cover methods related to producing humidity sensitive materials and manufacturing humidity sensors. The main inventive features focus on the composition of materials, processing steps, and integration techniques to achieve the humidity sensitivity and printable forms.
Material composition and preparation
Providing particles of barium oxide, titanium dioxide, and lanthanum hydroxide with average grain diameters in a specified nanoscale range and mixing them in defined weight percentages to form a particle mixture that is then sintered in a nitrogen atmosphere to form a sintered mixture.
Formation of composite dielectric material
Milling the sintered mixture to specified particle sizes, mixing the milled particles with an alkali hydroxide co-dopant in precise proportions, then milling and heating this composite dielectric powder in a nitrogen atmosphere below specified temperatures, followed by cooling.
Formation and deposition of homogeneous liquid mixture
Mixing a defined weight percent of the composite dielectric powder with a liquid polymeric binder to produce a homogeneous liquid mixture, which is then deposited onto a substrate by printing techniques such as 3D printing, and followed by processing (curing) to remove liquid portions.
Curing and processing techniques
Processing the deposited material on the substrate using room temperature curing, heating below 110° C., ultraviolet (UV) curing, laser curing, or combinations thereof to solidify the humidity sensitive material for use in sensors.
Manufacturing humidity sensors with electrodes
Providing electrodes on a substrate, printing the homogeneous liquid mixture onto a first electrode, curing to remove liquids, and then providing a second electrode on the cured layer to form humidity sensors with defined layer thicknesses.
The claims collectively cover a process for creating a humidity sensitive ceramic material doped and co-doped with specific components, processed in controlled conditions, combined with polymeric binders to form printable inks, deposited and cured using low-temperature techniques, and integrated into sensor devices with electrodes.
Stated Advantages
The humidity sensitive material exhibits rapid and large changes in capacitance and impedance for relatively small humidity changes, enabling fast and sensitive detection.
The material maintains large changes in impedance and capacitance across a broad 10-90% relative humidity range, ensuring wide applicability.
The log-linear response of the material simplifies calibration processes in humidity sensing devices.
The manufacturing method eliminates cumbersome and time-consuming high-temperature firing steps, allowing curing at low temperatures using room-temperature thermal curing, laser curing, ultraviolet curing, or combinations thereof.
The printable form via a polymeric liquid binder allows manufacturing by 3D printing, facilitating scalable and precise deposition.
Sensors made with thin layers of the material have low mass and small environmental footprints, making them suitable for sensitive and space-constrained applications.
Documented Applications
Use in humidity sensors with resistor-type (impedance-based) configurations.
Use in humidity sensors with capacitor-type (capacitance-based) configurations.
Applications requiring fast detection of volatile vapors in critical environments, such as the International Space Station and other manned spacecraft.
Use in space suits, sensitive hygrometers, electronic weather stations, aerospace vehicles, and other applications requiring fast and sensitive response to humidity changes.
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