Electrospun Nickel Manganite (NiMn2O4) Nanocrystalline Fibers for Humidity and Temperature Sensing

Abstract

Nickel manganite nanocrystalline fibers were obtained by electrospinning and subsequent calcination at 400 °C. As-spun fibers were characterized by TG/DTA, Scanning Electron Microscopy and FT-IR spectroscopy analysis. X-ray diffraction and FT-IR spectroscopy analysis confirmed the formation of nickel manganite with a cubic spinel structure, while N2 physisorption at 77 K enabled determination of the BET specific surface area as 25.3 m2/g and (BJH) mesopore volume as 21.5 m2/g. The material constant (B) of the nanocrystalline nickel manganite fibers applied by drop-casting on test interdigitated electrodes on alumina substrate, dried at room temperature, was determined as 4379 K in the 20–50 °C temperature range and a temperature sensitivity of −4.95%/K at room temperature (25 °C). The change of impedance with relative humidity was monitored at 25 and 50 °C for a relative humidity (RH) change of 40 to 90% in the 42 Hzπ1 MHz frequency range. At 100 Hz and 25 °C, the sensitivity of 327.36 ± 80.12 kΩ/%RH was determined, showing that nickel manganite obtained by electrospinning has potential as a multifunctional material for combined humidity and temperature sensing.

Nickel Manganite-Sodium Alginate Nano-Biocomposite for Temperature Sensing

“…This value was slightly lower than for the pure powder obtained by sol-gel combustion (−5.4%/K [33]), slightly higher than for NiMn 2 O 4 electrospun nanofibers (−4.95%/K [46]), comparable with commercial devices [1] and within the range previously determined for as-deposited and annealed NiMn 2 O 4 thick films obtained by aerosol deposition [7,47].…”

“…The measured resistance for the nano-biocomposite film was overall lower, on average by three orders of magnitude, than the values previously obtained for the powder (≈31 to 7 MΩ in the temperature range of 20-50 °C [33], also at RH 50%), ranging from ≈39 kΩ for 20 °C to ≈10 kΩ for 50 °C at a relative humidity (RH) of 50%, reflecting the influence of the alginate component, as shown in the inset in Figure 7. The material constant (B-value) estimated from the linear fit shown in Figure 7 as 4523 K was slightly lower than the value determined for the pure powder, but well within the range of commercial spinel based NTCR ceramics [1] and slightly higher than the value of 4379 K obtained for electrospun NiMn2O4 powder [46]. The temperature sensitivity at room temperature (25 °C) was determined to be −5.09%/K by differentiation of equation (1) into:…”

“…The resistance decreased with increase in relative humidity from ≈104 kΩ at RH 40% to ≈0.6 kΩ at RH 90%. NiMn2O4 has previously been shown to be a potential humidity-sensing material [46,53]. The time delay between adsorption (condensation) and desorption (evaporation) was low (1.5%) with the curves almost overlapping, as shown in Figure 10a, indicating that the sensing material displayed a good hysteresis curve [34].…”

“…In the lower humidity range (40-60%) the grain effect was dominant, with this semicircle gradually decreasing and becoming less dominant as the RH increased. For lower RH water molecules were first only chemisorbed on the surface, followed by physisorption, and with further increase in RH forming multiple physisorbed layers, resulting in proton hopping between water molecules [46], reduced resistance and impedance values and, in this case, increased dominance of the grain boundary and electrode effects. Increased capacitive behavior at the interface between the electrode and sensor material at high RH is due to diffusion and polarization of charged species [53].…”

Extended Positron–Positronium Trapping Defects in the MgAl2O4 Spinel Ceramics

“…Among the significant number of porous ceramic materials, which are widely used for the manufacture of active elements of humidity sensors, dielectric spinel types are considered as one of the most promising. [1][2][3] The crystallographic structure of this spinel creates a real possibility of isotropic grain growth, formation of grain boundaries in ceramics, and, consequently, a more uniform surface distribution of humidity-absorbing pores. The MgAl 2 O 4 ceramics are more stable in comparison with other types of porous ceramics.…”