High Relative Humidity Range Research Articles

Cation-oxygen dual-defective ACu3Ti4O12 (A = Sr, Ba) perovskites enable high-performance humidity sensors for human-body related moisture monitoring

ACu3Ti4O12 (A = Sr, Ba) double perovskites are attractive dielectric materials, yet they have not been reported in the field of gas and humidity sensors. In this work, SrCu3Ti4O12 (SCTO) and BaCu3Ti4O12 (BCTO) powders were synthesized by a facile modified solid-phase sintering method with characteristic of abundant cation-oxygen dual-defects (oxygen vacancy, metal deficiencies of Cu+ and Ti3+). For the first time, SCTO and BCTO are explored as humidity sensing materials, while the SCTO sensor holds a response value of four orders of magnitude (Sr = 2.8× 104), which is over a thousand times higher than that of BCTO (Sr = 25). In addition, the SCTO sensor is featured in fast response (7 s), reliable linearity (R2 = 0.97), small hysteresis (ΔHmax = 0.8%) and good repeatability in a wide relative humidity (RH) range (11%–97%). The boosted humidity sensing performance enables the SCTO sensor to possess great potential in human-body related moisture monitoring of breath and finger detection. Finally, the complex impedance analysis reveals different majority carriers of SCTO (H+) and BCTO (H3O+) under high RH range. The enhanced humidity sensing performance of SCTO can be attributed to the synergistic effects of richer dual-defects and larger ion potential. This work provides an excellent humidity sensing material of SCTO, and furthermore, gives new insights on defect sensitization strategy of perovskites for high-performance electronic sensory devices.

A Highly Responsive Graphene Oxide Humidity Sensor Based on PVA Nanofibers.

Graphene oxide (GO) humidity sensors based on poly(vinyl alcohol) (PVA) nanofibers have been proposed. The PVA nanofiber layers of different densities were obtained by adjusting the electrospinning time. Then, GO films were deposited on PVA nanofibers by a spin-coating method. The electrical properties of GO films are improved due to the increased distribution of PVA nanofibers in the GO films. The humidity sensors exhibit good sensitivity under a high relative humidity range of 40-80%. The response of sensors has reached 98.44% at a humidity level of 80% RH. The GO/PVA sensors have good stability at various humidity levels for 1 week. Furthermore, the GO/PVA sensors were used for respiration monitoring under different statuses. These sensors have good application prospects in the respiratory detection and analysis of diseases.

Comparison of shrinkage and mass change of hardened cement paste under gradual drying and rapid drying

To identify the impact of drying rate on mechanisms of drying shrinkage, two hardened cement paste (hcp) samples were prepared. Mature samples were dried directly at the target relative humidity (RH), “rapid drying”, or at RH decreasing from 95% step by step till 11%, “gradual drying”. When comparing the relation of mass change versus drying shrinkage, at high RH range over 80%, gradually dried samples showed less mass change for same amount of shrinkage comparing to rapid drying samples. For the range of RH of 80%-40%, the incremental values of both mass change and drying shrinkage were same for two drying methods. The specimens were characterized by XRD, TG-DTA and water vapor sorption isotherms. By combining the results with findings in the literature, we postulated that an additional part of drying shrinkage is activated when dried at high relative humidity for a longer time and we attributed this additional part to gel pores of calcium silicate hydrates.

Isomer-Resolved Reactivity of Organic Peroxides in Monoterpene-Derived Secondary Organic Aerosol.

Organic peroxides play a vital role in the formation, evolution, and health impacts of atmospheric aerosols, yet their molecular composition and fate in the particle phase remain poorly understood. Here, we identified, using iodometry-assisted liquid chromatography mass spectrometry, a large suite of isomer-resolved peroxide monomers (C8-10H12-18O5-8) and dimers (C15-20H22-34O5-14) in secondary organic aerosol formed from ozonolysis of the most abundant monoterpene (α-pinene). Combining aerosol isothermal evaporation experiments and multilayer kinetic modeling, bulk peroxides were found to undergo rapid particle-phase chemical transformation with an average lifetime of several hours under humid conditions, while the individual peroxides decompose on timescales of half an hour to a few days. Meanwhile, the majority of isomeric peroxides exhibit distinct particle-phase behaviors, highlighting the importance of the characterization of isomer-resolved peroxide reactivity. Furthermore, the reactivity of most peroxides increases with aerosol water content faster in a low relative humidity (RH) range than in a high RH range. Such non-uniform water effects imply a more important role of water as a plasticizer than as a reactant in influencing the peroxide reactivity. The high particle-phase reactivity of organic peroxides and its striking dependence on RH should be considered in atmospheric modeling of their fate and impacts on aerosol chemistry and health effects.

Effects of Annealing on the Structural and Optical Properties of V2O5 Thin Films Prepared by RF Sputtering for Humidity Sensor Application

In this work, vanadium pentoxide (V2O5) thin films were prepared using rf magnetron sputtering on silicon wafer and glass substrates from V2O5 target at 200 °C substrate temperature, followed by annealing at 400 and 500 °C in air for 2 h. The prepared thin films were examined by X-ray diffraction (XRD), forier transform infra-red spectroscopy (FTIR), UV-visible absorbance, and direct current coductivity to study the effects of annealing temperature on their structural and optical properties. The XRD analysis exhibited that the annealing promoted the highly crystallized V2O5 phase that is highly orientated along the c direction. The crystalline size increased from 22.5 nm to 35.4 nm with increasing the annealing temperature to 500 °C. The FTIR spectroscopy showed the enhancement of the characteristics band for the V2O5 with increasing annealing temperature to 500 °C. The optical study showed that the energy gap for the sample deposited on glass slides decreased from 2.85 eV, for as deposited sample, to 2.6 eV upon annealing the sample to 500 °C. There was a linear dependence between sensitivity and relative humidity (RH) at the range from 25% to 70%, while the behavior was exponential at high RH range.

In Situ Quantitative Observation of Hygroscopic Growth of Single Nanoparticle Aerosol by Surface Plasmon Resonance Microscopy.

Aerosol particle hygroscopicity is an important factor in visibility reduction, cloud formation, radiation forcing, and the global climate. The high number concentration of nanoparticles (defined as particles with diameters below 100 nm) means that their hygroscopic growth abilities and potential contributions to the climate and environment are significant. Therefore, a rapid and accurate in situ analysis method for single nanoparticle hygroscopic growth in an atmospheric environment is important to characterize the effects of the particle's physical and chemical properties in this process. In this work, surface plasmon resonance microscopy with azimuthal rotation illumination (SPRM-ARI) is used to observe the hygroscopic growth and water content of single nanoparticles in situ. The hygroscopic growth results of a single-component nanoparticle are well matched with the extended aerosol inorganic model (E-AIM) results, and the proposed method remains reliable even when the relative humidity (RH) exceeds 90%. For a bicomponent nanoparticle (with NaCl as the primary content), the presence of a component without deliquescence phase transitions under increasing humidity conditions causes the measured data to differ from both the Zdanovskii-Stokes-Robinson (ZSR) model and E-AIM predictions in the low RH range. However, because of their complete liquefaction, the growth factor (GF) variation of the bicomponent nanoparticle is close to the model predictions in the high RH range. Finally, based on the positive correlation between particle volume and the gray intensity of SPRM-ARI, GF values can be obtained from the cube root of the gray intensity and the actual water content of single nanoparticles can then be derived.

Surface acoustic wave humidity sensor based on three-dimensional architecture graphene/PVA/SiO2 and its application for respiration monitoring

A quartz surface acoustic wave (SAW) delay line humidity sensor based on three-dimensional architecture graphene (3DAG)/polyvinyl alcohol (PVA)/SiO2 layered sensing film have been proposed and applied in respiration monitoring. An amorphous SiO2 nanolayer was deposited on the total surface of the SAW delay line by radio frequency magnetron sputtering method as a protect coating and sensing film. Then, 3DAG grown on Ta substrate using CVD method was in-situ transformed to the delay area of the SAW device using PVA film to construct a humidity sensor. The prepared humidity sensor exhibits high sensitivity especially under high relative humidity range of 55 %–90 % due to the synergetic effects of the viscoelastic effect of the PVA film, the large absorption and transportation effect of 3DAG, and the mass loading effect of the SiO2. The humidity sensor also has short response and recovery times, good stability, repeatability, and selectivity. Furthermore, the developed humidity sensor was used for respiration monitoring and exhibit excellent capability of monitoring different respiration rates and depths. The respiration variations before and after water drinking can also be recognized by the sensor.

Ultra-smooth TiO2 thin film based optical humidity sensor with a fast response and recovery.

An ultra-smooth $\text{TiO}_2$TiO2 thin film based optical humidity sensor was fabricated via a modified dip coating process. The $\text{TiO}_2$TiO2 film possessed a root mean square roughness of ${2.6 \pm 0.3}\;\text{nm}$2.6±0.3nm. Measurement of relative humidity (RH) was performed by modulation in the intensity of laser transmitted at room temperature. The optical humidity sensor based on $\text{TiO}_2$TiO2 film exhibited two-segmented linearity in the whole RH range. The response time and recovery time were determined to be 27 s and 23 s, respectively. To our knowledge, the optical humidity sensor achieved the fastest recovery to date among those modulated in optical power. The fast response and recovery are attributed to the smooth surface of sensing film, which allows the rapid equilibrium between adsorption and desorption of water molecules on the film surface. In addition, this optical humidity sensor possessed an excellent reproducibility and long-term stability after aging. The sensing mechanism is based on the chemisorption of water molecules in the low RH range and formation of water droplets in the high RH range on the surface of ${\text{TiO}_2}$TiO2 film.

Hydric characterisation of rammed earth samples for different lime concentrations

The rehabilitation of ancient rammed earth houses, as well as the use of earthen materials in modern constructions, are a growing matter of concern, especially in area such as Rhône-Alpes, France, where 40% of old constructions are in rammed earth. A current pathology observed for this type of construction is related to the rising damps, for which the water from the ground is absorbed by the wall. This situation leads to a very saturated state. As it has been proven that the compressive strength is altered by the presence of water in the pores, a better understanding on high relative humidity range is necessary to be able to predict the mechanical behavior of buildings and thus ensure a better risk assessment. The present study describes experimental results of the water uptake experiments and moisture storage at high relative humidities.

2D TiO2 nanosheets for ultrasensitive humidity sensing application benefited by abundant surface oxygen vacancy defects

To realize the sensitive and rapid sensing of humidity, 2D as-prepared TiO2 nanosheets (hereafter shorted as TiO2 nanosheets) with characteristics of surface oxygen vacancy defects and large surface area were designed and synthesized. The TiO2 nanosheets-based sensor exhibit superior humidity sensing performance with an ultrahigh sensitivity evidenced by the dramatic impedance variation of more than four orders of magnitude from relative humidity (RH) 11% to 95%, fast response (3 s) and recovery (50 s) process, as well as a small hysteresis (∼4.6%). Additionally, a systematic study of the sensing performances of sensors fabricated from TiO2 nanosheets and two counterparts calcined in N2 and O2 with decreased specific surface area and controlled surface defects, namely TiO2-400 (N2) and TiO2-400 (O2), has been conducted. The results show that at low RH level of 33% and 54%, TiO2-400 (N2) with highest surface oxygen vacancy defects concentration exhibits the highest response of 6.26 and 34, respectively, while at high RH range of 85% to 95%, the TiO2 nanosheets with largest specific surface area shows the highest response which is almost 10 times higher than that of the calcined counterparts. Combining the complex impedance analysis, the overall ultrahigh humidity sensing performance of TiO2 nanosheets-based sensor is attributed to the dissociating promotion by the abundant surface defect and enhanced electrolytic conduction by the large specific surface area.

Risk of Climate‐Induced Damage in Historic Textiles

AbstractEleven wool and silk historic textiles and two modern artist's canvases were examined to determine their water vapour adsorption, moisture dimensional response and tensile behaviour. All the textiles showed a similar general pattern of moisture response. A rise in ambient relative humidity (RH) from dry conditions produced expansion of a textile until a certain critical RH level after which a contraction occurred to a greater or lesser degree depending on the yarn crimp and the weave geometry. The largest expansion recorded between the dry state and 80% RH was 1.2 and 0.9% for wool and silk textiles, respectively. The largest shrinkage of 0.8% at high RH range was experienced by a modern linen canvas. Two potential damage mechanisms related to the moisture response of the textiles—stress building as a result of shrinkage of the textile restrained in its dimensional response and the fretting fatigue when yarns move with friction one against another—were found insignificant in typical textile display environments unless the textiles are severely degraded or excessively strained in their mounting.

Reduced graphene oxide for fiber-optic humidity sensing.

Graphene-based electrical chemical vapor sensors can achieve extremely high sensitivity, whereas the comparatively slow sensing response and recovery, the research focused on only low concentration detection, have been known as drawbacks for many applications requiring rapid and high concentration detection. Here we report a novel graphene-based fiber-optic relative humidity (RH) sensor relying on fundamentally different sensing mechanism. The sensor can achieve power variation of up to 6.9 dB in high relative humidity range (70-95%), and display linear response with correlation coefficient of 98.2%, sensitivity of 0.31 dB/%RH, response speed of faster than 0.13%RH/s, and good repeatability in 75-95%RH. Theoretical analysis of sensing mechanism can explain the experimental result, and reveal the broad applying prospect of the sensor for other kinds of chemical vapor detection. This novel graphene-based optical sensor provides a beneficial complement to the existing electrical ones, and will promote the employment of graphene in chemical sensing techniques.

Prediction of water loss and viscoelastic deformation of apple tissue using a multiscale model

A two-dimensional multiscale water transport and mechanical model was developed to predict the water loss and deformation of apple tissue (Malus × domestica Borkh. cv. ‘Jonagold’) during dehydration. At the macroscopic level, a continuum approach was used to construct a coupled water transport and mechanical model. Water transport in the tissue was simulated using a phenomenological approach using Fick’s second law of diffusion. Mechanical deformation due to shrinkage was based on a structural mechanics model consisting of two parts: Yeoh strain energy functions to account for non-linearity and Maxwell’s rheological model of visco-elasticity. Apparent parameters of the macroscale model were computed from a microscale model. The latter accounted for water exchange between different microscopic structures of the tissue (intercellular space, the cell wall network and cytoplasm) using transport laws with the water potential as the driving force for water exchange between different compartments of tissue. The microscale deformation mechanics were computed using a model where the cells were represented as a closed thin walled structure. The predicted apparent water transport properties of apple cortex tissue from the microscale model showed good agreement with the experimentally measured values. Deviations between calculated and measured mechanical properties of apple tissue were observed at strains larger than 3%, and were attributed to differences in water transport behavior between the experimental compression tests and the simulated dehydration-deformation behavior. Tissue dehydration and deformation in the high relative humidity range ( > 97% RH) could, however, be accurately predicted by the multiscale model. The multiscale model helped to understand the dynamics of the dehydration process and the importance of the different microstructural compartments (intercellular space, cell wall, membrane and cytoplasm) for water transport and mechanical deformation.

Graphene/LiNbO3 surface acoustic wave device based relative humidity sensor

This study described relative humidity (RH) sensing using a graphene/128° YX LiNbO3 surface acoustic wave (SAW) device. The resonant frequency of the device decreased in a two-stage manner as the RH increased. For a low RH range (RH<50%), a frequency downshift of 1.38kHz per 1% RH change was observed. This was attributed to mass loading of the SAW propagation surface due to the adsorption of water molecules by the graphene surface. For a high RH range (RH>50%), a frequency downshift of 2.6kHz per 1% RH change was obtained, which was due to the change in elastic grapheme properties. The mass loading effect of the water layer was less effective at high temperature, resulting in a lower temperature coefficient of resonant frequency (TCF).

Interlamellar Space Configuration under Variable Environmental Conditions in the Case of Ni‐Exchanged Montmorillonite: Quantitative XRD Analysis

Interlamellar space organization of low‐charge montmorillonite was studied by modeling of X‐ray diffraction (XRD) patterns recorded under controlled relative humidity (RH) conditions on Ni saturated specimens. The quantitative XRD investigation, based on an indirect method consisting of the comparison of experimental reflections with the other calculated from structural models, is used to characterize eventual nanostructural changes along c* axis of Ni‐exchanged montmorillonite. This method allowed us to determine, respectively, the relative layer types contribution, the layer thickness, nanoconfiguration of the interlamellar space, and position, amount, and organization of water molecules and exchangeable cations. Obtained theoretical models exhibit heterogeneous hydration state which is the dominating character detected all over studied cycles. Along RH cycle a modification in the main structure of the host materials is performed and the presence of a mixed layer structure (MLS) is noted. The hydration hysteresis at the low and the high RH range can be explained by fluctuations in the water retention mechanism and hydration heterogeneities created within the smectite crystallite.

Special Section on Advances in Internally Cured Concrete

Special Section on Advances in Internally Cured Concrete

Graphene oxide thin film coated quartz crystal microbalance for humidity detection

In this paper, we demonstrated that chemically derived graphene oxide (GO) thin film as a humidity sensitive coating deposited on quartz crystal microbalances (QCMs) for humidity detection. By exposing GO thin film coated QCMs to various relative humidity (RH) environments at room temperature, the humidity sensing characteristics of the QCMs such as sensitivity and linearity, response and recovery, humidity hysteresis were investigated. The experiment results show that GO thin film coated QCMs exhibit an excellent humidity sensing performance. Moreover, the possible humidity sensing mechanism of GO thin film coated QCMs was also investigated by monitoring the crystal's motional resistance change. It is suggested that the frequency response of the QCMs is dependent on water molecules adsorbed/desorbed masses on GO thin film in the low RH range, and on both water molecules adsorbed/desorbed masses on GO thin film and variations in interlayer expansion stress of GO thin film derived from swelling effect in the high RH range.

Study on Dielectric and Humidity Sensing Properties of La1-x Sr x FeO3 Materials

In this paper, single-phase nanocrystalline La1-x Sr x FeO3 (x = 0.1, 0.2, 0.3, 0.4 and 0.5) with perovskite structure were prepared by employing sol-gel method. XRD and TEM were used to characterize the materials. Dielectric properties of La1-x Sr x FeO3 (x = 0.1, 0.2, 0.3, 0.4 and 0.5) were investigated. The experiments were carried out as a function of Sr doping (0.1 ≤ x ≤ 0.5) and frequency (10–105 Hz) in different relative humidity (RH) at 25°C. The results revealed that capacitance decreased as the frequency increased, and the peaks of dielectric loss appeared at high relative humidity range. Humidity sensing properties were also studied in this work. It was found that La0.7Sr0.3FeO3 exhibited high humidity sensitivity and small hysteresis from 33% RH to 98% RH.

Dynamic water vapour sorption properties of wood treated with glutaraldehyde

The dynamic water vapour sorption properties of Scots pine (Pinus sylvestris L.) wood samples were studied to investigate the modifying effects of glutaraldehyde. Pine sapwood was treated with solutions of glutaraldehyde and a catalyst (magnesium chloride) to obtain weight per cent gains of 0.5, 8.6, 15.5, and 21.0%, respectively. The sorption behaviour of untreated and treated wood was measured using a Dynamic Vapour Sorption apparatus. The results showed considerable reduction in equilibrium moisture content of wood and the corresponding equilibrium time at each target relative humidity (RH) due to glutaraldehyde treatment. The moisture adsorption and desorption rates of modified and unmodified wood were generally faster in the low RH range (up to approximate 20%) than in the high range. Modification primarily reduced the adsorption and desorption rates over the high RH range of 20–95%. Glutaraldehyde modification resulted in a reduction in sorption hysteresis due to the loss of elasticity of cell walls.

Sensitivity and complex impedance of nanometer zirconia thick film humidity sensors

Nanometer zirconia (ZrO 2) with grain size 20 nm was used to make thick film humidity sensor on silicon substrate. The impedance of the sensor changed from 10 6 Ω to 10 2 Ω when the relative humidity (RH) varied from 11% to 98%. The curve of impedance vs frequency showed good linearity when the measured frequency was in between 100 Hz and 1 kHz. The temperature influenced the impedance of the sensor. Complex impedance (Nyquist) diagrams of the sensor at different relative humidities and temperatures were drawn. An equivalent circuit with resistors and capacitors was built to explain the conduction process of the sensor. In low RH range, the conduction process was dominated mainly by conduction and polarization of the grains of nanometer zirconia, while in high RH range, by decomposition and polarization of the absorbed water.