Study On Humidity Sensitivity Of Hydroxyapatite

In modern production and life,humidity detection plays an increasingly important role.Hydroxyapatite is a non-toxic,harmless,acid and alkali resistant material with good thermal stability.Because it has a polar surface,it can effectively detect and capture water molecules and give sensitive humidity sensing signals,so it is very promising to apply it to humidity detection devices.Based on the above reasons,we have done the following work:Firstly,hydroxyapatite film was deposited on PET-ITO interdigital electrode by electrochemical deposition.By optimizing the deposition parameters,hydroxyapatite with excellent humidity sensing properties was obtained.The XRD results show that the sample has a preferred orientation on the a-plane.Based on the crystal structure of hydroxyapatite,more hydroxyl groups can be exposed on the surface.The SEM images of the samples verified this point and showed that the micro-morphology of the sample was a two-dimensional long strip.Two-dimensional banded structure can provide large specific surface area and abundant active adsorption sites.SEM images also show that hydroxyapatite has a loose spatial structure,which can achieve the rapid transport of water molecules.Testing the humidity sensitivity performance of the hydroxyapatite sensor,it was found that the humidity sensor has high sensitivity,low humidity hysteresis and good linearity.In particular,hydroxyapatite showed a response time of 0.9 s and a recovery time of 5.6 s,respectively.In addition,the adsorption mechanism of hydroxyapatite was discussed in detail by combining the impedance spectrum of hydroxyapatite at different humidity.Secondly,hydroxyapatite powder with hexagonal prism structure was synthesized by hydrothermal method.It was coated on a glass-based ITO interdigital electrode to make a humidity sensor.The humidity sensitivity of the sensor was tested,the response current of the sample at a humidity level of 12% to 97% was measured twice in a row in a complete test.The results show that hydroxyapatite is a positive humidity sensing material,and the response current increases with the increase of humidity.But when the first relative humidity changes from 12% to 97%,there is an abnormal response peak at the boundary between low relative humidity and high relative humidity.In order to study the mechanism of HAp and the reason of abnormal response peak,Grand Canonical Monte Carlo(GCMC)method was used to simulate the adsorption behavior of hydroxyapatite.Four types of HAp(300)supercells were established: and no adsorption?H2O adsorption?N2 adsorption and O2 adsorption.The GCMC method simulates the reloading behavior of water molecules by four HAp(300)supercell models.Based on the simulation results and experimental data,the adsorption mechanism and abnormal response peak of hydroxyapatite were discussed in detail.