Preparation And Properties Of Near-infrared Reflective Pigments And Films

Most energy of sunlight is concentrated in the near infrared and visible range.Applying high near-infrared reflective coatings on the surfaces of buildings,warehouses,oil tanks,can decrease the inner temperature of these facilities,meeting the goal of saving energy,enhancing security and improving living and working conditions.The purpose of this paper is to grow functional film on glass,which has high visible light transmittance and high near-infrared reflection.We adopted the method of sol-gel method and solid state reaction method to compound the Yttrium molybdate and strontium copper silicate pigments.Ceramic targets of yttrium molybdate and strontium copper silicate were prepared.Yttrium molybdate and strontium copper silicate films were prepared by magnetron sputtering and the effect of sputtering technology on the properties of the films was studied.Yttrium molybdate pigment was prepared by solid-state reaction and sol-gel method using yttrium oxide,neodymium oxide,ammonium molybdate and citric acid as raw materials.The effects of pigment composition and preparation technology on pigment grain size and reflectivity were studied.The result shows that when the molar ratio of citric acid to total metal particles is 1.0 and the gel temperature is 70?,the uniform and transparent gel can be obtained in a short time.Calcining the precursor at 900? can obtain yttrium molybdate pigments with grain size of 50-70 nm.While using solid-state reaction method,the raw material should sinter at 1450? for 4h to get pigment with grain size of about 200 nm.The highest near-infrared reflectance of the pigments synthesized by the two techniques are both about 100%.When 3%Nd3+is doped in the matrix,the near-infrared reflection of the pigment can reach 104%.The properties of yttrium molybdate target prepared by hot pressing sintering and non-pressing sintering were compared with each other.The hot pressing sintering process not only reduces the sintering temperature,but also increases the density and decreases the grain size.The yttrium molybdate ceramics sintered at 1200? and 30 MPa has a relative density of 97.3%and strength of 66 MPa.And the near-infrared reflectance of yttrium molybdate ceramics is more than 80%in all near-infrared bands.Yttrium molybdate thin films were prepared on glass substrates by magnetron sputtering with hot pressing yttrium molybdate ceramics as the target material.The effects of sputtering parameters on the morphology,crystallinity and near-infrared reflectance of yttrium molybdate thin films were studied.The results show that with the increase of sputtering time,the film thickness increases and the average near-infrared reflectance also increases.Under the condition of 25?-2Pa-80W and the deposition rate of 150 nm/h,the thickness of the film reaches 530 nm and the near-infrared reflectance reaches 18%when sputtering for 3.5 h.With the increase of sputtering power,the near-infrared reflectance of the film increases firstly and then decreases.The edge of the near infrared reflectance band moves to the shortwave direction,showing blue shift.Under the conditions of 25?-0.5Pa-2h and sputtering power of 80 W,the film has the maximum near-infrared reflectance reaches 16.3%.With the increase of sputtering pressure,the roughness of the film increases.And it make the NIR reflectance decrease slightly.lt shows that increasing the sputtering pressure has a bad effect on reflectance.With the increase of sputtering temperature,the NIR reflectance increases.When the sputtering temperature increases from normal temperature to above 250?,the maximum NIR reflectance increases from 15%to 25%.Annealing treatment can promote the crystallization of the films and improve their reflectivity greatly.The reflectivity of the amorphous films prepared at 25?-2Pa-80W-3h increases from 11.5%to 17%after annealing at 800? for 4h.The results of energy spectrum analysis of yttrium molybdate films show that all elements are uniformly distribute in the films.High resolution transmission electron microscopy(HRTEM)showed that the film was tightly bonded to the substrate and the crystals were highly oriented.The hardness test of film prepared at 300?-100W-2Pa-8h by nanomechanical test system shows that the hardness of the film is 11.58 GPa.The results also show that the transmittance of yttrium molybdate films prepared on glass substrate is more than 80%in visible light band.Using SiO2,CuO and SrCO3 as raw materials,CuCrSi4O10 pigment were synthesized by solid-state reaction process,with particle size of 200?250 nm at 900?.With the increase of wavelength in the band of 700?1250 nm,the near-infrared reflectance of pigments increases gradually from 45%to 70%.The near infrared reflectance ranges from 70 to 75%in the band of 1250?2500 nm.The doping of Eu3+in CuCrSi4O10 can improve the reflectivity.When the doping amount of Eu3+is 4%,the near-infrared reflectance in the 700-2500 nm band is increased by 10%,up to 83%.CuSrSi4O10 ceramics were prepared by pressure-free sintering.When the sintering temperature was 1000?,the target sample with relative density of 95.1%and strength of 98.89 MPa could be obtained.The near-infrared reflectance of ceramic is consistent with the properties of powder pigments.It also increases with the increase of wavelength,and the best near-infrared reflectance is 63%.We acquired CuSrSi4O10 thin films on glass through magnetron sputtering with CuSrSiO10 ceramics as the target material.Studied the sway of sputtering parameters on the morphology,crystallicity and near-infrared reflectance of CuSrSi4O10 thin film.The results show that the sputtering time is positively correlated with the film thickness.The sputtering time is positively correlated with the thickness of the film,while the reflectance of the film is the same before 2h and opposite after 2h.The average near-infrared reflectance of the films is 16.1%and the highest value reaches 20%when the sputtering time is 2 h at 300?-1.5Pa-80W.With the increase of sputtering power,the near-infrared reflection increases firstly and then decreases.When the magnetron sputtering power is 100 W,the maximum near infrared reflectance of the sample is 21.6%at 300?-1.5 Pa-2h.With the increase of sputtering pressure,the near-infrared reflection of the film increases firstly and then decreases,and the near-infrared reflection of the sample shows blue shift.At 300?-80W-2h,the best near-infrared reflection performance is 22.3%at sputtering pressure of 2 Pa.Under the preparation condition of 100W-2Pa-2h,at the sputtering temperature of 100?,the film begins to crystallized.When the sputtering temperature is 300?,the sample shows the highest near-infrared reflectance of 23%.After annealing at 600?,the sample begins to crystallise.When the annealing temperature reaches 1000?,the film exhibits the maximum near-infrared reflectance.The reflectance of the film is higher than 18%in the full near-infrared band,and the maximum reflectance is 22.4%at 900 nm wavelength.The obtained strontium copper silicate films maintain a transmittance of more than 70%between 550 nm and 700 nm.The hardness of CuSrSi4O10 thin film is 9.26 GPa.In this paper,the NIR reflective film has good NIR reflectance,visible light transmittance and temperature resistance in the NIR range,and the hardness reaches about 10 GPa,which can meet the application requirements of vehicles,buildings and other fields.