Xudong Cheng

Synthesis of NiCr2O4 spinel coatings with high emissivity by plasma spraying

Air plasma spraying (APS) was used to produce high emissivity coatings with a NiCr2O4 spinel structure. The relationship between the emissivity and the crystal structure was investigated. X-ray diffraction (XRD) analyses show that NiCr2O4 spinel has been fabricated with the space group Fd3m. Scanning electron microscope (SEM) photographs show that the coating consists of a laminated structure with homogeneous grains and high porosity because of the unique feature of plasma spraying. The emissivity measurement and Fourier transformation infrared radiation (FT-IR) spectra show that NiCr2O4 has a high emissivity of about 0.91 because of its special spinel structure. APS is a suitable method to produce high emissivity coatings.

Preparation of high emissivity NiCr2O4 powders with a spinel structure by spray drying

Spray-drying was used to produce the high emissivity NiCr2O4 powders with a spinel structure. Preliminary investigations focused on fabricating the high emissivity powders for infrared radiation coatings and finding the relationship between microstructure and emissivity. The NiCr2O4 powders were characterized for composition, microstructure, and infrared emissivity by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared radiant instrument, and Fourier transform infrared spectra (FT-IR). Thermogravimetry and differential thermal analysis show that the appropriate baking temperature for NiCr2O4 powder preparation is about 1200°C. The emissivity measurement and FT-IR spectra show that, because of the special spinel structure, the NiCr2O4 powders have a high emissivity about 0.91. Spray-drying is a suitable method to produce the high emissivity ceramic powders.

The effect of annealing under non-vacuum on the optical properties of TiALN non-vacuum solar selective absorbing coating prepared by cathodic arc evaporation

TiAlN solar selective absorbing coatings which were deposited on 304L stainless steel using cathodic arc evaporation method were annealed under non-vacuum at different temperatures with different times. The optical properties (absorptance and emittance) of the coatings were measured by a spectrophotometer. It was found that, after being annealed for 2 hours at different temperatures, the absorptance of the coatings reached the highest value of 0.92 at 700 °C while the emittance got the lowest value of 0.38 at 800 °C. When the coatings were annealed at 600 °C for 24 hours, the optical properties changed to 0.92/0.44 (absorptance/ emittance). By measuring the structure, morphology, elements and surface roughness of the coatings, it was found that both the elemental composition and the surface roughness of the coatings changed as a result of annealing, and these changes caused the change of the optical properties of the coatings.

Effect of coated PHB on properties of abradable seal coating

As pore-forming materials, the coated poly-p-hydroxybenzoate(short for PHB) and h-BN can be applied in the preparation of abradable seal coatings at high temperature. The characteristics of coating such as morphology, thermal stability and composition were studied by SEM, EDS and FTIR. The results show that the modified PHB will change the remained carbon amount, porosity and pore morphology of the coating, which can affect the properties of coatings. If the pore is small enough in uniform distribution, the coating with 5 MPa bond strength, 30–55 HR45Y superficial hardness and certain of carbon can be suitable to well abradability.

Preparation and characterization of high infrared emissivity Mn-doped NCO spinel composites

NiCr2O4 (NCO) spinel composites with different Mn/Ni atomic ratios (Mn/Ni = 0.05, 0.10, 0.15, and 0.20) were synthesized via solid state reaction method. Phase compositions and microstructure of samples were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The TG-DSC curves showed that the appropriate baking temperature for Mn-doped NCO spinel preparation was approximately 1 320 °C. X-ray diffraction patterns exhibited the formation of NCO spinel with Fd-3m space group. Valence state of the Mn ions was determined from 2p and 3s X-ray photoelectron spectra. Manganese ions were mostly in divalent and trivalent states, and the ratio of Mn2+/Mn3+ was 0.78-0.98. Fourier transform infrared spectroscopy (FTIR) was used to analyze the spectral emissivity of Mn doped NCO spinel. It was revealed that the infrared emissivity of Mn-doped NCO spinel in 1.8-5 μm could be significantly enhanced with increasing content of Mn2+, reaching as high as 0.9398. Mn-doped NCO spinel showed excellent radiation performance and good prospect in high emissivity applications in the temperature range of 800-1 200 °C.