Research On Preparation And Properties Of Electroless Ni-W-P-PTFE Anti-fouling Deposits On Heat Transfer Surface

The heat exchanger is the key equipment for the heat and mass transfer in industry,which is also widely used in other fields concerned. Fouling deposition was widely appeared on heat transfer surfaces in engineering applications. The accumulations of fouling on the surfaces of heat transfer equipment can result in a decrease of the operating efficiency and service life of equipment, and cause the energy loss and safe trouble.Obviously, it was a most serious problem to solve the fouling on heat exchanger surface. It is a key research point for anti-fouling by using modifying surface on the surface of heat exchanger. In this thesis, we mainly study on the anti-fouling properties of the Ni-W-P-PTFE deposits with the different PTFE content. The main results of this studying are summarized as follows(1)The electroless Ni-W-P-PTFE deposits with various PTFE content were prepared by adjusting the PTFE emulsion concentration in electroless solution, which were based on the Ni-W-P bath. And the influence of process parameters on Ni-W-P-PTFE deposits composition and deposition rate was studied. The results show that the mount of PTFE particles which been co-deposited in the deposits would increase to maximum when the concentration of PTFE was 12ml/L and decrease with the further increasing PTFE of plating solution. The trend of the deposition rate was inversely proportion to the PTFE content in electroless solution.(2)The surface morphology was observed by Scanning Electron Microscopy(SEM).The composition distribution and microstructure were analyzed based on Energy Dispersive Spectrometer(EDS) and X-ray Diffraction(XRD), respectively. The corrosion resistance properties of the deposits were investigated by the further corrosion test. The results show that the addition of PTFE particles hardly affected the microstructure of the deposits, and the composition was distributed uniformly on the deposit surface. The deposits presented mixed crystal. Moreover, the corrosion resistance properties of the deposits becamed decreased slightly with the increase of the PTFE content in the deposits.(3)The effect of PTFE content on the mechanical properties of the Ni-W-P-PTFE deposits was assessed using Vickers hardness tester and MFT-4000 surface property tester,respectively. The results show that the hardness, elastic modulus and friction coefficient of the deposits were decreased with the addition of the PTFE content in the deposits and the deposits presented excellent wearable property. The adhesion strengths were affected bythe PTFE content in the deposits and surfactant in bath. In addition, there is not special influence on surface smoothness of the deposits for different PTFE content.(4)The effect of temperature and PTFE content on the anti-fouling property of the deposits was investigated base on the rapid fouling adhesion experiment. The relation among the surface smoothness, the surface free energy and the anti-fouling property was studied, and the fouling deposition was predicted by theorizing the experimental results.The results show that the Ni-W-P-PTFE deposits had better anti-fouling property than the uncoated mild steel surface and the anti-fouling property of the deposits became improved with the increase of the PTFE content in the deposits. It was found that the anti-fouling property of the deposits are related to the surface free energy, but not to the surface roughness. The Gray models were used to predict the fouling deposition, and it could provid fundamental with making clearing period of the fouling on the surface of heat exchangers.