微粒聚四氟乙烯-苯乙烯辐射接枝物的红外光谱定量测定法

本文叙述粉末状材料辐射接枝工艺中测定接枝单体含量的红外光谱方法。在粉末聚四氟乙烯—苯乙烯接枝体系中使用同种材料制备具有不同接枝率的薄膜作为标准物质,选择1493cm~(-1)和2362cm~(-1)谱带作为组分的分析谱带,利用最小二乘法计算了二谱带的吸光度比对接枝率(g)的回归方程。此方法对难以称量求得接枝率的微粒接枝共聚物的定量测定具有准确、方便的优点。     

Surface characterization of polytetrafluoroethylene (PTFE) transfer films during rolling-sliding tribology tests using X-ray photoelectron spectroscopy

A disk-on-disk Amsler wear tester simulating the rolling-sliding motion and high pressure during wheel/rail contact, was used to study the wear performance of PTFE including its film transfer and material flow properties. The chemical composition of the transfer film formed on the wheel-disk surface at various test stages were analyzed by X-ray photoelectron spectroscopy (XPS). The friction curve of the PTFE films obtained on the Amsler can be divided into three regions, according to the friction level and disk surface morphology. Initially, there is a rapid increase of friction coefficient which is presumably accompanied by a fast material transfer from pre-coated rail-disk to the wheel-disk surfaces. In the second region, the friction remains stable throughout and the XPS results show the presence of PTFE on the wheel-disk surface which confirms a transfer of material between the two contact surfaces. In addition, the splitting of F 1s and C 1s photoelectron peaks of PTFE, as a result of a discrepancy in surface charging, suggests that the transfer film exists in two forms: thick patch and thin film. With an increase in rolling cycles, the thick patches become thinner, as well as its coverage reduces. By contrast, the thin film gains both in thickness and coverage. Using a simple model, the thin film is calculated to be only a few nanometers thick. At the beginning of the third region, only a thin film is left on the surface. Additional rolling leads to a rapid rise in friction and the transfer film thickness continues to decrease. The evidence supports the removal of PTFE out of the contact zone, and a high friction coefficient (μ = 0.6) is reached at the end of the test indicating an un-lubricated metal-metal contact. No major tribochemical reaction of PTFE is observed during this study.     

填充材料对聚四氟乙烯基复合材料摩擦学特性的影响

聚四氟乙烯基复合材料是重要的自润滑材料,应用广泛。根据填充材料的类别不同对聚四氟乙烯基复合材料进行了合理地分类,并阐述了不同填料对聚四氟乙烯基复合材料摩擦学特性的影响,分析和比较了不同填料的减摩抗磨机理,对于聚四氟乙烯基复合材料的科学研究和工程应用具有一定的借鉴和指导意义。     

聚四氟乙烯成型加工新技术

介绍了聚四氟乙烯(PTFE)成型的特殊性,并对现有各种加工方法的优缺点进行了比较.为了弥补现有各种加工方法的不足,设计了新型聚四氟乙烯加工设备--柱塞冲压式挤出机,并阐述了它的加工工艺过程和成型原理.     

Effect of Addition of Polytetrafluoroethylene (PTFE) and Silicon Carbide (SiC) on Properties of Electroless Nickel Alloy Coatings

IN RECENT YEARS,electroless deposition hasbecome an important technology to prepare compositematerials[1][2',especially the metallic matrix compositematerials with characteristics of Ni-P alloy andcomposite phases,and the prepared process which canbe used to design the functional materials131[41.Both theelectrolytic and electroless codeposited compositesdisplay the flexibility and potential advantagesThe ternary and even the polyalloys(such as Ni-Co-P,Ni-Mo-P,Ni-Cu-P,Ni-W-P-B)have mu…     

聚四氟乙烯膜辐射接枝反应条件的研究

采用了共辐射接枝技术，在室温下将苯乙烯接枝到聚四氟乙烯薄膜上，合成了辐射接枝膜。研究了溶剂种类、单体浓度、辐射剂量以及剂量率等因素对接枝反应的影响。结果表明，单体浓度和辐射剂量率是反应的主要影响因素，两者对接枝反应速率的影响指数分别为1．2和0．4。     

Thermal degradation of polytetrafluoroethylene in flowing helium atmosphere II. Product distribution and reaction mechanism

The thermal degradation of polytetrafluoroethylene was studied in the helium flowing atmosphere and the temperature range 510–600°C. The products of the thermal degradation of polytetrafluoroethylene were analyzed by an on-line gas Chromatograph and the product distribution was obtained. The products consist of tetrafluoroethylene (TFE), perfluoropropene (PFP) and cyclic-perfluorobutane (c-PFB). Under most conditions the main product was TFE. The c-PFB was regarded as the secondary product formed from TFE because the formation of c-PFB strongly depended upon the degradation rate. However, the production of PFP was not related to the degradation rate, but it was influenced by diffusion limitation of gaseous product in the sample matrix. These phenomena were also verified with Curie-point pyrolyser. The results showed that the production of PFP reached a maximum point under diffusion limitation condition. The degradation mechanism of polytetrafluoroethylene was proposed in terms of unzipping mechanism and other mechanism like radical chain transfer reaction.     

Thermal degradation of polytetrafluoroethylene in flowing helium atmosphere

The thermal degradation of polytetrafluoroethylene in flowing helium atmosphere was studied in the temperature range 510–600C. The products of thermal degradation were analyzed by an on-line gas chromatography and the rates of degradation were obtained. At relatively lower temperatures (less than 530°C) the rate curves as a function of time showed two peaks. This phenomenon was explained in terms of diffusion limitation of the gaseous products. Further research was carried out by scanning electron microscopy (SEM) in order to observe the diffusion limitation and these facts were confirmed by observing the matrix of partially degraded polymer. The rate curves which have two peaks indicated that the diffusion limitation was disappeared above ca. 50% conversion. The activation energy in diffusion limitation free region was 78.1 kcal/mole and it was very similar to the result obtained by Madorsky (80.5 kcal/mole). The activation energy was also consistent with that obtained by thermogravimetry.     

Filtration and regeneration behavior of polytetrafluoroethylene membrane for dusty gas treatment

With micron talcum particles and nano-CaCO₃ powder as test dust, a series of experiments have been carried out to systematically study the gas filtration and regeneration behavior of polytetrafluoroethylene membrane, and some comparisons were made with common filter media. The experimental results showed that the PTFE membrane had a filtration efficiency of above 99.99% for micron particles, and excellent regeneration behavior was obtained, though a much higher initial pressure drop existed. Based on the results, it was concluded that the PTFE membrane is an excellent surface-filtration media for micron particles. Effects of operation parameters, including airflow velocity, particle concentration and particle characteristics were also investigated. To better understand the evolution of pressure drop during the filtration process, a mathematical model with operation parameters and characteristics of particles was derived from the gas-solid two-phase flow theories. A novel method on the determination of regeneration period of the filter media was put forward based on the analysis of the pressure drop according to this model.     

A novel approach to determine the in-plane thermal conductivity of gas diffusion layers in proton exchange membrane fuel cells

Heat transfer through the gas diffusion layer (GDL) is a key process in the design and operation of a proton exchange membrane (PEM) fuel cell. The analysis of this process requires determination of the effective thermal conductivity. This transport property differs significantly in the through-plane and in-plane directions due to the anisotropic micro-structure of the GDL.A novel test bed that allows separation of in-plane effective thermal conductivity and thermal contact resistance in GDLs is described in this paper. Measurements are performed using Toray carbon paper TGP-H-120 samples with varying polytetrafluoroethylene (PTFE) content at a mean temperature of 65-70 °C. The measurements are complemented by a compact analytical model that achieves good agreement with experimental data. The in-plane effective thermal conductivity is found to remain approximately constant, k ≈ 17.5 W m⁻¹ K⁻¹, over a wide range of PTFE content, and its value is about 12 times higher than that for through-plane conductivity.