The Electrochemistry of the FPL (Forest Products Laboratory) Process and its Relationship to the Durability of Structural Adhesive Bonds

The FPL (Forest Products Laboratories) Process for preparing aluminum for structural adhesive bonding has been used in the aerospace industry since the early 1950's. Problems were encountered with the use of the process when the industry changed from phenolic to epoxy adhesives. In-service disbonds followed by corrosion were observed. This review article describes an investigation of the electrochemistry of the FPL etch process. Through a combination of electrochemical polarization measurements, surface chemical and surface morphological investigations and a thorough application of the Boeing wedge test, we are able to provide a mechanism of action of the FPL etch process. An oscillating electrochemical reaction was observed for low alloy aluminum which was ascribed to the dissolution and redeposition of copper on the aluminum during the etching process. A spatial variation in wedge test performance was found in that edge specimens demonstrated lower crack extensions than center specimens when using a low alloy aluminum that was etched in an FPL etch bath that was low in copper. These results are positioned in a historical perspective providing some insight into possible reasons for the irreproducibility of durability of structural adhesive bonds made with low alloy aluminum adherends that were prepared in a low copper content FPL etch bath.     

Room Temperature Curing Epoxy Adhesives for Elevated Temperature Service. Part III. The Effect of Silane Coupling Agents

The effect of silane coupling agents incorporated into the bulk of previously-developed room-temperature-curing epoxy adhesives^8,9,10 was studied. The physical and mechanical properties of corresponding aluminum bonded joints were characterized in ambient and humid-hot environments. Experimental results have demonstrated significant advantages of silane addition to the performance of these epoxy adhesives, especially under exposure to humid atmosphere. Thermal analysis of the polymerization processes, taking place during curing of the various low-temperature-curing formulations containing silane coupling agents, indicates that curing is not complete after seven days at room temperature, showing an exotherm at 80-100°C and a residual small one at 120°C. The basic formulation, comprising a tetra- and trifunctional epoxy resin blend and a multifunctional amine and ATBN cross-linking mixture, developed a three-phase matrix-rubber microstructure when the silane was added to the system.     

Plasma-sprayed coatings as adherend surface pretreatments

As part of the National Center for Manufacturing Sciences contract on adhesive bonding of dissimilar materials, UTRC, as a sub-contractor, is evaluating environmentally acceptable surface preparation techniques for selected metals and composites. The selected processes are automatable and capable of being transferred into the manufacturing arena. One aspect of the programme is the evaluation of plasma-sprayed, microporous, thin coatings as surface pretreatments for both resin-based composites and metals. Mechanical test results are presented which demonstrate the viability of this approach to achieve acceptable joint strengths with steel, titanium and aluminium bonded to several types of resin-matrix composite. The environmental impact, by elimination of organic primer systems and strong acid etching and anodizing solutions, will be discussed.     

矿渣微粉对混凝土抗冻融耐久性的影响

试验研究了矿渣微粉对混凝土强度和抗冻性能的影响.结果表明,同基准混凝土相比,掺入20%～50%比表面积为475m2/kg的矿渣微粉,可以明显提高混凝土的后期强度,并降低冻融循环后重量和动弹性模量的损失率.这说明矿渣微粉对混凝土具有显著的增强作用,并对混凝土的抗冻性能具有很好的改善作用.     

硫铝酸盐水泥体系高温稳定性研究

针对硫铝酸盐水泥水化产物易转变和国际上对延迟性钙矾石形成和破坏的争议,研究了硫铝桎卤水泥在不同温度下的膨胀和性能变化行为,结果证明,无论是压蒸或蒸养处理,在120℃温度下形成的稳定产物是单硫型水化硫铝酸钙,常温下转化为Aft,并伴随一个快速的结构破坏过程,而在80℃条件下,硫铝酸盐水泥石的结构是稳定,未出现DEF破坏。     

丙烯酸酯齐聚物和微凝胶增韧环氧粘接件的湿热耐久性

以铝合金LY12CZ为基材 ,以丙烯酸酯齐聚物和微凝胶分别改性环氧树脂粘合剂 ,进行了湿热老化试验和楔子试验 ,观察了粘接件在湿热条件下剪切强度的变化和耐久性。结果表明丙烯酸酯齐聚物作为增韧剂 ,经湿热老化试验后 ,PACR1、PACR2有较好的湿热老化性 ,剪切强度保留率分别为 81.7%、80 .0 % ,而且PACR2耐久性较好 ;微凝胶作为增韧剂 ,微凝胶 1# 有较好的湿热老化性和耐久性     

Durable,Sensitive, and Wide‐Range Wearable Pressure Sensors Based on Wavy‐Structured Flexible Conductive Composite Film

Flexible pressure sensors have potential applications in human motion monitoring and electronic skins. To satisfy the practical applications, pressure sensors with a high sensitivity, a low detection limit, a broad response range, and an excellent stability are highly needed. Here, a piezoresistive pressure sensor based on wavy‐structured single‐walled carbon nanotube/graphite flake/thermoplastic polyurethane (SWCNT/GF/TPU) composite film is fabricated by a prestretching process. Due to the random wavy structure, high conductivity, and good flexibility, the prepared sensor displays a low detection limit of 2 Pa, a wide sensing range of 0–60 kPa, and a high sensitivity of 5.49 kPa^?1 for 0–50 Pa. Furthermore, the sensor shows a remarkable repeatability of over 1.1 × 10⁴, 9.0 × 10³, and 2.0 × 10³ pressure loading/unloading cycles at 50 Pa, 500 Pa, and 30 kPa, respectively, and a fast responsibility of 100–150 ms of loading response time and 400–600 ms of relaxation time. Therefore, the pressure sensor is successfully adopted to monitor both the large‐scale human activities (e.g., walk and jump) and the small‐scale signals (e.g., wrist pulse). Furthermore, a sensor array is assembled to map the weight and shape of an object, indicating its various potential applications including human–machine interactions, human health monitoring, and other wearable electronics.     

抗硫化返原剂PK900在全地形轮胎胎面胶中的应用

研究抗硫化返原剂PK900在全地形轮胎胎面胶中的应用。结果表明:在全地形轮胎胎面胶中添加抗硫化返原剂PK900,胶料硫化速度变化不大,抗硫化返原性能提高,在过硫条件下硫化胶可保持较好的物理性能;成品轮胎的耐久性能提高,使用寿命延长。     

Preparation of Gd2Zr2O7 nanoceramics from two-step thermal treatment and the aqueous durability analysis

Gd₂Zr₂O₇ ceramics demonstrate important prospect in the immobilization of high-level radioactive wastes (HLWs). In this study, Gd₂Zr₂O₇ nanoceramics were fabricated using two-step method, where Gd₂Zr₂O₇ nanopowder was firstly synthesized by solvothermal method and Gd₂Zr₂O₇ nanoceramics were subsequently sintered via self-propagating chemical furnace plus quick pressing (SCF/QP). The characterization results display that the Gd₂Zr₂O₇ nanocrystalline ceramics with average grain size of 78 nm and bulk density of 5.53 g cm⁻³ were successfully prepared. The results of MCC-1 static leaching experiments show that the normalized release rate (LR_i) of Gd is 2.2 × 10⁻² g m⁻²•d⁻¹ on the first day and converges to 1.2 × 10⁻³ g m⁻²•d⁻¹ after 42 days. Zr shows superior chemical stability as the 21 days LR_Zr value is as low as 2.7 × 10⁻⁶ g m⁻²•d⁻¹, which becomes constant as the leaching duration prolongs.     

Effects of pyrochlore content on the phase,structure, and properties of uranium-rich glass ceramics

In this study, the effects of the pyrochlore content on the phase, structure, and properties of uranium-rich glass ceramics were studied by modifying the mass ratio of the uranium pyrochlore in the glass ceramics. The results indicate that U has a high occupancy rate of approximately 0.7 f.u. at the A position of pyrochlore, and the crystal pyrochlore phase in the glass matrix can increase or decrease according to the U amount in the waste. Specifically, at a high occupancy rate and crystallization amount, the U loads reach 20 wt% in the sample, which exceeds the reported 16 wt% maximal U loads of pyrochlore-based glass ceramics. Furthermore, all the samples have excellent mechanical properties and chemical stabilities. The bulk density of each sample is more than 90% the theoretical density, which is 10–20% higher than those of the glass ceramics prepared by pressure sintering. Moreover, the Vickers hardness values of all samples exceed 6 GPa, and the U leaching rate after 21 days is only 6.7 × 10⁻⁵ g m⁻² d⁻¹, which is an order of magnitude lower than those of brannerite glass ceramics under equal leaching conditions.