Degradation Mechanisms of Silicones
Abstract
Nowadays, silicones are used in multiple applications. They are available as linear fluids, cyclics, gels, and resins, depending on the degree of cross-linking, or as elastomers, when fillers are incorporated in cross-linked polymers. This chapter deals with the key properties of silicones. It describes degradation behavior in terms of physical and chemical effects currently understood by detailed analysis of the aged material. With their low moisture uptake and ability to withstand harsh environmental conditions, silicone-based materials are frequently used in the electronics industry to protect fragile components against damages and corrosion.
... Silicone semistructural adhesives have been used in jet engines for more than 30 years where, for instance, they prevent bimetallic corrosion even at high temperatures. They are also used in electrical, micro-and optoelectronics [112], optical assemblies, and in the mounting of optics, resistors, connectors, and other components. Additional benefits stemming from the use of silicone adhesives are a wide operating temperature range; easy repairability; good physical and electrical stability over a range of frequencies, temperatures, and humidities; and the protection of components from temperature extremes, high humidity, radiation, thermal shock, and mechanical vibration. ...
Silicone elastomers are widely used because of their myriad useful properties. However, their synthesis requires a high energy input. We report that the amount of silicone, per application, can be...
Unstretched films of natural rubber (NR) from Hevea brasiliensis were exposed to ozone flow of 15 ml min−1 from 4 to 300 min. The efficiency of reaction was determined by ozone consumption of NR films. Plots of reacted ozone mass versus film thickness show that the ozone penetration and the ozone reaction progressed into deeper layers (170 µm) than described in the literature (∼0.5 µm). The previous proposed model based on viscometry measurements was corroborated by ozone consumption results. The effect of thickness on the O3/NR stoichiometric ratio indicated that the diffusion process that controls the ozonation in unstretched film does not consist of the boundary progression behind which all reactive sites have been saturated. Ozonation in unstretched rubber film, while being less efficient than ozonolysis in solution, does have a reaction efficiency of the same order of magnitude. NMR spectroscopy was used to characterise the products formed by ozonation. Copyright © 2004 Society of Chemical Industry
This paper discusses a method for data analysis of early failures that are typically due to defects from production and/or installation. The approach is based on Weighted Linear Regression and aims at estimating the next failure moment and the failure probability in an interval. As an additional goal, methods are intended to be suitable for light computing devices.
Liquid silicone rubber (LSR) is an elastomer molded into critical performance components for applications in medical, power, consumer, automotive, and aerospace applications. This article reviews process behavior, material modeling, and simulation of the (LSR) injection molding process. Each phase of the LSR injection molding process is discussed, including resin handling, plastication, injection, pack and hold, and curing; and factors affecting the molding process are reviewed. Processing behavior of LSR is marked by transient interactions between curing, shear rate, temperature, pressure, and tooling. Therefore, current LSR models for curing, viscosity, pressure, and temperature are discussed. Process dynamics and material modeling are combined in LSR injection molding simulations with applications in mold design, troubleshooting process‐induced defects, and management of shear stress and non‐uniform temperatures between LSR and substrates during overmolding. Finally, case studies using commercial simulation software are presented, which have shown cavity pressure and flow front advancement within 3% of experimental values. Optimization of LSR materials, data collection, model fitting, venting, and bonding remain areas of continued interest.
Silver sintering is receiving increasing attention due to its novel die-attach technique for high-temperature power electronics. Excellent thermal conductivity, high melting point/remelting temperature and low-temperature sintering behaviors of the silver sintered attachment meet the requirements of high-temperature applications for power devices, specifically SiC devices. The merits and demerits of the existing pressure-assisted sintering and pressure-less sintering techniques using nano-scale, micro-scale and micro-nano-scale hybrid silver sintered materials are separately presented. The emerging rapid sintering approaches, such as the electric-assisted approach, are briefly introduced and the technical outlook is provided. In addition, the study highlights the importance of creating a brief resource guide on using the correct sintering methods.
Light‐emitting diodes (LEDs) are among the key innovations that have revolutionized the lighting industry, due to their versatility in applications, higher reliability, longer lifetime, and higher efficiency compared with other light sources. The demand for increased lifetime and higher reliability has attracted a significant number of research studies on the prognostics and lifetime estimation of LEDs, ranging from the traditional failure data analysis to the latest degradation modeling and machine learning based approaches over the past couple of years. However, there is a lack of reviews that systematically address the currently evolving machine learning algorithms and methods for fault detection, diagnostics, and lifetime prediction of LEDs. To address those deficiencies, a review on the diagnostic and prognostic methods and algorithms based on machine learning that helps to improve system performance, reliability, and lifetime assessment of LEDs is provided. The fundamental principles, pros and cons of methods including artificial neural networks, principal component analysis, hidden Markov models, support vector machines, and Bayesian networks are presented. Finally, a discussion on the prospects of the machine learning implementation from LED packages, components to system level reliability analysis, potential challenges and opportunities, and the future digital twin technology for LEDs lifetime analysis is provided.
This new edition includes better values of properties already reported, properties not reported in time for the earlier edition, and entirely new properties becoming important for modern polymer applications. It also contains 217 total polymers, 15 of which are all-new, particularly in high-technology areas such as eletrical conductivity, non-linear optical properties, microlithography, nanophotonics, and electroluminescences. Examples of specific polymers include silsesquoxane ladder polymers, ‘foldamer’ self-assembling polymers, and block copolymers that phase separate into ‘mushrooms’, ellipsoids, and sheets with on surface radically different in properties from the other.
The use of adhesives is widespread and growing, and there are few modern artefacts, from the simple cereal packet, to the jumbo jet, that are without this means of joining. Adhesion Science provides an illuminating account of the science underlying the use of adhesives, a branch of chemical technology which is fundamental to the science of coatings and composite materials and to the performance of all types of bonded structures. This book guides the reader through the essential basic polymer science, and the chemistry of adhesives in use at present. It discusses surface preparation for adhesive bonding, and the use of primers and coupling agents. There is a detailed chapter on contact angles and what can be predicted from them. A simple guide on stress distribution joints and how this relates to testing is included. It also examines the interaction of adhesives and the environment, including an analysis of the resistance of joints to water, oxygen and ultra-violet light. Adhesion Science provides a comprehensive introduction to the chemistry of adhesives, and will be of interest not only to chemists, but also to readers with a background in physical or materials science.
In this paper, we are concerned with the reliability models and analysis methods for the case where catastrophic and degradation failure modes are considered simultaneously. First, the existing degradation models and analysis methods are reviewed and classified. In particular, the existing methods for analyzing degradation data are classified into the “horizontal axis” and “vertical axis” methods. Second, based on the above degradation models and analysis methods, a systematic procedure for simultaneously analyzing catastrophic failure times and degradation measurement data are presented. Finally, using the data in Huang and Askin (2003), comparative analysis results are presented with respect to the direction of analysis (i.e., horizontal versus vertical).