Surface pretreatments purpose

The purpose of surface pretreatment is to remove contaminants, such as dust and films, from the substrate surface. The surface contamination can be extrinsic, composed of organic debris and mineral dust from the environment or preceding processes. It can also be intrinsic, such as a native oxide layer. Contaminants and films interfere with bonding, which can cause poor adhesion and even prevent deposition. Therefore, surface pretreatment is important to ensure plating quality. Most (metal) surface treatment operations have three basic steps surface cleaning, surface treatment, and rinsing. 

The most important tests on bonded joints are targeted at the determination of the strength under precisely defined conditions. In order to obtain comparable results from such tests on different test stations, for example, at the adhesive manufacturer and the adhesive user, the test conditions have to be stipulated in detail and must be binding. For this purpose, test standards have been issued by the German Institute for Standardization (DIN) and the European Standards (EN) in cooperation with interested technical groups. The standards for tests in the held of adhesive technology, for example, contain indications regarding material and dimensions of test pieces, the test method to be applied (test equipment, test speed), if required even surface pretreatment of test pieces and other test criteria to be taken into account. 

The purpose of surface preparation is to remove contamination and weak surface layers, to change the substrate surface geometry, and/or introduce new chemical groups to provide, at least in the case of metals, an oxide layer more receptive to the adhesive. An appreciation of the effects of pretreatments may be gained from surface analytical or mechanical test techniques. Experimental assessments of the effects of surface pretreatment, even when using appropriate mechanical tests, are of limited value unless environmental exposure is included. Self-stressed fracture mechanical cleavage specimens, as discussed in Chapter 4 and in the texts edited by Kinloch(2,5) for example, are therefore referred to wherever possible. 

A wide range of surface pretreatment procedures has been developed for different plastic adherends available in the current market. As with other adherends mentioned above, it is the purpose of any surface pretreatment to establish a surface condition for good wetting by the adhesive. 

Various reviews [1 6] have given details of the common surface pretreatments that have been developed, mainly empirically, both for non-metals and metals to give adhesive joints which possess the maximum strength, a low coefficient of variation on the strength values (i.e. are reproducible) and have long service lives in hostile environments. It is not the purpose of the present chapter to repeat the many recipes that are listed in these reviews but rather to indicate the types of pretreatment that are employed for different substrates and identify the scientific principles involved. 

The purpose of any particular surface pretreatment may be manifold but the main aims are usually one or more of the following ... 

Such peel tests can be valuable to industry for the purposes of selecting a suitable adhesive for a given substrate material, for developing a surface pretreatment, or for investigating the effects of altering one test parameter (e.g. temperature, humidity or rate of peel). However, the results obtained in one peel test are rarely transferable to other geometries and have limited predictive capability. For this reason, much recent attention has been directed toward the development of geometry-independent peel tests, as is discussed in the next section. 

For this purpose we studied a temperature-programmed interaction of CH with a-oxygen. Experiments were carried out in a static setup with FeZSM-5 zeolite catalyst containing 0.80 wt % Fe203. The setup was equipped with an on-line mass-spectrometer and a microreactor which can be easily isolated from the rest part of the reaction volume. The sample pretreatment procedure was as follows. After heating in dioxygen at 823 K FeZSM-5 cooled down to 523 K. At this temperature, N2O decomposition was performed at 108 Pa to provide the a-oxygen deposition on the surface. After evacuation, the reactor was cooled down to the room temperature, and CH4 was fed into the reaction volume at 108 Pa. 

It has been demonstrated that ILMs are suitable for qualitative and quantitative analyses of low-molecular weight compounds of biological interest, for example, carbohydrates, vitamins and amino acids [38], and glycolipids [40]. ILMs were further used for fhe direct analysis of alkaloids, anesthetics and antibiotics, separated by thin-layer chromatography (TLC) [46]. For this purpose, the ILM was spotted onto the fractions on the TLC-plates and the complete plate was measured in MALDI MS without the need for additional pretreatment of the TLC-samples. The mass deviation inherently caused by the inhomogeneous surface of fhe TLC-plafe was balanced by using the... 

Pretreatment for fillers. When used as a surface treatment for fillers or reinforcing materials, in which the silane is applied to the filler or fibre before incorporation into a resin matrix, the same factors as for pretreatment primers apply. In addition, the particle size and the absence/presence of water are important, and in a sense this application is only a variation on the former. It should be noted that silane treated fillers may have, or impart, different rheological properties to non-treated fillers, particularly particulates. A major disadvantage of this approach is that a general purpose silane may have to be used by a manufacturer rather than one specifically tailored to the use of a particular resin type and less than optimum properties are likely to be achieved in some cases. 

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