Adhesives metals

Moisture acts as a debonding agent through one of or a combination of the following mechanisms 1) attack of the metallic surface to form a weak, hydrated oxide interface, 2) moisture assisted chemical bond breakdown, or 3) attack of the adhesive. (2 ) A primary drawback to good durability of metal/adhesive bonds in wet environments is the ever present substrate surface oxide. Under normal circumstances, the oxide layer can be altered, but not entirely removed. Since both metal oxides and water are relatively polar, water will preferentially adsorb onto the oxide surface, and so create a weak boundary layer at the adhesive/metal interface. For the purposes of this work, the detrimental effects of moisture upon the adhesive itself will be neglected. The nitrile rubber modified adhesive used here contains few hydrolyzable ester linkages and therefore will be considered to remain essentially stable. 

Some categories of nonglazing uses for PVB are as follows phe-nolic/adhesives metal/glass binders hard copy printing and coat-ings/additives. 

A critical problem with adhesion layers arises from grain boundary diffusion. Deposited films tend to be polycrystalline and granular. The electrochemistry of the adhesion film is frequently much less desirable than the electrochemistry of the primary film. Moreover, minute contamination of the primary metal film surface by adhesion components can dramatically degrade the electron transfer properties (e.g., electrochemical reversibility, as evidenced by cyclic voltammetric peak potential separation) of the film [58], Thus it is essential that the adhesion layer is not exposed to solution. While the rate of diffusion of adhesion metals through the bulk of the primary layer is quite slow, grain boundary diffusion along the surfaces of grains is much faster. In many cases, the adhesion layer can seriously compromise the performance of the electrode. This is particularly a problem for chromium underlayers. Recently a codeposited Ti/W adhesion layer has been recommended as an alternative to chromium, with reportedly better adhesion and fewer interferences than Cr. A procedure was also described to recondition these electrodes to minimize interference by adhesion layer metals [58]. 

The adhesion of noble metals to the insulating substrates is generally poor. In order to overcome this problem, a thin layer (10-50nm) of adhesive metal (Cr, Ti, W) is deposited under the noble metal. Often this adhesive metal migrates through the noble metal and forms an oxide layer that significantly alters its surface... 

The physical and chemical nature of the metal substrate surface depends on the bulk alloy composition, processing conditions used, and any preconditioning environments that the substrate may be exposed to during fabrication and storage. Once the joint is assembled, the physical and chemical nature of the adhesive-metal interface may change due to the environment and to the chemical nature of the adhesive. 

Adhesive, Epoxy Resin, Metal to Metal Structural Bonding Strong Linoleum Cement Adhesive, Metal to Wood... 

Wood glue, wallpaper paste, labelling adhesive, metal adhesive as reference to a certain purpose of use. 

Bonding of metal materials In the case of bonding with hot-melt adhesives, metal materials require preheating to the melt temperature to develop sufficient adhesive bonded joints, due to the high thermal conductivity. 

MAJOR USES Used in the production of pesticides, resins, finishes, lacquers, printing ink, paints, adhesives, metals and gasoline. 

ORIGIN/INDUSTRY SOURCES/USES manufacture of pesticides polyvinyl and nitrocellulose resins in solvent mixtures for finishes solvent in lacquers, printing inks, paints, adhesives metals gasoline... 

EXPOSURE ROUTES inhalation ingestion of contaminated drinking water skin and eye contact skin adsorption coal-fired power plants exposure to ink, paints, lacquers, and adhesives metal coating industries... 

KEYAVORDS Yield strength, adhesives, metallic materials, strain energy density, environment, relative humidity, temperature, strain rate... 

The scanning Kelvin probe, which measures the Volta potential difference between a specimen and the calibrated sensing probe, is introduced as the only electrochemical technique which allows nondestructive, real-time measurements of electrode potentials at adhesive/metal oxide interfaces in situ, even if they are covered with an adhesive layer. 

Fig. 31.2 shows profiles of electrode potentials across the three-layer boundary which reveal the ingress of ions into the intact adhesive/metal interface as a function of time. The potential profile can be assumed to reflect the ion concentration at the interface. This was proven by XPS small-spot analysis of the adhesive/metal interface after the removal of the adhesive [35]. Based on this assumption the profile can be evaluated and used as a basis for the calculation of the diffusion coefficient according to one-dimensional molecular diffusion in a medium with a constant diffusion coefficient. 

For the evaluation of the diffusion constant D at a time t, the potential difference relative to the potential of the intact, electrolyte-free metal/adhesive interface is fitted with respect to Eq. (22). For the ingress of sodium chloride from an aqueous solution of 0.5 m NaCl into the defect area as shown in Fig. 31.2, a diffusion coefficient of 1 x 10 cm s is calculated, even for highly stable adhesive/metal interfaces modified with an aminosilane adhesion promoter. Performing the diffusion measurement with other metal hahde solutions shows that an effective diffusion coefficient of the hydrated ion-pair, is measured by this method. This could be shown by changing the size of either the hydrated cation or anion, which resulted in a corresponding change in the measured diffusion coefficient (with smaller hydrated ions diffusing faster). 

The pressurized blister test is an excellent method to combine electrochemical reactions at polymer/metal interfaces with a mechanical load. It allows the application of a mechanical stress from a homogeneously pressurized electrolyte on the adhesive/metal interface in a sample geometry that is accessible for the HR-SKP [28]. Depending on the adjusted conditions, information on the synergy of mechanical stresses, elastic or inelastic deformations of the adhesive, transport processes, and corrosive reactions could be obtained with this method. 

In adhesion science and technology, the manifestations of acid-base interactions have been observed at both macroscopic and microscopic scales (wetting, adhesion, metallization, etc.). The development of scanning probe microscopic methods (scaiming tunneling microscopy (STM) and atomic force microscopy (AFM)) over the past decade has led to the possibility of measuring adhesion forces on the molecular scale in addition to imaging surfaces in atomic resolution. 

Chem. Descrip. Aliphatic urethane aciylate resin/SR 306 (tripropylene glycol diacrylate) blend with < 400 ppm MEHQ inhibitor Uses Urethane-acrylic, adhesion promoter in pressure-sensitive adhesives, metal coating, electronics, and inks... 

Uses Urethane-acrylic for adhesives, metal coalings, paper coalings, PVC floor coatings, wood coatings, electronics Features Good weatherability, chem. resist., adhesion, hardness, heat resist., abrasion resist., impact str., water resist., shear resist. tow shrinkage... 

Chem. Descrip. Aromatic urethane acrylate oligomer Uses Urethane-acrylic for adhesives, metal coatings, paper coatings, plastic coatings, textile coatings, wood coatings, leather coatings... 

Chem. Descrip. Bisphenol A epoxy diacrylate diluted with 20% OTA-480 Uses Epoxy-acrylic in clear coatings tor paper, laminates, adhesives, metal decorating, and screen inks... 

Uses Urethane-acrylic in clear coatings for paper and wood laminates, adhesives, metal decorating, plastics Features Exc. flexibility, toughness, abrasion resist. 

Features High solids good hardness, adhesion, metal wetting and color retention low VOC... 

Chem. Descrip. N-Ethyl o/p-toluene sulfonamide CAS 80-39-7 EINECS/ELINCS 201-275-1 Uses Plasticizer for nylon, shellac, cellulose acetate, protein materials, PVAc adhesives (metal-to-rubber joins, bookbinding, shoe), nitrocellulose lacquers food pkg. adhesives, coatings, paper, cellophane Features Makes compds. resist, to oils, soivs., and greases Reguiatory FDA 21CFR 175.105,175.300,175.320,176.170,176.180, 177.1200,177.1210... 

Uses Biocide, preservative for aq. systems, paints/coatings, latexes, resin emulsions, pigment slurries, dispersed colors, Joint cements, adhesives, metal working fluids, textile processing sol ns. 

Figure 4.5 displays the ctdculated distrihution of the shrinkge stresses over the adhesive-honded plate cross-section. At the adhesive-metal interface a concentration of stresses is observed that can exceed twice those in the hulk adhesive. 

Application of mechanical work to the adhesive-metal interface (by adhesive flow through the gap between the dollies at various speeds) had greater effect on the adhesion strength when cementing was performed in the liquids than in the air (see Fig. 5.2). This can be explained by the fact that the work done facihtates the selective wetting of the substrate by the adhesive the flowing adhesive picks up drops of liquid from the substance surface and removes them. 

For interphase tension below 220-230 mN/m and use of hydrolytically stable adhesives, the joints do not fail along the adhesive—metal interface even after hold-up in water for periods of years. Presumably with this interphase tension the process of substitution of adhesive... 

Two other specific problems complicate the process of sealing pipelines with adhesives. One is that gas in gas mains is transported under 70-75 atmospheres pressure, and noticeable increase of gas main diameter is observed under this pressure. Thus, on the adhesive-metal interphase boimdary heavy internal stresses occur, which can lead to strength reduction or to failure of the adhesive joint. Joint failiu-e will also be promoted by vibration, which occurs with passage of fluid or gas through a deformed section of the pipe. 

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