Wedged sample layers

The XPS analysis of the samples primed at 34% RH indicated that there was a consistent failure of the wedge samples which occurred mainly within the alkoxide layer in all systems. Partial hydrolysis may have resulted in the formaton of a weak hydrated oxide layer and was the zone through which the crack propagated to debond the samples. Based on the relative humidity in the chamber during the priming process and the failure surface analysis results, it was concluded that this level of 34% RH was not sufficient to complete the hydrolysis of the alkoxides and produce a stabilized oxide structure. As noted above, however, the wedge crack results did not indicate any instability. 

The XPS analysis of the failure surfaces of the wedge samples primed at 51% RH and bonded with PES and immersed in DI water at 100°C are reported in Table 3. The concentration of sulfur in all of the primed samples bonded with PES was about 5% and suggests that failure occurred primarily within the adhesive. The atomic concentrations of aluminum, silicon, and titanium were below 0.5%, precluding assignment of failure within the alkoxide layer. The control sample failed at the interface between the steel and the adhesive. 

There is an apparent optimum relative humidity level required to achieve good adhesion and durability. Priming the steel adherends at 18% RH caused failure in the wedge samples within the steel (oxide) layer. Adherends primed at 34% RH failed within the alkoxide primer layer, whereas at 51% RH failure occurred primarily within the adhesive layer. This change in locus of failure with humidity was not evident using the wedge crack test when the adherends were primed with aluminum alkoxides. A peel-type test would probably be more sensitive in detecting these shifts in failure mode. 

The failure surfaces produced following tests of lap shear or wedge samples of titanium alloy bonded with epoxy depended on the surface pretreatment (34). Simple add etching of the adherend produced primarily interfacial failure between the oxide and epoxy whereas chromic acid anodization of the adherend resulted in failure within the oxide layer as in the case discussed above. 

Analtech Preparative Uniplate-T wedge-shaped layers are tapered from a thickness of 1700 pm at the top to 300 pm at the bottom, and have a 700 pm-thick preadsorbent area at the bottom for manual or instrumental sample application. Sample concentration occurs in the preadsorbent zone, and low bands tend to separate better in the thinner lower layer region. 

In the preparation of standards, diffusional techniqnes are of special importance. Using snch techniqnes diffusion layers are formed. With a special modification by use of wedge-type samples, these layers are broadened and are thus better accessible for the microprobe.The samples consist of several diffusion bands because of the various phases in the respective carbide system. Usually, however, the samples should be single phase and homogeneous in order to make chemical gross compositional analysis applicable. Only with a comparison of different techniques a real standardization is possible. Such transition metal carbide standards have been made from the phases VC, NbC, TaC and Cr3C2. ... 

Figure 15 Wedge-type sample of the Hf-N system with various diffusion layers ...

Figure 2. Dimensions of wedge-shaped briquettes employed as specimens of marble and limestone. Also shown are locations of areas sampled in layers to assess depth of chemical alteration caused by atmospheric exposure.

Figure 19. Diffusion layers of hafnium nitrides formed in a wedge-type sample. Note the thiekness enhancement upon decreasing sample thickness [82].

Figure 4.23. Passage of IR radiation through layer of powdered sample deposited on transparent (a) plane-parallel and (b) wedge-shaped plates a = angular aperture of radiation beam /3 = angle of Inclination of wedge-shaped plate.

The figures in this column refer to the use of the wedge technique, i.e. the sample is applied at the upper part of the straight strip of adsorbent between two hexagonal areas (1.5 cm-side) from which the adsorbent layer has been removed (see 130). 

A unique plate for PLC combining a 700-pm-thick preadsorbent area and a wedge-shaped silica gel G layer is manufactured by Analtech (Uniplate-T Taper Plate). The silica gel layer is thin (300 pm) adjacent to the preadsorbent and varies uniformly to a thickness of 1700 pm at the top. Sample concentration occurs in the preadsorbent, and low-Rf zones are better separated on the thin, bottom area of the silica gel than they would be on a 1000-pm constant-thickness preparative layer. The solvent flow pattern in the tapered layer causes the lower portions of the zones to travel at a faster rate than the top portions, reducing vertical band spreading and leading to tighter, better resolved zones. Nyiredy... 

A liquid that was originally a layer of constant thickness on a vertical wall eventually forms a parabolic wedge shape and the thickness /zx as a function of the distance x from top of the liquid sample is given by... 

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