Column preparation etching

Several types of surface modification have been employed [37,38] such as etching or deposition of very fine inert supports before application of the phase. The latter are referred to as support coated open tubular (SCOT) or by others as porous layer open tubular (PLOT) columns. They have a higher sample capacity than liquid coated columns due to the greater amount of phase per unit length. Several recent papers have described modified methods of column preparation [39-41] using Silanox 101 as the support. 

Capillary Modification. The capillary was etched with a fluoride compound at high temperature to prepare a whisker column with a 1000-fold increased inner surface area as compared to an unmodified capillary... 

The preparation of polymer-coated capillaries consists of four consecutive, main steps, as illustrated in Figure 8.2 etching of the bare silica capillary, silylation of the etched surface, in situ polymerization, and evaporation of the solvent. Of the four steps, photopolymerization and evaporation of the solvent appear to be the most critical for obtaining uniform layers. The major drawback of the polymeric phases is the poor column efficiency that arises from the small diffusions of solutes in these retentive layers. 

ZnS nanotubes have been prepared by sulfidizing ZnO templates obtained in columnar form by electrochemical deposition.77 Heating the ZnO column in H,S above 400 °C gave the ZnS coated ZnO columns. The ZnO cores were then etched out giving hollow ZnS lubes. 

Patents [102, 103] describe the preparation of open tubular columns with an inside thickness-fixed porous layer by etching. First, the authors prepared a capillary column from a two-layer workpiece composed of two concentric tubes, one of them (external) being made of sodium borosilicate glass. To obtain an adsorption layer of defined thickness, the inner layer of the two-layer capillary was entirely leached. The method relies on porous glasses as the adsorbents. Porous glasses have been successfully used in gas capillary (see, for example, [104]). 

Table 1 summarizes some microstructural and electrochemical properties of porous Si anode materials, as pertaining to the second approach mentioned above, collected from the literature published since 2005. Several synthesis methods have been identified for preparing the porous Si anode materials (column 1, Table 1). One of the two most adopted methods is known as the metal-assisted chemical etching (MACE denoted as E in Table 1). The fundamental principle of this method can be found in the handbook chapter Porous Silicon Formation by Metal Nanoparticle Assisted Etching. Figure 2 shows an example of the MACE-derived porous Si particle. The other most adopted method is magnesiothermic reduction (denoted as M in Table 1). In this method (see handbook chapter Porous Silicon Formation by Porous Silica Reduction ), porous Si oxide materials are reduced by magnesium vapor under high-temperature thermal treatment. The porous Si oxide precursors may be synthesized via the conventional sol-gel processes. Porous Si particles with unique pore structures, such as hollow interior and ordered mesoporosity, may be obtained from Si oxides having the same pore structures which are achieved by using proper templates.

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