Inert substrates

Color Additives. The FDA has created a unique classification and strict limitations on color additives (see also CoLORANTS FOR FOOD, DRUGS, COSMETICS, AND MEDICAL DEVICES). Certified color additives are synthetic organic dyes that ate described in an approved color additive petition. Each manufactured lot of a certified dye must be analyzed and certified by the EDA prior to usage. Color lakes are pigments (qv) that consist of an insoluble metallic salt of a certified color additive deposited on an inert substrate. Lakes are subject to the color additive regulations of the EDA and must be certified by EDA prior to use. Noncertifted color additives requite an approved color additive petition, but individual batches need not be EDA certified prior to use. 

Thin films of metals, alloys and compounds of a few micrometres diickness, which play an important part in microelectronics, can be prepared by die condensation of atomic species on an inert substrate from a gaseous phase. The source of die atoms is, in die simplest circumstances, a sample of die collision-free evaporated beam originating from an elemental substance, or a number of elementary substances, which is formed in vacuum. The condensing surface is selected and held at a pre-determined temperature, so as to affect die crystallographic form of die condensate. If diis surface is at room teiiiperamre, a polycrystalline film is usually formed. As die temperature of die surface is increased die deposit crystal size increases, and can be made practically monocrystalline at elevated temperatures. The degree of crystallinity which has been achieved can be determined by electron diffraction, while odier properties such as surface morphology and dislocation sttiicmre can be established by electron microscopy. 

It is a valve metal and when made anodic in a chloride-containing solution it forms an anodic oxide film of TiOj (rutile form), that thickens with an increase in voltage up to 8-12 V, when localised film breakdown occurs with subsequent pitting. The TiOj film has a high electrical resistivity, and this coupled with the fact that breakdown can occur at the e.m.f. s produced by the transformer rectifiers used in cathodic protection makes it unsuitable for use as an anode material. Nevertheless, it forms a most valuable substrate for platinum, which may be applied to titanium in the form of a thin coating. The composite anode is characterised by the fact that the titanium exposed at discontinuities is protected by the anodically formed dielectric Ti02 film. Platinised titanium therefore provides an economical method of utilising the inertness and electronic conductivity of platinum on a relatively inexpensive, yet inert substrate. 

The electrochemical preparation of metal chalcogenide compounds has been demonstrated by numerous research groups and reviewed in a number of publications [ 1-3]. For the most part, the methods that have been used comprise (a) cathodic co-reduction of the metal ion and a chalcogen oxoanion in aqueous solution onto an inert substrate (b) cathodic deposition from a solvent containing metal ions and the chalcogen in elemental form (the chalcogens are not soluble in water under normal conditions, so these reactions are carried out in non-aqueous solvents) (c) anodic oxidation of the parent metal in a chalconide-containing aqueous electrolyte. 

At the next level of abstraction are measurements performed at a thin film of fuel cell catalyst immobilized on the surface of an inert substrate, such as glassy carbon (GC) or gold (Fig. 15.2c). Essentially, three versions of this approach have been described in the fiterature. In the first case (a porous electrode ), an ink containing catalyst and Nafion ionomer is spread onto an inert nonporous substrate [Gloaguen et al., 1994 Gamez et al., 1996 Kabbabi et al., 1994]. In the second case (a thin-fihn electrode ), the ink does not contain Nafion , but the latter is... 

The normalized steady-state current vs. tip-interface distance characteristics (Fig. 18) can be explained by a similar rationale. For large K, the steady-state current is controlled by diffusion of the solute in the two phases, and for the specific and y values considered is thus independent of the separation between the tip and the interface. For K = 0, the current-time relationship is identical to that predicted for the approach to an inert substrate. Within these two limits, the steady-state current increases as K increases, and is therefore diagnostic of the interfacial kinetics. 

Our future work towards the investigation of the catalytic potential of our novel catalysts will involve more inert substrates such as aryl chlorides and bromides. 

Metallocenes are homogeneous catalysts that are often soluble in organic solvents. Therefore, polymerization can occur via a solution process with a non-polar diluent dissolving the propylene gas, the catalyst, and the co-catalyst system. They can also be adsorbed onto an inert substrate which acts as part of the fluidized bed for gas phase polymerization processes. 

Nickel hexacyanoferrate (NiHCF) films can be prepared by electrochemical oxidation of nickel electrodes in the presence of hexacyanoferrate(III) ions,141 or by voltammetric cycling of inert substrate electrodes in solutions containing nickel(II) and hexacyanoferrate(III) ions.142 NiHCF films do not possess low-energy intervalent CT bands, however, when deposited on ITO they are observed to reversibly switch from yellow to colorless on electroreduction.143... 

Asap is a projected geometric or superficial area of the substrate. Aact is the active surface area through which current may pass. For circuit lines flush with an inert substrate, a is smaller than one. For a deep feature, whose walls admit current, a may be larger than one (see Fig. 5). 

Fig. 5. Illustration of the real and superficial current density. Top Current ditribution over lines on an inert substrate. Middle Current distribution over an array of trenches. Bottom Current distribution over a branching aggregate.

In another electrode structure, a porous hydrophobic membrane is compressed on an electrode structure ( 3,0. The hydrophobicity of the membrane prevents the weeping of the electrolyte and allows the gas to penetrate freely into the electrode structure. This electrode consists mainly of an electroactive material (usually precious metals) dispersed on an inert substrate (typically carbon) and these components are bound together by some partially hydrophobic agent (PTFE) the mechanical support and electrical contact is... 

The concept of impedance microbiology is more than a century old however, it gained its popularity only in the mid-seventies. Impedance is based on the changes in conductance in a medium due to the microbial breakdown of inert substrates into electrically charged ionic compounds and acidic by-products. The detection time, that is, the time necessary for... 

Porous MIP disks may be made, e.g., by incorporating MIP particles in a meshlike inert network or by polymerizing MIPs in the pores of a porous inert membrane. The MIP so generated may either fill the pores (without clogging the membrane since the MIP is itself porous) or the MIP may form a thin film on the pore walls of the inert substrate. 

There continues to be major problems with coupling HPLC to FTIR (Fourier transform infrared) due to the interference caused by water. The interface is the critical component in the system [126]. The two basic types of interfaces are continuous and capture. A continuous interface has been developed that uses a liquid-liquid extraction. In this approach, the analytes are extracted from the mobile phase by mixing postcolumn with a stream of IR (infrared) transparent, water-immiscible solvent. In the ca-pure technique, the eluent is deposited on a continuously moving, IR transparent, inert substrate from which the eluent can be easily removed by evaporation. These techniques have been applied to identification of racemic precursors of diltizam, AZT derivatives, and steroids [127]. 

Adsorption from the liquid phase is experimentally much easier (cheaper), but requires, even for highest-purity solvents, chemical inert substrates, e.g., hopg, or selective adsorbate systems, like thiols on gold. 

Figure 20. The SECM-induced desorption experiment. Chronoamperometric characteristics for the reduction of H+ on (a) a rutile (001) surface with d — 2.6 pm, and (b) an albite (010) surface with d — 2.8 pm In each case, solid curves from bottom to top represent the theoretical behaviors for an inert substrate and for specified adsorption rate constant values. Adapted with permission from Ref. [79]. Copyright (g) 1992, American Chemical Society.

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