Chloride surfaces

Surface chlorides, too, were formed on diamond. The samples were outgassed in a high vacuum at 800° and immediately afterwards treated with chlorine at temperatures from 100 to 500°. With reaction temperatures up to 400°, 20 meq/100 gm were bound on the diamond surface, a quantity which is equivalent to the amount of potassium retained after treatment with this alkali metal. (Table XIII). The chlorine on... 

Rhe(CO)ie] on the Sur ce of MgO When RhCl3 H20 or [Rh(CO)2Cl]2 supported on MgO is treated with CO (latm) at room temperature, [Rh,5(CO)i,5] is formed and can be extracted with CH2CI2 (yields not reported) (Scheme 16.10). The unusual stabihty of a neutral cluster on the highly basic MgO surface was attributed to the formahon of surface chloride ions, which modify the strong basic character of surface sites close to the Rh atoms through formation of acidic Mg-Cl sites [104]. 

Upon illumination, photogenerated holes could convert surface chloride groups... 

As in the mechanism proposed by d Hennezel and Ollis, UV illumination was predicted to initiate the conversion of surface chloride groups into chlorine radicals. 

Reactor Component Development — Corrosion of heat-transport tubing — Growth of passive oxides — Hydrogen embrittlement — Surface chloride contamination... 

This present paper discusses in more detail three separate nuclear-related studies where surface analysis has been used extensively borosilicate glass leaching, surface chloride contamination, and gas phase oxidation of some nickel alloys. 

In order to minimize the temperature drop at the reactor inlet caused by the rapid, endothermic naphthene dehydrogenation, the catalyst bed was diluted by a low-surface, chloride-free alumina. The degree of dilution was varied in three different zones of the reactor, with the highest dilution at the reactor inlet. The first zone, comprising 33% of the reactor volume, contained only 6% of the total amount of catalyst. The temperature drop at the reactor inlet, measured with the axial thermocouple, did not exceed 5°C. 

Although the surface chloride of silica cannot be burned off as easily, it will react with H2 or CH3OH and these can then be burned off. This treatment sometimes also produced an increase in RMIP. However, the effect was minor by comparison to the bromide and iodide, probably because water was formed during the burn-off. 

Other materials were prepared by converting silica to silica chloride by treatment with thionyl chloride, and then reacting the surface chloride groups with amines as shown below ... 

Since bonding of chloride to platinum is stronger than water to platinum, the reported processes should be viewed in terms of a competitive chemisorption between two active surfactants surface chloride and an organic adsorbate. 

Furthermore, Eq. (1) is also used for the prediction of long-term performance of structures exposed to chloride environments, e. g. during the design stage or the evaluation of the residual life of existing structures. In principle, if D pp and Q are known and can be assumed to be constant in time, it is possible to evaluate the evolution with time of the chloride profile in the concrete and then to estimate the time t at which a particular chloride threshold will be reached and corrosion will initiate. For example. Figure 6.6, plots chloride profiles calculated for a surface chloride content of 5 % by mass of cement and a time of 10 y as a function of the apparent difiusion coefficient. Figure 6.7 shows the initiation times that can be estimated from those profiles as a function of the thickness of the concrete cover when a chloride threshold of 1 % by mass of cement is assumed. 

Figure 6.7 Initiation time of corrosion as a function of cover thickness and apparent diffusion coefficient assuming that the surface chloride concentration is 5 % and the critical threshold is...

Table 6.1 Composition, surface chloride content, apparent diffusion coefficient, corrosion rate and resistivity data for three mixes in marine-splash zone [23, 32] and motorway exposure [33] and strength from [23]...

The initiation time ( ) may be calculated as a function of the chloride transport properties of concrete (usually the apparent diffusion coefficient), the surface chloride content dictated by the environment, the thickness of the concrete cover and the critical chloride content determining the onset of corrosion. The arrival of the critical chloride content at the steel at depth x at time t is calculated using Fick s second law of diffusion (Chapter 6). 

Further omitting safety factors, the surface chloride content is calculated by... 

For electrochemical chloride extraction (abbreviated CE, also called chloride removal, or desalination), a direct current is applied between the reinforcement (cathode) and an anode that is placed temporarily on the outer surface of the concrete. The anode is an activated titanium wire mesh or a reinforcing steel mesh. The anode is surrounded by tap water or saturated calcium hydroxide solution in ponds (upper, horizontal surfaces) or tanks (vertical or overhead surfaces) or as a paste that can be sprayed onto all types of surface. Chloride ions migrate from the reinforcement to the anode. Due to a relatively high current density of 1 to 2 A/m, relatively large amounts of chloride can be removed from the concrete within a relatively short time, usually 6 to 10 weeks. After that, the anode, the electrolyte and the incorporated chloride ions are removed from the stracture. The principle layout and electrode reactions involved are indicated in Figure 20.8. 

Cs in Eq. (12.2) is surface chloride content. Least squares predicted data at 1 mm depth increments. 

Surface Chloride Concentration The main source of chloride ions arises from salt added during road and bridge deicing. Sodium chloride (NaCl) and calcium chloride (CaCy have been traditionally used as deicing salts. In the United States, 282 kg of salt are used per lane-mile. Normally the number of apphcations varies from less than 8 to more than 16 per year depending on climate conditions. Annual salt estimates for various states are given in Table 12.1. Rebar surface can be exposed to the following... 

The chloride ingress into concrete follows Pick s law of difiusion for cured concretes. Concrete mixtures and admixtures affect the diffusivity of chloride ions. Figure 12.7 shows the transport of chloride ions through the concrete deck under moderate corrosion environment. The surface chloride concentration is assumed to be equal to 3.56 kg/m, which corresponds to moderate corrosive conditions. Chloride diffusion follows an exponential decay into the concrete. Chloride concentration at the rebar surface increases with time. 

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