Whetlerites

Hilaski R, Katz S, Salem H. 1992. Inhalation toxicity of chromium from Whetlerite dust in rats. 

Since carbon molecular sieves are amorphous materials, the dimensions of their pore structures must be measured phenomenologically by the adsorption of small probe molecules with different critical dimensions. There is insufficient long range order to utilize standard x-Ray diffraction methods for characterization. The earliest reports of molecular sieving carbons dealt primarily with coals and charcoals. Sorption of helium, water, methanol, n-hexane, and benzene was measured and related to the porosity of the carbon. Pore-sizes were estimated to be two to six angstroms (3-6). In a classic paper P.H. Emmett described methods for tailoring the adsorptive properties and pore size distributions of carbon Whetlerites. 

E.s.r. signals were not obtained after treatment with HCl, t-C4H9NH2, and CO. The effect of amine treatments on the reactivity of whetlerites, with respect to CNCl, has also been studied." " ... 

Charcoal Charcoal, activated Charcoal briquettes, shell, screenings, wood, etc. Charcoal, except activated EINECS 240-383-3 HSDB 2017 NA1361 Swine fly ash Whetlerite. 

The main applications of the carbon support include hydrogenation reactions (Pd/C, Pt/C, Pt-Fe/C, Fe-Ru/C, Fe-Co/C, Ni/C/Co/C), oxidation reactions (Sn/C, Ni/C), and environmental automotive catalysis (Cu/C, Cu-Cr/C) [341], The examples of carbons working as catalyst supports are discussed in the following chapters. The best known examples are whetlerites used for military filters... 

So, very generally, the complete chemisorption mechanism for HCN on an ASC whetlerite can be described by Eq.l6 ... 

CNCl + whetlerite-HjO HOCN + HCl 2 HCl + (NHtjaCOs 2 NH4CI + H2CO3 H2C03 C02 + H20... 

As for chromium-free whetlerites, e.g. ASZM-TEDA, there is very little known about the actual processes involved in the CNCl retention. As there seems to be very little difference in the capacity to remove CNCl between ASZ (Cu, Zn " and ASZM (Cu ", Zn , Mo ) carbons [52], it is safe to suggest that the Zn " takes over the tasks of Cr , as catalyst,... 

This effect will be even more pronounced when a high number of nitrogen atoms is present on the surface, i.e. when tlie surface basicity of the carbon increases [81]. Given the impregnation process of whetlerites (see section 4.2.2.1), it is clear that the residual ammonia from the impregnation solution will enhance the capacity of the carbon for SO2 adsorption. The presence of the basic TEDA molecules will reinforce this effect. 

As TEDA is present on all modem types of whetlerite, military filters exhibit a rather good retention of radioactive gases by direct chemisorption. However, one has to bear in mind this is only a retention, not a destruction. This means that the filter itself will become a radioactive source, much like when retaining radioactive aerosol particles (see section 2.3.8), and has to bo replaced, and disposed of, as soon as possible. 

From the previous sections it is clear that military filters filled with whetlerite carbon retain most industrial vapours and gases at least as eifectively as dedicated industrial filters, especially when the supplementary impr nation with TEDA is added. This is also illustrated in Fig.l5, where the breakthrough times for a number of gases of some typical military filters (filled with whetierites) are compared with the minimum requiremoits of an industrial filter ABEK-2, tested confoim the European Standard EN141 [83]. This norm describes the testing conditions and requirements of the most common types of industrial filters. The data presented arc for tests with a flow rate of 30 litres/min, an inlet concentration of 5000 ppmv and a relative humidity of the air stream of 70%. 

The protection against Chemicd Warferc Agents is a very small, but highly specialised field amongst activated carbon applications. Even after several decades of intensive use and elaborate research, many aspects of the military carbons, most of which are knovm as whetlerites, remain unclear. Much as is the case for other applications, activated carbon provides an adequate answer to a wide variety of problems, but raises a lot of questions as to the how and why of its excellent performance. This will, however, not prevent it from continuing to play its role as the first line of defence against the threat of CWAs in the near and even in the not so near future. 

The effectiveness of modern masks depends on both physical adsorption and chemical inactivation of the threat agent. For example, in the M17 protective mask the adsorbent, known as ASC Whetlerite charcoal, is charcoal impregnated with copper oxide and salts of silver and chromium.6 The M40 protective mask uses an ASZ impregnated charcoal, which substitutes zinc for the hexavalent chromium (CrVI). The Centers for Disease Control and Prevention and the National Institute for Occupation... 

Liang, S. H. Harrison, B. H. Pagotto, J. G. Analysis ofTEDA on ASC-Whetlerite Charcoal Defense Research Establishment, Ottawa. Available at httD //handle.dtic.mil/100.2/ADA192035. 

Saxena et al. studied the adsorption of dimethyl methyl phosphonate (DMMP) as a stimulant for Sarin, which is a highly toxic warfare gas agent. The adsorption was carried out on an activated carbon, a whetlerite and activated carbon impregnated with copper hexafluorocacetylacetonate (1) copper trifluoro acetyl-acetonate and a copper oxime. The adsorption isotherms are Type 1 of the BET classification and show maximum adsorption in the case of activated carbon (1). The amount adsorbed was 68.5 weight percent on (1). The adsorption involved both physisorption and chemisorption. TGA and IR studies of DMMP loaded activated carbons, and mass spectric analysis of the decomposition products showed that the decomposition products were methyl methyl phosponic acid and methylphosphonic acid. 

Emmett, P. H. (1948). Adsorption and pore-size measurements on charcoals and whetlerites. Chem. Rev. 43(1), 69-148. 

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