De Boer method

The nitrides can be prepared by heating a metal powder in an N2 or NH3 atmosphere to temperatures above 1100°C. The carbides form upon heating mixtures of the metal powders with carbon to temperatures of about 2200 °C. Both the nitrides and carbides can also be made by chemical transport reactions by the van Arkel-de Boer method if the metal deposition takes place in an atmosphere of N2 or a hydrocarbon. Their remarkable properties are ... 

SBA-15 samples with diameters from 5 to 10 nm have been prepared by tuning the temperature of the first step of the synthesis [5], MCM-41 has been prepared in the presence of hexadecyl trimethyl ammonium by using methylamine as pH-controlling agent [6], The pore size from N2 adsorption at 77 K has been evaluated by the Broekhoff and de Boer method, shown to correctly evaluate the pore size of ordered mesoporous silicas [7]. 

Very highly pure titanium metal can be prepared in small amounts by decomposition of pure titanium tetraiodide, (Tih) vapor on a hot wire under low pressure (Van Arkel-de Boer method). 

Extremely pure Ti can be made on a small scale by the van Arkel-de Boer method (also used for other metals) in which pure Til4 vapor is decomposed on a hot wire at low pressure. 

Reduction to elemental titanium was first commercialized in the 1950s. A successful laboratory method is reduction of the dioxide with excess calcium hydride in a molybdenum boat. The reaction is carried out at 900 °C in a vacuum or an atmosphere of hydrogen (equation 1). Extremely pure titanium can be prepared on a laboratory scale by the van Arkel-de Boer method in this method, pure TiLi is vaporized and decomposed on a hot wire in a vacuum. 

Table 2 shows that the specific surface Sbet and the Dubinin micropore volume Vp increase with the EDAS/TEOS ratio. Figure 2a presents the evolution of the cumulative surface distribution over the micro- and the mesopore range obtained by applying the Brunauer and the Broekhoff-de-Boer methods in their respective domains. For low EDAS content, 0.025 < EDAS/TEOS < 0.06, the structure is mainly microporous, whereas for high EDAS content, 0.1 < EDAS/TEOS < 0.2, mesopores are also present. Indeed, a large mesopores distribution... 

Figure 2. (a) Cumulative surface area as function of pore diameter obtained by applying Brunauer and Broekhoff-de-Boer methods, (b) FHH plots (Equation 1). The exponents m and the linear range A(p/p ) used for their extraction are presented in Table 2. 

Lukens, W.W., Jr, Schmidt-Winkel, P., Zhao, D., et al. (1999). Evaluating pore sizes in mesoporous materials a simplified standard adsorption method and a simplified BroekhofF-de Boer method. Langmuir, 15, 5403-9. 

The highest purity (0.03% C and 0.006% N) is attained via the elegant recovery process of van Arkel and de Boer (method V below). This is based on the thermal decomposition of titanium iodide at 1100-1500 °C. 

Broekhofif-de Boer method are in good agreement with transmission electron microscopy data. 

The last section has shown the basic concepts of capillary condensation and how they can be utilized in the determination of pore size distribution (PSD). In this section, we address a number of practical approaches for PSD determination. One of the early approaches is that of Wheeler and Schull and this will be presented first. A more practical approach is that of Cranston and Inkley, and this will be discussed next. Finally, the de Boer method is presented, which accounts for the effect of pore shape on the calculation of the statistical film thickness and the critical pore radius. 

---