Gaseous boron oxides

It is postulated that HOBO then reacts with BO to form gaseous boron oxide hydride, HBO, and boron dioxide, B02 (OBO). 

Active oxidation of B4C at a low partial oxygen pressure leads to the formation of gaseous boron oxides and removal of them from the surface of the specimen. Similar to other materials, porosity increases the reactive surface of boron carbide specimens and weight gain on oxidation [106]. 

Although most of the fluorine calorimetry has been done with the elements, it has been used to burn oxides, carbides, nitrides, and chal-cogenides and hence determine their heats of formation. In some instances it has proved superior to oxygen bomb calorimetry. Thus the oxidation of boron tends to be incomplete because of oxide coating, whereas fluorination produces gaseous boron trifluoride without surface inhibition. A summary of modem fluorine calorimetry results is assembled in Table III. 

In a high-temperature atmosphere created by the combustion of a host hydrocarbon fuel, there will be an abundance of hydroxyl radicals. Thus, boron monoxide reacts with hydroxyl radicals to form gaseous metaboric oxide HOBO. 

Most borides are chemically inert in bulk form, which has led to industrial applications as engineering materials, principally at high temperature. The transition metal borides display a considerable resistance to oxidation in air. A few examples of applications are given here. Titanium and zirconium diborides, alone or in admixture with chromium diboride, can endure temperatures of 1500 to 1700 K without extensive attack. In this case, a surface layer of the parent oxides is formed at a relatively low temperature, which prevents further oxidation up to temperatures where the volatility of boron oxide becomes appreciable. In other cases the oxidation is retarded by the formation of some other type of protective layer, for instance, a chromium borate. This behavior is favorable and in contrast to that of the refractory carbides and nitrides, which form gaseous products (carbon oxides and nitrogen) in air at high temperatures. Boron carbide is less resistant to oxidation than the metallic borides. 

Methyl tetra-O-acetyh/S-D-glucopyranoside (1 g. dried over phosphorus pent-oxide) in anhydrous chloroform was saturated with gaseous boron trifluoride and the solution was kept for 24 hr. The gelatinous precipitate was decomposed by shaking with sodium bicarbonate solution, and the chloroform layer was washed with water. After drying with calcium chloride, it yielded 0.98 g. of the a anomer m. p. 97-98 [ Id +121°. Recrystallization from ethanol gave material of m. p. 100-101° [q ]d +130°. 

Gaseous boric acid removes a boron oxide film. The rates of formation and removal of the B2O3 film are equal at 550-600°C in air with a dew point of 25-70°C and at 650°C with a dew point of 88°C. At higher temperatures, B2O3 is formed at a higher rate than it is removed by the interaction with water vapor. Therefore, at low temperatures boron carbide is oxidized with water vapor more rapidly than with dry air, at high temperatures the situation is quite the opposite [2]. 

The highly corrosive gaseous boron trifiuoride is prepared by the action of concentrated sulfuric acid on a mixture of the oxide and calcium fiuoride [Equation (14.4)] ... 

Because the breadth of chemical behavior can be bewildering in its complexity, chemists search for general ways to organize chemical reactivity patterns. Two familiar patterns are Br< )nsted acid-base (proton transfer) and oxidation-reduction (electron transfer) reactions. A related pattern of reactivity can be viewed as the donation of a pair of electrons to form a new bond. One example is the reaction between gaseous ammonia and trimethyl boron, in which the ammonia molecule uses its nonbonding pair of electrons to form a bond between nitrogen and boron ... 

---