Boric oxide, formation

From Boric Oxide and Alcohol. To avoid removing water, boric oxide, B2O3, can be used in place of boric acid. The water of reaction (eq. 4) is consumed by the oxide (eq. 5). Because boric acid reacts with borates at high temperatures, it is necessary to filter the reaction mixture prior to distillation of the product. Only 50% of the boron can be converted to ester by this method. In cases where this loss can be tolerated, the boric oxide method is convenient. This is particularly tme for methyl borate and ethyl borate preparation because formation of the undesirable azeotrope is avoided. 

A common constituent of salt baths is boric oxide and the use of such mixtures in contact with nickel-rich alloys containing Ti, A1 or other strong reducing elements is to be avoided, owing to the possible formation of a nickel-boron eutectic of low melting point. 

The borothermic reduction of a metal oxide is easiest when there is no formation of dodecaboride. The boric oxide is volatile and is completely eliminated > 1500°C under vacuum. 

Ellis Wilson (1991, 1992) examined cement formation between a large number of metal oxides and PVPA solutions. They concluded that setting behaviour was to be explained mainly in terms of basicity and reactivity, noting that cements were formed by reactive basic or amphoteric oxides and not by inert or acidic ones (Table 8.3). Using infrared spectroscopy they found that, with one exception, cement formation was associated with salt formation the phosphonic add band at 990 cm diminished as the phosphonate band at 1060 cm" developed. The anomalous result was that the acidic boric oxide formed a cement which, however, was soluble in water. This was the result, not of an add-base readion, but of complex formation. Infrared spectroscopy showed a shift in the P=0 band from 1160 cm" to 1130 cm", indicative of an interaction of the type... 

Myers et al. reported that partially dehydrated APB is an effective intumescent flame retardant in thermoplastic polyurethane.77 APB at 5-10 phr loading in TPU can provide 7- to 10-fold improvement in burn-through test. It is believed that in the temperature range of 230°C-450°C, the dehydrated APB and its released boric oxide/boric acid may react with the diol and/or isocyanate, the decomposed fragments from TPU, to produce a highly cross-linked borate ester and possibly boron-nitrogen polymer that can reduce the rate of formation of flammable volatiles and result in intumescent char. 

Zinc borates are predominately a condensed phase fire retardant. In a halogenated system such as flexible PVC, it is known to markedly increase the amount of char formed during polymer combustion whereas the addition of antimony trioxide, a vapor-phase flame retardant, has little effect on char formation. Analyses of the char show that about 80%-95% of the antimony is volatilized, whereas the majority of the boron and zinc from Firebrake ZB remains in the char (80% and 60%, respectively).48-56 The fact that the majority of the boron remains in the condensed phase is in agreement with the fact that boric oxide is a good afterglow suppressant. The mode of action can be summarized in the following equation (not balanced). 

Sometimes, usually because of the difficulty of obtaining some elements completely pure, one is faced with a bewildering variety of values for the same heat of formation. For example, the thermochemistry of boron compounds has been hampered for some time by lack of a reliable value of the heat of formation of boric oxide, B2O3. Recent values for c) at 25° C have ranged from... 

Boric acid and boric oxide and probably many other boron compounds are converted in sulfuric acid to boron tri (hydrogensulfate), B(HS04)3, which behaves as a strong acid, HBfHSO ). The evidence for the formation of this acid and its salts provides an interesting example of the application of the cryoscopic and conductimetric methods for determining modes of ionization ( 4). 

The enthalpy changes for the following three reactions, which represent the formation of dilute boric acid solution, the dissolution of crystalline boric oxide, and the formation of liquid water respectively, are as follows ... 

Phenolic ester formation between a phenol and a higher carboxylic acid catalysed by a 4A molecular sieve has been described with a modification that after 1 hour at 120 C under nitrogen, boric oxide B2O3, was added, presumably to absorb water and the refluxing continued for 5 hours at 185°C (ref.1). 

Addition of alkali oxides to vitreous silica result in the formation of NBO. Examination of property trends for alkali silicate versus alkali borate glasses, however, suggests that this is not the case for alkali borate glasses. Small additions of alkali oxides to silica cause a decrease in Tg, while similar additions to boric oxide cause an increase in Tg. Conversely, small additions of alkali oxides to silica cause an increase in the thermal expansion coefficient, while similar additions to boric oxide cause a decrease in the thermal expansion coefficient. Any potential structural model for alkali borate glasses must directly address this extreme difference in behavior. 

If the effect of alkali oxide additions to boric oxide cannot be explained on the basis of NBO formation, how can they be explained ... 

Combinations of boric oxide with polyacrylic and polyphosphonic acid exhibit quick setting and hardening based on the formation of hydrogen-bonded complexes. 

Boron alkoxides form the oxide or boric acid when reacted with excess watCT. Oxide formation can be written as... 

Mineralizer. A substance that, even though present in only a small amount, assists the formation and/or crystallization of other compounds during firing. A small amount of alkali, for example, mineralizes the conversion of quartz to cristobalite boric oxide acts as a mineralizer in the synthesis of spinel (MgAl204) the presence of iron compounds facilitates the growth of mullite crystals. 

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