Pentaborate

CFIO chromophore, 278 KBjOg (potassium pentaborate, KPB) harmonic generation, 346... 

Boron. The principal materials used are borax [1303-96-4] sodium pentaborate, sodium tetraborate, partially dehydrated borates, boric acid [10043-35-3] and boron frits. Soil appHcation rates of boron for vegetable crops and alfalfa are usually in the range of 0.5—3 kg/hm. Lower rates are used for more sensitive crops. Both soil and foHar appHcation are practiced but soil appHcations remain effective longer. Boron toxicity is not often observed in field appHcations (see Boron compounds). 

The polyions postulated in solution all have known structural analogues in crystalline borate salts. Investigations of the Raman (66) and B nmr (67) spectra of borate solutions have confirmed the presence of three of these species the triborate (3), B202(0H) 4, tetraborate (4), [B40 (0H) 4], and pentaborate (5) B O (OH) 4, polyanions. Skeletal stmctures were assigned based on coincidences between the solution spectra and those soHd borates for which definitive stmctural data are available (52). These same ions have been postulated to be present in alkah metal borate glasses as well. 

Fig. 5. Solubility—temperature curves for boric acid, borax, sodium pentaborate, and sodium metaborate (71).

A single-crystal x-ray diffraction study has shown that the borate anion in anhydrous borax is polymeric in nature and is formed via oxygen bridging of triborate and pentaborate groups (83). The chemistry of anhydrous borax has been reviewed (73,84). 

Sodium Pentaborate Pentahydrate. Sodium pentaborate pentahydrate, NaB Og -5H20 or Na20 -5B203 -10H2O formula wt, 295.11 monoclinic sp gr, 1.713 exists in nature as the mineral sborgite [12272-01 -4]. Heat capacity, entropy, and other thermal measurements have been made at 15-345 K (85). 

Crystalline sodium pentaborate pentahydrate is stable in the atmosphere. When heated in vacuum, it is stable to 75°C however, above 75°C, four of its five H2O molecules are lost (73). 

A single-crystal x-ray diffraction study gives a stmctural formula of Na2 [B5 0g (0H)4]-3H2 0 and contains the pentaborate ion analogous to that found in the corresponding potassium compound (86). 

Whereas there is no commercial production of sodium pentaborate pentahydrate, the compound can be prepared by crystallizing a borax-boric acid solution having a Na20 B202 mol ratio of 0.2. 

Potassium Pentaborate Tetrahydrate. Potassium pentaborate tetrahydrate, KB Og 4H2O or K2O -5B202 8H20 formula wt, 293.20 orthorhombic prisms sp gr, 1.74 heat capacity, 329.0 J/(mol-K) [78.6 cal/(mol-K)] at 296.6 K is much less soluble than sodium pentaborate (Tables 9 and 10). Heat capacity measurements on the soHd have been made over a broad temperature range (85). 

The sohd-state stmctural formula is K[B Og(OH)4] H2O (123), which is analogous to that found ia sodium pentaborate (5). 

The a-form, which crystallines as the kinetic product, is the commercial form of ammonium pentaborate tetrahydrate and the P-form is the thermodynamic product but is slow to crystalline. Its heat capacity has been measured over a broad temperature range (85). Solubihty data are given ia Table 9 and pH data ia Table 10. 

Ammonium pentaborate tetrahydrate is very stable ia respect to ammonia loss. On heating from 100 to 230°C, it loses 75% of its water content but less than 1% of the ammonia. At 200°C, under reduced pressure, the water content drops to 1.15 mol, but only 2% of the ammonia is lost (61). At still higher temperatures all ammonia and water are expelled to give boric oxide (125). 

Ammonium tetraborate tetrahydrate is prepared by crystallization from an aqueous solution of boric acid and ammonia having a B202 (NH4)20 ratio of 1.8 2.1. Ammonium pentaborate is similarly produced from an aqueous solution of boric acid and ammonia having a B202 (NH4)20 ratio of 5. Supersaturated solutions are easily formed and the rate of crystallization is proportional to the extent of supersaturation (130). A process for the production... 

Sodium Calcium Pentaborate Pentahydrate. Sodium calcium pentaborate pentahydrate, NaCaB O 5H20 or Na20 2CaO 5B2O2 10H2O formula wt 351.19 monoclinic sp gr, 2.14 exists ia nature as the mineral probertite. Probertite can be prepared by heating a... 

Fig. 9. The borate glass stmctural groups where = boron Q — oxygen (a) boroxol (b) pentaborate (c) triborate and (d) diborate (142).

This system is backed-up by a Standby Liquid Control System (SLCS) that injects sodium pentaborate into the moderator using a positive displacement pump (shown as a piston pump). Steam that originates in the core of a BWR, unlike the primary coolant in a PWR, exits the containment. The closing of the MSIVs isolates the radioactivity from the environment but when this is done, normal heat removal is not possible. The Residual Heat Removal (RHR) system... 

Potassium oxide in cement, 5 468 in dental ceramics, 8 275 Potassium ozonide, 18 417, 418 Potassium pentaborate tetrahydrate, 4 242t, 276... 

Sodium calcium pentaborate pentahydrate, 4 242t, 278-279 Sodium carbide, 22 765 Sodium carbonate, 20 631, 22 765, 787-797, 23 669, 3 416. See also Soda ash applications of, 22 794-795 from brine, 5 799-800 carbon dioxide recovery from natural gas using, 4 811... 

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