Borax, dehydration

The main boric raw materials are boric acid H3BO3 and borax (Na2B4.07.10 H2O) or borax dehydrated to pentahydrate. Boron-containing natural raw materials have also been used in some instances they are based on the minerals datolite (2 CaO. ... 

Synonyms/Trade Names Anhydrous borax, Borax dehydrated, Disodium sait of boric acid. Disodium tetrabromate. Fused borax. Sodium borate (anhydrous). Sodium tetraborate... 

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). 

Heats of dehydration per mole of water vapor are (74) decahydrate to pentahydrate, 54.149 kj (12.942 kcal), and decahydrate to tetrahydrate, 54,074 kj (12.924 kcal). Borax stored over a saturated sucrose-sodium sucrose—sodium chloride solution maintains exacdy 10 moles of water and can thus be used as an analytical standard. Commercial borax tends to lose water of crystallisation if stored at high temperature or ia dry air. 

Rapid heating of either borax decahydrate or pentahydrate causes the crystal to dissolve before significant dehydration, and at about 140°C, puffing occurs from rapid vaporisation of water to form particles having as high as 90% void volume and very low bulk density (78). 

Pentahydrate is reversibly converted to an amorphous dihydrate, at 88°C and 0.26 kPa (2 mm Hg) or by boiling with xylene (73,75). The heat of dehydration for the pentahydrate to tetrahydrate has been calculated to be 53.697 kj (12.834 kcal) per mole of water (74). Thermogravimetric analyses show that 2.75 moles of water are lost on heating to 140°C. Like borax, pentahydrate puffs when heated rapidly to give a product having a bulk density of 0.042 g/mL (79). 

The dihydrate loses water slowly at room temperature. Its heat of dehydration to NaB02 0.5H2O has been calculated as 58.1 kJ/mol (13.9 kcal/mol) of H2O (88). Sodium metaborate dihydrate reacts with atmospheric CO2 to produce sodium carbonate and borax. The melting point is 90—95°C, compared to 54°C for the tetrahydrate. Some crystallographic work has been done (91). 

Commercial preparation of sodium perborate tetrahydrate is by reaction of a sodium metaborate solution, from sodium hydroxide and borax pentahydrate, and hydrogen peroxide followed by crystallization of tetrahydrate (95). The tnhydrate and monohydrate can be formed by reversible dehydration of the tetrahydrate. 

Very recently, ball milling was also nsed to synthesize sodium borohydride, NaBH, by mechano-chemical reaction of dehydrated borax (Na B O,), MgH and Na COj (at room temperature) according to the following reaction [176]... 

Z.P. Li, N. Morigazaki, B.H. Liu, S. Suda, Preparation of sodium borohydride by the reaction of MgHj with dehydrated borax through ball milling at room temperature , J. Alloys Compd. 349 (2003) 232-236. 

Dehydration gives pentahydrate, Na2B407 5H20 and other lower hydrates. Calcination at elevated temperatures gives anhydrous borax. 

Borax pentahydrate occurs in nature as mineral tincalconite, formed by dehydration of borax. It has several industrial applications, mostly the same as its decahydrate. The pentahydrate is used in the manufacture of borosili-cate glass. It also is used in cleaning agents ceramic glaze adhesives cosmetics antifreeze and herbicide formulations. It is added to fertihzers to provide boron as a nutrient to the plants. 

The production methods of BA from BPH or borax dec-ahydrate may be categorized into three main groups. These are (a) azeotropic distillation, (b) melting and (c) dehydration in fluidized bed. 

Production of BA without fusion is very attractive with respect to energy consumption and corrosion. Thus, the attempts have mostly been in dehydration borax pentahydrate in a fluidized bed via a stage-wise calcination [4,5]. The main disadvantage of this process is the puffing of the par-... 

Only a few borates of cadmium are known. Cadmium monoborate monohydrate CdO B203 H20 is formed in cadmium nitrate/borax solutions. The 1 2 5 borate precipitates from hot boric acid solutions containing cadmium acetate (206). Its dehydration occurs in three stages, with one water molecule lost at 100°C, three at 100-150°C, and the last at over 300°C. 

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