Orthophosphate

As discussed in Chapter 3, though phosphates exist in three structural forms, orthophosphates, pyrophosphates and metaphosphates, they are found in nature mainly as orthophosphates. The acid phosphates used in the synthesis of CBPCs, as well as the resulting products that constitute CBPCs are also orthophosphates, and therefore, this chapter is focused on orthophosphate minerals. Readers interested in other types of phosphates are referred to the excellent review by Corbridge et al. [1]. 

The interatomic bonds that produce the crystalhne structures of minerals are briefly discussed first. This is followed by general mles used in constmcting models of crystal structures of phosphate minerals, then the crystal structures of orthophosphate mineral forms. The discussion is brief because the emphasis of the book is on practical aspects of novel phosphate ceramics and cements. Readers interested in more details are referred to Corbridge et al. [1] and Kanazawa [2]. 

The basic budding block of the orthophosphates is the PO4 unit, which is briefly discussed here. This helps us to better understand various mineral forms that constitute the orthophosphate ceramics and cements. For additional discussion on crystal chemistry and crystal stmctures, see Refs. [1-3]. 

Phosphoric acid forms several series of salts in which the acidic H atoms are successively replaced by various cations there is considerable commercial application for many of these compounds. 

Lithium orthophosphates are unimportant and differ from the other alkali metal phosphates in being insoluble. At least 10 crystalline hydrated or anhydrous sodium orthophosphates are known and these can be grouped into three series  

Likewise, there are at least 10 well-characterized potassium orthophosphates and several ammonium analogues. The presence of extensive H bonding in many of these compounds leads to considerable structural complexity and frequently confers important properties (see later). The 

In all of these alkali-metal and alkaline earth-metal orthophosphates there are discrete, approximately regular tetrahedral PO4 units in 

Phosphaies are used in an astonishing variety of donicsiic and industrial applications but their ubiquitous presence and their substantial impact on everyday life is frequently overlo(4ted. It will be convenient first lo indicate the specihc uses of individual compounds and the properties on which ihey are based, then to conclude with a brief summary of many diffcreni types of application and their interrelation. TTie most widely used compounds are the various phosphate salts of Na, K. NH4 and Ca. TTie uses of di-. iri- and poly-phosphaie.s are mentioned on pp. 527-29. 

As mentioned in Section 5.2.5.1, zinc phosphate, while having many desirable properties as an anticorrosive pigment, does not demonstrate the degree of corrosion protection offered by lead and chromate pigments [5.55]. Therefore the pigment industry has concentrated on developing phosphate-based pigments with improved 

By controlled chemical modifications under consideration of different points of view with suitable elements and compounds connected with the optimization of the manufacturing processes, it has become possible to improve the effectiveness of zinc phosphate for many applications [5.68, 5.70]. 

An overview of modified orthophosphate pigments that have gained economic importance is given in Table 5.6. When looking at Table 5.6, it becomes obvious that the pigment industry has developed several variations of zinc phosphate to improve 

The aim of phosphate borate combinations was to accelerate the readiness to hydrolyze [5.78] because,e as discussed in Section 5.2.5.1, the hydrolyzation process is one prerequisite for the effectiveness of zinc phosphates but these pigments need a certain time for activation. The improved anticorrosive activity of zinc phosphate molybdates is attributed to the inhibitive effect of water-soluble molybdate ions [5.55]. 

Zinc-free phosphates compounds variation of the cations e.g. with [5.54,5.81] 

Crystalline diphosphoric acid. The reaction discovered by Geuther  

Is recommended by Partington and Wallsom for obtaining very pure H 4P P 7. 

A mixture of H3PO4 and POCI3 carefully evaporated in a platinum dish at 180°C. The residue Is allowed to crystallize In a cooled desiccator. 

Vitreous crystals. M.p. 61 C. Soluble without change In Ice water gradually forms orthophosphoric acid at higher temperature. 

Pentasodlum triphosphate Is prepared by annealing a quenched melt of solid (NaPOg)n (Graham s salt) and Na PgO, between 300 and 500°C (Huber)  

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The prefix is also used in orthophosphates, orthocarbonates, orthoformates and ortho-silicates, which are derivatives of POCOH), the hypothetical C(OH)4, HC(OH)3 and Si(OH)4 respectively in these the word ortho is always written in full. 

The above is a general procedure for preparing trialkyl orthophosphates. Similar yields are obtained for trimethyl phosphate, b.p. 62°/5 mm. triethyl phosphate, b.p. 75-5°/5 mm. tri-n-propyl phosphate, b.p. 107-5°/5 mm. tri-Mo-propyl phosphate, b.p. 83-5°/5 mm. tri-wo-butyl phosphate, b.p. 117°/5-5 mm. and tri- -amyl phosphate, b.p. 167-5°/5 mm. The alkyl phosphates are excellent alkylating agents for primary aromatic amines (see Section IV,41) they can also be ua for alkylating phenols (compare Sections IV,104-105). Trimethyl phosphate also finds application as a methylating agent for aliphatie alcohols (compare Section 111,58). 

A convenient method for preparing pure AW-dialkyl anilines and substituted anilines directly from the corresponding amines consists in heating the latter with trialkyl orthophosphates ... 

Chapter IV. a-Chloromethylnaphthalene (IV,23) benzylamine (Gabriel synthesis) (IV,39) i r.N -dialkylanilines (from amines and trialkyl orthophosphates) (IV,42) a-naphthaldehyde (Sommelet reaction) (IV,120) a-phenyl-cinnamic acid (Perkin reaction using triethylamine) (IV,124) p-nitrostyrene (IV,129) p-bromonaphthalene and p naphthoic acid (from 2 naphthylamine-1 -sulphonic acid) (IV,62 and IV,164) diphenic acid (from phenanthrene) (IV,165). 

The ability of various selenium heterocycles to check the loss of orthophosphate caused by irradiation of ATP has been studied by Brucker and Bulka (92). They found that only 2-amino-4,5-dimethyiselenazole shows radioprotective properties, while other 2-aminoselenazoles, selenosemicarbazides, and acetone selenosemicar-bazones possess no such activity but are in addition very sensitive to radiation (93). 

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