Phosphoric acid solutions

The essential basis of the scheme for the separation of water-soluble compounds is, therefore, distillation of (a) an aqueous solution of the mixture, (b) an alkaline (with sodium hydroxide) solution of the mixture, and (c) an acidic (with sulphuric oj phosphoric acid) solution of the mixture. The residue will contain the non-volatile components, which must be separated from inorganic salts and from each other by any suitable process. 

However, the peroxomonophosphate ion decomposes relatively rapidly ia aqueous solution. A mixture of peroxodiphosphoric and peroxomonophoshoric acids can be produced by treatiag a cold phosphoric acid solution with elemental fluorine (qv) (49). Peroxodiphosphoric acid is not produced commercially. Ammonium, lithium, sodium, potassium, mbidium, cesium, barium, 2iac, lead, and silver salts have all been reported. The crystal stmctures of the ammonium, lithium, sodium, and potassium compounds, which crysta11i2e with varyiag numbers of water molecules, have been determined (50). 

Extensive hydrogen bonding takes place in phosphoric acid solutions. In concentrated (86% H PO solutions, as well as in the crystal stmctures of the anhydrous acid and the hemihydrate, the tetrahedral H PO groups are linked by hydrogen bonding. At lower (75% H PO concentrations, the tetrahedra are hydrogen-bonded to the water lattice. Physical properties of phosphoric acid solutions of various concentrations are Hsted in Table 2 the vapor pressure of aqueous H PO solutions at various temperatures is given in Table 3. 

Table 3. Vapor Pressure of Phosphoric Acid Solutions., kPa ...

At equihbrium, the specific composition of a concentrated phosphoric acid is a function of its P2 s content. Phosphoric acid solutions up to a concentration equivalent of about 94% H PO (68% P2O5) contain H PO as the only phosphoric acid species present. At higher concentrations, the orthophosphoric acid undergoes condensation (polymerization by dehydration) to yield a mixture of phosphoric acid species (Table 5), often referred to genericaHy as polyphosphoric or superphosphoric acid, H20/P20 = - 3, or ultraphosphoric acid, H20/P20 = - 1. At the theoretical P2O5 concentration for orthophosphoric acid of 72.4%, the solution is actually a mixture containing 13% pyrophosphoric acid and about 1% free water. Because the pyrophosphoric acid present is the result of an equihbrium state dependent on the P2 5 content of the solution, pure orthophosphoric acid can be obtained because of a shift in equihbrium back to H PO upon crystallization. 

Titanium corrodes very rapidly in acid fluoride environments. It is attacked in boiling HCl or H2SO4 at acid concentrations of >1% or in ca 10 wt % acid concentration at room temperature. Titanium is also attacked by hot caustic solutions, phosphoric acid solutions (concentrations >25 wt%), boiling AlCl (concentrations >10 wt %), dry chlorine gas, anhydrous ammonia above 150°C, and dry hydrogen—dihydrogen sulfide above 150°C. 

Phosphorsaure, /. phosphoric acid, -anhydrid, n. phosphoric anhydride (phosphorus pentoxide). -losimg, /. phosphoric acid solution, -salz, n. phosphate. 

Phosphoric acid The austenitic grades are resistant to all strengths up to 80°C but are limited to 30-40% concentration at boiling point, the molybdenum-bearing types having the best corrosion resistance. Some test data for various types is shown in Fig. 3.28. Industrially, this acid is often encountered in an impure state with appreciable amounts of sulphuric and hydrofluoric acid present so that process testing is likely to be particularly necessary. The super-austenitic steels have enhanced resistance to phosphoric acid solutions. 

Fig. 3.28 Corrosion rates of various stainless steels in phosphoric acid solutions at boiling...

All conventional phosphate coating processes are based on dilute phosphoric acid solutions of iron, manganese and zinc primary phosphates either separately or in combination. The free phosphoric acid in these solutions reacts with the iron surface undergoing treatment in the following manner ... 

In the polarization curve for anodic dissolution of iron in a phosphoric acid solution without CP ions, as shown in Fig. 3, we can see three different states of metal dissolution. The first is the active state at the potential region of the less noble metal where the metal dissolves actively, and the second is the passive state at the more noble region where metal dissolution barely proceeds. In the passive state, an extremely thin oxide film called a passive film is formed on the metal surface, so that metal dissolution is restricted. In the active state, on the contrary, the absence of the passive film leads to the dissolution from the bare metal surface. The difference of the dissolution current between the active and passive states is quite large for a system of an iron electrode in 1 mol m"3 sulfuric acid, the latter value is about 1/10,000 of the former value.6... 

Figure 3. Current vs. potential curve for iron dissolution in phosphoric acid solution at pH 1,85. Ep, Flade potential Ep, passivation potential Epii- critical pitting potential EiP, transpassivation potential. Solid and broken lines correspond to the cases without and with CF ions, respectively.

Cellulase enzyme complexes consist of three major types of proteins that synergistically catalyze the breakdown of a cellulosic substrate. Because the enzymes are strictly substrate-specific in their action, any change in the structure or accessibility of the substrate can have a considerable influence on the course of the hydrolysis reaction. A pretreatment method based on exposing cellulosic substrate to phosphoric acid solution [9] and addition of the nonionic... 

C04-0029. Calculate the volume of 0.108 M NaOH solution required to react completely with 145 mL of phosphoric acid solution that is 1.15 X 10 M. 

Reactions between oxides and phosphoric acid solutions... 

We have noted earlier that aluminium is unusual in forming alumino-phosphate complexes in phosphoric acid solution which may be of a polymeric nature. Bearing in mind the analogies between aluminium phosphate and silica structures, it may well be that during cement formation an aluminium phosphate hydrogel is formed. Its character may be analogous to that of silica gel, where a structure is built up by the... 

Zinc phosphate cement, as its name implies, is composed principally of zinc and phosphate. It is formed by mixing a powder, which is mainly zinc oxide, with a solution based on phosphoric acid. However, it is not as simple chemically as it appears because satisfactory cements caimot be formed by simply mixing zinc oxide with phosphoric acid solution. 

Mg(H2P04)2.4H2O as was the case in the reaction between MgO and simple phosphoric acid solutions. Inspection of the diagrams of Belopolsky, Shpunt Shulgina (1950) shows that newberyite is the stable phase at lower concentrations of phosphate. Presiunably, in the present case, aluminium locks up some phosphate and so reduces the phosphate available for the magnesium phosphate phase. 

Figure 3. A model of a porous oxide film formed at 120 V in a phosphoric acid solution, according to Heber.10...

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