Ultraphosphate crystals

A base glass composed of Ca0 P205 = 0.85 (molar ratio) was used to produce these fibers. Crystallization took place at 600 C for 48 h. Unidirectional crystallization techniques were not conducted. Crystallization of P-Ca(P03)2 proceeded in needle form, with random orientation yielding an isotropic body. An ultraphosphate of the substantially lower chemical durability of the glass matrix and the ultraphosphate crystals compared with that of the P-Ca(P03)2, the matrix was easily extracted by aqueous leaching. These P-Ca(P03)2 fibers were subsequently used in a composite material with a very low modulus of elasticity (Kasuga 1996). 

When crystallization is completed the fibrous phosphate can be extracted from the ultraphosphate matrix by leaching the system with hot water. 

Polyphosphate is defined in this work as any linear, condensed phosphate, in which the phosphate, but not necessarily the system containing the phosphate exhibits the conditions 1 < M2O/P2O5 < 2, where M is any single or mixed metals with a total equivalency of unity. The definition is required to differentiate the total composition of a system from the polyphosphates crystallizing in a melt. An example is a polyphosphate crystallizing from a melt of ultraphosphate composition where several metal oxides may be involved. 

A large number of samples of [Ca(PO3)2]n were made in batches from a few grams to fifty pounds or more. In all cases the samples were heated to 1000 C and allowed to slowly crystallize from a sodium ultraphosphate melt. Under the best conditions fibers of three inches in length were prepared from the large melts where crystallization could be controlled. (6)... 

If the calcium phosphate fibers grown from ultraphosphate melts are slurried with a solution of sodium ethylene diamine tartaric acid the calcium crystals can be converted to a sodium phosphate glass that dissolves very slowly yielding very long chains. 

Three possibilities exist when a salt with a polyphosphate x-ray pattern crystallizes from a melt containing an excess of phosphorus pentoxide. 1. The phosphorus pentoxide is incorporated into the polyphosphate chains converting the chains to crystalline ultraphosphates. 2. The excess phosphorus pentoxide does not enter the polyphosphate crystal structure, but forms an amorphous phase between the crystals of polyphosphate. The amorphous phase is not detected by x-ray. 3. The excess phosphorus pentoxide does not enter the crystal structure of the polyphosphate, but forms as an ultraphosphate between the crystalline polyphosphate crystals as a eutectic phase. (This latter case is precisely what happens in the calcium sodium ultraphosphate system from which calcium phosphate fibers are grown (21) and the phase diagram of Hill et. al. is obeyed as it should be.)... 

In the potassium Kurrol s salt phase system the crystalline analogues to Ca2P60i7 or CaP O i were not found by a literature search. (22) The amorphous potassium ultraphosphate systems have been studied. (23) Amorphous condensed phosphates are seldom, if ever, single compounds, but are a random mixtures of compounds and can be large and very complex. If the ultraphosphates were embedded between crystals of pure potassium phosphate fibers they would be very difficult to detect. 

It is concluded that the crystalline phase of potassium Kurrol s salt is not cross-linked. The mixture of very long chain polyphosphates and amorphous ultraphosphates dissolve to form highly viscous aqueous solutions. It is also concluded that the seed crystals aiding the growth of ultra long polyphosphate molecule-ions is built up from small segments of polyphosphate formed in a phosphate melt. 

T-Ray data indicate that BiPsOi4 is an isotype of the ultraphosphate LaP50j4, and there are strong structural relations with the holmium compound. The latter can be obtained in both orthorhombic Pnmd) and monoclinic (C2Jc) forms, and the ultraphosphate structure for both is shown by single-crystal measurements. ... 

Calcium polyphosphates, [Ca(P03)2] , crystals grown in sodium ultraphosphate melts in the preparation of fibers, were grown in a manner similar to how [KPOaln is grown in melts of ultraphosphoric acid. These systems yield salts referred to as cross-linked Kunol s salts. Since potassium Kurrol s salts can be easily and quickly solubilized in water containing some diverse ions, such as sodium, potassium phosphates are much more easily studied. Potassium Kurrol s... 

There is no question whether or not cross-linking is a necessary part of a system with an ultraphosphate composition. It is a structural-composition requirement, but where does cross-linking reside in potassium Kurrol s salt crystallized in ultraphosphate melts Are cross-links contained in crystalline phases and cause the formation of crystalline potassium ultraphosphates, or does a salt obey its phase diagram for a two-component K2O-P2O5 system (See Figure 3.1.)... 

Let us approach question 1 first. Assume that when preparing cross-linked Kurrol s salt, all phosphoric oxide added to crystalline [KP03]n enters potassium Kurrol s salt as a cross-linking agent. Assume that all phosphate crystallizes to cross-linked Kurrofs salt. If these assumptions are true, cross-linked Kurrol s salt is an ultraphosphate and not a polyphosphate because the M2O-P2O5 must be less than unity. Moreover, there must be two different compounds present in a phase system exhibiting different X-ray patterns. 

Two different potassium Kurrofs salt compounds, one cross-linked and the other linear chains, do not appear in this phase diagram, nor could a crystalline compound other than potassium Kurrofs salt be found in ultraphosphate areas of this system. Other choices are (1) an amorphous phase is formed, or (2) some new undetected crystalline potassium ultraphosphate is formed. No other crystalline potassium ultraphosphates are known, and no new ones were discovered in this work. Both phase studies and X-ray analyses suggest that an amorphous phase is formed in all potassium Kurrofs salt systems crystallized in ultraphosphate phase systems. 

Polyphosphates crystallized in an ultraphosphate melt may be superlong chains of linear molecules with only defect cross-linking. Also, cross-linking may be contained in an amorphous phase, where it is very difficult to detect directly, rather than as a part of a crystal structure. Cross-linking is probably a random event and does not constitute a thermodynamically stable state, even in the absence of moisture. 

Kurrol s salt is very slowly soluble in distilled water and ultraphosphate glasses are infinitely and quickly soluble in water, it is possible to estimate the quantity of amorphous phase contained in a well-crystallized Kurrol s salt system. Sample mixtures of crystalline and amorphous phases are first milled to a fine powder and then any soluble phase dissolved from crystalline phases with distilled water. The aqueous filtrate solution is then analyzed both for ratios and concentrations of dissolved phosphates. The soluble part of a sample should be amorphous since potassium Kurrol s salt is almost insoluble under these conditions. 

All attempts to form crystals in ultraphosphate systems with K2O-P2O5 ratios of 0.5 or less have been unsuccessful. Thermal analyses reveal an endothermic region extending from about 200 °C to the eutectic temperature at 450 °C. This amorphous region becomes more and more pronounced as M2O-P2O5 ratios are decreased to 0.5, where the total system is amorphous. 

Although the above approach is easy and straightforward, care must be exercised when applying it to more complex systems. Growth of calcium polyphosphates in sodium ultraphosphate melts is a three-component system rather than two, even when all water is driven from the system. It is recommended that the simpler method of assuming all sodium and no calcium reported to an amorphous phase (as was done in Chapter 6, Section 6.5) be used to estimate ratios of amorphous to crystalline phases or portions of a melt that is expected to be water soluble when the melt is fully crystallized. These estimates will not be precise, but are useful in estimating potential yields. 

In an attempt to obtain direct evidence for the presence of cross-linking in potassium polyphosphates crystallized from ultraphosphates melts, two tools were chosen. Cross-linking should in theory be observed by either phase chemistry or X-rays. Also, the existence of end and middle group phosphorus is well established... 

Once the ratio of sodium ultraphosphate to calcium polyphosphate had been more or less standardized, the game of adding crystal habit modifiers was undertaken in an attempt to determine the influence of modifiers. No reliable generalizations could ever be stated as to how foreign ions influenced these systems, but... 

All ultraphosphates contain PO4 tetrahedra linked by three vertices to neighboring tetrahedra (fig. 8). The further coordination of the phosphate groups varies, giving rise to three different crystal structures monoclinic I (La - -Tb), monoclinic II (Dy-Lu, Y), and orthorhombic (Dy-Er, Y) (Beucher, 1970 ... 

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