Thermogravimetric study of uranium phosphates

The thermal decomposition of (UO₂)₃(PO₄)₂ and U(HPO₄)₂ ·xH₂O in the temperature range 25–1600?, was investigated. (UO₂)₃(PO₄)₂ decomposed first to 1/3[U₃O₈ + 3U₂O₃P₂O₇] and then to U₃O₅P₂O₇ before a loss of phosphorus was observed above 1350?. Decomposition in air and in inert atmospheres was nearly identical. Reduction with H₂ or with carbon black in argon gave U₃O₅P₂O₇ and [UO₂ + + (UO)₂P₂O₇] before pure UO₂ was formed. U(HPO₄)₂ ·xH₂O decomposed to UP₂O₇ in argon. It oxidized partly in air before the same product was obtained. The high temperature stability of UP₂O₇ and U₃(PO₄)₄ was also investigated.     

DTA-TG and XRD study on the reaction between ZrOCl2·8H2O and (NH4)2HPO4 for synthesis of ZrP2O7

In this paper, we report results of thermoanalytical investigation on the reaction between ZrOCl₂·8H₂O and (NH₄)₂HPO₄ in molar ratio 1:2. Differential thermal-thermogravimetric and X-ray diffraction analyses were performed in order to reveal the chemical transformations, which took place during heating of the individual compounds ZrOCl₂·8H₂O, (NH₄)₂HPO₄ and the mixture ZrOCl₂·8H₂O:2(NH₄)₂HPO₄. It was shown that the transformations in the mixture below 160 °C were connected with dehydration of ZrOCl₂·8H₂O and interaction between the components of the mixture, which resulted in the formation of NH₄Cl, NH₄H₂PO₄ and a mainly amorphous zirconium phase, most likely t-ZrO₂. The zirconium component subsequently reacted with ammonium dihydrophosphate (below 200 °C) or with dehydrated phosphate derivatives (above 200 °C), which in both cases yielded an amorphous product. The interaction between the components of the mixture resulting in the formation of ZrP₂O₇ was completed by its crystallisation at 610 °C. Our study indicates an alternative low-temperature approach for the synthesis of the technologically important ZrP₂O₇ material.     

Non-isothermal kinetics of thermal decomposition of NH<Subscript>4</Subscript>ZrH(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>·H<Subscript>2</Subscript>O

Nanocrystalline NH₄ZrH(PO₄)₂·H₂O was synthesized by solid-state reaction at low heat using ZrOCl₂·8H₂O and (NH₄)₂HPO₄ as raw materials. X-ray powder diffraction analysis showed that NH₄ZrH(PO₄)₂·H₂O was a layered compound with an interlayer distance of 1.148 nm. The thermal decomposition of NH₄ZrH(PO₄)₂·H₂O experienced four steps, which involves the dehydration of the crystal water molecule, deamination, intramolecular dehydration of the protonated phosphate groups, and the formation of orthorhombic ZrP₂O₇. In the DTA curve, the three endothermic peaks and an exothermic peak, respectively, corresponding to the first three steps' mass losses of NH₄ZrH(PO₄)₂·H₂O and crystallization of ZrP₂O₇ were observed. Based on Flynn–Wall–Ozawa equation and Kissinger equation, the average values of the activation energies associated with the NH₄ZrH(PO₄)₂·H₂O thermal decomposition and crystallization of ZrP₂O₇ were determined to be 56.720 ± 13.1, 106.55 ± 6.28, 129.25 ± 4.32, and 521.90 kJ mol⁻¹, respectively. Dehydration of the crystal water of NH₄ZrH(PO₄)₂·H₂O could be due to multi-step reaction mechanisms: deamination of NH₄ZrH(PO₄)₂ and intramolecular dehydration of the protonated phosphate groups from Zr(HPO₄)₂ are simple reaction mechanisms.     

Salze von Halogenophosphorsäuren. XIX. Über die Darstellung von Kupfer(II)-monofluorophosphat-Solvaten und die Kristallstruktur von Aquamonofluorophosphatokupfer(II)-1,4-Dioxan 2/1, 2[Cu(H2O)PO3F] · C4H8O2

Salts of Halogenophosphoric Acids. XIX. Preparation of Copper(II) Monofluorophosphate Solvates and the Crystal Structure of Aquamonofluorophosphatocopper(II)-1,4-Dioxane 2/1, 2[Cu(H₂O)PO₃F] · C₄H₈O₂ The mixed solvate Aquamonofluorophosphatocopper(II)-1,4-Dioxane 2/1 1 was obtained by the reaction of aqueous solutions of NH₄HPO₃F and acidified (NH₄)₂PO₃F, respectively, using 1,4-dioxane as precipitating agent. 1 crystallizes in the monoclinic space group C2/m with a = 2130.9(2), b = 655.45(6), c = 447.30(4) pm, b? = 96.207(7)° and Z = 2. Copper(II) monofluorophosphate-methanol 1/1, CuPO₃F · CH₃OH 2 was obtained by the reaction of copper(II) salts with alkaline or ammoniummonofluorophosphates in methanol. 1 and 2 react in the presence of water vapor to copper(II) monofluoro phosphate dihydrate, CuPO₃F · 2H₂O 3 , which reacts reversibly with dioxan or CH₃OH under formation of 1 and 2 , respectively.     

Thermal stability and X-ray luminescence properties of cesium fluorophosphatohafnates

The thermal stability of cesium fluorophosphatohafnates (crystalline CsHf₂F₂(HPO₄)₂PO₄ · 2H₂O, CsHfF₂PO₄ · 0.5H₂O, CsHf₂F₆PO₄ · 4H₂O and X-ray amorphous Cs₂Hf₃O_1.5F₅(PO₄)₂ · 5H₂O, Cs₅H₄Hf₃F₇(PO₄)_3.66(NO₃)₃ · 5H₂O) was determined. The weight ratios Cs⁺/Hf and PO ₄ ^3? /ZrHf in CsHf₂F₂(HPO₄)₂PO₄ · 2H₂O were confirmed by identifying the calcination production CsHf₂(PO₄)₃ (～1000°C). A new crystalline compound CsHf₂F(HPO₄)(PO₄)₂ was found by thermogravimetric and X-ray powder diffraction analysis during heating. A new method for hydrothermal synthesis of CsHf₂(PO₄)₃, which was different from the already known one, was proposed. It was ascertained that CsHf₂(PO₄)₃ possesses a significant X-ray luminescence; whereas in fluorophosphatehafnates show low luminescence intensity.     

Proton conductivity and spectral data of Cs<Subscript>2</Subscript>HPO<Subscript>4</Subscript> · 2H<Subscript>2</Subscript>O

The Cs₂HPO₄ · 2H₂O single crystals synthesized from an aqueous solution containing equimolar amounts of H₃PO₄ and Cs₂CO₃ were studied by impedance and IR spectroscopy, X-ray diffraction analysis, and differential scanning calorimetry (DSC). The IR spectra were analyzed in accordance with the structural data, and the absorption bands were assigned. The proton conductivity was studied at temperatures in the range 20–250°C. The conductivity of dehydrated Cs₂HPO₄ was low, ~10^–5–10^–9 S cm^–1 at 90–250°C with an activation energy of conductivity E _a = 1.1 eV at 130–250°C. The processes determining the character of the temperature dependence of conductivity were consistent with the DSC and thermogravimetry data. According to these data, dehydration of the crystalline hydrate Cs₂HPO₄ · 2H₂O starts at 60°C and occurs in three stages, forming Cs₂HPO₄ · 1.5H₂O below 100°C; anhydrous Cs₂HPO₄ at t > 160°C, which is stable up to 300°C; and Cs₄P₂O₇ above 330°C.     

Ammonium-exchanged phase of γ-titanium phosphate

The monoammonium salt of γ-titanium phosphate has been prepared by hydrothermal treatment of π-Ti₂O(PO₄)₂·2H₂O in the presence of urea and phosphoric acid, and its crystal structure was obtained by Rietveld analysis using powder X-ray diffraction data. γ-Ti(PO₄)(NH₄HPO₄) crystallizes in the monoclinic space group P2₁/m with a = 5.0725(3) Å, b = 6.3101(3) Å, c = 11.2435(5) Å, β = 97.980(3)° (Z = 2). The structure consists of 2D titanium phosphate layers in the ab-plane. The titanium atoms and one of the phosphate groups are located nearly in the ab-plane of the layer. All the oxygen atoms of this phosphate group are involved in titanium coordination sphere. The other phosphate group located in the layers edges links two neighboring titanium atoms in the a-direction through two of its oxygen atoms. The remaining two oxygens are pointed toward the interlayer space being involved in hydrogen bond interactions with the ammonium ions. Each ammonium ion is shared by four oxygens belonging to four different phosphate hydroxyl groups. γ-Ti(PO₄)(NH₄HPO₄) is stable until 453 K, while above this temperature, it transforms to γ’-Ti(PO₄)(NH₄HPO₄) high temperature polymorph stable until 573 K. Thermal decomposition of this material leads to cubic TiP₂O₇ structure, with previous formation of two intermediate pseudo-layered compounds: Ti(PO₄)(NH₄HP₂O₇)_0.5 and Ti(PO₄)(H₂P₂O₇)_0.5. The activation energy of thermal decomposition has been calculated as a function of the extent of conversion applying the Kissinger–Akahira–Sunose (KAS) isoconversional method to the thermogravimetric data.     

Thermoanalytical study on the oxidation of uranium dioxides derived from uranyl nitrate,uranyl acetate and ammonium diuranate

The oxidation of UO₂ was investigated by TG, DSC and X-ray diffraction . UO₂ samples were prepared by the reduction of UO₃ at P_H2 + P_N2 = 100 + 50 mm Hg and 5°C min^?1 up to 800°C. In order to obtain six UO₂ samples with different preparative histories, UNH, UAH and ADU were used as starting materials and their thermal decomposition was carried out at 450–625°C for 0–9 h at an air flow rate of 100 ml min^?1. α-UO₃, γ-UO₃, UO₃ - 2 H₂O, and their mixtures were obtained. The reduction of UO₃ gave β-UO_2+x with different x values from 0.030 to 0.055. The oxidation carried out at P_O2 = 150 mm Hg was found to consist of oxygen uptake at room temperature. UO₂ - U₃O₇ (Step I) and U₃O₇ → U₃O₈ (Step II). TG and DSC curves of the oxidation showed two plateaus and two exothermic peaks corresponding to Steps I and II. In the case of two of the samples, the DSC peak of Step II split into two substeps, which were assumed to be due to the different reactivities of U₃O- formed from α-CO₃ and that from other types of UO₃. The increase in O/U ratio due to the oxygen uptake at room temperature changed from 0.010 to 0.042 except for a sample prepared from ADU which showed an extraordinarily large value of 0.445. TG curves showed an increase in O/U from room temperature to near 250°C for Step I and the plateau at 250–350°C where O/U was about 2.42, and showed a sharp increase in O/U above 350°C for Step II and the plateau above 100°C where O/U was 2.72–2.75. It is thought that the prepared UO₂ had a defective structure with a large interstitial volume to accommodate the excess oxygen.     

Darstellung und Kristallstruktur von [Co(NH3)6]2P4O13 · 5 H2O

Preparation and Crystal Structure of [Co(NH₃)₆]₂P₄O₁₃ 7·5H₂O Single crystals of [Co(NH₃)₆]P₄O₁₃ · 5 H₂O were obtained by diffusion controlled growth. To this end sodium polytetraphosphate was prepared by column chromatography and allowed to react with [Co(NH₃)₆]Cl₃. The compound [Co(NH₃)₆]₂P₄O₁₃ · 5 H₂O contains the novel isolated polytetraphosphate anion. The expected systematic variation in bond length in the P? O? P bridges of the poly tetraphosphate anion was verified. The conformation of the anion is discussed.     

Standard enthalpy of formation of disodium hydrogen phosphate hexahydrate and sodium diphosphate

Commercial disodium hydrogen phosphate dodecahydrate (Na₂HPO₄·12H₂O) was used as a precursor for synthesizing disodium hydrogen phosphate hexahydrate (Na₂HPO₄·6H₂O) and sodium diphosphate (Na₄P₂O₇). The purity of the synthesized products was checked up by IR spectroscopy and X-ray diffraction. The heat of dissolution of these compounds, in acid solutions of several concentrations (w/w) of H₃PO₄ was measured in a C-80 SETARAM calorimeter. Many dilution and mixing processes were also realized in the calorimeter in order to get the standard enthalpy of formation of these products. The values obtained for the enthalpies of formation are: (?3210.5) and (?3516.5) kJ · mol^?1 for sodium diphosphate (Na₄P₂O₇) and disodium hydrogen phosphate hexahydrate (Na₂HPO₄·6H₂O), respectively.     

Thermal and X-ray diffraction analysis studies during the decomposition of ammonium uranyl nitrate

Two types of ammonium uranyl nitrate (NH₄)₂UO₂(NO₃)₄·2H₂O and NH₄UO₂(NO₃)₃, were thermally decomposed and reduced in a TG-DTA unit in nitrogen, air, and hydrogen atmospheres. Various intermediate phases produced by the thermal decomposition and reduction process were investigated by an X-ray diffraction analysis and a TG/DTA analysis. Both (NH₄)₂UO₂(NO₃)₄·2H₂O and NH₄UO₂(NO₃)₃ decomposed to amorphous UO₃ regardless of the atmosphere used. The amorphous UO₃ from (NH₄)₂UO₂(NO₃)₄·2H₂O was crystallized to γ-UO₃ regardless of the atmosphere used without a change in weight. The amorphous UO₃ obtained from decomposition of NH₄UO₂(NO₃)₃ was crystallized to α-UO₃ under a nitrogen and air atmosphere, and to β-UO₃ under a hydrogen atmosphere without a change in weight. Under each atmosphere, the reaction paths of (NH₄)₂UO₂(NO₃)₄·2H₂O and NH₄UO₂(NO₃)₃ were as follows: under a nitrogen atmosphere: (NH₄)₂UO₂(NO₃)₄·2H₂O → (NH₄)₂UO₂(NO₃)₄·H₂O → (NH₄)₂UO₂(NO₃)₄ → NH₄UO₂(NO₃)₃ → A-UO₃ → γ-UO₃ → U₃O₈, NH₄UO₂(NO₃)₃ → A-UO₃ → α-UO₃ → U₃O₈; under an air atmosphere: (NH₄)₂UO₂(NO₃)₄·2H₂O → (NH₄)₂UO₂(NO₃)₄·H₂O → (NH₄)₂UO₂(NO₃)₄ → NH₄UO₂(NO₃)₃ → A-UO₃ → γ-UO₃ → U₃O₈, NH₄UO₂(NO₃)₃ → A-UO₃ → α-UO₃ → U₃O₈; and under a hydrogen atmosphere: (NH₄)₂UO₂(NO₃)₄·2H₂O → (NH₄)₂UO₂(NO₃)₄·H₂O → (NH₄)₂UO₂(NO₃)₄ → NH₄UO₂(NO₃)₃ → A-UO₃ → γ-UO₃ → α-U₃O₈ → UO₂, NH₄ UO₂(NO₃)₃ → A-UO₃ → β-UO₃ → α-U₃O₈ → UO₂.     

NaH(ZnPO4)2及α-磷锌矿的低热固相反应合成与调控

对合成层状磷酸锌氢钠（NaH(ZnPO4)2）的新路线进行了研究,用Na2HPO4·12H2O及Zn(NO3)2·6H2O作为起始原料,聚乙二醇-400（PEG-400）为表面活性剂,通过一步固相反应于60 ℃下陈化得到了层状磷酸锌氢钠。用XRD, TG/DTG 及 FTIR表征了产物。实验结果表明,NaH(ZnPO4)2在500 ℃附近有一个主要的失重峰,归属为HPO42-脱水变成P2O74- 离子。因此,作为有机反应的非均相催化剂时,该化合物具有足够的热稳定性。对照实验的结果显示陈化温度调控着反应产物的生成。即,当反应混合物在60 ℃陈化时,生成的是NaH(ZnPO4)2,当反应混合物在室温陈化时,生成的则是α-Zn3(PO4)2·4H2O。     

A Study of Ammonium Mono-, Di- and Triphosphate Heterogeneous Systems in View of their Use as Liquid Fertilizers

Abstract

Ammonium phosphates belong among principal compounds of multicomponent liquid fertilizers and thus this study has been directed toward agrochemical application. For this reason, in the system of NH⁺ ₄, H⁺ PO³ ₄, P₂O⁴ ₇, P₃O^5- ₁₀ - H₂O, the subsystem, NH₄H₂PO₄ - (NH₄)₂H₂P₂O₇ - (NH₄)₃H₂P₃O₁₀?(NH₄)₃PO₄ - (NH₄)₄P₂O₇ - (NH₄)₅P₃O₁₀ - H₂O, was studied in which the pH of saturated solutions varies from 5 to 8. The solubility was studied in the partial pseudoternary systems. The experimental temperatures were selected immediately above the corresponding cryohydratic points, from 0 to -8°C. The sum of the results obtained can be schematically represented as a set of the curves of simultaneous crystallization of two solids on the mantle of a trigonal prism which represents the salt composition of the studied system.     

A Study of Ammonium Mono-, Di- and Triphosphate Heterogeneous Systems in View of Their Use as Liquid Fertilizers

Abstract

Ammonium phoaphates belong among principal compounds of rnulticomponent liquid fertilizers and thus this study has been directed toward agrochernical application. The system NH₄H₂PO₄-(NH₄) ₂H₂PO₄- (NH₄)₂H₂P₂O_7- (NH₄)₃ H₂P₃O₁₀- (NH₄) ₃PO₄-(NH₄)₄) ₄P₂O₇-(NH₄)₅P₃O₁₀-H₂O was studied in which the pH of saturated solutions varies from 5 to 8. The solubility was studied in the partial pseudoternary systems. The experimental temperatures were selected immediately above the corresponding cryohydratic points, from 0 to -8 °C, The results were discussed using a computer. The procedure used makes it possible to find a smoothing equation for each branch of the solubility diagram at issue. Simultaneously, a set of coefficienta Q related to the ideality of the respective solutions was found, From practical point of view, it can be seen from the results obtained that the highest concentrations of agrochemically effective components(nitrogen and phosphorus pentaoxide) are attained in saturated solutions containing triphosphate with a nutritional value of more than 50%.     

Novel Method for Preparing NH4NiPO4·6H2O: Hydrogen Bonding Coacervate Selective Self-assembly

The single phase NH₄NiPO₄·6H₂O was synthesized by solid‐state reaction at room temperature using NiSO₄·6H₂O and (NH₄)₃PO₄·3H₂O as raw materials. The NH₄NiPO₄·6H₂O and its calcined products were characterized using X‐ray powder diffraction (XRD), thermogravimetry and differential thermal analyses (TG/DTA), Fourier transform IR (FT‐IR), ultraviolet‐visible (UV‐vis) absorption spectroscopy, and scanning electron microscopy (SEM). The results showed that the product dried at 80°C for 3 h was orthorhombic NH₄NiPO₄·6H₂O [space group Pmm2(25)], and surfactant polyethylene glycol (PEG)‐400 can direct growth of crystal NH₄NiPO₄·6H₂O. The thermal process of NH₄NiPO₄·6H₂O experienced three steps, which involve the dehydration of the five crystal water molecules at first, and then deamination, dehydration of the one crystal water, intramolecular dehydration of the protonated phosphate groups together, at last crystallization of Ni₂P₂O₇. The product of thermal decomposition at 150°C for 2 h, orthorhombic NH₄NiPO₄·H₂O, is layered compound with an interlayer distance of 0.8370 nm.     

ZrONO3)2-H3PO4-KF(HF)-H2O system at molar ratios of PO 43? /Zr = 0.5?1.6 as the basis for phase formation

The system ZrO(NO₃)₂-H₃PO₄-KF(HF)-H₂O was studied at ∼20°C along sections at molar ratios of PO₄³⁻ = 0.5, 1.0, and 1.6; KF: Zr = 1−5; and HF: Zr = 2−6. Phases in precipitates were identified by X-ray powder diffraction; IR spectroscopy; and crystal-optical, chemical, X-ray fluorescence and thermal analyses. The following crystalline phases were isolated: potassium fluorozirconates K₃ZrF₇, K₂ZrF₆, δ-KZrF₅, and KZrF₅ · H₂O; zirconium hydrophosphate Zr(HPO₄)₂ · 0.5H₂O; and potassium fluorophosphate zirconate K₃Zr₃F₃(HPO₄)₃(PO₄)₂. The following amorphous basic oxo(hydroxo)fluorohydrophosphate nitrates were isolated: K₄Zr₄O_2.5F₈(HPO₄)₂(NO₃)₃ · 6H₂O, K₂Zr₃O₃F₂(HPO₄)₂(NO₃)₂ · H₂O, and KZr₃O_1.5F₃(HPO₄)₂(NO₃)₃ · 2H₂O. Fields of solid phases were constructed, and the roles of anions and cations in the phase formation were considered.     

Synthesis and crystal structure of a neutral open framework cobalt(II) phosphate Co6(PO4)4·7H2O with a channel structure

Using tri-ethyl phosphate as a phosphate source, the hydrothermal reaction of cobalt(II) oxalate di-hydrate, zinc oxide and 1,8 di-amino octane at 200°C gave purple crystals of Co₆(PO₄)₄?·?7H₂O (1), along with a mixture of open-framework zinc–cobalt phosphates Co–Zn–HPO₄, and Co₃(HPO₄)₂(2OH). Compound 1, has been characterized by thermal analysis, FTIR and single crystal X-ray diffraction. The single crystal structure of Co₆(PO₄)₄?·?7H₂O reveals cobalt in four, five and six-fold coordination with linkages through the bridging water molecules and the oxygen atoms of the phosphate in the subunits. Four subunits are connected together through the oxygen atoms (PO₄), to form the three dimensional open framework structure, with a 20-member ring channel that hosts two uncoordinated water molecules. Thermal removal of the water molecules occurs between 400–600°C, with the collapse of the structure above 600°C.     

Synthesis and physicochemical characterization of carboxymethylcellulose-containing calcium hydroxylapatite

The CaCl₂-(NH₄)₂HPO₄-C₈H₁₁O₇Na-NH₃-H₂O system was studied at 25°C using the solubility method (Tananaev’s residual concentration method) and pH measurements. The solid phases isolated from the system were characterized using chemical analysis, X-ray powder diffraction, IR spectroscopy, and thermogravimetry. Nanocrystalline carboxymethylcellulose-containing calcium hydroxylapatites Ca₁₀(PO₄)₆(OH)₂ · xH₂O · yC₈H₁₁O₇Na with x = 6–12 and y = 0.1–0.5 were found as a result of the characterization.     

Kinetics and thermodynamics of thermal decomposition of NH<Subscript>4</Subscript>NiPO<Subscript>4</Subscript>·6H<Subscript>2</Subscript>O

The single phase NH₄NiPO₄·6H₂O was synthesized by solid-state reaction at room temperature using NiSO₄·6H₂O and (NH₄)₃PO₄·3H₂O as raw materials. XRD analysis showed that NH₄NiPO₄·6H₂O was a compound with orthorhombic structure. The thermal process of NH₄NiPO₄·6H₂O experienced three steps, which involves the dehydration of the five crystal water molecules at first, and then deamination, dehydration of the one crystal water, intramolecular dehydration of the protonated phosphate groups together, at last crystallization of Ni₂P₂O₇. In the DTA curve, the two endothermic peaks and an exothermic peak, respectively, corresponding to the first two steps’ mass loss of NH₄NiPO₄·6H₂O and crystallization of Ni₂P₂O₇. Based on Flynn–Wall–Ozawa equation, and Kissinger equation, the average values of the activation energies associated with the thermal decomposition of NH₄NiPO₄·6H₂O, and crystallization of Ni₂P₂O₇ were determined to be 47.81, 90.18, and 640.09 kJ mol⁻¹, respectively. Dehydration of the five crystal water molecules of NH₄NiPO₄·6H₂O, and deamination, dehydration of the crystal water of NH₄NiPO₄·H₂O, intramolecular dehydration of the protonated phosphate group from NiHPO₄ together could be multi-step reaction mechanisms. Besides, the thermodynamic parameters (ΔH ^≠, ΔG ^≠, and ΔS ^≠) of the decomposition reaction of NH₄NiPO₄·6H₂O were determined.     

Sur L'Existence d'un Intermediaire Reactionnel Entre Phosphate et Pyrophosphate Acide de Potassium: Cas de K2H8(PO4)2P2O7

On the Existence of Intermediate Reaction Products of Potassium Hydrogen Phosphate and Diphosphate: K₂H₈(PO₄)₂P₂O₇ The crystal structure of K₂H₈(PO₄)₂P₂O₇ has been determined from diffractometer data obtained using MoKα radiation. The space group is Pca2₁ with a = 9.364(2), b = 7.458(2) and c = 19.560(2) Å, V = 1 366.0 ų; d_m = 2.17(1) g/cm³. Z = 4 · μ(MoKα) = 12.47 cm^?1. The structure was solved by direct methods. The crystal structure was refined to R = 0.025 for 416 independent reflexions. Two kinds of PO₄ exist and the mean value of P? O is 1.55(2) Å for one and 1.53(2) Å for the other. In P₂O₇ the angle P? O? P is 135(1)°. The distances P? O of bridge are 1.59(2) and 1.57(2) Å the mean value of P? O in terminals ? PO₃ is 1.51(2) Å. The coordination numbers of the potassium ions are nine and eight. K₂H₈(PO₄)₂P₂O₇, compound with mixed anion PO₄/P₂O₇ may be considered as reactional intermediary between acid orthophosphate and pyrophosphate.