Aluminum Metaphosphate Research Articles

The structure of phosphate glass evidenced by small angle X-ray scattering

Numerous phosphate glass systems with compositions covering the entire glass forming range have been examined by small angle X-ray scattering. The experiments were carried out in a widely extended interval of s values between 0.055 and 31 nm −1. A small angle scattering effect was detected for all samples investigated with the exception of the aluminium metaphosphate glass. The small angle scattering recorded indicates the presence of two differently-sized heterogeneity regions of electron density. The small-scale heterogeneities are present in magnesium and zinc phosphate glasses only. Their size is about 1 nm diameter in the magnesium and about 2 nm in the zinc phosphate glasses. The species do not result from liquid–liquid phase separation. Examinations to extract information on the nature of these heterogeneity regions are described in detail. There is no fundamental knowledge on the large-scale heterogeneities established. The small angle scattering suggests that their occurrence is related to water contamination. Anomalous small angle X-ray scattering experiments of a series of zinc polyphosphate glasses and a strontium metaphosphate glass sample are performed to examine the distribution of the Zn or Sr atoms, respectively.

Aluminum Phosphates Derived from Alumina and Alumina‐Sol–Gel Systems

Aluminum phosphate products formed by the reactions of alumina and alumina‐gel systems with acidic phosphates were analyzed. Drying of alumina‐gel to form microcrystalline boehmite and conversion to γ‐alumina by thermal treatment was indicated by the appearance of octahedral, pentacoordinate, or tetrahedral sites, which were established using 27Al magic‐angle‐spinning solid‐state nuclear magnetic resonance spectroscopy. Crystalline aluminum phosphate products and amorphous material were identified using this technique. α‐alumina and heat‐treated alumina‐gel that were reacted with phosphate in an Al:P ratio of 1:1 yielded dramatically different aluminum orthophosphate:aluminum metaphosphate product ratios of 8.2:1 and 1:1.1, respectively. When alumina‐gel was heat‐treated with phosphate, an abundance of aluminum orthophosphate, aluminum metaphosphate, and hydrated aluminum phosphate products were affected by varying conditions of temperature and time of heat treatment and by the amount of phosphate present. An α‐alumina/alumina‐gel composite sol–gel phase that was reacted with phosphoric acid (H3PO4) in a Al:P ratio of 1:1 exhibited an increased quantity of aluminum metaphosphate products compared with an α‐alumina:H3PO4 ratio of 1:1 and a higher percentage of reaction (79%) compared with the reactions of an α‐alumina:H3PO4 ratio of 1:1 or an alumina‐gel:H3PO4 ratio of 1:1. The morphologies of aluminum triphosphate hydrate and aluminum metaphosphate product phases were observed using scanning electron microscopy.

The Influence of Silicon Oxide on the Mechanical Properties of Metaphosphate Glasses

The possibility of improving the mechanical properties of potassium aluminum metaphosphate glasses through the introduction of silicon oxide into the glass composition is analyzed. It is shown that the elastic moduli (Young modulus, shear modulus, Poisson ratio) and the hardness remain almost unchanged with an increase in the content of silicon oxide in the glass. At the same time, the structural strength increases by a factor of 1.7 and the fracture toughness increases by a factor of 1.3. The assumption is made that the observed increase in the structural strength is associated with the incorporation of silicon ions into the structure of the metaphosphate glass in the octahedral coordination.

Local Structure of Sodium Aluminum Metaphosphate Glasses

High‐resolution solid‐state 31P, 27Al, and 23Na nuclear magnetic resonance (NMR), Raman spectroscopy, differential scanning calorimetry, and density measurements were used to characterize the local structure of the glasses (1−x)(NaPO3)3·xAl(PO3)3. A systematic increase in density, glass transition temperature (Tg), and frequencies of P–O stretching vibrations for terminal nonbridging oxygens (NBOs) was observed as the Al content was increased. A change of slope in the behavior of Tg as a function of x was clearly detected around x= 0.25 ± 0.03. Also, changes of behavior in the 23Na NMR line shape and in the Raman band of the PO2 symmetric vibration are detected for concentrations higher than x= 0.17. According to these facts, a reorganization of the network affecting the degree of connectivity between phosphate chains is proposed to explain the observed behaviors of Tg and P–NBO vibrations in these glasses.

Oxidation protection of carbon materials by acid phosphate impregnation

Acid phosphate impregnation, with ozone pre-treatment, improves the oxidation resistance of carbon materials (polycrystalline graphite and pitch-based carbon fiber), as shown by weight measurement in air up to 1500 °C. The impregnation involves using phosphoric acid and dissolved aluminum hydroxide in the molar ratio 12:1 and results in a rough, white and hard aluminum metaphosphate coating of weight about 20% of that of the carbon before the treatment. Without ozone pre-treatment, the impregnation is not effective. Without aluminum hydroxide, the impregnation even degrades the oxidation resistance of the carbon.

Structure of sodium phosphate glasses containing Al 2O 3 and/or Fe 2O 3. Part I

The relationship between the composition and structure for three series of glasses: Na 2O–Al 2O 3–P 2O 5 (NAP); Na 2O–Al 2O 3–Fe 2O 3–P 2O 5 (NAFP), and Na 2O–Fe 2O 3–P 2O 5 (NFP) has been studied. The structural changes in the NAP, NAFP and NFP glasses have been investigated by Raman and by Raman difference spectroscopy (RDS). The Raman spectra show that the addition of Al 2O 3 content to sodium phosphate glasses has a different effect on the phosphate network than the addition of Fe 2O 3. With increasing Fe 2O 3 content up to 20 mol% the structure changes from the chain-like metaphosphate to the pyrophosphate structure. The iron ions play an important role in forming P–O–Fe bonds that strengthen the cross-bonding of shorter pyrophosphate chains. On the other hand, with increasing Al 2O 3 content up to 20 mol%, the sodium metaphosphate is replaced by aluminium metaphosphate where Al(OP) 6 units cross-link phosphate chains. The addition of Fe 2O 3 to Al 2O 3 in phosphate glasses containing both Al 2O 3 and Fe 2O 3 (NAFP series), enhances the formation of pyrophosphate units because iron ions have stronger effect on the depolymerization of metaphosphate chains if compared to the aluminium ions.

Aluminum Metaphosphate (Al(PO3)3) by XPS

The XPS spectra of aluminum metaphosphate were collected with a VSW HA150 using monochromatic Al Kα x-radiation. Monochromatic radiation provides a distinct clarity to the rich peak structure in the valence band of aluminum metaphosphate due to the absence of interfering x-ray satellites from the intense O 2s region. The valence band, survey, and the Al 2s, Al 2p, O 1s, and C 1s core levels are reported. The valence band region of metaphosphate is significantly different from that of phosphate.

Geometric and Electronic Structure of Amorphous Aluminophosphates. Ab Initio and Experimental Studies

A combination of experimental (diffuse reflectance infrared Fourier transform spectroscopy, DRIFTS, and X-ray photoelectron spectroscopy, XPS) and ab initio studies of model clusters is used to understand the geometric and electronic structure of aluminophosphate (AlPO) systems used as catalytic materials. The presence of an intense IR band in the DRIFTS spectra, around 1300 cm-1, together with literature data suggested to represent the system using cluster models based on metaphosphate-like structures. By varying the P/Al atomic ratio the basic features of AlPO4−Al2O3 catalysts are modeled. The calculated geometrical parameters (bond distances and associated stretch force constants) are discussed in relation to the structure of the catalyst and, despite the inherent approximations in modeling solids with cluster models, fits quite well-the experimental X-ray data for aluminum metaphosphate. The computed ionization potentials (IP), OKVV transitions, and IR spectra are in reasonable agreement with experime...

Particles of aluminum metaphosphate containing closed pores. Preparation, characterization and optical properties

Admixture of aluminum nitrate, sodium metaphosphate and ammonium hydroxide aqueous solutions yields noncrystalline solid precipitates. Using various aluminum: phosphorus ratios in the reacting mixtures, a range of particulate solids is obtained, the thermal behavior of which depends largely on the Al: P molar ratio in each solid. Upon heating to 600–700°C for times ranging from 30 s to 10 min, closed pores are formed within the particles of the solids in which the Al: P ratio is less than unity. The particles which are thus obtained are powerful light backscatterers. Closed-pore formation and growth can be monitored in real time by heating the particles under the condensed beam of a transmission electron microscope.

Improvement of the temperature resistance of aluminium-matrix composites using an acid phosphate binder

Binders are used in preforms from which metal-matrix composites are fabricated by liquid-metal infiltration. This paper (Part I) reports the preparation and characterization of various binders (by themselves). The characterization was in terms of the composition (by atomic absorption spectrometry and X-ray spectrometry), morphology, phases (by X-ray diffraction) and changes upon heating to 1200 °C (by thermogravimetric analysis and mass spectrometry). The binders studied include silica, phosphates (prepared from Al (OH)3 and H3PO4) with the P/Al molar ratio ranging from 1–23, sodium silicate and acrylic emulsion. A phosphate binder was in the form of type B aluminium metaphosphate (Al(PO3)3) at 500 °C when the P/Al atom ratio = 2.2 in the liquid binder, and was in the form of type A aluminium metaphosphate (Al/(PO3)3) when the atom ratio ≥ 5.8 in the liquid binder. Most of the phosphate binders formed type A aluminium metaphosphate (Al(PO3)3) after heat treatment at 800 °C. The phosphate binder with P/Al atom ratio = 2.2 in the liquid binder formed cristobalite aluminium orthophosphate (AlPO4), and the phosphate binder with P/Al atom ratio = 24 in the liquid binder formed a combination of cristobalite aluminium orthophosphate (AlPO4) and metaphosphate glass after heat treatment at 1200 °C in argon.

Aluminium metaphosphate glass-ceramics

AIP3O9 glass-ceramics were prepared by crystallization of glasses at 750–1100°C. Crystallization of AIP3O9 and AIPO4 at lower temperatures is favoured by addition of 5–10 mol % Li2O, Na2O or AIF3, whereas crystallization is hindered by 5–10 mol % B2O3, BPO4, SiO2, TiO2, Nb2O5 or Ta2O5. Additives such as TiO2, ZrO2, MgF2, CaF2 and Pt, frequently useful in nucleating silicate glasses, are ineffective in AIP3O9 glasses. AIPO4, resulting from the P2O5 loss during melting, forms at the surface of melted glass samples. AIP3O9 forms in the bulk as elongated columnar or lamellar crystals with grain sizes of 0.5–2.0 μm. Li2O-doped AIP3O9 is inhomogeneous with coarse intergranular regions and glassy regions. Dielectric constants vary from 5.0–5.2.

Phosphate bonding with several calcined aluminas

Reactivities of several calcined aluminas with orthophosphoric acid at fairly low curing temperatures were studied. Studies showed that compressive strengths were inversely proportional to the surface area of the calcined alumina used in the bond, due to the formation of crystalline AIPO 4 phase. A glassy phase and possibly an aluminum metaphosphate phase are effective bonding phases.

Analysis of the lithium ion conductivity in aluminium metaphosphate glasses

Glass formation and electrical conductivity have been studied in the system LiF-Li 2O-Al(PO 3) 3. Compositions have been specified by the ratio, N, of Li ions to the sum of glass-formers, Al + P, and by the ratio, X, of fluorine atoms to phosphorus atoms. Clear glasses were obtained with N=1 to 2.3 and X=0.5 to 2.5. Limited substitutions of Br for F and of BO 3 2 for 1 4 Al(PO 3) 3 were found possible. A correlation was found between the activation energies for conduction, E a, and the pre-exponential constants, A. Both E a and A were found to decrease with increasing N and to increase with increasing X. Anderson and Stuart's method of calculating activation energy is criticized, and a simple electrostatic calculation of E a is introduced in which E a depends on the Li + ion jump distance calculated from the mean Li + ion concentration. However this model cannot explain the large observed variations of A and its correlation with E. It is suggested that large variations of jump distance with small variations of composition occur due to a change of mechanism from single to multiple-ion jumps.

OPTICAL AND OTHER PHYSICAL PROPERTIES OF Al (PO3)3 - CONTAINING FLUOROPHOSPHATE GLASSES

OPTICAL AND OTHER PHYSICAL PROPERTIES OF Al (PO₃)₃ - CONTAINING FLUOROPHOSPHATE GLASSES

Aluminum Metaphosphate as a Hydrofluoric Acid Resistant Raman Cell Material

Aluminum Metaphosphate as a Hydrofluoric Acid Resistant Raman Cell Material

On Aluminium Phosphate Hydrates

A new crystal of aluminium pyrophosphate 18-hydrate, Al4(P2O7)3⋅18H2O, was obtained by double decomposition from mixed aqueous solution of ammonium phosphate and ammonium alum in the pH range below 2.5. In the pH range 3-6, two different crystals of aluminium orthophosphates (A-type and B-type) AlPO4⋅2H2O, whose structures remain unknown, were obtained. The pure A-type crystal was able to be crystallized by this method, while the B-type was always acompanied by the A-type. We found that the pure B-type can be crystallized by autoclave treatment on amorphous precipitate from the mixed solution under the pressure of 10 atm. at 182°C. The physical and chemical properties of these new crystals were studied.When aluminium orthophosphate crystals (A-type and B-type) were heated they became amorphous anhydrites after missing their crystallization water near 200°C. At about 400°C they changed directly to tridymite form AlPO4 without passing quartz-form AlPO4 (berlinite) even if no alkali existed at all, and holding for 2 weeks in the stable temperature range of berlinite caused no inversion to berlinite. The amorphous anhydrites changed also to cristobalite- form AlPO4 at about 800°C. These cristobalite-form AlPO4 obtained at relatively low temperatures had imperfect structures having enlarged lattice spaces.The extra pure cristobalite-form AlPO4 obtained by heating aluminium orthophosphates above 1, 350°C, did no more invert to tridymite-form or quartz-form AlPO4, but with alkalis coexisted these inversions were able to take place smoothly.Aluminium pyrophosphate crystal lost its crystallization water at about 180°C, and at a little higher temperatures some P2O5 vapourized from the amorphous anhydrate, which decomposed to aluminium metaphosphate Al(PO3)3 and cristobalite-form AlPO4. At above 1, 050°C more vapourisation of P2O5 and decomposition of metaphosphate to cristobalite-form AlPO4 occured.On heating the pyrophosphate a new phase appeared prior to the metaphosphate and this coexisted with the metaphosphate and cristobalite-form AlPO4 up to about 1, 000°C.

Colour Centres in Metaphosphate Glass

IN a recent communication1, Basu states that we have attributed the coloration of metaphosphate glasses, induced by X-rays, to the activating influence of the metal (aluminium, barium, silver, etc.) in the glass, and that his results with sodium metaphosphate glasses show that ‘F-centres’ can be produced without these activators. In the references to our work cited by Basu2,3, the point is made that radiophotoluminescent centres having certain specific properties are connected with the presence of silver in potassium–barium–aluminium metaphosphate glass. It is clearly shown, we believe, in the publications from this Laboratory3–5 that a visible coloration is produced upon X-irradiation of the above silver-free base glass, two broad bands appearing with peaks at about 420 mµ and 530 mµ. These colour centres were not attributed to any ‘activating’ influence of the aluminium, barium or other metallic constituents of the glass.