Thermal expansion studies on the Sodium Zirconium Phosphate family of compounds A1/2M2 (PO4)3: effect of interstitial and framework cations

Thermal expansion of the sodium zirconium phosphate (NZP) family of compounds A_1/2M₂(PO₄)₃ (A = Ca or Sr; M = Ti, Zr, Hf or Sn) has been measured in the temperature range 298–1273 K by high-temperature X-ray powder diffractometry. Some of the compounds in the series (calcium zirconium phosphate and calcium hafnium phosphate) display the typical thermal expansion behaviour of NZP compounds, namely expansion along the hexagonal c axis and contraction along the a axis. The other compounds, depending on their interstitial and framework composition, behave differently. The observed axial thermal expansion and contraction behaviour is explained on the basis of the crystal chemistry of the compounds. Low-expansion compounds in this series are identified and their expansion anisotropy examined. Infared spectra of the compounds are reported. Differential scanning calorimetry measurements on the tin compounds indicate the occurrence of a diffuse phase transformation at high temperatures.     

Structural model for thermal expansion in MZr2P3O12 (M=Li,Na, K,Rb, Cs)

A structural model is proposed to describe the highly anisotropic thermal expansion in the sodium zirconium phosphate NaZr₂P₃O₁₂ structure as a result of the thermal motion of the polyhedra in the structure. In the proposed model the rotations of the phosphate tetrahedra are coupled to the rotation of the zirconium octahedra. Of the two versions considered, the first one allows angular distortions to occur only in the ZrO₆ octahedra; the second one permits all polyhedra to be distorted.     

Synthesis,crystallographic characterization and ionic conductivity of iron substituted sodium zirconium phosphate Na<Subscript>1.2</Subscript>Zr<Subscript>1.8</Subscript>Fe<Subscript>0.2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Sodium zirconium phosphate NaZr₂P₃O₁₂ (hereafter NZP) crystallizes in rhombohedral (hexagonal) symmetry with the space group R-3c. The NZP-related phase of synthetic iron substituted NZP has been prepared by partial substitution on zirconium site by Fe(III). The material has been synthesized by sintering the finely powdered oxide mixture in a muffle furnace at 1,050 °C. The polycrystalline phase of Na_1.2Zr_1.8Fe_0.2(PO₄)₃ has been characterized by its typical powder diffraction pattern. The powder diffraction data of 3,000 points have been subjected to general structural analysis system (GSAS) software to arrive at a satisfactory structural fit with R _p = 0.0623 and R _wp = 0.0915. The following unit cell parameters have been calculated: a = b = 8.83498(18) ?, c = 22.7821(8) ? and α = β = 90.0° γ = 120.0°. The structure of NZP consists of ZrO₆ octahedra and PO₄ tetrahedra linked by the corners to form a three-dimensional network. Each phosphate group is on a two-fold rotation axis and is linked to four ZrO₆ octahedra. Each zirconium octahedron lies on a threefold rotation axis and is connected to six PO₄ tetrahedra. AC conductivity of the solid solution has been measured between 303 and 773 K. The material exhibits temperature-dependent enhancement of ionic conduction by ≈400 times at elevated temperatures. The activation energies show significant change in slope at 1,000/T = 2.23(448 K).     

Ge、Si元素对ZrO2和Zr(Fe,Cr)2能量与电子结构的影响

采用基于密度泛函理论的第一性原理计算方法,研究Ge、Si元素对锆合金中与腐蚀相关的ZrO_2氧化膜相和Zr(Fe,Cr)_2第二相能量与电子结构的影响。合金形成热、结合能的计算结果表明:ZrO_2四方相结构不稳定,立方相易形成且结构稳定,氧化膜晶体结构从四方相向立方相发生转变影响锆合金的耐腐蚀性能;Ge、Si元素均降低ZrO_2立方相的结构稳定性和形成能力,与Ge相比,Si易取代Zr(Fe,Cr)_2第二相中的Cr,增加锆合金Fe/Cr原子比。电子态密度和Mulliken电子占据数的计算结果表明:ZrO_2中Zr与O存在杂化共振与较强的离子键作用,Ge、Si降低ZrO_2立方相结构稳定性的原因主要在于削弱了Zr-O之间的离子键作用;ZrO_2氧化膜相和Zr(Fe,Cr)_2第二相是影响锆合金耐腐蚀性能的两个重要因素,对Si而言,形成含Si的Zr(Fe,Cr)_2第二相对锆合金耐腐蚀性能产生不利影响,改善锆合金耐腐蚀性能需要ZrO_2晶体结构改变占主导地位;对Ge而言,含Ge的Zr(Fe,Cr)_2第二相难形成,第二相对锆合金耐腐蚀性能的影响相对Si较小,减缓ZrO_2由四方相向立方相的转变倾向,是Ge改善锆合金耐腐蚀性能的重要原因。     

Encapsulation of heterovalent ions of two simulated high-level nuclear wastes and crystallization into single-phase NZP-based wasteforms

Preliminary data were obtained on the immobilization of various heterovalent ions present in the two selected high-level nuclear waste compositions. The entire set of ions present in the waste compositions were immobilized into sodium zirconium phosphate (NZP) structure. The waste loading was in the range 5–25%. The two types of wasteforms loaded with the simulated high-level waste compositions were characterized by powder X-ray diffraction, FT-IR, TGA/DTA, and scanning electron microscopy. The difference in the compositions of the two simulated wastes was reflected in the waste loading percentage and the crystallization of the wasteforms into NZP structure. Up to 12% waste loading, single phase isostructural with NZP was obtained as a major product in the case of the first waste composition. An increase in the waste loading led to the segregation of ZrP₂O₇ as a secondary phase. With the second waste composition, an NZP-like phase was obtained as the major product even at 25% waste loading.     

Erbium zirconium phosphate Er<Subscript>0.33</Subscript>Zr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> of the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> family. Structure contraction on heating

Erbium zirconium phosphate Er_0.33Zr₂(PO₄)₃, a member of the family of structural analogs of NaZr₂(PO₄)₃ (NZP), was prepared by the sol-gel process and studied by X-ray phase analysis, IR spectroscopy, and differential scanning calorimetry. The behavior of erbium zirconium phosphate on heating in the temperature interval from 25 to 625°C was studied by high-temperature X-ray diffraction. Expansion and contraction along different crystallographic directions and contraction of the structure as a whole were found. The overall contraction is due to higher contribution of the negative axial thermal expansion coefficients α _a and α _b to α_av and hence to the volume expansion of the phosphate. On heating to 900°C, the NZP structure is preserved.     

溶胶凝胶法制备磷酸锆钠陶瓷材料

以Zr(NO3)4.5H2O、NH4H2PO4和NaNO3为原材料,采用溶胶凝胶法合成了磷酸锆钠(NaZr2(PO4)3)陶瓷粉体,采用TG-DTA,XRD和SEM测试方法对粉体性能进行了表征,研究了烧结温度和pH值等反应条件对粉体合成的影响.结果表明,要获纯的磷酸锆钠粉体,合成温度需控制在800～1 000℃之间,其中最合适合成温度为900℃左右.前驱体pH值对合成温度基本没有影响,但会影响产物微观形貌.当合成温度为900℃,pH值为9时可以制备出团聚较少、颗粒均匀、分散性较好且平均粒径为100nm的磷酸锆钠粉体.     

Isomorphism in Crystalline Phosphates of the NaZr2(PO4)3 Structural Type and Radiochemical Problems

The problems of isomorphism in phosphates that are structural analogs of sodium zirconiumorthophosphate NaZr₂(PO₄)₃ (NZP) are discussed. Data on the crystal chemistry of orthophosphates of theframework structure are systematized according to the suggested classification of their formula types. Thetheoretically possible, actually occurring isomorphism of cations in phosphates, in particular, isomorphisminvolving f-element cations, is discussed. The isomorphous capacity of the NZP structure toward variouscations was evaluated. Data on isomorphism in phosphates are necessary for choosing a suitable single-phase ceramic matrix for incorporation of radionuclides and adjusting its composition to actual nuclear waste.     

对两种不同晶型磷酸锆载银工艺探索

磷酸锆是一种具有离子交换性能的无机载体,被广泛应用于离子交换体。研究不同晶型磷酸锆的载银工艺,探索银离子交换的机理并制备出高载银量的磷酸锆载银抗菌粉。以锆磷比为1∶2的α-Zr(HPO4)2.H2O和锆磷比为2∶3的六面体磷酸锆为对象,研究在不同离子交换环境下对银离子的交换率。发现α-Zr(HPO4)2.H2O在层间隙扩大的情况下,银离子交换量大于8.47%,而六面体磷酸锆在强酸高温环境中,银离子交换量大于4.45%。具有层状间隙的α-Zr(HPO4)2.H2O比六面体磷酸锆对银离子具有更高的交换容量。为研制具有高效长效抗菌要求的制品,如抗菌医用导管做好准备。     

Ca1-xBaxZr4(PO4)6磷酸盐陶瓷材料的热膨胀特性

Ca1-xBaxZr4(PO4)6(0≤X≤1.0)属于NZP族磷酸盐陶瓷材料,它是新的一类低热膨胀陶瓷材料。研究发现CaZr(PO4)6(X=0)及BaZr4(PO4)6(X＝1)时的轴膨胀特性正好相反,因此当X为某一值时热膨胀系数将为零。本研究采用共沉淀法合成了Ca1-xBaxZr4(PO4)6磷酸盐陶瓷材料,当X＝0时,热膨胀系数为－0．86×10-61／℃;当X＝0．25时热膨胀系数为2．7×10-61／℃;当X＝0．75时其热膨胀异向性最小。为了得到热膨胀异向性和热膨胀系数均小的Ca1-xBaxZr4(PO4)6磷酸盐陶瓷材料,X应在0．6至0．9之间,并通过控制烧结条件抑制晶粒的生长。     

Synthesis and characterization of srilankite nanowires

We describe the synthesis and characterization of srilankite (Ti2ZrO6) nanowires. The nanowires are produced via hydrothermal synthesis with a TiO2/ZrO2 mixture under alkaline conditions. The zirconium titanate nanowires have median diameters of 60 nm and median lengths of 800 nm with the (022) axis along the length of the nanowire. Electron microscopy, energy dispersive X-ray spectroscopy, powder X-ray diffraction, and electron diffraction are used to characterize the phases and compare nanowires produced with varying molar ratios of Ti and Zr. Electron diffraction patterns produced from single nanowires show highly crystalline nanowires displaying a compositional-ordering superlattice structure with Zr concentrated in bands within the crystal structure. This is in contrast to naturally occurring bulk srilankite where Zr and Ti are randomly substituted within the crystal lattice. Streaking is observed in the electron diffraction patterns suggesting short-range ordering within the superlattice structure.     

Structure and Lattice Dynamics of R $$_2$$ 2 Sn $$_2$$ 2 O $$_7$$ 7 and R $$_2$$ 2 Zr $$_2$$ 2 O $$_7$$ 7 (R = La–Lu) Crystals: Ab Initio Calculation

Journal of Superconductivity and Novel Magnetism - Crystal structure and phonon spectrum of rare-earth stannates R $$_2$$ Sn $$_2$$ O $$_7$$ and zirconates R $$_2$$ Zr $$_2$$ O $$_7$$ (R =...     

The sodium ytterbium orthophosphate Na3(1+x)Yb(2-x)(PO4)3

A new sodium ytterbium orthophosphate with general formula Na_3(1+x)Yb_(2-x)(PO₄)₃ (0.07 ? x ? 0.50) has been prepared and characterized. Its crystal structure has been determined from a single crystal for x = 0.50. The space group is R3?c, the lattice constants are : $\text{a}\text{= 9.12(1)}\text{A}\text{?}$, $\text{c}\text{= 21.81(6)}\text{A}\text{?}$. The structure of Na_4.50Yb_1.50(PO₄)₃ is related to that of NaZr₂(PO₄)₃. The PO₄ tetrahedra and the (Yb,Na)O₆ octahedra form a three-dimensional skeleton in which the remaining sodium atoms are inserted. This structural type is also found for the phases Na_4.50Ln_1.50(PO₄)₃ (Ln = Tm, Lu) and Na_4.50Ln_1.50(AsO₄)₃ (Ln = Er, Tm, Yb, Lu).     

ZrO2-Si3N4陶瓷复合材料中的化学不相容性

ＺｒＯ_２与Ｓｉ_３Ｎ_４之间存在化学反应生成ＺｒＮ或氧氮化锆,ＺｒＯ_２也可能被氮稳定形成氨稳定的ＺｒＯ_２本文对ＺｒＯ_２－Ｓｉ_３Ｎ_４陶瓷复合材料中的化学不相容性及抑制措施进行了综述．     

Crystal chemistry of the NaZr2(PO4)3, NZP or CTP,structure family

The NaZr₂(PO₄)₃ type structure (abbreviated as NZP or CTP, CaTi₄(PO₄)₆), has emerged as a new family, which has extraordinary technological utility in three fields: fast-ion conductors, radwaste solidification and zero expansion ceramics. NZP or CTP is formed by an extraordinary range of discrete compositions and crystalline solutions. In this paper these compositions are classified according to their crystal chemical substitution scheme, and some uncommon trends in the systematic variation of their lattice parameters are shown. Some of the major trends are explained by correlation with the rotation of polyhedra in the structure.     

Zr/ZrO2 sensors for in situ measurement of pH in high-temperature and -pressure aqueous solutions

The aim of this study is to develop new pH sensors that can be used to test and monitor hydrogen ion activity in hydrothermal conditions. A Zr/ZrO2 oxidation electrode is fabricated for in situ pH measurement of high-temperature aqueous solutions. This sensor responds rapidly and precisely to pH over a wide range of temperature and pressure. The Zr/ZrO2 electrode was made by oxidizing zirconium metal wire with Na2CO3 melt, which produced a thin film of ZrO2 on its surface. Thus, an oxidation-reduction electrode was produced. The Zr/ZrO2 electrode has a good electrochemical stability over a wide range of pH in high-temperature aqueous solutions when used with a Ag/AgCl reference electrode. Measurements of the Zr/ZrO2 sensor potential against a Ag/AgCl reference electrode is shown to vary linearly with pH between temperatures 20 and 200 degrees C. The slope of the potential versus pH at high temperature is slightly below the theoretical value indicated by the Nernst equation; such deviation is attributed to the fact that the sensor is not strictly at equilibrium with the solution to be tested in a short period of time. The Zr/ZrO2 sensor can be calibrated over the conditions that exist in the natural deep-seawater. Our studies showed that the Zr/ZrO2 electrode is a suitable pH sensor for the hydrothermal systems at midocean ridge or other geothermal systems with the high-temperature environment. Yttria-stabilized zirconia sensors have also been used to investigate the pH of hydrothermal fluids in hot springs vents at midocean ridge. These sensors, however, are not sensitive below 200 degrees C. Zr/ZrO2 sensors have wider temperature range and can be severed as good alternative sensors for measuring the pH of hydrothermal fluids.     

Synthesis of castable sodium zirconium phosphate monoliths employing reactions between zirconyl nitrate hydrate and condensed phosphates

Reactions between zirconyl nitrate hydrate and condensed phosphates can be used to produce castable low CTE sodium zirconium phosphate (NZP) monoliths. Reaction between sodium nitrate, zirconyl nitrate hydrate and condensed phosphoric acid at room temperature (alkali nitrate method) produces monoliths having a heterogeneous microstructure, which are multiphasic in appearance. Except for the presence of crystalline sodium nitrate, they are X-ray amorphous. Differential thermal analysis revealed two distinct exothermic crystallization events when these materials are heated. The first event, with an onset temperature of 650°C, is the result of NZP and ZrO₂crystallization. The second is the result of ZrP₂O₇ crystallization. Reaction between zirconyl nitrate hydrate and condensed sodium phosphate (condensed alkali phosphate method) results in a more homogeneous microstructure in which crystalline zirconium hydrogen phosphate hydrate and sodium nitrate are present. Two exothermic peaks, with onset temperatures of approximately 570 and 860°C, are observed. The first exotherm is the result of NZP, ZrO₂ and ZrP₂O₇ crystallization; the second exotherm is the result of a further NZP formation. After heating materials made by these two methods at 940°C for 24 h, the condensed-alkali-phosphate-method-derived material converted to phase-pure NZP, while the alkali-nitrate-method-derived material contained ZrP₂O₇. The differences in phase evolution between the materials prepared by these two methods are attributable to the differences in chemical and microstructural homogeneity that result from the reactants used. This revised version was published online in September 2006 with corrections to the Cover Date.     

A new mixed valent molybdenum monophosphate with a tunnel structure: Cs3Mo8O11(PO4)8

A new mixed valent molybdenum monophosphate, Cs₃Mo₈O₁₁(PO₄)₈, with a tunnel structure, has been synthesized. It crystallizes in the space group C2/m with a=20.203 (2) Å, b=6.370 (1) Å, c=14.379 (1) Å and β=99.827 (7)°. Its [Mo₈P₈O₄₃]_∞ 3D-framework consists of single phosphate groups, single MoO₆ octahedra, and bioctahedral units of corner-sharing octahedra Mo₂O₁₁ and of edge-sharing octahedra Mo₂O₁₀. The entire host lattice can be described by the association of [MoPO₈]_∞ chains running along b, through the corners of their octahedra and tetrahedra, and through the edges of their octahedra, forming large tunnels running along b where the Cs⁺ cations are located. Bond valence calculations show that in the bioctahedral units, the electrons are delocalized between the two Mo atoms.     

Calcium phosphate coating of Ti–Nb–Zr–Sn titanium alloy

This study focuses on rapid formation of calcium phosphate coating on a β type Ti–Nb–Zr–Sn biomedical titanium alloy by alkali treatment. The results show that a bioconductive surface layer forms on specimens immersed in 1–5 M KOH solution but only treatment in 1 M KOH avoids formation of crevices, producing a potassium titanate layer with porous network structure. Heat treatment at 600 °C after the alkali treatment promotes titanate growth. Following the above treatments, a continuous apatite layer forms within 4 h of soaking in a calcium phosphate solution with high ionic concentration. Such rapid apatite formation is due to high concentration of calcium ions in the solution used in this study and the buffering function of NaHCO₃. Results of dissolution experiment show that Ca and P ions release gradually from the coating during soaking in a 0.9% NaCl solution, which may be helpful to the formation of natural bone if implanted in human body. Cell culture experiment shows that the apatite layer favours adhesion and proliferation of rat osteoblast as compared with coating-free Ti–Nb–Zr–Sn alloy and commercially pure titanium (CP Ti).     

含Ag0.16Na0.84Zr2(PO4)3抗菌喷雾剂

叙述了含Ag_(0.16)Na_(0.84)Zr_2(PO_4)_3抗菌喷雾剂的制法、性能与应用