The synthesis and thermal behaviour of sodium phosphorodiamidate

Sodium phosphorodiamidate pentahydrate, NaPO₂(NH₂)₂·5H₂O, was made by saponifying phenyl phosphorodiamidate with a 4 mol dm^–3 aqueous sodium hydroxide solution. The product was stable below 5° C, but it decomposed gradually to phosphoramidate and orthophosphate at 30° C. The phosphorodiamidate produced imidopolyphosphates and polyphosphates other than phosphoramidate and orthophosphate when it was heated above 30° C, and was finally converted to sodium metaphosphate above 300° C in air.     

Synthesis and thermal reorganization of sodium cyclo-hexaphosphate

Sodium cyclo-hexaphosphate hexahydrate was prepared by passing an aqueous solution of lithium cyclo-hexaphosphate through cation-exchange resin, neutralizing the resulting solution with an aqueous sodium hydroxide solution, and then adding ethanol into the solution. The sodium cyclo-hexaphosphate was dehydrated upon heating above 180°C without decomposing to other phosphates and anhydrous sodium cyclo-hexaphosphate was produced. The anhydrous cyclo-hexaphosphate was stable and did not exhibit any thermal change up to 450 °C, and was transformed to sodium cyclo-triphosphate above 450 °C. The cyclotriphosphate melted at about 650 °C.     

Synthesis and thermal property of sodium triimidocyclotriphosphate

Sodium triimidocyclotriphosphate tetrahydrate was made by reacting phosphorus pentachloride with ammonium chloride and then hydrolysing the resulting product in an aqueous sodium acetate solution. When the cyclotriphosphate was heated in air, it was directly converted to sodium cyclotriphosphate according to the reaction (NaPO₂NH)₃ + 3H₂O → (NaPO₃)₃ + 3NH₃     

Synthesis and thermal behaviour of alkaline earth cyclo-octaphosphates

Hydrated alkaline earth cyclo-octaphosphates were made by adding an aqueous solution of alkaline earth chlorides into an aqueous solution of sodium cyclo-octaphosphate. Thermal properties of the compounds were studied by TG-DTA analysis. The water of crystallization was removed below 200°C. The cyclo-octaphosphates decomposed to produce many phosphate species up to about 500°C, and they finally reorganized to metaphosphates. The overall thermal reaction of alkaline earth cyclo-octaphosphates can be written by the equation. M4(PO3)8 · nH2O 4M(PO3)2 + nH2O     

Synthesis and thermal behaviour of potassium sialate geopolymers

The geopolymers potassium polysialate (K-PS) and potassium sialate disiloxo (K-PSDS) have been found to possess extremely good thermal stability. K-PS shows little sign of melting up to 1400 °C, its amorphous structure being replaced by the crystalline feldspars leucite and kalsilite at 1000 °C. ²⁷Al and ²⁹Si MAS NMR confirm the ease of this thermal reaction which involves only slight changes to the tetrahedral Al environment. Silica-rich K-PSDS becomes friable and porous at >1200 °C, with less complete crystallisation of K-feldspar, the formation of some cristobalite and the retention of a degree of amorphous geopolymer. ³⁹K NMR suggests that the charge-balancing alkali ions in the K-PS and K-PSDS geopolymer networks behave similarly to those of Na geopolymers, dehydrating on heating and moving into the feldspar lattice >1000 °C.     

Synthesis and thermal behaviour of ammonium and guanidine cyclo-hexaphosphates

Ammonium cyclo-hexaphosphate monohydrate and guanidine cyclo-hexaphosphate dihydrate were prepared by a wet chemical process from an aqueous solution of lithium cyclo-hexaphosphate. Thermal properties of the compounds were studied by using a TG-DTA apparatus.     

Synthesis,characterisation and thermal behaviour of lithium aluminosilicate inorganic polymers

Lithium aluminosilicate inorganic polymers were synthesised from dehydroxylated kaolin-type clay (halloysite) by the conventional method under highly alkaline conditions with lithium hydroxide or lithium silicate solutions of two different Li₂O/SiO₂ molar ratios. Variants were also developed of a solid-state synthesis method involving the thermal reaction of dehydroxylated halloysite with LiOH followed by hydration of the product. The molar compositions of the materials prepared by all three methods (SiO₂/Al₂O₃ = 2.41–3.27, Li₂O/SiO₂ = 0.30–0.61, and H₂O/Li₂O = 9.33–10.40) fall within the range of compositions previously reported to produce viable geopolymers. Curing at 40 °C produces solid samples of varying viability depending on the amount of synthesis water. The cured materials are not characteristically X-ray amorphous, but contain the lithium zeolites Li-ABW and fibrous Li-EDI, the latter in the materials synthesised by solid-state reaction. The ²⁷Al and ²⁹Si MAS NMR spectra of the cured materials contain narrow resonances more characteristic of zeolites than of inorganic polymers. Heating the synthesised products at <800 °C produces β-eucryptite, LiAlSiO₄. In a further series of thermal reactions, β-spodumene, LiAlSi₂O₆ is formed at 900 °C, decomposing at 1100 °C to form additional β-eucryptite. At 1275 °C, β-spodumene reappears in the samples of higher silica content. Judicious manipulation of the composition and thermal treatment of the Li-zeolites formed in these lithium aluminosilicate syntheses could make them useful precursors to β-eucryptite and β-spodumene ceramics.     

Synthesis and thermal behaviour of nanostructured ZrO2 powders obtained under hydrothermal conditions

Nanocrystalline zircone (ZrO2) powders were synthesized from zirconium oxyacetate aqueous solution treated up to 240 degrees C under autogeneous pressure. Depending on experimental conditions, colloidal particles of 26-150 nm are formed by aggregation of zirconia crystallites. The effect of some experimental conditions over the colloidal particle size or zirconia phase composition was studied. The powder sintering behaviour is also presented.     

The synthesis and thermal behaviour of zinc diphosphates

Zinc diphosphates (Zn₂P₂O₇ · 5H₂O, Zn₂P₂O₇ · 3H₂O, 5K_1.4Zn_1.3P₂O₇ · 16H₂O, and 5K_0.8Zn_1.6P₂O₇ · 9H₂O) were made by the wet process. The composition of the products was dependent on the conditions (concentration, pH, and dropping rate of the solution) of the process. When the products were heated, decomposition of the diphosphates to orthophosphate took place below about 150 ·C. Polymerization of the phosphates to phosphates with longer chains was observed in the temperature range 150 to 400 ° C. The amorphous phosphates thermally produced by heating diphosphates other than 5K_1.4Zn_1.3P₂O₇ · 16H₂O, showed reorganization to diphosphate above 400 ° C according to the reaction M₂O₃PO[P(O₂M)O] _n PO₃M₂ +nM₃PO₄(n + 1)M₄P₂O₇ where M represents K and/or 1/2Zn.     

以柠檬酸钠为分散剂一步法合成Cu-水导热纳米流体

以柠檬酸钠为分散剂,KBH4为还原剂,CuSO4·5H2O为氧化剂,采用一步法直接合成了Cu-水导热纳米流体。其最佳合成工艺条件为:n(CuSO4·5H2O)∶n(KBH4)=2.5∶1,柠檬酸钠的用量为0.07mol/L,温度为40℃,反应时间为100 min。TEM表征表明该导热纳米流体中Cu纳米粒子分散较均匀;经激光光散射仪粒度分析得其分散粒子平均尺寸为1.1nm;在25℃时测得该导热纳米流体的导热系数为0.7812 W/(m·K),比纯水的导热系数提高30%。     

Dielectric behaviour of sodium and potassium doped magnesium titanate

Pure phase of magnesium titanate (MgTiO $_{\boldsymbol{3}})$ was obtained at 1100°C by both the conventional solid-state method as well as by the flux method starting from hexahydrated magnesium nitrate and titanium dioxide as the reactants. MgTiO $_{\boldsymbol{3}}$ doped with Na or K was also prepared by the solid-state route. Na and K doped compositions led to monophasic MgTiO $_{\boldsymbol{3}}$ below 5 mol % dopant concentration while biphasic mixture of MgTiO $_{\boldsymbol{3}}$ (major phase) and MgTi $_{\boldsymbol{2}}$ O $_{\boldsymbol{5}}$ (minor phase) were obtained at higher dopant concentration. The dielectric constant and dielectric loss of MgTiO $_{\boldsymbol{3}}$ were found to be almost the same irrespective of the preparative method. MgTiO $_{\boldsymbol{3}}$ doped with 5 mol % of Na and K ions displayed optimum dielectric properties.     

Synthesis and characterization of sodium alkoxides

Alcohol route is being adopted for cleaning sodium from sodium-wetted small components of coolant circuits of fast reactors. For better understanding of sodium-alcohol reactions and their energetics, the data on thermo-chemical properties such as heats of sodium-alcohol reactions, heats of dissolution, heat capacities, thermal decomposition behaviour, etc of their end products are essential. In order to generate such data, high purity sodium alkoxides, viz. sodium methoxide, sodium ethoxide and sodium n-propoxide, were prepared by reacting sodium metal with respective alcohol. These compounds were characterized using X-ray diffraction technique and IR spectroscopy. The elemental analysis was carried out by CHNS analyser and atomic emission spectroscopy. Normal chain sodium alkoxides were found to exhibit tetragonal crystal structure. Crystal structures of sodium ethoxide and sodium n-propoxide are reported for the first time. The IR spectrum of sodium n-propoxide is also reported for the first time.     

Characterization and thermal behaviour of gel-grown gadolinium tartrate crystals

Gadolinium tartrate crystals in the form of spheru!itoe were synthesized by using a controlled diffusion system in sillica gel. Characterization of the material was performed by utilizing the techniques of chemical analysis, X-ray and electron diffraction, infrared and mass spectroscopy, and by As thermal behaviour. The material turns out to be a dihvdrate and the chemical composition vvoethus established as Gd₂(C₄H₄O₆)₃ · 2H₂O. The data obtained from the thermal analysis show the tendency of the material to decompose, and this is further confirmed by mass spectroscopy The decomposition process is completed in four steps until gadolinium oxide is obtained at 840* C. The energetics of the reactions at each stage of decomposition have been examined and mechanisms for the decomposition reactions are proposed.     

Microporous titanosilicate AM-2: Rb-exchange and thermal behaviour

Rb-exchange and thermal stability of the microporous titanosilicate AM-2 were analysed by powder X-ray diffraction, thermo-gravimetric analysis, and chemical analysis of the mother liquid after exchange. The dehydration and thermal stability of the exchanged structure were monitored with in situ high temperature powder X-ray diffraction. Crystal structures were refined with Rietveld methods at 25 and 400 °C. The AM-2 structure was found to incorporate Rb⁺ by replacing K⁺. After four exchange cycles and 166 h reaction time at 90 °C, the chemical composition was refined to K_0.18Rb_1.82TiSi₃O₉·H₂O. Extrapolation suggests that higher exchange ratios may be obtained after further cycles. H₂O was expelled by heating, leading to a dehydrated structure at 360 °C. Dehydration was associated with a change of space group symmetry from orthorhombic P2₁2₁2₁ to monoclinic P2₁, which proved to be reversible after rehydration. This change of symmetry leaves the AM-2 characteristic structural topology uninfluenced and causes only minor distortions. The monoclinic AM-2 structure breaks down above 600 °C to become X-ray amorphous, and at 750 °C a wadeite-type phase (K_xRb_2−xTiSi₃O₉) crystallises. This transformation is irreversible and leads to immobilisation of Rb⁺.     

The zircon thermal behaviour: effect of impurities

The effect of impurities on zircon thermal behaviour is discussed and explained from a thermodynamic point of view. Based on the data obtained from the ZrO₂-Al₂O₃-SiO₂-TiO₂ system, previously studied by the authors, the influence of the impurities, normally present in zircon sands, on the dissociation and initial melting temperatures in natural zircon, has been studied.     

Modeling of droplet dynamic and thermal behaviour during spray deposition

Mathematical modeling of supersonic gas atomization for spray forming has been investigated. Influence of the droplet dynamic and thermal behaviour on the resultant microstructure has been studied. Analytical models have been constructed taking into account the higher Reynolds number owing to supersonic gas flow. The impact velocity profiles of the droplets lend credence to the evolution of equiaxed grain morphology through dendrite fragmentation. The thermal history profile along with the fraction solid plot could yield optimized standoff distance to obtain a mushy droplet. A comparison of secondary dendrite arm spacing obtained from the mathematical model showed good agreement with experimental observations.