Sol-Gel Fabrication of Rare-Earth Doped Photonic Components

The use of sol-gel to fabricate silica-on-silicon waveguides, and particularly erbium-doped waveguide amplifiers, is reviewed. In particular, efforts to use sol-gel to improve molecular homogeneity in heavily Er-doped silica-based films is discussed. A variety of material studies carried out to investigate the gain limitations found in these materials is then presented. These include x-ray diffraction, ellipsometry and Rutherford backscattering. Excess heat treatment is used to force crystallisation of the films, and analysis of the resulting structure is used to infer properties of the glass before the additional heating. The use of erbium alkoxide precursors is shown to alter the erbium environment in the final glass, in comparison to the use of inorganic erbium salts.     

Crystallisation and performance characteristics of high‐temperature annealed electroless Ni‐W‐P coatings

Electroless deposition of Ni–P based alloys is a well‐known commercial process that has numerous applications because of their excellent anticorrosive and wear properties. However, for some special occasions, like the components for gas making furnaces in chemical fertiliser industry, the coatings must be reinforced to withstand short‐term high temperatures between 600 °C and 700 °C as well as light erosive wear. Therefore, co‐deposition of high melting point metallic element, W, has been considered as a preferred choice. In the present study, two Ni–W–P alloy coatings were deposited on mild steel panels from different alkaline baths. The microstructures of the annealed coatings were characterised by quantitative XRD, XPS and SEM/EDS analysis techniques and their microhardness, friction and wear behaviour, corrosion mechanism as well as microstrain and residual stress are discussed in comparison with the as‐plated state. The results indicate that the hardness mainly depends on the volume fraction and crystallite size of Ni₃P phase; the uniform corrosion in sulfuric acid solution is closely related to the ratio of I_Ni/I_Ni3P as well as grain size. The wear mechanism of the high‐temperature annealed coating is dominated by abrasive wear, but the wear in the early stages started from mild adhesive wear caused by adhesion between the friction couples. Electroless deposited Ni‐W‐P alloys with high phosphorus present relatively good properties, including hardness, wear and corrosion resistance when 700 °C is applied for annealing process.     

Thermal Behaviour of Silicate-Phosphate Glasses in Relation to Their Biochemical Activity

Glasses of theK₂O–MgO–CaO–SiO₂ and K₂O–MgO–CaO–P₂O₅–SiO₂ systems with microelements (Fe, Mo, Zn, B, Mn, Cu) were obtained by melting of apatite and serpentinite rocks, K₂CO³ and oxides of appropriately metals mixtures. The amorphous state of glasses and the structural changes during their heating were determined by RDF and DTA/DSC methods. The solubility of the glasses in 2 mass% citric acid solution was studied by chemical analysis (ICP-AES, EDS) and SEM observations.It has been found that the biochemical activity of silicate-phosphate glasses depends on the content of P₂O₅ and K₂O in their framework and is related to crystallisation ability of these glasses.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal investigation of the crystallisation nucleant formed between 2,4,6 trinitrotoluene, (TNT) and 2,2′,4,4′,6,6′ hexanitrostilbene (HNS)

Hexanitrostilbene (HNS), is added to trinitrotoluene (TNT), in order to improve the grain structure of cast munitions. The formation and composition of the nucleant material has been investigated by thermal methods using mixtures of HNS and TNT, with composition in the range 0.5%, the normal casting level, to 50% w/w HNS to TNT. These were cycled between ambient and upper temperatures in the range 160 to 235°C. Endotherms in the DSC traces, due to nucleant decomposition, have been observed in situ without the need for separation and purification. DSC enthalpy measurements, before and after thermal decomposition, were used to determine the composition of separated nucleant. Nucleant regeneration after decomposition, was investigated by thermal methods. Nucleant could not be recrystallised from solvents. Results have been interpreted on the basis of the formation of a, solid solution of TNT in HNS, rather than a complex of formula TNT₂HNS.     

Determination of nucleating ability ofwood for non-isothermal crystallisation of polypropylene

Composites made from an isotactic polypropylene matrix and wood (pine or beech) have been prepared and tested. To improve adhesion between components, the wood modification was performed by esterification with maleic, propionic, crotonic, succinic and phthalic anhydrides. The surface of wood fillers was also modified by chemical treatment with NaOH as well as by extraction process. Non-isothermal crystallisation of polypropylene in wood composites is studied by DSC, and the basic parameters of crystallisation are determined. We discovered that the composites containing chemical treated wood fillers showed the tendency reduction the nucleation efficiency of polypropylene. The ability of wood filler to induce nucleation in polypropylene matrix is dependent on the kind of chemical modification of surface wood     

Crystallization and melting behaviour of poly(m-xylene adipamide)

The melting and crystallisation behaviour of poly(m-xylene adipamide) (MXD6) are investigated by using the conventional DSC, X-ray diffraction and polarised light microscopy. Triple, double or single melting endotherms are obtained in subsequent heating scan for the samples after isothermal crystallisation from the melt state at different temperatures. The lowest melting peak can be ascribed to the melting of secondary crystals. The melting of primary crystals causes the medium melting peak and the highest melting peak is attributed to the melting of recrystallised species formed during heating. Following the Hoffman–Weeks theory, the equilibrium melting temperature is equal to 250°C and the equilibrium melting enthalpy ΔH _m ⁰ to 175 J g^–1. Then, using the Lauritzen–Hoffmann theory of secondary crystallisation, the analyse of the spherulitic growth shows that the temperature of transition between the growing regimes II and III is equal to 176°C. Finally the Gibbs-Thomson relationship allows the determination of the distribution function of crystalline lamellae.     

Abtrennung von Ceriterden aus Gemischen mit Yttererden durch fraktionierte Kristallisation der Magnesiumdoppelnitrate in großem Maßstab

Summary The fractional crystallisation of magnesium double nitrates was used to separate cerium earths from 112 kg yttrium earth mixtures; they were recovered in three different fractions. By using excess magnesium nitrate the crystallisation could be extended at least to gadolinium without using HNO₃ as solvent. In the resulting solutions (69 kg oxide) there remained yttrium and nearly all erbium and heavy yttrium earths.

     

Hydrothermal synthesis and structure of organically templated chain, layered and framework scandium phosphates

Four scandium phosphate-based structures have been prepared hydrothermally in the presence of the primary diamines ethylenediamine and diaminobutane and the primary amine cyclohexylamine and characterised by single crystal and powder X-ray diffraction, ³¹P and ⁴⁵Sc solid-state MAS NMR and chemical analysis. Charge balancing protons in the structures are located using bond valence sum calculations and postulated hydrogen bonding networks. Compound 1, [(H₃NC₂H₄NH₃)₃][Sc₃(OH)₂(PO₄)₂(HPO₄)₃(H₂PO₄)], , a=5.4334(6), b=8.5731(9), , α=79.732(4), β=83.544(4), γ=80.891(5)°, Z=2, is built up of scandium phosphate ribbons, based on trimers of ScO₆ octahedra linked by OH groups. These trimers are joined through phosphate groups bound through three oxygens, and are decorated by phosphate groups linked by a single oxygen atom. The ribbons are arranged parallel to the a-axis and linked one to another by fully protonated ethylenediammonium ions. Compounds 2, [(H₃NC₄H₈NH₃)₃][(Sc(OH₂))₆Sc₂(HPO₄)₁₂(PO₄)₂], , a=13.8724(3), , Z=1, and 3, [(H₃NC₄H₈NH₃)₂(H₃O)][Sc₅F₄(HPO₄)₈], C2/m, a=12.8538(4), b=14.9106(4), , β=101.17(9)°, Z=2, were prepared using diaminobutane as the organic template in the absence and presence, respectively, of fluoride ions in the gel. Compound 2 has a pillared layered structure, in which ScO₆ octahedra are linked by three vertices of hydrogenphosphate groups into sheets and the sheets pillared by ScO₆ octahedra to give a three-dimensionally connected framework isostructural with a previously reported iron(III) hydrogenphosphate. The protonated diaminobutane molecules occupy cavities between the layers. Compound 3 has a layered structure in which isolated ScO₆ octahedra and tetrameric arrangements of ScO₄F₂ octahedra, the latter linked in squares through fluoride ions, are connected by phosphate tetrahedra that share two or three oxygens with scandium atoms. In this structure, the protonated diaminobutane molecules connect the layers, the -NH₃⁺ groups fitting into recesses in the layers. Compound 4, [(C₆H₁₁NH₃)][ScF(HPO₄)(H₂PO₄)], Pbca, a=7.650(3), b=12.867(5), , Z=8, the first scandium phosphate to be prepared with a monoamine, is also a layered solid. In this case, the layers contain single chains of ScO₄F₂ octahedra which share fluoride ions in trans positions. Phosphate tetrahedra bridge across scandiums via two of their four oxygens, both within the same chain and also to neighbouring chains to make up the layer. The protonated amine groups of the cyclohexylamine molecules achieve close contact with phosphates of the layer, while the cyclohexyl moieties, which are in the chair configuration, project into the interlayer space.     

Large strain requirements for shear-induced crystallization of isotactic polypropylene

We studied strain effects on the crystallization of a series of isotactic polypropylenes (iPP) of various molecular weights using rheology, rheo-optical measurements, differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). The samples were pre-sheared and then crystallized both at the same temperature. Transmitted light intensity measurements demonstrate that the effect of pre-shear on crystallization rate keeps increasing with strain up to surprisingly large strain levels, much beyond strains that are required to reach steady shear flow (at given We). Crystal orientation sets in at a total strain of about or higher. WAXD and DSC measurements corroborated the light transmission results. Total shear strains to 1000 were applied to the iPP samples at the beginning of a crystallization experiment, after the samples had reached the crystallization temperature of 145°C (under-cooled state). A constant Weissenberg number We=1 (We is defined as the product of shear rate and a relaxation time) was maintained for all pre-shearing of this study. We=1 corresponds to the onset of shear thinning in steady shear. Deborah number values were low, De<<1, indicating that steady shear flow had been reached in all pre-shearing runs (De is defined as the ratio of relaxation time to pre-shearing time). Further studies are needed at high We as there are indications that strain requirements are much reduced at high We. A fundamental understanding is still missing.     

Optical Transmittance Thermal Analysis of the Poly(Ethylene Terephthalate) Foils

The optical transmittance of poly(ethylene terephthalate) foils has been investigated using the linear heating as well as the isothermal heating. It was found out that transmittance records obtained at linear heating show the crystallisation and melting processes distinctly. These results are in accordance with those achieved by DSC measurements. The isothermal heating was especially applied to investigate PET cold crystallisation. In its course the optical transmittance first decreases to a certain minimal value, regaining some of the transmittance in the final period of crystallisation (crystal growth). The used method is suitable for investigating crystallisation processes of polymers accomplished at very slow rates.This revised version was published online in November 2005 with corrections to the Cover Date.