Gian Carlo Pellacani

Enhancing the mechanical properties of porcelain stoneware tiles: a microstructural approach

Abstract This paper focuses on the complexities of the microstructure and phase development in porcelain stoneware tiles produced following industrial fast single firing cycles. A microstructural investigation was conducted to determine if the addition of selected low cost minerals would improve mechanical properties. The minerals tested were quartz, mullite and kyanite. Uniaxially pressed samples were submitted to the same industrial firing schedule and tested according to the European tile standards before further microstructural analysis. All the requirements specified in UNI EN normative concerning BIa class tiles were fulfilled; moreover, mullite and kyanite added formulations showed sensible increases in mechanical properties, especially as far as flexural strength and abrasion resistance are concerned.

Crystallization of some anorthite-diopside glass precursors

Anorthite and diopside have been obtained from complete devitrification of glasses belonging to the quaternary system MgO-CaO-Al2O3-SiO2. Microstructure, the natural trend of the nucleation mechanism and kinetic studies on the crystallization phenomenon have been investigated by means of optical and electron microscopies, thermal and thermomechanical techniques and X-ray powder diffractometry. All the glasses investigated show a complete crystallization starting from a simple surface nucleation process. The activation energy for the crystallization process proved to be higher than that for viscous flow, leading to an important aspect modification in the sample during ceramization. Thermal stability and physical properties of both glass and glass-ceramic materials have been tested, suggesting the possible use of these materials in industrial application.

Effects of nucleating agents on diopside crystallization in new glass-ceramics for tile-glaze application

The effect of crystallization produced by addition of TiO2, ZrO2 and P2O5 oxides to glass-ceramic of the system CaO-MgO-SiO2 was studied using structural and thermal techniques. The devitrification process was independent of thermal treatment. X-ray diffraction studies performed on the glass-ceramic system indicated that diopside crystalline phase was more thermodynamically favourable than other phases. The effect of the nucleating agent depends on its nature: TiO2 decreased the activation energy while P2O5 and ZrO2 did not. SEM analysis of the doped glass-ceramics showed randomly distributed crystals with significant dimensional variations from those of the undoped system. All these formulations, showing a high crystallization rate, and a fast heating rate, can be used as tile glazes and/or tile-glaze components.

Effect of TiO2 addition on the properties of complex aluminosilicate glasses and glass-ceramics

The nucleating effect of titania during glass crystallization has been studied in a complex glassy system where some particular oxides, such as ZnO and MgO, which present chemical and thermodynamic affinity for titanium have been added. Such additions tend to produce phase separation in the glass and leads to titanate phases formation in the glass-ceramic. Moreover, the presence of lithia has a promoting effect on both mechanisms because the lowered viscosity increases cation diffusion. Various thermal, microscopic, and diffractometric techniques have been used to investigate the amorphous and the crystalline phase.

Nickel(II) complexes with dithiooxamide, N,N′-di-methyl- and N,N′-di-hydroxyethyl-dithiooxamide

Abstract Some complexes of Ni II with dithiooxamide (DH 4 ), N,N′-dimethyldithiooxamide (Met 2 DH 2 ) and N,N′-dihydroxyethyldithiooxamide (HOEt 2 DH 2 ) were investigated in the solid state and in solution. The solid complexes Ni(DH 4 ) 2 (Cl,Br,ClO 4 ,HSO 4 ) 2 , Ni(Met 2 DH 2 ) 2 (Cl,Br,ClO 4 ) 2 2H 2 O, Ni(Met 2 DH 2 ) 2 Cl 2 H 2 O . 0.5 Et- OH, Ni(Met 2 DH 2 ) 2 (HSO 4 ) 2 . 0 5 HAc and Ni(HOEt 2 DH 2 ) 2 (ClO 4 ) 2 are diamagnetic. Their electronic spectra show a square planar coordination; the splitting parameters Δ 1 (cm −1 ), evaluated for the perchlorate complexes, are in the sequence DH 4 (18420)⪡HOEt 2 DH 2 (19060)⪡Met 2 DH 2 (19550). The compounds Ni 2 (HOEt 2 D) 2 glycol and Ni 2 (HOEt 2 DH) 2 (SO 4 ) 1.5 glycol are binuclear and polymer complexes containing one diamagnetic square planar and one paramagnetic octahedral nickel atom (μ eff = 3.33 and 3.27 B.M.), as indicated also by their electronic spectra. The complexes investigated in solution by the Job method show that in glacial acetic acid containing HCl or HClO 4 , the metal:ligand ratio is always 1:2, in methylcellosolve DH 4 and HOEt 2 DH 2 give with NiCl 2 the ratio 1:1 while the stronger ligand Met 2 DH 2 still gives the ratio 1:2; with the less competitive perchlorate all the three ligands give the ratio 1:2. The I.R. and far I.R. spectra of the soldis show that DH 1 and Met 2 DH 2 are cordinated to the metal through both sulphur and nitrogen atoms. In the NiL 2 Y 2 complexes this coordination results in a splitting of the ν(CN) band in the region of 1500 cm −1 and of the ν(CS) band in the region of 800 cm −1 corresponding to the coordinated and uncoordinated halves of the molecules. This splitting is larger for the DH 4- than for the Met 2 DH 2- complexes, presumably because of the inductive effect of the methyl group in this latter ligand.

Solubility, reactivity and nucleation effect of Cr2O3 in the CaO-MgO-Al2O3-SiO2 glassy system

The effect of Cr2O3 on some anorthite-diopside glass-ceramics has been investigated up to amounts of 5 mol%. The solubility in the glassy compositions analysed is total for the oxide, but for amounts higher than 0.5 mol%, an insoluble spinel form, MgCr2O4, precipitates. Ultraviolet-visible spectroscopy has proved to be the most sensitive technique to the presence of Cr(III) in a crystalline spinel site, followed by X-ray diffraction and scanning electron microscopy observations. Electron spin resonance and X-ray photoelectron spectroscopy techniques excluded any oxidation state, other than Cr3+. The influence of the transition cation on glass nucleation is that of an increasing bulk effect with chromium, and thus chromium-spinel, content. The magnesium content affects spinel formation, while heat treatments up to 1100 °C do not. The spinel formation influences the anorthite-diopside ratio in the glass-ceramic, with a large favour towards the pyroxene.

STRUCTURAL AND ELECTRICAL CHARACTERIZATION OF POLYMERIC HALOPLUMBATE(II) SYSTEMS

The synthesis and the structural, thermal, and electrical characterization of haloplumbate(II) systems are described. The counterions are diprotonated linear aliphatic amines, such as the 2-methylpentane-1,5-diamine (2meptH2) and propane-1,3-diamine (pnH2) dications. The (2meptH2)[PbCl4] and (2meptH2)[PbBr4] are isostructural, space group Cc, with a = 24.140(4) A, b = 7.720(2) A, c = 7.795(2) A, β = 98.1(1)°, Z = 4 for the chlorine compound and a = 24.539(4) A, b = 8.031(2) A, c = 8.198(2) A, β = 99.6(1)°, Z = 4 for the bromine compound; the (2meptH2)[Pb1.5I5] crystallizes in the triclinic P1 space group, with a = 11.803(3) A, b = 12.565(3) A, c = 8.494(8) A, α = 106.2(1)°, β = 100.5(1)°, γ = 117.4(1)°, Z = 2; the crystals of (pnH2)[PbCl4] are orthorhombic, space group P212121, a = 19.247(4) A, b = 7.862(2) A, c = 7.581(2) A, Z = 4; the (pnH2)2[Pb1.5Br7]·H2O crystallizes in the triclinic P1 space group, with a = 11.517(3) A, b = 14.122(3) A, c = 8.149(2) A, α = 104.1(1)°, β = 109.8(1)°, γ = 77.5(1)°, Z ...

Densification of glass powders belonging to the CaO–ZrO2–SiO2 system by microwave heating

Abstract Densification and microstructural changes of two glassy compositions belonging to the wollastonite and zirconia stability fields in the ternary CaO–ZrO 2 –SiO 2 system were studied in a 2.45 GHz multimode microwave cavity. The effect of microwaves is to lower the sintering and devitrification temperature with stronger influence for high zirconia content composition. Correlation was found between dielectric properties and heating rate, showing lower interaction temperature for high zirconia content composition which starts to absorb microwave energy at about 400°C compared to 800°C for the low-zirconia one. Sintering and crystallization processes evolved in complex ways during heat treatment so that the two final glass-ceramic materials exhibit different microstructures, crystalline phases and mechanical properties.

On the complexes of tetramethyl- and tetraethyl-dithiooxamide with manganese(II), iron(II), cobatl(II), nickel(II) and copper(II)

Abstract The complexes of the ligands (L): tetramethyldithiooxamide (Met 4 D) and tetraethyldithiooxamide (Et 4 D) with metals (M): Mn II , Fe II , Co II , Ni II , and Cu II , were investigated in various media; the complexes identified by the Job method have the same metal: ligand ratios and the same electronic spectra (except those of Cu) as the corresponding solids, having the general formulae ML 3 A 2 (A=ClO 4 − , FeCl 4 − ) and Cu-LX 2 (X=Cl, Br); copper percholorate gives with Met 4 D only the 1:2 complex Cu(Met 4 D) 2 (ClO 4 ) 2 . I.R. and far I.R. spectra and magnetic susceptibilities, in the range 100–300°K, were also investigated. The octahedral high-spin, sulphur-coordinated ML 3 A 2 complexes show a greater deformation for the Met 4 D- than for the Et 4 D-derivatives. CuLX 2 complexes have a cis configuration. All dd bands were assigned, and the Dq, B, and β values were evaluated; the spectrochemical series Ni>Co>Fe>Cu> was obtained. The lower Dq-values for the Et 4 D-complexes are attributed to a greater steric effect of the Et 4 D-ligand.

Organic-inorganic composite materials: structural archetypes of linear polymeric chlorocadmates(II)

Abstract Structural considerations on the monodimensional polymeric chlorocadmates(II) are reported and two types of structural arrangement are recognized; truly monodimensional linear structures and polymeric endless ribbons. Regarding the linear structures, the hydrogen bonding capability of the cations is considered to favour the presence of the terminal chlorine ions on the inorganic chains and is therefore responsible for their structural motifs. The ribbon structures are favoured by particular concurrent conditions such as the weak hydrogen bonding capability and opportune size dimensions of the cations. The CdCl and Cd…Cd distances in the different structural archetypes have been discussed and a graphical representation illustrating the stacking patterns of halocadmates is reported.