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Although nickel(II) oxide (NiO) is a potential carcinogenic agent, it is still used in the synthesis of ceramic pigments because during their preparation at high temperature, NiO is thought to combine with other compounds, crystallizing as new phases with spinel-like structures. Unfortunately, there are no widely accepted methods for the determination of free NiO in ceramics, the main reason being experimental dif®culties. In fact, quantitative phase analysis (QPA) by X-ray powder diffraction (XRPD) may fail because diffraction peaks of NiO with space group Fm3 Å m and a 9 4.18 A Ê overlap with those of the spinel with space group Fd3 Å m and a 9 8.4 A Ê . To overcome this problem, in this work QPA has been performed in situ at high temperature to resolve the peak overlap of NiO and spinel by taking advantage of the different thermal expansion of each phase. It is believed that this is the ®rst report of the application of this technique.

Nickel(II) oxide (NiO) still is extensively used as a raw material for the synthesis of traditional ceramic pigments, despite the fact it is potentially carcinogenic. One of the reasons is that, unfortunately, no widely accepted methods exist for its determination in ceramics so far (the main reason being experimental difficulties). Quantitative phase analysis via powder X-ray diffractometry, for example, may fail because of the presence of glass and because NiO diffraction peaks overlap those of spinel in spinel-based pigments. This communication elucidates how to address these experimental difficulties and determine free NiO in the case of black ceramic pigments.

Several compounds containing crystal water showed rather interesting behaviour during heat treatment. In temperature regions below phase transformations caused by partial or total loss of "structural" crystal water an anisotropic lattice deformation occured /T. Sato, T. Nakamura, Thermochimica Acta /1982/ 21, 281/. In the case of GaOOH this phenomenon was proved to be connected with the departure of water being in excess to the "structural" wa-, ter bounded within the GaOOH lattice, but nevertheless this excess water was fixed somehow inside the lattice, because the temperatur O region of its leaving was between 100-270 C even when using very low heating rates /M. Farkas-Jahnke, Eight European Crystallographic Meeting, Liege /1983/ Abstract 241/. The amount of water was very large, about 20 w% of the "structural" water. Similar phenomenon, i.e. the presence of excess "fixed" NH3 was observed in ammonium paramolybdate tetrahydrate samples prepared at different pH values. The "apparent" structure of the material in all cases was alike, i.e. the site and intensity distribution of the reflections in room temperature X-ray patterns made in focusing Guinier-cameras were the same. The ]ltt 3 content of samples, however, prepared at basic pH values was about 50 w% higher than the value corresponding to stoichiometry, while of those prepared at acidic pH values was approximately equal to the stoichiometric NH3 content. These two kinds of materials, looking thus alike according to the room temperature X-ray diffraction investigations differ significantly in the way of their thermal decomposition, investigated in a high temperature Guinier-Lenne type camera. When ageing the samples containing excess "fixed" NH3 for several days at room temperature solid state reaction was observed between the "mother" ammonium paramolybdate tetrahydrate lattice and the excess ~li3 fixed in the lattice, resulting in an other molybdate compound having higher NH3 content stoichiometrically. Not only the mentioned compounds, but also several other lattices may contain considerable amount of excess "fixed" species /water, ammonium etc./ which can influence the further chemical and physical behaviour of the material. The results of such investigations led us to the conclusion that it would be necessary to revise the present conception of the stoichiometry. Complex investigations would be required using beside the room temperature X-ray diffraction measurements high temperature X-ray techniques, DTA, DTG, mass spectrometry, JlTJlIIR and many other methods to reveal the real stoichiometry of the material and its relation to the lattice stoichiometry, i.e. to the ratio of the building elements of the crystal lattice. Due to this recognized flexibility of lattices, being able to incorporate excess water, or other species by expanding themselves anisotropically great care has to be taken when characterizing the structure of such a compound by its room temperature unit cell parameters.04.2-6 DISTORTED OCTAHEDRAL COPPERIII) COMPLEX OF CIMETIDINE. refle...