D. de Waal

Rapid determination of CaCO3 in mixtures utilising FT—IR spectroscopy

Abstract The quantitative determination of limestone in various mixtures is a very important analytical problem for several industrial processes, especially so for the cement and lime industries where the determination of limestone in building-related products is required. Errors can result from the presence of several minerals, such as Ca(OH) 2 and clays, when the common loss-on-ignition method is used. Infrared spectroscopy is one method of quantitatively measuring a specific substance, providing that the vibrational mode used does not overlap with those of other substances present in the mixture. For this reason FT—IR spectroscopy has been used here to illustrate its potential as an analytical tool in the determination of CaCO 3 in mixtures of CaCO 3 and Ca(OH) 2 .

Raman analysis of ancient pigments on a tile from the Citadel of Algiers

A micro-Raman spectroscopy study of a multi-coloured (yellow, blue, white, redish-brown and brown-black) tile shard from the Citadel of Algiers was undertaken. XRD and EDX were used as complementary techniques. The study shows that the heterogeneous three-shade yellow pigment on the tile is composed largely of the ancient ternary (Pb-Sn-Sb) pyrochlore oxide with a dominant Pb-O vibration at 127 cm(-1) consistent with the Pb2SnSbO6.5 structure as verified by XRD. The literature assignment of this band at 132 cm(-1) probably comes from a mixture of pigments. The redish-brown and the brown-black pigments are found to be Naples yellow (Pb2Sb2O7) and lead(II) stannate (Pb2SnO4), respectively, while cobalt blue (CoAl2O4) gives the blue colour and cassiterite (SnO2) is the origin of the white colour. The bulk of the tile body is composed mainly of hematite (alpha-Fe2O3), maghemite (gamma-Fe2O3), magnetite (Fe3O4) and Quartz (alpha-SiO2) with traces of calcite (CaCO3) and amorphous carbon. Micro-Raman spectroscopy proved to be very useful in the characterization of pigments as well as the tile body. These results further establish Raman spectroscopy as a technique of choice for the analysis of pigments on archaeological artifacts. The results obtained here could be used in the restoration and preservation programme of the Citadel itself which stands today as a symbol of pre-colonial Algerian heritage.

Vibrational spectra of two phases of copper pyrovanadate and some solid solutions of copper and magnesium pyrovanadate

Infrared and Raman spectra of both the α- and β-phases of Cu2V2O7 are presented. Of the 13A′ + 8 A″ vibrational modes of V2O4−7 all of the ones predicted to be terminal stretching modes can be distinguished for both phases in the Raman. Both the symmetric and asymmetric bridge stretching modes are observed for α-Cu2V2O7. The Raman spectra of the solid solution series Cu2−xMgxV2O7 (x = 0.5; 0.67) are similar to that of β-Cu2V2O7. The influence of magnesium substitution in the copper pyrovanadate lattice can be observed from the shift of vibrational bands.

Preparation and structural characterization of two new titanium phosphates NaCa0.5Ti(PO4)3 and Ni0.5TiOPO4

Summary The titanium phosphate Na 4 Ca 0.5 Ti(PO 4 ) 3 crystallizes in the trigonal space group R32 (a h = 9.008 ± 0.002 A, c h = 21.814 ± 0.003 A and Z = 6). Its structure belongs to the nasicon type family. The titanyl phosphate Ni 0.5 TiOPO 4 crystallizes in a monoclinic unit cell, P2 I ,/c, (a = 7.383 ± 0.001 A, b = 7.323 ± 0.001 A, c = 7.344 ± 0.001 A, β = 120.23 ± 0.01° and Z = 4). The structure of these two compounds is based on a three-dimensional framework built of TiO 6 octahedra and PO 4 tetrahedra. The PO 4 tetrahedra are isolated in both Na 4 Ca 0.5 Ti(PO 4 ) 3 and Ni 0.5 TiOPO 4 . The TiO 6 octahedra are isolated in the former and linked together by “titanyl” oxygen atoms to form -Ti-O-Ti-O- infinite chains in the latter. These structural data are confirmed by the Raman spectroscopy study.

Quantitative Determination of CaCO3 in Cement Blends by FT-IR

Fourier transform infrared (FT-IR) spectra have been recorded of cement blends containing between 0 and 25% limestone, as well as for 100% limestone. Integrated intensity of the out-of-plane vibration of the carbonate ion was used in relation to the integrated intensity of a peak remaining fairly constant in the cement blends itself. Calibration curves were set by using five measurements of each particular sample. The results are compared to ordinary weight loss measurements. FT-IR is found to be a quick and accurate method for the quantitative analysis of limestone in cement blends.

Vibrational spectra of a solid solution of cadmium and calcium pyrophosphate

Abstract Infrared and Raman spectra of the solid solution Cd1.25Ca0.75P2O7 are presented. The spectra of this phase are unique as a result of the C1 site for P2O4−7 and the crystal structure of C11 which should not result in any splitting of the predicted vibrational modes for this ion with the eclipsed conformation, leaving it essentially free of interference arising due to crystal effects.

KINETIC STUDY OF THE DECOMPOSITION OF NITRITE TO NITRATE IN ACID SAMPLES USING RAMAN SPECTROSCOPY

Raman spectroscopy was employed as a means of determining the rate of decomposition of nitrite in solutions at various pH values. Nitrite decomposes with time in acidic medium, with an increase in decomposition rate as the concentration of acid increases. The mean decomposition rate of 0.625 mol/L NO−2 in 1 mol/L HCl is 1.18 × 10−5 s−1, with t1/2 = 16 h. This rate explains the problems encountered when the flow injection analysis (FIA) version of the Shinn reaction is applied to certain nitrite samples mainly from acidic origin. Nitrite is potentially unstable, and all food and water samples should be analyzed as soon as possible after collection. If it is necessary to store the samples prior to analysis, the effects of the storage conditions on the stability of the analyte must be established in prior trials.

Structural and vibrational studies of NaZr2(AsO4)3

The structure of NaZr{sub 2}(AsO{sub 4}){sub 3}, which belongs to the Nasicon-type family, was solved by the Rietveld method in the R3-barc space group, from X-ray powder diffraction data. The hexagonal unit cell parameters are a{sub h}=9.1518(2) A and c{sub h}=23.1097(4) A. The structure is formed by a three-dimensional network of AsO{sub 4} tetrahedra and ZrO{sub 6} octahedra sharing corners. Na atoms occupy totally the M1 site. Raman and infrared spectra were recorded and assignments of the As-O stretching and bending modes were made.

Vibrational spectra and factor group analysis of Mn(0.5+x)Ti(2−2x)Cr2x(PO4)3 {0≤x≤0.50}

Abstract Raman and infrared spectra of a series of phosphates Mn 0.5+ x Ti 2−2 x Cr 2 x (PO 4 ) 3 {0≤ x ≤0.5} have been recorded in crystalline state. Factor group analysis has been performed for space group R3 ( x =0, 0.1, 0.15) and R3c ( x =0.25, 0.5) and assignments of the internal modes of the PO 4 tetrahedra have been made.

Crystal chemistry, vibrational spectra and factor group analysis of Ba(3-x)Srx(PO4)2 (0≤x≤3) solid solution series

Abstract A new solid solution series, Ba (3− x ) Sr x (PO 4 ) 2 (0≤ x ≤3), has been prepared by solid state reaction. The existence of a continuous solid solution is confirmed by X-ray diffraction as well as Raman and infrared spectroscopy. The vibrational spectra of this crystalline orthophosphate solid solution series are interpreted by means of factor group analysis in terms of space group R 3 m . Assignments of the P–O vibrational stretching and bending modes, as well as some of the external modes, have been made.