The structure and solubility of carbonated hydroxyl and chloro lead apatites

The properties of carbonated hydroxyl and chloro lead apatites, Pb₁₀(PO₄)₆(OH)₂ and Pb₁₀(PO₄)₆Cl₂, serve as models for the incorporation of carbonate into their medically important calcium analogs, and there is likely incorporation of carbonate in an insoluble lead phosphate phase during lead remediation. We have synthesized a series of carbonated lead hydroxyl- and lead chloro-apatites at 60–80 °C. The incorporation of carbonate into the apatite structure was documented by X-ray powder diffraction, IR and Raman spectroscopy, ²⁰⁷Pb solid state NMR spectroscopy, and elemental analysis. The carbonate content was determined by combustion analysis and confirmed by Raman spectroscopic analysis. As carbonate content increases in hydroxyl lead apatite, Raman spectra show changes in the phosphate stretching modes at 925 and 950 cm⁻¹, an increase in intensity and downshift of a new peak at 1050 cm⁻¹, and changes in the spectral features of the O–H stretch at about 3560 cm⁻¹. The variation in unit cell parameters for the chloro lead apatite as a function of carbonate content is similar to that documented for B-type substitution in calcium apatites. The ²⁰⁷Pb NMR spectra corroborate B-type substitution. For the hydroxyl lead apatite, the changes in cell parameters suggest a combination of A- and B-type substitution. Solubilities of the carbonated lead apatites, determined by ICP-MS, increase slightly at low to moderate carbonate content, but more strongly at ca. 5.0 wt.% carbonate content. K_sp values extrapolated to zero carbonate content reveal that the chloro lead apatite is indeed less soluble than the hydroxyl analog.     

Etude de la decomposition thermique de fluorapatites carbonatees

Using a precipitation method, variably carbonated samples of fluorapatite-like francolite were prepared from solutions containing diammonium phosphate, ammonium fluoride and ammonium carbonate. Thermal analysis, gas chromatography and IR spectroscopy were performed. The results show that cyanate ions (CNO^?) appear between 400 and 500 °C, probably as a result of the thermal evolution of ammonium ions. Above 500°C, nitrogen gas was detected with CO₂. N₂ arises presumably from cyanate ion decomposition. Decarbonation of these apatites occurs in three steps, the first of these is attributed to carbamate ions.     

Termal decomposition of carbonated calcium phosphate apatites

The thermal stability of AB-type carbonated calcium phosphate apatites prepared by precipitation from aqueous media was studied. The behavior of powders was investigated using temperature programmed XRD, infrared spectroscopy and thermogravimetry. In N₂ atmosphere, two successive peaks of decarbonatation with maxima at about 700 and 950°C occurred. This behavior is explained by different substitution modes for carbonates in the apatite. The decarbonatation peaks were shifted to higher temperature under CO₂ (around 900 and 1150°C). The analysis of the thermal stability allowed further densification of carbonate apatite ceramics without important carbonate loss. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Sintering-wet Carbonation of Nano-sized Carbonated Hydroxyapatite

Synthetic carbonated apatite ceramics are considered as promising alternative to auto- and allograft materials for bone substitute. In this study, Carbonated hydroxyapatite (CHA) was synthesized by nanoemulsion method. The powder produced was B-type CHA in nano-sized and had 8.25% carbonate content. The CHA samples were made into pellets and were sintered to 800 °C. Upon cooling down to 150, 200, 250 and 300 °C, carbonation with wet CO₂ was performed on the CHA in a desiccator to re-compensate the carbonate loss due to sintering and improve densification. The aim of this study was to investigate and compare the effect of cooled down temperatures on dense CHA with two kind of wet CO₂ atmospheres: direct wet CO₂ and dry CO₂ through water. Sintered CHA carbonated by using dry CO₂ through water had overall higher amount of carbonate content as compared to carbonation from wet CO₂ directly from tank. D200, sample undergone carbonation by carbonated by dry CO₂ through water at 200 °C had the highest carbonate content (3.35%).     

Mechanism of Substitution in Carbonated Apatites

Single-phase AB-type carbonate apatites were prepared by sintering appropriate mixtures of CaHPO₄ and CaCO₃ at 870°C in a CO₂ atmosphere with a partial water vapor pressure of 5 mm Hg. Chemical and physical analyses indicate that at a constant CO₃^2?/OH^? ratio in the hydroxyl sublattice, carbonate substitutes for phosphate on a 1:1 mole basis. For every three PO₄^3? ions substituted, two vacancies in the Ca²⁺ sublattice and one in the OH^? sublattice are created. The same substitution mechanism seems to apply in pure B-type carbonate apatite.     

Thermal analysis of apatite structure

Two types of thermal effects, caused by substitutions (Ca²⁺↔ Na⁺, ↔ CO₃ ^2-, SO₄ ^2-, OH^-↔ F^-) in synthetic precipitated apatites as well as by sorption of Cd²⁺, Zn²⁺, and Cr³⁺ ions from the solutions were studied by TG/DTA, XRD and FTIR analysis. The temperatures of exothermic effect at 330-340°C and of decomposition of carbonate and sulfate apatites at 650-950°C were shown to depend on the substitutions in the apatite structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sodium and carbonate distribution in substituted calcium hydroxyapatite

Hydroxyapatites containing sodium and carbonate are prepared according to a double decomposition method. Two samples have been investigated by IR absorption spectroscopy and X-ray powder pattern fitting methods. Results confirm that both compounds pertain to the apatite family crystallising in a hexagonal system, space group P6₃/m. The cell parameters of the lower carbonate content apatite are a=9.3892(4) and c=6.9019(3) Å, while those of the higher one are a=9.3249(1) and c=6.9213(1) Å. Occupancy factors show that sodium is localised mainly in a 6h cationic site. Furthermore, carbonate ions occupy phosphate sites leading to a B-type carbonate apatite. These simultaneous substitutions affect the OH⁻ position in the channel, as well as the metaloxygen interatomic distances. The substitution mechanism can be described using two of the six known elementary mechanisms.     

Influence of the thermal treatment in the crystallization of NiWO4 and ZnWO4

NiWO₄ and ZnWO₄ were synthesized by the polymeric precursor method at low temperatures with zinc or nickel carbonate as secondary phase. The materials were characterized by thermal analysis (TG/DTA), infrared spectroscopy, UV–Vis spectroscopy and X-ray diffraction. NiWO₄ was crystalline after calcination at 350 °C/12 h while ZnWO₄ only crystallized after calcination at 400 °C for 2 h. Thermal decomposition of the powder precursor of NiWO₄ heat treated for 12 h had one exothermic transition, while the precursor heat treated for 24 h had one more step between 600 and 800 °C with a small mass gain. Powder precursor of ZnWO₄ presented three exothermic transitions, with peak temperatures and mass losses higher than NiWO₄ has indicating that nickel made carbon elimination easier.     

Thermal decomposition of the composite hydrotalcites of iowaite and woodallite

The thermal stability and thermal decomposition pathways for synthesized composite iowaite/woodallite have been determined using thermogravimetry analysis in conjunction with evolved gas mass spectrometry. Dehydration of the hydrotalcites occurred over a range of 56–70°C. The first dehydroxylation step occurred at around 255°C and, with the substitution of more iron(III) for chromium(III) this temperature increased to an upper limit of 312°C. This trend was observed throughout all decomposition steps. The release of carbonate ions as carbon dioxide gas initialised at just above 300°C and was always accompanied by loss of hydroxyl units as water molecules. The initial loss of the anion in this case the chloride ion was consistently observed to occur at about 450°C with final traces evolved at 535 to 780°C depending of the Fe:Cr ratio and was detected as HCl (m/z=36). Thus for this to occur, hydroxyl units must have been retained in the structure at temperatures upwards of 750°C. Experimentally it was found difficult to keep CO₂ from reacting with the compounds and in this way the synthesized iowaite-woodallite series somewhat resembled the natural minerals.     

Effect of Li2O-doping on the thermal stability of cobaltic oxide

The influence of lithium oxide-doping on the thermal stability of Co₃O₄ was studied using DTA, TG, DTG and X-ray diffraction techniques. Pure and doped cobaltic oxide specimens were prepared by thermal decomposition of pure basic cobalt carbonate and the basic carbonate mixed with different proportions of LiOH, in air, at different temperatures between 500 and 1100°C.Pure Co₃O₄ was found to start partial decomposition when heated in air at 830°C yielding the CoO phase. The complete decomposition was effected by heating at 1000°C.Doping of Co₃O₄ with different proportions of Li₂O was found to much increase its thermal stability. The temperatures at which the doped oxide samples started to undergo decomposition were increased to 865, 910 and 1050°C for 0.375, 0.75 and 3% Li₂O-doped solids, respectively. The DTA revealed that the 1.5% Li₂O-doped cobaltic oxide did not undergo any thermal decomposition till 1080°C. The X-ray investigation showed that the prolonged heating of 1.5 and 3% Li₂O-doped solids at 1100°C for 36 h effected only a partial decomposition of Co₃O₄ into CoO. Heating of these solids at temperatures varying between 900 and 1100°C led also to the formation of a new lithium oxide cobaltic oxide phase, the composition of which has not yet been identified.The role of Li₂O in increasing the thermal stability of Co₃O₄ was attributed to the substitution of some of its cobalt ions by Li⁺ ions, according to Verwey and De Boer's mechanism, leading to the transformation of some of the Co²⁺ into Co³⁺ ions thus increasing the oxidation state of the cobaltic oxide lattice.     

Thermal and structural properties of sodium,potassium and carbonate doped strontium hydroxyfluorapatite

Ion-doping in hydroxyapatite bioceramics has attracted a lot of interest particularly for biomedical applications in repairing and replacing failure parts of musculoskeletal systems. Thus the multiple doping aims to mimic and resemble the chemical composition of the bone mineral component. Herein strontium hydroxyapatites bioceramics containing sodium Na⁺ and potassium K⁺ as cationic substituent and carbonate CO₃^2? and fluoride as anionic substituent were synthesized and characterized by several analysis techniques. Therefore the chemical assays indicated that obtained compounds were less stoichiometric comparably to bone tissues. The X-ray diffraction diagrams and the infrared spectra revealed that pure phases of hydroxyfluorapatite containg the cited ions were obtained. The triple insertion of sodium, potassium and carbonate into the apatite structure leaded to the B-type carbonate apatite. The FE-SEM micrographs of the powders were formed by agglomerates. Moreover, the particles' morphology strongly depends on the ions nature and amount. The D-GTA curves indicated that the heating of the powders from the room temperature to 1000 °C didn't affect the structural and thermal stability of the materials apart from a partial decomposition of the apatite inducing the formation of the β-tristrontium phosphate phase and enhancing the biomaterial character of the materials.     

Mineralogical and chemical investigation of Tunisian phosphate washing waste during calcination

Phosphate washing waste (PWW) is one of the wastes generated by the phosphate mine with a very high amount. This waste was investigated in this work to study the effect of the calcination of the PWW at four different temperatures 600 °C, 700 °C, 800 °C and 900 °C on its mineralogical and chemical composition. The samples were investigated by X-ray powder diffraction, Fourier transform infrared, differential scanning calorimetry and thermogravimetric analysis, solid-state magic angle spinning nuclear magnetic resonance of ²⁹Si, ²⁷Al and ³¹P and scanning electron microscope. The results show that the PWW presents a complex system and it suffers a significant change on its mineralogical and chemical composition after calcination. It reveals the presence of carbonate, natural zeolite, fluorapatite, quartz and clay. After calcination, the waste shows the disappearance of some of these phases and the appearance of others and some other phases remain steady.

     

Some features of the incorporation of oxygen in different oxidation states in the apatitic lattice—II On the synthesis and properties of calcium and strontium peroxiapatites

New apatites: peroxiapatites, containing in their lattices oxygen in an oxidation state — I, are found with calcium and strontium phosphate apatites. The oxygen (-I) containing groups are peroxide ions, which are associated with vacancies. Peroxiapatites are formed at high temperatures by a reaction involving O²⁻ of the oxyapatites and molecules of oxygen, provided the treatment atmosphere is sufficiently free of water. The peroxiapatite formation must be correlated with the very high reactivity of oxyapatites, which has been shown in the first part of this paper.When peroxiapatites are heated, in air, inert gases or vacuum, the peroxide ions disproportionate: molecular oxygen originating from this disproportionation reaction, is practically retained till 350°C by the lattice of strontium apatites, while it is released on formation from calcium apatites.     

Thermal analysis applied in the crystallization study of SrSnO3

SrSnO₃ was synthesized by the polymeric precursor method with elimination of carbon in oxygen atmosphere at 250 °C for 24 h. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After calcination at 500, 600 and 700 °C for 2 h, samples were evaluated by X-ray diffraction (XRD), infrared spectroscopy (IR) and Rietveld refinement of the XRD patterns for samples calcined at 900, 1,000 and 1,100 °C. During thermal treatment of the powder precursor ester combustion was followed by carbonate decomposition and perovskite crystallization. No phase transition was observed as usually presented in literature for SrSnO₃ that had only a rearrangement of SnO₆ polyhedra.     

Crystal morphology, composition, and dissolution behavior of carbonated apatites prepared at controlled pH and temperature

A range of carbonated apatites was prepared by aqueous precipitation at 37, 60, and 85°C and at controlled pH values varying from 6.00–9.50 in 0.25 increments. The products were analyzed for Ca, P, Sr, Mg, Na, F, and carbonate. Their initial dissolution rates were measured in a pH 4.5, 0.01 mol · liter⁻¹ acetate buffer. Information about crystal morphologies and crystal defects was obtained by x-ray diffraction and high-resolution transmission electron microscopy (TEM). The molar ratios of the products, together with their Sr and Mg contents, increased with increasing pH. Initial dissolution rates of the products, when adjusted for carbonate content, were in the order 37 > 60 > 85°C whereas apparent particle sizes determined by TEM and x-ray diffraction were ordered 37 < 60 < 85°C. Carbonated apatites precipitated at pHs of 7.0 or less were observed to have planar defects parallel to (100) that were identified as unit-cell-thick intergrowths of octacalcium phosphate. Carbonated apatites precipitated at higher pHs and noncarbonated apatites did not have these defects. A crystal growth mechanism is proposed to account for the presence of the (100) defects.     

The thermal decomposition of Mg-containing carbonate apatites

Carbonate apatites precipitated from an aqueous solution and containing Mg²⁺ and Sr²⁺ ion were studied by thermogravimetric, infrared absorption, and X-ray diffraction methods. In the temperature range of 25–350°C water evolves and at 350–905°C carbonate decomposes. Two effects characterize the Mg-containing system: Weight loss during decomposition is related to carbonate in the apatite and to an additional ion; increased formation of whitlockite. The interrelation between these two phenomena and the presence of carbonate and Mg is discussed.     

Investigation on drying conditions and assays of amidosulfuric acid and sodium carbonate by acidimetric coulometric titration and gravimetric titration

Amidosulfuric acid and sodium carbonate as standards for acid–base titrimetry were assayed by coulometric titration and gravimetric titration. Amidosulfuric acid was directly assayed by coulometric titration with electrogenerated hydroxide ions, and sodium carbonate was assayed by gravimetric back-titration. For sodium carbonate, excess amount of sulfuric acid, whose concentration was determined by coulometric titration, was added to sodium carbonate, and then gravimetrically back-titrated using a sodium hydroxide solution whose concentration was determined by gravimetric titration using the sulfuric acid. The accuracy of the coulometric titration for amidosulfuric acid and sulfuric acid was evaluated by examining the current efficiency of pulse electrolysis, the amount of the electrolysis current used, and the time spent for a titration. In addition, the drying conditions for high purity primary standards have a significant effect on the titration results due to changes in the acid–base assay. The suitable drying conditions for amidosulfuric acid and sodium carbonate were evaluated by mass-change measurements, coulometric titration and gravimetric titration. The measurement uncertainties were estimated from the uncertainties on the titration processes. Finally, the assays of amidosulfuric acid and sodium carbonate were 99.986% ± 0.010% (k = 2) after drying at 50 °C for 2 h, and 99.970% ± 0.016% (k = 2) after drying at 280 °C for 4 h, respectively. In addition, the international consistency was confirmed by measuring certified reference materials (CRMs) available from different National Metrology Institutes, and the compatibility of values among CRMs was experimentally ascertained.     

Analyzing the calcination of sulfur-rich calcareous oil shales using FT-IR spectroscopy and applying curve-fitting technique

The thermal processes during progressive calcination of sulfur-rich calcareous oil shales were analyzed using FT-IR spectroscopy and applying curve-fitting technique. The spectroscopic analysis is advantageous in the analysis of amorphous and short-range ordered thermal phases lacking of XRD peaks. The raw calcareous oil shales are composed of organic matter, kaolinite, smectite, calcite, and apatite (francolite). The principal thermal phases are metakaolinite, meta-smectite, free lime, anhydrite, gehlenite, and ellestadite. The thermal reactions observed with increase temperatures includes decomposition of organic matter followed by release of sulfur gas; dehydroxylation of kaolinite; and smectite at 500–600 °C; and thermal transformation to metakaolinite and meta-smectite; decarbonation of microcrystalline calcite to free lime at 600 °C; reaction of the sulfur gas with the free lime; formation of anhydrite at 600 °C; reaction of apatite and formation of ellestadite at 800 °C; reaction of the metakaolinite; the meta-smectite with the free lime; formation of gehlenite at 900 °C. Owingto the sulfatization process, a great part of the sulfur content of the raw oil shales is retained in the calcined ashes and the release of sulfur gas to the atmosphere decreases. Thus, the combustion of calcareous oil shales for energy source has less pollution effect than that of the clayey oil shales. FT-IR spectroscopy and spectral analysis seems to be useful methods for phase analysis of oil shales in combustion industry.     

Influence of Calcination on the Properties of Nickel Oxide-Samarium Doped Ceria Carbonate (NiO-SDCC) Composite Anodes

Apart from its composition, the starting powder properties such as particle size potentially affect the triple phase boundary and the electrochemical performance. Calcination process has been identified as one of the factors that influence the particle size of the composite anode powders. This study investigates the correlation between calcination temperature and properties (i.e., chemical, physical, and thermal) of NiO–samarium-doped ceria carbonate (SDCC) composite anodes. NiO–SDCC composite anode powder was prepared with NiO and SDCC through high-energy ball milling. The resultant composite powder was subjected to calcination at various temperatures ranging from 600 °C to 800 °C. Characterizations of the composite anode were performed through X-ray diffraction (XRD), Fourier transform infrared spectroscopy, energy dispersive spectroscopy, field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), dilatometry, and porosity measurements. The composite anodes exhibited good chemical compatibility during XRD after calcination and sintering. The FTIR result verified the existence of carbonates in all the composite anodes. The increment in calcination temperature from 600 °C to 800 °C resulted in the growth of nanoscale particles, as evidenced by the FESEM micrographs and crystallite size. Nonetheless, the porosity obtained remained within the acceptable range for a good anodic reaction (20% to 40%). The TGA results showed gradual mass loss in the range of 400 °C to 600 °C (within the low-temperature solid oxide fuel cell region). The composite anodes calcined at 600 °C and 700 °C revealed a good thermal expansion coefficient that matches that of the SDCC electrolyte.     

Thermal stability of crandallite CaAl<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)<Subscript>5</Subscript>·(H<Subscript>2</Subscript>O)

Thermogravimetry combined with evolved gas mass spectrometry has been used to characterise the mineral crandallite CaAl₃(PO₄)₂(OH)₅·(H₂O) and to ascertain the thermal stability of this ‘cave’ mineral. X-ray diffraction proves the presence of the mineral and identifies the products of the thermal decomposition. The mineral crandallite is formed through the reaction of calcite with bat guano. Thermal analysis shows that the mineral starts to decompose through dehydration at low temperatures at around 139 °C and the dehydroxylation occurs over the temperature range 200–700 °C with loss of the OH units. The critical temperature for OH loss is around 416 °C and above this temperature the mineral structure is altered. Some minor loss of carbonate impurity occurs at 788 °C. This study shows the mineral is unstable above 139 °C. This temperature is well above the temperature in the caves of 15 °C maximum. A chemical reaction for the synthesis of crandallite is offered and the mechanism for the thermal decomposition is given.