Crystalline Phase Composition Research Articles

Phase Composition of ProRoot Mineral Trioxide Aggregate by X-Ray Powder Diffraction

Introduction Composition and crystalline phases of the endodontic material mineral trioxide aggregate (MTA) is of fundamental importance for understanding its physical and chemical properties. This research was done to determine the composition of crystalline phases for ProRoot MTA. Methods For phase identification, powder of ProRoot MTA was analyzed by x-ray diffraction (XRD), comparing the MTA peaks with the data contained in the Powder Diffraction File of the International Centre for Diffraction Data (ICDD). To help the task of identifying a phase, chemical analysis by energy-dispersive spectrometry (EDS) and particle-induced x-ray emission (PIXE) were applied. Quantitative phase analysis was performed by applying Rietveld refinement to the XRD data. Results ProRoot MTA is composed of bismuth oxide (19.8%), tricalcium silicate (51.9%), dicalcium silicate (23.2%), calcium dialuminate (3.8%), and calcium sulfate dehydrated (1.3%). The trace elements detected were Fe, Ni, Cu, and Sr. Conclusions Rietveld refinement was able to analyze the composition of ProRoot MTA, which is based basically on a mixture of Portland cement (with smaller quantities of calcium dialuminate and calcium sulfate dehydrated) and bismuth oxide for radiopacity.

Phosphoric acid treated AlN powder for aqueous processing of net-shape dense AlN and β-SiAlON parts

Due to fast hydrolysis of AlN when in contact with water, AlN based ceramics are processed in organic solvents, which are volatile, expensive, harmful to the health and environment. The present work intends to protect AlN powder against hydrolysis in order to enable aqueous processing of AlN based ceramics. A commercial AlN powder was treated in an ethanol solution of H3PO4 and Al(H2PO4)3 kept at 80°C for 24 h to protect it from hydrolysis. The dispersing behaviour of the treated AlN powder in water and the ability to consolidate defect free parts of AlN and β-Si4Al2O2N6 ceramics from aqueous suspensions by slip casting and gelcasting techniques were studied. The consolidated parts were then sintered in a graphite furnace and the sintered bodies exhibited properties [bulk density (BD), apparent porosity (AP), crystalline phase composition and microstructural features] similar to those reported in literature for the same materials processed from organic media.

Microstructure and Thermal Behavior of Thermal Barrier Coatings

Yttria stabilized zirconia thick coatings were thermally sprayed from two different feedstock powders. Coating characteristics such as density, crystalline phase composition, and microstructure were evaluated. The thermal expansion coefficient and thermal diffusivity were measured as a function of temperature up to 800 °C and analyzed in terms of the microstructural features. The ability of available models to relate the measured thermal properties to the microstructural features as characterized by readily available methods was assessed. The importance of pore shape and orientation on the thermal conductivity was evidenced. The thermal contact resistance between the substrate and the coating in these samples was estimated from the thermal diffusivity data, and found to change during cooling from 800 °C.

In vitro investigation of oxide nanoparticle and carbon nanotube toxicity and intracellular accumulation in A549 human pneumocytes

If released in the environment, nanomaterials might be inhaled by populations and cause damage to the deepest regions of the respiratory tract, i.e., the alveolar compartment. To model this situation, we studied the response of A549 human pneumocytes after exposure to aluminium oxide or titanium oxide nanoparticles, and to multi-walled carbon nanotubes. The influence of size, crystalline structure and chemical composition was investigated. After a detailed identification of nanomaterial physico-chemical characteristics, cells were exposed in vitro and viability and intracellular accumulation were assessed. In our conditions, carbon nanotubes were more toxic than metal oxide nanoparticles. Our results confirmed that both nanotubes and nanoparticles are able to rapidly enter into cells, and distribute in the cytoplasm and intracellular vesicles. Among nanoparticles, we demonstrate significant difference in biological response as a function of size, crystalline phase and chemical composition. Their toxicity was globally lower than nanotubes toxicity. Among nanotubes, the length did not influence cytotoxicity, neither the presence of metal catalyst impurities.

Effect of the addition of mullite–zirconia to the thermal shock behavior of zircon materials

Ceramics and refractories are subjected to local temperature and atmosphere gradients due to the successive application of heating cooling cycles, during service. These situations originate thermal stresses that cause certain degree of damage to the material defining the potential usage of the refractory. The favorable effect of the addition of a second phase for improving the thermal shock resistance (TSR) of dense ceramics have been proved previously. However the addition must be controlled because it can excessively affect the densification and microstructure. The objective of this work is to study the TSR of pure zircon ceramic materials and to quantify the influence of the addition of mullite–zirconia (MZ) grains in a range between 15 and 45 wt.%. Cool water quenching test was carried out on slip cast prismatic bars in order to study the TSR. For the thermal shock tests temperatures differences (Δ T) between 200 and 1200 °C were applied. The elastic dynamic modulus ( E) was evaluated by the impulse excitation technique as a function of the temperature difference of the quenching test. The decrease in the E modulus was also correlated with the number of thermal cycles. The materials were characterized by density measurements and mechanical properties. The XRD and Rietveld method were employed for determining the crystalline phase composition. Finally, the microstructure of the materials was examined by SEM. Significant changes in the E modulus were observed for Δ T over 400 °C for all composites studied.

Crystal structure stability and catalytic activity of magnetoplumbite (MP) catalyst doped with Mn and Mg

LaMgxMn1−xAl11O19 catalysts with Magnetoplumbite (MP) structure were prepared by the reverse microemulsion method, where x values were varied in the range of 0–1. The effects of Mn and Mg introductions on crystalline phase compositions, texture and activities of the catalysts were investigated. The catalysts were characterized by XRD, N2 adsorption, TEM, H2-TPR, TG-DTA, etc. The results showed that LaMg0.5Mn0.5Al11O19 catalyst had high surface area (40.1m2g−1/1200°C 5h); LaMg0.5Mn0.5Al11O19 catalyst exhibited the high activity for CH4 combustion (T10=470°C, T90=690°C). It was believed that a synergetic effect of Mg and Mn is beneficial to enhance the stability and catalytic activity of the crystals.

Chemical composition of glass and crystalline phases in coarse coal gasification ash

A procedure has been developed for determining the chemical composition and relative abundance of the amorphous or glassy material, as well as crystalline phases, present in coarse coal gasification ash, in order to assist in predicting the behaviour of the material in cement/brick/concrete applications. The procedure is based on a combination of quantitative X-ray diffraction (XRD), chemical analysis and electron microprobe studies. XRD analysis indicates that the clinker samples contain a number of crystalline high temperature phases, including anorthite, mullite, cristobalite, quartz and diopside. Quantitative evaluation using Rietveld-based techniques has been used to determine the percentages of both the individual crystalline phases and the glass component. These data were then combined with the chemistry of the crystalline phases and the overall chemical composition of the ash to estimate the chemical composition of the glass phase, which is typically the most abundant component present in the different materials. Although there is some degree of scatter, comparison between the inferred glass composition from XRD and bulk chemistry and actual data on the glass composition using electron microprobe techniques suggest that the two approaches are broadly consistent. The microprobe further indicates that a range of compositions are present in the glassy and crystalline components of the ashes, including Si–Al-rich glass, metakaolin and Fe–Ca–Mg–Ti phases, as well as quartz, anorthite and an aluminophosphate material. Electron microprobe and XRD studies also show that pyrrhotite (FeS), representing a high temperature transformation product of pyrite, is present in some clinker and partially burnt carbonaceous shale samples.

Anatase/rutile TiO 2 composites: Influence of the mixing ratio on the photocatalytic degradation of Malachite Green and Orange II in slurry

The present study is directed to clarify the influence of the ratio of anatase to rutile phase, containing in the TiO 2 samples, on their activity as photocatalysts in slurry. A series of samples corresponding to different percentages of anatase is prepared from commercial anatase and rutile TiO 2 brands (KRONOS). The crystalline phase composition of the samples is characterized by X-ray diffraction. The photocatalytic action of the mixtures is tested in photodegradation of the commercial organic dyes Malachite Green Hydrochloride and Orange II in aqueous solutions under UV irradiation. Comparative tests with Degussa P-25 are performed. The apparent rate constants of the process are determined from the kinetic curves using appropriate models. They generally increase with the anatase ratio, being always larger for Malachite Green than for Orange II.

Recycling of CRT panel glass as fluxing agent in the porcelain stoneware tile production

In the present work, the feasibility to substitute feldspar raw material in a porcelain stoneware body with Panel Cathode Ray Tube (CRT) glass was investigated. A standard batch and a composition, where 35 wt.% Na-feldspar was substituted by CRT glass, were sintered at different temperatures in the range of 1000–1250 °C. The degree of the densification was studied by evaluation of the closed and total porosity, while the sintering rate was estimated by non-isothermal dilatometric measures. The variation of the crystalline phase composition was evaluated by XRD analysis. From the preliminary study other ceramic samples with different percentages of CRT glass (i.e. 2.5, 5 and 10 wt.%) were prepared and fired in industrial kiln. The sintering parameters, the microstructure and the mechanical properties were measured and compared with the standard composition.

Influence of Pressure on the Crystallization in SiO<sub>2f</sub>/SiO<sub>2</sub> Composites

The influence of pressure on the crystallization behavior in SiO2f/SiO2 composites hotpressed at 1350°C was studied. The crystalline phase composition analysis on SiO2f/SiO2 composites revealed that the formation of cristobalite was promoted when the hot-pressing pressure ≤ 12 MPa, however suppressed with higher pressure applied. It can be ascribed to the nucleation mechanism change from surface nucleation to bulk nucleation. Analysis on relative density as well as fracture microstructure of SiO2f/SiO2 composites confirmed the conclusion.

Micro X-ray diffraction for painting and pigment analysis

Micro-X-ray diffraction (Micro-XRD) offers many opportunities for non-destructive, in situ crystalline phase composition analysis of varied artworks. This paper discusses the application of this technique to paintings. Painting surfaces and cross-sections can be examined to characterise pigments and provide additional information complementary to existing investigative analyses, which often rely only on elemental information. This study was completed in three parts: proprietary tube paints were examined showing differences in pigment composition on the basis of paint quality; analysis of cross-sections from Tiepolo’s Banquet of Cleopatra provided information on ground layer composition; and a small panel painting was examined non-destructively by placement within the instrument. Through these examples the utility and versatility of the technique is demonstrated.

Rapid, accurate phase quantification of multiphase calcium phosphate materials using Rietveld refinement

Rietveld refinement has been employed to estimate the crystalline phase compositions of multiphase calcium phosphate mixtures containing calcium hydroxyapatite [Ca5(PO4)3OH], and alpha and beta tricalcium phosphate [Ca3(PO4)2]. Two methods were employed using fixed structural models for all three phases and refining the zero offset, scale factors, lattice parameters and one peak breadth parameter using either a constant background (method A) or a background with two refined parameters (method B). Analysis of a matrix of quantitative standards across a broad spectrum of phase compositions indicates that method A results in small systematic deviations of the Rietveld phase compositions (< 1 wt%) from the nominal values, but the systematic deviations are eliminated by refining the background (method B). The methods require approximately 10 min to complete, and are suitable for quality control of calcium phosphate production (and potentially other multiphase systems) when accuracy, precision and time are all significant considerations.

Evolution of Phases and Habit during the Crystallization of Freeze-Dried Lactose/Salt Mixtures in Humid Air

Phase compositions, transient phases, and morphology of the crystallization of freeze-dried lactose/salt mixtures in humid air were estimated by in situ X-ray diffraction analysis complemented by ex situ scanning electron microscopy, powder diffraction, and analysis of the solid state α/β anomeric ratios by gas-liquid chromatography. The salts studied are calcium chloride (CaCl 2 ), magnesium chloride (MgCl 2 ), potassium chloride (KCl), and sodium chloride (NaCl) with lactose/salt molar ratios of 2:1, 4:1, and 9:1 mol/mol. Following an induction period during which water is sorbed, crystallization is rapid and the predominant phases observed using the in situ method in freeze-dried lactose/magnesium chloride (MgCl 2 ), sodium chloride (NaCl), and potassium chloride (KCl) are mixtures of α-lactose monohydrate and β-lactose. In general, the α/β ratio of the solid state as measured by gas-liquid chromatography was similar to the crystalline phase composition as measured by X-ray diffraction. A transient phase appears in lactose/KCl (4:1 and 9:1 mol/mol), lactose/MgCl 2 (9:1 mol/mol), and lactose/NaCl (9:1 mol/mol), namely, α/β mixed phase. Another transient effect observed with nearly all the lactose-salt mixtures was the observation of a subtle shift in the lattice parameters of α-lactose from a = 8.006 A, b = 21.562 A and c = 4.800 A for short crystallization times to a = 7.982 A, b = 21.562 A, and c = 4.824 A for longer times. The transient effects, namely, the observation of the α/β mixed phase and the distortion in α-lactose monohydrate lattice parameters, are explained in terms of stresses induced during the rapid onset of crystallization.

Effect of TiO2 Crystalline Phase Composition on the Physicochemical and Catalytic Properties of Pd/TiO2 in Selective Acetylene Hydrogenation

Pd/TiO(2) catalysts have been prepared using TiO(2) supports consisting of various rutile/anatase crystalline phase compositions. Increasing percentages of rutile phase in the TiO(2) resulted in a decrease in Brunauer-Emmett-Teller surface areas, fewer Ti(3+) sites, and lower Pd dispersion. While acetylene conversions were found to be merely dependent on Pd dispersion, ethylene selectivity appeared to be strongly affected by the presence of Ti(3+) in the TiO(2) samples. When TiO(2) samples with 0-44% rutile were used, high ethylene selectivities (58-93%) were obtained whereas ethylene losses occurred for those supported on TiO(2) with 85% or 100% rutile phase. X-ray photoelectron spectroscopy and electron spin resonance experiments revealed that a significant amount of Ti(3+) existed in the TiO(2) samples composed of 0-44% rutile. The presence of Ti(3+) in contact with Pd can probably lower the adsorption strength of ethylene resulting in an ethylene gain. Among the five catalysts used in this study, the results for Pd/TiO(2)-R44 suggest an optimum anatase/rutile composition of the TiO(2) used to obtain high selectivity of ethylene in selective acetylene hydrogenation.

Lead-strontium titanate glass ceramics: I – crystallization and microstructure

The crystallization behaviour of glasses in the system [(Pb\(_{1-x}\)Sr\(_{x}\)) O·TiO2]-[2SiO2· B2O3]-[K2O]-[BaO] (0.2 ≤ x ≤ 0.9) have been studied. Perovskite titanate was found to be the major phase in all the glass ceramic samples investigated. The actual composition of crystalline phases could not be confirmed on the basis of shift in the X-ray diffraction (XRD) peak positions because of similar effects due to solid solution formation and strain due to crystal clamping. Comparison of the observed intensities of various XRD peaks of the perovskite titanate phase with the calculated intensities for (Pb\(_{1-x}\)Sr\(_{x}\))TiO3 with same lead/strontium ratio confirmed the formation of lead strontium titanate solid solution. Microstructural characteristics of various glass ceramics are also discussed. The advantages of using K2O and BaO as additives instead of only K2O are also discussed.

Effect of the casting solvent on the crystal characteristics and pervaporative separation performances of P(VDF- co-HFP) membranes

In this paper, two different crystalline phase compositions appear in the isothermally dried solvent-cast poly(vinylidene fluoride- co-hexafluoropropylene) (P(VDF- co-HFP)) membranes, which was explained based on the different solvent–polymer interactions. The dipolar intermolecular interaction between P(VDF- co-HFP) and dimethylacetamide (DMAc) induces polar γ phase with trans conformation, which is absent in the P(VDF- co-HFP)–acetone system. The different pervaporation behavior of the two solvent-cast membranes in separating ethyl acetate (EtAc) from water was explained based on the different permeant–polymer interactions which were further deduced from the affinity differences. The difference of polarity between EtAc molecules and the acetone-cast P(VDF- co-HFP) membrane is smaller than that between EtAc molecules and the DMAc-cast P(VDF- co-HFP) membrane, which makes for the different solubilities and diffusivities of EtAc in the two different solvent-cast membranes. And the separation properties of them in pervaporation of EtAc/water mixture are inevitably varied.

A fine route to tune the photocatalytic activity of TiO2

Different nanocrystalline photoactive TiO2 catalysts were prepared by the hydrolysis of titanyl sulphate (TiOSO4). Some important parameters in the preparation procedure, such as pH, calcination temperature, hydrolysing agent and temperature and ageing time were varied, leading to TiO2 with very different physical properties, i.e. crystalline phase composition, crystallite size, surface area, light absorption properties and bandgap energy. The photocatalytic activity of the TiO2 catalysts was evaluated using the photooxidation of dichloroacetic acid (DCA) as probe reaction. The experimental results revealed that the photocatalytic activity of the samples was greatly affected by their physical properties and therefore by the experimental conditions employed in their preparation. Using the optimum preparation parameters, TiO2 with an activity notably higher than the commercial TiO2 Degussa P-25 was obtained. Photoelectrochemical properties of both materials were studied for the hypothesis of enhanced activity.

Mullite-zirconia composites: Effect of citric acid addition on slip and cast properties

Dispersion of mixed suspensions of zircon and α -alumina using citric acid as dispersant followed by pressure filtration produced after sintering (1600∘C—2 h) dense mullite-zirconia composites. The effect of citric acid addition and pH on the rheological behavior of the mixed suspensions (57 vol%) was examined. Most of flow curves showed a shear thinning behavior at low shear rates reaching the viscosity a plateau at high shear rates. Newtonian viscosity at high shear rates values decreased to a minimum and then increased with increasing the amount of dispersant added. Compacts prepared from well stabilized suspensions achieved a maximum relative density of 72% (theoretical) which is slightly higher than that obtained from suspensions dispersed with a polyelectrolyte. Characteristics of sintered compacts such as density and crystalline phase composition by XRD were determined.

Temperature and Orientation Induced Polymorphic Behavior of Syndiotactic Polypropylene

Syndiotactic polypropylene (sPP) was rapidly quenched from the melt to room temperature, obtaining films in the disordered form I, with the chains in helical conformation. A significant portion of chains in the trans-planar mesophase was found, as evidenced by X-ray diffraction and FTIR spectroscopy. The quenched films were drawn to a draw ratio of 6 at 25, 60, and 90 °C and analyzed before and after releasing the tension. A large shrinkage was observed unhooking the fibers, and this parameter, expressed as (lmax − lf)/lmax, almost linearly decreased on increasing the drawing temperature. The crystalline phase composition was investigated by diffraction techniques in both the fixed and relaxed fibers. The fully extended fibers drawn at all the investigated temperatures contain a significant amount of the trans-planar mesophase while the fraction of the crystalline trans-planar form III decreases on increasing the drawing temperature and it is absent in the fiber drawn at 90 °C. Upon relaxation, we found evidence that the trans-planar mesophase in the fixed fiber crystallizes into form II while form III in the fixed fibers tends to transform into the trans-planar mesophase. An infrared and dynamic-mechanical analysis on the fibers was also performed to confirm the structural results. The analysis evidenced that on increasing the drawing temperature, the mesophase in the fixed fibers more and more transforms into the helical form II. On the other hand trans-planar chains remain in the amorphous fraction of all the relaxed fibers. The experimental results allow one to better clarify the role of the trans-planar mesophase in phase transitions of sPP and, taking into account also literature data, to propose a more detailed scheme of transformations between different polymorphs of this polymer.

Effect of cryogenic treatment on nickel‐titanium endodontic instruments

To investigate the effects of cryogenic treatment on nickel-titanium endodontic instruments. The null hypothesis was that cryogenic treatment would result in no changes in composition, microhardness or cutting efficiency of nickel-titanium instruments. Microhardness was measured on 30 nickel-titanium K-files (ISO size 25) using a Vicker's indenter. Elemental composition was measured on two instruments using X-ray spectroscopy. A nickel-titanium bulk specimen was analysed for crystalline phase composition using X-ray diffraction. Half of the specimens to be used for each analysis were subjected to a cryogenic treatment in liquid nitrogen (-196 degrees C) for either 3 s (microhardness specimens) or 10 min (other specimens). Cutting efficiency was assessed by recording operator choice using 80 nickel-titanium rotary instruments (ProFile 20, .06) half of which had been cryogenically treated and had been distributed amongst 14 clinicians. After conditioning by preparing four corresponding canals, each pair of instruments were evaluated for cutting efficiency by a clinician during preparation of one canal system in vitro. A Student's t-test was used to analyse the microhardness data, and a binomial test was used to analyse the observer choice data. Composition data were analysed qualitatively. Cryogenically treated specimens had a significantly higher microhardness than the controls (P < 0.001; beta > 0.999). Observers showed a preference for cryogenically treated instruments (61%), but this was not significant (P = 0.21). Both treated and control specimens were composed of 56% Ni, 44% Ti, 0% N (by weight) with a majority in the austenite phase. Cryogenic treatment resulted in increased microhardness, but this increase was not detected clinically. There was no measurable change in elemental or crystalline phase composition.