The existence of amorphous phase in Portland cements: Physical factors affecting Rietveld quantitative phase analysis

Rietveld quantitative phase analysis has become a widespread tool for the characterization of Portland cement, both for research and production control purposes. One of the major remaining points of debate is whether Portland cements contain amorphous content or not. This paper presents detailed analyses of the amorphous phase contents in a set of commercial Portland cements, clinker, synthetic alite and limestone by Rietveld refinement of X-ray powder diffraction measurements using both external and internal standard methods. A systematic study showed that the sample preparation and comminution procedure is closely linked to the calculated amorphous contents. Particle size reduction by wet-grinding lowered the calculated amorphous contents to insignificant quantities for all materials studied. No amorphous content was identified in the final analysis of the Portland cements under investigation.     

膨润土中蒙脱石物相的定量分析

膨润土中蒙脱石物相定量分析的传统方法分析的精度低,而且由于蒙脱石标准样品很难制得,无法对蒙脱石物相定量分析的结果进行验证和评估.运用X射线衍射定量相分析的Rietveld全谱图拟合法、直接分析法(外标法)和K值法(内标法),以及吸蓝量法、化学成分分析法,对典型膨润土样品的蒙脱石进行了定量相分析,讨论了不同分析方法的优缺点,认为Rietveld全谱图拟合法的分析结果精度和可信度最高.     

Evolution with Temperature of Crystalline and Amorphous Phases in Porcelain Stoneware

Porcelain stoneware tile is a ceramic building material characterized by high technological properties, especially regarding water absorption, chemical and frost resistance, bending strength and abrasion resistance. Because mineralogy is one of the main factors affecting the mechanical properties of porcelain stoneware, a complete determination and quantification of the mineral and amorphous phases is of special importance in the study of porcelain stoneware tiles. In the present work, a reference industrial composition (50% kaolinitic clay, 40% feldspar, and 10% quartz) of porcelain stoneware tiles fired at different temperatures (400°–1400°C) was characterized by X-ray powder diffraction combined with quantitative full-phase analysis using the Rietveld method, including amorphous content. The green composition contained albite, microcline, and muscovite as fluxing agents, which start to decompose at low temperatures (400°–800°C range) and are completely dissolved above 1200°C. The mullite phase is formed from 1100° to 1230°C and at the latter temperature, quartz particles start to dissolve. Studies of mineralogical evolution have revealed that the high heating rate (45°–50°C/min) required in ceramic tile manufacture leads to significant differences in comparisons with whiteware ceramics fired at a lower heating rate (10°C/min). Thus, the formation of mullite in porcelain stoneware occurs at higher temperatures (1100°C) whereas the transformation of β-quartz to β-cristobalite does not take place. The experimental results of this study show that qualitative mineralogical analysis, based on the intensity of a particular diffraction peak for each crystalline phase, is a suitable methodology to obtain preliminary knowledge of mineralogical changes with temperature.     

Comprehensive phase characterization of crystalline and amorphous phases of a Class F fly ash

A comprehensive approach to qualitative and quantitative characterization of crystalline and amorphous constituent phases of a largely heterogeneous Class F fly ash is presented. Traditionally, fly ash composition is expressed as bulk elemental oxide content, generally determined by X-ray fluorescence spectroscopy. However, such analysis does not discern between relatively inert crystalline phases and highly reactive amorphous phases of similar elemental composition. X-ray diffraction was used to identify the crystalline phases present in the fly ash, and the Rietveld quantitative phase analysis method was applied to determine the relative proportion of each of these phases. A synergistic method of X-ray powder diffraction, scanning electron microscopy, energy dispersive spectroscopy, and multispectral image analysis was developed to identify and quantify the amorphous phases present in the fly ash.     

Full quantitative phase analysis of hydrated lime using the Rietveld method

Full quantitative phase analysis (FQPA) using X-ray powder diffraction and Rietveld refinements is a well-established method for the characterization of various hydraulic binders such as Portland cement and hydraulic limes. In this paper, the Rietveld method is applied to hydrated lime, a non-hydraulic traditional binder. The potential presence of an amorphous phase in this material is generally ignored. Both synchrotron radiation and a conventional X-ray source were used for data collection. The applicability of the developed control file for the Rietveld refinements was investigated using samples spiked with glass. The results were cross-checked by other independent methods such as thermal and chemical analyses. The sample microstructure was observed by transmission electron microscopy. It was found that the consistency between the different methods was satisfactory, supporting the validity of FQPA for this material. For the samples studied in this work, the amount of amorphous material was in the range 2–15 wt.%.     

Quantitative phase analysis of hydraulic limes using the Rietveld method

Quantitative phase analyses of three commercial samples of hydraulic limes have been performed using the Rietveld method. Although the Rietveld method has been already applied to cement analysis, we report here the first application to different classes of hydraulic binders, such as hydraulic limes (HL) and natural hydraulic limes (NHL). Unlike HL, that are simple diluted cement, NHL are specific product of great interest for its application in building restoration and conservation.Samples were also characterized by laser granulometry and chemical analysis. Thermogravimetric analysis/Differential Scanning Calorimetry (TG/DSC) and calcimetric analyses were conducted to compare the results of such well-established techniques with those obtained with the Rietveld method. Taking advantage of the Rietveld method with the addition of an internal standard, the phase fraction of all the crystalline phases as well as the amorphous component, have been accurately determined. This technique offers a valid support for the characterization of hydraulic limes in the light of the EN classification of such industrial products.     

Influence of body composition on the technological properties and mineralogy of stoneware: A DOE and mineralogical-microstructural study

This paper reports a systematic and comprehensive investigation of the effects of the starting mixture composition on the mineralogy and properties of porcelain stoneware tiles using mixture design and full quantitative phase analyses by the Rietveld method. Functional relationships between properties and the raw material mixture proportions were obtained and related to the mineralogical composition of the fired product. Mullite crystallisation depended on the chemical environment. Dissolved quartz mounted to 10 wt% of the dry body regardless on initial amount, indicating saturation of the surrounding melt. The paramount role of the amorphous content on the stoneware properties was disclosed quantitatively. Open porosity decreased with increasing amount of amorphous content, and consequently both the stain and wear resistance increased. The CIE-Lab colour parameters a* and b* increased with increased amorphous content due to interaction with surface iron in hematite. The mullite content increased wear resistance, thus supporting the mullite strengthening theory.     

Crystallinity Analysis of Glass-Ceramics by the Rietveld Method

The crystallinity of multicomponent glass-ceramic mixtures has been analyzed via the Rietveld method, using powder X-ray diffractometry data. The Rietveld technique uses an internal standard but requires no calibration data to determine the total amorphous phase content of a mixture. This method of analyzing the crystallinity of synthetic mixtures gives high-precision results, with an error of generally less than ±3.0%, for several glass-ceramics.     

Structural study of mullite based ceramics derived from a mica-rich kaolin waste

Mullite-based ceramics have been synthesized by reactive sintering of a mixture containing kaolin and a mica-rich kaolin waste. Samples fired in the temperature range from 1300 to 1500 °C were characterized by X-ray diffraction (XRD). The quantitative phase analysis and unit cell parameters of the mullite were determined by Rietveld refinement analysis of the XRD data. Mullite-based ceramics with 1.2 wt% quartz, 56.3 wt% glass (amorphous phase), 2.64 g/cm³ of apparent density, and 35±1.2 MPa of flexural strength were obtained after firing at 1500 °C. A liquid phase sintering mechanism activated by a total mica content of 13.3 wt% allowed to increase the mullite content to 47.6 wt% (2.3 wt% quartz and 50.1 wt% glass phase) and improve the flexural strength (70±3.9 MPa) after firing at 1400 °C.     

Mechanical Properties of Dental Porcelain with Different Leucite Particle Sizes

This research aims to investigate the effect of leucite particle size on the mechanical properties of dental porcelain with a similar leucite content and chemical composition. Leucite powders of different particle sizes were synthesized by a hydrothermal method and a high-temperature fusing-crystallization method, respectively. Dental porcelains with different average leucite particle sizes (i.e., 0.5±0.2, 1.2±0.3, and 5±2 μm) were prepared by sintering the mixture of different leucite powders and a low temperature frit. The crystalline phase, crystalline content, relative density, hardness, flexural strength, and fracture toughness of the porcelains were measured by X-ray diffraction (XRD), quantitative XRD analysis, the Archimedes method, a Vickers microhardness tester, a universal testing machine, and a single-edge precracked beam method, respectively. The microcrack density and the distribution of leucite particles were also quantitatively assessed from micrographs. The results showed that the leucite particle size did not have a significant effect on the average of the measured flexural strength, fracture toughness, and hardness of dental porcelains. However, because of a existence of the large number of microcracks, the relative density and the Weibull modulus of the sample groups with an average leucite particle size of 5 μm were statistically lower.     

Using phase diagrams to deal with moisture expansion

Consensus has it that the post-fabrication moisture expansion of fired clay-based materials is governed by the presence of amorphous and/or vitreous phases. In this work, very simple calculations using the lever rule and the phase diagram of the Al₂O₃–SiO₂–K₂O (A–S–K) system, were used to show that the experimentally observed dependencies between moisture expansion and the A/S and K/A weight ratios in clay-based compositions can be correlated with the amount of liquid phase formed during the initial melting of the composition, which remains in the fired body as a vitreous phase. This correlation might, if judiciously used, help ceramists in the choice of additives and/or processing conditions, while avoiding changes in the firing temperatures. Also, the results obtained throw a sharper light in the dual and, in this respect, antagonistic role played by the liquid phase during firing.     

Quantitative Analysis of Crystalline and Amorphous Phases in Glass–Ceramic Composites Like LTCC by the Rietveld Method

Glass–ceramic composites like low-temperature cofired ceramics are densified at temperatures below 900°C via liquid-phase sintering. For high-frequency applications, materials with low dielectric losses are needed. At these frequencies glass exhibits higher dielectric losses than a crystalline phase; therefore, the glass amount is reduced after densification by crystallization. To perform a quantitative X-ray analysis of such glass–ceramic composites, a method based on Rietveld refinement was developed. For optimum results, the X-ray diffraction patterns were fitted using the software TOPAS 2.1 from Bruker AXS. With this method, it is possible to determine quantitatively the amount of crystalline phases and also the amount of the remaining amorphous phase.     

Quantitative Phase-Composition Analysis of Liquid-Phase-Sintered Silicon Carbide Using the Rietveld Method

Accurate quantitative X-ray diffraction analysis of SiC-based ceramics is difficult because of the significant overlap of the Bragg reflections from the different SiC polytypes. In this regard, the Rietveld method is a powerful tool for the accurate and precise analysis of the phase/polytype compositions in these materials. In this study, we have used two different types of Rietveld codes for the quantitative phase/polytype analysis of a liquid-phase-sintered SiC specimen: FULLPROF, which is based on the classical Rietveld approach, and BGMN, which is based on the new fundamental parameter approach. In both cases, the effect of texture corrections on the precision of the analysis also was studied. The accuracy of the analysis, in terms of the weight percentage of SiC (all polytypes) and yttrium aluminum garnet liquid phase, as determined from the starting powder composition, is within the standard deviation of the analysis in both cases (FULLPROF and BGMN), with and without the texture corrections. In addition, in the case of the classical code (FULLPROF), inclusion of the texture corrections has been shown to improve the precision. In contrast, the precision of the analysis using the BGMN code without the texture corrections is better. However, inclusion of the texture corrections is expected to improve the accuracy of the analysis.     

Raman spectroscopic and SEM/EDXS analyses of high translucent Nantgarw porcelain

In the first quarter of the 19th Century the factory established at Nantgarw created some of the finest quality porcelain in the world, rivalling that of Sevres, but beset by economic difficulties resulting from extraordinarily high kiln losses approaching 90 %, the production which started in 1817 (ceased by 1820) produced the finest translucency ever achieved in Georgian porcelains. An opportunity has arisen to analyse rare Nantgarw porcelain shards excavated archaeologically from the Nantgarw China Works site. Two types of compositions, bone china and silica-rich pastes are identified by Raman and SEM-EDXS analyse, confirming some ancient studies. The spectral data from “sagged” silica-rich shards are interpreted to reveal potential explanations of the manufacturing fault which significantly contributed to the demise of the ceramics factory. Finally, the pigments and glaze used in Nantgarw porcelain decoration have been analysed and identified for the first time.     

Aluminum-rich belite sulfoaluminate cements: Clinkering and early age hydration

Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO₂ into the atmosphere when compared to ordinary Portland cements. Here, we discuss the laboratory production of three aluminum-rich BSA clinkers with nominal mineralogical compositions in the range C₂S (50-60%), C₄A₃$ (20-30%), CA (10%) and C₁₂A₇ (10%). Using thermogravimetry, differential thermal analysis, high temperature microscopy, and X-ray powder diffraction with Rietveld quantitative phase analysis, we found that burning for 15 min at 1350 ºC was the optimal procedure, in these experimental conditions, for obtaining the highest amount of C₄A₃$, i.e. a value as close as possible to the nominal composition. Under these experimental conditions, three different BSA clinkers, nominally with 20, 30 and 30 wt.% of C₄A₃$, had 19.6, 27.1 and 27.7 wt.%, C₄A₃$ respectively, as determined by Rietveld analysis. We also studied the complex hydration process of BSA cements prepared by mixing BSA clinkers and gypsum. We present a methodology to establish the phase assemblage evolution of BSA cement pastes with time, including amorphous phases and free water. The methodology is based on Rietveld quantitative phase analysis of synchrotron and laboratory X-ray powder diffraction data coupled with chemical constraints. A parallel calorimetric study is also reported. It is shown that the β-C₂S phase is more reactive in aluminum-rich BSA cements than in standard belite cements. On the other hand, C₄A₃$ reacts faster than the belite phases. The gypsum ratio in the cement is also shown to be an important factor in the phase evolution.     

Suspension high velocity oxy-fuel spraying of TiO2: A quantitative approach to phase composition

A range of coatings from a water based suspension of anatase has been prepared by suspension high velocity oxy-fuel spraying with the aim to study effects of heat power of the flame on phase composition, microstructure and surface topography. Three most commonly used approaches of quantitative phase analysis have been scrutinized with respect to their applicability and as some of the coatings showed presence of preferred orientation and it was argued that quantitative Rietveld refinement is the most accurate method for phase composition determination. Coatings had a layered duplex anatase/rutile microstructure with fraction of rutile increasing exponentially with heat power. Spraying at the lower heat power led to a lower surface roughness and higher power resulted in surfaces with pronounced humps, which were distributed homogeneously on the surface. The emergence of humps is related to an increase in macroscopic surface area of up to 30% with respect to the flat coating.     

Melting Equilibria of the Bi-Sr-Ca-Cu-O (BSCCO) System in Air: The Primary Crystallization Phase Field of the 2212 Phase and the Effect of Silver Addition

The subsolidus and primary crystallization phase field of the "2212" (Bi:Sr:Ca:Cu) phase in the BSCCO system have been investigated. At 830°C, this phase was observed to be in equilibrium with ten phases. Sixteen four-phase equilibrium regions that surround the 2212 phase have been identified at this temperature. The melting events as-sociated with these four-phase regions were studied with differential thermal analysis, quenching experiments, and wicking experiments, in which samples of the liquid for analysis were absorbed by capillary action. The melt com-positions were obtained by using quantitative energy-dis-persive X-ray spectrometry. The 2212 phase melts incon-gruently, beginning at ∼825°C. Its primary crystallization field encompasses a compositional range of 24–42 mol% BiO^1.5, 7–33 mol% SrO, 2–27 mol% CaO, and 19–43 mol% CuO. The compositions of melts in equilibrium with the 2212 phase were mostly on the calcium-deficient side of the 2212 solid solution. An approximate polygonal model of the 2212 primary crystallization field has been presented. The addition of silver depresses the melting temperatures in the vicinity of the 2212 phase, from 4°C to 22°C. Silver entered the melt at a saturation level of 2–8 mol%. In the more copper-rich liquids, silver replaced some of the copper, which resulted in a shift of the 2212 crystallization field away from the copper oxide corner.     

Phase content controlled TiO2 nanoparticles using the MicroJetReactor technology

In this paper, a method for the continuous preparation of nanoscaled titania with controlled phase content is presented. The method bases on the MicroJetReactor technology. The synthesis process was carried out by using the hydrolysis of titanium tetraethylate (TET). Synthesis with flow rates to 14 ml/min are implemented, and temperatures are varied between 20 and 210 °C. Particle size distribution measurements by dynamic light scattering (DLS) show monomodal particle size distributions from 1 to 10 nm, stable for more than 24 h. There is no correlation between hydrolysis temperature and the particle size distributions.XRD (X-ray diffractometry) investigations showed, that crystal structures of anatase, brookite, rutile and an amorphous content can be detected in all samples. Quantitative analysis using the Rietveld refinement shows a significant effect of the synthesis temperature on the phase content. The relative phase content of anatase can be raised from 40 wt% up to 75 wt%, accompanied by a loss of all other phases.     

Characterisation of the glass fraction of a selection of European coal fly ashes

Fly ash largely consists of the inorganic content of coal that remains after combustion. The crystalline phases present in fly ash may form upon cooling of a molten alumino‐silicate glass. This view is supported by the spherical shape of many fly ash particles, inferring that they have gone through a viscous fluid state. The amorphous content in fly ash is believed to dominate reactivity behaviour, under both alkaline and acid conditions, because glasses have a higher potential energy than the equivalent crystal structure and the variation of bond angles and distances in a glass makes the bond breakage easier. It is the degradation behaviour under alkaline conditions, and the subsequent release of silica from the glass phase, that is important in the use of fly ash for conversion to zeolites and for pozzolanic applications in cement. This research comprehensively studies the composition, quantity and stability of the glass phase in a series of nine fly ashes sourced from Spanish and Italian power plants. The quantitative elemental composition of the glass phase in each fly ash was determined. Samples of the ashes then underwent a series of tests to determine the internal structure of the ash particles. Heat treatment of most of the ashes results in mullite crystallising from the glass phase; this is the crystalline phase that is predicated to form by both the relevant phase diagrams and also by NMR spectroscopy. In the ashes, mullite is present as a spherical shell, tracing the outline of the particle but in some specific cases the mullite skeleton is made up of coarse crystals reach also the internal parts of the particles. The morphology and density of the mullite crystals in these shells varies greatly. This work has supported the view that some crystalline phases present in fly ashes, such as mullite, form upon cooling of the amorphous glass melt as opposed to direct conversion from existing mineral phases in the coal during the combustion process. Copyright © 2004 Society of Chemical Industry     

Mineralogical Composition of Clinker as an Indicator of Sulfate Resistance: A Rietveld XRD/Takashima Approach

This study aims to optimize quantitative X‐ray diffraction (XRD) mineralogical analysis of the minority phases in clinker. The proposed method consists of applying Rietveld quantitative refinement to the XRD patterns for both clinker and the insoluble residue remaining after it is attacked with methanol and salicylic acid (Takashima method). The method was tested with industrial clinker and the same material after modifying its mineralogy by refiring at 1500°C followed by slow cooling. The findings showed that the C₄AF/C₃A ratios for quickly and gradually cooled clinker were much higher when the clinker diffractograms were refined with the Rietveld procedure than when the proposed method was used. The proportion of C₃A found with the proposed method was ≈2.8‐fold higher than when Rietveld only was applied to the diffractograms for clinkers. Taken together, the refinement data for the two materials (clinker and Takashima residua) revealed that Rietveld quantitative XRD applied to clinker underestimates the low C₃A content. These findings are supported by postsulfate attack durability studies conducted on cements prepared with the two clinkers.