Fraction Of Crystalline Phase Research Articles

Effect of milling parameters on the formation of nanocrystalline hydroxyapatite using different raw materials

Abstract The influence of milling parameters (time and atmosphere) on the mechanochemical synthesis of nanocrystalline hydroxyapatite (n-HAp) using different raw materials was studied. Two distinct chemical reactions were activated for various milling times under air or in a high purity argon (99.998 vol%) atmosphere. Then, the mechanically activated powder was heat treated at 800 °C for 1 h to produce n-HAp with high degree of crystallinity. Results revealed that the phase purity of products under both milling atmospheres was strongly influenced by the chemical composition of raw materials. The synthesized powders exhibited average sizes about 32 and 27 nm under air atmosphere, and about 32 and 34 nm under argon atmosphere. The fraction of crystalline phase drastically decreased after 80 h of milling under both atmospheres. In addition, the fraction of crystalline phase for the annealed sample at 800 °C was higher than the mechanosynthesized specimens. The results of morphological evaluation confirmed the formation of n-HAp with different morphologies each of which can be used for particular purpose.

Microstructure and Mechanical Properties of Cr-W-B-N Coating Deposited by DC Reactive Magnetron Co-Sputtering

Nanocomposite Cr-W-B-N coatings with various tungsten contents were synthesized on silicon wafer substrates. The used technique is a DC reactive magnetron co-sputtering deposition equipped with a Cr-B alloy target with 20 at.% B and a W target in a mixed argon/nitrogen plasma atmosphere. Composition and microstructure of the obtained coatings were investigated using X-ray diffraction, X-ray Photoelectron Spectroscope and transmission electron microscope while the micro-hardness was measured using a depth-sensing nano-indenter. The results have shown that the microstructure and the mechanical properties of Cr-W-B-N coatings were strongly dependent on either the tungsten content or the volume fraction of W-N crystalline phases. It was observed that the micro-hardness of Cr-W-B-N coatings is lower than that of Cr-B-N coating as the tungsten content is less than 24 at.% and the volume fraction of W-N crystalline phases is lower than 37 vol.%. As the tungsten content further increased to 30 at.% and the volume fraction of W-N crystalline phases increased to 55 vol.%, the micro-hardness of Cr-W-B-N coating was found enhanced to 19 GPa and higher than Cr-B-N film. It was also obtained that the volume fraction of Cr-N crystalline phases is inversely proportional to the volume fraction of W-N crystalline phases.

Structural Characterization of Nanocrystalline Ni<sub>(50-x)</sub>Ti<sub>50</sub>Cu<sub>x</sub> (X = 5, 9 wt%) Alloys Produced by Mechanical Alloying

Nanocrystalline Ni(50-x)Ti50Cux(X = 5, 9 wt%) alloys were successfully produced by mechanical alloying. Mechanical activation was performed at different milling times under a high purity argon (99.998 vol%) atmosphere. Phase analysis and structural features of the samples were examined by X-ray diffraction (XRD). Results revealed that NiTiCu (B2) phase was achieved after 600 min of milling. The formation of this phase was mostly related to the critical factors in determining the site replacement of elements in Ni-Ti-Cu ternary system. After 600 min of milling, the average crystallite size and lattice strain of the samples were about 5 - 10 nm and 1.057% - 1.967%, respectively. Evaluation of the full width at half maximum (FWHM) values for all the samples indicated the occurrence of anisotropic line broadening. The determined amounts of crystallinity revealed that the fraction of crystalline phase decreased with increasing weight percentage of copper up to 9% and reached a minimum value after 600 min of milling. The lattice parameters and the unit cell volume of the milled samples were always larger than the standard values. In addition, lattice parameter deviation influenced by the weight percentage of copper. Based on the obtained data, mechanical alloying process can be used for production of nanocrystalline NiTiCu alloys with different structural features.

Microstructural Investigations of Rapidly Solidified Al-Co-Y Alloys

The alloys with different compositions in the Al-rich corner of the Al-Co-Y ternary system were prepared by conventional casting and further processed by melt-spinning technique. The microstructure and the thermal behavior of the alloys were analyzed by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and differential thermal analysis (DTA). It was found that only rapidly solidified Al85Co7Y8alloy exhibited the best glass forming ability (GFA) and a fully amorphous structure. Besides, Al85Co13Y2and Al85Co2Y13alloy ribbons were fully crystalline, whereas Al85Co10Y5and Al85Co5Y10alloy ribbons consisted of some crystalline phases within an amorphous matrix. The SEM results showed the same trend that the crystalline phase fraction decreases with the approaching into best glass former. From DSC results, only Al85Co7Y8amorphous alloy exhibited a glass transition temperature (Tg) at 569 K, and its supercooled liquid region (ΔTx=Tx−Tg) was found to be 17 K. Moreover, other calculated GFA parameters for this alloy system were also discussed.

Preparation and Characterization of Fe-Based Metallic Glasses with Pure and Raw Elements

Amorphous alloys with a composition (at.%) Fe48Cr15Mo14C15B6Y2 were prepared by using either pure elements (alloy B1) or a commercial AISI430 steel as a base material (B2). When prepared from pure elements, alloy (B1) could be cast in plate form with a fixed thickness of 2 mm and variable lengths between 10 and 20 mm by means of copper-mold injection in an air atmosphere. In the case of alloy B2, prepared by using commercial grade raw materials, rods of 2 mm diameter are obtained. Ribbons (B1 and B2) of width 5 mm and thickness about 30 μm are prepared from the arc-melted ingots using a single roller melt spinner at a wheel speed of 40 m/s. The thermal and structural properties of the samples are measured by a combination of differential scanning calorimetry (DSC), x-ray diffraction and scanning electron microscopy. Chemical compositions are checked by energy dispersive spectroscopy analysis. X-ray diffraction and scanning electron microscopy observations confirm that an amorphous structure is obtained in all the samples. A minor fraction of crystalline phases (oxides and carbides) is detected on the as-cast surface. Values of hardness and Young modulus were measured by nanoindentation for both the alloys. The effects of adverse casting conditions (such as air atmosphere, non-conventional injection copper mold casting and the partial replacement of pure elements with commercial grade raw materials) on the glass formation and properties of the alloy are discussed.

Influence of heat treatment on structure and some physical properties of lithium boro-niobate glass

The glass composition (90 mol% Li2B4O7–10 mol% Nb2O5) was prepared by the melt quenching technique. The quenched sample was heat treated at 480°C, 545°C and 630°C for 5 h and heat treated at 780°C with different time. The times were 5, 10, 15, 20, 28, and 36 h. The glass and glass ceramics were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and dc conductivity as a function of temperature. Lithium niobate (LiNbO3) and lithium diborate (Li2B4O7) were the main phases in glass ceramic addition to traces from LiNb3O8. Crystallite size of the main phases determined from the X-ray diffraction peaks are in the range <100 nm. The fraction of crystalline (LiNbO3) phase increases with increase the heat treatment temperature and time. The relation between physical properties and structure were studied.

Effect of cryogenic treatment on microstructure and mechanical properties of Cu&amp;lt;sub&amp;gt;40&amp;lt;/sub&amp;gt;Zr&amp;lt;sub&amp;gt;44&amp;lt;/sub&amp;gt;Ag&amp;lt;sub&amp;gt;8&amp;lt;/sub&amp;gt;Al&amp;lt;sub&amp;gt;8&amp;lt;/sub&amp;gt; bulk metallic glass composite

The effect of cryogenic treatment on microstructure and mechanical properties of Cu₄₀Zr₄₄Ag₈Al₈ bulk metallic glass composite (BMGC) has been investigated. The microstructure and mechanical properties of BMGC before and after cryogenic treatment were characterized through optical micrograph (OM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Vickers micro hardness (<italic>H</italic>_v). The results show that the formation of crystalline phase of Cu₄₀Zr₄₄Ag₈Al₈ BMGC can be obtained through the cryogenic treatment with 2 h. The dimension and volume fraction of crystalline phase increases with increasing of the cryogenic treatment duration from 2h to 24 h, which result in the improvement of micro hardness of BMGC. The Cu₁₀Zr₇ and AgZr phases were formed in Cu₄₀Zr₄₄Ag₈Al₈ BMGC after cryogenic treatment. The glass transition temperature of amorphous matrix of BMGC increases with the increase of cryogenic treatment duration. However, the crystallization exothermal heat of BMG decreases with the increasing of the cryogenic treatment duration. The internal stress induced by cryogenic treatment was associated with the microstructure evolution of Cu₄₀Zr₄₄Ag₈Al₈ BMGC.

Analysis of the crystal phases of Na+-beta-aluminas synthesized by infiltration of alkali molten salts

Na+-beta-aluminas in ternary Na2O–Al2O3–Li2O systems were synthesized by infiltration of alkali molten salts into porous α-Al2O3 pre-form. The effects of calcination temperature, infiltration time, and starting materials on phase formation were investigated. Pre-forms were fabricated by pressureless powder packing (PLPP), slip casting, and cold isostatic pressing (CIP) with fused and calcined α-Al2O3 powder. They were heated and infiltrated by alkali molten salts at [Na2O]:[Al2O3]=1:5 (Li2O=0.4 w/o). Each infiltrated specimen was calcined at 1100–1300°C to form Na+-beta-aluminas, whose crystalline formations, phase fractions, and alkali ion contents were analyzed. The pre-form prepared by PLPP with 1μm-calcined α-Al2O3 powder showed the highest Na-β″-Al2O3 phase fraction (59.5%), without residual α-Al2O3 phase.

Fine-Tuning of Relative Fraction of Amorphous and Crystalline Phases in Hydrogenated Silicon Prepared by PE-CVD Method

In the present study, nc-Si:H thin films have been deposited from rf-PE-CVD method. A set of depositions was achieved by varying deposition pressure from 234 mTorr to 1 Torr, while all other deposition parameters were kept constant. Structural, optical and electrical properties of the films were investigated in detail. Deposition pressure is found to be a crucial parameter in fine-tuning the material properties including relative fraction of amorphous and crystalline phases. Results indicate that film growth rate critically depends on plasma chemistry/gas phase chemistry governed by variation in deposition pressure. Deposition rate increased monotonically with increase in deposition pressure. Structural properties were studied by Raman spectroscopy and low angle XRD and the results shows that films are nanocrystalline over entire range of deposition pressure studied. Hydrogen content in the films was found < 11 at. % and decreases with increase in deposition pressure. Bandgap was found independent of deposition pressure while photoconductivity decreased by one order from 10-4 S/cm. Surface morphology of films was studied by AFM.

Effect of different conventional melt quenching technique on purity of lithium niobate (LiNbO3) nano crystal phase formed in lithium borate glass

The glass system (45Li2O+45B2O3+10Nb2O5) was fabricated by the conventional melt quenching technique poured in water, at air, between two hot plates and droplets at the cooled surface. The glass and glass ceramics were studied by differential thermal analysis (DTA) and X-ray diffraction (XRD).The as quenched samples poured in water and between two hot plates were amorphous. The samples poured at air and on cooled surface were crystalline as established via X-ray powder diffraction (XRD) studies. Differential thermal analysis was measured. The glass transition temperature (Tg) and the crystallization temperatures were calculated.Lithium niobate (LiNbO3) was the main phase in glass ceramic poured at air, droplets at the cooled surface and the heat treated glass sample at 500, 540 and 580°C in addition to traces from LiNb3O8. Crystallite size of the main phases determined from the X-ray diffraction peaks is in the range of <100nm. The fraction of crystalline (LiNbO3) phase decreases with increase in the heat treatment temperature.

Origin and influence of water‐induced chain relaxation phenomena in chitosan biopolymers

AbstractChain dynamics, probed by dielectric spectroscopy, provide a route to further understanding of the molecular interactions induced by hydration, degree of crosslinking, and microstructural changes occurring on swelling of biopolymers such as chitosan, which is becoming a focus for biomedical engineering and therapeutic delivery. The basis of the β‐wet relaxation peak is established as segmental chain relaxation between chitosan water bridges and related to its hysteresis induced by microstructural changes during wetting and dewetting cycles. Linear expansion probes the hysteresis arising from bridging water interactions during the hydration–dehydration paths which is also shown in the resultant ionic conductivity. β‐wet relaxation and ionic conductivity exhibit identical hysteresis behavior with both degrees of chemical crosslinking and water contents. X‐ray diffraction shows that the degree of crosslinking and hydration also influences the degree of disorder of the polymer chains changing both the crystalline phase fraction and lattice dimensions. These molecular interactions provide power law behavior between β‐wet relaxation dynamics and ionic mobility over five orders of magnitude for all degrees of chemical crosslinking and water bridging which is independent of the significant hysteresis in these properties indicative of scaling behavior within the noncrystalline gel phase. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Preparation and characterization of Fe-based bulk metallic glasses in plate form

Amorphous alloys with composition (at%) Fe48Cr15Mo14C15B6Gd2 (alloy A) and Fe48Cr15Mo14C15B6Y2 (alloy B) were prepared either using pure elements (A and B1) and a commercial AISI430 steel as a base material (B2). When prepared from pure elements both alloys (A and B1) could be cast in plate form with a fixed thickness of 2mm and variable lengths between 10 and 20mm by means of copper-mold injection in air atmosphere. In the case of alloy B2, prepared using commercial grade raw materials, rods of 2mm diameter were obtained.X-ray diffraction and scanning electron microscopy observations confirmed that an amorphous structure was obtained in all the as-cast samples. A minor fraction of crystalline phases (oxides and carbides) was detected on the as-cast surface. Differential scanning calorimetry measurements showed a glass transition temperature at 856K for alloy A and 841K for alloy B1, and an onset crystallization temperature of 887K for alloy A and 885K for alloy B1. In the case of alloy B2 a slightly different crystallization sequence was observed.Values of hardness (∼13GPa) and the Young modulus (∼180GPa) were measured by nanoindentation for both the alloys.The effects of adverse casting conditions (such as air atmosphere, non-conventional injection copper mold casting and partial replacement of pure elements with commercial grade raw materials) on the glass formation and properties of the alloy are discussed.

Structural and thermal characterization of CaO–MgO–SiO2–P2O5–CaF2 glasses

The paper presents the influence of varying CaO/MgO ratio on the structure and thermal properties of CaO-MgO-SiO2-P2O5-CaF2 glasses. A series of eight glass compositions in the glass forming region of diopside (CaMgSi2O6) - fluorapatite [Ca5(PO4)3F] - wollastonite (CaSiO3) ternary system have been designed and synthesized by varying diopside/wollastonite ratio in glasses. The as prepared melt-quenched glasses have been characterized for their structure by infrared spectroscopy (FTIR) and magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy. Silicon is predominantly present as Q2 (Si) species, while phosphorus tends to coordinate in orthophosphate environment in all the investigated glasses. The change in CaO/MgO ratio had an insignificant affect on the structure of glasses. The thermal sintering and crystallization parameters for the studied glasses have been obtained from differential thermal analysis (DTA) while crystalline phase fractions in the sintered glass-ceramics have been analyzed by X-ray diffraction adjoined with Rietveld refinement. Diopside, fluorapatite, wollastonite and pseudowollastonite have crystallized as the main crystalline phases in all the glass-ceramics with their content varying with respect to variation in CaO/MgO ratio in glasses. Scanning electron microscopy (SEM) has been used to shed light on the microstructure of glass-ceramics. The possible implications of structure and sintering behaviour of glassesmore » on their bioactivity have been discussed.« less

Mechanical and functional properties of amorphous-crystalline ribbons of Ti40.7Hf9.5Ni44.8Cu5 alloy

The mechanical behavior and functional properties in amorphous-crystalline thin ribbons of Ti40.7Hf9.5Ni44.8Cu5 alloy with a different volume fraction (from 0 to 100%) of crystalline phase were studied. The results obtained showed that a fully amorphous sample was deformed elastically up to 6%. The existence of the crystalline phase in the sample resulting in the deformation was realized by reorientation of martensite at the early stage. The strain accumulated at this stage was fully recoverable during subsequent heating through the temperature range of reverse martensitic transformation. It was found that an increase in the volume fraction of crystalline phase led to a rise in the value of the shape memory effect. This was due to the increase in the volume fraction of the sample deforming by the mechanism of martensite reorientation. It was observed that the amorphous-crystalline Ti40.7Hf9.5Ni44.8Cu5 alloy was deformed by three mechanisms of unelastic deformation: reorientation of martensite crystals, plastic deformation of the amorphous phase, and dislocation slip. It was shown that the change in the deformation mechanism was determined by the volume fraction of crystalline phase and the value of preliminary strain. It was found that the Ti40.7Hf9.5Ni44.8Cu5 alloy exhibited a two-way shape memory effect only if the amorphous and the crystalline phase coexisted in the alloy.

Debranched cassava starch crystallinity determination by Raman spectroscopy: Correlation of features in Raman spectra with X-ray diffraction and 13C CP/MAS NMR spectroscopy.

Because starch crystallinity influences the physical, mechanical, and technological aspects of numerous starch-based products during production and storage, rapid techniques for its assessment are vital. Samples of different levels of crystallinity were obtained by debranching gelatinized cassava starch, followed by subjection to various hydrothermal treatments. The recrystallized products were further subjected to partial hydrolysis with a mixture of α-amylase and glucoamylase prior to freeze-drying. Crystallinities were determined using X-ray diffraction (XRD) and 13C CP/MAS NMR spectroscopy, and correlated with FT-Raman spectra features. XRD crystallinities ranged between 0 and 58%, and agreed with crystalline-phase fractions (R2=0.99) derived from the respective 13C CP/MAS NMR spectra. A strong linear correlation was found between crystallinities and integrated areas of the skeletal mode Raman band at 480cm-1 (R2=0.99). With appropriate calibration, FT-Raman spectroscopy is a promising tool for rapid determination of starch crystallinity.

Structure and functional properties of rapidly quenched ribbons of Ti2NiCu alloy with different fractions of the crystalline phase

The controllable annealing of amorphous Ti2NiCu ribbons by a pulsed electric current was developed, and samples with different fractions of crystalline phase were obtained. The samples’ structure was studied using high-resolution electron microscopy. Annealing conditions allowing us to obtain an amorphous nanocrystalline structure with grain sizes of less than 10 nm were determined. Conditions for obtaining samples with the two-wave shape memory effect were found. A prototype micromanipulator was designed and successfully tested.

Microstructure and formation kinetics of a freeze lining in an industrial copper FSF slag

The freeze lining of an industrial copper flash smelting furnace slag, its growth kinetics and microstructure have been studied using a water cooled probe technique in a rotating crucible furnace at 1350°C. The first layers of iron silicate slag solidify on the water cooled metal surface as amorphous or glassy material with a minor fraction of crystalline spinel phase precipitated. At a distance of 4–5 mm from the cold face about 50% of the structure is composed of crystalline olivine (fayalite) and spinel phases embedded in a glassy matrix. Major thickness of the freeze lining is formed within first 15 min of slag contact with a cooled metal surface. The solidified microstructures obtained were compared with equilibrium phase assemblages calculated. The equilibrium solidification in the near solidus reactions includes the formation of pyroxene and rhodonite type phases, but they were not identified in the lining microstructures.

Silver Ion Dynamics in Ag2S-Doped Silver Molybdate–Glass Nanocomposites: Correlation of Conductivity and Scaling with Structure

This work reports the study of silver ion dynamics in Ag2S-doped silver molybdate–glass nanocomposites of compositions xAg2S–(1 – x)(yAg2O–(1 – y)MoO3). The volume fraction of crystalline phases in these glass nanocomposites increases with the increase of Ag2S content and considerably influences the dc conductivity. It is observed that a significant amount of volume fraction of crystalline phases for x ≥ 0.15 for the y = 0.20 series and for x = 0.20 for the y = 0.30 series causes the conductivity to decrease. The power law exponent has been obtained from ac conductivity spectra using the power law model and is observed to be almost constant at lower volume fraction of the nanocrystalline phases embedded in the glass matrix, but it decreases for samples with high crystalline volume fraction. The electric modulus data have been analyzed on the basis of the Havriliak–Negami (HN) equation. The Kohlrausch–Williams–Watts (KWW) stretched exponent β, obtained from modulus data, indicates a strong nonexponential relaxation. The scaling of the conductivity spectra reveals that the relaxation dynamics is independent of temperature but is dependent on compositions affected by the increased volume fraction of crystalline phases of the glass nanocomposites.

Calorimetric study of non-isothermal crystallization kinetics of Zr 60Cu 20Al 10Ni 10 bulk metallic glass

The non-isothermal differential scanning calorimetric techniques were used to evaluate the thermal stability and crystallization kinetics of Zr 60Cu 20Al 10Ni 10 bulk metallic glass. Various models were used to analyze the non-isothermal DSC at the heating rates ( ϕ) ranging from 1 to 80 K/min. The Kissinger equation, Ozawa equation, Augis-Bennett equation, Lasocka equation, and Vogel–Fulcher–Tammann non-linear equation were employed to describe the relationship between the crystallization peak temperatures and the heating rates. The overall crystallization activation energies of the metallic glass were estimated using the Kissinger, Ozawa and Augis–Bennett methods, respectively. The local activation energies at various volume fraction of crystalline phases were obtained by general Ozawa's isoconversional method. The crystallization kinetics was specified by a function reflecting crystallization mechanism. It has been found that a critical heating rate exists at around 20 K/min, beyond which the shapes of the DSC curves and the various relationships are varied. The crystallization process of the metallic glass can be divided into two groups, i.e. a slow heating rates region with ϕ = 1–20 K/min, and a rapid heating rates region with ϕ = 30–80 K/min. The overall crystallization activation energy for the slow heating rates regions is much larger than that for the rapid heating rates region. The crystallization activation energy derived from the Kissinger's peak temperatures is 326.4 ± 11.3 kJ/mol for the slow heating rates region, and 202.2 ± 26.6 kJ/mol for rapid heating rates region, respectively. The crystallization mechanisms were discussed with Johnson–Mehl–Avrami (JMA) and normal grain growth (NGG) mode. The crystallization mechanisms are different for the two heating rates regions. A transition point was found at the NGG-controlled crystallization stage for the higher heating rates, while it was absent for the slower heating rates.

Addressing the amorphous content issue in quantitative phase analysis: the certification of NIST standard reference material 676a

A non-diffracting surface layer exists at any boundary of a crystal and can comprise a mass fraction of several percent in a finely divided solid. This has led to the long-standing issue of amorphous content in standards for quantitative phase analysis (QPA). NIST standard reference material (SRM) 676a is a corundum (α-Al(2)O(3)) powder, certified with respect to phase purity for use as an internal standard in powder diffraction QPA. The amorphous content of SRM 676a is determined by comparing diffraction data from mixtures with samples of silicon powders that were engineered to vary their specific surface area. Under the (supported) assumption that the thickness of an amorphous surface layer on Si was invariant, this provided a method to control the crystalline/amorphous ratio of the silicon components of 50/50 weight mixtures of SRM 676a with silicon. Powder diffraction experiments utilizing neutron time-of-flight and 25 keV and 67 keV X-ray energies quantified the crystalline phase fractions from a series of specimens. Results from Rietveld analyses, which included a model for extinction effects in the silicon, of these data were extrapolated to the limit of zero amorphous content of the Si powder. The certified phase purity of SRM 676a is 99.02% ± 1.11% (95% confidence interval). This novel certification method permits quantification of amorphous content for any sample of interest, by spiking with SRM 676a.