Crystallization Behavior Of Glasses Research Articles

Crystallisation characteristics and properties of glasses based on fluorapatite–anorthite eutectic system

The effect of partial replacement of CaO by MgO or ZnO on the crystallisation behaviour of glasses based on 30 fluorapatite–70 anorthite eutectic composition has been investigated using the differential thermal analysis, X-ray diffraction and scanning electron microscopy. Minor additive of TiO2 oxide was added on the glass batches as nucleating agents. The main crystalline phases formed after controlled heat treatment of the glasses were fluorapatite, anorthite, wagnerite and gahnite. The resultant glass–ceramic samples were characterised by the thermal expansion coefficient and Knoop microhardness. The α values of the crystallised glasses in the range of 25–500°C varied from 67×10−7 to 79×10−7 °C−1. In this case, the microhardness values of glass–ceramic samples decreased in the range of 6117–6884 MPa with increasing thermal expansion coefficient value. Precipitation of the wagnerite or gahnite phases in the crystallised glasses causes an improvement in wear resistance of the glass ceramic samples.

Mutual Influence of Special Components in Baotou Steel Blast Furnace Slag on the Crystallization Behavior of Glass

In the process of glass-ceramics prepared with Baotou steel blast furnace slag, quartz sand, and other raw materials by melting method, the mutual influence of the special components such as CaF2, REXOY, TiO2, K2O, and Na2O in the blast furnace slag on the crystallization behavior of parent glass was investigated using differential thermal analysis (DTA) and X-ray diffraction (XRD). The results show that the special components in slag can reduce the crystallization temperature and promote crystallization of glass phase, which belongs to surface crystallization of glass, and they cannot play the role of the nucleating agent; the major crystal phase composed of diopside, diopside containing aluminum and anorthite, is slightly different from the expected main crystal phase of diopside. Therefore, the nucleating agents of proper species and quantity must be added into the raw materials in order to obtain glass-ceramics. The results have important theoretical guidance meaning for realizing industrial production of Baotou steel blast furnace slag glass-ceramics preparation.

Control of the thermal properties of slow bioresorbable glasses by boron addition

This work studied the properties of glasses with the molar composition 63.8SiO 2-(11.6-x)Na 2O-(0.7 + x)B 2O 3-19.2CaO-3MgO-1.5Al 2O 3-0.2P 2O 5, in which x = 0, 1, 2, 3. These glasses are of interest for the development of slowly dissolving fibers to be incorporated in composites for medical applications. The thermal properties were recorded using hot stage microscopy, differential thermal analysis, and heat treatments in the range of 800°-1000 °C. The glass crystallization behavior was determined based on calculated values of the activation energy of crystallization and the Johnson-Mehl-Avrami exponent. The structural units in the glass network were identified using infrared spectroscopy. Finally, in vitro dissolution was tested in SBF solution. The addition of B 2O 3 increased the glass transition temperature and reduced the working temperature. When heat treated at 900 °C, the glass with the smallest amount of B 2O 3 formed two crystalline phases: magnesium silicate MgSiO 3 and wollastonite CaSiO 3. In the other compositions, only CaSiO 3 was observed after heat treatment at 950 °C. All the glasses crystallized preferentially from the surface. Changes in the liquidus and crystallization temperatures were related to changes in the glass structure. The formation of [BO 3] units led to glasses with improved resistance to crystallization and decreased liquidus temperature. In the glasses with 2.7 and 3.7 mol% B 2O 3, [BO 3] units were transformed into [BO 4] units. The formation of [BO 4] led to an increase in fragility and a decrease in resistance to crystallization. All the glasses dissolved slowly in simulated body fluid.

Dependence of thermal properties on crystallization behaviors of (1 − x)MgSiO 3– xCaMgSi 2O 6 glass-ceramics

Effects of crystallization behaviors on thermal properties of (1 − x)MgSiO 3– xCaMgSi 2O 6 (0.36 ≤ x ≤ 0.90) glass-ceramics were investigated. The crystallization behaviors of glasses were confirmed from the activation energy of crystallization ( E a), crystallite size ( L) and crystalline phases of clino-enstatite (MgSiO 3) and diopside (CaMgSi 2O 6). The specific heat capacity of the specimens sintered at 800 °C for 5 h was affected by the E a of glasses. The thermal conductivity and thermal diffusivity of the sintered specimens were dependent on the L of glass-ceramics. The temperature dependence of thermal conductivity was also discussed for the application of lighting-emitting diode (LED) package and substrate materials.

Synthesis and characterization of clinopyroxene based glasses and glass-ceramics along diopside (CaMgSi2O6)–jadeite (NaAlSi2O6) join

The crystallization behavior and mechanical characterization of glasses based upon the compositions along diopside (CaMgSi2O6)–jadeite (NaAlSi2O6) join has been investigated. Six glasses were obtained by the melt-quenching technique. Structural and thermal behaviors of these glasses were investigated by density and molar volume, infrared spectroscopy (FTIR) and dilatometry. The crystallization behavior of glasses was investigated by using differential scanning calorimetry (DSC). Sintering and crystallization behavior of the glass-ceramics were investigated under non-isothermal heating conditions up to temperatures of 850°C. Mechanical characterization of glasses was investigated by using the measurement of Vickers indentation hardness and elastic constants such as Young's modulus (E), shear modulus (G), bulk modulus (K) and Poisson's ratio (ν). These data of the glasses were correlated with the structure of glasses, nature and role played by glass forming cations.

Synthesis of nanocomposites based on MO-Bi2O3-B2O3 (M = Ca, Sr, Ba) glasses

This work examines the effect of KBF4 additions on the crystallization behavior of glasses based on the multicomponent systems MO-Bi2O3-B2O3 with M = Ca, Sr, and Ba. The glass-ceramic composites obtained contain a δ-Bi2O3-based crystalline phase with a crystallite size of ≃7 nm, evenly distributed over the glass matrix. The 400°C electrical conductivity of the nanocomposites reaches 2 × 10−4 S/cm, and the activation energy is 1.1 eV, typical of anion conduction. These values are comparable to those reported for δ-Bi2O3 ceramics.

Effect of phase separation on crystallization of glasses in the BaO-TiO2-SiO2 system

The effects of phase separation on the crystallization behavior of glasses were investigated in order to materialize a high-luminous glass-ceramic phosphor, which consists of fine phosphor crystals and a transparent glass matrix prepared due to phase separation. The glass ceramics in BaO-TiO2-SiO2 has the potential to show high photoluminescence intensity, because of multiple light scattering at the boundary between the phosphor crystal and the glass matrix. The crystallization behaviors of the glasses were examined using both the XRD analyses for an isothermal heat treatment process and the DTA measurements as a non-isothermal treatment process. The phase-separation in the glass significantly affected the subsequent crystallization behavior. In the non-phase-separated glasses, surface crystallization occurred first, and crystallization then proceeded inside the glasses. In the phase-separated glasses, the crystallization was considered to start at the boundary of two glass phases inside the glass and the crystals grew in BaO-TiO2-rich phases. This apparent bulk crystallization owing to the phase separation has the potential to materialize a high-performance phosphor composite.

Interfacial crystalline behavior in glass-fiber/polypropylene composites modified by block copolymer coupling agents

A kind of di-block copolymer polystyrene-block-poly(γ-methacryloxy-propyltrimethoxysilane) (PS-b-PMPS) with different PS block length and a kind of tri-block copolymer polystyrene-block-poly(n-butylacrylate)-block-poly(γ-methacryloxypropyltrimethoxysilane) (PS-b-PnBA-b-PMPS) with different PnBA block length were synthesized by atom transfer radical polymerization (ATRP), in which PS was a ‘hard’ block and PnBA was a ‘soft’ block. The interfacial crystallization behaviors of glass fiber/polypropylene systems modified with different coupling agents MPS, PS-b-PMPS, and PS-b-PnBA-b-PMPS were investigated on different crystallization conditions. Transcrystallinity could not be induced on non-isothermal crystallization or without maleic anhydride (10%) in polypropylene, but it appeared when glass fibers were treated with common silane coupling agent γ-methacryloxypropyltrimethoxysilane (MPS) and di-block copolymer coupling agent PS-b-PMPS in 135 °C isothermal crystallization without shear and 150 °C isothermal crystallization with shear. However, it disappeared at the interface when the samples were treated with tri-block copolymer coupling agent (PS-b-PnBA-b-PMPS) either under static or shear-induced condition. It might be that the flexible interlayer formed by the flexible block PnBA of PS-b-PnBA-b-PMPS could relax not only the thermal stress resulted from interface temperature gradient arising from sample cooling for crystallization, but also the shear stress induced by fiber/matrix interface shear.

The Influence of Metal Diffusion and Interfacial Reactions on the Crystallization Behaviour of Glasses Employed in the Manufacture of Glass-Ceramic-to-Metal Seals

One of the major attributes of glass-ceramics is an ability to tailor their thermal expansion characteristics and this makes them ideal candidates for sealing to a wide variety of metals and alloys; however, during the sealing process, reaction of diffusing metal species with glass constituents may occur, and this can lead to the formation of undesirable phases within the interfacial region. In addition, diffusion of metal species into the bulk glass away from the interface may affect the overall crystallization kinetics and can result in the formation of unwanted crystalline phases which may be detrimental to the lifetime behaviour of a seal component. This contribution outlines and discusses the factors affecting the crystallization behaviour of glasses employed in seal manufacture and describe methods by which undesirable reactions can be alleviated or minimized through effective control of the process parameters and starting glass composition.

Nanosized structural transformation and nonlinear optical properties of lithium niobium germanate glasses

Glass formation in Li2O–Nb2O5–GeO2 (LNG) system, the structure and crystallization behavior of glasses that have compositions near the ratio Li2O/Nb2O5∼1 corresponding to stoichiometry of ferroelectric phase LiNbO3 were examined by differential thermal analysis, X-ray diffraction, small-angle neutron scattering and second harmonic generation (SHG). LNG glasses were subjected to heat treatments at temperatures in the range between Tg and temperature of the first exothermic peak in order to initiate nonlinear optical activity by nanoheterogeneity formation. Transparent nanostructured glasses with second-order optical nonlinearity were obtained for compositions characterized by the Li2O/Nb2O5 molar ratio ranging from 0.83 to 1.2 and GeO2 40–45mol%. As prolonged heat treatments of nanostructured glasses result in crystallization of ferroelectric LiNbO3 the origin of SHG in transparent LNG glasses is supposed to be connected predominantly with polarity of nanoheterogeneities formed at the initial stage of phase separation.

Crystallization behavior of glasses in the system of Na 2O–CaO–MgO–Fe 2O 3–Al 2O 3–SiO 2 with high contents of nickel oxide

The structural behavior of nickel oxide in glassy and glass-ceramic materials, obtained in the system of Na 2O–CaO–MgO–Fe 2O 3–Al 2O 3–SiO 2, was investigated. The influence of the NiO content on the vitrification, crystallization, structure and exploitation properties of two model compositions, with different ratios [CaO]/[MgO] was analyzed. On the basis of DSC and XRD data, it is shown that NiO promoted the formation of bunsenite crystals, as nuclei for crystallization. On the other hand, NiO promoted formation of pyroxenes even for compositions with low MgO contents, which formed gehlenite without NiO admixtures. It is shown that in the composition with relatively high MgO contents, NiO could participate in the formation of two types of pyroxenes with the structure and chemical composition similar to (MgO 0.4NiO 0.6)(CaO 0.9NiO 0.1)Si 2O 6 and diopside–hedenbergite solid solutions. The optimal contents of NiO in both model compositions was about of 7 wt%, since higher contents reduced the exploitation properties. The glass-ceramics with optimal contents of NiO were also produced using Ni bearing galvanic slurry and coal ash; the resulting materials showed similar exploitation properties to those mentioned above.

Influence of alumina addition on crystallization and texturing behavior of LaBGeO 5 glass

The structure and crystallization behavior of glasses with 25La 2O 3 · 25B 2O 3 · 50GeO 2 composition, melted in platinum (P glass) and corundum (A glass) crucibles, were studied by DTA, X-ray diffraction and FTIR spectroscopy. The Al 2O 3 dissolved from corundum crucible in the A glass was estimated to be in the range 5–7 wt%. This alumina content had almost no influence on glass transition temperature but strongly affected the structure and crystallization behavior of the A glass. In fact, the P glass showed good texture-forming ability: high quality textured glass-ceramic plates based on stillwellite-like LaBGeO 5 crystals were easily obtained. On the contrary, the presence of alumina stabilized the A glass from which binary phases crystallize first, and only afterwards they are transformed in stillwellite by secondary crystallization: so in this glass texturing is hindered. Crystallization and texturing behavior of P and A glasses were well related to FTIR data. P glass contained both threefold and fourfold coordinated boron while in the A glass the presence of aluminum forced boron to assume almost exclusively threefold co-ordination. Hence the easier crystallization of stillwellite phase and the good textures obtained from the P glass contrary to the A glass, can be well understood since all boron atoms have tetrahedral co-ordination in stillwellite LaBGeO 5 crystal.

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.

Crystallization behavior and microstructure of powdered and bulk ZnO–Al 2O 3–SiO 2 glass-ceramics

The crystallization behavior of glass with the composition: 55.6 mol% SiO 2, 22.8 mol% Al 2O 3, 17.7 mol% ZnO and 3.84 mol% of TiO 2 as nucleating agent and with different particle sizes has been studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and tranmission electron microscopy (TEM). In glass powders two crystalline phases: zinc–aluminosilicate s.s. with high-quartz structure, Zn x/2 Al x Si 3− x O 6, ( x varies dependent on heat-treatment temperature) and gahnite are formed. The ratio of these phases depends on particle sizes. In bulk glass, however, gahnite is the sole crystalline phase. The composition of initially formed zinc–aluminosilicate s.s. was determined by Rietveld refinement of XRD patterns to be Zn 0.69Al 1.38Si 1.62O 6. With temperature increase, the amount of zinc–aluminosilicate s.s decreased with simultaneous reduce of zinc and aluminum incorporated in the structure. Eventually at 1423 K almost pure high-quartz structure was formed. The activation energies of zinc–aluminosilicate s.s. and gahnite crystallization were determined by non-isothermal method to be 510 ± 18 and 344 ± 17 kJ mol −1, respectively. The latter value matches well with those cited in literature for crystal growth of gahnite in similar glasses. That is attributed to the fact that the high-quartz structure acts as a precursor for gahnite crystallization.

Nano-Phased Crystallisation of Ferroelectrics from Glasses in the K2O-TiO2-P2O5 and K2O-Nb2O5-SiO2 Systems

Crystallisation behaviour of glasses in the K2O-TiO2-P2O5 (KTP) has been studied by DTA, XRD, EM and SHG techniques to isolate composition ranges where bulk precipitation of ferroelectric phase KTiOPO4 occurs. It was found that bulk crystallisation of KTiOPO4 at temperatures slightly exceeding Tg is initiated by addition of SiO2. Controlled heat treatment leads to formation of optically non-linear KTiOPO4 nano-particles in KTP glasses (like amorphous nanostructuring in KNS glasses) in initial stages of phase separation and produces nanoscaled modulation of polarisability and SHG effect. The results are compared to the xK2O xNb2O5(1-2x)SiO2 (KNS) systems.

Bulk metallic glasses: A new class of engineering materials

Bulk glass-forming alloys have emerged over the past fifteen years with attractive properties and technological promise. A number of alloy systems based on lanthanum, magnesium, zirconium, palladium, iron, cobalt and nickel have been discovered. Glass-forming ability depends on various factors like enthalpy of mixing, atomic size and multicomponent alloying. A number of processes is available to synthesise bulk metallic glasses. The crystallisation behaviour and mechanical properties of these alloys pose interesting scientific questions. Upon crystallisation many of these glasses transform to bulk nanocrystals and nanoquasicrystals. A detailed study of the structure and the crystallisation behaviour of glasses has enabled the elucidation of the possible atomic configuration in liquid alloys. Their crystallisation behaviour can be exploited to synthesise novel nanocomposite microstructures and their mechanical properties can be enhanced. A broad overview of the present status of the science and technology of bulk metallic glasses and their potential technological uses is presented.

KTiOPO 4 precipitation from potassium titanium phosphate glasses, producing second harmonic generation

Glass formation in the K 2O–TiO 2–P 2O 5–SiO 2 system, and the structure and crystallization behavior of glasses having compositions near the stoichiometry of KTiOPO 4 (KTP) have been examined by differential thermal analysis (DTA), X-ray diffraction (XRD), fast Fourier transform infrared (FTIR) spectroscopy and second harmonic generation (SHG). Pure glasses may be obtained adding an appropriate amount of P 2O 5 as well as of SiO 2 to the KTP composition. Transparent and homogeneous glasses were synthesized for the 56(K 2O·2TiO 2·P 2O 5)·44P 2O 5 (KTP–44P) and the 90(K 2O·2TiO 2·P 2O 5)·10SiO 2 (KTP–10Si) molar compositions. In contrast, for the 80(K 2O·2TiO 2·P 2O 5)·20SiO 2 (KTP–20Si) and for higher SiO 2 contents, the obtained glasses were partially opaque and phase separated. KTP glasses with lower P 2O 5 content cannot be obtained as they crystallize during quenching. The KTP–10Si glass shows the only exothermic peak connected to KTP phase crystallization whereas the KTP–44P and the KTP–20Si glasses devitrify in two steps. Firstly the same unidentified phase is formed in both these glasses and the KTP phase is formed only at higher temperatures. Transparent and opalescent KTP glasses exhibiting SHG activity may be produced by careful heat treatments at temperatures just above T g. The origin of SHG in transparent glasses is supposed to be connected with either precipitation of KTiOPO 4 nanocrystallites or very early stages of liquid-type phase separation.

Structure and crystallization behavior of glasses in the BaO–B 2O 3–Al 2O 3 system

The structure and the devitrification behavior of barium aluminoborate glasses, examined by Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction are reported. The glass compositions are expressed by the general formula: (50 − x/2)BaO·(50 − x/2)B 2O 3· xAl 2O 3 with x=2, 4 and 8. All the as-quenched glasses were phase separated. Aluminum acting as glass former gives a more polymerized structure increasing the glass stability with respect to the devitrification process. Surface crystallization was found to be dominant for all glasses, forming βBaB 2O 4 nanocrystals as the main crystalline phase.

Glass ceramic textures based on new ferroelectric complex oxides

The possibility to produce polar phases from glass has been examined for ternary oxide systems of the stillwellite family (trigonal LnBXO5, where Ln=La,Ce,Pr,Sm; X=Si,Ge and RBPO5, where R=Ca,Sr,Ba,Pb), tetragonal K2(NbO)2Si4O12 and orthorhombic PbLiPO4. Both original and literature data on crystallization behaviour of glasses in the Ln2O3-B2O3-XO2, RO-B2O3-P2O5, K2O-Nb2O5-SiO2, and Li2O-PbO-P2O5 systems are reviewed. The anisotropy in properties and morphology of polar crystals is considered as the main reason of grain-oriented crystallisation of glasses. Three new types of ferroelectric glass ceramic textures in the systems mentioned are reported and their specific features are described.

Crystallization kinetics of fluorophosphate glasses: Part I Effect of composition and heating rate

Crystallization behaviour of glasses from the system AlF3-MF2-Ba(PO3)2 (M=Ca, Mg, Sr, Ba) have been studied using differential thermal analysis as a function of Ba(PO3)2. The kinetic parameters for crystallization, namely, the activation energy, E, frequency factor, ν, and Avrami exponent, n, were determined. E, ν and n decreased with increasing Ba(PO3)2. Crystallization commenced at higher temperatures and the crystal growth mechanism changed from bulk to surface with increasing Ba(PO3)2. X-ray diffraction analysis revealed that CaAlF5, SrAlF5, CaAlF7 and CaSrAlF7 crystallize from these glasses when heated. The infrared transmission spectra indicated that AlF6, PO3F and Ba(Ca,Mg,Sr)P2O7 groups were present in these glasses.