Good Glass Formers Research Articles

Toward In Silico Prediction of Glass-Forming Ability from Molecular Structure Alone: A Screening Tool in Early Drug Development

We present a novel computational tool which predicts the glass-forming ability of drug compounds solely from their molecular structure. Compounds which show solid-state limited aqueous solubility were selected, and their glass-forming ability was determined upon spray-drying, melt-quenching and mechanical activation. The solids produced were analyzed by differential scanning calorimetry (DSC) and powder X-ray diffraction. Compounds becoming at least partially amorphous on processing were classified as glass-formers, whereas those remaining crystalline regardless of the process method were classified as non-glass-forming compounds. A predictive model of the glass-forming ability, designed to separate between these two classes, was developed through the use of partial least-squares projection to latent structure discriminant analysis (PLS-DA) and calculated molecular descriptors. In total, ten of the 16 compounds were determined experimentally to be good glass-formers and the PLS-DA model correctly sorted 15 of the compounds using four molecular descriptors only. An external test set was predicted with an accuracy of 75%, and, hence, the PLS-DA model developed was shown to be applicable for the identification of compounds that have the potential to be designed as amorphous formulations. The model suggests that larger molecules with a low number of benzene rings, low level of molecular symmetry, branched carbon skeletons and electronegative atoms have the ability to form a glass. To conclude, we have developed a predictive, transparent and interpretable computational model for the identification of drug molecules capable of being glass-formers. The model allows an assessment of amorphization as a formulation strategy in the early drug development process, and can be applied before compound synthesis.

Glass-forming ability and thermoplastic formability of a Pd40Ni40Si4P16 glassy alloy

The glass-forming ability of a Pd40Ni40Si4P16 alloy has been investigated. This alloy exhibits a wide supercooled liquid region of 107 K, a high reduced glass transition temperature of 0.596 and a small fragility parameter of 28, indicating that this alloy is a good glass former. Using flux treatment, the Pd40Ni40Si4P16 alloys can be easily produced as centimeter-scale metallic glasses. The glass transition and crystallization kinetics of this alloy were investigated by means of both differential scanning calorimetry (DSC) and differential isothermal calorimetry (DIC). Thermoplastic forming of the Pd40Ni40Si4P16 glassy alloy is easily performed due to the high thermal stability and low viscosity of the supercooled liquid. By pressing a “flat” silicon wafer onto a sample within the thermoplastic forming region, the surface of the Pd40Ni40Si4P16 metallic glasses could be significantly smoothened. The final surface showed a reduced root mean square roughness Rq as low as ~2 nm. This indicates a simple approach to prepare “flat” surfaces for metallic glasses.

Ti–Zr–Be ternary bulk metallic glasses correlated with binary eutectic clusters

In this paper, the reported scheme for locating good glass formers based on the concept of binary eutectic clusters is applied to predict alloy compositions with high glass-forming ability (GFA) in the Be–Ti–Zr system. Around the predicted composition, a series of novel bulk metallic glasses with high GFA, high strength and large compressive plastic strain of up to 15% was successfully developed. In particular, the specific strength of these newly developed BMGs reaches up to 450 kN m/kg and the supercooled liquid region is as high as 118 K, indicating a great potential to be used as aerospace materials.

Prediction of cooling rate dependent ordering in metallic glass transition using a two-state model

A two-state theoretical model is proposed to study the evolution of local order when a good metallic glass former is cooled down from the liquid state. We find that the development of order depends strongly on the cooling rate and that the ordered fraction converges to an upper limit at low cooling rates. We compare our model predictions with molecular dynamics (MD) simulation results for the Zr 35.5Cu 64.5 binary system, revealing good agreement for the fast cooling rates accessible through MD. The analytical model proposed here, however, can be extended to much lower rates which correspond to experimentally accessible processing routes.

Effect of Fe on the glass-forming ability, structure and devitrification behavior of Zr–Cu–Al bulk glass-forming alloys

We report on the glass-forming ability and devitrification behavior of Zr60Cu30Al10, Zr60Cu25Al10Fe5 and Zr62.5Cu22.5Al10Fe5 bulk glass-forming alloys on heating. The effect of Fe addition on the structure of Zr–Al–Cu alloys is also discussed. Crystallization kinetics and structural changes in the glassy alloys were studied using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The results indicate that good glass-formers, such as Zr62.5Cu22.5Al10Fe5, are located somewhat beyond the equilibrium eutectic point. Possible phase separation in the supercooled liquid on heating and electron beam-induced in situ crystallization are observed and discussed.

Co–B–Si–Ta bulk metallic glasses designed using cluster line and alloying

The formations of Co-based Co–B–Si–Ta bulk metallic glasses, as well as their mechanical and corrosion properties have been explored in this work. The alloy compositions were designed by using the cluster line approach and the alloying strategy, where the cluster line referred to a straight composition line linking a specific binary cluster to the third element in a ternary alloy phase diagram. The base ternary compositions in the Co–B–Si ternary system were first determined by the intersection points of two cluster lines, Co–B cluster to Si and Co–Si cluster to B. Then these basic ternary compositions were a small amount of Ta alloyed to further improve the glass-forming abilities. Experimental results revealed that good glass formers with 4 mm in diameter occurred at Co 62.2B 26.9Si 6.9Ta 4, obtained by Ta alloying of the base intersection compositions of Co 7B 3–Si with Co 9Si–B. This bulk metallic glass have not only high thermal stabilities with high T g and T x values, but also exhibit high fracture strength of about 4760 MPa, high Vickers hardness of about 1460, a Young's modulus of 198 GPa, and good corrosion resistances in 1 mol/L HCl and 3 mass% NaCl solutions.

Statistical composition-structure-property correlation and glass-forming ability based on the full icosahedra in Cu–Zr metallic glasses

Using the large-scale atomic/molecular massively parallel simulator, fraction of the Cu-centered ⟨0,0,12,0⟩ full icosahedra (fico) is obtained from a statistical analysis over a broad compositional range with high resolution in the Cu–Zr binary system. Weak but significant peaks are observed at certain compositions which coincide with good glass formers. This correlation implies that the change in fico is a fundamental structural factor in determining the ease of glass formation. In this regard, fico can be an indicator of glass-forming ability. Our work provides further understanding on the atomic structure of the Cu–Zr system and its effect on glass formation.

The role of rare earth elements in the structures of FeB-based glass forming liquid alloys

The structures of liquid Fe72RE6B22 (RE=Sc, Er, Ho, Dy, Y, Sm, Gd, Nd, and Ce) alloys were investigated by ab initio molecular dynamics simulation. The results show that the chemical affinity of Fe-RE and RE-B may influence the glass forming ability more than the atomic size of RE atom in these alloys. As expected, the ⟨0,3,6,0⟩ polyhedron dominates around B atoms and is significantly enriched by adding RE elements to the liquid Fe78B22 alloy. The good glass formers do not correspond to the larger percentages but to more RE atoms in the shell of ⟨0,3,6,0⟩ polyhedron. These features suggest that the effect of the chemical composition of ⟨0,3,6,0⟩ polyhedron on the glass forming ability may be larger than that of its quantity in these alloys.

Effect of low diffusion coefficient on glass phase formation in Pd77Cu6Si17 alloy

The microstructure evolution of laser rapidly solidified Pd77Cu6Si17 alloy was investigated. The experimental results showed that with increasing growth velocity, a phase transition series of Pd3Si dendrite+eutectic-ξ dendrite+eutectic-eutectic grain-regular eutectic-amorphous phase occurred. The critical velocity of amorphous transition was determined to be about 6 mm/s and the smallest lamellar spacing was 35 nm. Compared with those of Al-25 wt% Sm and Al-32.7 wt% Cu alloys, it was proposed that low diffusion coefficient is the main reason for the good glass formation ability of Pd77Cu6Si17 alloy.

Amorphization of a crystalline active pharmaceutical ingredient and thermoanalytical measurements on this glassy form

Amorphization is nowadays a method that is frequently applied in the pharmaceutical industry. The primary aim of this study is to achieve the amorphization of clopidogrel hydrogen sulphate as an active pharmaceutical ingredient (API) with various solvents and to choose the most suitable one. A secondary aim was to determine the glass-transition temperature (Tg) of this API and to classify it as a good or poor glass former. To investigate the amorphous form, differential scanning calorimetry, X-ray powder diffraction, and FT-IR analysis were applied. The melting point (Tm) was 177.4 C (450.6 K), and Tg was determined to be 88.9 C (362.1 K). The quotient Tg/Tm was 0.80, and this API was therefore classified as a good glass former.

Glass forming ability of materials: A thermodynamic approach

The glass forming ability of materials has been studied on the basis of the critical cooling rate ( R c ) for the glass formation. The study is made by obtaining an analytical expression for the nose temperature ( T n ) of the time–temperature–transformation ( T–T–T) diagram using the expressions for the thermodynamic quantities Gibbs free energy difference (Δ G), entropy difference (Δ S) and enthalpy difference (Δ H) between the undercooled liquid and solid phases obtained on the basis of Taylor’s series expansion. The study is made for oxide as well as for polymeric glasses by calculating R c for SiO 2, B 2O 3, O-terphenyl, 2-methylpentane, glycerol and ethanol. The variations of R c with the reduced ideal glass transition temperature ( T K / T m ) as well as with the ratio of specific heat and entropy differences ( Δ C p m / Δ S m ) at the melting temperature ( T m ) have been analyzed, where T K is the ideal glass transition temperature. It is found that material having a large value of the reduced ideal glass transition temperature ( T K / T m ) results a lower value of R c . It is also found that R c decreases with increasing Δ C p m / Δ S m . Attempt has also been made to study the glass forming ability of materials on the basis of reduced residual entropy ( Δ S R / Δ S m ) and ( T g - T K ) / T m , where T g is the glass transition temperature and it is found that the material having a lower reduced residual entropy ( Δ S R / Δ S m ) requires a lower R c to convert into a glassy structure. It is also found that the materials having low ( T g - T K ) / T m require low R c and consequently such materials can be said as a good glass former.

Viscoelastic properties of crystals

We examine the question of whether fluids and crystals are differentiated on the basis of their zero frequency shear moduli or their limiting zero frequency shear viscosity. We show that while fluids, in contrast with crystals, do have a zero value for their shear modulus, in contradiction to a widespread presumption, a crystal does not have an infinite or exceedingly large value for its limiting zero frequency shear viscosity. In fact, while the limiting shear viscosity of a crystal is much larger than that of the liquid from which it is formed, its viscosity is much less than that of the corresponding glass that may form assuming the liquid is a good enough glass former.

On the glass-forming ability and short-range bond ordering of liquids

The problem discussed is the relation between the glass-forming ability and short-range bond ordering of liquids, leading to the locally favored structures. Short-range bond ordering temperature was assumed to be equal to T A , which is the temperature of transition from an Arrhenius-like to a non-Arrhenius behavior for the α-relaxation time dependence on temperature. For a number of substances, it was shown that T A / T m ⩾ 1.05 for good glass-formers and T A / T m ⩽ 1.02 for poor glass-formers, where T m is melting temperature. An interpretation of this finding is proposed.

Thermodynamic properties of the Pd 77.5Cu 6Si 16.5 undercooled liquid

Proper understanding of glass formation implies the knowledge of the thermodynamics of the undercooled melts. Specifically, high values of the excess specific heat of the liquid are expected for good glass-formers. Extending the work of Gillessen and Herlach [F. Gillessen, D.M. Herlach, J. Non-Cryst. Solids 117–118 (1990) 555–558], we re-propose a calculation of the temperature dependence of entropy difference between amorphous-liquid and crystal states. An amorphous Pd 77.5Cu 6Si 16.5 alloy has been produced by injection casting in a cylindrical copper mould. DSC measurements in the liquid, amorphous and crystalline states were performed with samples sliced from the cylinder to determine the heat of fusion, of crystallization and the difference in specific heat capacity between amorphous-liquid and crystal phases. These thermodynamic quantities are used to calculate the thermodynamic functions of the liquid-glass with reference to the equilibrium crystal mixture. The data are compared to those of other bulk glass-formers in terms of fragility plots.

Glass-transition behavior of Ni: Calculation, prediction, and experiment

Vitrification of metals and alloys has received much attention in the field of materials science. Although some progress has been made, this phenomenon has yet to be fully understood. Herein, we investigate the vitrification process of pure Ni using an ab initio molecular dynamics simulation. The results of the molecular dynamics simulation and predictions from the specific volume and density diagrams as well as a casting experiment indicate that Ni may have a high reduced glass transition temperature but due to kinetic reasons is not a good glass former. The results of the present work provide new information about the glass-transition phenomenon and suggest that the reduced glass transition temperature is only an indicator of how easily can glass be formed and that its stability is a significantly more important feature.

Relaxation process of the 4I13/2 level of Er3+ in a borosilicate glass

Abstract Relaxation of 1.54 μm emission of the erbium doped borosilicate glasses with high rare earth solubility was investigated. When the erbium content is less than 0.2 wt%, multi-phonon relaxation is the predominant process of non-radiative relaxation. It is difficult to increase the quantum efficiency higher than 70% for erbium ions in this glass due to multi-phonon relaxation. Because of the good glass-formation ability and high rare earth solubility, this glass will be suitable as a host for rare earth ions with a large energy gap, such as Yb3+, Eu3+ or Tb3+.

Glass forming ability and short-range order in a binary bulk metallic glass by ab initio molecular dynamics

We have performed a series of ab initio molecular dynamics simulations of Cu64Zr36 alloy, in order to study the glass forming ability in connection to the local order. The results show that Cu64Zr36 is characterized by a pronounced icosahedral short-range order (ISRO) in the liquid, undercooled, and amorphous states associated with the existence of Cu7Zr6 and Zr6Cu10 clusters centered by Cu and Zr atoms, respectively. The latter increase the structural incompatibility of liquid and amorphous states with competing crystalline phases and give support to the view that good glass formers have high degree of ISRO already present in the liquid.

Intracellular glasses and seed survival in the dry state

So-called orthodox seeds can resist complete desiccation and survive the dry state for extended periods of time. During drying, the cellular viscosity increases dramatically and in the dry state, the cytoplasm transforms into a glassy state. The formation of intracellular glasses is indispensable to survive the dry state. Indeed, the storage stability of seeds is related to the packing density and molecular mobility of the intracellular glass, suggesting that the physico-chemical properties of intracellular glasses provide stability for long-term survival. Whereas seeds contain large amounts of soluble non-reducing sugars, which are known to be good glass formers, detailed in vivo measurements using techniques such as FTIR and EPR spectroscopy reveal that these intracellular glasses have properties that are quite different from those of simple sugar glasses. Intracellular glasses exhibit slow molecular mobility and a high molecular packing, resembling glasses made of mixtures of sugars with proteins, which potentially interact with additional cytoplasmic components such as salts, organic acids and amino acids. Above the glass transition temperature, the cytoplasm of biological systems still exhibits a low molecular mobility and a high stability, which serves as an ecological advantage, keeping the seeds stable under adverse conditions of temperature or water content that bring the tissues out of the glassy state. To cite this article: J. Buitink, O. Leprince, C. R. Biologies 331 (2008).

Quaternary Fe-based bulk metallic glasses with a diameter of 5 mm

Bulk metallic glasses with a diameter of 5 mm were obtained by drop casting in the quaternary Fe–B–Y–Nb and Fe–B–Y–Mo systems. Starting from the best glass former Fe 71.2B 24Y 4.8 in the ternary Fe–B–Y system, the search quickly led to the discovery of the quaternary good glass formers (Fe 71.2B 24Y 4.8) 96Nb 4, (Fe 73.2B 22Y 4.8) 95Mo 5 and (Fe 70.7B 24Y 5.3) 95Mo 5 after trying only around a dozen of alloys. No obvious glass transition event was observed for these quaternary alloys. No Nb and Mo containing crystalline phases were detected in the alloys studied. The potential beneficial effects of Nb and Mo in enhancing the glass forming ability (GFA) of the Fe–B–Y alloy system are discussed.

Topological Instability as a Criterion for Design and Selection of Easy Glass-Former Compositions in Cu-Zr Based Systems

In the present work we propose a new approach for predicting the best glass-former composition(s) in multi-component metallic glasses. By applying the λ criterion, a topological instability criterion proposed to predict the crystallisation behaviour of Al-based systems, we show that it is also successfully possible to reproduce compositional ranges where binary and ternary bulk metallic glasses (BMGs) have recently been obtained. Our results indicate that the good glass-former composition(s) lie(s) within fields of mutual and simultaneous topological instability of all the crystalline phases competing with glassy phase.