Overheating-Dependent Heterogeneous Crystal Nucleation in a Lithium Disilicate Melt

The viscosity of high-temperature metallic melt, which is an important index for evaluating dynamics of liquid melt, is one of the basic physical properties. It not only influences the mold-filling capacity of melting metal in traditional casting techniques, but also exhibits more distinct influence on the fabrication of advanced material, such as metallic glass. According to the variation tendency of viscosity with temperature in alloy melt, the fragility of superheated melt could be obtained, which has proved to correlate with the ability of alloy to form glass. Besides, the viscosity of alloy well above the liquidus temperature also plays a key role in probing into the characteristic of liquid-liquid phase transition, the fragile-to-strong transition phenomenon, how the potential energy landscape evolves during cooling, etc. It has been generally accepted that the viscosity of metallic melt at high temperatures increases with temperature decreasing and could be fitted by an Arrhenius curve in the whole temperature range. However, recently more and more studies show that the viscosity of metallic melt cannot be fitted by only one Arrhenius curve. Instead, there exists at least one specific temperature below which the viscosity data begins to deviate from the Arrhenius curve at high temperature during cooling. These data could be described by another Arrhenius curve. In order to in depth understand this phenomenon, in this paper we summarize the viscosity data of different metallic melts in the literature. On the basis of introducing the method of detecting high-temperature melt viscosity, we discuss comprehensively the changing tendency of viscosity with temperature and the characteristics of abnormal viscosity changes in pure metal, binary and multivariate alloys well above the liquidus temperature. It is found that the abnormal viscosity changes generally occur in alloys that could form the types of intermetallic compounds. The abnormal viscosity change in metallic melt is accompanied with exothermic or endothermic effect, depending on alloy system, and reflects the existence of liquid-liquid transition well above the liquidus temperature. Besides, such an abnormal change of viscosity influences the ability to form metallic glass liquids. Although the abnormal dynamic change of metallic melt hints the existence of complexity of structural change in liquid during cooling, what is the key factor underlying this phenomenon remains a mystery. By combining the advanced experimental techniques such as high-energy X-ray diffraction and neutron scattering with the computer simulation method, this problem may be understood further. Besides, the relation between viscosity abnormity and the phase diagram is another problem that deserves to be noticed in the future.

Viscosity is one of the most important physical properties of slags, which needs to be controlled to improve the efficiency of operation of a wide range of industrial processes. The present investigations deal with viscosity measurements in the molten metal oxides as applicable to the pyrometallurgical and power generation industries. The effect of temperature and composition on the viscosities of the silicate melts was the topic of primary interest during present investigations. Viscosity measurements were carried out in the systems ‘FeO’ – SiO2, ‘FeO’ – MgO – SiO2, and Al2O3 - ‘FeO’ – SiO2 at metallic iron saturation conditions; and the CaO – K2O – SiO2 system during the course of the present program. Upon critically reviewing the existing literature in the systems of interest, it was found that there was a serious lack of reliable and systematic experimental data. The compositions selected for measurement in the present investigation will enable the systematic study of the effects of the different components in the melt on the viscosity of the melt. The temperature range was chosen keeping in mind the limiting factors, such as, the liquidus temperatures of the various slag compositions and the maximum operating temperature of the furnace. The high-temperature viscosity measurement apparatus that was recently constructed by the Pyrometallurgy Research Centre at The University of Queensland, was commissioned to operate under controlled atmospheres and used for experimental measurements during the present program. An experimental methodology, inclusive of sample preparation methods, viscosity measurement procedure and post-experimental analysis of samples, was established for conducting successful experiments using the viscosity apparatus. Rotational cylinder viscometry was employed as the technique to measure viscosity, as it was found to be suitable for the range of viscosities under consideration for present investigations. The viscometers were calibrated against standard liquids to determine the equipment constant to be used in converting the raw viscometer data into absolute values of viscosities. The viscosity measurements were typically conducted at 50 K intervals, after equilibrating the sample at each temperature. The sample was quenched from above the liquidus temperatures to analyse the phase and compositional homogeneity of the melt, using the unique quenching mechanism available on the viscosity apparatus. The microstructures of the slag samples after viscosity measurements were studied using Scanning Electron Microscopy (SEM); composition analysis was done using Electron Probe X-ray Micro Analysis (EPMA); and the bulk compositions of the slag samples were determined using X-ray Florescence (XRF) technique, to determine the phase homogeneity and bulk compositions of the quenched samples. This approach provided a way of determining any possible deviations from target compositions and presence of any crystal phases during the course of the experiment, and enabled the reduction of uncertainty associated with the measurements. Slag compositions in the systems ‘FeO’ – SiO2, Al2O3 – ‘FeO’ – SiO2, ‘FeO’ – MgO – SiO2 and CaO – K2O – SiO2 have been selected for investigations to enable systematic studies of the effects of compositional variation to be undertaken. In the ‘FeO’ – SiO2 system at metallic iron saturation, measurements were conducted for four compositions with SiO2 concentration varying between ~31 mol % to ~41 mol %, over the temperature range 1523 K – 1773 K. In the Al2O3 – ‘FeO’ – SiO2 system at metallic iron saturation, measurements were conducted for seven compositions over the temperature range 1473 K – 1773 K. In the ‘FeO’ – MgO – SiO2 system at metallic iron saturation, measurements were conducted for seven compositions over the temperature range 1523 K – 1773 K. Measurements in the CaO – K2O – SiO2 system were conducted for three synthetic slag samples and two natural slag samples for compositions pertaining to biomass ash slags in the temperature range 1270 K – 1873 K. The new experimental viscosity data obtained from the experiments were critically analysed and were found to match well with expected trends in terms of dependence of viscosity on composition and temperature variations. The data obtained ivfrom the present investigations were compared with results reported by other researchers. The present data were shown to be self-consistent and reproducible, the uncertainties in absolute values of viscosity were demonstrated to be significantly lower than most previous studies. The new data enable the individual effects of changing Al2O3, CaO, FeO, K2O MgO and SiO2 concentrations on the viscosities of fully liquid silicate slags to be identified in a systematic way. This systematic approach is particularly useful in resolving the effects of complex interactions in the melts, such as, charge compensation reactions (Me+, Me2+)O – Al2O3. The modified-Urbain viscosity model, one of the predictive models developed at the Pyrometallurgy Research Centre, was used to compare with results from experiments and validate the model parameters. In most cases, the absolute viscosities from present measurements were found to be slightly higher than model predictions, although the slopes of plots of logarithm of experimental viscosities as a function of inverse temperature were found to match well with the predictions by the model. The new data from the present investigations will be used to optimise the modified Urbain model parameters to improve the accuracy of viscosity predictions. The present investigations have resulted in: • Improved procedures for slag viscosity measurements • Systematic measurement of uncertainties in viscosity as a function of geometry of the crucible/bob assembly • New experimental data in a number of important slag systems, data of importance to both industrial applications and the improvement of predictive slag viscosity models.

Variation of the chemical diffusivity of oxygen and viscosity of an andesite melt with pressure at constant temperature

The fracture and failure behavior of in-situ polymerized polyamide-12 (PA-12) belends prepared by reactive extrusion were studied in instrumented highspeed (v = 1.2 m/s) impact bending tests using the linear elastic fracture mochanics approach. PA-12 was polymerized in presence (up to 9 wt.-%) of ethylene/butyl acrylate copolymers (E/BA) of varying BA content and melt viscosity. From the tests performed en injection molded specimens at ambient temperature and -40°C, respectively, the fracture toughness (K d ) and initiation fracture energy (G d,i ) were derived. K d was less sensitive to either testing temperature of E/BA type and content. G d,i , on the other hand, went through a maximum at m temperature and monotonously increased at T = -40°C as a function of modifier centent. E/BA with higher melt viscosity and lower polarity (lower BA content) performed better than the lower melt viscosity, higher polarity E/BA counter-part. The dominant failure modes and their change both with temperature and modifier content were studied by fractography and discussed.

An optical falling needle rheometer was employed to measure the melt viscosity of high density polyethylene (HDPE) and low molecular weight poly (tetrafluoroethylene) (PTFE). The temperature dependence of the melt viscosity of these two polymers was obtained and described by an empirical Arrhenius relation. At the present time, this method has been confirmed to be a simple and fast (within several tens of seconds for each measurement) approach to determine polymer melt viscosities of up to at least 1×105 Pa s. The sample cell containing ∼ 2.5 cm3 materials can be vacuum sealed and disposed of without the need of subsequent cleaning each time, which could be a useful feature. In comparison with HDPE, the PTEF sample melt was found to show a much higher melt viscosity with about the same degree of polymerization. © 1993 John Wiley & Sons, Inc.

The paper presents original experimental data on the viscosity and electrical resistivity of liquid cast irons IChKh28N2 and ICh310Kh24M2F4TR. The authors discuss the measurement results within the framework of the concept of metal melts microheterogeneity. Liquid cast iron in a micro­heterogeneous state is considered as a dispersed system consisting of dispersed Fe – 30 % Cr particles distributed in a Fe – 3 % C dispersion medium. The concept of colloidal microheterogeneity (microheterogeneity) of Fe – C melts was first formulated by Wertman & Samarin more than 80 years ago and found another confirmation in this work. The introduction of theoretical approaches to the rheology of dispersed systems into the analysis of the temperature dependences of the viscosity of microheterogeneous melts made it possible to estimate the parameters of microheterogeneity: the volume fraction and size of dispersed particles. The volume fraction of dispersed particles was determined using the Taylor equation for the viscosity of dispersed systems and size of dispersed particles – within the framework of the theory of absolute reaction rates. Analysis of the temperature dependences of microheterogeneous melts electrical resistivity within the framework of the theory of transport phenomena (in this case, conductivity) in inhomogeneous media (microheterogeneous melts) made it possible to estimate the volume fraction of dispersed particles. The volume fraction of dispersed particles based on data on the electrical resistivity of liquid cast iron was determined using the Odelevsky equation for the inhomogeneous media conductivity. The cluster size was determined by the ratio of the melt electrical resistivity at the liquidus temperature and the analysis temperature, taking into account the known data for the mean free path and the electron scattering coefficient of liquid iron. The volume fraction of dispersed particles in liquid cast iron was 0.2 – 0.1 at the liquidus temperature. With increasing temperature, the volume fraction of dispersed particles decreases. The cluster size in liquid cast iron was about 3 nm at the liquidus temperature, and with increasing temperature the cluster size decreased to 1 – 2 nm. The results obtained are of practical importance: increasing the performance properties of cast iron castings is possible by high-temperature melt treatment (HTMT) in order to change the crystallization conditions and obtain a modified structure. Studies of the microheterogeneous structure of liquid cast irons and assessment of microheterogeneity parameters make it possible to substantiate and propose the optimal HTMT mode in order to improve the performance characteristics of products made of wear-resistant cast irons alloyed with chromium.

The pre-experiment of the present study revealed that polyurethane (PU) synthesized using poly (hexamethylene carbonate) glycol (PHC) has high melt viscosity and is difficult to process. Therefore, poly (trimethylene carbonate) glycol (PTC) was employed to synthesize a PU product with low melt viscosity. First, four types of thermoplastic polyurethane (TPU) were formed through one-step solvent-free synthesis. TPU is presented in the format “TPU-X-Y,” with X representing the polyol (PTC or PHC, around 1000 molecular weight) and Y the chain extender (1,3-propane diol [PDO] or 1,4-butane diol [BDO]) used. The TPU was synthesized using a fixed molar ratio of (isocyanate):(polyol):(chain extender) = 2:1:1 and compared. The results indicated that chain entanglement often occurred among the long carbon chains of PHC. The synthesized TPU employed a property of PTC, namely converting polarity into reverse polarity in high temperatures, to resolve the high melt viscosity of TPU of the PHC series, which causes processing difficulties. The synthesized TPU-PTC-PDO exhibited favorable molecular arrangements. Given its polarity, TPU-PTC-PDO has outstanding tensile properties (strength at break: 41.10 ± 10.78 MPa; 100% modulus = 6.73 ± 0.12 MPa), making processing at lower temperatures (180 or 190 °C) feasible. With the inclusion of PTC, the synthesized polycarbonate TPU exhibits the advantages of polycarbonate and is suitable for a wide range of applications.

Poly( L ‐lactic acid) (PLLA) films containing various concentrations of two natural antioxidants, α‐tocopherol and resveratrol, were fabricated by a melt compounding and compression molding process. The influence of the antioxidants on the optical properties such as color and UV‐visible light transmission was analyzed. The thermal, mechanical, rheological and physical properties of PLLA films with added antioxidants were assessed. PLLA films with added α‐tocopherol and resveratrol showed a yellowish brown color and the lightness was influenced by the presence of the antioxidants. The glass transition and melting temperatures were significantly reduced with the addition of antioxidants while enhanced thermal stability was observed, which could be a benefit and important for processing and production. PLLA films with added antioxidants were slightly more hydrophobic than neat PLLA. The combination effect of plasticizing and enhancement of the elastic modulus with differing concentrations of two antioxidants played a critical role in the mechanical and thermomechanical properties of PLLA films. The melt viscosity of the PLLA films with added antioxidants was substantially higher than that of neat PLLA. The higher melt viscosity and G ′(ω) could be an indication of formation of entanglement between PLLA and the two antioxidants. Copyright © 2012 Society of Chemical Industry

This study presents the first reconstruction of the smelting conditions in 16th‐ to 18th‐century smelters from Miedziana Góra (Holy Cross Mountains, Poland). Based on geochemical (inductively coupled plasma mass spectrometry/emission spectrometry, X‐ray fluorescence) and mineralogical analysis (X‐ray diffractometry, scanning electron microscopy, electron probe micro‐analysis) of historical slags, their chemical/phase composition and the basic smelting parameters (temperature, melt viscosity, and oxygen fugacity) were determined. Due to the differences in chemical and phase composition, slags from different smelting stages have been distinguished: hypocrystalline slags (MG6) from speiss/matte production and glassy (MG1–MG5) from matte conversion. In glassy slags, pyroxenes, quartz/cristobalite grains, and aggregates composed of metallic Cu and PbO are dispersed in the glass. Hypocrystalline slags are composed of wollastonites, anorthites, and metallic Cu. The temperature range at which the slags were formed was from ~1100°C (solidus temperature) to 1150–1200°C (liquidus temperature). The silicate melt's viscosity was from log η = 1.19 to 4.42 Pa s (at 1100–1200°C). The higher viscosity of MG1–MG5 slags indicates that, unlike MG6 slags, they were not formed during gravity separation. Information about the phase composition made it possible to determine the oxygen fugacity in the range of log fO2 = −4 to −12 atm. High oxygen fugacity indicates the oxidizing nature of the smelting process.

This research examined the torque rheological properties of cocoa pod husk (CPH)‐filled polypropylene (PP) composites. Composites with varying filler loading ranging from 10 to 40 phr and formulation with or without palm oil‐based green coupling agent (GCA‐P) were analyzed using a Brabender Plastrograph torque rheometer. The GCA‐P synthesized from fatty acid of palm oil was used to enhance adhesion at the filler–matrix surface interfaces. The results reveal that PP/CPH composites containing 40 phr filler loading and GCA‐P exhibited higher processing torque and power law index (n). Higher melt viscosity was recorded at higher filler loading, owning to filler agglomeration and more effective filler‐matrix adhesion in the presence of GCA‐P. As a result, higher energy was required to compound PP/CPH composites, which could be attributed to the increase in activation energy (Ea) at higher melt viscosity.

The authors propose a mathematical model of non-equilibrium crystallization of a binary alloy with modifying refractory nano-sized particles. The model describes heat transfer processes, as well as heterogeneous nucleation and crystallization of two components of the melt. The nucleation of the crystalline phase occurs on the surface of the nanoparticles during the supercooling of the melt. The liquidus temperature in the melt depends on the concentration of the dissolved alloying component, which is determined by the non-equilibrium lever equation. When the metal is cooled down to the eutectic temperature, the solidification of the alloy α-phase takes place, followed by solidification of β-phase if the cooling continues. The growth rate of the crystal phase is proportional to the supercooling value. The volume of the solid phase formed around the nucleus determines the size of the grain structure in the solidified alloy. The article depicts numerical simulation of aluminum melt solidification in cylindrical ingot mold, carried out by the authors. The parameters of heat exchange of the melt-mold system with the environment are available from experiments. The conditions of nucleation, crystallization rate, supercooling and solidification time prove to significantly differ within the cast. The area with the finest structure of the solidified metal is located near the wall of the mold. The calculated size of the grain structure in the casting is consistent with the experimental results. Comparing the results of numerical calculation with the data of a physical experiment on measuring the temperature during solidification of the melt and studying the properties of the cast confirm reliability of the proposed model.

Viscosities of diopside-anorthite melts were measured over the wide range of temperature (near the glass-transition temperature−1580°C/1bar) and pressure (5–20 kb/above the liquidus temperature). The measurements were carried out by the fibre-elongation method for low temperature and the counter-balanced sphere method for high temperature at 1 bar, and the sinking and floating spheres method for high temperature at high pressure. Some of the values obtained deviated slightly from those in the literature. The data on viscosity and the glasstransition temperature have been interpreted on the basis of the configurational entropy theory, by which temperature and compositional effects on viscosity were explained well. The configurational entropies at the glasstransition temperature of magmatic silicate melts are almost constant if we use an average molecular weight (amw) or “bead” as a unit; 8.0±1.2 J/K·amw, 1.1 ±0.2cal/K·bead. The latter value coincides well with the value from the literature for organic polymers. The negative deviation from linearity of the glass-transition temperature of intermediate melts may be interpreted as the effect of the mixing entropy. The calculated glasstransition temperature-composition curve using the mixing entropy agreed well with the experimental values.

Structural investigation of sodium borate glasses and melts by Raman spectroscopy. II. Conversion between BO 4 and BO 2O − units at high temperature

Effect of MgO/Al2O3 and CaO/SiO2 on the Metallurgical Properties of CaO–SiO2–Al2O3–MgO–TiO2 Slag

Compared to thermosetting resins, thermoplastic polymers offer many advantages as fiber reinforced composite matrices, such as excellent toughness, superior corrosion resistance, weldability, and recyclable, etc. However, the processibility of thermoplastic composites is commonly considered as a challenge because of the high viscosity of polymer melts (e.g., polypropylene, polyetheretherketone, etc.), which remarkably hinders their applications. Using low viscosity and in situ polymerizable thermoplastic resins to manufacture continuous fiber reinforced thermoplastic composites have been deemed as a cost‐effective emerging approach to surpass the processibility challenges. Therefore, this paper presents an overview of advancement in the engineering, high‐performance and room‐temperature‐processible liquid methyl methacrylate (MMA) resins and their composites up to date. First, the polymerization behavior and kinetic modeling of the MMA resins are reviewed, and the effects of initiators on the polymerization are summarized. In the second part, the pultrusion process and modeling including impregnation, temperature distribution and pulling force are discussed. Next, the mechanical properties and durability of the carbon fiber‐, glass fiber‐reinforced MMA‐matrix composites are presented. Finally, the challenges of the preparation and application of the MMA‐matrix composites are identified.