Glassy Part Research Articles

A Unified Model for Non-Fickian Diffusion and Anomalous Swelling of Glassy Polymer Gels.

A sheet of glassy polymers placed in a solvent shows swelling behaviors quite different from that of soft polymers (rubbers and gels). (1) Non-Fickian diffusion (called case II diffusion): As solvent permeates into the sample, a sharp front is created between the swollen part and the glassy part, and it moves toward the center at constant speed. (2) Nonmonotonous swelling: The thickness of the sample first increases and then decreases toward the equilibrium value. Here we propose a theory to explain such anomalous behavior by extending the previous theory for swelling of soft gels. We regard the material as a continuum mixture of a glassy polymer network and solvent. We assume that the polymer network is a viscoelastic gel of glassy polymers, and its relaxation time depends strongly on solvent concentration. We show that this theory explains the above two characteristics of glassy polymers in a simple and unified framework. The theory predicts how the permeation speed of the solvent and the characteristic times of the swelling process depend on material parameters and experimental conditions, which can be checked experimentally.

On modeling the infiltration of water in a PEG-DA hydrogel and the resulting swelling under unconstrained and mechanically-constrained conditions

Polyethylene glycol-diacrylate (PEG-DA) hydrogels are the most extensively studied synthetic gels in biomaterial science, and mathematical modeling of the diffusion of water into this polymer and the resultant swelling of these hydrogels is of central importance for quantitatively predicting the coupled diffusion–deformation response of these materials. Lee (2011) in his Ph.D. thesis reported on some novel experiments on diffusion and swelling of initially dry rods of PEG-DA when put in contact with water at one end — under two different mechanical boundary conditions: (a) when the rods were free to swell, with no mechanical constraints, and (b) when the rods were mechanically-constrained in a glass tube. In the unconstrained case he observed a sharp diffusion “front” that separated the swollen rubbery part and the dry glassy part of the rod, while in the constrained case no sharp diffusion front was observed. His experimental results have not been mathematically modeled in the literature. Here, we build on an existing theory for gels (Chester and Anand, 2010; 2011; Chester et al., 2015) and modify it to account for a dependence of the diffusivity of the solvent on the polymer volume fraction, and a dependence of the Flory–Huggins interaction parameter on the pressure. We show that results from our numerical simulations based on the modified theory can satisfactorily reproduce the experimental observations of Lee (2011).

Structural interaction of semi-interpenetrating polymer network polyurethane/styrene acrylonitrile latex particles

A series of novel structured latex particles with semi-interpenetrating polymer network (IPN) of glassy styrene-acrylonitrile copolymer (SAN) cores and rubbery polyurethane (PU) shells were synthesized to improve damping property. The inverted core/shell synthesis method (rubbery part first, then the glassy part) was applied to control morphology of core/shell latex particles. The glass transition temperature and mechanical property of the obtained semi-IPN were characterized by DMA and UTM, respectively. The effect of composition on the mechanical properties of core/shell latex IPN particles was studied. It was found that the core/shell latex particles with high crosslinking density are more miscible than those with low crosslinking density. Additionally, the improved tensile strength and elongation were observed. Therefore, the crosslinking efficiency of PU plays an important role in governing phase miscibility in core/shell latex IPN particles.

Partially amorphous stainless steel coatings: Microstructure, annealing behavior and statistical optimization of spray parameters

A stainless steel powder of a mixed amorphous and crystalline structure was HVOF sprayed in an effort to produce coatings with a large glass fraction. In the first part of this work, the microstructure and annealing behavior of powder and coatings are studied. The coatings consisted of a glassy part and a martensitic part, the latter with boride, borosilicide and boro-carbide dispersions. The annealing behavior of powder and coatings is characterized by glass crystallization and martensite tempering. Annealing of the powder leads to complete microcrystallization of the glassy part, whereas annealing of the coatings eventually leads to nanocrystallization of the residual glass phase. In the second part, the effects of selected spraying parameters (oxygen-to-fuel ratio, powder feed rate, spraying distance and spraying stages) on characteristic coating properties are investigated by means of the Taguchi analysis. The oxygen-to-fuel ratio mostly affected the coating hardness and porosity. The powder feed rate had a significant effect on all the coating properties but mostly on the deposition rate and crack extension force. Spraying in stages significantly increased the deposition rate, whereas it promoted coating amorphicity. A spraying experiment under the optimum conditions determined by the Taguchi analysis, showed a good fit between the predicted and the attained property values.

Investigation of the Role of Nucleating Agents in MgO−SiO2−Al2O3−SiO2−TiO2 Glasses and Glass-Ceramics: A XANES Study at the Ti K- and L2,3-Edges

We report a X-ray absorption study at Ti K- and L2,3-edges to determine the role of TiO2 content as a nucleating agent in glass ceramics. It is found that the local Ti environment is not modified with TiO2 addition, indicating that medium range organization is responsible for its ability to promote internal versus bulk nucleation. We have identified a Ti coordination change between the nucleation front and the crystallized part of the glass ceramic. These changes correspond to conversion from 5-fold coordinated to 4-fold coordinated Ti in the remaining glassy part, resulting from compositional changes. This reveals that active sites for nucleation could be experimentally detected and that reorganization of the glass matrix during nucleation has a major influence on the ongoing nucleation processes.

Channeling investigation of the crystalline structure ofU4O9−y

The crystallographic structure of ${\mathrm{U}}_{4}{\mathrm{O}}_{9\ensuremath{-}y}$ crystals can be described in terms of a spatial arrangement of special aggregates of oxygen atoms distributed throughout the basic fluorite framework of ${\mathrm{UO}}_{2}$. The structure of ${\mathrm{U}}_{4}{\mathrm{O}}_{9\ensuremath{-}y}$ single crystals was investigated with the ion-channeling method by recording angular scans across major crystallographic directions and along major atomic planes. Monte Carlo simulations were performed to interpret the channeling data. The presence of various anionic clusters previously proposed (such as the Willis-type 2:2:2 aggregate and Bevan-type cuboctahedral cluster), as well as more recent models involving the incorporation of extra oxygen atoms as oxo groups forming uranyl-type bonds and a structural disordering of part of the uranium sublattice, were investigated. Channeling data exhibit satisfactory agreement with both the Willis and Bevan-type aggregates. They are incompatible with the presence of a glassy part in the uranium sublattice and indicate that the presence of uranyl-type bonds is unlikely.

Microstructural characterization of the oxide scale on nitride bonded SiC-ceramics

The microstructure of the oxide scale formed at 1510 °C by oxidation of silicon nitride-bonded SiC-ceramics was studied by scanning electron microscopy (SEM). Etching by diluted HF etchants was used to help microstructural observation. This method revealed individual cristobalite crystallites as well as interfaces or interlayers between silica and non-silica phases. The ceramics–scale interface was covered by cristobalite crystallites showing that the devitrification of oxide scale begins here. Crystallites grown on SiC were smaller than those grown on binding phase. A thin HF-soluble interlayer was observed between SiC grains and cristobalite. No interlayer was found between cristobalite and oxynitride-type binding phases. The applied etching procedure gave supplementary information on the cracking, too. Partial etching by diluted HF delineated cracks in the scale. These cracks originate in the cristobalite and extend nearly perpendicularly to the substrate through the whole glassy part of the scale.

Local Structure and Charge Distribution in the UO2—U4O9 System

AbstractFor Abstract see ChemInform Abstract in Full Text.

Local Structure and Charge Distribution in the UO2−U4O9 System

Analysis of X-ray absorption fine structure spectra of UO(2+x) for x = 0-0.20 (UO(2)--U(4)O(9)) reveals that the adventitious O atoms are incorporated as oxo groups with U--O distances of 1.74 A, most likely associated with U(VI), that occur in clusters so that the UO(2) fraction of the material largely remains intact. In addition to the formation of some additional longer U--O bonds, the U sublattice consists of an ordered portion that displays the original U--U distance and a spectroscopically silent, glassy part. This is very different from previous models derived from neutron diffraction that maintained long U--O distances and high U--O coordination numbers. UO(2+x) also differs from PuO(2+x) in its substantially shorter An-oxo distances and no sign of stable coordination with H(2)O and its hydrolysis products.

南長岡ガス田における火山岩貯留岩の分布と変質作用

Volcanic rock units in the Minami-Nagaoka gas field are very heterogeneous because of their facies change and intense alteration. ln this study, a geological model of the Minami-Nagaoka gas field is constructed to explain such heterogeneity for optimizing further exploitation. This model emphasizes two aspects of this volcanic reservoir. The first is distribution of primary volcanic body, and the second is secondary alteration processes. Primary volcanic body is identified on the basis of the difference of the primary plagioclase type in phenocrysts. This volcanic rock is divided into 6 zones according to types of primary feldspar in phenocryst; zone 1, oligoclase; zone 2, oligoclase with labradorite and anorthite; zone3, albite; zone 4, oligoclase and andesine; zone 5, labradorite and anorthite; zone 6, albite. It is clarified that the very productive intervals are within the glassy rhyolite of “zone 3” which extends widely in this field. The glassy rhyolite in zone 3 of the southern area is characterized by perlitictexture, and dissolution pores are dominant in such glassy part. In the northern area, such glassy rhyolite underwent intense silicification and dissolution pores are underdeveloped compared with those in the southern area. It is inferred that such heterogeneity of porosity is due to the difference in recrystallization of glass by the influence of the overlying volcanic activity. Dissolution pores are generated by the process of montmorillonitization in which cations such as potassium and sodium leached out. Montmorillonite changes to sericite (illite) when provided with potassium and to chlorite with iron and/or magnesium. In the lower part of zone 3, chlorite occurs as fill of the pores. This means that the iron and magnesium leached from underlying mafic or intermediate rock units deteriorated reservoir quality with chlorite precipitation in the lowermost interval.

Direct Conversion of Bulk Materials into MFI Zeolites by a Bulk-Material Dissolution Technique

Publisher Summary This chapter discusses the direct conversion of bulk-materials into MFI Zeolites by a bulk-material dissolution technique. By using a novel synthetic technique, dynamic bulk-material dissolution (DBMD), succeeded in converting glass bulk materials by replacing the glassy part to MFI zeolite crystals from the surface to the inside. A thoroughly converted zeolitic tube and partially converted zeolitic fibers and fabric are prepared with this technique. Seed crystals accelerated crystallization and improved both the coverage and uniformity of the crystals.

Morphology, design and characterization of IPN-containing structured latex particles for damping applications

We have prepared a series of novel structured latex particles with interpenetrating polymer network (IPN) cores and glassy SAN shells. The IPN cores were composed of two polymers: polybutadiene-based and acrylic-based. The morphologies of these latex particles were determined by TEM. The glass transition temperature and mechanical behavior of the polymers were characterized by DMS. The effect of different components on the final core/shell particle morphologies and mechanical properties was studied. The mechanical behavior of core/shell particles with IPN cores was also compared with that of separate core/shell and multilayered core/shell particles. In addition, normal core/shell synthesis (rubbery part first, then the glassy part) and inverted core/shell synthesis (glassy part first, then the rubbery part) were performed to provide another access for morphology design and control. It was found that the core/shell latex particles with poly(butyl acrylate)-based copolymers are more miscible than poly(ethylhexyl methacrylate)-based copolymers. The high grafting efficiency of poly(butyl acrylate) plays an important role in governing phase miscibility. The latex particles synthesized by the inverted core/shell mode showed higher miscibility than the normal synthesized ones. The damping properties of different core/shell particles were evaluated based on the loss area (LA) from dynamic mechanical spectroscopy measurements. The IPN core/shell polymers were found to be the best dampers due to their more miscible chemistry. The highest level of damping was achieved by inverting core/shell particles with dual-phase continuity compared to normal core/shell particles.

Variations of noble gas abundances and isotope ratios in a single MORB pillow

To evaluate variations of noble gas signatures within a single MORB pillow caused at its extrusion, all noble gas abundances and isotope ratios (from He to Xe) were analyzed in different portions of a pillow basalt from the glassy rim to the interior by slicing off at every 2.5mm in thickness (#1 to #7). 40Ar/36Ar and He contents are high in glassy parts, and rapidly decrease toward the inner crystallized parts. Although ³He/4He is almost uniform among glassy parts (#1 to #3), the outermost part (#1) has a lower 40Ar/36Ar than the inner glassy parts (#2 and #3). This indicates incorporation of low 40Ar/36Ar component into the glassy rim from the surrounding materials at its solidification. Abundances of heavier noble gases, especially Xe, greatly increase toward crystallized parts. It could not be explained by incorporation of surrounding noble gases dissolved in the seawater and requires some other component such as fractionated product during crystallization by solid‐melt partition or derived from fine sediments. In order to obtain magmatic signature, outermost glassy part should be eliminated as well as crystalline parts.

Long-term stability of PEO-Li 2O:3B 2O 3-LiClO 4 composite solid electrolyte

Poly(ethylene oxide) (PEO)-based composite solid electrolytes are of interest for their applications in solid-state electrochemical devices. In this paper we study both thermal and electrical stability of a PEO-Li 2O:3B 2O 3(glass)-LiClO 4 solid electrolyte vs a month-long ageing performed at room temperature under dry atmosphere. A comparison is performed with homologous films prepared from different solvents without the lithium triborate. We show that the composite electrolyte is the most amorphous one immediately after preparation and better resists crystallization. The conductivity after three months ageing is well above that of the reference films. Some anomalies have been found which are attributed to the glassy part of the composite.

Multicomponent latex IPN materials. I. Morphology control

A series of novel structured latex particles with interpenetrating polymer network (IPN) cores and glassy SAN shells were developed in an attempt to investigate the feasibility of these polymers as both toughening and damping agents in thermoplastics. The IPN cores were composed of one impact part (polybutadiene based) and one damping part (acrylic based, with Tg around +10°C). The particle morphologies of these polymers were determined by TEM. The glass transitions and mechanical behavior of the polymers were characterized from DMS. The effect of different components on the final core/shell particle morphologies and mechanical properties was studied. The mechanical behavior of core/shell particles with IPN cores was also compared with that of separate core/shell and multilayered core/shell particles. In addition, normal core/shell synthesis (rubbery part first then the glassy part) and inverted core/shell synthesis (glassy part first then the rubbery part) were performed to provide another access for morphology control. It was found that the core/shell latex particles with poly(butyl acrylate) based copolymers are more miscible than poly(ethylhexyl methacrylate)-based copolymers. The high grafting efficiency of poly(butyl acrylate) plays an important role in governing phase miscibility. The latex particles synthesized by the inverted core/shell mode showed higher miscibility than the normal synthesized ones. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2193–2206, 1997

Local Structure of Simplified Waste Glass: Complementarity of XAS and MD Calculations

ABSTRACTX-ray Absorption Spectroscopy (XAS) together with x-ray diffraction methods were used in inactive analogues of the French nuclear waste glass to analyze Pd-Te precipitates and the peculiarity of the sites occupied by some structural probe elements such as Mo, Zn, Zr and Si in the glassy part of the material. The influence of the precipitates on the structure of the glassy matrix around these structural probes was investigated by comparing noble metal bearing compositions together with noble metal free glasses.In noble metal bearing glasses, Pd is associated to Te as (Pd90Te10) precipitates. Pd K-edge EXAFS shows the presence of Te in the Pd coordination shell and is in accordance with a non-metallic character of the Pd-Te bond. Mo K-edge EXAFS shows that Mo occurs as molybdate groups non connected to the glassy matrix, which may be related to the occasional separation of Mo-rich phases in some compositions. Zr is located in an octahedron with d(Zr-O)=2.08Å 0.01Å whereas Zn is 4-fold coordinated with d(Zn-0)=-1.95 ű 0.01Å. Beyond this well defined first coordination shell, XAS detects some degree of medium range order which gives insight on the bonding of the site to the polymeric borosilicate network. The interatomic Zn-Si and Zr-Si EXAFS-determined distances agree with a ZnO4and Si04tetrahedra sharing corners geometry and Zr-Si octahedra sharing corner with Si04tetrahedra. A third shell of neighbors around Zr was evidenced in the noble metal bearing glasses and in a four oxide glass, indicating that Zr is an element useful for detecting subtle changes in the local structure of complex borosilicate glasses. Si K XANES shows modifications in the connection between Si04tetrahedra when noble metals are present. To obtain accurate and precise structural interpretations, a direct comparison between EXAFS data and Molecular Dynamic (M.D.) calculations on simplified nuclear glass comprising six oxides has been performed. MD calculations show that the distribution of the Zr-O distances is harmonic in the k-range accessible with EXAFS in glasses.

Cation Exchange Properties of Hydrothermally Treated Coal Fly Ash

Two samples of fly ash were treated for 2-48 h in 3.5 M NaOH at 100 °C. Powder XRD patterns of resulting products were obtained, and their CEC was determined. Zeolite P and/or hydroxysodalite formed during the treatment from the glassy part of fly ash, while quartz gradually dissolved and mullite remained stable. Approximately 50% of fly ash could be converted to zeolites with the CEC of resulting products reaching 2.5-3 mequiv/g. Concentrations of extractable B, Mo, and Se in fly ash considerably decreased upon treatment. Adsorption isotherms of lead on treated fly ash suggested that at low initial lead concentrations and at pH lower than 6 precipitation of lead compounds is not likely. A desorption experiment indicated incomplete reversibility at higher concentrations, suggesting that part of the adsorption may not have been cation exchange related. Treated fly ash displayed high selectivity for Pb 2+ > Sr 2+ > Cu 2+ > Cd 2+ > Zn 2+ > Cs + in competition with Na + , especially at low concentrations of these cations, and was effective in removing Pb and Zn from industrial wastewaters. It was not selective for Ni 2+ and UO 2 2+ . In a column test, 160 bed vols of NH 4 + -contaminated fish-pond water was filtered through treated fly ash until NH 4 + breakthrough occurred.

A model for the effect of physical ageing on the stress relaxation behavior of high density polyethylene

The stress relaxation behavior of high density polyethylene (HDPE) can be affected by ageing processes; e.g., with increasing storage time at a low temperature following a quench from a high temperature (close to the melting point) the relaxation curves change shape. More specifically, the stress level approached after very long loading times in a stress relaxation experiment increases with the ageing time. Here this stress level is denoted “the internal stress”σ i. Struik has pointed out that physical ageing may also occur in semicrystalline polymers like HDPE. The physical ageing should then be associated with that part of the amorphous phase which is closest to the surfaces of the crystallites. This part of the amorphous phase of HDPE can be assumed to have a restricted mobility at room temperature and may have a partially “glassy” character. In this paper a model for explaining the increase inσ i for HDPE with increasing ageing time is proposed and discussed. It is based on the separation of the amorphous phase into two parts as suggested by Struik. The glassy part of the amorphous phase ages in a way similar to that of an entirely amorphous polymer quenched to a temperature below its glass transition, while the more rubbery phase is assumed not to undergo any physical ageing.

Subaerial volcanism in the Archean Uchi-Confederation volcanic belt

The Uchi-Confederation Lakes area, within the Uchi subprovince of the Canadian Shield has three major cycles of mafic to felsic metavolcanic rocks forming a section 8500-11,240 m thick, folded about a central syncline. A rhyolite tuff about 300 m thick is exposed over a strike length of 16 km at the top of the second cycle. The tuff is eutaxitic in texture and consists of relict shards, fiamme and essential pumice and lithic fragments. The unit forms two flow units and one cooling unit approximately 300 m thick, with a lateral extent of 12 km, consisting of a vitrophyric base, a densely welded mid-portion about 200 m thick and the upper 40 m which is less densely welded. The fiamme, up to 38 cm long and 5 cm thick, are draped over lithic fragments and wholly replaced by very fine-grained quartz. Snowflake texture is observed in feldspar grains in the relict glassy part of the unit. Pronounced reverse size grading is present with pumiceous and lithic fragments concentrated in the upper part. The upper portion contains breccia-filled fractures indicative of fumarolic activity. The unit is underlain by subaqueous ash flows and overlain by stromatolitic carbonate. Reconstruction based upon poor stratification, reverse size grading, abundant relatively fine pumiceous clasts and great lateral extent suggest a Plinian eruption and caldera collapse. The unit represents subaerial deposition and welding based on replacement of fiamme by silica, development of snowflake texture, and deformation of fiamme and welding of shards. Submergence and deposition of shallow water sedimentary carbonate followed.

Crystals Formed by Devitrification of Glasses in the System CaO-MgO-P<sub>2</sub>O<sub>5</sub>

Phenomena in the devitrifying process of phosphate glasses containing both CaO and MgO were studied by DTA, X-ray diffraction and chemical resistivity test. Crystals formed by heat-treatment of the glass were identified to be magnesium metaphosphate in CaO/MgO mole ratio smaller than 1 and β-calcium metaphosphate larger than 4. A schematic phase diagram of CaP2O6-MgP2O6 system in which the existence of a double salt 2CaP2O6⋅MgP2O6 was assumed from the results was given. The gush of a melt through a crevice formed in the crystallized layer was observed during the heat-treatment of a cylindrical specimen. Such strongly separating tendency seems to occur because of difference of the anion structure between CaP2O6 and MgP2O6. A considerable difference of the chemical resistivity between the crystal part and the glassy part in a specimen was detected by a dissolution test by using 1:1 hydrochloric acid.