Vitreous Phase Research Articles

Estimating the reduction of the firing temperature produced by the addition of energetic fluxes in porcelain tiles through the Fluegel’s model

Abstract Reducing the firing temperature and accelerating the densification process bring economic and environmental benefits. This study used Fluegel’s viscosity model, developed for glasses, to estimate the decrease of the firing temperature produced by the introduction of energetic fluxes in a porcelain body. The experimental results confirmed the prediction of the model, a 30 ºC reduction in the temperature, for the addition of wollastonite. However, for the addition of spodumene, the reduction was slightly higher than the predicted. These results suggested that Fluegel’s model may be used to estimate the effects of the introduction of energetic fluxes in porcelain tile compositions. However, the predictions should be seen as a general orientation. Among the limitations of the model were the extrapolation of limit values established by the model for the composition and, above all, the initial hypothesis that the chemical composition of the vitreous phase in porcelain tiles is constant.

Sintering Behavior and Technological Properties of Low-Temperature Porcelain Tiles Prepared Using a Lithium Ore and Silica Crucible Waste

Porcelain tiles are a building material that has been widely used in recent years and that consumes substantial resources during the sintering process. This study reports on the production of low-temperature porcelain tiles by using low-grade lithium ore (LO) and silica crucible waste (SCW) in a new SiO2–Al2O3–Na2O–K2O–Li2O system. The firing temperature of the porcelain tiles was reduced from 1260 °C to 1070 °C by adding 30% LO instead of feldspar in a modified triaxial ceramic body, and SCW was recycled and used as a raw material. These actions help to reduce the carbon emissions produced during sintering and achieve sustainable development. The effect of phase transitions on the sintering and technological properties of the porcelain tiles was studied by quantitative phase analysis, using X-ray diffraction (XRD). Secondary mullite (0–19%) can be formed at 1040–1100 °C, where more quartz and cristobalite will be retained, which increases the rupture modulus of the porcelain tiles. While the vitreous phase increases rapidly at 1100–1160 °C, the closed pores (0.1–33.1%) will simultaneously expand, causing a decrease in compactness. The results show that low-grade LO (with a cost similar to that of feldspar) allows for the production of porcelain tiles with better process performance at lower temperatures (≤1100 °C).

Fine analysis of interaction mechanism of bioactive glass surface after soaking in SBF solution: AFM and ICP-OES investigations

Bioactive glasses have the physical characteristics enabling them to be used in bone tissue engineering applications. However, the exact mechanism of the interactions between the glass surface and environment leading to the transition from the vitreous phase to the crystalline phase remains a subject of study. This work focuses on the growth of a calcium phosphate layer on the surface of the glass after immersion in a mineral solution, which mimics the mineral phase of human blood. The investigations use the Inductively Coupled Plasma and the Atomic Force Microscopy to establish the kinetic of crystallization, the kinetic of chemical reactivity and the surface transformations such as structure, texture and morphology of the bioactive glass. Obtained results show the progressive formation of a hydroxyapatite layer within 2 weeks. This crystal which is that of the bone belongs to the crystallographic structure within space group of P63/m. In addition, results show a decrease of the gradient of thickness which varies according to the immersion time from 7.5 µm to 2.8 µm and an increase of the homogeneity of the surface visible by the lowering of the gradient in the phase measurement from 60 Å to 15 Å.

Synthesis and Stability of the Strontium Cobaltite Thermally Treated in Air

This paper reports, the studies on chemical transformations at thermal treatment of a mixture of SrCO3 and Co3O4 corresponding to stoichiometric ratio of SrCoO3 compound. The mixture of raw materials was prepared by mechanical activation. Thermal analysis, X-ray diffraction and scanning electron microscopy were used for these studies. It was found that SrCoO3 forms at 930oC but is not stable and turn immediately into Sr2Co2O5 by eliminating of oxygen. This compound, Sr2Co2O5, is unstable and by increasing of the temperature decomposes in Sr3Co2O6 and cobalt oxide. At temperatures above the 1250oC, the samples melt and Sr3Co2O6 crystallizes from vitreous phase by cooling.

Reactive sintering behavior of Moroccan clay “Ghassoul”

Abstract The aim of this work is to study the sinterability of Ghassoul clay in order to manufacture a magnesium-based ceramics. Phases transformations and mechanical properties, were investigated at temperatures ranging between 1000 and 1250 °C. Several experimental techniques (particle size analysis, TGA/DTA, X-ray diffraction, IR spectroscopy, dilatometric analysis, mechanical three-point bending tests) were carried out on the raw and sintered specimens. The results obtained indicate that Ghassoul consists essentially of stevensite as clay mineral, accompanied by quartz and dolomite. The thermal treatment at 1000 °C leads to the disappearance of stevensite and dolomite as well as the formation of diopside and enstatite. The rise in temperature reveals the transformation of theses phases into clinoenstatite at 1200 °C. The sintering temperature has a strong influence on the mechanical properties. In fact, the increase in temperature is accompanied by a degradation of the mechanical properties, coinciding with the increase of the quantity of the vitreous phase and the total dissolution of the quartz.

Interconnection of Structure with Whiteness and Translucency in Soft Porcelain

The structures of two types of English soft porcelain (bone china and parian) were investigated. The structural features of these materials that make it possible for the distinct properties of whiteness and translucency — uniformity, high content of the vitreous phase, well-developed interface of particles of the dispersed phase — to be combined in them are identified. It was found that a change in the conditions of firing affects the color characteristics of such porcelains. Parian possesses a more uniform structure than bone china, since the spread in the data on the average intergrain distance is significantly smaller with the same confidence probability 0.95 than in bone china.

Polyampholytes as Emerging Macromolecular Cryoprotectants.

Cellular cryopreservation is a platform technology which underpins cell biology, biochemistry, biomaterials, diagnostics, and the cold chain for emerging cell-based therapies. This technique relies on effective methods for banking and shipping to avoid the need for continuous cell culture. The most common method to achieve cryopreservation is to use large volumes of organic solvent cryoprotective agents which can promote either a vitreous (ice free) phase or dehydrate and protect the cells. These methods are very successful but are not perfect: not all cell types can be cryopreserved and recovered, and the cells do not always retain their phenotype and function post-thaw. This Perspective will introduce polyampholytes as emerging macromolecular cryoprotective agents and demonstrate they have the potential to impact a range of fields from cell-based therapies to basic cell biology and may be able to improve, or replace, current solvent-based cryoprotective agents. Polyampholytes have been shown to be remarkable (mammalian cell) cryopreservation enhancers, but their mechanism of action is unclear, which may include membrane protection, solvent replacement, or a yet unknown protective mechanism, but it seems the modulation of ice growth (recrystallization) may only play a minor role in their function, unlike other macromolecular cryoprotectants. This Perspective will discuss their synthesis and summarize the state-of-the-art, including hypotheses of how they function, to introduce this exciting area of biomacromolecular science.

Analysis of pellets mineral composition using the solutions trees and k-means methods

Metallurgical properties of pellets to a great extent depend on the peculiarities of their microstructure. Therefore, understanding of the regularity of its evolution in the process of the pellets burning and elaboration on this base optimal methods of technological process control is a rather actual task. Analysis of experiment data of iron ore pellets microstructure accomplished using the methods of solutions trees and cluster analysis. The pellets were produced of ferrous quartzite concentrates. As the base for the investigation results of study of seven samples of iron ore pellets used, made of regular Mikhajlovsky deposit magnetite concentrate (8.3 % SiO2; 65.4 % Fe) with various basicity and MgO content. Processing of the data made in the Orange Canvas media. Classification of phase composition presented by application of decision tree concept. It was shown, that for the pellets glassy binding, an increased content of Na2O and relatively low content of FeO is typical, since the glass phase is formed basing on fusible silicates of waste rock with a high content of alkalis. Sodium and potassium are concentrated in the amorphous (vitreous) phase with a high silicon content. Increasing the MgO content leads to the appearance of a crystalline phase with a decrease in the concentration of alkalis. The decrease of the concentration of alkalis in this case linked with the general increase of the melt due to the pellets fluxing. The pellets fluxing also contributes to the change of composition of iron-bearing phases: with increasing amount of MgO in the pellets, the natural average content of MgO increases in iron-bearing minerals, crystallizing from the melt. CaO is accumulated by silicate components of the pellet structure.

Prognostic factors of postoperative intraretinal cystoid spaces after primary pars plana vitrectomy for vitreomacular traction

PurposeTo study the anatomical and surgical prognostic factors related to developing postoperative intraretinal cystoid spaces (ICS) six months after 25-gauge pars plana vitrectomy (PPV) for vitreomacular traction (VMT). MethodsThe study is a retrospective case series of patients presenting with VMT treated primarily with PPV. All patients underwent 25-gauge PPV by the same retina surgeon. Intra-operative parameters were all recorded. Postoperative visual acuity (VA), foveal thickness, and ICS were collected over six months of follow-up. ICS were defined as hyporeflective cysts divided by hyperreflective septa on optical coherence tomography (OCT). Patients with ICS persistence 3 months postoperatively received topical treatment extension. The primary outcome measure was odds of preoperative ICS in patients with postoperative ICS compared to controls. Secondary outcome measures were odds of presence of an attached hyaloid to the optic disc, presence of pseudophakia, the use of intra-operative air, and the use of more than one intra-operative indocyanine green (ICG) injections in patients with postoperative ICS compared to controls. ResultsTwo hundred and eighty treatment-naïve patients with preoperative diagnosis of epiretinal membrane (ERM) were reviewed. Thirty patients with VMT, confirmed both preoperatively on OCT and intra-operatively, were included. Postoperatively, 40% (n = 12) presented with ICS at 6 months. Among these, 83% (n = 10) had ICS prior to PPV. Patients presenting with preoperative ICS were significantly more at risk of having persistent ICS postoperatively (P < 0.05). The following factors did not statistically affect ICS occurrence: optic disc hyaloid attachment status, phakia/pseudophakia, intra-operative air vs. sulfur hexafluoride (SF6), and the number of intra-operative ICG injections. ConclusionsOur data demonstrate a predictive relationship between the occurrence/persistence of ICS post-PPV for VMT and the initial foveal status. Specifically, having preoperative ICS is a major risk factor for its persistence postoperatively. Our data highlight the pathophysiological importance of the vitreous phase and its effect on visual prognosis.

Comparison of microwave and furnace melting for glasses to immobilise Fe-corrosion products

ABSTRACTThis study reports a comparison between Fe-based corrosion products immobilised by direct vitrification through furnace melting versus microwave melting. Although microwave melting is faster, the Fe-corrosion product does not dissolve in the melt and is encapsulated by the vitreous phase. In comparison, for furnace melting, complete dissolution of the corrosion product in the glass is obtained till the solubility limits are exceeded. In both cases, Fe release is low indicating that either strategy may be employed for immobilisation depending upon the species captured in the Fe-corrosion product.

The structure of model glasses of the amorphous phase of glass-ceramic glazes from the SiO2[sbnd]Al2O3[sbnd]CaO[sbnd]MgO[sbnd]Na2O[sbnd]K2O[sbnd]ZnO system

In this work, particular attention was paid to the structural characteristics of the amorphous phase in glass-ceramic glazes from the SiO2Al2O3CaOMgONa2OK2OZnO system. The study was carried out on model glasses whose chemical composition corresponds to the chemical composition of the vitreous phase of the glazes determined on the basis of electron probe micro-analyzer (EMPA). Structural investigations of the obtained model glasses were carried out using the mid-infrared (MIR) and solid-state magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The solid-state MAS-NMR study carried out on 27Al and 29Si nuclei showed that all aluminum and silicon ions have tetrahedral coordination and thus form the glass network. The results of the 29Si solid-state MAS-NMR measurements also showed that with the increase of ZnO content in the glass chemical composition, the number of Q3 and Q2 silicon-oxygen units increases at the expense of Q4 (where n is the number of bridging oxygens), thus indicating an increase in the degree of depolymerization of the alumino-silico-oxygen network of studied of glasses. Analysis of the MIR spectra of the obtained glasses confirmed the conclusions from the solid-state MAS-NMR research, i.e. that Zn2+ ions cause depolymerization of the glass network of glazes. The weakening of the network of glasses resulted in lowering of the transformation and dilatometric softenings temperature. The tests carried out on model glasses allow drawing conclusions about the structure and properties of the vitreous phase of real glazes.

High-Temperature Mineral Phases Generated in Natural Clinkers by Spontaneous Combustion of Coal

The aim of this study is to analyze natural clinkers (= calcined clays by coal combustion) from a lower Cretaceous coal outcrop in Ariño (Teruel, NE Spain) in order to describe mineral and textural transformations produced during the spontaneous combustion of coal. To achieve this aim, samples were analyzed using X-ray diffraction and optical and electron microscopy. Spontaneous combustion resulted in the melting of the surrounding clays, with the generation of an Al–Si-rich vitreous phase. Subsequently, high-temperature phases crystallized from this vitreous phase. These new minerals are interesting due to their similarity with those formed during ceramic processes, used in the manufacture of stoneware and ceramic tiles, as well as in refractory ceramics, and with natural events such as metamorphic and igneous processes. The studied natural clinkers are composed of vitreous phase mullite, hematite, hercynite, cristobalite, quartz, pyroxenes, cordierite, gypsum, pyrite, and calcium oxides. A trend from hematite to hercynite composition indicates compositional variations at sample scale, which evidence d-spacing differences in hercynite and may be related to the Al and Fe content in hercynite depending on its texture. The mullite shows higher Si/Al ratio (1.21) than the theoretical composition (0.35), indicating that this mullite is more Si-rich. Three pyroxene-type compositions (diopside-type, ferrosilite-type, and a Ca–Al-rich pyroxene) were found. Both the mullite and the pyroxenes are nonstoichiometric.

Glass ceramic for the vitrification of high level waste with a high molybdenum content

Vitrification has been selected in France as the immobilization process for high-level waste arising from spent fuel reprocessing. Several high-level waste solutions from the reprocessing of legacy UMo spent fuel, used in gas cooled reactors, have been stored in the Orano La Hague facility in stainless steel tanks since the mid-1960s. A special glass-ceramic formulation has been developed and qualified through lab and pilot testing to meet standard waste acceptance criteria for the final disposal of the UMo waste. These solutions are very rich in molybdenum and phosphorus whose contents make the molten glass quite corrosive and require a high-temperature glass formulation to obtain sufficiently high waste loading factors (12% in molybdenum oxide). Molybdenum is known to be sparingly soluble in conventional borosilicate glass. The formulated glass-ceramic matrix comprises a major vitreous phase containing secondary phase particles less than 100 μm in diameter. These are formed by phase separation and crystallization as the molten glass cools. The physical and microstructural properties of the UMo glass in the solid and liquid states are reported here. Evolution of microstructure as a function of the cooling profile was investigated, given the sensitivity of the crystallization process to the cooling profile. The chemical durability of the UMo glass-ceramic was also studied. The feasibility of this process has been demonstrated in a full-scale pilot facility with inactive surrogate solutions.

Investigation of the effect of beef moisture content on the amount of bound moisture with the calorimetric method

With the development of food processing and storage at near-cryoscopic temperatures, more and more attention is being paid to the development of methods for frozen out moisture and cryoscopic temperature calculating based on their component composition data. There is a significant dispersion among the existing experimental data of various researchers and calculation methods for beef thermophysical properties. In the study given, the authors determined the enthalpy of phase transitions, beet heat capacity with different moisture content and its cryoscopic temperature with the method of differential scanning calorimetry. With the analysis of the phase transitions enthalpy, it was found out that the share of non-freezing water for beef is n = 0.35 (g of water per 1 g of dry matter). The presence of the vitreous phase in the temperature range of about -85 ° С was established, most noticeably manifested when the moisture content of the samples is w = 37–45.8%, which indicates the formation of amorphous solutions in the process of food products freezing. Beginning of moisture melting peak Tm.b. takes place at temperatures range from -35 ° C till -25 ° C for the samples with low and normal moisture content respectively. Acccording to the theoretical Heldman ratio, a dependence for cryoscopic temperature calculating was proposed . The given semi-empirical dependences of the phase transitions enthalpy and the frozen moisture fraction provide an increase in the accuracy of calculations at low values of moisture content in the product. The research results can be used as input data in mathematical modeling of heat exchange processes and the development of calculating methods for the thermophysical properties of food products based on their composition.

Glass softening kinetics in the limit of high heating rates.

Surface-facilitated, front-propagated softening of glassy materials is now a well-known phenomenon, which is common to stable vapor deposited glasses. As we demonstrate in our recent communication, this softening pathway is not unique to vapor-deposited vitreous phases and can be observed in ordinary melt-cooled glasses in the limit of high heating rates [Cubeta et al., J. Chem. Phys. 147(7), 071101 (2017)]. Expanding on this preliminary report, we use our thin-wire, quasi-adiabatic fast scanning calorimetry technique to investigate softening kinetics of micrometer scale, viscous liquid methylbenzene, and 2-propanol films, which are fully equilibrated at distinct temperatures near the compounds' standard glass hardening transition ranges. Heating of each sample with rates in excess of 105 K·s-1 results in softening kinetics that are well approximated by an Arrhenius temperature function. Remarkably, the apparent activation energy barriers to non-equilibrium, front-propagated softening matches the barriers to near-equilibrium self-diffusivity at the samples' initial temperatures. Furthermore, our analysis also shows an exceptionally strong correlation between the high temperature softening rate and the self-diffusion coefficients at low initial temperatures. Finally, our front softening velocities are also strongly dependent on the samples' initial states, much more so than previously observed. Based on these results, we propose an extended Wilson-Frenkel model of non-equilibrium phase transformations as a general theoretical framework to describe front propagated softening in glassy materials.

Receiving of Ceramic Veneer with the Use of Unsorted Container Glass Breakage

The results of studies on the production of ceramic material, which can be used for face veneer and pedestals are presented. This material was obtained on the basis of stiff clay with the addition of 30 % by weight of unsorted container glass breakage as a flux-hardening additive, which forms a vitreous phase during baking, and 2.5 % by weight of a fluxing agent that increases the amount of the vitreous phase and lowers the temperature of the liquid-phase sintering material. In turn, the vitreous phase acts as a binder in the bulk of the material due to the vitrification of the surface of the ceramic particles and their connection into a strong frame and creates the effect of self-glazing products. Studies have been conducted showing that the highest compressive strength and the lowest water absorption of the material being developed were obtained using boric acid as a fluxing agent and baking at a maximum burning temperature of 1050 °C.

The Formation of Pitted Features on the International Simple Glass during Dynamic Experiments at Alkaline pH

ABSTRACTThe forward rate of dissolution of the International Simple Glass (ISG) was determined under alkaline conditions at 40 °C using the Single Pass Flow Through (SPFT) method. Forward rates were consistent with those obtained in the literature for this glass composition. The formation of altered gel layers and surface pits was observed on the surface of glass particles, especially at the very highest pH values, despite the application of high flow rates to prevent the build-up of solubility limiting phases. These features could be attributed to preferential localized dissolution at sites with a higher alkali concentration or from a separate, less durable, vitreous phase. These results may indicate that surface pit and altered gel formation occurs under the forward rate of dissolution as imposed by the SPFT method, particularly for simplified borosilicate glass materials.

Polymer waste as a combustible additive for wall ceramics production

The research presents the experimental results devoted to the charge composition development for the production of wall ceramic products, based on low plasticity clay using additives. One of the additives is polymer waste in the amount of 15 wt. %, in particular it is unplasticized polyvinyl chloride used as a combustible additive for increasing ceramics porosity thus decreasing its density and consequently the load on the basement when the walls are constructed. Besides it decreases thermal conductivity and improves energy efficiency of developed wall ceramics application. Boric acid is a second additive used as a fuse thus reducing the temperature of ceramics liquid-phase sintering and forming a vitreous phase, which increases the strength characteristics and reduces water absorption, and therefore increases the product frost resistance. However the vitreous phase amount is insignificant and the products still are characterized by porosity sufficient for density and thermal conductivity reduction up to the level of conditionally effective thermal performance. Thus the application of the developed wall ceramics facilitate the production of energy effective products, which can be used for multi-layers walls construction providing modern thermal engineering standards and rational consumption of building materials. Herewith the developed materials properties correspond to the requirements of solid ceramic bricks used in Russian climatic conditions and help to combine the functions of bearing, heat-insulating and partly facing layers to a certain extend thus expanding their application.

Production of facing ceramic material using cullet

The research presents experimental results concerning the charge composition development for ceramics, used for cladding facades and basements of buildings and structures. The given composition is suggested to be based on the low plasticity clay as a basic component, which cannot be used to produce crackless, durable and frost resistant ceramics without introducing functional additives. The following functional additives were applied in the conducted experiments: boric acid, used as a fuse for the reduction of liquid phase sintering temperature and the increase of vitreous phase amount; various empties cullet, used as a fluxing and strengthening additive, which is the source of vitreous phase, forming the rigid frame of interconnected ceramic particles through a layer of vitreous phase. The research experiments stated that the highest compressive strength and frost resistance and the least water absorption can be achieved when 30 wt. % of colorless empties cullet and 2,5 wt.% of boric acid are introduced into the charge. Besides the research demonstrates the results of determining the dependence of bending strength, density, thermal conductivity, open and total porosity. The developed charge composition on the one hand stipulates the solution environmental and technical-economic problems of natural resources rational use and waste management, and on the other hand allows producing high quality facing ceramic products at a reduced cost and using low demand resources.

Pozzolanic Activity of Old Volcanic Tuffs of Mako Area (Senegal-Oriental, West African Craton): An Economic and Environmental Interest

The volcanic tuffs of Senegal-Oriental in Mako area are produced during a calc-alkaline volcanism which occurs in this region and which is dated from about 2.3 - 1.95 Ga. Despite their altered appearance, the X-Ray diffractions show mineral paragenesis: Quartz-Kaolinite-Illite and an important amorphous phase. On the Ternary Keil-Rankin diagram for the CaO-SiO2-Al2O3 the volcanic tuffs of Mako area are situated between pozzolan and the fly ash. The difference between silica and lime is greater than 34% in these volcanic tuffs. In this study, they have been mixed with Portland cement to obtain pozzolanic cements respectively with 20%, 30%, 35% and 40% of addition of volcanic tuffs. The pozzolanic reactivity is highlighted by the compressive strength increase until 90 days of conservation in water. It supposes that the vitreous phase of the volcanic tuffs reacts with the free CaO (CaOf) of Portland cement to produce new hydrated minerals. This study has a positive economic and environmental impact. Because the time of grinding of pozzolanic cements is reduced. Also, the addition of volcanic tuffs reduces the production of clinker, then the CO2 emission.