Redox behavior of glasses doped with copper and arsenic, antimony or tin

Soda-lime-silicate glasses (16Na2O-10CaO-74SiO2, in mol %) doped with copper and arsenic were studied by high temperature UV-vis spectroscopy. The base glass is a model for sheet glasses. Arsenic was one of the classical fining agents and is still used as an oxidizing additive in heavy metal oxide glasses. During heating, the Cu2+ absorptivity slightly decreased up to a temperature of 470 °C. At further increasing temperatures, the absorptivity decreased more notably and after reaching a minimum at temperatures >600 °C strongly increased again. At smaller heating rates, the minimum was more pronounced and was shifted to lower temperatures. This was explained by the redox reaction: 2Cu2+ + As3+ ↔ 2Cu+ + As5+ This reaction is shifted to the left during heating. At temperatures 600 °C, it is in equilibrium. In-between, the kinetics play an important part. Rate constants of the redox reaction were determined from relaxation times. The rate constants showed Arrhenius behavior and were inserted into a kinetic differential equation. Numerical solutions of this differential equation were in good agreement with the results from high temperature spectroscopy. The activation energy is 210 kJ∙mol-1. This value is much smaller than the activation energy of viscous flow and hence the rate determining step is assumed to be the diffusion of Cu2+. Sodium borasilicate glasses (25 Na2O-15 B2O3-60 SiO2, in mol%) doped with copper and arsenic, antimony, or tin as redox agents were studied by optical absorption spectroscopy in the temperature range from 25 to 620 °C. In general, the redox agents decrease the Cu2+-concentration in the glasses. Increasing the temperature to 620 °C resulted in a shift of the Cu2+ absorption band from 12,600 to 11,800 cm-1. In glasses solely doped with copper or with copper and tin, the absorptivity decreased by about 5 % in that temperature range. In principle, glasses doped with both copper and arsenic or antimony showed the same behaviour up to a temperature of 420 °C. For these glasses, heating to higher temperatures resulted in a minimum absorptivity at around 540 to 500 °C and a subsequent strong re-increase in absorptivity. The rate constants showed Arrhenius behavior and were inserted into a kinetic differential equation. The activation energy are 270 kJ.mol-1 (Cu/As) and 265 kJ.mol-1 (Cu/Sb). During cooling from 620 °C, a steep decrease in absorptivity down to a temperature of 520 °C and after passing through a minimum a slight re-increase was observed. The Cu2+ concentration, and hence the absorptivity after cooling depends on cooling rate (10 to 0.5 K·min-1)

Melting behaviour of waste glass cullet briquettes in soda-lime-silica container glass batch

The melting behaviour of representative container glass batch with and without the addition of 15wt % briquettes produced from waste cullet fine particles was investigated in the context of reducing both waste and glass melting energies. Carbonate raw material decomposition and reactions during melting were studied by DTA-TGA-MS. The decomposition kinetics of two batches, representing typical container glass batches with 0% and 15% briquette additions, were calculated by transformation degree based on the Ginstling-Brounstein and Arrhenius equations. High temperature phase transitions and fractions of silica reaction in each batch were obtained from X-ray diffractometry (XRD). The briquette additions accelerated the decomposition reactions and the silicate reaction kinetics by decreasing the activation energy for carbonate decomposition. Silica sand in the batch was shown to melt at lower temperatures with the addition of briquettes. Batch melting processes at different temperatures and briquette melting on top of the molten glass at high temperatures, were investigated by macroscopic investigations of sample cross-sections post-melting. The positive effects of briquette additions to container glass batches, in terms of increased melting rate and reduced batch reaction and decomposition temperatures, are supported by the results of this study

Improve melting glass efficiency by Batch-to melt conversion

AbstractSoda–lime silicate glasses are composition used recently in container, table ware, float glass, etc. Most of soda-lime silicate glasses are produced by major component sand (silica, SiO2), soda ash (Na2CO3) and lime stone (CaCO3) by adding effective minor additive such as dolomite (CaMg(CO3)2), sodium sulfate (Na2SO4), alumina (Al2O3), etc. During melting process, around 550°C, soda ash is reacted with lime stone to produce sodium calcium carbonate, Na2CO3(s) + CaCO3(s) ⇒ Na2Ca(CO3)2, melting at 780°C. Sodium calcium carbonate is reacted with sand generate formation of sodium silicate and wollastonite, Na2Ca(CO3)2 + 2SiO2 ⇒ Na2SiO3 + CaSiO3 + 2CO2, at 900°C. The alternative way of Batch-to Melt conversion is to replace lime stone by natural wollastonite (CaSiO3). This reaction has occurred by crossing over the step of the reaction Na2Ca(CO3)2. This means that the melting process can be emerged easier than batch with lime stone; batch with wollastonite requires lower energy. From the calculated thermodynamic exploited heat of glass batch includes wollastonite which is required 10% lower than using lime stone. When the lime stone is replaced by wollastonite, the kinetic is investigated by Thermal gravity and Differential Scanning Calorimeterv (TG/DSC). Then the next analysis is the melting process of both batches by using Batch-Free Time method with the same condition. The concern of wollastonite is minor impurity, especially iron oxide (Fe2O3), because iron can present in green color for clear glass production. From this experiment, wollastonite can be replaced lime stones and some parts of silica. Regarding to this experiment, batch containing wollastonite melts easier than lime stone batch. In conclusion, the results demonstrated that the two composite glasses were of the same properties

Modification of silicophosphate glass composition, structure, and properties via crucible material and melting conditions

Abstract Ceramic crucibles are known to corrode in contact with glass melts. Here, we investigate the effect of alumina and fused silica crucibles on the composition, structure, and properties of silicophosphate glasses. Glasses in the system 0.3 Na2O‐0.6 P2O5‐0.1 SiO2 were melted in platinum, alumina, or fused silica crucibles at 900°C or 1200°C for 0.5‐12 hours. Al2O3 and SiO2 were found to leach from the crucibles into the glass melt and alter the glass composition: Al2O3 content increased with melting temperature and time, resulting in up to 10 mol% Al2O3; SiO2 from fused silica crucibles was also introduced into the glass, resulting in a 25% higher SiO2 content compared to the nominal composition. Glass density, transition temperature, thermal expansion, and mechanical properties were strongly affected by these compositional changes. Based on vibrational spectroscopy, this is explained by increasing numbers of P–O–Al or P–O–Si bonds, resulting in a depolymerization of the phosphate network, and ionic cross‐linking by high field strength aluminum or silicon ions. With increasing alumina content, P–O–Si bonds were replaced by P–O–Al bonds. 31P and 27Al MAS NMR spectra revealed that aluminum is present in sixfold coordination exclusively and fully bonded to phosphate species, connecting phosphate groups by P–O–Al–O–P bonds

Relating type of mold materials to crystal morphology and properties of glass-ceramics with YSZ additions as a dental material

YSZ was added to glass frit in order to improve properties of the glass-ceramic dental materials by casting into a graphite mold and a cast iron mold and then crystallized via heat treatment. XRD results presented the similar crystalline phases of phlogopite-calcium mica and tetragonal zirconia in both molds. Microstructures by SEM showed the different crystal morphology due to casting molds. The slow cooling of graphite mold produced the equiaxed crystals whereas the fast cooling of cast iron mold promoted rod-like, and YSZ addition increased the number of crystals. The properties depended on the crystal morphology and crystallinity. The 5 wt% YSZ added glass-ceramic from graphite mold developed the equiaxed crystals to present the desirable properties of 147.15 MPa, flexural strength, 251.80 µg/cm2, chemical solubility and 9.26 × 10-6/°C CTE. The results were accepted by ISO 6872:2015 (Dentistry-Ceramic Materials) in type II class 2b as a partially and fully covered single substructure and matched with commercial porcelains

The influence of yttria-stabilised zirconia and cerium oxide on the microstructural morphology and properties of a mica glass-ceramic for restorative dental materials

The addition of yttria-stabilized zirconia and cerium oxide to this mica glass ceramic was found to increase mechanical properties and decrease chemical solubility. They were also found to be able to control translucency. X-ray diffraction showed no significant change in phase formation with phlogopite-Ca mica, fluorapatite and tetragonal zirconia the main phases present with their addition. Scanning electron microscopy showed that the additives did affect the grain morphology significantly and this was the controlling factor in the observed changes in strength, hardness, and solubility. The microstructures consisted of mainly plate-like and interlocking crystals. The largest increased in strength and hardness and the largest decreased in chemical solubility can be attributed to the largest change in grain morphology by the addition of both the YSZ and CeO2. The values of hardness, biaxial flexural strength and chemical solubility were 3.5\u20136.2 GPa, 105\u2013120 MPa and 142\u2013732 \ub5g/cm2, respectively making them acceptable for dental materials according to ISO 6872:2015. The addition of YSZ increased the opacity, whilst the CeO2 improved translucency and influenced the color to a yellowish to yellow-brownish shade close to Thais\u2019 teeth