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On-site pXRF analysis in various French collections (Musée du Louvre, Musée national des Arts asiatiques-Guimet, Paris) of porcelains decorated with painted enamels from the Qing Dynasty, in particular porcelains bearing an imperial mark, identifies the types of enamels/glazes, the ions and coloring phases or the opacifier. The study of the elements associated with cobalt (nickel, manganese, arsenic, etc.) and of the impurities of the silicate matrix (yttrium, rubidium and strontium) differentiates the use of ‘Chinese/Asian’ raw materials from ones imported from Europe by the initiative of the European missionaries (chiefly Jesuits) present at the Court (Beijing). Particular attention is paid to the analysis of the blue color of the marks and to the elements associated with the use of gold or copper nanoparticles as well as to the compositions of the pyrochlore phases (tin yellow, Naples yellow). The comparison is extended to pXRF and Raman microspectroscopy measurements previously made on other Qing imperial porcelains as well as on Cantonese productions (on porcelain or metal) from different Swiss and French museums and blue-and-white wares of the Ming and Yuan Dynasties (archaeological and private collections).

Inorganic fibers and opacifiers are indispensable for improving the strength and high temperature insulation performance of the fumed silica-based thermal insulation material. However, zirconia fiber enhances the strength of the fumed silica-based thermal insulation material and reduces the radiative heat transfer to replace the opacifier. The sample of fumed SiO2/Al2O3 doped with 7% zirconia fiber (FZ7) has a lower density of 0.70 g/cm3 and a high porosity of 75.0%. In addition, the thermal conductivity of FZ7 at 800 °C is 0.077 W/(m·K), which is lower than the sample of fumed SiO2/Al2O3 doped with 7% glass fiber (FG7) and 0.089 W/(m·K) at 800 °C. The effective extinction coefficient of the thermal insulation material containing zirconia fiber is larger than that of the glass fiber by Fourier transform infrared spectroscopy analysis and calculation, indicating that the zirconia fiber has a distinct absorption and scattering effect on infrared radiation to reduce the radiative heat transfer. Therefore, zirconia fiber enhances the strength and decreases the high temperature thermal conductivity of the composites with the dual effect on the insulation and mechanical performance of the fumed silica-based thermal insulation material.

PURPOSE: To evaluate the color stability and mechanical properties of two commonly used maxillofacial silicone elastomers after addition of pigments and opacifiers and before and after artificial aging. MATERIALS AND METHODS: This study evaluated two maxillofacial silicone elastomers: A-2000 and M511. Two different pigment and opacifier systems (e-Skin and Reality Series) were used with the elastomers. Control groups (no pigment or opacifier) and experimental groups (each with subgroups containing additional pigments and/ or opacifiers) were fabricated for each of the silicone elastomers. A total of 51 specimens were evaluated for color stability, and 100 for mechanical properties. A spectrophotometer was used to assess CIE L*a*b* values before and after aging. CIELAB 50:50% perceptibility threshold (ΔE* = 1.1) and acceptability threshold (ΔE* = 3.0) were used to interpret color changes. A durometer and universal testing machine were used to evaluate the mechanical properties. ANOVA and Fisher least significant difference (LSD) test were performed to determine the statistical significance of the results (P < .05). RESULTS: Significant differences in color measurements (ΔE*) were found for all silicone groups following artificial aging (P < .05). ΔE* values for the mixed pigment/opacifier subgroups of both elastomers were below the perceptibility threshold. Additionally, after aging, the hardness, tear strength, and tensile strength significantly increased for all silicone groups (P < .05), while percent elongation significantly decreased (P < .05). CONCLUSION: Artificial aging affected the color stability and mechanical properties of the pigmented silicone elastomers with added opacifier. Overall, A-2000 with e-Skin group displayed the most color stability, with its mechanical properties being the least affected by artificial aging.

As compared with silica aerogels, alumina aerogels have excellent high-temperature stability, and hence, are regarded as a promising candidate for high-temperature thermal insulation materials. However, heat transfer mechanisms for such materials remain insufficiently explored. In this study, based on real material microstructures, an analytical thermal conductivity model for alumina aerogel-fiber-opacifier composites is developed via a modified parallel-series equivalent electrical circuit approach. The model takes into account solid, gaseous, and solid-gas coupling heat conduction in aerogels, solid heat conduction in both fibers and opacifier particles, and radiation in aerogels, fibers, and opacifier particles. The model is validated by comparing its predictions with measured thermal conductivity data. The model predictions reveal that there are two kinds of solid-gas coupling heat transfer mechanisms, which occur in the corner regions between interconnected secondary particles and in the slit regions between adjacent chains, respectively. Because of this coupling, the contribution of gaseous heat conduction is comparable to that of solid heat conduction and radiation of aerogels, fibers, and opacifier particles, which is well supported by experimentally measured data of thermal conductivity. The model is also used to analyze effects of various parameters on the thermal insulation performance of the composites, such as diameters and volume fractious of both fibers and opacifier particles.

TiO2 is a potential alternative opacifier to ZrSiO4, but it is restricted because it easily causes glaze yellowing due to the formation of rutile. Herein, the CaCO3-TiO2 composite with close interface combination was added into the raw glaze for sanitary ceramics to prepare white glaze with negligible radioactivity. The glaze added CaCO3-TiO2 exhibits the surface properties similar to the glaze added ZrSiO4 and its excellent opacifying effect with L* value of 89–94 is achieved by the crystallization of titanite. Moreover, the optimal glaze added CaCO3-TiO2 shows a white surface with b* value of 2.73, while the glaze added pure TiO2 shows a yellowish surface with b* value of 7−10. Mechanism analysis indicates that the tight interface combination between CaCO3 (CaO) and TiO2 can promote their combination reaction to form perovskite and further promote the formation of titanite. Therefore, the formation of rutile is inhibited, resulting in the white glaze surface.

Ternary mullite fibrous felt/opacifier/aerogel composites (MYTC) were prepared by impregnating the TiO2 opacifier/Y2SiO5 aerogels into mullite felts. The effect of the TiO2 opacifiers on the thermal insulation property of aerogel composite was investigated by adjusting the TiO2 opacifier contents from 0 to 15 wt%. The as-prepared MYTC exhibited low density of 0.195 g/cm3 and low thermal conductivity of 0.042 W/m/K. The high-temperature resistance of MYTC was tested using a self-designed thermal insulation test system. It was found that the addition of Y2SiO5 aerogels and TiO2 opacifiers significantly improved the thermal insulation performance of aerogel composites. The results demonstrated that MYTC showed more efficient heat insulation property as the back surface temperature of the MYTC was 157 °C lower than that of the mullite fiber felts as the front surface temperature of both was about 1200 °C. The as-prepared MYTC exhibited excellent high-temperature thermal insulation performance, making the materials potential application to high-temperature thermal insulation.

An experimental investigation is carried out to study the effect of operating parameters such as filling ratio, input heat, number of wick layers and thin coated wick on the thermal performance of a heat pipe .A film coating is a thin polymer- based coat applied to wick .the thickness of such a coating is usually between 20-100 micro meter .film coating formulations usually contain the following components: polymer, plasticizer, colourant, opacifier, and solvent. Coated material is a covering that is applied to the surface of an object ,the purpose of applying the coating may be decorative ,functional, or both ,The coating itself may be an allover coating, completely covering the substance, Functional coatings may be applied to change the surface properties of the wick, demineralized water used as working fluid. The total thermal resistance decreases with increasing filling ratio until filling ratio around between 0.5 and 0.6 then increases with increasing filling ratio, The total thermal resistance decreasing with increasing the number of coated layers of wick ,The total thermal resistance decreases with increasing heat input .

The reduction of radiation heat transfer in VIPs is an important issue. In VIPs, the radiation heat transfer is reduced by the use of opacifier. However, the amount of opacifier also significantly affects the cost of VIP. In this study, the effect of different types and sizes of opacifiers on VIP thermal conductivity was investigated. For this purpose, 6 VIP samples containing different opacifiers (SiC, graphite and calcium aluminate in 3 different grain sizes) were produced. Fumed silica, glass fiber and opacifier were used as fillers in VIP cores at 65%, 20% and 15% (by mass), respectively. VIP samples were vacuumed up to 0.1 Pa, and their thermal conductivity coefficients were measured according to TS EN 12667 standard. In addition, transmittance ratios (%T) of fumed silica, glass fiber, opacifiers and core samples were measured by FTIR spectrophotometer and the mass extinction coefficients of each sample were calculated. The silicon carbide (F1000) as the opacifier (e: 399 m(2) kg(-1)) and the graphite-containing core among the VIP core samples (e: 149 m(2) kg(-1)) exhibited the highest mass absorption coefficient. In addition, the thermal conductivity of the core samples without barrier was measured under 1 Pa vacuum and then the radiation conductivities were calculated from the obtained data. F800 type SiC significantly reduced radiation heat transfer, while the solid conduction of the core was increased due to its relatively coarse grain size. VIP sample with SiC (F1200) provided the lowest thermal conductivity at 0.1 Pa (3.94 mW mK(-1)). As a result, F1200 type SiC was found to be the most efficient type of opacifier among the investigated opacifiers.

High performance thermal insulation material was prepared by fumed silica as thermal insulation matrix, white cement as binder. SiC powder was incorporated as an opacifier. Short glass fibers were added to increase stiffness and minimize contraction. The samples were produced within 4 days under ambient pressure with no complicated equipment. The influences caused by white cement amount on the properties were investigated to achieve the optimal performance. A low thermal conductivity 0.033 W·m−1·K−1 at 25 °C and a low thermal conductivity 0.038 W·m−1·K−1 at 800 °C were achieved based on the experimental results. The linear shrinkage of the insulation up to 800 °C in air for 30 min was 7.54%. In addition, the insulation exhibited a compression stress above 0.15 MPa (3% strain). The relation between structure and performances was revealed. That we here publicly reported thermal insulation materials synthetized by nano-powder and inorganic binder might reveal a new method for synthesis high performance thermal insulation materials. Based on the simplicity of the manufacturing process, the optimized material properties and cheap cost of raw materials, we believe this technology can act as an effective thermal insulation material for buildings and myriad applications requiring improved thermal efficiency.

Non-invasive methods including micro-Raman spectroscopy (μ-Raman), micro X-ray fluorescence (μ-XRF), fibre optics reflectance spectroscopy (FORS) and environmental scanning electron microscopy (ESEM) were used to study thirty-five ceramic shards from Afrasiyab and forty-seven potshards from Nishapur. These shards are dated from the ninth to the tenth century AD and include various types of underglaze and inglaze decoration. Non-invasive scientific studies indicated that tin oxide was employed as a white opacifier in both sites while silicates including quartz, olivine, diopside and feldspar served as opacifier in Afrasiyab shards thus demonstrating a technological connection with the pre-Islamic tradition of glaze opacification. The white slip of most of the wares excavated at Nishapur contained dehydrated pyrophyllite which may be indicative of local production. Furthermore, while a dense distribution of chromite was found in the black underglaze decoration of the so-called yellow staining black ware from Nishapur, a diluted chromite probably obtained from a different source was used in the imitated lustre wares from Afrasiyab. Mixtures with different proportions of manganese oxide and black haematite were utilised as the black colouring agents. Taking all of these findings into account, it is proposed that a consistent ceramic technology and production is represented by the entire set of the shards from Afrasiyab while different materials and technologies are evinced in the Nishapur ceramics.

Poly(methyl methacrylate) (PMMA) bone cement is used to anchor the majority of total joint replacements (TJRs). Many brands of cement are used, both with and without the addition of antibiotics to reduce the risk of infection. The present study involved determination of various parameters in tensile fatigue loading: (1) energy absorbed (U) vs number of loading cycles (N) and creep strain (e) vs N, during fatigue tests on specimens of an antibiotic-containing cement (SmartSet GHV) and a plain cement (CMW1) and (2) crack length (a) vs fatigue loading cycles (N) and crack growth rate (da/dN) vs Mode I stress intensity factor range (ΔKI), during Fatigue Crack Propagation (FCP) tests. In the fatigue tests, four different sample types (round, machined; round, directly moulded; rectangular, machined, and rectangular, directly moulded) and tension-tension loading were used. In the FCP tests, compact tension specimens under tension-tension loading were used. It was found that there were limited effects of sample type, except at the highest stress levels, but that these two cements had different rates of crack propagation. These differences were reflected in the fracture surfaces with SmartSet GHV showing accumulation of opacifier around the particles and crack progression around the initial beads, while for CMW1 the opacifier was evenly distributed and the cracks went through the initial beads.

A novel method was developed to uniformly disperse sub-micron TiO2 opacifier into fiber reinforcements using agar and silica as binders via freeze drying. TiO2 opacifier/ fiber/ alumina-based aerogel ternary (TFA) composites with high strength and excellent high-temperature thermal insulation were successfully prepared by sol-gel route, impregnation process and supercritical fluid drying. The microstructure, mechanical and thermal insulation properties of TFA composites were investigated comprehensively. The results show that the mechanical property of TFA composites can be significantly enhanced by mullite fiber felt and the incorporation of SiO2 binder. The effect of TiO2 opacifier on the high-temperature thermal conductivity was studied by adjusting the content of TiO2 from 0 to 15 wt%. The obtained TFA composites exhibit high Young's modulus of up to 3.58 MPa and low high-temperature thermal conductivities of 0.129 W/m·K at 800 °C and 0.168 W/m·K at 1000 °C, respectively. The mechanism of heat transfer in TFA composites at high-temperature was also analyzed.

This study investigated the effects of inorganic silicone coatings on the load resistance of heat treated glass beams. The authors performed destructive load tests on 192 heat treated glas...

The processing and validation of the zircon sand concentrate process into the zircon opacifier have been carried out. The purpose of this research was to determine the optimal processing conditions and the process validation parameters, namely the production repeatability, and product consistency. The optimum conditions were zircon sand concentrate 100 g was roasted with 15% NaOH at 400 °C for 3 hours, zircon opacifier leaching with 0.1 N HCl for 2 hours, drying at 105 °C, and milling until particle size escapes 200 mesh. The dominant mineral in the zircon opacifier by the XRD method was zirconium silicate (ZrSiO4). The processing zircon sand concentrate with seven replications, an average weight of zircon opacifier was obtained: (92.754 ± 1.707)%, and the production repeatability was 98.293%. So, the production repeatability was quite satisfying. The zircon opacifier composition from the seven replication processing, was obtained 10 oxides, including ZrO2: (85.220 ± 0.124)%, SiO2: (8.760 ± 0.206)%, HfO2: (2.475 ± 0.013)%, Al2O3: (1.183 ± 0.024)%, TiO2: (0.364 ± 0.018)%, Fe2O3: (0.131 ± 0.003)%, etc, the standard deviation of composition test results was 0.146% - 4.839% (lower than 5%), meaning that the consistency of the product was satisfactory.

The purpose of this work is to produce more excellent opaque wall tile glazes by using sapphirine instead of zirconium silicate as an opacifier. In order to achieve it, the chemical compositions were precisely adjusted in the system of SiO2-Al2O3-MgO-K2O-Na2O-B2O3. The morphological characteristics of the glaze were determined by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). And the optical properties of the glaze were characterized by a spectrophotometer and a gloss meter. The results reveal that well-shaped crystals of sapphirine (Mg2Al4SiO10) with needle-like morphology were formed as only crystal phase. The glaze is provided with better opacity whiteness and gloss compared with commercial zircon-based glass-ceramic glazes, and it is mainly composed of cheap mineral raw materials. Those features make it as an alternative one for improving the properties of conventional opaque ceramic glazes.

Opacifiers are usually doped in the silica aerogels to reduce the radiative heat transfer at high temperature. However, the doped opacifiers will enhance the heat conduction in the solid phase and increase the density of silica aerogels dramatically. For developing lightweight and efficient opacifiers, in this paper, different types of core/shell opacifiers are designed, and their extinction performance is investigated, theoretically. Then the optimal temperature-dependent particle size and doping amount of these opacifiers are obtained by maximizing the Rosseland mean extinction coefficient and minimizing the total thermal conductivity of silica aerogel composite. The results show that the hollow carbon black opacifiers might greatly reduce the densities of the opacifier-doped silica aerogels without deteriorating appreciably their insulating capability, and the carbon/SiC, carbon/TiO2 and carbon/Al2O3 core/shell opacifiers exhibit excellent extinction performance and would be strong candidates for high temperature due to their high extinction performance, low density and high-temperature stability. Finally, a core/shell opacifier-gradient-doped silica aerogel based on the optimal opacifier types and doping amount is designed, which significantly improves the insulating performance and reduces the density of silica aerogel composite. The results of this paper present important references for the process design and improvement of comprehensive performance of opacifier-doped silica aerogels.

This paper investigated the effects of laboratory synthesised rocket composite propellants’ formulations on propellant performance parameters using response surface methodology (RSM). For the sake of a safe environment, the propellant is made of chemical constituents that have less severe effects on air quality. Experimental measurements of propellant performance parameters were carried out using the ballistic evaluation method. The thrust generated during combustion, the burn time and the propellant combustion temperature were measured using a data acquisition facility equipped with a button load cell and a thermocouple. Specific impulse, density, temperature, characteristic velocity, molecular weight and heat ratio were computed from the measured parameters. The resulting optimum rocket composite propellant formulations were 65.1%, 18.1%, 9.1%, 3.6%, 2.2% and 1.9% for the oxidiser, binder, fuel, opacifier, burning rate enhancer and catalysts, respectively. The corresponding performance indices i...

This study focuses on a group of decorated glass beads (twelfth–tenth century BC), belonging to a larger assemblage that was excavated from the prehistoric burial tumulus at Lofkend, Albania. The bulk glass, opaque glass decorations, and corroded areas were examined and analyzed using variable pressure-scanning electron microscopy with energy-dispersive spectroscopy (VP-SEM-EDS) and X-ray diffraction (XRD). The four glass beads analyzed were made using a plant ash-based alkali and colored with an iron containing chromophore which gave the glass its dark green color. Calcium antimonate was the predominant white opacifier used. Sodium antimonate was found as the opacifier in one sample. Its occurrence is likely accidental and formed due to a low concentration of calcium in the glass. Lead antimonate was identified in one sample and, along with calcium antimonate which was also present, would have acted as an opacifier for the white glass.

The paper presents aerogel SiO2–TiO2 composites used for thermal insulation of hydrothermal reactor for biomass-to-hydrogen conversion and the method of their production. The technology of aerogel composites production includes the following stages: ion exchange of liquid Na-glass resulting in production of silica hydrosol; hydrosol concentration; hydrogel production and its maturing; SiO2–TiO2 alcogel production; modification of its surface; subcritical drying of alcogel resulting in production of SiO2–TiO2 ambigel; its thermal treatment, granulating and classification. The influences of infrared opacifier (titanium dioxide) and thermal treatment temperature of SiO2–TiO2 composite on its structural and thermal characteristics have been investigated. Possibilities of hydrogen yield increase by reduction of power waste by means of vacuumized thermal insulation for reactor walls have been examined.

A facile and effective polymer-derived ceramics (PDCs) emulsification-crosslinking-pyrolysis method was developed to fabricate SiCN@TiO2 core-shell ceramic microspheres with polyvinylsilazane (PVSZ) and tetrabutyl titanate (TBT) as precursors. The TBT: PVSZ mass ratios, emulsifier concentrations and the pyrolysis temperature were examined as control parameters to tune the size and morphology of microspheres. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the synthesized SiCN@TiO2 microspheres to be comprised of SiCN core coated with TiO2 crystals, with an average size of 0.88 μm when pyrolyzed at 1400 °C. The analysis of Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) ensured that SiCN@TiO2 core-shell ceramic microspheres composed of rutile TiO2, β-SiC and Si3N4 crystalline phases, The thermal properties were characterized by thermogravimetric analysis (TGA). The obtained SiCN@TiO2 core-shell ceramic microspheres were the promising candidate of the infrared opacifier in silica aerogels and this technique can be extended to other preceramic polymers.

Radiative properties such as spectral extinction coefficient, Rosseland mean extinction coefficient and radiative thermal conductivity are the key features of porous insulation materials. For silica aerogel composites with fiber and opacifier, it is difficult to determine the spectral extinction coefficient and radiative thermal conductivity via experiment accurately. The spectral extinction coefficient of such composites is usually determined by a transmittance test using KBr as a diluent. The traditional model has several assumptions on determining the extinction coefficient from the transmittance measurement: the diluents are assumed as a pure transparent medium, the pressed pellet has no reflection, and the composite powder is in series with the KBr when calculating the effective thickness of the composite. Thus, the extinction coefficient determined from the traditional model with these assumptions will result in some uncertainty on predicting the radiative thermal conductivity. To overcome the drawbacks, improved models are proposed by considering the absorption of KBr diluents, sample reflection and random distribution of sample powder in the diluents. KBr diluted silica aerogel composite pellets with the same constituents and concentrations but different thicknesses are prepared using the pressed pellets method. The transmittances of the pressed pellets are measured by Fourier transform infrared spectroscopy (FTIR). The spectral extinction coefficients are calculated from the measured transmittances with proposed models. The radiative thermal conductivity of silica aerogel composite is calculated with the measured Rosseland mean extinction coefficient determined from different models. This study found that the developed models could eliminate the assumptions of the traditional model.

The thermal insulation material composed of fiber-reinforced fumed silica (in the raw and opacified with silicon carbide, zirconia or titania powders) was produced and analyzed. Optical properties (scattering and absorption coefficients) were experimentally examined in the spectral range of 0.9 – 4.7 µm by the solution of the inverse problem of radiative transfer. The inverse problem was based on the invariant embedding equation and the measured spectral directional-hemispherical reflectance. The effect of silicon carbide opacifier addition on the optical properties, effective and radiative thermal conductivity was estimated. The calculated radiative thermal conductivity of thermal insulations with various volume fractions of SiC opacifier was compared to the one deduced from the effective thermal conductivity using the calorimetric technique of conductive and radiative components separation. The effective thermal conductivity was measured by the quasi-stationary technique in the temperature range of 373 – 1173 K. The results of the inverse problem solution were compared to the calculations based on the Mie theory and the measured size distribution of silicon carbide particles. The experimental scattering coefficient was shown to be smaller than the calculated one. At the same time, absorption coefficients demonstrated mutual consent. Possible uncertainties in SiC powder size and the complex refractive index of the basic material were considered as a probable explanation of the obtained results. The size distribution of SiC opacifier was numerically optimized to obtain as low Rosseland mean radiative thermal conductivity as possible. The influence of the opacifier chemical composition was analyzed by collating radiative thermal conductivity deduced from the measured effective thermal conductivity to ones calculated using Mie theory. Finally, the effect of Fe2O3, Si3N4, TiO2, graphite, ZrO2, TiN, TiC, AlN opacifiers was numerically analyzed using Mie theory. Compounds based on titanium and an iron sesquioxide were shown to be promising opacifiers for high temperature applications.

The composition and production of pre-modern glazed tiles in Pakistan are not well understood. Here, 38 glazed tile samples sourced from various monuments at Makli Hill and Lahore Fort in Pakistan, dating mainly from the sixteenth and seventeenth centuries CE, were investigated with scanning electron microscopy and energy dispersive X-ray spectrometry for a comprehensive technological study to understand the methods used in their production. The analyses were supplemented by laser ablation-inductively coupled plasma-mass spectrometry to more fully characterise the raw materials used for the glazes. The Makli tile bodies are composed of clay-based ceramic whereas those from Lahore are stonepaste. Both are coated with soda-lime-silica glazes made using plant ash. Cobalt, copper, lead‑tin yellow and lead‑tin orange are identified as the glaze colorants. White glazes do not have an added opacifier or colorant, but are white due to the presence of an underlying layer of silica particles. Technological variations between the Makli and Lahore tiles are highlighted in the discussions, the former found to resemble traditional kashi ware of Sindh-Multan in their make-up, while the latter matches Mughal tile-work that prevailed for a while locally in the seventeenth century.

Eighteen glazed objects from Nimrud, Hasanlu and Borsippa dated to a period from the ninth to sixth century BCE were analysed by micro X-ray fluorescence (μ-XRF), X-ray diffractometry (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) and micro-Raman spectroscopy (μ-Raman). While calcium antimonate (CaSb 2 O 6 ) and lead pyroantimonate (Pb 2 Sb 2 O 7 ) were the main white and yellow opacifiers of the glazes, respectively, white sodium antimonate (NaSbO 3 ) was also sporadically observed in the Nimrud glazes. Copper sulphide associated with cassiterite (SnO 2 ) was used as colouring agent – or probably as opacifier – in a green glaze from Hasanlu. Cassiterite associated with the slag of Cu-Sn copper alloys was also observed in a green glaze from Nimrud suggesting a close tie between metallurgy and glaze-making. Pyromorphite (Pb 5 (PO 4 ) 3 Cl) and arsenian pyromorphite were observed in spherical forms embedded in the yellow glazes of Nimrud and Borsippa.

Due to pure silica aerogel is fragile and nearly transparent to 3–8 μm infrared beam, reinforced fiber and opacifier are composited with silica aerogel to optimize its performance. The suppression of radiative heat transfer is related to opacifier type, size and content. However, the addition of opacifier will enhance solid conduction inevitably. In addition, the influence of doping opacifier will also be affected by temperature since thermal radiation is temperature and wavelength dependent. Therefore thermal conductivities of 10 fiber and opacifier doped silica aerogel composites are studied experimentally and theoretically. Transmittances of silica aerogel doped with opacifier of different type, size and content are measured within 1.4–25 μm by FTIR. The spectral extinction coefficient of fiber/opacifier loaded silica aerogel composite is obtained by considering the practical absorption of KBr diluents. The thermal conductivity of silica aerogel composite is measured by transient plane source method at different temperature and gas pressure. Effective model with considering heat conduction via gaseous molecules, matrix skeleton, fiber, opacifier and thermal radiation via skeleton, fiber and opacifier is developed for fast predicting the thermal conductivity of fiber/opacifier doped silica aerogel composite. It is found that the silica aerogels doped with SiC or TiO 2 particles has lower radiative thermal conductivity than that doped with ZrO 2 particles with volume fraction of 3.75% and diameter of 3.5 μm. Silica aerogel doped with 3.75%, 3.5 μm SiC particles has the lowest thermal conductivity at temperature less than 1000 K.

A novel sol-gel chemistry approach was developed to enable the simple integration of a cast-in-place, ambiently-dried insulation into high temperature applications. The insulation was silica-based and synthesized using methyltrimethoxysilane (MTMS) as the precursor. MTMS created a unique silica microstructure that was mechanically robust, macroporous, and superhydrophobic. To allow for casting into and around small, orthogonal features, zirconia fibers were added to increase stiffness and minimize contraction that could otherwise cause cracking during drying. Nano-sized titania powder was incorporated as an opacifier to reduce radiative heat transport. To assess relevance to high temperature thermoelectric generator technology, a comprehensive set of materials characterization experiments were conducted. The silica gel was thermally stable, retained superhydrophobicity with a water contact angle >150°, and showed a high electrical resistance >1 GΩ, regardless of heating temperature (up to 600 °C in Ar for 4 h). In addition, The silica-based thermal insulation exhibited a Young's modulus ∼3.7 MPa and a low thermal conductivity

Silica aerogel as a super-insulating material is widely used in thermal protection system of spacecraft and aircraft. However, the significant radiative heat transfer causes obvious deterioration in the insulation capability of silica aerogel at high temperature because the pure silica aerogel is almost transparent to infrared radiation in such a spectrum range. Doping fibers or opacifiers could greatly improve the thermal insulation properties at high temperature. In this paper, we determine the optimal temperature-dependent size for typical opacifiers and silica fibers by calculating radiative properties. Suppose that the opacifier particles are spherical and the fiber is an infinite cylinder. According to the Mie scattering theory, the extinction efficiency factor of single opacifier particle and single fiber could be obtained. Then, the extinction coefficient could be calculated which characterizes thermal insulation performance of aerogel composites. The results show that the radiative thermal conductivity increases with increasing temperature, thus smaller particles and thinner fibers are more suitable for doping at high temperature. In addition, the carbon black has the best extinction characteristic in the four types of studied opacifiers (carbon black, SiC, ZrO2 and TiO2), but it will be oxidized at high temperature. Compared with TiO2 and ZrO2, the insulating performance of the SiC opacifier is more effective at high temperature. Although doping opacifier or fiber in silica aerogel provides a better extinction function, it might increase the heat conduction. Therefore, we could achieve an optimal doping amount at the minimum effective thermal conductivity, in other words, the highest insulating capability. The effective thermal conductivity in doped silica aerogel is equal to the sum of the conductive thermal conductivity and the radiative thermal conductivity. The optimal temperature-dependent doping amount is obtained by minimizing the effective thermal conductivity. The results show that the optimal doping of both opacifier and fiber amount in silica aerogel increases with the temperature. In addition, the carbon black behaves the strongest ability to inhibit heat transfer when the temperature is below 600K, while the SiC doped silica aerogel has the most effective performance in suppressing heat transfer when the temperature is higher than 600K. Optimized results were applied to design multi-layer doping with a temperature gradient. Each layer is doped with the corresponding optimal size and amount of opacifiers and fibers according to the temperature. Assuming that the temperature changes linearly in the direction of heat transfer, we studied four multi-layer solutions as follows. Solution 1 is the only SiC opacifier multi-layer doping. Solution 2 is SiC and carbon black opacifier multi-layer doping. Carbon black opacifier only exists in the temperature below 600K, otherwise the SiC is doped, which could ensure that only a single type of opacifier was doped for each layer. Solution 3 is the only silica fiber multi-layer doping. Solution 4 is the optimal co-doping of opacifier and silica fiber, which is similar to Solution 2 but mingled with silica fiber in each layer. The results show that the silica fiber only doping has the smallest effective thermal conductivity, and the co-doped silica aerogel with carbon black, SiC opacifier and silica fiber has the smallest radiative thermal conductivity. To verify the above results, the back temperature curve of doped silica aerogel was measured. Silica aerogel doped with various types of opacifiers and SiC in different particle sizes and doping amounts were considered. In addition, the back temperature of SiC-multi-layer doped silica aerogel was investigated. The predictions agree with experimental results qualitatively.

In ceramic industry, zircon sand is widely used in different applications because zirconia plays a role as common opacifying constituent. In particular, it is used as a basic component of glazes applied to ceramic tiles and sanitary ware as well as an opacifier in unglazed bulk porcelain stoneware. Natural zircon sands are the major source of zirconium minerals for industrial applications. In this paper, long, medium, and short range studies were conducted on zirconium minerals originated from Australia, South Africa, and United States of America using conventional and less conventional techniques (i.e., X-Ray Diffraction (XRD), Positron Annihilation Lifetime Spectroscopy (PALS), and Perturbed Angular Correlations (PAC)) in order to reveal the type and the extension of the regions that constitute the metamict state of zircon sands and themodifications therein produced as a consequence of the industrial milling process and the thermal treatment in the production line. Additionally, HPGe gamma-ray spectroscopy confirms the occurrence of significant levels of natural radioactivity responsible for metamictization in the investigated zircon samples. Results from XRD, PALS, and PAC analysis confirm that the metamict state of zircon is a dispersion of submicron disordered domains in a crystalline matrix of zircon., Facultad de Ciencias Exactas

Ceramics are the most ancient material used by humankind, in the form of earthenware. Whiteware encompasses many subcategories, such as sanitary ware, porcelain ware, earthenware, and stoneware. Clays used in the whiteware body are classified into two types: plastic clay and non-plastic clay. The clay–quartz–feldspar phase diagram represents the composition of all types of whiteware bodies, such as porcelain stoneware, white stoneware, soft porcelain, hard porcelain, laboratory porcelain, stoneware, earthenware, and dental porcelain. Transparent glazes are prepared without the addition of any opacifier. A translucent glaze is applied purposefully for decoration as a glossy surface. The glaze on a ceramic body is a thin coating of glaze or glass-ceramics. The presence of glaze defects after firing may render the final products rejected or discarded as scrap. Peeling or shivering is a glaze defect in which the glaze breaks away from the body/ceramic ware mainly due to a mismatch in the thermal expansion coefficient between the glaze and the body.

Statement of problem A significant challenge of craniofacial prostheses is their limited service life because of degradation and color instability. In spite of improvements in the materials and techniques used for the fabrication of silicone maxillofacial prostheses, undesirable color change over time remains a challenge. Zn and Ti nano-oxides (nano-TiO2) have been reported to impart an ultraviolet- (UV) shielding property to silicone elastomers. However, studies examining the effects of nanopigments on the color stability of craniofacial prostheses are sparse. Purpose The purpose of this in vitro study was to evaluate the color stability of a room-temperature vulcanizing (RTV) silicone elastomer with the addition of iron oxide and titanium dioxide nanopigments under accelerated artificial aging. Material and methods Sixty disks (O15×2 mm) were fabricated from RTV silicone 4408 Q. The specimens were divided into 5 groups containing iron oxide nanopigment, iron oxide nanopigment and rutile nano-TiO2 (as an opacifier), burnt sienna pigment, burnt sienna and nano-TiO2, and silicone without pigment or opacifier. The specimens were subjected to accelerated aging in a Xenotest chamber for 1000 hours. CIELab color coordinates and the total color difference (ΔE∗) values were determined before and after aging. ΔE∗ values were compared between the groups by using 1-way ANOVA and Tamhane multiple comparisons (α=.05), and a standard deviation of 1.09 was considered. Results ANOVA showed that the values of ΔE∗ differed among all groups (P Conclusions Nano-TiO2 with burnt sienna groups had a lower color change than the other groups. The color change in all groups was within a clinically acceptable range.

Five scarabs and one scaraboid found in Vinha das Caliças 4 (Beja, Portugal) were analyzed using a micro-analytical methodology in order to determine their mineralogical and chemical composition. Microstructural characterization and chemical analysis revealed that all were composed of a white body of crushed feldspathic sand covered by a lead-rich, alkaline-depleted silicate blue-green glaze showing evident signs of glass deterioration. Variable pressure scanning electron microscopy with X-ray energy dispersive spectrometry, handheld X-ray fluorescence spectroscopy, and micro X-ray diffraction results show that blue-green color of the glaze was produced by using copper ions (Cu2+) in conjunction with the lead antimonate bindheimite, a yellow-colored opacifier. The introduction of small amounts of tin in the structure of bindheimite enabled the production of a ternary Pb–Sb–Sn oxide. Tin, which was most likely added with the copper source (bronze scrapings), is known to facilitate the crystallization of bindheimite. The results are consistent with the five scarabs and one scaraboid being manufactured in Egypt. This study, the first archeometric study of scarabs found in the Iberian peninsula, has greatly contributed to the understanding of the influence of the Eastern and Central Mediterranean world in the Southwestern Iberia during the first millennium B.C.

A vacuum super insulation for temperatures up to 1073 K has been developed using an opacified powder mixture with high-density ( ρ = 180 kg m−3) expanded perlite as base material. To analyze radiative transfer, the mass-specific extinction coefficient e of expanded perlite and various opacifiers (SiC, B4C, FeTiO3, TiO2) has been determined by FTIR spectrometry. For reduction of radiative transfer, a SiC powder with mean grain diameter of 2 μm–4 μm and bulk density of 870 kg m−3 has been identified as most suitable opacifier, also under economic aspects. Subsequently, six homogeneous powder mixtures with weight fraction w of SiC between 0% and 60% have been prepared. In order to determine the optimum w , guarded hot plate (GHP) measurements under high vacuum conditions ( p λ e = 13∙10−3 W m−1 K−1 for w = 40% and ρ = 263 kg m−3. This mean temperature corresponds to an insulation application with 950 K hot-side and ambient temperature cold-side. For the optimum mixture with w = 40%, e has likewise been determined with FTIR spectrometry. Furthermore, λ e has been measured with the GHP method also at mean temperatures between 373 K and 873 K, where excellent values between 4∙10−3 W m−1 K−1 and 20∙10−3 W m−1 K−1 have been obtained. For the evaluation of these measurements, two different methods have been applied in order to separate radiative thermal conductivity λ r and solid thermal conductivity λ s : first the common plot of λ e versus T 3 , and second an improved method, which includes the temperature dependencies of e and λ s . Expanded perlite, opacified with SiC, has proven as a highly efficient and economic vacuum super insulation material for industrial applications up to 1073 K.

A representative group of lead-glazed ceramics excavated from the Medieval city of Aktobe, in what is today southern Kazakhstan, was analyzed to reconstruct the production technology. Fifteen sherds, which date from the 9th–12th c. CE, were previously identified by neutron activation analysis as locally produced ( Klesner et al., 2019 ). The ceramics, which represent four common Early Islamic wares (monochrome, underglaze painted, underglaze slip-painted, and opaque) were examined by scanning electron microscopy and electron microprobe analysis to establish the variability of local artisans’ use of raw materials, glazing methods, and decorative techniques. Early Islamic ceramics are the first glazed wares produced in southern Kazakhstan, and through their technological reconstruction, we determined how this new ceramic technology was produced. We show evidence that the ceramics were introduced by skilled craftspeople who knew the production technology that was being used in Islamic centers in southwest and Central Asia. The ceramic technology differs, however, in the use of antimony as an opacifier in opaque glazes containing high-lead oxide. This research adds to the growing body of knowledge about glazing technologies in Central Asia and helps to define the technological and cultural ties present in the Early Islamic Period.

For polymer foams with low-density, the thermal radiation propagating through the foam still contributes significant to the total thermal transfer. It is very promising to enhance the absorption or reflection of IR radiation by the foam matrix. However, it is still a question which of the reflected infrared or absorbed infrared is more effective in reducing radiative thermal conductivity. In this work, we studied theoretically and experimentally the effectiveness to reduce the radiative thermal conductivity of polymer foams by reflection mode and absorption mode. The relationship between the optical parameters of foam and the heat radiation transmission in the foams was quantitatively investigated. It was found that, taking into account the re-emission, the radiative thermal conductivity was further reduced merely by increasing the absorption coefficient, but in theory it could continue to drop to zero by increasing the reflection fraction. Both the flake aluminum powder (FAP) that mainly reflects infrared and the flake graphite powder (FGP) that mainly absorbs infrared were added to the rigid cross-linked PVC (c-PVC) foam. The results demonstrated that the reduction of radiative thermal conductivity of the c-PVC foam with FAP was more significant than of the c-PVC foam with FGP. The experimental results were in good agreement with the theoretical prediction.

Rigid poly (vinyl chloride) [PVC] composites with 0 to 4 wt% of either conventional or nanoscale rutile titanium dioxide filler were injection molded. Rutile titania absorbs solar UVR efficiently and is typically used in rigid PVC formulations as an opacifier and protects the polymer from light-induced degradation. A comparison of the stabilization effectiveness of the two types of fillers were assessed by monitoring the change in tensile properties and development of light-induced surface yellowing of the composites on exposure outdoors as well as under laboratory accelerated conditions. A comparison of the conventional and nanoscale uncoated rutile tiania as a light-stabilizer in rigid PVC is reported. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

Radiative heat transfer at high temperature deteriorates the insulating capability of silica aerogel due to its poor extinction characteristics for wavelength below 8 μm. Both the infrared opacifier doping and fiber doping can reduce the heat transfer and improve insulating capability of silica aerogel efficiently at high temperature. We determine the optimal temperature-dependent size for typical opacifiers and silica fibers by combining the spectral extinction coefficient with blackbody radiation. The optimal temperature-dependent doping amount is obtained by minimizing the effective thermal conductivity. Based on the obtained temperature-dependent optimal parameters and the graded temperature distribution in silica aerogel, four solutions of multi-layer graded doping are presented and the insulating capability is improved effectively. The measured back temperature curves of doped silica aerogel in the experiment qualitatively verify the optimization predictions.

The efficacy of titanium dioxide as an opacifier for glass ceramic, wear-resistant, semi-fritted, glaze coatings with the required physical, chemical, and operating characteristics for floor tiles is determined. Infrared spectroscopy, x-ray phase analysis, and electron microscopy are used to perform a comprehensive study of the formation of composition-optimized glaze coatings.

In tile manufacturing alumina acts as an opacifier in porcelain tile bodies and as a matting agent in glazes. Calcined alumina is a versatile and a new material for glaze industry due to it’s the densest and more stable crystalline form of alumina. The study was accented on examining of the effect of alumina characteristics and concentration on thermal behavior, phase evolution and optical properties of wall tile glazes. For this purpose several wall tile glazes which contain different phases of alumina and a different concentration were prepared and fired in industrial firing cycle. In the study it was showed that softening and melting temperatures of the wall tile glazes were increased with the increment of the alumina concentration. The crystal phases were detected as anorthite, corundum and gahnite. Depending on the forming of new crystalline phases, glazes with different aesthetic properties were obtained in the study.

This paper presents aerogel SiO2–TiO2composites used for thermal protection of biomass-to-hydrogen hydrothermal reactor and the method of their production. The technology of aerogel composites production includes the following stages: ion exchange of liquid Na-glass leading to formation of hydrosol silica; hydrosol concentration; formation and maturing of hydrogel; production of SiO2-TiO2alcogel; modification of its surface; subcritical drying of alcogel leading to formation ofSiO2-TiO2 ambigel; its heat treatment, granulating and classification. The influence of the infrared opacifier (titania) and the heat treatment temperature of SiO2-TiO2composite on its structural and thermal characteristics is investigated. Possibilities of increasing the hydrogen yield by reduction of energy losses using vacuum thermal insulation for reactor walls are examined.

The paper presents a historical evolution of compositions and applications of glazes on various ceramics (majolica, facing tile, glazed pottery, porcelain). The origin and development of artistic and industrial enameling processes for metals are described. The effect of additions in glazes and enamels on the color and transparency of decorative, artistic, and technical vitreous coatings on metallic and nonmetallic materials is exemplified by objects created in different historical epochs.

The present study focuses on calcium phosphate identified in some late-Antique glass tesserae, green or blue in colour, from Padova (Italy) and Tyana (Turkey). It is generally accepted that calcium phosphate is a primary opacifier, probably obtained by deliberate addition of bone powder to a transparent glass. However, no specific crystallographic-chemical-spectroscopic studies have been performed on this important type of opacifier until now. Multi-methodological investigations on calcium phosphate, on its reaction rim, and on interactions with surrounding soda-lime-silica glass were carried out in this work by means of scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), electron microprobe (EMPA), and micro-Raman spectroscopy, in order to clarify the nature of these inclusions and provide new insights into the production technologies of such kind of glass tesserae. Our results show that calcium phosphate grains are actually hydroxyapatite characterised by an evident reaction rim, which is enriched in sodium derived from the surrounding glass and replacing calcium of the opacifier. Such a cation replacement process between opacifier and glassy matrix is also confirmed by the presence of newly formed crystals composed of sodium calcium phosphate (beta-rhenanite) and calcium silicate (wollastonite, polytype 1-T). beta-Rhenanite and wollastonite are generally found in the proximity of calcium phosphate grains. Notwithstanding the geographical distance between Padova and Tyana (more than 2000 km), comparable results were found in all the tesserae from both sites, suggesting similar and highly standardised production technologies of late-Antique tesserae with calcium phosphate as opacifier. (C) 2015 Elsevier B.V. All rights reserved.

Spherical opacifier doping aerogels for thermal insulation have been investigated in the past decades. However, the cylindrical fiber doping is seldom studied, in particular, there are no thermal analysis on non-silica fiber-loaded aerogels which can satisfy thermal insulation and mechanical requirements in harsh thermal environment simultaneously. The radiation inhibition property and overall insulation performance of non-silica fiber doping method are numerically investigated in the present work. Our results reveal that the optimal diameter of non-silica fiber dopant is significantly lower than that of opacifier doping at identical temperature. Carbon fiber has incomparable infrared radiation suppression ability of about 4 times that of carbon opacifier in the whole temperature range. Compared with the opacifier doping, the non-silica fiber doping method is demonstrated to provide stronger light shielding effect, lower thermal conductivity at a certain doping fraction, and much higher mechanical properties. Moreover, a stratified core-shell design for oxidizable carbon fiber is proposed to extend its excellent radiation suppression ability to high temperature. These findings provide useful guidance for the application of fiber-reinforced aerogels for high temperature thermal insulation.

A solvothermal deposition method using no TiO2 seed layers was employed to grow a dense TiO2 coating on ZrO2 fibers as infrared opacifier. The crystal phase and microstructure of the obtained heterogeneous fibers were characterized by XRD, SEM, EDS and TEM. The mechanical stability and heat endurance of the TiO2 coating were studied. The infrared shielding performance of the TiO2-coated ZrO2 fibers was characterized by DRS and effective specific extinction (e*). In the infrared range of wavelengths from 2.5 to 10 μm, the TiO2 coating on the fiber surface could increase the e* of the ZrO2 fibers by 70%. The results suggest that the TiO2-coated ZrO2 fibers are promising candidates as infrared opacifiers at high temperatures.

High-performance submicron ZrSiO4 powder is prepared by a sol-gel-microemulsion-hydrothermal method (S-G-M-H). In this method, the transformation from sol to gel is constrained in the droplets of the microemulsion and accelerated by the hydrothermal process. The interface change of sol/oil to gel/oil makes the emulsion automatic demulsificate without demulsifiers, which means that the organic solvents can be recycled. The preparation process is low-cost and environmentally friendly. The results show that the synthesized ZrSiO4 powder owns the optimized median diameter (D50) of 0.67 μm under the optimized preparation condition of hydrothermal treatment at 150 °C for 7 h. The ZrSiO4 particles are the agglomeration of the primary particles with a size of about 100 nm. As an opacifier, 15 wt% submicron ZrSiO4 powder added give a whiteness value of 85 to the opaque glaze, which is significantly better than commercial ZrSiO4 powder with the same amount added. Meanwhile, the obtained submicron powder has excellent sintering activity. After sintered at 1300 °C for 2 h, the ZrSiO4 pellets has the density of 4.32 g cm−3 and the porosity of 0.31%.

Many pharmaceutical tablets have a coating. This chapter discusses the critical quality attributes of coating liquids, their preparation, and the coating process of the tablets. Moreover, it describes how the requirements can be fulfilled in practice. A coating layer can be applied for many reasons, from cosmetic purposes to advanced drug delivery. A coating liquid generally consists of a polymer, a plasticizer, a colorant or opacifier, and sometimes components to stabilize the coating liquid or to improve wetting of the tablets. In the coating process, the liquid is sprayed onto the tablet cores whilst they are moving. The inlet air ensures drying of the tablets. During this drying phase the polymers coalesce and form a smooth thin layer around the tablet of more or less constant thickness. Good quality of the coating liquid is the basis for well coated tablets. Therefore, the preparation of a coating liquid should ensure a lump free, viscous liquid with a set amount of solids.

The Hutterites and Habans produced coloured-glazed, mostly blue- and yellow-coloured vessels alongside their white-glazed faience ware. However, the production technology of the coloured-glazed vessels, specifically the nature of the glaze, is a matter of debate among scholars. Both coloured tin glaze and coloured engobe covered with a transparent lead glaze were thought to have been applied on the ceramics. Around 140 objects of blue-glazed Hutterite and Haban museum objects and archaeological artefacts were analysed using a handheld XRF spectrometer. In addition, small fragments of selected ceramics were studied by electron microprobe analysis (EMPA). According to the XRF measurements the blue glaze of all except one of the studied Hutterite and Haban ceramics contains tin in variable amounts (from about 0.015 wt% up to 13 wt%). The EMPA technique showed that tin in the form of tin oxide opacifier was deliberately added to the single-layered alkali– lead or lead–alkali glaze. These data confirm that the tin glaze technique was used during production of blue-glazed ceramics, and in this respect they can be regarded as faience. The blue glaze of the Haban vessels produced by a “mining town” workshop contains tin in very low concentrations (Sn

A collection of tesserae and two fragments from rounded cakes of coloured glass, probably dating to the 2nd century AD, were found at West Clacton Reservoir, Essex, in the UK, by Colchester Archaeological Trust. A selection of the finds were analysed using SEM-EDS and ICP-MS. This paper provides data on the composition of the different glass colours and discusses how each colour was made. Colourants and opacifiers were added to a base glass, most often one of the transparent, naturally coloured (blue-green) natron glass types widely available at the time, but there appear to be preferences in the type of base glass used for certain colours, which affects the type of antimonate opacifier precipitated. Possible reasons for using different types of base glass to make strongly coloured Roman glass are discussed.

Zircon (ZrSiO4) is widely used as a glaze opacifier in the ceramic industry. The crystallization mechanism of ZrSiO4 from a CaO-riched zirconium-based frit glaze was studied by XRD, SEM, and DSC in this work. Isothermal and non-isothermal heat treatments were used to study the phase development and microstructural evolution during the firing process. It was found that t-ZrO2 and Ca2ZrSi4O12 were first crystallized at a relative low temperature and then converted to ZrSiO4 with the increasing of temperature. ZrSiO4 originating from t-ZrO2 has an inward growth and an outward growth, while ZrSiO4 transformed from Ca2ZrSi4O12 only has an outward growth. SEM showed that ZrSiO4 appeared to be a rod shape in fired samples. The calculated activation energy for ZrSiO4 is 311.2 kJ/mol, and the Avrami index (n) is 0.35–0.39. This indicates the one-dimensional diffusion-controlled growth of ZrSiO4, which explains the formation of rod-shape ZrSiO4 crystal.

This study focuses on polychrome glass tesserae from the palaeo-Christian mosaic, still in situ , which decorates the vaults of the votive chapel of St. Maria Mater Domini in Vicenza (Veneto region, NE Italy). Aims are characterisation of the “base composition” of the glassy matrix and identification of opacifiers and colourants and these are performed by means of a multi-methodological approach (SEM-EDS, EMPA, XRPD, IS). Systematic comparisons between the Vicenza tesserae and those from the votive chapel of St. Prosdocimus in Padova, part of the remains of the only other palaeo-Christian mosaic located in the Veneto, coeval in age and with comparable colour palettes, are also carried out in order to improve our knowledge of production technologies of these materials during the 6th century AD in the Northern Adriatic area. Textural, chemical, diffractometric and spectroscopic data indicate multiple production technologies in the Vicenza tesserae , with evidence of several glassy matrices, opacifiers/pigments and/or ionic colourants/decolourants, all variously mixed in order to obtain the desired shades. In particular, the matrices of the Vicenza tesserae , mostly comparable with compositional reference groups typical of both Roman and Late Roman times, and opacifiers/pigments mainly composed of antimony-based compounds typical of Roman tradition, indicate the extensive availability of older glass for re-use and/or a preference for recycling, rather than the preparation of new batches. Peculiar is also the finding, in one Vicenza Aquamarine sample, of an opacifier composed of sodium antimonate, never found in ancient glass tesserae until now. Comparisons between the Vicenza and Padova mosaics indicate technological connections between the sites, as testified by the many chromatic groups with high degree of comparability. However, when differences are observed into chromatic groups compared, the Vicenza tesserae generally show older technological features than those of Padova. The hypothesis advanced here, related to the different geographical location of the two sites, explains such experimental evidence in terms of the different speeds at which innovative technologies spread in north-eastern Italy.