Lightweight glass–ceramic tiles from the sintering of mining tailings

Modern thermally-insulating building façades comprise lightweight structural panels, in turn mostly composed of porcelain stoneware with engineered porosity. Sintered glass–ceramics may represent a valid alternative, mainly considering layered articles, with a dense surface layer on a highly porous body that could be manufactured by double pressing. In this paper we present a low cost route to lightweight tiles, developed starting from mining tailings, such as waste from the mining of boron-rich minerals and basalt rock, and recycled glasses, such as common soda-lime glass and pharmaceutical borosilicate glass. A highly porous body was obtained by direct sintering of mixtures of mining tailings and soda-lime glass; despite the homogeneity of porosity and the formation of new crystal phases (at only 1000 °C), favorable to good mechanical properties, the water absorption remained far above the limits (>2 wt%). The water absorption was minimized by introduction of a dense glaze, associated to the firing of mixtures coated by a thin layer of recycled borosilicate glass powders; both color and shrinkage were optimized by the mixing of borosilicate glass with powders of zircon mineral and vitrified boron waste/basalt/soda-lime mixture.     

Formation of an Alkali Diffusion Barrier and Stain-Resistant Glass Surface

As it is well known, the structures of silica and soda-lime-silica glasses are subjected to alkali ion diffusion. This diffusion can lead to staining of the glass surface, thus detrimentally affecting its optical functions. In this work, an effective alkali diffusion barrier layer is created by boron diffusion into the top 10 to 50-nm thick layer of glass surface. In this layer, alkali mobility is electrochemically arrested by a coordination change of boron. As a result, the glass surface stays pristinely clear, even under sustained exposure to hot and humid conditions. Structural studies indicate that when three-coordinated boron diffuses into a pre-existing glass network, it converts nonbridging oxygens, associated with alkali ions, into bridging oxygens by changing its coordination from 3 to 4. This forces alkali ions to change their bond association from nonbridging oxygens to the charge sphere of boron due to the required charge neutrality. This new bond arrangement immobilizes the alkali ions at these sites. As a result of the alkali ion immobilization, and the reduction in nonbridging oxygens in the network, the glass surface becomes resistant to nucleophillic attack, as well as resistant to stain formation, and crystallization.     

Effect of alumina content on surface area and micropore distribution of porous glass prepared from borosilicate glass

The surface area and micropore distribution of porous glass prepared from borosilicate glass were controlled by the addition of alumina up to 8 wt%. The surface area increased with increased alumina content in the range from 0 to 3 wt%, but it suddenly decreased when the percent alumina exceeded 4 wt%. The mean pore diameter and micropore volume also decreased with increased alumina content. When nickel ion was supported into the porous glass, the surface area decreased to about one-half that of the original glass. Since the amount of nickel supported on the porous glass increased directly with surface area, the silanol group was considered to be uniformly distributed on the glass.     

Interaction between porous glass and ammonium molybdate solution in acidic medium

The results obtained by treating porous high-silica glass with ammonium molybdate are reported. The structural changes occur both in the pore space and on the surface of the porous glass.     

Aminopropylsilane treatment for the surface of porous glasses suitable for enzyme immobilisation

During silylation of porous glass with 3-aminopropyltriethoxysilane, the properties of the carrier affected the concentration of bound amino groups, the formation of aminopolysiloxane mono- or multilayer on the surface, and the hydrolytic stability of the layer formed. The influence of the carrier depended on the specific surface area and the size of pores. In contrast to silylation performed in organic solvents, in aqueous solutions a monolayer of aminopolysiloxane of high hydrolytic stability was formed on the surface of porous glass. Tetraethoxysilane modification of porous glass prior to silylation with aminosilane yields carriers of increased hydrolytic stability. Glucoamylase immobilised on carriers, that were modified in aqueous solutions, exhibit higher enzymatic activity.     

Double-layer waste-derived glass-ceramics prepared by low temperature sintering/sinter-crystallisation

Lightweight glass-ceramics with a dense surface layer were produced by a novel sintering approach. The surface porosity of a glass-ceramic body from the direct sintering of an engineered mixture of fly ash from thermal power plants, recycled soda-lime glass and boron waste (residues of the mining and purification of valuable boron containing minerals) was sealed by a glaze, deriving from the sinter-crystallisation of glass powders produced from the same mixture. The use of boron waste, providing B₂O₃, allowed a substantial viscous flow, for the substrate, even at the relatively low temperature (850–950°C) adopted for a single firing treatment (simultaneous sintering of substrate and sinter-crystallisation of glaze). The dense sinter-crystallised layer, besides imparting improvements in the mechanical properties, was found to feature an enhanced chemical stability.     

Photocatalytic activity of transparent porous glass supported TiO2

A porous glass tube with a composition of 96SiO₂·4B₂O₃ (wt%) supported TiO₂ shows high photooxidation activity due to its transparency and large surface area. The surface area of the porous glass tube supported TiO₂ is 10,000 times larger than that of conventional materials. TiO₂ crystals supported are anatase type. Transparency of the porous glass tube is very important. Herein, sol–gel and chemical vapor deposition (CVD) processes were employed as TiO₂ supporting processes. CVD process is more effective. For instance, an aqueous methylene blue solution with 1 ppm concentration almost thoroughly decomposes at a contact time of 300 s using porous glass tube supported TiO₂ prepared by CVD process under irradiating with 10 W low-pressure mercury lamp, on the other hand, opaque porous alumina tube supported TiO₂ was only 25%. The smaller the pore size of the porous glass tube, the larger the transparency and the permeation resistance through porous glass tube. Hence, porous glass tube with ca. 40 nm pore diameter is suitable from the standpoint of a practical use.     

Nano-TiO2-Coated Unidirectional Porous Glass Structure Prepared by Freeze Drying and Solution Infiltration

A unidirectional porous glass structure coated with a nanometer TiO₂ thin film on pore walls was successfully fabricated by a two-step process. Firstly, a water-based slurry of sheet glass was frozen while controlling the growth direction of ice crystals, and then sublimation of the ice under vacuum formed the green body. The green body was subsequently sintered to produce porous glass with unidirectional pores. Secondly, the sintered porous glass was infiltrated by a titanium (IV) butoxide solution, and then dried and calcined at a moderate temperature to generate a nanometer TiO₂ film on pore walls. The present porous glass with nanometer TiO₂ has more total surface area than the TiO₂ film on glass plates, which is believed to be more effective in the phtotocatalysis application for air or water purification.     

石油焦系活性炭抗氧化性能研究

活性炭在高温下极易被氧化,极大的限制了其在催化领域的应用,为了提高活性炭在高温下的抗氧化能力,文章以NaOH化学活化法制备的活性炭为原料,通过固体渗硼对活性炭进行基体改性。实验结果表明：渗硼后活性炭表面的活性点数量明显减少,抑制了氧化性气体与活性炭的反应,从而提高了活性炭的抗氧化能力。并且渗剂在活性炭中含量为10%、渗剂中B4C含量为25%、热处理时间为5 h时,与活性炭原料相比,基体改性后600℃活性炭氧化失重率由70%左右降低到20%左右,比表面积降低10%~20%,活性炭材料的微反活性仍可达到70.25。     

Silicon carbide fiber oxidation behavior in the presence of boron nitride

The oxidation behavior of Sylramic SiC fibers without a boron nitride surface layer was compared to Sylramic iBN SiC fibers with a boron nitride surface layer by conducting thermogravimetric analysis in dry O₂ at temperatures ranging from 800 to 1300°C for times up to 100 hours. Sylramic fibers followed the Deal and Grove oxidation kinetic model. A transient period of accelerated oxidation kinetics was observed with Sylramic iBN fibers. Raman spectroscopic analysis of oxidized fibers provided evidence for a borosilicate glass structure. The boron concentrations in the oxides, quantified by inductively coupled plasma‐optical emission spectrometry, were correlated with the weight change behavior, oxide thickness, and fiber recession of the oxidized fibers. Oxides formed from Sylramic iBN fibers were typically higher in boron concentration, which led to initial rapid oxidation rates that were 3‐10 times faster than observed for pure SiC. Slower oxidation rates followed as the oxide surface became increasingly enriched with SiO₂ due to boria volatilization, thus limiting boria effects on SiC fiber oxidation kinetics. The accelerated high‐temperature oxidation of SiC fibers due to the presence of BN are discussed in terms of the borosilicate glass structure and composition.     

Subcritical Water Treatment: A Simple Method to Prepare Porous Glass with a Core–Shell Structure

This paper presents a subcritical water treatment method for preparing porous glass with a core–shell structure from ordinary soda-lime glass beads in one step. In this method, reactive subcritical water rather than any other chemical additive was utilized to selectively corrode the glass and mainly leach the alkali ions from the glass. The core–shell structure has been characterized by scanning electron microscope observation. The mesoporous structure of the porous glass beads has been confirmed by a nitrogen adsorption–desorption measurement. The treated alkali–lime–silicate glass beads have mesopores with a narrow distribution ranging around 4 nm, and a uniform nanoflake array on the surface. The shell structure can be easily tailored by changing the treatment temperature and water flow rate. A possible mechanism of a corrosion-ion immigrating-recondensation pattern was hypothesized to explain the formation of the core–shell porous structure.     

Synthesis and characterization of sol-gel bioactive glass nanoparticles doped with boron and copper

In this work the sol-gel synthesis of bioactive glass nanoparticles containing both boron and copper oxides is reported for the first time in the literature. Two acid/base co-catalysed methods were compared. The obtained glasses have been characterized in terms of morphology, composition, particle surface area, phase analysis and bioactivity in acellular simulated body fluids. The almost spherical nanoparticles (<100 nm diameter) obtained are characterized by a certain degree of aggregation and have compositions, which are coherent with the theoretical ones. Each glass revealed the ability to promote the growth of hydroxyapatite on its surface during soaking in simulated body fluid, thus we can assume that the addition of boron and copper did not negatively affect the bioactivity of the sol-gel derived glasses. Future investigations will be devoted to biological characterizations for cytotoxicity, antibacterial properties and pro-angiogenetic abilities.     

Structural Parameters of Membranes from Porous Glass in Aqueous Solutions of Electrolytes,Containing Singly-Charged (Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>) and Triple-Charged (Fe<Superscript>3+</Superscript>) Cations

The structural parameters of micro- and macroporous glass-like membranes in the solutions containing sodium, potassium, and iron counterions were investigated. The dependences of the volumetric porosity of the membranes, structural resistance coefficients, filtration coefficients, specific surface, average pore radius on the conditions of obtaining porous glass, the composition of the electrolyte, and the contact time of the porous glass with the solution are analyzed.     

Influence of the composition and temperature of heat treatment of porous glasses on their structure and light transmission in the visible spectral range

The pore structure and light transmission of high-silica porous glasses in the visible spectral range have been investigated as a function of the heat treatment temperature and the composition of the initial two-phase alkali borosilicate glass. The character of light transmission in porous glasses has been analyzed in the framework of the concepts of structural features of their pore space and the processes occurring in the porous glass during heating. It has been demonstrated that an increase in the temperature of heat treatment of porous glasses with different compositions leads to an increase in the pore size and a decrease in their specific surface area (with a nearly constant total porosity), which is associated with the processes of overcondensation of pores due to the rearrangement and the change in the packing density of secondary silica particles. It has been revealed that the introduction of phosphate and fluoride ions into the initial sodium borosilicate glass results in an increase in the light extinction coefficient of porous glasses due to the increase in the sizes of phase-separated inhomogeneity regions in the initial two-phase glasses, the formation of larger pores, and the presence of nanosized microcrystalline phases in porous glasses.     

Preparation of a Translucent, Conductive, Porous Nanocomposite

A translucent, conductive, porous nanocomposite was designed and prepared by depositing SnO₂ on the inner surfaces of the pores of a porous glass plate and on its outer surface using a chemical vapor deposition method. The porous nanocomposite almost maintained its large surface area and pore volume because the pores remained open after they were deposited with SnO₂. Conductivity between the two outer surfaces of the nanocomposite plate was confirmed for the first time.     

铝硼硅酸盐玻璃纤维结构与耐水动力学

采用红外光谱、示差扫描量热分析等手段研究了氧化硼对铝硼硅酸盐玻璃结构及转变温度的影响,并用粉末法测试了玻璃的耐水性。结果发现,随着氧化硼含量增加,玻璃转变温度先降低后升高。玻璃与水反应初期受硼酸盐的水解动力学控制,后期主要为水分子对硅氧骨架的侵蚀和Ca2 与H 离子的离子交换过程。分析认为,引入少量的B2O3主要与碱性的CaO结合,生成含有非桥氧的端氧键B-O-Ca,破坏了玻璃网络结构,B2O3过量时,更多的硼酸盐基团与硅酸盐基团结合,生成桥氧键B-O-Si键,增强了玻璃结构。     

SYNTHESIS AND CHARACTERIZATION OF BORON CARBIDE FILMS BY PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION

The plasma-enhanced chemical vapor deposition of boron carbide was investigated on quartz glass and alumina substrates from a gas mixture of BCl 3 , H 2 , and CH 4 in an inductively coupled plasma (ICP) medium produced by a radio frequency (RF) discharged onto the gases passing through a tubular reactor under atmospheric pressure. A thin solid boron carbide coating with a gray color was deposited on both substrates. The results of XRD revealed that the major solid phase formed in the coating material was β-rhombohedral B 4 C. The SEM analysis showed that the surface homogeneity increased with an increase in the exposure time, and different boron carbide structures were formed at different RF powers and exposure times.     

Synthesis and characterization of boron carbide films by plasma-enhanced chemical vapor deposition

The plasma-enhanced chemical vapor deposition of boron carbide was investigated on quartz glass and alumina substrates from a gas mixture of BCl 3 , H 2 , and CH 4 in an inductively coupled plasma (ICP) medium produced by a radio frequency (RF) discharged onto the gases passing through a tubular reactor under atmospheric pressure. A thin solid boron carbide coating with a gray color was deposited on both substrates. The results of XRD revealed that the major solid phase formed in the coating material was β-rhombohedral B 4 C. The SEM analysis showed that the surface homogeneity increased with an increase in the exposure time, and different boron carbide structures were formed at different RF powers and exposure times.     

漫谈高硼玻璃的电熔

阐述了高硼玻璃的熔制特性,通过对窑内玻璃液流温度分布的分析,认为用全电熔窑熔化高硼玻璃比较理想,并提出了相关注意事项.     

锂辉石在低硼硅医药玻璃中的应用研究

以锂辉石中的氧化锂等质量替代低硼硅医药玻璃(简称7.0医药玻璃)化学组成中的氧化钠、氧化钾和氧化硼,研究了氧化锂对7.0医药玻璃高温黏度特性、低温黏度特性、工艺性能的影响。研究结果表明,锂辉石可降低玻璃熔化温度(Tm)17～34℃、玻璃火焰加工温度(T3)20～35℃、玻璃应变点温度(Tst)30～76℃;另外,玻璃拉管成形温度范围(△T)提高到426～445℃,可促进玻璃成形精度提高,因此,锂辉石可促进低硼硅医药玻璃的节能减排。