Mg-bearing quartz solid solutions as structural intermediates between low and high quartz

Glass powder samples of cordierite composition (doped with 8 mol% TiO₂) were heat-treated to produce a series of increasingly SiO₂-enriched Mg-bearing quartz solid solutions (Qss). The obtained materials were then analyzed by X-ray diffraction: Rietveld structural refinements revealed that Mg-bearing Qss phases possess trigonal symmetry and a compositionally dependent intermediate structural arrangement between those of low and high quartz. High-temperature diffraction measurements were performed up to 700°C to characterize the thermal expansion behavior of the crystals. At SiO₂-rich compositions, a reversible high-to-intermediate inversion of the quartz structure is observed, which shifts with increasing stuffing to lower temperatures than the conventional 573°C for pure quartz. Similarities and differences to the better-established Li-bearing Qss are discussed in the text.     

Towards new zero-thermal-expansion materials: Li-free quartz solid solutions stuffed with transition metal cations

Stuffed aluminosilicate quartz solid solutions (Qss) represent the main functional component of state-of-the-art zero-thermal-expansion glass-ceramics. For the first time, we present the synthesis of Li-, Mg- and Zn-free Qss solely stuffed with transition metal cations (Fe²⁺, Ni²⁺, Co²⁺); partial Li⁺ co-doping enables also significant Mn²⁺ incorporation. They were obtained by glass powder crystallization; Qss crystals exhibit compositionally tunable coefficients of thermal expansion (CTEs), from ? 2 × 10^?6 K^?1 to ～10 × 10^?6 K^?1 in the range 30–300 °C. Co²⁺-bearing crystals exhibit the closest-to-zero CTE value (0.2 ×10^?6 K^?1) and the most isotropic behavior in the whole Qss family, opening up new perspectives for the development of Li-free low-expansion materials. From a structural point of view, we identified the unit cell volume (and not the pseudo-hexagonality of the aluminosilicate framework) as the key structural parameter leading to low or negative CTEs in Qss, with a linear correlation extending to non-stuffed non-silicate quartz-like phases.     

Thaumasite-ettringite solid solutions in degraded mortars

The thaumasite form of sulfate attack (TSA) has been observed in mortar prisms made from Portland-limestone cements after laboratory storage in 1.8% magnesium sulfate solution at 5 °C for 5 years. The prisms all showed evident signs of degradation, which increased with increasing limestone content. X-ray powder diffraction indicated that a solid solution was formed in all the prisms, which was based on the crystal structure of thaumasite, but extended towards the chemical composition of ettringite. The prism made from the cement with the highest level (35%) of limestone replacement gave the greatest amount of the thaumasite solid solution and had a composition close to the thaumasite end member, whereas those cements with lower (15%, 5% and 0%) levels of replacement gave reduced amounts of the solid solution and had greater lattice parameters. The solid solutions that have been observed are compared with those reported by Barnett et al. for synthetic thaumasite samples grown from sucrose solution.     

Glass-to-metal seals for solid oxide cells at the Politecnico di Torino,an overview

A summary and update of the research on the design, process, and testing of glass and glass-ceramic to metal seals for solid oxide cells (SOC) conducted during the last 13 years at the Politecnico di Torino, Italy, within our research group and with several international collaborations, is presented and discussed. Glass and glass-ceramic-based materials play a key role in SOC performance and durability as well as in the sealing and joining of metallic interconnects. The sinter-crystallization method is a powerful technique that is used to obtain dense and reliable glass-ceramics capable of providing hermetic joining and seals. The issues, learned from our experience, that have an impact on the lifetime behavior of glass and glass-ceramic to metal seals are briefly reviewed in terms of challenges and working conditions. The mechanical characterization of glass-to-metal seal materials has a crucial impact on the overall performance, as the metal–glass interface plays a key role on the final joining strength and reliability. Several glass compositions are presented along with results on their characterization and behavior as joining materials for metallic interconnects, with a focus on their potential use as SOC seals.     

Reticulated ceramic foams from alumina-chromia solid solutions: A feasibility study

Open cellular ceramic foams were manufactured from plain and chromia-doped alumina, with a chromium concentration ranging between 1.25 mol% and 5.0 mol%. The (AlCr)₂O₃ starting powders were prepared by precipitation of a chromia precursor onto the surface of an alumina powder and subsequent calcination. Characterization of the starting powders as well as the foam samples made therefrom were carried out with respect to the chromium concentration in the alumina phase and the influence of the dopant on the cellular structure and sintering behavior of the doped material. While no positive effect on the compressive strength of the ceramic foams was found, the dopant influences the sintering behavior resulting in an increased shrinkage and in a reduction of total porosity.     

受污NHD溶剂石英砂过滤工艺的改进

采用床高为600 mm、粒径为0.60～0.80 mm的石英砂过滤器,通过添加配料对NHD溶剂中固体杂质进行表面改性处理,然后对添加配料后的NHD溶剂进行净化处理,研究了配料粒径、添加量及操作压力等因素对过滤效果的影响,确定了对添加配料后的NHD溶剂进行过滤的最佳操作条件。实验结果表明:在室温,配料粒径为20～25μm、添加量为m(配料)∶m(固体杂质)=0.32、操作压力为0.03 MPa的条件下,NHD溶剂经过滤后,固体杂质去除率可达92.3%,且处理后的NHD溶剂的吸收性能未变。     

氧化铁浸染型石英中性正浮选制备低铁石英砂

氧化铁含量是决定石英在不同领域应用的主要因素,尤其是氧化铁浸染型石英砂,因氧化铁的赋存状态、共伴生、浸染程度及粒度差异,常规擦洗、强磁选及酸法反浮选难以有效降低石英中三氧化二铁含量。中性条件下,以抑制剂抑制含铁矿物、采用捕收剂使充分解离的石英上浮,通过粗选、精选进一步降低石英精砂中三氧化二铁含量。研究表明：自然pH下,采用淀粉基抑制剂CTSS、两性捕收剂兼起泡剂ZD-3联合作用,可将此类石英砂三氧化二铁含量由130～150mg/kg降至60～100mg/kg,满足超白光伏玻璃用硅质原料的质量要求;入浮砂粒度上限为0.6mm,以≤0.5mm为宜;对含铁铝硅酸盐矿物、氧化铁浸染型石英砂,中性正浮选石英精砂三氧化二铁含量低于酸性反浮选石英精砂中该指标;热力学计算表明pH≥5.5时淀粉基抑制剂CTSS与氧化铁表面铁离子发生化学键合的标准自由能变化ΔG为负值,化学键合具有自发趋势,抑制剂CTSS与含铁矿物的优先吸附是实现石英中性正浮选提纯的关键之一。     

XRD, EDX and IR analysis of solid solutions between thaumasite and ettringite

Solid solutions between thaumasite and ettringite were prepared by methods analogous to those well established for the preparation of thaumasite and ettringite. The extent of immiscibility in this system is investigated by varying the Al:Si and SO₄²⁻:CO₃²⁻ ratios in reactant mixtures. The solids produced were analysed by quantitative X-ray diffraction, with Rietveld refinement also providing accurate unit cell dimensions, energy-dispersive X-ray analysis and infrared spectroscopy. The compositional and unit cell variations in the solid solution are discussed. A wide variety of solid solution compositions were produced with both the thaumasite and ettringite structures, but all preparations were considerably diluted by secondary amorphous products.     

A threshold heating rate for single-stage heat treatments in glass-ceramics containing seed formers

The development of glass-ceramic materials is often achieved using an elementary microstructural strategy that splits the tasks of seed formation and functionality between two types of crystals. This strategy requires customized time-temperature ceramization protocols, which have been so far implemented using empirical parameters. Here, a more fundamental approach is proposed: the extent of overlap O_e between seed formation and volume crystallization is evaluated by calorimetric and dilatometric measurements, targeting the computation of a threshold heating rate q_t for effective single-stage heat treatments. The applicability of this novel parameter is tested in TiO₂-doped lithium magnesium aluminosilicate glass-ceramics, whose seed formation stage is thoroughly characterized by Raman spectroscopy and STEM. High-temperature X-ray diffraction demonstrates that insufficient seeding results in potentially weaker performances of the final products, due to large sizes and silica deficiency of the functional quartz solid solution crystals.     

铌酸催化水解葡萄糖的研究

研究了铌酸催化水解葡萄糖溶液的反应,考察了不同热处理温度对铌酸催化剂活性的影响。研究发现,当热处理温度为400 ℃时,此类催化剂对葡萄糖催化水解生成乙酰丙酸（LA）的活性和选择性较好。对不同制备方法得到的铌酸催化剂活性进行比较,结果表明,直接水洗法制备得到的铌酸较有利于LA的生成。对用磷酸处理的铌酸催化剂进行考察发现,对于本反应体系,催化剂酸性的增加反而使活性下降。用XRD对催化剂的结构表征结果表明,催化剂活性与其表面是否结晶无明显关系。     

过渡金属掺杂铈-锆固溶体催化剂制备及其评价

选取过渡金属Cu、Co、Ni和Fe对Ce-Zr固溶体(CZO)进行掺杂改性,采用CO催化氧化为探针反应对其进行活性评价,考察过渡金属种类、掺杂量和掺杂方式对催化剂活性的影响.结果表明,对于过渡金属掺杂Ce-Zr固溶体,低温还原峰温度值越低,表面氧反应活性越高,催化剂活性越大,Cu掺杂的催化剂活性最高.共沉淀法与浸溃法制...     

Enhanced ferroelectric and ferromagnetic properties of BiFeO3-PbTiO3 multiferroic solid solutions with Ba substitutions

Dense 0.6(Bi_0.9La_0.1)(Ga_0.05Fe_0.95)O₃-0.4(Pb_1-xBa_x)TiO₃ (BLGF-PBT, x = 0, 0.1, 0.2, 0.3, and 0.4) ceramics with different Ba contents were prepared by the solid-state reaction method, and effects of Ba contents on the structure and multiferroic properties were investigated. X-ray diffraction results indicate that the Ba-modified BLGF-PBT ceramics exhibit single perovskite structure without detectable secondary phases, and a transition from tetragonal phase to rhombohedral one takes place with the increase of Ba content. The piezoelectric constant d₃₃, remanent polarization P_r, and remanent magnetization M_r are improved by the Ba substitution simultaneously. Values of P_r, M_r, and d₃₃ of BLGF-PBT ceramics for the composition of x = 0.3 with the coexistence of tetragonal and rhombohedral phases are 20 μC/cm², 0.05 emu/g, and 256 pC/N, respectively, much higher than those without Ba modification. The significantly improved d₃₃ and M_r indicate that BLGF-PBT ceramics with Ba modification provide alternative materials for multifunctional devices.     

An unusual promotion of the redox behaviour of CeO2-ZrO2 solid solutions upon sintering at high temperatures

The reduction behaviour of a high surface area CeO₂-ZrO₂ solid solution is compared with that of a high surface area CeO₂. It is shown that, upon sintering induced by repetitive reduction/oxidation processes, the temperature of reduction of the solid solution decreases from 900 to 700 K. In contrast, the reduction at low temperatures of the CeO₂ sample is strongly retarded after such treatments. The role of ZrO₂ in promoting the reduction at low temperatures is discussed.     

Electromagnetic wave absorbing properties of glucose-derived carbon-rich SiOC ceramics annealed at different temperatures

A kind of glucose-derived carbon-rich silicon oxycarbide (glucose-SiOC) nanocomposite with excellent electromagnetic wave absorbing performance is obtained via solvothermal method, and then pyrolyzed at high temperature (1300°C and 1400°C) under argon atmosphere. The structural evolutions and the electromagnetic wave absorbing capabilities of the nanocomposites have been systematically investigated. The resultant 3 mol/L glucose-SiOC ceramic exhibits a heterostructure, in which nanosized glucose-derived carbon and SiC particles decorate on amorphous SiOC network. Benefitting from the nanosized carbon, SiC particles and the heterostructure attributes, the 3 mol/L glucose-SiOC ceramic displays a strong electromagnetic wave-absorbing property. The minimum reflection coefficient of the 3 mol/L glucose-SiOC ceramic pyrolyzed at 1400°C reaches −27.6 dB at 13.8 GHz. The widest effective absorption bandwidth attains 3.5 GHz in Kμ-band. This work opens up a novel and simple route to fabricate polymer-derived ceramics with excellent electromagnetic wave-absorbing performance.     

Synthesis and thermal stability of (Co,Ni)O solid solutions

(Co,Ni)O solid solutions are considered as promising protective materials of O₂-evolving anodes for Al production. In this context, two solid-state synthesis methods, namely high-energy ball milling (HEBM) and calcination, have been evaluated for the synthesis of (Co,Ni₎O solid solutions. In all cases, Co_xNi_1−xO solid solutions can be formed over the whole composition range. However, undesired WC contaminant is observed using the HEBM method due to the erosion of the milling tools. Their thermal stability in air has been analyzed by thermogravimetric analyzes (TGA) complemented by X-ray diffraction (XRD) analyses. It is shown that Co_xNi_1−xO solid solutions are stable at 1000°C over the whole composition range whereas they are only stable for x ≤ 46 and x ≤ 22 at 800°C and 700°C, respectively. For higher Co contents, the formation of Co₃O₄ is observed. This is a relevant information for their future use for Al production, which can be done at different temperatures (~700-1000°C) depending of the electrolyte composition.     

Stable structure and electronic properties of Ru1−xTixO2 rutile type solid solutions from DFT calculations

To design solid solution is an effective strategy for functional materials. The complex electron correlation and non-equilibrium atomic interaction are the primary factors to impact the macro-/micro-structure and application performances of solid solution. Hence, this article concentrates on the stable crystal structure and the corresponding electronic structure of Ru_1−xTi_xO₂ solid solution by using density functional theory calculations. Based on analyzing the atomic interaction between solute and solvent atoms, the most stable supercell models for the specific solid solubility were obtained. In Ru_1−xTi_xO₂ solid solution, solute (and solvent) atoms preferentially arrange along the [110] direction, and tend to occupy the nearest sites of identical atoms, to arrange the symmetric ordered substitution configurations. Using the subregular solution model, the mixing enthalpy can be represented by the following expression: . The calculated phase diagram is consistent with the experimental results. Thus, the calculated results in this article are reliable and can provide more meaningful information. In the cases of Ru-rich solid solutions, the metastable phase exists in the range of x < 0.27; while in the cases of Ti-rich solid solutions, the metastable phase exists in the range of x > 0.81. Interestingly, the electron density of Ru_1−xTi_xO₂ solid solutions at Fermi level has a stronger dependence on the Ru composition, which intrinsically influences its electronic structure and optical properties. According to the basic application principle, Ru_1−xTi_xO₂ solid solutions with lower (x < 0.27) and higher (x > 0.81) solid solubility could act as suitable candidate for the applications in field electrochemistry and photocatalysis.     

Formation of high entropy metal diborides using arc-melting and combinatorial approach to study quinary and quaternary solid solutions

High entropy metal diborides (HEBs) represent a radically new approach to extend the chemical composition window of ultra-high temperature ceramics (UHTCs). In this work, arc-melting was used to produce dense HEBs starting from UHTC powders. In order to understand the influence of each individual diboride within the quinary system (HfB₂, ZrB₂, TiB₂, TaB₂ and CrB₂), we investigated five quaternary equimolar solid solutions e.g. Hf-Zr-Ti-Ta, Hf-Zr-Ti-Cr, Hf-Zr-Ta-Cr, Hf-Ti-Ta-Cr, Zr-Ti-Ta-Cr and the overall quinary equimolar combination. Arc-melting allowed a rapid screening of favorable and unfavorable combinations. The produced HEBs were free from undesired oxides and characterized by linear variation of lattice parameters typical of diborides and binary solid solutions. Because of evaporation during arc melting, CrB₂ was hardly found in the solid solution, suggesting that vapor pressure should be taken into account when designing HEB compositions especially for operating temperatures exceeding 2000 °C. Finally, Vickers microhardness ranged between the typical values of starting diborides.     

Synthesis and characterization of doped nano-sized ceria–zirconia solid solutions

Two compositions Ce_0.50Zr_0.39La_0.04Y_0.07O_2−δ and Ce_0.25Zr_0.65La_0.04Y_0.06O_2−δ based on ceria-zirconia solid solutions were prepared as nanopowders using a continuous hydrothermal flow synthesis reactor, followed by either freeze-drying or hotplate-drying of the slurry. Each dried nanopowder was then subjected to 10 h heat-treatment at 1000 °C, 1100 °C or 1200 °C in air (to simulate accelerated ageing). The reducibility and hydrogen consumption of the oxidised samples were measured using temperature programmed reduction (TPR) up to 1000 °C. The effects of composition, drying method and heat-treatment temperature were evaluated on the TPR profiles of the materials. The powders were further investigated using a range of analytical methods including UV/Vis spectroscopy (which yielded colour data), Raman spectroscopy, powder X-ray diffraction, BET surface area measurements and X-ray photoelectron spectroscopy (XPS). Chemometric methods were used to investigate relationships between the spectroscopic and total oxygen storage capacity (OSC) data. Principal component analysis (PCA) was used to provide a simple interpretation of the effects of various synthesis and treatment parameters on Raman spectra. Principal component regression (PCR) was used to build regression models relating the Raman spectra and the temperature of hydrogen consumption peak at several set temperatures in the TPR. The total hydrogen consumption of the materials was generally high, while the drying and heat-treatment conditions appeared to have a significant effect on the final properties of the resulting powders, such as the surface area and total oxygen storage capacity.     

Synthesis of carbon nitrides with graphite-like or onion-like lamellar structures via a solvent-free route at low temperatures

Carbon nitrides with graphite-like or onion-like lamellar structures were synthesized at low temperatures by the reactions of cyanuric chloride (C₃N₃Cl₃) with NaNH₂, K, or NaN₃. The synthesized samples were investigated by powder X-ray diffraction, elemental analysis (from C-N combustion), X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, mass spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and high-resolution electron microscopy. The synthesized carbon nitride with a graphite-like lamellar structure was obtained and observed for the first time. The formation mechanism of the carbon nitride was discussed.