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In this work, a metal–glass joint between Ti and K9 glass was obtained by vacuum diffusion bonding after Ti was pre-oxidized at different temperatures to explore the effect of the pre-oxidation procedure on the properties of diffusion bonding joints. For the oxide layer, X-ray diffraction revealed that the oxide film consisted of TiO2 and some low-valence Ti–O compounds such as Ti6O, Ti3O, TiO, etc. The x/y ratio of TixOy decreased as oxidation temperature increased. Scanning and transmission electron microscopy showed that the morphology of the oxide layer gradually changed from dense to loose and porous, and the oxidized particle size gradually increased and distributed in layers from inside to outside, with the increase in temperature. From the results of diffusion bonding at 700 °C for 2 h, good Ti-K9 joints without cracks and pores can be obtained when the pre-oxidation temperature attained 900 °C. A transition layer appeared at the Ti-K9 interface with the diffusion of elements Ti, Si, and O, etc. Shear strength tests showed that the structure of the oxide layer at different conditions can directly affect the strength of the joint between Ti and glass. The joint to Ti pre-oxidized at 900 °C exhibited the highest shear strength, producing an average failure strength of 20.6 ± 1.2 MPa. An appropriate amount of oxide layer can improve the quality of the Ti-K9 joint. The feasibility of diffusion bonding added to process versatility for the use of Ti-K9 joint on practical application. [ABSTRACT FROM AUTHOR]

The isothermal wetting and spreading behaviors of Sn-Ti/ZrO2 systems were investigated by the sessile drop method, and the interfacial microstructures were characterized by XRD and TEM. The wettability improved significantly with the increase in Ti content or with the increase in temperature as a result of the interfacial phenomena. For example, for tests at 1000 °C, we found that: (1) XTi = 0 to XTi = 2.0%, the final contact angle decreased from 144° to 42° along with the increase in the coverage of ZrO2 by a Ti2O3 interfacial layer; (2) XTi = 2.0% to XTi = 4.0%, the contact angle decreased to 22° because of the replacement of Ti2O3 by a more metallic layer; (3) XTi = 4.0% to XTi = 8.0%, no further decrease in the angle was observed as the interfacial layer remains Ti11.31Sn3O10. For XTi = 4.0%, the temperature increase from 900 to 1000 °C led to a decrease in contact angle from 47° to 22°, respectively, due to the interfacial layer shifting from Ti2O3 to Ti11.31Sn3O10. For all the systems, the Ti enhanced the loss of oxygen from zirconia leading to the formation of black ZrO2-x. Spreading kinetics of Sn-Ti/ZrO2 systems was controlled by the reaction-limited dynamics. The diffusion of released oxygen changed the spreading rate in the rapid-spreading stage. [ABSTRACT FROM AUTHOR]

Geopolymer with Si/Al ratios from 2 to 4 were prepared by adding different contents of fused silica into geopolymer matrix. Effects of Si/Al ratios on the structure, mechanical properties and chemical stability in air of the obtained geopolymer were systematically investigated. The results showed that all the geopolymer samples were XRD amorphous. Geopolymer with Si/Al ratios of 2 and 2.5 showed similar structure and property and they were classed as KGP-I; and geopolymer with Si/Al ratios of 3, 3.5 and 4 were similar and they were class as KGP-II. In alkaline solution, reactivity of fused silica were higher than that of metakaolin, resulting in higher content of both residual metakaolin and free alkaline cation in KGP-II than in KGP-I. Fused silica partially reacted with the alkaline solution in KGP-II indicating chemical interfacial bonding between silica and binder phase. With the increase in Si/Al ratios, KGP-II especially for geopolymer with Si/Al of 4 showed much higher mechanical properties than KGP-I due to the increased Si-O-Si bonds and residual silica as reinforcement. However, KGP-II showed worse chemical stability in air than KGP-I, with the presence of efflorescence on the surface, which was attributed to their higher residual free K + . [ABSTRACT FROM AUTHOR]

In this paper, synthetic metakaolin with fixed composition (Al2O3·2SiO2) was produced by a simple chemosynthetic route. The chemosynthetic metakaolin can eliminate the influence of impurities in metakaolin from natural kaolin minerals. The synthetic metakaolin together with NaOH and SiO2-sol were used to prepare Na-based geopolymer precursors with various molar ratios of Si/Al. The molar ratios of Si/Al from 1 to 2 were tailored by adding different contents of SiO2-sol. Zeolite/geopolymer composites or monolith-type zeolite were successfully fabricated from synthetic metakaolin-based geopolymer through a hydrothermal process. The effects of Si/Al ratios on the phase composition and microstructure of the produced zeolite/geopolymer composites or zeolites were studied. The results proved that the composition of synthetic metakaolin and geopolymer precursors can be facilely tuned, and the monolithic geopolymer precursors can be mostly, or even totally, transformed into zeolite after hydrothermal treatment. [ABSTRACT FROM AUTHOR]

Abstract: The thermal evolution of cesium-substituted potassium-based geopolymer ((K1−x Cs x )2O·Al2O3·5SiO2·11H2O, x =0, 0.1, 0.2, 0.3, and 0.4) on heating is studied by a variety of techniques. Phase compositions and thermal expansion behaviors of the ceramics derived from the geopolymer are characterized. All of the geopolymer specimens with or without cesium substitution exhibit similar thermal evolution trends. Major weight losses before 600°C from all the geopolymer specimens are observed and are resulted from evaporation of free water and hydroxyl groups. Thermal shrinkage of these specimens can be divided into four stages, i.e. structural resilience, dehydration, dehydroxylation and sintering, according to the dilatometer results. For these specimens, significant difference is observed in the viscous sintering stage and the effect of cesium is to reduce the thermal shrinkage in this stage due to the increased matrix viscosity. In the ceramics derived from geopolymer, the amount of stabilized leucite increases with the amount of cesium and with 20% cesium substitution leucite is fully stabilized in cubic phase. [ABSTRACT FROM AUTHOR]

Abstract Brazing and soldering following pre-metallization were employed to obtain reliable ZrO 2 /Sn-Ti/ZrO 2 joints. Both the metallization and brazing depend on the wettability of ZrO 2 by Sn-Ti alloys. The interfacial microstructure of joints was analyzed by SEM, XRD and TEM, and the shear strength of joints was evaluated. Good brazed joints and fully covered metallization layers, leading to good soldered joints, were obtained by the Sn-4Ti and Sn-8Ti alloys, while unsatisfactory results were obtained with Sn-1Ti and Sn-2Ti alloys owing to their limited wettability on ZrO 2. Both kinds of ZrO 2 /Sn-Ti/ZrO 2 joints possessed a β-Sn matrix with Ti 6 Sn 5 and Ti 2 O 3 interfacial layers. A higher Ti concentration per unit area induced the formation of a Ti 11.31 Sn 3 O 10 layer along with the reduction of the Ti 2 O 3 layer thickness at the interface in the soldered joints. All the joints exhibited a similar shear strength of 22 ∼ 28 MPa and fractured through the β-Sn matrix. [ABSTRACT FROM AUTHOR]

Abstract: Unidirectional carbon fiber reinforced geopolymer composite (Cuf/geopolymer) is prepared by a simple ultrasonic-assisted slurry infiltration method, and then heat treated at elevated temperatures. Effects of high-temperature heat treatment on the microstructure and mechanical properties of the composites are studied. Mechanical properties and fracture behavior are correlated with their microstructure evolution including fiber/matrix interface change. When the composites are heat treated in a temperature range from 1100 to 1300°C, it is found that mechanical properties can be greatly improved. For the composite heat treated at 1100°C, flexural strength, work of fracture and Young''s modulus reach their highest values increasing by 76%, 15% and 75%, respectively, relative to their original state before heat treatment. The property improvement can be attributed to the densified and crystallized matrix, and the enhanced fiber/matrix interface bonding based on the fine-integrity of carbon fibers. In contrast, for composite heat treated at 1400°C, the mechanical properties lower substantially and it tends to fracture in a very brittle manner owing to the seriously degraded carbon fibers together with matrix melting and crystal phases dissolve. [Copyright &y& Elsevier]

Abstract: A kind of sheet-like carbon fiber preform was developed using short fibers (2, 7 and 12mm, respectively) as starting materials and used to strengthen a geopolymer. Mechanical properties, fracture behavior, microstructure and toughening mechanisms of the as-prepared composites were investigated by three-point bending test, optical microscope and scanning electron microscopy. The results show that the short carbon fibers disperse uniformly in geopolymer matrix. The Cf/geopolymer composites exhibit apparently improved mechanical properties and an obvious noncatastrophic failure behavior. The composite reinforced by the carbon fibers of 7mm in length shows a maximum flexural strength as well as the highest work of facture, which are nearly 5 times and more than 2 orders higher than that of the geopolymer matrix, respectively. The predominant strengthening and toughening mechanisms are attributed to the apparent fiber bridging and pulling-out effect based on the weak fiber/matrix interface as well as the sheet-like carbon fiber preform. [Copyright &y& Elsevier]