Journal of the American Ceramic Society

doi: 10.1111/jace.12947pmid: N/A

Microstructure of a carbonated alkali‐activated slag binder, showing calcium carbonate formation and residual silicate gel regions. Image: S.A. Bernal. Please see feature article, “Durability of alkali‐activated materials: progress and perspectives” by Susan A. Bernal and John L. Provis.

doi: 10.1111/jace.12948pmid: N/A

MS&T 2013 ACerS Ceramographic Exhibit & Competition Category: TEM, 2nd Place

Bernal, Susan A.; Provis, John L.; Green, D. J.

doi: 10.1111/jace.12831pmid: N/A

In the last decade, there has been rapid growth in interest in alternative binders, as part of the toolkit of cement technologies needed to mitigate the carbon footprint associated with the construction industry. Alkali‐activated materials (AAMs), including geopolymer binders and other related systems, have been identified as a key component of this move to lower CO2 cements and concretes. These are clinker‐free cements which can exhibit comparable performance to conventional portland/blended cements, when they are adequately formulated and cured. However, AAMs have a somewhat limited record of durability in service, and this is one of the main limitations facing their commercial adoption at present. To provide the best possible answers to the question of long‐term durability within an experimentally accessible timeframe, standardized accelerated degradation testing methods have been widely adopted, in an attempt to simulate natural processes. It has been identified that the interactions between material and environment, which take place on microstructural and nanostructural levels, have a very significant influence on the outcomes of the durability tests. Here, we present an overview of the results obtained when AAMs are exposed to aggressive testing conditions such as elevated concentrations of CO2, sulfates or chlorides. The key outcome of this article is a broader synthesis of the available data regarding the interactions between these new materials and their surrounding environment, which is then available to be used in the design, development, and implementation of environmentally sustainable, high‐performance cements and concretes for the 21st century.

Hu, Lei; Chen, Jun; Fan, Longlong; Deng, Jinxia; Yu, Ranbo; Xing, Xianran; Wilkinson, A.

doi: 10.1111/jace.12855pmid: N/A

With a simple ReO3‐type structure, ScF3 exhibits a rare property of isotropic negative thermal expansion over a large temperature range. In this study, a rapid and low‐temperature synthesis route has been developed to prepare pure phase of ScF3 in which NaNO3 or KNO3 as reaction media and Sc(NO3)3 and NH4HF2 as precursors (i.e., 30 min and 310°C). The sample of ScF3 has relatively regular morphology and shows high crystallinity as well as single‐crystalline nature. The type of molten salts has obvious impact on morphologies of the particles. Substituting NaNO3 with KNO3, cubes of ScF3 turns to be nanosticks. The thermal stability of the as‐prepared ScF3 was investigated by thermal analysis. Molten salts play a significant role in eliminating the nonstoichiometric impurity of ScF2.76 which is a common impurity during the conventional chemical reaction. This study reveals that molten salt is in favor of preparing those fluorides and relatives which is inert with moisture.

Xie, Zhipeng; Li, Shuang; An, Linan; Franks, G.

doi: 10.1111/jace.12869pmid: N/A

We report a novel oscillatory pressure‐assisted hot‐pressing process for preparing high‐quality ceramics. Compared with the samples prepared by conventional pressureless sintering (PS) and hot‐pressing (HP), the zirconia ceramic prepared by oscillatory pressure‐assisted hot‐pressing (OPAHP) exhibited a higher density, smaller grain size, and more homogeneous structure. More remarkably, the strength of the OPAHP sample reached 1556 MPa, which is much higher than the samples prepared by other two techniques. The results suggest that OPAHP is a more effective technique for preparing high‐quality zirconia, which is likely applicable to other material systems.

Zhao, Yong‐Li; Zhao, Chun‐Hua; Huang, Juan; Zhao, Bing; Park, D.‐S.

doi: 10.1111/jace.12870pmid: N/A

A bilayer concept was proposed to adjust the electrical properties of NTC thermistors. The conventional NTC material Ni0.75Mn2.25O4 was chosen as the sensitive layer, and high conductive LaMnO3–Ni0.75Mn2.25O4 composite was chosen as the support layer. The bilayer NTC thermistors were successfully fabricated by classical uniaxial pressing method. After cosintering at 1235°C for 4 h, the two layers adhered well to each other without any cracking or delamination. The resistance decreased linearly with the decrease in the thickness of Ni0.75Mn2.25O4 layer, and the B values varied between 3868 and 3901 K. After annealing at 150°C in air for 500 h, the resistance shifts at 25°C were less than 1%, which mean that the bilayer NTC thermistors had high stability.

Tseng, Ching‐Fang; Lin, Po‐An; Lanagan, M.

doi: 10.1111/jace.12880pmid: N/A

Novel glass–free low temperature firing microwave dielectric ceramics Li2CeO3 with high Q prepared through a conventional solid‐state reaction method had been investigated. All the specimens in this paper have sintering temperature lower than 750°C. XRD studies revealed single cubic phase. The microwave dielectric properties were correlated with the sintering conditions. At 720°C/4 h, Li2CeO3 ceramics possessed the excellent microwave dielectric properties of εr = 15.8, Q × f = 143 700 (GHz), and τf  = −123 ppm/°C. Li2CeO3 ceramics could be excellent candidates for glass‐free low‐temperature co‐fired ceramics substrates.

Sun, Shi‐Kuan; Zhang, Ya‐Ru; Masubuchi, Yuji; Motohashi, Teruki; Kikkawa, Shinichi; Troiler‐McKins, S.

doi: 10.1111/jace.12806pmid: N/A

The maintaining of the chemical composition and electrical insulativity of SrTaO2N ceramics was investigated during sintering and annealing, using powders prepared by the nitridation of Sr2Ta2O7. Due to the low thermal stability of SrTaO2N, the partial loss of SrO and nitrogen induced the formation of a TaO0.9 impurity after heat‐treating at above 1100°C. The sintering additive SrCO3 and postannealing in NH3 were employed to compensate for the loss of SrO and nitrogen to obtain ceramics with the original chemical composition. The as‐sintered SrTaO2N ceramics with various relative density (RD) were annealed in NH3 to observe the recovery of color and electrical insulativity. It was found that the inner part of the well‐sintered samples with RD = 95.1% could not be recovered by annealing, and continued to exhibit semiconducting behavior and a black color. On the other hand, for the as‐sintered SrTaO2N ceramics with RD < 84%, both the nitrogen content and electrically insulating behavior were completely recovered after annealing. The postannealed SrTaO2N ceramics (RD = 83.3%) possessed a relatively large dielectric constant of 450 with a low dielectric loss of less than 0.1 at 100 Hz, almost independent of frequency and temperature.

Manthina, Venkata; Patel, Tulsi; Agrios, Alexander G.; Riman, R.

doi: 10.1111/jace.12819pmid: N/A

ZnO nanorods have been studied extensively due to facile synthesis and useful optoelectronic properties for applications in nanoscale devices. In a common two‐step procedure, an ethanolic Zn2+ precursor solution is used to deposit ZnO seed crystals on a substrate, which is then immersed in an aqueous Zn2+ precursor solution to grow the nanorods. Here, a forced hydrolysis technique was employed based on additions of water and heat to the seed precursor solution before depositing the seeds on commercial fluorine‐doped tin oxide (FTO)/glass substrates. ZnO nanorods were then grown from these seeds by chemical bath deposition. Analyses showed that the forced hydrolysis resulted in an increase in seed crystallite size and a decrease in the number of seeds deposited. With increasing seed size, the number density of nanorods decreased, while the length and diameter of each rod increased. These findings offer a simple method for exerting control over the number density of ZnO nanorods that is compatible with the rough FTO surface, unlike other methods that require smoother substrates.

Von Hagen, Robin; Sneha, Mahima; Mathur, Sanjay; Derby, B.

doi: 10.1111/jace.12832pmid: N/A

Hollow tin‐oxide (SnO2) nanospheres were synthesized by coating, carbon nanospheres (CNs) as hard templates, with a tin(IV) sol obtained by partial hydrolysis of [Sn(OBut)4] under ambient conditions. Formation of crystalline SnO2 spheres upon calcination was confirmed by powder X‐ray diffraction data, whereas the hollow interiors of SnO2 particles were verified by scanning and transmission electron microscopy of both intact and broken spheres. The shell of SnO2 nanospheres sintered at 700°C consisted of a single layer of nanocrystallites (~6 nm) self‐assembled in a ball‐like superlattice. Tin‐oxide hollow spheres showed an average diameter of 150 nm and could be homogeneously dispersed in water/ethylene glycol (50:50 vol%) mixture to form stable inorganic inks viable for their use in commercial ink‐jet printers demonstrated by printing porous ceramic structures on an interdigitated sensor chip. The integration of large surface and nanoscopic voids in the final structures imparted higher sensitivity to the as‐printed sensors toward both oxidizing (nitrogen dioxide) and reducing gases (methane and ethanol), which validates the enormous potential of printable inorganics in functional applications.