As with all alloys, the grain structure of the nickel-base superalloy 625 has a significant impact on its mechanical properties. Predictability of the grain structure evolution in this material is particularly pertinent because it is prone to inter-metallic precipitate formation both during manufacture and long term or high temperature service. To this end, analysis has been performed on the grain structure of Alloy 625 aged isothermally at temperatures between 600-800 • C for times up to 3000 hours. Fits made according to the classical Arrhenius equation describing normal grain growth yield an average value for the activation energy of a somewhat inhomogeneous grain structure above 700 • C of 108.3±6.6 kJ mol −1 and 46.6±12.2 kJ mol −1 below 650 • C. Linear extrapolation between 650-700 • C produces a significantly higher value of 527.7 ± 23.1 kJ mol −1 . This result is ultimately a consequence of a high driving force, solute-impeded grain boundary migration process operating within the alloy.Comparison of the high and low temperature values with the activation energy for volume self-diffusion and grain boundary diffusion identifies the latter as the principle governing mechanism for grain growth in both instances. A decrease in the value of the time exponent (n) at higher temperatures despite a reduction in solute drag is attributable to the Zener pinning imposed by grain boundary M 6 C and M 23 C 6 particles identified from Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDXS) analysis.Vickers hardness results show the dominance of intermetallic intragranular precipitates in 1 the governance of the mechanical properties of the material with grain coarsening being accompanied by a significant increase in hardness. Furthermore, the lack of any correlation with grain growth behaviour indicates these phases have no significant effect on the grain evolution of the material.

We report the use of diatom frustules as scaffolds for the growth of molybdenum disulfide nanosheets. The frustules were impregnated with a single source molecular precursor complex which is converted to MoS 2 by solventless thermolysis. Randomly oriented few-layer thick MoS 2 nanosheets are found to coat both the exterior surface and internal pores of the scaffold.Nature displays exquisite control of phase and morphology during biomineralisation and the resulting mineralised structures have been found to possess attractive functional properties, particularly in the area of photonics. [1][2][3][4] Consequently there is considerable scientific interest in replicating the intricate architectures found in nature, 5-9 as well as enhancing the intrinsic properties of biomineralised structures' by decoration with inorganic nanostructures. [10][11][12][13] Diatoms are marine-dwelling eukaryotic unicellular algae, 14 which produce biomineralised silica exoskeletons known as frustules. Diatom frustules comprise the majority of the biosilica found in oceans, 14 and bulk quantities of the fossilised shells are recovered by dredging. This material is known as diatomaceous-earth (DE). It is widely available and inexpensive and finds use in a number of products including toothpaste and as a laboratory filter aid (under the trade name Celite™). Additionally, the intricate hierarchical nanostructures found in diatom frustules have attracted considerable interest for nanotechnology applications. 15,16 Diatom frustules have the highest strength-to-weight ratio of all reported natural biomaterials, 17 their periodic nanoscale pores result in both high surface areas and unique photonic properties which enhance light uptake. 15, 18 In the living diatom this aids photosynthesis but the functional structures persist in the deceased organisms' biomineral shell. 15, 18, 19 Biosilica is an inert insulator which provides an ideal scaffold or template for functional materials. 13, 15,[20][21][22] By introducing semiconducting materials into the biomineralised architecture it is potentially possible to exploit the frustules' photonic properties for light harvesting or its large surface area for sensing and catalytic applications. 15, 19, 20 For example, diatom frustules coated with TiO 2 have been incorporated into dye sensitised solar cells, where the devices' enhanced performance was attributed to improved light scattering by the diatoms. 15 A surface sol-gel process has been used to coat diatom frustules with a ~50 nm thick layer of SnO 2 ; the resulting structures were used as NO gas detectors. 20 Bao et al. have reported the conversion of the insulating silica of diatom frustules to semiconducting silicon by magnesiothermic reduction, 23 after which the photocatalytic properties of the resulting structures was enhanced by subsequent deposition of CdS on the frustule's surface. 19 However, to-date, there have been no reports of the functionalization of biomineralised structure with twodimensional (2D) semiconductor materials.Mol...

The paper reports on the performance of 34 different concrete mixes containing glass crushed to ¾-in. (19-mm) maximum size as coarse aggregate and six reference mixes made with gravel of the same size. Two cements of alkali equivalent 0.58 and 1.13, classifiable as low and high alkali (ASTM C 150-72), in amounts ranging from 400–900 lb/yd3 (237–534 kg/m3 were used in combination with glass both with the fines removed and in the as-crushed condition. Partial cement replacement with fly ash and mixing of glass with gravel aggregate were included in an attempt to find a suitable method of overcoming the expected adverse effects of the reaction between glass and cement alkalis. On the basis of compressive strength, flexural strength, expansion, and visible surface deterioration recorded up to an age of one year, the results show that in many cases the direct combination of glass with portland cement yields concrete which exhibits marked strength regression and excessive expansion due to alkali-aggregate reaction. The conditions under which performance is satisfactory appear to relate to limiting maximum values of cement content and alkali equivalent. Replacement of 25 to 30 percent by weight of the cement, whether low or high alkali, appears to be an effective and widely applicable method of ensuring good long-term concrete performance, although the minimum required in any given case may be related to cement composition.

Sulfate attack on concrete can either be of expansion-cracking type due to ettringite formation or of surface deterioration type due to acidic nature of sulfate solutions. The present test methods for determining sulfate resistance generally evaluate the expansive attack phenomenon. Since low C3A portland cements are not susceptible to this type of attack, new methods need to be developed to test the long-time resistance of these cements to the acidic type of sulfate attack. An attempt to develop a laboratory method involving immersion of small specimens of cement paste in a sulfate solution held at constant pH is described. Preliminary results are given for five different types of cements tested in accordance with the new method.

Ultrasonic testing using contacting transducers such as quartz or PZT is well established. However, standard measurement techniques used require physical contact of the sample and ultrasonic transducer and some sort of couplant between the two. With this configuration there is a possibility of damaging the sample, transducer or bond during testing, thermal cycling, or removal of the transducer. We present results taken using recent advances in non-contact methods of ultrasound generation and detection using electromagnetic acoustic transducers (EMATs), which offer some significant benefits over contact ultrasonic techniques. Circumventing the need for couplant removes the possibility of contaminating the system, which is an issue for some material property measurements, and allows easier measurements over a wider range of temperatures. An automated data analysis system has been developed which allows the velocity of sound in the sample, and hence the elastic constants, to be determined to a high accuracy. This technique is illustrated using measurements of the alloy Gd64Sc36.