Profiling hot isostatically pressed canister–wasteform interaction for Pu-bearing zirconolite-rich wasteforms

Zirconolite-rich full ceramic wasteforms designed to immobilize Pu-bearing wastes were produced via hot isostatic pressing (HIP) using stainless steel (SS) and nickel (Ni) HIP canisters. A detailed profiling of the elemental compositions of the major and minor phases over the canister–wasteform interaction zone was performed using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS) characterization. Bulk sample analyses from regions near the center of the HIP canister were also conducted for both samples using X-ray diffraction and SEM-EDS. The sample with the Ni HIP canister showed almost no interaction zone with only minor diffusion of Ni from the inner wall of the canister into the near-surface region of the wasteform. The sample with the SS HIP canister showed ∼100–120 μm of interaction zone dominated by high-temperature Cr diffusion from canister materials to the wasteform with the Cr predominantly incorporated into the durable zirconolite phase. We also examined, for the first time, changes to the HIP canister wall thickness caused by HIPing and demonstrated that no canister wall thinning occurred. Instead, in the areas examined, the canister wall thickness was observed to increase (up to ∼20%) due to the compression occurring during the HIP cycle. Further, only sparse formation of (Cr, Mn)-rich oxide particles were noted within the HIP canister inner wall area immediately adjacent to the ceramic material, with no evidence for reverse diffusion of ceramic materials. Though the HIP canister–wasteform interaction extends to ∼120 μm when using an SS HIP canister for the system investigated, this translates to <<1 vol.% for an industrial scale HIPed wasteform. Importantly, the HIP canister–wasteform interactions did not produce any obviously less durable phases in the wasteform or had any detrimental impact on the HIP canister properties.     

Air-Coupled Ultrasonic Resonance Imaging of Hexagonal SiC and Alumina Tiles

Resonant ultrasound spectroscopy (RUS) is an NDE technique that evaluates a sample based on its predicted resonant behavior, but RUS is limited by lack of spatial resolution and small specimen size. Air-coupled ultrasonic resonance imaging (ACURI) is a new NDE technique that is based on RUS but introduces a spatial resolution by generating an image of the flexural vibration modes. This paper presents experimental results of ACURI applied to hexagonal silicon carbide tiles. Frequency sweep scans demonstrate the ability of air-coupled transducers to detect resonance modes. Several mode shapes are imaged and compared to Finite Element simulations with good agreement. Visual comparison allows for easy detection of material differences such as density variations.     

Role of MoS2 morphology on wear and friction under spectrum loading conditions

One of the ways by which grease is evaluated is by using a four‐ball wear test using ASTM D2266. However, actual applications may require bearings to be subjected to spectrum loading conditions. This study focuses on using ball milling to mitigate the wear from sharp edges in the MoS₂ particles. Two different blends of greases were formulated using MoS₂ in the as‐received state (unmilled) and milled MoS₂; they were tested under spectrum loading conditions where the load and frequency of the tests were treated as variables. It was found that ball milling of the MoS₂ significantly reduces the wear under spectrum loading condition both for ramp‐up and ramp‐down conditions. It was also shown that shortening the time step for both the ramp‐up and ramp‐down cycles resulted in larger wear for unmilled MoS₂ particles in comparison with milled MoS₂ particles in grease. The milling process did not play a significant role when frequency of the test was either ramped up or down. Copyright © 2015 John Wiley & Sons, Ltd.     

XANES analysis of calcium and sodium phosphates and silicates and hydroxyapatite–Bioglass®45S5 co-sintered bioceramics

Bioglass®45S5 was co-sintered with hydroxyapatite at 1200 °C. When small amounts (< 5 wt.%) of Bioglass®45S5 was added it behaved as a sintering aid and also enhanced the decomposition of hydroxyapatite to β-tricalcium phosphate. However when 10 wt.% and 25 wt.% Bioglass®45S5 was used it resulted in the formation of Ca₅(PO₄)₂SiO₄ and Na₃Ca₆(PO₄)₅ in an amorphous silicate matrix respectively. These chemistries show improved bioactivity compared to hydroxyapatite and are the subject of this study. The structure of several crystalline calcium and sodium phosphates and silicates as well as the co-sintered hydroxyapatite–Bioglass®45S5 bioceramics were examined using XANES spectroscopy. The nature of the crystalline and amorphous phases were studied using silicon (Si) and phosphorus (P) K- and L_2,3-edge and calcium (Ca) K-edge XANES.Si L_2,3-edge spectra of sintered bioceramic compositions indicates that the primary silicates present in these compositions are sodium silicates in the amorphous state. From Si K-edge spectra, it is shown that the silicates are in a similar structural environment in all the sintered bioceramic compositions with 4-fold coordination.Using P L_2,3-edge it is clearly shown that there is no evidence of sodium phosphate present in the sintered bioceramic compositions. In the P K-edge spectra, the post-edge shoulder peak at around 2155 eV indicates that this shoulder to be more defined for calcium phosphate compounds with decreasing solubility and increasing thermodynamic stability. This shoulder peak is more noticeable in hydroxyapatite and β-TCP indicating greater stability of the phosphate phase. The only spectra that does not show a noticeable peak is the composition with Na₃Ca₆(PO₄)₅ in a silicate matrix indicating that it is more soluble compared to the other compositions.     

Influence of Inclusion and Specimen Orientations on Intergranular Corrosion Testing of AISI 316LN Stainless Steel

Fabricated components must be free from sensitization for using these in critical applications in aggressive environments. During fabrication of a hollow bar from solid bar, deep hole drilling was employed which introduces residual stresses. Stress-relieving heat treatment was employed by heating the hollow bar from room temperature to 1,065°C @ 40°C/h and soaking at 1,065°C for 1 h followed by cooling @ 40°C/h as well as 70°C/h. To detect the susceptibility to IGC, specimens were taken from both circumferential direction as well as longitudinal direction and subjected to ASTM A 262 Practice E test. In U bend, the specimens from the circumferential direction failed whereas longitudinal specimens did not fail. However specimens of both orientations showed Step structure in Practice A test indicating that no carbide has nucleated during the stress-relieving heat treatment ensuring that the cooling rates are faster than the critical cooling rates and the material is not susceptible to IGC. EDAX studies indicated the presence of numerous MnS inclusions enriched in chromium which might have led to chromium depletion around the inclusions resulting in poor passivity at these locations. This study presents the influence of orientation of MnS inclusions in causing failure in U bend test. The need to select specimens of correct orientation during IGC testing is emphasized in this investigation.     

Studies on Hg(II) ion retention properties of cross-linked graft copolymer of acrylic acid and its analytical application

The effects of different parameters such as time, concentration, pH and temperature, on metal ion retention properties of the polymer have been investigated. Metal ion adsorption kinetics, isotherms and thermodynamics have been studied. A plausible mechanism for mercury ion retention has been suggested. Mercuric ion has been isolated quantitatively from various synthetic mixture containing metal ions (Ni²⁺, Cd²⁺, Pb²⁺ and Zn²⁺).     

Conceptual Design of Unpressurized Shelters on Lunar Surface

Three concepts for the shelters on the moon are presented here. It is envisaged that the first robots will land on the moon and start preparing sites for advanced bases and also for future human presence. These robots will encounter severe radiation and micrometeor hits when they are exposed to the lunar atmosphere. During the period of intense solar radiation these robots have to be temporarily sheltered, since shielding on the robots may not be adequate to protect the instruments. The construction of these shelters has to be performed with very little equipment support. This paper presents concepts and their feasibility analysis for the fabrication of shelters under such stringent constraints.     

A new efficient optimal path planner for mobile robot based on Invasive Weed Optimization algorithm

Planning of the shortest/optimal route is essential for efficient operation of autonomous mobile robot or vehicle. In this paper Invasive Weed Optimization (IWO), a new meta-heuristic algorithm, has been implemented for solving the path planning problem of mobile robot in partially or totally unknown environments. This meta-heuristic optimization is based on the colonizing property of weeds. First we have framed an objective function that satisfied the conditions of obstacle avoidance and target seeking behavior of robot in partially or completely unknown environments. Depending upon the value of objective function of each weed in colony, the robot avoids obstacles and proceeds towards destination. The optimal trajectory is generated with this navigational algorithm when robot reaches its destination. The effectiveness, feasibility, and robustness of the proposed algorithm has been demonstrated through series of simulation and experimental results. Finally, it has been found that the developed path planning algorithm can be effectively applied to any kinds of complex situation.