Anthony Cook

Preliminary Evaluation of Digital Image Correlation for In-situ Observation of Low Temperature Atmospheric-Induced Chloride Stress Corrosion Cracking in Austenitic Stainless Steels

Digital image correlation has been used to observe the growth of atmospheric-induced chloride stress corrosion cracking in type 304L stainless steel under controlled conditions of temperature, relative humidity and chloride-deposition density in a nondestructive manner. The technique is capable of detecting changes in crack dimensions that are difficult to discern via conventional optical microscopy, i.e. crack growth beneath salt layers and adherent corrosion product deposits, and measurement of crack opening displacements. Our results also demonstrate that suitable specimen design, combined with digital image correlation, will provide the means of comparing the growth behaviour of short atmospheric-induced chloride stress corrosion cracks with data obtained from conventional pre-cracked compact tension specimens as a function of mechanical “driving force”.

A new method for the polymer-supported synthesis of cyclic oligoesters for potential applications in macrocyclic lactone synthesis and combinatorial chemistry

Attachment of ω-hydroxyalkanecarboxylic acids to Merrifield beads followed by treatment with a catalytic amount of di-n-butyltin oxide in chlorobenzene at 133 °C for 4–18 h brought about the formation of the corresponding cyclic oligomers (COs) as the main (>92%) soluble products in yields of 56–83%. Similar results were obtained with polymer-supported (PS) ricinoleic acid, which has a secondary hydroxy group, but attempts to carry out analogous reactions with PS lithocholic acid failed. PS 20-hydroxyicos-10-enoic acid and N-(11-hydroxyundecanoyl)-11-aminoundecanoic acid reacted well to give COs, the cyclic monomers being the major products. Samples of these cyclic monomers were isolated. The latter two hydroxy acids were also successfully assembled on the beads (the former using olefin metathesis) and then cyclo-oligomerised. There are several possible applications for this PS synthetic method. Thus, the COs might be used, via transesterifications, for the preparation of soluble combinatorial libraries of macrocycles, or used as starting materials for the small-scale combinatorial synthesis of copolyesters. For both of these applications the fact that the PS syntheses afford families of COs is not a problem because the applications involve the establishment of equilibria into which all of the COs can feed. Finally, these PS reactions may provide a useful approach to the small-scale synthesis of macrocyclic lactones with 15 or more ring atoms, since with these ring sizes the cyclised monomers are formed in >67% yield.

Assessing the risk of under-deposit chloride-induced stress corrosion cracking in austenitic stainless steel nuclear waste containers

Abstract This paper provides a short summary of investigations that have focused on the occurrence of the phenomenon that is commonly referred to as atmospheric chloride-induced stress corrosion cracking (AISCC) in types 304L and 316L austenitic stainless steels; the materials from which storage containers for the UK’s intermediate level nuclear waste are currently fabricated. A brief overview of the relationship between localised corrosion phenomena (pitting or crevice corrosion) and stress corrosion cracking from observations derived under conditions of immersion in chloride-containing environments is provided. The impact of environmental variables such as the relative humidity, temperature and chloride deposition density on the development of AISCC and potential difficulties in extrapolating data derived from laboratory investigations to an in-store situation are also discussed. Proposals for the development of laboratory protocols that may more accurately reflect behaviour in an actual storage situation, including the possibility of employing accelerated testing methods, are also briefly addressed.

Investigation into composition and deposition of artificially produced marine aerosols on austenitic stainless steels

Abstract This study focused on the effect of organic species on the occurrence of atmospheric-induced stress corrosion cracking (AISCC) in intermediate level waste (ILW) container materials under ‘wetted’ deposits of artificial sea-water (SW). Artificial SW solutions enriched with one of two bio-exudates – with organic carbon concentrations of between 92 and 451 μM – were employed to investigate changes in interfacial behaviour, associated with organic content, at the liquid–solid boundary on type 304L stainless steel (SS). These effects were determined in terms of contact angle and deposit diameter. On evaporation organically-enriched SW droplets deposited on 304L SS maintain a constant contact diameter on exposure to a relative humidity (RH) of 70±1%. By contrast deposits produced from artificial SW alone contract radially inwards. The bio-exudate that remained on the SS surface following the cleaning of deposits formed from organically enriched SW was visualised via cyanoacrylate fuming. This technique confirmed that bio-exudate adheres to 304L SS after removal of the inorganic components. The impact of organic enrichment on AISCC was investigated using droplets of test solutions on 304L U-bend specimens exposed to environmental conditions of 50·0±0·5°C and 30±1% RH.

Pit Propagation in Pure Aluminum Investigated via the 1D Artificial Pit Technique: Growth Regimes, Surface Morphology and Implications for Stability Criteria

The growth kinetics of various diameter aluminum artificial pitswere investigated under potential control in 1 mol dm-3 HCl. Pitsof diameter ? 50 ?m display mass transport control at highpotentials, Ohmic growth at intermediate values followed by atransition to a further region of potential-independent dissolution atca. 100 mV prior to repassivation. X-ray computed tomographicexamination of pit cross sections suggests the onset of Ohmicpropagation coincides with a transition to non-uniform dissolutionover the pit surface. By contrast 25 ?m diameter pits show noevidence of dissolution below their limiting current density andappear to grow without surface roughening until 20 mV above therepassivation potential. Investigation into the nature of growthprior to this potential via step-potential procedures confirmeddissolution proceeds under mass transport control. Overall theseobservations support the hypothesis that sustained pit propagationrequires a high degree of saturation, near 100%, in AlCl3.

Styrene-containing mesogens. Part 1: photopolymerisable nematic liquid crystals

Several members of a novel series of styrene-containing liquid crystal monomers, based on the cyanobiphenyl mesogenic group, possess thermally stable nematic phases. These materials display a large odd–even effect, relating to the length of the flexible spacer between the styrene and cyanobiphenyl units, which is very similar to previously described liquid crystal ‘dimers’ composed of two cyanobiphenyl units. It is shown that styrene (i.e. 4-vinylphenoxy) is an excellent terminal group for cyanobiphenyl mesogens as compared to a number of other phenyloxy groups. In addition, a compatible bifunctional mesogenic crosslinker is described. Photopolymerisation of an aligned film of a low-melting eutectic mixture derived from these compounds is achieved using cationic initiation in aerobic conditions.

A novel series of styrene-based liquid crystal monomers displaying either nematic or chiral nematic phases

A new series of liquid crystalline styrene‐based monomers is described. These monomers are prepared by the DCC‐mediated esterification reaction between 4‐[11‐(4‐vinylphenoxy)undecyloxy]benzoic acid and a range of phenols chosen due to their proven utility in the synthesis of liquid crystals. Most members of the series display thermally stable (enantiotropic) nematic phases, although a few give only monotropic nematic phases. By incorporating the (S)‐2‐methylbutyl side chain, monomers that exhibit the chiral nematic phase can be obtained. Predictably, monomers derived from phenols containing an additional ring as substituent (e.g. 4‐cyano‐4′‐hydroxybiphenyl) display relatively high transition temperatures. In contrast, monomers derived from simple 4‐n‐alkylphenols possess a nematic phase, which is accessible at moderate temperatures. In addition, a eutectic mixture derived from these monomers has a melting point only just above room temperature, which is an advantage for the fabrication of robust films via the in situ photopolymerization process. Standard free radical polymerization of a number of these monomers provides side chain liquid crystal polymers, SCLCPs, with mesophases that are stable over a wide temperature range. For a homologous series of SCLCPs containing a terminal n‐alkyl chain on the mesogenic group, an unexpected but distinct odd–even effect is observed.

Phthalocyanine-containing polystyrenes

An unsymmetrical phthalocyanine derivative containing a single styrene unit, prepared using a mixed phthalonitrile cyclotetramerisation, can undergo free radical polymerisation to give well-defined polystyrenes in which the macrocyclic components aggregate even in dilute solution.

Postgrads fight back

Tony Hughes states (November, Letters p17) that the SERC postgraduate studentship stipend has increased by a total of £1000 per annum since October 1989. He means, of course, that the stipend has risen by a total of £1000 over the two years from October 1989, not £2000. This increase is almost entirely consumed by the governments removal of housing benefit (about £10 per week in a £30 per week house – if you can find one that cheap) and inflation.