26 research outputs found
A study of hexavalent and trivalent chromium conversion coatings on zinc surfaces
Physical, chemical and corrosion properties of a hexavalent chromium conversion coating
(CCC) and that of a commercial third generation trivalent chromium system; Tripass LT1500,
on zinc electrodeposited steel has been studied. Moreover, the role of additives has been
studied to elucidate film formation and corrosion resistance mechanisms. Micro-cracking and
self-repair corrosion protection behaviour commonly associated with hexavalent CCCs has
also been investigated.
Scanning Electron Microscopy (SEM) studies showed that for both hexavalent and trivalent
CCCs were in general, flat with a spherical-like structure and in the case of the former microcracked
beyond 122 nm conversion coating thickness. In general, the micro-crack pattern
observed e.g. a dense crack network, depended upon the underlying zinc substrate
morphology. The study has also demonstrated the effect of SEM imaging and prior specimen
preparation conditions on hexavalent CCC micro-cracking and blistering.
X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Infrared
(IR) data has indicated that the hexavalent CCC film formation appears to be a
electrochemical / sol-gel mechanism given the lack of zinc content at surface and subsurface
regions within the conversion coating, presence of H2O and in particular the contribution of
Cr(OH)3 as opposed to Cr2O3. An alternative film formation mechanism may exist for
trivalent CCC given a higher proportion of zinc at surface and sub-surface regions, IR data
analysis indicating that chromium is possibly deposited from a chromium (III) complex ion
such as [CrC2O4(H2O)4]
+
, moreover as Cr(OH)3 and Cr2O3 compounds as indicated by XPS
data analysis. The role of cobalt nitrate during film formation is unclear given that cobalt was
not detected within the trivalent CCC from XPS and AES data.
Electrochemical LPR measurements, polarisation curves and XPS data has shown in general,
self-repair corrosion protection properties for hexavalent CCC to be lacking. Instead, it is
proposed that the corrosion protection behaviour for hexavalent and trivalent CCC to be
barrier. Polarisation curves and LPR data showed that the corrosion resistance performance
for trivalent CCC was higher than hexavalent CCC, in general. LPR data showed that the
omission of cobalt nitrate and increased addition of sodium molybdate content within the Tripass LT1500 treatment solution formulation was found to overall decrease corrosion
resistance within the trivalent CCC.
In addition, silica based topcoat and black trivalent CCCs was also investigated and
characterised using AES, SEM and LPR. Zinc whiskers was also observed from zinc
electrodeposits following exposure to thermal treatment (150°C for 1 h). Elemental analysis
and grain pattern investigations failed to help determine the cause of zinc whisker initiation.
Zinc whiskers was seen to protrude out of hexavalent and trivalent CCCs, with the latter
requiring a longer thermal exposure time
One-pot methodology for the synthesis of polysubstituted pyridines and terpyridines
Polysubstituted pyridines are prepared by a one-pot three-component cyclocondensation process, developed by modification and improvement of the traditional Bohlmann-Rahtz reaction. The synthesis combines a 1,3-dicarbonyl compound, ammonia, and an alkynone without the use of an additional acid catalyst. This three-component heteroannulation reaction proceeds by tandem Michael addition-heterocyclization with total control of regiochemistry and the resulting library of pyridines is isolated in good yield. Modified Bohlmann-Rahtz procedures were applied to the synthesis of a range of terpyridines, by a two- and three-component condensation of 2,6-propynoylpyridine derivatives and a range of enamines, or 1,3-dicarbonyl compounds and ammonia, proceeding in moderate to good yield using a range of conditions. The synthesis of fluorescent cyanopyridines with desirable photophysical properties from p- aminocrotononitrile and a variety of heterocyclic alkynones was established by one-pot Bohlmann-Rahtz reaction in excellent yields. These cyanopyridines can be generated in good yield, rapidly, using microwave irradiation. Primary thioamides are prepared in excellent yield from the corresponding nitriles by treatment with ammonium sulfide in methanol, at room temperature for electron deficient aromatic nitriles or under microwave irradiation at 80 C or 130 C in 15-30 minutes for other aromatic and aliphatic nitriles without the need for chromatographic purification.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
One-pot methodology for the synthesis of polysubstituted pyridines and terpyridines
Polysubstituted pyridines are prepared by a one-pot three-component cyclocondensation process, developed by modification and improvement of the traditional Bohlmann-Rahtz reaction. The synthesis combines a 1,3-dicarbonyl compound, ammonia, and an alkynone without the use of an additional acid catalyst. This three-component heteroannulation reaction proceeds by tandem Michael addition-heterocyclization with total control of regiochemistry and the resulting library of pyridines is isolated in good yield. Modified Bohlmann-Rahtz procedures were applied to the synthesis of a range of terpyridines, by a two- and three-component condensation of 2,6-propynoylpyridine derivatives and a range of enamines, or 1,3-dicarbonyl compounds and ammonia, proceeding in moderate to good yield using a range of conditions. The synthesis of fluorescent cyanopyridines with desirable photophysical properties from p- aminocrotononitrile and a variety of heterocyclic alkynones was established by one-pot Bohlmann-Rahtz reaction in excellent yields. These cyanopyridines can be generated in good yield, rapidly, using microwave irradiation. Primary thioamides are prepared in excellent yield from the corresponding nitriles by treatment with ammonium sulfide in methanol, at room temperature for electron deficient aromatic nitriles or under microwave irradiation at 80 C or 130 C in 15-30 minutes for other aromatic and aliphatic nitriles without the need for chromatographic purification
Effect of heat treatment on zinc whisker growth from electrodeposited coatings
The effects of simple heat treatments on electrodeposited zinc coatings formed on
mild steel substrates were examined. It was found that over a temperature range of
50-200°C for 1 and 24 h periods zinc whisker growth was evident. The additional
effects of electrodeposited coating thickness and subsequent chromium-based
passivation processes were also examined in terms of their effect on whisker growth.
Individual whisker morphologies were investigated utilising a field emission gun
scanning electron microscopy (FEGSEM) and focused ion beam field emission gun
scanning electron microscopy (FIB-FEGSEM)
An X-ray photoelectron spectroscopy investigation of chromium conversion coatings and chromium compounds
Hexavalent and trivalent chromium based conversion coatings on zinc
electrodeposited steel have been investigated using X-ray photoelectron
spectroscopy (XPS) with the aim of elucidating their film chemistry. Furthermore, a
monochromatic Al Kα X-ray source was utilised and the spectra produced evaluated
using curve fitting software to elucidate oxidation state information. In addition, a
number of chromium compounds were investigated and used to complement the
curve fitting analysis for the conversion coatings.
High resolution Cr2p spectra from chromium compounds exhibited multiplet splitting
for Cr2O3. Additional satellite emissions can also be observed for Cr2O3 and Cr(OH)3.
Curve fitting of hexavalent chromium conversion coating (CCC) 2p3/2 spectra
contained both Cr(VI) and Cr(III) species with the content of the former slightly higher
when the X-ray beam take-off angle (TOA) was reduced to determine more surface
specific information. The Cr(III) content was determined to be mainly composed of
Cr(OH)3 with some Cr2O3. In comparison, trivalent CCCs were largely composed of
Cr2O3 as opposed to Cr(OH)3. Survey scans of both coatings revealed that the
trivalent CCCs had a higher relative zinc content
Healthcare Resource Utilization Associated with Intermittent Oral Corticosteroid Prescribing Patterns in Asthma
Acknowledgments We would like to thank Anna Mett of in Science Communications, Springer Healthcare, UK, for providing medical writing support, which was funded by AstraZeneca.Peer reviewe
Trends in systemic glucocorticoid utilization in the United Kingdom from 1990 to 2019 : a population-based, serial cross-sectional analysis
Acknowledgments The authors thank the members of the Forum for reducing Oral Corticosteroid Use in Severe asthma (FOCUS) for their involvement in the conception of the study (Table S5). Medical writing support, including preparation of the draft manuscript under the direction and guidance of the authors, incorporating author feedback, and manuscript submission, was provided by Lea Anne Gardner, PhD, RN (CiTRUS Health Group), in accordance with Good Publication Practice 2022 (GPP 2022) guidelines. This support was funded by AstraZeneca (Cambridge, UK). Data from OPCRD were obtained under license from Optimum Patient Care Limited. The interpretation and conclusions contained in this report are those of the authors alone. Funding This work was funded by AstraZeneca. In collaboration with the steering committee, AstraZeneca was involved in the study design; in the collection, analysis, and interpretation of data; in the writing of the manuscript; and in the decision to submit the article for publication. All authors had full access to the data, agreed to be accountable for the accuracy and integrity of the work, and shared responsibility for the decision to submit the article for publication. Steering committee members were not compensated for their participation.Peer reviewe
Investigation of whisker growth from alkaline non-cyanide zinc electrodeposits
Electroplated zinc finishes have been widely used in the packaging of electronic products for many years as a result of their excellent corrosion resistance and relatively low cost. However, the spontaneous formation of whiskers on zinc electroplated components, which are capable of resulting in electrical shorting or other damaging effects, can be highly problematic for the reliability of long-life electrical and electronic equipment. This work investigated the mechanism for whisker growth from zinc electrodeposited mild steel substrates. The incubation time for whisker growth from the surface of nodules on the surface of the electrodeposit was considerably reduced compared with that from the planar deposit surface. Recrystallisation of the as-deposited columnar structure was observed at the whisker root. This result is consistent with some recent whisker growth models based on recrystallisation. There was no evidence of iron-zinc (Fe-Zn) intermetallic formation at the iron/zinc (Fe/Zn) interface or within the zinc coating beneath the whiskers