A Microstructural and Kinetic Investigation of the KCl-Induced Corrosion of an FeCrAl Alloy at 600 A degrees C

The corrosion behaviour of a FeCrAl alloy was investigated at 600 A degrees C in O-2 + H2O with solid KCl applied. A kinetics and microstructural investigation showed that KCl accelerates corrosion and that potassium chromate formation depletes the protective scale in Cr, thus triggering the formation of a fast-growing iron-rich scale. Iron oxide was found to grow both inward and outward, on either side of the initial oxide. A chromia layer is formed with time underneath the iron oxide. It was found that although the alloy does not form a continuous pure alumina scale at the investigated temperature, aluminium is, however, always enriched at the oxide/alloy interface

Development and validation of a new clinical decision support tool to optimize screening for retinopathy of prematurity

Background/Aims Prematurely born infants undergo costly, stressful eye examinations to uncover the small fraction with retinopathy of prematurity (ROP) that needs treatment to prevent blindness. The aim was to develop a prediction tool (DIGIROP-Screen) with 100% sensitivity and high specificity to safely reduce screening of those infants not needing treatment. DIGIROP-Screen was compared with four other ROP models based on longitudinal weights. Methods Data, including infants born at 24–30 weeks of gestational age (GA), for DIGIROP-Screen development (DevGroup, N=6991) originate from the Swedish National Registry for ROP. Three international cohorts comprised the external validation groups (ValGroups, N=1241). Multivariable logistic regressions, over postnatal ages (PNAs) 6–14 weeks, were validated. Predictors were birth characteristics, status and age at first diagnosed ROP and essential interactions. Results ROP treatment was required in 287 (4.1%)/6991 infants in DevGroup and 49 (3.9%)/1241 in ValGroups. To allow 100% sensitivity in DevGroup, specificity at birth was 53.1% and cumulatively 60.5% at PNA 8 weeks. Applying the same cut-offs in ValGroups, specificities were similar (46.3% and 53.5%). One infant with severe malformations in ValGroups was incorrectly classified as not needing screening. For all other infants, at PNA 6–14 weeks, sensitivity was 100%. In other published models, sensitivity ranged from 88.5% to 100% and specificity ranged from 9.6% to 45.2%. Conclusions DIGIROP-Screen, a clinical decision support tool using readily available birth and ROP screening data for infants born GA 24–30 weeks, in the European and North American populations tested can safely identify infants not needing ROP screening. DIGIROP-Screen had equal or higher sensitivity and specificity compared with other models. DIGIROP-Screen should be tested in any new cohort for validation and if not validated it can be modified using the same statistical approaches applied to a specific clinical setting

Oxidation behaviors and microstructural alterations of a Mo(Si,Al)(2)-based composite after heating at 1580 degrees C either in a furnace (ex-situ) or via alternating current (in-situ)

The commercial heating element Kanthal Super ER (Mo(Si,Al)(2)-based composite) was oxidized at 1580 degrees C for 24 h up to 1 year using two methods: (1) a furnace set at the desired temperature, (2) passing an alternating current (AC) through the material. Initially, the oxidation behaviors appeared similar for the AC- and furnace-exposed materials. However, at longer exposure times, the level of Al depletion was more pronounced in the furnace-exposed material. A dense alumina scale formed with the same thickness during the two types of exposures, although a porous outer alumina scale was also formed on the composite that was heated in the furnace. The bulk microstructures were also different, in that dark regions in a circle were noted on the AC-exposed material, while the dark regions were evenly distributed on the furnace-exposed material. These dark regions consisted of agglomerated Mo-5(Si,Al)(3) and Al2O3. The AC-exposed material also has "bands" where Al2O3 have agglomerated

Oxidation behaviour of a Mo(Si,Al)2 based composite at 1500 degrees C

The oxidation of a Mo(Si,Al)(2) composite is investigated at 1500 degrees C in dry air using exposure times from 1 to 1000 h. Cross sections are examined with Scanning Electron Microscopy (SEM) and the phase composition is analyzed by X-ray diffraction (XRD). The material forms a continuous and protective alumina layer, the growth of the alumina layer following parabolic kinetics. Immediately below the scale Mo(Si,Al)(2) is replaced by a Mo(5)(Si,Al)(3) layer due to the flux of aluminum to the scale. The Al concentration in the Mo(Si,Al)(2) phase in the underlying substrate decreases from 27% before exposure to 16-17% after 1000 h. The continuous alumina layer becomes covered by a top layer consisting of alumina grains embedded in a viscous melt with approximate composition 7 Na(2)O-15 Al(2)O(3)-78 SiO(2). With time, sodium is volatilized from the melt and the top scale layer transforms to a mixture of alumina, mullite and silica melt

First Three-Dimensional Atomic Resolution Investigation of Thermally Grown Oxide on a FeCrAl Alloy

Thermally grown Al2O3 scales formed on a FeCrAl alloy, Kanthal APMT, were successfully analysed using pulsed green laser atom probe tomography. The alloy was exposed to 5 vol.% O-2 + 95 vol.% N-2 at 900 A degrees C for 1 h, and covered by a thin layer of Al2O3. Cr segregation to some of the Al2O3 grain boundaries was observed. The continuous Cr-rich band, which contains a large number of Cr- and/or Fe- enriched nano-sized particles, was studied in detail. Four types of nanoparticles were found and analysed. Oxidation mechanisms at the initial stages are discussed based on the observations

The Oxide Scales Formed on a Dispersion-Strengthened Powder Metallurgical FeCrAl Alloy at 900 A degrees C in O-2 and in O-2 + H2O

Early oxide scale growth on an oxide dispersion strengthened rapidly solidified powder FeCrAl material, Kanthal(A (R)) APMT, was investigated at 900 A degrees C in an O-2 + N-2 and an O-2 + H2O + N-2 environment for up to 168 h. Gravimetry was used to follow oxide growth and the oxide scale was examined with XRD. Scale morphology was investigated in detail with SEM/EDX, TEM/EDX/CBED. The alloy rapidly formed a protective two-layered alpha-alumina scale containing oxide nodules. Between the top and bottom alumina layers there was a zone containing chromia-rich particles 5-20 nm in diameter, corresponding to the original sample surface. The alumina scale mainly grew inward after 1 h of oxidation. Alumina scale growth at 900 A degrees C was initially somewhat faster in an O-2 + H2O + N-2 environment than in an O-2 + N-2 environment

KCl-Induced Corrosion of an FeCrAl Alloy at 600\ub0C in O2 + H2O Environment: The Effect of Pre-oxidation

The present study investigates the influence of H2O and KCl on the high temperature corrosion of an FeCrAl alloy at 600 A degrees C. Polished samples were exposed to O-2 or O-2 + H2O and to O-2 + H2O with KCl applied. The samples were investigated using SEM/EDX, XRD, IC, AES and SIMS. It was found that KCl accelerates corrosion and that a rapidly growing iron-rich oxide forms with time. Chromate formation is shown to initiate the formation of a non-protective oxide scale. Pre-oxidising the alloy before exposure in the presence of KCl had a strongly beneficial effect on the corrosion

KCl-Induced Corrosion of an FeCrAl Alloy at 600\ub0C in O2 + H2O Environment: The Effect of Pre-oxidation

The present study investigates the influence of H2O and KCl on the high temperature corrosion of an FeCrAl alloy at 600 A degrees C. Polished samples were exposed to O-2 or O-2 + H2O and to O-2 + H2O with KCl applied. The samples were investigated using SEM/EDX, XRD, IC, AES and SIMS. It was found that KCl accelerates corrosion and that a rapidly growing iron-rich oxide forms with time. Chromate formation is shown to initiate the formation of a non-protective oxide scale. Pre-oxidising the alloy before exposure in the presence of KCl had a strongly beneficial effect on the corrosion

A Comparative Study of the Initial Corrosion of KCl and PbCl2 on a Low-Alloyed Steel

Heat exchange surfaces in biomass- and waste-fired boilers are exposed to corrosive species due to the considerable amounts of alkali chlorides and PbCl2 which are released during combustion. The corrosivity of alkali chlorides toward superheater alloys exposed at high temperature has been studied extensively. However, at lower material temperatures, i.e., at waterwall conditions, considerably less research has been performed. In order to investigate the effect of small amounts of KCl and PbCl2 during the initial stages of the corrosion attack, a Fe–2.25Cr–1Mo steel was exposed for 24\ua0h in an atmospheres consisting of O2\ua0+\ua0H2O\ua0+\ua0N2 at 400\ua0\ub0C. Both KCl and PbCl2 resulted in an increased corrosion rate compared to the reference. The aim of the present paper is to investigate the influence of KCl and PbCl2 on the initial oxidation of a Fe–2.25Cr–1Mo steel. The work involves a detailed microstructural investigation as well as thermodynamic equilibrium calculations

The Initial Oxide Scale Development on a Model FeNiCrAl Alloy at 900 degrees C in Dry and Humid Atmosphere: A Detailed Investigation

The investigated alumina forming FeNiCrAl model alloy shows protective oxidation behavior in dry and humid environment at 900 A degrees C. Hence, this type of alloy may replace conventional chromia forming austenitic alloys in aggressive oxidizing/reducing environments. A detailed investigation of the oxide scale development reveals a complex initial scale development. Firstly, at alloy grain boundaries, a thin Al rich oxide forms which is replaced by transient alumina platelets in dry and equiaxed alpha-Al2O3 crystallites in humid atmosphere. The scale at alloy grain centers develops via a layered scale of external chromia:Fe/Ni metal inclusions:internal alumina to a layered external spinel:internal alumina scale in dry atmosphere. In humid condition an additional oxide feature appears on the center of large alloy grains i.e. thick oxide protrusions. Despite the initially different phase compositions a continuous protective alpha-Al2O3 scale forms both atmospheres