Synthetic Ash Research Articles

Effect of grain boundary serration on the fatigue, creep and cyclic creep strengths of a nickel-base superalloy in air and in hot corrosive environment.

Fatigue, creep and cyclic creep tests have been carried out at 800°C for the variously heat-treated nickel-base superalloy Inconel 751. The heattreatments given are simple aging (SA), two-stages solution treatment (TS) and direct aging (DA), with and without coating of synthetic ash mixture composed of 90% Na2SO4 and 10% NaCl. Effect of grain boundary topography, particularly of the serrated grain boundary produced by the direct aging, on the strength properties is, then, investigated.It is clarified that hot corrosion can alter the fracture mechanism completely. In hot corrosive environment, a stress-enhanced aggressive intergranular penetration of sulfides, oxides and/or chlorides can cause a grain boundary weakening to induce a premature intergranular fracture in a brittle manner regardless of the grain boundary topography. In particular, the cyclic creep is shown to result in minimization of failure life in hot corrosive environment because the combined creep and fatigue loadings promote the aggressive intergranular attack, in contrast to the case in air in which the failure life is mainly determined by the creep damage.In general, the effect of grain boundary topography on the strength properties is significant in hot corrosive environment rather than in air. In hot corrosive environment, both the chromium-depleted zone and the straight grain boundary appear to enhance the aggressive intergranular attack, because the former can induce the low melting nickel sulfides formation and the latter is easily subjected to the locally increased strain concentration so as to provide a stress-activated path. The development of the chromiumdepleted zone tends to give a detrimental effect on the strength properties under all the loading conditions, while the detrimental effect of the straight boundary is more pronounced under the creep-dominant loading conditions. Consequently, in order to improve the strength properties in hot corrosive environment, it is important to eliminate such undesirable microstructures associated with the grain boundary, depending on the loading conditions.It is also confirmed that even in hot corrosive environment, the serrated grain boundary contributes notably to improve the strength under creepdominant loading conditions by virtue of the suppression of such an aggressive intergranular attack.

Studies of sintering of coal ash relevant to pulverized coal utility boilers: 1. Examination of the Raask shrinkage—electrical resistance method

The Raask shrinkage and electrical resistance method for determining the onset of sintering of fly ash has been tested on a soda lime glass, coal ASTM ashes, fly ashes and pulverized synthetic mineral mixtures. Results with the glass confirmed those of Raask and showed that particle size distribution and bulk density affected the resistance values: the sinter point was indicated by a change in the characteristic temperature coefficient of resistance. The shrinkage and electrical sinter points were usually the same, but a high Na content lignite gave 850°C for shrinkage but 600°C for characteristic resistance change. Sinter points were 200°C less for fly ash than for ASTM ash. The fly ashes had a slight enrichment of alkalies and a decrease in Fe content compared to the total ash. Holding a compact at a temperature above the sinter point gave increased strength and shrinkage, but no decrease in electrical resistance, indicating that the decrease in resistance as temperature increased was due to the establishment of contact points between particles, with little effect of the continued growth of a contact neck. Addition of pulverized sodium silicate or iron silicate glasses to a synthetic ash also reduced the sinter points, as did alkali additions, whereas addition of pyrite did not. It was concluded that the method was a valuable tool, but sources of variability had to be determined and controlled.

Hot salt corrosion test procedures and coating evaluation

There is considerable uncertainty regarding the relevance to practical applications of the various test procedures used to assess the resistance of superalloys to hot salt corrosion. A description is given of work to evaluate the applicability of the results obtained from current test methods in comparison with the performance of components in service. The test methods used were (i) burner rigs, (ii) crucible tests with and without electrochemical acceleration and (iii) various furnace tests such as the Dean test and those using a synthetic ash. The morphology of the corrosion product obtained was compared with that formed on blades and other parts during service exposure. The results indicate that burner rig testing gives the most realistic simulation of service behaviour and that some of the other tests can be modified to be more relevant. A highly significant aspect is the influence of contaminants on corrosion behaviour, which can vary depending on test method and must therefore be understood in detail when a particular test procedure is defined. It is shown that the deposition rate of sulphate from the vapour phase is an important factor controlling corrosion rates in burner rigs and Dean tests. In burner rigs the obvious correlation with contaminant concentration was not found, and a more important parameter is believed to be the contaminant mass flux. Tests in which the flux was close to that in operating gas turbines gave the best simulation of corrosion. The corrosion resistance of coatings can be assessed using similar procedures, but more care is required in the interpretation of results since failure of a coated component may result from a single defect. A statistical approach to the interpretation of behaviour is therefore discussed.

Studies on slag deposit formation in pulverized coal combustors. 2. Results on the wetting and adhesion of synthetic ash drops on different steel substrates

A simple sticking apparatus has been further developed to study the comparative wetting and adhesion properties of a synthetic coal ash slag on boiler steels. Both the wetting and adhesion behaviour appears to be affected by the physical nature of the oxide layer on the steel surface (i.e., thickness and microporosity). The adhesion force is also found to be a function of the chemical nature of the surface oxide layer on the steel (i.e., whether the layer is predominantly ferrous (FeO) or ferric (Fe 2O 3) oxide). The presence of a sodium salt (either sulfate or carbonate) on the steel surface enhances both the wetting and adhesion properties by dissolution in the molten drop creating a less viscous glass with a lower liquidus temperature at the drop-surface interface. At this time it is difficult to establish whether the bonding between the slag and steel oxide layer is mechanical, chemical, or a combination of both.

Some Results of the Wetting and Adherence of Synthetic Coal Ash Droplets on Steel

As part of a study of slagging in boiler furnaces the sticking temperature, strength of adhesion and contact angle of molten mineral glass drops on various oxidized steel substrates have been investigated. The freezing of the interface between the drop and the metal substrate occurs in milliseconds and in this time a bond is formed between the glass and the oxide coating on the steel. Mineral compositions of low melting point which have reduced liquidus temperatures when iron is dissolved from the surface appear to give the lowest sticking temperatures. Stainless steels which were not heavily oxidized gave low strengths of adhesion. Pyrrhotite formed from melting of pyrite wetted the oxidized surfaces well and gave low sticking temperatures.

Corrosion of Type 310 Stainless Steel By Synthetic Fuel Oil Ash★

Abstract In an investigation of the corrosion of Type 310 stainless steel in synthetic fuel oil ash, the minimum temperatures at which the steel was attacked by a mixture of V2O5 and Na2SO4 and by mixtures of V2O5 and NaVO3 were determined. The minimum temperatures ranged from 1075 F for a mixture of 67 percent V2O5 and 33 percent NaVO3 to 1220 F for a mixture of 88.5 percent V2O5 and 11.5 percent NaVO3. An unidentified phase was produced at the interface between the steel and a vanadium compound or mixtures of compounds in the temperature range 1075 F to 1890 F. There was evidence that this phase penetrated into the steel at grain boundaries. Steel heated above 1700 F in contact with a vanadium compound or a mixture of these contained nodules of an unidentified phase at the grain boundaries. Spectrochemical analyses of the slag (fused synthetic mixture) indicated that it contained some of the components of the steel in the same proportions as they were present in the steel. 4.3.3

Acceleration of vitamin E deficiency by Torula yeast. II. Effect of Torula yeast ash and lipid.

SummaryWhen added to a purified basal diet low in vit. E and selenium, the ash of Torula yeast was found to promote exudative diathesis. This effect could not be demonstrated by any of the minor elements, nor by any of the major components, of the ash. The lipid isolated from Torula yeast also promoted exudates; this effect could be duplicated by tall oil. A combination of lipid and ash from Torula yeast produced an incidence of exudative diathesis similar to that produced by an equivalent amount of the intact yeast. A combination of tall oil and a synthetic ash was just as effective. It is concluded that the anti-vit. E property of Torula yeast is due essentially to both its unsaturated fatty acid and mineral contents. The relatively high content of dienoic acid in the lipid of Torula yeast was confirmed.

Blood Regeneration in Severe Experimental Anemia. Influence of Inorganic Elements.

We have recently reported in these Proceedings1 a rather startling reaction to the inorganic ash of liver, kidney and apricots. This ash incorporated in a standard anemia diet2 given to dogs kept constantly anemic by bleeding will effect a notable increase in blood hemoglobin production above control periods. This may amount to 30 to 50 gm. hemoglobin per 2-week period.We have made various analyses of these ashes and from such data have made various synthetic ash compounds, but such synthetic mixtures so far have not proved to be potent. These experimental data will be published in due time.We wish to report briefly our findings when these dogs are given various simple salts added to the standard ration. It is apparent that in the doses given iron is more potent than either copper or zinc.These observations dealing with copper salts are of considerable interest when contrasted with the recent reports of Hart, S teen-bock, Waddell and Elvehjem,3 who report a distinctly favorable reaction to copper salts an...