Water based processing of iron powder utilising starch consolidation

The effects of water based shaping, by means of starch consolidation (SC), of an iron powder system regarding oxygen/carbon content and sintering performance were evaluated. Specifically, the influence of the drying conditions and the use of two different thickeners, xanthan gum and cellulose ether, were studied. The results showed that cellulose ether gave lower sintered density than xanthan gum, mainly because of less favourable rheological impact and air/gas entrapment at mould filling and consolidation. Due to less oxidation at drying and less removal of carbon at sintering, freeze dried specimens sintered to a higher density than room temperature air dried ones. The degree of oxidation and removal of carbon also influenced the as sintered microstructure. Ferrite grains surrounded by iron phosphide were found m both air dried and freeze dried specimens. However, the higher carbon content in freeze dried specimens also resulted in a significant amount of iron carbide grains (inclusions), which can be a potential strength limiting factor

Evaluation of ceramic sacrificial coatings for improved alkaliinduced corrosion protection in biofuel-fired boilers

In the combustion of bio-based fuels the critically exposed burner parts in small boilers are typically uncooled and are usually made of FeCrNi alloys. These materials can suffer attack from the ashes because of the formation of alkali chromate. The reaction depletes the protective oxide in chromia, leading to accelerated corrosion. Selected "acidic" ceramic coatings based on Ti, Si, B and P have been evaluated for use as sacrificial layers to prevent the initial reaction of alkali and chromium. An accelerated oxidation test method including mild thermal shock has been utilized that previously proved useful to provide application-relevant results. A comparison of coated and uncoated specimens was performed with an austenitic high temperature steel as a substrate. The results indicate that the alkali released from the ash reacts with the respective "acidic" elements in the deposited coatings. This reaction has promoted initial formation of a thin and continuous chromium-rich protective oxide sub-layer. In addition, the oxide scale formed on the coated specimens appeared more coherent and crack-free. A significant enrichment of Ni at the steel-oxide interface also occurred that can promote high temperature corrosion resistance

Evaluation of ceramic sacrificial coatings for improved alkaliinduced corrosion protection in biofuel-fired boilers

In the combustion of bio-based fuels the critically exposed burner parts in small boilers are typically uncooled and are usually made of FeCrNi alloys. These materials can suffer attack from the ashes because of the formation of alkali chromate. The reaction depletes the protective oxide in chromia, leading to accelerated corrosion. Selected "acidic" ceramic coatings based on Ti, Si, B and P have been evaluated for use as sacrificial layers to prevent the initial reaction of alkali and chromium. An accelerated oxidation test method including mild thermal shock has been utilized that previously proved useful to provide application-relevant results. A comparison of coated and uncoated specimens was performed with an austenitic high temperature steel as a substrate. The results indicate that the alkali released from the ash reacts with the respective "acidic" elements in the deposited coatings. This reaction has promoted initial formation of a thin and continuous chromium-rich protective oxide sub-layer. In addition, the oxide scale formed on the coated specimens appeared more coherent and crack-free. A significant enrichment of Ni at the steel-oxide interface also occurred that can promote high temperature corrosion resistance

Mechanical characterisation of porous glass reinforced hydroxyapatite ceramics: Bonelike®

In the present study, mechanical properties of porous glass reinforced hydroxyapatite bioceramics were assessed by microhardness, bending and compression tests and fracture toughness determination. Porous discs were produced by a dry method using wax spheres as pore formers. Green bodies were sintered and the final microstructure of the composites consists of hydroxyapatite, alpha and beta tricalcium phosphate (alpha and <FONT FACE=Symbol>b</font>-Ca3(PO4)2)due to the reaction between the glassy phase and the hydroxyapatite matrix. The results of the mechanical tests showed that the glassy phase yielded higher fracture toughness and bending strength when comparing with literature data for single hydroxyapatite. There is a compromise between mechanical properties and the porosity level for bioceramics: for example, according to Weibull statistics for composites with 65% porosity the maximum bending stress level is 0.2 MPa for 100% survival probability whereas this stress level increases to 2.5 MPa for composites with 40%. However, only the 65% porosity composite samples seem to have the complete adequate morphology for bone ingrowth