Directed Metal Oxidation Process Research Articles

Experimental Results of SiC reinforced Al2O3 Matrix Ceramic Matrix Composites Validated with Finite Element Method

In this paper, SiCp/Al2O3 composites were fabricated through directed metal oxidation process. Experimental results of these composites validated or compared with Finite Element Method (FEM). Finite Element has become one in all the foremost necessary tools offered to an engineer. The finite part methodology is employed to resolve advanced analysis issues. In this paper, Finite Element Method based ANSYS software is used to FEM model to determine mechanical properties of SiC reinforced Al2O3 matrix composite by changing volume fractions of SiC. The comparison of experimental results with Finite element analysis provides detailed information about the results of these comparisons. The FA was competent of predict the information for several scenario quite fine.

Growth of Al2O3/Al Composite by Directed Metal Oxidation of Al Surface Doped with Sodium Source

Both an unreinforced Al₂O₃/Al matrix and a α-Al₂O₃ particulate reinforced composite have been produced by the oxidation of an Al surface doped with NaOH in the absence of any other dopant. Fabrication of the matrix was initiated by the formation of NaAlO₂, which provides a favorable surface structure for the matrix formation by breaking the protective Al₂O₃ layer on Al. During the matrix growth, the external surface of the growth front was covered with a very thin sodium-rich oxide. A cyclic formation process of the sodium-rich oxide on the growth surface was proposed for the sodium-induced directed metal oxidation process. This process involves dissolution of the sodium-rich oxide, motion of Na to the growth front, and re-formation of the oxide on the surface. Near-net-shape composites were fabricated by infiltrating an Al₂O₃/Al matrix into a α-Al₂O₃ particulate preform, without growth barrier materials. The infiltration distance increased almost linearly in the NaOH-doped preform.

Mechanical properties of SiC p/Al 2O 3 ceramic matrix composites prepared by directed oxidation of an aluminum alloy

Silicon carbide particulate reinforced alumina matrix composites were fabricated using DIrected Metal OXidation (DIMOX) process. Continuous oxidation of an Al–Si–Mg–Zn alloy with appropriate dopants along with a preform of silicon carbide has led to the formation of alumina matrix surrounding silicon carbide particulates. SiC p /Al 2O 3 ceramic matrix composites fabricated by the DIMOX process, possess enhanced mechanical properties such as flexural strength, fracture toughness and wear resistance, all at an affordable cost of fabrication. SiC p /Al 2O 3 matrix composites were investigated for mechanical properties such as flexural strength, fracture toughness and hardness; the composite specimens were evaluated using standard procedures recommended by the ASTM. The SiC p /Al 2O 3 ceramic matrix composites with SiC volume fractions from 0.35 to 0.43 were found to possess average bend strength in range 158–230 MPa and fracture toughness was found to be in range of 5.61–4.01 MPa√m. The specimen fractured under three-point loading as observed under scanning electron microscope was found to fail in brittle manner being the dominant mode. Further the composites were found to possess lower levels of porosity, among those prepared by DIMOX process.

Functionally graded reaction layers produced by directed metal oxidation process

The directed metal oxidation process has been attempted for the fabrication of a functionally graded layer on the Al–Mg/Al 2O 3 powder compact. It was found that the reaction of the Al–Mg/Al 20 3 at 900°C under air atmosphere leads to the formation of reaction layers with varying ceramic phase contents. Two different types of reaction layers were observed, depending on the Mg contents: ceramic/channel/composite or channel/ceramic/channel/composite arrangements from the sample surface. The microstructural development of the reaction layers at various reaction stages was investigated and the mechanism of the reaction layers was discussed on the basis of MgO phase formation on the surface of the reaction layer.

Kinetics of directed oxidation of Al-Mg alloys into A1 2O 3 preforms

Synthesis of oxide matrix composites by the directed metal oxidation process offers significant advantages over traditional composite processing routes. Much of the previous work on directed oxidation has been focused on the understanding of the microstructural evolution during the process. In this work, growth kinetics of Al 2O 3/Al composites through Al 2O 3 preforms has been studied. The mechanism of oxidation of Al-Mg alloys into Al 2O 3 preforms has been investigated theoretically and experimentally. Analysis of the oxidation kinetics for various preform particle sizes and durations of oxidation demonstrates that the preform provides preferential sites for Al 2O 3 nucleation. Furthermore, the weight gain rate increases with decreasing Al in2O 3 particle size. With increasing oxidation time, liquid metal transport to the oxidation front slows down and becomes a factor in controlling the weight gain rate. The oxidation rate of Al alloys into Al 2O 3 preforms can be tailored by the control of preform particle size.

Creep Deformation in an Alumina–Silicon Carbide Composite Produced via a Directed Metal Oxidation Process

Flexural creep studies were conducted in a commercially available alumina matrix composite reinforced with SiC particulates (SiCp) and aluminum metal at temperatures from 1200° to 1300°C under selected stress levels in air. The alumina composite (5 to 10 μm alumina grain size) containing 48 vol% SiC particulates and 13 vol% aluminum alloy was fabricated via a directed metal oxidation process (DIMOX(tm))† and had an external 15 μm oxide coating. Creep results indicated that the DIMOX Al2O3–SiCp composite exhibited creep rates that were comparable to alumina composites reinforced with 10 vol% (8 (μm grain size) and 50 vol% (1.5 μm grain size) SiC whiskers under the employed test conditions. The DIMOX Al2O3–SiCp composite exhibited a stress exponent of 2 at 1200°C and a higher exponent value (2.6) at ≥ 1260°C, which is associated with the enhanced creep cavitation. The creep mechanism in the DIMOX alumina composite was attributed to grain boundary sliding accommodated by diffusional processes. Creep damage observed in the DIMOX Al2O3‐SiCp composite resulted from the cavitation at alumina two‐grain facets and multiple‐grain junctions where aluminum alloy was present.

Oxidation and Corrosion of SiC(particulate)/Al/Al2O3 Composites in Sodium Silicate at Elevated Temperatures

Ceramic‐matrix composites (CMCs) fabricated by the directed metal oxidation process (DimoxTM) may have applications in heat exchangers in high‐temperature corrosive environments such as those in the glass industry. The oxidation and corrosion properties of such CMCs with and without preformed metal‐free surface layers have been investigated in the temperature range of 1000–1300°C. The untreated CMCs experienced rapid oxidation in air leading to mass increases of 100 to 140 mg/cm2 in less than 1 h. This occurred by oxidation of residual metal in the composite to form Al/Al2O3 deposits on the surface. After the initial formation of the oxidation product, there is little further reaction during up to 300‐h exposures to oxidizing atmospheres. Experimental composite coupons with metal‐free surfaces were resistant to oxidation except for localized events associated with flaws. Small amounts of sodium silicate (2 to 40 mg/cm2) painted on the surfaces produced no corrosive effects on any of the specimens. Dynamic corrosion experiments, in which a continuous mist of sodium silicate was sprayed onto the surfaces, produced corrosion at 1300°C.

Directed oxidation/nitridation of Al alloys: The orientation of the oxides/nitrides formed adjacent to Al2O3 or AlN reinforcement particles

The search for a new generation of fine grained metallo-ceramic materials with tailorable properties has led to studies of the directed oxidation of aluminium alloys, first in oxidizing and later in nitriding atmospheres. (The directed oxidation technology is patented by Lanxide Corporation and included under the trade name DIMOX TM directed metal oxidation process.) Initial investigations of the matrix provided a detailed description of the complicated microstructure of the AI203/AI oxidation product, when no reinforcement filler material was present [1-3]. It was observed [1, 2] that during oxidation in air initial nucleation results in oxide regions of 10-100 ~tm with random crystallographic orientation, followed by formation of millimetre sized A1203 columns with (0001) parallel to the

Advanced Ceramics for Environmental Protection

AbstractAdvanced ceramic materials offer significant thermodynamic efficiency advantages over metals and alloys because of their higher use temperatures. Using ceramic components results in higher temperature industrial processes which convert fuels to energy more efficiently, reducing environmental emissions. Ceramics have always offered high temperature strength and superior corrosion and erosion resistance. However, brittleness, poor thermal shock resistance and catastrophic failure have slowed industrial adoptions of ceramics in environmental applications.This paper will focus on environmental applications of three new advanced ceramic materials that are overcoming these barriers to industrial utilization through improved toughness, reliability, and thermal shock performance. PRD-66, a layered oxide ceramic with outstanding thermal shock resistance and high use temperature with utility in catalyst support, insulation, and hot gas filtration applications, is discussed. Tough silicon carbide fiber reinforced silicon carbide (SiC/SiC) and carbon fiber reinforced silicon carbide (C/SiC) ceramic composites made by chemical vapor infiltration, and silicon carbide particulate reinforced alumina (SiCp/A12O3) composites made through Lanxide Corporation's DIMOX™ directed metal oxidation process are described. Applications of these materials to pollution reduction and energy efficiency in medical and municipal waste incineration, heat management, aluminum remelting, pyrolysis, coal combustion and gasification, catalytic pollution control, and hot gas filtration, will be discussed.

Influence of Magnesium‐Aluminum Spinel on the Directed Oxidation of Molten Aluminum Alloys

The directed oxidation of some molten aluminum alloys was studied. Alloys containing Si, Zn, and Mg are readily converted into Al2O3/Al composites with the characteristic directed metal oxidation process (DIMOX) metal‐channel structure. No reaction took place when alloys without Mg were used. However, when Mg‐free melts containing Si and Zn were in contact with bulk spinel (MgAl2O4), the typical reaction product grew from the metal pool, although without formation of the spinel starter layer which was thought to be a prerequisite for DIMOX growth. Furthermore, the growth front was more planar than when Mg‐containing alloys were used.