Lanxide process

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

Lanxide process (a) infiltration of preform (b) wicking of liquid metal along grain boundaries (reproduced by permission of Woodhead Publishing Limited)74. 

The Lanxide process, developed by the Lanxide Corporation, involves the formation of a ceramic matrix by the reaction between a molten metal and a gas, e.g., molten aluminum reacting with oxygen to form alumina. Growth... 

FIGURE 20.18 Illustration of the Lanxide process for making a shaped CMC. 

In the Lanxide process for the synthesis of fiber-reinforced ceramic composites a liquid alloy (A1 based), impregnated in a whisker felt or fiber preform, is gradually oxidized in air to form an oxide matrix. 

Melt infiltration into fibrous preforms combined with oxidation of the metal matrix can produce ceramic matrix composites. Since this type of process was developed by Lanxide Corporation, it is called the Lanxide process [49]. For example, a Nicalon SiC fiber and alumina matrix composite was produced as follows [50] stacked fibrics of Nicalon fiber were coated by CVD. The major purposes of the coating were to protect the fiber from aluminum alloys during... 

Lanxide Process. The directed oxidation of molten metal precursors, injected into a mass of filler. (Lanxide, Newark, Delaware, USA. See Ceram. Eng. Sci. Proc. 8 (7/8), 879, 1987). 

Studies on the influence of polymers on the crystallization of calcium carbonates in vitro have shown that metastable liquid complexes with anionic polymers can be formed that subsequently transform to calcite. Studies of carbonate biomineralization have shown that amorphous calcium carbonate forms either transiently or as a stable phase. It has also been shown that absorbed proteins modify the fracture properties of carbonates. In particular, fracture surfaces show smooth conchoidal fracture, like glass, rather than the faceted fracture characteristic of normal crystals. This suggests that we have much to learn about the modification of the properties of crystals and amorphous solids by entrained polymer (see Fig. 3). There are parallels with the Lanxide process for... 

Alternatively, tows of fibers can be passed through a Hquid metal bath, where the individual fibers are wet by the molten metal, wiped of excess metal, and a composite wine is produced. A bundle of such wines can be consoHdated by extmsion to make a composite. Another pressureless Hquid metal infiltration process of making MMCs is the Prim ex process (Lanxide), which can be used with certain reactive metal alloys such as Al—Mg to iafiltrate ceramic preforms. For an Al—Mg alloy, the process takes place between 750—1000°C ia a nitrogen-rich atmosphere (2). Typical infiltration rates are less than 25 cm/h. 

Lanxide A process for making composites of metals with oxides. A molten metal reacts with an adjacent oxidant and is progressively drawn through its own oxidation product so as to yield a ceramic/metal composite. Fibres or other reinforcing materials can be placed in the path of the oxidation reaction and so incorporated in the final product. The Lanxide Corporation was founded in 1983 in Newark, DE, to exploit this invention. In 1990 it formed a joint venture with Du Pont to make electronic components by this process. Variations are Dimox (directed metal oxidation), for making ceramic metal composites, and Primex (pressureless infiltration by metal), for making metal matrix composites. 

New types of ceramic composites with high thermal shock resistance have recently been developed that show some promise for gas turbine applications. These composites consist of a ceramic matrix reinforced by ceramic fibers or platelets inside the matrix. The fibers pull out of the matrix during fracture to resist crack propagation. Such composites can be readily fabricated using a new process developed by Lanxide Corporation [18]. The process uses directed oxidation reactions of molten metals to grow a ceramic matrix around a reinforcing material. 

One approach for fabricating fiber reinforced ceramic matrix composites is the directed oxidation of metals, a process first introduced by Lanxide Corporation [1, 2] and later used successfully to produce turbine engine and aerospace components. Rights to the DIMOX technology, as it was identified, were ultimately acquired by Power Systems Composites, L.L.C., a subsidiary of the Power Systems business of the General Electric Company. 

The Lanxide Corporation (now intellectual property within MSE Inc.) have patented the PRIMEXTM pressureless metal infiltration process and the PRIMEX CASTTM foundry process, which are able to infiltrate ceramic reinforcements with molten metals without application of pressure or vacuum and it is believed that the processes can be used with carbon fiber. 

Lanxide A process for making composites of metals with oxides. A molten metal reacts with an adjacent oxidant and is progressively drawn through its own oxidation product so as to yield a ceramic-metal composite. Fibers or other reinforcing materials can be placed in the path of the oxidation reaction and so be incorporated... 

Another type of reaction processed composite is that under development by Lanxide Corporation They have reported "growth" of Al O by reaction of molten A1 at the interface between the AI2O2 product (fed by capillary action along microscopic channels in the Al20 product) and a gaseous source of O2 (e.g. air). Since this is a growth process it can "grow" around particulates, or fibers to form composites. The extent to which such composites can be varied in composition and microstructure is not yet fully known, but appears to be quite broad. The process can also apparently be applied to other matrix materials such as AIN, TIN, and ZrN. 

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