Reaction-Ceramic Matrix Composites

Reaction-Ceramic Matrix Composites

 

In the last Blog we looked at analyzing fluid flow into a porous medium, in the manufacture of CMCs using the RMI process simultaneously with the fluid infiltration a reaction takes place between the infiltrating molten liquid and the porous preform. Thus the second step in developing a computational analysis of the RMI process for producing CMCs is to integrate the reaction behavior between the infiltrating liquid silicon and the porous carbon preform.

The reaction kinetics of the SiC formation are calculated using a general reaction kinetics equation with constants for the Si+C reaction:

 

Reaction Kinetics Equation                                (4)

 

Where:

Reaction Kinetics Equation Explained

 

 

 

 

 

 

 

 

 

 

 

The volume fraction of Si is obtained as:

volume fraction of Si                                                            (5)

 

The mass balance assumes that reaction proceeds to full completion and all Si transforms into SiC. To account for the effect of reaction termination, the mass balance can be modified as:

 

Reaction Termination Mass Balance Miodification              (6)

 

Where

DefEq6

 

Integration of this approach in the model allows the distribution of SiC and Si species to be predicted as a function of both spatial location and time into the infiltration (Figure 6). Convection of the moving fluid and the reaction rate define the distribution of both species. The sum of the volume fractions of Si and SiC equals the total volume fraction of fluid.

 

Fig6

Figure 6. Distribution of (a) SiC and (b) Si volume fractions along x=0


The next blog in this series will consider the issue of heat transfer associated with infiltration of molten silicon, reaction between the liquid silicon and the carbon preform, and heat evolved on solidification.

Ideation

Ideation – What is that?

 

To Ideate or not to Ideate? That is the question.

 

“Ideate” simply means to form an idea, thought or image of; to form ideas, think. (Dictionary.com)

 

“Ideation” is the process of forming and relating ideas. Ideation means to conceive or generate an idea and implement it. Ideation means to conceptualize an idea. It is the thought processes involved in apprehending and expressing a new concept, often in a graphical format. Here at AltaSim, we talk about “Tomorrow’s Technology Today” in most everything we do. Tomorrow’s technology started with today’s (or yesterday’s) idea. Almost all of the projects we get to work on are time sensitive for various reasons. Somebody somewhere was practicing Ideation before we got involved.

 

What happens when Ideation is constantly interrupted? What happens when today’s solution is delayed because yesterday’s tools cannot get us quickly to tomorrow? What happens when different users in different departments using different tools try to communicate about the same solution? Ideation comes to a screeching halt.

 

CAD is a great tool. We all know that. But often, CAD becomes a bottleneck when different users in different departments try to communicate with each other during the process of Ideation. Somewhere between Concept, Design, Analysis, Production, and Go-to-Market, this process often becomes “hurry-up-and-wait”. This kills Ideation. So on one end of the spectrum, there are people being encouraged to ideate more and more. On the other end of the spectrum, there are people frustrating and discouraging those ideating, without really knowing it. And somewhere there’s a group of people who are saying… “This product NEEDS to get to Market!”  We believe SpaceClaim solves this problem!

SpaceClaim=Ideation

SpaceClaim-3D Direct Modeling Software

 

What would it look like in your organization if the bottleneck never occurred? What could happen to revenues if so much time wasn’t lost in the process? Can you imagine what tomorrow’s products you would already have conceptualized, designed, analyzed, produced and on the market today? Think about it… now that’s some really good Ideation.

 

Fluid Flow in Ceramic Matrix Composites

Fluid Flow in Ceramic Matrix Composites

In a previous Blog we discussed some of the background to the production of Ceramic Matrix Composites (CMCs) using the Reactive Melt Infiltration (RMI) process. In this Blog we will address some of the issues associated with the first step in the process: infiltration of molten material into a porous preform.

 

Unsaturated flow through a porous media can be simulated using modified Richard’s and Darcy’s equation:

Eq1(1)

 

 

 

 

In this formulation, Darcy’s law provides the fluid velocity in the unsaturated media as:

 

Eq2 (2)

 

 

 

 

For which:

 

DefEq2

 

The effective saturation, relative permeability, and moisture capacity are functions of pressure:

Eq3 (3)

 

 

 

Results of the infiltration analysis show agreement with experimental results published by Einset for non-reactive flow (Figure 1) and reactive flow (Figure 2) in systems with different pore sizes.

 

Ceramics Matrix Composites-Fluid Flow1

Figure 1. Calculated and experimental acetone infiltration profiles for different pore diameter parameters.

 

Ceramics Matrix Composites-Fluid Flow2

Figure 2. Calculated and experimental infiltration profiles for silicon.

 

Once validated the analyses can predict other critical factors such as the flow front and its velocity during processing, examples are provided in 3 through 5.

Ceramics Matrix Composites-Fluid Flow3

Figure 3. Calculated saturation level as a function of infiltration time and distance from inlet.

Ceramics Matrix Composites-Fluid Flow4

Figure 4. Results of saturation during flow of Silicon into perform for infiltration times of 1s, 10s and 20s.

Ceramics Matrix Composites-Fluid Flow5

Figure 5. Distribution of the velocity in the fill direction for both layers at t= 1s.

The next blog in this series will consider the issues associated with the chemical reaction between infiltrating liquid and the porous preform, with specific focus on the infiltration of molten silicon into a porous carbon preform to produce a silicon carbide composite.