In this lecture, we'll talk a little bit about processing of ceramics and how we use network modifiers to reduce or alter the processing temperatures of ceramics. We mentioned previously. The purpose of the network modifiers is just as it says here we have the nice network, the nice directional Covalin bonds. But once we add network modifiers, whether that could be soda lime, we actually break up the network and introduce more vandal walls type bonding. Hence the overall bond energy has been reduced and it allows us to process the materials at lower temperature. Whereas pure courts you have to process at a very high temperature, very difficult hits, makes it very expensive. Whereas the introduction of soda and lime, you introduced the network modifiers you break up the network see and it allows you to process at lower energies lower temperatures. So now we have to become familiar with some of the terms associated with processing of ceramics. And often we look at the processing temperatures in terms of the viscosity. Okay, so if I look at the melting temperature here the tip, the ceramic is actually a glass of liquid and then we have our working point and softening point. So this is the point where the material is actually soft but it remains, it maintains its shape so you can mold it shape, it, blow it however you want, it will maintain the shape. So this is the range which we do the working, hence the working range. Then we have the kneeling point. This is where you can reduce the stress in the ceramic. Okay, so say if you want to temper it, you want to be at the kneeling point. And then finally the strain point is any viscosity above this value. You will have brittle failure. No plastic deformation below. You can have a substantial amount of plastic deformation when we're in this range. But here at viscosity is above the strain point. You will have brittle failure sheet forming typically involves trying to cast a continuous sheet of ceramic typically from the molten ceramic material. And we do this by float the floating the glass on liquid tin. So here we have the raw material, we have the molten glass, we convey it down, we have heaters. Now the glasses on liquid tin, it's it's going to have a very very smooth finish. Okay, and here we fire and polish it the cooling zone and then we bring it out. We do another Neil to remove any stress. And then you cut it again, we do this continuous casting over molten tin. Okay, raw material in, we create the molten glass. Then we bring it into a hot zone. Fire polish, cool it, remove any stress, then cut it to size. Another very useful processing technique is blowing glass. Here you have the molten soft glob, you put it in a mole, you do a pre press, okay, gets it near the shape but it's not the final shape. Then we take the suspension, put it in the finishing mode compressed air and we have our net shape. Now again, this has to be in the working temperature range because you think about it. Glass is extremely brittle at room temperature. So to do to conduct this type of process and we have to be at elevated temperatures pressing you can do that for plate inexpensive glassware. Generally you put it in a mold that has a graphite lining. Press end up with your final part. You can also do fiber winding. Typical process used to fabricate fiberglass as well as other fibers. Basically you have a melt, then you pull and you wind it okay? So the glass is actually cooling as you wind it.
