I have been trying to understand the concept of a component in relation to phase diagrams in my materials class. I have tried searching online and found that the definition is supposed to be that a component is a singular element, however I have also found a water (a 2 element compound) phase diagram is listed as a singular component phase diagram, which contradicts the previous definition of a component.
So is a component all relative to the temperatures/concentrations it operates under? Like, if a liquid is made of two elements and you're looking at it between 20-100 degrees Celsius and it only separates into its individual elements after 100 degrees Celsius, then would it be classified as a singular component phase diagram under 100 degrees Celsius?
So in short I need help understanding what a component is in relation to phase diagrams.