Are the differences, if they exist merely semantic ("First World War" vs "World War One") or are they more substantial; for example one's a historical trend and the other's a broader philosophical system? Speaking only as philosophical amateur I suspect Materialism is an outlook and Empiricism is a methodology but I could be wrong.
Materialism is a global assumption while Empiricism is often a method or practice. Stoicfury is right in placing Materialism as metaphysics.
However, John Locke is the founder of British Empiricism. Yet Locke found God a sensible concept, despite how un-empirical God remains. Bishop Berkeley followed Locke, and is almost an idealist in his disbelief of the necessity of matter through an analysis of the empirical facts as "impressions". David Hume followed after Locke and Berkeley and set yet a different tone, altogether.
Locke is closest to an empiricist, Berkeley is practically an idealist, and Hume, practically a materialist. What is primary for Empiricism is the sufficiency of the brain to process sensory stimuli, regardless of the sufficiency of the mechanics of matter to enable such processes.
Empiricism too strictly defined actually strays from empirical practice as a gathering of knowledge as it presents itself, and a confidence that the most reliable, universal, or repeatable experiences are the most fruitful for establishing understanding.
What is the empirical experience of empiricism absent Locke, Berkeley, and Hume?
Empiricism can best be described as a practice or method(-ology, if you must).
Philosophically, materialism and empiricism are quite different, so much so that it would not even be useful to speak of their differences. We're not merely talking apples and oranges here, we're talking apples and Lamborghini Gallardo's. Let me show you where each concept resides in philosophy:
Note: While there are no "official" categories, people typically use at least 4 major top-level categories when sorting theories in philosophy: Metaphysics (what is out there? what is it like?), Epistemology (what is the source and scope of knowledge?), Ethics (what is right and wrong?), and Logic (study of reason and inferences).
Materialism is the theory that all that exists is material (physical); it clearly falls under metaphysics because it tries to assert what things are (made of). (Specifically, it falls under philosophy of mind which itself falls under metaphysics.) As a theory regarding the ontological makeup of the universe, and it is often contrasted with dualism and idealism.
Empiricism is a theory of knowledge which asserts that knowledge can only (primarily) come from sensory experience, which places it clearly within the realm of epistemology because it tries to assert how we can know things. It is often contrasted with rationalism or idealism.
I hope that clears things up.
Aristotle is probably the greatest empiricist to date. In practically all of his philosophy, including his ethics, he thought the correct place to start was with observations of the world. This is the crux of empiricism; we apply reason to our experiences of the external in order to do philosophy. You will note that Aristotle was by no means a materialist; he believed in a great number of immaterial things. Aristotle did not find materialism tenable given his experience of the world, so he rejected it.
Empiricism can be contrasted with idealism, such as that of Aristotle's teacher, Plato.
Both empiricism and idealism are advocated by a significant number of present day philosophers of widely varying qualifications and backgrounds.
Materialism has not (yet?) had any particularly notable proponents in the same way empiricism has. Materialism is a particular metaphysics which holds that matter is the fundamental substance in nature, and that all phenomena, including mental phenomena, spiritual phenomena, and consciousness, are the result of material interactions. It has largely been replaced by philosophical physicalism, which states that all that is is physical in some sense, and is, in general, a much easier position to hold.
You can read more about Materialism here
To supplement the other answers here, I thought to quote from PhilosophyForums.com, but I modify the writing and omit blockquotes for easier reading.
Source: Posted Oct 31, 2009 by user 'Hamandcheese'
As a materialist I think every thing is made of matter, akin to naturalism. If someone claims, say, that a statue of Mary cried a tear, the materialist would point out: the substance that the rock is made out of, is all it is, and is no different than the rock before it was extracted from the earth, only that it has been shaped. Thus materialism is an important premise for my deductive and inductive reasoning.
Empiricism is the statement that everything that we know, we know through our direct senses, or some other aided observation (an empiricist would be fine with a microscope). Traditionally empiricists reject the idea of innate ideas, being entirely skeptical that intuitions and instinct could reliably inform our knowledge.
So the difference is pretty substantial. There are plenty of materialists who are not strict empiricists: that is, they think that only matter exists, but that some truth is innate in our brain and certain facts can be determined through intuitive reasoning. Empiricists, on the other hand, don't necessarily have to believe that all that exists is matter. Indeed, George Berkeley is famous for being both a strong empiricist and 'immaterialist'.
Source: Posted Nov 1, 2009 by user 'mrnormal5150'
empiricism tends to be an epistemological position while materialism is a metaphysical one. Sometimes one entails the other, but not always.