Expository writing is often used in academic settings as a style of prose that is thought of more in terms of creative writing. Essays are a typical example of expository writing used to convince others of a particular opinion. The purpose of expository writing is to explain further through critical analysis and not to simply focus on the facts themselves.
Technical writing's main objective is to teach others how a product or procedure works. Technical writing is usually geared to those who have advanced knowledge in a particular subject so that they would understand testing protocols or an industrial report. A pharmaceutical company might use technical writing to explain how a particular medication works, for example, so it is more like reading a textbook than an argument.
Technical writing is sharing information in an impersonal way whereas expository writing may involve the writer's personal impressions and opinions on a certain topic. Expository writing is geared toward providing information that supports an argument with a large reader audience while technical writing is more fact-based for an audience with a particular knowledge base.
College students need to know the difference when completing assignments. A math analysis or lab report should be written in a technical style whereas a philosophical essay should be written in expository style. Some occupations may require you to blend both styles at times, such as using the technical style for ads and expository style for describing how a product works.