Lesson Alloy Advantage

Learning Objectives

After this lesson, students should be able to:

• Define and classify alloys as mixtures.
• Compare and contrast the physical and chemical properties of alloys and elements.
• Determine the advantages of using alloys compared to pure substances

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Worksheets and Attachments

Pre-Req Knowledge

Students should be familiar with the composition of matter and be able to define elements, compounds and mixtures. They should also be able to distinguish between physical and chemical properties, and be familiar with the periodic table of elements.

Introduction/Motivation

(Prior to the lesson, give students time to complete the Reviewing Pure Substances and Mixtures Pre-Assessment.)

All substances on our planet can be classified as either pure substances or mixtures. In addition to the elements that make up the periodic table of elements, pure substances also include compounds that you encounter every day, like water. Mixtures include substances like Kool Aid and bronze. Bronze is a mixture of the elements copper and tin. Bronze is considered an alloy of copper. An alloy is a metal that is made by mixing two or more metallic elements, or made by mixing a metal and a nonmetal.

Let’s take a closer look and share the responses you wrote down for question three on the pre-assessment. What might be some advantages of using a copper mixture rather than using pure copper? (Pause for students to share responses.) As stated by some of you, when copper is mixed with other elements, forming alloys, some benefits might be to lower the materials cost and make it easier to produce the material. In order to understand the advantages of alloys, we are going to play the role of materials engineers who use their understanding of the properties of alloys in order to determine the ways in which they can be used. Refer students to the activity Alloy the Way to Mars to have them investigate different alloys and populate a class table with their findings and calculations of different material properties.

(Show students Table 1. Titanium and Its Alloys.) Using the information in this table, we can determine why—for a given application—it may be more beneficial to use an alloy rather than a pure substance. (Discuss the table as a class. Then proceed to Lesson Closure.)

Lesson Background and Concepts for Teachers

Alloys are created in order to enhance specific properties and characteristics of a given material. For example, the hardness, strength and corrosion-resistance of titanium are heightened when mixed with other substances, such as aluminum or chromium. Today, most commonly used metals are not pure; rather, they are alloys.

Since most design problems involve the selection of materials, it is important for scientists and engineers to study materials properties in order to understand and sometimes redesign the structure of a given substance. For example, an engineer who designs hip or knee replacement implants must understand the properties of a material to determine whether it will survive in the human body for a given period of time without side-effects to the person. A material used for hip replacement parts needs to be ductile, resistant to corrosion, biocompatible and, among other things, strong. Alloys are most often selected for such applications because of the properties they exhibit.

Associated Activities

• Alloy the Way to Mars - Mirroring real-world engineering, student teams take measurements and make calculations for various metal alloys to determine their specific strengths and compile a class data table. After analysis of the class data, they write letters to NASA to communicate and defend their findings for the alloy they recommend be used to construct the engine and engine turbines for a space launch system being designed to transport astronauts to Mars.

Lesson Closure

As we learned from our examination of the properties of titanium and its alloys, when a pure substance (like titanium) is mixed with other elements, the material’s properties can be enhanced, resulting in its suitability for more applications. For example, with the creation of titanium alloy 6al-4v, hip replacements and engine turbines became a reality. With the support of materials scientists, materials engineers can design newer, more efficient alloys, and then apply these substances to broader applications. (Next, administer the summary assessment.)

Vocabulary/Definitions

alloy: A metal made by mixing two or more metallic elements, or by mixing a metal with a nonmetal. For example, bronze is a mixture of copper and tin, and steel is a mixture of iron and carbon.

atomic number: The total number of protons (positive charges) found in the nucleus of an atom of an element. Also the total number of electrons surrounding the nucleus of an atom of an element.

brittleness: A characteristic of a substance that is hard and rigid and breaks with smooth fractures, such as glass.

corrosiveness: The ability of a substance to deteriorate over time due to chemical means.

density: The amount of mass in a given volume; expressed in grams per cubic centimeter (g/cm3).

ductility: A characteristic of a substance that is malleable and can be physically changed without breaking, such as plastic.

element: A substance made of one type of atom, which cannot be broken down into smaller parts. For example, titanium (Ti).

malleability: A characteristic of a substance that describes its ability to be shaped and molded through hammering or pressing.

melting point: The temperature at which a substance melts.

mixture: A substance made by mixing two or more substances together. For example, bronze is a mixture of copper and tin.

oxidation: The ability of a substance to react with oxygen.

pure substance : A substance made of only one type of atom, or one type of molecule, or one type of compound. For example, gold (Au), oxygen gas (O2), or water (H2O).

reactivity: The ability of a substance to react with other substances.

Assessment

Pre-Lesson Assessment

Review: Before the lesson, give students time to complete the Reviewing Pure Substances and Mixtures Pre-Assessment, which asks them to categorize substances as either pure substances or mixtures, and explain the benefits of alloys. During the Introduction/Motivation section, ask students to share their answers. Students’ responses to the three questions reveal their base knowledge of the topic.

Lesson Summary Assessment

Concluding Questions: After the Lesson Closure, administer the Alloy Advantage Summary Assessment, which gives students a chance to show their comprehension of the learning goals. They define alloys, compare and contrast alloy properties to those of the elements from which they are composed, and explain the advantages of alloys. Review their answers to gauge their depth of comprehension before moving on to conduct the associated activity.

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed through the Robotics Engineering for a Better Life and Sustainable Future research experience for teachers under National Science Foundation RET grant number CNS 1300794. However, these contents do not necessarily represent the policies of the NSF and you should not assume endorsement by the federal government.