Chemistry, Physics and Modern Materials

Introduction

This multi-demonstration kit is a great way to explore new advanced materials and techniques used in today’s technology! The demonstrations incorporate chemistry and physics to teach the importance of diffraction, nitinol wires, photoresistors and piezoelectricity.

Set of four demonstrations includes:

• Diffraction—Simulate the concept of X-ray diffraction for your students without using expensive equipment. Using optical transform samples and a laser pointer, your students will see the unique diffraction patterns of electromagnetic radiation when passed through each selected barrier.
• Nitinol wires—Made of nickel-titanium metal alloy, nitinol is known as a “memory” wire. At cooler temperatures the crystal structure of the wire may be easily deformed (i.e., coiled or twisted). At higher temperatures, the crystal structure returns to its original state.
• Photoresistors—Also known as a semiconductor, photoresistors are commonly made of cadmium sulfide. A photoresister is simply a material whose resistance depends on incident light upon it.
• Piezoelectricity—Get a striking reaction when you see the LED light upon hitting the piezoelectric element with a pencil! The piezoelectric buzzer element is made of a crystalline material that generates a charge upon mechanical stress.

Concepts

• Diffraction (scattering)
• Lasers
• Optical transforms
• Metal alloys
• Crystal structures
• Resistors
• Photoconductivity
• Energy bands
• Piezoelectric materials
• Electricity
• Mechanical stress

Background

Demonstration I. Diffraction
Diffraction is the concept of passing electromagnetic radiation, such as monochromatic light from a laser, through a barrier and observing the resulted wave scattering or wave distortion projected on a screen. This has been an effective technique in discovering the molecular structure of unknown compounds. The unknown compound, in its crystalline form, acts as the barrier in the diffraction technique and the structure of the crystal may be determined. Today this technique is known as X-ray diffraction and is usually performed with a standard specialized instrument called a diffractometer. Scientists have been able to determine positions of atoms, bond distances, and bond angles to discover the beautiful geometries that crystalline compounds display. Show to your students that chemistry is fun with this simulation of X-ray diffraction.

Demonstration II. Nitinol Wire
See a “live” wire snap back into its remembered shape when it is put into hot or cold water.

Demonstration III. Photoresistors
The functionality of photoresistors depends upon the light illuminated on its surface. The unique design of the photoresister allows for amazing applications in technology. Conduct a simple demonstration with your students and show them how fascinating photoresistors are!

Demonstration IV. Piezoelectric Effect
Piezo buzzers contain a material inside called the piezo element. This element is made out of a material that generates an electrical charge when struck.

Experiment Overview

Demonstration I. Diffraction
The purpose of this activity is to conduct a diffraction experiment using a laser pointer and an optical transform slide in a darkened room to decipher the structure of the simulated crystal based on the observed light scattering pattern.

Demonstration II. Nitinol Wire
Demonstrate the unique properties of a Shape Memory Alloy by bending Nitinol wire at one temperature, then submerging the wire into water, of a different temperature. Watch it reform into its original shape.

Demonstration III. Photoresistors
Illustrate the properties of photoresistors by connecting the photoresistor to a multimeter and shining a flash light to the top of the photoresister. The resistance may be observed when the photoresistor is illuminated.

Demonstration IV. Piezoelectric Effect
Piezo buzzers contain a material inside called the piezo element. This element is made out of a material that generates an electrical charge when struck.

Materials

Safety Precautions

Do not aim the laser pointer directly into anyone’s eyes and never look into the laser beam. The low-power, coherent light can cause damage to the sensitive retina and may lead to permanent eye damage. Do not aim the laser at any reflective surfaces, such as mirrors or highly polished metal. Prevent stray laser light from projecting beyond the classroom to eliminate any unintentional exposure to the laser light. When refracting the laser light, it is best to do this on a low work surface to keep the refracted laser light below “normal” eye level. For people with sensitive eyes it is recommended that dark, IR-protective safety glasses be worn. Caution should be used whenever handling Bunsen burners and hot water. Always wear chemical splash goggles whenever chemicals, glassware or heat are used. Handle photoresistor leads with caution, as they are sharp. If resistor becomes hot, allow time to cool before touching. Wear chemical splash goggles or safety glasses for eye protection when striking the piezo element. Take caution to avoid striking fingers with pencil while conducting experiment. Follow all other laboratory safety guidelines.

Disposal

All materials may be kept and used again for additional classes. Dry the nitinol wire with a paper towel and store. LED or piezo elements that no longer function may be disposed of in the trash.

Prelab Preparation

Demonstration I. Diffraction

1. Cut each white index card into four equal pieces.
2. Carefully cut out each optical transform pattern and place one in the center of each small piece of index card. Trace the
   outline of the transform slide on the card.
3. Cut out the square in the center of the small index card piece.
4. Tape the transform slide into the small square. Note: Only tape on the sides of transform slide (see Figure 1).
   {13758_Preparation_Figure_1}
5. Label each card alphabetically.

Procedure

Demonstration I. Diffraction

1. Set up the demonstration across from a white screen or plain white wall.
2. Use the large binder clip to hold the laser pointer in place.
3. Set the large paper clip, holding the laser pointer, on a surface such that the transmitted image will be on the white screen or white wall.
4. Hold one index card in front of the laser light, so that the light shines through the optical transform slide. Try holding the slide at various distances from the laser light and determine which distance provides the clearest diffraction pattern. Note: For best results, determine this step ahead of time.
5. Instruct students to sketch the image they see projected on the screen for each card on the student worksheet for the diffraction demonstration.
6. Repeat steps 4–5 with the remaining optical transform slides.

Demonstration II. Nitinol Wire

Part A. See the wire remember its straight shape

1. Start with the nitinol wire in a “straight” form.
2. Hold one end of the wire and place it into the beaker of ice water until it is thoroughly chilled.
3. Remove the wire and quickly use your hands to bend the wire into crazy shapes (or better yet, if you can, bend the wire while it is still in the ice water).
4. Use pliers or tongs to hold one end of the bent nitinol wire, and carefully dip it into the near-boiling water. The wire should instantaneously pop back straight again (see Figure 2).

Part B. “Train” the wire to remember a new shape

1. Starting with the straight wire, use your hands or pliers to bend the wire at room temperature into a desired shape.
2. While firmly holding the wire in this shape with pliers or (you may need 2 pairs), heat the wire in a Bunsen burner flame (or candle flame) until it is just slightly red. The wire will at first “fight” and want to straighten out. (You must “train” it.) Note: Overheating will not help in this procedure and may actually damage the wire.
3. Allow the wire to cool to room temperature, still holding it in its “trained” shape.
4. Chill the wire by dipping it into ice water. Remove the wire from the ice water and immediately straighten it out.
5. Using tongs, dip the wire into a near-boiling water bath.
6. The wire should “remember” the bent shape in which you “trained” it and form back into that shape.

Demonstration III. Photoresistors

1. Connect the leads of the photoresistor to a mulimeter.
2. Read the resistance. Note: The multimeter range should be set to 20 kΩ resistance.
3. Shine a flashlight at the top of the photoresistor and read the resistance display from the meter.
4. Cover the top of the photoresistor with hand and read the resistance reading again.

Demonstration IV. Piezoelectric Effect

1. For better results conduct this demo in a slightly darkened room or area of the room.
2. Tape the leads of the LED to the piezo element (see Figure 3).
   {13758_Procedure_Figure_3}
3. Using a pencil point, tap or strike the center of the piezo element until you see the LED blink.

Student Worksheet PDF

13758_Student1.pdf

13758_Teacher1.pdf

Teacher Tips

• A higher power laser, such as Flinn Scientific Catalog No. AP8934, will give a sharper diffraction image for the Diffraction demonstration.
• Have a student stand close to the wall where the refracted imagine is located and determine the pattern.
• Both Parts A and B on the Nitinol Wire demonstration may be repeated indefinitely if the wire’s unique crystal structure is not damaged by overextending or overheating.
• Nitinol is named for its elemental composition, nickel (Ni) and titanium (Ti) and the Naval Ordnance Laboratory (NOL) where it was discovered.
• For the Piezoelectric Effect demonstration, hold the piezo element with fingers around the edges.
• Start by tapping the piezo element first with the pencil and then increase the force to light the LED.
• It might take a few tries of tapping the piezo element in the same place to light the LED.

Sample Data

Answers to Questions

1. Briefly explain the experimental setup to observe the best diffraction pattern.

   The laser was placed inside of a binder clip and set on a shelf, in a darkened room. The teacher pressed the laser button and held the cubic cell in front of the laser light, where the laser light was shined through the cubic cell. The diffraction pattern was seen on the blank wall 5 ft to 10 ft away from the laser pointer. Different cubic cells gave different patterns.

2. In the nitinol wire demonstration, explain how temperature plays a role in the shape of the wire.

   The alloy has crystal structures that have different shapes at different temperatures. When cooled the crystal structure is easily changed and returns to its original shape when heated in near-boiling water.

3. The photoresistor provided is made from cadmium sulfide (CdS). Are photoresistors made from other materials? If so, conduct an internet search to find an example.

   Photoresistors are also made from lead sulfide and lead selenide.

4. Conduct an internet search and find a real-world application for piezo elements.

   Piezo buzzers contain a piezo element and they are used for making sounds. Examples include: electrical alarms, buzzers at sporting events or a door bell.

Discussion

Demonstration I. Diffraction
In nature and laboratories, many compounds form solid structures known as crystals. The atoms that make up each crystal bond and form beautiful solids that exhibit geometric shapes and sometimes fascinating colors. The use of diffraction, specifically X-ray diffraction, was an amazing discovery that helped scientists in many fields determine the chemical structures of molecules— which in some cases were complex and difficult to determine. In fact, it was possible to determine the structures of fibrous proteins using X-ray diffraction, a task that was often strenuous due to the many polymerized molecules positioned in unique folds within the protein.

X-rays are a form of electromagnetic radiation. Other types of electromagnetic radiation are radio waves, microwaves, visible and UV light. All types of electromagnetic radiation have a wave-like nature and travel at the speed of light, c (3 x 10¹⁰ cm/s). At the beginning of the century, scientists discovered that using X-rays as a form of electromagnetic radiation for diffraction experiments to solve the chemical structures of crystals was superior to other forms of electromagnetic radiation. X-rays have wavelengths of atomic dimensions (Å, angstroms), thus it is possible for atoms to scatter X-rays. When X-rays shine upon the crystal, the crystal scatters the incoming X-ray and the refracted patterns are analyzed to determine the positions of atoms within the crystal structure. Laser light resembles X-rays in that it has a very specific wavelength of light. When the laser light passes through a barrier, in this case an optical transform instead of a crystal, the patterns on the optical transform scatter the laser light. The demonstration thus effectively and inexpensively simulates X-ray diffraction patterns observed when atoms in a crystal scatter X-ray light.

Demonstration II. Nitinol Wire
Nitinol wire is part of a class of metals known as Shape Memory Alloys (SMAs). These alloys have different crystal structure phases that form at distinct temperatures. The crystal structure is easily deformed at cool temperatures (see A), and then when heated, the solid state structure returns to its original arrangement with great speed and force (see B).

The live wire is a nickel–titanium alloy and thus is given the acronym Nitinol. Nitinol consists of nearly equal percentages of the two metals and is specially alloyed and annealed to produce a small grained, extremely uniform crystal structure. A difference of less than 1% in composition will change its transition temperature by 150 °C. Therefore, the materials require very careful formulation and processing.

The Shape Memory Effect (SME) of the nickel–titanium alloy was accidentally noticed by William Beuhler and his research team at the U.S. Naval Ordnance Laboratory in 1961. However, the first SME was discovered in 1932 by Arne Ölander, a Swedish researcher, who observed the Shape Memory Effect of a gold–cadmium alloy. During the 1960s and 1970s, other Shape Memory Alloys were found. Researchers around the world studied alloys of titanium, copper, iron and gold which had this newly found property.

The most successful applications have come more recently. Raychem Corporation came out with Shape Memory Alloy pipe connectors that will shrink, thus producing a better seal in jet engines and hydraulic systems. Toki Corporation of Tokyo, Japan, improved nitinol for specific use by electrical activation. At the 1986 International Symposium on SMAs, papers were presented on possible applications including basic alloy research and development, crystal structures, medical applications (such as using SMA wires like electric muscles in robotic or prosthetic devices), product designs, and manufacturing studies. Since not all areas of Shape Memory Alloys have been explored, the research and interest are still growing today.

Demonstration III. Photoresistors
Traditional resistors, such as carbon-film resistors, which are most commonly used in laboratories, are designed to limit the current flow by producing a voltage drop. The color codes on the body of the resistor indicate the tolerance or the resistance value of the resistor (see Figure 4). These electrical components are very important in circuits as they control the current flow in the circuitry.

The resistor symbol in a circuit is shown in Figure 5. One may imagine a resistor as being a water pipe. The diameter of the water pipe controls the flow rate of the water passing through the pipe. Among the vast and growing applications, various types of resistors reduce current to delicate circuit components, split voltage to bring power to multiple components, create heat, act as fuses, and now use light as a factor to control the resistivity. Since all resistors conduct electricity, the resistance value of most resistors determines the amount of current that flows through it and is related to current and voltage by the equation:

V/R = I

where

V is the voltage drop
I is the current
R is the resistance

A photoresistor, also known as a light-dependant resistor (LDR), has the ability to conduct electricity dependent upon the incident light, as opposed to carbon-film resistors, which contain fixed-resistance values. Fascinatingly, the resistance of a photoresistor is inversely proportional to the incident light. The resistance increases in darkness or when not directly illuminated and decreases when directly exposed to light.

The mechanism is simple. When the top layer of the photoresistor, known as the semiconductor material, CdS, is directly illuminated, the semiconductor absorbs the photons from the light and produces a change in resistance from the production of charge carriers. The symbol for a photoresistor (see Figure 6) differs from that of a common resistor (see Figure 5). The circular shape represents the semiconducting material and the arrows represent the incoming illumination. The physical appearance of the photoresistor is shown in Figure 7. The zig-zag represents the CdS semiconducting material connected to two leads. Today, photoresistors have vast applications in electronics. Demonstration IV. Piezoelectric Effect
The piezoelectric effect was an amazing phenomenon discovered in 1880 by brothers Pierre Curie—who was awarded the Nobel Prize in physics in 1903—and Jacques Curie, also known as Paul. The piezoelectric effect is translated to ‘press’ in the Greek language. When mechanical stress is applied to certain crystalline materials, the material forms electrical charges. The charge produced is proportional to the applied weight or the striking of the material. The crystal does not have a center of symmetry and behaves like a generator to produce electricity from mechanical energy. In addition, these materials are able to produce what is called a converse piezoelectric effect. In a converse piezoelectric effect electricity is applied to the crystalline material to produce energy. One example of a crystalline material is quartz, SiO₂. Typically, piezoelectric materials are made today from zinc and silicon salts.

The piezoelectric effect led to several important industrial applications. For example, quartz was glued between steel plates and named the “Langevin sandwich.” Paul Langevin was Pierre Curie’s student and developed this piece of technology, which was used in World War I to produce ultrasonic waves for the detection of submarines. Other applications of piezoelectric materials are in aerospace and aircraft structures, vibration and noise control and microsensors.

References

Lisenky, G. C.; Kelly, T. F.; Neu, D. R.; Ellis, A. B. J. Chem. Ed. 1991, 2, 68, 91–96.

Properties of 6 mil BioMetal™ Wire, Mondo-tronics, Inc., Sunnyvale, California, 1987.

Seymour, R. B.; Kauffman, G. B. J. Chem. Ed. 1990, 9, 67, 763–765.

Special thanks to Dr. Ainissa Ramirez, New Haven, CT for providing the idea and the instructions for this activity to Flinn Scientific.