1. Silver Nitrate on Copper Wire
Growing Crystals
Silver Nitrate on
Copper Wire

2. Growing Silver Crystals
Place a flattened 1” piece of Cu wire on a microscope slide.
Focus one end of wire under stereoscope.
Have the teacher drop AgNO3 (silver nitrate) on the wire.
Make observations:
Low and high power
Light from above and below

3. Crystal Definitions Dendrites crystal branches
crystal growth pattern – directional
grow until they eventually become large enough to impinge upon (interfere with) each other
spaces between the dendrite arms
crystallize to make a more regular
crystal

4. Once nucleated, the dendrites spread sideways and the secondary arms generate further tertiary arms and so on. When solidification is complete, all the dendrites that have formed knit together to form grains (or crystals).

6. Snow - ice
Snow - Ice

7. Dendritic copper crystals

8. Crystal Defects What does crystalline mean?
How easy is it to grow a perfect crystal?
What types of defects are possible?

9. CRYSTAL TERMS Grains individual crystals
They grow in different directions and meet up with each other
Grain Boundary
boundaries where grains meet

11. “Crystal grains” are regions of regularity
“Crystal grains” are regions of regularity. At the grain boundaries, atoms have become misaligned.
Heating a metal tends to shake the atoms into a more regular arrangement - decreasing the number of grain boundaries, and so making the metal softer. Banging the metal around when it is cold tends to produce lots of small grains. Cold working therefore makes a metal harder. To restore its workability, you would need to reheat it.
You can also break up the regular arrangement of the atoms by inserting atoms of a slightly different size into the structure. Alloys such as brass (a mixture of copper and zinc) are harder than the original metals because the irregularity in the structure helps to stop rows of atoms from slipping over each other.
Crystal Grains

12. Crystal Defects and Imperfections
impurities and disruptions in the pattern of atoms
affect many physical properties
three main types
Ask the students what comes to mind when you hear the word “defect”. They usually say something “bad” or “unwanted” or “negative”. When discussing that point defects can be used to make alloys point out that we create “defects” on purpose b/c they result in useful changes in properties.
Reinforce the idea that defects can lead to positive changes when discussing that line defects can increase the hardness or strength of metals.
Ask students to predict how crystals may “mess up”.

13. 1. Interfacial Defects grain boundaries affected by size of grains
Use BB board to show

15. By cooling more quickly, a smaller grain size results and this has the effect of making the resulting solid stronger. Figure 2 and Figure 3 are examples of metals with different grain size – the one exhibited in Figure 3 will be significantly stronger than its counterpart in Figure 2.
Figure 2
Figure 3

16. Phenyl Salicylate Demo
freezing a liquid to grow crystals
nucleation site – location where a crystal starts growing
watch for grains and grain boundaries
journal a description

17. 2. Dislocation (Line Defects)
regions in crystals where atoms are not perfectly aligned – an extra partial plane
can move
a small number make a metal more workable
a large number make a metal harder to work
dislocations can get “jammed” or “pinned”
makes the metal harder = work-hardening
-use overheads to illustrate
Deck of cards with one partial card inserted

24. Dislocation Movement

25. 3. Point Defects
single atom defects

26. Substitutional replace some of the original atoms with different atoms
used in making alloys
examples – brass and bronze

27. Interstitial
extra atoms inserted in the gaps between the regular atoms
used in making alloys
example - steel

28. Vacancy atom is missing (void) move around in crystal by diffusion
-use BB board to illustrate
Have students draw an example in their journals

29. Iron Wire Demo

30. Iron Wire – Crystal Structure Change
Iron Wire 72-S to 76-S
BCC slow heating causes the wire to sag due to thermal expansion. The crystal structure of the wire changes to FCC at transition temperature 910o C and the density of the wire increases. As the wire cools back, at the transition temperature, the crystal becomes BCC and the wire will suddenly sag or dip bounce, then return slowly continue to contract to its original length.
Repeat the experiment with a small area of the wire cleaned to remove oxidation. This part of the wire will glow brighter.
The metal magnets will fall off at ~770o , the Curie Temperature
The glowing wire is an example of incandescence – raising the temperature until light is emitted
BCC is loosely packed, at 910C (transition) the wire structure becomes FCC closely packed
Iron atoms are arranged in a body-centered cubic pattern (BCC) up to 1180 K. Above this temperature it makes a phase transition to a face-centered cubic lattice (FCC). The transition from BCC to FCC results in an 8 to 9% increase in density, causing the iron sample to shrink in size as it is heated above the transition temperature.
How it works: A three meter length of iron wire is horizontally stretched above the lecture bench. A Variac supplies the adjustable AC heating current. As the current is increased, the wire will heat up, expand, and sag. The hotter, the more the sag. If the wire is heated to below the transition temperature and allowed to cool (heating current turned off), the wire shrinks back to its original length as is evident by a reduction of the sag to its original. However, if the wire is heated to a temperature above 1180 K (910 C) and then allowed to cool, it behaves in a remarkable way. Initially there is a reduction in the sag as it begins to cool (no surprise). But when it reaches the transition temperature and goes from FCC to BCC, its density decreases, resulting in an increase in overall length (about 2%) and a visible increase in the sag. As it continues to cool back to room temperature the wire shrinks back to approximately its original length. Note that the increase in sag (at the transition temperature) happens very quickly and it is helpful to repeat the demonstration for the class.

31. IRON WIRE OBSERVATIONS AND TERMS
Thermal Expansion
expansion of material due to heat
Incandescence
the emission of light as a result of a material being heated
Curie temperature
the temperature at which magnetic metals lose their magnetism
Curie temperature for iron is 770 °C
Note: 3 naturally magnetic metals: Fe, Ni, Co
In inudstry when moving stell ignets they used to use electromagnets to move it from one part of the plant to the other…you got to wait it to cool below the cuire point before the electromagnet can work

32. OBSERVATIONS Oxidation rusting REMEMBER: METALS ARE CERAMIC WANNABES!
Other observations
heat sink

33. OBSERVATIONS Solid state phase
when a solid material changes crystal structure while remaining a solid
Iron starts off as BCC then changes to FCC it is heated
When it cools it changes back from FCC (more dense) to BCC (less dense) and that is where you see the dip
This occurred at 912 °C
Coffee roasters (true hard core ones) use variac to control the the rate at which the coffee bean was extracted
This demo illustrates thermal explansion and packing factor

34. Face Centered-Densely Packed
Iron Wire – Crystal Structure Change
Face Centered-Densely Packed
Body Centered
More Loosely Packed
912o
Heating
Cooling

35. Iron Wire Crystal Structure
The Curie point of a ferromagnetic material is the temperature above which it loses its characteristic ferromagnetic ability (768°C for iron). At temperatures below the Curie point the magnetic moments are partially aligned within magnetic domains in ferromagnetic materials. As the temperature is increased towards the Curie point, the alignment (magnetization) within each domain decreases. Above the Curie point, the material is purely paramagnetic and there are no magnetized domains of aligned moments.
64-S, 54-M

36. EXAMPLES OF HOW TO MAKE CRYSTALS
Liquid to Solid (freezing a melt)
Phenyl salicylate
monoclinic crystals of sulfur
2. From a Chemical Reaction
silver nitrate on copper wire
AgNO Cu › Ag CuNO3
3. From Solution
making copper sulfate crystals OR alum crystals
Borax
each crystal growing activity has its own purpose and why we do it ….You can actually watch the crystals grow and you can see the crystals grow into each other and watch grains and grain boundaries…that is why we do this one…
The light from the stereoscope will be hot enough to keep the phenyl salicylate hot so use a doc camera
Use a bic lighter to melt the phenyl salicylate on a slide and then find the edge of the liquid and drop a seed crystal on it—you can sometimes see crystals appear from no where

37. SOLUTION TERMS Solute- stuff being dissolved
Solvent-stuff doing the dissolving
Water is considered the universal solvent

38. Solution Terms Continued…
Unsaturated Solution
a solution that can dissolve more solute
Saturated Solution
a solution that has dissolved the max amount of solute
the amount of solute a solvent can dissolve increases with temperature
Supersaturated solution
solution that has dissolved more solute than it “theoretically” should

39. Solubility curve: graph that shows how much of a solute will dissolve in water at different temperatures
supersaturated
saturated
unsaturated

40. Solubility Graph Examples
1. How many grams of potassium nitrate can be dissolved in 100g of water at 30 degrees C?
2. If 70 g of potassium nitrate is dissolved in 100g of water at 40 degrees C...is the solution saturated, supersaturated, or unsaturated?
3. If 10g of potassium nitrate is dissolved in 100g of water at 50 degrees C, can more potassium nitrate be dissolved?
if so, how much more?

41. 3 Ways to form Crystals From a solution Liquid to Solid (melting)
Precipitation from a chemical reaction
Precipitate - a solid that forms when 2 solutions react

42. Forming Copper Sulfate Solutions

44. Ways to form Crystals Cooling a liquid from a melt (freezing)
phenyl salicylate demo
sulfur – monoclinic crystals (Part B)
Grow as a precipitate from a chemical reaction
silver nitrate on copper wire
AgNO Cu › Ag CuNO3
silver nitrate + copper wire -----› silver crystals + copper nitrate
From a solution as the solvent cools or evaporates
growing single crystals – copper sulfate or potassium alum
sodium acetate demo
sulfur – rhombic crystals (Part A)

45. Growing Single Crystals Lab
copper sulfate or potassium alum

46. Day 1
Measure amount of water it takes to fill jar 3/4 full. Use a graduated cylinder. Record in mL.
Determine amount of chemical needed to make a supersaturated solution.
Copper sulfate = _____ mL of water x 0.43 g/mL Or
Potassium alum = _____ mL of water x 0.16 g/mL
Record in grams.
Describe appearance of chemical.

47. Add the amount of water from step #1 to the beaker.
Mass proper amount of chemical into a mL beaker using a balance.
Define the term “tare” in your journal.
Add the amount of water from step #1 to the beaker.
Use a hot plate to heat the contents of the beaker until all of the chemical is dissolved. Stir as you heat.
Pour a small amount of the solution into a watch glass. Place remaining solution into your jar and loosely cap.
Record observations.

49. Day 2 Select a seed crystal from your watch glass.
Cut cm of thread and use it to tie a knot around the seed crystal.
Make a sketch actual size, record the mass and describe the seed crystal in your journal.
Run the thread through the hole in the jar lid and tape it down so that the seed will suspend in the middle of the solution.

50. Clean the seed crystal and thread by gently and quickly dipping them in a beaker of water a couple of times.
Suspend the seed crystal in the jar of solution.

51. Day 2- Journaling
Look at your watch glass under a stereoscope and find examples of each of the following:
single crystal
grains
grain boundary
dendrites are difficult to find – but look in case
Make a labeled sketch of each of these structures.
Choose a seed crystal – sketch it actual size, record the mass and describe it.

52. Day 3+
Check the crystal daily. Record observations, mass, sketches, and describe “maintenance” techniques used.
If crystals appear on bottom of jar – reheat the solution to re-dissolve the chemical. Use a beaker. Allow solution to cool before replacing the crystal.
If dendrites grow on the crystal or thread try to remove them.
use forceps
dip in water
?????????

53. If crystal stops growing, re-supersaturate the solution.
Add 2 or 3 grams of chemical for each 100 mL of solution and reheat in a beaker to dissolve.
Let solution cool before replacing the crystal in solution.

54. Uses of Single Crystals
Turbine blades
PET scanners – scintillating crystals
Lasers
Silicon – computer chips
Uses of Single Crystals

57. Sodium Acetate Demo
growing crystals from a supersaturated solution – sodium acetate and water
journal a description
+acetate&hl=en&sitesearch=# - tower
instant hand warmer