Why the water is so "dirty"?

                                                                                                                                      ---Genesee River Water Residual Study


Wenjie Bi

University of Rochester
Materials Science Program

OPT407: Electron Microscopy
Spring 2010

Sample preparation
Analysis Methodology
Results and Discussion



Colorful stones sit in the bottom of the water; happy fishes swim back and forth in the Genesee river. What a beautiful view! Mm... I cannot help imaging this scene... Ok, I admit I am cheating myself. Let's go back to the real world. The river isn't that clean. I wonder what is in the water to make it so "dirty"?  Our lovely Electron Microscopies jumped to my mind at once. So, the wonderful jounery of exploring begins. Let's see....

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Sample preparation

The water was fetched from the nearest spot from the Hopeman Building of our school. They were dried in oven which was set at temperature of 40 degree C after serval hours. Then I put the residual powder onto carbon tape and sit it on a stub. After this, the sample was sputtered with gold for 50 seconds. The coating was applied using a Dento Vacuum Desk 2 system. Now the sample was ready for SEM examination.

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Analysis Methodology

Scanning electron microscope analysis was done using a Zeiss SUPRA40-VP model SEM and  Transmission Electron Microscope analysis was done by a FEI Tecnai F20 at the Institute of Optics at the University of Rochester. 
In SEM analysis, secondary electron detector (SE2), backscatter electron detector (BSD), and energy dispersive spectroscopy (EDS) were used to examine the content and compositions of the water.  
In TEM analysis, bright field image was used for further inspection.

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Results and Discussion

1. SEM-Secondary Electron Imaging

The following images are all micrographs taken using the secondary electron imaging technique (SE2). As we can see in the imaging proecess, there are abundant "stones" in the water as shown in figure 1. Through EDS analysis (the graph is shown below), we know their compositions are CaCO3. The turbidity of water are caused by this kind of stuff. There are also diatoms in the water, as seen in figure 2 and 3. A crystal shape matter is also identified, see figure 4. EDS analysis indicates that it consists of Ca, P, O.

 CaCO3 and fiber  color film layers
Figure 1. CaCO3 and Fiber

diatom    diatom-colored            
Figure 2 Diatom                                                                                                   

diatom-high mag    diatom-high mag-colored
Figure 3 Diatom with high magnification                                                          

Ca, P compound    yellow purple    light green
Figure 4 Ca, P compound

2. SEM-Backscatter Electron Imaging

The following micrographs, CaCO3 grains and diatom, were taken with backscatter electron imaging technique. As we can see, we can not see to much information from this technique for lacking of heavy metals.

BSE-CaCO3    BSE-Diatom    
Figure 5  CaCO3 grains by BSE                                                                                Figure 6  
Diatom by BSE


EDS is also used to characterize the stones shape matters which turns out to be CaCO3, the microorganism which is diatom, and the crystalline shape stuff which shows the Ca, P compositions.

bw se bsd    mix
Figure 7 CaCO3 grains
                                                                                                    Figure 8  Diatom

Figure 9 Crystal Shape Compound

4. TEM

I also tried to find intereting stuff by TEM technique and used TEM-EDS to characterize the composition of matters. There seems to be some heavy metals in the water, which means the water might be polluted slightly.                                                          

tem-heavy metal    TEM-EDS
Figure 9 Image of Heavy Metal by TEM                                                                Figure 10 Heavy metal composition by TEM-EDS

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I would like to thank Brian McIntyre for his guidence, advise and help to prepare samples, and use TEM.  

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