My research experience was in the Electrical and Systems Engineering Group under Dr. Jorge Santiago at the University of Pennsylvania. I worked in the lab with Dr. Mariem Rosario-Canales and Ms. Preethi Gopu.
The research project I participated in was: The Preparation and Characterization of Electrospun MnFe2O4 Nanofibers
Background: Manganese ferrite(MnFe2O4) has generated interest due to its properties of high magnetic permeability and high electrical resistance. These properties lend themselves to potential applications for magnetic storage, microwave and electrical devices. Historically nanoparticles of manganese ferrite have been produced by several methods such as ball-milling, co-precipitation,reverse micelle synthesis,pulsed laser deposition,solid phase reactions, thermal decompostion and the sol-gel method. Many research efforts have been concentrated on enhancing the magnetic properties of the ferrites. Since magnetic properties depend on morphology research has been done on nanorods because the magnetic property is easily grown along the magnetic axis.
Our research focused on using the sol-gel method and subsequent electro-spinning to produce ferrite nanofibers.
Manganese Ferrite sol was prepared by the dissolution of:
iron(III) nitrate nonahydrate(2.02g),manganese(II) nitrate(0.6mL 45-50 wt%solution), 3 grams citric acid and 15mL water. Subsequent removal of water produced the gel. The gel was then combined with a polyvinyl acetate polymer solution(15 wt% in a 4:6 cosolvent of DMF/THF in a 1.5 polymer to 1 gel ratio.
The above method resulted in a non homogeneous solution that was not condusive to electrospinning. As a result, a modification was made to the method where the "gel" was placed in an oven to completely remove the water from the solution producinging a fine powder. The powder was then mixed with the PVAce polymer solution and stirred for several hours. The resulting material was then electrospun by placing the material in a syringe on a syringe pump at 15mL/hr. Approximately 8.5kV was applied to the tip of the needle and the nanofibers were collected onto silicon wafers. Additionally, some of the material was retained prior to electrospinning to allow direct analysis of the dried,calcined sol-gel material.
The nanofibers were first dried at 80 degrees celsius for 4 hours.
The nanofibers were then calcined at 400, 600 and 800 degrees celsius for 6 hours. The material that was not subjected to electrospinning was also calcined at the above temperature conditions.
Results and analysis:
The calcined nanofibers were examined by optical microscopy after the calcining step. The control,non calcined nanofibers contained many areas of the ferrite that was not homogeneous within the fibers. Only the 400 degree calcined sample retained any nanofiber features. The 600 and 800 degree samples no longer contained any fibers and only very minute areas of metallic material.
SEM Analysis(Scanning Electron Microscopy)
The non calcined and the 400 degree calcined samples were examined by electron microscopy and are shown below.
X-Ray Diffraction Analysis
The 800 degree calcined(non electrospun) samples was examined by XRD. The sample was placed on a quartz low background holder and preparation by an acetone slurry preparation. The diffraction pattern and the matched phases are found below.
There were several problems encountered with the preparation of the ferrite. The major problem was inhomogeneity of the gel or dried powders with the polymer solution. The resulting nanofibers were also of poor quality. We were not able to produce the MnFe2O4 phase. Future work should include investigation into different sample preparation methods and the used of other polymers