Chapter 7 summarized this dissertation and provide some future thinking
3.2. Materials and Methods
3.2.1 Cordierite Substrate Sample Preparation
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An uncoated commercial, 400 cpsi cordierite substrate (NGK, Japan) was used to prepare cordierite substrate samples. The 4inch (10.16cm) length x 3.5 inch (8.89cm) diameter round substrate was cut between channel walls to form a rectangular substrate sample. The individual cordierite substrate samples were 10 cm long, 1.6 cm wide, and 0.7 cm thick.
Each sample was approximately 14 channel widths wide, and 5 channel widths thick, with estimated wall thickness of 10 mils. The target mass of each sample was 5 grams. The prepared cordierite samples were rinsed with deionized water to remove any dust or debris from the cutting process, and then dried in an 105oC oven for 24 hours. Each sample was weighed and recorded.
3.2.2Deposition of Na2CO3, K2PO4, FeSO4 on the Cordierite Substrate Sample
Water based solutions containing 5gL-1 of Na2CO3, FeSO4 and K3PO4 were prepared in 1 L beakers as three separate solutions. And 20 g/L of calcium acetate and zinc phosphate were prepared in 1 L beakers as two separate solutions on the other hand. Two dried rectangular, cordierite substrate samples were then placed into the 1 L beaker containing one of the solutions. The sample was completely submerged in solution. The samples were exposed to the solution for one week. The samples were removed from the beakers and dried in an 105oC oven for 24 hours. The cordierite substrate samples were
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then cleaned with dehydrated ethanol solution. The samples soaked in the solution under ultrasonic treatment for 5 minutes to remove unreacted, residual crystals from the sodium, iron, potassium, zinc and calcium solutions. The samples were removed from the ethanol solution and dried in an 105oC oven for 24 hours. The mass of each sample was recorded, and the weight difference for each sample was calculated. As detailed in Table 1, the target mass loading was 5% for sodium, 10% for iron, 5% for potassium, 10% for zinc and 20%
for calcium. If the target mass loading was not achieved, the same procedure was repeated
to obtain the target mass loading of each substrate sample.
Table 3.1. Sample preparation and treatment description: ash mass loading (% dry weight), thermal treatment temperature (oC) and thermal exposure time (hour).
Ash-substrate Composition Temperature (oC) and Time (hour) of Thermal Exposure
Table 3.2 Sample preparation and treatment description corresponding for Zn and Ca doped substrate
Ash-substrate composition Temperature (oC) and time (hr) of thermal exposure
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3.2.3 In-situ Lab simulation of DPF thermal conditions
The heat treatment of the prepared cordierite substrate samples was carried out under temperatures ranging from 300-1100oC. A section of sample was cut from each doped cordierite substrate sample. A section of substrate was also cut from a clean, undoped (blank) cordierite substrate sample. The sections of cut substrate were approximately 3 channels by 3 channels (0.4 cm by 0.4 cm) in size, and weighed approximately 0.5grams.
The sample was heated in a thermogravimetric analyzer (TG209, NETZCH) to hold temperatures of 300oC, 500oC, 900oC, and 1100oC. The TGA heating rate was 25K min
-1 in an atmosphere of high purity nitrogen, which was set to a flow rate of 25 ml min-1.
Once the TGA cooled down to room temperature, the sample was removed and rinsed by dehydrated ethanol in an ultrasonic bath. This additional step of dehydrated ethanol and ultrasonic cleaning was intended to remove any residual chemicals which did not react with the cordierite surface. Once removed from the ethanol, the samples were dried in an oven at a temperature of 105oC for 24 hours. It should be noted that a separate cordierite sample was used for each temperature condition and time of exposure.
Therefore, with one pristine sample and three different chemical solutions (sodium
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carbonate, iron sulfate, and potassium phosphate), four different temperature conditions (300oC, 500oC, 900oC and 1100oC).
3.2.4 SEM, WDS and XRD analysis of Cordierite substrate aging samples
3.2.4.1 SEM analysis of cordierite substrate aging samples
The surface microstructures of the thermal-chemically treated cordierite samples were characterized by a Hitachi 4300 SEM. Prior to SEM analysis, the samples were coated with iridium and palladium. Samples were placed on a metal stand and anchored to the stand by double sided carbon tape. The surface microstructures of thermal-chemically treated samples were compared to pristine cordierite samples.
3.2.4.2 Element Distribution by EPMA
Each cordierite sample was placed standing vertically (channel walls running vertically) then embedded into an epoxy resin. The epoxy resin was allowed to cure for 24 hours.
After curing, the epoxy resin bound sample was then ground and polished with 6 µm and 3 µm diamond paste coated polishing pads. An additional fine polish process was carried out utilizing a 1 µm polishing pad with aluminum oxide paste. The aluminum oxide powder was first dispersed in dehydrated ethanol, prior to use in the fine polishing process. The cross-sectional distribution of elements was appraised with WDS (JXA-8900, Japan). The cordierite porosity was calculated via adjusting the threshold color of the BSE images using
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Image J2X (National Institutions of Health, US). Select one area on the BSE images and the contrast of the original image is automatically enhanced and black pixels after adjustment indicate the porosity. The equation is shown as:
Porosity (%)=Sp/ST (1)
Sp: Porous area
ST: Total area
The average cross-section element concentrations were calculated by converting the entire scanning area element concentration including the pore area, which were read directly from the WDS, to cordierite cross-section element concentration based on J2X. The equation is shown as:
Concentration (%)= C1/µ (2)
µ= Sc/Ss
C1: element concentration read from WDS
µ: cordierite substrate area fraction based on J2X
Sc: cordierite substrate area
Ss: entire scanning area
3.2.4.3 XRD analysis of cordierite substrate aging samples
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XRD was utilized to characterize the physico-chemical properties of doped and pristine cordierite substrate samples to reveal the crystalline phases change before and after the thermal-chemical treatment. Samples for XRD analysis were prepared by grinding the TGA thermal-chemical treated cordierite samples using a mortar and pestle. The ground powder samples were appraised via x-ray diffraction (MiniFlex, Rigaku). The XRD analyses were carried out under electric voltage/current of 30kV/15 mA. The scanning angle ranges from 10-90o with the scanning step of 0.01o.