The effect of preparation and mechanical properties of CIP and HIP fabricated alumina ceramics
Date
2016
DOI
Authors
Gelani, Hatem
Version
OA Version
Citation
Abstract
Objectives: This in-vitro study was designed to investigate the mechanical properties, and translucency of alumina processed by two methods: Cold Isostaic Pressing (CIP) and Hot Isostaic Pressing (HIP).
Materials and Methods: The alumina specimens used in this study were made from Almatis CT-SDP-3000 powder using both the CIP and HIP methods. Sixty cylinders were fabricated and cut into discs, and forty rectangular blocks were pressed and then made into crowns using the Sirona inLab MCXL milling machine. All cylinders and crowns were sintered in a (Vita Zycromat furnace), and the thirty cylinders and twenty crowns were sent for hot isostaic pressing at the (American Ohio Pressing company). For flexural testing, ten specimens for each of the three CIP and HIP disc groups were polished using 6 µm, 15 µm, and 25 µm micro-grit diamond-polishing pads, then loaded under compression using a universal mechanical testing machine (5566A, Instron) at a crosshead rate of 0.5 mm/min until fracture occurred. The crowns were cemented onto prefabricated aluminum dies using (Durelon) Zinc Polycarboxylate Cement. Ten crowns were subjected to a static load to failure test in universal mechanical testing machine. Another ten crowns from both groups were subjected to cyclic loading at 30% of the mean failure load in a water baths for I 05 cycles at a frequency of 1 Hz, and then their load to failure was tested under compression. Twenty CIP and HIP discs were subjected to translucency testing using the Benchtop spectrophotometer (i5, Xrite), and another ten _ CIP and HIP discs were tested for Vicker's hardness number using a microhardness tester (Micromet 2003, Buehler). Both the cylinders and rectangular blocks were tested for density before and after sintering. The grain size measurements were conducted under a Field Emission Scanning Electron Microscope (FESEM, SU6600, Hitachi). Selected failed specimens were also subjected to fractographic analysis using FESEM.
Results: The biaxial flexural test found that the load to failure of CIP specimens was 307.5 ± 34.2 MPa for the 6µm group, 293 ± 24 MPa for the 15µm group, and 302.7± 48 MPa for the 25µm group. The load to failure of HIP specimens was 373 ± 53 MPa for the 6µm group, 300.5 ±78 MPa for the 15µm group, and 281 ± 28 MPa for the 25µm group. The mean failure loads and standard deviation values for Both CIP and HIP crowns under static and cyclic loading are as follows: The CIP specimens failed at 4527 ± 1272 N under static loading and 2843 ± 1078 N under cyclic loading. The HIP specimens failed at 4912 ± 1505 N under static loading and 4676 ± 1489 N under cyclic loading. The microhardness test showed that the CIP group had a mean hardness of 2389 ± 297 and the HIP group had a mean hardness of 3049 ± 544. The translucency test found that the CIP group had a mean transparency of 1.99 ±1.74, and the HIP group had a mean transparency of 6.75 ± 1.34.
Conclusions:
1) Effect of different polishing grit size on discs showed higher effect on the strength of HIP specimens, but not on CIP specimens. Specifically, polishing with a smaller grit size increased the strength of the HIP specimens.
2) Cyclic loading fatigue had a significant effect on the failure load of CIP crowns, but not on HIP crowns, that is, the HIP crowns were much stronger under cyclic loading than the CIP crowns.
3) Microhardness tests showed significant differences between CIP and HIP alumina, as the HIP specimens were much stronger than the CIP specimens.
4) Translucency test showed there was a significant difference between CIP and HIP alumina as the HIP specimens were much translucent than the CIP specimens. The fact that HIP resulted in much greater strength and transparency is promising for its use in creating both durable and cosmetically attractive dental repairs.
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Thesis (MSD)--Boston University, Henry M. Goldman School of Dental Medicine, 2016 (Department of Restorative Sciences and Biomaterials)
Includes bibliographic references: leaves 87-94.
Thesis (MSD)--Boston University, Henry M. Goldman School of Dental Medicine, 2016 (Department of Restorative Sciences and Biomaterials)
Includes bibliographic references: leaves 87-94.
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This work is protected by copyright. Downloading is restricted to the BU community. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.