Titanium casting into phosphate bonded investment with zirconite.
OBJECTIVE
Reaction layer structure of the titanium castings surface was investigated when a new centrifuge-vacuum-pressure cast titanium machine and a zirconite inner investment was used.


METHODS
The micro-hardness of titanium castings was measured using a Knoop's hardness tester. The structure of reaction layers and the distribution of elements on the surfaces of titanium castings were analysed by SEM and EDS, respectively, when zirconite was used as the inner investment for cast titanium.


RESULTS
Knoop's micro-hardness at distances of 50 and 75 microm from the titanium casting surfaces made directly in phosphate investment molds had significantly harder surfaces than those made in zirconite coating molds. The thickness of the reaction layer on the surface of titanium castings was <35 microm with zirconite coating and was >50 microm without zirconite coating. The structure of reaction layer was divided into four layers from the outer surface to the inner including: sintering layer, alpha-Case, Si-rich layer, acicular crystal structure. The distribution of elements was different on each layer.


CONCLUSIONS
The thickness of the cast titanium reaction layer was reduced when the wax patterns were coated with zirconite. The surface of the titanium castings was smooth and without cracks, and the investment on the surface of titanium castings was easily removed.
Department of Prosthodontics, Nanjing Stomatological Hosptial, School of Medicine, Nanjing University, 30 Zhongyang Road, Nanjing 210008, China. lj961016@public1.ptt.js.sn
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D003734:Dental Casting Investment; D003735:Dental Casting Technique / Q000295:instrumentation*; D004577:Electron Probe Microanalysis; D006244:Hardness; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D016062:Porosity; D012824:Silicic Acid / Q000737:chemistry; D012822:Silicon Dioxide; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*; D015040:Zirconium
D003734:Dental Casting Investment; D012824:Silicic Acid; D012822:Silicon Dioxide; D015040:Zirconium; D014025:Titanium; C028541:zirconium oxide