Design of a substrate heater for calcium hydroxyapatite coating by pulsed laser ablation Page: 4 of 28
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Design of a Substrate Heater for Calcium Hydroxyapatite Coating
by Pulsed Laser Deposition
Abstract
Calcium hydroxyapatite (HA) is the main chemical constituent of bone. When replacement
hip joints are coated with this chemical, the body may be more likely to accept the artificial
joint, forming new bone that bonds the joint to the original leg bone. HA deposited by laser
ablation in vacuum adheres to the substrate better at high temperatures of up to 700'C. This
heater should be capable of uniformly heating to 700C a silicon disk 150 mm in diameter.
The heater consists of two wire heating coils brazed into a disk of stainless steel, with
tantalum shields on top and at the sides of the heater to minimize radiation loss. Three
spring-rotation clamps at the bottom of the heater hold the substrate disk in place.
This report describes the heater and how it was developed, including design evolution and
thermal modeling. Also, detailed information about parts is discussed.
1.0 Introduction
Calcium hydroxyapatite (HA) is the main chemical constituent of bone[l]. When
replacement hip joints are coated with this chemical, the body is more likely to accept the
artificial joint, forming new bone that bonds the joint to the original leg bone. HA deposited
by laser ablation adheres to the substrate better at high temperatures of up to 700C. This
heater should be capable of uniformly heating to 700 C a silicon disk 150 mm in diameter.
This heater will be used in a vacuum system with pressures less than 1x10-7 torr. The
copper vapor laser used for ablation operates with 200 kW, at 4.4 kHz, and at wavelengths
of 578 and 514 nm.
The heater consists of two wire heating coils brazed into a disk of stainless steel, with
tantalum shields on top and at the sides of the heater to minimize radiation loss. Three
spring-rotation clamps at the bottom of the heater hold the substrate disk in place.
This report describes the heater and how it was developed, including design evolution and
thermal modeling. Also, detailed information about parts is discussed.
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Chang, T. & Havstad, M. A. Design of a substrate heater for calcium hydroxyapatite coating by pulsed laser ablation, report, July 24, 1995; California. (https://digital.library.unt.edu/ark:/67531/metadc626531/m1/4/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.