Yttria Stabilized Zirconia Bulk Ceramic Fibres ( ZrO2 ) Type ZYBF from Zircar Zirconia

Topics Covered

Background
Product Overview
Properties
Microstructure of Zircar Type ZYBF-1 Bulk Zirconia Ceramic Fiber
Microstructure of Zircar Type ZYBF-2 Bulk Zirconia Ceramic Fiber
Microstructure of Zircar Type ZYBF-3 Bulk Zirconia Ceramic Fiber
Microstructure of Zircar Type ZYBF-4 Bulk Zirconia Ceramic Fiber
Microstructure of Zircar Type ZYBF-5 Bulk Zirconia Ceramic Fiber
Phase Stabilization in Zirconia
Yttria Stabilized Zirconia as a Semicionductor
Applications of Type ZYBF Yttria Stabilized Zirconia Fiber

Background

Typical features of ZIRCAR Zirconia’s ZYBF yttria stabilized zirconia ceramic fiber products include:

• Available in Five Different Forms
• Low Thermal Conductivity
• Highly Refractory
• Low Heat Storage
• Extreme High Temperature Stability
• Fibers Stabilized with ~10 wt% Yttria
• Lightweight
• Available “Off the Shelf”

Figure 1. Zirconia Bulk Fiber Type ZYBF-2.

Product Overview

Zircar Zirconia Bulk Fibers Type ZYBF are yttria stabilized zirconia fibers available in five different forms, all having useful properties up to 2200°C. These polycrystalline fibers can be vacuum formed into rigid shapes, placed into cavities as loose fill insulation, or added to ceramic bodies and coatings for reinforcement. They are differentiated by fiber length, surface area, crystallite size and porosity. However, they all share the same fiber diameter and calcined chemical composition. All five forms of ZYBF are made using the “Zircar Process” which replicates the gross physical structure of an organic precursor fiber with a ceramic. Typically these fibers are 6 to10 microns in diameter and have a serrated outside surface.

Properties

Typical Properties of Zircar ZYBF yttria stabilized zirconia ceramic fiber products.

* 1 - 2 wt% hafnia occurs naturally with zirconia and does not affect performance.

1 Based on Pore Volume
2 Based on Surface Area

Microstructure of Zircar Type ZYBF-1 Bulk Zirconia Ceramic Fiber

Zircar Type ZYBF-1 is a grayish colored, low-fired, very fine grained, hollow fiber which has some apparent fiber to fiber binding as supplied. ZYBF-1 has a very high BET surface area (75 m²/g) and may be dispersed with grinding media to a submicron particle size. ZYBF-1 is the longest of the five ZYBF fiber types with lengths in excess of 1 cm.

Figure 2. Photomicrograph of Type ZYBF-1 Fibers originally at 50X magnification. ZYBF-1 is the longest of our zirconia fibers.

Figure 3. Photomicrograph of Type ZYBF-1 Fiber originally at 4500X magnification. Note the hollow nature of the fiber.

Microstructure of Zircar Type ZYBF-2 Bulk Zirconia Ceramic Fiber

Zircar Type ZYBF-2 is a high-fired, fine grained, hollow fiber which has some significant fiber to fiber binding as shown in the photo (figure 4).

Figure 4. Photomicrograph of Type ZYBF-2 originally at 200X magnification.

Figure 5. Photomicrograph of Type ZYBF-2 originally at 5000X magnification.

Microstructure of Zircar Type ZYBF-3 Bulk Zirconia Ceramic Fiber

Zircar Type ZYBF-3 is a high-fired, medium grained, porous fiber which has minimal fiber to fiber binding as shown in the photo in figure 7. ZYFB-3 fibers are shorter fibers on the order of a few hundred microns long.

Figure 6. ZYBF-3 Photomicrographs originally at 50X magnification.

Figure 7. ZYBF-3 Photomicrographs originally at 5,000X magnification.

Microstructure of Zircar Type ZYBF-4 Bulk Zirconia Ceramic Fiber

Zircar Type ZYBF-4 is a medium-fired, medium-grained, mostly solid fiber which has minimal fiber to fiber binding.

Figure 8. ZYBF-4 Photomicrographs originally at 100X magnification.

Figure 9. ZYBF-4 Photomicrographs originally at 9,010X magnification.

Microstructure of Zircar Type ZYBF-5 Bulk Zirconia Ceramic Fiber

Zircar Type ZYBF-5 is a high-fired, large-grained, mostly solid fiber which has minimal fiber to fiber binding.

Figure 10. ZYBF-5 Photomicrographs originally at 50X magnification.

Figure 11. ZYBF-5 Photomicrographs originally at 4,000X magnification.

Phase Stabilization in Zirconia

All of Zircar’s Zirconia Bulk Fibers are phase stabilized with ~10% yttria (yttrium oxide - Y₂O₃) to maintain a stable tetragonal / cubic structure. The yttria, in a solid solution within the zirconia, stabilizes the tetragonal / cubic structure by preventing the monoclinic to tetragonal crystal transformation that occurs at 1170°C in pure un-stabilized or insufficiently stabilized zirconia. This undesirable transformation causes an 11% volume change in the crystal unit cell size that can cause micro-cracking and reduced physical strength in the bulk solid.

Yttria Stabilized Zirconia as a Semicionductor

Yttria stabilized zirconia is an electrical semiconductor at elevated temperatures. This conductivity arises from the different valences of ionic Zr⁺⁴ and Y⁺³. Electricity is conducted at elevated temperatures (~700-800°C) as oxygen ions are induced to flow through the stabilized zirconia structure. This phenomenon forms the basis of zirconia oxygen sensors.

Applications of Type ZYBF Yttria Stabilized Zirconia Fiber

• Zircar’s Type ZYBF can be vacuum formed into rigid shapes.
• Zircar’s Type ZYBF is used as an additive in ceramic fiber vacuum formed products to improve refractoriness.
• Zircar’s Type ZYBF can be added to Zircar’s Zirconia Cement Type ZR-CEM and used as a coating or as a filler for holes, bonding of mis-matched surfaces, and repairing cracks and openings in furnace walls composed of zirconia insulation.
• Zircar’s Type ZYBF can be placed into cavities as loose fill insulation or used as furnace packing.
• Zircar’s Type ZYBF is used as thermal insulation in many industrial furnace applications. It is ideal for applications where an insulation exhibiting extremely low thermal conductivity is required.
• Zircar’s Type ZYBF is used in aggressive chemical environments due to its high purity stability and stability. It is stable in vacuum, inert or reducing atmospheres.

Source: Zircar Zirconia

For more information on this source please visit Zircar Zirconia.