PRODUCTION METHOD OF TRANSPARENT POLYCRISTALLINE SILICON NITRIDE CERAMICS WITH SPARK PLASMA SINTERING TECHNIQUE

Abstract

Invention relates to the production method of transparent polycrystalline silicon nitride ceramics which are obtained by sintering raw materials in powder form with powder metallurgy in the field of advanced technical ceramics and are used in the aviation and defense industry. More specifically, the present invention relates to a transparent polycrystalline silicon nitride ceramic material production method which allows obtaining transparent polycrystalline silicon nitride ceramic material at lower temperature and pressure values compared to the prior art in order to reduce production costs, facilitate the production process and reduce quantity/number of material and devices used, for this, unlike conventional sintering technique, spark plasma sintering technique in which heat is produced under high electrical current is used.

Claims

1. A production method for transparent polycrystalline silicon nitride ceramic material and characterized by; comprising following steps: obtaining the initial powder mixture by adding only one of powders Y2O3, Dy2O3 and Eu2O3 each time (composition) with different proportions between 0-10% to the silicon nitride (Si3N4) powder, ensuring a homogeneous mixture of them, carrying out sintering process by using spark plasma sintering technique.

2. A production method according to claim 1 for transparent polycrystalline silicon nitride ceramic material and characterized by; comprising following steps while a pressure of 15-50 MPa is applied during sintering process: firstly; reaching sintering temperatures of 1700-1800° C. with heating rates of 50-100° C./min, keeping the temperature constant at the sintering temperatures of 1700-1800° C. for 5-20 minutes, then reducing the temperature to the room temperature with cooling rates of 350-600° C./min.

3. A production method according to claim 1 for transparent polycrystalline silicon nitride ceramic material and characterized by; in order to ensure homogeneous mixture of initial powder mixture; comprising following steps: mixing the initial powder mixture in alcohol environment for 3-5 hours by using an axial ball mill, then removing the alcohol by means of rotating evaporator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0024] The invention presents a transparent polycrystalline silicon nitride ceramic material production method which allows obtaining transparent polycrystalline silicon nitride ceramic material at lower temperature and pressure values compared to the prior art, for this, unlike conventional sintering technique, spark plasma sintering technique in which heat is produced under high electrical current is used. Thus, reducing production costs of transparent polycrystalline silicon nitride ceramic material, facilitating the production process of it and reducing quantity/number of material and devices used during production of it are aimed.

[0025] First of all, obtaining polycrystalline silicon nitride ceramic with spark plasma sintering technique applied in the present innovative method brings important advantages. Unlike conventional sintering techniques, spark plasma sintering technique produces heat under high electric current. In this technique, by applying high-density electric current under the applied mechanical pressure, arc is created on the powders and sintering is carried out with the effect of the pressure and temperature occurred. In this way, it is possible to produce polycrystalline transparent silicon nitride ceramic materials which have high purity, high density and high mechanical properties in shorter times. In addition, thanks to method applied here, the production of polycrystalline silicon nitride ceramic materials at lower temperatures (1700-1800° C.) and lower pressure (15 MPa-50 MPa) compared to conventional production methods reduces the product cost and makes easier the production process.

[0026] In the present innovative production method of the polycrystalline transparent silicon nitride ceramic material, α-Si.sub.3N.sub.4, Y.sub.2O.sub.3, Dy.sub.2O.sub.3 and Eu.sub.2O.sub.3 powders are used separately in each composition as initial material. Firstly, only one of the powders Y.sub.2O.sub.3, Dy.sub.2O.sub.3 and Eu.sub.2O.sub.3 is added with different proportions of 0-10% to the silicon nitride (Si.sub.3N.sub.4) powder. In order to obtain homogeneous mixture, the initial powder mixture is mixed in alcohol environment for 3-5 hours by using an axial ball mill. Subsequently, homogeneous initial powder mixture is obtained by removing the alcohol with the rotating evaporator. Sintering process with spark plasma sintering technique is started by using the homogeneous initial powder mixture obtained.

[0027] In the sintering process carried by using spark plasma sintering technique; first of all, sintering temperatures of 1700-1800° C. are reached with heating rates of 50-100° C./min. The temperature is kept constant at the sintering temperatures of 1700-1800° C. for 5-20 minutes. Then, the temperature is reduced to the room temperature with cooling rates of 350-600° C./min. A pressure of 15-50 MPa is applied during the sintering process. With the characterization tests applied at the end of the process, it has been proven that the Si.sub.3N.sub.4 ceramics sintered has a polycrystalline structure and transparent optical feature.

[0028] Unlike the conventional methods, with the present innovative method; permeability is obtained by directly sintering the initial raw material in the form of Si.sub.3N.sub.4 by controlling grain size and secondary phase by changing liquid phase amount and pressure. In addition, unlike other methods, there is no new product and phase transformation in the system as well as there is no change or effect related to the initial powder size.

[0029] Applying different sintering pressures and adding the amount of additives in the present innovative method makes the method of the invention different from the sintering conditions used in SiAlON ceramics. Using SPS (Spark Plasma Sintering) as sintering technique in this system is not monotony, there are no techniques other than SPS, GPS (Gas Pressure Sintering), HIP (Hot Isostatic Pressure) and HP (High-pressure) due to the high pressure requirement for the production in this area. The important difference achieved by the present innovative method is the optimization of sintering parameters and minimum phase formation, and all of them have been achieved in Si.sub.3N.sub.4 ceramic. Also here, in addition to the application areas based on the commonly used structural properties of Si.sub.3N.sub.4, product development for application of optical properties functionally has been provided. Besides, in the present innovative method, this product has been developed by only controlling the sintering pressure and, grain boundary phase amount via additive material. Moreover, the initial material was absolutely not transformed, it was preserved as Si.sub.3N.sub.4.

[0030] Shortly, in our present patent application titled “Production Method of Transparent Polycrystalline Silicon Nitride Ceramics with Spark Plasma Sintering Technique”, instead of SiAlON which is a solid solution produced from Si.sub.3N.sub.4, a method for increasing the transparency of Si.sub.3N.sub.4 directly by liquid phase sintering of it by using SPS (Spark Plasma Sintering) technique is presented. Here, unlike the prior art, there is a study about gaining transparency by just sintering Si.sub.3N.sub.4 without using extra initial raw materials (such as AlN, Al.sub.2O.sub.3) and without creating any new phase.