High temperature strain gages

Abstract

A ceramic strain gage based on reactively sputtered indium-tin-oxide (ITO) thin films is used to monitor the structural integrity of components employed in aerospace propulsion systems operating at temperatures in excess of 1500° C. A scanning electron microscopy (SEM) of the thick ITO sensors reveals a partially sintered microstructure comprising a contiguous network of submicron ITO particles with well defined necks and isolated nanoporosity. Densification of the ITO particles was retarded during high temperature exposure with nitrogen thus stabilizing the nanoporosity. ITO strain sensors were prepared by reactive sputtering in various nitrogen/oxygen/argon partial pressures to incorporate more nitrogen into the films. Under these conditions, sintering and densification of the ITO particles containing these nitrogen rich grain boundaries was retarded and a contiguous network of nano-sized ITO particles was established.

1 . A high temperature ceramic strain gauge, said gauge comprising: 
 an indium-tin-oxide substrate;    a strain element positioned on the substrate    a data acquition system couplable to the substrate via leads and pads such that the strain gage may be used to monitor systems operating in excess of 1500° C.    
   
   
       2 . The strain gage of  claim 1 , wherein the gage has little signal draft.  
   
   
       3 . The strain gage of  claim 1 , wherein the gage has a gage factor of about 0.00001%/hr at 1538° C.  
   
   
       4 . The strain gage of  claim 1 , wherein the lead lines and pads are platinum.  
   
   
       5 . The strain gage of  claim 1  wherein a layer of alumina is deposited on the substrate.  
   
   
       6 . The strain gage of  claim 1  has a partially sintered microstructure comprising a contiguous network of submicron indium-tin-oxide particles.  
   
   
       7 . A method of preparing a high temperature strain gage, said method includes: 
 providing a substrate;    cleaning the substrate;    prebaking the cleaned substrate;    spincoating the prebaked substrate to form a coating of photoresist material;    softbaking the substrate;    spincoating to complete the coating of photoresist material    baking the coated substrate;    applying a photomask in a desired pattern;    exposing the coated substrate to UV light;    removing the photomask;    developing the substrate;    cleaning the exposed and developed substrate in and oxygen plasma to remove all organics;    depositing a thin film of indium-tin-oxide and platinum;    cleaning unexposed photoresist materials and a portion of the coated thin film;    annealing the strain sensor.    
   
   
       9 . The method of  claim 7 , wherein the substrate is cleaned with acetone, deionized water and methanol, followed by nitrogn blow dry.  
   
   
       10  The method of  claim 7 , wherein the substrate is pre-baked at temperature of about 150° C. for 45 minutes.  
   
   
       11  The method of  claim 7 , wherein the substrate is softbaked at a temperature of about 140° C. for about 45 seconds.  
   
   
       12 . The method of  claim 7 , wherein the substrate is postbaked at temperature of about 110° C. for about 150 seconds.  
   
   
       13 . The method of  claim 7 , including doping the substrate with alumina.