On the weak absorption of microwave heating auxiliary substances
As the microwave heating characteristics of selective , for some room temperature, a small dielectric constant and loss factor of the material , the weak microwave absorbing material , the microwave heating of their effect is not significant , or even can not be heated , thus limiting microwave energy technology heat treatment of these substances , shows the drawbacks of the microwave energy . However, the disadvantage through clever use of certain characteristics of microwave and substance to be improved, even make shortcomings into advantages . Some researchers have reported the solution, are briefly introduced .
Auxiliary heating methods: adding a strong microwave absorbing material
 According to other studies have shown J.W.Walkiewicz alumina weak microwave absorbing material . Use it in a certain power microwave heating 4.5min, the temperature reached only 78 `C. The iron oxide is a strong microwave absorbing material , only microwave heating 2.75min, the temperature as high as 1258 `C. W.H.Sutton the strong absorption of microwave and other substances added to the iron oxide alumina weakly absorbing material into the microwave to make the added iron oxide alumina can be significantly microwave heating . When alumina is added 10% iron oxide , the microwave has been able to carry the samples heated ; when alumina is added to 50% of iron oxide , the samples can be rapidly heated by microwaves . They also
1% - 90% of the strong absorption of microwave substances (such as NiO, CrN, Fe3O4, MnO2, Ni203, aluminum , calcium , etc. ) is added to a weak absorption of microwave substances (such as A12O3, SiO2-MgO) among these weak absorption solution microwave microwave heating problem substances .
    M.L.Levinson the weak absorption of microwave ceramic material were placed around a very thin toner , iron ore, magnetite and ferrite powder RF , leaving the microwave to heating the ceramic material. His study also showed that high iron stick
The soil is easy to microwave heating , the clay is more difficult without iron .
 Because poor thermal conductivity of nylon , R.A.Peterson in microwave heating nylon encountered difficulties . His solution is coated with a second nylon material, such as triethylene glycol . Compared with the nylon , triethylene glycol to absorb micro
Wave, and the nylon will occur when the temperature of the thermal runaway effect , triethylene glycol volatilized . Initially, the microwave heating is largely triethylene glycol , nylon, triethylene glycol at a low temperature by indirect heat transfer is heated , reaches a certain temperature , the nylon can be directly heated by microwaves . After evaporation in triethylene glycol , nylon may be heated to the desired temperature . According to this method , the microwave can be nylon in a wide temperature range for heating.
T.Nishtani that the microwave heating by the material of the various components within the dielectric loss factor and the conductivity of the particles . If the substance is to be microwave heated to a high temperature of 1000 ℃ , the conductivity must be at least 10 - s. ' , And the particles should be directly exposed to the substance penetration depth 5 to 10 times less. He once 0.1%-to% of good-conductive particles ( such as aluminum , silicon carbide , silicon, magnesium , iron- silicon alloy , R -alumina , chromium oxide , etc. ) was added to the matrix of a refractory oxide ( such as alumina, mullite, pyrophyllite , magnesium oxide , etc. ) , so that these weak material can rapidly absorb microwave heating by microwaves .
C.E.Holcombe put a lot of good conductivity powder (Nb, TaC, SiC, Cu, Fe) and aluminum nitrate nitrate mixed into memory microwave heating , in addition , surrounded by insulation material placed zirconia . They believe that the microwave heating of these substances are divided into three phases . The initial stage, the microwave heating of the surrounding insulation material zirconia , zirconia part by heat conduction of the heat transfer to the sample ; at 700 `C - 1000 ℃ , the second stage, as well as the added nitrate particles begin directly microwave heating ; third phase , the main material M combined microwave rapidly heated by microwaves , in most cases , the third stage temperature above 1000 ℃ .
The two complementary methods : "Picket fence" method
  H.D.Kimmy and R. L. Smith and " 36 -39 ] The " Picket fence " method for supporting the microwave heated by the heat sintering of ZrO2 ZrO2 fiber insulation surrounded by enclosed , and in its surrounding SiC rod arrangement ; at low temperatures, the dielectric should be C loss factor than ZrO: large ( Figure 4- 53 ) Therefore , SiC absorb most of the microwave energy , the microwave heating of SiC ZrO2 faster rate than at a temperature below the critical point before , ZrO: mainly by thermal conductivity of SiC is heated when the temperature exceeds a critical point after , ZrO: dielectric loss factor than the sudden increase in addition to the sample and local overheating , ZrO2 easily be microwave heated to the desired sintering temperature , and the sample does not appear burst phenomenon .
The three auxiliary heating methods : microwave absorber lined with SiC
     University of Florida professor D.E.Clark designed a complementary microwave heating method lined with SiC microwave absorber on the weak absorption of microwave sample above . Microwave heating alone 25g, alumina, temperature and time, the microwave power is increased to 5kW, the internal temperature of the alumina is still more than 500 ; , therefore , from the 03 requires the use of microwave heating auxiliary heating .
SiC has a microwave absorber lining , the microwave heating temperature of the alumina 8g and time, it can be seen , when the microwave heating is started , SiC liner are heated rapidly , and then transfer energy radiation to the surface of the alumina , alumina surface is rapidly heated , the heat by heat conduction into the inside of alumina , the process is continued until a temperature above 800 ℃ , the aluminum begins to absorb microwave by microwave heating quickly within aluminum , while the aluminum surface SiC is still receiving the microwave absorber lining of heat , this heat is also conducted to the inside of alumina , so that the alumina inside to heat a double heat to the internal temperature is higher than the surface temperature . In addition , the heat to the surroundings through surface diffusion and sample loss among the following brick .
The four auxiliary heating method : M.C.L.Patterson other invented a heating sintered Si3N; helper methods .
 They put 90 root causes of Si3 N; composition tools are regularly inserted into the alumina dried , pliers pot filled with SiC, BN and Si3 N; mixture ((40% SiC, 30% BN, 30% Si3N4) , these powders for supporting the tool , but also has other functions , such as the initial stage of the microwave heating , the microwave energy can be used as absorbent , but also to prevent Si3N; reacts with the surrounding environment , and to prevent decrease in temperature during high etc. 90 Si3N; cutter ring and through the use of carefully controlled electric conduction type is evenly heated . Additional insulation material on the increase around a conducted ring used minimally reduce heat loss and maintain growth within the glass can be uniformly heated .
The five auxiliary heating method : A single-mode microwave cavity coupling with adjustable window Shanghai Institute of Ceramics , Chinese Academy of Shi Jianlin , TIAN responsible for such single-mode microwave cavity coupled with adjustable windows, and adjust microwave input power , short piston so as to maintain the resonant cavity and the best fit condition a so as to maintain the sample at a constant heating rate , and final temperature stable .