Microwave furnace

On the other hand, improvements in ceramic powder processing technology, the routine preparation of high-purity ceramics of nanometre scale, and the new techniques for the processing of these powders such as HIP, SPS, microwave furnace, etc., will be the driving forces for a very active study on nanoceramics in the near future, probably opening up new phenomena and new applications. 

There are two types of systems for the hazardous waste treatment with heating. Microwave furnaces with the operating area on the top are used for the treatment... 

Figure 3.2 Dry ashing microwave furnace. (Reproduced by kind permission of CEM Corporation)...

Zhao, C. Vleugels, J. Groffils, C. Luypaert, P.J. Van der Biest, O. Hybrid sintering with a tubular susceptor in a cylindrical single-mode microwave furnace. Acta Mater. 2000, 48, 3795-3801. 

The furnace treatment is continued until a constant weight is obtained unlike in the previous standard where constant (short) ashing time is used. The method permits the use of a microwave furnace which typically shortens the time to 2 to 6 hours. 

Lead levels were analyzed in venous blood samples. 2 ml samples were obtained in sterile vacutainer, reconstituted with 1.5 mg K2EDTA/ml blood, stored at +4°C and transported during the same day. Using AAS (atomic absorption spectrometer) with a Perkin Elmer 4100 HGA 700 graphite furnace fitted with an AS-70 brand Auto sampler. Lead was extracted into a mixture of nitric (HN03) and hydrochloric acid (HC1) under pressure with microwave digestion. A PAAR PHYSICA - PERKIN ELMER microwave furnace designed for laboratory practice was used. The research was approved by the ethics committee, as well by the parents of the examined children. The parents of the children have been informed about the results of the blood lead levels. 

Approximately 1 g of sample is weighed into a crucible. Vycor or platinum crucibles have both been used for this work. The MAS 7000 furnace insert allows the use of metal vessels in the microwave unit. The crucible is placed into the microwave furnace. The temperature is ramped up to 525 C over a two-hour period. It then holds the temperature for one hoiu. After the sample cools, approximately S mL of a 1 1 nitric acid-water solution are added to the cmcible and heated gently to dissolve the ash. It is critical that nitric acid only be added after the organic matrix has been ashed and cooled. The sample is quantitatively transferred to a 25-mL volumetric and brought to volume with water. 

FIGURE 8.3 XRD patterns of precursor powders heated in a microwave furnace for different times (peaks have been identified as (x) F-A1203 and (a) a-Al203). (Reproduced with permission from Ebadzadeh, T. Sharifi, L., J. Am. Cer. Soc., 2008,91,3408-3409. Copyright Wiley-Blackwell.)... 

Electric furnace Hot press Reaction sinter Vapor deposition Plasma spraying Microwave furnace... 

The main disadvantage of electric heating is that it usually costs more per energy unit than gas heating. However, the total energy usage for electric furnaces may often be lower than for gas-fired furnaces. The cost issue is not normally a problem in a university laboratory, but it can be a major concern for industrial applications. Two other types of furnace that use electricity are induction furnaces and microwave furnaces. 

Microwave furnaces. Microwave heating is an application of induction heating using higher frequencies. In many ways microwave furnaces are just expensive micro-wave ovens. 

Microwave furnaces currently are used for research and small-scale production because the available power sources are limited in size. Microwave processing is an area in which considerable research is being performed. The main direction for this research, and the possibility for future commercial applications, is in the reduction of production times and lowering the amount of energy consumption required for part processing. 

Water-based coatings require a drying treatment. The application of microwave furnaces for this purpose gives operational advantages over the use of ambient or heated air drying. Microwaves of 2450 MHz frequency are used, and have the following properties ... 

Table 4.23 Results of test campaigns on core drying, using hot air and microwave furnaces [143, Inasmet and CUF, 2002]...

Water (1.51) was brought in a storage vessel and 200 pg of each of scandium and samarium were added as nitrate solution to serve as internal standards. The sample was then irradiated with 30 MeV bremsstrah-lung (mean electron beam current 150 pA) from an electron linear accelerator for 5h in a 0.7-1 flow-chamber under slow continuous cyclic flow. Thereafter, the components of interest (Sc, Cr, Mn, Co, Ni, Cu, Zn, As, Y, Zr, Nb, Mo, Cd, Sn, Sb, I, Ba, Tl, Pb, and U) were separated by a sulfur-substituted cellulose-based sorbant filter switched into the flow cycle after activation. This sorbant was then dried in a microwave furnace and pressed to a thin (1mm thick) pellet. Product activities were counted with a large coaxial germanium detector (where was... 

Previous results showed Sl3N4-6% Y203-2% AI2O3 (with and without TIN and SIC additions) could be sintered in the 28-GHz microwave furnace to densities of 90 to 93% TD at 1750°Cfor 1 h. Compositions of Sl3N4-12%Y203-4%Al203 (with and without the TIN, TIC, and SIC additions) were fabricated and fired in the 2.45-GHz and 28-GHz furnaces at 175CTC. 

Fig. 1. Temperature profile h 2.45-GHz microwave furnace for sintering of Si3N4-6% Y203-2% AI2O3 which showed specimen cracking.

Previous resuits showed enhanced reaction rates for the nitridatlon of silicon in the 2.45-GHz microwave furnace as compared to conventional heating. While the nitridatlon was usually uniform, the center of the samples always contained some unreacted silicon that would experience melting In some cases. The sample sizes were typically 100 g of Si-6% 203-2% AI2O3 with cross sections of <3.8 mm (1.5 In.). Such samples are rather thick in comparison to others in much of the nitridation experiments in the literature. To establish the parameters reauired to nitride samples of this size, a series of tests were done varying the heating rate, insulation configurations, and nitrogen gas additions. 

As reported previously, an annealing study was performed to Investigate microstructural development of silicon nitride in a microwave furnace. Samples of SI3N4-4% 203 and Si3N4-6% 203-2% AI2O3 were hot-pressed to full density and annealed both by microwave and conventional heating at 1200.1400. and 1500 0 for times of 10 and 20 h. 

A new microwave furnace was constructed and is currently being tested under manual control. Test loads have been heated and controller adjustments are being performed. The furnace will operate at 2.45 GHz with up to 12 kW of power and have more than double the volumetric capacity of the previous cavity. These additional features will significantly increase the capabilities over the current furnace. Of most importance will be the improved uniformity of the microwave field,... 

Figure 12.29 Heating patterns in conventional and microwave furnaces. (From Ref 42.)...

An AA spectrometer is also available with a graphite furnace and vapor generation accessories for the trace analysis of lead, antimony, arsenic, and mercury at parts-per-billion levels. AA is used for quantitative analysis of these metals in polymers as well as finished formulations. It has been used to determine the elemental composition of catalysts and plastic additives, polymer formulations, and composite materials. Samples may be rapidly acid digested prior to analysis using a microwave oven or similar techniques. Microwave furnaces are also available for dry ashing. 

Fig. 1. Microwave furnace with thermal pod, thermocouple, and controller.

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