This paper provides an overview of the macroscopic properties of porcelain tableware fired in a microwave furnace with six magnetrons (each with a nominal power of 900 W) operating at the frequency of 2.45 GHz. The dependence of firing temperature on physical properties such as shrinkage, water absorption, apparent porosity, bulk density, and impact resistance was analyzed. Emphasis is on the differences in the macroscopic properties of microwave and conventionally (gas and electric) fired porcelain. Batches were fired from room temperature up to above the optimum firing temperature (1380°C). Results show similar macroscopic properties for both firing methods, microwave heating required lower firing temperatures (between 1300°C and 1350°C), and shorter processing times (about 70 minutes). The main differences between microwave and electric firing methods occur in a temperature band of 300°C above the porcelain eutectic temperature (close to 1000°C).

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cement produces very soluble hydroxides that easily migrate from the cement to the ceramic brick. The reaction of these A study of the eVect of cement in the formation of hydroxides with the calcium sulphate (CaSO 4 ) present in eZorescence on the surface of ceramic building materthe brick produces alkali sulphates that migrate and crystalials was conducted. W icking tests were performed with lise on the material surface. Hydrated lime (Ca(OH) 2) is bricks covered with cement, and a test procedure, where also formed and produces calcium carbonate by cartemperature and water pressure applied to the samples bonation with CO 2 . could be controlled, has been developed. Salts formedIn order to evaluate the susceptibility to efflorescence of at brick surfaces consist of arcanite (K 2 SO 4). Results ceramic building materials -heavy clay material and morshow that salt deposition kinetics are enhanced by tars -some tests4,5 have been developed for bricks and higher test temperature and particularly by imposing mortar, based on humidification and drying of materials. It water pressure around the brick. A method to quantify is a difficult exercise since the parameters that influence the eZorescence was developed in order to avoid any process are numerous. Nevertheless, the tests are based on subjectivity in the assessment of the test results. Image the same principle: the material is humidified for a certain analysis oVers an alternative for quantification of this time, and the formation of efflorescence is observed after phenomenon. Study of eZorescence digital images lead drying. The humidification process can be carried out in to the definition of an eZorescence coeYcient. A set of different ways, the most common being immersion in water samples with low to high levels of eZorescence was (wicking test), or the presence of water on the upper face used and the results show a clear distinction between (percolating test), or conditioning in a humid atmosphere diVerent degrees of eZorescence. It is concluded that by imposing wet/dry cycles. this process is a valid one for quantifying the eZor-Studies undertaken until now have investigated the influescence phenomenon.BCT /420 ence of various parameters that contribute to the salt deposition process, especially in cements. For instance, L . Hennetier, J. V. Almeida, and A. M. S. Correia are recent studies have been made to understand the deposition in the Centro T ecnolo ´gico de Cera ˆmica e V idro, 3020 kinetics. For that purpose, some tests have been developed Coimbra, Portugal. V. M. Ferreira

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Following some previous work, we report here considerable improvements on the counting rate capability of timing RPCs by the use of ceramic electrodes with a resistivity of 10 9 Ω•cm. The X-ray sensitivity of the detector depends linearly on the counting rate with a slope of 9% per 100 kHz/cm 2 , free from charge depletion effects, while keeping a timing accuracy, measured with 511 keV synchronous photon pairs, around 90 ps σ up to 75 kHz/cm 2 .

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The energy dependence on fossil resources and the increasing competitiveness of the stoneware industry, which is a relevant natural gas consumer, leads to new and more environmentally friendly firing methods. Microwave radiation is herein presented as an alternative heating technology for stoneware firing. The samples were fired in a multimode furnace with 6 magnetrons in its core, each one operating at a nominal power of 900 W and frequency of 2.45 GHz. A pyrometer and a thermocouple were installed in the microwave furnace for temperature measuring, control and monitoring. Pyrometer was calibrated in an electric furnace for accurate temperature measurements. During calibration, the thermocouple used in the microwave furnace was installed in the electric furnace, giving a temperature difference from the control (electric furnace) of 2 to 5 ºC, from room temperature up to 1450 ºC. To help the stoneware firing, a silicon carbide (SiC) plate was used as microwave susceptor, also working as a support base for the stoneware samples (mugs). The microstructure of the microwave fired stoneware shows features similar to those of conventionally fired samples (gas and electric heating), with the microwave requiring lower firing temperature to reach an equal structure. X-Ray diffraction and scanning electron micrograph show the relevant transformations taking place for lower temperatures when using microwave heating.