Evolution of Specific Heat Capacity with Temperature for Typical Supports Used for Heterogeneous Catalysts

Heterogeneous catalysts are widely used in the chemical industry. Compared with homogeneous catalysts, they can be easily separated from the reaction mixture. To design and optimize an efficient and safe chemical process one needs to calculate the energy balance, implying the need for knowledge of the catalyst’s specific heat capacity. Such values are typically not reported in the literature, especially not the temperature dependence. To fill this gap in knowledge, the specific heat capacities of commonly utilized heterogeneous catalytic supports were measured at different temperatures in a Tian–Calvet calorimeter. The following materials were tested: activated carbon, aluminum oxide, amberlite IR120 (H-form), H-Beta-25, H-Beta-38, H-Y-60, H-ZSM-5-23, H-ZSM-5-280, silicon dioxide, titanium dioxide, and zeolite 13X. Polynomial expressions were successfully fitted to the experimental data.

Optimization of a sensor for a Tian–Calvet calorimeter with LTCC-based sensor discs

In this work, it is shown how a finite element method (FEM) model of a Tian–Calvet calorimeter is used to find improvements in the sensor design to increase the sensitivity of the calorimeter. By changing the layout of the basic part of the sensor, which is a low temperature co-fired ceramics (LTCC) based sensor disc, an improvement by a factor of 3 was achieved. The model was validated and the sensors were calibrated with a set of measurements that were later used to determine the melting enthalpies and melting temperatures of indium and tin samples. Melting temperatures showed a maximum deviation of 0.2 K while the enthalpy was measured with a precision better than 1 % for most samples. The values for tin deviate by less than 2 % from literature data.

First steps to develop a sensor for a Tian–Calvet calorimeter with increased sensitivity

Initial steps to apply a ceramic multi-layer technique to build a new sensor for a Tian–Calvet calorimeter are presented in this contribution. The new sensor has a stacked design of ceramic sensor discs and insulating rings. The development was finite-element method (FEM) supported to design the sensor disc. In the next step, the function of the sensor disc was proven up to a temperature of 600 °C. Finally, the entire stack was tested at room temperature, delivering a resolution of 5 µW and a maximum sensitivity of 8.5 µV mW−1. The time constant is strongly dependent on the mass of the cuvette. We show that the time constant of the sensor can be more exactly characterized when using a novel low temperature co-fired ceramic (LTCC) cuvette with a low mass and an integrated heater. Then, the time constant can be reduced to T1∕e = 118 s. The new sensor shows similar specifications as commercial devices and presents a good starting point for future high temperature applications.

Sensor stack for Tian-Calvet Calorimeter made in LTCC-Technology

The paper presents the construction and first tests of a new sensor stack for a Tian-Calvet Calorimeter made in LTCC Technology. In contrast to typical construction where wired thermocouples are directly connected, the here-presented solution replaces wired thermocouples by screen-printed thick-film thermocouples placed on a structured disc made of Low Temperature Co-fired Ceramics (LTCC). The advantage of screen-printed thermocouples is the ease of integration of them into thick-film hybrid structures, and to simplify the device setup. Moreover, using thermocouples integrated into a ceramic disc can increase the sensitivity of the system and simultaneously reduce the production costs. The paper shows the design and fabrication of the sensor stacks. It consists of several LTCC discs and ceramic spacers. On each LTCC disc, 34 Au/Pt thermocouples were deposited. The design of the disc was supported by FEM-modelling under consideration of device specific requirements. The very initial measurements, which we conducted using two sensor stacks already exhibited a sensitivity of 8 μV/mW, which is more than satisfactory in this stage of development.

Excess Enthalpy and Luminescence Studies of SnO2 Nanoparticles

The extra reactivity of nano materials is attributed to the excess surface energy stored in the sample. The excess enthalpy of SnO2 nano-particles were measured as a function of particle size using a calvet calorimeter. SnO2 with particle size 11, 27, 47 nm and bulk samples (1 μm) were dropped from room temperature to 987, 936 and 885 K and their HT–H298 values were determined. The excess enthalpies for SnO2 samples with particle sizes 11, 27and 47 nm compared to the bulk sample calculated from the difference between HT–H298 values of the nano and the bulk samples were found to be 15.06, 3.05, 2.21 kJ · mol−1 respectively. Luminescence experiments reveal that the surface trap electron density decreases with increase of particle size. The excess enthalpy is related to the surface trap intensity.