Gert Roebben - Academia.edu (original) (raw)

Papers by Gert Roebben

Materials Letters, 2003

This paper is focussed on the reinforcing phases developing in a Si 3 N 4 -based composite micros... more This paper is focussed on the reinforcing phases developing in a Si 3 N 4 -based composite microstructure when sintering a powder mixture of 74 wt.% Si 3 N 4 , 20 wt.% TiO 2 , and 6 wt.% Y 2 O 3 . Micron-and submicron-sized as well as Al 2 O 3 and Al 2 O 3 + SiO 2 -coated submicron-sized TiO 2 powders were used to prepare these in situ composites consisting of Si 2 N 2 O, a-Si 3 N 4 , h-Si 3 N 4 , and TiN. The impulse excitation technique was used to evaluate the intergranular glass phase, which affects crack growth and high-temperature deformation. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to investigate the reinforcing phases. The influence of the TiO 2 -additive powder characteristics on the microstructure and properties of the ceramics is reported. D

Materials Science and Engineering: A, 2006

A powder mixture of α-Si3N4, Al2O3, and TiO2 was hot-pressed using different sintering cycles to ... more A powder mixture of α-Si3N4, Al2O3, and TiO2 was hot-pressed using different sintering cycles to search for an optimum in situ formed β-O-sialon–TiN composite. The impulse excitation technique (IET), high-temperature X-ray diffraction (HTXRD), and scanning electron microscopy (SEM) were used to investigate the microstructure. Below the temperature of 1300°C, the high-temperature internal friction (Q−1) decreases with the increase of sintering

Journal of Nanoparticle Research, 2011

The Institute for Reference Materials and Measurements has organised an interlaboratory compariso... more The Institute for Reference Materials and Measurements has organised an interlaboratory comparison (ILC) to allow the participating laboratories to demonstrate their proficiency in particle size and zeta potential measurements on monomodal aqueous suspensions of silica nanoparticles in the 10-100 nm size range. The main goal of this ILC was to identify competent collaborators for the production of certified nanoparticle reference materials. 38 laboratories from four different continents participated in the ILC with different methods for particle sizing and determination of zeta potential. Most of the laboratories submitted particle size results obtained with centrifugal liquid sedimentation (CLS), dynamic light scattering (DLS) or electron microscopy (EM), or zeta potential values obtained via electrophoretic light scattering (ELS). The results of the laboratories were evaluated using method-specific z scores, calculated on the basis of consensus values from the ILC. For CLS (13 results) and EM (13 results), all reported values were within the ±2 |z| interval. For DLS, 25 of the 27 results reported were within the ±2 |z| interval, the two other results were within the ±3 |z| interval. The standard deviations of the corresponding laboratory mean values varied between 3.7 and 6.5%, which demonstrates satisfactory interlaboratory comparability of CLS, DLS and EM particle size values. From the received test reports, a large discrepancy was observed in terms of the laboratory's quality assurance systems, which are equally important for the selection of collaborators in reference material certification projects. Only a minority of the participating laboratories is aware of all the items that are mandatory in test reports compliant to ISO/IEC 17025 (ISO General requirements for the competence of testing and calibration laboratories. International Organisation for Standardization, Geneva, 2005b). The absence of measurement uncertainty values in the reports, for example, hindered the calculation of zeta scores.

Key Engineering Materials, 2002

Energy & Fuels, 2004

The European Union's reference method for the determination of a common fiscal marker of gas oil ... more The European Union's reference method for the determination of a common fiscal marker of gas oil for heating purposes, Solvent Yellow 124 (SY124), was validated. A total of 12 different batches of samples using various commercially available gas oils and various colorants with SY124 concentrations from 0.12 to 9 mg L -1 were prepared. Various other dyes were added to check for potential interferences in the separation and detection of SY124. A total of 26 laboratories participated in the validation study. Outliers were identified using the Cochran and Hawkins test, and the resulting datasets were checked for normal distribution using normal probability plots. At a level of 6 mg L -1 , the relative repeatability and reproducibility standard deviations were 0.68% and 3.8%, respectively. At 0.12 mg L -1 , the repeatability and reproducibility standard deviations were 5.4% and 13.5%. A limit of detection of 0.020 mg L -1 and a limit of quantification of 0.065 mg L -1 were estimated. The method was found to be without significant bias and is therefore suitable as a reference method for the determination of SY124 in gas oil.

Nanostructure Science and Technology, 2011

... Reference materials (RMs) are essential tools in the quest for compa-rable and reliable measu... more ... Reference materials (RMs) are essential tools in the quest for compa-rable and reliable measurement results, a quest which laboratories, worldwide, are tasked with every day. ... Chapter 3 Nanoscale Reference Materials Gert Roebben, Hendrik Emons, and Georg Reiners ...

Journal of Nanoparticle Research, 2014

ABSTRACT Transmission electron microscopy (TEM) in combination with a systematic selection proced... more ABSTRACT Transmission electron microscopy (TEM) in combination with a systematic selection procedure for unbiased random image collection, semi-automatic image analysis, and data processing has been validated for size, shape, and surface topology measurements of silica nanoparticles. The validation study, assessing the precision and accuracy of the TEM method, consists of series of measurements on two colloidal silica-certified reference materials, with number-based modal area-equivalent circular diameters (ECD) of 19.4 nm (ERM-FD100) and 27.8 nm (ERM-FD304). The measurement uncertainties are estimated for the modal and median particle size, shape, and surface topology parameters of single primary particles. The single primary particles are distinguished from agglomerates using a linear discriminant analysis approach. After optimization of the binning process, the mode associated with the number-based particle size distribution is obtained by lognormal fitting. The methodology described in this paper relies on a high level of automation of calibration, image acquisition, image analysis, and data analysis and gives robust results for the modal ECD. The expanded uncertainty of the modal ECD is estimated to be about 3 %. The largest contribution to the expanded uncertainty stems from the uncertainty associated with the trueness of the TEM method.

Materials Letters, 2003

This paper is focussed on the reinforcing phases developing in a Si 3 N 4 -based composite micros... more This paper is focussed on the reinforcing phases developing in a Si 3 N 4 -based composite microstructure when sintering a powder mixture of 74 wt.% Si 3 N 4 , 20 wt.% TiO 2 , and 6 wt.% Y 2 O 3 . Micron-and submicron-sized as well as Al 2 O 3 and Al 2 O 3 + SiO 2 -coated submicron-sized TiO 2 powders were used to prepare these in situ composites consisting of Si 2 N 2 O, a-Si 3 N 4 , h-Si 3 N 4 , and TiN. The impulse excitation technique was used to evaluate the intergranular glass phase, which affects crack growth and high-temperature deformation. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to investigate the reinforcing phases. The influence of the TiO 2 -additive powder characteristics on the microstructure and properties of the ceramics is reported. D

Materials Science and Engineering: A, 2006

A powder mixture of α-Si3N4, Al2O3, and TiO2 was hot-pressed using different sintering cycles to ... more A powder mixture of α-Si3N4, Al2O3, and TiO2 was hot-pressed using different sintering cycles to search for an optimum in situ formed β-O-sialon–TiN composite. The impulse excitation technique (IET), high-temperature X-ray diffraction (HTXRD), and scanning electron microscopy (SEM) were used to investigate the microstructure. Below the temperature of 1300°C, the high-temperature internal friction (Q−1) decreases with the increase of sintering

Journal of Nanoparticle Research, 2011

The Institute for Reference Materials and Measurements has organised an interlaboratory compariso... more The Institute for Reference Materials and Measurements has organised an interlaboratory comparison (ILC) to allow the participating laboratories to demonstrate their proficiency in particle size and zeta potential measurements on monomodal aqueous suspensions of silica nanoparticles in the 10-100 nm size range. The main goal of this ILC was to identify competent collaborators for the production of certified nanoparticle reference materials. 38 laboratories from four different continents participated in the ILC with different methods for particle sizing and determination of zeta potential. Most of the laboratories submitted particle size results obtained with centrifugal liquid sedimentation (CLS), dynamic light scattering (DLS) or electron microscopy (EM), or zeta potential values obtained via electrophoretic light scattering (ELS). The results of the laboratories were evaluated using method-specific z scores, calculated on the basis of consensus values from the ILC. For CLS (13 results) and EM (13 results), all reported values were within the ±2 |z| interval. For DLS, 25 of the 27 results reported were within the ±2 |z| interval, the two other results were within the ±3 |z| interval. The standard deviations of the corresponding laboratory mean values varied between 3.7 and 6.5%, which demonstrates satisfactory interlaboratory comparability of CLS, DLS and EM particle size values. From the received test reports, a large discrepancy was observed in terms of the laboratory's quality assurance systems, which are equally important for the selection of collaborators in reference material certification projects. Only a minority of the participating laboratories is aware of all the items that are mandatory in test reports compliant to ISO/IEC 17025 (ISO General requirements for the competence of testing and calibration laboratories. International Organisation for Standardization, Geneva, 2005b). The absence of measurement uncertainty values in the reports, for example, hindered the calculation of zeta scores.

Key Engineering Materials, 2002

Energy & Fuels, 2004

The European Union's reference method for the determination of a common fiscal marker of gas oil ... more The European Union's reference method for the determination of a common fiscal marker of gas oil for heating purposes, Solvent Yellow 124 (SY124), was validated. A total of 12 different batches of samples using various commercially available gas oils and various colorants with SY124 concentrations from 0.12 to 9 mg L -1 were prepared. Various other dyes were added to check for potential interferences in the separation and detection of SY124. A total of 26 laboratories participated in the validation study. Outliers were identified using the Cochran and Hawkins test, and the resulting datasets were checked for normal distribution using normal probability plots. At a level of 6 mg L -1 , the relative repeatability and reproducibility standard deviations were 0.68% and 3.8%, respectively. At 0.12 mg L -1 , the repeatability and reproducibility standard deviations were 5.4% and 13.5%. A limit of detection of 0.020 mg L -1 and a limit of quantification of 0.065 mg L -1 were estimated. The method was found to be without significant bias and is therefore suitable as a reference method for the determination of SY124 in gas oil.

Nanostructure Science and Technology, 2011

... Reference materials (RMs) are essential tools in the quest for compa-rable and reliable measu... more ... Reference materials (RMs) are essential tools in the quest for compa-rable and reliable measurement results, a quest which laboratories, worldwide, are tasked with every day. ... Chapter 3 Nanoscale Reference Materials Gert Roebben, Hendrik Emons, and Georg Reiners ...

Journal of Nanoparticle Research, 2014

ABSTRACT Transmission electron microscopy (TEM) in combination with a systematic selection proced... more ABSTRACT Transmission electron microscopy (TEM) in combination with a systematic selection procedure for unbiased random image collection, semi-automatic image analysis, and data processing has been validated for size, shape, and surface topology measurements of silica nanoparticles. The validation study, assessing the precision and accuracy of the TEM method, consists of series of measurements on two colloidal silica-certified reference materials, with number-based modal area-equivalent circular diameters (ECD) of 19.4 nm (ERM-FD100) and 27.8 nm (ERM-FD304). The measurement uncertainties are estimated for the modal and median particle size, shape, and surface topology parameters of single primary particles. The single primary particles are distinguished from agglomerates using a linear discriminant analysis approach. After optimization of the binning process, the mode associated with the number-based particle size distribution is obtained by lognormal fitting. The methodology described in this paper relies on a high level of automation of calibration, image acquisition, image analysis, and data analysis and gives robust results for the modal ECD. The expanded uncertainty of the modal ECD is estimated to be about 3 %. The largest contribution to the expanded uncertainty stems from the uncertainty associated with the trueness of the TEM method.