Determination Of Particle Size Distribution Research Articles

New Prospects for Particle Characterization Using Analytical Centrifugation with Sector‐Shaped Centerpieces

AbstractAnalytical centrifugation (AC) has recently shown great potential for the accurate determination of particle size distributions. The well‐established LUMiSizer(R) is customized by a new design allowing for higher rotor speeds, improved thermal insulation, and measurement cell assembly. The latter enables sedimentation analysis of nanoparticles (NPs) in sector‐shaped centerpieces. The measurement window of AC experiments is assessed by the Peclet (Pe) number. It is shown that at low Pe numbers (0.7 < Pe < 30), sedimentation, and diffusion can be accurately and simultaneously analyzed from the sedimentation boundaries within one experiment. Moreover, sedimentation properties can be reliably determined up to Pe numbers of 4000. The thermal characteristic throughout the sedimentation analysis is validated by measuring polystyrene particles at elevated temperatures. Moreover, the performance of the setup is demonstrated by determining the sedimentation properties of SiO2 NPs at intermediate Pe numbers in excellent agreement with results from analytical ultracentrifugation experiments. Finally, for the first time, an accurate analysis of the core–shell properties of Au NPs via AC is presented. By combining the analysis of sedimentation and diffusional properties at low Pe numbers, the shell thickness of the stabilizer cetyltrimethylammonium bromide alongside the core diameter distribution of the Au NPs is determined.

The impact of cyclic fuels on the formation and structure of soot

This paper investigates the impact of cyclic fuels on the nanostructure, nucleation and overall production of soot in an n-heptane (C7H16) laminar coflow diffusion flame. The fuels selected to dope the n-heptane flame are cyclopentene (C5H8), cyclohexene (C6H10) and methylcyclohexane (C7H14). These fuels were chosen for their differences in their structure and sooting tendency. The flame structure was studied with Differential Mobility Spectrometry (DMS) for particle size distribution determination, two-colour ratio pyrometry to calculate the soot volume fraction and soot temperature. The soot nanostructure was investigated using Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). The addition of cyclic fuels was found to promote the formation of soot nanoparticles earlier in flames. In addition, the soot volume fraction was increased significantly by the addition of the cyclic fuels, especially by the addition of cyclopentene. The addition of 20% of cyclopentene increased the soot volume fraction by a factor of 2. HRTEM results suggest a significant influence of cyclopentene on the soot nanostructure; cyclopentene addition promotes the incorporation of five-membered rings (pentagonal rings) leading to highly curved fringes. This suggests cyclopentene could be used as a fuel to promote curvature in different carbonaceous materials to modify their properties.

Transferencia de oxígeno en una columna de tres fases utilizando polímeros sólidos como vectores de transferencia de masa

Three solid polymers; Kraton, Elvax, and Desmopan, previously suggested to be used in three-phase reactors, were evaluated for their ability to enhance oxygen transfer in a bubble column. These vectors were first characterized through determination of particle size distribution, surface roughness, specific surface area, density, void fraction and thermal stability. Oxygen transfer was then determined with a non-coalescing medium using polymer volume fractions from 0 to 75% in a 4 L bubble column operated at air flow rates ranging from 1 to 6 L/min. The results showed that the oxygen transfer was significantly improved in presence of 10 and 25% of Kraton and Elvax, compared with control experiment with no polymer. A maximum oxygen transfer improvement of 90%, compared with control, was observed with 10% Kraton. With Desmopan, no positive effect on oxygen transfer was observed regardless of the vector percentage used. Phase’s dispersion and oxygen transfer was further explored in presence of 10% Kraton. Gas holdup, Sauter mean bubble diameter and vector dispersion were characterized by means of high speed digital image analysis. The results showed that the enhancement of oxygen transfer mediated by Kraton was mainly caused by an increase of gas holdup and consequently of the gas/liquid surface area.

Towards a new and general method for decoding the soil texture from laser diffraction spectra

Laser diffraction (LD) is a modern method for determining particle size distribution of soils and sediments. When deciphering particle size distribution, the area under the differential LD-spectrum is determined, limited by the vertical boundaries at the group edges according to the FAO-classification. In fact, there are no real vertical boundaries between the fractions of the particles, and the fractions themselves are distributed on a scale of size according to normal distribution. To eliminate the errors in the fractions content, deconvolution procedure for separating the original particle size distribution LD-spectrum is proposed. It resulted in a different share of the fractions compared to the common calculation method of the fractions content by FAO-classes. It is possible to detect new invisible fractions and, conversely, to exclude fractions defined within FAO vertical boundaries. In addition, the new indicator dispersion of LD-fractions (D) is proposed, which provides information on the property of individual fractions by particle size. Vertisols’ texture was heavier after deconvolution, especially in the Stavropol Vertisols. Vertisols had relatively low dispersion D < 0.7, which means relative homogeneity of LD-fractions. Northern Italy Andosols, however, had lighter texture after deconvolution. The number of LD-fractions was less than the number of FAO-fractions, while clay and fine sand (63–200 μm) LD-fractions were absent. It is likely due to the increase in LD-fractions dispersion, as evidenced by the high value of D (1.5).

INFLUENCE OF BACKGROUND ELECTROLYTE AND SURFACE-ACTIVE SUBSTANCES ON EFFICIENCY OF ELECTRO-FLOTATION EXTRACTION OF HARDLY SOLUBLE EUROPIUM COMPOUNDS

Europium and its compounds are widely used in high-tech processes of nuclear and hydrogen energy, electronics, medicine and other fields. In this work, the regularities of electroflotation extraction of hardly soluble europium compounds from model systems were obtained and analyzed. The aim of the work is to obtain data on the process of electroflotation extraction of hardly soluble europium (III) compounds from model systems with background electrolyte and the addition of surface-active substances, establishing optimal conditions for efficient extraction of hardly soluble europium (III) compounds. The research was conducted at room temperature (20 ± 2 °C) in a non- current electric flotator of periodic action, which is made in the form of a vertical column. The cross-sectional area of the electric flotator is 10 cm2, the volume of the treated solution is 500 ml, the height of the apparatus is 800 mm, and the sampling valve is located at a height of 40 mm from the electrode unit. The electrode unit consists of an insoluble anode made of ORTA (titanium with ruthenium oxide coating) and of a cathode made of stainless steel mesh (cell size 0.5 × 0.4 mm, wire thickness 0.3 mm). The mass concentration of europium (III) was determined by a mass-spectrometer with inductively coupled plasma of Termo Scientific brand. Determination of particle size and particle size distribution, surface charge of particles of the dispersed phase (ξ) were carried out using a Photocor Compact-Z laser particle analyzer. The efficiency of the process of extracting hardly soluble compounds of Eu3+ was evaluated by the degree of extraction α (%). The objects of study are colloid-dispersed systems of poorly soluble compounds of europium (III) in aqueous solutions in the presence of surface-active substances of various nature and background electrolytes. The initial aqueous solution contains: СEu3+ - 0.1 g/l, Cbackground electrolyte - 1 g/l, background salts: NaCl, NaNO3, Na2SO4; Csas - 5 mg/l. It has been shown that for each type of solution the efficiency of the electroflotation process is achieved at certain pH. It is established that the optimal conditions for the extraction of europium (III) compounds are: volume current density, Jv = 0.4 A/l; process duration 10 min. For nitrate background the degree of extraction is maximum at pH 10 - 11 and at the presence of an anionic surfactant additive in the solution (Оxy surfactant A1218). When extracting europium (III) compounds from a system with a sulphate background the best results were obtained at pH values of 8 and 10, as well as the addition of an anionic and, or cationic (Septa surfactant XEV70) surfactant. Chloride background showed the best conditions for the extraction of europium (III) at pH 7 with the addition of a non-ionic surfactant of PEO-1500 brand. The degree of extraction of europium is 98-99%.

Role of dimethyl ether in incipient soot formation in premixed ethylene flames

Emissions of soot particles exert crucial impact on human health and the environment. Previous researches show that a partial replacement of fossil fuels with oxygenated fuels is supposed to reduce soot emission. However, the crucial information of soot size distributions is unclear, although small particles are more dangerous than large particles. In this paper, dimethyl ether (DME) is selected among the oxygenated fuels for the investigation of the doping effect on nascent soot formation. DME was doped in the burner-stabilized rich premixed ethylene/oxygen/argon flames at various mixing ratios. Flame temperature profiles were measured using R-type thermocouples with radiation correction. A scanning mobility particle sizer (SMPS) with a sampling system was used to determine particle size distributions (PSDs) of soot-containing combustion products with immediate dilution. Thermo-gravimetric analysis (TGA) complemented with elemental analysis (EA) was conducted to detect the chemical properties of formed soot particles. Additionally, species profiles of the experimental flame conditions were provided from simulations. The experimental PSDs showed that DME addition could slow down soot evolution process, while lead to a slight increase in incipient soot with size below 4 nm. When DME added, the production of benzene was suppressed due to the reduced concentrations of acetylene and propargyl, and thus soot nucleation. Meanwhile, soot oxidiation was enhanced because the OH radical and the oxidizability of soot particles are both increased. Considering the slight increase of sub-4 nm soot, the effect of oxygenated-PAHs (OPAH) was emphasized. The production of OPAH suppressed soot surface growth, which leading to the relatively lower consumption of sub-4 nm soot in DME added flames.As a result, DME cannot be simply regarded as a clean fuel due to the enhanced formation of sub-4 nm soot particles. When applying oxygenated fuels into practice, it is necessary to pay more attention to the size distributions of the emitted particles, and conduct appropriate post-processing techniques to reduce the emissions of small particles.

Comparison of pipette method and state of the art analytical techniques to determine granulometric properties of sediments and soils

The determination of particle size distribution is a crucial issue in various fields of earth sciences (e.g., Quaternary research, sedimentology, stratigraphy, structural geology, volcanology), environmental sciences as well as diverse industrial applications (e.g., pharmaceuticals, cement industry). New measurement techniques developed as a result of industrial demands have also gained ground in environmental and Earth sciences research. The new techniques (especially laser diffraction) have enabled the particle characterisation in the broader size-range with a more detailed resolution. Still, they have to be compared with data obtained by classical methods. In light of the above, the primary aim of our research is to examine the methods of particle size determination critically. Excessive oversimplifications of particle size analyses routinely have used in paleo-environmental and paleo-climatological reconstructions, and other sedimentary studies, as well as insufficient knowledge of the background of the applied methods, distort the interpretation of the results. Over the past four decades, laser diffraction particle size analysers have proven to be practical tools of particle size characterisation. However, the shape of the natural sediment and soil particles are irregular and, therefore, affects the particle size distribution results obtained by different methods. The results of the traditional pipette method differed from laser diffraction results. The presence or absence of the pretreatments did control the differences between the two techniques. The results of Fraunhofer optical method were significantly different from Mie theory because it can detect much lower volume percentages of finer particles. Grain size results of coarse-grained samples measured by different laser diffraction devices were more comparable than the results of more clayey samples. The ratios of different sizes were changed due to the hydrochloric acid and hydrogen peroxide pretreatments. The comparison of different techniques is necessary to revaluate standards in grain size measurements which can enable the shift from conventional methods to more productive and reproducible methods. Still, light scattering techniques have not yet been able to displace classical methods in Earth sciences completely, in contrast to industrial applications.

Production of instant coffee from cold brewed coffee; process characteristics and optimization

This study aimed to develop a process for producing instant coffee from cold brewed Arabica and Robusta roasted coffee beans. The process starts by selecting an appropriate mixture of Arabica and Robusta coffee beans, degree of roasting (light, medium, dark) and degree of grinding (coarse, fine). Sensory evaluation by a trained panel showed that a mixture of 92.5% Arabica and 7.5% Robusta medium roasted, coarsely ground coffee beans produces instant cold brewed coffee equally or better accepted from other instant coffees available to consumers. The selected coffee beans were subjected to vacuum assisted cold extraction and the extract was spray dried. Spray drying conditions (inlet temperature, air volumetric flow and air aspiration rate) were optimized by a 33 full factorial design. Response variables were solids yield, process thermal efficiency and anti-oxidant capacity of the produced powder measured as %DPPH scavenging ability, FRAP and total phenolic content. The produced powder was analysed for its physicochemical characteristics (caffeine content, phenolics, moisture content, hygroscopicity, bulk density, solubility, particle size distribution, acrylamide content and shelf life determination).

Digital UV/VIS imaging: A rapid PAT tool for crushing strength, drug content and particle size distribution determination in tablets.

The Process Analytical Technology (PAT) and the Quality-by-Design (QbD) approaches can efficiently facilitate the shift to the desired continuous manufacturing and real time release testing (RTRT). By this, it is vital to develop new, in-line analytical methods which fulfil the pharmaceutical requirements. The fast-developing digital imaging-based machine vision systems can provide revolutionary solutions not just in the automotive industry but in the pharmaceutical technology, as well. This study aimed to explore the capabilities of UV/VIS-based machine vision in tablet inspection as a PAT tool for the determination of compression force and crushing strength, drug content and drug distribution in tablets using meloxicam a yellow model drug. In the case of determining the compression force and crushing strength, the application of multivariate wavelet texture analysis (MWTA) based models provided relatively low prediction errors. To predict the drug content of meloxicam tablets CIELAB or RGB colorspace based algorithms were successfully developed and validated. UV/VIS imaging was also used to map the particle size distribution and spatial distribution of meloxicam, the results were compared to chemical maps obtained by Raman microscopy. Digital imaging combined with multivariate data analysis might be a valuable, high throughput, in-line PAT tool for automated inspection of pharmaceutical tablets.

Milk homogenization monitoring: Fat globule size estimation from scattering spectra of milk

The fat globule size distribution of raw milk and milk with an increasing degree of homogenization was estimated based on their bulk light scattering properties in the Vis/NIR wavelength range. The particle size distribution (PSD) was approximated as a lognormal distribution, of which the parameters were estimated simultaneously with the fat concentration. This resulted in a good agreement between the estimated PSDs and the reference PSDs obtained by laser diffraction in case of raw and strongly homogenized samples. The accuracy increased if a known fat concentration was incorporated, or when the scattering coefficient and anisotropy factor spectra were used simultaneously as input. For mildly homogenized samples, the lognormal distribution was unable to fit the bimodal PSD correctly and focused on the largest fat globules. In this case, the estimated PSDs provided still relatively accurate information on D90, D32 and the right distribution tail, which contains the largest fat globules. Industrial relevanceThe presented estimation method demonstrates the potential of bulk scattering spectra for determining the PSD and concentration of scattering particles in turbid media. Further development of this technology can lead to new solutions for spectroscopic PSD determination, allowing on-line monitoring systems for a wide range of food and non-food products.

Particle Size Distribution of Natural Clayey Soils: A Discussion on the Use of Laser Diffraction Analysis (LDA)

Particle size distribution is one of the most significant factors determining physical soil properties. Laser diffraction analysis (LDA) is an alternative method to the traditional hydrometric methods (HM) used to determine particle size distribution in soils. However, significant differences in fraction content are found in relation to the applied methods of a particle size test. Above all, measurements performed by LDA for clayey soils usually produce different results to those based on Stokes’ equation. Methodical problems, such as an appropriate method of dispersing the sample and the selection of LDA calculation theory, also play a significant role in fine soils. This paper contains the results of analyses of Neogene clays from Poland, which are characterized by differentiation with regard to the content of clay fraction particles. In this article, the validity of using laser diffraction analysis (LDA) for the identification and characterization of clayey sediments with common genesis is assessed. The possibility of finding reliable pedotransfer functions to the convert LDA results to a hydrometric analysis is discussed.

Particle size determination from magnetization curves in reduced graphene oxide decorated with monodispersed superparamagnetic iron oxide nanoparticles

Reduced graphene oxide (RGO) decorated with superparamagnetic iron oxide nanoparticles (SPION) is a novel composite nanomaterial with a myriad of promising applications. However, processes such as the fast and simple synthesis of non-agglomerated monodispersed SPION on RGO and the accurate characterization of particle size distributions remain challenging. Here we present how to solve these two problems. Firstly, we introduce a new microwave-assisted synthesis of stabilized SPION on RGO which is fast, simple and up-scalable but at the same time renders well dispersed SPION with narrow size distributions. The coverage of the RGO flakes with SPION is extensively tuned and the results are compared with a non-stabilized microwave-assisted method. Secondly, we implement an accurate method for the determination of particle size distributions from magnetization curves in RGO-SPION composite nanomaterials. This method is applied to the prepared composites with different particle size distributions, degrees of particle agglomeration and coverage of the RGO flakes. The influence of sample characteristics in the size determination method is discussed and the results are compared with the values obtained from transmission electron microscopy (TEM) and X-ray diffraction (XRD), showing that the method is well suited for these and potentially other types of superparamagnetic composite nanomaterials.

Determination of particle size distributions and transformation enthalpies from the temperature course of a phase transformation

The presented analysis of the temperature course of a phase transformation of nanoparticles offers a powerful tool to obtain data for the particle size distribution and the enthalpy of transformation. The analysis starts with the temperature distribution within an ensemble of nanoparticles and a functional relation between particle size and transformation temperature. In contrast to the Maxwell-Boltzmann distribution, in case of nanoparticles, the distribution of the temperature of the particles follows a normal distribution. Finally a reliable characterization of the specimen and the transformation in question are presented. These results, particularly the particle size distribution, represent – in many cases – a statistically more significant result as compared to the outcome, obtained by evaluation of electron micrographs. Looking at the problems of microcalorimetric determination of reaction enthalpies, one may realize comparable problems. By comparison of the experimental data with the calculated ones, one may obtain additional information about the interaction of the particles within the ensemble.

Self-constructed automated syringe for preparation of micron-sized particulate samples in x-ray microtomography

In X-ray microtomography the sample has to meet special requirements regarding (1) mechanical stability (blurring), (2) geometry (FOV - field of view, rotational symmetry) and (3) composition (high attenuating phases). When analyzing micron-sized particulate material (e.g. powders), the particles in the FOV have to be (4) statistically representative and fixation (embedding matrix) becomes a critical issue due to segregation and agglomeration effects. The authors describe a self-constructed, low-cost automated syringe that allows controlling aspiration speed and suctioning volume. The carrier matrix is a wax structure that is shock frozen within a small polymeric tube. With this, the authors could successfully validate the method to determine particle size distributions (PSD). The described method is used in a related study by Ditscherlein et al. (2019).•Low-cost automated syringe constructed with LEGO-parts and automatized with Arduino-microcontroller.•Particle sample embedded within a shock-frozen wax matrix.•Reproducibility successfully demonstrated by determining particle size distributions.

Determination of particle size distribution based on dynamic light scattering measurements in the near field

Particle size distribution (PSD) measurement is important for improving product quality, inhibiting environmental pollution, and safeguarding human health. The near-field scattering (NFS) technique offers many substantial advantages over conventional techniques. However, the reconstruction equations are ill-posed and it is difficult to get a reliable solution. In this paper, we propose a new method that can solve the reconstruction equations. This method combines the Backus-Gilbert eclectic theory with truncated singular value decomposition (TSVD) method to obtain a non-negative approximation solution as the initial value of Chahine algorithm for fine calculation. Our method exhibited good performance with several numerical cases of unimodal and bimodal PSDs. It was then used for PSD measurement of two standard particles (GBW(E) 120,028 and 120,047) using the NFS techniques. The relative errors of the length mean diameter, with respect to the peak size of these two standard particles, were 0.18% and 0.76%, respectively.

Determination of Size Distribution of Precipitation Aggregates Using Non-Invasive Microscopy and Semiautomated Image Processing and Analysis

Particle size distribution (PSD) determination is a typical practice for the characterization of the slurries generated in a precipitation plant. Furthermore, the precipitates generated in these processes form colloidal or aggregated suspensions. Nevertheless, the conventional methods used to estimate PSD (e.g., laser diffraction and/or a cyclosizer) have not been designed to measure particles that tend to aggregate or disaggregate, since they include external forces (e.g., centrifugal, agitation, pumping and sonication). These forces affect the true size of the aggregates formed in a unit operation, thereby losing representativeness in terms of aggregates particle size. This study presents an alternative method of measuring the size distribution of particles with aggregation behavior, particularly, by using non-invasive microscopy and image processing and analysis. The samples used were obtained from an experimental precipitation process by applying sulfidization to treat the cyanide-copper complexes contained in a cyanidation solution. This method has been validated with statistical tools and compared with a conventional analysis based on laser diffraction (Mastersizer). The PSD results obtained with optical microscopy show a bi-modal behavior of the precipitates. However this behavior could be not determined when using the laser diffraction technique. The PSD obtained for the sample tested by microscopy had a mean of 119.7 μm, a median of 147 μm and a 90% distribution reached a particle size of 312.5 μm. These values differ with those obtained by the laser diffraction technique. Our results show significant differences between the methods analyzed, demonstrating that the image processing and analysis obtained by optical microscopy is an excellent and non-invasive alternative to obtain size distributions of aggregates in precipitation processes.

Mechanism of an asphaltene inhibitor in different depositing environments: Influence of colloid stability

Additives are used to reduce unwanted carbonaceous deposits of asphaltenes on surfaces during petroleum production from natural oil and gas reservoirs. The working mechanism of formulated additive packages can be multifaceted. Additives may be effective in the bulk fluid by preventing asphaltenes aggregation, as well as at the surface by preventing asphaltenes adhesion. In this paper, we investigate the numerous different mechanisms by which an asphaltene inhibitor can interfere with the formation of carbonaceous deposits using a combination of techniques including dynamic light scattering to determine particle size distribution, quartz crystal microbalance with dissipation monitoring to examine deposition behaviour and atomic force microscopy to probe deposit morphology. The tested inhibitor prevents deposition of asphaltenes in toluene, where asphaltenes exist as a stable colloidal dispersion of nanoaggregates, by forming barrier-type films that inhibit asphaltenes adhesion and displacing adsorbed thin films of asphaltenes. However, inhibitor performance in heptane-toluene, where asphaltenes are destabilised, depends on the degree of destabilisation. At low heptane volume fraction, inhibitor slows the rate of deposition and deposition rate decreases with increasing inhibitor concentration. However, at high heptane volume fraction, inhibitor can increase the deposition rate, particularly when used in high concentration. At high heptane volume fraction, inhibitor addition alters the morphology of the deposit from that consisting of large flocculent aggregates to that consisting of smaller, submicrometer aggregates. This is consistent with the finding that inhibitor acts as an anti-agglomerant and prevents the formation of large aggregates in the bulk liquid. This paper shows that the impact of inhibitor addition depends on the environmental conditions encountered and the degree of destabilisation of the asphaltenes. Where inhibitor addition alters the nature of depositing species from large flocculent aggregates to smaller submicrometer aggregates, an increase in deposition rate may be observed.

Hydrogeological Properties of Gypseous soils in South Africa

Abstract Gypseous soils occur in the western arid and semi-arid regions of South Africa and Namibia. These soils exhibit a complex nature and abnormal behaviour due to their gypsum content and as such they have become more prevalent in research. As these soils are finding more use in industry, an astute understanding of their hydrogeological properties and behaviour is required. Powdery gypseous soil samples collected from the Northern Cape (Geelvloer) and Western Cape (Rooiberg and R355) Provinces, as well as a prepared sample, are subject to XRD analysis, particle size distribution determination and falling-head permeability tests using both water and brine. The testing served as preliminary research to guide further studies into the topic. The prepared sample, with 19% fines, comprises 35% gypsum and 65% sand. Geelvloer samples, with 91.95% gypsum content, are comprised mostly of sand-sized particles with 45% fines. Rooiberg samples contain 75% fines with a slightly lower gypsum content of 83.25%, while R355 samples have 50% fines with 75.35% gypsum. It is generally understood that particle size distribution contributes to the hydraulic conductivity of soils, where a higher portion fines will result in a lower conductivity. In the case of gypseous soils, the solubility is of importance as well, as it may have long term effects. With the intent of evaluating the effect of the aforementioned factors on the hydraulic conductivity of gypseous soils in South Africa, the samples taken represent differences in particle size distribution and origin. Geelvloer had k-values in the order of 8.82×10-6 m/s, with the brine sample giving 9.43×10-6 m/s, while the k-values for Rooiberg and R355 were in the order of 3.90×10-6 m/s and 5.87×10-6 m/s, respectively. The brine resulted in 5.63×10-6 m/s for Rooiberg and 9.90×10-6 m/s for the R355 sample. The made sample, having less fines, had k values in the order of 2.15×10-5 m/s, and 4.19×10-5 m/s for the brine. The differences between the results are largely negligible and show that despite what is believed to influence the hydraulic conductivity, in the case of gypseous soils in South Africa, on a small scale, it remained unaffected.

Dimethyl carbonate (DMC) and Methyl Formate (MeFo): Emission characteristics of novel, clean and potentially [formula omitted]-neutral fuels including PMP and sub-23 nm nanoparticle-emission characteristics on a spark-ignition DI-engine

Dimethyl carbonate (DMC) and methyl formate (MeFo) are oxygenate fuels characterized by a very high octane number and boiling points in the range of commercial gasoline (DMC: 90°C/363,2K, MeFo: 31.5°C/304,7K). Due to their molecular structure without C–C bonds (C1-fuel) and their high oxygen content of 53.3%, DMC and MeFo are expected to avoid the formation of soot precursors in combustion and thus to distinctly reduce particulate number (PN) emissions.Beyond todays solid particle number (PN) limits, which are based on the definition of the particle measurement program (PMP) using a 23 nm cut-off of the counter, sub-23 nm particles are currently discussed to be a health concern. The measurement of smaller solid particles is not standardized yet and is potentially impeded by the presence of volatile nucleation mode particles below 23nm. Moreover, standard techniques for additionally determining particle size distributions usually are below their sensitivity limit due to the low particle concentrations produced by oxygenate fuels.At the Technical University of Munich, DMC and MeFo were tested as pure substances in their emission and performance behavior compared to conventional gasoline fuel, using a single-cylinder, direct injection SI-engine. Primary (limited: CO, HC, NOx) and secondary (non-limited: CH2O,CH3OH,NH3) gaseous emissions pre- and after a TWC as well as particle number (PN) emissions were investigated.Regarding the challenges of particle number measurements, this work presents our method to also assess the properties of such ultra-low concentration aerosols from engine exhaust considering trends in particle size and potential artifacts caused by volatile, sub-23 nm particles. The method described uses two differently constructed PMP PN counting systems, operating in parallel, using largely different dilution schemes and rates. Both systems are equipped with two condensation particle counters (CPC) each, which are set to cut-off ratios of 23nm and 10nm, allowing to gain further insights using the ratios of the different systems (indication of potential artifacts) as well as ratios of the two CPC (indicating size trends) respectively.The test outcomes of steady-state operating points during lambda-sweeps show positive effects of the fuels on raw gaseous emissions while still maintaining high conversion rates over the TWC. PN emissions drop significantly and are even below ambient concentrations both for DMC and MeFo in DI-mode. However, a higher relative share of sub-23 nm particles is observed among the low number of remaining particles, and the data of both particle systems is used for further analysis of size trends and volatility.While displaying ultra-low pollutant emissions, DMC and MeFo are also potentially CO2neutral substances, and their potential sustainable production using green electricity and waste CO2 will be also summarized.

Components of the Co3Cr4(PO4)6–Cr(PO3)3 system and the compound CoCr2(P2O7)2 as new ceramic pigments

The compounds: Co3Cr4(PO4)6, Cr(PO3)3 and CoCr2(P2O7)2 were tested for possible application as ceramics and anticorrosive pigments. They were characterized by SEM analysis, determination of particle size distribution and thermal stability. All phosphates were thermally stable up to 1100 °C so they can be used for colouring of middle-temperature ceramic glazes. The gravimetrical determination of corrosive loss of steel sheets and other corrosion factors characterizing the resistance to corrosion in an aqueous environment of the phosphates were discussed. The colour properties of the compounds were studied for powders and pigments introduced into organic matrix and several single-firing ceramic glazes. It is shown that the investigated phosphates can be used as ceramic pigments only for leadless single-firing ceramic glaze. The optimum pigment concentration sufficient for colouring glaze was close to 2 wt %. Generally, the examined phosphates have interesting green, greenish-blue and cyan shades.