Function Of Grinding Time Research Articles

Flow properties of single origin chocolates: Effect of product formulation and particle size.

The objective of this research was to evaluate changes in flow behavior of chocolate during chocolate grinding using a stone grinder as affected by chocolate formulation. Three different types of chocolates were evaluated. Two chocolates without milk added (70% chocolate) and two chocolates with milk added and with different amounts of cocoa nibs (30% chocolate and 14% chocolate) were tested. For the 70% chocolates, nibs of two different origins were used; therefore, a total of four samples were evaluated. Chocolates were processed in a stone grinder, and samples were taken as a function of grinding time. For each timepoint, the flow behavior of the samples was measured using a rotational rheometer and fitted to the Casson model. Particle size was measured using a laser scattering instrument. Results showed that yield stress increased linearly while the Casson plastic viscosity decreased exponentially with grinding time (smaller particles). Particle size distribution of the chocolates showed a prominent bimodal distribution for short grinding times (∼9 h) with small (∼15 µm) and large (∼100 µm) particles; with longer grinding time, the population of larger particles decreased. Yield stress values were higher for the 70% chocolate, but they were not very different between the two milk chocolates tested. The Casson plastic viscosity was greatest for the 70% chocolate, followed by the 30% chocolate. The 14% chocolate had the lowest Casson plastic viscosity. Changes of Casson plastic viscosity with particle size were more evident for the dark chocolates compared to the milk ones. These results are helpful to small chocolate producers who need better understanding of how the formulation and grinding of chocolate affect its flow behavior, which will ultimately affect chocolate handling during production.

The distribution of oxygen in submicron silicon powders produced by ultrafine grinding

The distribution of oxygen in submicron silicon powders produced by ultrafine grinding was studied as a function of grinding time, grinding liquid composition, air exposure during the grinding experiments and post-grinding handling. Grinding in isopropyl alcohol resulted in relatively low oxygen concentrations. Here, a maximum SiO2 oxide layer thickness of 0.24 nm was calculated for a product with a total oxygen concentration of 3.35 wt%, a mean particle size of 122 nm and a BET specific surface area of 72 m2/g. When excluding the contribution from adsorbed or trapped grinding liquid and alkoxy groups the layer thickness was reduced to 0.07 nm. The addition of ion exchange water to the isopropyl alcohol produced a non-linear increase in the oxygen concentration. The effect of exposure to air during drying was small compared to the effect of exposure to air during the grinding process or during heat treatment at higher temperatures.

Phase Purity Regulated by Mechano-Chemical Synthesis of Metal–Organic Frameworks for the Electrocatalytic Oxygen Evolution Reaction

Three new metal organic frameworks (ZnTIA-1mc, CuTIA-1mc, and CoTIA-1mc) were synthesized by the mechanochemical grinding (mc) method in the unadulterated form. They compared with their solvothermally synthesized (st) counterparts, where the mixtures of isomeric forms have been isolated. Kinetics study with the function of grinding time during the mechanosynthesis process revealed the formation of new metastable phases. Less crystallinity and short of mechanical defects in the structure of synthesized mc metal organic frameworks showed enhanced electrocatalytic activity toward oxygen evolution reaction (OER). Among all, CoTIA-1mc showed high OER activity with 289 mV overpotential, 10 mA cm-2 current density, and 55.4 mV dec-1 Tafel slope in 1 M KOH which is close to the commercially used RuO2.

Feed hardness and acoustic emissions of autogenous/semi-autogenous (AG/SAG) mills

In this study, the relationship between acoustic emissions and hardness of different rock types (model quartz, model calcite, and real iron ore) coupled with binary mix ratios of model quartz and iron ore (1:3, 1:1 and 3:1) was investigated in a laboratory-based AG/SAG mill. The acoustic emission response and sensitivity of the mill were compared, along with its product particle size distribution. Features, such as discrete wavelet transform (DWT), power spectral density estimate (PSDE), and statistical root mean square (RMS) were extracted from the mill acoustic emissions. From the results, it was evident that the mill acoustic emission response can be used to classify different rock hardness and their binary mixtures. Model quartz emitted the highest acoustic response, followed by iron ore and model calcite at the initial stages of grinding (5 min). The results further indicated that as the rock feed sizes reduced, the average mill noise also increased as a function of grinding time. Accordingly, the acoustic emission presented a contrasting effect with model calcite and model quartz emitting the highest and lowest noise emission, respectively. The proportions of different mineral types (model quartz and iron ore) were reflected well in the acoustic emissions. The study has demonstrated that the integration of acoustic sensing techniques in AG/SAG mills can serve as a proxy for online measurement of different rock/ore hardness, for example, as a fast track method to determine the hardness of ores in comparison to the traditional ore grindability procedures, such as Bond work index (BWI) and SAG power index(SPI) tests which can be laborious and time-consuming.

Температура отверстий колец подшипников при шлифовании сборным текстурированным кругом

The problem of reducing the thermal stress of the grinding process of bearing rings has been viewed. The possibility of reducing the temperature of the treated surface based on the use of precast textured grinding wheels has been presented. Experimental models of pulse, contact, average temperature, velocities and rates of their change in the function of grinding time are found.

Effects of grinding time on morphology and collectorless flotation of coal particles

The impact of particle shape and surface properties has been mainly overlooked in the literature for different mineral systems. In this study, to investigate the effects of morphological variations, samples of clean coal particles (−0.212 + 0.075 mm) were used and the flotation experimental in a batch condition (2 L Denver cell) were conducted in the absence of collectors by keeping the particle size constant. Binocular microscopic images were used to determine the shape factors of coal particles. A dry ball milling process was carried out as a function of grinding time (60–960 s) and representative samples were taken for determining both shape and floatability of particles. Further, particle-bubble attachment, zeta potential, roundness, surface roughness values and flotation kinetics were measured. It was indicated that by increasing milling duration from 60 s to 960 s, the roundness and roughness increased from 0.792 to 0.809 and 23 nm to 57 nm, respectively. This led to increasing flotation rate constant from 0.4482 ± 0.02 to 0.4856 ± 0.03 1/min. In addition, the theoretical calculations for energy barrier showed that upon increasing the roughness degree from 0 to 57 nm, the energy barrier significantly decreased from 2.79E-16 to 6.51E-17 J/m2, which also proved our findings from a theoretical point of view. Thus, it was finally concluded that the more the roughness, the higher the flotation kinetics and the lower the energy barrier.

Structural collapse in phlogopite mica-rich mine tailings induced by mechanochemical treatment and implications to alkali activation potential

The alkali activation of mine tailings is of interest to diminish the impoundment storage of large waste stream from mining industry. However, most of the mine tailings, like phosphate mine tailings generated in Finland, are rather inert and need pre-treatment to induce the reactivity for alkali activation. In this work, mechanochemical treatment was conducted to improve the reactivity of phosphate mine tailings. The ground specimens were subjected to the crystal structural analysis of X-Ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermal analyses by Thermogravimetry/Differential Thermal Analysis (TG/DTA), showing the increment of amorphous content and structural degradation as a function of grinding time. The subsequent alkaline reactivity test illustrated incremental alkaline dissolution of Si, Al and K and a schematic diagram of altered phlogopite structure (sources of aluminosilicates in tailings) was also proposed. Additionally, the mineralogical composition of individual particles was carried out by mineral liberation analysis (MLA), thereby evaluating the influence of pre-treatment on the mineralogy of tailings. The results indicate profound micromorphological changes and structural cleavage of the precursor due to grinding, which strongly increase alkaline reactivity.

Silicon Powder Properties Produced in a Planetary Ball Mill as a Function of Grinding Time, Grinding Bead Size and Rotational Speed

Mechanical milling is a promising route for production of submicron and nano sized silicon powders, but it is challenging to predict and control the product properties. In this study a metallurgical grade silicon quality was milled in a planetary ball mill and the properties of the powder were investigated as a function of grinding time, grinding bead size (20 mm, 2 mm, 0.25 mm) and rotational speed based on the concepts presented in the stress model. The finest powder was characterized by a d50 of 0.62 μm. This powder was produced with the 2 mm grinding beads and 4 h of grinding (i.e. the highest specific energy input to the mill with this bead size). The largest BET specific surface area, the highest concentration of iron contamination and the smallest amount of crystalline silicon phase were characterized in the powder produced using the 0.25 mm grinding beads and 4 h of grinding (i.e. the highest stress number). Aggregates consisting of silicon and iron were formed. An acid wash to reduce the concentration of iron contaminant revealed that silicon did form an amorphous phase as well as the specific surface area increased. With a constant specific energy input to the mill, a reduction in rotational speed (i.e. reduced stress energy) produced similar powder properties with the exception of the particle size distribution.

Characterization and structure of cold-extruded whey protein isolate: impact of ball milling

The effect of ball milling on physicochemical, functional and rheological properties and structural characteristics of cold-extruded whey protein isolate (TWPI) was investigated as a function of grinding time. Ball milling decreased the free sulfhydryl content of all the samples. Furthermore, ball milling and cold extrusion could enhance surface hydrophobicity, emulsifying and rheological properties of WPI. The solubility of cold-extruded WPI was far higher than the traditional heat-extruded WPI. The viscoelastic modulus of TWPI, ground by ball milling for 10 h, dramatically increased compared to that of WPI at 85 °C. Scanning electron microscopy revealed that a ball-milling treatment of 2 h remarkably decreased the particle size of all the samples. FTIR demonstrated that ball-milling treatment decreased the ordered secondary structure (α-helix and β-sheet) of WPI. Therefore, a combination of cold extrusion and ball milling could remarkably enhance the emulsifying and rheological properties of WPI, an effective way for providing novel functional ingredients to the dairy industry.

Changeing of fly ash leachability after grinding

Effect of grinding on the reactivity of fly ash used for geopolymer production was tested. Extraction technique using different alkaline and acidic solutions were used for detect the change of the solubility of elements due to the physical and mechano-chemical transformation of minerals in function of grinding time. Both the extraction with alkaline and acidic solution have detected improvement in solubility in function of grinding time. The enhancement in alkaline solution was approx. 100% in case of Si and Al. The acidic medium able to dissolve the fly ash higher manner than the alkaline, therefore the effect of grinding was found less pronounced.

Effects of Grinding Time on Rheological, Textural and Physical Properties of Natural Peanut Butter Stored at Different Temperatures

AbstractThe effects of ultrahigh speed grinding process duration of 2–4 min and its storage temperature on rheological, textural and physical properties of natural peanut butter produced from peanuts of Virginia and Spanish varieties were investigated. Both types of peanut butter samples exhibited food suspension with multimodal particle size distribution, fitted adequately to the Casson model and demonstrated nonNewtonian shear‐thinning behavior with apparent yield stress. The storage (G′) and loss (G′′) modulus decreased as a function of grinding time and temperature. Grinding time and storage temperature gave significant effects on all the responses (P < 0.05) while peanut variety only has impact on the particle size distribution. Identical trends were observed for the natural peanut butter from both Virginia and Spanish peanut varieties.Practical ApplicationsProcessing and storage temperature are among factors influencing texture of food suspension such as butter and spreads. Our research investigated the effect of grinding time and storage temperature on rheological, textural and physical properties of natural peanut butter in the effort of producing optimum quality in terms of finest texture. The relationship between particle size distribution and textural properties is useful in the development of natural peanut butter with this study focusing on grinding effects as its processing and stability in terms of storage temperature.

Effect of Home Grinding on Properties of Brewed Coffee

<p>We present measurements of particle size distribution, density, loss of coffee on brewing and caffeine content in brewed coffee (as measured using Fourier Transform Infrared Spectroscopy) as a function of grinding time using a blade-type grinder. In general, there is not a lack of correlation between coffee properties and grinding for grinding times in excess of 42 s, but mass loss on brewing and caffeine content are both increased with grinding times between 0 and 42 s. In addition, we present evidence that this dependence of the composition of brewed coffee on grinding time is a function of increased coffee particle surface area that results from grinding, rather than increased loss of grounds into the brewed beverage or increased percolation time. Finally, we present a general recommendation for determining equivalency between small amounts of finely ground coffee and larger amounts of coarser-ground coffee.</p>

A simple heatsink for planetary mills

This paper proposes the use of a copper disk as a simple heatsink for planetary mills in order to limit or slow down the temperature increase during prolonged grinding. A series of grinding experiments have been performed in which the surface temperature of different parts of the grinding bowl has been determined as a function of grinding time. Three different experimental series were conducted: a reference series without the heatsink, and two series where the heatsink had been given the respective initial temperatures of 25 °C and −25 °C. As demonstrated in this paper, the proposed concept represents a cheap but effective way of limiting or slowing down the temperature increase occurring in the grinding bowl. The effect is of a magnitude that can be of considerable practical importance, and the concept can be employed on most planetary mills where the grinding bowl holder is designed to accommodate different bowl sizes.

Influence of suspension stability on wet grinding for production of mineral nanoparticles

Grinding behavior of nanoparticles in an attritor mill and the minimum achievable particle size are strongly influenced by the suspension stability. In the present work, suspension stability (i.e. ζ-potential) of nanoparticles was studied by measuring pH as a function of grinding time in the wet milling process. It was found that after a certain time in an attritor mill, there is no further size reduction and the average product particle size increases monotonically. One of the reasons is that the production of submicron particles leads to more particle–particle interactions and consequently pH of the suspension decreases with grinding time. Usually pH value is related to suspension stability and it can be enhanced by addition of NaOH solution. The maximum negative ζ-potential of −51.2 mV was obtained at pH of 12 for silica. The higher the ζ-potential with the same polarity, higher will be the electrostatic repulsion between the particles. Hence, the maximum electrostatic repulsion force was maintained by the adjustment of pH value in wet milling. The experiments were conducted at different pH conditions which were maintained constant throughout the experiments and nanosized particles were obtained consequently.

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A graphitized coke material obtained from petroleum residua was mechanically ground at different milling times between 0 and 100 h. Electrochemical reactions with both lithium and sodium are significantly altered as a function of grinding time. Short-time ball milling of graphite (1 and 5 h) induces a limited decrease in particle size and an increase in microstrain content. Simultaneously, alkali metal intercalation and electrolyte decomposition are hindered, and thus the irreversible and reversible capacities decrease. For longer milling time (up to 100 h), average crystallite size decreases and particles adopt a lamellar shape. Simultaneously, the irreversible capacity increases and correlates with an increase of the resistance, as obtained by impedance spectroscopy. Ex-situ XRD shows that extensively ground graphite samples need a higher discharge specific capacity to reach the formation of n-stages as compared to non-ground graphite, this being indicative of lithium incorporation in energetically different sites to the interlayer space. Sodium storage capacity increases with prolonged grinding time. This effect is shown here for the first time for graphitized cokes.

Electrochemical, textural and microstructural effects of mechanical grinding on graphitized petroleum coke for lithium and sodium batteries

A graphitized coke material obtained from petroleum residua was mechanically ground at different milling times between 0 and 100 h. Electrochemical reactions with both lithium and sodium are significantly altered as a function of grinding time. Short-time ball milling of graphite (1 and 5 h) induces a limited decrease in particle size and an increase in microstrain content. Simultaneously, alkali metal intercalation and electrolyte decomposition are hindered, and thus the irreversible and reversible capacities decrease. For longer milling time (up to 100 h), average crystallite size decreases and particles adopt a lamellar shape. Simultaneously, the irreversible capacity increases and correlates with an increase of the resistance, as obtained by impedance spectroscopy. Ex-situ XRD shows that extensively ground graphite samples need a higher discharge specific capacity to reach the formation of n-stages as compared to non-ground graphite, this being indicative of lithium incorporation in energetically different sites to the interlayer space. Sodium storage capacity increases with prolonged grinding time. This effect is shown here for the first time for graphitized cokes.

Kinetics of comminution in micro- and sub-micrometer ranges

Fine grinding in the area of particle size of a few micrometers is becoming an increasingly conventional process. For this range of grinding, the most suitable are the various types of agitated-ball mills. Despite the fact that this is a well known area of grinding, in terms of the required conditions, there are still many unknowns regarding the kinetics of grinding, particularly in the submicron range when we are approaching the lower grinding limit. We are often satisfied if the upper limit of granulation of the product (100% undersize) is obtained. We know that the significant parameters for very fine grinding are primarily the following: the size of grinding balls, the concentration of solid phase, the medium, the dispersion agent, the design of the pearl mill and, of course, the time of grinding (which relates, of course, to the energy consumption). All of these parameters can not be generalized for each grinding process separately, but the knowledge of the speed of grinding for individual particle size is very useful. In this paper we refer precisely to this range of granulation, investigating the laws of kinetics of wet grinding. The paper deals with the grinding of various substances, primarily fillers and pigments for commercial use. For the sake of comparison we also present the data regarding the kinetics of grinding in the planetary and vibration ball mills. The experimental data are presented in the form of a median particle size ( d 50) as a function of grinding time.

Effects of grinding and compression on crystal structure of anhydrous caffeine

The extent of the polymorphic transformation of anhydrous caffeine has been studied as a function of grinding time and compression pressure by using quantitative X-ray diffraction analysis. The measurements show that both grinding and compression induce the transformation from the metastable form I into the stable form II. The transformation can be observed even after 1 min grinding or by using a compression pressure of about 50 MPa in tableting. The degree of transformation is greater near the surface than in the middle part of the tablet.

Microsurface finishing of borosilicate glass with magnetic fluid grinding

Abstract A new microsurface finishing method of local area using magnetic fluid, abrasive grains and magnet is proposed. The profile of grinding surface of borosilicate glass is observed as a function of grinding time and magnetic fluid strength. Magnetic fluid and magnetic field can provide efficient and uniform finishing in a local area.

Effects of Ball Size and Particle Size on the Rate of Wet Ball-Milling

A lead-based relaxor material for multilayer ceramic capacitors was ground by ball-milling with partially stabilized zirconia balls of 1, 3 and 15mm in diameter and the effects of ball size and particle size of powder on milling rate were studied. Particle size distribution and specific surface area of powders were examined as a function of grinding time. Small zirconia balls in ball milling were effective to grind the powder to submicronmeter. In order to explain these experimental results on the milling rate, an equation for expressing the milling rate was proposed. The new equation is characterized by two parameters, ball size and particle size of the powder. The calculated and observed milling rates agreed well, and the effects of ball size and particle size on the milling rate were quantitatively confirmed It was found by estimating the proposed equation that milling rate of a powder had a maximum value at a ball size. Tha ball size which showed the maximum milling rate increased as particle size and mechanical strength of the powder increased.