The Upper Cretaceous (Maastrichtian) Whitemud Formation is a potentially commercial kaolin deposit located in southern Saskatchewan and southeastern Alberta. The Whitemud Formation contains a lower kaolinitic sandstone, a middle lignite and carbonaceous shale, and an upper interbedded siltstone and claystone. The sediments that comprise the rocks of the Whitemud Formation were deposited on alluvial or upper deltaic plains located along the northwest flank of the Williston Basin.

Mineralogy and textures were determined by X-ray powder diffraction, scanning electron microscopy, and optical microscopy. Kaolinite abundance increases upward from the underlying rocks of the Eastend Formation through the Whitemud Formation, and the abundance of smectite, micas, and feldspars decreases from the Eastend Formation into the Whitemud Formation. Vermiform kaolinite crystals are in close spatial association with feldspar and mica grains. Near the top of the Whitemud Formation, etched quartz and feldspar grains, and gibbsite suggest the presence of a strong chemical leaching environment.

Mineral distributions, presence of root remains, pedologic mottles, grain coatings composed of clay, and soil horizons indicate the Whitemud Formation sediments were modified by intense weathering in a paleosol environment.

Kaolin concentrated from selected kaolinitic sandstone deposits, and beneficiated by oxidation, leaching, and high-intensity wet-magnetic separation has a product brightness up to filler quality. Recovery of lowabrasion kaolin is low and viscosity of a fine-particle kaolin fraction is high. Economics of producing a wet-processed filler-grade kaolin is marginal.

Ice skates are remarkably slippery across a wide range of conditions. We propose, based on earlier observations and new modeling, that an ice-rich slurry forms rapidly beneath a skate blade during each stride to lubricate the interface. Crushing from normal load and abrasion from sliding provide ice particles and heat to the slurry, with average contact pressures approaching melting pressures for the bulk ice. Shearing of the slurry by forward motion generates additional heat to melt the ice particles at the pressure-reduced temperature. We model these mechanics and link the viscosity of the resulting slurry to its ice fraction, which controls slurry-film thickness via lateral squeeze-flow. The slurry properties quickly converge to establish a highly efficient lubricating film that provides the characteristically low skate friction across a wide range of conditions. Although our 1D model greatly simplifies the complex interaction mechanics, its predictions are insensitive to most assumptions other than the average contact pressure. The presence of ice-rich slurries supporting skates merges pressure-melting, crushing, abrasion and lubricating films as a unified hypothesis for why skates are so slippery across broad ranges of speeds, temperatures and normal loads.

The mechanics underlying ice–skate friction remain uncertain despite over a century of study. In the 1930s, the theory of self-lubrication from frictional heat supplanted an earlier hypothesis that pressure melting governed skate friction. More recently, researchers have suggested that a layer of abraded wear particles or the presence of quasi-liquid molecular layers on the surface of ice could account for its slipperiness. Here, we assess the dominant hypotheses proposed to govern ice–skate friction and describe experiments conducted in an indoor skating rink aimed to provide observations to test these hypotheses. Our results indicate that the brittle failure of ice under rapid compression plays a strong role. Our observations did not confirm the presence of full-contact water films and are more consistent with the presence of lubricating ice-rich slurries at discontinuous high-pressure zones (HPZs). The presence of ice-rich slurries supporting skates through HPZs merges pressure-melting, abrasion and lubricating films as a unified hypothesis for why skates are so slippery across broad ranges of speeds, temperatures and normal loads. We suggest tribometer experiments to overcome the difficulties of investigating these processes during actual skating trials.

Growers desire more techniques to control weeds in horticultural crops that are grown organically and consumed directly, such as red raspberry. Abrasive grit emited via high air pressure is a new method for controlling weeds. Grit derived from corn cobs was examined for its efficacy during the year of raspberry establishment for 2 to 3 years at three sites (seven site-years) and compared with efficacy of hand-weeding as well as no weed control. Grit was applied once or twice weekly after raspberry transplantation in spring until weed emergence ceased in mid to late July. Weeds and raspberry growth were assessed in August. Grit was effective in controlling broadleaf weeds, averaging 94% control across site-years, but control of grass weeds was less than 10%. Total weed (broadleaf plus grass) control across site-years ranged from 51% to 96% and averaged 78%. Raspberry cane growth was affected by weeds, and grit-weeding at least partially alleviated these effects. Thus, abrasive grit allows growers to manage broadleaf weeds effectively without herbicides or soil tillage. However, additional research is needed to determine the correct amounts and timing of grit applications, as well as more efficacious types of grit, to control grass weeds.

Sequences of quartz-rich coarse (20−63 μm) silt occur in many low- and midlatitude unglaciated arid and semiarid areas and have been termed “desert loess.” The processes by which these deposits are generated have been debated for decades. All hypotheses to explain their origin seek to provide mechanisms for the generation of silt-sized material without glacial grinding, which is the main process involved in the production of coarse silt at high latitudes. Possible mechanisms for the formation of coarse silt in arid regions include derivation from preexisting siltstones, mechanical weathering of silicate rocks, and abrasion of sand grains in active dune environments during intense transport events. Examination of the characteristics of desert loess and field and laboratory experiments to assess the role of dune areas as a source of coarse silt by abrasion and/or resuspension of residual fines suggests that many loess sequences are dominated by locally derived coarse silt. Improvements in the characterization of desert loess particle size, mineralogy, and geochemistry are needed, however, to identify sources and sinks of coarse silt, especially when combined with climatic back-trajectory analysis. Properly scaled experiments and modeling of particle collisions will also help to better quantify the effectiveness of abrasion in the generation of coarse silt in support of field observations.

The long-accepted theory to explain why snow is slippery postulates self-lubrication: frictional heat from sliding melts and thereby lubricates the contacting snow grains. We recently published micro-scale interface observations that contradicted this explanation: contacting snow grains abraded and did not melt under a polyethylene slider, despite low friction values. Here we provide additional observational and theoretical evidence that abrasion can govern snow kinetic friction. We obtained coordinated infrared, visible-light and scanning-electron micrographs that confirm that the evolving shapes observed during our tribometer tests are contacting snow grains polished by abrasion, and that the wear particles can sinter together and fill the adjacent pore spaces. Furthermore, dry-contact abrasive wear reasonably predicts the evolution of snow-slider contact area, and sliding-heat-source theory confirms that contact temperatures would not reach 0°C during our tribometer tests. Importantly, published measurements of interface temperatures also indicate that melting did not occur during field tests on sleds and skis. Although prevailing theory anticipates a transition from dry to lubricated contact along a slider, we suggest that dry-contact abrasion and heat flow can prevent this transition from occurring for snow-friction scenarios of practical interest.

The unique properties of clays make them suitable for a large number of applications. Among the procedures that can be used to characterize clayey materials, the assessment of the abrasion and the abrasiveness index can be employed to predict the mechanical behaviour of clay samples. However, only a limited number of references to these testing procedures are available in the literature. Several Portuguese clayey samples were collected and the <63 μm fraction was analysed. The main clay minerals present are kaolinite, illite and smectite. The abrasiveness index depends on the granulometric and mineralogical compositions. A lower abrasiveness is induced by the presence of a high abundance of the <2 μm fraction, small mean particle size and a large phyllosilicate content . Kaolinite and illite show good correlation with the abrasiveness index, while smectite decreases abrasion.

The mechanics of snow friction are central to competitive skiing, safe winter driving and efficient polar sleds. For nearly 80 years, prevailing theory has postulated that self-lubrication accounts for low kinetic friction on snow: dry-contact sliding warms snow grains to the melting point, and further sliding produces meltwater layers that lubricate the interface. We sought to verify that self-lubrication occurs at the grain scale and to quantify the evolution of real contact area to aid modeling. We used high-resolution (15 µm) infrared thermography to observe the warming of stationary snow under a rotating polyethylene slider. Surprisingly, we did not observe melting at contacting snow grains despite low friction values. In some cases, slider shear failed inter-granular bonds and produced widespread snow movement with no persistent contacts to melt (μ < 0.03). When the snow grains did not move and persistent contacts evolved, the slider abraded rather than melted the grains at low resistance (μ < 0.05). Optical microscopy revealed that the abraded particles deposited in air pockets between grains and thereby carried heat away from the interface, a process not included in current models. Overall, our results challenge whether self-lubrication is indeed the dominant mechanism underlying low snow kinetic friction.

Organic growers need additional tools for weed control. A new technique using abrasive grit propelled by compressed air was tested in field plots. Grit derived from corncobs was directed at seedlings of summer annual weeds growing at the bases of corn plants when the corn was at differing early stages of leaf development. Season-long, in-row weed control exceeded 90% when two or three abrasion events were coupled with between-row cultivation. Timing of weed abrasion was critical, with highest levels of control corresponding to the one- and five-leaf stages or the one-, three-, and five-leaf stages of corn development. Corn yields associated with these treatments were equivalent to those of hand-weeded controls in which no abrasive grit was applied. Thus, air-propelled abrasive grit applications at the one-, three-, and five-leaf stages of corn controlled weeds sufficiently to prevent weed-induced reductions in corn grain. Additionally, these applications were not harmful to corn plants. This new concept for weed control may be of interest to organic crop managers.

Spectral observations show that volcanic glass is the dominant ingredient of the aeolian landforms which cover the northern lowlands on Mars. Surface winds subject these sands to physical alteration processes in the present-day surface environment. This work highlights the role of glaciovolcanism throughout Mars’ geologic history and the parallels with landforms and materials found in Iceland. As the physical properties of Martian volcanic glass particles are difficult to constrain from orbit, Icelandic materials can provide valuable insights in their transport and modification characteristics. The processing of glass grains by environmental processes by means of the dune transport cycle is discussed. Experiments targeted the grain-size alteration effects experienced during the dune transport cycle, including the effect of ‘low-energy’ avalanching and ‘high-energy’ aeolian regimes (i.e. particle rolling and saltation). Saltation transport was found to rapidly alter grains and particle size distributions, which contributes to a positive feedback loop where the new smaller grains are mobilised more easily after fracturing and surficial abrasion. Post-depositional physical alteration therefore needs to be reconciled with the present-day silicic spectral signatures of these glasses in order to infer the relevant landform genetic. This effort is especially relevant in respect to the loss of possible signatures of biochemical alteration from microbial interactions, as glaciovolcanic environments are favourable habitats for life. As chemical and physical weathering is limited to the grain exterior, the grain interior may still retain a geochemical record of the subglacial eruption environment in which these grains were formed. Quantification of the volatiles sequestered in the glass can therefore be used to identify the formative conditions of the amorphous component in aeolian sediments.

This paper addresses the formation processes at an unparalleled Bronze Age settlement in the Iberian Meseta. The site of El Cerro (Burgos, Spain) presents a series of challenging features: the simultaneous inhumation of three subadults alongside a dwelling quarter and adjacent pits, some of them filled with apparent formality, including such anachronistic elements as Neolithic and Beaker items and several placed deposits, such as a leg of a cow. A critical evaluation of the contextual dataset, a re-fitting operation, and an assessment of the abrasion and size of a ceramic sample were carried out. The archaeological peculiarities of the site are explained as a contextually specific cultural response to a grievous and traumatic episode: the death of three young siblings, which entailed the abandonment of the settlement through prescribed practices. Some depositions are a product of recognizable intentionality, while others are regarded as unintended cumulative outcomes.

Dental wear is deterioration as a result of use. It has existed since the beginning of mankind in all civilizations and cultures. It occurred routinely and intensely in early populations but was considered to be a physiological process. Ideas about dental wear are not as clear today because while it is less pronounced it sometimes appears in pathological patterns. Moreover, it is produced by many complex mechanisms acting in synchrony or sequentially, in synergy or additive, in patterns that often mask its true origins. In an effort to ameliorate the means of preventing and diagnosing dental wear and improving our understanding of its diverse manifestations, the primary objective of this article will be to present the principal mechanisms that produce it as well as their consequences. To organize our presentation we have adopted a tribological approach, focusing on the friction, wear, and lubrication of interacting surfaces.

Face au réchauffement climatique lié à l’effet de serre, les constructeurs automobilespoursuivent leurs efforts dans la réduction des émissions de CO2. Le ticketd’entrée pour répondre à ces contraintes, tout en réduisant les coûts d’investissement,est d’optimiser les technologies de finition des fûts de carter cylindres des moteurs.Toutefois, l’acceptation des surfaces issues de ces technologies de finition, notamment lerodage, est pilotée par un contrôle visuel associé à des critères empiriques d’état etaspect de surface. Le but du présent travail est de proposer une méthodologie objective decaractérisation de la qualité de surface, basée sur une analyse multi-échelle de latexture. Différents critères de topographie et d’aspect de surface ont été définis. Ilsont été appliqués pour l’étude de l’impact de la vitesse d’expansion des rodoirs sur lesvariations de la qualité de surface obtenue. Des essais instrumentés ont été menés, afinde suivre l’évolution des paramètres physiques relatifs au rodage, tels que les énergiesspécifiques requises à chacune des configurations. Cette étude démontre le potentiel de laméthode développée à définir des corrélations objectives entre les paramètres process etla qualité de surface après rodage.

Les succès des applicationsde superfinition par toilage ont été longtemps attribués à l'artd'appliquer des combinaisons variées de conditions et de séquences,pour un dispositif de toilage particulier, sans aucune méthodeapparente établie. Du point de vue laïque ceci pourrait semblervrai. Toutefois il y a des mécanismes physiques bien définis quisont essentiellement de nature fondamentale. Une descriptionénergétique du procédé de toilage est introduite. La variabled'énergie dissipée est considérée pour étudier l'effet du temps detoilage et observer l'influence supposée d'"alignement" (oscillationaxiale de la bande abrasive). Deux régimes de toilage sontidentifiés et ainsi discutés.

Nous proposons dans cet article d'analyser un nouveau procédé de polissage automatique : Ecoclean, qui est développé principalement pour la préparation de prothèses dentaires. En faisant varier les conditions expérimentales (matériau étudié, durée de traitement, présence ou non d'acide, présence ou non d'aiguilles) nous obtenons des états de surface différents. Pour chaque échantillon l'état de surface est caractérisé à l'aide d'un rugosimètre tactile et le calcul d'une centaine de paramètres de rugosité. Nous recherchons ensuite à l'aide du logiciel MESRUG, que nous avons développé dans notre laboratoire, les paramètres de rugosité qui sont les plus pertinents pour caractériser l'état de surface en fonction des conditions expérimentales. Le polissage automatique est comparé au polissage manuel. Cette méthode peut être utilisée pour définir les conditions expérimentales permettant d'obtenir un état de surface répondant à des critères de rugosité déterminés.

Le temps de cycle et la fréquence d'oscillation sont des variables "process" majeurs en technologies avancées de superfinition par toilage. Cet article examine leur rôle en liaison avec les mécanismes physiques activés (coupe, labourage ou glissement). On introduit ainsi une description énergétique du procédé de toilage. Celle-ci exploite la variable d'énergie dissipée pour étudier l'effet du temps de toilage et observer l'influence supposée d'alignement (oscillation axiale de la toile abrasive). Deux régimes de toilage sont identifiés et ainsi discutés.

La topographie de surface est une caractéristique à prendre en considération au même titre que la composition chimique pour décrire la fonctionnalité d'une surface. Cette topographie peut être décrite par des paramètres de rugosité d'amplitude, de fréquence ou hybrides. L'évolution de deux paramètres d'amplitude Ra et Rt en fonction de la longueur d'évaluation est ici étudiée sur un acier inoxydable de type 316L dont la surface est obtenue par polissage pour différents grades de papier. Cette étude montre l'existence de trois régimes en fonction de l'échelle d'observation des valeurs de Ra et Rt. Un premier régime où l'endommagement des surfaces ne comporte pas de loi d'échelle entre les différents grades de papier. Un régime transitoire est aussi identifié et caractérisé par un paramètre d'évaluation appelé Cut-Off qui suit une loi logarithmique en fonction de la taille de grain du papier. Enfin un troisième régime où les paramètres de rugosité suivent une parfaite loi d'échelle prouve que pour ce régime les mécanismes d'endommagement sont identiques à des échelles différentes.

The lack of botanical remains from farming sites in Africa remains a serious archaeological problem. This paper discusses how the indirect evidence of pottery may help to evaluate grain farming in African archaeology.