ФИЗИКО-ХИМИЧЕСКИЕ СВОЙСТВА УЛЬТРАДИСПЕРСНЫХ ПОРОШКОВ КРЕМНИЯ

Experimental investigations of ultradispersed silicon powder produced by mechanical grinding are conducted. The process of scaling powders using mechanochemical grinding was studied. It was found that the dimension of crystallites of the silicon powder determines their physical and chemical properties. Finely divided powders of silicon with a particle size ≤10 nm easily decompose water at room temperature into hydrogen and oxygen, they are easily oxidized by air oxygen and actively interact with hydroxides and acids with the release of significant amount of heat. The rate of saturation of micro- and ultradispersed powders with hydrogen at a constant rate of flow in the flow system depends on the temperature of the hydrogen hydrogenation process. It was found that the hydride formed at a low temperature (≤573 K) is in an equilibrium state when it is being hydrogenated in a flow reactor. The treated powder passes into a metastable state with the termination of the thermal action after hydrogenation. Hydrogen, entering the volume of micro- and ultradispersed silicon powder in the temperature range 373–723 K due to the diffusion process, can react not only with silicon atoms to form hydrides of the SiH2 type, but also with hydrides of less active radicals of the type of Si2H4, Si2H6. The hydrogenation process has two distinct stages. It is shown that the temperature of the transition between the stages is determined by the dispersion of micro- and ultradispersed silicon powders and by the structure of hydrides on the particle surface. As a result, it is established that the optimum temperature of hydrogenation should be taken at a temperature of 623 K, at which the maximum mobility of silicon atoms is reached during the formation of hydride. Sharp decrease in the hydrogen content is observed at a temperature above 723 K for the Si2H4 (SiH2).Проведены экспериментальные исследования ультрадисперсного порошка кремния, полученного путем помола полупроводникового монокристаллического кремния, изучен процесс масштабирования порошков с использованием механохимического измельчения. Установлено, что размерность кристаллитов порошков кремния определяет их физико-химические свойства. Ультрадисперсные порошки кремния с размером частиц ≤10 нм легко разлагают воду при комнатной температуре на водород и кислород, они легко окисляются кислородом воздуха и активно взаимодействуют с гидрооксидами и кислотами с выделением значительного количества тепла. Скорость насыщения микро- и ультрадисперсных порошков водородом при постоянной скорости потока в проточной системе зависит от температуры процесса гидрирования водорода. Установлено, что гидрид, образующийся при низкой температуре (≤573 К) находится в равновесном состоянии при гидрировании в проточном реакторе. С прекращением термического воздействия после гидрирования обработанный порошок переходит в метастабильное состояние. Водород, поступающий в объем микро- и ультрадисперсного порошка кремния в диапазоне температур 373–723 К за счет диффузионного процесса, может реагировать не только с атомами кремния с образованием гидридов типа SiH2, но и с гидридами менее активных радикалов типа Si2H4, Si2H6. Процесс гидрирования имеет две явно выраженные стадии. Показано, что температура перехода между стадиями определяется дисперсностью микро- и ультрадисперсных порошков кремния и структурой гидридов на поверхности частиц. В итоге установлено, что за оптимальную температуру гидрирования следует принять температуру 623 К, при которой достигается максимальная подвижность атомов кремния при формировании гидрида. При температуре выше 723 К для гидрида Si2H4 (SiH2) наблюдается резкое уменьшение содержания водорода

Methodology for generating a global forest management layer

The first ever global map of forest management was generated based on remote sensing data. To collect training data, we launched a series of Geo-Wiki (https://www.geo-wiki.org/) campaigns involving forest experts from different world regions, to explore which information related to forest management could be collected by visual interpretation of very high-resolution images from Google Maps and Microsoft Bing, Sentinel time series and normalized difference vegetation index (NDVI) profiles derived from Google Earth Engine. A machine learning technique was then used with the visually interpreted sample (280K locations) as a training dataset to classify PROBA-V satellite imagery. Finally, we obtained a global wall-to-wall map of forest management at a 100m resolution for the year 2015. The map includes classes such as intact forests; forests with signs of management, including logging; planted forests; woody plantations with a rotation period up to 15 years; oil palm plantations; and agroforestry. The map can be used to deliver further information about forest ecosystems, protected and observed forest status changes, biodiversity assessments, and other ecosystem-related aspects

Global forest management data for 2015 at a 100 m resolution

Spatially explicit information on forest management at a global scale is critical for understanding the status of forests, for planning sustainable forest management and restoration, and conservation activities. Here, we produce the first reference data set and a prototype of a globally consistent forest management map with high spatial detail on the most prevalent forest management classes such as intact forests, managed forests with natural regeneration, planted forests, plantation forest (rotation up to 15 years), oil palm plantations, and agroforestry. We developed the reference dataset of 226 K unique locations through a series of expert and crowdsourcing campaigns using Geo-Wiki (https://www.geo-wiki.org/). We then combined the reference samples with time series from PROBA-V satellite imagery to create a global wall-to-wall map of forest management at a 100 m resolution for the year 2015, with forest management class accuracies ranging from 58% to 80%. The reference data set and the map present the status of forest ecosystems and can be used for investigating the value of forests for species, ecosystems and their services