Iron and aluminum association with microbially processed organic matter via meso-density aggregate formation across soils: organo-metallic glue hypothesis

Global significance of iron (Fe) and aluminum (Al) for the storage of organic matter (OM) in soils and surface sediments is increasingly recognized. Yet specific metal phases involved or the mechanism behind metal–OM correlations frequently shown across soils remain unclear. We identified the allocation of major metal phases and OM to density fractions using 23 soil samples from five climate zones and five soil orders (Andisols, Spodosols, Inceptisols, Mollisols, Ultisols) from Asia and North America, including several subsurface horizons and both natural and managed soils. Each soil was separated into four to seven density fractions using sodium polytungstate with mechanical shaking, followed by the sequential extraction of each fraction with pyrophosphate (PP), acid oxalate (OX), and finally dithionite–citrate (DC) to estimate pedogenic metal phases of different solubility and crystallinity. The concentrations of Fe and Al (per fraction) extracted by each of the three reagents were generally higher in meso-density fractions (1.8–2.4 g cm−3) than in the lower- or higher-density fractions, showing a unique unimodal pattern along the particle density gradient for each soil. Across the studied soils, the maximum metal concentrations were always at the meso-density range within which PP-extractable metals peaked at 0.3–0.4 g cm−3 lower-density range relative to OX- and DC-extractable metals. Meso-density fractions, consisting largely of aggregated clusters based on SEM observation, accounted for on average 56 %–70 % of total extractable metals and OM present in these soils. The OM in meso-density fractions showed a 2–23 unit lower C : N ratio than the lowest-density fraction of the respective soil and thus appeared microbially processed relative to the original plant material. The amounts of PP- and OX-extractable metals correlated positively with co-dissolved C across the soils and, to some extent, across the density fractions within each soil. These results led to a hypothesis which involves two distinct levels of organo-metal interaction: (1) the formation of OM-rich, mixed metal phases with fixed OM : metal stoichiometry followed by (2) the development of meso-density microaggregates via “gluing” action of these organo-metallic phases by entraining other organic and mineral particles such as phyllosilicate clays. Given that OM is mainly located in meso-density fractions, a soil's capacity to protect OM may be controlled by the balance of three processes: (i) microbial processing of plant-derived OM, (ii) dissolution of metals, and (iii) the synthesis of organo-metallic phases and their association with clays to form meso-density microaggregates. The current hypothesis may help to fill the gap between well-studied molecular-scale interaction (e.g., OM adsorption on mineral surface, coprecipitation) and larger-scale processes such as aggregation, C accrual, and pedogenesis.

Iron and aluminum association with microbially processed organic matter via meso-density aggregate formation across soils: organo-metallic glue hypothesis

Global significance of iron (Fe) and aluminum (Al) for the storage of organic matter (OM) in soils and surface sediments is increasingly recognized. Yet specific metal phases involved or the mechanism behind metal-OM correlations frequently shown across soils remain unclear. We identified density fraction locations of major metal phases and OM using 23 soil samples from 5 climate zones and 5 soil orders (Andisols, Spodosols, Inceptisols, Mollisols, Ultisols), including several subsurface horizons and both natural and managed soils. Each soil was separated to 4 to 7 density fractions using sodium polytungstate with mechanical shaking, followed by the sequential extraction of each fraction with pyrophosphate (PP), acid oxalate (OX), and finally with dithionite-citrate (DC) to estimate pedogenic metal phases of different solubility and crystallinity. The extractable Fe and Al concentrations (per fraction) generally showed unique unimodal distribution along particle density gradient for each soil and each extractable metal phase. Across the studied soils, the maximum metal concentrations were always at meso-density range (1.8–2.4 g cm−3) within which PP-extractable metals peaked at 0.3–0.4 g cm−3 lower density range relative to OX- and DC-extractable metals. Meso-density fractions, consisted largely of microaggregates based on SEM observation, accounted for on average 56–70 % of total extractable metals and OM present in these soils. The OM in meso-density fractions appeared microbially processed from the original plant material. The amounts of PP- and OX-extractable metals correlated positively with co-dissolved C among the soils and, to some extent, across the density fractions within each soil. These results led to a hypothesis which involves two distinct levels of organo-metal interaction – the formation of OM-rich, mixed metal phases having relatively fixed OM : metal stoichiometry and subsequent development of meso-density microaggregates via gluing properties of these organo-metallic phases by incorporating other organic and mineral particles such as phyllosilicate clays. Given that stable OM is mainly located in meso-density fractions, soil's capacity to protect OM may be controlled by the balance of following three processes: (i) microbial processing of plant-derived OM, (ii) dissolution of metals, and (iii) the synthesis of organo-metallic phases and their association with clays to form meso-density microaggregates. The current hypothesis may help to fill the gap between well-studied molecular scales interaction (e.g., OM adsorption on mineral surface, coprecipitation) and larger-scale processes such as aggregation, C accrual, and pedogenesis.

PERALUMAN 300

PERALUMAN 300 is a 5754 aluminum alloy in the wrought aluminum-magnesium family (5000 or 5xxx series). It is closely related to the alloys 5154 and 5454 (Aluminum Association designations that only differ in the second digit are variations on the same alloy). Of the three 5x54 alloys, 5754 is the least alloyed (highest composition % of aluminum), but only by a small amount. It is used in similar applications. As wrought alloy, it can be formed by rolling, extrusion, and forging, but not casting. It can be cold worked to produce tempers with a higher strength but a lower ductility. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance and surface qualities as well as forming, machining, and joining. Filing Code: Al-454. Producer or source: Lamineries Matthey SA.

Refino de grão de ligas alumínio- silício com ante-ligas Al-B

RESUMO Com o objetivo de conhecer a influência das partículas AlB2 e AlB12 na capacidade de refino de grão de uma liga Al-4B sobre ligas de fundição à base de alumínio-silício, realizou-se testes de refino TP1 da Aluminum Association variando-se as concentrações de AlB2 e AlB12. Para a caracterização química foram utilizadas as técnicas de espectrometria de emissão óptica e espectrometria de energia dispersiva (EDS). O método utilizado para medir os tamanhos de grão foi o do intercepto, através de uma lupa estereoscópica. Os resultados foram comparados com os do refinador convencional Al-5Ti-1B. A liga alumínio-silício utilizada foi a Al-11Si-0,1Mg, comum na produção de rodas automotivas. A liga Al-4B com 100% de partículas AlB2 apresentou a melhor capacidade de refino, proporcionando tamanhos médios de grãos de 0,26 mm na liga Al-11Si-0,1Mg, no tempo de amostragem de 5 minutos. A liga Al-4B com 100% de partículas AlB12 apresentou um resultado intermediário, com tamanhos médios de grãos de 0,43 mm na liga Al-11Si-0,1Mg, no tempo de 5 minutos. A liga Al-11Si-0,1Mg refinada usando-se o refinador convencional Al-5Ti-1B apresentou tamanho médio de grão de 0,63 mm após 5 minutos de amostragem, o pior resultado quando comparado com os refinadores Al-4B com 100% de partículas AlB2 e AlB12 respectivamente.

Uso do Nióbio como refinador de grão para Ligas de Alumínio-Silício

Com o objetivo de encontrar alternativas para o refino de grão de ligas alumínio-silício, um novo refinador foi experimentalmente produzido à base de nióbio, boro e alumínio (Al-3%Nb-1%B). Esta nova liga foi caracterizada quimicamente por espectroscopia de emissão óptica por plasma acoplado indutivamente (ICP-OES), microestruturalmente por microscopia eletrônica de varredura (MEV) e por espectrometria de energia dispersiva (EDS). Foi utilizado o teste TP1, da Aluminum Association, para medir a capacidade de refino desta nova liga sobre a liga Al-11%Si-0,1%Mg e compará-la com o refinador convencional TiBAl 5/1 (5% de titânio e 1% de boro). O tamanho de grão foi medido com uma lupa estereoscópica utilizando o método do intercepto da ABNT. Para os cinco minutos iniciais, o teste TP1 realizado com 1 kg/t da liga Al-3%Nb-1%B apresentou tamanhos de grãos semelhantes ao teste realizado com 5 kg/t de TiBAl 5/1, indicando que este novo refinador pode ser utilizado industrialmente para o refino de grão de ligas alumínio-silício, desde que o tempo de residência seja próximo de 5 minutos.

INFLUENCIA DA CONCENTRAÇÃO DE ALB2, TITÂNIO E ESTRÔNCIO NA MACRO E MICROESTRUTURA DE UMA LIGA ALUMÍNIO-SILÍCIO

Com o objetivo de verificar o efeito das possíveis interações entre AlB2, Ti e Sr sobre a macro e a microestrutura de uma liga Al-Si quase-eutética, foram feitos testes de refino de grão da Aluminum Association, variando-se a concentração de AlB2 (de 40 a 280 ppm de B), Ti (de 100 a 700 ppm) e Sr (de 50 a 200 ppm). O tamanho médio de grão das amostras foi medido através do método do intercepto e a modificação da estrutura eutética foi avaliada utilizando-se padrões internacionais. Observa-se que um aumento no teor de Ti favorece o refino da fase primária Al-alfa pelo AlB2. Para níveis de 300 ppm de Ti e 120 ppm de B, a modificação da estrutura eutética pelo Sr não foi deteriorada após a adição do AlB2, o que ocorre para taxas mais altas de adição de AlB2, devido a formação da fase SrB6. Portanto a adição de Ti é recomendada (quando propriedades elétricas e térmicas não são requisitos), por permitir trabalhar com taxas mais baixas de adição de AlB2 (120 ppm de B), obtendo excelente de refino de grão ( ~ 200 microns) e sem que ocorra o envenenamento do Sr pelo AlB2.

Organic Coatings to Prevent Molten Metal Explosions

Over 60 years ago the first reported molten metal explosion from a bleed-out during direct chill casting in an aluminium mill was reported. Soon thereafter, testing was performed to determine the root cause of the explosion. Upon determination of the root cause, an investigation to determine if any preventive measures could be instituted to prevent the explosions was conducted. Results found that a specific organic coating (e.g., Wise Chem E-212-F) prevented molten metal explosions, whereas some specific organic coatings initiated the explosions. Fifteen years ago the U.S. Department of Energy in conjuncture with the Aluminum Association reinvestigated the root cause of molten metal explosions. Testing revealed that an initiation or trigger had to be present for a molten metal explosion to occur. Testing identified three additional coatings that could afford protection.

AA 2524

Aluminum alloy 2524 is an advanced heat treatable alloy offering toughness and improved fatigue crack growth versus existing alloys. This datasheet provides information on composition, and physical properties as well as fatigue. It also includes information on corrosion resistance as well as heat treating. Filing Code: AL-389. Producer or source: The Aluminum Association Inc.