Thermal stability of potassium carbonate near its melting point

Lehman, Richard; Gentry, Jefffery S; Glumac, Nick

doi:10.1016/s0040-6031(98)00289-5

Cited by 140 publications

(79 citation statements)

References 8 publications

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“…The destabilization of support through reaction with alkali metal carbonate requires (i) the disappearance of potassium carbonate, which is otherwise stable at higher temperature, 51 and (ii) the release of CO 2 . In the samples under investigation, the increase of thermal treatment temperature really causes the progressive disappearance of carbonate (not yet decomposed after the drying at 373 K), as demonstrated by infrared spectroscopy on PdK4 samples treated in the 373-823 K range (see Figure 5a).…”

Section: Support Modifications Upon Catalyst Preparation and Treatmentsmentioning

confidence: 99%

Pd-Supported Catalysts: Evolution of Support Porous Texture along Pd Deposition and Alkali-Metal Doping

Pellegrini¹,

Leofanti²,

Agostini

et al. 2009

Langmuir

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Adsorption of N 2 at 77 K and scanning electron microscopy have been used to measure the changes in the support morphology, at nano-and microscale level, along the processes involved in the preparation of a supported Pd catalyst: Pd deposition, doping, and thermal treatments. Among the investigated supports, viz., activated carbons, γ-Al 2 O 3 , SiO 2 , and SiO 2 -Al 2 O 3 (SA), the SA one was found particularly sensitive to these processes, as a result of its high plasticity and reactivity. Involved processes can be summarized as follows: (i) During the Pd deposition, the support itself is partially dissolved and removed as a result of both the basicity of the precipitating agent and the final washing.(ii) When the undoped sample is thermally treated up to 823 K, only modest phenomena are observed. (iii) Upon doping with potassium carbonate, the support dissolution continues, and the greater the carbonate concentration, the greater the dissolution extent. In this case the dissolved material is not removed, but reprecipitates (partially outside the pores), during the subsequent drying at 393 K. (iv) When doped samples are thermally treated, the reaction between carbonate and support causes the mobilization of the support itself, with sintering phenomena that can reach the total collapse of the porous structure. The starting temperature of the pore collapse decreases with increasing potassium carbonate concentration. The modification of the support influences, directly or indirectly, the surface properties and the availability of Pd particles that can be doped or even covered by materials from support and made more or less accessible or even inaccessible by pore narrowing, widening, or blocking.

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Section: Support Modifications Upon Catalyst Preparation and Treatmentsmentioning

confidence: 99%

Pd-Supported Catalysts: Evolution of Support Porous Texture along Pd Deposition and Alkali-Metal Doping

Pellegrini¹,

Leofanti²,

Agostini

et al. 2009

Langmuir

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“…2 The preparation of dense and stoichiometric KNN ceramics 3,4 has however been a persistent challenge due to the hygroscopic nature of alkali carbonate precursors, 5 volatility of alkali oxides [6][7][8] and narrow sintering interval close to the solidus temperature. [9][10][11] As denser ceramics typically yield improved piezoelectric coefficients, many have endeavored to improve performance through optimizing synthesis and sintering procedures.…”

Section: Introductionmentioning

confidence: 99%

Sintering of sub-micron K 0.5 Na 0.5 NbO 3 powders fabricated by spray pyrolysis

Haugen

Madaro

Bjørkeng

et al. 2015

Journal of the European Ceramic Society

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K0.5Na0.5NbO3 (KNN)-based ceramics are promising lead-free piezoelectrics, but processing of these materials is an ongoing challenge. Here, we present a spray pyrolysis route to highquality KNN-based powders. Fine-grained (<100 nm as-prepared, ~130 nm calcined at 800 °C) and phase-pure KNN and Li0.03K0.485Na0.485Nb0.8Ta0.2O3 (KNNLT) powders were obtained from aqueous precursor solutions. Ceramics with 95 % of theoretical density and with normalized strain of 333 pm/V were obtained by conventional sintering. The sintering of KNN remained challenging even for the fine grained powders, and the origins of these processing challenges were investigated by dilatometry and electron microscopy. Coarsening into cuboidal grains, which strongly reduced the sinterability, was observed in alkali-oxide excess KNN, caused by the formation of a liquid phase at ~650 °C. We propose that the reactivity of alkali oxide with moisture and carbon dioxide at lower temperatures cause the formation of the liquid phase at the surface even for stoichiometric KNN powders.Evaporation, mainly of potassium oxide, at high temperatures was shown to cause the formation of a Nb-rich secondary phase. The segregation of a secondary phase and inhomogeneous distribution of K/Na are discussed in relation to sintering above the solidus temperature of KNN.

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“…Na análise termogravimétrica da CBLA (AM02), Fig. 2a, percebeu-se que o resíduo apresentou quatro perdas de massa características: a) de 30 a 220 °C, 3% provenientes da água adsorvida; b) de 380 a 480 ºC, 1,5% correspondente à matéria orgânica e à decomposição do Ca(OH) 2 indicadas em [21][22][23]. Na Fig.…”

Section: Resultsunclassified

“…4a percebe-se que a AM04 (cal de CBLA) apresentou três perdas de massa características: a) de 30 a 220 °C, 3% proveniente da água adsorvida; b) de 380 a 480 ºC, 19% correspondente à decomposição do Ca(OH) 2 em CaO+H 2 O; e c) acima de 600 °C, uma pequena perda decorrente da decomposição de K 2 CO 3 em K 2 O+CO 2 . Estas faixas de temperatura foram similares às indicadas em [21][22][23]. Salienta-se que o valor de 19% para a decomposição do Ca(OH) 2 em CaO+H 2 O obtido pela análise termogravimétrica confirmou o percentual de 24% de água combinada obtida durante a etapa de hidratação da AM04 (cal de CBLA, Tabela I), ratificando que a metodologia empregada utilizando hidratação com excesso de água, seguida de secagem em estufa, foi efetiva.…”

Section: Avaliação Da Produção De Cal De Cbla (Am02)unclassified

Cal produzida a partir de cinza de biomassa rica em cálcio

et al. 2018

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Resumo Neste artigo propõe-se a obtenção de cal hidratada a partir da cinza de lenha de algaroba (Prosopis juliflora), biomassa rica em cálcio. Devido à concentração expressiva de potássio na cinza de algaroba, uma etapa de lavagem se fez necessário uma vez que age como um fundente, impedindo a formação de estruturas de óxido de cálcio reativas na temperatura de decomposição do carbonato de cálcio. Assim, o processo de beneficiamento consistiu na coleta, peneiramento em malha ANBT NBR n° 200 (0,074 mm), lavagem em água quente (100 °C) para redução da concentração do potássio, calcinação e hidratação. A cal de cinza de algaroba produzida foi caracterizada pelas seguintes técnicas: análise granulométrica por difração a laser, fluorescência de raios X, difração de raios X e análise termogravimétrica TG/DTG. Após caracterização, os resultados da cal de cinza de algaroba foram comparados com os da cal CHI comercial e a norma ABNT. Os resultados obtidos evidenciaram que a cal de cinza de algaroba produzida apresentou propriedades físico-químicas e mineralógicas correspondentes às da cal comercial e composição química com 78% de hidróxido de cálcio (CaOH2), além de atender às especificações químicas e finura recomendada pela ABNT, sendo classificada assim como uma cal CHI do tipo cálcica.

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Thermal stability of potassium carbonate near its melting point

Cited by 140 publications

References 8 publications

Pd-Supported Catalysts: Evolution of Support Porous Texture along Pd Deposition and Alkali-Metal Doping

Pd-Supported Catalysts: Evolution of Support Porous Texture along Pd Deposition and Alkali-Metal Doping

Sintering of sub-micron K 0.5 Na 0.5 NbO 3 powders fabricated by spray pyrolysis

Cal produzida a partir de cinza de biomassa rica em cálcio

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