Hiroyuki Mizuta

GROWTH CONDITIONS AND GENESIS OF SPHERICAL AND PLATY KAOLINITE

Spherical and platy kaolinite crystals were prepared under several hydrothermal conditions. Spherical kaolinite was produced mainly at high solid/water ratio (1/4) and at low temperatures (150°-200°C). Platy kaolinite predominated in products from experiments with intermediate solid/water ratios (1/256-1/16) and at high temperatures. Boehmite predominated at low solid/water ratios (1/4096) at all experimental temperatures (180°-220°C). The results indicate that the growth of the spherical kaolinite was favored at high degrees of supersaturation, whereas the growth of the platy kaolinite was favored at relatively low degrees of supersaturation.

Spherical kaolinite; synthesis and mineralogical properties

Spherical kaolinite has been synthesized for the first time from noncrystalline aluminosilicate material in hydrothermal experiments conducted between 150° and 250°C and under autogenous vapor pressure. Spherules, whose mean diameters depended on growth conditions (0.1–0.6 μm), were formed surrounding the noncrystalline aluminosilicate in all products of 150° and 200°C runs and coexisted with platy or lath-shaped kaolinite in the products of 250°C runs. The estimated percentages of spherules in the products increased from about 1% in the 150°C-15 days product to about 74% in 200°C-8 days product, and decreased from about 21% in 250°C-2 days product to 0% in 250°C-8 days product. Lattice images by high-resolution electron microscope indicated that the spherules consisted of nearly concentric stackings of layers with a unit spacing of 7Å, which were sectored by radiating boundaries. The mean chemical composition of the spherules (Al2O3/SiO2 = 0.58) analyzed by the analytical electron microscope is similar to that of kaolinite (Al2O3/SiO2 = 0.5). Even in the case of the product abundant in spherule (200°C-8 days), X-ray powder diffraction patterns of the wetted products, e.g., of the 200°C-8 day run, showed the 7.14-Å (001) reflection of kaolinite. The 020 reflection was broad, indicating the existence of abundant (001) layer displacements. The b axis (8.94 Å) were within the kaolinite range (8.93–8.94 Å). No infrared absorption peaks were observed at 3550 cm−1 which would correspond to halloysite. The differential thermal analysis slope ratios of the endothermic peak at about 550°C (1.4–2.3) were in the kaolinite range (0.78–2.39).РезюмеСферический каолинит был первый раз синтезирован из некристаллического алюминосиликатного материала путем гидротермических экспериментов, проведенных при температурах от 150°С до 250°С и при автогенном давлении пара. Шарики, средние диаметры которых зависили от условий роста (0,1-0,6 μм), были образованы вокруг некристаллических алюминосиликатов во всех продуктах экспериментов при 150°С и 200°С и существовали с пластинчатым каолинитом в продуктах экспериментов при 250°С. Определенное процентное содержание шариков увеличивалось от 1% в продуктах, образованных при 150°С в течение 15 дней, до около 74% в продуктах, образованных при 200°С в течение 8 дней, а также уменьшалось от около 21% в продуктах при условиях 250°С-2 дня до 0% в условиях 250°С-8 дней. Отображения решетки при помощи электронного микроскопа с высокой равщиряющей способностью указывают на то, что эти шарики состояли из почти концентрических групп слоев с элементарным расстоянием 7 Å, которые были расчленены излучающими границами. Средний химический состав шариков (А12O3/SiO2 = 0,58), анализированный при помощи аналитического электронного микроскопа, был похож на состав каолинита (А12О3/SiO2 = 0,5). Даже в случае наличия избытка шариков в продуктах (200°С-8 дней), образы рентгеновской порошковой дифракции влажных продуктов экспериментов показали отражение 7,14 Å (001) каолинита. 020 отражение было широким, указывая на существование перемещений слоев 001. Оси Ь (8,94 Å) находились в каолинитовом диапазоне (8,93-8,94 Å). Не наблюдалось полос инфракрасной абсорбции при 3550 цμ−1, которые соответствовали бы галлоизиту. Отнощения наклонов эндотермических пиков дифференциального термического анализа при около 550°С (1,4–2,3) находились в каолинитовом диапазоне (0,78–2,39). [Е.О.]ResümeeKugeliger Kaolinit wurde zum ersten Mal aus nichtkristallinem Alumosilikatmaterial in hydrothermalen Experimenten synthetisiert, die zwischen 150° und 250°C und unter autogenem Dampfdruck durchgeführt wurden. Die Kugeln, deren durchschnittlicher Durchmesser von den Wachstumsbedingungen abhing (0,1–0,6 μm), umgaben in allen zwischen 150° und 200°C gebildeten Produkten das nichtkristalline Alumosilikat. In den bei 250°C entstandenen Produkten bildeten sie sich neben plattigen und leistenförmigen Kaoliniten. Der geschätzte Anteil der Kugeln in den Produkten nahm von etwa 1% in den bei 150°C nach 15 Tagen entstandenen Produkten auf etwa 74% in den bei 200°C nach 8 Tagen enstandenen Produkten zu. Weiters nahmen sie von etwa 21% in den bei 250°C nach 2 Tagen entstandenen Produkten auf 0% in den bei 250°C nach 8 Tagen entstandenen Produkten ab. Die Gitterbilder mittels hochauflösender Elektronenmikroskopie zeigten, daß die Kugeln aus einer nahezu konzentrischen Anordnung von Schichten mit einem Schichtabstand von 7 Å bestehen, die durch radiale Grenzen unterteilt sind. Der Durchschnittschemismus der Kugeln (Al2O3/SiO2 = 0,58), der mittels Mikrosonde bestimmt wurde, ist ähnlich dem von Kaolinit (Al2O3/SiO2 = 0,5). Selbst wenn in dem Produkt die Kugeln überwiegen (200°C, 8 Tage), zeigen die Röntgenpulverdiffraktometeraufnahmen der feuchten Produkte, z.B. das aus dem Experiment bei 200°C und 8 Tagen, den 7,14 Å (001) Reflex von Kaolinit. Der 020 Reflex war breit, was auf eine häufige Fehlordnung der 001 Schichten hindeutet. Der Abschnitt auf der b-Achse (8.94 Å) war innerhalb der bei Kaoliniten üblichen (8,93–8,94 Å). Bei 3550 cm−1 wurden keine Infrarot-Absorptionspeaks gefunden, die auf Halloysit hingedeutet hätten. Die Neigungsverhältnisse des endothermen Peaks bei 550°C (1,4–2,3) der differentialthermoanalytischen Untersuchung lag im Bereich der Kaolinite (0,78–2,39). [U.W.]RéuméLa kaolinite sphérique a été synthétisée pour la première fois à partir de matériel aluminosilicate non-cristallin dans des expériences hydrothermiques menées entre 150°C et 250°C et sous une pression de vapeur autogène. Des sphérules dont les diamètres moyens dépendaient des conditions de croissance (0,1–0,6 μm) ont été formées autour de l’aluminosilicate non-cristallin dans tous les produits des expériences à 150°C et 200°C et coexistaient avec la kaolinite en plaquettes ou en forme de lattes dans les produits des expériences à 250°C. Les pourcentages de sphérules estimés dans les produits ont augmenté d’à peu près 1% dans le produit 150°C-15 jours à à peu près 74% dans le produit 200°C-8 jours, et a diminué d’à peu près 21% dans le produit 250°C jours à 0% dans le produit 250°C-8 jours. Des images de lattice par microscope électronique à haute résolution ont indiqué que les sphérules consistaient d’empilement de couches presque concentriques avec un espacement d’unités de 7 Å, sectionnés par des limites radiantes. La composition chimique moyenne des sphérules (Al2O3/SiO2 = 0,58) analysée par le microscope électronique analytique est semblable à celle de la kaolinite (Al2O3/SiO2 = 0,5). Même dans le cas du produit abondant en sphérules (200°C-8 jours), les clichés de diffraction des rayons-X des produits mouillés, e.g., de l’expérience à 200°C-8 jours, ont montré la réflection 7,14-Å (001) de la kaolinite. La réflection 020 était large, indiquant l’existence d’abondants déplacements de couche (001). L’axe b (8,94 Å) est darts la gamme de la kaolinite (8,93–8,94 Å). Aucun sommet d’absorption infrarouge n’a été observé à 3550 cm−1, ce qui corresponderait à l’halloysite. Les proportions de courbes d’analyse différentielle thermique du sommet endothermique à à peu près 550°C (1,4–2,3) étaient dans la gamme de la kaolinite (0,78–2,39). [D.J.]

Effects of solution chemistry on the hydrothermal synthesis of kaolinite

The hydrothermal synthesis of kaolinite was examined in the Al2O3-SiO2-H2O system to study inhibitory effects of additional ions on the formation of kaolinite. Syntheses were carried out with amorphous starting materials and salt solutions of various concentrations in Teflon pressure vessels at 220°C for 5 days. The reaction products were characterized by XRD, IR, DTA-TG, NMR and TEM. In all of the runs using solutions with cation concentrations less than 0.001 M, no significant effect on the formation of kaolinite was observed. The inhibitory effect of the univalent cations Li+, Na+ or K+ was less than that of divalent cations such as Mg2+ or Ca2+. The addition of trivalent Fe3+ or excess Al3+ ions interfered with the formation of kaolinite significantly. Sulfate and acetate solutions interfered with the formation of kaolinite more than chlorides and nitrates. No crystalline product was obtained using a 1.0 M basic solution of carbonate or hydroxide. The addition of the lithium ion to the system affected the crystallization of kaolinite only slightly. The use of 0.1 M LiCl and LiNO3 solutions for the syntheses improved crystallization of kaolinite along the [001] direction.

Preparation of High-Density and High-Strength Alumina by Hip

Well-dispersed slurry was prepared for high-purity and submicron alumina powder, and dense green compact was formed by the slip casting system assisted with vacuum-pressure. The sample, sintered at 1240°C for 2 h in air, was subjected to the HIP treatment without capsule at 1050°-1400°C for 1 h in argon atmosphere. Extremely high-density (99.9%) and fine-grain (0.7-15 um in diam.) alumina ceramics were obtained. The HIP′ed sample showed high bend strength (-780 MPa).

Plasticity of Bodies of Synthetic Kaolinite Exchanged with Several Cations

In order to investigate the effect of exchangeable cations on rheology of clay body, plasticity of the synthetic kaolinite body whose surface cations were replaced by a particular one were measured by using Pfefferkorn methods. Unfrozen water (binding water) on the synthetic kaolinite surface were also measured by using low temperature differencial scanning calorimetory to estimate the binding forth of cations with water. Following results were obtained.1) The plasticity is encouraged by exchanging cations on synthetic kaolinite surface.2) Thickness of unfrozen water on the kaolinite surface is about 9-13A.3) Plasticity and thickness of unfrozen water film on the synthetic kaolinite closely relate to ionic radius and hydration energy of exchanged cation.