Use of wollastonite in nonfritted zirconium glazes

Abstract

The possibility of using wollastonite as one of the main components in non-fritted opacified glazes for sanitary ceramics is demonstrated. The main physicochemical properties of synthesized coatings are determined, the specifics of their structure and phase composition are analyzed.A topical problem of ceramic production is the expansion of material resources for the porcelain-faience industry and simultaneous upgrade of product quality. Wollastonite is of great interest in this respect.This raw material is white-colored powder belonging to pyroxenoides made up by [SiO 4 ] tetrahedron chains, whose bases are not in the same plane, even approximately, but are differently oriented in such a way that the chain pattern is repeated after each third tetrahedron. Two modifications of wollastonite are known: a-CaSiO 3 (pseudowollastonite) and b-CaSiO 3 (proper wollastonite), which are closely interrelated [1]. Pseudowollastonite crystallizes in the pseudohexagonal syngony and wollastonite in the triclinic syngony. At a temperature of 1125°C wollastonite is irreversibly transformed into pseudowollastonite with a slight volume alteration. Its melting temperature is 1540°C, the density of a-wollastonite is 3.09´10 3 kg/m 3 , and that of b-wollastonite 2.87´10 3 kg/m 3 . Its Mohs hardness is 4.5 -6.0. The CLTE of a-wollastonite is 118´10 -7 K -1 , and that of b-wollastonite 65´10 -7 K -1 . Wollastonite crystals have a needle-like shape; besides, fibrous and discoid crystals are found as well [2].Analysis of published data [2,3] indicates that wollastonite is most frequently used in the production of construction materials, in particular, in the production of facing tiles. Wollastonite additives range from 15 to 65% (here and elsewhere wt.%) depending on the chemical composition. It is known that wollastonite is used in the production of lowmelting glazes, which makes it possible to lower the frit content to 20% and, accordingly, decrease the cost of the glaze. However, no published data have been found on the use of this component in nonfritted glazes and its effect on the properties of coatings.We have attempted to fill this vacancy in the systematic study of the physicochemical (luster, whiteness, CLTE, microhardness) properties of coatings and to reveal a correlation between the said properties and the compositions of nonfritted glazes for sanitary ware made from porcelain mixtures.For our study we selected wollastonite concentrate VP-25 (hereafter "wollastonite") produced by the TransResurs Company (Russia) according to standard TU 5726-001-50889697-01. The averaged chemical composition of wollastonite is as follows (%): 50.00 SiO 2 , 0.16 Fe 2 O 3 , 45.20 CaO, and 0.61 calcination loss.X-ray phase analysis of wollastonite concentrate indicated that the material mainly includes wollastonite; a-quartz is present in insignificant quantities.Wollastonite concentrate was introduced in an amount of 55% into previously analyzed glazes of series 1, 2, and 3 [3] with zircosil content equal to 10.0, 12.5, and 15.0%, respectively...

Use of colemanite for improving the quality of unfritted glazes

“…When heated colemanite dissolves in hydrochloric acid, and it is insoluble in water. Accompanying minerals are gypsum CaSO 4 , kernite Na 2 B 4 O 6 (OH) 2 3 ] triangle, which are joined at common vertices, forming a closed ring. Calcium atoms and water molecules are present between the chains.…”

“…The base composition chosen for the investigations was a composition consisting of unfritted opacified glaze [3], containing Chupitskoe pegmatite, quartz sand, zircobite, wollastonite concentrate, Belgorod chalk, Vesko-Granitik refractory clay, and Glukhovetskoe kaolin. It should be noted that in our investigations we used, instead of ordinary quartz To investigate the influence of colemanite on the properties of glass-crystalline coatings for ceramic sanitary ware, the coatings were synthesized by introducing colemanite into the batch compositions in amounts ranging from 3 to 15% (above 100%) with a 3% step variation.…”

Esmaltes para baldosas cerámicas preparados con una nueva materia prima borácica

“…En unos casos, aunque estos eran rápidos, las temperaturas máximas necesarias eran superiores a 1200ºC (44) , y en otros, aunque las temperaturas máximas utilizadas se encontraban entre 1180ºC y 1200ºC, eran necesarios ciclos de cocción muy largos. (45) En otros trabajos encontrados en la bibliografía se evaluaba la posibilidad de preparar esmaltes sin fritas con agentes fundentes tales como residuos de la industria de la minería o materias primas borácicas tradicionales, pero los vidriados resultantes, o bien estaban fuertemente coloreados (12-15 % Fe 2 O 3 ) (46) , siendo por tanto de escaso interés cerámico, o bien eran muy fundentes, con temperaturas de sellado inferiores a 1100ºC (47,48) , presentando además un aspecto mate (49,50) o coloreado (51) . Por estas razones puede considerarse que, en la práctica y hasta la fecha, no hay constancia del uso industrial de esmaltes no fritados en la fabricación de baldosas cerámicas.…”

“…Tradicionalmente, si sólo se dispone de datos a gradientes de velocidad altos, también se utiliza otro tipo de representación gráfica para describir el tipo de flujo, en la que se muestra la variación de la tensión de cizalla con el gradiente de velocidad, en coordenadas lineales (Figura 2.31 b). En estas gráficas se puede apreciar fácilmente, a partir de la forma de la curva (lineal, convexa, cóncava), el tipo de comportamiento del fluido (45) (newtoniano, pseudoplástico, dilatante) en el intervalo de gradientes de velocidad altos (>10 s -1…”

“…La matidez del vidriado resultante se debe a la considerable cantidad de grandes cristales de wollastonita uniformemente distribuidos en el vidrio residual. 196 En consecuencia, en las nuevas composiciones a ensayar se introdujeron materias primas que contuvieran calcio en su composición, como la wollastonita.…”