Chrome Flour

Pó de cromo em cerâmica
O pó de cromo é cromite em pó fino, também conhecido como pó de cromite, cromite de ferro e pó de cromo 325. Ocorre em abundância no sul da África. Embora tenha inúmeras aplicações que dependem das suas propriedades refratárias, uma das suas principais aplicações é no sector de cerâmica, como pigmento e esmalte. É valorizada também pela sua capacidade de coloração no fabrico de vidro, oferecendo um tom verde agradável em cenários rotineiros. É o principal minério do metal cromo. Como pigmento, o pó de cromo tem sido usado intencionalmente desde o século XIX.
Como é usada em pigmentos para cerâmica?
Com os estilos arquitectónicos e de design de interiores recentes virando na direção da escolha máxima para o consumidor final, é vital que todos os tipos de revestimentos de parede estejam disponíveis num conjunto de cores. Ladrilhos de cerâmica, tijolos e pavimentação não são excepção. Os pigmentos são adicionados durante o processo de fabrico.
A cromite tem sido associada a pigmentos castanhos para cerâmica, normalmente quando misturada com cromite de ferro e zinco, o que se deve aos sítios cristalográficos específicos que esses cromóforos ocupam no pó de cromo. Essas cores são produzidas a partir da mistura de óxidos de zinco, cromo e ferro que ocupam os sítios tetraédrico, octaédrico e intersticial, respectivamente, do espinélio, quando calcinados a mais de 1.000°C. Fundamentalmente, o pó de cromo é estável em temperaturas que excedem os 1.000°C, temperatura importante pois todas as cerâmicas são cozidas até certo grau.
Misturar o pó de cromo em proporções iguais com óxido de ferro, por exemplo, dará um pigmento que irá colorir o porcelanato de preto após calcinação a 1.200°C. Usar limonite (óxido de ferro hidratado) com pó de cromo numa proporção de 3:1 (a favor do cromo), irá resultar numa cor castanha convencional - ambas com apenas 3% em peso no ladrilho geral. Aumentar a proporção de limonite para pó de cromo de 1:1 irá, após a calcinação, produzir uma cerâmica com o tom altamente específico de "castanho chocolate". No exemplo do pigmento preto, podem ser feitas outras poupanças de custo, usando hematite residual como uma fonte de óxido de ferro.

Shades of pink are attainable when chromite is used in concert with zinc and aluminium oxides; at low firing temperatures alongside antimony and titanium oxides, chromite affords a yellow-orange hue. Classic green pigments - akin to those found when chromite is used to colour glass - can be obtained with using pure chromite, but care needs to be taken so as not to react with other metals present. If tin is present then a pink colour may be formed, zinc can cause a dirty brown pigment if present in large amounts. The presence of manganese alongside chrome flour can lead to colours varying between red and green depending on manganese concentration.

Grey pigmentation, especially prevalent for bricks and pavers, can be easily obtained using chromite. When used in a roof tile setting, it brings the added benefit of heat resistance. Shades between pale grey and almost black are also available by variations in powder size, with base body amounts of chromite of up to 10% in the ceramic. As a general rule of thumb, the particle size for most pigmenting applications has chromite in the region of 45um or 325mesh

How is it used in glazes for ceramics?

In comparison to pigments, glazes are applied after the manufacturing process and bear more similarities in behaviour to chromite as a glass colourant. Chromite materials have been identified in ceramic glazes dating from the late Bronze Age, providing for a muted grey-ish glaze alongside other materials. In some cases, chromite in a glaze can act as a nucleation point for the crystallisation of other components dissolved in the glaze; potentially giving rise to glazes that are metallic and/or lustrous in appearance.

Acting alone, like in glass, chrome flour provides for the customary green colour in a glaze. Adding more iron oxide will cause a change in favour of a greenish brown. Like in pigments for ceramics, the zinc iron chromite manifold presents a brown colouration in the glaze world. Should lead be present in large amounts, the colour is modulated to a more yellowish tint, whereas in the complete absence of lead, near black is observed. The presence of lead oxide compounds can also have an effect on the perceived vividness of a glaze, even with a high chromite content.

Chromite should be considered as distinctive from chromium oxide - the latter does not have iron present and can be combined with other metals to afford glazes in pink and purple.

Packaging

Choose the packaging and shipping arrangement that best suits your needs, from small packaging to bulk bags or custom sizes made just for you. We can accommodate virtually any size, from one metric ton to thousands.

Convenience

We maintain competitive pricing in an effort to win and retain your business for as long as you need us. Our goal is to meet the needs of every customer, including those with special requests and demanding production schedules.

A 15-day general turnaround for manufacturing allows us to get your compounds to you as quickly as possible, so you can keep up with the demands of your business. Contact us to get in touch with a distributor in your area if you don’t have time to wait for materials.

We currently ship to 44 countries across the world and we’re happy to ship to yours, too. The dependable and professional logistics channels we have in place make it easy to offer great pricing and service regardless of your location.

African Pegmatite

With 48 years as professionals in mining and manufacturing, we have the insight, network, and experience to offer you the very best in quality, service, and efficiency. We’ve been accredited by the ISO 9001 since 2002 and have most recently met the 2015 standard.

We aim to provide the very best materials available to our customers, and become your one-stop shop for colourants, minerals, compounds, and more. Take a look at our general clay and ceramic page to see all the other clay and ceramic products we have available.

If you’d like to become a distributor of African Pegmatite products, get in touch with us and we’ll customise an arrangement with you.