News AND Events

Faster Firing Glazes: Borates in Ceramics

:: Wednesday, March 7, 2018

Pre-dating the wheel by a few thousand years, pottery is one of the oldest human technologies. Shaped by Neolithic hands, the earliest objects were vessels for transporting goods as well as small figurines. As people developed, so did their means of creating pottery: Firing in open pits progressed to using higher temperature ovens and kilns. Later, humans created a variety of means for protecting and decorating their work. Yet, ceramic manufacturing remained mostly unchanged for centuries. Finally, the industrial revolution created a whiteware ceramics industry which included everything from the mass production of floor and wall tiles to porcelain sinks and electrical insulators. Comparable developments in raw material formulation have been less radical. For most of human history, potters have used the unchanged clay they pulled directly from the earth. The advent of industrial production necessitated consistent, standardized product manufacturing.

What Is Whiteware?

The term whiteware covers most categories of ceramics apart from heavy clays (bricks, blocks, and roof tiles), concrete and cement, refractories, and technical ceramics. Today, the huge whitewares market mainly consists of floor and wall tile, sanitary ware, and tableware. Nearly all whiteware products are glazed; the glazes for tile typically contain borates.

Frits and Glazes for Ceramics

Glazes are thin coatings applied to ceramic substrates before the firing process. The glaze can be applied using a variety of techniques, including wet methods such as waterfall and spray applications, and dry methods such as dry pressing. During firing, the glaze melts and forms an impervious, glassy coating which is fused onto the ceramic substrates to protect and beautify it. Although by weight glazes tend to account for less than 5% of the whiteware body, they provide most of the aesthetic appeal and technical characteristics—especially protection from physical or chemical damage.

Glazes consist of a mixture of various raw materials including clay, water and “frits”. Frits are a powdered glass, created by fusing and then quenching raw materials. This glass is milled to a powder and added to the glaze. Fritting has the following benefits:

  • Soluble components are rendered insoluble
  • Glaze melting point is reduced
  • Elimination of water
  • Fewer total materials in the process

Frit formulations depend upon a number of factors including:

  • Product type
  • Application method
  • Firing process, time, and temperature

How Has the Formulation of Frits Changed?

Multiple factors have created complex, new demands on frit makers and glaze manufacturing:
  • Advancements in whiteware process technology
  • Faster firing at higher temperatures
  • Exacting worldwide quality standards Increasing legislation relative to health and emissions

Certain tried and tested frits perform well in the new processes; others may seem adequate for the job but in practice fall short of optimizing the advanced technology. Some frits are less able to cope technically with the new firing speeds, quality standards, or emissions controls.

Correct borate use remains a key factor in optimal frit performance. The choice of borate depends on many factors, including:

  • Processing conditions of the final ceramic articles
  • Composition of the final glaze and its requirement for secondary oxides, such as sodium and calcium
  • Cost and local availability of borates and other raw material ingredients

Anhydrous borax is usually the preferred sodium borate on technical grounds, since it removes the necessity of driving off water of crystallization; Neobor® pentahydrate borax is the lower-cost alternative that is widely used.

A Global Partner for the Ceramics Industry

U.S. Borax has contributed to the development of successful frit formulations. The company’s laboratories assess the performance of borates in fritting and glazing and cooperate in new product development. Much work has been undertaken for, or in conjunction with, partners in various segments of the ceramic industry. U.S. Borax now has a unique corpus of (non-proprietary) data and experience that is at the service of frit and whiteware manufacturers globally.

Using borates to control the melt and fine-tune the final glaze properties is a particular area of expertise for U.S. Borax. We have also refined borate use in:

  • Initiation of glaze formation
  • Increasing the refractive index
  • Improving surface durability
  • Reducing the thermal expansion coefficient of the glaze coating which can ensure a perfect thermal fit between glaze and body

The move to higher temperatures for faster tile firing necessitates changes in the boric oxide (B2O3) content of frits and the near elimination of alkali and lead oxides. Originally used as the principal fluxes in standard frit bases, those oxides are now being replaced by increasing amounts of calcium, magnesium, and zinc oxides. In formulations where sodium is undesirable, boric acid, boric oxide, and hydroboracite are viable sources of B2O3.

Such, typically, are implications of any new technology. Changes cause chain reactions throughout the industry—and form the essential reason why U.S. Borax relies on a multi-disciplinary ceramics team consisting of chemists, materials scientists, chemical engineers, and market experts in Europe and America. U.S. Borax research and support helps to improve product and manufacturing performance, maximize borate benefits, and develop frit recipes that take full advantage technically, economically, and aesthetically of the newest possibilities.

Where will borate research take us next?

Read more about borates in glazes and enamels
 


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U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 500 customers with more than 1,700 delivery locations globally. We supply 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles east of Los Angeles.  Learn more about Rio Tinto

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