Amine-reactive surface chemistry of zinc phosphate glasses
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Surface chemical studies on zinc phosphate glasses were carried out with an ammonia probe using FTIR and XPS. Low softening point zinc phosphate glasses can be co-extruded with high softening point polymers to form polymer filled blends. NH 3 reacts with P - O H groups (Br0nsted acid sites) to form bound NH 4 + and with the zinc ions (Lewis acid sites) to form coordinately bound NH 3 . Bulk nitridation reactions, forming various P - N bonds to >100 nm, occur concurrently. The glass surfaces were depleted in Zn compared to the batch compositions. Exposure to ambient water vapor removed Lewis acid bound ammonia; aqueous washing removed both types. Di- and tri-methyl amines also reacted with surface Br0nsted and Lewis acid sites. These amine reactions have the potential for binding polymer chains to the glass surface.
I. INTRODUCTION
II. EXPERIMENTAL
Melt blends are a mixture of a low melting point zinc phosphate glass and a polymer with overlapping softening temperatures (typically 300°-400 °C) which can be co-extruded and molded in a single step.1"3 The advantages of inorganic phase filled polymers are well known: these fillers contribute hardness, stiffness, impermeability, fire retardency, and lower cost. Some polymers with suitably high softening points include aromatic polyetherketones, polyetheretherketones, and polyetherimides. Glasses with overlapping softening temperatures include some of the zinc phosphate glasses. In heterogeneous systems the interfacial properties determine many of the macro-properties. Although an increasing number of papers, with infrared data, are appearing in the literature on the surface and catalytic properties of amorphous aluminum phosphates,4"6 there is little published information on the surface properties of glassy and crystalline phosphates and no information on the zinc phosphates. This paper describes studies of zinc phosphate glass surfaces. To facilitate the experimental interpretation, two of the glasses consisted of binary zinc phosphates with different Zn/P ratios; the third glass had 24 mol % other cations in the composition, which enhanced the hydrolytic stability. An ammonia probe was used and the chemical responses observed with FTIR, XPS, and wet chemical analyses. The ammonia probe gas allows one to determine the presence of the Br0nsted ( H + donating) and Lewis acid (electron accepting) sites. Concurrent nitridation reactions with the glass are also believed to take place under the conditions used. Reactions were also carried out with substituted amines (di- and trimethyl amines).
A. Glass compositions
2120 http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 8, Aug 1995 Downloaded: 14 Mar 2015
The batch compositions of the glasses used are listed in Table I. B. Glass preparation and treatments The batches were melted at 1100 °C in covered silica crucibles and annealed at 300 °C. The glass powder was prepared by dry gauge milling to a coarse powder, followed by extensive grinding in a motorized agate mortar and pestle under a dry nitrogen atmosphere
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