Editing Zirconium tungstate (section)

==Zirconium tungstate-copper system==
[[File:XRD Spectra.jpg|left|thumb|416x416px|XRD Spectra from Verdon & Dunand (1997).]]
[[File:Reaction Mechanism.jpg|thumb|373x373px|Proposed reaction mechanism in the HIP process of zirconium tungstate-copper system from Verdon & Dunand (1997).]]
Through hot-isostatically pressing (HIP) a ZrW<sub>2</sub>O<sub>8</sub>-Cu composite (system) can be realized. Work done by C. Verdon and D.C. Dunand in 1997 used similarly sized zirconium tungstate and copper powder in a low carbon steel can coated with Cu, and they were HIPed under 103MPa pressure  for 3 hours at 600&nbsp;°C. A control experiment was also conducted, with only a heat treatment (i.e., no pressing) for the same powder mixture also under 600&nbsp;°C for 3 hours in a quartz tube gettered with titanium.

The results from X-ray diffraction (XRD) in the graph in Verdon & Dunand's paper shows expected products. (a) is from the as received zirconium tungstate powder, (b) is the result from the control experiment , and (c) is the ceramic product from the HIP process. Apparently there are new phases formed according to Spectrum (c) with no ZrW<sub>2</sub>O<sub>8</sub> left. While for the control experiment only partial amount of ZrW<sub>2</sub>O<sub>8</sub> was decomposed.

While complex oxides containing Cu, Zr, and W were believed to be created, selected area diffraction (SAD) of the ceramic product has proven the existence of Cu<sub>2</sub>O as precipitates after reaction. A model consisted of two concurrent processes were surmised (as presented): (b) the decomposition of the ceramic and loss of oxygen under low oxygen partial pressure at high temperature leads to Cu<sub>2</sub>O formation; (c) copper diffuses into the ceramic and forms new oxides that absorb some oxygen upon cooling.

Since only very few oxides, those of noble metals which are very expensive, are less stable than Cu<sub>2</sub>O and Cu<sub>2</sub>O was believed to be more stable than ZrW<sub>2</sub>O<sub>8</sub>, kinetic control of the reaction must be taken into account. For example, reducing reaction time and temperature helps alleviate the residual stress caused by different phases of the ceramic during reaction, which could lead to a delamination of the ceramic particles from the matrix and an increase in the CTE.<ref>C. Verdon and D.C. Dunand, High-Temperature Reactivity in the ZrW<sub>2</sub>O<sub>8</sub>-Cu System. ''Scripta Materialia'', 36, No. 9, pp. 1075-1080 (1997).</ref>