docs: def refractory_VDI_Cp(ID, T=None):
      r'''Returns heat capacity of a refractory material from a table in
      [1]_. Here, heat capacity is a function of temperature between
      673.15 K and 1473.15 K according to linear interpolation among 5
      equally-spaced points. Here, heat capacity is not a function of
      porosity, affects it. If T is outside the acceptable range, it is
      rounded to the nearest limit. If T is not provided, the lowest temperature's
      value is provided.
  
      Parameters
      ----------
      ID : str
          ID corresponding to a material in the dictionary `refractories`
      T : float, optional
          Temperature of the refractory material, [K]
  
      Returns
      -------
      Cp : float
          Heat capacity of the refractory material, [W/m/K]
  
      Examples
      --------
      >>> [refractory_VDI_Cp('Fused silica', i) for i in [None, 200, 1000, 1500]]
      [917.0, 917.0, 956.78225, 982.0]
  
      References
      ----------
      .. [1] Gesellschaft, V. D. I., ed. VDI Heat Atlas. 2nd edition.
         Berlin; New York:: Springer, 2010.
      '''
      if T is None:
          return float(refractories[ID][2][0])
      else:
          Cps = refractories[ID][2]
          if T < _refractory_Ts[0]:
              T = _refractory_Ts[0]
          elif T > _refractory_Ts[-1]:
              T = _refractory_Ts[-1]
          return float(np.interp(T, _refractory_Ts, Cps))